Zwitterion-coated graphene-oxide-doped composite membranes for proton exchange membrane applications

Zwitterion-coated graphene oxide (ZC-GO) containing ammonium and sulfonic acid groups was synthesized, and various amounts were incorporated into polybenzimidazole (PBI). The effect of the ZC-GO content on the properties of PBI/ZC-GO composite membranes for direct methanol fuel cell (DMFC) applications was investigated. The structure of ZC-GO was confirmed using Fourier-transform infrared spectroscopy, and the purity and structure of PBI were investigated using proton nuclear magnetic resonance spectroscopy. With increasing ZC-GO content, the proton conductivity, methanol permeability, water uptake, and swelling ratio of the composites increased, whereas the thermal stability decreased. Notably, the composite membrane containing 25   wt% ZC-GO exhibited a high proton conductivity (4.12×10 −2   S   cm −1 at 90   °C and RH 100%) and low methanol permeability (1.38×10 −7   cm 2   s −1 at 25   °C), which is much lower than that of Nafion 117 under the same conditions. The excellent properties of the composite membranes can be attributed to the homogeneous dispersion of ZC-GO and the formation of proton-transport channels in the membranes. This investigation demonstrates the potential of PBI/ZC-GO composite membranes for DMFC applications.