Stabilization of Lattice Oxygen Evolution Reactions in Oxophilic Ce‐Mediated Bi/BiCeO_1.8H Electrocatalysts for Efficient Anion Exchange Membrane Water Electrolyzers

Abstract The lattice oxygen mechanism (LOM) offers an efficient reaction pathway for oxygen evolution reactions (OERs) in energy storage and conversion systems. Owing to the involvement of active lattice oxygen enhancing electrochemical activity, addressing the structural and electrochemical stabilities of LOM materials is crucial. Herein, a heterostructure (Bi/BiCeO_1.8H) containing abundant under‐coordinated oxygen atoms having oxygen nonbonding states is synthesized by a simple electrochemical deposition method. Given the difference in reduction potentials between Bi and Ce, partially reduced Bi nanoparticles and surrounding under‐coordinated oxygen atoms are generated in BiCeO_1.8H. It is found that the lattice oxygen can be activated as a reactant of the OER when the valence state of Bi increases to Bi⁵⁺, leading to increased metal–oxygen covalency and that the oxophilic Ce³⁺/⁴⁺ redox couple can maintain the Bi nanoparticles and surrounding under‐coordinated oxygen atoms by preventing over‐oxidation of Bi. The anion exchange membrane water electrolyzer with Bi/BiCeO_1.8H exhibits a low cell voltage of 1.79 V even at a high practical current density of 1.0 A cm⁻². Furthermore, the cell performance remains significantly stable over 100 h with only a 2.2% increase in the initial cell voltage, demonstrating sustainable lattice oxygen redox.