Confocal Raman spectroscopic investigations of fuel cell tested sulfonated styrene grafted poly(vinylidene fluoride) membranes

We report on a confocal micro-Raman spectroscopic study of fuel-cell-tested proton conducting polymer membranes. The membranes are based on poly(vinylidene fluoride), which is irradiated, grafted with styrene, and finally sulfonated. We have determined the composition of the membrane before and after fuel cell testing. The fuel cell tests result in a gradual loss of poly(styrene sulfonic acid), which is also reflected in a decreasing conductivity. The degradation is an inhomogeneous process that differs both over the membrane surface and through the membrane depth. Most notably we detect an aggravated degradation at the cathode side of the membrane. Cross-linking the membranes with bis(vinyl phenyl)ethane or divinyl benzene does not prevent membrane degradation. (C) 2002 The Electrochemical Society.