The Electrochemical Synthesis of the Graphite Intercalation Compounds Containing Tetra-n-alkylammonium Cations

The electrochemical intercalation of tetra-n-alkylammonium (TAA) cations into graphite is investigated using galvanostatic reduction and cyclic voltammetry in TAABr/ dimethylsulfoxide (DMSO) electrolytes. Structural and compositional analyzes by X-ray diffraction, thermogravimetric and elemental analyzes show that stable graphite intercalation compounds (GICs) are formed with highly-flattened TAA cation bilayers for (C5H11)4N+, (C6H13)4N+, (C7H15)4N+, (C8H17)4N+, with gallery expansions of 0.81 nm. (C4H9)4N+ forms a mixed-phase product including a stable GIC with monolayer TAA arrangement and a gallery expansion of 0.48 nm. The GICs with bilayer galleries incorporate 0.7–1.2 DMSO co-intercalate molecules per cation; the monolayer galleries contain relatively little DMSO. Although cyclic voltammetry shows that TAA cations smaller than (C4H9)4N+ do intercalate into graphite, they do not form stable GICs. The GICs obtained by galvanostatic reduction are compared to those prepared using chemical ion-exchange reactions. A surface passivation model is introduced to explain the relative stabilities of GICs formed with larger TAA cation intercalates.