Comb-shaped ether-free poly(biphenyl indole) based alkaline membrane

High-conductive and alkali-resistant alkaline membranes are needed for fuel cells and water electrolysis. In this work, the ether-free poly(biphenyl indole) (PBN) was synthesized by the means of super acid catalysis. Then comb-shaped piperidinium-functionalized PBN (PBN-Pip) membranes were prepared by the incorporations of 1-bromohexyl-N-methylpiperidinium and 1-bromohexane. The comb-shaped long side chains facilitated the formation of wide and connected ion transport channels. The PBN-Pip membrane possessed the conductivity of as high as 108 mS cm−1 at 80 °C. The ether-free backbone and the hexyl spacers endowed the membrane with excellent stability. No degradation can be observed after immersion in 1 M KOH at 80 °C for 1000 h. The single cell with this membrane exhibited the open circuit voltage of 1.02 V and the peak energy density of 404 mW cm−2 at 80 °C. After the cell durability test for 120 h, the ohmic resistance of the cell and the chemical structure of the membrane both had no changes. All these suggest that the comb-shaped PBN membrane is very promising.