BiVO4-modified anodic nanocoral WO3 structures for enhancement of photoelectrochemical performance

Description of BiVO4/anodic WO3 nanocoral structures and the mechanism of water oxidation. The band alignment between BiVO4 and WO3 improved the photoelectrochemical water-splitting performance. [Display omitted] •Four-step forming mechanism of anodic nanocoral WO3 structures on W foil was demonstrated.•Nanocoral WO3 optimized for photoelectrochemical performance by annealing at 500 °C.•Use of BiVO4/anodic WO3 as photoanodes enhanced photoelectrochemical efficiency.•IPCE of BiVO4/WO3 photoanode 21 times higher than that of pristine nanocoral WO3. Nanostructuring of metal oxides is a straightforward strategy for enhancing photoelectrochemical (PEC) performance. The present work demonstrates the anodization of W metal to determine the optimum WO3 nanostructure for use in photoanodes. Anodization was performed in a fluoride-containing 1 M Na2SO4 electrolyte. Under optimum conditions, WO3 nanocoral structures were fabricated. The forming mechanism of the nanocoral structures was elucidated by the generation and development of nanobubbles at the metal/oxide interface. To enhance the PEC performance, BiVO4 layers were coated on the anodic WO3 nanocoral structures and annealed at 500 °C in air atmosphere. The prepared BiVO4/WO3 nanocoral layers were characterized by SEM, XRD, EIS and UV–vis spectroscopy. They were then used as photoanodes for PEC and IPCE measurements. Consequently, photocurrent density was improved to 0.42 mA/cm2 at 1.23 V vs. RHE and IPCE at 400 nm (21%) was enhanced by 21 times due to the producing band alignment between BiVO4 and WO3.