Assessment of mechanical properties of fluoroelastomer and EPDM in a simulated PEM fuel cell environment by microindentation test

The elastomeric materials used as seals/gaskets in Polymer Electrolyte Membrane (PEM) fuel cells are exposed to acidic environment, humid air and hydrogen, and subjected to mechanical compressive load. Both sealing and electrochemical performance of the fuel cell depend heavily on the long-term mechanical and chemical stability of these materials. In this paper, mechanical property degradation of two elastomeric materials, Fluoroelastomer and EPDM, which are being considered as gasket materials for PEM fuel cells, was investigated using microindentation. Test samples were subjected to various compressive loads to simulate the actual loading in addition to soaking in a simulated PEM fuel cell environment. Two temperatures, based on actual fuel cell operation, 80 and 60 °C, were selected in this study. Mechanical properties of the samples before and after exposure to the environment were assessed. Hysteresis loss energy, indentation load, elastic modulus and hardness were obtained from the loading and unloading curves. Indentation deformation was studied using Hertz contact model. It was found that the mechanical properties of the Fluoroelastomer samples changed significantly after exposure to the simulated environment over time. The exposure medium, temperature and applied compressive load contributed to the degradation of the material. On the other hand, the change of mechanical properties for the EPDM samples was not apparent. It is concluded that EPDM is much more stable than Fluoroelastomer for PEM seal applications.