Vacancy Engineering of Fe-Doped CoNi₂S₄@CC Boosting the Oxygen Evolution Reaction and Overall Water Splitting

Transition metal sulfides have emerged as promising alternatives to precious metal catalysts for sustainable electrocatalytic hydrogen production. However, achieving simultaneous optimization of active site exposure and vacancy-electron interplay remains a critical challenge. Herein, we develop a dual-regulation strategy integrating Fe-doping and high-temperature annealing to synthesize sulfur-deficient Fe-doped CoNi₂S₄@CC nanocatalysts (Fe-CoNi₂S_4-x@CC). The approach innovatively combines heteroatom doping and vacancy engineering, where iron doping leads to lattice dilation and sulfur vacancies create vacancy defects, thereby exposing a large number of active sites. The designed catalysts have iron-induced charge redistribution and vacancy tailored adsorption energies synergistically in the dual active center and expose more active sites to accelerate charge transfer. Intriguingly, the Fe-CoNi₂S_4-x@CC achieves a low overpotential of 194.72 mV@10 mA cm^-2 in alkaline media, surpassing most reported CoNi-based sulfides. More remarkably, it demonstrates exceptional kinetics with a Tafel slope of 43.2 mV dec^-1 and enhanced active site utilization evidenced by its high electrochemical double layer capacitance value (31.3 mF cm^-2). This work presents a significant advance for the rational design of high-performance OER catalysts by demonstrating a synergistic modulation strategy that integrates cation doping and vacancy engineering in Fe-doped CoNi₂S₄@CC, which not only optimizes the electronic structure but also increases the rate of charge transfer to enhance the catalytic activity.