Abstract
The effect of interlayer distance and oxygen content on proton conductivity of graphite oxide is presented. Bulk-state proton conductivities were measured using coin-shaped pellets of three different graphite oxide samples, namely, H-GO, S-GO, and B-GO, generated respectively from the techniques of Hummers, Staudenmaier, and Brodie. The extent of oxidation, nature of functional groups, interlayer distances, and morphologies are studied through Raman spectroscopy, XPS, powder XRD pattern, and SEM images. The proton conductivities follow the trend H-GO > S-GO > B-GO. In the XPS study, the total oxygen contents were found to follow the trend H-GO > B-GO > S-GO, whereas the interlayer distances obtained from the powder XRD patterns show the trend H-GO > S-GO > B-GO. Beside the nature of the functional groups and extent of oxidation, the interlayer distance displays a significant effect on the proton conductivity values. The temperature-dependent Arrhenius plots reveal the activation energy (E-a) of the samples as 0.274, 0.291, and 0.296 eV. These low E-a values imply the Grotthuss mechanism for proton conduction. The high conductivity value and low activation energy of H-GO with a maximum interlayer distance indicate that hydronium ion's rotational movement and re-formation of hydrogen bonds by the Grotthuss mechanism are supported by a more flexible interlayer. We propose that this physical insight might be considered to improve the proton conductivity through modulating layer distances not only in carbon allotropes but also in other materials.