A sudden cathodic jump appearing on the potentiodynamic curves during subsequent electrochemical intercalation of 18 m sulphuric acid into chromium trioxide-graphite intercalation compounds (CrO3-GICs) is preserved for CrO3-GICs heated at a temperature lower than that of the decomposition of the intercalate, but vanishes completely after CrO3-GICs are thermally transformed into the physical mixture of graphite and lower chromium oxides. The results have shown that CrO3-GICs can be prepared, not only by the solvent method but also by the impregnation-dry method. Using a potentiodynamic technique involving the thermal modification of CrO3-GICs it has been possible to demonstrate the presence of an intercalation phase for CrO3-GICs which have unclear X-ray diffraction patterns.