Deoxygenation‐Induced Lattice Distortion in CuO _x for Efficient Methane Diolate Anion Oxidation and Bipolar Hydrogen Evolution

Abstract Hybrid water electrolysis represents apromising approach for energy‐efficient hydrogen (H 2 ) production. Herein, a highly active and selective electrocatalyst is reported for formaldehyde oxidation reaction (FOR), comprised of electrochemically deoxygenated copper nanosheet arrays supported on copper foam (D O ‐Cu‐NS/CF). Comprehensive in‐situ and ex‐situ characterization confirms the formation of a Cu‐rich, defect‐abundant surface during deoxygenation. Using solid paraformaldehyde (p‐HCHO) as anodic feedstock, D O ‐Cu‐NS/CF achieves remarkable current densities of 500 and 963.3 mA cm −2 at low potentials of merely 0.199 and 0.495 V versus RHE, respectively. Theoretical simulations demonstrate that p‐HCHO exists primarily as methane diolate anions (MDA) in alkaline media, and the lattice distortion in D O ‐Cu‐NS/CF significantly enhances MDA adsorption and oxidative dehydrogenation, leading to outstanding FOR performance. A membrane electrode assembly (MEA) utilizing D O ‐Cu‐NS/CF as the anode enables efficient bipolar H 2 production at 0.7 V for 280 h with a current density up to 500 mA cm −2 . This work highlights the crucial role of lattice engineering inenhancing FOR activity and offers new insights into the electrooxidation process of p‐HCHO. The D O ‐Cu‐NS/CF electrode developed shows significant potential for use as a cost‐effective anode for energy‐saving, high‐rate production of H 2 through hybrid water electrolysis.