A Type II n-n staggered orthorhombic V2O5/monoclinic clinobisvanite BiVO4 heterojunction photoanode for photoelectrochemical water oxidation: Fabrication, characterisation and experimental validation.

Graphical abstract Highlights • A Type II n-n staggered heterojunction photoanode of V 2 O 5 /BiVO 4 was synthesized. • A high photocurrent density of 1.53 mA/cm2 at 1.5 V vs Ag/AgCl was measured. • This was due to lower charge resistance and faster transit time showed by EIS/IMPS. • Photo-excitons transfer in V 2 O 5 /BiVO 4 was validated by theoretical band diagram. Abstract Conventional photoanode using a singular semiconductor material is not technically viable for photoelectrochemical (PEC) water oxidation owing to the properties relating to its wide band gap, sluggish charge mobility, as well as poor separation and rapid recombination of photogenerated charge carriers. The main aim of this study was to fabricate an n-n heterojunction photoanode of V 2 O 5 /BiVO 4 via a facile electrodeposition synthesis method in order to overcome the technical bottlenecks encountered in conventional singular photoanode structures. Additionally, the synergistic effect of band potentials matching and conductivity difference between BiVO 4 and V 2 O 5 were studied using LSV, IMPS, EIS, HR-TEM, XRD, XPS, Raman and ultraviolet-visible spectroscopies. This was followed by the performance evaluation of the light-induced water splitting using a standard three-electrode assembly PEC cell under 1.5 AM solar simulator. Results showed that the V 2 O 5 /BiVO 4 heterojunction photoanode achieved a significantly improved photocurrent density of 1.53 mA/cm2 at 1.5 V vs Ag/AgCl, which was a 6.9-fold and a 7.3-fold improvement over the individual pristine BiVO 4 (0.22 mA/cm2) and V 2 O 5 (0.21 mA/cm2), respectively. The improvement was attributed to the lower charge resistances at the FTO/semiconductor, semiconductor/FTO and semiconductor/electrolyte interfaces as well as the fast transit time (τ) of 6.4 ms for photo-injected electrons in the V 2 O 5 /BiVO 4 heterojunction photoanode. Finally, the experimental results were used to reconstruct a theoretical band diagram in validating the heterojunction alignment between V 2 O 5 and BiVO 4 as well as in elucidating the photogenerated charge carriers transfer mechanism in the V 2 O 5 /BiVO 4 heterojunction photoanode. [ABSTRACT FROM AUTHOR]