3D meso/macroporous Ni 3 S 2 @Ni composite electrode for high-performance supercapacitor

Abstract Ni 3 S 2 @Ni composite electrode for supercapacitor is synthesized via a one-step solvothermal treatment of Ni foam at 120 °C, exhibiting a 3D meso/macroporous network structure. The structure contains Ni 3 S 2 nanosheets with 15–20 nm in thickness and meso/macropores with an average pore size of 24.69 nm, and its formation is regulated through the slow release of S 2− ions and the solid/liquid interfacial reactions in absolute ethanol. At a current density of 17.15 A g −1 , the composite electrode demonstrates a high specific capacitance of 945.71 F g −1 , and at various current densities below 17.15 A g −1 , it retains capacitance retention ratios above 100% after 2000 charge/discharge cycles. A two-step oxidation and three-step reverse reduction process occurs during the reversible Faradaic reaction of Ni 3 S 2 in KOH aqueous solution, which is due to the valence transitions of Ni 0 in Ni 3 S 2 between Ni 0 and Ni 3+ . The homogeneous cracking in Ni 3 S 2 layer is a critical factor for achieving its long-term cycling stability, however, the cycling results in its amorphization. An asymmetric supercapacitor is assembled using Ni 3 S 2 @Ni composite electrode as the positive electrode and Ni foam as the negative electrode, which delivers an energy density of 55.79 Wh kg −1 at the power density of 938.98 W kg −1 .