Preparation of Polymer Electrolyte Membranes via Radiation-Induced Graft Copolymerization on Poly(ethylene-alt-tetrafluoroethylene) (ETFE) Using the Crosslinker N,N′-Methylenebis(acrylamide)

Abstract

Polymer electrolyte membranes (PEM) prepared by radiation-induced graft copolymerization are investigated. For this purpose, commercial poly(ethylene-alt-tetrafluoroethylene) (ETFE) films were activated by electron beam treatment and subsequently grafted with the monomers glycidyl methacrylate (GMA), hydroxyethyl methacrylate (HEMA) and N,N′-methylenebis(acrylamide) (MBAA) as crosslinker. The target is to achieve a high degree of grafting (DG) and high proton conductivity. To evaluate the electrochemical performance, the PEMs were tested in a fuel cell and in a vanadium redox-flow battery (VRFB). High power densities of 134 mW∙cm−2 and 474 mW∙cm−2 were observed, respectively.

Polymer Electrolyte Membranes Prepared by Graft Copolymerization of 2-Acrylamido-2-Methylpropane Sulfonic Acid and Acrylic Acid on PVDF and ETFE Activated by Electron Beam Treatment

“…Previously, graft copolymerization on ETFE after pre-activation via EB treatment was studied in detail [39,44]. It was shown that EB doses ranging from 40 to 100 kGy in the activation step are well suited to achieve high degrees of branching ( DG ) and very good proton conductivity of the PEMs.…”

“…%. Higher monomer fractions are not feasible, since polymerization may occur in the liquid phase due to transfer of radicals to the monomers or solvent leading to polymerization in the reaction mixture [44]. DG increased from 28% to 1335% and the conductivity from 0.3 to 93.5 mS∙cm −1 in going from 10 to 30 vol.…”

“…In addition, it is seen that the power density is higher for AAP421, the membrane with the higher DG and consequently the higher number of sulfonic acid groups incorporated. For comparison, for Nafion 117 at 50 °C a value of 122 mW∙cm −2 was determined in the same fuel cell at identical operating conditions after 90 min [44].…”

“…Firstly, the ETFE or PVDF backbone material was activated by electron beam treatment with 50 to 200 kGy and stored at −30 °C prior to grafting. The details are given elsewhere [44]. The graft polymerizations were carried out in a double-walled glass reactor (100 mL volume) equipped with a condenser under continuous nitrogen flow for removal of oxygen and mixing of the reaction mixture.…”

“…The fuel cell tests were carried out at 40 and 50 °C with a stoichiometric gas excess ratio of 1.1 for both gases (λ H2 , anode = 1.1, λ O2 , cathode = 1.1) in a single fuel cell device as detailed previously [44].…”