Browsing by Author "Lin, Yu-Chang"

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Effective hydrogenation of TiO2 photocatalysts with CH3OH for enhanced water splitting: A computational and X-ray study
(2019-09-15)
Wang, Tsai-Te
;
Raghunath, Putikam
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Lin, Yu-Chang
;
Lin, Yan-Gu
;
Lin, Ming-Chan
We have investigated computationally and experimentally the efficacy of CH3OH treatment of anatase TiO2 nanoparticles (NPs) and compared the results obtained with H-2 as the hydrogenation source. The results indicate that TiO2 NPs heated at 300 degrees C in 120 Torr of CH3OH vapor is more effective than the samples heated under 800 Torr of H-2 at the same temperature. Ultraviolet-visible spectroscopy (UV-VIS), Photoluminescence spectroscopy (PL) and X-ray diffraction spectroscopy (XRD) were employed to study the optical property. The effect of temperature of hydrogenation has been systematically studied for NPs in the 200-450 degrees C range for both H-sources based on H-2 evolution, employing Xe lamp as the light source. The hydrogenated TiO2 NPs using H-2 and CH3OH have been analyzed by soft X-ray absorption near-edge structure analyses with and without Xe lamp irradiation in situ. The result indicates that CH3OH hydrogenation can induce a much stronger Ti-O interaction along direction d(z)(2) and increase the unoccupied DOS of Ti t(2g) states. This is why the CH3OH treated TiO2 exhibits a greater photo-activity. The crucial role of the hydrogenation using CH3OH was also investigated systematically and confirmed by quantum-chemical calculations with complementary synchrotron-based X-ray techniques. The results are consistent with the predicted barriers for the formation of H atoms on the TiO2 surface, 4-9 kcal/mol, considerably lower than that in the H-2 case, 48 kcal/mol.
Electrodeposited Fe2TiO5 nanostructures for photoelectrochemical oxidation of water
(2016-09-20)
Lin, Yan-Gu
;
Hsu, Yu-Kuei
;
Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
Electrodeposition was used to fabricate nanostructured films of Ti-containing hematite for application to the photoelectrochemical (PEC) splitting of water. The morphology and microstructure of Ti-doped hematite were examined with a scanning electron microscope, X-ray diffraction, Raman spectra and X-ray photoelectron spectra. Optical absorption spectra indicated an enhanced light absorbance in Ti-doped hematite. This Ti doping increased the carrier concentration about ten-fold, confirmed with a Mott-Schottky analysis. The prepared Ti-doped hematite showed a photocurrent enhanced four-fold relative to pristine hematite. Synchrotron-based soft X-ray absorption spectra clearly revealed that a local Fe2TiO5 structure in hematite formed a heterojunction, which decreased the accumulation of photogenerated holes and improved the performance. (C) 2016 Elsevier Ltd. All rights reserved.
Electrodeposited Fe2TiO5 nanostructures for photoelectrochemical oxidation of water
(2016-09-20)
Lin, Yan-Gu
;
Hsu, Yu-Kuei
;
Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
Electrodeposition was used to fabricate nanostructured films of Ti-containing hematite for application to the photoelectrochemical (PEC) splitting of water. The morphology and microstructure of Ti-doped hematite were examined with a scanning electron microscope, X-ray diffraction, Raman spectra and X-ray photoelectron spectra. Optical absorption spectra indicated an enhanced light absorbance in Ti-doped hematite. This Ti doping increased the carrier concentration about ten-fold, confirmed with a Mott-Schottky analysis. The prepared Ti-doped hematite showed a photocurrent enhanced four-fold relative to pristine hematite. Synchrotron-based soft X-ray absorption spectra clearly revealed that a local Fe2TiO5 structure in hematite formed a heterojunction, which decreased the accumulation of photogenerated holes and improved the performance. (C) 2016 Elsevier Ltd. All rights reserved.
