A sulfophenylated polysulfone as the DMFC electrolyte membrane - an evaluation of methanol permeability and cell performance

A sulfophenylated polysulfone (PSU-sph), carrying 0.8 sulfonic acid units per repeating unit of the polymer, is evaluated as a membrane electrolyte for DMFC applications. The liquid uptake, methanol transport characteristics, electrolyte conductivity, and fuel cell performance are investigated. The methanol transport and DMFC performance results are compared to those of Nafion® 117. The PSU-sph membrane investigated shows superior qualities with regard to methanol crossover, with a methanol permeability of approximately 25% compared to that of Nafion®. The conductivity was measured to be 15% compared to that of Nafion®. However, this could not fully account for the internal resistance of the cell, implying that the contact resistance between the electrodes and electrolyte is higher when PSU-sph is used, probably because the electrodes are developed for use with Nafion® membranes. The stability of the PSU-sph membrane seems promising, with very low degradation observed over a period of 72 hours. It was concluded that although the mass transport properties of the PSU-sph membrane sample investigated were superior, it could not match the performance of Nafion® 117 in a DMFC application. However, a higher degree of sulfonation may have a significant positive effect on cell performance. The results also showed that a fully intergrated MEA is needed to fully assess new menbrane materials.