The role of sp-hybridized boron atoms in the highly efficient photocatalytic N2 reduction activity of boron-doped triphenylene-graphdiyne

Photocatalytic nitrogen (N-2) reduction with H2O under ambient conditions is a fascinating approach by which to realize clean ammonia (NH3) production. However, the high overpotential of N-2 activation and low solar-to-chemical conversion efficiency remain challenging in practical application. In the present work, we propose that introducing sp-hybridized boron atoms into metal-free triphenylene-graphdiyne monolayer (B@TP-GDY) would be a promising solution to achieve highly efficient nitrogen reduction reaction (NRR) under visible and even infrared light. Based on first-principles calculations and the nonadiabatic molecular dynamics method, we find that spin-polarization on sp-hybridized B sites plays a key role in activating N-2 molecules through the "acceptance-donation" concept, enabling the NRR process to be driven effectively by the photogenerated electrons. Besides, B@TP-GDY monolayers exhibit a high selectivity towards NH3 production with perfect suppression of the competing hydrogen evolution reaction. Moreover, the defect states induced by B atoms not only enhance the light absorption ability, but also significantly suppress the recombination of photogenerated carriers. The predicted photogenerated carrier lifetime of B@TP-GDY, 198 ps, is about twice that of the pristine TP-GDY monolayer, 110 ps. Our finding broadens the understanding of B-based photocatalytic mechanism for N-2 fixation and provides a feasible route to design metal-free NRR photocatalysts.