Identification of in situ Generated Iron-Vacancy Induced Oxygen Evolution Reaction Kinetics on Cobalt Iron Oxyhydroxide

Developing highly efficient and low-cost electrocatalysts towards oxygen evolution reaction (OER) is essential for practical application in water electrolyzers and rechargeable metal-air batteries. Although Fe-based oxyhydroxides are regarded as state-of-the-art non-noble OER electrocatalysts, the origin of performance enhancement derived from Fe doping remains a hot topic of considerable discussion. Herein, we demonstrate that in situ generated Fe vacancies in the pristine CoFeOOH catalyst through a pre-conversion process during alkaline OER result from dynamic Fe dissolution, identifying the origin of Fe-vacancy-induced enhanced OER kinetics. Density functional theory (DFT) calculations and experimental results including X-ray absorption fine-structure spectroscopy, in situ UV-Vis spectroscopy, and in situ Raman spectroscopy reveal that the Fe vacancies could significantly promote the d-band center and valence states of adjacent Co sites, alter the active site from Fe atom to Co atom, accelerate the formation of high-valent active Co4+ species, and reduce the energy barrier of the potential-determining step, thereby contribute to the significantly enhanced OER performance.