Activating the O−O Coupling through NiMoO ₄ ‐CeO ₂ Nano‐Heterojunction with Abundant Oxygen Vacancies for Efficient Electrocatalytic Water Oxidation

ABSTRACT The primary bottleneck in electrochemical water splitting efficiency is the sluggish kinetics of the anodic oxygen evolution reaction (OER), which involves a multi‐step, proton‐coupled electron transfer (4e − ) process. Bimetallic oxides stand out as ideal candidates for OER electrocatalysis owing to their low cost and high stability; however, their practical application is constrained by insufficient intrinsic catalytic activity. In this study, we synthesized a flower‐like microsphere of a defect‐engineered NiMoO 4 ‐CeO 2 heterojunction with abundant oxygen vacancies (denoted as NiMoO 4 @CeO 2 ‐O v ) via a facile hydrothermal method. This catalyst exhibits a remarkably low overpotential of 229 mV at a current density of 100 mA cm −2 , along with excellent stability and long‐term durability. X‐ray absorption fine structure (XAFS) characterization and density functional theory calculations indicate that the combination of defect engineering and heterojunction formation can activate lattice oxygen. In situ spectroscopy and 18 O isotope‐labeled differential electrochemical mass spectrometry (DEMS) unambiguously confirm the occurrence of direct intramolecular lattice oxygen coupling through the lattice oxygen mechanism (LOM) in NiMoO 4 @CeO 4 ‐O v during the OER process. This methodology provides a feasible and practical pathway for the efficient deployment of nickel‐molybdenum‐based electrocatalysts in industrial‐scale water electrolysis for hydrogen generation.