Introduction Underground coal gasification (UCG) technology is critical to coal development in China, which has attracted recent attention. UCG technology can directly convert coal into syngas rich in CH4, H2, CO2, and CO beneath the earth surface, which is appropriate for the employment of coal resources with a low value (i.e., coal resources in large depths or with restricted thickness). UCG technology significantly reduces the economic cost and safety risks of coal mining and improves the overall efficiency of coal utilization. Syngas obtained from UCG technology is used to produce higher-value-added chemicals, such as methanol, ammonia, ethylene, and Fischer-Tropsch synthesis products, and the fuel for heating and power generation. Using syngas produced by UCG technology for power generation is mainly carried out through internal combustion engines. The energy conversion efficiency is limited by the Carnot cycle, usually about 30%, which diverges from the goal of clean and efficient use. Solid oxide fuel cells (SOFCs) convert the chemical energy in syngas fuel directly into electrical energy through electrochemical reactions. The conversion efficiency is considerably high and is not limited by the Carnot cycle. Power generation efficiency of > 60% and combined heat and power (CHP) efficiency of > 90% can be achieved. Therefore, SOFCs can efficiently employ the syngas from UCG, which is important for the clean and efficient development and utilization of coal. Flat-tube SOFCs exhibit high thermal shock resistance and stability under the redox cycle and are capable of being used in harsh environments. This paper was to investigate power generation using flat-tube SOFCs fed with carbon-containing fuels. In addition, the performance and durability of anode-supported flat-tube SOFCs with direct internal reforming of syngas from UCG were also analyzed. Methods The flat-tube Ni/yttria-stabilized zirconia (YSZ) anode-supported cell contains a porous NiO-3YSZ (3% yttria-stabilized zirconia, in mole fraction, ~1 mm thick) anode support, a NiO-8YSZ (8% yttria-stabilized zirconia, in mole fraction, 15-20 μm thick) anode functional layer, a dense 8YSZ electrolyte layer (15-20 μm thick), a gadolinia-doped ceria (GDC) barrier layer (~3 μm thick), and a porous (La0.6, Sr0.4)(Co0.2, Fe0.8)O3) (LSCF)-GDC cathode layer (15-20 μm thick). The cell was indicated as NiO-3YSZ|NiO-8YSZ 8YSZ|GDC|LSCF-GDC. The cell dimensions were 155 mm × 65 mm × 5.5 mm with an active cathode area of 60 cm2. The cell was heated in air at 750 ℃after assembly. The anode was reduced under 0.3 L·min1 H2 prior to the electrochemical tests. H2 or syngas was fed to the anode to evaluate the cell performance. To evaluate the electrochemical cell performance, the open-circuit voltage (OCV), current-voltage (I-V) characteristics, and electrochemical impedance under different conditions were measured by a model VMP3B-20 electrochemical workstation (BioLogic Co., France). The electrochemical impedance spectra (EIS) were recorded under OCV condition in the frequency range of 30 mHz to 30 kHz at an alternating current of 10 mV.Results and discussion The increasing temperature reduces a carbon deposition in SOFC fueled with different syngas. Especially at 750 ℃, the carbon deposition is not favorable for most types of UCG syngas. When the flow rates of H2, CO, CH4, and CO2 are fixed, the composition of N2 does not affect the carbon deposition. Increasing the composition of CO2 mitigates the carbon deposition. The power density of SOFC with H2 at 750 ℃ is 260.3 mW·cm2 at 0.8 V, and the maximum power density is 395.1 mW·cm2. The power density of a cell fueled with syngas (Swan Hills) at 0.8 V is 240.1 mW·cm2, and the maximum power density is 361.9 mW·cm2, reaching 91.6% of that with H2. The power densities of SOFC fueled with other types of UCG syngas are lower than those fueled with syngas (Swan Hills). The stability test of the flat-tube SOFCs fed with syngas (Swan Hills) is conducted at 750 ℃ under 300 mA·cm2. During the test, the composition of CO2 is changed. The flat-tube SOFC can discharge stably for 960 h. When the CO2 content is higher than or equal to 20% (in volume fraction), the degradation rate is less than 2.7% every 100 h in each stage. No sudden performance degradation emerges, indicating that the flat-tube SOFCs can run stably under such conditions. Since the original composition of syngas (Swan Hills) is similar to that of stage 2 (for 112-214 h), a stable power generation from flat-tube SOFCs directly using UCG syngas (Swan Hills) is viable. The CO2 content reduces to 10% at approximately 460 h. The voltage fluctuates sharply at 520 h. Subsequently, when CO2 further decreases to 0, the cell operates stably for another 144 h. However, when N2 flow is stopped at 750 h, the performance deteriorates significantly. After the long-term test, two characteristic peaks of carbon deposition appear in the Raman spectrum, i.e., the D peak (at 1 335-1 350 cm1) and the G peak (at 1 580-1 600 cm1). The result indicates that the carbon deposition is formed on the surfaces of the fuel channels. The SEM images show that after the test at 960 h, a significant Ni particle agglomeration occurs in the active anode layer of the cell fed with syngas (Swan Hills), and the average Ni particle size is increased by 17.0%. The Ni content loss in the active anode layer appears. Especially, the Ni content near the electrolyte layer (0-5μm) decreases from 30.0% (pixel, same below) to 19.2%. Carbon deposition, nickel agglomeration, and nickel particle loss result in a performance degradation.Conclusions The cell performance and durability of flat-tube solid oxide fuel cells by direct internal reforming of syngas from underground coal gasification were investigated. The peak power density of the cell with syngas (Swan Hills) from underground coal gasification was 361.9 mW·cm2 at 750 ℃ (Note: Swan Hills is a coal mine in Canada), which was approximately 91.6% of that with H2. Astable operation with a constant current of 300 mA·cm2 at > 960 h was realized. The ohmic resistance and polarization resistance increased from 0.108 Ωcm2 and 0.485 Ω·cm2 to 0.190 Ω·cm2 and 0.494 Ω·cm2, respectively. The increased rates of the ohmic resistance and polarization were 0.085 Ω·cm2·kh1 and 0.009 Ω·cm2·kh1, respectively. The main degradation mechanisms were the carbon deposition on the anode, Ni percolation loss, and Ni particle agglomeration, detected by Raman spectroscopy and scanning electron microscopy. Elevating CO2 concentration suppressed the carbon deposition, improving the cell stability.

Introduction Compared with conventional solid oxide fuel cell, using one material as both the cathode and anode to construct a symmetrical solid oxide fuel cell (SSOFC) configuration can simplify the fabrication processes and reduce the cost, while mitigating the chemical incompatibility and thermal mismatching issues. A-site double perovskite PrBaMn2O5+δ, with a matched thermal expansion coefficient with electrolytes, good structural stability in both oxidizing and reducing atmospheres as well as a modest catalytic activity is a promising symmetrical electrode. However, PrBaMn2O5+δ has a low electrical conductivity in reducing atmosphere and an inferior catalytic activity towards fuel oxidation. To address these issues, a lattice doping strategy was employed to regulate the charge carrier and oxygen vacancy concentrations, as well as the energy band structure. In addition, theoretical calculation could predict the properties of the material, and screen doping elements for high-performance material. The A site elements have a great impact on the properties of material in terms of structure, conductivity, and catalytic activity. In this paper, first-principles calculation was employed to investigate the effect of A-site Re (rare-earth) element species (i.e., La, Pr, Nd, Sm, Gd, and Y) on the structure and properties of ReBaMn2O5+δ materials, and the calculated results were verified by experimental data.Methods The Cambridge sequential total energy package (CASTEP) module in Material Studio software was utilized to calculate the binding energy, formation energy from oxides, and density of states (DOS) of LaBaMn2O5+δ (LBM), PrBaMn2O5+δ (PBM), NdBaMn2O5+δ (NBM), SmBaMn2O5+δ (SBM), GdBaMn2O5+δ (GBM), and YBaMn2O5+δ (YBM) materials, respectively. The selected materials were prepared by a sol-gel method. The phase structure of the synthesized powder was examined by X-ray diffraction (XRD). The electrical conductivities of the samples were measured by the DC four-terminal method in air and 5% H2/Ar atmosphere, respectively. The electrochemical impedance spectroscopy (EIS) and current-voltage curves of the La0.8Sr0.2Ga0.8Mg0.2O3?δ (LSGM, 300 μm) electrolyte supported symmetrical cell were obtained using Solartron 1260 with 1287.Results and discussion The theoretical lattice parameters of ReBaMn2O6 and ReBaMn2O5 were obtained through geometric optimization in DFT calculation. The ReBaMnO5 shows an enlarged lattice volume rather than that of ReBaMnO6. Also, the lattice volume of RBM shrinks with decreasing Re3+ ion radius. The binding energy results show that GBM has the maximum absolute value of binding energy, indicating an intense structural stability, which is related to the half-filled electronic configuration (4f7) of Gd3+. YBM has the minimum binding energy, indicating a poor structural stability. For the formation energy, SBM and GBM show a negative formation energy from corresponding oxides, inferring an intense synthesis preference. LBM and YBM exhibit a positive formation energy, and they prefer to maintain two phases, i.e., La(Y)MnO3 and BaMnO3. The energy difference between the O 2p orbital center and the Fermi surface of perovskite materials is related to the catalytic activity. Based on the conduction mechanism of B—O—B small polaron of electrons in perovskite structure, the energy difference between O 2p and Mn 3d orbital center can be related to the conductivity of the material. In this regard, the DOS of ReBaMn2O6 and ReBaMn2O5 is calculated to predict the corresponding properties. The results show that ReBaMn2O5+δ exhibits a better catalytic activity towards oxygen reduction than fuel oxidation because of the lower energy difference between the O 2p orbital center and Fermi surface of ReBaMn2O6 than that of ReBaMn2O5. In addition, PBM shows the minimum O 2p-Fermi energy difference, indicating a superior catalytic activity. While YBM and LBM possess high these values, indicating a poor catalytic activity. For the energy difference between O 2p and Mn 3d orbital center of the material, ReBaMn2O6 shows a smaller value than that of ReBaMn2O5, inferring that a higher electrical conductivity can be obtained in oxidizing atmosphere than in reducing atmosphere. PBM and NBM exhibit lower O 2p-Mn 3d energy difference values, indicating that they can realize a high conductivity. While YBM and LBM show the opposite results, indicating a low conductivity of the material. To verify these calculation results, ReBaMn2O5+δ with La, Nd, and Gd A-site elements are synthesized for properties characterization.[1]The XRD patterns demonstrate that NBM and GBM show a tetragonal structure with P4/mmm space group in both air and 5% H2/Ar atmosphere, while LBM sample consists of BaMnO3, La1-xM1-zO3, and MnO phases. This result is consistent with the calculation results that LBM possesses a positive formation energy, showing a thermodynamic instability. NBM and GBM exhibit a higher conductivity in air rather than in 5% H2/Ar, and NBM displays higher conductivities than GBM. At 900 ℃, the conductivities of NBM are 48.8 S·cm-1 and 10.0 S·cm-1 in air and 5% H2/Ar, respectively, which are higher than those of GBM (i.e., 38.9 and 8.8 S·cm-1). For the EIS results, NBM and GBM-based symmetrical cells exhibit lower polarization resistance in air than that in 3%H2O/H2. In addition, NBM shows superior catalytic activity than GBM, as confirmed by a lower polarization resistance of NBM than GBM (i.e., 1.78 vs. 3.4 Ω?cm2 in air, 2.60 vs. 3.7 Ω?cm2 in 3% H2O/H2). The conductivity and EIS results both are in accordance with the theoretical calculation results.Conclusions The computation results indicated that LBM is not stable at single phase layered perovskite structure. GBM showed the maximum binding energy, indicating the optimum structural stability, while NBM exhibited a smaller energy difference between Mn 3d and O 2p orbital center, and a lower energy difference between the O 2p orbital center and Fermi surface, implying the good conductivity and excellent catalytic activity among the investigated materials. Based on the calculation results, La, Nd and Gd were selected as A-site elements for verification. The results manifested that LBM was difficult to form single-phase perovskite, but it was easy to synthesize the single phases NBM and GBM. They showed a good structural stability in both reducing and oxidizing atmospheres. NBM exhibited higher conductivities in both air and 5% H2/Ar, compared to GBM. In addition, NBM electrode displayed much lower polarization resistance than GBM, demonstrating a superior catalytic activity. The LSGM electrolyte (300 μm) supported symmetrical cell with NBM electrode delivered a maximum power density of 335 mW?cm-2 at 850 ℃.

Introduction Optimizing the nanostructure of the cathode is an effective approach to enhance the performance of solid oxide fuel cells at a triple-phase boundary (TPB). The most commonly used method is an impregnation method, which can produce nano-sized particles on the cathode framework structure. However, it is not able to achieve the related large-scale application due to its laborious preparation process and unstable performance. In this paper, nano-sized and submicron-sized composite powders of La0.6Sr0.4CoO3?δ?Ce0.8Gd0.2O2?δ (LSC?GDC) were synthesized by flame spray pyrolysis (FSP) and spray drying (SD) methods for the preparation of cathode, respectively. Methods A uniform submicron-sized LSC?GDC composite powder was prepared by SD with a solution of metal nitrates as a precursor solution. Also, a uniform nano-sized LSC?GDC composite powder was directly synthesized by FSP with a solution of metal acetates as a precursor solution. The submicron-sized and nano-sized powders were blended in different mass ratios (i.e., 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, and 40:60) to produce cathode slurries. These slurries were then screen-printed onto the button cells of NiO?GDC|GDC|3YSZ|GDC|LSC?GDC|LSC structure with an effective electrode area of approximately 0.5 cm2. The voltammetric characteristics of the cells were tested by an electrochemical workstation. The electrochemical characterization was performed by electrochemical impedance spectroscopy (EIS) at open circuit voltage (OCV), and the impedance spectra were analyzed via distribution of relaxation time (DRT) analysis.Results and discussion Nano-sized particles synthesized by FSP and submicron-sized particles synthesized by SD can be distinguished via microscopic analysis. In addition, the fine particles are evenly distributed around the coarse particles, having a porous structure that meets an expected cathode microstructure. Under the experimental conditions, the overall ohmic impedance and polarization impedance both increase and then decrease as the proportion of nano-sized particles increases. The cathode performance is optimal when a mass ratio of SD powder: flame FSP powder is 70:30. Under SOFC mode at 850 ℃, the maximum power density of the button cell is 0.47 W/cm2, with an area specific resistance of 0.62 Ω·cm2. The corresponding ohmic impedance and polarization impedance values are 0.36 Ω·cm2 and 0.26 Ω·cm2, respectively. Combined with the results by DRT analysis, the doping of an appropriate amount of nano-sized powder significantly enhances the cathode O2 reduction reaction (ORR) process and cathode oxygen diffusion process.Conclusions Nano-sized and submicron-sized LSC?GDC composite materials were prepared by FSP and SD as one-pot methods, respectively. The feasibility of these two approaches for the large-scale preparation of SOFC cathode powders was investigated. The results showed that incorporating an appropriate amount of nano-sized powder into the submicron-sized powder for the preparation of the cathode could effectively enhance the cell performance.

Introduction Hydrogen energy, as an environmentally friendly and clean energy source, is expected to optimize the energy structure and alleviate energy consumption due to its high energy density, good combustion characteristics and abundant reserves. Hydrogen production from photolyzed water is considered as the most ideal way to obtain hydrogen source in the future. However, the disadvantages of weak visible light response, low catalytic activity, and poor chemical stability are one of the main factors limiting the application of traditional photocatalytic materials in photolytic water hydrogenation to real life. Zinc indium sulfide (ZIS) is proved to be an ideal semiconductor photocatalyst due to its good chemical stability, moderate forbidden bandwidth (2.2-2.5 eV), suitable conduction band position (0.79 eV), and good visible light absorption (absorption edge about 540 nm). However, ZIS suffers from a high photogenerated carrier complex rate and a weak photostability. Scholars optimized the ZIS energy band structure, expanded the spectral absorption range, improved the photoelectron dynamics behavior, and enhanced the photostability of ZIS by different approaches like morphology regulation, elemental doping, co-catalysis, and heterojunction. S-type heterojunctions have attracted recent attention due to their excellent photogenerated carrier dynamics and highly efficient photodissociation of hydrogen from water. In this paper, CWO/ZIS composite nanomaterials were synthesized by a two-step hydrothermal/water-bath method, and the photocatalytic mechanism of CWO/ZIS heterojunctions was discussed via constructing S-type heterojunctions, using the built-in electric field to enhance the photogenerated electron/hole separation efficiency and the migration rate.Methods Cobalt tungstate (CWO) nanoparticles were firstly prepared by a hydrothermal method, and then S-type CWO/ZIS heterojunctions were prepared by a water bath method. The composite samples named as CWO/xZIS were prepared at different molar ratios of Co2+ to Zn2+ (i.e., x = 0, 1%, 2%, 3%, 4%, 5%, 6%, and 10%). The properties of the samples (i.e., physical phase components, morphology, crystal structure, elemental distribution, chemical state, photocatalytic hydrolysis performance, photogenerated carrier separation efficiency, photogenerated charge transport rate, and photogenerated electron/hole pair recombination rate) were characterized.The photocatalytic hydrogen production performance of the samples was tested by a 30 mL customized photoreactor and a Timex GC7900 gas chromatograph. A 300 W Xenon lamp was equipped with a cut 420 nm filter (wavelength range: 420-780 nm) and an all-reflector was used as a visible light source. 5 mg of the sample was added to a mixed solution containing 9 mL of deionized water and 1 mL of triethanolamine (TEOA) and transferred to a 30 mL photoreactor sealed well. The air in the reactor was removed via charging the reactor with argon gas for 10 min. Afterwards, the reactor was mounted on the reaction platform, the circulating cooling water was turned on, the temperature of the reaction system was controlled at 10 ℃, and a stirrer was used for continuous stirring. A Xenon lamp 10 cm away from the reactor was turned on for illumination, and 100 μL of gas was extracted from the reactor for each 30 min and injected into the gas chromatograph for gas analysis for 3 h. The cyclic experiments were repeated under the same conditions for several times.Results and discussion According to the experimental results by X-ray diffraction (XRD), pure ZIS and pure CWO samples can be prepared. The characteristic peaks of ZIS and CWO both appear in the XRD patterns of the CWO/xZIS sample, indicating that CWO and ZIS are compounded. The surface morphology and microstructure of pure ZIS, pure CWO nanomaterials and their composite samples are determined by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Based on the FESEM images, pure ZIS appears a typical two-dimensional nanosheet structure, and the size of pure CWO nanoparticles is approximately 50 nm. The FESEM images of CWO/3%ZIS samples show that CWO nanoparticles are attached to ZIS nanosheets. The HRTEM images show that the coexistence of lamellar and granular forms on the CWO/3%ZIS sample occur, confirming that the product contains both CWO and ZIS. Two sets of different lattice stripes corresponding to different crystalline surfaces of pure ZIS and CWO appear in the product, which further confirms that CWO and ZIS are composited. The X-ray photoelectron spectra indicate that CWO/3%ZIS samples contain ZIS and there is astrong intense interaction between CWO and ZIS. From the results of hydrogen production tests on CWO/xZIS samples, the samples of CWO/3%ZIS show the maximum hydrogen production activity with a photocatalytic hydrogen production rate, which is twice greater than that of pure ZIS. The reproducibility test proves that the samples of CWO/3%ZIS have a good photochemical stability. From the results of electrochemical performance tests on different samples, CWO/3%ZIS sample has the maximum photocurrent density and the minimum electrochemical impedance, thus indicating that it has the maximum photogenerated carrier separation efficiency and transport rate, which is also consistent with the photocatalytic hydrolysis to production hydrogen performance. Conclusions Pure CWO nanoparticles were synthesized by a hydrothermal method and S-type CWO/ZIS heterojunctions were prepared via loading CWO nanoparticles onto ZIS nanosheets by a water bath method. The results of XRD, FESEM, HRTEM, and XPS confirmed the formation of a close contact between CWO and ZIS and the construction of a good heterogeneous interface. The results of visible-light water splitting hydrogen production tests showed that the hydrogen production performance of the CWO/xZIS composite samples was improved, compared with that of pure ZIS, in which the hydrogen production rate of the CWO/3%ZIS samples reached 4 296.8 μmol·g1·h1, which is twice greater than that of pure ZIS (i.e., 2 178.2 μmol·g1·h1). The electrochemical performance test results showed that the S-type heterojunction photogenerated carrier transport channel was constructed due to the well-matched energy band structures of CWO and ZIS, resulting in the composite samples with a higher separation efficiency of the photogenerated electron/hole pairs, a faster photogenerated charge transport rate, and a smaller electron/hole recombination rate, thus leading to the enhancement of the photocatalytic hydrolysis into hydrogen generation efficiency of the CWO/xZIS heterojunction.

