When electrocatalytic nitrate reduction meets copper-based atomic site catalysts

Human activities have elevated the nitrate (NO3-) levels in water, posing significant threats to human health and the ecosystem. The electrocatalytic nitrate reduction reaction (NO3RR) is a potential technology that eliminates NO3- and converts it to harmless N2 and value-added NH3. Copper (Cu)-based catalysts are strong contenders for the NO3RR due to their low cost, fast reduction kinetics, and flexible electronic structure. Single-atom catalysts (SACs), as an epitome of atomic site catalysts, have attracted considerable attention owing to their remarkable atom utilization efficiency and distinctive coordination geometries. With the ongoing development of SACs, two types of atomic site catalysts, Cu-based single-atom alloys (SAAs) with more stable alloy bonds and Cu-based dual-atom catalysts (DACs) featuring two adjacent metal sites, have gradually come into prominence. This comprehensive review delves into the recent advancements in Cu-based atomic site catalysts for the NO3RR. It discusses the diverse coordination structures, single-atom reconstruction, and coexistence phenomena in Cu-based SACs. Furthermore, it examines the doping of different single atoms at the Cu matrix interface in Cu-based SAAs, and the synergistic effects observed in Cu-based DACs. Lastly, we highlight the challenges and prospects facing Cu-based atomic site catalysts in future, with the aspiration of contributing to the advancement of Cu-based atomic site catalysts in the NO3RR. This manuscript comprehensively reviews the recent advancements in Cu-based atomic site catalysts in the NO3RR, following a sequential order with six sections: Introduction, Mechanism, Cu-based SACs, Cu-based SAAs, Cu-based DACs, and Perspectives.