Preparation and characterization of PVA proton exchange membranes containing phosphonic acid groups for direct methanol fuel cell applications

In this paper, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), which is an organic phosphonic acids (OPA), is selected as the protic media to prepare phosphonated proton exchange membranes based on polyvinyl alcohol (PVA) by solution casting technique. The obtained PVA membranes were characterized using fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and wide angle X-ray diffraction (WAXD). The proton conductivities and the methanol permeabilities through the membranes were investigated in terms of various OPA content. The proton conductivity of the PVA membrane measured at room temperature was close to that of the nafion-117 membrane measured under the same test conditions (1.02 × 10−3 S·cm−1). But in the low relative humidity (50%), the proton conductivity of the phosphonic proton exchange membrane has a conductivity of up to 8.17 × 10−5 S·cm−1, which was significantly higher than that of the sulfonate proton exchange membrane. The methanol permeabilities of the PVA membranes were in the range of 10−7 to 10−6 cm2/s in the room temperature, depending on the OPD content. The thermal stability of the composite membrane was enhanced with incorporating of PBTCA by presenting high initial decomposition temperature.