Cluster Model And Numerical Analysis Of The Membrane Electrode Assembly Of Proton Exchange Membrane Fuel Cells

The proton exchange membrane fuel cell (PEMFC) is one of the most promising power sources for future electric vehicles due to it's high power density and energy conversion efficient. However the accurate, systematic and in-deepth acquaintance with MEA, where mass transfer processes and electrochemical reactions proceed simultaneously, has not been obtained yet. So it is completely necessary to make more comprehensive study about MEA. The optimization design of the structure and composition of the MEA can be carried out on a computer economically.In the thesis, we proposed a random cluster model of MEA. The cluster model consists of a randomly distribution of three kinds of particles, Pt/C, Nafion and PTFE (poly-tetra -fluoro-ethylene). They were generated on a computer by the means of Monte Carlo method. Base on such a cluster model. The catalyst utilization was calculated through counting the number of Pt/C clusters and Nafion particles clusters. It was supposed that the effective Pt/C clusters were only those that not only have electron channels via carbon particles to current collector but also have proton channels via Nafion polymer particles to the Nafion membrane. The purpose of the work, in a word, is to look for how many Pt/C, which have two-type channels. The simulation program was written by VC language and MATLAB. The factors influcing catalyst utilization was thoroughly discussed.The following results have been concluded:(1) The catalyst utilization could be improved through reduction of the catalyst layer thickness. So the thinner MEA, the higher utilization would be.(2) There is an optimum loading of Nafion for a certain loading of catalysts. Too much Nafion particles would lead to catalyst overlaid. In turn, it may isolate catalyst clusters from current collector (carbon paper/cloth).(3) The thickness of an electrode could be reduced and accordingly the catalyst utilization could be increased by using catalyst with a high Pt containing catlalysts Pt/C.However, it will also reduce the reaction area of the MEA at the same time, the efficiency of Nafion membrane will drop unfortunately.(4) A relative lower loading of PTFE does not ruin the utilization of Pt/C. But with the increase of PTFE, for example, greater than 10%, it does no good to catalyst utilization.