Enhanced light extraction in wafer-bonded p-side-up thin-film AlGaInP light emitting diodes via zinc oxide nanorods
(2016-10-01)
Tseng, Ming-Chun
;
Wuu, Dong-Sing
;
Chen, Chi-Lu
;
Lee, Hsin-Ying
;
Lin, Yu-Chang
ZnO nanorods grown via hydrothermal method on the aluminum-doped zinc oxide (AZO) thin film were used to fabricate high-brightness p-side-up thin-film AlGaInP light-emitting diodes (LEDs). The AZO thin film was not only used as current spreading layers but also as a seed layer of ZnO nanorods. The AZO thin film was prepared using atomic layer deposition. The ZnO nanorods improved light extraction, thus increasing the light output power of the LEDs. The output powers of LEDs with optimum ZnO nanorod structures were increased by 32% at an injection current of 700 mA, as compared with that of an LED with AZO thin film. The emission wavelength shifts of LEDs with an AZO thin film and optimum ZnO nanorod structure were 18 and 11 nm, respectively, when the injection current was increased from 20 to 1000 mA. The ZnO nanorods not only provide more light extraction but also keep the thermal stability of the LED device without any degradation. The results are promising for the developed high brightness AlGaInP LED applications with low fabrication cost through ZnO nanorods grown by hydrothermal method to enhance the light extraction efficiency. (C) 2016 Optical Society of America
Hierarchical Fe2O3 nanotube/nickel foam electrodes for electrochemical energy storage
(2016-10-20)
Lin, Yan-Gu
;
Hsu, Yu-Kuei
;
Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
An iron-oxide (Fe2O3) nanotube (NT) array is grown directly as a hierarchical nanoarchitecture on a nickel-foam (NF) surface via a simple and cost-effective immersive process. The morphology and microstructure of Fe2O3 NT arrays are systematically examined by scanning electron, transmission electron, Raman, and X-ray photoelectron spectroscopies. The results reveal that the walls of Fe2O3 NT are composed mainly of agglomerated small alpha-Fe2O3 (hematite) monocrystalline nanoparticles filled with a few ZnO monocrystalline particles. The microstructural influence on the pseudocapacitive performance of the obtained Fe2O3 NT/NF electrodes is also investigated via in-situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in-situ XAS results regarding charge storage mechanisms of the Fe2O3 NT/NF electrodes show that a Li+ can reversibly insert/desert into/from the 3D mesoporous textures between the Fe2O3 subunits depending on the applied potential. The electrochemical results indicate that the Fe2O3 NT/NF electrode shows highly reversible features and satisfactory rate abilities. Most significantly, the excellent specific capacitance achieved in Fe2O3 NT/NF nanoelectrodes is as great as 300.1 Fg(-1); energy density 75 W h kg(-1) and power density 4.5 kW kg(-1) are obtained, and the Fe2O3 NT/NF nanoelectrode has acceptable cycling stability after 3000 cycles. (C) 2016 Elsevier Ltd. All rights reserved.
Hierarchical Fe2O3 nanotube/nickel foam electrodes for electrochemical energy storage
(2016-10-20)
Lin, Yan-Gu
;
Hsu, Yu-Kuei
;
Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
An iron-oxide (Fe2O3) nanotube (NT) array is grown directly as a hierarchical nanoarchitecture on a nickel-foam (NF) surface via a simple and cost-effective immersive process. The morphology and microstructure of Fe2O3 NT arrays are systematically examined by scanning electron, transmission electron, Raman, and X-ray photoelectron spectroscopies. The results reveal that the walls of Fe2O3 NT are composed mainly of agglomerated small alpha-Fe2O3 (hematite) monocrystalline nanoparticles filled with a few ZnO monocrystalline particles. The microstructural influence on the pseudocapacitive performance of the obtained Fe2O3 NT/NF electrodes is also investigated via in-situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in-situ XAS results regarding charge storage mechanisms of the Fe2O3 NT/NF electrodes show that a Li+ can reversibly insert/desert into/from the 3D mesoporous textures between the Fe2O3 subunits depending on the applied potential. The electrochemical results indicate that the Fe2O3 NT/NF electrode shows highly reversible features and satisfactory rate abilities. Most significantly, the excellent specific capacitance achieved in Fe2O3 NT/NF nanoelectrodes is as great as 300.1 Fg(-1); energy density 75 W h kg(-1) and power density 4.5 kW kg(-1) are obtained, and the Fe2O3 NT/NF nanoelectrode has acceptable cycling stability after 3000 cycles. (C) 2016 Elsevier Ltd. All rights reserved.
