Understanding the Activity Trends in Electrocatalytic Nitrate Reduction to Ammonia on Cu Catalysts

Cu-based catalysts possess great potential in the electrocatalytic nitrate (NO₃^-) reduction reaction for ammonia (NH₃) synthesis. However, the low atomic economy limits their further application. Here we report a Cu single-atom (SA) incorporated in nitrogen-doped carbon (Cu SA/NC) with high atomic economy, which exhibits superior NH₃ Faradaic efficiency (FE) of 100% along with an impressive NH₃ yield rate of 7480 μg h^-1 mg_cat.^-1. As counterparts, Cu_s+n/NC, with mixed SA and nanoparticles (NPs), shows decreasing NH₃ FE with decreasing SA content, but the production of N₂ and N₂O increases gradually, which reaches the maximum on pure Cu NPs. In situ characterizations and theoretical calculations reveal that a higher NH₃ FE of Cu SA/NC is ascribed to a lower free energy of the rate-limiting step (HNO* → N*) and effective inhibition for the N-N coupled process. This work provides the intuitive activity trends of Cu-based catalysts, opening an avenue for subsequent catalysts design.