Introduction Supercapacitors are widely used due to their fast charging and discharging processes, high power density (i.e., 10 kW·kg-1), fast charging and discharging (i.e., minutes or even seconds), and long cycle term (i.e., up to 100 000 cycles theoretically). The electrode materials determine the electrochemical energy storage performance of the supercapacitor. It is thus important for the development of high-performance electrode materials to improve the performances of the supercapacitor. Many electrode materials are explored for supercapacitors, such as transition metal oxides, transition metal hydroxides and transition metal sulfide. The electrode materials show the promising practical applications. To further optimize the electrochemical performances of the electrode materials, the supercapacitors with the composites are developed as electrode materials. Among the composites, transition metal sulfide-based electrode materials have attracted much attention because of their outstanding performances for energy performances of supercapacitors. In this paper, Ni3Se2/Ni3S2 nanocomposites were synthesized on nickel foam by a solvothermal and selenization method, and their structures and electrochemical energy storage performances were systematically investigated.Methods 4.4 g Na2S·9H2O was dissolved in 40 mL methanol under stirring vigorously for 30 min. The solution was moved to 2 Teflon-lined stainless steel autoclaves, equally, and two cleaned Ni foams were immersed in the solution, respectively, then the autoclaves were kept in an oven 140 ℃ for 16 h. After the reaction, Ni3S2 nanorods on Ni foam (Ni3S2/Ni ) were obtained.0.01 g Se powder was dissolved in 6 mL hydrazine?hydrate (resolution A). 9 mL DI-water and 15 mL ethanol were added into resolution A, obtaining resolution B. Resolution B was transfered to 2 autoclaves. Two Ni3S2/Ni samples were put into two autoclaves with resolution B. The autoclaves were kept in an oven at 140 ℃ for 10 h. The samples were prepared at different growth temperatures and time.The crystal structure and morphology of the samples were determined by X-ray diffraction (XRD, Bruker-D8, λ=0.154 05 nm), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The chemical elements and valence bond states were analyzed by X-ray photoelectron spectroscopy (XPS, Al Kα) and X-ray energy spectrometry (EDS). The electrochemical properties were examined on an electrochemcial system with Ni3Se2/Ni3S2 nanocomposites as working electrodes at room temperature.Results and discussion The SEM images of Ni3Se2/Ni3S2 nanocomposites show that Ni3Se2 nanoparticles cover Ni3S2 nanorods. Besides, some Ni3Se2 clusters are on the top of Ni3S2 nanorods. Moreover, the HRTEM images of Ni3Se2/Ni3S2 nanocomposites reveal the interfaces between Ni3Se2 and Ni3S2.Under the optimized growth conditions, the specific capacitance of Ni3Se2/Ni3S2 nanocomposites can reach 2 482.00 mF·cm-2 (@1 mA·cm-2), and the specific capacitance retention rate is still 68.45% after 2 000 charge-discharge cycles at 10 mA·cm-2, and the coulombic efficiency is 97.20%-99.28%. The assembled liquid (6 mol/L KOH) Ni3Se2/Ni3S2//AC asymmetric supercapacitor demonstrates a specific capacitance of up to 768.75 mF·cm-2 (@2.5 mA·cm-2). The assembled Ni3Se2/Ni3S2//AC all solid-state supercapacitor (ASS) has a specific capacitance of 983.57 mF·cm-2 (@7.5 mA·cm-2). The outstanding electrochemical performances of Ni3Se2/Ni3S2 nanocomposites can be since: 1) Ni3Se2/Ni3S2 nanocomposites are fabricated on Ni foam, directly, reducing the contact resistance due to the good conductivity of Ni foam; 2) Ni3Se2/Ni3S2 nanocomposites on Ni foam have a three-dimensional structure, exhibiting the large specific surface area for the electrochemical reactions; and 3) the synergies of Ni3Se2 and Ni3S2 can improve the electrochemical performances. In addition, the integrated circuits with Ni3Se2/Ni3S2//AC solid-state capacitor are also analyzed. The series Ni3Se2/Ni3S2//AC ASSs demonstrate a typical increase in the operating voltage window, and the parallel ones show the improvement of the specific capacitance, indicating the promising practical applications for energy storage of Ni3Se2/Ni3S2 nanocomposites.Conclusions Ni3Se2/Ni3S2 nanocomposites were prepared as electrode materials for supercapacitors and their the electrochemical performances were investigated. As the electrode material, Ni3Se2/Ni3S2 nanocomposites showed the outstanding properties for energy storage. At 1 mA·cm-2, the constructed supercapacitor in 6 mol/L KOH solution exhibited the specific capacitance of 2 482 mF·cm-2. the ASS devices were also constructed with Ni3Se2/Ni3S2 nanocomposites, showing good electrochemical performances for energy storage. Furthermore, the ASS devices with Ni3Se2/Ni3S2 nanocomposites as electrode material showed the typical integrated features in series and parallel circuits. Singe ASS device demonstrated 0-1.4 V working voltage window, and two series devices could work well in 0-2.8 V, while the specific capacitance presented the obvious improvement for two parallel ASS devices. Therefore, the study could demonstrate a potential application of Ni3Se2/Ni3S2 nanocomposites, and provide an approach to design the new materials for energy storage.