Crystal Facet Engineering of TiO 2 Nanostructures for Enhancing Photoelectrochemical Water Splitting with BiVO 4 Nanodots.

Although bismuth vanadate (BiVO) 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, titanium dioxide (TiO) has been considered unsuitable because of its relatively positive valence band edge and low electrical conductivity. Herein, a crystal facet engineering of TiO nanostructures is proposed to control band structures for the hole blocking layer of BiVO nanodots. We design two types of TiO nanostructures, which are nanorods (NRs) and nanoflowers (NFs) with different (001) and (110) crystal facets, respectively, and fabricate BiVO/TiO heterostructure photoanodes. The BiVO/TiO NFs showed 4.8 times higher photocurrent density than the BiVO/TiO 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 nanodots and TiO 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.