(376aq) Highly Hydroxide Conductive Quaternized Polybenzimidazole Anion Exchange Membranes

Polybenzimidazole (PBI) is a polymer with excellent mechanical, thermal and chemical stabilities. However, most anion exchange membranes (AEMs) based on quaternized PBI reported in the literature suffer from extremely poor hydroxide conductivity compared to other AEM categories. In this study, it is found that the poor hydroxide conductivity might be caused by the electrostatic interaction between imidazole anion and quaternary ammonium cation, which makes quaternization of PBI difficult and limits the formation of ion clusters in PBI AEM. Based on this analysis, highly hydroxide conductive quaternized PBI AEM are prepared by a two-step method to avoid the electrostatic interaction: First, PBI was grafted non-ionic side chains via N-substitution reaction, and then reacted with tri-quaternization reagent. The designed membrane exhibits high hydroxide conductivity (154 mS cm^-1) and low swelling ratio (23%) at 80°C. After immersion in 60 °C, 1 M KOH solution for 168 h, this hydroxide conductivity of the membrane still remains constant. The two-step method mentioned in this work provides a universal promising method to prepare high hydroxide conductivity and alkaline stability quaternized PBI anion exchange membranes.

The authors thank the National Science Foundation of China (21476044, 21406031 and 21776034), the National Key Research and Development Program of China (2016YFB0101203) for financial support of this work.