Graphene quantum dot reinforced hyperbranched polyamide proton exchange membrane for direct methanol fuel cell

Abstract

The hyperbranched macromolecule (HBM) polyamide proton exchange membrane with uniform 3D matrix topology is beneficial to the enhancement of proton conductivity. In order to extend the application of HBM in direct methanol fuel cell (DMFC), graphene oxide (GO) and graphene quantum dot (GQD) are incorporated into HBM to enhance the proton/methanol selectivity of the membrane. The functional groups on GO and GQD surface would interact with –SO3H groups in HBM by the hydrogen-bond interaction and participate in the proton conductive channel construction. And the GO and GQD in the composite can effectively prevent the permeation of methanol molecules. Most important, the HBM membrane filled by GQD (GQD-HBM) can effectively avoid large scale phase separation which occurs in HBM membrane filled by GO (GO-HBM) due to the greater size of GO. Proton conductivity of GQD-HBM (0.30 S/cm) is 17% improved compared with the pristine HBM while methanol permeability is significantly reduced by ca. 50% due to the physical barrier of GQD. The proton/methanol selectivity is therefore enhanced by more than 80% and the DMFC performance is also significantly enhanced.