Browsing by Author "Wu, Cheng-Yeou"

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A combined electrochemical route to fabricate large-area and free-standing inverse opaline film
(2016-07)
Liao, Chen-Hong
;
Hung, Pei-Sung
;
Wu, Cheng-Yeou
;
Chen, Hsin-Yi
;
Wu, Pu-Wei
A combined electrochemical route involving electrophoresis and electrodeposition is developed to fabricate a large-area unsupported nickel inverse opaline film with thickness less than 10 pm. A vertical electrophoresis allows for the packing of 495 nm polystyrene microspheres on an ITO-coated glass to form a colloidal crystal with significantly reduced defects. Subsequently, a nickel electrodeposition is employed to fill the interstitial voids among the close-packed polystyrene microspheres, followed by the removal of the colloidal template in a two-stage process, leaving a robust nickel skeleton with hexagonally arranged pores and interconnected pore channels. This nickel skeleton is then detached from the ITO-coated glass via a liquid nitrogen treatment, rendering a free-standing nickel inverse opaline film in 2 x 2 cm(2). Porometer measurements indicate a narrow pore size distribution consistent with images from scanning electron microscope. We determine that the intensity ratio of (111)/(100) diffraction peak is an indicator for the strength of the Ni inverse opals, and thus affects its structural integrity upon detachment from the ITO-coated glass. (C) 2016 Elsevier B.V. All rights reserved.
Evaluation on carbon nanocapsules for supercapacitors using a titanium cavity electrode
(2010-08-01)
Wu, Cheng-Yeou
;
Wu, Pu-Wei
;
Lin, Pang
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We synthesize carbon nanocapsules (CNCs) by a flame combustion method and evaluate their potential as the electrode material for electrochemical double layer capacitor using a titanium cavity electrode (TCE). Identical process is conducted on commercially available carbonaceous materials such as Vulcan XC72R, Black Pearl 2000 (BP2000), multi-walled carbon nanotubes (MWCNTs), and active carbon (AC1100) for comparison purposes. Images from Scanning electron microscope and Transmission electron microscope on the CNCs demonstrate irregular-shaped particles in average size of 10-20 nm with graphene layers on perimeter compassing a hollow core. Electrochemical characterizations including cyclic voltammetry (CV), current reversal chronopotentiometry (CRC), and impedance spectroscopy are carried out in 1N H(2)SO(4) to determine the specific capacitance and cycle life time. Among these samples, the BP2000 still delivers the highest specific capacitance in F g(-1) but the CNCs demonstrate the largest value in mu F cm(2). In addition, the CNCs exhibit impressive life time for 5000 cycles without notable degradation. Consistent results are obtained by CV, CRC, and impedance measurements, validating the TCE as a facile tool to perform reliable electrochemical evaluations. (C) 2010 Elsevier B.V. All rights reserved.
Mechanical alloying preparation of La0.6Ca0.4CoIr0.25O3.5-delta as a bifunctional electrocatalyst in alkaline electrolyte
(2008)
Chang, Yun-Min
;
Wu, Pu-Wei
;
Wu, Cheng-Yeou
;
Hsieh, Yi-Fan
;
Chen, Jing-Yu
La0.6Ca0.4CoIr0.25O3.5-delta was prepared by a mechanical alloying process from mixtures of La0.6Ca0.4CoO3 and IrO2. Scanning electron microscopy images on the resulting powders exhibited particles with irregular shape at 300-500 nm in size. X-ray diffraction analysis confirmed formation of a perovskite with complete disappearance of rutile signals from IrO2, indicating successful incorporation of Ir4+ at the Co3+ sites. Supported on carbon nanocapsules, the La0.6Ca0.4CoIr0.25O3.5-delta demonstrated superior performance over those of La0.6Ca0.4CoO3 in both charging and discharging current density-voltage polarizations. In addition, galvanostatic charging and discharging measurements at 25 and 100 mA/cm(2) indicated that the electrocatalytic abilities of La0.6Ca0.4CoIr0.25O3.5-delta are stable and sustainable.
