Preparation and study of spirocyclic cationic side chain functionalized polybiphenyl piperidine anion exchange membrane

Abstract

Research on the ion conductivity and mechanical stability of anion exchange membranes (AEMs) has achieved great progress, it is more urgent to prepare AEMs with high alkali stability. Azaspirocyclic cations are among the most alkali-stable cations. In this study, a synthesized long-chain 3-(3-(1-(8-bromooctyl) piperidin-4-yl) propyl)-6-azaspiro[5.5] undecan-6-ium bromide(BOP-ASU) cation was introduced into a portion of a piperidine ring on a PBP backbone to prepare PBP-BOP-ASU, and AEMs based on PBP-ASU and PBP-BOP-ASU were prepared. The structure of each product was characterized (1H NMR, MS), and the prepared anion exchange membrane was also characterized using micromorphology (SEM, TEM, AFM) and performance tests (TGA, WU, SR, ion conductivity, alkali stability). The PBP-BOP-ASU (8% membrane) showed the highest ion conductivity (117.43 mS/cm) at 80 °C. In addition, it showed excellent alkali stability in a test environment of 2 M NaOH solution at 80 °C for 1400 h. Moreover, the introduction of side chain spiro cations could improve the microscopic phase separation structure of the AEMs, and it also increased their ionic conductivity, thus ensuring the potential for their application in anion exchange membrane fuel cells.