Chemical degradation of Nafion ionomer at a catalyst interface of polymer electrolyte fuel cell by hydrogen and oxygen feeding in the anode

Chemical degradation products of a Nafion membrane on the catalyst interface of polymer electrolyte fuel cell (PEFC) by hydrogen and oxygen feeding into the anode were studied by high-performance liquid chromatography (HPLC). An acidic solution of pH 5.3 was obtained after the anode reaction and 5.0 x 10(-6) mol.l(-1) of hydrogen fluoride was detected by HPLC. Degradation mechanisms of the ionomer induced by trace radical species were simulated by means of quantum chemical calculations using a model side chain terminal of trifluoromethanesulfonate (TFMS). The results indicate that H radicals and OH radicals generated by the reaction on the interface induce the production of hydrogen fluoride, carbonyl fluoride and sulfonic acids. The bond dissociation energies (BDE) of C-S and C-F bond in TFMS are calculated to be 214.5 and 569.6 kj.mol(-1), respectively. It was clarified that the degradation of TFMS is affected not only by BDE but also by the behavior of fluorine atoms. (C) 2012 Elsevier B.V. All rights reserved.