Single-Metal-Atom Dopants Increase the Lewis Acidity of Metal Oxides and Promote Nitrogen Fixation

Exploring
Earth-abundant metal oxides for ambient N2 (Lewis base)
reduction to value-added NH3, an essential
commodity for modern industries, has extreme significance. However,
due to their insufficient Lewis acidity and unfavorable electronic
parameters, resulting in poor N2 adsorption, instability
of key N intermediates (NNH*/NNH2*/N*), and preference
for hydrogen evolution, the NH3 selectivity and yield rate
with metal oxides are far from satisfactory. Herein, theoretical predictions
reveal that tuning the electronic structure of defective Co3O4 (Co3O4‑x) via a single-Ru-atom dopant can cooperatively enhance the N2 adsorption, driven by strong Ru4d-N2p orbital coupling, and stabilize the key N-intermediates, further
suppressing the H* dimerization and significantly boosting the NH3 selectivity. Motivated by DFT predictions, we introduced
optimal single-Ru-atom dopants to maximize the Lewis acidity of Co3O4 with in situ-generated oxygen
defects (Ru1.4Co3O4‑x), which exhibited an excellent N2-fixation activity
with a high NH3 Faradaic efficiency (40.2%) and yield rate
(39.4 μg/h/mgcat; 2.67 mg/h/mgRu) at 0
V (vs RHE), along with long-term stability and 2.5 times higher selectivity
than pristine Co3O4‑x, outperforming the state-of-the-art Ru/C.

探索地球储量丰富的金属氧化物，用于常温常压下将氮气（Lewis碱）还原为高附加值氨气（NH3）——后者是现代工业不可或缺的基础化工原料，这一研究具有极其重要的意义。然而，由于此类氧化物路易斯酸性不足且电子结构参数欠佳，导致氮气吸附能力不佳、关键含氮中间体（NNH*/NNH2*/N*）稳定性差，且倾向于发生析氢反应，因此金属氧化物基催化剂的氨气选择性与产率远未达到理想水平。本研究通过理论计算预测，借助单原子钌掺杂调控缺陷型四氧化三钴（Co3O4‑x）的电子结构，可依托Ru4d与N2p轨道的强耦合作用协同增强氮气吸附，并稳定关键含氮中间体，同时进一步抑制氢质子（H*）的二聚反应，从而显著提升氨气选择性。基于密度泛函理论（DFT）的预测结果，我们引入最优剂量的单原子钌掺杂剂，结合原位生成的氧缺陷，制备出最大化路易斯酸性的Ru1.4Co3O4‑x催化剂。该催化剂在0 V（相对于可逆氢电极RHE）条件下展现出优异的固氮活性，氨气法拉第效率高达40.2%，产率分别为39.4 μg/h/mgcat与2.67 mg/h/mgRu，同时具备长期稳定性，其氨气选择性较原始缺陷型四氧化三钴提升2.5倍，性能优于当前主流的Ru/C催化剂。