Cross-Linkable Polymeric Ionic Liquid Improve Phosphoric Acid Retention and Long-Term Conductivity Stability in Polybenzimidazole Based PEMs

A series of composite cross-linked membrane based on fluorine-containing polybenzimidazole (6FPBI) and a cross-linkable polymeric ionic liquid (cPIL) have been prepared for high temperature proton exchange membrane (HT-PEM) applications. Particularly, the obtained composite cross-linked membranes showed excellent phosphoric acid doping ability and proton conductivity. On the basis of the trade-off between mechanical strength and proton conductivity of composite membranes, the optimal content of cPIL is 20 wt % (6FPBI-cPIL 20 membrane). For instance, the 6FPBI-cPIL 20 membrane with a PA doping level of 27.8 exhibited a proton conductivity of 0.106 S cm(-1) at 170 degrees C, which is much higher than that of pristine 6FPBI membrane. The most outstanding contribution of this work is that the 6FPBI-cPIL membranes showed improved phosphoric acid retention and long-term conductivity stability under harsh conditions (80 degrees C/40% RH) for 96 h. In particular, the proton conductivity and PA doping level of the 6FPBI-cPIL 20 membrane remained at a high level of 0.064 S cm(-1) and 8.5 after 96 h of the test, respectively.