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

Abstract

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.