INTERCALATION OF SULFURIC-ACID INTO GRAPHITE - FOLLOWED BY POTENTIAL MEASUREMENT

Electric potential of graphite during intercalation of sulfuric acid by chemical oxidation was found to increase in stepwise to positive direction, and reflect the change in stage structure of graphite intercalation compounds with sulfuric acid (H2SO4-GICs). It was shown that the intercalation behavior of sulfuric acid into graphite by the chemical oxidation method could be followed by in-situ measurement of electric potential. From the potential change, the intercalation process of sulfuric acid by the chemical oxidation method was found to be fundamentally the same as that by electrochemical one. The intercalation reaction is divided into two processes; one is charging process of host carbon layers corresponding to the potential increase and another is transformation process of stage structure in GICs showing the plateau on the potential curve. The potential increase of graphite in sulfuric acid solution by the chemical oxidation process was limited by the equilibrium potential of redox reaction of oxidant used, which is determined on the activities of each chemical species in the solution. Effects of dilution of sulfuric acid on the formation of H2SO4-GICs could be explained in term of the balance between the upper limit of saturated potential in the chemical oxidation and the onset potential for each stage structure. The intercalation behavior of sulfuric acid by the chemical oxidation process depended strongly on the structure and the texture of host carbon materials. The effect of host carbon materials on the potential change during the chemical intercalation could be explained on the basis of competition of reaction rates between the charging of carbon layers and the stage transformation in the gallery.