Coordination Tailoring of Epitaxial Perovskite-Derived Iron Oxide Films for Efficient Water Oxidation Electrocatalysis

Cost-effective perovskite oxides have recently offered intriguing promise for electrochemical energy storage and conversion systems. Despite the breadth of previously studied electronic structures and properties, the sluggish kinetics of the oxygen evolution reaction (OER) of perovskite oxides basically restrict their applications in metal-air batteries and electrolytic cells. In this work, we report on a highly efficient OER activity of perovskite-derived SrFeO_3−δ (0.0 ≤ δ ≤ 1.0) single-crystal films by selectively tuning the Fe-O coordination structure and film orientation. Our findings show that the facile anionic oxygen-induced topotactic brownmillerite phase of the SrFeO_2.5 film possesses superior electrocatalytic performance with a small overpotential and Tafel slope, which is mainly attributed to the peculiar Fe-O coordination framework along with ordered oxygen vacancy channels. Moreover, the low adsorption free energy and small charge transfer resistance could further boost the electrocatalytic OER performance of the (111)-oriented BM-SrFeO_2.5 films. This delicate tailoring of the epitaxial SrFeO_3−δ films enables the tunable catalytic reaction pathways and concomitantly efficient OER kinetics, which has significant implications for the rational design of cost-effective and high-performance perovskite-based electrocatalysts.