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.