Nanospace-confined worm-like BiVO4 in TiO2 space nanotubes (SPNTs) for photoelectrochemical hydrogen production

Abstract

Titanium dioxide (TiO2) space nanotubes (SPNTs) have attracted considerable attention in the fields of photocatalysis and photoelectrochemical energy conversion because of their large surface area and good physical and chemical stability. However, their large bandgap (3.0–3.2 eV) and poor charge-carrier separation and transport properties lead to unsatisfactory photo-conversion efficiency. To overcome these drawbacks, we performed in vivo and in vitro deposition of BiVO4 (BVO) on SPNTs, obtaining a sophisticated BVO/SPNTs heterojunction via electrochemical anodization and microwave-assisted synthesis. Unlike conventional TiO2 nanotube structures, TiO2 SPNTs possess empty spaces between the tubes (tube-to-tube interface), which can effectively admit BVO particles and generate worm-like BVO, yielding an intimate heterojunction interface and enlarged surface area. The prepared BVO/SPNTs exhibited a narrow bandgap (2.32 eV), small charge-transfer resistance, and accelerated reaction kinetics, as confirmed by incident-photon-to-current conversion efficiency, ultraviolet diffuse reflectance spectroscopy, and electrochemical impedance spectroscopy. These salient features, together with a strong response to visible light, resulted in a photocurrent density of 0.68 mA/cm2 without any co-catalyst at 1.23 V vs. a reversible hydrogen electrode in 0.5 M Na2SO4, which is 14 times higher than that of the pure SPNT electrode film. Thus, this study highlights that the integration of the materials with different dimensions by tailoring the surface properties may yield efficient and stable catalysts for multiple applications, particularly for hydrogen production at a significantly improved rate.