POTENTIAL CHANGE WITH INTERCALATION OF SULFURIC-ACID INTO GRAPHITE BY CHEMICAL OXIDATION

Potential of graphite during the intercalation of sulfuric acid by chemical oxidation with either nitric acid or potassium permanganate in H2SO4 of 18 mol/dm3 was found to increase to positive direction in stepwise. On potential change, a distinct plateau corresponding to the transformation from stage two to one compound and a faint one for the formation of stage three were observed, exactly the same as those observed during galvanostatic oxidation. The intercalation of sulfuric acid into graphite by chemical and electrochemical oxidations was shown to be fundamentally the same processes; potential of graphite increases with oxidation and the intercalation of sulfuric acid proceeds by showing potential plateaux. On the change of potential of graphite by chemical oxidation, there was found to be an upper limit of saturated potential, depending strongly on the oxidizer used and also on the concentration of sulfuric acid even if enough amounts of oxidizer was used. The relation between the threshold potential for stage transformation in H2SO4-GICs, increasing with dilution of sulfuric acid, and the upper limit of saturated potential by chemical oxidation, decreasing with dilution of the acid, governed the intercalation reaction by chemical oxidation in sulfuric acid with various concentrations. © 1990.