Properties, degradation and high temperature fuel cell test of different types of PBI and PBI blend membranes

Polybenzimidazoles (PBIs) with synthetically modified structures and their blends with a partially fluorinated sulfonated aromatic polyether have been prepared and characterized for high temperature proton exchange membrane fuel cells. Significant improvement in the polymer chemical stability in terms of the oxidative weight loss, molecular weight decrease and onset temperatures for the thermal SO2 and CO splitting-off was achieved with the electron-deficient polybenzimidazoles containing –S(O)2– and –C(CF3)2– bridging groups. Ionical cross-linking in the form of acid–base blends was found to further improve the polymer stability and assist maintaining the membrane integrity. Upon acid doping the membrane swelling was reduced for the modified PBI and their blend membranes, which, in turn, results in enhancement of the mechanical strength, proton conductivity and high temperature fuel cell performance.