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 ternary junction that leverages the unique benefits of for efficient electron transport, for broadband light absorption, and Au nanoparticles (NPs) for surface plasmon effects. The binary junction was constructed by depositing a layer onto the surface of the nanobricks via consecutive drop casting. Au NPs were subsequently integrated into the structure through electrochromic activation of . The optimal loading for the highest-performing 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 to , while work function measurements corroborated the formation of a Schottky barrier between the incorporated Au NPs and , improving charge separation. The best-performing Au NP-sensitized photoanode thin films exhibited a photocurrent density of 0.578 mA 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 and photoanodes, respectively. This study presents a promising and scalable route for fabricating noble metal-sensitized, metal oxide-based nanocomposite photoanodes for solar water splitting.