Chemical modification of proton exchanger sulfonated polystyrene with sulfonated graphene oxide for application as a new polymer electrolyte membrane in direct methanol fuel cell

Abstract

A novel composite membrane is prepared by the dispersion of sulfonated graphene oxide (SGO) in sulfonated polystyrene–polyethylene (SPS-PE) for electrolyte in direct methanol fuel cell. For sulfonated polystyrene used the method that patented by Makowski et al. Graphene oxide (GO) is prepared by modified Hummer's method and is further functionalized with SO3-H. SGO is then incorporated in SPS-PE matrix using solvent cast method to form composite membrane. The composite membranes are characterized by FT-IR, TGA and SEM. Oxidative resistance, water uptake, ionic conductivity and methanol permeability are measured to evaluate its performance in a direct methanol fuel cell with cation exchanger membrane. The membranes were confirmed to retain 1–5% water vapor at 80–140 °C in air due to the hydrophilic of highly SPS and SGO. The ionic conductivity and permeability of the membrane to methanol was found to increase with temperature increasing. The membrane SGO-SPS–PE shows the proton conductivity of 2.74 × 10-2 S cm-1 at 100 °C without extra humidity supply and is very promising for high temperature with low humidity. The high proton conductivity is ascribed to the unique composition in which the heterocyclic polymer provides the proton motion by construction diffusion and the highly SGO-SPS copolymer retains water vapor to lower the activation energy for proton conduction.