Modulating the electronic structure of nickel sulfide via defect engineering for efficient bifunctional overall water splitting

Defect-enriched nickel sulfide (D-Ni₃S₂) nanosheets grown on Ni foam are designed as an efficient bifunctional electrocatalyst for overall water splitting (OWS). The optimal (D₂-Ni₃S₂) catalyst exhibits overpotentials of 52 mV for hydrogen evolution reaction and 210 mV for oxygen evolution reaction at 10 mA cm⁻². With regard to the OWS, the assembled two-electrode (D₂-Ni₃S₂//D₂-Ni₃S₂) alkaline electrolyzer requires a low cell voltage of 1.52 V at 10 mA cm⁻², with robust stability over 100 h, outperforming the commercial Pt/C-IrO₂ couple and is even comparable to the most reported Ni₃S₂-based heterostructure electrocatalysts. Combined with density functional theory calculations, the rich defects can improve the electric conductivity and tune the chemisorption of H⁺ and OH⁻, thus remarkably enhancing the OWS activity. This work offers a promising avenue to design efficient bifunctional catalysts toward OWS by defect engineering.