| Summary: | 碩士 === 元智大學 === 化學工程研究所 === 89 === A mathematical model is developed to investigate transport phenomena as well as electrochemical reaction occurring in the cathode of a proton exchange membrane fuel cell (PEMFC). The main goal of the present research is to explore the two-dimensional effects that have been ignored by most previous investigators. Restriction of the access of oxygen to the catalyst layer of the cathode by the ribs of bipolar plates is taken into account in the model presently studied.
In the catalyst layer, Nernst-Planck equation is used to describe the mass transport of proton in the ionomer, and the electrochemical reaction is assumed to follow the Butler-Volmer equation. In addition, the Stefan-Maxwell equation is applied to calculate the local mole fraction of gaseous species in the diffusion layer.
A method of collocation on finite elements based on B-spline interpolation is employed for the numerical solution of the coupled nonlinear differential equations. The computational results reveal that the one-dimensional model would overestimate the cathode performance since it ignores the concentration and potential gradients along the plane direction. The two-dimensional model is likely to yield more accurate presentation of the cathode performance due to its realistic considerations. Though the existence of diffusion layer could obviously reduce the differences between the one-dimensional model and the two-dimensional model, an inappropriate thickness or porosity may also adversely affect the performance of the fuel cell. The effects of percentage of Nafion in catalyst layer, oxygen pressure and other parameters are also discussed.
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