Sulfate-Terminated High-Entropy Oxyhydroxide Porous Nanocubes for Efficient Nitrate-to-Ammonia Conversion

Electrochemically coupling the nitrate reduction reaction (NO 3 RR) with the oxygen evolution reaction (OER) enables simultaneous pollution mitigation and efficient ammonia synthesis. However, slow kinetics in both reactions, particularly water dissociation and NO 3 – hydrogenation, limit Faradaic efficiency (FE), yield rate, and energy consumption. Designing catalysts that overcome these dual kinetic barriers is challenging. High-entropy materials (HEMs) offer promise due to compositional diversity and lattice distortion effects, but precise synthesis is difficult. This work employs porous high-entropy sulfide nanocubes (NiCoFeCuMn-S) as precatalysts. These electrochemically transform into sulfate-terminated oxyhydroxides (NiCoFeCuMnOOH–SO 4 2– ), which serve as the active species. The resulting catalyst delivers exceptional bifunctional performance in alkaline electrolyte: an ultralow OER overpotential (216 mV @ 10 mA cm –2 ), high NH 3 FE (94.5%), and yield rate (21.8 mg h –1 mg cat –1 ). In situ spectroscopy shows that multimetallic synergy enables efficient OER mechanisms. Density functional theory reveals that coordinated sulfate lowers the water dissociation barrier, facilitating proton transfer and accelerating NH 3 synthesis. This work presents a promising design strategy for efficient bifunctional high-entropy electrocatalysts.