Unveiling the Activity Origin of Ag Decorated BiVO4 Photoanodes for Enhanced Photoelectrochemical Water Splitting: The Approach of Electronic Structure
Thi Thuy Nga Ta1,2*, Yu-Cheng Huang1,2, 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