Novel bilayer well-aligned Nafion/graphene oxide composite membranes prepared using spin coating method for direct liquid fuel cells

The objective of this study was to prepare Nafion/graphene oxide (GO) composite membranes for direct liquid fuel cell applications with the aim of decreasing fuel permeability and further increasing cell performance. Nafion 212 (N212) composites of different GO content and local packing density were manufactured using drop coating and spin coating methods. The GO loading in the resulting composites had a positive correlation with the water uptake, ion exchange capacity, and ionic conductivity of the samples. However, the fuel permeability and water diffusivity were not dependent on the GO content in the composite membranes. Rather, the fuel permeability was related to the arrangement, including orientation and local packing density, of the GO in the composites. The Cussler model was used to describe the fuel barrier property of the N212/GO, and the spin-coated composite membranes had a higher effective aspect (width to thickness) ratio, leading to a higher degree of permeability reduction than was achieved in the drop-coated samples. The spin-coated composite with 0.067% GO loading exhibited double peak power densities than the pristine N212 in direct methanol, ethanol, and formic acid fuel cells. The well-aligned thin top layer of GO contributed to the excellent fuel cell performance.