Synthesis of intercalation compounds in the graphite-HNO3-H3PO4 system

The highly oriented pyrolytic graphite-HNO3-H3PO4 system was studied by x-r ay diffraction and potentiometry at different acid concentrations. The resu lts demonstrate that chemical and electrochemical intercalation in the grap hite-98% HNO3-85% H3PO4 system yields graphite nitrate, a binary graphite i ntercalation compound (GIC). H3PO4 is shown to have an ambiguous effect on the concentration ranges of different stages of graphite nitrate, shifting them to lower HNO3 concentrations as compared to the graphite-HNO3-H2O syst em. In the graphite-98% HNO3-100% H3PO4 system, a stage II ternary GIC is o btained, with an intercalate layer thickness d(i) similar or equal to 4.7 A ngstrom. Stages II-VI of this GIC were prepared via exchange reaction betwe en graphite nitrate and 100% H3PO4 A mechanism for the formation of the ter nary GIC is proposed. The synthesis of the cointercalated GIC is likely to involve two steps: in the first step, graphite nitrate is formed; subsequen t reaction in the intercalate layer leads to partial replacement of solvate d HNO3 by H3PO4 molecules.