Preparation of Sandwich-like NiCo2O4/rGO/NiO Heterostructure on Nickel Foam for High-Performance Supercapacitor Electrodes

Supercapacitors have attracted wide attention because of their ultra-high power density, long cycling stability, fast charge/discharge rate, and bridging function for the power and energy gaps between batteries and traditional dielectric capacitors [ 1 , 2 ]. Generally, the electrode materials used for supercapacitors can be divided into two categories based on the different energy storage mechanisms: electrical double-layer capacitors (EDLCs) and pseudo-capacitors (PCs) [ 3 ]. In fact, PCs exhibit much larger capacitance values and energy density than EDLCs due to their fast and reversible redox reaction [ 4 ]. Therefore, considerable efforts have been focused on improving the performance of PCs. It has been recognized that the most used PCs’ electrode materials, including RuO 2 , NiO, Co 3 O 4 , and MnO 2 , possess multiple oxidation states/structures, which enable rich redox reactions on the surface of the electrodes and provide high specific capacitance. However, the poor conductivity and cycling stability of these materials restrict their applications [ 5 – 8 ].