Browsing by Author "Chang, Yun-Min"

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A Promising Approach to the Synthesis of 3D Nanoporous Graphitic Carbon as a Unique Electrocatalyst Support for Methanol Oxidation
(2010)
Tiwari, Jitendra N.
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Tiwari, Rajanish N.
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Chang, Yun-Min
;
Lin, Kun-Lin
;
材料科學與工程學系
A 3D nanoporous graphitic carbon (g-C) material is synthesized by using an adamantane (C(10)H(16)) flame, and utilized to support a Pt(50)-Ru(50) alloy catalyst. The physico-chemical properties of the Pt(50)-Ru(50)/3D nanoporous g-C electrode are examined by a range of spectroscopy techniques as well as Brunauer-Emmett-Teller surface area analysis. Cyclic voltammetry measurements are used for electrochemical characterization of the Pt(50)-Ru(50)/3D nanoporous g-C electrode. The electrochemical investigations show that the supported Pt(50)-Ru(50) has excellent activity and stability towards methanol electro-oxidation. Good CO tolerance is also shown, and considered to be due to the presence of Ru nanoparticles. It is proposed that Ru is able to promote the oxidation of strongly adsorbed CO on Pt by supplying an oxygen source: RU(OH)(ad). Moreover, the presence of 3D nanopores in the g-C support may also contribute to the observed higher current density by virtue of the easy transport of methanol and the oxidation products through these nanopores.
Displacement Reaction in Pulse Current Deposition of PtRu for Methanol Electro-Oxidation
(2009)
Hsieh, Yu-Chi
;
Wu, Pu-Wei
;
Lu, Yung-Jean
;
Chang, Yun-Min
;
材料科學與工程學系
Galvanostatic depositions in rectangular pulses and nitrosol precursors were employed to prepare PtRu nanoparticles on carbon clothes in various sizes and compositions. Variables including current on-time (T(on)), current off-time (T(off)), and current density were explored to identify the optimized catalytic performances for methanol electro-oxidation. Electrochemical characterizations including cyclic voltammetry and hydrogen desorption were carried out. Images from a transmission electron microscope on the PtRu nanoparticles revealed a moderate size distribution. Signals from X-ray patterns indicated a slight shift of diffraction peaks, suggesting that the Ru was alloyed successfully in the Pt lattice. In addition, the amount of alloyed Ru was found to decrease with reduced duty cycles. Composition determinations from inductively coupled plasma mass spectrometry and analysis on the oxidation states from X-ray photoelectron spectroscopy suggested a displacement reaction in which the Ru was alternately deposited and dissolved during T(on) and T(off), while the Pt was deposited continuously. As a result, we observed substantial enrichment of Pt in the PtRu nanoparticles when the duty cycle was shortened.
Displacement reaction of Pt on carbon-supported Ru nanoparticles in hexachloroplatinic acids
(2011-03-14)
Hsieh, Yu-Chi
;
Chang, Li-Chung
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Wu, Pu-Wei
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Chang, Yun-Min
;
Lee, Jyh-Fu
The displacement reaction of Pt on Ru to form a Ru core and Pt shell (Ru@Pt) bimetallic structure is investigated by immersing the carbon-supported Ru nanoparticles in hexachloroplatinic acids with pH of 1,2.2. and 8, followed by a hydrogen reduction treatment. Results from inductively coupled plasma mass spectrometry suggest that the dissolution of Ru is mostly caused by the reduction of Pt cations. Images from transmission electron microscopy demonstrate a uniform distribution of Ru@Pt in size of 3-5 nm. Spectra from X-ray absorption near edge structure and extended X-ray absorption fine structure confirm that the pH value of hexachloroplatinic acid determines the type of ligands complexing the Pt cations that affects their activity and consequently the severity of displacement reaction and alloying degree of Ru@Pt nanoparticles. As a result, the samples from pH 1 bath reveal a desirable core-shell structure that displays a reduced onset potential in CO stripping and stable catalytic performance for H(2) oxidation while the samples from pH 8 bath indicate the formation of Pt clusters on the Ru surface that leads to poor CO stripping and H(2) oxidation characteristics. (C) 2011 Elsevier B.V. All rights reserved.
