Enhanced active hydrogen supply promotes interfacial tandem electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction to ammonia (NRA) provides a promising approach for both nitrogen pollution mitigation and green ammonia production. However, its efficiency is hindered by the slow kinetics of multi-proton-coupled electron transfer and the competing hydrogen evolution reaction (HER). In this work, a Cu₃P/Co(PO₃)₂ heterojunction electrocatalyst was rationally designed, where Co sites serve as main active centers for adsorbing and activating NO₃^-, and Cu sites effectively supply critical active hydrogen (*H) species. Theoretical calculations further validate interfacial charge redistribution at the heterointerface and resulting optimized electronic structure, particularly confirming kinetically favorable *H generation at Cu sites for the Volmer step. This Cu₃P/Co(PO₃)₂ achieves an outstanding NH₃ Faradaic efficiency (FE) of 98.1 ± 0.8 % and yield rate of 5.4 ± 0.2 mg h^-1 cm^-2 at -0.3 V versus the reversible hydrogen electrode (RHE). In situ characterizations and theoretical calculations reveal a well-defined reaction pathway dominated by efficient stepwise deoxygenation and hydrogenation. Moreover, a practical Zn - NO₃^- battery system employing Cu₃P/Co(PO₃)₂ as the cathode is successfully assembled, which concurrently delivers electrical energy and green ammonia synthesis with robust cycling stability.