Nanohybrid membranes with hydroxide ion transport highways constructed from imidazolium-functionalized graphene oxide

Abstract

Graphene oxide (GO) and functionalized GO have been widely employed to design and fabricate polymer–inorganic nanohybrid materials for electrochemical applications. In this study, a series of imidazolium-functionalized graphene oxide (ImGO) nanosheets bearing different types of ligands (namely butyl, decyl, carbethoxy, and benzyl groups) on quaternary ammonium (QA) groups are prepared via distillation–precipitation polymerization and quaternarization, and then embedded into chitosan (CS) to fabricate nanohybrid membranes. The addition of ImGO significantly enhanced the thermal, mechanical, and anti-swelling stabilities of membranes due to the strong electrostatic attractions at CS/ImGO interface. More importantly, hydroxide ion transport highways were constructed at CS/ImGO interface via interfacial interactions. Meanwhile, the influence of the ligands on QA groups on the physicochemical properties, OH⁻ conductivity, and conduction mechanism is systematically elucidated. Due to the optimal hydrophilicity and ion exchange capacity, ImGO with carbethoxy group as the ligand confers the highest OH⁻ conductivity on nanohybrid membrane (up to 1.02 × 10⁻² S cm⁻¹ at 90 °C and 100% RH, about four times of that of CS control membrane). Correspondingly, a fuel cell with such a membrane shows an OCV of 0.71 V and a maximum power density of 75.8 mW cm⁻² at a current density of 298.8 mA cm⁻².