Browsing by Author "Huang, Yu-Cheng"

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A novel hybrid artificial photosynthesis system using MoS2 embedded in carbon nanofibers as electron relay and hydrogen evolution catalyst
(2017-08-01)
Niu, Fujun
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Dong, Chung-Li
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Zhu, Changbao
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Huang, Yu-Cheng
;
Wang, Miao
Inspired by photosynthesis in nature, artificial photosynthesis (AP) systems have been widely investigated in the context of energy and environmental research. Here we report a noble-metal-free AP system for visible-light-driven H-2 generation from aqueous solutions consisting of fluorescein (FL) as photosensitizer, single-layer ultrasmall MoS2 nanoplates embedded in carbon nanofibers (CNF) as electron relay and redox catalyst, and triethanolamine (TEOA) as sacrificial electron donor. This CNF-MoS2/FL system exhibits outstanding H-2 evolution performance, with an H-2 generation rate that exceeds not only both MoS2/FL (by 100%) and CNF/FL (by 1100%), but also the Pt/FL system (by 40%). The excellent photocatalytic activity of this CNF-MoS2/FL system can be ascribed to the synergistic effects of CNF and MoS2 coupling: (1) the simultaneous presence of MoS2 with its delocalized and increased Mo 4d unoccupied states and of CNF with increased graphitic characteristics enables electron transfer from FL* to MoS2 via CNF electron relay; (2) the single-layered ultrasmall MoS2 nanoplates with short effective lengths for electron transfer and high density of reactive S-edges effectively catalyze the H-2 evolution reaction (HER). The presented work successfully fabricated a highly efficient AP system for solar H-2 production from a fully aqueous solution and indicated CNF-MoS2 as a promising candidate to replace Pt for solar fuel conversion. (C) 2017 Elsevier Inc. All rights reserved.
Au-BINOL Hybrid Nanocatalysts: Insights into the Structure-Based Enhancement of Catalytic and Photocatalytic Performance
(2019-04-10)
Patolla, Shashank Reddy
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Kao, Chen-Rui
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Chen, Guan-Wei
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Huang, Yu-Cheng
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Chuang, Yu-Chun
Advances in new systems of organic-inorganic hybrid nanocomposites are less prevalent, owing to a lack of facile strategies for precise control of their structures, compositions, and, hence, their properties. In this work, Au-BINOL hybrid nanocomposites with eccentric and concentric nanostructures were produced. The hybrid nanocomposites containing two distinct moieties of inorganic Au nanocrystals and organic BINOL nanospheres were applied to the catalytic hydrogenation of 4-nitrophenol with NaBH4 in the aqueous phase with and without the illumination of visible light. Here, we demonstrate that the existence of Au-BINOL interfaces offers benefits to their performance. The eccentric nanostructures made with CTAC show the superior activity from large Au-BINOL interfaces formed between the BINOL nano spheres and the faces of Au nanoplates. They further exhibit a high Au localized surface plasmon resonance (LSPR)-enhancement effect on the photoreduction of 4-nitrophenol, which is attributed to the strong LSPR absorption of exposed Au nanocrystals unaffected by the coverage of BINOL shells.
Bifunctional cobalt phosphide nanoparticles with convertible surface structure for efficient electrocatalytic water splitting in alkaline solution
(2019-03-01)
Wang, Miao
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Dong, Chung-Li
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Huang, Yu-Cheng
;
Shen, Shaohua
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電子物理學系
Highly efficient non-noble materials for water splitting are essential for renewable energy application. Herein, cobalt phosphide nanoparticles with high P/Co ratio are synthesized and display overpotentials of 348 mV (or 343 mV) for oxygen evolution reaction (OER) with surface oxidized active species formed and 200 mV (or 184 mV) for hydrogen evolution reaction (HER) in 1 M NaOH (or 1 M KOH) at 10 mA cm(-2). The improved OER could be ascribed to the smaller particle size for increased active site number and more importantly the improved intrinsic activity probably assisted by more phosphates formed during electrocatalytic reaction; while the improved HER performance is mainly attributed to the increased active sites in the form of Co-P bonds. In a two-electrode configuration, the catalysts exhibit excellent overall water splitting performance, with 10 mA cm(-2) at 1.58 V and a long-time reaction stability without attenuation during 10 h operation. (C) 2019 Elsevier Inc. All rights reserved.
