Browsing by Author "Li, Jing-Mei"

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A more accurate, reliable method to evaluate the photoelectrochemical performance of semiconductor electrode without under/over estimation
(2018-03-20)
Li, Jing-Mei
;
Wang, Yu-Ting
;
Hsu, Yung-Jung
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材料科學與工程學系
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Department of Materials Science and Engineering
A more accurate and reliable method is proposed to evaluate the photoelectrochemical (PEC) performance of semiconductor toward water splitting. Conventionally, I-t measurements are conducted at a fixed potential relative to the reference electrode, e.g., 0 V vs. Ag/AgCl, to monitor the photocurrent, which has been regarded as a direct indicator for performance comparison among different electrodes. Considering that the open-circuit potential (OCP) varies from electrode to electrode, the photocurrent comparison at a fixed potential may misrepresent the actual differences between samples. Here, we study the PEC performance by applying two distinct external bias values, one at 0 V vs. Ag/AgCI deriving from the conventional practice and the other at 0.1 V vs. OCP representing the exactly fixed applied overpotential. Two experimental groups are designed to address the arguments, including the influence of heat treatment for ZnO nanorod arrays and the global comparison among ZnO, TiO2, Au particle-decorated TiO2, and CdS electrodes. Different trends in photocurrent are observed at the two distinct biases, with the results from 0.1 V vs. OCP conforming to the general considerations. The results suggest that application of a fixed potential relative to the OCP will provide a more fair comparison for accurate PEC performance evaluation without under-or over-estimation. (C) 2018 Elsevier Ltd. All rights reserved.
Au-decorated GaOOH nanorods enhanced the performance of direct methanol fuel cells under light illumination
(2016-05-15)
Hsu, Yi-Han
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Nguyen, An T.
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Chiu, Yi-Hsuan
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Li, Jing-Mei
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Hsu, Yung-Jung
We reported for the first time that GaOOH nanorods, which were prepared using a facile chemical precipitation method, may display noticeable photocatalytic activities toward methanol oxidation under light illumination, a significant revelation for demonstrating their use as the anode photocatalyst in the half cell reaction of direct methanol fuel cells (DMFCs). The GaOOH nanorods were further decorated with Au nanoparticles to endow them with increasingly pronounced charge separation, which conduced to a remarkable enhancement in the photocatalytic performance. Time-resolved photoluminescence spectroscopy was employed to depict the charge transfer event across the interface of GaOOH/Au, from which a correlation between photocatalytic efficiency and interfacial charge dynamics was realized. By incorporating GaOOH nanorods into the traditional Pt-catalyzed half-cell reaction, a 12.7% increase in anodic current generation can be attained under light illumination, demonstrating the promising potential of GaOOH as a practical anode photocatalyst in DFMCs. A further enhancement in methanol oxidation current up to 70.8% can be achieved by employing Au-decorated GaOOH nanorods, which was attributed to the efficient charge carrier transfer rendered by the Au decoration. The current study delivers both fundamental and practical importance as it broadens the scope of electrocatalysts for fuel cells, specifically by introducing a new class of highly efficient photocatalysts for promoting electrochemical reactions. (C) 2015 Elsevier B.V. All rights reserved.
Electroless deposition of RuO2-based nanoparticles for energy conversion applications
(2019-01-01)
Li, Jing-Mei
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Hu, Chi-Chang
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Wu, Tzu-Ho
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Hsu, Yung-Jung
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材料科學與工程學系
This study reports a delicate electroless approach for the deposition of RuO2 center dot nH(2)O nanoparticles on the VOx center dot mH(2)O nanowires and this method can be extended to deposit RuO2 center dot nH(2)O nanoparticles on various material surfaces. Electrochemical characterizations, including linear sweep voltammetry (LSV), electrochemical quartz crystal microbalance (QCM) analysis and rotating ring-disc electrode (RRDE) voltammetry, were carried out to investigate the growth mechanism. The deposition involves the catalytic reduction of dissolved oxygen by the V4+ species of VOx center dot mH(2)O, which drives the oxidation of RuCl3 to proceed with the growth of RuO2 center dot nH(2)O. This core/shell VOx center dot mH(2)O/RuO2 center dot nH(2)O shows a better catalytic activity of the oxygen reduction reaction (ORR) than RuO2 center dot nH(2)O, which is ascribed to the pronounced dispersion of RuO2 center dot nH(2)O. Such an electroless approach was applicable to the preparation of a RuO2-based nanoparticle suspension as well as the deposition of nanocrystalline RuO2 center dot nH(2)O on other functional supports like TiO2 nanowires. The thus-obtained RuO2-decorated TiO2 nanorods exhibit significantly an enhanced photoactivity toward photoelectrochemical water oxidation. The versatility of the current electroless approach may facilitate the widespread deployment of nanocrystalline RuO2 center dot nH(2)O in a variety of energy-related applications.
