Interface-Engineered Co-Ni-S 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 report a novel interface-engineered Co-Ni-S electrode synthesized via a two-step electrodeposition-sulfurization strategy that retains cobalt active sites while promoting optimized 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 electrode delivers an ultrahigh specific capacitance of 3,586 F g⁻ 1 at 1 A g⁻ 1 and maintains 97% capacity retention over 5,000 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 nextgeneration energy storage and water-splitting technologies.