Impact of synthesis conditions on physicochemical and transport characteristics of graphene oxide laminates

In this study, the effect of oxidation conditions during the synthesis process of graphene oxide (GO) flakes on transport characteristics of GO laminates is investigated. Transport properties of the GO laminates synthesized by different oxidation methods are characterized by measuring their ionic conductivity (via proton conductivity) and mass diffusion of species (via methanol permeability). These properties are observed to be significantly different for each sample owing to the difference in their physicochemical properties. It is determined that the two key parameters that dictate the transport characteristics of a GO laminate are the GO oxidation level and flake size. Through a parametric study, it is determined that at a constant oxidation level methanol permeability decreases linearly with increasing the GO mean flake size while changes in proton conductivity remain insignificant. This behavior is attributed to difference in adopted conduction pathways of protons and methanol molecules. With increasing the oxidation level, proliferation of surface defects is deductively reasoned to be the dominant factor responsible for a large increase in the measured methanol permeability. The proton conductivity is also significantly increased with increasing the oxidation level because of greater number of ion exchange sites, shortened transport pathway and increased GO flakes inter-layer spacing.