Defect‐Rich High‐Entropy Spinel Oxide as an Efficient and Robust Oxygen Evolution Catalyst for Seawater Electrolysis

ABSTRACT Overall seawater splitting driven by regenerable electricity is an ideal pathway for mass production of green hydrogen. Nonetheless, its anodic oxygen evolution half‐reaction (OER) confronts sluggish kinetics, competitive chlorine evolution, and chloride corrosion or poisoning problems, needing to develop high‐efficient and robust electrocatalysts toward those challenges. Herein, novel defect‐rich single‐phase (NiCoMnCrFe)3O4 high‐entropy spinel oxide (HEO) is fabricated by low‐temperature annealing of high‐entropy layered double hydroxide precursor. Due to the presence of abundant defects, unique “cocktail” effect, and efficient electronic structure regulation, such (NiCoMnCrFe)3O4 can deliver 500 mA cm−2 current density at the overpotentials of 268/384 mV in alkaline freshwater/seawater, outperforming its counterparts, commercial IrO2, and most reported OER catalysts. Moreover, it manifests exceptional OER durability and anticorrosion capability. Theoretical calculations reveal that the eg occupancies of surface Mn atoms are closer to 1.0, which may be the activity origin of such HEO. Importantly, the constructed (NiCoMnCrFe)3O4||Pt/C electrolyzer only requires 1.57 V cell voltage for driving overall seawater splitting to reach 500 mA cm−2 current under real industrial conditions. This work may spur the development of advanced OER electrocatalysts by combining entropy and defect engineering and accelerate their applications in seawater splitting, metal–air batteries, or marine biomass electrocatalytic conversion fields.