Browsing by Author "Sone, Masato"

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Cathodic deposition of TiO2 thin films with supercritical CO2 emulsified electrolyte
(2013-08-01)
Chang, Tso-Fu Mark
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Lin, Wei-Hao
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Hsu, Yung-Jung
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Chen, Chun-Yi
;
Sato, Tatsuo
TiO2 thin films were fabricated by cathodic deposition with a supercritical CO2 (sc-CO2) emulsified TiCl3 + NaNO3 electrolyte. Morphology and average grain size were evaluated by SEM, TEM and XRD. SEM micrographs showed that the TiO2 films fabricated by TiCl3 + NaNO3 electrolyte were porous, and the films were composed of particles and aggregates of the particles. Also, size of the particles increased when the sc-CO2 emulsified electrolyte was used. Average grain size of the TiO2 films was calculated using Scherrer equation. The average grain size was found to increase when the sc-CO2 emulsified electrolyte was used. In addition, both particle sizes observed from SEM and average grain size calculated using Scherrer equation were found to increase when pressure was increased from atmospheric pressure to 20 MPa. (c) 2013 Elsevier B.V. All rights reserved.
Effects of Fluorinated Surfactant in Cathodic Deposition of TiO2 Films with Supercritical CO2 Emulsified Electrolyte
(2014)
Chang, Tso-Fu Mark
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Lin, Wei-Hao
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Hsu, Yung-Jung
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Sato, Tatsuo
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Sone, Masato
Effect of a fluorinated surfactant, F(CF(CF3)CF2O)(3)CF(CF3)COO(CH2CH2O)CH3, in pore structure and grain size of the TiO2 films deposited cathodically was studied. Increase in pore size and decrease in grain size were observed when the fluorinated surfactant was used. When supercritical CO2 was introduced into the system, synergetic effect on increasing the pore size was observed. Also, grain coarsening was observed for the films deposited with supercritical CO2. Therefore, the fluorinated surfactant combining with supercritical CO2 demonstrated the ability to control morphology and grain size of the deposited TiO2 films at the same time. (C) 2014 The Electrochemical Society. All rights reserved.
Effects of Pressure in Cathodic Deposition of TiO2 and SnO2 with Supercritical CO2 Emulsified Electrolyte
(2016-08-01)
Lin, Wei-Hao
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Chen, Chun-Yi
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Chang, Tso-Fu Mark
;
Hsu, Yung-Jung
;
Sone, Masato
This study reports the effect of the high pressure on properties, especially the crystallinity, of the TiO2 and SnO2 films cathodically deposited in supercritical CO2 emulsified electrolyte. The as-deposited metal oxides are usually amorphous when cathodic deposition is applied. An additional heat treatment process is needed to have crystalline metal oxides. In this study, the TiO2 and SnO2 thin films cathodically deposited at elevated pressure showed an improvement in the crystallinity with an increase in the pressure using X-ray diffraction analysis. The high-resolution transmission electron microscopy and selected-area electron diffraction confirmed that the TiO2 deposited at 35 MPa had the anatase crystal structure. An enhancement in the charge carrier dynamics at the TiO2 electrode/electrolyte interface with an increase in the pressure was observed from the electrochemical impedance spectroscopy, which is a result of the improved crystallinity. The effect of the pressure on the crystallinity of the SnO2 was more obvious than that on the TiO2. Grain size of the SnO2 films estimated by the Scherrer equation was increased from 3.5 to 14.8 nm when the pressure was increased from 5 to 25 MPa. (C) 2016 Elsevier Ltd. All rights reserved.
Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production
(2018-07-11)
Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
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Chen, Chun-Yi
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Hsieh, Ping-Yen
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Ozasa, Kazunari
Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.
Incorporating graphene quantum dots to enhance the photoactivity of CdSe-sensitized TiO2 nanorods for solar hydrogen production
(2020-07-28)
Chang, Yung-Shan
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Hsieh, Ping-Yen
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Chang, Tso-Fu Mark
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Chen, Chun-Yi
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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.
Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts
(2019-05-01)
Chiu, Yi-Hsuan
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Chang, Tso-Fu Mark
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Chen, Chun-Yi
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Sone, Masato
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Hsu, Yung-Jung
Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems.
