Facet-dependent solar ammonia synthesis of BiOCl nanosheets via a proton-assisted electron transfer pathway

Under the pressure of a fossil fuels shortage and global climate change, solar ammonia synthesis and the need to develop N-2 fixation under mild conditions is becoming more urgent need; however, their intrinsic mechanisms still remain unclear. Herein, we demonstrate that the kinetic inertia of N-2 can be overcome using oxygen vacancies (OVs) of BiOCl as the catalytic centers to create lower energy molecular steps, which are amendable for the solar light driven N-N triple bond cleavage via a proton-assisted electron transfer pathway. Moreover, the distinct structures of OVs on different BiOCl facets strongly determine the N-2 fixation pathways by influencing both the adsorption structure and the activation level of N-2. The fixation of terminal end-on bound N-2 on the OVs of BiOCl {001} facets follows an asymmetric distal mode by selectively generating NH3, while the reduction of side-on bridging N-2 on the OVs of BiOCl {010} facets is more energetically favorable in a symmetric alternating mode to produce N2H4 as the main intermediate.