Electrocatalytic conversion of nitrate (NO₃⁻) to ammonia (NH₃) holds significant potential in the control of nitrogen oxide (NO_x) 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.

硝酸盐 (NO ₃ ^- ) 向氨 (NH ₃ ) 的电催化转化在控制来自固定源的氮氧化物 (NO _x ) 方面具有巨大潜力。然而，之前对反应中间体的研究仍不清楚。在这里，我们报告了具有介孔空心球结构的PdCu/Cu ₂ O 杂化物显示出从 NO ₃ ^-合成NH _{3 的}高选择性（96.70%）和法拉第效率（94.32%）。详细表征表明 (1) Pd 能够实现电子转移 (Pd 3d → Cu 3d) 并通过形成部分 PdCu 合金导致 Cu 3d 轨道极化，这使得 Pd 电子缺乏但提供空轨道来吸附 NO ₃ ^-，(2)富电子Cu更有利于NO ₃ ^-还原的发生。在线微分电化学质谱和密度泛函理论计算的相互证实表明，PdCu合金阻止了*NOH中间体的生成并促进了*N的形成，为从NO ₃ ^-还原反应合成NH ₃提供了新的机制。