Estimating the Durability of Polymer Electrolyte Fuel Cell Membranes Using a Fracture Percolation Model

Abstract

During fuel cell operation, the polymer electrolyte membranes are subjected to chemical and mechanical degradation that have an adverse impact on the membrane lifetime and thus overall durability of the fuel cell. To understand the synergistic effect of these two fundamentally different modes of degradation, it is therefore essential to consider both these effects when modeling membrane failure. A kinetic approach using a fracture percolation model is presented in this work that takes into consideration the hazard rates of chemical and mechanical degradation of the membrane incorporated into a two-dimensional membrane lattice network. While the chemical hazard rate is based on the rate of mass loss occurring during fuel cell operation, the mechanical hazard rate is evaluated based on a stress-induced, thermally activated process. The model captures the characteristic mechanisms of failure under the action of these fundamentally different modes, and converts the hazard functions into realistic time scale. The individual effects of the two modes are then incorporated in the model to predict in agreement with measured data, the time to fracture initiation in the membrane for a given combination of chemical and mechanical load.