Browsing by Author "Lo, An-Ya"

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A High Efficiency Surface Modification Process for Multiwalled Carbon Nanotubes by Electron Cyclotron Resonance Plasma
(2008-11-27)
Tseng, Wen-Shou
;
Tseng, Chyuan-Yow
;
Chuang, Pi-Kai
;
Lo, An-Ya
;
Kuo, Cheng-Tzu
A novel process of surface modification for multiwalled carbon nanotubes (MWCNTs) by using electron cyclotron resonance plasma is proposed. The process uses a H(2)/O(2) gas mixture as etching gas and applies a bias voltage of -250 DCV to the process stage to extract and accelerate hydrogen and oxygen cations. The generated high density and high incident energy cations are employed to create defects on the surface of nanotubes through ion bombardment. The oxygen cations with high reduction potential are simultaneously applied, oxidizing the surface of the nanotubes so as to form functional groups on the side walls most effectively. Additionally, being far from the plasma sheath, the MWCNTs can be maintained at a lower temperature to prevent from being decomposed under the high energy plasma. The efficiency of this method was systematically analyzed using X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The experimental results have shown that the proposed method is a highly effective way to functionalize MWCNTs, resulting in the nanotubes with high concentration of oxygen-containing functional groups and minimal structural damage within very short process time.
An in situ fabrication process for highly electrical conductive polyimide/MWCNT composite films using 2,6-diaminoanthraquinone
(2013-10-18)
Huang, Yi-Chia
;
Lin, June-Hua
;
Tseng, I-Hsiang
;
Lo, An-Ya
;
Lo, Teng-Yuan
We present a valuable in situ fabrication process for synthesizing high electrical conductive polyimide/multiwalled carbon nanotube (PI/MWCNT) composite films. The success of this process was achieved the addition of 2,6-diaminoanthraquinone (DAAQ). The DAAQ is not only an excellent dispersion agent to stably disperse pristine MWCNTs in solvent but also a monomer to directly synthesize PI. The strong interaction between DAAQ with MWCNT was verified by FTIR, UV-Vis, Raman, and fluorescence spectra. The highest value of electrical conductivity of 55.6 S/cm are achieved by the PI composite containing 40 wt.% of MWCNT. Moreover, the electrical conductivity of this film further enhanced to 106 S/cm after the thermal compression process. The MWCNT content at the percolation threshold of conductivity is 0.50 wt.% (or 0.32 vol.%) and the critical exponent is equal to 2.52. The developed in situ fabrication process through DAAQ-derived molecules can also be applied to synthesize other polymers requiring diamine structure. (C) 2013 Published by Elsevier Ltd.
Effect of Temperature Gradient Direction in the Catalyst Nanoparticle on CNTs Growth Mode
(2010-09-01)
Lo, An-Ya
;
Liu, Shang-Bin
;
Kuo, Cheng-Tzu
;
材料科學與工程學系
;
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
;
Yu, Ningya
;
Huang, Shing-Jong
;
Hung, Chin-Te
;
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
;
Liu, Shou-Heng
;
Huang, Shing-Jong
;
Kuo, Cheng-Tzu
;
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.
Process and properties of the carbon nanotube assisted LiCoO(2) thin-film battery electrode by pulsed laser deposition
(2009-11-01)
Lo, An-Ya
;
Sun, Chuan-Shu
;
Tseng, Wen-Shou
;
Kuo, Cheng-Tzu
;
材料科學與工程學系
In this study, a pulsed laser deposition process was developed to deposit a carbon nanotube (CNT) assisted LiCoO(2) electrode to improve its power density. The electrodes were deposited on Pt-coated Si substrates with Ar and O(2) as sputtering gases and LiCoO(2)+C as the target. The results indicate that the working pressure is the most important parameter to control the composition of the electrode. Therefore, electrodes with a three-layer structure (i.e., LiCoO(2)-rich/CNT-rich/LiCoO(2)-rich) were fabricated by a three-step deposition process by varying the pressures from 13 to 1.3x10(4) Pa and then 13 Pa again, and it was found that the charge/discharge capacity became approximately 1.5 times greater than that in the corresponding electrode without a CNT-rich layer. The results also indicate that a higher substrate temperature is favorable for improving the crystallinity of the electrode to approach LiCoO(2) crystals.
Process and properties of the carbon nanotube assisted LiCoO2 thin-film battery electrode by pulsed laser deposition
(2009-11-01)
Lo, An-Ya
;
Sun, Chuan-Shu
;
Tseng, Wen-Shou
;
Kuo, Cheng-Tzu
;
材料科學與工程學系
In this study, a pulsed laser deposition process was developed to deposit a carbon nanotube (CNT) assisted LiCoO2 electrode to improve its power density. The electrodes were deposited on Pt-coated Si substrates with Ar and O-2 as sputtering gases and LiCoO2+C as the target. The results indicate that the working pressure is the most important parameter to control the composition of the electrode. Therefore, electrodes with a three-layer structure (i.e., LiCoO2-rich/CNT-rich/LiCoO2-rich) were fabricated by a three-step deposition process by varying the pressures from 13 to 1.3x10(4) Pa and then 13 Pa again, and it was found that the charge/discharge capacity became approximately 1.5 times greater than that in the corresponding electrode without a CNT-rich layer. The results also indicate that a higher substrate temperature is favorable for improving the crystallinity of the electrode to approach LiCoO2 crystals.
Significant improvement in the thermoelectric properties of zwitterionic polysquaraine composite films
(2013-09-16)
Ho, Mei-Chan
;
Chao, Ching-Hsun
;
Lo, An-Ya
;
Chen, Chun-Hua
;
Wu, Ren-Jye
In this study, the polysquaraine SQI(0.1), a zwitterionic pi-conjugated polymer, was adopted as the matrix for the preparation of flexible and freestanding films; the low band gap of this semiconducting polymer made it a natural choice for use as a thermoelectric (TE) polymer. To enhance their TE applications, both single-walled carbon nanotubes (SWNTs) and mesoporous carbon (i.e., CMK-3) were integrated into the SQI(0.1)-based films and the effects of doping with iodine were also investigated. Using scanning electron microscopy, the variations in morphology of these SQI(0.1)-based films were examined. Raman spectroscopy was used to study the pi-pi interactions between iodine and the carbon materials (Le., SWNT, CMK-3); X-ray diffraction and Raman spectroscopy to investigate the intercalation of the doped iodine in the composite films; and X-ray photoelectron spectroscopy to determine the valence state of the doped iodine. The TE properties of these materials were characterized in terms of the electrical conductivity (sigma), thermal conductivity (kappa), and Seebeck coefficient (S). The TE properties of the iodine-doped composite film prepared from SWNTs, CMK-3, and SQI(0.1) included a notable value of ZT (Figure of Merit) of 4.563 x 10(-3), which was 143% of that of the corresponding iodine-doped SQI(0.1) film. (c) 2013 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
;
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
;
Liu, Shou-Heng
;
Huang, Shing-Jong
;
Shen, Huang-Kai
;
Kuo, Cheng-Tzu