Introduction La1?xSrxCr0.5Mn0.5O3 (LSCM) perovskite as a SOC fuel electrode material has attracted much attention due to its excellent comprehensive performance. However, there is still a lack of systematic and in-depth research on the its structural stability that is affected by some factors such as Sr content, temperature, and atmosphere under operating conditions of SOC. In particular, previous work indicate that this material exhibits different electrode performances and crystal structures under Sr-free and Sr-containing conditions, having the Sr content impact on its structural stability and electrochemical performance. Therefore, this paper was to analyze the crystal structures of La1?xSrxCr0.5Mn0.5O3 heat-treated in a reducing atmosphere at elevated temperatures from 500 ℃ to 1 000 ℃. In addition, the mechanism of crystal structural transformation of LSCM in a high-temperature reducing atmosphere was also discussed.Methods The LSCM precursors with different Sr contents (i.e., x of 0, 0.1, 0.2, and 0.3) were prepared by a citric acid sol-gel method. The precursors were calcined into LSCM powders in a muffle furnace at 1100 ℃. The LSCM powders were then thermally reduced in a reducing atmosphere at 500 ℃?1 000 ℃. After reduction, the phase transformations of each sample were characterized by X-ray diffraction (XRD). The lattice constants of the samples were calculated based on the Rietveld method using a software named Rietica. In addition, the first-principles calculations, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were also performed to reveal the effects of Sr content and reduction heat treatment on the crystal transformation of LSCM.Results and discussion The samples with different Sr contents were calcined in air at 1 100 ℃. A single trigonal phase appears when the Sr contents x≤0.2, while a small amount of SrCrO4 phase occurs besides the perovskite phase when x=0.3. After reduction at elevated temperatures, the sample with x of 0 transforms from a trigonal phase to an orthorhombic phase, and its crystal structure is relatively stable according to the fact that there are no other phases formed with increasing the reduction temperature. The XRD patterns of LCM samples reduced at different temperatures are analyzed using the Rietveld method. The results show that the unit cell volume of the reduced perovskite samples increases with the increase of heat treatment temperature from 700 ℃ to 1 000 ℃. However, the unit cell volume of the sample reduced at 600 ℃ is smaller than that at 500 ℃. This is because the sample begin to lose a considerable amount of oxygen at 500-600 ℃ during the reduction heat treatment, leading to a significant change in the shape of the crystal unit cell. For the samples with x of 0.1 and 0.2, trigonal and orthorhombic phases co-exist, and the proportion of trigonal phase increases with increasing x value but decreases with increasing reduction temperature. A layered perovskite oxide phase of (La,Sr)2MnO4 appears in the sample with x of 0.2 when the reduction temperature increases to 900 ℃, indicating that this sample has a poorer structural stability, compared with the sample with x of 0.1. According to the XPS results, compared with the LCM without Sr, the Mn3+ concentration in the reduced LSCM is relatively low as the Sr content increases, which can alleviate the Jahn-Teller distortion. Therefore, LSCM tends to form a trigonal phase, while LCM undergoes a more significant Jahn-Teller distortion, making it tends to transform into a more stable structure of orthorhombic phase than trigonal phase. The FTIR spectra reveal that the Mn/Cr—O bond energy increases in the LSCM perovskite with the increase of Sr content. The lattice parameters of each sample are calculated using the Rietveld method based on the XRD data, and subsequently the lengths of Mn/Cr-O bonds of each crystal are calculated. The results demonstrate that the length of Mn/Cr—O bond in the crystals decreases with the increase of Sr content, which is consistent with the conclusion derived from the FTIR spectra. However, the first-principles calculations confirm that the binding energy of the crystal of LSCM gradually increases with the increase of Sr content. Therefore, in summary, the existence of trigonal phase and the increase of binding energy caused by Sr doping jointly lead to the fact that the structural stability of Sr-containing LSCM perovskite is lower than that of Sr-free LCM under high-temperature reduction atmosphere conditions.Conclusions The structural transformation process and regularity of the LSCM perovskites under high-temperature reducing atmosphere were mainly controlled by the Jahn-Teller distortion, which depended on the concentration of Mn3+. The LCM without Sr underwent a more significant Jahn-Teller distortion, making it form an orthorhombic phase. The increase of Sr content mitigated the Jahn-Teller distortion, making the Sr-containing LSCM perovskites more likely to form a trigonal phase as well as possess an increased binding energy, thus reducing the structural stability of LSCM.

With the rapid development of modern society and escalating energy demands, the widespread use of traditional non-renewable fossil fuels has exacerbated environmental pollution and the greenhouse effect worldwide. The ‘carbon peak, carbon neutral’ goal propels wind power and photovoltaic-based renewable clean energy for power generation capacity in China. However, the intermittent and variable nature of renewable energy, along with a limited grid load regulation capacity, hinders the large-scale conversion or storage of intermittent power. Hydrogen serves as a sustainable fuel option due to its impressive high-energy potential at 140 MJ/kg and its capability for extensive, long-term storage, positioning it as a crucial element in transitioning towards a world underpinned by green, low-carbon energy sources. Generating green hydrogen through the electrolysis of water, powered by the variable outputs of renewable energy sources, becomes the most viable strategy for producing green hydrogen, while also leveraging the surplus energy from these renewables. At present, the widely adopted technique for hydrogen generation through water electrolysis is alkaline water electrolysis (AWE) with significant advantages of large single-unit size and low equipment cost, thus being a preferred technology route for large-scale hydrogen production.However, alkaline water electrolyzer is difficult to use for the new situation of fluctuating power supply to produce green hydrogen efficiently due to the problems of low current density, massive equipment, and poor dynamic operation capability. Alkaline water electrolysis has a problem of low current density. For electrode materials, the lower intrinsic catalytic activity of non-precious metal electrode materials makes the kinetics of the electrolytic water reaction, compared with precious metal catalysts such as platinum and iridium oxide. For the diaphragm materials, the typical thickness of PPS diaphragms offers a significant resistance to the movement of hydroxide ions and potential risks for gas crossover. Also, frequent stops and starts can induce reverse current, resulting in corroded electrodes and reduced lifespan.To confront these challenges, this review mainly summarized the research progress on transition metal catalysts and the development of industrial electrode technology. Alkaline water electrolysis electrode materials are mainly classified into three categories, i.e., precious metals, transition metals, and nonmetals. Among these, transition metal-based catalysts (i.e., Ni, Fe, Co, and Mol, and their compounds) have the advantages of low cost, simple preparation, and various structural compositions. They are considered as ideal materials to replace precious metal catalysts. The main types of these catalysts include single transition metals, sulfides, phosphides, and nitrides. They are often modified via electronic environment regulation, nanostructure optimization, and multi-component synergistic effects to enhance their intrinsic catalytic activity.For an efficient and reliable alkaline water electrolysis system, a high-performance diaphragm is also essential. The diaphragm separates the cathode and anode, prevents the mixing of hydrogen and oxygen, and transfers hydroxide ions. This review also represented the research progress on a new generation of composite diaphragms, and discussed the modifying industrial PPS diaphragms. Simple organic fiber diaphragms have a poor pore structure and a high ionic resistance, and their thickness and gas barrier properties are difficult to fully address. Applying an inorganic functional coating to the surface of PPS fabric to create an organic-inorganic composite diaphragm becomes the main aspect of diaphragm research. The inorganic functional coating on the surface of the composite diaphragm improves hydrophilicity and gas barrier properties and reduces the thickness and ionic resistance of the diaphragm.Alkaline electrolyzer downtime can produce a reverse current due to the potential difference between the conductive metal bipolar plate formed by the electronic pathway and the ionic pathway constituted by the alkaline circulation. This can cause a significant corrosion to the cathode material in the large volume intermediate compartment of the alkaline electrolyzer and creates a potential safety issue. Therefore, some studies addressing the mechanisms of reverse current formation and mitigation strategies are crucial for alkaline water electrolyzers for frequent shutdown and startup.Summary and prospects Alkaline water electrolysis is a highly mature, simple, and low-cost hydrogen production technology that is widely applied to a large-scale hydrogen production in China. In the future, the construction of new power systems will urgently need a large-scale wind power consumption capacity as well as a low-cost, green hydrogen supply in chemical and transportation industries. This requires electrolysis cells capable of adapting to fluctuating power sources, i.e., wind power. However, the existing industrial technology mainly focuses on a single-tank hydrogen production for incremental improvements. Limited progress is made to address some issues like a low current density and a poor dynamic performance. The emerging demand for green electricity to produce green hydrogen leads to higher requirements for the key materials and equipment technology of alkaline water electrolysis. The next generation of this technology can feature a high current density and a low energy consumption, operate across a wide and variable load, and have rapid start/stop capabilities to accommodate the fluctuating hydrogen production scenarios of renewable energy. The lab-research of AWE electrode catalysts should consider the needs of industrial applications. Simple organic fiber diaphragms have a poor pore structure and a high ionic resistance. Hence, thick membranes (typically >0.8 mm) are required to meet the gas barrier properties. Organic-inorganic composite diaphragms are promising for future industrial applications, although their long-term durability still requires a further verification. Moreover, there is a significant lack of research on the effect of fluctuating working conditions (i.e., variable loads and start-stop cycles) on the dissolution of electrode catalysts, detachment, and mechanical damage to the diaphragm. Beyond materials, further studies on system operation control and optimization are needed to improve dynamic performance (i.e., strategies to mitigate reverse current that limits the start-stop frequency of alkaline water electrolyzers.

Hydrogen is considered as a clean energy carrier in the global energy transition and development due to its high energy density (142 kJ·g-1), cleanliness, and sustainability. At present, hydrogen is mainly produced through steam reforming of fossil fuels under harsh conditions, which are restrained by the complex operation and emission of carbon dioxide. Hydrogen production through water electrolysis is an effective and clean method for generating high-purity hydrogen using renewable energy sources without pollution. The electricity utilized in this process is obtained from renewable sources such as solar, hydropower, wind, and nuclear energy, enabling carbon-free and green hydrogen production. With the advancements in renewable energy generation technologies and electrolysis cell techniques over the past a few decades, the production of green hydrogen through water electrolysis is flourishing. Based on the type of electrolyte and operating conditions, water electrolysis technologies are primarily classified into four categories, i.e., alkaline water electrolysis (AWE), proton exchange membrane (PEM) water electrolysis, anion exchange membrane (AEM) water electrolysis, and solid oxide electrolysis cell (SOEC) water electrolysis. PEM water electrolysis technology, distinguished by its prompt start-up and power modulation capabilities, is currently a sole technology capable of producing high-purity hydrogen coupled with renewable energy generation. This review firstly introduced several major hydrogen production technologies, emphasizing the advantages of PEM water electrolysis technology. Subsequently, we represented the latest developments in iridium (Ir) and ruthenium-based (Ru) oxygen evolution reaction (OER) electrocatalysts in acidic electrolyte, and summarized the strategies for developing acidic OER electrocatalysts with a high performance. Finally, this review highlighted the challenges associated with acidic OER electrocatalysts and outlined prospective avenues for future research.The electrolysis efficiency of PEM water electrolysis primarily depends on the overpotentials at the anode and cathode. Compared to the hydrogen evolution reaction involving a 2-electron transfer step at the cathode, the OER at the anode involving a 4-electron transfer step is considered as a rate-limiting step. The anodic overpotential is significantly higher than the cathodic overpotential, typically requiring an overpotential of 200?500 mV to drive a current density of 10 mA·cm-2. Unfortunately, the choice of anodic catalytic materials is greatly limited by the strong acid characteristics and the high anodic electrolysis voltage, which demands that the anodic catalysts can operate stably in a strong acid and oxidizing environment. According to the OER activity and stability of different metals, the precious metal iridium dioxide (IrO2) is commercially employed as a benchmark anodic catalyst of PEM electrolysis cells. However, Ir is one of the most expensive metals in the world. For Ir-based catalysts, researchers focus on reducing the Ir content in the catalyst, but the Ir content still generally exceeds 40% (in mass fraction). Therefore, developing efficient, stable, and low-cost non-Ir-based OER catalysts is also important in the development of PEM water electrolysis technology. Compared to Ir, metal Ru possesses a higher OER activity and is only one-tenth the price of Ir, that has a significant potential for application in PEM water electrolysis. In recent years, various types of Ru-based catalysts are developed in the acidic OER field, showing a promising potential as substitutes for Ir-based catalysts. Therefore, this review could provide a detailed overview of the research progress on Ir- and Ru-based catalysts in PEM water electrolysis for hydrogen production.Summary and Prospects The development of PEM water electrolysis for hydrogen production is currently flourishing, yet achieving a large-scale commercialization still requires overcoming several technical challenges. The extensive research on Ir- and Ru-based materials notably advances the development of highly active and stable OER catalysts, playing a crucial role in designing commercially viable PEM water electrolysis technology. Despite significant advancements in the research of such OER catalysts, there are still some issues that need to be addressed. The challenge of Ir-based catalysts remains in reducing the Ir content in catalysts and the Ir loading in membrane electrodes, while ensuring high activity and stability. Developing low-cost metal-supported catalysts with high stability and conductivity is an effective approach to reduce Ir usage. Metal oxides of specific elements (i.e., Ti, Ta, Nb, W, and Mo) can stably exist under strong acidic and oxidizing conditions, demonstrating a good corrosion resistance, which is the potential candidates for substrates. Furthermore, enhancing the continuity of Ir-based catalysts and forming a dense conductive layer can improve the conductivity of these metal oxide supports. Enhancing the stability of Ru-based catalysts is a challenge to commercial application. Reducing the proportion of unstable Ru elements through supported or solid solution-type Ru-based catalysts can stabilize catalysts under acidic OER conditions. Suppressing the lattice oxygen participation in OER can prevent the structural collapse of Ru-based catalysts, and the mechanisms of Ru self-deposition phenomenon are required a further exploration. Finally, it is important to establish a unified and comprehensive testing standard system for assessing the activity of catalysts in the PEM water electrolysis, particularly under high current density conditions.

Hydrogen storage alloys are considered as the most promising solid-state hydrogen storage materials with reliable safety, outstanding hydrogenation/dehydrogenation rate and a large quantity of hydrogen storage capacity. Among the common Mg-based, rare-earth-based, Zr-based and Ti-based hydrogen storage alloys, Ti-based hydrogen storage alloys are rapidly developed due to their low cost and supreme hydrogen storage capacity at room temperature and smooth pressure. Note that the Ti-Mn based AB2-type hydrogen storage alloys (i.e., A for Ti, Zr, rare metals and other hydride-forming elements, B for late transition metals and other non-hydride-forming elements) have a wide range of adjustable composition and a single Laves hydrogen-absorbing phase. The excellent thermodynamic properties of Ti-Mn alloy make it be an attractive hydrogen storage material, but difficult activation and high plateau pressure are still challenges for the large-scale application of Ti-Mn based hydrogen storage alloys.The optimization of the hydrogen storage properties of the materials is mainly achieved via compositional design of the elements, oxygen content control and achievement of the preparation process. The increase of cell volume brings more space for hydrogen to occupy with the increase of elements with larger atomic radii. Also, the interatomic force or bonding energy weakens, and the energy required for hydride decomposition reduces, which are conducive to the hydrogen absorption and desorption reaction of the material. For instance, an increase in the number of elements (e.g., Zr) that bind hydrogen more intimately than Ti usually promotes the hydrogen absorption reaction. A small amount of Cr and V instead of Mn can lower the slope of the hydrogen absorption and release plateau and significantly reduce the reaction hysteresis. The phase transition of the metal hydride is restricted, and the plateau pressure is subsequently increased as the valence electron concentration is increased. On this basis, it is still necessary to strengthen the in-depth research on the oxygen control method of materials to improve the hydrogen absorption kinetics of materials. This is because the incubation period before the activation process or the initial hydrogen absorption process is usually caused by the oxide film on the metal surface. The surface oxide scale prevents hydrogen from squeezing into the interior of Ti?Mn based hydrogen storage alloys and reduces the hydrogen absorption kinetic performance of the materials. Also, the oxide scale dissolves at high temperatures, and some oxygen atoms are solidly dissolved into the crystal lattice of the alloy, which reduces the interstitial space available for H to occupy and the hydrogen storage capacity of the material. At present, the commonly used access of oxygen removal is to replace the oxygen in Ti using metals with a lower Gibbs free energy. In addition, unlike conventional methods such as arc melting to prepare Ti-based hydrogen storage alloys, a low-cost, high-performance preparation process is developed for the perspective of modulating the microstructure to provide channels for hydrogen transport. Finally, the application of Ti-Mn hydrogen storage alloys in the field of hydrogen storage tanks is elaborated. The addition of cooling materials inside and outside the tank, the expansion of the contact area between the cooling structure and the hydrogen storage alloys as well as the mixing of phase change material can provide a positive effect of mass and heat transfer for reactor and maintain the hydrogenation/dehydrogenation rate of the metal hydride reactants, which lays the foundation for the design of metal hydride reactors in the future.Summary and prospects Ti?Mn hydrogen storage alloys are practically applied in the field of compressed hydrogen storage due to their advantages of low cost, satisfying dynamics, high hydrogen storage capacity and cycling stability. It is necessary for the further development and application of Ti-Mn hydrogen storage alloys to specifically investigate the bonding of hydrogen atoms with metal atoms as well as the distribution of hydrogen atoms. However, it is difficult to utilize the micro-scale analysis of X-ray diffraction and transmission electron microscopy to achieve this goal. Therefore, some cutting-edge characterization tools, such as differential phase contrast (DPC) imaging, can be used to accurately characterize the positions of interstitial hydrogen atoms as well as the hydrogen binding energies at different positions, which is a key to understanding the hydrogen storage mechanism and chemical properties of metal hydrides. It should not be ignored that the cost issues also need to be considered in the application. At present, the commonly used methods are vacuum self-consuming electrode or induction melting followed by heat treatment to achieve the homogenization of the sample composition. Hence, there is an urgent need to further explore the methods for low-cost and large-scale preparation of Ti-Mn system hydrogen storage alloys in the future.

