Sulfonated graphene oxide/Nafion composite membranes for high-performance direct methanol fuel cells

An easy and effective method for producing low methanol-crossover membranes is developed by dispersing sulfonated graphene oxide (SGO) into a Nafion matrix. A SGO/Nafion mixture with low SGO content exhibits unique viscosity behavior and allows for better SGO dispersion within the Nafion. After film casting, the composite membranes show lower methanol and water uptakes, a reduced swelling ratio, improved proton conductivity in low relative humidity, and extremely high methanol selectivity, which can be implemented in direct methanol fuel cells (DMFCs). The regular backbone of the composite membrane shows a higher storage modulus, increased α-relaxation (transition temperature), and improved tolerance to pressure during membrane electrode assembly (MEA). The small angle X-ray spectra indicate the shrinkage of the ionic clusters in the composite membranes, which thus reduce methanol crossover. The hybrid membranes applied to DMFCs demonstrate performances superior to that of the commercial Nafion 115 in 1 M and 5 M methanol solutions.