Diazoniabicyclo-type poly (ionic liquid) cross-linked polybenzimidazole membrane with improved phosphoric acid retention for HT-PEMFCs

Poly (ionic liquid)s with ion-pair aggregates are recognized as excellent modifier for high-temperature proton exchange membranes. Herein, a bulky ionic liquid, N-(4-chlorobutyl)-N'-(5-Pentenyl)-1,4-diazoniabicyclo-[2.2.2]-octane bromide ([CPDOc]Br2), is synthesized and incorporated into polybenzimidazole (PBI) polymer as side groups. During the membrane fabrication, the cross-linked networks and poly(ionic liquid) are formed simultaneously through an in-situ free radical reaction. Finally, the anions are exchanged into H2PO4− with base-acid doped. As a result, the PBI-CPDOc30 membrane with low PA uptake (139%) exhibits the highest conductivity (0.121 S cm−1 at 170 °C), higher than that of PBI (0.083 S cm−1) with a PA uptake of 221%. Moreover, the PBI-CPDOc20 membrane exhibit a PA retention of up to 81% after the 400 h-test at 160 °C.