Proton conductivity and properties of sulfonated polyarylenethioether sulfones as proton exchange membranes in fuel cells

A series of high molecular weight proton exchange membrane (PEM) materials, based on sulfonated polyarylenethioether sulfone (SPTES) copolymers, has been developed utilizing an all aromatic polymer backbone with bulky organic endcaps, along with a high sulfonic acid content that enhances water retention and high temperature application. The SPTES copolymers containing up to two sulfonic acid units per polymer repeat unit are expected to maximize the membrane water uptake as well as the proton conductivity. The evaluation of these PEMs resulted in a wide variation of proton conductivities in the range of 100–215 mS/cm at 65 °C and 85% relative humidity; the measured proton conductivities were found to be temperature and humidity dependent. This new class of SPTES copolymer materials for PEMs has been demonstrated to be superior to the state-of-the-art Nafion membranes with respect to proton conductivity as well as high temperature PEM use.