Synthesis of nickel cobalt sulfide on Ni foam for improved electrochemical energy storage: Effect of binder-free reverse pulse potentiostatic electrodeposition and redox additive

Nickel cobalt sulfide (Ni-Co-S) was grown on 3D conductive Ni foam (NF) using binder-free electrochemical deposition to serve as a positive electrode (NCS@NF) for electrochemical energy storage application. Multiple cycles of reverse pulse potentiostatic electrochemical deposition (RPP-ED) were systematically applied to study their influence on the physico-chemical properties of NCS@NF. During the 300 optimized RPP-ED cycles uniform mesoporous interconnected nanoflakes of Ni-Co-S were formed on NF. The NCS@NF electrode demonstrated remarkable electrochemical storage performance, achieving a maximum areal capacity of 0.590 C cm⁻² (590 C g⁻¹) in 2 M KOH electrolyte. This remarkable property of NCS@NF can be associated with the improved ionic diffusion at the interconnected nanoflake structure and improved redox transitions at the active sites of nanoflakes. Moreover, the addition of K₄(CN)₆ as a redox additive improved the areal capacity of NCS@NF to 2.56 C cm⁻² (2560 C g⁻¹). Furthermore, an aqueous hybrid supercapacitor was assembled by integrating activated carbon on NF as the negative electrode, while employing NCS@NF as the positive electrode. The aqueous hybrid supercapacitor exhibited an enhanced charge-discharge potential of 1.5 V and demonstrated remarkable stability, maintaining 89% of its performance over 10,000 cycles. Notably, it achieved maximum energy and power densities, 33 μWh cm⁻² and 6019 μW cm⁻², respectively. These results establish its suitability for hybrid supercapacitor applications.