Sulfonic acid functionalized graphene (S-graphene) is explored as a potential inorganic filler as well as a solid acid proton conducting medium to realize a hybrid membrane with Nafion for a direct methanol fuel cell (DMFC). The simple, but effective, functionalization of graphene is performed by sulfonic acid containing aryl radicals to increase the number of sulfonate groups per unit volume of graphene domain. Nafion-S-graphene hybrid membranes increase compactness of ionic domains and enhanced proton conductivity while restricting the methanol crossover across the membrane. DMFCs with a Nafion-S-graphene (1 wt %) hybrid membrane deliver a peak power density of 118 mW cmc at a load current density of 450 mA cm(-2) while operating at 70 degrees C under an ambient pressure. By contrast, operating under identical conditions, a peak power density of 54 mW cm(-2) at a load current density of 241 mA cm(-2) is obtained with the pristine recast Nafion membrane. The Nafion-S-graphene hybrid membranes are extremely beneficial and useful for DMFCs in addressing many critical problems associated with commercial Nafion membranes.