▎ 摘　　要

Recent experimental reports on in-plane proton conduction in reduced graphene oxide (rGO) films open a new way for the design of a proton-exchange membrane essential for fuel cells and chemical filters. In humid conditions, water molecules attached to the rGO sheet are expected to play a critical role in this membrane, but theoretical studies of their involvement are scarcely found in the literature. In this study, we investigate proton migration on water-adsorbed monolayer and bilayer rGO sheets using first-principles calculations to reveal the mechanism. We devise a series of models for water-adsorbed rGO films by systematically varying the reduction degree and water content, and we optimize their atomic structures in reasonable agreement with experiments using a density functional that accounts for van der Waals correction. After suggesting two different transport mechanisms, epoxy-mediated hopping and water-mediated hopping, we determine the kinetic activation barriers for these in-plane proton transports on the rGO sheets. Our calculations indicate that water-mediated transport is more likely to occur due to its much lower activation energy than epoxy-mediated transport and reveal new prospects for developing efficient solid proton conductors.