Surface modification of sulfonated poly(ether ether ketone) membranes using Nafion solution for direct methanol fuel cells

Sulfonated poly(ether ether ketone) (SPEEK) membranes were used as support material for Nafion–SPEEK–Nafion (NSN) composite membranes. The NSN composite membrane was prepared by immersing the SPEEK in the Nafion-containing casting solution. The resulting composite membranes were mechanically durable as we selected a suitable degree of sulfonation (DS) of PEEK, and we expect the composite membranes to be of low methanol permeability and high proton conductivity relative to pure SPEEK membranes. The proton conductivity and methanol permeability properties of the composite membrane were measured, and the effect of proton conducting layer was discussed with an empirical equation. It was found that the proton conductivity of the composite membrane exceeded that of the SPEEK membrane under the same condition. The methanol permeability of NSN membrane was higher than that of the same thick SPEEK membrane. The direct methanol fuel cell (DMFC) performance of the NSN membrane was better than that of the SPEEK membrane at 60 °C using 1 M methanol solution.