Electronic Structure Evolution in Tricomponent Metal Phosphides with Reduced Activation Energy for Efficient Electrocatalytic Oxygen Evolution
(2018-08-29)
Wang, Miao
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Dong, Chung-Li
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Huang, Yu-Cheng
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Li, Yanrui
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Shen, Shaohua
Non-noble metal catalysts for high-active electrocatalytic oxygen evolution reaction (OER) are essential in large-scale application for water splitting. Herein, tricomponent metal phosphides with hollow structures are synthesized from cobalt-contained metal organic frameworks (MOFs), i.e., ZIF-67, by tailoring the feeding ratios of Ni and Fe, followed by a high-temperature reduction and a subsequent phosphidation process. Excellent OER activity and long-time stability are achieved in 1 M NaOH aqueous solution, with an overpotential of 329 mV at 10 mA cm(-2) and Tafel slope of 48.2 mV dec(-1), even superior to the noble metal-based catalyst. It is evidenced that the formed (oxyhydr)oxide/phosphate species by in situ electrochemical surface oxidation are responsible for active OER. Accordingly, the simultaneous introduction of external Ni and Fe elements significantly influences the electronic structures of the parent metal phosphides, leading to the in situ electrochemical formation of surface active layer with decreased OER activation energy for greatly improved water oxidation performance. This electronic structure tuning strategy by introducing multicomponent metals demonstrates a versatile method to use MOFs as precursors for synthesizing high-efficient water splitting electrocatalysts.
Electronic structures associated with enhanced photocatalytic activity in nanogap-engineered g-C3N4/Ag@SiO2 hybrid nanostructures
(2020-06-01)
Huang, Yu-Cheng
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Arul, K. Thanigai
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Chen, Chi-Liang
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Chen, Jeng-Lung
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Chen, Jie
Graphitic carbon nitride (g-C3N4) has attracted considerable attention with regard to its use in photocatalytic solar hydrogen production by the splitting of water. High charge carrier recombination critically limits the photocatalytic activity of g-C3N4. Plasmonic metal nanoparticles that can generate localized surface plasmon resonance (LSPR) have been suggested to enhance the harvesting of visible light and to improve water splitting efficiency. However, direct contact between metal nanoparticles and g-C3N4 reduces the hydrogen generation efficiency owing to energy loss by Forster resonance energy transfer (FRET), which competes with plasmon resonance energy transfer (PRET). Decorating g-C3N4 with Ag@SiO2 core-shell plasmonic nanoparticles increases its photocatalytic ability. Tuning the size of the SiO2 nanogap can optimize the photocatalytic performance of g-C3N4/Ag@SiO2, which involves a trade-off between PRET and FRET. X-ray absorption spectroscopy (XAS) is utilized to investigate the electronic structure of g-C3N4 and its modulation with Ag@SiO2. In situ XAS reveals the dynamics of the charge carriers under solar illumination. Analytic results suggest charge redistribution, shifting of the conduction band, modification of the unoccupied states, and consequent improvement in photocatalytic activity by solar illumination. This work sheds light on the effect of LSPR on this photocatalyst with reference to its electronic structure.
