Investigation of proton conductivity of PVDF based anhydrous proton exchange membranes (PEMs) obtained via a facile “Grafting Through” strategy

Abstract

In this work, alkaline treated PVDF was used as a macromolecule in conjunction with GMA in the graft copolymerization. Synthesized PVDF-g-PGMA copolymers were functionalized with 5-aminotetrazole (ATet), and subsequently doped with triflic acid (TA) at several mole ratios with respect to tetrazole units. Finally PVDF-g-PGMA-ATet-(TA)x membranes were fabricated. The composition and the structure of the membranes were characterized by Energy Dispersive X-ray spectroscopy (EDS), 1H-NMR, 19F-NMR and FTIR. According to EDS results, 97 % functionalization with 5-aminotetrazole was achieved. The crystallinity and morphology of the polymers were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Proton conductivity of the materials was investigated by dielectric-impedance analyzer. The proton conductivity increased with increasing temperature and acid doping level. In the absence of humidity, the highest proton conductivity was found as 0.04 S/cm at 150 °C for PVDF-g-PGMA-ATet-(TA)3 membrane. Thermogravimetric analysis (TGA) showed that PVDF-g-PGMA-ATet(TA)3 was thermally stable up to 250 °C. The water uptake of the membranes decreased with triflic acid content. Methanol permeability experiments exhibited that the obtained graft copolymer membranes have similar methanol permeability values with Nafion 112.