Water free operated phosphoric acid doped radiation-grafted proton conducting membranes for high temperature polymer electrolyte membrane fuel cells

Official URL: http://dx.doi.org/10.1002/fuce.201300110

The present study uses the radiation-induced grafting method and applies it onto poly (ethylene-alt-tetrafluoroethylene) (ETFE) for the synthesis of proton-exchange membranes by using monomers 4-vinyl pyridine (4VP), 2-vinyl pyridine (2VP), N-vinyl-2-pyrrolidone (NVP) followed by phosphoric acid doping. Phosphoric acid that provides Grotthuss mechanism in proton mobilization is used to transform the graft copolymers to a high temperature membrane state. Resultant proton-exchange membranes are verified with their proton conductivity, water uptake, mechanical and thermal properties, phosphorous distribution as ex situ characterization. Our most important finding as a novelty in literature is that ETFE-g-P4VP phosphoric acid doped proton-exchange membranes exhibit proton conductivities as 66 mS/cm at 130 °C, 53 mS/cm at 120 °C, 45 mS/cm at 80 °C at RH 100% and 55 mS/cm at 130 °C, 40 mS/cm at 120 °C, 35 mS/cm at 80 °C at dry conditions. Moreover, ETFE-g-P4VP membranes still conserves the mechanical properties, i.e., tensile strength up to 48 MPa. ETFE-g-P4VP membranes were tested in PEMFC at 80 °C, 100 °C and 120 °C and RH <2% and exhibit promising performance as an alternative to commercial Nafion® membranes. The single cell testing performance of ETFE-g-P4VP membranes is presented for the first time in literature in our study.