Browsing by Author "Liu, Shang-Bin"

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Effect of Temperature Gradient Direction in the Catalyst Nanoparticle on CNTs Growth Mode
(2010-09-01)
Lo, An-Ya
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Liu, Shang-Bin
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Kuo, Cheng-Tzu
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材料科學與工程學系
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Department of Materials Science and Engineering
To improve the understanding on CNT growth modes, the various processes, including thermal CVD, MP-CVD and ECR-CVD, have been used to deposit CNTs on nanoporous SBA-15 and Si wafer substrates with C(2)H(2) and H(2) as reaction gases. The experiments to vary process parameter of Delta T, defined as the vector quantities of temperature at catalyst top minus it at catalyst bottom, were carried out to demonstrate its effect on the CNT growth mode. The TEM and TGA analyses were used to characterize their growth modes and carbon yields of the processes. The results show that Delta T can be used to monitor the temperature gradient direction across the catalyst nanoparticle during the growth stage of CNTs. The results also indicate that the tip-growth CNTs, base-growth CNTs and onion-like carbon are generally fabricated under conditions of Delta T > 0, < 0 and similar to 0, respectively. Our proposed growth mechanisms can be successfully adopted to explain why the base- and tip-growth CNTs are common in thermal CVD and plasma-enhanced CVD processes, respectively. Furthermore, our experiments have also successfully demonstrated the possibility to vary Delta T to obtain the desired growth mode of CNTs by thermal or plasma-enhanced CVD systems for different applications.
Fabrication of CNTs with controlled diameters and their applications as electrocatalyst supports for DMFC
(2011-03-01)
Lo, An-Ya
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Yu, Ningya
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Huang, Shing-Jong
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Hung, Chin-Te
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Liu, Shou-Heng
A facile synthesis procedure based on chemical vapor deposition (CVD) process has been developed to fabricate carbon nanotubes (CNTs) with controlled diameters and high yields utilizing Fe-containing ordered hexagonal mesoporous silicas (HMSs) such as MCM-41 and SBA-15 having varied pore sizes as the catalysts as well as the templates. It is found that unlike Fe/HMS catalysts prepared by co-precipitation method, samples prepared by the impregnation method gave rise to multi-wall CNTs with uniform diameters, which were largely dictated by the pore size of the Fe/HMS catalysts. Among these uniform MWCNTs, sample with a larger diameter (>= 8 nm) was found to be more favorable as support for Pt catalyst, leading to a homogeneous dispersion of metal nanoparticles. Consequently, the Pt/CNT electrocatalysts so prepared gave rise to superior methanol oxidation activities as well as tolerances for CO poisoning compared to Pt supported on commercial single-wall CNT (Pt/SWCNT) and XC-72 activated carbon (Pt/XC-72) having a similar metal loading. (c) 2011 Elsevier B.V. All rights reserved.
Hollowed carbon capsule based Pt-Fe/carbon electrodecatalysts prepared by chemical vapor infiltration method
(2008-07-01)
Lo, An-Ya
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Liu, Shou-Heng
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Huang, Shing-Jong
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Kuo, Cheng-Tzu
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Liu, Shang-Bin
A new type of hollowed carbon capsule (HCC) material has been fabricated and utilized as a support for Pt-Fe catalyst by means of chemical vapor infiltration (CVI) method. The supported Pt-Fe/HCC catalyst was found to possess cavities with sizes around 20-40 nm and well-dispersed Pt-Fe alloy particles embedded on the internal graphitic carbon walls and hence can be used as potential electrodecatalyst for fuel cells. Preliminary performance tests by cyclic voltammetry revealed that the supported Pt-Fe/HCC catalyst has electrochemical properties compatible to a common commercial catalyst. The formation mechanism of the HCC material is also proposed. (c) 2008 Elsevier B.V. All rights reserved.
Syntheses of carbon porous materials with varied pore sizes and their performances as catalyst supports during methanol oxidation reaction
(2012-12-01)
Lo, An-Ya
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Hung, Chin-Te
;
Yu, Ningya
;
Kuo, Cheng-Tzu
;
Liu, Shang-Bin
Carbon porous materials (CPMs) with extended ranges of pore size and morphology were replicated using various porous silicas, such as zeolites, mesoporous silicas, and photonic crystals, as templates by means of chemical vapor infiltration (CV!) method. The micro-, meso-, and macro-porous carbons so fabricated were adopted as supports for the metal (Pt) catalyst for direct methanol fuel cells (DMFCs), and the supported Pt/CPM electrocatalysts were characterized by a variety of different spectroscopic/analytical techniques, viz transmission electron microscopy (TEM), Raman, X-ray photoelectron spectroscopy (XPS), gas physisorption/chemisorption analyses, and cyclic voltammetry (CV). That these Pt/CPMs were found to exhibit superior electrocatalytic activities compared to the commercial Pt/XC-72 with a comparable Pt loading during methanol oxidation reaction (MOR) is attributed to the presence of Pt nanoparticles (NPs; typically 1-3 nm in size) that are highly dispersed in the CPMs, facilitating an improved tolerance for CO poisoning. While the MOR activity observed for various Pt/CPMs tend to increase with increasing pore size of the carbon supports, Pt catalyst supported on carbon substrates possessing microporosities was found to have superior stability in terms of tolerance for CO poisoning than those with greater pore size or having meso- and macroporosities. (C) 2012 Elsevier Ltd. All rights reserved.
Syntheses of carbon porous materials with varied pore sizes and their performances as catalyst supports during methanol oxidation reaction
(2012-12-01)
Lo, An-Ya
;
Hung, Chin-Te
;
Yu, Ningya
;
Kuo, Cheng-Tzu
;
Liu, Shang-Bin
Carbon porous materials (CPMs) with extended ranges of pore size and morphology were replicated using various porous silicas, such as zeolites, mesoporous silicas, and photonic crystals, as templates by means of chemical vapor infiltration (CV!) method. The micro-, meso-, and macro-porous carbons so fabricated were adopted as supports for the metal (Pt) catalyst for direct methanol fuel cells (DMFCs), and the supported Pt/CPM electrocatalysts were characterized by a variety of different spectroscopic/analytical techniques, viz transmission electron microscopy (TEM), Raman, X-ray photoelectron spectroscopy (XPS), gas physisorption/chemisorption analyses, and cyclic voltammetry (CV). That these Pt/CPMs were found to exhibit superior electrocatalytic activities compared to the commercial Pt/XC-72 with a comparable Pt loading during methanol oxidation reaction (MOR) is attributed to the presence of Pt nanoparticles (NPs; typically 1-3 nm in size) that are highly dispersed in the CPMs, facilitating an improved tolerance for CO poisoning. While the MOR activity observed for various Pt/CPMs tend to increase with increasing pore size of the carbon supports, Pt catalyst supported on carbon substrates possessing microporosities was found to have superior stability in terms of tolerance for CO poisoning than those with greater pore size or having meso- and macroporosities. (C) 2012 Elsevier Ltd. All rights reserved.
Synthesis of uniform carbon nanotubes by chemical vapor infiltration method using SBA-15 mesoporous silica as template
(2007)
Lo, An-Ya
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Liu, Shou-Heng
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Huang, Shing-Jong
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Shen, Huang-Kai
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Kuo, Cheng-Tzu