Browsing by Author "Chen, F"

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Effects of porosity change of gas diffuser on performance of proton exchange membrane fuel cell
(2003-09-15)
Chu, HS
;
Yeh, C
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Chen, F
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機械工程學系
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Department of Mechanical Engineering
An investigation is made of the effects of the change of the porosity of the gas diffuser layer (GDL) on the performance of a proton exchange membrane (PEM) fuel cell. The analysis of fuel cell performance with non-uniform porosity of GDL is a necessity because the presence of liquid water in the GDL leads to a non-uniformly distributed porosity in the GDL. To implement this performance analysis, a half-cell model which considers the oxygen mass fraction distribution in the gas channel, the GDL and the catalyst layer, and the current density and the membrane phase potential in the catalyst layer and the membrane is investigated. Four continuous functions of position are employed to describe the porosity, and differential equations are derived based on oxygen transportation and Ohm's law for proton migration and solved numerically. Results show that a fuel cell embedded with a GDL with a larger averaged porosity will consume a greater amount of oxygen, so that a higher current density is generated and a better fuel cell performance is obtained. This explains partly why fuel cell performance deteriorates significantly as the cathode is flooded with water (i.e. to give a lower effective porosity in the GDL). In terms of the system performance. a change in GDL porosity has virtually no influence on the level of polarization when the current density is medium or lower, but exerts a significant influence when the current density is high. This finding supports the scenario proposed by previous studies that the polarization at high current density corresponds mainly to mass transfer through (or the concentration activation of) the membrane assembly. (C) 2002 Elsevier Science B.V. All rights reserved.
HRTEM and EFTEM studies of the evolution of Cu/Ta/SiO2/Si interfaces in ULSI devices
(1999)
Yin, KM
;
Chang, L
;
Chen, FR
;
Kai, JJ
;
Chuang, CCCG
The Cu/Ta/SiO2/Si films have been annealed at temperatures from 500 degreesC to 600 degreesC in various vacuum conditions. Transmission electron microscopy has been used to characterize the microstructure of the films after annealing. It shows that different thicknesses of amorphous interlayer were formed between Cu and Ta under various vacuum conditions. Energy dispersive spectroscopy confirmed this interlayer to be tantalum oxide. It has also found that tantalum oxidation is caused by oxygen from the outside atmosphere diffusing along grain boundaries in copper films.