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), H-1-NMR, F-19-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 A degrees 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 A degrees 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.