Improving the photo-oxidative capability of BiOBr via crystal facet engineering

Bismuth oxybromide (BiOBr) has emerged as a potential visible-light-driven photocatalyst with relatively high photocatalytic activity although modifications are still necessary to further promote its photocatalytic performance. Here, a facile chemical precipitation process was used to synthesize tetragonal BiOBr with a predominance of either {001} or {010} exposed crystal facets. Scanning electron microscopy revealed that BiOBr particles dominated by the {010} facet possessed a large plate-like morphology while the {001}-dominated BiOBr comprised smaller, more irregular particles. Ultraviolet-visible diffuse reflectance spectra and Mott-Schottky analysis highlighted a difference in electronic band structure of the two materials; BiOBr-010 possessed a valence band potential and a band-gap of 2.71 and 2.95 eV versus normal hydrogen electrode (NHE), respectively, while BOBr-001 exhibited values of 2.63 and 3.15 eV versus NHE, respectively. BiOBr-010 displayed a better photo-oxidative capability than BOBr-001 for both water oxidation and formic acid degradation (aqueous phase). The higher photo-oxidative capability of BiOBr-010 was attributed to the suppression of photo-induced electron/hole recombination. Additionally, the improved charge transfer efficiency and reduced charge transfer resistance in BiOBr-010 was revealed to be beneficial for enhancing photoelectrochemical (PEC) performance. The findings account for the better photo-oxidative activity and higher current density of BiOBr-010 despite its smaller specific surface area and illustrate the use of crystal facet engineering to promote photocatalytic performance.