A Review on the Recent Developments and Perspectives of Copper-Based Nanoparticles for the Electrochemical Reduction of NOx and COx.

Anthropogenic emissions of carbon oxides (COx) and nitrogen oxides (NOx) arising from industrial activities contribute to environmental and health problems, motivating the development of effective strategies for their mitigation and valorization. Among the available approaches, electrochemical reduction offers the additional possibility of converting COx and NOx species into value-added products that may serve as chemical feedstocks or energy carriers, thereby contributing to carbon and nitrogen resource recovery. However, the practical development of these processes requires catalysts with high activity, selectivity, and stability, supported by synthesis strategies capable of controlling their active structures. Several metals, including Ir, Pt, Rh, Ru, Pd, Ni, Ag, Au, and Cu, have been investigated for the electrochemical reduction of COx and NOx in aqueous media. Among them, Cu is particularly attractive because of its relatively high abundance, tunable oxidation states, and ability to catalyze both reaction families. This review examines Cu-based nanomaterials prepared through different synthesis strategies and analyzes how composition, oxidation state, morphology, exposed facets, defects, alloying, and interfacial structure influence COx and NOx electroreduction. By comparing both reaction families, the review identifies shared structure-active-site-performance relationships together with reaction-specific requirements for intermediate stabilization and product formation. Particular attention is given to in situ and operando evidence showing that Cu-based catalysts may reconstruct under electrochemical conditions, so that the catalytically relevant material can differ from the as-synthesized structure. These insights support catalyst optimization with mechanistically informed design of dynamic Cu-based interfaces for selective COx and NOx electroreduction.