Unraveling the Water-Mediated Proton Conduction Mechanism along the Surface of Graphene Oxide

The proton conduction capability of graphene oxide (GO) sheets opened up a new avenue for the design of high-performance solid-state electrolytes, which is urgently needed in areas such as fuel cells and flow batteries. However, the proton conduction mechanism of GO sheets is still unclear, impeding the optimization and further utilization of GO-based proton-conducting electrolytes. In this work, we systematically investigate the proton conduction behavior on the surface of GO sheets with water molecules involved. We find that both epoxide and hydroxyl functional groups can effectively attract water molecules onto the surface of GO sheets to form a dense hydrogen-bonding network. Protons can hop between adjacent as well as nonadjacent hydroxyl functional groups with low energy barriers through the hydrogen-bonding network. On the other hand, the proton conduction capability of epoxide functional groups is relatively low, and spontaneous proton conduction can rarely be observed. Our work suggests that increasing the content of hydroxyl functional groups can lead to a higher proton conductivity of GO sheets.