Tuning Iron Active Sites of FeOOH via Al3+ and Heteroatom Doping‐Induced Asymmetric Oxygen Vacancy Electronic Structure for Efficient Alkaline Water Splitting

Abstract Oxygen evolution reaction is the essential anodic reaction for water splitting. Designing tunable electronic structures to overcome its slow kinetics is an effective strategy. Herein, the molecular ammonium iron sulfate dodecahydrate is employed as the precursor to synthesize the C, N, S triatomic co‐doped Fe(Al)OOH on Ni foam (C,N,S‐Fe(Al)OOH‐NF) with asymmetric electronic structure. Both in situ oxygen vacancies and their special electronic configuration enable the electron transfer between the d‐p orbitals and get the increase of OER activity. Density functional theory calculation further indicates the effect of electronic structure on catalytic activity and stability at the oxygen vacancies. In alkaline solution, the catalyst C,N,S‐Fe(Al)OOH‐NF shows good catalytic activity and stability for water splitting. For OER, the overpotential of 10 mA cm −2 is 264 mV, the tafel slope is 46.4 mV dec −1 , the HER overpotential of 10 mA cm −2 is 188 mV, the tafel slope is 59.3 mV dec −1 . The stability of the catalyst can maintain ≈100 h. This work has extraordinary implications for understanding the mechanistic relationship between electronic structure and catalytic activity for designing friendly metal (oxy)hydroxide catalysts.