EPR investigation of HO/ radical initiated degradation reactions of sulfonated aromatics as model compounds for fuel cell proton conducting membranes

Abstract

In order to predict hydroxy radical initiated degradation of new proton conducting polymer membranes based on polystyrene, polyethersulfone, polyetheretherketone, or on polymers obtained by radiation grafting of styrene on different fluoropolymers, eight sulfonated aromatics were chosen as model compounds for EPR experiments, aiming at the identification of products of HO• radical reactions with these polymers. Photolysis of H 2 O 2 was employed as the source of hydroxyl radicals. A detailed investigation of the pH profile was carried out for p-toluenesulfonic acid. Besides benzyl-and hydroxy-cyclohexadienyl radicals at lower pH values, phenoxyl radicals were identified, predominating in the pH range 10.5-13.0. A large number of new radicals give evidence of multiple hydroxylation of the aromatic rings, confirming reaction mechanisms proposed on the grounds of product analysis, but no evidence of dimerisation was found. The result as regards stability of organic proton exchange membranes for fuel cells is, that all unsaturated bonds and weakly bound atoms are subject to immediate attack by HO•. Ether links open by HO• ipso addition. Strategies for the reduction of membrane degradation should focus on a minimisation of HO• formation and of its access to the interior of the membrane.xylene-4-sulfonate were carried out in order to study radical

Investigations of conductivity in FEP-based radiation-grafted alkaline anion-exchange membranes

“…5) At high in situ pH, the oxidative radical mechanism for polymer degradation is suppressed [10] and potentially enables the use of hydrocarbon only membranes (C-H backbone) with enhanced green credentials (manufacturing and disposal)…”

Consecutive reactions of aromatic-OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

“…2058 R. Koch et al: Reaction of the OH-adducts of aromatics with NO, NO 2 and O 2 of H 2 O. Hübner and Roduner (1999) studied hydroxylation of p-methoxy-benzenesulphonate and observed various phenoxyl radical anions, i.e. the ether link was broken.…”

(2009 ECS Battery Division Technology Award) Development of Highly Durable PFSA Membrane for PEMFC under High Temperature and Low Humidity Conditions

“…Therefore, the performance loss of the MEA was attributed to the degradation of the cathode catalyst. Regarding the corrosion mechanism of the carbon support, Hubner et al reported on the "Hydroxyl radical initiated degradation reactions of sulfonated aromatics for fuel cell membrane" (22). They reported that the hydroxyl radical addition occurs on the aromatic ring, and is followed by the addition of an oxygen molecule.…”