Modified CNTs/Nafion composite: The role of sulfonate groups on the performance of prepared proton exchange methanol fuel cell's membrane

A novel Nafion®-based nanocomposite membrane was synthesized to be applied as direct methanol fuel cells (DMFCs). Carbon nanotubes (CNTs) were coated with a layer of silica and then reacted by chlorosulfonic acid to produce sulfonate-functionalized silicon dioxide coated carbon nanotubes (CNT@SiO2-SO3H). The functionalized CNTs were then introduced to Nafion®, and subsequently, methanol permeability, proton conductivity, ion exchange capacity (IEC) and water uptake properties of the prepared membranes were investigated. The experimental results showed that the water uptake and IEC of the Nafion®/CNT@SiO2-SO3H (1 wt%) membrane increased in comparison with the recast Nafion®. IEC was enhanced from 0.9 meq/g for the recast Nafion® to 0.946 meq/g for Nafion® /CNT@SiO2-SO3H, which could be attributed to the presence of sulfonate groups on the surface of CNTs. In addition, the proton conductivity of the sulfonate modified CNT/Nafion® composite was enhanced in a wide range of temperatures. Selectivity of the fabricated membrane was found to be more than 8-fold higher than that of recast Nafion® 117, demonstrating the promising potential of the produced membranes for DMFC applications.