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

Abstract

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.