Poly(terphenyl piperidinium) containing hydrophilic crown ether units in main chains as anion exchange membranes for alkaline fuel cells and water electrolysers

Abstract

Poly(arylene piperidinium) polymers are recognized as promising anion exchange membrane (AEM) materials for alkaline fuel cell and water electrolysis, due to the aryl-ether free polyaromatic backbones and stable piperidinium cations. Herein, hydrophilic crown ether units have been introduced into poly(terphenyl piperidinium) (PDTP) by readily superacid-catalyzed polycondensation of dibenzo-18-crown-6 (DE), p-terphenyl and N-methyl-4-piperidine followed via quaternization. The obtained PDTP membranes showed much higher hydroxide conductivity than the control poly(terphenyl piperidinium) (PTP) sample without DE units, due to their high water uptake. The highest hydroxide conductivity of 110 mS/cm was reached at 80 °C for PDTP-10 (where 10 denoted the molar content of crown ether units) membrane with an ion exchange capacity (IEC) of 2.57 meq./g. The introduction of DE units alleviated the chemical degradation of PDTP membrane in 1 M NaOH at 80 °C as compared to the PTP membranes. Furthermore, membrane electrode assemblies based on PDTP-10 membrane shown a peak power density of 621 mW/cm2 at 60 °C in AEM fuel cells and a current density of 2000 mA/cm2 at 2.1 V for water electrolysers circulated with 1 M NaOH at 80 °C. The in-situ stability tests in fuel cells and water electrolysers also manifested that the chemical structure of PDTP-10 membrane remained intact during short-term durability tests under galvanostatic mode. The above results manifested that AEMs containing hydrophilic crown ether units in the polymer mainchain showed potential in the application for AEM based electrochemical devices.