Electrochemical Nitrate Reduction on CuPd Dilute Alloys: Enhancing Ammonium Selectivity and Activity by Tuning Trace Pd Doping

The electrochemical reduction of nitrate offers a pathway to convert industrial nitrate waste into valuable ammonia. However, developing dilute alloy catalysts (often referred to as “single-atom alloys”) that achieve both high selectivity and activity for the electrochemical nitrate reduction reaction (NO 3 RR) is limited by an incomplete mechanistic understanding of composition−activity relationships. Here, we prepared a series of shape-controlled, phase-pure, surfactant-free CuPd dilute alloys with systematically varied Pd dopant loadings at trace levels (0.05–0.9 wt%) into the Cu surface. Electrochemical studies in acidic phosphate buffer reveal a strong dependence of NO 3 RR performance on Pd content. Specifically, CuPd with 0.15 wt% Pd showed a marked enhancement in ammonium yields and Faradaic efficiency—achieving a maximum yield of 258 μmol mg cat −1 h −1 with over 80% Faradaic efficiency for NH 4 + production at −0.8 V vs RHE. This rate of ammonium formation is greater than that observed on Cu 2 O, Cu, and other CuPd dilute alloys with lower (0.05 wt%) and higher (0.45 and 0.9 wt%) Pd loadings under identical conditions. Grand-canonical density functional theory calculations (GC DFT) reveal a Pd ensemble-size-dependent shift in selectivity between nitrate reduction to ammonium and the competing hydrogen evolution reaction. Post-electrolysis analysis demonstrates that the CuPd catalyst undergoes no substantial change in the morphology or composition after the NO 3 RR. These results underscore the advantages of trace Pd incorporation and ensemble control in tuning activity and selectivity, providing design principles for efficient NO 3 RR electrocatalysts.