Integration of Gold Nanoparticles into BiVO ₄ /WO ₃ Photoanodes via Electrochromic Activation of WO ₃ for Enhanced Photoelectrochemical Water Splitting

The development of highly efficient photoanodes is crucial for enhancing the energy conversion efficiency in photoelectrochemical water splitting. Herein, we report an innovative approach to fabricating an Au/BiVO₄/WO₃ ternary junction that leverages the unique benefits of WO₃ for efficient electron transport, BiVO₄ for broadband light absorption, and Au nanoparticles (NPs) for surface plasmon effects. The BiVO₄/WO₃ binary junction was constructed by depositing a BiVO₄ layer onto the surface of the WO₃ nanobricks via consecutive drop casting. Au NPs were subsequently integrated into the BiVO₄/WO₃ structure through electrochromic activation of WO₃. The optimal BiVO₄ loading for the highest-performing BiVO₄/WO₃ heterostructure and the light intensity dependence of the photocurrent efficiency were also determined. Flat-band potential measurements confirmed an appropriate band alignment that facilitates electron transfer from BiVO₄ to WO₃, while work function measurements corroborated the formation of a Schottky barrier between the incorporated Au NPs and BiVO₄/WO₃, improving charge separation. The best-performing Au NP-sensitized BiVO₄/WO₃ photoanode thin films exhibited a photocurrent density of 0.578 mA cm^-2 at 1.23 V vs RHE under AM 1.5G (1 sun) illumination and a maximum applied-bias photoconversion efficiency of 0.036% at 1.09 V vs RHE, representing an enhancement factor of 12 and 2.3 compared to those of pristine BiVO₄ and WO₃ photoanodes, respectively. This study presents a promising and scalable route for fabricating noble metal-sensitized, metal oxide-based nanocomposite photoanodes for solar water splitting.