Integration of Gold Nanoparticles into BiVO4/WO3 Photoanodes via Electrochromic Activation of WO3 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.