Characterization of statistical co-polymer vinylidene fluoride-hexafluoropropylene-phenylphosphonic acid functionalized hexafluoropropylene for potential applications as a proton electrolyte membrane

Abstract

Meeting the world’s growing demand for energy without contributing to the emergent problem of anthropogenic climate change requires the use of renewable, carbon-free energy sources which in turn are contingent on advances in materials science. A newly synthesized statistical co-polymer of vinylidene fluoride, hexafluoropropylene and phenylphosphonic acid functionalized hexafluoropropylene (PolyPPA) shows potential for use as a polymer electrolyte membrane (PEM) in a variety of green-energy applications including proton pumps, flow batteries and high temperature-low relative humidity fuel cells. Preliminary testing of PolyPPA samples synthesized using a high molecular weight and low molecular weight feedstock show comparable conductivity, thermal stability and water uptake. Both high and low molecular weight PolyPPA exhibit minimal water uptake, are thermally stable to 160 °C, contain tightly bound water and exhibit low but measurable conductivity with best relative performance in high temperature and low relative humidity conditions. Despite a relatively low conductivity, the absence of liquid acid and the thermal stability suggests possible high temperature and high pressure applications. Future work needs to be conducted to determine how the degree of phenylphosphonic acid functionalization affects the conductivity and mechanical properties to determine an optimal formulation to minimize area specific resistance.