Surface and in-depth chemistry of sulfuric and perchloric acid intercalated graphite explored through secondary ion mass spectrometry (SIMS) and atomic force microscopy (AFM)

Graphite can be considered one of the most studied materials for technological application in batteries, energy, electronics, catalysis, and water purification. The intercalation of ions and molecules is often the fundamental mechanism behind these technological applications. Thirty years after the publication of the model, there are still several unclear mechanisms related to the intercalation of solvated anions into graphite that deserve to be more deeply investigated. In this article, we describe how ToF-SIMS can be combined with in situ and ex-situ AFM to correlate changes in the topographical features with changes in the surface and in-depth chemistry of GIC samples obtained from HOPG electrochemically intercalated in sulfuric and perchloric acid aqueous solution. Thanks to this combined approach, the interpretative model of intercalation mechanism was revised demonstrating that graphite structural defects are areas of preferential access for the solvated electrolytes. EGO formation, gas evolution, and blister growth can take place at the subsurface as well as in the bulk of the electrode by penetration through rifts or diffused step edges. Finally, the reduction of the intercalated carbon lattice is not usually accompanied by complete ejection of the intercalated electrolyte anions.