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

Abstract Electrocatalytic nitrate reduction reaction (NO ₃ RR) presents a sustainable paradigm for green NH ₃ synthesis and NO ₃ ⁻ wastewater valorization. However, overcoming sluggish NO ₃ RR kinetics under industrial‐current operation persists as a critical challenge. Herein, robust oxygen vacancy‐enriched heterostructures (O _v ‐Co(OH) ₂ /Cu) are engineered through in situ electrochemical reconstruction. By coupling Cu‐mediated NO ₃ ⁻ ‐to‐NO ₂ ⁻ conversion with O _v ‐Co(OH) ₂ ‐accelerated NO ₂ ⁻ ‐to‐NH ₃ transformation, this heterostructured system delivers an unprecedented NH ₃ 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 O _v 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 ( ^* NO ₂ to ^* NOOH). To demonstrate practical viability, a membrane‐electrode‐assembly electrolyzer integrating NO ₃ RR with glycerol oxidation reaction achieves highly effective co‐production of NH ₃ 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 NO ₃ RR applications.