Thermal Stability of Proton Conducting Acid Doped Polybenzimidazole in Simulated Fuel Cell Environments

Abstract

Recently, polybenzimidazole membrane doped with phosphoric acid (FBI) was found to have promising properties for use as a polymer electrolyte in a high temperature (ca. 150th 200°C) proton exchange membrane direct methanol fuel cell. However, operation at 200°C in strongly reducing and oxidizing environments introduces concerns of the thermal stability of the polymer electrolyte. To simulate the conditions in a high temperature fuel cell, FBI samples were loaded with fuel cell grade platinum black, doped with ca, 480 mole percent phosphoric acid (i.e., 4.8 H3P()4 tolecules per PBI repeat unit) and heated under atmospheres of either nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identification. In all cases weight loss below 400°C was found to be due to loss of water. Judging from the results of these tests, the thermal stability of FBI is more than adequate for use as a polymer electrolyte in a high temperature fuel cell.

Sulfonated Polybenzimidazoles for High Temperature PEM Fuel Cells

“…This indicates there is a strong dependence of polymerization process on both doping level and conductivity, and is reiterated by Bai and Ho in their work. 33 Typical doping levels reported in the literature for m-PBI prepared via the conventional organic solvent route are between 6 and 10 mol PA/PBI, 14,15,[17][18][19][20][21] although some films with higher doping levels and poor mechanical properties have been achieved. 52 Average doping levels for s-PBI membranes developed in this work are between 30 and 35 mol PA/PBI, although some membranes retain 40-50 mol PA/PBI.…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…These membranes are capable of operating at temperatures up to 200 • C [53]. Moreover, these membranes promise low cost and high performance [52,54]. Early work was done on a variety of PBI identified as mPBI.…”

In-Situ Dynamic Characterization of Energy Storage and Conversion Systems

“…So far, phosphoric acid (H3PO4, abbreviated to PA) doped polybenzimidazole (PBI) has been found to be one of the most commercially promising materials for PEM fuel cell operating at temperature higher than 100°C. The advantages of PBI over other polymers, including low cost [54], high glass transition temperature [55], excellent textile fiber properties [56], and great thermal stability [57], promised it to be an excellent polymer for membrane fabrications. One of the most significant advantages of a PA doped PBI membrane over a PFSA based membrane is that its conductivity no longer relies on the water content due to its unique proton conduction mechanism [50,[58][59][60], but strongly depends on the PA doping level [50,[61][62][63] and the operating temperature [50,63,64].…”