Valorizing Nitrate in Electrochemical Nitrogen Cycling: Copper-Based Catalysts from Reduction to C-N Coupling

Electrochemical nitrate reduction (NO₃RR) offers a sustainable approach to mitigating nitrogen pollution while enabling the resourceful conversion of nitrate (NO₃ ^-) into ammonia (NH₃), nitrogen gas (N₂), and value-added chemicals such as urea. Copper (Cu)-based catalysts, with their versatile catalytic properties and cost-effectiveness, have emerged as pivotal materials in advancing NO₃RR. This review systematically summarizes recent progress in Cu-based catalysts for NO₃RR, focusing on their catalytic mechanisms, tuning strategies, and applications across diverse product pathways. The intrinsic self-reconstruction behavior and synergistic effects of Cu-based catalysts are elucidated alongside advanced in situ characterization techniques that reveal dynamic structural evolution and intermediate interactions during reactions. We comprehensively discuss the performance of Cu-based catalysts in steering NO₃RR toward NH₃ or N₂ production, emphasizing the role of catalyst design (e.g., single atoms, alloys, oxides, hydroxides) in enhancing selectivity and efficiency. Furthermore, the multifunctionality of Cu catalysts is exemplified through carbon-nitrogen (C-N) coupling reactions, where reactive nitrogen intermediates are valorized into urea. Key challenges and future directions are outlined to guide the rational design of Cu-based systems for efficient electrochemical nitrogen cycling.