As a device capable of converting electrical energy into chemical energy, solid oxide electrolysis cell (SOEC) has superior characteristics such as high energy conversion efficiency, reversible operation capability, and environmental friendliness. The hydrogen electrode as the direct site for the hydrogen evolution reaction (HER) is a crucial component of SOEC. Excellent hydrogen electrode materials require a chemical-structural stability under high-temperature reducing atmosphere, outstanding electrocatalytic activity, long-term operational stability, and cost-effectiveness. To meet these requirements, various types of hydrogen electrode materials are developed. However, their performance stability issues are evident, necessitating the overcoming of these challenges through materials development aligned with the unique demands of SOEC materials. It is thus essential to provide a systematic discussion on aspects such as the hydrogen electrode reaction mechanism (i.e., hydrogen spillover, oxygen spillover), material requirements, physicochemical properties of electrode materials, electrochemical performance, and material degradation. This will facilitate subsequent research endeavors in this field.This review introduced cermet-based hydrogen electrodes, exemplified by materials such as Ni-Zr0.92Y0.08O2 (YSZ) and Ni-Gd0.2Ce0.8O2 (GDC). Cermet hydrogen electrodes composed of Ni and ceramic phases are widely used due to their excellent electrocatalytic performance of Ni, good mechanical strength, and lower cost. However, some issues such as Ni oxidation, migration, agglomeration, carbon deposition, and poor redox cycle stability during electrolysis of H2O and CO2 operations restrict the application of Ni-based cermet. This compels to seek novel hydrogen electrode materials to address these challenges, leading to the proposal of perovskite, with perovskite oxides as a representative category. Perovskite oxide is mixed ionic-electronic conductors (MIEC) material, so the reactive region can be expanded to the entire surface of the whole electrode to reduce the activation resistance. Also, perovskite has an excellent resistance to carbon deposition, sulfur poisoning, and redox cycle stability. The A, B, and O sites have a potential to be replaced by other ions, and the above characteristics lead to a wide range of interest in perovskite-based materials. The physicochemical characteristics and the pros and cons of each type materials of perovskite, i.e., single perovskite (ABO3, i.e., La1?xSrxCrO3?δ, SrFeO3?δ, SrTiO3?δ), double perovskite (A2B2O6, i.e.,PrBaFe2O5+δ, Sr2Fe2?xMoxO6?δ), and Ruddlesden-Popper perovskite (RP, An+1BnO3n+1) were discussed. The review also provides a comprehensive discussion on various strategies for improving material performance, including A-site vacancy, A/B-site doping, in-situ exsolution, second-phase composites, and microstructure optimization. Other materials like spinel with good stability and conductivity are explored as the alternatives for hydrogen electrodes.Under electrolysis conditions, the degradation issues of Ni-based cermet materials primarily revolve around the oxidation, migration, agglomeration of Ni, and external poisoning by sulfur and silicon. The oxidation of Ni leads to deactivation and loss of electronic conductivity, necessitating the protection of Ni-based cermet electrodes via introducing a reducing gas. Furthermore, the oxidation, migration, and agglomeration of Ni can disrupt the original structure and composition distribution of the electrode, resulting in a poor cyclic stability of the cermet-based electrode during redox cycles. The deposition of carbon can block triple phase boundaries (TPBs), reduce active reaction sites, and disrupt the microstructure of the electrode. Simultaneously, trace impurities in the reaction gas, such as sulfur, have a pronounced poisoning effect on Ni metal. Measures such as alloying, introducing materials with a high ionic conductivity, and regulating electrode structure can effectively mitigate these deteriorative effects and slow down the degradation process.Summary and prospects The existing research on hydrogen electrode materials for SOEC involved the systematic theoretical and experimental studies. To commercialize hydrogen production through SOEC, it is still necessary to further investigate hydrogen electrode materials. At the mechanistic level, advanced characterization techniques, such as in-situ transmission electron microscopy and X-ray photoelectron spectroscopy, combined with first-principles calculation and distribution of relaxation time method, can be employed to investigate the reaction mechanisms of SOEC hydrogen electrodes. This approach guides subsequent development and application of electrode materials. The degradation of hydrogen electrode materials is a primary obstacle to the current commercialization of SOEC. The existing research predominantly focused on Ni-based metal ceramic hydrogen electrodes. For Ni-based metal ceramics, the main issues involve the oxidation, migration, and coarsening of nickel. Based on the fundamental mechanisms of electrode reactions, a comprehensive exploration of material degradation phenomena and their mechanisms is conducted. The severity of the impact of the mentioned changes on the elementary reactions of the electrode is assessed, and the corresponding improvement strategies are proposed. At the material level, it is essential to conduct in-depth studies based on the actual requirements of the electrodes. Combining theoretical predictions with experimental data, some performance-enhancing novel hydrogen electrode materials can be obtained through ion doping and in-situ exsolution for the regulation of electronic structure, charge carrier migration capability, and surface oxygen vacancy formation energy. At the application level, improvements in large-scale cell manufacturing process, optimization of the microstructure of Ni?YSZ electrodes, and the incorporation of high-performance catalytic materials such as perovskites using methods like ion liquid injection are crucial for advancing the practical application of SOEC.

Solid oxide fuel cell (SOFC) is a power generation device that can directly convert chemical energy into electrical energy, which has a high power generation efficiency. Compared with the conventional power generation mode, the use of the SOFC to generate electricity can greatly reduce the environmental pollution. Solid oxide fuel cells can be divided into tubular and flat plate types according to their structure. The structural characteristics of SOFC determine that its high temperature sealing difficulty is lower than that of plate structure, and the special tubular SOFC structure design can completely solve the high-temperature sealing problem, especially in the tubular SOFC structure with multiple single cells in series integrated design on one battery tube. One battery tube is equivalent to a small stack with unique output characteristics of a high voltage and a low current, which can significantly reduce the ohmic polarization loss of tubular cells. The reduced sealing difficulty of tubular SOFC makes the tubular battery stack relatively easy, and the thermal stress constraint in the operation of the stack is small, which is conducive to the long-term stable operation of the stack. Compared with plate batteries, their volumetric power density and output current density are relatively low under the same conditions. In addition, tubular SOFC can be also operated under pressure due to its good sealing characteristics, further improving the power generation efficiency. After continuous development, significant breakthroughs in the technology of tubular SOFC are mode, especially for establishing kilowatt level SOFC power generation systems and achieving commercialization. Most of the single tube batteries used are multi-cell structures. The development of SOFC technology starts relatively late in China, so although it is commercialized, it is mostly a single tube single cell structure, and there is little research on multiple cells. This review represented the typical structural design of tubular SOFC, and classified the geometry of tubular SOFC and the material types of battery supports, including anode supported type, cathode supported type, ceramic tube supported type, and metal/cermet supported type according to the battery support materials. The bamboo round tube, bamboo flat tube, single-section round tube and single-section flat tube structure were classified according to the geometry of the tubular SOFC. Also, a small-sized microtubule SOFC was introduced, having a higher power density, compared to large-sized tubular batteries due to their smaller size. Also, the common materials and preparation methods of tubular SOFC were reviewed, for instance, high-temperature sintering method and spraying method. Finally, the further development on tubular SOFC was prospected.Summary and Prospects The main feature of tubular SOFC is its relatively easy high-temperature sealing performance and low thermal stress during stack integration and operation. Each type of tubular battery structures has its own unique characteristics. In general, multi-section tubular structures are more suitable for the construction of high-power power plants, while single section tubular batteries are more suitable for small systems. At present, regardless of the structure of a single cell, there is already a relatively mature material system that can achieve a stable battery performance. The existing work mainly focus on the development and preparation of new materials, process optimization, and the development of different hydrocarbon fuel cells. Among the tubular battery supports, round tube multi-section and flat tube multi-section batteries are more suitable for single tube high-power output. The mainstream of this multi-section design battery is a single tube output of over 100 W, which is more suitable for large distributed functional systems. In addition, tubular batteries with metal or metal ceramic support structures can significantly improve the startup speed of SOFC. Tubular batteries can also be used as electrolytic cells due to the reversible structure of SOFC and SOEC. This type of battery with a fast start-up speed is more suitable for coupling with photovoltaic and wind power, achieving an efficient energy utilization. For cylindrical multi-cell batteries, one battery tube is equivalent to a stack, so the manufacturing process of tubular batteries is relatively complex, and their commercialization process lags behind that of flat panel batteries. For battery stacks, there are some issues such as battery array arrangement, heat exchange, and airflow distribution. At present, there are not many publicly reported experimental data, a further experimental research is thus needed. Although there are still some challenges for tubular SOFC, the performance, stability, and reliability of SOFC can be improved through the development of novel materials and technological innovations, thereby enhancing their application prospects in the field of sustainable energy and enabling commercial SOFC technology to be implemented.

Energy is a foundation and driving force for the progress of human civilization. It is vital to the national economy, people livelihood, national security, human survival, and development, which is crucial to promoting economic and social development. SOFCs have the advantages of an all-solid structure, high energy conversion efficiency, no need to use precious metal catalysts, easy-to-achieve modularization, flexible fuel types, etc., which are widely used. As a kind of SOFC, protonic ceramic fuel cells (PCFCs) with protons as charge carriers have a unique conduction mechanism and can effectively convert chemical energy into electric energy at relatively low temperatures (i.e., 400?700?°C). The feature that PCFCs can be operated at medium and low temperatures can effectively avoid a reaction between the cell components at high temperatures, making the microstructure more stable while extending the service life. Therefore, PCFCs have attracted recent attention.As one of the core components of PCFCs, the catalytic activity of the cathode is important to the electrochemical performance of PCFCs. The oxygen reduction reaction (ORR) at the cathode of PCFCs is a high-temperature driven process, and the dynamic reaction of ORR at the cathode side of PCFCs becomes slow as the operating temperature decreases and the polarization loss of the cathode increases, resulting in a sharp decline in the electrochemical performance of a single cell at lower temperatures. Therefore, the design of cathode materials with high catalytic activity and stability is one of the effective ways to achieve high-performance low-temperature PCFCs.However, the performance of PCFCs is highly dependent on the material structures of cathodes, which in principle should have sufficient electrical conductivity, structural stability, electrochemical catalytic activity, and durability. Many PCFCs cathodes with a variety of different air electrode structures are developed. This review represents the development on perovskite oxides, double perovskite oxides, RP perovskite oxides, and spinel oxides in PCFCs cathodes, and compared the properties of different cathode materials. Some studies are carried out to modify cathode materials via doping certain elements. The doping of certain elements or compounds can increase the conductivity of the cathode, thereby reducing the resistance and increasing the current density. Also, doping can change the crystal structure and chemical bonding state of the cathode material, improving its stability in different environments. In addition, some dopants may enhance the reaction activity on the cathode surface and reduce the activation energy of the reaction, thus increasing the reaction rate. The preparation of composite structure is also an effective approach to improve the performance of cathode materials. Composite cathodes with comprehensive performance advantages can be constructed via combining different materials with different advantages. In a composite cathode, a synergistic effect can be created between different materials to further enhance the overall performance of the cathode. In addition, the flexible design of the composite structure enables the optimization of the material composition and structure in micron-scale and nano-scale, resulting in the better performance.Summary and prospects Protonic ceramic fuel cells can efficiently convert chemical energy directly into electrical energy, overcoming the potential problems of fuel gas dilution and gas separation in oxygen ion conductor solid oxide fuel cells. However, the electrochemical performance of PCFCs does not exceed that of O-SOFCs, and the development and improvement of cathode materials with a high catalytic activity is the most important issue to promote the development of PCFCs at low temperatures. The future research aspects of PCFCs cathode are as follows: (a) Development and performance of high entropy perovskite oxides. High entropy perovskite oxides can exhibit the properties of many different oxides simultaneously, and achieve a good performance in PCFCs; (b) In-situ characterization and detection of reaction mechanisms. In the future, the in-depth study of in-situ characterization is expected to provide a theoretical support for further understanding of the relationship between electrode structure and performance and further optimization of cathode performance; (c) The development of low-cost cathodes. Cobalt-based perovskite materials are widely used in PCFCs. However, the thermal mismatch between cobalt-based materials and common proton-conducting electrolytes, chemical instability, and rising price of cobalt greatly limit the application of cobalt-based materials in PCFCs cathodes; (d) Optimization of nanostructures. The nanostructured electrodes and interfaces formed via atomic layer deposition or impregnation can increase the number of active sites and reduce the length of ion diffusion to active sites; and (e) Development of composite cathode. The introduction of electrolyte material in the cathode, that is, proton conduction phase, can effectively reduce the polarization resistance of the cathode, expand the length of the three-phase interface, and reduce the thermal expansion coefficient of the cathode, which can better match the electrolyte and solve the problem of delamination between the cathode and the electrolyte.

Introduction Ferroelectric ceramics generate a strain property in electric field due to the inverse piezoelectric effect and ferroelectric domain swiching, and these ceramics can be made as key components of actuators. Lead-based ferroelectric ceramics are widely used in actuators, but their high lead level is harmful to human-being health and environment. (K1-xNax)NbO3-based ceramics replace lead-based ceramics for actuators applications. (K1-xNax)NbO3-based ceramics with a multi-phase coexistence structure at room temperature have a high strain due to the possible increasing polarization direction. The classical (1-x)(K1-yNay)(Nb1-zSbz)O3- xBi0.5(Na1-wKw)0.5ZrO3 (0≤x≤0.05, 0.40≤y≤0.68, 0≤z≤0.08, 0≤w≤1) (KNNS-BNKZ) system can be adjusted to have rhombohedral-tetragonal (R-T), rhombohedral-orthogonal-tetragonal (R-O-T), orthogonal-tetragonal (O-T) phases coexisted structures to increase the strain property. When the system is used to construct the coexistence structure, the composition and process need to be finely regulated, especially the raw material calcination or pre-firing process. Pre-firing is a solid-phase reaction of various raw materials at a certain temperature, and the purpose is to synthesize the crystal structure of the target component without raw material components. The activity, particle size and uniformity of the pre-fired powder have a great influence on the difficulty of green sintering and the electrical properties of ceramics. The pre-firing temperature affects the phase coexist structures of 0.96(K0.5Na0.5)(Nb0.96Sb0.04)O3-0.04Bi0.5(Na0.5K0.5)0.5ZrO3 ceramic coming from KNNS-BNKZ system, but the effect of the strain properties of ceramics is not reported yet. In this paper, 0.97(K0.48Na0.52)(Nb0.97Sb0.03)O3-0.03Bi0.5(K0.48Na0.52)0.5ZrO3 (0.97KNNS-0.03BNKZ) with R-T was designed according to KNNS-BNKZ system. KNN-based ceramics with multi-phase coexistence for improving their strain properties were constructed via adjusting the pre-firing temperature. In addition, the effect of pre-firing temperature on the phase structure, dielectric properties, ferroelectric properties and strain properties of 0.97KNNS-0.03BNKZ ferroelectric ceramics was investigated.Methods For the preparation of 0.97KNNS-0.03BNKZ ferroelectric ceramics by a solid-phase sintering method, the ingredients were made according to the chemical formula, and various raw materials were mixed and ground with absolute ethanol in a ball mill with zirconia balls. After 12-h milling, the slurry was dried. The mixture of 0.97KNNS-0.03BNKZ components of 20.0 g in a crucible was calcined at 600-950 ℃ for 3 h. After milling and drying, the powder was pressed into green discs with the diameter of 13 mm. The upper and lower surfaces of the green discs were buried with the same calcination powder, covered with alumina crucible then sealed with alumina powder. Finally, the green discs were sintered in a high-temperature furnace at 1 180 ℃ for 3 h. The ceramic samples were obtained after cooling in the furnace.The samples were not polished and thermally corroded. The surface morphology of the ceramics was determined by a model Smartlab 3 kW scanning electron microscope after direct cleaning and drying. The density of the samples was analyzed by the Archimedes drainage method. After grinding the surface of samples, the phase structure of the ceramics was characterized by X-ray diffracometer (XRD). Their ferroelectric and strain properties were determined at 10 Hz by a model Precision Premier II ferroelectric system. Their permittivity was measured at 10 kHz by a model TZDM permittivity instrument.Results and discussion The effect of calcination temperature (i.e., 600-950 ℃) on the diameter shrinkage, density, relative density, microstructure, crystal structure, dielectric properties, ferroelectric properties and strain properties of 0.97KNNS-0.03BNKZ ceramics was analyzed. The results show that the diameter shrinkage density and relative density of these ceramics firstly increase and then decrease with the increase of the calcination temperature. The ceramics calcinated at 800 ℃ have the maximum relative density (i.e., 94.9%), while the ceramics calcinated at 600 ℃ and 950 ℃ have the minimum relative density (i.e., 80.3% and 80.4%). All of the ceramics have the same distorted orthogonal crystal structure based on the XRD patterns and temperature-dependence of dielectric constant. Their Curie temperature increases from 280 ℃ to 320 ℃, while their dielectric constant increases from 4 520 to 7 769. The maximum polarization strength (Pmax) of the ceramics at 600, 800 ℃ and 950 ℃ is obtained due to the easy domain swiching for the high or small relative density of ceramics. At 950 ℃, the bipolar strain of the ceramics reaches 0.5% at 60 kV/cm because the ferroelectric domain is easy to swiching, and the interacts between V'K\Na-VO defect dipoles and domain swiching. At 600-900 ℃, the strain properties of the ceramics change slightly (i.e., 0.2%-0.3% strain). The unipolar strain properties of ceramics calcinated at different temperatures are similar.Conclusions The pre-firing had little effect on the crystal structure of 0.97KNNS-0.03BNKZ ceramics, but had a great effect on the density and strain performance of the ceramics. When the calcination temperature was 950 ℃, the bipolar strain of the ceramics reached 0.5% at 60 kV/cm, because the ferroelectric domain was easy to swiching and the interacts between V'K\Na-VO defect dipoles and domain swiching.

Introduction With the rapid development of wireless communication and information technology, the electromagnetic wave generated by electronic equipment and communication facilities will cause serious damage to human health and living environment. Electromagnetic wave absorbing materials can convert electromagnetic waves into heat or other forms of energy, which plays an important role in reducing electromagnetic wave pollution. Electromagnetic wave absorbing materials have attracted recent attention. Common electromagnetic wave absorbing materials include magnetic materials and dielectric materials, such as ferrite, magnetic metals, carbon materials (i.e., carbon nanotubes, graphite carbon, etc.), oxide ceramics (i.e., zinc oxide, tin oxide, etc.) and silicon carbide, etc.. However, these materials are prone to oxidization and impedance mismatch at high temperatures. It is thus important to develop new dielectric materials with intense electromagnetic loss characteristics at high temperatures. Polymer-derived silicon boron carbon nitrogen (SiBCN) ceramics have superior corrosion resistance and high-temperature oxidation resistance, as one of electromagnetic wave absorbing materials that can be applied in harsh environments. However, pure phase SiBCN ceramics have the poor absorption of electromagnetic waves due to their low dielectric constant and low conductivity.At present, in-situ generation or addition of high electromagnetic loss phases are often used to improve the absorption ability of SiBCN ceramics for electromagnetic waves. In this paper, SiZrBCN composite ceramics were prepared via introducing Zr into a polymer-derived SiBCN ceramic precursor. The evolution of the physical phase composition and microstructure of SiZrBCN composite ceramics by Zr addition was investigated, and the effect of physical phase compositions on the electromagnetic wave absorption performance of SiZrBCN ceramics was discussed. Methods Under the condition of ice bath, THF (280 mmol), DCMVS (150 mmol) and (CH3)2S?BH3 (250 mmol) were injected into a three-necked round-bottomed flask and stirred thoroughly for 24 h to obtain an intermediate dichloromethylmethylsilyl ethylborane (TDSB). DCMS (180 mmol) and HMDZ (450 mmol) were sequentially added to TDSB. DCMS (180 mmol) and HMDZ (450 mmol) were added sequentially to TDSB and stirred for 24 h. Subsequently, the material in a three-necked flask was heated at 110 ℃for 4 h, and then slowly heated at 170 ℃ for 4 h to obtain a clear liquid. The above products were distilled at a reduced pressure for three times to obtain PBSZ, and ZrCl4 (12.5 mmol) was added into PBSZ and heated at 80 ℃ for 12 h and distilled at a reduced pressure to obtain a beige precursor named as sample Z5. The above experiments were repeated to prepare samples Z0, Z5, and Z10, respectively, and the experiments were carried out in Ar atmosphere throughout the whole process. The resulting samples Z0, Z5 and Z10 were heated at a heating rate of 2 ℃ at 280 ℃ for curing, and then the cured samples were heated in N2 atmosphere at 1 600 ℃ to obtain samples Z0-1600, Z5-1600 and Z10-1600.The chemical bonding and group compositions of SiBCN ceramic precursors were investigated by a model VERTEX 70 Fourier infrared spectrometer. The physical phase composition of SiBCN ceramics was investigated by a model X'Pert MPD Pro X-ray diffractometer under the following conditions (i.e., Cu as an anodic target, Kα-rays as a radiation source, voltage and current of 40 kV and 40 mA, respectively, and scanning range (2θ) of 10° to 90°. The chemical bonding composition of SiBCN ceramics was analyzed by a model ESCALAB250XI X-ray electron spectrometer. The microstructure of SiBCN ceramics was determined by a model Apreo S HiVac scanning electron microscope with a model TalosF200X transmission electron microscope. The electromagnetic parameters of the ceramics were examined by a model E5071C vector network analyzer.Results and discussion ZrCl4 reacts with the Si—H bond/N—H bond of PBSZ, and atom Zr replaces atom H to generate Si—Zr and N—Zr bonds. The addition of Zr inhibits the formation of SiC nanocrystals inside the ceramics, increases the generation of Si3N4 inside the ceramics, and increases the size of graphitic carbon inside the ceramics from 1.50 nm to 1.77 nm and 1.82 nm. SiZrBCN ceramics with Zr addition of 5% have the superior electromagnetic wave absorption performance, and the RLmin of SiZrBCN ceramics reach -21.8 dB at 7.8 GHz when the thickness is 2.5 mm.Conclusions 1) During the precursor synthesis, ZrCl4 reacted with Si—H bond/N—H bond of PBSZ, and Zr replaced H atoms to generate Si—Zr and N-Zr bonds, which grafted Zr onto the active sites of PBSZ.2) After the ceramic precursor was heat-treated at 1 600 ℃, the crystals of Zr2CN, SiC, Si3N4 and graphitic carbon were generated in-situ inside the ceramic, in which the addition of Zr suppressed the formation of SiC nanocrystals, increased the generation of Si3N4 inside the ceramic, and improved the impedance matching of the substrate. The presence of Zr promoted the generation of graphitic carbon inside the ceramic, and caused the in-plane crystallization of the graphitic carbon size increasing from 1.50 nm to 1.77 nm and 1.82 nm.3) SiZrBCN ceramics with 5% Zr addition had the optimum electromagnetic wave absorption performance due to the large number of dielectric crystals generated inside the ceramics and the good impedance matching performance. The RLmin of the SiZrBCN ceramics reached -21.8 dB at 7.8 GHz when the thickness was 2.5 mm. The generation of a variety of dielectric crystals could improve the absorption performance of the material. The crystals could improve the electromagnetic wave absorption ability of the material, indicating that SiZrBCN ceramics could be used as an effective candidate in the field of wave-absorbing materials.

