Synthesis and properties of anion conductive ionomers containing fluorenyl groups for alkaline fuel cell applications

Abstract

A series of anion conductive aromatic ionomers, poly(arylene ether)s containing different polymer backbones and quaternized ammonio-substituted fluorenyl groups, were synthesized via nucleophilic substitution polycondensation, chloromethylation, quaternization, and the subsequent ion exchange reactions. The ion exchange capacity (IEC) of the ionomers was controlled to be from 0.68 to 2.54 meq. g⁻¹ by the chloromethylation reaction conditions. The designed chemical structures were well-characterized by the ¹H NMR spectra. The ionomers provided ductile and transparent membranes. The ionomer membranes were thermally stable up to 180 °C under nitrogen and mechanically stable with 48 MPa of the maximum stress at 80 °C and 60% RH (relative humidity). High hydroxide ion conductivity up to 50 mS cm⁻¹ was achieved at 30 °C in water for the ionomer membrane bearing sulfone/ketone structures and the highest IEC (2.54 meq. g⁻¹). The membranes were durable in hot water (80 °C) for 1000 hours. These properties of the ionomer membranes seem promising as an anion exchange membrane for alkaline fuel cells.