Polybenzimidazoles incorporating imidazole N-spirocyclic quaternary ammonium cation for anion exchange membranes water electrolysis

Abstract

In the present work, a polybenzimidazole copolymer (cPBI) containing rigid benzene and flexible alicyclic segments was synthesized as the backbone of anion exchange membranes (AEMs). Then the N-spirocyclic quaternization based on the imidazole of cPBI was innovatively developed to prepare the cPBI-spiro AEM, which exhibited excellent mechanical properties and chemical stability to oxidative and alkaline conditions. To optimize the conductivity and stability, a series of cPBI-xp-ys AEMs were further prepared by balancing the ratio of long side chain piperidinium and spirocyclic quaternization ammonium (QA). As a result, the cPBI-0.6p-0.4s AEM with apparent microphase separation structure displayed the OH− conductivity of 110.35 mS/cm and swelling ratio of 17.1% at 80 °C. The cPBI-0.4p-0.6s AEM maintained 75.67 wt% mass in Fenton's reagent (3% H2O2 and 4 ppm FeSO4) at 80 °C for 72 h and 83.20% conductivity in 2 M NaOH at 80 °C for 2016 h. Moreover, the current density of the anion exchange membrane water electrolysis (AEMWE) with cPBI-0.4p-0.6s AEM was 553 mA/cm2 at 2.1 V, the AEMWE could be operated stably under 200 mA/cm2 at 80 °C for 10 h. These results indicate that the cPBI-based AEMs containing long side chain piperidinium and spirocyclic QA structures have great potential application in AEMWEs.