Effect of Fe2O3 Coating on ZnO Nanowires Probed by Scanning Transmission X-ray Microscopy and in Situ X-ray Absorption Spectroscopy
Y. R. Lu1,2,3*, Y. F. Wang3, H. W. Chang3, Y. C. Huang1,2, Y. X. Chen2, J. L. Chen4, C. L. Chen4, Y. C. Lin4, Y. G. Lin4, W. F. Pong3, T. Ohigashi5, N. Kosugi5, W. C. Chou2, C. L. Dong3
1Program for Science and Technology of Accelerator Light Source, National Chiao Tung University, Hsinchu, Taiwan
2Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
3Department of Physics, Tamkang University, New Taipei City, Taiwan
4National Synchrotron Radiation Research Center, Hsinchu, Taiwan
5Institute for Molecular Science, Editorial Board, UVSOR Facility, Okazaki, Japan
* presenting author:Ying-Rui Lu, email:waney200@yahoo.com.tw
An array of Fe2O3/ZnO core-shell nanowires (NWs) for photoelectrochemical (PEC) water splitting is developed for highly efficient absorption of light and carrier collection. The synergistic effect of ZnO NWs decorated with a thin layer of α-Fe2O3 results in a higher PEC performance than pure ZnO or α-Fe2O3. However, the electronic structure and charge transfer processes of the Fe2O3/ZnO core-shell NWs remain unclear. In this study, we investigated the electronic structure evolution and surface electronic states of the ZnO/Fe2O3 core-shell NWs under PEC conditions using synchrotron-based spectroscopic techniques coupled with microscopic approaches (i.e., X-ray absorption spectroscopy (XAS) and scanning transmission X-ray microscopy (STXM)). The STXM result shows strong anisotropic effects of O 2p orbitals for both of bare and Fe2O3-coated ZnO NWs based on polarized-XAS. Stronger hybridization between O 2p-Zn 4sp states is revealed in Fe2O3/ZnO and may favor the electron conduction along the NW. The Fe2O3 could consolidate the ZnO surface and thus the core-shell NW exhibits more uniformized electronic structure than bare ZnO. In situ XAS further demonstrates that the Fe 3d and Zn 4p state are the active sites for the photoelectrochemical reaction in the Fe2O3/ZnO core-shell NWs. The enhanced photoelectrochemical water splitting is likely owing to the extra photogenerated electrons from Fe2O3 layer is transferred from Fe 3d to Zn 4p orbital revealed by XAS under operational PEC condition.

Keywords: Fe2O3/ZnO, Photoelectrochemical (PEC), Water splitting, X-ray absorption spectroscopy(XAS), scanning transmission X-ray microscopy(STXM)