IntroductionThe advancement of solid oxide cells (SOCs) technology has led to a reduction in the operating temperature to 700-800 ℃, substantially enhancing the long-term stability of cells. However, as the temperature declines, the sluggish oxygen reduction/oxygen evolution reaction (ORR/OER) at the oxygen electrode emerges as a critical constraint on SOCs power output efficiency. (La_0.6Sr_0.4)0_.95Co_0.2Fe_0.8O₃-_δ (LSCF), renowned for its excellent ORR/OER catalytic and electrical conductivities, is widely adopted in SOCs oxygen electrodes. However, its inherent drawback lies in the incompatibility of its thermal expansion coefficient (TEC) with traditional electrolytes like GDC and YSZ, often inducing fuel cell or stack failure during cycling due to thermal stress. To address this interface compatibility issue, combining LSCF with an electrolyte material, specifically Sm_0.2Ce_0.8O₂-_δ (SDC), to form a composite electrode proves to be viable. This not only mitigates the average TEC but also optimizes the reaction kinetics. In this study, LSCF and SDC materials were synthesized via the sol-gel method, and the impacts of varying SDC content in the composite electrode on phase structure, conductivity, thermal expansion, and ORR/OER performance were meticulously examined. Results indicate that SDC incorporation effectively curtails the material TEC, enhances ionic conductivity, and boosts ORR/OER activity. Ultimately, the LSCF/40SDC composite electrode manifests remarkable electrochemical performance and long-term stability in fuel cell and water electrolysis mode.MethodsA series of LSCF/xSDC composite electrodes were synthesized using the sol-gel method. Detailed structural analyses of the materials were conducted by X-ray diffraction (XRD). Electrical conductivity and thermal expansion coefficient of electrode strips were measured from room temperature to 800 ℃. Electrochemical impedance spectroscopy of symmetrical cells was performed, while the electrochemical performance and long-term stability of single cells were evaluated by electrochemical workstation.Results and DiscussionXRD results confirm pure phase LSCF and SDC were prepared via sol-gel method. LSCF exhibits a hexagonal perovskite structure, and SDC oxide adopts a cubic fluorite configuration. The composite powders exhibit only the characteristic diffraction peaks of LSCF and SDC, confirming their excellent chemical compatibility. The conductivity of LSCF/xSDC materials ascends steadily within 200-600 ℃. Above 600 ℃, the conductivity declines with the increasing temperature. Thermal expansion tests clearly demonstrate that combining strategy with SDC electrolyte markedly diminishes the TEC of LSCF electrode, achieving better alignment with the TECs of YSZ and SDC (10.5×10^-6 K^-1 and 11.4×10^-6 K^-1 respectively).Impedance analysis of symmetrical cells shows that increasing SDC content leads to a continuous reduction in polarization impedance. This stems from SDC-induced enhancements in material ionic conductivity and expansion of the electrode reaction three-phase interface, thereby improving oxygen catalytic capacity. The Distribution of Relaxation Times (DRT) outcomes for LSCF/40SDC at 650-850 ℃ signify that elevated temperatures notably propel each electrode reaction step, particularly influencing the oxygen surface and interface charge transfer processes.Electrochemical performance analysis of single cells indicates that a higher SDC proportion correlates with stronger oxygen electrode catalytic ability and improved cell performance, with the LSCF/40SDC cell exhibiting best performance. Moreover, composite SDC significantly boosts hydrogen production efficiency during water electrolysis, attributable to enhanced oxygen electrode OER activity and reduced electrode reaction polarization resistance. After 400 h of stable operation, the cell voltage diminishes marginally from 0.70 V to 0.68 V, yielding an degradation rate of 7.15%/1000 h The cell microscopic morphology remains intact, with tight cohesion among the oxygen electrode, isolation layer, and electrolyte without devoid of detachment or separation. La, Sr, Co, and Fe are uniformly distributed, with no interdiffusion or chemical reaction occurrences after the long-term test.Conclusion(La_0.6Sr_0.4)_0.95Co_0.2Fe_0.8O₃-_δ perovskite and Sm_0.2Ce_0.8O₂-_δ powders were synthesized by sol-gel method, The effect of SDC content on material crystal structure, conductivity, thermal expansion coefficient, and electrochemical performance were investigated. The LSCF/40SDC material offers a superior TEC match with the electrolyte. In symmetrical cell tests, LSCF/40SDC presents the lowest polarization resistance and reduced activation energy. In full cell tests at 750 ℃, the peak power density surges to 1132 mW/cm², 1.87 times that of the base LSCF electrode. During water electrolysis at 1.3 V, the full cell with the LSCF/40SDC electrode attains a current density of -875 mA/cm². Notably, the LSCF/40SDC cell sustains stable operation for 400 h under 750 ℃ and 1000 mA/cm² discharge conditions, with an ultra-low attenuation rate of 7.15%/1000 h epitomizing outstanding long-term stability.