Improvement of homogeneity and interfacial properties of radiation grafted membranes for fuel cells using diisopropenylbenzene crosslinker

A novel crosslinked radiation grafted poly(ethylene-alt-tetrafluoroethylene) (ETFE) based membrane has been obtained by use of the crosslinker 1,3-diisopropenylbenzene (DIPB). The investigated membranes are based on 25 μm thick ETFE film grafted with styrene/DIPB. Grafted films and proton-exchange membranes with varying DIPB concentration and fixed graft level (∼25%) were prepared. The influence of the crosslinker on various ex situ and in situ fuel cell relevant membrane properties was investigated in detail. The composition of the styrene/DIPB in the bulk and in the near-surface region was determined. Infrared spectroscopy analysis revealed homogeneous crosslinker distribution in the surface and bulk of the grafted films, whereas XPS showed a poorer grafts concentration at the surface in the highly crosslinked samples. A qualitative relationship between the surface hydrophilicity measured by the contact angle and the interfacial property of the membrane–electrode assembly (MEA) determined by electrochemical impedance spectroscopy during fuel cell operation was observed. The interfacial properties, dimensional stability and hydrogen barrier properties of the membranes improved substantially with increasing DIPB concentration.