Introduction Lead zirconate titanate (PZT) piezoelectric ceramics are widely used in electronic components. With the continuous development of intelligent, integrated and lightweight piezoelectric devices, the shape and structure of piezoelectric ceramic components become more complex. 3D printing technology has potential advantages in the personalized manufacturing of complex ceramic parts, especially the fused deposition modeling (FDM) method, which has the advantages of high efficiency, low cost, and wide material adaptability. This paper was to prepare PZT piezoelectric ceramics by FDM. In addition, the process optimization, printing performance, sintering behavior, and electrical properties were also investigated.Methods A PZT powder with an average particle size of 2.85 μm was used. An organic binder was composed of 58% paraffin wax (PW, purity: 99% in mass fraction, the same below), 5% stearic acid (SA, 98%), 20% Polyethylene (PE, 99%), and 17% ethylene-vinyl acetate copolymer (EVA, 98%). The ceramic powder and organic binder were thoroughly mixed by a double-roller mixing machine at 130 ℃ for 60 min, and then crushed into granules of less than 5 mm. The solid loading of the feedstock was set to 83%, 85%, 87%, and 89%. A commercial extrusion printer (UP-R200, Shenzhen Uprise 3D Technology Co., Ltd., China) with the extrusion nozzle diameter of 0.5 mm, and the layer thickness of 0.2 mm for FDM was used in this study. The printing condition was printing temperature of 120 ℃, print speed of 40 mm/s, and printing platform temperature of 85 ℃. Some complex shaped parts like ring array, rectangular array, and thin-walled cylindrical structures were printed. The printed green bodies were firstly placed in kerosene for solvent debinding at 40 ℃ for 20 h and then dried in an oven at 40 ℃ for 15 h. The dried parts were heated at 600 ℃ for 2 h. After thermal debinding, the samples were put into a crucible with a lid, buried on PZT powder, and sintered in the furnace at 1 100 ℃ for 2 h. The PZT ceramics coated with silver electrodes were polarized in an electric field of 2.5 kV/mm in silicone oil at 120 ℃ for 20 min. The phase composition and structure of the sample were determined by a model D8 Advance X-ray diffractometer (XRD, Germany) with detect angles ranging from 10° to 80°. The rheological properties of the printing consumables were tested at 180 ℃ by a model Rosand RH2000 capillary rheometer (Malvern Co., UK). The microstructures of samples were analyzed by a model JSM-6700F field emission scanning electron microscope (SEM, JEOL Co., Japan). The density of the samples was measured by a drainage method. The dielectric constant εr and dielectric loss δ were measured by a model Agilent-4294A impedance analyzer (USA). The ferroelectric properties were analyzed by a model aix ACCT-TF Analyzer 2000 ferroelectric tester (Germany). The piezoelectric constant of the polarized sample was measured by a model ZJ-3AN quasi-static d33 meter (Institute of Acoustics, Chinese Academy of Sciences, China).Results and discussion At a constant solid loading, the shear viscosity of the feedstock at 180 ℃ decreases with the increase of shear rate, and has obvious shear thinning characteristics, which is beneficial to the extrusion process. At a constant shear rate, the higher the solid loading is, the higher the measured shear viscosity will be. At a shear rate of 100 s-1, the shear viscosity is 30.30, 45.07, 47.08 Pa·s and 655.21 Pa·s respectively as the solid loading increases. Annular arrays with a wall thickness of 1 mm, rectangular arrays with an element spacing of 0.25 mm, and annular thin-wall blank samples with an inclination angle of 30° are printed, indicating that the prepared feedstock has a good printing performance. The SEM images show that the prepared PZT ceramic samples have a good interlayer bonding. Each layer is straight, uniform and continuous. After debinding and sintering, the interior of the material is uniform and dense without obvious pore defects, which shows that PZT ceramics with a good interlayer bonding can be obtained by the FDM method. The density of both green body and sintered body increases with the increase of solid loading, and the density of sintered body increases from 7.55 g/cm3 to 7.84 g/cm3. The results show that the sintering shrinkage in the Z direction is higher than that in the X-Y direction. The SEM images of PZT samples at each stage show that the two-step debinding process of solvent debinding + thermal debinding is beneficial to eliminating organic binders without causing defects. PZT piezoelectric ceramic sheets with a diameter of 17.5 mm and a thickness of 1.35 mm are prepared using a feedstock with a solid loading of 87%. The electrical property analysis indicates that the Curie temperature reaches 295℃, the coercive electric field E is 7.57 kV/cm, the remnant polarization Pr reaches 3.66 μC/cm2, and the piezoelectric constant d33 reaches 316 pC/N.Conclusions The prepared feedstock with a high solid content and a low viscosity exhibited a typical shear thinning rheology and an excellent printing performance. A PZT spherical shell structure without support was prepared. The PZT ceramic samples had good interlayer bonding and no interlayer cracks. The density of PZT ceramics increased with increasing the solid loading. At a solid loading of 87%, the density of PZT ceramic reached 7.82 g/cm3, and the piezoelectric constant d33 was 316 pC/N. This study provided an effective approach for the preparation of complex structure PZT piezoelectric ceramics.

Introduction Piezoelectric ceramics for the exchange of mechanical energy and electric energy are widely used in the production of piezoelectric sensors, piezoelectric energy harvesters, piezoelectric transducers and other functional devices. Among the piezoelectric ceramics, Pb(Zr, Ti)O3 (PZT) based perovskite piezoelectric ceramic with high piezoelectric properties is popular. However, the serious thermal depolarization behavior of PZT at a high temperature makes it difficult to meet the application requirements of high-temperature piezoelectric applications in aerospace, nuclear industry and other fields. The Curie temperature of BiScO3-PbTiO3 (BS-PT) perovskite piezoelectric ceramic, located at the morphotropic phase boundary (MPB), is nearly 100 ℃ higher than that of PZT-based piezoelectric ceramics when their piezoelectric coefficient (d33) values are similar. Therefore, BS-PT piezoelectric system is considered as a matrix with a great potential for high-temperature piezoelectric applications. Obtaining BS-PT-based high-temperature piezoelectric ceramics with both high temperature (d33) and high thermal depolarization temperature (Td) remains a key challenge. For perovskite-type piezoelectric ceramics, the Curie temperature is like-inversely proportional to the tolerance factor, and ferroelectric active ions are usually attributed to promoting the polarization coupling. These indicate that introducing the small tolerance factor and ferroelectric active ions into BS-PT matrix could break through the bottleneck above. In this paper, Bi(Zn2/3Nb1/3)O3 (BZN), with ferroelectric active Bi/Zn ions and a tolerance factor similar to BS was introduced into BS-PT matrix, and the related microstructure, electrical properties and their correlation mechanism were investigated.Materials and method For the preparation of BS-xPT-BZN (0.60≤x≤0.63) piezoelectric ceramics by a high-temperature solid-state reaction method, the raw materials were mixed and ground in a ball mill, and then sintered at 850 ℃ for 2 h. Afterwards, the sintered materials were pressed, and further sintered at 1 140 ℃ for 2 h. The BS-xPT-BZN piezoelectric ceramic with silver electrodes was placed in a silicone oil bath at 120 ℃ and loaded in a DC electric field of 50 kV/cm for 30 min for artificial polarization. The phase composition, grain morphology, ferroelectric, piezoelectric and dielectric properties of the BS-xPT-BZN ceramics were characterized by a model D8-Advance type X-ray diffractometer, a model Sigma-300 type field emission scanning electron microscope, a model ZJ-6A type quasi-static d33 meter, and a model TZDM-RT-1000 high-temperature dielectric temperature spectrum test system.Results and discussion All the BS-xPT-BZN ceramic samples have a dense microstructure, and the average grain sizes are 2.29-3.91 μm. Meanwhile, the BS-xPT-BZN piezoelectric ceramics sintered have a perovskite phase structure. The tetragonal phase content gradually increases and all the ceramic samples maintain the characteristics of two phases coexist as the PT content increases. As a result, the composition with a high Curie temperature and located at the morphotropic phase boundary (MPB) is obtained. Among all the compositions studied, the ceramic sample with x of 0.62 has a maximum room temperature d33 value, and thus is considered as MPB composition. This is because the maximum d33 value is usually obtained in the MPB composition with a flatter Gibbs free energy profile. In addition, the Curie temperature of the MPB is as high as 438 ℃, which is conducive to the acquisition of Td and high-temperature application. Also, the in-situ variable temperature d33 test results show that the depolarization temperature of MPB sample with x of 0.62 is up to 409 ℃ and accompanied by a large high temperature d33 (709 pC·N-1), which is much better than that of reported Pb-based perovskite piezoelectric ceramics. The excellent high-temperature piezoelectric performance is due to the vertical MPB phase boundary characteristics of BS-PT matrix itself, and the increase of tetragonal phase content of BS-PT matrix results from the introduction of BZN, which has a small tolerance factor and contains ferroelectric active ions. This study demonstrates that BS-xPT-BZN piezoelectric ceramics are advanced high-temperature piezoelectric materials suitable for electromechanical applications at elevated temperatures.Conclusions BS-xPT-BZN (0.60≤x≤0.63) ternary system high-temperature piezoelectric ceramics were prepared by a high-temperature solid-phase reaction method. The results showed that the ceramic samples had a good grain development and compact structure. The ceramics with x of 0.62 located at the morphotropic phase boundary had the optimal comprehensive high-temperature performance (i.e., the Curie temperature TC of 438 ℃, thermal depolarization temperature Td of 409 ℃, and the maximum in-situ high-temperature quasi-static piezoelectric coefficient d33 of 709 pC·N-1). The excellent high temperature piezoelectric properties could be mainly related to the MPB characteristics that maintained multi-phase coexistence in a wide temperature region. The large high-temperature piezoelectric properties and high thermal depolarization temperature indicate that BS-xPT-BZN piezoelectric ceramics could be a promising candidate for the preparation of advanced high-temperature piezoelectric devices.

Introduction In recent years, 5G communication and smart devices become popular, but the electromagnetic pollution that they produce affects human-being health and the normal operation of electronic devices. Therefore, electromagnetic wave strong attenuation materials have attracted much attention, especially polymer-derived ceramics (PDCs) due to their tunable microstructure and superior high-temperature performance. The amorphous structure of the ceramics has a high-temperature stability, but the dielectric constants are low, making them weak to electromagnetic wave dissipation. To address this problem, catalysts for increasing heat treatment temperature or direct addition of high conductive loss phases (CNTs, RGO, etc.) are usually used to improve the attenuation ability of the ceramics to electromagnetic waves. Rare-earth element metals can modulate the electronic energy band structure of the materials due to the presence of empty d-orbitals, thus modulating their optical, electrical, and magnetic properties. In this paper, the effect of samarium doping on the microstructure and dielectric properties of SiBCN ceramics was thus investigated via introducing the transition metal Sm into polyborosilazane as a catalyst.Methods Based on the 'Schlenk' technology, 20 mL THF, 21 mL DCMVS and 24 mL borane dimethyl sulfide complex were slowly added to a reaction bottle in an ice bath, and the reaction was carried out in argon atmosphere for 24 h to obtain dichlorodimethylsilylethylborane (TDSB). Afterwards, 11 mL DCMS and 72 mL HMDZ were stirred in a three-neck flask at room temperature for 24 h. The reaction bottle was heated at 110 ℃ for 4 h to remove THF, trichloromethylsilane and other by-products, and was further heated at 170 ℃ for 3 h. After three cycles of filtration, a yellow viscous precursor was obtained. To obtain Sm-containing polyborosilazane, PBSZ was weighed and dissolved in THF before SmCl3 dissolving in DMF was added. The precursors without and with different SmCl3 mass fractions of 0, 1% and 3% were named as samples PS0, PS1 and PS3. The PBSZ was slowly heated in a tube furnace (TL1700, Nanjing Boyuntong Co., Ltd., China), in argon atmosphere at 180 ℃ for 1 h, and then further heated at 400 ℃ for 3 h to obtain a cured PBSZ. The cured PBSZ was ground and cold-pressed into φ20×2 mm wafers at 80 MPa. SiBCN ceramics were acquired via heating the wafers in argon atmosphere at 1 000 ℃ for 1 h in, and then further heated at 1 600 ℃ for 2 h. The physical phase composition of the ceramics was determined by a model X'Pert MPD Pro X-ray diffractometer (XRD, The Netherlands) with Cu target at a tube voltage of 40 kV and a tube current of 30 mA. The elemental species, atomic valence states, and binding states of SiBCN ceramics were analyzed by a model AXIS SUPRA+ X-ray photoelectron spectroscope (XPS, Shimadzu Co., Japan). The microstructure and morphology were determined by a FEI NOVA 400 scanning electron microscope (SEM, USA). The microstructure and distribution pattern of the ceramics were characterized by a model JEM-F200 transmission electron microscope (TEM, Japan). The oxidation resistance of SiBCN ceramics was determined by a model STA 449F3 thermogravimetric analyzer (TG, Netzsch Co., Germany) in air at a heating rate of 10 ℃/min. The electromagnetic parameters of the ceramics were determined by a model Keysight E5071C vector network analyzer (Malaysia).Results and discussion Sm doping promotes the increase of dielectric crystals such as SiC and SiCN in the ceramics. This is due to the better promotion of polymer ceramic crystallization by transition metals. The optimum oxidation resistance of the ceramics is obtained at Sm doping of 1%. The BN phase generates a great mass of B2O3 during high temperature oxidation due to the massive crystals generated, which is closer to the oxidative weight loss of free carbon. Also, B2O3 forms a liquid-phase protective layer that covers the ceramic surface and prevents a further diffusion of air into the interior of the material, improving the material antioxidant properties.The superior impedance matching is obtained and the absorption performance of the ceramics for electromagnetic waves is enhanced due to the generation of dielectric crystals such as SiC and SiCN. At Sm doping of 1%, the ceramics have the optimum attenuation performance for electromagnetic waves due to the presence of conductivity loss and polarization loss in SiBCN ceramics, and the maximum attenuation constant α. When the thickness is 2 mm, the ceramic achieves the RAmin of -40.00 dB at 17.36 GHz and the effective absorption bandwidth (EAB) of 5.12 GHz.Conclusions The generation of SiC, SiCN and Si3N4 crystals was promoted by Sm doping, and the intensity of diffraction peaks of each crystal phase increased with the increase of Sm doping. The generation of SiC and SiCN dielectric crystals and their heterogeneous interfaces enhanced the attenuation performance of SiBCN ceramics against electromagnetic waves. The RAmin of the ceramics reached -40.00 dB at 17.36 GHz with an EAB of 5.12 GHz at a thickness of 2 mm.

Introduction SiCf/SiC ceramic matrix composites can replace high-temperature alloys in manufacturing high-temperature structural parts of aerospace engines due to their excellent properties. In a gas environment, SiCf/SiC composite materials have a challenge from corrosion by water vapor and oxygen. The specific process of SiCf/SiC corrosion by water vapor-oxygen coupling is not yet clarified. Therefore, investigating its corrosion behavior is of extremely important significance in guiding the protection of SiCf/SiC from corrosion and ensuring the application of high-temperature components.In this paper, the water-oxygen corrosion behavior of SiCf/SiC was simulated via hydrothermal corrosion experiment in water environment and water-oxygen corrosion experiment in water-oxygen coupling environment, respectively. Methods In the hydrothermal corrosion experiment, SiCf/SiC was placed in deionized water in a closed container and kept in an oven at 200 ℃ for 2 450 h. The pressure inside the container was approximately 2 MPa. After the corrosion was completed, the aqueous solution was taken out and dried in an oven at 35 ℃, and the dried powder was characterized. In the water-oxygen corrosion experiment, SiCf/SiC was placed in a closed high-temperature furnace tube, and water vapor-oxygen mixed gas (A volume ratio of 90%:10%) was injected into the furnace tube. The pressure inside the furnace tube was normal pressure, the temperature was maintained at 1 300 ℃ for 50?200 h.The crystal structure of water-oxygen corrosion products was analyzed by X-ray diffraction (XRD, Smart Lab., Japan). The morphology and composition of SiCf/SiC and its corrosion products were determined by scanning electron microscopy (SEM, Zeiss Co., Germany). The Si content in hydrothermal corrosion products dissolved in aqueous solution was measured by inductively coupled plasma (ICP, Leeman Prodigy 7, USA). The electronic states of Si and O in the hydrothermal corrosion products were characterized by X-ray photoelectron spectroscopy (ESCALAB 250Xi, XPS). The thermal stability of hydrothermal corrosion products was analyzed by thermal gravimetric analysis-differential scanning calorimetry (TGA-DSC, Netzsch Co., Germany).Results and discussion Based on the observation of the microstructure, the connected pores of SiCf/SiC composite materials are the entry and exit channels for corrosion media/products. Corrosion products mainly exist in three types of areas, i.e., pores remaining during the precursor impregnation process, lamellar holes produced in the gaps between fiber cloths, and suture holes in the z direction.In a hydrothermal environment at 200 ℃, the corrosion of SiCf/SiC in water is a volume expansion process, the matrix becomes loose, and the pores are filled with corrosion products. After hydrothermal corrosion for 2 450 h, the Si content in the milky white colloid measured is 1 045.4 mg/L. According to the EDS analysis, the O/Si atomic number ratio is 2.9, and the chemical composition is close to H2SiO3 (SiO2?H2O). The comprehensive analysis by XRD (PDF 38-0448) and XPS (O 1s has two chemical states, namely Si—O and Si—O—H) indicates that the milky white product is H2SiO3.In the water-oxygen coupled corrosion environment at 1 300 ℃, the fibers and interface layers of the SiCf/SiC composite material are corroded, and cracks are formed. After corrosion for 200 h, the thickness of the sample expands from 4.85 mm to 6.66 mm, which is increased by 37%. The internal structure of the sample becomes loose, the corrosion intermediate product is H2SiO3, and the final product is cristobalite SiO2.Conclusions This article studied the corrosion process of SiCf/SiC composite materials in hydrothermal (oxygen-free) and water-oxygen coupling environments. The connected pores of SiCf/SiC composite materials were channels for corrosive media/products, which could not be avoided. In an oxygen-free hydrothermal environment at 200 ℃, the corrosion of SiCf/SiC by water was a volume expansion process, forming a milky white product H2SiO3. In a water-oxygen coupled corrosion environment at 1 300 ℃, the SiCf/SiC composite material expanded in volume and formed cracks. The fibers and interface layers were corroded and the structure became loose. The corrosion product was cristobalite SiO2.

