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

Abstract

The highly oriented pyrolytic graphite–HNO3–H3PO4system was studied by x-ray diffraction and potentiometry at different acid concentrations. The results demonstrate that chemical and electrochemical intercalation in the graphite–98% HNO3–85% H3PO4system yields graphite nitrate, a binary graphite intercalation compound (GIC). H3PO4is shown to have an ambiguous effect on the concentration ranges of different stages of graphite nitrate, shifting them to lower HNO3concentrations as compared to the graphite–HNO3–H2O system. In the graphite–98% HNO3–100% H3PO4system, a stage II ternary GIC is obtained, with an intercalate layer thickness di≃ 4.7 A. Stages II–VI of this GIC were prepared via exchange reaction between graphite nitrate and 100% H3PO4 . A mechanism for the formation of the ternary GIC is proposed. The synthesis of the cointercalated GIC is likely to involve two steps: in the first step, graphite nitrate is formed; subsequent reaction in the intercalate layer leads to partial replacement of solvated HNO3by H3PO4molecules.