Ex-situ soft X-ray absorption spectroscopic investigation of NiCo2O4 annealed in different gases for hydrogen generation by electrolysis of urea
(2019-06-14)
Chang, Han-Wei
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Dong, Chung-Li
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Lu, Ying-Rui
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Huang, Yu-Cheng
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Chen, Chi-Liang
Electrochemical and ex-situ X-ray absorption spectroscopic (XAS) measurements of NiCo2O4 that have been annealed in different gases (Ar and air) were made to evaluate the efficiency of its electrocatalysis of hydrogen generation by the electrolysis of urea. The electrochemical and XAS measurements demonstrated that NCO-Ar contain significant amounts of Co2+ in octahedral coordination was more favorable than NCO-air for urea electrolysis owing to the effective exposure of electrochemical active sites to participate in the Faradic redox reaction. Further insight into the electrocatalytic mechanism of NiCo2O4-based materials during urea electrolysis was obtained using ex-situ soft XAS. The results of ex-situ soft XAS revealed that the variation of the octahedral and tetrahedral coordinations of Co2+ in NCO-Ar and NCO-air importantly contributes to electrocatalytic behavior. NCO-Ar exhibits excellent electrocatalytic activity towards the Co redox couples in a repetitive cycling process owing to the creation of highly efficient active sites (octahedral Co2+). This study presents importantly x-ray spectroscopic determination of the change in electronic structure of catalyst for hydrogen production. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
In situ evolution of highly dispersed amorphous CoOx clusters for oxygen evolution reaction
(2017-09-07)
Chen, Dawei
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Dong, Chung-Li
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Zou, Yuqin
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Su, Dong
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Huang, Yu-Cheng
Electrocatalytic water splitting is a key technique to produce hydrogen fuels, which can be considered as an efficient strategy to store renewable energy. Oxygen evolution reaction (OER) that occurs at the anode side requires a four-electron transfer under highly oxidizing conditions. OER has a large overpotential and therefore determines the overall efficiency. Certain electrocatalysts can efficiently help to improve the reaction kinetics. Owing to the high cost of precious metals such as Pt, Ru, and Ir, non-precious metal oxide catalysts have been vigorously investigated under alkaline conditions. Herein, we synthesized novel highly dispersed amorphous CoOx for the first time in the form of a cluster favorable to enhance the OER activity using a facile method via the air dielectric barrier discharge (DBD) plasma. Compared with the pristine biopolymer-cobalt complex, the amorphous CoOx cluster exhibits a much higher current density and a lower overpotential for OER, e.g., the overpotential of 290 mV at 10 mA cm(-2) and the overpotential of only 350 mV at 300 mA cm(-1). The excellent electrocatalytic OER activity was attributed to the unsaturated catalytic sites on the amorphous CoOx cluster. In addition, we studied the reaction mechanism, and it was observed that pure O-2 DBD plasma could lead to the evolution of crystalline CoOx; however, the presence of N-2 and O-2 in DBD plasma could ensure the facile evolution of amorphous CoOx clusters. This study provides a new strategy to design amorphous materials for electrocatalysis and beyond.
Interlayer interaction in ultrathin nanosheets of graphitic carbon nitride for efficient photocatalytic hydrogen evolution
(2017-08-01)
Zhao, Daming
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Chen, Jie
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Dong, Chung-Li
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Zhou, Wu
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Huang, Yu-Cheng
Two-dimensional graphitic carbon nitride (g-C3N4) nanosheets (CNNS) have attracted intense interest in photocatalysis, given their small thickness and high specific surface area favoring charge transfer and surface reactions. Herein, a facile strategy of breaking and following repolymerizing the heptazine units in bulk g-C3N4 (BCN) is developed to synthesize ultrathin CNNS with thickness of 1 nm in relatively high product yield (similar to 24%). The as-prepared 1 nm-thick CNNS show significantly enhanced photocatalytic performance for hydrogen evolution than BCN and even the 3 nm-thick CNNS acquired by thermal oxidation etching of BCN. It is evidenced that the disordered layer structure of the obtained ultrathin CNNS causes strong interlayer C-N interaction, tunneling electron transport between the C-N layers. Meanwhile, the broken in-plane C-N bonds create more unsaturated N sites in the 1 nm-thick CNNS, facilitating the electron excitation from the occupied states in g-C3N4 to its unoccupied states for water reduction reaction. (C) 2017 Elsevier Inc. All rights reserved.
