Durability Testing of Silicone Materials for Proton Exchange Membrane Fuel Cell Use

Silicone resins are ideal candidates for Proton Exchange Membrane Fuel Cells (PEMFC) sealing and gasketing. They have many advantages for PEMFC application such as superior stability and longevity under harsh environments, low water absorption, and broad temperature range. However, as this work shows, silicone based materials have one big drawback:  low molecular weight siloxanes, oligomers, and/ or degradation byproducts may readily migrate from the base material into the fuel cell membrane, forming glassy structures, reducing the mechanical durability and ultimately fracturing the proton exchange membrane (PEM). A novel, in-situ testing method has been developed to test the effect of siloxanes on PEMFCs. The mechanism for migration of cyclic siloxanes to the PEM interface, causing it to failure in a brittle fashion is presented. A commercially available silicone gasket material was used as a case study to validate the mechanism.  Optical microscopy, scanning electron microscopy (SEM) and inductively coupled plasma (ICP) were used to perform failure analysis of the tested samples. Thermogravimetric analysis (TGA) was used to measure the removal rate of low molecular weight cyclic siloxanes. Gas chromatography-mass spectrometry (GC-MS) was used to separate the organic molecules off gassing from the material at temperature and provide a mass spectrum of each component.