Browsing by Author "Chang, Yung-Shan"

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AgAu alloy nanoshell: Decorated BaTiO3/TiO2 and SrTiO3/TiO2 for photoelectrochemical catalysis
(2019-08-25)
Chang, Yung-Shan
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Lee, T. Randall
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Hsu, Yung-Jung
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Medhi, Riddhiman
;
Srinoi, Pannaree
CdS/CdSe co-sensitized brookite H:TiO2 nanostructures: Charge carrier dynamics and photoelectrochemical hydrogen generation
(2018-06-05)
Chang, Yung-Shan
;
Choi, Mingi
;
Baek, Minki
;
Hsieh, Ping-Yen
;
Yong, Kijung
In this study, we have synthesized CdS/CdSe co-sensitized brookite TiO2 nanostructures with hydrogen doping (H:TiO2/CdS/CdSe) in a facile solution reaction and studied their PEC performances. Compared to undoped brookite TiO2, the H:TiO2/CdS/CdSe composites exhibit much enhanced photocurrent generation, which originates from the improved charge transfer kinetics endowed by hydrogen doping and sensitization. Time-resolved photoluminescence (PL) and electrochemical impendence spectroscopy (EIS) are employed to explore the charge transfer dynamics between sensitizers and TiO2 and charge carrier kinetics at the semiconductor/electrolyte interface. According to the analytical results, sensitizations of TiO2 are found to enhance the charge separation efficiency. Besides, the hydrogen doping into TiO2 generates oxygen vacancy states, providing additional charge transfer pathway and prohibiting charge recombination, beneficial for enhancing the PEC performances as well. Based on the charge dynamics data, we further develop charge transfer models for TiO2/CdS/CdSe and H:TiO2/CdS/CdSe. The findings from this work can help understanding the charge transfer dynamics in brookite TiO(2)based composite systems as well as designing versatile photoelectrodes for solar energy conversion.
Enhanced photoelectrochemical hydrogen generation in neutral electrolyte using non-vacuum processed CIGS photocathodes with an earth-abundant cobalt sulfide catalyst
(2019-02-28)
Wang, Mingqing
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Chang, Yung-Shan
;
Tsao, Chun-Wen
;
Fang, Mei-Jing
;
Hsu, Yung-Jung
This work reports the novelty of using eco-friendly and cost-effective non-vacuum Electrostatic Spray-Assisted Vapour Deposited Cu(In, Ga) SSe (CIGS) thin films as photocathodes, combined with the earth abundant cobalt sulfide (Co-S) as a catalyst to accelerate the kinetics of photogenerated electron transfer and hydrogen generation for photoelectrochemical water splitting. CdS and ZnO layers were subsequently deposited on top of the selenised CIGS films to increase the charge separation and lower the charge recombination for the photocathodes. In order to improve the lifetime and scalability of the CIGS photocathode and the other cell components, a photoelectrochemical test was conducted in a neutral electrolyte of 0.5 M Na2SO4 under simulated sunlight (AM 1.5G). Both the photocurrent densities and the onset potentials of the photocathodes were significantly improved by the electro-deposition of the low cost and earth-abundant Co-S catalyst, with a photocurrent density as high as 19.1 mA cm(-2) at -0.34 V vs. reversible hydrogen electrode (RHE), comparable with and even higher than that of the control photocathode using rare and precious Pt as a catalyst.
Fabrication of WO3 photoanode decorated with Au nanoplates and its enhanced photoelectrochemical properties
(2019-10-20)
Liu, Ying
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Chang, Yung-Shan
;
Hsu, Yung-Jung
;
Hwang, Bing-Joe
;
Hsueh, Chun-Hway
In the present work, we improved the photoelectrochemical (PEC) performance of tungsten trioxide (WO3) photoanode by decorating WO3 plates with Au nanoplates. WO3 plates were fabricated on FTO-coated glass by hydrothermal treatment and Au nanoplates were incorporated by immersing the substrates in Au nanoplates solution under different periods of time. Our study revealed that compared with pristine WO3, the Au-WO3 nanocomposite performed enhanced photocurrent density under irradiation of the simulated sunlight. This improved PEC performance was benefited from the extension of light absorption resulting from the surface plasmon resonance effect of Au nanoplates at about 650 nm wavelength, and it was verified by UV-vis absorption spectra. The incident photon-to-current conversion efficiency measurements revealed improved photoactivity after decoration of WO3 with Au nanoplates. This study provided a facile method to decorate Au nanoplates on WO3 photoanodes with enhanced performance for solar energy conversion. (C) 2019 Elsevier Ltd. All rights reserved.
Incorporating graphene quantum dots to enhance the photoactivity of CdSe-sensitized TiO2 nanorods for solar hydrogen production
(2020-07-28)
Chang, Yung-Shan
;
Hsieh, Ping-Yen
;
Chang, Tso-Fu Mark
;
Chen, Chun-Yi
;
Sone, Masato
This work demonstrated that the incorporation of graphene quantum dots (GQDs) can greatly improve the photoelectrochemical (PEC) efficiency of CdSe-sensitized TiO2 nanorods (TiO2/CdSe), a TiO2-based visible light-responsive photoelectrode paradigm, for solar hydrogen production. For TiO2/CdSe, the accumulated holes at CdSe may induce photocorrosive oxidation to decompose CdSe, deteriorating the long-term stability of the photoelectrode and degrading the PEC performance. With the introduction of GQDs, the delocalized holes can further transfer from CdSe to the GQDs, which eases the hole accumulation at the CdSe sites, thus retarding photocorrosion. Compared to the binary TiO2/CdSe photoanode, the ternary TiO2/CdSe/GQD photoanode displays higher photocurrent and better photostability toward PEC hydrogen production. This superiority can be attributed to vectorial charge transfer and enhanced reaction kinetics provided by the introduction of GQDs. The findings from this work highlight the importance of the introduction of GQDs as a potential solution to the photocorrosion issue of chalcogenide-sensitized semiconductor photoelectrodes.