Unveiling the Activity Origin of Ag Decorated BiVO₄ Photoanodes for Enhanced Photoelectrochemical Water Splitting: The Approach of Electronic Structure

Thi Thuy Nga Ta^1,2*, Yu-Cheng Huang^1,2, Jeng-Lung Chen³, Dinh Phong Tran⁴, Chi-Liang Chen³, Ping-Hung Yeh², Chao-Hung Du², Way-Faung Pong², Chung-Li Dong², Wu-Ching Chou¹

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
²Research Center for X-ray Science & Department of Physics, Tamkang University, New Taipei City 25137, Taiwan
³National Synchrotron Radiation Research Center, Hsinchu 30010, Taiwan
⁴Department of Fundamental and Applied Sciences, University of Science and Technology of Hanoi, Hanoi, Viet Nam

* Presenter:Thi Thuy Nga Ta, email:thuynga.guta@gmail.com

Bismuth vanadate (BiVO₄) has attracted substantial attention in hydrogen production via photoelectrochemical (PEC) water splitting. The full exploitation of BiVO₄ potential remains restricted due to the severe charge recombination in the bulk of BiVO₄, which is caused by the short diffusion length of the photoexcited charge carriers and inefficient charge separation. Enormous efforts have been paid to improve the photocurrent density and solar-to-hydrogen conversion efficiency of BiVO₄. In this study, we report that modulating the electrode composition and the electronic configuration of BiVO₄ through silver nanoparticles (Ag NPs) decoration could be an effective strategy not only to enhance charge carrier concentration but also to suppress charge recombination in the solar water-splitting process. With the small amount of Ag NPs decoration, the photocurrent density of BiVO₄ is enhanced significantly, and it increases with the increase of Ag NPs concentration. At 0.5% Ag NPs, the photocurrent density approaches a noticeable value of 4.1 mA.cm^-2 at 1.23 V versus RHE and under solar illumination, which is much higher than 2.3 mA.cm^-2 of pure BiVO₄ at the same condition. X-ray absorption spectroscopy (XAS) is utilized to study the electronic structure of pure BiVO₄ and how it is modified by the Ag NPs decoration. Analytical results indicate that an increased distortion in VO₄ tetrahedron via V-O bond prolongation alters the V 3d - O 2p hybridized states. Additionally, upon the increasing of Ag concentration, the oxygen-vacancy defects that act as recombination centers in BiVO₄ could be diminished accordingly. Furthermore, in-situ XAS which are conducted under dark and solar illumination conditions reveal the significantly enhanced PEC performance could be attributable to the localized surface plasmon resonance effect of nanosized Ag particles.

Keywords: Bismuth vanadate (BiVO₄), Solar Hydrogen Production, Photoelectrochemical (PEC) Water Splitting, X-ray Absorption Spectroscopy (XAS), Electronic Structure