Single atom (Co, Fe, Ni)/MIL-125(SH)2 photocatalyst for ammonia synthesis synergistically mediated by N2 activation and proton generation

The fabrication of single atoms on MIL-125(Ti) for photocatalytic ammonia synthesis. • SAs modulate the local electronic structure for charge mobility and separated active site. • The favorable N 2 activation and protons supply optimizes the reduction kinetics. • Magnetic field-induced spin flipping to charge utilization further boost the activity. Photocatalytic nitrogen fixation is an attractive alternative to the energy-intensive traditional ammonia synthesis. However, the major challenge is that most photocatalysts are limited by their low charge mobility, insufficient molecules activation and sluggish reaction kinetics. Herein, we integrated single atoms (Co, Fe, Ni) on MIL-125(Ti) functionalized with sulfhydryl (MIL-125(SH) 2 , MTS) to afford Co-MTS, Fe-MTS and Ni-MTS for photocatalytic nitrogen reduction. Through uniformly dispersed SAs (single atoms) coordinated with O and S atom, such intimate interaction and charge redistribution can efficiently regulate the unsaturated Ti sites for N 2 adsorption and activation. Moreover, the introduced SAs species also serve as separated active center for water oxidation to promote H 2 O adsorption and protons release, kinetically optimizing protons supply and energy barrier of rate rate-determining step for N 2 hydrogeneration. Benefited from the spatially separated metal node-SAs dual sites and favorable reaction energy barrier, the optimized Ni-MTS sample shows an ammonia yield rate of 72.6 μmol·g −1 ·h −1 with an apparent quantum efficiency of 0.49% at 400 nm. This can be further enhanced by magnetic field-induced spin flipping contributed to charge utilization. This work would inspire the development of other high-efficiency single atom/MOFs that combining molecular activation and protons supply for photocatalysis.