【作者】 冉洪波；

【导师】 魏子栋；

【作者基本信息】 重庆大学 ， 物理化学， 2004， 硕士

【摘要】 质子交换膜燃料电池(PEMFC)具有较高的功率密度和能量转化效率，最有可能成为电动汽车的动力源。但是目前人们对质子交换膜燃料电池膜电极的结构、传输过程和电极的微观性质还缺乏准确、系统和深层次的认识，质子交换膜燃料电池的开发和研究还有大量的工作要做。用计算机对膜电极的结构和组成进行优化设计，从理论上解决膜电极的设计的某些问题，对改善膜电极结构和提高催化剂的利用率是有现实意义的研究课题。 本文首先建立了质子交换膜燃料电池的膜电极的随机立方网格模型，在电极模型各格点位置，用Monte Carlo方法生成随机分布的Pt／C粒子、Nafion粒子和聚四氟乙烯(PTFE)团粒，通过建立质子交换膜膜电极的团簇模型，统计有传导电子能力的Pt／C粒子团簇和有传导质子能力的Nafion粒子团簇，认为只有那些既有质子传输通道又有连续的电子通道和气体扩散通道的团簇才产生有效的电流，而其余团簇不产生电流，把电极的输出电流转化成一个概率事件。进而实现对膜电极的催化剂利用效率的数值分析。运用VC语言编写了模拟程序，实现了对膜电极催化剂利用率的统计，探讨了电极结构和电极制备工艺对催化剂利用率的影响。 通过对膜电极(Membrane electrode assembly，简称MEA)的Monte carlo模拟获得以下结论： (1)催化剂利用率随电极厚度的增加而减小，所以膜电极的薄型化可以提高电极中的催化剂的利用率。 (2)Nafion在电极中提供质子通道，Nafion含量在不同厚度电极中存在一最佳值，并不是越多越好，过多的Nafion使催化剂被Nafion团簇所隔离，降低了其通向集流网的团簇数量，从而降低了Pt／C的利用率。 (3)高负载比的Pt／C作催化剂可以降低催化层厚度，提高催化剂利用率，但同时也会降低三维反应区，使膜电极膜的利用率下降。 (4)适量PTFE的用量不会造成Pt／C利用率的下降，但随着PTFE的增加，Pt／C的利用率明显下降。更多还原

【Abstract】 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.更多还原