Electrochemical Performance Measurements of PBI-Based High-Temperature PEMFCs

Acid-doped poly(2,2'-m-phenylene-5,5'-bibenzimidazole) membranes have been prepared and used to assemble membrane electrode assemblies (MEAs) with various contents of PBI (1-30wt.%) in the gas diffusion electrode (GDE). The MEAs were tested in the temperature range of 140 degrees C-200 degrees C showing that the PBI content in the electrocatalyst layer influences strongly the electrochemical performance of the fuel cell. The MEAs were assembled using polyphosphoric acid doped PBI membranes having conductivities of 0.1 S cm(-1) at 180 degrees C. The ionic resistance of the cathode decreased from 0.29 to 0.14 Ohm-cm(2) (180 degrees C) when the content of PBI is varied from 1 to 10wt.%. Similarly, the mass transfer resistance or Warburg impedance increased 2.5 times, reaching values of 6Ohm-cm(2). 5wt.% PBI-based MEA showed the best performance. The electrochemical impedance measurements were in good agreement with the fuel cell polarization curves obtained, and the optimumperformance was obtained when overall resistance was minimal.