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

Abstract

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.

Crystal facet and phase engineering for advanced water splitting

“…6b), Lee et al hydrothermally synthesized (001) facet dominant-TiO 2 NRs and (110) facet-dominant nanoflowers (NFs) and electrodeposited BiVO 4 on TiO 2 NRs and NFs. 110 Although TiO 2 NRs show higher photoactivity than TiO 2 NFs, the photocurrent of BiVO 4 /TiO 2 NRs significantly decreases after heterojunction, while that of BiVO 4 /TiO 2 NFs increases. This is because BiVO 4 and TiO 2 with (110) facets form type II band alignment, where charge separation is strengthened.…”

Selective Nitridation Crafted a High‐Density, Carbon‐Free Heterostructure Host with Built‐In Electric Field for Enhanced Energy Density Li–S Batteries

“…The calculated work function values of VN and TiO 2 in our work are fairly close to those reported in literatures. [ 42 , 43 , 44 , 45 ] The difference in the work function suggests that there would be band bending and self‐driven electron transfer from VN to TiO 2 at their coupling interfaces during contact until the work function equilibrium is reached. According to the schematic energy band diagrams illustrated in Figure 2i,h , a spontaneous built‐in electric field pointing toward the TiO 2 side can be formed when the quasi‐metallic VN and semiconducting TiO 2 are in contact.…”

Enhanced solar water splitting of BiVO4photoanodes byin situsurface band edge modulation

“…1–8 This technique has great potential in practical applications because it can be integrated by thin-film photoelectrodes of photocathode and photoanode that act as a device with a self-biased independent structure. 9,10 Among the candidate materials for the photoanode, n-type semiconductor materials, such as TiO 2 , 11,12 ZnO, 13 BiVO 4 , 14–17 WO 3 , 18,19 Fe 2 O 3 , 20,21 and Ta 3 N 5 , 22 have been widely used as photoanodes. BiVO 4 in particular has attracted extensive attention due to its suitable band gap (2.4 eV with 10% theoretical photo-to-hydrogen conversion efficiency) and a reasonable energy band structure.…”