Stabilizing Lattice Oxygen Evolution with Oxophilic Ce and Active Ni Oxide Composite Electrocatalysts for Efficient Anion Exchange Membrane Water Electrolyzers

In transition metal oxide (TMO) based oxygen evolution reactions (OER) electrocatalysts, the lattice oxygen-mediated mechanism (LOM) has emerged as a more efficient pathway for OER compared to the traditional adsorbate evolution mechanism (AEM). LOM activation critically depends on covalency of transition metals (TMs) with high-valence states. In this study, we leverage the high electron affinity and strong oxophilicity of cerium (Ce) to fine-tune the TM-O bonding state of NiO through a one-step electrodeposition method. Ce and Ni co-electrodeposition forms a CeO₂/NiO heterostructure that shifts from AEM to LOM via enhanced covalency between high- valence Ni and lattice oxygen and promotes electron transfer from NiO to CeO₂. This CeO₂/NiO heterostructure achieves a low overpotential of 160 mV and a Tafel slope of 32.68 mV dec^⁻1 at 10 mA cm^⁻2. Additionally, it exhibits a low cell voltage of 1.84 V and only a 1.19% voltage increase over 100 h at a high current density of 1 A cm^⁻2 in an anion exchange membrane water electrolyzer. These results represent the role of oxophilic Ce and CeO₂ in stabilizing the Ni oxidation states, thereby ensuring superior LOM-driven OER performance.