Proton exchange membranes prepared by radiation grafting of styrene/divinylbenzene onto poly(ethylene-alt-tetrafluoroethylene) for low temperature fuel cells

The radiation grafting method is of interest for the preparation of proton exchange membranes for fuel cell and other electrochemical applications. Being based on low-cost starting materials and established process technologies, the method offers the prospect of cost-competitive membranes for the polymer electrolyte fuel cell (PEFC). In this study, a range of membranes have been prepared by pre-irradiation grafting of styrene/divinylbenzene onto poly(ethylene-alt-tetrafluoroethylene) (ETFE), with graft level, defined as mass of graft component added with respect to base film mass, spanning from 2.3% to 69%, and characterized ex situ for their fuel cell relevant properties. A selection of samples was evaluated in the single cell. The optimum graft level was found to be between 20% and 30%. In this range, fuel cell performance comparable to Nafion® standard was obtained, and a preliminary durability experiment over 770 h showed no signs of membrane degradation. At graft levels below 20%, the membrane resistance becomes excessively high, whereas above 30%, the mechanical properties of the membranes are insufficient, leading to rapid failure in the single cell. Room for improvement was identified in the quality of the interface between membrane and electrodes.