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

Although bismuth vanadate (BiVO₄) 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 BiVO₄, titanium dioxide (TiO₂) has been considered unsuitable because of its relatively positive valence band edge and low electrical conductivity. Herein, a crystal facet engineering of TiO₂ nanostructures is proposed to control band structures for the hole blocking layer of BiVO₄ nanodots. We design two types of TiO₂ nanostructures, which are nanorods (NRs) and nanoflowers (NFs) with different (001) and (110) crystal facets, respectively, and fabricate BiVO₄/TiO₂ heterostructure photoanodes. The BiVO₄/TiO₂ NFs showed 4.8 times higher photocurrent density than the BiVO₄/TiO₂ 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 BiVO₄ nanodots and TiO₂ 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.