Poroelastic PEM fuel cell catalyst layer and its implication in predicting the effect of mechanical load on flow and transport properties

This study experimentally and numerically investigates the polymer electrolyte fuel cell (PEFC) catalyst layers (CLs) to analyze the coupled pore-fluid diffusion and resultant stress distribution. In the study, effect of nanoporosity on mechanical strength is explored by analyzing the CL structure based on the elastic modulus and the yield strength scaling laws of open-cell foams. A finite element analysis of the CL is performed by adopting the biphasic consolidation theory. The biphasic theory in combination with the transient consolidation principle of a porous body is formulated to account for the variation in the external loading conditions as well as the internal pore pressure. The CLs are observed to have the elastoplastic ionomer matrix and anisotropic nanoporosity, which are responsible for the localized plastic densification on indentation. The indentation behavior of the CLs appears to respond similar to the conventional low-density nanoporous foams leading to the localized nonlinear response of contact stiffness. The mechanical properties were found to be insensitive to the constituents' (Pt and Carbon) concentration gradation over the CL thickness. In the numerical results, effect of porosity loss on the transport properties is discussed to highlight the importance of estimating the stress levels. It is outlined from the present study that under critical loading conditions, the yield limits of the CL play a crucial role in estimating the extent of transport losses. The effective proton conductivity and oxygen diffusivity losses are dependent on the macroscopic strength of the ionomer and the effective electronic conductivity loss is a function of intrinsic strength of the CL, which is also responsible for the overall durability of the CL. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.