Modification of proton-conducting perfluorinated membranes with graphene oxide

Composite proton-conducting membranes with graphene oxide based on a perfluorinated copolymer of the Aquivion${}^\circledR$ type were obtained by casting a mixture of components onto a substrate with subsequent evaporation of the solvent. At fractions of $C_{\mathrm{GO}}\ge$ 0.05 weight%, graphene oxide as a modifier in the matrix created large-scale fibril-type structures (cross size $\sim$1 mm) with parallel packing on scales $\sim$10 mm. Within the fibrils, scanning electron microscopy data revealed a parallel packing of graphene oxide sheets alternating with polymer layers. At $C_{\mathrm{GO}}$ = 0.1 and 0.2 weight% tensile tests of samples along the fibrils showed increased elastic modulus and elastic limit relative to the data for transverse deformation. Less modifier fractions (0.02; 0.05 weight%) caused strengthening, an increase in the deformation resource and proton conductivity ($\sim$10%, data for 22; 50$^\circ$С) mainly along the fibrils. The found relationship between the structure, mechanical and conductive properties of composites with variation in the modifier fraction will allow for the targeted design of the membranes, regulating their properties and degree of anisotropy.