| dc.description.abstract | Abstract
In this study, a two-dimensional, steady, and isothermal single cell model for a PEM fuel cell is established using a two phase flow theory. Backing layer, including gas diffusion layer (GDL) and micro porous layer (MPL), and catalyst layer (CL) are discussed to build the mathematical model with boundary conditions. Effects of various source terms, operating conditions, and properties on the performance of fuel cells are discussed.
The fluid in the backing layer is composed of nitrogen, oxygen, steam, and liquid water. Their distributions are presented and discussed. The MPL can prevent the catalysts from falling into the GDL and con reduce the interface resistance between the MPL and GDL due to their fine pores. The liquid water can be more easily drawn out of the CL due to the enhanced capillary force at the interface. The effects of the porosity, the permeability, and the contact angle of the gas diffusion layer and the micro porous layer are studied. Effects of compressed thickness of the GDL and the above three factors on the production of water and the performance of the fuel cell are studied, The transport of oxygen in the electrochemical reaction, the current density, and the distribution of liquid water in catalysis layer are also investigated. The electrochemical reaction is described by the Bulter-Volmer equation.
The results of this study indicate that the evaporation and condensation of water has significant effects on the performance of fuel cells and the production of liquid water. The drag force between the gas and the liquid slows down the speed of liquid water. The accumulated liquid water in the catalyst layer and the gas diffusion layer degrades the performance of the fuel cells. As far the effects of the contact angle, very lag or very small contact angles in the GDL facilitate the removal of liquid water and results in better cell performance.
Finally, the effects of the porosity and the permeability of the compressed regions in the GDL are analyses. The influx of oxygen to the CL would change because of the smaller porosity and permeability due to compression. More oxygen is directed to the CL, and the cell performance is there fore enhanced. | en_US |