ИСТИНА

The aim of this work was to investigate the solvent’s influence on the formation and properties of graphite intercalation compounds (GIC) obtained in the graphite – H2SO4 – R system, R = H2O, C2H5OH, CH3COOH, C2H5COOH. Synthesis of GICs was carried out by anodic polarization of HOPG in complex electrolyte with different H2SO4 concentration (10 – 94 %) under galvanostatic conditions. The investigation of graphite – H2SO4 – H2O system shows decreasing H2SO4 concentration in the electrolyte leads to stage number increasing. It was confirmed that threshold of sulfuric acid intercalation in aqueous solutions is about 10 % H2SO4. Substitution of water for ethanol is accompanied by the rise of intercalation threshold to 70 % H2SO4, where graphite bisulphate (GB) II stage could be obtained. Use a number of physicochemical methods confirmed the absence of water or ethanol co-intercalation into graphite matrix. And the final product is GB with composition C7.7nH2SO4, n – stage number. Ternary GICs, contained molecules of sulfuric and organic acids, were synthesized with carbonic acids such as CH3COOH and C2H5COOH. The mechanism of TGIC with C2H5COOH formation differs from the one for TGIC with CH3COOH or HCOOH. Two – steps mechanism proposed for the formation of ternary GICs with HCOOH or CH3COOH: firstly only H2SO4 intercalation takes place and then organic acid or its mixture with sulfuric acid intercalates. In case of C2H5COOH – H2SO4 solutions firstly unstable TGIC are obtained and further polarization leads to GB formation. The concentration areas of H2SO4 where TGIC at identical stage number exists are the same for acetic and propionic solutions. The compositions of ternary GIC were determined by complex of physicochemical methods: C7.8n(H2SO4)0.52(CH3COOH)0.48, C7.6n(H2SO4)0.75(C2H5COOH)0.25, n – stage number. The results obtained in the graphite – H2SO4 – R system shown that decreasing of H2SO4 concentration caused 1) smoothing of charging curves and their displacement to higher potentials, 2) increasing of the stage number. Thermal analysis, including STA (TG + DSC) coupled with IR – spectroscopy and mass – spectrometry, of the samples shown that GIC obtained in the complex electrolyte are less stable than GB. It is reflected in decrease of TGIC’s decomposition temperature for 20 – 30 oC. The enthalpies and temperatures of decomposition were determined.