(255q) Characterization of Degradation of Acid Doped Nanocomposite PBI and PEEK Proton Exchange Membranes

Acid-doped PBI nanocomposite is one of the most promising membrane materials for the low-humidity high-temperature fuel cell. The ion conductivity is derived from the doping of inorganic acid (phosphoric acid). The fuel cell performance depends on the acid doping level, the leaching of the doped acid, and the degradation of the membrane. The incorporation of nanoscale inorganic particles in the polymer is expected to help bind and entrap the doped acid to the polymer. In this project, we prepared both PBI and PEEK nanocomposite membranes using different nanoscale surface modified silica particles with different acid doping levels. The resulting membranes were characterized for its thermal stability and mechanical properties against its acid doping level and variation of nanoparticle loading. The membranes were tested in a Scribner Fuel Cell Testing System, and the electrochemical impedance spectroscopy was obtained using Autolab instrument. The results were compared between PBI and PEEK membranes and design-of-experiment model was developed to reflect the influence of the doping level and the particle loading. Detailed fuel cell performance tests were conducted using membrane electrode assembly (MEA) prepared using PBI and Pt/C at different operating conditions, such as pressures, temperatures, and H2/O2 gas compositions. Preliminary results show that the phosphoric acid doped PBI and PEEK membranes both exhibited high ion conductivity of 0.11 and 0.24 S/cm at 120 and 160 °C, respectively. The power density output of PBI MEA equipped fuel cell increased from 0.92 W/cm2 to 1.15 W/cm2 when the pressure was increased from 1 to 2 atm at 160 °C. Results show that PBI and PEEK membrane is capable of operating fuel cells at working temperature greater than 120 °C without the need of water management.