Oxidation-resistance of Hydrocarbon Electrolyte Membranes for PEFC

Abstract

The polymer electrolyte membranes (AAc/SSS membrane) were synthesized by the radiation-induced graft polymerization of acrylic acid (AAc) and sodium 4-vinylbenzenesulfonate (SSS) on a polyethylene film. The single cells using the synthesized polymer films as the electrolyte were tested continuously. In the case of AAc/SSS membrane contacted directly with the oxidizing catalyst (Pt) in oxygen electrode at 55°C, the cell voltage dropped significantly after only 5 h operation due to an oxidative degradation of the membrane. When the oxygen electrode was impregnated with an ionomer of perfluorocarbon- sulfonic acid to prevent the AAc/SSS membrane from its direct contact with Pt ele ctrocatalysts, the cell worked continuously for 212 h at 55°C and 71 h at 70°C. When a thin fluorinated polymer electrolyte membrane (F-membrane, thickness = 11μm) was sandwiched between the AAc/SSS membrane and the oxygen electrode impregnated with the ionomer, the significant degradation of the AAc/SSS membrane was delayed until 190 h at 70°C. It is considered that the AAc/SSS membrane was oxidized by active oxygen (radical) species and/or hydrogen peroxide produced at the cathode side.