Silver-carbon nanocapsule electrocatalyst for oxygen reduction reaction
(2007)
Wu, Cheng-Yeou
;
Wu, Pu-Wei
;
Lin, Pang
;
Li, Yuan-Yao
;
Lin, Ying-Mei
The types of carbonaceous material and electrocatalyst are the critical components in fabrication of gas diffusion electrodes for fuel cells and metal-air batteries. In this study, carbon nanocapsule (15-30 nm) and Ag-carbon nanocapsule powders were synthesized and characterized for their electrochemical performances as oxygen reduction electrocatalyst in alkaline electrolyte using commercial noncatalyzed gas diffusion electrode as substrate. The i-V polarization response of the carbon nanocapsule demonstrated enhanced electrocatalytic capability over those of XC-72R and vapor growth carbon fiber, delivering 0.80 V at 200 mA/cm(2). In addition, Ag-carbon nanocapsule powders exhibited a value of 0.99 V at 200 mA/cm(2), surpassing commercially available Mn-catalyzed, and MnCo-catalyzed gas diffusion electrodes. Galvanostatic discharge of these Ag-carbon nanocapsule powders from 10 to 200 mA/cm(2) confirmed their stability and sustainability. This report identified a class of carbon material that not only exhibits electrocatalytic capability itself but also provides opportunity as substrate for known electrocatalysts. (c) 2007 The Electrochemical Society.
Synthesis and Characterization of La(0.6)Ca(0.4)Co(0.8)Ru(0.2)O(3) for Oxygen Reduction Reaction in an Alkaline Electrolyte
(2010-01-01)
Chang, Yun-Min
;
Chang, Yin-Fang
;
Wu, Pu-Wei
;
Wu, Cheng-Yeou
;
Lin, Pang
We employed an amorphous citrate precursor (ACP) method to synthesize stoichiometric La(0.6)Ca(0.4)Co(0.8)Ru(0.2)O(3) powders. Result from X-ray diffraction demonstrated a perovskite La(0.6)Ca(0.4)CoO(3) lattice, indicating the incorporation of Ru(3+) at the Co(3+) sites. Image from the scanning electron microscope revealed a foamlike microstructure with various pores at 0.5-3 mu m. La(0.6)Ca(0.4)Co(0.8)Ru(0.2)O(3) exhibited a higher H(2)O(2) decomposition rate in KOH solution as opposed to that of ACP-derived La(0.6)Ca(0.4)CoO(3), which suggested an improved catalytic ability for oxygen reduction reaction (ORR). A similar behavior was observed during the ORR current-potential polarization using La(0.6)Ca(0.4)Co(0.8)Ru(0.2)O(3) supported on Black Pearl 2000 as a gas diffusion electrode. In addition, impedance spectra at the open-circuit voltage and selective cathodic overpotentials also confirmed a smaller charge-transfer resistance for La(0.6)Ca(0.4)Co(0.8)Ru(0.2)O(3). In galvanostatic measurements and lifetime evaluation, La(0.6)Ca(0.4)Co(0.8)Ru(0.2)O(3) demonstrated steady voltage profiles with negligible degradation. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3384665] All rights reserved.
Synthesis and Characterization of La0.6Ca0.4Co0.8Ru0.2O3 for Oxygen Reduction Reaction in an Alkaline Electrolyte
(2010-01-01)
Chang, Yun-Min
;
Chang, Yin-Fang
;
Wu, Pu-Wei
;
Wu, Cheng-Yeou
;
Lin, Pang
We employed an amorphous citrate precursor (ACP) method to synthesize stoichiometric La0.6Ca0.4Co0.8Ru0.2O3 powders. Result from X-ray diffraction demonstrated a perovskite La0.6Ca0.4CoO3 lattice, indicating the incorporation of Ru3+ at the Co3+ sites. Image from the scanning electron microscope revealed a foamlike microstructure with various pores at 0.5-3 mu m. La0.6Ca0.4Co0.8Ru0.2O3 exhibited a higher H2O2 decomposition rate in KOH solution as opposed to that of ACP-derived La0.6Ca0.4CoO3, which suggested an improved catalytic ability for oxygen reduction reaction (ORR). A similar behavior was observed during the ORR current-potential polarization using La0.6Ca0.4Co0.8Ru0.2O3 supported on Black Pearl 2000 as a gas diffusion electrode. In addition, impedance spectra at the open-circuit voltage and selective cathodic overpotentials also confirmed a smaller charge-transfer resistance for La0.6Ca0.4Co0.8Ru0.2O3. In galvanostatic measurements and lifetime evaluation, La0.6Ca0.4Co0.8Ru0.2O3 demonstrated steady voltage profiles with negligible degradation. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3384665] All rights reserved.