NiCo2O4/graphene quantum dots (GQDs) for use in e fficient electrochemical energy devices: An electrochemical and X-ray absorption spectroscopic investigation
(2020-05-15)
Chang, Han-Wei
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Fu, Ji-Xuan
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Huang, Yu-Cheng
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Lu, Ying-Rui
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Kuo, Chun-Hong
NiCo2O4/graphene quantum dots (GQDs) were synthesized by the incorporation of GQDs into NiCo2O4 as electrode materials for use in electrochemical energy devices. The electronic structure and the electrochemical performance of NiCo2O4/GQDs were investigated by X-ray absorption spectroscopy (XAS) and electrochemical measurements. The rich redox active sites were revealed on the NiCo2O4/GQDs, which were formed by the strong CeOeNi/Co interaction between NiCo2O4 and GQDs. The synergetic double-layer capacitive and pseudocapacitive properties were suggested to provide favorable electrochemical characteristics. In/ex situ XAS elucidates local electronic and chemical environments and provides insights into the energy storage/conversion mechanisms. Analytical results demonstrate that the NiCo2O4/GQDs have strong oxygen-carbon bridges and have more Ni active sites than does NiCo2O4, favoring metal-to-ligand charge transfer at the interface between NiCo2O4 and GQDs, critically influencing electrochemical performance. This work contributes importantly to the field by elucidating an energy storage/conversion mechanism for electrochemical energy devices.
Operando Spectral and Electrochemical Investigation into the Heterophase Stimulated Active Species Transformation in Transition-Metal Sulfides for Efficient Electrocatalytic Oxygen Evolution
(2020-02-07)
Wang, Miao
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Dong, Chung-Li
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Huang, Yu-Cheng
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Shen, Shaohua
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交大名義發表
In-depth understanding of electrocatalytically active species transformation during oxygen evolution reaction (OER) is highly guidable to design effective electrocatalysts for water splitting. Herein, cobalt sulfide (CoSx) nanovesicles decorated with iron sulfide (FeSx) heterophases were successfully synthesized by using a metal-organic framework precursor through a solvothermal method. The obtained CoSx/FeSx exhibited much elevated OER activity as compared to pristine CoSx and even most previously reported cobalt-based electrocatalysts, with the overpotential of 304 mV at 10 mA cm(-2) in 1 M KOH. As revealed by operando Raman and X-ray absorption spectroscopy measurements, the electrocatalytically active species transformation in CoSx nanovesicles could be stimulated by the incorporated FeSx heterophases due to the increased average valence state of cobalt and lowered coordination of cobalt sites. As a result, the electrocatalytically active cobalt oxyhydroxides could be more easily formed on the catalyst surface during OER and thus contributed to the highly improved performance. This real-time spectral and electrochemical insight into the electrocatalytically active species transformation may guide the rational design of highly efficient electrocatalysts for water splitting from the viewpoint of electronic structure-electrocatalytic activity relationship.
Synergy of Dopants and Defects in Graphitic Carbon Nitride with Exceptionally Modulated Band Structures for Efficient Photocatalytic Oxygen Evolution
(1970-01-01)
Zhao, Doming
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Dong, Chung-Li
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Bin Wang
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Chen, Chao
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Huang, Yu-Cheng
Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by simply calcining the mixture of graphitic carbon nitride (g-C3N4) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g-C3N4. The resultant boron-doped and nitrogen-deficient g-C3N4 exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 mu mol h(-1) g(-1), much higher than previously reported g-C3N4. It is well evidenced that with conduction and valence band positions substantially and continuously tuned by the simultaneous introduction of boron dopants and nitrogen defects into g-C3N4, the band structures are exceptionally modulated for both effective optical absorption in visible light and much increased driving force for water oxidation. Moreover, the engineered electronic structure creates abundant unsaturated sites and induces strong interlayer C-N interaction, leading to efficient electron excitation and accelerated charge transport. In the present work, a facile approach is successfully demonstrated to engineer the electronic structures and the band structures of g-C3N4 with simultaneous introduction of dopants and defects for high-performance photocatalytic oxygen evolution, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion.
