Electrochemical Synthesis of Graphite-Tetrafluoroaluminate Intercalation Compounds

Abstract

Graphite tetrafluoroaluminate intercalation compounds (AlF4-GICs) have been prepared by electrochemical oxidation of a natural graphite electrode in a 1.0 M nitromethane solution of tetraethylammmonium tetrafluoroaluminate ([TEA][AlF4]). Galvanostatic electrolysis suggests that the intercalation reaction occurs above 0.8 V vs. Ag + /Ag. Powder X-ray diffraction measurements of the AlF4-GIC obtained by potentiostatic electrolysis reveal that the most AlF4-rich phase is the stage-3 GIC with a gallery height of 0.79 nm. This gallery height agrees with the theoretical value calculated from the size of AlF4that locates its twofold axis perpendicular to the graphite layers. Co-intercalation of the solvent is suggested by the composition of the stage-3 GIC (C55AlF4) and is confirmed by release of the solvent above 350 K during thermogravimetric analysis. Although the AlF4-GIC shows the higher air stability than those of the GICs with typical inorganic complex anions, it slowly decomposes into GICs at higher stages after exposure to the air over 1000 h. Increase of gallery height was observed during this period, which possibly results from reorientation of AlF4between the layers. The thermodynamic stability of AlF4-GIC is evaluated based on a Born-Harber cycle.

Expansion of tetrachloroaluminate-graphite intercalation compound by reaction with anhydrous hydrogen fluoride

“…The AlCl 3 -GIC compound prepared from HOPG was reacted with aHF at three different temperatures, 25, −30, and −80 °C and the products of these reactions are abbreviated as EG (25), EG(−30), and EG(−80). In contrast to our expectation, this reaction did not result in formation of tetrafluoroaluminate-GIC [22,23] but in formation of expanded graphite. During the reaction, bubbles, which were clearly visible in aHF, were generated from surface of AlCl 3 -GIC at all the reaction temperatures.…”

Preparation, Characterization, and Structure Trends for Graphite Intercalation Compounds Containing Pyrrolidinium Cations

“…Graphite is a prototypical and also technologically important intercalation host, and graphite intercalation compounds (GICs) have long been studied for their interesting and useful structures and properties. − Either cations or anions, sometimes accompanied by neutral co-intercalates, can be introduced between the graphene layers via chemical or electrochemical redox reactions to form a variety of GICs. The accompanying reduction or oxidation of the graphene sheets results in so-called donor-type or acceptor-type GICs, respectively. − Graphite is unique in forming highly ordered stages, i.e., ordered sequences of graphene sheets and intercalate galleries, where the stage number is the sequence descriptor . In a stage-1 GIC, each graphene sheet is separated from the others by intercalate galleries, whereas a stage-2 GIC has two adjacent graphene sheets contained between intercalate galleries, etc.…”

Anion Intercalation into Graphite Cathodes in K+‐containing High‐Voltage Electrolytes: Problems Associated with Counter Anodes

“…A number of anionic species were proved appropriate for this purpose, including PF 6 − , AlCl 4 − , (CF 3 SO 2 ) 2 N − , and so . For example, PF 6 − is known to form PF 6 − /C 24 + , corresponding to a theoretical capacity of 93 mAh/g .…”