Browsing by Author "Hung, Tsung-Chi"

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Catalyst-free, low-temperature growth of high-surface area carbon nanoflakes on carbon cloth
(2009-01-01)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Chen, Chien-Chung
;
Whang, Wha-Tzong
;
材料科學與工程學系
We have used a microwave plasma-enhanced chemical vapor deposition system to synthesize two-dimensional (2D) and three-dimensional (3D) structures of carbon nanoflakes (CNFs). This catalyst-free, low-temperature synthesis involved introducing CO(2) and CH(4) as reactants at a specified ratio of 2:3. We obtained uniform 2D arrays of CNFs at lower microwave powers (200 or 300 W) and substrate temperatures (up to 420 degrees C); their thickness was close to 1 mm. At a microwave power of 400 W, we obtained a 3D architecture comprising the smallest nanoflakes reported to date. The specific surface area of the 3D structure was double that of the corresponding 2D arrays. We suspect that such structured carbon materials might have great potential for energy storage applications. (C) 2008 Elsevier B. V. All rights reserved.
Deposition of Carbon Nanowall Flowers on Two-Dimensional Sheet for Electrochemical Capacitor Application
(2009)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Whang, Wha-Tzong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have used bias-assisted microwave plasma chemical vapor deposition to synthesize (i) two-dimensional carbon nanowalls [(2D CNWs), monolayer] and (ii) three-dimensional carbon nanowalls [(3D CNWs), double-layer] on carbon cloth in a CH(4)/CO(2) system. The specific surface area of the 3D CNW electrode (1580 m(2)/g) was considerably larger than that of the 2D CNW electrode (364 m(2)/g). This higher surface area and more porous structure of the 3D CNW electrode resulted in its capacitance reaching as high as ca. 198 F/g at a scan rate of 10 mV/s. Electrochemical measurements suggested that this 3D electrode is a promising material for application in electrical storage devices.
One-step fabrication and field emission properties of petal-like carbon nanotubes
(2009-02-01)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Whang, Wha-Tzong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have used bias-assisted microwave plasma chemical vapor deposition to synthesize (i) carbon nanotubes (CNTs) possessing a graphitic carbon nanoflake (CNF) morphology, (ii) CNF spheres, and (iii) a pure carbon nanoflake film (CNFF) on stainless-steel substrates. We employed CH(4) and CO(2) as the precursors to these carbon nanomaterials(CNMs); the use of CO(2) aided the destruction of the CNT surfaces and reduced the growth temperature range to 380-450 degrees C at 300 W, as a result of the presence of oxygen-based species in the plasma. Applying an external bias of - 150 V led to the growth of CNTs possessing specifically oriented graphitic CNFs. We used scanning electron microscopy and high-resolution transmission electron microscopy to observe the morphologies and graphitic structures of these CNMs. Field emission measurements of a CNT/CNF-coated electrode revealed that the turn-on field was ca. 2.73 V/mu m. (c) 2008 Elsevier B.V. All rights reserved.
One-Step Fabrication of Carbon Nanotubes Decorated with Graphitic Nanoflakes for Energy Storage Systems
(2010-07-01)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Chen, Chien-Chung
;
Whang, Wha-Tzong
;
材料科學與工程學系
We have used a bias-assisted microwave plasma chemical vapor deposition system to synthesize carbon nanotubes presenting graphitic nanoflakes, named coral-like carbon nanotubes, and well-aligned carbon nanotubes on carbon cloth substrates. Applying an external bias of -100 V led to the growth of well-aligned carbon nanotubes. In the absence of an external bias, the coral-like nanotubes presenting graphite nanoflakes were formed. The specific surface areas of the well-aligned and coral-like carbon nanotubes electrodes were 90.31 and 143.69 m(2)/g, respectively. In terms of energy storage, we estimated the capacitance of the coral-like carbon nanotube electrode to be ca. 194 F/g in an electrolyte of 1 M H(2)SO(4). This value is almost double that of the well-aligned carbon nanotubes electrode (104 F/g), presumably because the presence of the carbon nanoflakes had a positive influence on the migration and adsorption of ions within the electrode. The fitting results indicated that the coral-like carbon nanotubes electrode behaved as a traditional electrochemical capacitor. Durability tests revealed that the coral-like carbon nanotube electrode was reliable, with a decay of 9% in capacitance over 1000 cycles.
Quantitative limitation of active site and characteristics of chemical oxidized well-aligned carbon nanotubes
(2008-06-30)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Chen, Mi
;
Chen, Chien-Chung
;
材料科學與工程學系
For many years, acid treatment processes have been used to modify substances for their applications on energy storage devices, such as electrochemical capacitors, fuel cells, etc. It is obvious that the increase of surface area and functional groups has beneficial influence on the amount of reactant adsorption. However, the quantitative limitation of active site has been poorly discussed until today. In this experiment, nitric acid (2 M and 14 M) was introduced at 90 degrees C over different periods of time to oxidate the well-aligned multi-wall carbon nanotubes (MWNTs), which were synthesized directly using carbon cloth (CC) as the substance. Quinoidal functional groups on active CNTs, such as -COOH and -OH, were found to be the result of chemical reaction. Pt catalyst, which was extracted from H2PtCl6 center dot 6H(2)O, was deposited onto the carbon nanotubes using electroless plating in chloroplatinic acid solution. The extent of Pt adsorption was measured and was substantially larger than the as-prepared CNTs. It was found that the state of quantitative limitation existed in both 2 M and 14 M systems. A model was also developed to illustrate the limitation in the active site due to the chemical oxidation. (C) 2007 Elsevier B.V. All rights reserved.