A Redox-Buffering System for Stabilizing the Lattice Oxygen Mechanism in CeO₂/FeOOH Heterostructure Electrocatalysts for Highly Stable Anion Exchange Membrane Water Electrolyzers

Lattice oxygen participation is crucial for oxygen-evolution reaction (OER) performance, but stabilizing the active high-valence cation remains a major challenge. This study focuses on iron oxyhydroxide (FeOOH), which exhibits a delicate balance between high-valence states and stability. A heterostructure (CeO₂/FeOOH) with an electron-rich, high-valence-state interface was synthesized via a simple co-precipitation method. Due to the work-function disparity between CeO₂ and FeOOH, electron accumulation occurs in CeO₂, while FeOOH attains a high-valence state. This enhanced valence state strengthens Fe–O covalency, facilitating lattice oxygen participation in oxygen-evolution reaction. Furthermore, electron-abundant CeO₂ functions as a redox buffer, where the electron-reservable Ce³⁺/Ce⁴⁺ redox couple stores excessive oxygen and donates electrons to stabilize high-valence FeOOH. By incorporating this “redox-buffering system,” Fe dissolution was minimized, significantly improving catalyst stability under harsh oxidizing conditions. The anion exchange membrane electrolyzer exhibited outstanding performance, delivering a current density of 500 mA cm⁻² at 1.69 V, with remarkable stability over 100 h at 1 A cm⁻². These findings provide a new strategy for stabilizing high-valence-state oxygen-evolution reaction catalysts, offering valuable insights for designing efficient and durable electrochemical systems.