Crystal size dependent photogenerated charge separation on an octahedral bismuth vanadate photocatalyst

Abstract

Although size engineering has been recognized as a useful strategy in elevating the photocatalytic performance, the significant role of crystal size in the charge separation process within semiconductor photocatalysts remains enigmatic. Herein, by taking bismuth vanadate (BiVO₄) as a platform, we present dramatic charge separation differences for the fabricated octahedral crystals with varying sizes, ranging from approximately 8 μm to 100 nm. Our findings reveal that in larger-sized octahedral BiVO₄ crystals, photogenerated electrons and holes are spatially separated between facets and edges. However, for octahedral BiVO₄ with a smaller size of about 100 nm, photogenerated charges are distributed non-selectively across both facets and edges. The diverse spatial distribution of photogenerated charges is presumably attributed to the differences in the magnitude of band bending caused by varying crystal sizes. Remarkably, a nearly seven-fold improvement in charge separation efficiency can be achieved solely by decreasing the size of BiVO₄, due to the reduced bulk charge recombination. This work sheds light on the crucial role of crystal size in photogenerated charge separation of semiconductor photocatalysts.