| Summary: | Bismuth vanadate (BiVO<sub>4</sub>) has attracted substantial attention on account of its usefulness in producing hydrogen by photoelectrochemical (PEC) water splitting. The exploitation of BiVO<sub>4</sub> for this purpose is yet limited by severe charge recombination in the bulk of BiVO<sub>4</sub>, which is caused by the short diffusion length of the photoexcited charge carriers and inefficient charge separation. Enormous effort has been made to improve the photocurrent density and solar-to-hydrogen conversion efficiency of BiVO<sub>4</sub>. This study demonstrates that modulating the composition of the electrode and the electronic configuration of BiVO<sub>4</sub> by decoration with silver nanoparticles (Ag NPs) is effective in not only enhancing the charge carrier concentration but also suppressing charge recombination in the solar water splitting process. Decoration with a small number of Ag NPs significantly enhances the photocurrent density of BiVO<sub>4</sub> to an extent that increases with the concentration of the Ag NPs. At 0.5% Ag NPs, the photocurrent density approaches 4.1 mA cm<sup>−2</sup> at 1.23 V versus a reversible hydrogen electrode (RHE) under solar simulated light illumination; this value is much higher than the 2.3 mA cm<sup>−2</sup> of pure BiVO<sub>4</sub> under the same conditions. X-ray absorption spectroscopy (XAS) is utilized to investigate the electronic structure of pure BiVO<sub>4</sub> and its modification by decoration with Ag NPs. Analytical results indicate that increased distortion of the VO<sub>4</sub> tetrahedra alters the V 3d–O 2p hybridized states. Additionally, as the Ag concentration increases, the oxygen vacancy defects that act as recombination centers in BiVO<sub>4</sub> are reduced. In situ XAS, which is conducted under dark and solar illumination conditions, reveals that the significantly enhanced PEC performance is attributable to the synergy of modulated atomic/electronic structures and the localized surface plasmon resonance effect of the Ag nanoparticles.
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