Crystal Facet Engineering of TiO2 Nanostructures for Enhancing Photoelectrochemical Water Splitting with BiVO4 Nanodots

Abstract Although bismuth vanadate (BiVO 4 ) has been promising as photoanode material for photoelectrochemical water splitting, its charge recombination issue by short charge diffusion length has led to various studies about heterostructure photoanodes. As a hole blocking layer of BiVO 4 , titanium dioxide (TiO 2 ) has been considered unsuitable because of its relatively positive valence band edge and low electrical conductivity. Herein, a crystal facet engineering of TiO 2 nanostructures is proposed to control band structures for the hole blocking layer of BiVO 4 nanodots. We design two types of TiO 2 nanostructures, which are nanorods (NRs) and nanoflowers (NFs) with different (001) and (110) crystal facets, respectively, and fabricate BiVO 4 /TiO 2 heterostructure photoanodes. The BiVO 4 /TiO 2 NFs showed 4.8 times higher photocurrent density than the BiVO 4 /TiO 2 NRs. Transient decay time analysis and time-resolved photoluminescence reveal the enhancement is attributed to the reduced charge recombination, which is originated from the formation of type II band alignment between BiVO 4 nanodots and TiO 2 NFs. This work provides not only new insights into the interplay between crystal facets and band structures but also important steps for the design of highly efficient photoelectrodes.