Revealing the Mechanism of Graphene Oxide Reduction by Supercritical Ethanol with First-Principles Calculations

Recently, graphene and graphene oxide (GO) have become renowned for versatile applications in clean-energy technology, motivating extensive research for a large-scale production of graphene by GO chemical reduction. In this work, we investigate the mechanism of GO reduction by the supercritical liquid of ethanol using first-principles calculations. The supercell and cluster models for graphene sheet with an epoxy group are built, and the pseudopotential plane-wave and Gaussian-type atomic orbital methods are applied to the supercell and cluster models, respectively. After careful identification of intermediate states for GO + CH3CH2OH complexes along three different routes, we determine the reaction pathways and activation barriers, revealing which route has the fastest reaction velocity. We calculate the reaction enthalpies, demonstrating that the hydrogen donations from ethanol are endothermic reactions, but the GO reductions by ethanol accompanied with its hydrogen donation are exothermic reactions. We further highlight the solvent and entropy effects, which can significantly enhance the GO reduction, especially above the supercritical temperature. Our work may reveal the mechanism of GO reduction with supercritical alcohol and also contribute to opening an alternative way of graphene synthesis.