Mo as a Bifunctional Active Site in a High-Entropy Oxide for Stable and Selective Seawater Electrolysis

The anode corrosion and competitive chlorine evolution reaction due to the existence of high-concentration Cl− are significant obstacles for the commercialization of hydrogen production through seawater electrolysis. Herein, a high-entropy (FeCoNiCuMo)2O4 incorporating a highly selective OH− adsorption active site was designed and synthesized as an efficient and robust anode material for alkaline seawater oxidation. For the oxygen evolution reaction (OER) over this high-entropy oxide, low overpotentials of 232 and 313 mV at 10 and 100 mA cm−2 in 1 M KOH + seawater, respectively, are achieved. Crucially, it demonstrates impressive stability under an industrial-level current density of 1 A cm−2 over 1000 h without obvious activity degradation and hypochlorite species generation, which should be primarily attributed to the existence of Mo in the high-entropy oxide. Post characterizations confirm the increased proportion of oxygen vacancy, and the strong pH-dependent OER performance suggests that the OER proceeds predominantly via the lattice oxygen oxidation mechanism. Density functional theory calculations reveal that Mo as the primary active site is also the only site that can stably adsorb Cl−. More notably, it demonstrates that the stronger competitive adsorption of OH− over Cl− guarantees selectivity and stability. Additionally, the partially leached Mo for the generation of MoO42− also contributes to mitigating Cl− adsorption, providing a second safeguard for selectivity and stability. This study provides an insight into developing stable and selective anodic electrocatalysts for seawater electrolysis.