Surface reconstruction-driven WCuNiMo alloy for efficient ammonia oxidation and hydrogen evolution

The global transition toward renewable energy necessitates the development of highly efficient electrocatalysts for sustainable hydrogen production. Herein, a multimetallic WCuNiMo catalyst was synthesized via a hydrothermal-calcination route, followed by post-treatment under reductive (H₂/Ar) and oxidative (air) atmospheres to obtain a metallic WCuNiMo alloy and its oxidized counterpart (WCuNiMoO_x), respectively. The resulting WCuNiMo alloy features a nanostructured architecture with enhanced electrical conductivity and abundant electrochemically accessible active sites. Owing to the synergistic electronic interactions among W, Cu, Ni, and Mo and favorable structural characteristics, the catalyst demonstrates outstanding bifunctional electrocatalytic activity toward the ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) in alkaline media. Specifically, the WCuNiMo alloy achieves a current density of 100 mA cm^-2 at an ultralow potential of 1.37 V vs. RHE for AOR, which is significantly lower than the 1.65 V required for the oxygen evolution reaction (OER) under identical conditions. Meanwhile, it delivers a low HER overpotential of 186 mV at 10 mA cm^-2, outperforming its oxidized counterpart. Electrochemical impedance spectroscopy coupled with in situ Fourier-transform infrared (FTIR) spectroscopy reveals accelerated charge transfer kinetics and a stepwise ammonia dehydrogenation pathway governed by the Oswin-Salomon (O-S) mechanism. When integrated into a model alkaline electrolyzer, the symmetric WCuNiMo∥WCuNiMo configuration operates at a low cell voltage of 1.67 V to deliver 100 mA cm^-2, accompanied by a high hydrogen evolution rate of 1.366 mmol h^-1 cm^-2 with nearly 100% faradaic efficiency and 64% ammonia removal after 24 hours. This work demonstrates the critical influence of calcination atmosphere on structural and functional optimization, offering a promising strategy for efficient hydrogen production and ammonia-containing wastewater remediation.