Introduction In recent years, heat accumulation occurs with the emergence of the “heat island effect”. The high temperature can affects human living environment, and increases the energy consumption of refrigeration equipment. It is thus necessary to develop color thermal insulation materials with a high near-infrared reflectance. The existing components used for insulation coatings are mostly rare-earth transition metal composite oxides. However, a higher cost of using rare earth materials restricts the large-scale application to some extent. Transition metal high-entropy ceramic inorganic powder can be used as cheap raw materials, which has the advantages of multi-component characteristics (i.e., great component adjustment space, unique entropy effect, and adjustable material properties. However, little work on the use as high reflective pigments has been reported yet. In this paper, high-entropy ceramic carbonate powders were prepared and the color of the powders was innovatively adjusted via changing the transition metal components. In addition, the phase, color and optical reflection properties of the prepared high-entropy ceramic carbonate powders with different element combinations were also analyzed.Methods For the hydrothermal preparation of high-entropy carbonate powders (i.e., (Mg0.2Co0.2Ni0.2Zn0.2Cu0.2)CO3, (Mg0.2Co0.2Ni0.2Zn0.2Fe0.2)CO3, and (Mg0.2Co0.2Ni0.2Zn0.2Mn0.2)CO3), pure MgSO4, CoSO4, NiSO4, ZnSO4, FeSO4, MnSO4, CuSO4 and Na2CO3 were used as raw materials according to a stoichiometric coefficient ratio. Firstly, a certain proportion of five metal sulfate solids was mixed with deionized water in a beaker under stirring until fully dissolved. The sulfate solution was put into a sodium carbonate solution, and mixed under stirring. Afterwards, the mixture in a high-pressure reactor with a PTFE lining was heated at 160 ℃ for 12 h for hydrothermal treatment. A high-entropy carbonate powder was obtained after centrifugation, washing, and drying.The phase composition of the powder was determined by a model Empyrean X-ray diffractometer (XRD, PANalytical Co., The Netherlands). The microstructure of the powder was analyzed by a model SUPRA 55 field emission scanning electron microscope (FESEM, Carl Zeiss Co., Germany). The UV visible near-infrared diffuse reflectance of the powder was characterized by a model LAMBDA 750 ultraviolet-visible-near infra-red spectrometer (UV-VIS-NIR, PerkinElmer Co., USA). The near-infrared solar reflectance R* in the wavelength range of 780-2 500 nm was calculated according to the national standard ASTMG159-98. The L*a*b* color parameters of the powder were determined by a model CS-5960GX spectrophotometer.Results and discussion Three types of five-component equimolar high-entropy carbonate solid solutions were prepared by a hydrothermal method. Based on the morphology characterizations, three high-entropy carbonates synthesized have the same crystal structure and the same spatial group as R3c. The diffraction peak gradually shifts towards a lower diffraction angle with the order of the components Cu, Fe, and Mn. This is because the radius of the element ions gradually increases, resulting in a corresponding increase in the crystal plane spacing. Moreover, there are significant differences in the morphology characteristics of three high-entropy carbonates, which are the result of the multiple effects of factors such as the number of extranuclear electrons, the Jahn Teller distortion, magnetism, and bond length of Cu, Fe, and Mn ions. The Jahn Teller distortion and para-magnetism of Cu lead to the formation of irregular spherical particles with surface density and particle aggregation in the MgCoNiZnCu carbonate solid solution. The ferromagnetism of Fe causes MgCoNiZnFe carbonate solid solution to form the spheres with dense and regular surface morphology. The combination of ion bonding bond length and antiferromagnetism of Mn results in the formation of loose aggregates of MgCoNiZnMn carbonate solid solutions. In addition, the colorimetric characterization indicates that the color of three high-entropy powders is different (i.e., grayish green for MgCoNiZnCu, orange red for MgCoNiZnFe, and light purple for MgCoNiZnMn). The band gap value Eg gradually increases with the order of the component Fe, Cu, and Mn, and the absorption wavelength of the sample gradually decreases (i.e., the absorption wavelengths are 497.14, 393.99 nm and 242.71 nm, respectively), and the absorption edge gradually shifts blue. Three types of high-entropy carbonate solid solutions have a high near-infrared solar reflectance in the near-infrared band, with a maximum of 78.64%, which can be used as thermal insulation materials.Conclusions Three high-entropy carbonate powders with different elemental compositions were prepared by a hydrothermal method, and the phase composition, reflectance, and color properties of the synthesized powders were comprehensively investigated. The results showed that changing a single element in the compositions could change the color of the powder (i.e., grayish green for MgCoNiZnCu, orange red for MgCoNiZnFe, and light purple for MgCoNiZnMn), and the color coordinate L*a*b*c* value also changed accordingly. Meanwhile, the bandgap width of the powder gradually increased from 3.11 eV to 3.40 eV and 5.49 eV with the order of the component Fe, Cu, and Mn. The three compositions of high-entropy carbonate powders had three different shades in the visible light region, and a high near-infrared solar reflectance (R*) of 78.64%. Therefore, the high-entropy carbonate powders prepared via changing the component element had the characteristics of stable structure, tunable color, and high near-infrared reflectance, having broad application prospects in architecture, automotive, and chemical engineering.

Introduction Micron-sized SiO2 hollow microspheres were prepared by a hard template encapsulation method and an ethyl acetate etching process with polystyrene (PS) as a template, hexadecyltrimethylammonium bromide (CTAB) as a surface modifier, and tetraethyl orthosilicate (TEOS) as a silicon source, and vertically deposited self-assembled into micron-sized SiO2 hollow microsphere photonic crystals. The effects of TEOS content and etching conditions on the morphology of hollow microspheres, as well as the effect of vertical deposition self-assembly solution concentration on the infrared properties of micrometer sized SiO2 hollow microsphere photonic crystals were investigated. Methods For the preparation of micron-sized PS@SiO2 microspheres, 0.15 g of polystyrene microspheres with the size of 1.5 μm were dissolved in 160 mL of deionized water and 80 mL of anhydrous ethanol. After ultrasonic dispersion, 0.03 g of CTAB was added to modify the surface of the polystyrene template under stirring. After 30 min, 3 mL of 25% ammonia water was added to prepare solution A. 0.2 mL of ethyl orthosilicate was dissolved in 5 mL of anhydrous ethanol to prepare solution B. Solution B was mixed with solution A under stirring at room temperature for 24 h. The reacted solution was filtered and washed with anhydrous ethanol and deionized water for three times. PS@SiO2 material was obtained after drying. For the preparation of micron-sized SiO2 hollow microspheres, 0.5 g of PS@SiO2 microspheres were dispersed in 20 mL of ethyl acetate, and heated at 60 ℃ for 10 min after ultrasonic dispersion. The PS template was etched off by ethyl acetate. Subsequently, the slurry was filtered and washeda with anhydrous ethanol and deionized water for three times to obtain micron-sized SiO2 hollow microspheres.For the preparation of micron-sized SiO2 hollow microsphere photonic crystals, a microsphere suspension was dispersed for a certain time, and then a cleaned hydrophilic glass substrate was vertically immersed into the microsphere suspension, and dried at 60 ℃. As the mixed solvent evaporates, the microspheres self-assemble on the surface of the substrate into a photonic crystal thin film with an opal structure.Results and discussion Micron-sized SiO2 hollow microspheres with a low damage rate, a good dispersibility, and a high sphericity were prepared with PS spheres as a template, CTAB as a surfactant, and TEOS as silicon source. PS template was removed via ethyl acetate etching. At TEOS content of 0.2 mL, PS@SiO2 microspheres are tightly coated, and there are no secondary microspheres. When ethyl acetate is used for etching for 10 min, the hollow SiO2 microspheres with the diameter of 1 570 nm and thickness of 65 nm are prepared. Moreover, micron-sized SiO2 hollow microspheres are self-assembled into photonic crystal materials by a vertical deposition method. As the concentration of self-assembly solution increases, the arrangement of SiO2 hollow microspheres is tightly ordered without obvious vacancies and with a hexagonal periodic structure. The number of layers increases from 6 to 16, and the reflectivity gradually increases. When the solubility of the self-assembled solution is 0.005 g/mL, the maximum reflectivity is 85%.Conclusions The micron-sized SiO2 hollow microspheres with a good dispersion, a high uniformity, a less damage, and a high sphericity were prepared by a template encapsulation method and an ethyl acetate etching process. Also, micron-sized SiO2 hollow microsphere photonic crystals with a good thermal insulation performance, a low density, and a reflectivity of 85% as infrared band hollow microsphere photonic crystals were prepared by a vertical deposition self-assembly method.

Introduction Strontium zirconate titanate is an important dielectric material with a high dielectric constant and a low dielectric loss. Also, as a semiconductor catalytic material, it has an application potential in the fields of photocracking water and photodegradation of organic matter. However, as a semiconductor catalytic material, SrTixZr(1-x)O3 has a wide band gap and a low carrier migration rate. Element substitution is commonly performed via ion doping at the B site (i.e., Ti element site) in the lattice. The resulting lattice defects inhibit photogenerated electron-hole recombination and narrow the band gap, thereby improving the catalytic efficiency. At present, the doping of transition metal elements such as Nb, Co, Rh, Fe and Ce is beneficial to reducing the band gap and promoting its response to visible light. Little studies have been reported to explain the morphology of single crystal particles by theoretical calculations. In this paper, SrTixZr(1-x)O3 single crystal nanoparticles with different Ti/Zr molar ratios were synthesized by a hydrothermal method. The micro-morphology, crystal size and light response characteristics of SrTixZr(1-x)O3 single crystal nanoparticles were investigated. In addition, the micro-morphology of SrTixZr(1-x)O3 single crystal nanoparticles was also revealed based on the first-principles calculation.Methods Strontium chloride hexahydrate (SrCl2·6H2O) and titanium tetrachloride (TiCl4) from Sinopharm Chemical Reagent Co., Ltd., China, were used as raw materials, respectively. Zirconium tetrachloride (ZrCl4) and lithium hydroxide (LiOH) from Shanghai McLean Biochemical Technology Co., Ltd., China, were used as zirconium source and pH regulator. SrTixZr(1-x)O3 nano-single crystal particles with different molar ratios of titanium to zirconium were prepared by a hydrothermal method at 180 ℃ for 12 h.The phase composition, microstructure and element distribution of the samples were determined by X-ray diffractometer and thermal field emission scanning electron microscope with energy dispersive spectrometer. The light response characteristics of the samples were characterized by UV-visible spectrophotometer. Based on the first-principles density functional theory (DFT), 3 kinds of SrTi0.25Zr0.75O3, 6 kinds of SrTi0.5Zr0.5O3 and 3 kinds of SrTi0.75Zr0.25O3 2×2×2 supercell configurations were designed and calculated.Results and discussion SrTixZr(1-x)O3 nano-single crystal exhibits a perovskite structure. The diffraction peak becomes wider when element Zr gradually replaces elemen Ti. SrCO3 as an impurity phase can be removed by calcining at 1 200 ℃. The hydrothermal reaction synthesized SrTiO3 with a cubic phase shows a regular hexahedron morphology. Most of SrZrO3 crystals with an orthorhombic phase are flat octahedron morphology. The particles basically tend to be regular hexahedron morphology when Ti:Zr= 1:3 and 3:1. However, the lattice distortion effect of SrTixZr(1-x)O3 crystal reaches the maximum, and some of the morphologies are star-shaped when Ti:Zr=1:1.The lattice parameters of SrTixZr(1-x)O3 unit cell configuration were calculated by first-principles density functional theory. In SrTi0.5Zr0.5O3 system, the configurations (iv), (viii) and (ix) are transformed into orthorhombic crystals, and the maximum lattice constant c reaches 9.5 ?. The ground state energies of configurations (iii), (v) and (xii) are 2.538, 1.530 eV and 0.949 eV, respectively. Based on the principle of energy minimization, the crystal grows preferentially according to these configurations. Thus, SrTixZr(1-x)O3 (x=0.25, 0.75) grains exhibit a uniform hexahedral morphology. The octahedral dip angle, bond lengths and angles of four configurations (iii), (v), (ix) and (vii) are selected to analyze the symmetry change and lattice distortion of the crystals. The octahedral bond angles are more than 179.9° in the three lowest ground state energy configurations, which maintain a structural symmetry. However, Ti(Zr)O6 octahedron tilt angles of the configuration (ix) are mainly concentrated at 145°-153°. The Ti(Zr)—O bond lengths are distributed in the range of 1.711-2.926 ?. This indicates that equimolar Ti/Zr causes the lattice distortion due to the change of bond length and angle. The lattice distortion promotes the formation of star-like morphology. The light response characteristics show that the band gap of SrTixZr(1-x)O3 nano-single crystal particles decreases with the increase of Ti4+ proportion. The band gaps of SrTi0.25Zr0.75O3, SrTi0.5Zr0.5O3 and SrTi0.75Zr0.25O3 are 3.70, 3.47 eV and 3.34 eV, respectively, which are consistent with those obtained via the first-principles calculations.Conclusions Perovskite structure SrTixZr(1-x)O3 nano-single crystal particles with different Ti/Zr molar ratios were synthesized by a hydrothermal method. SrTi0.25Zr0.75O3 and SrTi0.75Zr0.25O3 both were transformed into a hexahedral morphology. A special star-shaped polyhedron morphology appeared in SrTi0.5Zr0.5O3 sample. The lattice parameters and energy band structure of SrTixZr(1-x)O3 were obtained via the first-principles calculations. The lattice distortion effect appeared as Ti/Zr=1. There were lattice parameters of three configurations in the supercell lattice arrangement are a=b≠c, where c can be up to 9.570 ?. The actual crystal growth process of the SrTi0.5Zr0.5O3 system was partially carried out according to these arrangements. The heterogeneous nucleation mechanism was induced by different crystal configurations and the lattice distortion, which promoted the formation of star-shaped grains. The band gap change rule of the samples was verified by ultraviolet-visible spectrophotometer. The increase of element Ti ratio led to the decrease of the band gap since the energy level of Ti 3d orbital was lower than that of Zr 4d orbital.

Introduction Na-ion batteries (NIBs) have a great potential as next-generation large-scale energy storage devices. Among various cathode materials for NIBs, P2-type layered transition metal oxides have attracted much attention because of their excellent kinetics and easy processability. In P2-type layered oxides, Na ion occupies two different sites, i.e., Nae and Naf. The triangular prism polyhedron of Naf site shares faces with two TmO6 octahedrons, while Nae shares edges with six TmO6. The migration behavior of Na ions at different positions is diverse due to the distinction of distance and electrostatic force between Na+?Tmn+. The migration of Na ions at Nae site has a lower migration energy barrier, compared to that of Naf position. Namely, more Na ions at Nae site and increasing the occupation ratio of Nae/Naf can effectively improve the electrochemical performance of P2 layered oxides. Previous research indicates that the ratio of Na ions at different sites can be modulated by introducing inactive ions to transition metal layers. However, the introduction inevitably results in the capacity sacrifice. The ration of Nae/Naf is mainly affected by two aspects, i.e., the interaction between Tmn+ and Na+, and the interaction between Na+ and Na+. In the case with the same transition metal component, the design of Na content is expected to achieve the regulation of Nae/Naf ratio, mainly from the following three reasons: 1) Na content affects the valence state of transition metals, and thus modulates the interaction between Tmn+ and Na+; 2) Na content changes the Na interlayer distance, and then affects the distance between Na+ and Tmn+ and the corresponding interaction between Na+ and Tmn+; and 3) Na content regulates the distance between Na+ and Na+. In this paper, we proposed a novel strategy to optimize the Nae/Naf occupancy ratio with the same transition metal composition via adjusting Na content in the material. This strategy could open up new opportunities to design high-performance cathode materials for NIBs.Methods NaxNi0.1Mn0.9O2 (x = 0.45, 0.55, and 0.65, denoted as Na45, Na55, Na65) were prepared by a simple high-temperature solid-phase method. The precursors were Na2CO3, NiO and Mn2O3 and weighed according to a required stoichiometry ratio with a 5% excess of Na2CO3. After grinding, they were heatd in an alumina crucible in a muffle furnace at an elevated rate of 5 ℃/min up to 950 ℃. After heated at 950 ℃ for 15 h, the powdered materials were obtained by natural cooling and finally transferred to an argon-filled glove box. The working electrodes were prepared via spreading the slurry of active materials, acetylene black and polyvinylidene difluoride with a mass percent of 75:15:10 on Al foil. After drying in vacuum at 80 ℃ for 12 h, the electrodes were transferred to an argon-filled glove box and assembled into CR2032-type button cells. The counter electrode was metal sodium, the separator was a glass fiber, and the electrolyte was 1 M NaClO4 in propylene carbonate (PC) solution with 5% fluoroethylene carbonate (FEC) additive.Results and discussion The effect of Na content on the occupancy ratio of Nae/Naf positions and the corresponding evolution of structure and electrochemical properties was investigated. All the Nax compounds have a hexagonal P2 structure with P63/mmc space group. According to the XRD refinement and eletrochemical results, Na55 material has the maximum Nae/Naf occupancy ratio and specific discharge capacity, mainly originating from the better mobility of Na ions at Nae sites. Na55 exhibits a prominent capacity of 174.5 mAh·g?1 at 0.2 C, which is much higher than that of Na45 and Na65. Benefited from the optimized Nae/Naf ration, Na55 displays 10-10?10-12 cm2·s-1 of Na+ diffusion coefficient, which is much higher than 10-12?10-14 cm2·s-1 of the usual transition metal layered oxides cathodes. Also, Na55 exhibits an excellent rate performance with a capacity of 83.6 mAh·g?1 at 10 C rate, and a great cycling stability with a 92.95% capacity retention after 200 cycles. Conclusions Nae/Naf occupancy ratio of P2-type layered oxides was modulated by an extremely simple strategy for Na content optimization. The combined results of XRD refinement, electrochemical curve, transmission electron microscopy, cyclic voltammogram, ex-situ XRD and X-ray photoelectron spectroscopy showed that a higher Nae/Naf ratio in Na55 materials effectively enhanced the Na+ diffusion rate, consequently resulting in a high specific capacity (174.5 mAh·g?1 at 0.2 C), an outstanding kinetic performance (87 mAh·g?1 at 10 C) with an excellent cycling performance (92.95% capacity retention after 200 cycles). Compared to conventional P2 materials with common Na content, Na55 had a smaller volume change without any phase transition during electrochemical process. The simple and effective strategy could offer an insight into the rational design of high-performance layered cathode materials and also enhance the practical application of NIBs.

