A new nitrogen fixation strategy: the direct formation of *N2− excited state on metal-free photocatalyst

N2 fixation under mild conditions using renewable electricity or solar energy is a promising alternative to the century-old Haber–Bosch process; however, it is generally impeded by the initial hydrogenation and competitive hydrogen evolution reaction. Herein, a new N2 fixation strategy is proposed via directly forming *N2− excited state on metal-free boron-decorated diamond clusters (BDCs). Surface-doped B atoms facilitate the adsorption of N2 and simultaneously suppress H+ due to the repulsion of Lewis acids. Excited state dynamics simulations demonstrate that valence electrons using the valence-band edge of BDCs as springboard are directly excited into the π* orbitals of *N2 under the illumination of ∼4 eV light (far below ∼11 eV for free N2), which not only further improves the selectivity but also forms activated *N2− excited states with sufficient lifetime (∼10 ns) for the initial hydrogenation. This work affords fresh insight to advance photocatalysis for sustainable NH3 production.