Acid-Base Chemistry and HT-Polymer Electrolyte Membrane

The project aim is to understand and mitigate phosphoric acid related problems in PBI based High Temperature PEM Fuel Cell (HT-PEMFC). During the past one year, topics which were investigated are: phosphoric acid dehydration, effects to gas crossover, and phosphoric acid migration.  Phosphoric acid dehydration into its polymerized form effectively reduces conductivity and happens spontaneously at the operation temperature of HT-PEMFC. FT-IR spectrum at different temperatures shows a growing peak in the region of 1800 – 2500 cm-1 which might be related to acid dehydration. The growing FT-IR peaks happens both when there are enough free acid in the membrane and when no free acid (all acids are bonded) are present. In addition to the FT-IR, 31P NMR is being investigated as one of the ways for quantifying pyrophosphoric acid formation in HT-PEMFC.

Figure 1 FT-IR Spectrum for PBI-H3PO4 with increasing temperature

Phosphoric acid migration from the electrolyte was also studied during this project. Migration through means of evaporation was measured from its vapor pressure. The relatively low amount of evaporated phosphoric acid proved to be the greatest obstacle for quantifying them. Movement of acid due to electrochemical movement was also tried to be measured using the help of impedance spectroscopy.

No journal publication has been made during the past year. Dissemination activities were done once by presenting one poster during the DTU Energy PhD Symposium in November 2015.