Insights into the Dynamics of In Situ Formed Active Cuδ+ Clusters in CuOx Electrocatalysts during the Nitrate Reduction Reaction

Abstract Hetero-structured Cu-based systems with positively charged active centers have emerged as a promising catalyst for the nitrate reduction reaction (NO3RR). We systematically investigate the factors governing long-term NO3RR performance through comprehensive electrochemical analysis and post-catalytic characterization of CuO, Cu2O, and Cu catalysts. Among the studied systems, Cu2O exhibits superior performance, achieving a maximum ammonia yield rate of 945.75 μg h−1 mgcat−1 at −1.4 V (vs Ag/AgCl(sat.KCl)) with a Faradaic efficiency (FE) of 62.69%, outperforming CuO and Cu under identical conditions. CuO and Cu2O demonstrate enhanced selectivity toward ammonia over nitrite across all potentials, whereas metallic Cu shows significantly higher nitrite formation (31% FE), nearly fourfold greater than that of the oxides. The higher NO3RR to ammonia performance of CuOx catalysts is attributed to the feasible in situ formation of polarized Cuδ+ species/clusters, supported by the insights gained through in situ X-ray absorption spectroscopy and post-mortem analysis. This study elucidates the relationship between the dynamically formed Cuδ+ species/clusters and the retention of interfacial active surface area, which is sustained through the dissolution−redeposition dynamics of copper ions at the catalyst−electrolyte interface.