Enhancing hydroxide conductivity of anion exchange membrane via incorporating densely imidazolium functionalized graphene oxide

Abstract

This study presents a generic method to increase the hydroxide conductivity of anion exchange membranes by tuning the microphase separation structure. Graphene oxide was functionalized with macromolecular brushes for the first time by a precipitation polymerization method. Densely-functionalized imidazolium groups were aligned in the configuration of macromolecular brushes to act as hydroxide-conductive groups, which endow the functionalized graphene oxide with a high ion exchange capacity value of 3.05 mmol g−1. Polymer-inorganic composite membrane for anion exchange membrane fuel cell was fabricated by incorporating the imidazolium-functionalized graphene oxide into imidazolium-functionalized bisphenol A-type polysulfone. The dense imidazolium groups manipulated the aggregation of conductive groups at the polymer/filler interfaces to induce the well-defined microphase structure of composite membranes, constructing low-resistance channels for ionic transport. The activation energy of hydroxide transport in composite membranes was reduced to 25.17–13.62 kJ mol−1, in comparison with 28.63 kJ mol−1 for control membrane. The hydroxide conductivity of composite membrane was elevated to 22.02 mS cm−1 at 30 °C, which is 2.10 times of that for control membrane. The maximum power density of single fuel cell of 78.7 mW cm−2 at 60 °C was thus achieved.