Introduction Two-dimensional transition metal dichalcogenides (TMDCs) have attracted much attention due to their unique “sandwich” structure. As a typical two-dimensional layered transition metal sulfide, MoS2 has a layered structure composed of S-Mo-S triple layers with covalent bonds. The atoms in MoS2 layer are combined by covalent bonds, while the interaction between layers depends on the van der Waals forces. This special S—Mo—S layered structure is conductive to the rapid diffusion of lithium ions, and the intercalation of lithium ions between layers during a charging and discharging process does not affect the volume change. However, MoS2 has some problems such as poor conductivity and easy decomposition of the structure, severely hindering the development of MoS2 electrode materials. This paper was to composite a liquid metal (LM) with MoS2 materials. Among them, LM has an excellent ion and electron conductivity, which can improve the conductivity of MoS2. The moderate interlayer distance of MoS2 can restrict LM droplets within the framework, thereby allowing LM to better exert its self-healing properties for the preparation of negative electrode materials with self-healing capabilities.Methods 400 mg of LM was firstly added into 50 mL of N, N-Dimethylformamide (DMF), and then a certain amount of phosphomolybdic acid was added into the LM and DMF under ultrasound. Also, the required thiourea and catalyst NaBH4 were mixed in a beaker in a molar Mo:S ratio of 1.0:2.6. Afterwards, the two solutions were transferred to a polytetrafluoroethylene liner and reacted at 200 ℃ for 24 h. The resulting reaction solutions were washed with deionized water, N, N-Dimethylformamide, and anhydrous ethanol, respectively. Finally, the washed materials were dried in a vacuum drying oven at 70 ℃ for 12 h to obtain the final reaction product. The prepared active material was mixed with acetylene carbon black and polyvinylidene fluoride (PVDF) in a ratio of 8:1:1. The material was fully ground in a ball mill in the presence of an appropriate amount of solvent N-Methyl-2-pyrrolidone (NMP) to obtain a uniformly mixed slurry. The slurry was evenly coated on a copper foil and dried in a vacuum at 70 ℃ for 12 h. The dried material was cut into 12 mm discs with a slicer as a battery negative electrode, and it was assembled into a CR2016 button battery in a glove box filled with argon. Among them, the metal lithium sheet was a counter electrode, the polypropylene porous membrane (Celgard2400) was a separator, the electrolyte solute was 1 mol·L-1 LiPF6, the solvent was a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a ratio of 1:1:1, and the foam nickel was a gasket.Results and discussion The results show that the liquid metal effectively combines with MoS2 via electrostatic adsorption and coordination bonds to form a stable composite structure. In addition, the composite material has a higher deformability and a chemical stability, promoting the repair of the crack surface of the electrode material, reducing the internal redox reaction, and improving the cycle stability of the lithium-ion battery. When a mass ratio of LM:MoS2 is 2:1, the composite material shows the optimum performance. At a current density of 0.1 A·g-1, after 100 cycles, the specific capacity of the composite material is stable at 656.1 mA·h·g-1, the capacity retention rate reaches 74.3%, effectively improving the cycle stability of the electrode material.Conclusions A lithium-ion battery negative electrode material LM@MoS2 with self-healing characteristics was prepared by a hydrothermal method. The cracks generated in the electrode during the charging and discharging process were repaired via utilizing the fluidity and high surface tension of liquid metal, effectively improving the cycle life of the electrode material. The optimum cycle stability of the electrode was obtained at a mass ratio of LM:MoS2 of 2:1. The LM@MoS2 prepared could reduce the internal redox reaction of the battery, thereby improving the electrochemical performance of the battery in the process of repeated insertion and extraction of lithium ions, reducing mechanical fractures, and improving the electrochemical performance of the battery.

Introduction As a positive material with a low cost, a high energy density and a good power performance, spinel lithium manganese nickel oxide (LiNi0.5Mn1.5O4) has attracted much attention in the industry of lithium ion battery. Reducing the surface oxygen release behavior and the resolution of Ni or Mn during charging and discharging is a main method to improve the electrochemical performance. The conventional coating technique is to construct a coating layer on the surface of the material particles, which can isolate the electrolyte and reduce side reactions at the interface. Since the solid-phase coating method cannot form the uniform and compact coating layer, the improvement of the electrochemical performance is limited. In this paper, a precursor with Li3PO4 layer that was produced by a wet coating method was sintered at 850 ℃. In addition, the impact of coating method was also analyzed by the first-principles calculation and characterizations.Methods According to a molar ratio of LiNi0.5Mn1.5O4, a certain amount of Ni0.25Mn0.75(OH)2 precursor and Li2CO3 were weighed and mixed. The mixed material was ground in a mortar evenly. Afterwards, the ground material was sintered in a muffle furnace at 950 ℃ for 10 h, finally obtaining a LNMO positive electrode material (i.e., sample P0) after cooling in the furnace.According to the designed coating amount of 3% Li3PO4, NH4H2PO4 and LiOH·H2O were weighed and sequentially added to alcohol solution with LNMO particles. After stirring and evaporation, the collected products were sintered in a muffle furnace to obtain conventional coating LNMO@Li3PO4 material (i.e., sample P1).Also, Ni0.25Mn0.75(OH)2 precursor was mixed with deionized water in a mass ratio of 1:5. LiOH·H2O was added to the coating at 3% under stirring until fully dissolved. Also, NH4H2PO4 was added in another beaker and mixed with deionized water in a mass ratio of 1:20 until fully dissolved. The above two solutions were mixed thoroughly and filtered. The obtained filtered product was dried in a blast drying oven at 90 ℃for 24 h to obtain Ni0.25Mn0.75(OH)2 precursor pre-coated with Li3PO4. Li2CO3 in a ratio of Li:(Ni+Mn) of 1:2 was mixed evenly with the pre-coated precursor, and heated in a furnace at 950 ℃ for 10 h to obtain a wet coated LNMO cathode material with Li3PO4 after cooling (i.e., sample P2).The morphologies and structures of the cathode materials were examined by a model S-4800 scanning electron microscope (SEM, Hitachi Co., Japan) a model F20 aberration-corrected transmission electron microscope (TEM) with a cold field emission gun at 200 kV (TECNAI), and a model Panalytical X’Pert X-ray diffractometer (XRD) in the 2θ range of 10°-75° with Cu Kα radiation (λ=1.540 5 ?). The compositions of TMs in materials were measured by a model IRIS IntrepidⅡinductively coupled plasma atomic emission spectroscope (ICP-AES, XSP). Density functional theory (DFT) calculations were carried out through a named Vienna ab initio package (VASP), in which the cut-off energy was set to 520 eV for an accurate test, and the projector augmented wave (PAW) was used to describe the interaction between ions and electrons. For the optimization of crystal structures, the exchange correlation function was used as the Perdew-BurkesEmzerhof (PBE) form of generalized gradient approximation (GGA). The lattice vector and the atomic position were sufficiently optimized until the resultant force was less than 0.01 eV/(?·atom-1). The Brillouin zone was adopted with a 4×4×4 k-mesh. Each material was mixed with carbon black and polyvinylidene fluoride binder in N-methyl-2-pyrrolidone with a mass ratio of 90:5:5 to prepare the electrode slurry. Subsequently, the slurry was casted on the Al foil and dried in vacuum at 100 ℃. Pouch cells were assembled with graphite as an anode, and 1 mol/L LiPF6 solution in EC/EMC/DEC (3:5:2 by volume) as an electrolyte. Pouch cells were tested at 3.50-4.95 V and 0.1 C (1 C=150 mA·h·g-1) for the first cycle on a model Maccor S4000 battery testing system. The cycling performance, EIS, and rate capability at 25 ℃ were tested at 3.5-4.9 V.Results and discussion Based on the powder XRD patterns of samples P0, P1, and P2, all the samples have a typical spinel structure, since the Li3PO4 coating layer has no impact on the LNMO’s crystal structure. The SEM images of samples reveal that the coating process has a slight effect on the surface appearance and particle size distribution. Based on the TEM and SEM-EDS analysis, the coating layer of sample P2 has higher homogeneity than that of sample P1, which can provide a better protective effect and reduce the corrosion of the electrolyte. According to the cycling data, the capacity retention is 90.47%, which is obvious improvement from sample P0 after running 300 cycles, and the superior cycling performance indicates an outstanding structural stability of sample P2, which can be proved by the Mn dissolution data. The capacity retention of 92.45% at 2C discharging can verify that sample P2 has a uniform coating layer. As a result, the precursor pre-coating Li3PO4 technique affects the phase structure and morphology of spinel LNMO slightly, and improves the electrical properties effectively. Conclusions The main phase structure and micromorphology of spinel LNMO remained unchanged after Li3PO4 coating, and the characteristic peak of Li3PO4 appeared. The rate discharging and cycling performance was significantly improved, and the charge transfer impedance was reduced by Li3PO4 layer. This study indicated that precursor pre-coating Li3PO4 technique could be an effective approach to reduce the dissolution of transition metal and could be thus a potential method to improve the electrochemical performance of lithium manganese nickel oxide.

Introduction The rapid development of radar and radio communication technology plays a critical role in enhancing the competitiveness of national defense, while subsequent electromagnetic interference seriously threatens the stealth and information security of military equipment. Consequently, electromagnetic wave absorption (EWA) materials that can eliminate or reduce electromagnetic waves by converting electromagnetic energy into thermal energy or other energy through their own electromagnetic loss mechanism have attracted much attention. Nevertheless, the development of EWA materials is still a challenge to simultaneously satisfy efficient microwave absorption and excellent anticorrosive performance in the case of the complex and changeable marine military environment. Reduced graphene oxide (rGO) with a unique sheet structure, a great chemical stability and a high electrical conductivity can extend the diffusion path of corrosive media and provide conductive loss, which is an excellent candidate for anticorrosion and wave absorption material. To improve the environmental adaptability of EWA materials for practical applications, constructing nanocomposites via combining rGO and MOFs derivatives is an effective strategy to achieve significant EWA and anticorrosion properties. In this paper, metal nanoparticle uniformly loaded carbon skeleton-rGO composites were prepared with MOFs as precursors to improve the impedance matching and EWA performance via utilizing the synergistic effect of magnetic nanoparticles and dielectric rGO. In addition, a theoretical and experimental reference for the development of new multifunctional materials with a high-efficiency electromagnetic wave absorption and an anticorrosion performance was also provided. Methods For the preparation of Ni/Zn/NC@rGO nanocomposites, graphene oxide (GO) was prepared by a modified Hummer method. Also, white ZIF-8 precursor powder was obtained via dissolving zinc nitrate in 2-methylimidazole solution in methanol system. Meanwhile, nickel nitrate was dissolved into ZIF-8 precursor powder, and GO with different mass ratios of nickel nitrate was added. Finally, the obtained powder was treated at a high temperature to obtain Ni/Zn/NC@rGO nanocomposites. The composition of Ni/Zn/NC@rGO nanocomposites was determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The magnetic properties of the composites were measured via hysteresis curves. The microstructures of the nanocomposites were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic parameters of Ni/Zn/NC@rGO nanocomposites were examined by a vector network analyzer. The dynamic potential polarization of bare carbon steel, carbon steel coated with pure epoxy resin coating, carbon steel coated with 3% (in mass fraction) doped Ni/Zn/NC epoxy resin (Ni/Zn/NC/EP), and carbon steel coated with 3% doped Ni/Zn/NC@rGO epoxy resin (Ni/Zn/NC@rGO/EP) were analyzed by an electrochemical workstation for three times to ensure the accuracy of the results.Results and discussion The XRD patterns of Ni/Zn/NC and Ni/Zn/NC@rGO nanocomposites show a crystalline facet C(002) of rGO as well as crystalline facets (111), (200) and (220) of Ni metal, indicating that Ni2+ is reduced to magnetic Ni monomers at a high temperature. The XPS spectra show that the Ni/Zn/NC@rGO nanocomposites consist of elements C, N, Ni, O and Zn. Ni/Zn/NC@rGO-1:1 nanocomposite has the maximum degree of graphitization and more structural integrity, possibly due to the promotion of wave absorption and anticorrosion properties. Besides, the SEM and TEM images of Ni/Zn/NC@rGO nanocomposites reveal that the nanocomposites have a large number of pore structures, which allow electromagnetic waves to be dissipated through multiple reflection and scattering. Furthermore, Ni nanoparticles are uniformly dispersed on rGO nanosheets, and the multiple interfaces formed lead to the polarization relaxation phenomenon, which is beneficial for the attenuation of electromagnetic waves through polarization loss.Ni/Zn/NC@rGO-1:1 nanocomposite has the maximum electromagnetic wave storage and attenuation capabilities, which can be attributed to that the interface polarization induced by the rGO multilayer structure and the uniformly dispersed Ni nanoparticles and the rGO sheets, as well as the dipole polarization originated from the defects created by N atoms doping during the pyrolysis process. Moreover, the imaginary part of the complex permittivity of Ni/Zn/NC@rGO-1:1 shows slight fluctuations, indicating that the existence of multiple polarization relaxation processes, which is also confirmed by the Cole-Cole semicircle plots. As a result, Ni/Zn/NC@rGO-1:1 exhibits the optimum EMA performance. The minimum reflection loss value (RLmin) is -63.70 dB with a matching thickness of 1.67 mm, and the effective absorption bandwidth (RL<-10 dB) reaches 5.36 GHz at the thickness of 1.63 mm. The synergistic benefits of magnetic nanoparticles and dielectric rGO optimize the impedance matching characteristics of Ni/Zn/NC@rGO-1:1 sample, while the porous structure and abundant interface polarization effectively improve the attenuation constant of the sample.Compared with carbon steel of other coating samples, Ni/Zn/NC@rGO/EP coating sample possesses a higher corrosion potential and a lower corrosion current, thus showing the most excellent anticorrosion performance. Ni/Zn/NC@rGO nanoparticles fill the micropores of the epoxy resin, which can effectively inhibit the infiltration of corrosive ions. In addition, the unique sheet structure of graphene is also easy to stack and thereby extend the diffusion pathway of corrosive media to achieve the purpose of improving the anticorrosion performance.Conclusions Ni/Zn/NC@rGO nanocomposites derived from MOF were synthetized via co-precipitation and pyrolysis processes., The outstanding impedance matching and microwave attenuation ability was realized via adjusting the mass ratios between the Ni source and GO. At a mass ratio of 1:1, the effective absorption bandwidth and the RLmin values were 5.36 GHz and -63.70 dB with the thicknesses of 1.63 mm and 1.67 mm, respectively, which could be attributed to that the porous structure provide transmission paths for multiple reflections and scattering of electromagnetic waves, as well as multiple interfaces bring more polarization loss. In particular, the graphene layer structure also extended the diffusion path of the corrosive medium, resulting in a higher corrosion potential and a lower corrosion current in Ni/Zn/NC@rGO-doped nanocomposite coatings. This study provides a reference for the development of efficient anticorrosion and EWA materials, which could have a promising application in the field of marine environment.

Introduction Environmental pollution caused by personal care products and synthetic substances become worse. Bisphenol A (BPA) as a type of endocrine disrupting chemical is detected in water, soil, air, urban waste and food. BPA is difficult to be removed from water body due to its strong biological toxicity and environmental persistence, so it is beneficial to designing the related efficient treatments. At present, main methods removing BPA include adsorption, nanofiltration, photochemical oxidation and electrochemical oxidation, in which photocatalytic oxidation technology has received much attention. TiO2 is extensively investigated due to its advantages. Although TiO2 has an excellent photocatalytic performance, it has significant drawbacks, such as low visible light utilization and easy recombination of photo generated carriers. Loading is an effective method to improve photocatalytic capability. In this paper, Fe3+/CDs-TiO2 composite photocatalyst was prepared by a sol-gel method. Methods For the preparation of Fe3+/CDs-TiO2 catalyst, Ti(OBu)4, anhydrous ethanol and acetic acid were mixed under stirring to obtain a transparent solution. CDs and Fe(NO3)3·9H2O were added into the solution under stirring until forming a gel. The gel was heated in an oven at 70 ℃ to obtain yellow particles. The particles were ground into the finer particles and calcined in a muffle furnace at 300 ℃ for 4.5 h, hence obtaining Fe3+/CDs-TiO2. The photocatalytic performance of Fe3+/CDs-TiO2 was analyzed with BPA as a target pollutant. Fe3+/CDs-TiO2 was added into BPA aqueous solution, stirred in a dark environment for 20 min to achieve adsorption equilibrium. The photocatalytic reaction occurred after turning on an Xenon lamp. The concentrations of samples taken at regular intervals were determined by the HPLC method. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet visible diffuse reflection spectroscopy (UV-Vis DRS) and electrochemical method.Results and discussion Compared with TiO2, the absorption spectra of Fe3+/CDs-TiO2 range to visible light zone and photoinduced electrons transfer quickly through interface chemical bonds, indicating that the co-doping of Fe3+/CDs boosts a photocatalytic efficiency. The degradation efficiency of BPA can be 92.8% after 120 min with Fe3+/CDs-TiO2 at a loading ratio of Fe3+/CDs of 0.5% or 1.5%. Fe3+/CDs-TiO2 has a satisfied stable and reusable performance for 86% BPA, which is still degraded after 7 cycles. The photocatalytic degradation process of BPA with Fe3+/CDs-TiO2 follows the first-order kinetic equation, and the reaction rate constant is 0.022 16 min-1. Based on the results of free radical capture experiments, the holes are the dominant species for BPA degradation, and the toxicity of the intermediates decreases, which is simulated by Toxicity Estimation Software Tool (T.E.S.T). The mechanism of Fe3+/CDs-TiO2 photocatalytic degradation of BPA was analyzed based on main degradation substances and dominant intermediates. There is an electron coupling phenomenon between the orbital and the conduction band of TiO2, forming Ti—O—C bonds. Electrons can quickly transfer from the TiO2 conduction band through Ti—O—C bonds at the interface to the surface of the composite catalyst, and react with dissolved oxygen to generate ·O2-. The holes on the valence band can directly react with organic molecules or form hydroxyl radicals, which almost decompose organic molecules. In addition, the photogenerated electrons on the conduction band also reduce the loaded Fe3+ in-situ to Fe2+, which reacts with dissolved oxygen to generate Fe3+and ·O2-. The Fe3+→Fe2+→Fe3+ microcirculation effectively transfers photogenerated electrons.Conclusions The co-modification of Fe3+ and CDs widened the spectral response range of TiO2, and formed interface chemical bonds that provided channels for photoelectron transfer, suppressing carrier recombination and improving photocatalytic efficiency. When the loading amounts of Fe3+ and CDs were 0.5% and 1.5%, respectively, the composite material had the optimum degradation performance. In the presence of visible light, the degradation efficiency of BPA could reach 92.8% after 120 min. After 7 cycles, Fe3+/CDs-TiO2 still performed well and degradation efficiency was 86%. Fe3+/CDs-TiO2 photocatalytic reaction of BPA followed the first-order reaction kinetic equation, with a reaction rate constant of 0.022 16 min-1. According to the results of free radical capture experiments, the holes were the main species for the degradation of BPA, and the toxicity of the photocatalytic degradation products gradually decreased.

