Elucidating the dynamics and transfer pathways of photogenerated charge carriers in V2O5/BiVO4 heterojunction photoanodes: A transient absorption spectroscopy study

Pairing of bismuth vanadate (BiVO 4 ) with vanadium pentoxide (V 2 O 5 ) forms a Type II heterojunction photoanode, which has been proven to be a high-performance photoanode architecture for efficient photoelectrochemical (PEC) water oxidation. To further support for advanced rational design and improvement of the heterojunction photoanode, it is quintessential to understand the mechanics and properties of photogenerated charge carriers formed. This study aims to probe the dynamics of photogenerated electron-hole pairs formed in pristine photoanode as well as the heterojunction photoanodes using transient absorption spectroscopy (TAS). Relative to the BiVO 4 /V 2 O 5 structure, modelling and quantification of the decay constant helps in explaining why the V 2 O 5 /BiVO 4 heterojunction photoanode exhibited a longer lifetime of the photogenerated charge carriers with a lower decay rate constant that leads to a much-improved overall generation of photocurrent density. An oxygen evolving catalyst of nickel oxyhydroxide (NiOOH) was then anchored on the exterior surfaces of the heterojunction photoanode system to further investigate and modify the transfer pathways of the photogenerated charge carriers. Furthermore, the hole- and scavenger-assisted TAS measurements on the BiVO 4 /V 2 O 5 heterojunction photoanode revealed that the majority of trapped holes species are accumulated within the BiVO 4 layer. The findings suggested that the Type II heterojunction formation in V 2 O 5 /BiVO 4 could effectively reduce its charge recombination process. • Synthesized and characterized a novel V 2 O 5 /BiVO 4 heterojunction. • TAS confirmed the Type II charge transfer pathway over the Z-scheme. • Observed enhanced charge separation and extended carrier lifetimes. • TAS effectively elucidates charge carrier dynamics in heterojunctions.