Unveiling the mechanism of the Fe-doping-enhanced oxygen evolution reaction of CoSe

Abstract

Although iron doping is widely reported to boost the oxygen evolution reaction (OER) activity of transition metal-based catalysts, its role in triggering in situ structural evolution remains poorly understood. Herein, we synthesize an Fe-doped CoSe catalyst and systematically elucidate its activation mechanism. Under OER conditions, Fe doping weakens the Co–Se bond and shifts the d-band center toward the Fermi level, thereby triggering the structural evolution of CoSe into highly active CoOOH and Co₃O₄. This process is accompanied by in situ Se leaching, and the sequential oxidation of Se species to selenate, together with the oxidation of Fe³⁺/Co³⁺ to higher valence states species. The reconstructed CoFeOOH@SeO₄²⁻ lowers the energy barrier of the rate-determining *OH → *O step. As a result, the CoFeSe delivers an overpotential of only 265 mV to achieve a current density of 10 mA cm⁻² with a relatively low Tafel slope of 57.3 mV dec⁻¹. Moreover, the anion exchange membrane water electrolyzer (AEMWE) assembled with CoFeSe/NF‖NMF achieved a current density of 100 mA cm⁻² at a voltage of 1.82 V, which is lower than that of RuO₂‖NMF (1.98 V), highlighting its potential for practical implementation.