Novel concept of polymer electrolyte membranes for high-temperature fuel cells based on ETFE grafted with neutral acrylic monomers

Abstract

High temperature proton exchange membranes were synthesized via electron beam treatment of commercial poly(ethylene-alt-tetraflouroethylene) (ETFE) films and subsequent graft radical copolymerizations with 2-hydroxyethyl methacrylate (HEMA) and 2-hydroxyethyl acrylate (HEA). The maximum degree of grafting achieved was 193%. Both grafted monomers are hydrophilic and lead to high membrane affinity to phosphoric acid. Doping with phosphoric acid resulted in a maximum doping level of 310%. The grafted membranes combine stable ETFE backbone polymer with hydrophilic side chains. As indicated by stress–strain curves the graft copolymer membranes show good mechanical stability. In addition, the polymer–acid-composites are thermally stable up to around 210°C. The polymer–acid-composite materials were tested in H2/O2 fuel cells at 120°C. Power densities of up to 108mWcm‒2 were obtained at a current density of 200mAcm‒2. It is shown that the alternate concept of polymer–acid composites without any basic units is also suitable for the application in high temperature fuel cells.