Solar Hydrogen Production under Low Applied Bias Using Oxide Nanomaterials
Yan-Gu Lin1*, Yu-Chang Lin1,2, Hong-Jhe Lin1, Yu-Hsueh Chang1
1Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:Yan-Gu Lin, email:lin.yg@nsrrc.org.tw
Global climate warming and environment pollution have spurred scientists to develop new high-efficient and environmental-friendly energy technologies. Hydrogen is an ideal fuel for fuel cell applications. Hydrogen has to be produced from renewable and carbon-free resources using nature energies such as sunlight if one thinks of clean energy and environmental issues. In this regard, a photoelectrochemical (PEC) cell consisting of semiconductor photoelectrodes that can harvest light and use this energy directly for splitting water is a more promising way for hydrogen generation. Abundant and inexpensive oxide semiconductor such as ZnO has been recognized as a promising photoelectrode, but the photoconversion efficiency is substantially limited by its large band gap and rapid charge recombination. Recently, iron oxide (Fe2O3) with band gap 2.2 eV attracts increasing attention for the conversion of solar energy because iron is an abundant and cheap material. In this work, we propose a facile and simple fabrication of -Fe2O3 as a shell layer on the surface of ZnO nanowires (NW) as a core-shell nanoelectrode for application to the PEC splitting of water. The uniform coverages of the α-Fe2O3 shell at thickness a few nm and core diameter ~80 nm of ZnO NW were confirmed with SEM and TEM. With XRD and XPS we analyzed the structural and composition features of the ZnO/Fe2O3 core-shell NW. This n/n heterojunction structure would significantly cause a further negative shift of the flat-band potential and increase the surface band bending, relative to a bare α-Fe2O3 film electrode. These characteristics resulted in a doubling of photocurrent and a greater PEC stability at a less positive potential for the decomposition of water in a practical application. Our experiments improve our understanding of the heterojunction effect on PEC activity and provide a blueprint for the design of materials in the application of solar hydrogen.
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Keywords: ZnO, Fe2O3, water splitting, photoelectrochemical, solar hydrogen