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The sulfur-doped graphene oxide/graphite oxide composite material was synthesized in an original way, and a detailed study of its structural arrangement was carried out using XRD and Raman spectroscopy. Negative differential resistive properties of the obtained material were observed on the current-voltage curve at room temperature as a result of limited proton hopping through water molecules adsorbed on the hydrophilic surface of graphene oxide layers in the presence of a sulfur-enriched graphite oxide component with high electron conductivity, which promotes spatial charge separation and increases the efficiency of H+ transport. The obtained result offers a new way for the one-pot synthesis of new graphene-based composite materials with a wide range of possible applications.

The aim of this paper is the comparison of structural, morphological and electrical properties of thermally extended graphite synthesized by chemical oxidation of graphite with sulfur of nitric acids at all other same conditions. Thermal treatments of graphite intercalation compounds were performed at a temperature of 600°C on the air for 10 min but additional annealing in temperature range of 100-600oC for 1 hour was done. The obtained materials were characterized by XRD, Raman spectroscopy and impedance spectroscopy. The evolution of structural ordering of thermally extended graphite samples at increasing of annealing temperature was traced. It was determined that the additional annealing allows to control the electrical conductivity and structural disordering degree of extended graphite samples that is useful for preparation of efficient current collectors for electrochemical capacitors.

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Graphene oxide (GO) colloidal solution has been synthesised by the modified Tour method, in which the pH of the reaction medium has been increased to 2.0-2.2 at the final stage of graphite oxidation by adding NaOH solution. The solid-phase graphene oxide consists of multilayered graphene particles with a thickness of about 7.5 nm (9-10 layers of graphene) and an average size of about 7.7 nm. Reduced graphene oxide (rGO) has been prepared by hydrazine and microwave reduction. A comparative study of the structure, morphology, and electrical transport properties of rGO samples obtained by various methods has been carried out using XRD, SAXS, Raman spectroscopy, low-temperature nitrogen adsorption, and impedance spectroscopy. Structural analysis has shown the presence of two fractions of plate-like rGO particles for each reduction method, which consist of 4-6 layers of graphene in stacks and have a lateral size in the range of 7.1-7.6 nm. The BET specific surface area of the microwave-reduced rGO was higher than that of the chemically reduced one (296 and 237 m 2 g −1 respectively). The frequency dependence (10 −2 -10 5 Hz) of the AC conductivity of the GO and rGO samples has been analysed in the temperature range of 25 °C-175 °C. For the GO sample, the proton exchange conductivity mechanism dominates. A Drude-like response of electrical conductivity at frequencies above 10 3 Hz with transition to Johnscher's law response at 175 °C has been observed for rGO samples obtained using both chemical and microwave routes. Changes in activation energies and relaxation times have been interpreted using a model of a thermally activated frequency-dependent electron hopping mechanism between randomly coupled conducting sp 2 rGO packages separated by disordered sp 3 rGO regions with correspondingly higher resistivity.

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