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.

中文翻译：

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揭示氧化石墨烯表面水介导的质子传导机理

氧化石墨烯（GO）片的质子传导能力为高性能固态电解质的设计开辟了新途径，这在燃料电池和液流电池等领域迫切需要。然而，GO片的质子传导机理仍不清楚，阻碍了GO基质子传导电解质的优化和进一步利用。在这项工作中，我们系统地研究了涉及水分子的GO片表面的质子传导行为。我们发现，环氧基和羟基官能团都可以有效地将水分子吸引到GO片的表面上，形成致密的氢键网络。质子可以通过氢键网络在具有低能垒的相邻以及不相邻的羟基官能团之间跳跃。另一方面，环氧基官能团的质子传导能力较低，很少观察到自发的质子传导。我们的工作表明，增加羟基官能团的含量可以导致GO片的质子电导率更高。