Interface-engineered Co-Ni-S composite electrode for ultrahigh capacitance and water oxidation

Abstract

Transition metal sulfides (TMSs) are promising candidates for electrochemical energy storage and water splitting, but their practical application is hindered by limited conductivity and sluggish ion transport. Herein, we present an interface-engineered Co-Ni-S composite electrode prepared through a two-step process involving electrodeposition followed by hydrothermal sulfurization, which effectively preserves cobalt active sites while optimizing interfacial characteristics. This architecture enhances redox kinetics, electron mobility, and ion diffusion, resulting in a highly porous nanosheet structure with exceptional electrochemical performance. The Co-Ni-S composite electrode delivers an ultrahigh specific capacitance of 3586 F g⁻¹ at 1 A g⁻¹ and maintains 97% capacity retention over 5000 cycles. Simultaneously, it exhibits outstanding oxygen evolution reaction (OER) activity, requiring a low overpotential of 210 mV at 10 mA cm⁻² and showing long-term stability over 50 hours. Density functional theory (DFT) calculations confirm the presence of stable Co-Ni-S bonding and synergistic charge transfer. When assembled in an asymmetric supercapacitor device, the electrode achieves a remarkable energy density of 172 Wh kg⁻¹ and high-rate capability. These findings highlight the potential of interface-engineered bimetallic sulfides as multifunctional materials for next-generation energy storage and water-splitting technologies.