Graphite intercalation compounds (GICs) with a layered structure can be formed by an electrochemical process. The specific objective of the present study is to synthesize low- or non- sulfur graphite intercalation compounds which are friendly to the environment. The present work is focused on three aspects as follows: (1) to reduce the sulfur content by partially replacing sulfuric acid in H₂SO₄-GICs by co-intercalation of solvents in dilute sulfuric acid solution; (2) to electrochemically synthesize transition metal-GICs in aqueous solutions which are free of sulfuric acid; and (3) to synthesize organic acid-GICs which are totally free of any corrosive species. The criteria for selecting intercalates have been semiempirically summarized by surveying various kinds of synthesized accepto...[ Read more ]

Graphite intercalation compounds (GICs) with a layered structure can be formed by an electrochemical process. The specific objective of the present study is to synthesize low- or non- sulfur graphite intercalation compounds which are friendly to the environment. The present work is focused on three aspects as follows: (1) to reduce the sulfur content by partially replacing sulfuric acid in H₂SO₄-GICs by co-intercalation of solvents in dilute sulfuric acid solution; (2) to electrochemically synthesize transition metal-GICs in aqueous solutions which are free of sulfuric acid; and (3) to synthesize organic acid-GICs which are totally free of any corrosive species. The criteria for selecting intercalates have been semiempirically summarized by surveying various kinds of synthesized acceptor-type GICs. The data shows that the acidity of the electrolyte solution is more crucial than its oxidizing capability for the electrochemical intercalation.

The GICs have been electrochemically synthesized in ZnCl₂- and FeCl₃- aqueous solutions, in organic acid as well as in dilute sulfuric acid solutions. The synthesized GICs have been characterized using multi-techniques such as XRD, Raman spectroscopy, TGA in addition to chemical analysis. The study of electrochemical behaviors of natural graphite in the H₂SO₄-H₂O and H₂SO₄-CH₃COOH electrolytes shows that the reduction of sulfur content in GIC by diluting the sulfuric acid is possible. ZnCl₂-GICs of stage 3 to 7 and FeCl₃-GICs with stage 2 to 6 structures are electrochemically synthesized in ZnCl₂- and FeCl₃-aqueous solutions without addition of acid. The electrolyte concentration and applied potential play dominant roles in the synthesis process. Formation diagrams of electrochemical synthesis GICs are experimentally obtained in ZnCl₂- and FeCl₃-GICs in aqueous solutions at an elevated temperature. Formic acid-graphite intercalation compounds with stage 3 to 5 structures are synthesized by an electrochemical method wherein formic acid serves as both the electrolyte and the intercalate. The formic acid-GIC exhibits an excellent exfoliation ability at relatively low temperatures. The feasibility of electrochemical intercalation in other organic solutions has been also explored.

[italic]Key [italic]words: Graphite intercalation compounds (GICs), electrochemical synthesis, organic acid, aqueous solution and low- or no-sulfur.