Catalytic photo-redox of simulated air into ammonia over bimetallic MOFs nanosheets with oxygen vacancies

Solar-driven conversion of nitrogen (N 2 ) into ammonia (NH 3 ) is a promising alternative to the Haber-Bosch process, while still suffers from low conversion efficiency due to inactive N N bond. Herein, a novel pathway of photocatalytic air redox reaction (ARR) to ammonia via NO is proposed and tested over an effective catalyst of oxygen-vacancy-rich bimetallic Cu-Co organic framework ultrathin nanosheets (O VR -CuCo-MOFs NS) under visible light. The catalyst with unique oxygen defective sites shows an excellent NH 3 synthesis rate from air (287.76 ± 7.02 μmol g -1 ·h -1 ), which is 5.4-fold higher than that from pure N 2 . Moreover, experiments and theoretical calculations indicate that the transformation of air mainly follows a redox pathway, in which N 2 and O 2 can be trapped at the oxygen vacancies to generate nitric oxide (*NO) and further be reduced to ammonia by visible light. The ARR process shows a lower barrier of free energies in the onset activation step (*N 2 → *N-NO, −0.08 eV) and rate-limiting step (*NO → *NHO, 1.23 eV) compared with those of traditional nitrogen reduction (*N 2 → *N-NH, 1.48 eV and H 2 N-NH 2 → *NH 2 , 1.29 eV, respectively). This work provides a new and sustainable pathway for photo-driven ammonia synthesis. • Photocatalytic ammonia synthesis was achieved by a redox process of air. • Rich oxygen vacancies can promote the ammonia synthesis and photo/electro superiorities. • Experiment and theoretical calculation show less kinetic barrier of the redox possess. • The redox reaction provides a new strategy for green ammonia production.