Impacts of high-electroactive-surface-area buckypaper counter electrodes on the photovoltaic performance of dye-sensitized solar cells
(2015-09-09)
Cheng, Cheng-En
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Lin, Yu-Chang
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Tsai, Shang-Yi
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Lin, Zheng-Kun
;
Lee, Ping-Chen
In this paper we study the photovoltaic performance of dye-sensitized solar cells (DSCs) with high-electroactive-surface-area buckypaper (BP) counter electrodes (CEs). BP is made of entangled multi-walled carbon nanotubes and has a high electroactive surface area, which is effectively 11.5 times higher than that of Pt. The high surface area of BP causes a high I-3(-) reduction rate at the CEs and suppresses the charge recombination at the anodes. Accordingly, the open-circuit voltage, the filling factor, and the power conversion efficiency of DSCs with BP CEs are enhanced, and these photovoltaic parameters exhibit a better trend with the increase of solar power compared with conventional DSCs with Pt CEs.
KSCN-activation of hydrogenated NiO/TiO2 for enhanced photocatalytic hydrogen evolution
(2020-05-01)
Wang, Tsai-Te
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Chiang, Chao-Lung
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Lin, Yu-Chang
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Srinivasadesikan, Venkatesan
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Lin, Ming-Chang
It was investigated the efficiency of hydrogen production from NiO-loaded TiO2 treated by methanol hydrogenation and functionalized by SCN ligand (SCN-M:(NiO/TiO2)). The effects of a p-n junction created between NiO and TiO2 were demonstrated to enhance significantly the overall photocatalytic performance. The optical and microstructural properties of SCN-M:(NiO/TiO2) were studied with ultraviolet-visible spectra (UV-Vis), photoluminescence (PL), Raman spectra, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The atomic and electronic configurations of SCN-M:(NiO/TiO2) were investigated with analysis of the X-ray absorption near-edge structure (XAS) in situ under irradiation with Xe lamp incorporating a filter (AM 1.5G). An effective quantum yield of 1.34% for hydrogen production was attained with SCN-M:(NiO/TiO2). Quantum-chemical calculations revealed a synergistic decrease of the band gap upon loading Ni, Ni-linked O-2 and anionic SCN-ligand binding. The optimal energy bandgap was decreased to 2.70 eV for (SCN/O-2)-3Ni@TiO2, which reasonably supported the enhancement of H-2 evolution.
N,P co-coordinated Fe species embedded in carbon hollow spheres for oxygen electrocatalysis
(2019-06-28)
Zhu, Xiaofeng
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Tan, Xin
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Wu, Kuang-Hsu
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Chiang, Chao-Lung
;
Lin, Yu-Chang
The increasing interest in fuel cell technology and metal-air batteries has led to the need for stable and effective catalyst materials to replace noble metal (such as Pt) based benchmarks for the oxygen reduction reaction (ORR). In this study, carbon hollow spheres with highly dispersed nitrogen and phosphorus co-coordinated iron atoms (FeNPC) on their surface have been successfully fabricated, exhibiting exceptional ORR activity in both alkaline and acidic solutions. Specifically, the obtained FeNPC catalyst is capable of catalyzing the ORR with an onset potential of 1.03 V and a half-wave potential of 0.88 V (both vs. the reversible hydrogen electrode) in alkaline solution, outperforming the commercial Pt/C catalyst under identical conditions. Experimental results and theoretical simulations reveal that the quasi-octahedral O-2-FeNxPy species are the active sites of the FeNPC composite. These species modify the electronic configuration of Fe centers and weaken the adsorption of the OH* intermediate, thereby promoting the ORR process. Additionally, the FeNPC catalyst also displays a catalytic activity towards the anodic oxygen evolution reaction (OER), making it an active air electrode catalyst in rechargeable Zn-air batteries with a high peak power density of 233.2 mW cm(-2) and an excellent cycling stability at 3 mA cm(-2) for over 15 h.
