Substitution Boosts Charge Separation for High Solar-Driven Photocatalytic Performance

Bandgap engineering of photocatalysts is a common approach to achieving high effective utilization of solar resource. However, the difficulty in achieving bandgap narrowing and high activity simultaneously seems to be irreconcilable via the traditional modification pathway. Herein, we have substituted iodine for a fraction of bromine atoms in BiOBr to overcome this restriction and provided some deep-seated insights into how the substitution boosts the photocatalytic properties. The substituted BiOBr_0.75I_0.25 exhibited exceptional photoactivity, with photon-to-current conversion efficiency approximately 6 times greater than TiO₂ in UV region, and more than 10 times higher than BiOBr or BiOI in visible-light region. We found that the substitution narrowed the bandgap, facilitated the diffusion of electron with small effective mass, as well as induced oxygen vacancies on [Bi₂O₂]²⁺ layers. By virtue of the stronger dipole moments produced, the enhancement of intrinsic electric fields between [Bi₂O₂]²⁺ and halogen slabs was achieved in BiOBr_0.75I_0.25; thereby the distance the photogenerated electron could diffuse was sufficient to inhibit the recombination. Our findings not only shed light on the potential properties of hybrid-halide photocatalysts but also provide a strategy for developing high efficiency catalysts.