All room-temperature synthesis, N2 photofixation and reactivation over 2D cobalt oxides

Abstract

Ammonia is an indispensable chemical to the ecosystem and human beings. Storing solar energy in N-H bonds in NH3 is a promising sustainable alternative to the energy-consuming Haber Bosch process. However, nitrogen photofixation with this strategy still suffers from several unsolved issues, such as high-energy consumption with carbon footprint, short lifetime of photocatalysts, and nitrogen contamination in redox reactions. In this study, a room-temperature strategy is developed to two-dimensionally assemble the diminutive CoO-Co3O4 mixed-oxide composites on reduced graphene oxide. They proffer great surface area and deep-red-light absorbing defect states, which enable them to exhibit over 14 times higher photoactivity than template-free single components. The unveiled photoreaction-induced cation oxidation is reversely triggerable by photo-reactivating Co3O4 back to active CoO, with well-maintained photoactivity after six-cycles. All these room-temperature processes, from catalyst synthesis, nitrogen photofixation, to catalyst reactivation, offer facile way towards upscaling and hold great promise for practical zero-emission N2 photofixation.