Robust Oxygen-Vacancy-Engineered Co(OH)2/Cu Heterostructures Boost Nitrate Electroreduction to Ammonia beyond 2 A cm-2.

Electrocatalytic nitrate reduction reaction (NO3RR) presents a sustainable paradigm for green NH3 synthesis and NO3 - wastewater valorization. However, overcoming sluggish NO3RR kinetics under industrial-current operation persists as a critical challenge. Herein, robust oxygen vacancy-enriched heterostructures (Ov-Co(OH)2/Cu) are engineered through in situ electrochemical reconstruction. By coupling Cu-mediated NO3 --to-NO2 - conversion with Ov-Co(OH)2-accelerated NO2 --to-NH3 transformation, this heterostructured system delivers an unprecedented NH3 yield rate of 167.8 mg h-1 cm-2 and 97.7% Faradaic efficiency at >2 A cm-2, while maintaining exceptional current tolerance over 25 h. Operando spectroscopic characterizations and theoretical calculations reveal that the introduction of Ov in Co(OH)2 synergistically accelerates water dissociation to ensure continuous hydrogen supply and optimizes *NOOH adsorption, reducing the energy barrier for the rate-limiting step (*NO2 to *NOOH). To demonstrate practical viability, a membrane-electrode-assembly electrolyzer integrating NO3RR with glycerol oxidation reaction achieves highly effective co-production of NH3 and formate alongside wastewater treatment. This work offers new insights into the rational design of electrocatalysts through in situ reconstruction-induced vacancy engineering for scalable and practical NO3RR applications.