Transport Properties and Performance Evaluations of PBI Membranes for High Temperature Polymer Electrolyte Fuel Cells HT-PEMFCs

摘要

Acid-doped poly(2,2'-m-phenylene-5,5'-bibenzi-midazole) membranes have been synthesized and used to prepare MEAs using various contents of PBI (1-30% wt.) in the gas diffusion electrode (GDE). The MEAs were tested in the temperature range of 140-200 °C to study the effect of PBI content on oxygen mass transport resistance in the catalyst surface and electrochemical performance of the fuel cell. Poly phosphoric acid doped PBI membranes prepared in this work demonstrate the conductivity of 0.1 S cm~(-1) at 160 °C. The ionic resistance of the cathode decreased from 0.29 to 0.14 Ohm-cm~2 at 180 °C when content of PBI is varied from 1-10% wt. Alternatively, the mass transfer resistance or Warburg impedance was increased ～2.5 times, reaching a value as high as 6 Ohm-cm~2. 5% wt. Homemade PBI based MEA showed the best performance at 180 °C. The homemade membranes were compared with two commercial membranes purchased from Advent and BASF. Though the both the membranes are intended to be used as PEM for HT-PEMFCs, their chemistries are different. To quantify their relative merits, we have made a systematic study on these membranes and compared with in-house made MEAs. TPS polymer (Advent) is a pyridine-based poly (ether sulfone) performs in similar way than CELTEC (BASF) membranes that consist of phosphoric acid doped PBI. Commercial and homemade MEAs exhibit similar membrane resistances but commercial membranes exhibit better performance as a consequence of higher platinum loading. Homemade MEAs show less electrode resistances compared with the MEAs manufactured by Advent and BASF.