Effect of annealing on the electrodeposited Cu(2)O films for photoelectrochemical hydrogen generation
(2010-10-01)
Liang, Ru-Meng
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Chang, Yun-Min
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Wu, Pu-Wei
;
Lin, Pang
;
材料科學與工程學系
Cu(2)O films were electrodeposited on stainless steel substrates followed by Ar annealing for photoelectrochemical hydrogen generation. Plating variables including time and pH for the plating bath were explored to obtain desirable film qualities. X-ray diffraction (XRD) patterns indicated that the as-deposited Cu(2)O films exhibited preferred orientations in (200) and (111) planes from the plating bath of pH 9 and pH 11, respectively. Images from scanning electron microscope (SEM) revealed pyramid-like grains in 1 mu m size for the Cu(2)O films from pH 9 plating bath and large plate-like grains in 3-8 mu m size from pH 11 plating bath. Identical results from SEM and XRD were obtained from the Cu(2)O films at longer plating time. After annealing at 350 degrees C for 30 and 60 min, the Cu(2)O phase was nicely maintained but SEM images demonstrated coarser grains. Photoelectrochemical activity for H(2) generation was obtained on the Cu(2)O films before and after annealing by recording relevant photoelectrochemical currents at -0.3 V in 0.5 M aqueous Na(2)SO(4) solution. For the Cu(2)O films from both baths, substantial increments in photoelectrochemical current were observed for the annealed samples as opposed to as-deposited ones. The largest photoelectrochemical current was obtained at 0.143 mA/cm(2) from the Cu(2)O film of pH 9 plating bath with 60 min annealing, which exhibited a 560% increase over the as-deposited sample. We attributed the enhanced photoelectrochemical current to the improved crystallinity and reduced defects for the annealed Cu(2)O films. (C) 2010 Elsevier B.V. All rights reserved.
Effect of annealing on the electrodeposited Cu2O films for photoelectrochemical hydrogen generation
(2010-10-01)
Liang, Ru-Meng
;
Chang, Yun-Min
;
Wu, Pu-Wei
;
Lin, Pang
;
交大名義發表
Cu2O films were electrodeposited on stainless steel substrates followed by Ar annealing for photoelectrochemical hydrogen generation. Plating variables including time and pH for the plating bath were explored to obtain desirable film qualities. X-ray diffraction (XRD) patterns indicated that the as-deposited Cu2O films exhibited preferred orientations in (200) and (111) planes from the plating bath of pH 9 and pH 11, respectively. Images from scanning electron microscope (SEM) revealed pyramid-like grains in 1 mu m size for the Cu2O films from pH 9 plating bath and large plate-like grains in 3-8 mu m size from pH 11 plating bath. Identical results from SEM and XRD were obtained from the Cu2O films at longer plating time. After annealing at 350 degrees C for 30 and 60 min, the Cu2O phase was nicely maintained but SEM images demonstrated coarser grains. Photoelectrochemical activity for H-2 generation was obtained on the Cu2O films before and after annealing by recording relevant photoelectrochemical currents at -0.3 V in 0.5 M aqueous Na2SO4 solution. For the Cu2O films from both baths, substantial increments in photoelectrochemical current were observed for the annealed samples as opposed to as-deposited ones. The largest photoelectrochemical current was obtained at 0.143 mA/cm(2) from the Cu2O film of pH 9 plating bath with 60 min annealing, which exhibited a 560% increase over the as-deposited sample. We attributed the enhanced photoelectrochemical current to the improved crystallinity and reduced defects for the annealed Cu2O films. (C) 2010 Elsevier B.V. All rights reserved.
Enhancement of bifunctional catalysis by Ir doping of La0.6Ca0.4CoO3 perovskites
(2008-10-15)
Chang, Yun-Min
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Hsieh, Yu-Chi
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Wu, Pu-Wei
;
Lai, Chun-Han
;
Chang, Tin-Yu
La0.6Ca0.4Co0.8Ir0.2O3 was prepared by solid state reaction synthesis from mixtures of La(NO3)(3)center dot 6H(2)O, Ca (NO3)(2)center dot 4H(2)O, Co(NO3)(3)center dot 6H(2)O, and IrO2 at stoichiometric ratio. Images from scanning electron microscopy on the as-synthesized powders exhibited particles in irregular shape at 100-250 nm in size. X-ray diffraction analysis confirmed the formation of perovskite without the rutile signals from IrO2, suggesting successful incorporation of Ir4+ at the Co cation sites. The carbon nanocapsules (CNCs) were used as an electrocatalyst support. Electrodes for electrochemical measurements were fabricated by depositing mixtures of CNCs, La0.6Ca0.4Co0.8Ir0.2O3 and polymeric binders on commercially available noncatalyzed gas diffusion electrodes. In alkaline electrolyte, the La0.6Ca0.4Co0.8Ir0.2O3/CNCs demonstrated superior performances than those of La0.6Ca0.4Co0.8Ir0.2O3/CNCs and IrO2/CNCs in both charging and discharging current-potential polarization measurements. (c) 2008 Elsevier B.V. All rights reserved.