Visible light-induced electronic structure modulation of Nb- and Ta-doped alpha-Fe2O3 nanorods for effective photoelectrochemical water splitting
(2018-02-09)
Chang, Han-Wei
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Fu, Yanming
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Lee, Wan-Yi
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Lu, Ying-Rui
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Huang, Yu-Cheng
The photoelectrochemical (PEC) water splitting activity of Nb and Ta-doped hematite (alpha-Fe2O3) nanorods was investigated with reference to electronic structures by in situ synchrotron x-ray absorption spectroscopy (XAS). Current density-potential measurements demonstrate that the PEC activity of alpha-Fe2O3 nanorods depends strongly on the species and concentrations of dopants. The doping of alpha-Fe2O3 nanorods with a low level of Nb or Ta can improve their electrical conductivity and thereby facilitate charge transport and reduced electron-hole recombination therein. The photoconversion effects of Nb and Ta-doped alpha-Fe2O3 by in situ XAS in the dark and under illumination revealed opposite evolutions of the spectral intensities of the Fe L-edge and Nb/Ta L-edge, indicating that charge transfer and a conduction pathway are involved in the photoconversion. Analytic in situ XAS results reveal that the alpha-Fe2O3 that is doped with a low level of Nb has a greater photoconversion efficiency than that doped with Ta because Nb sites are more active than Ta sites in alpha-Fe2O3. The correlation between PEC activity and the electronic structure of Nb/Ta-doped alpha-Fe2O3 is examined in detail using in situ XAS and helps to elucidate the mechanism of PEC water splitting in terms of the electronic structure.
X-ray Absorption Spectroscopic Study on Interfacial Electronic Properties of FeOOH/Reduced Graphene Oxide for Asymmetric Supercapacitors
(2017-04-01)
Chang, Han-Wei
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Dong, Chung-Li
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Lu, Ying-Rui
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Huang, Yu-Cheng
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Chen, Jeng-Lun
The effects of growth time and interface between the iron oxyhydroxide (FeOOH) and carbon materials (carbon nanotubes (CNT) and reduced graphene oxide (RGO)) to form an asymmetric supercapacitor was studied by X-ray absorption spectroscopy (XAS) and electrochemical measurements. FeOOH/CNT (FCNT) and FeOOH/RGO (FRGO) were successfully synthesized by a simple spontaneous redox reaction with FeC13. The RGO functions as an ideal substrate, providing rich growth sites for FeOOH, and it is believed to facilitate the transport of electrons/ions across the electrode/electrolyte interface. FRGO has been identified as a supercapacitor and found to exhibit significantly greater capacitance than FCNT. To gain further insight into the effects of growth times and the interface of FeOOH for FCNT and FRGO, the electronic structures of FCNT and FRGO with various FeOOH growth times were elucidated by XAS. The difference between the surface electronic structures of CNT and RGO yields different nucleation and growth rates of FeOOH of FeOOH. RGO with excellent interface properties arises from a high degree of covalent functionalization, and/or defects make it favorable for FeOOH growth. FRGO is therefore a promising electrode material for use in the fabrication of asymmetric supercapacitors. In this work, coupled XAS and electrochemical measurements reveal the electronic structure of the interface between FeOOH and the carbon materials and the capacitance performance of asymmetric supercapacitors, which are very useful in the fields of nanomaterials and nanotechnology, especially for their applications in storing energy.