Electrochemical intercalation in the graphite–H2SO4–R(RCH3COOH, H3PO4) system Original Research Article

The anodic oxidation of highly oriented pyrolitic graphite (HOPG) in the mixture H2SO4–R (RCH3COOH, H3PO4) with concentration of H2SO4 in the range 0–100 wt% was investigated in this research work. Galvanostatic oxidation of graphite in H2SO4–R solution allows one to obtain stages 1–5 graphite intercalation compounds (GICs). The presence of R in the electrolyte solutions significantly expands the concentration limit for intercalation down to 1 wt% of H2SO4. The co-intercalated stages 1 and 2 H2SO4–CH3COOH–GICs with di=7.94 Å were obtained in 60–80 wt% of H2SO4 solution. The stages 1–3 co-intercalated H2SO4–H3PO4–GICs with di=8.08–8.20 Å were synthesized for the first time. It was shown that the form of galvanostatic curve E(Q) is determinated by the content of strong intercalate H2SO4. It was established that the potential of intercalation Eint of the stages 1–3 co-intercalated GICs and the quantity of electricity (Q) are higher than Eint and Q for the formation of binary GICs (graphite hydrogensulfate). The enhancement of the potential barrier for intercalation gives the evidence of the co-intercalation of H2SO4 with CH3COOH or H3PO4 in graphite matrix. The mechanism of co-intercalation of graphite was proposed.