Better Proton-Conducting Polymers for Fuel-Cell Membranes

Polyoxyphenylene triazole sulfonic acid has been proposed as a basis for development of improved proton-conducting polymeric materials for solidelectrolyte membranes in hydrogen/air fuel cells. Heretofore, the proton-conducting membrane materials of choice have been exemplified by a family of perfluorosulfonic acid-based polymers (Nafion7 or equivalent). These materials are suitable for operation in the temperature of 75 to 85 °C, but in order to reduce the sizes and/or increase the energy-conversion efficiencies of fuelcell systems, it would be desirable to increase temperatures to as high as 120 °C for transportation applications, and to as high as 180 °C for stationary applications. However, at 120 °C and at relative humidity values below 50 percent, the loss of water from perfluorosulfonic acid-based polymer membranes results in fuel-cell power densities too low to be of practical value. Therefore, membrane electrolyte materials that have usefully high proton conductivity in the temperature range of 180 °C at low relative humidity and that do not rely on water for proton conduction at 180 °C would be desirable.