SULFATE GRAPHITE-INTERCALATION COMPOUNDS - NEW ELECTROCHEMICAL DATA AND SPONTANEOUS INTERCALATION

During the electrochemical intercalation and deintercalation processes of sulfuric acid into graphite, the electrical resistivity along the graphene layers was followed with a contactless method. At 20 degrees C, the intercalation process is associated with a large decrease of resistivity; the lowest values are observed for stages 8 to 5 formation, and remain nearly constant until stage 1. However, the intercalation reaction is limited by the oxidation of sulfuric acid and by graphite overoxidation; these effects appear for an apparent charge transfer of C-10(+). Between 190 and 300 degrees C (1 or 1000 bar), pure sulfuric acid intercalates readily into graphite without external chemical or electrochemical oxidation. The formation of sulfate GIC is related to the decomposition of H2SO4 progressively evolving sulfur trioxide, which is a powerful oxidizing agent. Oxidation reaction, increasing with temperature above 250 degrees C, is expressed by the apparition of corrosion holes. The samples have been characterized by X-ray diffraction, resistivity measurements, and scanning electron microscopy.