Composite proton conducting membrane by radiation-induced grafting of 1 -vinylimidazole onto poly(ethylene- co -tetrafluoroethylene) and phosphoric acid doping

Composite membrane containing phosphoric acid (PA) for possible use in a fuel cell was prepared by radiation-induced grafting of 1-vinylimidazole (1-VIm) onto poly(ethylene-co-tetrafluoroethylene) (ETFE) films followed by protonation with PA doping. The preparation procedure involved three steps: (i) irradiation of ETFE films by an electron beam, (ii) grafting of 1-VIm onto the irradiated films under selected conditions and (iii) doping the grafted film with PA. The membrane composition, thermal properties and thermal stability were evaluated using Fourier-transformed infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry, respectively. The obtained membrane was found to have a degree of grafting of 54% and 6.6 mmol PA per poly-VIm repeating unit with ionic conductivity of 140 mS cm⁻¹ at 120°C and ∼20% relative humidity. The overall results suggest that the membrane has a promising combination of physicochemical properties appealing for possible application in polymer electrolyte membrane fuel cell above 100°C.