Browsing by Author "Hsieh, Yi-Fan"

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A facile route to prepare PdPt alloys for ethanol electro-oxidation in alkaline electrolyte
(2011-01-31)
Lin, Sheng-Chieh
;
Chen, Jing-Yu
;
Hsieh, Yi-Fan
;
Wu, Pu-Wei
;
材料科學與工程學系
We adopted a displacement reaction in acidic solution that enabled the spontaneous reduction of Pd and Pt cations in conjunction with corrosive dissolution of Ni. The composition for the PdPt was adjusted by varying the concentration of Pd and Pt cations. From SEM images and XRD patterns, the PdPt formed an fcc alloy uniformly deposited on the Ni substrate. Electro-oxidation of ethanol was conducted in alkaline electrolyte for samples of Pd, Pt, and PdPt alloys. In cyclic voltammetric profiles, the Pd(77)Pt(23) revealed the highest electrocatalytic ability in both apparent current and mass activity, followed by Pd(87)Pt(13), Pd, and Pt. Similar behaviors were observed in life time measurements in which stable performances for ethanol electro-oxidation were obtained. (C) 2010 Elsevier B.V. All rights reserved.
Effect of anodic dissolution in multi-element nanoparticles on methanol electro-oxidation
(2009-11-03)
Hsieh, Yi-Fan
;
Yeh, Kung-Yu
;
Wu, Pu-Wei
;
Hsieh, Yu-Chi
;
Lin, Pang
Radio frequency sputter deposition was used to deposit multi-element nanoparticles on carbon clothes for methanol electro-oxidation. Results from energy dispersive spectroscope confirmed the composition was Ft(35)Fe(12)Co(12)Ni(20)Cu(12)Ag(9). X-ray diffraction pattern suggested a fcc phase. An electrochemical de-alloying treatment was conducted in an acidic electrolyte with multiple potential sweeps at a scan rate of 20 mV/s for 0-0.3,0-0.5, and 0-0.7 V, respectively. Images from scanning electron microscope after anodic dissolutions demonstrated considerable variations in surface morphologies. Measurements on hydrogen desorption also revealed substantial increase in electrochemical active surface area. Current responses from cyclic voltammetry indicated the sample of 0-0.5 V anodic dissolution with notable enhancement. In mass activities, the same sample exhibited a comparable value to that Of Pt(43)Ru(57) (C) 2009 Elsevier B.V. All rights reserved.
Effect of platinum present in multi-element nanoparticles on methanol oxidation
(2009-06-10)
Tsai, Chih-Fang
;
Yeh, Kung-Yu
;
Wu, Pu-Wei
;
Hsieh, Yi-Fan
;
Lin, Pang
Nanoparticles of Pt(x)Fe((100-x)/5)Co((100-x)/5)Ni((100-x)/5)Cu((100-x)/5)Ag((100-x)/5) (x = 22, 29, 52, 56) were prepared by the sputter depositions on pretreated carbon clothes with their electrocatalytic abilities for the methanol oxidation investigated. XRD analysis of the deposited nanoparticles indicated crystalline fcc phases and SEM images revealed apparent growths of nanoparticulate nodules. Their average sizes were found to increase with the deposition time. Cyclic voltammetry of the deposited samples demonstrated enhancements in the current responses with increasing Pt amount and deposition time. In mass activity, the Pt(52)Fe(11)Co(10)Ni(11)Cu(10)Ag(8) exhibited the highest values of 462-504 mA/mg. Identical process was conducted to fabricate electrodes with sputtered Pt and Pt(43)Ru(57). In comparison, the Pt(52)Fe(11) Co(10)Ni(11)Cu(10)Ag(8) showed moderate improvements over that of Pt but was still outperformed by the Pt(43)Ru(57). (C) 2008 Elsevier B.V. All rights reserved.
Gravity-Assisted Seeding Control for 1-D Material Growth
(2009-07-01)
Chen, C. C.
;
Hsu, Lun-Hao
;
Rern, Kai
;
Cheng, Y. T.
;
Hsieh, Yi-Fan
This letter presents a seeding control scheme by utilizing gravity force to form an agglomeration of molten Co seeds on a patterned inverted silicon nanopyramid. Nanometer sized molten Co seeds formed on a nonwettable inverted pyramid surface can roll along the inclination followed by aggregation to form a singular seed with the size depending on the pyramid size and the thickness of as-deposited Co film inside the pyramid. The proposed scheme allowing the formation of well-aligned catalytic seeds with manipulated size will promise the control growth of 1-D material for practical integrated microelectronic device fabrication.
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.
Pulse Electrodepositions of PtRu on Large-Area Carbon Nanotubes for Enhancement of Methanol Electro-Oxidation
(2010)
Hsieh, Yi-Fan
;
Hsieh, Yu-Chi
;
Wu, Pu-Wei
;
Liao, Chen-Hong
;
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.
Structural characterizations of Cu3Pt electrocatalyst featuring Pt-rich surface layers synthesized via mechanical alloying and selective dissolution routes
(2013-03-05)
Hsieh, Yi-Fan
;
Hsieh, Yu-Chi
;
Tseng, Yuan-Chieh
;
Wu, Pu-Wei
;
Chao, Cheun Guang
We demonstrate a selective electrochemical dissolution route to prepare Cu3Pt catalysts featuring Pt-rich surface layers (Cu3Pt-Pt rich surface) from mechanically alloyed Cu3Pt. These catalysts were investigated by X-ray diffraction and X-ray absorption spectroscopy, and were subjected to electrochemical analyses to evaluate their catalytic properties. With appropriate anodization, Cu3Pt entered an oxygen-evolving regime where the corrosive dissolution of Cu dominated the reaction. Selective dissolution was carried out to prepare Pt-rich layers at the surface, while Cu3Pt was left unreacted at the core. An increase in the anodization duration modified the sample morphology, with the redistribution of Pt atoms to thicken the surface layers. A charge transfer from Pt to Cu accompanied the structural transition from Cu3Pt to Cu3Pt-Pt rich surface upon selective dissolution, rendering the sample to be electronically similar to a metal Pt. However, compared to the metal Pt and conventional Pt-based catalysts, the proposed structure is a more economical catalyst for direct methanol fuel cell, with less need of Pt in raw material but increased electrochemical surface area by exposing enormous Pt at the surface with an increase in the anodization duration. (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.