Hierarchical Engineering of CuCo2O4/Nickel–Cobalt–Sulfide Electrode for Improved Energy Storage

The CuCo2O4/nickel–cobalt–sulfide (NCS) composite electrode was fabricated on nickel foam (NF) substrate using a combination of hydrothermal method and constant-potential electrodeposition. Supported by the underlying CuCo2O4, the NCS layer was then systematically deposited by varying the deposition time to achieve the optimal deposition amount. This hierarchical architecture maximizes the exposure and utilization of electrochemically active sites from both components. The optimized CuCo2O4/NCS electrode delivers an areal specific capacitance (Cs) of 5.18 F cm−2 at a discharge current density of 2 mA cm−2, with a coulombic efficiency of 99.61%. Upon increasing the current density 30-fold to 60 mA cm−2, the electrode retains 67.95% of its original capacitance. The equivalent series resistance (RESR) is 0.96 Ω cm−2. Cycling stability tests show that 90% of the initial Cs is maintained after 2200 cycles, dropping to 80% at 2900 cycles and remaining stable thereafter.