Performance comparison of p-side-up thin-film AlGaInP light emitting diodes with aluminum-doped zinc oxide and indium tin oxide transparent conductive layers
(2016-04-01)
Tseng, Ming-Chun
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Wuu, Dong-Sing
;
Chen, Chi-Lu
;
Lee, Hsin-Ying
;
Lin, Yu-Chang
Transparent conductive layers (TCLs) deposited on a GaP window layer were used to fabricate high-brightness p-side-up thin-film AlGaInP light-emitting diodes (LEDs) by the twice wafer-transfer technique. Indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO) were used as TCLs for comparison. The TCLs improved droop of external quantum efficiencies (EQE) of LEDs and junction temperature, which result in increasing the light output power and thermal stability of the LEDs. The droop efficiency of Ref-LED, ITO-LED and AZO-LED were 64%, 27% and 15%, respectively. The junction temperature of ITO-LED and AZO-LED reduced to 49.3 and 39.6 degrees C at an injection current of 700 mA compared with that (80.8 degrees C) of Ref-LED. The LEDs with AZO layers exhibited the most excellent LED performance. The emission wavelength shifts of LEDs without a TCL, with an ITO layer, and with an AZO layer were 17, 8, and 3 nm, respectively, when the injection current was increased from 20 to 1000 mA. The above results are promising for the development of AZO thin films to replace ITO thin films for AlGaInP LED applications. (C) 2016 Optical Society of America
Performance of p-side-up thin-film AlGaInP light-emitting diodes with textured composite aluminum-doped zinc oxide transparent conductive layers
(2017-06-25)
Tseng, Ming-Chun
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Wuu, Dong-Sing
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Chen, Chi-Lu
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Lee, Hsin-Ying
;
Lin, Yu-Chang
Composite transparent conductive layers (TCLs) were deposited on the GaP window layer of p-side-up thin-film AlGaInP light-emitting diodes (LEDs) in order to enhance their light-extraction efficiency. The composite TCLs were fabricated from aluminum-doped zinc oxide (AZO) layers grown through atomic-layer deposition and pulsed-laser deposition. The results showed that wet-etching of composite AZO thin films improved the light extraction efficiency of the corresponding LED devices. The droop efficiencies of LEDs with flat AZO thin films, composite AZO thin films, and optimum textured composite AZO thin films were 29%, 30%, and 22%, respectively. LEDs with textured composite AZO layers exhibited favorable optoelectronic performance. When the injection current was increased from 20 to 1000 mA, the emission wavelengths of LEDs with flat AZO thin films, composite AZO thin films, and optimum textured composite AZO thin films shifted by 3, 5, and 3 nm, respectively. The optimum textured composite AZO thin film can not only improve LED performance but also effectively substitute flat TCLs in AlGaInP LED applications. (C) 2016 Elsevier B.V. All rights reserved.
