Dynamic tuning of d-p orbital hybridization during sulfur vacancy evolution in Co9S8 toward efficient overall water splitting

Defect engineering significantly enhances electrocatalytic performance by modulating electronic structures and interfacial coordination, yet the dynamic correlation between defect evolution and catalytic activity during reactions remains unclear. Herein, density functional theory (DFT) calculations first reveal the modulation of sulfur vacancy concentrations on Co₉S₈ electronic structures, predicting that optimized vacancy concentrations enable highly efficient electrocatalytic water splitting. Experimentally fabricated Co₉S₈ with appropriate sulfur vacancies exhibits superior bifunctional activity (HER: 164 mV@η₁₀; OER: 297 mV@η₁₀₀). The MCS-assembled overall water splitting system demonstrates stable operation at 1.57 V (10 mA cm⁻²) for over 60 h. Experimental studies illustrate that sulfur vacancies preferentially adsorb OH⁻ during reactions, inducing the formation of CoOOH active phases. DFT analysis further indicates that OH⁻ adsorption weakens d-p orbital hybridization, optimizing hydrogen/oxygen intermediate adsorption energy barriers and ultimately enhancing catalytic performance. This work establishes novel paradigms for systematic development of catalysts through synergistic analysis of defect dynamics, electronic structures and catalytic performance.