Preparation and characterization of proton exchange membrane by UV photografting technique

Abstract

Ultraviolet (UV)-induced graft copolymerization of glycidyl methacrylate GMA onto poly(ethylene terephthalate) (PET) films and the subsequent sulfonation on the monomer units in the grafting chain using sulfuric acid were carried out to prepare proton exchange membranes (PEMs) for fuel cells. A maximum grafting value of 23.5% was found for 15 vol% GMA after 4-h radiation time. Optimum concentration of sulfuric acid was selected for the sulfonation reaction to be 1 mol/L based on the degree of sulfonation and the tensile strength studies of the membrane. The radiation grafting and the sulfonation have been confirmed by titrimetric and gravimetric analysis as well as FTIR spectroscopy. The maximum ion exchange capacity (IEC) of 2.085 meq g−1 was found at 46.99% degree of sulfonation and the maximum proton conductivity was found to be 60.35 mS cm−1 at 30 °C and relative humidity of 100%. The various physical and chemical properties of the PEMs such as water uptake, mechanical strength, thermal durability, free-volume content, and methanol permeability were also studied as function of sulfuric acid concentration. To investigate the suitability of the prepared membrane for fuel cell applications, its properties were compared with those of Nafion 112 as standard membrane.