Pt crystalline ultrathin films as counter electrodes for bifacial dye-sensitized solar cells
(2017-01-01)
Cheng, Cheng-En
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Lin, Zheng-Kun
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Lin, Yu-Chang
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Lei, Bi-Chen
;
Chang, Chen-Shiung
This study is to develop the Pt crystalline ultrathin films as high-transparent, efficient, and low-Pt-loaded counter electrodes (CEs) for bifacial dye-sensitized solar cells (DSCs). The 1-nm-thick Pt ultrathin films are sputtered on fluorine-doped tin oxide substrates and thermal annealed at 400 degrees C. After annealing, as-prepared amorphous-nanocrystal-mixed Pt films become high-crystalline films with better optical transmittance and electrocatalytic ability to I-3(-) reduction for bifacial DSCs. The rear-to-front ratios of short-circuit current density and power conversion efficiency of DSCs with crystalline ultrathin Pt CEs are as high as 81 and 83%, respectively. (C) 2017 The Japan Society of Applied Physics
Room-temperature fabrication of Cu nanobrushes as an effective surface-enhanced Raman scattering substrate
(2016)
Hsu, Yu-Kuei
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Chen, Zhong-Bo
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Lin, Yu-Chang
;
Chen, Ying-Chu
;
Chen, San-Yuan
A facile route to manufacture an active surface-enhanced Raman-scattering (SERS) substrate based on brush-like Cu nanostructures directly grown on a Cu foil at 23 degrees C was systematically investigated. A hierarchical Cu nanobrush substrate was fabricated in two cycles of electro-oxidation and chemical reduction in sequence; Cu(OH)(2) nanowires (NW) were formed on electro-oxidation, and converted on chemical reduction to Cu NW. Two cycles of this process achieved a brush-like Cu nanostructure; its structure, morphology and composition were examined by XRD, SEM, HRTEM and XPS, respectively. With 4-mercaptobenzoic acid (4-MBA) and chlorothalonil as probe molecules, the SERS experiments showed that the brush-like Cu nanostructures exhibit excellent detection performance, which could serve as effective SERS substrates for ultrasensitive detection. This novel hierarchical SERS substrate shows satisfactory reproducibility and a linear dependence between the analyte concentration and intensity, revealing the advantage of this method for easily scaled production.
Sandwich-Nanostructured n-Cu2O/AuAg/p-Cu2O Photocathode with Highly Positive Onset Potential for Improved Water Reduction
(2019-10-23)
Lin, Yu-Chang
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Hsu, Liang-Ching
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Lin, Chia-Yu
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Chiang, Chao-Lung
;
Chou, Che-Min
An n-Cu2O layer formed a high-quality buried junction with p-Cu2O to increase the photovoltage and thus to shift the turn-on voltage positively. Mott-Schottky measurements confirmed that the improvement benefited from a positive shift in flat-band potential. The obtained extremely positive onset potential, 0.8 V-RHE in n-Cu2O/AuAg/p-Cu2O, is comparable with measurements from water reduction catalysts. The AuAg alloy sandwiched between the homo-junction of n-Cu2O and p-Cu2O improved the photocatalytic performance. This alloy both served as an electron relay and promoted electron-hole pair generation in nearby semiconductors; the charge transfer between n-Cu2O and p-Cu2O in the sandwich structure was measured with X-ray absorption spectra. The proposed sandwich structure can be considered as a new direction for the design of efficient solar-related devices.
Structural and Electronic Optimization of MoS2 Edges for Hydrogen Evolution
(2019-11-20)
Wang, Hao
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Xiao, Xu
;
Liu, Shuyuan
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Chiang, Chao-Lung
;
Kuai, Xiaoxiao
The activity and accessibility of MoS2 edge sites are critical to deliver high hydrogen evolution reaction (HER) efficiency. Here, a porous carbon network confining ultrasmall N-doped MoS2 nanocrystals (N-MoS2/CN) is fabricated by a self-templating strategy, which realizes synergistically structural and electronic modulations of MoS2 edges. Experiments and density functional theory calculations demonstrate that the N dopants could activate MoS2 edges for HER, while the porous carbon network could deliver high accessibility of the active sites from N-MoS2 nanocrystals. Consequently, N-MoS2/CN possesses superior HER activity with an overpotential of 114 mV at 10 mA cm(-2) and excellent stability over 10 h, delivering one of best MoS2-based HER electrocatalysts. Moreover, this study opens a new venue for optimizing materials with enhanced accessible catalytic sites for energy-related applications.