Nanocomposite membranes of surface-sulfonated titanate and Nafion® for direct methanol fuel cells

Various thiol and sultone groups were grafted onto the surface of titanate nanosheets to render organic sulfonic acid (HSO₃–) functionality. The nanocomposite membranes were cast together with Nafion^® using these materials as inorganic fillers. Nanocomposite membranes containing surface-sulfonated titanates showed higher proton conductivity than composite membranes containing untreated TiO₂ P25 particles. They showed better mechanical and thermal stability than Nafion alone. The methanol permeability of nanocomposite membranes decreased with increasing the content of the sulfonated titanate in the nanocomposite membranes. The relative permeability of methanol through these composite membranes with 2 and 5 M methanol solutions was reduced by up to 38 and 26%, respectively, relative to pristine Nafion 115 membranes. The membrane electrode assembly using Nafion/sulfonated titanate nanocomposite membranes exhibited up to 57% higher power density than the assembly containing a pristine Nafion membrane under typical operating conditions of direct methanol fuel cells.