Spatial Confinement Modulated Ru/WO3 Heterointerface for Tandem Nitrate-to-Ammonia Conversion in Neutral Electrolytes.

To address the challenges of weak NO3- adsorption, insufficient active hydrogen supply, and facile desorption of NO2- intermediates in neutral electrocatalytic nitrate reduction reaction (NO3RR), this study employs laser nano-welding technology to fabricate a Ru/WO3 heterojunction, and constructs a Ru/WO3/Cu(OH)2/FC spatially confined electrode using Cu(OH)2 nanorod arrays as the support. Laser welding achieves metallurgical-grade bonding between Ru and WO3 while retaining oxygen vacancies in WO3. Cu(OH)2 promotes NO3- adsorption via electrostatic and Lewis acid interactions, and its nanorod array structure confines NO2- intermediates. In 0.5 M K2SO4 + 50 mM KNO3 electrolyte, the electrode delivers an ammonia yield rate of 16.1 mg h-1 cm-2 and a Faradaic efficiency of 75.8% at -0.8 V vs. RHE, outperforming control groups. Potential-dependent electrochemical impedance spectroscopy (EIS) confirms that spatial confinement suppresses NO2- accumulation and optimizes interfacial charge transfer kinetics, providing a new strategy for electrode design in neutral NO3RR.