N2 reduction using single transition-metal atom supported on defective WS2 monolayer as promising catalysts: A DFT study

Nitrogen reduction reactions (NRRs) under mild conditions retain an enormous challenge in effective N2 activation on metal-based catalysts. Here, by spin-polarized DFT calculations, we systematically investigated the potential of single transition-metal atoms (Sc to Zn, Nb to Cd, W, Pt and Au) supported on the experimentally available WS2 nanosheets with sulfur vacancies as catalysts for N2 fixation and conversion. The results confirm that the WS2 nanosheet with sulfur vacancies is a good platform for anchoring single transition-metal atoms. Based on proposed several criteria, it is found that the single Ni atoms anchored to sulfur vacancies possess outstanding catalytic activity of NRR. Here, the Ni-WS2 nanosheet acts as likely Lewis-acid system and accepts electrons from the N2*, which causes the weakening of N–N bond. Reaction energy diagrams of the NRRs show that the whole NRRs on Ni-WS2 surface prefer to occur along the alternating associative pathway, and form the ammonia without the requirement of energy input. Overall, our results reveal that the Ni-WS2 system is a quite promising single-atom catalyst with less energy-consuming and good stability for NRRs. These findings could motivate more experimental and theoretical researches to further explore the potential of single transition-metal atoms anchored to two-dimensional substrate materials for NRRs.