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.