High-Entropy Metal Ammonium Phosphate Superstructure Nanocatalysts for Highly Efficient Water Oxidation and Methanol Oxidation.

Electrochemical water splitting faces a major challenge due to the sluggish kinetics of the oxygen evolution reaction (OER). This study proposes an innovative strategy to replace OER with the thermodynamically favorable methanol oxidation reaction (MOR) while producing high-value formic acid. The study develops a novel series of metallic ammonium phosphate electrocatalysts (NPOs·nH2O) through a facile chemical precipitation method, including the high-entropy FeCoNiCuMn-NPO·nH2O. The unique superstructure coupled with multi-element synergy enables abundant active site exposure, optimized electronic configuration, and enhanced charge transfer capability. Remarkably, the high-entropy catalyst demonstrates exceptional bi-functional performance: achieving ultralow overpotentials of 204/289 mV at 10/100 mA cm-2 for OER, and requiring only 1.3 V versus RHE to deliver 10 mA cm-2 in MOR-assisted electrolysis. Particularly, it exhibits high normalized activity (electrochemically active surface area activity: 16.6 mA cm-2, mass activity: 980 mA mg-1) with 94% Faradaic efficiency for formic acid production. The catalyst maintains >120 h stability at industrial-level current density (100 mA cm-2), outperforming most reported transition metal-based electrocatalysts. This work establishes a new paradigm for designing high-entropy electrocatalysts through structural engineering and composition optimization, providing crucial insights for sustainable energy conversion and biomass valorization.