Predicting fatigue lifetimes of a reinforced membrane in polymer electrolyte membrane fuel cell using plastic energy

Abstract

Limited mechanical durability remains a critical issue for the automotive application of polymer electrolyte membrane fuel cells (PEMFCs). Membrane fatigue cracking is a typical degradation mechanism that can lead to a failure of the PEMs. These cracks initiate and grow in the membrane due to hydration induced cyclic mechanical stresses, and the resistance to this type of damage is typically evaluated using relative humidity (RH) cycling as an accelerated stress test (AST) on the membrane. In this study, we simulate three RH cycling tests for a modern reinforced membrane. All the membrane material parameters used in the simulations were determined independently from the available experiments except for one: the material resistance to crack initiation, which is computed in terms of plastic energy in a representative unit fuel cell finite element model. This parameter was determined from one AST experimental data point and used to predict the cycle-to-failure of the membrane for the other two experimental conditions. Despite a number of assumptions used in the numerical analysis, the results show satisfactory agreement with experimental data. Although one test was used to calibrate the model, the proposed numerical scheme could replace numerous other long mechanical ASTs at the same temperature and humidity thereby significantly reducing the resources and time needed to evaluate the mechanical integrity of any particular modern membrane. Moreover, this model-based analysis could be used to correlate fuel cell operating conditions with membrane mechanical lifetime, thus aiding the development of system strategies in fuel cell vehicles for durability enhancement.