Understanding the hydrogenation behavior of *NO during electrochemical nitrate reduction reaction (NO3RR) is essential for designing catalysts with high selectivity toward ammonia (NH3) and valuable intermediates like hydroxylamine. Spinel cobalt oxides (Co3O4) are promising NO3RR electrocatalysts, yet the exact *NO hydrogenation mechanism remains unclear. Here, we integrate theoretical calculations and systematic experiments to reveal that the hydrogenation pathway is dictated by the coordination environment, which can be tuned via crystal facet engineering. Co3O4 nanoparticles enriched with (111) facets (o-Co3O4) and (100) facets (c-Co3O4) were synthesized to expose 4- and 6-coordinated Co sites, respectively. Theoretical results show that o-Co3O4 favors nitrogen-site hydrogenation (*NO → *NHO), while c-Co3O4 promotes oxygen-site hydrogenation (*NO → *NOH), leading to distinct ratedetermining steps. This selectivity is experimentally supported by in situ spectroscopy, which detects the *NH2OH intermediate exclusively on o-Co3O4. Consequently, o-Co3O4 achieves superior NO3RR performance, with a Faradaic efficiency of 99.4% and an NH3 yield rate of 12.8 mg h-1 cm-2 at −0.4 V. This work uncovers the coordination-governed mechanism of *NO hydrogenation and establishes facet engineering as an effective strategy for directing reaction pathways in NO3RR.

中文翻译：

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钴-氧配位控制 *硝酸盐电还原中的 NO 氢化

了解电化学硝酸盐还原反应 （NO3RR） 中 *NO 的氢化行为对于设计对氨 （NH3） 和羟胺等有价值的中间体具有高选择性的催化剂至关重要。尖晶石钴氧化物 （Co3O4） 是很有前途的 NO3RR 电催化剂，但确切的 *NO 加氢机制仍不清楚。在这里，我们整合了理论计算和系统实验，揭示了氢化途径是由配位环境决定的，这可以通过晶体刻面工程进行调整。合成了富含 （111） 个面 （o-Co3O4） 和 （100） 个面 （c-Co3O4） 的 Co3O4 纳米颗粒，以分别暴露 4 个和 6 个配位的 Co 位点。理论结果表明，o-Co3O4 有利于氮位氢化 （*NO → *NHO），而 c-Co3O4 促进氧位点氢化 （*NO → *NOH），导致不同的速率确定步骤。这种选择性得到了原位光谱法的实验支持，该光谱法仅在 o-Co3O4 上检测 *NH2OH 中间体。因此，o-Co3O4 实现了卓越的 NO3RR 性能，在 -0.4 V 下具有 99.4% 的法拉第效率和 12.8 mg h-1 cm-2 的 NH3 产率。这项工作揭示了 *NO 加氢的配位控制机制，并将分面工程确立为指导 NO3RR 反应途径的有效策略。