Nano-Au Catalysts Modified with TiO2: Enhancement of Electrocatalytic Activity for 1-Propanol Oxidation in Alkaline Media
(2019-07-16)
Chiu, Wan-Ting
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Chiu, Yi-Hsuan
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Hsieh, Ping-Yen
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Chang, Tso-Fu Mark
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Sone, Masato
Electrocatalytic activity of the anode for alcohols oxidation is a critical issue in fuel cell which is considered as a clean energy. Performance deterioration of the catalyst takes place due to the adsorption of carbonaceous residues on the electrode surface, which is also known as poisoning of the electrode. Desorption of carbonaceous residues is thought to be an essential solution but not has been studied systematically. In this work, we investigate both the desorption of carbonaceous residues and the promotion of electrocatalytic activity to alcohols oxidation reactions by using Au nanoparticles (NPs)-TiO2/polyaniline (PANI) composite to boost the overall activity of electrocatalytic alcohol oxidation reactions. Desorption of carbonaceous residues and electrocatalytic activity of alcohol oxidation reactions are evaluated by cyclic voltammetry (CV) measurements in various alcohols. The chronoamperometric i-t curves are measured to evaluate the stability. Mechanisms for desorption of carbonaceous residues and enhancement of the electrocatalytic activity are elaborated and summarized. Electrodes with TiO2 decoration show better performance than TiO2-free specimens. In addition, Au NPs-decorated composites not only show an extra characteristic peak of alcohol oxidation reactions but also perform a constructive effect on the already existing oxidation reaction, indicating the promotion of electrocatalytic oxidation of alcohols. (C) 2019 The Electrochemical Society.
Reduced graphene oxides-wrapped ZnO with notable photocatalytic property
(2020-07-01)
Hu, Wei-Chen
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Chen, Yi-An
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Hsieh, Ping-Yen
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Tsao, Chun-Wen
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Chiu, Yi-Hsuan
A facile, environmentally benign antisolvent method has been developed to prepare for reduced graphene oxides (RGO)-wrapped ZnO nanocrystals with controlled RGO contents. Because of the high electrical conductivity of RGO, the photogenerated electrons at ZnO mostly transported to RGO, leaving positively charged photoexcited holes in ZnO to result in charge separation. The steady-state photoluminescence, time-resolved photoluminescence spectroscopy and photovoltage decay analysis were employed to investigate charge carrier dynamics and charge transfer behaviors of RGO-ZnO. The influence of RGO content on the charge dynamics and photoconversion efficiency of RGO-ZnO toward dye degradation and water splitting has been realized. (C) 2020 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Supercritical CO2-Assisted Electrochemical Deposition of ZnO Mesocrystals for Practical Photoelectrochemical Applications
(2013-12-05)
Lin, Wei-Hao
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Chang, Tso-Fu Mark
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Lu, Yi-Hsuan
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Sato, Tatsuo
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Sone, Masato
We have successfully developed an effective supercritical CO2 (sc-CO2) emulsion-assisted electrochemical approach for cathodic deposition of ZnO mesocrystals. The sc-CO2 was introduced along with a nonionic surfactant in the process to form emulsified electrolyte, which significantly increased the supersaturation degree and promoted the molecular diffusion to affect the crystal growth of ZnO. The deposition involved the generation of primary nanocrystals with substantially high surface energy, followed by the preferred attachment of the primary nanocrystals along an energetically favorable orientation to form ZnO mesocrystals. The as-deposited ZnO mesocrystals exhibited remarkable optical properties at room temperature in terms of prominent near band-edge emission and substantially long exciton lifetime, attributable to the highly oriented crystallinity of mesocrystals that effectively suppressed the nonradiative charge recombination to extend the exciton decay dynamics. As compared to the structures prepared without the addition of surfactant or sc-CO2, ZnO mesocrystals from sc-CO2 emulsion displayed greatly improved photoactivity toward photoelectrochemical water oxidation, revealing their promising potential as photoanodes in relevant photoelectrochemical processes. The current study delivers the first demonstration of directly depositing ZnO mesocrystals on conductive substrates, which paves the way for utilization of mesocrystals as practical electrodes in technologically important energy conversion fields, such as electrochemical cells, photovoltaic devices, as well as photoelectrochemical water splitting, where the advantageous structural characteristics of mesocrystals, i.e., high crystallinity and abundant porosity, can be fully exploited.
The hydrobaric effect on cathodically deposited titanium dioxide photocatalyst
(2017-06-01)
Chang, Tso-Fu Mark
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Lin, Wei-Hao
;
Chen, Chun-Yi
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Hsu, Yung-Jung
;
Sone, Masato
The hydrobaric effect on photoactivity of titanium dioxide (TiO2) fabricated by cathodic deposition in an aqueous solution was evaluated in this study. When the applied pressure was increased to 35 MPa, the water-splitting performance was improved by almost fourfold of the performance of the TiO2 prepared at atmospheric pressure. The surface states effect was significant in the deposited TiO2, which was exploited to affect the charges recombination of TiO2, and thereby enhance the resultant photoelectrochemical water-splitting performance. The hydrobaric cathodic deposition could be extended to fabrication of other metal oxides to eliminate the negative influence from the high-temperature process.