The Analysis of Mass Transport Phenomena in Micro Porous Layer for High Current Density Operation in PEMFC for Automobile Application

Cost reduction is the most important issue for commercialization of Fuel Cell Electric Vehicle (FCEV). High current density operation is one of the solutions for it. In order to realize high current density operation, it is necessary to reduce both of electron and oxygen transport resistance in the porous materials such as gas diffusion layer (GDL) and micro porous layer (MPL). However, the impacts of MPL microstructure on their properties are not fully understood yet compared with GDL because of the necessity of higher spatial resolution. In previous study, the transport analysis on the micro-structure which were visualized by Nano X-ray CT and FIB-SEM were conducted for it. However, it was not enough to understand both of the electron and oxygen transport phenomena and find the dominant factors, because there is no study which focused on the comparison of the numerical and experimental results on both of the electron and oxygen transport. In this study, the comprehensive analysis on both of electron and oxygen transport phenomena in GDL and MPL was conducted with experimental and numerical study based on the three-dimensional (3D) micro structure data. As a result, it was found that pore structure, such as a local porosity and/or tortuosity significantly affected the oxygen transport phenomena. On the other hands, especially in the case of electron transport phenomena in MPL, our results suggested that the dominant factor is not the solid structure such as local solid fraction and/or tortuosity but the contact resistance between carbon particles. This fact revealed that it is effective way to reduce the contact resistance between carbon particles and/or the number of contact points in unit length of a transport path in order to improve electrical transport of MPL.