Oxygen Vacancy‐induced Electron Density Tuning of Fe₃O₄ for Enhanced Oxygen Evolution Catalysis

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction (OER) catalysts, there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts. Herein, Fe₃O₄ with oxygen vacancies (Fe₃O₄‐Vac) was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms. The electron density of Fe₃O₄‐Vac around Fe atoms increased compared to that of Fe₃O₄ according to the characterization of synchrotron‐based X‐ray absorption near‐edge structure (XANES), extended X‐ray absorption fine structure (EXAFS) spectra, and density functional theory (DFT) calculation. Moreover, the DFT results indicate the enhancement of the desorption of HOO* groups which significantly reduced the OER reaction barrier. Fe₃O₄‐Vac catalyst shows an overpotential of 353 mV, lower than that of FeOOH (853 mV) and Fe₃O₄ (415 mV) at 10 mA cm⁻², and a low Tafel slope of 50 mV dec⁻¹ in 1 M KOH, which was even better than commercial RuO₂ at high potential. This modulation approach provides us with valuable insights for exploring efficient and robust water‐splitting electrocatalysts.