Alloying effect-induced electron polarization drives nitrate electroreduction to ammonia

Electrocatalytic conversion of nitrate (NO3−) to ammonia (NH3) holds significant potential in the control of nitrogen oxide (NOx) from stationary sources. However, previous studies on reaction intermediates remain unclear. Here we report that PdCu/Cu2O hybrids with mesoporous hollow sphere structure show high selectivity (96.70%) and Faradaic efficiency (94.32%) for NH3 synthesis from NO3−. Detailed characterizations demonstrate that (1) Pd enables electron transfer (Pd 3d → Cu 3d) and causes the polarization of Cu 3d orbitals by forming partial PdCu alloys, which makes Pd electron deficient but offers empty orbits to adsorb NO3−, and (2) electron-rich Cu is more conducive to the occurrence of NO3− reduction. The mutual confirmation of online differential electrochemical mass spectrometry and density functional theory calculations demonstrates that PdCu alloys block the generation of ∗NOH intermediate and facilitate the formation of ∗N, providing a new mechanism for NH3 synthesis from NO3− reduction reactions.