Anhydrous proton exchange membranes comprising of chitosan and phosphorylated graphene oxide for elevated temperature fuel cells

Abstract

© 2015 Elsevier B.V. Phosphonic acid (PA) groups, as one kind of feasible proton carrier, possess the distinct intrinsic proton conduction ability and have triggered intensive attention in proton conducting materials. In this study, phosphorylated graphene oxide (PGO) nanosheets are incorporated into chitosan (CS) matrix to prepare nanohybrid membranes. The microstructure and physicochemical properties of PGO and the membranes are investigated systematically. The grafted polymer layer is found to be about 26wt% of PGO, which considerably increases the ion exchange capacity from 0.44mmolg-1 of GO to 0.79mmolg-1. Compared with CS control and GO-filled membranes, PGO-filled membranes achieve higher thermal and mechanical stabilities due to the strong electrostatic interactions between PGO (-PO3H) and CS (-NH2). PGO provides efficient hopping sites (-PO3H, -PO3-···+3HN-), which allow the formation of highly conductive channels along PGO surface. These channels are found to significantly facilitate proton conduction under both hydrated and anhydrous conditions. Particularly, nanohybrid membrane with 2.5% PGO acquires a 22.2-time increase in conductivity from 0.25mScm-1 to 5.79mScm-1 (160°C, 0% RH). With this benefit, the hydrogen fuel cell using PGO-filled membranes displays much higher cell performance than those using CS control and GO-filled membranes.