Thermodynamic data for anodic solid state graphite oxidation products in 96% sulphuric acid

Abstract

Graphite hydrogen sulphates (GHS) of stages 1 to 4 and graphite oxide (GO) with the nominal compositions C 8OH and C 2.65OH were prepared by anodic oxidation of natural graphite in 96% H 2SO 4. The degree of oxidation was controlled potentiostatically or galvanostatically, and it was determined by coulometry. From the oxidation potentials U and the negative temperature coefficients dU dT , the following thermodynamic data were derived for 298 K per mole graphitic carbon ( ΔG and ΔH in kJ mole −1, ΔS in J mol −1 K −1): C 48HSO 4 ΔG 0 = 2.06 C 24HSO 4 ΔG 0 = 4.98 ΔS 0 = −0.45 ΔS 0 = −1.27 ΔH 0 = 1.92 ΔH 0 = 4.59 C 8(OH) ΔG 0 = 19.9 C 2.65(OH) ΔG 0 = 66.2 ΔS 0 = −16.2 ΔS 0 = −61.5 ΔH 0 = 15.1 ΔH 0 = 46.9 Reasons are given for the possibility of a thermodynamic treatment of the electrochemical data obtained in the overoxidation region. A stoichiometric number of ν = 9 could be found for the number of water molecules cointercalated per anion and per two solvate acid molecules.