Fabrication of Ni nanowires for hydrogen evolution reaction in a neutral electrolyte
(2009-08-01)
Chen, Po-Chun
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Chang, Yun-Min
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Wu, Pu-Wei
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Chiu, Yu-Fan
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材料科學與工程學系
Hydrogen evolution reaction in 1 M Na(2)SO(4) was investigated using Ni nanowires in diameter of 250 nm with exposed lengths of 20, 35, and 45 mu m, respectively. The Ni nanowires were fabricated by a direct-current pulse electrodeposition technique using an anodic aluminum oxide template, followed by selective removal of the supporting pore walls. Scanning Electron Microscope images revealed structural stabilities and X-ray diffraction pattern indicated a polycrystalline fcc phase. In current-potential (i-V) polarizations, the Ni nanowires with longer exposed lengths demonstrated larger current responses. Analysis from impedance spectroscopy confirmed increasing double-layer capacitances with longer Ni nanowires. in galvanostatic lifetime experiments, the freestanding Ni nanowires exhibited a reduced overpotential over that of supported ones. Similar procedures were performed for the oxygen evolution reaction in both i-V and lifetime measurements. For the Ni nanowires of 45 pm length, we estimated the energy cost for hydrogen production was 5.24 x 10(5) J/mole. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Galvanostatic Pulse Plating of PtRu Nanoparticles for Direct Methanol Fuel Cells
(2008)
Hsieh, Yu-Chi
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Lu, Yung-Jean
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Wu, Pu-Wei
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Chang, Yun-Min
;
Chiu, Yu-Fan
A galvanostatic pulse electrodeposition technique of preparing nanoparticulate PtRu electrocatalyst for direct methanol fuel cells has been demonstrated. After extensive cyclic voltammetric analysis, we determined the optimized parameters for the methanol oxidation to be current on-time on 50 ms, current off-time of 400 ms, current density of 50 mA/cM, and total charge of 9.0 C/cm(2) In addition, the catalyst loading was measured at 68 mu g/cm(2) resulting in a mass activity of 213 mA/Pt. mg. The composition for the nanoparticles was confirmed as Pt(65)RU(35). High-magnification images on the specimen indicated fine particles in 4-20 nm with uniform distributions.
High-yield water-based synthesis of truncated silver nanocubes
(2014-02-15)
Chang, Yun-Min
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Lu, I-Te
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Chen, Chih-Yuan
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Hsieh, Yu-Chi
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Wu, Pu-Wei
A high-yield water-based hydrothermal synthesis was developed using silver nitrate, ammonia, glucose, and cetyltrimethylammonium bromide (CTAB) as precursors to synthesize truncated silver nanocubes with uniform sizes and in large quantities. With a fixed CTAB concentration, truncated silver nanocubes with sizes of 49.3 +/- 4.1 nm were produced when the molar ratio of glucose/silver cation was maintained at 0.1. The sample exhibited (100), (110), and (111) planes on the facets, edges, and corners, respectively. In contrast, with a slightly larger glucose/silver cation ratio of 0.35, well-defined nanocubes with sizes of 70.9 +/- 3.8 nm sizes were observed with the (100) plane on six facets. When the ratio was further increased to 1.5, excess reduction of silver cations facilitated the simultaneous formation of nanoparticles with cubic, spherical, and irregular shapes. Consistent results were obtained from transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and UV-visible absorption measurements. (C) 2013 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
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Wu, Pu-Wei
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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.
Pulse Electrodepositions of PtRu on Large-Area Carbon Nanotubes for Enhancement of Methanol Electro-Oxidation
(2010)
Hsieh, Yi-Fan
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Hsieh, Yu-Chi
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Wu, Pu-Wei
;
Liao, Chen-Hong
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Chang, Yun-Min
We employed an electroless deposition technique to prepare Ni seeds uniformly on a carbon cloth, followed by carbon nanotube (CNT) formation at an elevated temperature. Subsequently, a pulse electrodeposition was used to impregnate PtRu nanoparticles on the CNT structure. Similar procedures were performed on carbon supports including Vulcan XC72R, BP2000, and carbon nanocapsules (CNCs) for comparison purposes. Diffraction patterns from an X-ray confirmed a PtRu alloyed phase. An analysis from inductively coupled plasma-mass spectrometry indicated that the PtRu composition was relatively unchanged. Images from scanning and transmission electron microscopes revealed dense CNTs throughout the carbon cloth with nanoparticulate PtRu evenly impregnated. Considerable PtRu aggregations were found on the CNCs and BP2000. We observed a significantly improved coulomb efficiency and an electrochemically active surface area for the CNT-grown carbon cloth. In both apparent current density and mass activity for methanol electro-oxidation, the CNT-grown carbon cloth revealed the largest values. We attribute the performance enhancement to the large-area CNT structure that allowed facile access of electrolytes. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3246002] All rights reserved.
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
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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 for catelysis of bifunctional perovskite compound
(2010-06-10)
Wu, Pu-Wei
;
Chang, Yun-Min
This invention discloses the synthesis of a bifunctional La0.6Ca0.4Co1-xIrxO3 (x=0˜1) perovskite compound with a superb bifunctional catalytic ability for the oxygen reduction and generation in alkaline electrolytes. Synthetic routes demonstrated include solid state reaction, amorphous citrate precursor, and mechanical alloying. The interested compound demonstrates notable enhancements over commercially available La0.6Ca0.4CoO3.
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
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Wu, Pu-Wei
;
Wu, Cheng-Yeou
;
Hsieh, Yu-Chi
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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
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Wu, Cheng-Yeou
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Wu, Pu-Wei
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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.