Introduction The solubility of Mo in borosilicate glasses is relatively low. Therefore, molybdate is easy to separate from glass, forming Mo-yellow phase (alkali molybdates, such as Na2MoO4, CsLiMoO4, and Li2MoO4) or CaMoO4 crystals. The crystal CaMoO4 performs a superior water resistance ability, which can effectively reduce the Mo leaching rate of a high Mo content and high level waste (HLW) solidification glass. On the contrary, alkali-Mo-yellow phase is highly water-soluble, leading to a serious Mo-leaching, and thus decreases the chemical durability of the products. The duration of the chemical durability test of solidification glass is 7 or 28 days, thus retarding the whole cycle for the investigation of HLW solidification glass. Effective predicting Mo-yellow phase and the Mo leaching rate can accelerate the research via saving time on glass preparation and chemical durability test. Based on the glass structural gene modeling (GSgM), this paper proposed the Structure-Property (S?P) prediction models of chemical durability and the possibility of Mo-phase separation (PS, its value is xPS) for a simulated high Mo content (MoO3 2.6?3.3%) HLW borosilicate solidification glass. The key elements (i.e., Na, Li, B, and Mo) leaching rate rNa, rLi, rB, rMo as well as the Mo-phase separation xPS were predicted by the models. The reliability and practicability of the models were proved. In addition, combined with the Structure-Composition (S?C) modeling, the C?S?P analysis was also carried out for xPS and rMo.Methods Fifteen borosilicate glasses were designed by an one-component-at-a-time (OCAT) method. Glasses with different weights (130 g and 800 g) were prepared for each composition. Small samples with the mass of 130 g were melted and quenched. Large glass samples with the mass of 800 g were melted, and annealed. The properties of the samples were determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) with KBr, differential scanning calorimetry (DSC) and PCT-7 day chemical durability test, respectively. Mo-phase (xPS) was evaluated and scored for each sample by naked eyes (from 0?100%，high score means high probability of Mo-phase separation). The structural data used for modeling were derived from FTIR peak fitting area Ai. Each FTIR spectrum was decomposed into 10 Gaussian bands by a software named GRAMS AI 32 according to the same fitting rules. The S?P and S?C models were constructed by a software named JMP based on the Cornell first-order linear mixture formula. The sample (glass MV) for model validation was also prepared and measured by the same procedure.Results and discussion No Mo-phase appeats in the small samples (130 g), while a serious Mo-phase separation (i.e., yellow phase and white phase) occurs in some large samples (800 g), which can be attributed to the Mo-phase accumulation and the slow cooling rate of large size glasses. The XRD patterns indicate that the main components of Mo-phase are CsLiMoO4 (i.e., water-soluble yellow phase, yellow) and CaMoO4 (i.e., water-resistant crystal, white). The S?P models with satisfied statistical significance (i.e., P<0.0001) and model accuracy (i.e., Rsq≥0.87) are proposed based on the Ai and glass properties. The corresponding prediction formula of the target properties (i.e., Na, Li, B, Mo leaching rate ri, Tg, xPS) are (1) (2) (3) (4) (5) (6)In order to test the reliability of the models, a validation glass (i.e., MV) is designed. The Ai values of MV (130 g, without Mo phase separation) are used to calculate the target properties by formulas (1) to (6), and the predicted values of each property arerB =0.05 g·m2·d1,rLi =0.06 g·m2·d1,rNa =0.04 g·m2·d1,rMo =1.49 g·m2·d1.Tg=524.1℃, xPS=83%. The model prediction results show that MV glass can perform high Mo leaching rate, exceeding the EJ-1186 standard (ri<1 g·m2·d1). The Mo-phase possibility is 83%, indicating that MV glass has heavy Mo-phase separation. The rB, rLi, rNa meets the standard requirement. The large sample MV (800g) is prepared. Large area of MV glass is covered by Mo phase separation, which is scored by 70% by naked eyes, and the rB, rLi, rNa is qualified to EJ-1186. However, the rMo is as high as 0.91 g·m2·d1, which is close to the standard limit. Considering the test error, MV glass is not valuable for further investigation and measurement (such as viscosity, electrical resistance, liquidus temperature, etc.). The measured properties arerB =0.06 g·m2·d1,rLi =0.14 g·m2·d1,rNa =0.15g·m2·d1,rMo =0.91 g·m2·d1.Tg=524.4 ℃, xPS=70%. The S?P models indicate that within the designed glass composition, the Mo phase separation can prevent effectively with the decrease of Si—O—Si vibrations at 518?528 cm1, and the increase of B—O—B bending vibrations in [BO3] units. In order to figure out the components that affect the target structure as well as xPS and rMo, a detailed exploration of the components associated with the structure units that screen for PS and rMo from S?P models is simulated via S?C modeling. The results indicate that Li2O and CaO enhancement can increase the formation of Mo-phase, in which CaO can lead to the formation of the water resistance white crystal CaMoO4, while Li2O intensifies the precipitation of water-soluble Mo-yellow phase CsLiMoO4. SiO2 can affect the formation of CaMoO4 and CsLiMoO4. Certainly, Li2O can promote the Mo leaching rate.Conclusions A series of high Mo (MoO3 2.6%?3.3%), HLW borosilicate solidification glass was investigated by Glass Structural gene Modeling (GSgM) to establish the prediction models for the key elements (i.e., Na, Li, B, Mo) leaching rate rNa, rLi, rB, rMo and the Mo-phase separation. The rNa, rLi, rB, rMo and xPS with a satisfied accuracy were predicted. The results were summarized as bellow:1) The main components of Mo-phase were water-soluble yellow phase CsLiMoO4 (yellow) and water-resistant white crystal CaMoO4.2) The S?P models for all the target properties exhibited high accuracy (Rsq≥0.87) and satisfied statistical significance (P<0.000 1). The model validation proved the reliability of the models.3) Composition-structure-property analysis showed that SiO2 variation could affect the concentration of Si—O—Si (at 518?528 cm1) and B—O—B bending vibrations in [BO3] units, inducing two opposite effects on the Mo-phase separation, which could be evaluated via the simulated parameter calculation. Li2O enhancement increased the formation of water-soluble Mo yellow phase CsLiMoO4, and promoted the Mo leaching rate consequently. CaO could lead to the formation of the water resistance white crystal CaMoO4.

Introduction Studies on introducing phyllosilicate minerals into polymers to improve their tribological properties can provide some ideas for the development of intelligent self-healing composite materials. Polytetrafluoroethylene (PTFE) is widely used as one of engineering materials and solid lubricating materials due to its good self-lubricating ability, thermal stability, corrosion resistance and machinability. However, the molecular bond structure of PTFE exhibits unique slip characteristics during crystallization, making it prone to creep and resulting in a poor wear resistance. It is thus necessary for the modification of PTFE to improve the mechanical properties and tribological performance for engineering applications. The modification methods mainly include surface modification, blending modification, and filling modification. Recent studies indicate that the introduction of minerals such as serpentine, attapulgite, and sepiolite into PTFE can obtain PTFE-based composites with uniform mineral dispersion and excellent thermal stability, mechanical properties, and tribological properties due to the property of phyllosilicate minerals to intercalate monomer or polymer molecules. In this paper, antigorite and wollastonite minerals reinforced PTFE-based composites were prepared. The tribological properties of the composites were investigated, and the mechanism of the tribological properties improvement of PTFE caused by antigorite and wollastonite was discussed based on the worn surface analysis.Methods Antigorite (Atg) was extracted from natural deposited serpentine mineral in Anshan, China. Wollastonite (Wl) was provided by Dalian Global Mineral Co., Ltd., China. Polytetrafluoroethylene (PTFE) was purchased from Shandong Dongyue Co., China. The phase structure, functional groups and thermodynamic behaviors of the mixed raw powders were characterized by a model D8 Advance X-ray diffractometer (XRD), a model Nicolet 6700Fourier infrared spectrometer (FT?IR) and a model NETZSCH STA 449C simultaneous thermal analyzer (TG?DSC), respectively. The Shore hardness of the sintered composite samples was measured by a Shore hardness tester. The tribological properties of the composites were tested by a model Optimal SRV-IV ball-disc friction and wear tester. The 3D morphology, surface roughness and wear volume of the wear scars on the composites were determined by a model Olympus LEXT OLS4000 laser confocal microscope. The morphology and chemical composition of the worn composite and steel surfaces were examined by a model FEI Nova Nano SEM 450 field emission scanning electron microscope (FESEM) and an attached X-ray energy spectrometer (EDS). The chemical state of the major elements on the worn steel surface was analyzed by a model ESCALAB 250Xi X-ray photoelectron spectrometer (XPS).Results and discussion Compared to pure PTFE, the peak intensity of composite materials with different components obtained by adding minerals is reduced. The possible reason is that the addition of minerals hinders the nucleation and crystallization of PTFE, leading to a decrease in the crystallinity. In addition, no chemical reaction occurs during the process of introducing serpentine and wollastonite into PTFE by a pressureless sintering technology.The powders of antigorite and wollastonite are evenly dispersed in PTFE, with slight aggregation of antigorite. The mineral particles are tightly bound to the PTFE matrix, and there are no obvious defects such as pores and cracks in the composite. The average friction coefficient and wear volume of PTFE-based composites with simultaneous addition of 10% (in mass fraction) antigorite and 20% wollastonite are reduced by 44.2% and 71.4%, respectively, compared to pure PTFE. The composites exhibit excellent tribological properties due to the reinforcement of PTFE by minerals and the formation of a tribo-layer on the dual steel surface, which has high hardness and self-lubricating properties. Compared with the addition of a single antigorite, the addition of wollastonite minerals lowers the phase transition temperature of antigorite and promotes the formation of the tribo-layer, which has a good synergistic effect on the improvement of the tribological properties of the composites. Conclusions The mineral reinforced PTFE composite material was obtained via introducing antigorite and wollastonite minerals into PTFE and pressureless sintering, which had a dense structure, a uniform distribution of reinforcements, and an increased Shore hardness (from 11.5% to 23.7%), compared to pure PTFE.Single addition of antigorite could improve the wear resistance of PTFE and increased the frictional stability, while the simultaneous introduction of antigorite and wollastonite could improve both the anti-wear and friction reducing properties of PTFE. The average friction coefficient and wear volume of (10Atg+20Wl)/PTFE were reduced by 44.2% and 71.4%, respectively, compared to pure PTFE.The improvement of the tribological properties of mineral containing PTFE was attributed to the strengthening effect of minerals on the polymer and the formation of a tribo-layer with high hardness and self-lubricating properties on the dual surface. Compared with the addition of single antigorite, the simultaneous addition of wollastonite reduced the phase transformation temperature of antigorite, and promoted the formation of tribo-layer on the worn surface, thus having a good synergistic effect.

Introduction MgO-C refractories are extensively utilized as lining materials for smelting equipment (i.e., converters, ladles, and electric arc furnaces) due to their excellent resistance to slag erosion and thermal shock. Nevertheless, under high scrap ratio smelting conditions, MgO-C refractories are subjected to mechanical stress due to the introduction of scrap steel and thermal stress caused by frequent fluctuations in service temperatures, resulting in a substantial reduction in their operational lifespan. It is thus crucial to further enhance the mechanical properties and thermal shock resistance of MgO-C refractories. In recent years, effective approaches on the composition and structural design of materials are explored, which include the construction of nanostructure matrices, light-weighting and strengthening of magnesia-based aggregates, the introduction of novel additives, and the optimization of secondary carbon in binders. Among them, calcium magnesium aluminate (CMA) aggregates as a novel porous aggregate have attracted much attention. At elevated temperatures, it induces a partial liquid phase within the material matrix, effectively mitigating internal thermal stresses, repairing micro-cracks resulting from thermal shock, and facilitating the formation and growth of spinel whiskers. Consequently, a substantial enhancement in both toughness and thermal shock resistance of the material is achieved. In fact, ordinary sintered magnesia aggregates contain certain impurity phases, such as merwinite (with a melting point of 1 550 ℃) and andradite (with a melting point of 1 170 ℃). When conventional fused magnesia aggregates partially are substituted with ordinary sintered magnesia aggregates in the preparation of MgO-C refractories, localized liquid phases can be generated within the matrix at high temperatures, which may serve a similar function to CMA aggregates. Compared to CMA aggregates, ordinary sintered magnesia aggregates are more affordable, resulting in a substantial reduction in production expenses and facilitating the efficient utilization of low-grade magnesia. In this paper, ordinary sintered magnesia aggregates were selected to partially substitute conventional fused magnesia aggregates in the preparation of MgO-C materials. The microstructure evolution, mechanical properties, thermal shock resistance, and high-temperature fracture behavior of MgO-C refractories containing ordinary sintered magnesia aggregates were investigated.Methods MgO-C refractories were prepared via substituting 10% of ordinary sintered magnesia aggregates (w(MgO)=93.33%, w(SiO2)=1.72%, w(CaO)=3.12%, and w(CaO)/w(SiO2)=1.81, w is mass fraction) for conventional fused magnesia aggregates (w(MgO)=97.35%, w(SiO2)=0.5%, w(CaO)=1.12%, and w(CaO)/w(SiO2)=2.24) with a flake graphite as carbon source, metallic silicon powder and boron carbide as antioxidants, and thermosetting phenolic resin as a binder. After thoroughly blending the aforementioned materials, bar-shaped specimens with the sizes of 140 mm×25 mm×25 mm and standard brick specimens with the sizes of 230 mm×110 mm×70 mm were shaped at 150 MPa and then cured at 200 ℃ for 24 h. The cold modulus of rupture (CMOR) of the bar-shaped specimens, treated at different temperatures (i.e., 200, 1 000, 1 400 ℃ and 1 600 ℃) in a coke bed was measured by a model XD-117A three-point bending test machine. The microstructure and elemental composition of the specimens were determined by a model Nova Nano 400 field emission scanning electron microscope, combined with a model IE 350 PentaFET X-3 energy dispersive spectrometer. The bar-shaped specimens (140 mm×25 mm×25 mm) coked at 1 400 ℃ were selected for thermal shock test by an oil quenching method. Namely, these specimens were initially heated in a coke bed at 900 ℃ for 30 min, followed by quenching in an oil bath. After undergoing three thermal shock cycles, the residual strength index (CMOR after thermal shocks/CMOR before thermal shocks) of specimens was calculated. Subsequently, the bar-shaped specimens after thermal shock test were further heated in the coke bed at 1 600 ℃ for 3 h, and then the recovery strength index (the change of CMOR after reheating to 1 600 ℃/CMOR after thermal shocks) of MgO-C specimens was calculated. In addition, the standard brick specimens were processed into the wedge splitting specimens (100 mm×100 mm×70 mm), and heated in the coke bed at 1 000 ℃. Subsequently, high-temperature wedge splitting tests were conducted at 1 000 ℃ and 1 400 ℃ for 30 min, respectively. The specimens were surrounded in alumina crucibles filled with coke in a high-temperature furnace to establish a reducing atmosphere. Fracture parameters such as the nominal notch tensile strength (σNT), specific fracture energy (Gf), characteristic length (lch) and thermal shock resistance (Rst), were calculated to further quantitatively characterize the thermal shock resistance of specimens.Results and discussion Ordinary sintered magnesia aggregates remain intact in MgO-C refractories coked at 1 000 ℃. However, the impurities within some ordinary sintered magnesia aggregates dissolve and diffuse into the surrounding matrix as the temperature increases to 1 400 ℃, disintegrating the aggregates into a porous structure. In addition, Mg2SiO4 particles and whiskers, as well as SiC whiskers also appear in the matrix due to the introduction of silica powder. The dissolution and diffusion of impurities increase as the temperature further increases to 1 600 ℃, generating Mg2SiO4 particles and SiC whiskers in the matrix. These structural changes in MgO-C refractories at high temperatures enhance the strength, even the high-temperature flexural strength, and improve the thermal shock resistance of MgO-C refractories.The results of high-temperature wedge splitting test show that MgO-C specimens containing ordinary sintered magnesia aggregates exhibit an equivalent peak load to those of the control specimens, while their fracture displacements significantly enlarge. As evident from various fracture parameters, MgO-C specimens containing ordinary sintered magnesia aggregates exhibit higher Gf, lch, and Rst at 1 000 ℃ and 1 400 ℃, indicating that the introduction of ordinary sintered magnesia aggregates effectively reduces the material brittleness due to improving the thermal shock resistance of specimen Also, the specimens containing ordinary sintered magnesia aggregates exhibit a higher proportion of cracks along the aggregate-matrix interface in the crack propagation path. The enhancement of fracture toughness and thermal shock resistance of MgO-C refractories with ordinary sintered magnesia aggregates addition can be attributed to the stress relief provided by the porous structure of ordinary sintered magnesia, the promotion of sintering at 1 400 ℃ by the formation of liquid phases, and the formation of whiskers in the matrix.Conclusions The addition of ordinary sintered magnesia effectively enhanced the thermal shock resistance of MgO-C refractories due to the porous structure of ordinary sintered magnesia aggregate and its ability to form a liquid phase at high temperatures, thereby reducing the overall thermal expansion rate of the specimens. MgO-C specimens containing ordinary sintered magnesia aggregates exhibited higher Gf, lch, and Rst at 1 000 ℃ and 1 400 ℃ due to the higher porosity of the ordinary sintered magnesia aggregates, effectively mitigating the stress concentration. At 1 400 ℃, the impurities in the ordinary sintered magnesia aggregates dissolved and diffused into the matrix to form a liquid phase network that was conducive to absorbing stress at crack tips. The formation of this liquid phase promoted the whiskers formation and slowed down the crack propagation.

Introduction Al2O3-C refractories are one of the important categories of refractory materials in steel smelting. Improving their service life has a great application value. The service life of Al2O3-C refractories is closely related to their mechanical properties. Therefore, an effective approach to improve the mechanical properties of Al2O3-C refractories and further enhance their service life is to introduce a structural reinforcement such as carbon fibers. However, using commercial carbon fibers directly as a structural reinforcement cannot bind with other components of the material tightly at various temperatures due to its smooth surface and low reactivity, thus restricting the reinforcing effect of carbon fibers. Therefore, surface treatment such as thermal oxidation on carbon fibers is an effective way to improve the reinforcement effect of carbon fibers and improve the mechanical properties of carbon fibers reinforced Al2O3-C refractories. In this paper, short carbon fibers were treated by a thermal oxidation method, and Al2O3-C refractories were then prepared using the treated carbon fibers as a reinforcement. The structural evolution of short carbon fibers with different degrees of oxidation in Al2O3-C refractories, as well as the effect of adding thermal oxidation short carbon fibers on the mechanical and thermal shock resistance properties of Al2O3-C refractories were investigated. Methods White corundum, active alumina powder, silicon powder, boron carbide, flake graphite, nano carbon black, and short carbon fiber were used as raw materials, and thermosetting phenolic resin was used as a binder. In addition, some commercial carbon fibers were heated in air at 400, 500 ℃, and 600 ℃ for 0.5 h to prepare thermal oxidation carbon fibers in order to investigate the effect of thermal oxidation treatment of carbon fibers on their structural evolution and service performance in Al2O3-C refractories.The Al2O3-C samples without carbon fibers and with untreated carbon fibers, as well as thermal oxidation carbon fibers at different temperatures (i.e., 400, 500 ℃, and 600 ℃) were numbered as sample BK, sample F, sample FT4, sample FT5, and sample FT6, respectively. The raw materials were mixed evenly and then shaped into 25 mm×25 mm×140 mm at 120 MPa. Each sample was cured at 200 ℃ for 24 h, and then heated in a saggar filled with coke grit at 1 200, 1 300 ℃, and 1 400 ℃ for 5 h, respectively. The micromorphology of samples was determined by a field emission scanning electron microscope (TESEM). The apparent porosity and bulk density of samples were measured based on the Archimedes principle. The CMOR and HMOR of samples were measured by a three-point bending method. The CCS of samples were measured by a uniaxial compression method. The thermal shock resistance of the samples was evaluated according to the residual strength ratio of the CMOR (CMORrsr). The elastic modulus (E) of samples was analyzed by a resonance frequency and damping analyzer. The fracture-related parameters of samples were detected by a single-edge notched beam (SENB) method. Results and discussion Based on the TESEM images, the surface of the untreated carbon fibers are relatively smooth without obvious defects. After thermal oxidation at 400 ℃, the morphology of carbon fibers does not change much and still have a relatively smooth and intact surface. After thermal oxidation at 500 ℃ and 600 ℃, however, visible structural changes occur on the surface of carbon fibers, becoming rough in some areas. Also, the reaction between carbon fibers and Si heat-treated at 1200 ℃ occurs slightly, leading to that the surface morphology of carbon fibers is similar to their initial state. After heat treatment at ≥1300 ℃, some structures in the form of whiskers and particles appear on the surface of carbon fibers. In addition, for carbon fibers after thermal oxidation treatment, in addition to growing the structures outside the surface of fiber like the original carbon fibers, it is also possible to further react in fiber surface defects to generate new structures inside the fibers. This reaction process will continuously increase the defect size of the fibers and damage the structural integrity of the fibers.Although the addition of short carbon fibers reduces the compactness of Al2O3-C refractories, their introduction can still play a positive role in improving the mechanical properties. For instance, for Al2O3-C refractories containing carbon fibers treated at 500 ℃, after being heat treated at 1 400 ℃, their CMOR, CCS HMOR are increased by 28.2%, 22.4%, and 87.2%, respectively, compared with the control material. This can be due to the high-temperature chemical reaction between carbon fibers and other components of refractories, as well as the additional energy dissipation mechanism introduced by fibers, which greatly increases the energy required for crack propagation, thereby hindering crack propagation and improving the mechanical properties of refractories.Conclusions Thermal oxidation treatment could create defects on the surface of carbon fibers, thereby affecting their reactivity and mechanical properties. Adding them to Al2O3-C refractories could promote the formation of in-situ ceramic phases due to the surface defects, having positive impacts on the improvement of mechanical properties. However, the temperature of thermal oxidation treatment should be appropriate. If the temperature was too low or too high, it could not fully exert the reinforcing effect of carbon fibers. In addition, although the addition of thermal oxidation carbon fibers had a positive impact on the performance improvement of refractories in some cases, there were still weaknesses in the performance.

