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.

探索以地壳储量丰富的金属氧化物为催化剂，将常温常压下的氮气（路易斯碱）还原为高附加值氨气——现代工业不可或缺的大宗商品，具有极为重要的研究价值。
然而，由于此类材料路易斯酸性不足、电子结构参数不甚理想，导致氮气吸附能力较弱、关键氮中间体（NNH*/NNH2*/N*）稳定性欠佳，且更倾向于发生析氢副反应，因此金属氧化物基催化剂的氨气选择性与产率均远未达到理想水平。
本研究通过理论计算预测：借助强Ru4d与N2p轨道耦合作用，以单钌原子掺杂调控缺陷型四氧化三钴（Co3O4‑x）的电子结构，可协同增强氮气吸附能力，同时稳定关键氮中间体，进一步抑制氢质子二聚副反应，显著提升氨气选择性。
受密度泛函理论（Density Functional Theory, DFT）计算结果的启发，我们引入最优单钌原子掺杂量，结合原位生成的氧缺陷，最大化缺陷型四氧化三钴的路易斯酸性，制备得到Ru1.4Co3O4‑x催化剂。该催化剂在0 V（相对于可逆氢电极，vs RHE）下展现出优异的氮气固定活性：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；同时具备良好的长期稳定性，氨气选择性较原始缺陷型四氧化三钴提升2.5倍，性能优于当前顶尖的钌碳（Ru/C）催化剂。