Manipulating metal-oxygen local atomic structures in single-junctional p-Si/WO 3 photocathodes for efficient solar hydro
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Manipulating metal-oxygen local atomic structures in singlejunctional p-Si/WO3 photocathodes for efficient solar hydrogen generation Wu Zhou1, Chung-Li Dong2, Yiqing Wang1, Yu-Cheng Huang2, Lingyun He1, Han-Wei Chang2, and Shaohua Shen1 () 1
International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Shaanxi 710049, China 2 Department of Physics, Tamkang University, Tamsui 25137, Taiwan, China © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 28 August 2020 / Revised: 15 October 2020 / Accepted: 2 November 2020
ABSTRACT Self-passivation in aqueous solution and sluggish surface reaction kinetics significantly limit the photoelectrochemical (PEC) performances of silicon-based photoelectrodes. Herein, a WO3 thin layer is deposited on the p-Si substrate by pulsed laser deposition (PLD), acting as a photocathode for PEC hydrogen generation. Compared to bare p-Si, the single-junctional p-Si/WO3 photoelectrodes exhibit excellent and stable PEC performances with significantly increased cathodic photocurrent density and exceptional anodic shift in onset potential for water reduction. It is revealed that the WO3 layer could reduce the charge transfer resistance across the electrode/electrolyte interface by eliminating the effect of Fermi level pinning on the surface of p-Si. More importantly, by varying the oxygen pressures during PLD, the collaborative modulation of W–O bond covalency and WO6 octahedral structure symmetry contributes to the promoted charge carrier transport and separation. Meanwhile, a large band bending at the p-Si/WO3 junction, induced by the optimized O vacancy contents in WO3, could provide a photovoltage as high as ~ 500 mV to efficiently drive charge transfer to overcome the water reduction overpotential. Synergistically, by manipulating W–O local atomic structures in the deposited WO3 layer, a great improvement in PEC performance could be achieved over the singlejunctional p-Si/WO3 photocathodes for solar hydrogen generation.
KEYWORDS silicon, local atomic structure, water splitting, photocathodes, hydrogen generation
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Introduction
Photoelectrochemical (PEC) water splitting has been recognized as one of the most promising solar energy conversion technologies by rendering the photoexcited charge carriers for solar fuel synthesis, since the idea of photoelectrolysis using a semiconductor electrode was introduced by Fujishima in 1972 [1–6]. The key issue for the practical application of the PEC technology is to search for low cost and stable photoelectrode materials enabling high efficiency solar hydrogen generation [7–10]. During the past decades, tremendous research efforts have been dedicated to the exploration and development of photoelectrode materials, including oxides, sulfides, nitrides and III-V compounds [11–22]. However, the energy conversion efficiency and durability of these materials is still insufficient to large scale application. As widely used for
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