Phosphoric acid-doped sulfonated polyimide and polybenzimidazole blend membranes: high proton transport at wide temperatures under low humidity conditions due to new proton transport pathways

Abstract

We now demonstrate a new class of a polymer proton exchange membrane for fuel cells, capable of combining low cost and high proton conductivity under low humidity conditions. The novel phosphoric acid (PA)-doped sulfonated polyimide (SPI) and polybenzimidazole (PBI) blend membrane enables proton conductivities of approximately 0.5 and 0.1 S cm⁻¹ at 120 °C and 45%RH and at 30 °C and 30%RH, respectively. These conductivities were approximately two orders of magnitude higher than those of Nafion 117 due to a new proton transport pathway between phosphoric acid and sulfonic acid in the blend membrane. In addition, the membrane showed no signs of performance degradation at 120 °C and 0%RH after 1000 hours of operation, and maintained a proton conductivity value of more than 0.01 S cm⁻¹. Consequently, this material shows promise as a novel proton exchange membrane and may have potential applications for use in fuel cells.