Synthesis of La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3) perovskite for bi-functional catalysis in an alkaline electrolyte
(2009-04-15)
Chang, Yun-Min
;
Wu, Pu-Wei
;
Wu, Cheng-Yeou
;
Hsieh, Yu-Chi
;
材料科學與工程學系
The amorphous citrate precursor method was employed to prepare perovskite of La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3) as a bi-functional electrocatalyst for oxygen reduction and evolution in an alkaline electrolyte. The X-ray diffraction pattern of the as-synthesized powders exhibited a majority phase identical to that of La(0.6)Ca(0.4)CoO(3), indicating successful incorporation of Ir4(+) at the Co cation sites. Scanning Electron Microscope images demonstrated a foam-like microstructure with a surface area of 13.31 m(2) g(-1). For electrochemical characterization, the La(0.6)Ca(0.4)CO(0.8)Ir(0.2)O(3) particles were supported on carbon nanocapsules (CNCs) and deposited on commercially available gas diffusion electrodes with a loading of 2.4 mg cm(-2). In current- potential polarizations, La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3)/CNCs revealed more enhanced bifunctional catalytic abilities than La(0.6)Ca(0.4)CoO(3)/CNCs. Similar behaviors were observed in galvanostatic profiles for oxygen reduction and evolution at current densities of 50 and 100mAcm(-2) for 10 min. Moreover, notable changes from zeta potential measurements were recorded for La(0.6)Ca(0.4)Co(0.08)Ir(0.02)O(3) relative to La(0.06)Ca(0.4)CoO(3), In lifetime determinations, where a repeated 3 h sequence of oxygen reduction/resting/oxygen evolution/resting was imposed, La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3)/CNCs delivered a stable and sustainable behavior with moderate degradation. (C) 2008 Elsevier B.V. All rights reserved.
Synthesis of La0.6Ca0.4Co0.8Ir0.2O3 perovskite for bi-functional catalysis in an alkaline electrolyte
(2009-04-15)
Chang, Yun-Min
;
Wu, Pu-Wei
;
Wu, Cheng-Yeou
;
Hsieh, Yu-Chi
;
材料科學與工程學系
The amorphous citrate precursor method was employed to prepare perovskite of La0.6Ca0.4Co0.8Ir0.2O3 as a bi-functional electrocatalyst for oxygen reduction and evolution in an alkaline electrolyte. The X-ray diffraction pattern of the as-synthesized powders exhibited a majority phase identical to that of La0.6Ca0.4CoO3, indicating successful incorporation of Ir4(+) at the Co cation sites. Scanning Electron Microscope images demonstrated a foam-like microstructure with a surface area of 13.31 m(2) g(-1). For electrochemical characterization, the La0.6Ca0.4CO0.8Ir0.2O3 particles were supported on carbon nanocapsules (CNCs) and deposited on commercially available gas diffusion electrodes with a loading of 2.4 mg cm(-2). In current- potential polarizations, La0.6Ca0.4Co0.8Ir0.2O3/CNCs revealed more enhanced bifunctional catalytic abilities than La0.6Ca0.4CoO3/CNCs. Similar behaviors were observed in galvanostatic profiles for oxygen reduction and evolution at current densities of 50 and 100mAcm(-2) for 10 min. Moreover, notable changes from zeta potential measurements were recorded for La0.6Ca0.4Co0.08Ir0.02O3 relative to La0.06Ca0.4CoO3, In lifetime determinations, where a repeated 3 h sequence of oxygen reduction/resting/oxygen evolution/resting was imposed, La0.6Ca0.4Co0.8Ir0.2O3/CNCs delivered a stable and sustainable behavior with moderate degradation. (C) 2008 Elsevier B.V. All rights reserved.
