Characterization and fuel cell performance of divinylbenzene crosslinked phosphoric acid doped membranes based on 4-vinylpyridine grafting onto poly(ethylene-co-tetrafluoroethylene) films

Abstract

The effect of divinylbenzene (DVB) as crosslinker on the graft polymerization of 4-vinylpyridine (4VP) from poly(ethylene-co-tetrafluoroethylene) (ETFE) films was studied. The resulted films were doped with phosphoric acid (PA) and characterized for mechanical, surface, thermal properties, and fuel cell performance. The crosslinked membrane obtained from grafting a mixture of 4VP with 1% DVB improved the polymerization kinetics and resulted in about 50% graft level depending on graft conditions. The crosslinked membranes were also found to have better mechanical properties compared to its noncrosslinked counterpart. The resulted membrane exhibited proton conductivity as high as 75 mS/cm under 50% relative humidity (RH) at 120 °C, besides almost doubling the power output of fuel cell compared to a noncrosslinked membrane. To the best of our knowledge, DVB crosslinked 4VP based ETFE membranes were, for the first time, tested in practical fuel cell test station correlating their performance to operating temperature. Furthermore, surface properties of produced membranes were additionally correlated to the degree of crosslinking. Humidity dependence is less pronounced in the produced membranes resulting in strong potential for testing at intermediate temperature (80–120 °C) polymer electrolyte membrane fuel cells.