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

Abstract

© 2021 American Chemical Society.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.