Synthesis of large surface area carbon xerogels for electrochemical double layer capacitors
(2013-02-01)
Chang, Yun-Min
;
Wu, Cheng-Yeou
;
Wu, Pu-Wei
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A resorcinol formaldehyde (R-F) condensation reaction catalyzed by acetic acid (C) is employed to prepare carbon xerogels for electrochemical double layer capacitors. The samples are fabricated with an R:F ratio of 1:2 and R:C ratio of 10:1, followed by solvent exchange, pyrolysis, and carbon dioxide activation. The solvent exchange allows negligible structure contraction upon drying, and after pyrolysis and carbon dioxide treatment, we are able to produce porous carbons with a surface area of 3419 m(2) g(-1). Image from scanning electron microscope reveals an interconnected foam-like structure and BET confirms the presence of excessive micro- and mesopores. Electrochemical analysis including cyclic voltammetry (CV), current reversal chronopotentiometry (CRC), and impedance spectroscopy are conducted using a titanium cavity electrode so relevant capacitive characteristics and kinetic parameters could be determined. Both CV and CRC results indicate specific capacitances and life time behaviors that are comparable or even better than those of Black Pearl 2000. For example, the specific capacitance is 324.8 F g(-1) in 0.5 M H2SO4 aqueous solution at +/- 1 A g(-1) for potential window of 0-1 V. In contrast, sample without carbon dioxide activation displays a similar morphology but its surface area and specific capacitance are reduced considerably to 449 m(2) g(-1) and 34.7 F g(-1), respectively. (C) 2012 Elsevier B.V. All rights reserved.
Templated fabrication of nanostructured Ni brush for hydrogen evolution reaction
(2010-10-01)
Lin, Sheng-Chieh
;
Chiu, Yu-Fan
;
Wu, Pu-Wei
;
Hsieh, Yi-Fan
;
Wu, Cheng-Yeou
We fabricated a nanostructured brush by carrying out Ni deposition on a through-channel anodic aluminum oxide (AAO) template, followed by removal of the AAO skeleton. The AAO was prepared by a two-step anodization process resulting in pore diameter and thickness of 350 nm and 40 mu m, respectively. Subsequently, the AAO underwent an electroless deposition involving sensitization, activation, and Ni plating, in conjunction with polyethylene glycol used as the inhibitor to prevent premature closing of pore opening. After deliberate control in relevant parameters, we obtained a conformal Ni overcoat along every pore channel leading to a reduced average pore diameter of 78 nm. Afterward, the sample was immersed in a KOH solution to remove the AAO structure, forming freestanding Ni tubules in a brush configuration. The nanostructured brush revealed considerable enhancement for hydrogen evolution reaction in both current-potential polarization and galvanostatic measurements, which were attributed to the increment in apparent surface area.
Templated fabrication of nanostructured Ni brush for hydrogen evolution reaction
(2010-10-01)
Lin, Sheng-Chieh
;
Chiu, Yu-Fan
;
Wu, Pu-Wei
;
Hsieh, Yi-Fan
;
Wu, Cheng-Yeou
We fabricated a nanostructured brush by carrying out Ni deposition on a through-channel anodic aluminum oxide (AAO) template, followed by removal of the AAO skeleton. The AAO was prepared by a two-step anodization process resulting in pore diameter and thickness of 350 nm and 40 mu m, respectively. Subsequently, the AAO underwent an electroless deposition involving sensitization, activation, and Ni plating, in conjunction with polyethylene glycol used as the inhibitor to prevent premature closing of pore opening. After deliberate control in relevant parameters, we obtained a conformal Ni overcoat along every pore channel leading to a reduced average pore diameter of 78 nm. Afterward, the sample was immersed in a KOH solution to remove the AAO structure, forming freestanding Ni tubules in a brush configuration. The nanostructured brush revealed considerable enhancement for hydrogen evolution reaction in both current-potential polarization and galvanostatic measurements, which were attributed to the increment in apparent surface area.