TiO2-Au-Cu2O Photocathodes: Au-Mediated Z-Scheme Charge Transfer for Efficient Solar-Driven Photoelectrochemical Reduction
(2018-12-01)
Li, Jing-Mei
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Tsao, Chun-Wen
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Fang, Mei-Jing
;
Chen, Chun-Chi
;
Liu, Chen-Wei
An Au-mediated Cu2O-based Z-scheme heterostructure system is demonstrated for use as efficient photocathodes in photoelectrochemical (PEC) reduction. The samples are prepared by electrodepositing a Cu2O layer on the surface of Au particle-coated TiO2 nanorods. For TiO2-Au-Cu2O, the embedded Au particles function as a charge transfer mediator to enhance the electron transportation from the conduction band of TiO2 to the valence band of Cu2O. Such a vectorial charge transfer leads to the concentration of electrons at the conduction band of Cu2O and the collection of holes at the valence band of TiO2, providing TiO2-Au-Cu2O with substantially high redox abilities for reduction applications. Time-resolved photoluminescence spectra and electrochemical impedance spectroscopy analysis suggest that interfacial charge transfer is significantly improved because of the Au-mediated Z-scheme charge transfer mechanism. By virtue of the high redox ability and improved interfacial charge transfer, TiO2-Au-Cu2O performs much better as a photocathode in H2 production and CO2 reduction than pure Cu2O and binary TiO2-supported Cu2O do. Remarkably, the photocurrent density of TiO2-Au-Cu2O toward PEC CO2 reduction can reach as high as -1.82 mA/cm(2) at +0.11 V vs RHE. The incident photon-to-current conversion efficiency data manifest that TiO2-Au-Cu2O surpasses both pure Cu2O and binary TiO2-supported Cu2O in PEC reduction across the whole photoactive region. The current study paves a valuable approach of devising Z-scheme photocathode for the construction of sophisticated artificial photosynthesis systems capable of solar-to-fuel conversion.
ZnO-Au-SnO2 Z-scheme photoanodes for remarkable photoelectrochemical water splitting
(2016)
Li, Jing-Mei
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Cheng, Hao-Yun
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Chiu, Yi-Hsuan
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Hsu, Yung-Jung
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材料科學與工程學系
For the first time a ZnO nanorod-based Z-scheme heterostructure system was proposed and realized for efficient photoelectrochemical water splitting. The samples were prepared by depositing a thin layer of SnO2 on the Au surface of Au particle-decorated ZnO nanorods. For ZnO-Au-SnO2 nanorods, the embedded Au can mediate interfacial charge transfer by promoting electron transfer from the conduction band of SnO2 to the valence band of ZnO. This vectorial charge transfer resulted in the situation that the photoexcited electrons accumulated at ZnO while the photogenerated holes concentrated at SnO2, giving ZnO-Au-SnO2 substantially high redox powers. Time-resolved photoluminescence spectra suggested that the interfacial charge transfer across the ZnO/Au/SnO2 interface was significantly improved as a result of the Z-scheme charge transfer mechanism. With the substantially high redox powers and significantly improved interfacial charge transfer, ZnO-Au-SnO2 nanorods performed much better as a photoanode in photoelectrochemical water splitting than pristine ZnO, plasmonic Au-decorated ZnO and type-II SnO2-coated ZnO nanorods did. The present study has provided a viable approach to exploit Z-scheme photoanodes in the design of efficient artificial photosynthesis systems for solar energy conversion.