Interfacial defects for high-performance photoelectrochemical properties of core-shell BiVO₄ /ZnO nanodendrite: X-ray Spectro-Microscopic Investigation
Hsiao-Tsu Wang1,2*, Kuan-Hung Chen2, Abhijeet R. Shelke2, Chung-Li Dong2, Ping-Hung Yeh2, Chao-Hung Du2, Kandasami Asokan3, Shang-Hsien Hsieh4, Hung-Wei Shiu4, Chih-Wen Pao4, Huang-Ming Tsai4, Jih-Jen Wu5, Takuji Ohigashi6, Way-Faung Pong2
1Bachelor’s Program in Advanced Materials Science, Tamkang University, New Taipei City 25137, Taiwan
2Department of Physics, Tamkang University, New Taipei City 25137, Taiwan
3Inter-University Accelerator Center, New Delhi 110067, India
4National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
5Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan
6Institute for Molecular Science, Okazaki, Japan
* Presenter:Hsiao-Tsu Wang, email:hsiaotsu0108@gmail.com
Synchrotron-based X-ray spectro- and microscopic techniques, such as X-ray absorption spectroscopy (XAS) and scanning transmission X-ray microscopy (STXM), are powerful characterization tools in comprehensively and deeply understanding the mechanism of high-performance in advanced energy materials. The advantage of STXM provides not only chemically mapped information but spatially resolved electronic structures in the specific region of interest. In this study, XAS and STXM are used to investigate the origin of enhancement of photoelectrochemical (PEC) properties of photocatalytic core-shell BiVO₄/ZnO nanodendrites (here after referred to as BVO/ZnO). The atomic and electronic structures of core-shell BVO/ZnO nanodendrites have been well characterized. The variation of charge density between ZnO and BVO in core-shell BVO/ZnO nanodendrites with many unpaired O 2p-derived states at the interface forms interfacial oxygen defects and yields a band gap of approximately 2.6 eV in BVO/ZnO nanocomposites. Atomic structural distortions at the interface of BVO/ZnO nanodendrites, which supports the fact that many interfacial oxygen defects, affect the O 2p-V 3d hybridization and reduces the crystal field energy 10Dq ~2.1 eV. Such an interfacial atomic/electronic structure and band gap modulation increase the efficiency of absorption of solar light and electron-hole separation. This study provides evidence that the interfacial oxygen defects act as a trapping center and are critical for the charge transfer, retarding electron-hole recombination and the high absorption of visible light, which can result in favorable PEC properties of a nanostructured core-shell BVO/ZnO for PEC water splitting and related applications.
Keywords: Core-shell BVO/ZnO heterojunction, Photoelectrochemical properties, Interfacial defects, Scanning transmission X-ray microscopy (STXM), X-ray absorption spectroscopy (XAS)