Electronic Structure of BiVO4 Coated ZnO Nanodendrite Core- Shell Nanocomposite Using X-ray Spectroscopic Studies
Mandar M. Shirolkar1*, Y.-F. Wang1, Y. C. Shao1, K.-H. Chen1, X.-S. Qiu1, J.-S. Yang2, J.-J. Wu2, W. F. Pong1
1Department of Physics, Tamkang University, Tamsui, Taiwan
2Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan
* Presenter:Mandar M. Shirolkar
Recently, it has been reported that ZnO nanodendrites coated with BiVO 4 nanolayers core-shell nanocomposite thin film structure forms a multiple-level hierarchical heterostructure, which is remarkably beneficial for light absorption and charge carrier separation for the photoelectrochemical (PEC) properties. In this study, the electronic structure of the thin film of ZnO nanodendrite@BiVO4 nanolayers fabricated on FTO substrate was investigated using a set of X-ray spectroscopic methods. We have probed the origin and nature of localized electron states in core-shell structures using X-ray absorption spectroscopies and valance band spectroscopy, which essentially shows that in core-shell structure tetrahedral environment of V5+ in BiVO 4 is unusually distorted and the inter-band gap states related to multiple valence states of vanadium, namely, V4+ and V3+ are present. The presence of multiple valance states of vanadium affects the conduction band of BiVO 4, which disturbs small polaron formation, resulting due to electron localization phenomena. On the other hand, the BiVO 4 shell has improved Zn-O tetrahedral coordination through lattice oxygen sharing. Thus, our investigations show that alteration in deep trap state or small polaron formation in the conduction band maxima of BiVO4 due to multiple valance states of vanadium and improvement in Zn-O tetrahedral environment collectively increased carrier concentration in spite of increased carrier recombination rates, resulting in the enhanced PEC efficiency. These insights into the electronic structure of ZnO nanodendrite@BiVO 4 nanolayers may guide the development and optimization of this material for PEC applications.

Keywords: photoelectrochemical, nanocomposite, heterostructure, small polaron