Promoting Electroreduction of Nitrate to Ammonia in Neutral Media via the Synergistic Effect of Atomically Dispersed Fe, Cu, and Pd Sites

Electrochemical nitrate (NO₃⁻) reduction presents a multifunctional strategy to remediate NO₃⁻ contamination while enabling ammonia (NH₃) synthesis. However, it is still a challenge to achieve satisfied performance due to the multiple rate-limiting steps and competitive hydrogen evolution, particularly under neutral conditions and low concentrations. Herein, a set of single-atom catalysts (SACs) featuring high loading of multiple metal sites was synthesized as tandem catalysts for NO₃⁻ to NH₃. Fe/Cu/Pd−N−C SACs exhibit a superior performance with the high NH₃ Faradaic efficiency of 98%, 95%, and 82% at the NO₃⁻ concentration of 0.5, 0.1, and 0.01 M, respectively, which are much higher than these of other SACs. Moreover, it also performed very well in the stability and anti-interference measurements. The exceptional performance is proved to be attributable to the tandem interplay among Fe, Cu, and Pd sites. Specifically, NO₃⁻ undergoes reduction to NO₂⁻ over Cu single atoms, and NO₂⁻ then migrates to Fe single atoms for the subsequent conversion, benefiting from the high adsorption energy. Meanwhile, Pd sites can regulate the generation rate and consumption pathway of active hydrogen. This work offers a viable solution for the recycling and utilization of nitrate pollutants and provides a flexible design strategy for multifunctional electrocatalysts.