Reverse Built‐in Electric Field via Acid Etching for Efficient Oxygen Evolution Reaction

Developing efficient electrocatalysts for the oxygen evolution reaction (OER) is imperative for electrochemical energy conversion devices such as water electrolyzers and metal‐air batteries. Rationally modulating the charge localization by constructing a built‐in electric field (BEF) is a compelling strategy to boost OER performance, but it remains highly challenging. Here, this work successfully integrates the Ru/Ni co‐mixed oxide (RNO) and the acid‐etched perovskite oxide LaCo 0.9 Fe 0.1 O 3 (H‐LCFO) to construct a RNO/H‐LCFO heterojunction catalyst. Experimental characterization confirms that H‐LCFO increases the interfacial work function difference and reverses the direction of the built‐in electric field (BEF), driving electron transfer from the H‐LCFO to RNO and facilitating the lattice oxygen mechanism (LOM) for OER. Consequently, the RNO/H‐LCFO achieves an overpotential of 260 mV at a current density of 10 mA cm −2 in alkaline solution. When employed as an air cathode in a Zinc‐air battery, it delivers a higher peak power density of 124.2 mW cm −2 than that of Pt/C+RuO 2 and exhibits stable cycling over 180 h. This work demonstrates that defect engineering of perovskite oxides can effectively manipulate the interfacial BEF direction, offering a promising design strategy for high‐performance, cost‐effective OER electrocatalysts.