Proton conductivities of graphene oxide nanosheets: Single, multilayer, and modified nanosheets

Abstract

Proton conductivities of layered solid electrolytes can be improved by minimizing strain along the conduction path. It is shown that the conductivities (σ) of multilayer graphene oxide (GO) films (assembled by the drop-cast method) are larger than those of single-layer GO (prepared by either the drop-cast or the Langmuir-Blodgett (LB) method). At 60 % relative humidity (RH), the σ value increases from 1×10-6 S cm-1 in single-layer GO to 1×10-4 and 4×10-4 S cm -1 for 60 and 200 nm thick multilayer films, respectively. A sudden decrease in conductivity was observed for with ethylenediamine (EDA) modified GO (enGO), which is due to the blocking of epoxy groups. This experiment confirmed that the epoxide groups are the major contributor to the efficient proton transport. Because of a gradual improvement of the conduction path and an increase in the water content, σ values increase with the thickness of the multilayer films. The reported methods might be applicable to the optimization of the proton conductivity in other layered solid electrolytes. High proton conductivities in multilayer graphene oxide (GO) at room temperature facilitate the use of GO as a solid electrolyte in various cells. The conductivities of multilayer GO films are larger than those of single-layer films by several orders of magnitude, which implies that protons move more easily in the interlayers than on the surfaces. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.