Interfacial Stabilization of Cu^δ+ Sites for Durable Electroreduction of Nitrate to Ammonia

Copper-based materials are widely regarded as promising candidates for the electrochemical nitrate reduction reaction (NO₃^-RR) to ammonia. However, their practical deployment is often compromised by structural instability, specifically aggregation and undesirable reduction during electrolysis. To overcome these limitations, we engineer a cerium oxide-supported copper oxide catalyst featuring tunable interfacial interactions (denoted Cu^δ+O/CeO₂). In situ characterization reveals that robust Cu-O-Ce bonds effectively stabilize electron-rich Cu^δ+ species. This interfacial engineering not only promotes the formation of reactive *H but also effectively inhibits the accumulation of the byproduct NO₂^- and accelerates the hydrogenation of critical intermediates. Consequently, the catalyst 10Cu^δ+O/CeO₂ demonstrates a superior ammonia yield of 6.14 ± 0.35 mg h^-1 mg_cat.^-1 at -1.2 V vs reversible hydrogen electrode (RHE) and a Faradaic efficiency of 78.18 ± 9.30% at -0.8 V vs RHE. Furthermore, the catalyst exhibits exceptional durability, retaining over 95% of its initial activity across 10 consecutive cycles and maintaining stability for 240 h within a membrane electrode assembly. These findings offer a fundamental understanding and a versatile strategy for designing robust catalysts, emphasizing the critical role of strong interfacial synergy in enhancing the selectivity and longevity of nitrate-to-ammonia conversion.