The modulated oxygen evolution reaction performance of LaFeO₃ with abundant electronic structures via a design of stoichiometry offset

Transition metal oxides have been widely employed as electrocatalysts in various electrochemical processes such as oxygen evolution reaction (OER) owing to their designable adsorption/desorption ability of water intermediates by engineering their electronic structures. However, the coexistence of multiple chemical valences of the transition metal always hides the realization of the functional active phase in OER. In this study, we have performed the OER measurements on LaFeO₃ (LFO) catalysts to reveal the complex relationships between 3d electronic structure and its OER responses; herein, several electronic statuses, including t⁴_2ge²_g (S = 2), t⁵_2ge¹_g (S = 1), or t⁶_2ge⁰_g (S = 0) of Fe ions, can be dominantly achieved by the design of stoichiometry offset in LFO. It is found that the current density of LFO at 1.9 V shows a volcanic dependence on the oxygen content. After the comprehensive characterization of Fe and oxygen ions in LFO by X-ray photoelectron spectroscopy and magnetic hysteresis measurements, we have found the OH⁻ adsorption capacity and exchange interaction of Fe ions jointly determine the OER performance. Our research provides a stepwise evolution of the multiple spin states in LFO, and their subsequent OER responses are demonstrated, which can benefit the fundamental understanding of the link between 3d electronic structure and OER performance and the design for further promising transition metal oxide catalysts.