Hiroshi Shioyama

Electrochemical reactions of stage 1 sulfuric acid—Graphite intercalation compound

Abstract By means of cyclic voltammetry, a study of the redox reactions has been made on stage 1 sulfuric acid-graphite intercalation compound (H2SO4-GIC) prepared by anodic oxidation of graphite in sulfuric acid electrolyte. It was found that further oxidation of the stage 1 GIC gives rise to the reversible ionization reaction of carbon atoms in the graphite basal plane and also of sulfuric acid molecules produced in the interlayer spacing. This ionization reaction and the reverse deionization reaction are responsible for plateaus observed in the current vs. potential curve. These redox reactions between the stage 1 GIC and its ionized state were analyzed in situ by means of X-ray diffractometry.

Electrochemical preparation of the graphite bi-intercalation compound with H2SO4 and FeCl3

Abstract Stage-n FeCl3-GICs (n = 2,3) prepared in the standard two-zone method were oxidized galvanostatically in H2SO4. The electrode potential vs. electric quantity curves observed during the treatment and the X-ray powder patterns of the products showed clearly the intercalation of H2SO4 into FeQ3-GICs and the formation of the graphite bi-intercalation compounds (GBCs) of FeCl3 and H2SO4. The c axis repeat distance Ic of the GBCs, 17.38A, from the stage-2 FeCl3-GIC was equal to the sum of those of FeCl3-GIC, 9.38A, and of H2SO4-GIC, 8.00A. From the stage-3 FeCl3-GIC the compound with Ic of 25.38A ( = 9.38A + 8.00A + 8.00A), through the intermediate with Ic of 20.73A ( = 9.38A + 3.35A + 8.00A). The electrochemical reduction of these GBCs suggested that the intercalation of H2SO4 into FeCl3-GICs is reversible.

Electrochemical preparation of the ternary graphite intercalation compound with H2SO4 and H2SeO4

Stage-n H2SeO4-graphite intercalation compounds (GICs) (n = 2,3) prepared by galvanostatic oxidation of graphite in H2SeO4 were transferred into the electrolytic cell filled with H2SO4 and then continued the oxidation. From the observed electrode potential vs. electric quantity curves and the results of measured CSe atomic ratio, it was suggested that H2SO4 was intercalated into stage-n H2SeO4-GICs and the products were ternary GICs of H2SeO4 and H2SO4. When these ternary GICs were reduced electrochemically, at first H2SO4 was deintercalated and then H2SeO4 began to be released. These results may suggest that H2SO4 and H2SeO4 are intercalated in separate interlayer spaces of graphite, i.e. bi-intercalation. Intercalation of H2SeO4 into stage-2 H2SO4-GIC was also observed.