Fe single atom trigger asymmetric In-In polarized site pairs boosting near-infrared N2 photoreduction

Abstract

Building differentiated charge distributed polarized atomic pairs may be an alternative for N₂ activation. In this work, CuInS₂ atomic layers with asymmetric In-In polarized site pairs are prepared by doping Fe single atoms, as proved by X-ray absorption fine structure spectroscopy, quasi in situ X-ray photoelectron spectra and calculated atomic charge distribution. The engineered Fe single atoms tuned the surface atomic charge distribution, building local polarization center to boost directional surface charge separation. The formed In-In polarized site pairs with asymmetric charge distribution creates distinct interaction with two N atoms in N₂ molecule, contributing to the enhanced activation of N₂. The alternating pathway is regarded as hydrogenation pathway over Fe-CuInS₂ with *NNH formation as rate-determining step. The charge-redistributed surface atomic structure after engineered Fe single atoms strengthens intermediate interaction and lower the rate-determining step energy barrier. Benefiting from these features, Fe-CuInS₂ exhibits excellent photocatalytic activity under near-infrared (NIR) irradiation with an ammonia synthesis rate of 94.1 μmol g⁻¹ h⁻¹. In comparison, the N₂-NH₃ conversion rate of Fe-CuInS₂ under ultraviolet–visible (UV–Vis) irradiation could reach 137.4 μmol g⁻¹ h⁻¹, which is about 6.8 times higher than that of CuInS₂. The apparent quantum efficiencies of Fe-CuInS₂-2 at 380, 400, 450, 500, 550, 650, 700, 800, 850 and 1064 nm were 3.0 %, 3.3 %, 2.7 %, 2.1 %, 2.0 %, 1.5 %, 1.3 %, 0.4 %, 0.7 % and 0.6 %, respectively.