Browsing by Author "Hsieh, Ping-Yen"

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CdS/CdSe co-sensitized brookite H:TiO2 nanostructures: Charge carrier dynamics and photoelectrochemical hydrogen generation
(2018-06-05)
Chang, Yung-Shan
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Choi, Mingi
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Baek, Minki
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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.
Controlling the visible-light driven photocatalytic activity of alloyed ZnSe-AgInSe(2)quantum dots for hydrogen production
(2020-07-14)
Hsieh, Ping-Yen
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Kameyama, Tatsuya
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Takiyama, Takayuki
;
Masuoka, Ko
;
Yamamoto, Takahisa
Binary semiconductor quantum dots such as CdS and CdSe have been widely studied as photocatalysts for hydrogen production, but the high toxicity of Cd impedes their widespread deployment. Recently, multinary I-III-VI-based semiconductors,e.g., AgInS(2)and CuInS2, have emerged as promising alternatives for environmentally benign photocatalysts. In this work, we prepared quantum dots (QDs) composed of an alloyed ZnSe-AgInSe2(ZAISe) semiconductor and evaluated their photocatalytic activity for hydrogen (H-2) production. By individually controlling the fractions of Zn and Ag, that is, the ratios of (Ag + In)/(Zn + Ag + In) and Ag/(Ag + In), the band structure of ZAISe QDs could be finely tuned to improve their photocatalytic activity. The action spectra of the photocatalytic reaction of ZAISe QDs revealed vigorous activity across the whole visible region from 400 to 700 nm. The highest apparent quantum yield of H(2)production reached 3.4% under irradiation at 600 nm.
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
;
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
;
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.
Manganese ion implanted ultrananocrystalline diamond films: Optical and electrical characterization
(2019-04-01)
Kunuku, Srinivasu
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Chen, Chien-Hsu
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Hsieh, Ping-Yen
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Lin, Bo-Rong
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Tai, Nyan-Hwa
We report the optical and electrical properties of high-dose (10(15)-10(17) ions/cm(2)) Mn-ion implanted ultrananocrystalline diamond (Mn-UNCD) films. Mn-ion implantation and post-annealing of UNCD films lead to the formation of Mn-related color centers, characterized in Mn-UNCD films by their zero phonon line emissions at 621.2 nm and phonon sidebands at 611.2 nm and 630.3 nm. Raman spectra of Mn-UNCD films indicated amorphization via high-dose Mn-ion implantation and that the annealing process results in graphitization of the films. The Mn-UNCD film implanted with the Mn-ion dose of 1017 ions/cm(2) exhibits a conductivity of 122.25 (Omega cm)(-1), as well as enhanced field electron emission (FEE) properties such as a turn-on field of 10.67 V/mu m and a FEE current density of 0.85 mA/cm(2).
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
;
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.
Nitrogen-Doped Graphene Quantum Dots for Remarkable Solar Hydrogen Production
(2020-06-22)
Tsai, Kai-An
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Hsieh, Ping-Yen
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Lai, Ting-Hsuan
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Tsao, Chun-Wen
;
Pan, Hui
We synthesized nitrogen (N)-doped graphene quantum dots (N-GQDs) using a top-down hydrothermal cutting approach. The concentration of N dopants was readily controlled by adjusting the concentration of the N source of urea. When N dopants were incorporated into GQDs, visible absorption was induced by C-N bonds, which created another pathway for generating photoluminescence (PL). Time-resolved PL data revealed that the carrier lifetime of GQDs was increased upon doping with the optimized N concentration. The photoelectrochemical properties of N-GQDs toward water splitting were studied, and the results showed that 2N-GQDs prepared with 2 g of urea produced the highest photocurrent. The photocatalytic activity of 2N-GQDs powder photocatalyst for hydrogen production was also examined under AM 1.5G illumination, showing substantial enhancement over that of pristine GQDs. Electrochemical impedance spectroscopy data further revealed a significant improvement in charge dynamics and reaction kinetics and an increased carrier concentration as a result of N doping.
Photoelectrochemical cells for solar hydrogen production: Challenges and opportunities
(2019-08-01)
Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
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Kuo, Ming-Yu
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Hsieh, Ping-Yen
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Hsu, Yung-Jung
As the Holy Grail to a carbon-free hydrogen economy, photoelectrochemical (PEC) water splitting offers a promising path for sustainable production of hydrogen fuel from solar energy. Even though much progress has been made over the past decade, the effectiveness and robustness of PEC cells are still far from a mature phase that would allow for widespread deployment. This perspective discusses the key challenges facing the current level of PEC development and proposes experimental approaches and strategies that can be adopted to address the issues. Focuses are mainly placed on the employment of in situ and operando spectroscopic measurements, the introduction of alternative, high value-added oxidation reactions, and the creation of near infrared-responsive photoelectrodes. A brief outlook that may assist the future advancement of PEC technology is also presented. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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
;
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.
TiO2 Nanowire-Supported Sulfide Hybrid Photocatalysts for Durable Solar Hydrogen Production
(2019-01-23)
Hsieh, Ping-Yen
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Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
;
Fang, Mei-Jing
;
Wang, Yu-Ting
As the feet of clay, photocorrosion induced by hole accumulation has placed serious limitations on the widespread deployment of sulfide nanostructures for photoelectrochemical (PEC) water splitting. Developing sufficiently stable electrodes to construct durable PEC systems is therefore the key to the realization of solar hydrogen production. Here, an innovative charge-transfer manipulation concept based on the aligned hole transport across the interface has been realized to enhance the photostability of In2S3 electrodes toward PEC solar hydrogen production. The concept was realized by conducting compact deposition of In2S3 nanocrystals on the TiO2 nanowire array. Under PEC operation, the supporting TiO2 nanowires functioned as an anisotropic charge-transfer backbone to arouse aligned charge transport across the TiO2-In2S3 interface. Because of the aligned hole transport, the TiO2 nanowire-supported In2S3 hybrid nanostructures (TiO2 In2S3) exhibited improved hole-transfer dynamics at the TiO2-In2S3 interface and enhanced hole injection kinetics at the electrode surface, substantially increasing the long-term photostability toward solar hydrogen production. The PEC durability tests showed that TiO2-In2S3 electrodes can achieve nearly 90.9% retention of initial photocurrent upon continuous irradiation for 6 h, whereas the pure In2S3 merely retained 20.8% of initial photocurrent. This double-gain charge-transfer manipulation concept is expected to convey a viable approach to the intelligent design of highly efficient and sufficiently stable sulfide photocatalysts for sustainable solar fuel generation.