Chemical Aspects of Membrane Degradation

Membrane failure results from a complex interplay of mechanical stress and chemical attack; each have multiple origins. A picture of degradation is emerging where the polymer is attacked by hydroxyl-radicals generated on Pt particles within the membrane. We extend this picture to include several reactions of hydroxyl radicals with peroxide and the PFSA polymer. This extended picture allows us to explain three differences in behavior exhibited by membrane-degradation rates in Fenton's Reagent tests and in-cell tests regarding correlation of rate with end groups, spatial distribution of polymer loss and existence of induction periods. We postulate a 3-step degradation scenario: 1) hydroxyl radicals attack polymer end groups and side chains, 2) hydroxyl radicals are converted to peroxyl radicals which only attack polymer end groups, and 3) loss of polymer volume and membrane embrittlement leading to mechanical failure depending on the extent of degradation.