Activating lattice oxygen by a defect-engineered Fe₂O₃-CeO₂ nano-heterojunction for efficient electrochemical water oxidation

The sluggish anodic oxygen evolution reaction (OER) is currently the major hinderance for hydrogen production from water splitting. Iron-based materials are promising cost-effective candidates for OER electrocatalysts, however their low intrinsic activity limits their performance. Here we report a defect-engineered Fe₂O₃-CeO₂ heterojunction with rich oxygen vacancies (Fe₂O₃@CeO₂-O_V), exhibiting ultralow overpotential of 172 mV at 10 mA cm⁻² and 317 mV at 1000 mA cm⁻², respectively, alongside superior stability and durability. Advanced characterization and density functional theory calculations demonstrate that defect engineering combined with heterojunction formation activates the lattice oxygen, switching the reaction pathway from the conventional adsorbate evolution mechanism (AEM) to the lattice oxygen mechanism (LOM). The oxygen vacancies are revealed to form preferably on CeO₂ and induce not only electronic but also geometric modulation, contributing to strong Fe₂O₃-CeO₂ interfacial interaction and charge transfer from CeO₂ to Fe₂O₃, facilitating the O₂ desorption and boosting the intrinsic activity.