Improving electrocatalytic nitrate-to-ammonia conversion by balancing evolution and consumption with single-atom Pd doping

The efficient utilization of active hydrogen (*H) in electrocatalytic processes remains a critical challenge for achieving high selectivity in nitrate reduction to ammonia (NO 3 − RR), as excessive *H often promotes the competing hydrogen evolution reaction (HER), leading to reduced Faradaic efficiency and ammonia yield. Herein, we address this issue by designing a single-atom Pd-doped Cu/Cu 2 O electrocatalyst (SA Pd–Cu/Cu 2 O) that precisely modulates *H generation and consumption. The SA Pd–Cu/Cu 2 O catalyst achieves an exceptional NH 3 yield rate of 1634.14 μg h −1 mg −1 , a NO 3 − –N conversion of 97.56%, a NH 3 –N selectivity of 98.13%, and a Faradaic efficiency of 92.13% at −0.8 V vs. RHE. In situ spectroscopic studies and density functional theory (DFT) calculations reveal that single-atom Pd sites serve as hydrogenation centers that generate moderate *H, which is efficiently consumed by nitrogen-containing intermediates, thereby suppressing HER. In contrast, nanoparticle Pd doping produces excess *H, favoring HER. This work demonstrates an innovative strategy for balancing *H utilization via atomic-scale metal doping, offering new insights into the design of high-selectivity electrocatalysts for sustainable ammonia synthesis and environmental nitrate remediation.