Introduction Cement industry is one of the major carbon-emitting industries, which is characterized by a thermal efficiency below 54% and an energy consumption ranging from 3-4 GJ per ton of cement clinker. China annual average cement production reaches 2 341 million tons, contributing to approximately 14.3% of the total CO2 emissions. In addition to the CO2 emissions resulting from the high-temperature decomposition of limestone, which serves as a primary raw material, the cement production process significantly contributes to elevated CO2 emissions due to its substantial energy consumption. The cement rotary kiln is a pivotal equipment in the production process, with its high energy consumption primarily attributed to subpar performance of certain refractory materials and an irrational configuration. Consequently, this leads to elevated temperatures (reaching up to 350-400 ℃) in both the transition zone and firing zone of the kiln shell, resulting in a substantial energy loss accounting for 8%-15% of the total heat input. Previous studies demonstrated that the implementation of light weight refractory materials could effectively mitigate heat loss from the kiln shell, thereby enhancing energy efficiency. The CA6/MA composite material C2M2A14 has the excellent high-temperature performance and chemical stability of both CA6 and MA. It is proven to be an effective ladle lining material in the non-slag line part. Incorporating a proper quantity of Fe2O3 during the synthesis process of C2M2A14 results in a denser product under identical firing conditions. In this paper, C2M2A14 was introduced into magnesite refractories to achieve light weighting of magnesite refractories. In addition, the mechanism of achieving light weighting and the effects of addition amount and particle size on the microstructure and properties of magnesite refractories were also investigated.Methods Magnesium hydroxide, calcium carbonate and calcined α-alumina fine powders as raw materials were mixed. Also, 1% Fe2O3 was added to the mixture according to a specific mass ratio. The mixture was then pressed into cylindrical samples with a diameter of 36 mm×36 mm. C2M2A14 was synthesized via firing at 1 780 ℃ for 5 h. The synthesized material was crushed and sieved to obtain fine particles with different sizes of 1-3 mm, 0.088-1.000 mm, 0.5-1.0 mm, 0.088-0.500 mm, and≤0.088 mm. Magnesia and materials such as C2M2A14 were mixed according to the specified ratio, and then pressed into cylindrical samples with dimensions of 36 mm×36 mm and 36 mm×50 mm, as well as crucible samples with the dimensions of 50 mm×50 mm. These samples were fired at different temperatures (i.e., 1 600, 1 650 ℃ and 1 700 ℃) for 3 h. The bulk density, apparent porosity, true density, and cold crushing strength at room temperature of A sample with the size of 36 mm×36 mm were characterized according to national standards. The load softening temperature of a sample with the size of 36 mm×50 mm was measured. The pore size distribution of the original brick was determined by a fully automatic mercury porosimeter. Cement material in crucible was heated at 1 350 ℃ for 6 h to investigate its corrosion-resistance to cement material. The microstructure before and after corrosion of the crucible samples and original bricks was determined in a backscattered electron imaging mode by field corrosion scanning electron microscopy. The phase composition of the samples was characterized by X-ray diffraction with a software named Jade .Results and discussion The results show that at 1 600 ℃, the apparent porosity of sample increases while their bulk density and cold crushing strength decrease as the amount of C2M2A14 increases. Also, the load softening temperature decreases. The apparent porosity of samples with particle sizes ranging from 0.5-1.0 mm increases from 23.2% to 32.8% with increasing C2M2A14 from 10% to 40%. The bulk density decreases from 2.70 g/cm3 to 2.36 g/cm3, which is lower than the one of dense refractory (which is also made of the same material) at 2.94 g/cm3, indicating a trend towards light weighting. At the same addition amount of 10%, the particle size of C2M2A14 becomes smaller, the apparent porosity of the sample decreases, and the bulk density and cold crushing strength both increase. The load softening temperature is closer. The apparent porosity of samples with different particle sizes (i.e., 0.5-1.0 mm and 0.088-0.500 mm) gradually decreases, while the bulk density increases as the firing temperature increases. However, there is no corresponding increase in cold crushing strength. The maximum cold crushing strength is 56.6 MPa, and the particle sizes both exhibit a load softening temperature of >1 540 ℃, meeting the requirements for application in cement kiln transition zones. The presence of magnesia in the matrix during firing induces the decomposition of C2M2A14, as evidenced by XRD and SEM analysis. In the magnesite-spinel-aluminate ternary system, a liquid phase forms at elevated temperatures, facilitating a pore formation through liquid-assisted Kirkendall effect and achieving a light weighting in the samples. Furthermore, increasing the amount of C2M2A14 results in a higher apparent porosity, while leading to a decrease in bulk density, cold crushing strength, and load softening temperature. The corrosion resistance of group D and E samples with particle sizes of 0.5-1.0 mm and 0.088-0.500 mm was investigated at 1 350 ℃ by a static crucible method with the addition of 10% C2M2A14. The crucibles of D series samples exhibit a visible corrosion penetration, while those of group E samples show a negligible corrosion penetration. No adhering slag appears on the side walls in either group. The microstructural analysis reveals that different sizes of C2M2A14 particles are responsible for variations in penetration depth between the two group samples. Larger and more pores occur in group D samples, allowing cement material to penetrate through them. The introduction of C2M2A14 particles with the sizes of 0.088-0.500 mm in group E results in smaller pores resulted from the reaction between C2M2A14 particle and magnesia matrix, making them denser and effectively inhibiting the penetration by a low melting point cement phase.Conclusions 1) Introducing Ca2Mg2Al28O46 was introduced into magnesium refractor during firing. Magnesite-spinel-aluminate ternary system formed a liquid phase at a high temperature. The pores formed with a liquid phase assisted the Kirkendall effect and resulted in magnesium refractory to achieve lightweight. The apparent porosity of samples increased, the bulk density, compressive strength and the refractoriness under load decreased with increasing the amount of Ca2Mg2Al28O46 additions. At the same amount of Ca2Mg2Al28O46 added, the performance could be improved via reducing its particle size. 2) As the firing temperature increased, the apparent porosity of specimen decreased, the bulk density increased, but their compressive strength did not increase, and the refractoriness under a load maintained at a high level (>1 540 ℃). The refractoriness under a load could reach 1 603 ℃ when 10% (in mass fraction) of Ca2Mg2Al28O46 particles with the sizes of 0.50-1.00 mm were added and fired at 1 700 ℃. 3) The static crucible experiments at 1 350 ℃ showed that the specimens with the introduction of Ca2Mg2Al28O46 particles with the sizes of less than 0.50 mm at 10% addition had the optimum corrosion resistance to cement materials when the specimens were fired at 1 650 ℃.

With the rapid development of electronic information technology and the 5G, wireless electronic communication technologies and related products based on electromagnetic wave emission, transmission, and processing become popular. However, the consequent electromagnetic radiation and interference are serious, affecting human-being health and environment. Also, , the survival and penetration capabilities of weapon systems require minimizing radar cross-sections to achieve electromagnetic stealth with the continuous advancement of modern warfare radar detection technologies. The adoption of electromagnetic wave-absorbing materials currently represents the most effective and feasible approach to mitigate electromagnetic pollution and realize electromagnetic invisibility goals. For the dual needs of civil and defense applications, the development and production of high-performance electromagnetic wave absorbents becomes a hot research topic. Moreover, high-performance absorbing materials meet the basic requirements for traditional absorbents of "light weight, strong absorption, thin thickness, and wide band", and possess properties like high-temperature resistance, corrosion resistance, etc., to adapt to different complex environments.SiC fibers have attracted extensive attention due to their superior properties of low density, high strength, high modulus, high-temperature resistance, oxidation resistance, and corrosion resistance. SiC fibers have a tremendous application value in various extreme environments, including nuclear reactors, aeroengines, aircraft nozzles, etc.. Moreover, as a wide bandgap semiconductor material, SiC fibers also possess the advantage of tunable electrical resistivity, providing possibilities for their functional application in electromagnetic wave absorption. However, the electromagnetic absorption performance of conventional SiC fibers is far from ideal due to the presence of some issues such as single loss mechanism and impedance mismatch. It is thus necessary to improve the electromagnetic wave absorption capabilities of SiC fibers. To enhance the absorption performance of SiC fibers, efforts could be made in the following two aspects, i.e., tuning the electrical resistivity of SiC fibers to augment dielectric loss and optimize impedance matching, and introducing new loss mechanisms to increase electromagnetic wave attenuation paths. This review represented four approaches and underlying mechanisms to improve the electromagnetic wave absorption performance of SiC fibers, namely, elemental doping, surface coating design, structural design, and microstructure manipulation through thermal treatment. Furthermore, from the perspective of fibers, interface, matrix, and their structures, the related research progress on the electromagnetic wave absorption capabilities of SiC fiber-reinforced ceramic matrix and polymer matrix composites was summarized. The electromagnetic wave absorption properties could be effectively enhanced via the rational design of the SiC fibers and composites in multiple length scales.Summary and prospects The mechanisms underlying the four approaches to improve the electromagnetic wave absorption performance of SiC fibers are not entirely the same. Element doping can form conductive phases, magnetic loss phases, and heterogeneous interfaces inside SiC fibers to increase their electromagnetic losses, thus improving the electromagnetic wave absorption performance. Surface coating design can increase electromagnetic wave loss mechanisms, while optimizing impedance matching to attenuate electromagnetic waves. Structural design enables more electromagnetic waves to enter the interior of SiC fibers and utilizes structural features to increase electromagnetic wave transmission distance and multiple reflections, effectively attenuating electromagnetic waves and improving absorption performance. Thermal treatment can regulate the composition and crystallite size (microstructure) of SiC fibers, causing changes in fiber electrical resistivity and electromagnetic parameters, thereby improving electromagnetic wave absorption. For SiC fiber-reinforced composites, the multidimensional design of SiC fibers, interface, matrix, and their structures can enhance absorption performance. However, despite many achievements in the research of electromagnetic wave absorption properties of SiC fibers and their composites, studies on the synergistic improvement of structure absorption and other functional properties of SiC fiber-reinforced composites are still scarce. It is thus necessary for the functional application of SiC fibers in complex environments to strengthen the synergistic design of SiC fiber structural units in different scales and the research on structure-property evolution of SiC fiber reinforced electromagnetic wave absorbing composites under service conditions.

In the increasing severe energy crisis, the use of solar energy to replace traditional fossil fuels becomes a consensus in worldwide due to the non-renewable nature of fossil fuels and the inability of new energy sources such as hydrogen, wind, and nuclear energy. Among the forms of solar energy utilization, dye-sensitized solar cells (DSSCs) are a research hotspot in energy development and utilization due to their low cost, abundant raw materials, high efficiency, and long service life. The photoanode is an important component of DSSCs and plays a significant role in improving the photoelectric conversion efficiency of DSSCs. In recent years, various materials and modification methods for dye-sensitized solar cells are applied to design the photoanodes for the improvement of their photoelectric conversion efficiency. Among various photoanode materials, SnO2 is an ideal candidate due to its higher electron mobility (i.e., about 125 cm2·V-1·s-1) and larger bandgap width (i.e., 3.5 eV). However, SnO2-based dye-sensitized cells still have two main challenges, i.e., the lower open-circuit voltage (Voc) (Compared to TiO2, the conduction band edge of SnO2 shifts positively by up to 300 mV, resulting in a reduced difference between the conduction band potential and the redox potential of the electrolyte); and the lower current density (The isoelectric point of SnO2 is smaller, which reduces the binding force between SnO2 and acidic photosensitive dyes, leading to a decrease in dye adsorption and thus limiting the increase in current density from the source).This review represented recent research progress on tin SnO2 photoanodes in DSSCs, emphasizing the potential application of SnO2 in DSSCs and the challenges. This review introduced the structure and working principle of SnO2-based DSSCs, and analyzed the key factors affecting the photoelectric conversion efficiency, including short-circuit current density (JSC), VOC, and fill factor (FF). This review discussed the factors influencing these parameters and focused on the current state of research on improving SnO2 photoanodes, with the methods including surface coating, composite construction, ion doping, and metal doping. Although various modification methods are developed to improve the performance of SnO2 photoanodes, the overall photoelectric conversion efficiency is still lower, restricting its widespread application in a large scale. Therefore, developing more advanced modification techniques is a necessity to further enhance the performance of SnO2 (i.e., its stability and recyclability), and facilitate its wide application in the energy field, thus providing an effective solution to alleviate the energy crisis.Summary and prospects SnO2-based DSSCs have a potential to replace TiO2 DSSCs due to their outstanding charge transport capabilities and stable optical properties. However, a lower conduction band position of pure SnO2 makes it difficult to achieve an VOC beyond 500 mV. Also, the lower isoelectric point limits dye adsorption, inherently reducing the JSC. To address the poor performance of SnO2 nanoparticles, modifications such as changing their structural morphology, surface coating, and ion doping can be employed to enhance charge transport and suppress charge recombination, significantly improving the photoelectric conversion efficiency of SnO2 cells. To date, the photoelectric conversion efficiency of cells based on pure SnO2 is 8.74%, while that of SnO2-TiO2 composite cells is 9.53%. Although these are significant breakthroughs, there is still a gap, compared to TiO2 cells (i.e., 13%). It is evident that the current density of SnO2 is able to reach a high level (i.e., greater than 20 mA·cm-2) due to the good transport performance of SnO2, compared to that of TiO2, but there is still some gaps in open-circuit voltage and fill factor.Future research aspects are as follows:1) There is a great need for a deep understanding of electron generation, transport, loss, and collection within DSSCs, but many issues remain to be resolved. For instance, the recombination mechanism of photo-generated electrons with I3- is still unclear. The complex internal electron transport process has yet to be fully explained by any model, especially under certain light intensity disturbances affecting photo-generated current and voltage (IMPS/IMVS), necessitating further detailed theoretical studies. There are many possibilities for the process of electron injection from the semiconductor film to the FTO interface, such as thermal emission and tunneling, and there is currently no suitable theory to describe this interface, requiring a further research.2) The further use of transition metals with radii that are similar to Sn4+ (such as Ti4+, W4+, and In3+) or the synergistic effect of co-doping metals can be explored to specifically improve various properties of SnO2.3) To further break through the photoelectric conversion efficiency of SnO2, it is necessary to investigate the working process of DSSCs from a microscopic perspective and optimize each part to identify the processes limiting electron transport, improve electron yield, enhance electron transport processes, and reduce electron loss, aiming to achieve the optimum photoelectric conversion efficiency.

Supercapacitors have attracted recent attention because of their high power density, fast charging and discharging capability, long cycle life, and good stability. However, the generally low energy density of supercapacitors restricts their applications. The electrode material is the most critical part in the supercapacitor and significantly affects the performance. In recent years, a rational design of electrode materials is proved to be an effective way to improve the capacitance performance of supercapacitors. Among many electrode materials, layered double hydroxide (i.e., hydrotalcite and hydrotalcite-like) has the advantages of adjustable morphology and composition, high theoretical specific capacitance, low cost, easy synthesis and considerable energy density and power density, etc., and emerges in the field of supercapacitor electrode materials. The unique two-dimensional structure of the layered double hydroxide (LDH) and its energy storage mode through electrolyte ions embedded and dislodged in the interlayer dictate that an interlayer spacing modulation is an effective method to improve its capacitance performance. Enhancing the utilization of electrochemically active sites between LDH layers and reducing the ion transport velocity resistance via regulating the layer spacing become a commonly used and effective structural modulation method for two-dimensional electrode materials such as LDH. This review summarized the research progress on the application of LDH interlayer spacing regulation in the field of supercapacitors, introduced the structure of LDH, the energy storage mechanism, and the advantages of LDH as an electrode material, and described the influencing factors and the advantages and disadvantages about the interlayer spacing regulation from the two different perspectives of the ion-exchange method and the one-step synthesis method, respectively. The target anion intercalation in the two methods concerns the anion charge density and anion concentration in the reaction system. The interlayer spacing values of different guest intercalated LDH, such as inorganic anions, organic anions, and molecules, were discussed. The factors affecting interlayer spacing and capacitance performance were summarized. A small interlayer spacing significantly inhibits ion diffusion and charge transport, which is not conducive to achieving a high capacitance performance. Organic anion intercalation is more likely to achieve a larger interlayer spacing and a higher capacitance performance. Appropriate interlayer objects and interlayer spacing are crucial for achieving a high capacitance performance. The influence of metal cations ratio on the interlayer spacing and capacitance performance was evaluated, and three methods for regulating metal cations were summarized. The ratio of divalent and trivalent cations in the synthesis process can be adjusted to achieve the control of positive charge concentration in the basal layer and the control of interlayer force, thus controlling the interlayer spacing. The oxidation of divalent cations during or after synthesis is controlled to achieve a positive charge density. Selecting cations of different radii to synthesize LDH affects the distribution of basal layer charges, thereby affecting the interlayer spacing. This review elaborated on the method of adding intercalation agents during the process of regulating interlayer spacing, which can simultaneously increase the interlayer spacing and load mass, and is of great significance for obtaining high load and high capacitance electrodes. This review outlined common methods for improving capacitance performance by regulating interlayer spacing and the underlying mechanisms for improving the capacitance performance, playing an important role in promoting the in-depth research and application of LDH electrode materials.Summary and prospects Some prospects for future development were provided. In the future, with the continuous development of precise temperature control, uniform, and rapid heating synthesis technologies such as microwave synthesis, the combination of artificial intelligence control technology and synthesis equipment, the advancement of multi index observation in-situ experimental technology, and the precise observation and control of synthesis heating rate, temperature field, and concentration field are effective ways to achieve precise synthesis of hydrotalcite and precise control of interlayer spacing. And it is expected to achieve precise control of the types, quantities, and layout of interlayer objects according to demand. The influences of interlayer object types, quantities, arrangement attitudes, and pores on the electrolyte ion transport, and the related mechanism on the interlayer active site electrochemical reactions, and the related mechanism on the interlayer spacing and layer structure evolution can be investigated more accurately. The combination of multi-index observation in-situ synthesis experimental technology with the first-principles, molecular dynamics, and machine learning simulation methods can be ultilized to analyze the microstructure, electrochemical reactions, and other processes.