Anion Intercalation into Graphite Drives Surface Wetting

Abstract

The unique layered structure of graphite with its tunable interlayer distance establishes almost ideal conditions for the accommodation of ions into its structure. The smooth and chemically inert nature of the graphite surface also means that it is an ideal substrate for electrowetting. Here, we combine these two unique properties of this material by demonstrating the significant effect of anion intercalation on the electrowetting response of graphitic surfaces in contact with concentrated aqueous and organic electrolytes as well as ionic liquids. The structural changes during intercalation/deintercalation were probed using in situ Raman spectroscopy, and the results were used to provide insights into the influence of intercalation staging on the rate and reversibility of electrowetting. We show, by tuning the size of the intercalant and the stage of intercalation, that a fully reversible electrowetting response can be attained. The approach is extended to the development of biphasic (oil/water) systems that exhibit a fully reproducible electrowetting response with a near-zero voltage threshold and unprecedented contact angle variations of more than 120° within a potential window of less than 2 V.

Hydration Energy-Dependent Ion Intercalation on Graphite and the Asymmetric Electrowetting

“…In addition, we also found evidence of the intercalated Cl ions into the HOPG galleries via XPS analysis, as shown in Figures S5 and S6. However, all the studies focus on the anion intercalation-driven electrowetting on the HOPG substrate only qualitatively but do not explain any electrowetting response behavior, especially the nonintercalation of cation, at the same voltage range with negative polarity. ,, …”

“…reported threshold voltage-dependent electrowetting response behavior for Cl – anion intercalation for the positive polarity applied to the substrate. Despite the fact that many groups have advanced their understanding and applications of graphite ion intercalation-based electrowetting, their work did not reveal the underlying cause of these phenomena. ,− These unresolved issues inspired us to utilize the EWOC approach to reveal the underlying mechanism of the dependence of hydration energy and hydration shell size on the intercalation of ions into the graphite layers.…”

“…However, all the studies focus on the anion intercalation-driven electrowetting on the HOPG substrate only qualitatively but do not explain any electrowetting response behavior, especially the nonintercalation of cation, at the same voltage range with negative polarity. 26,27,31 Process of Ion Intercalation in Graphite and the Construction of a Physical Model. To quantitatively understand these phenomena in the electrowetting experiments, we develop a theoretical model considering the molecular-level interactions among the ions, water, and graphite layers.…”

Electrochemical Exfoliation of Graphene Oxide: Unveiling Structural Properties and Electrochemical Performance

“…Furthermore, we observed that below 2 V vs. Ag/AgCl (KCl 3 M) the intercalation step results in yields with low efficiency for the global process and that the current value increases with higher potentials (E E ), indicating an enhancement in SO 2À 4 intercalation at elevated potentials with the resulting increase in the graphite surface area due to the exfoliation of GO flakes, as reported in previous literature. [43][44][45] The method proposed in this study offers several advantages over traditional and other electrochemical methods. It operates under moderate reaction conditions, requires short processing times, is relatively cost-effective, and is environmentally friendly, as it avoids generating toxic or hazardous waste.…”

Aqueous electrolyte-mediated reversible K+ ion insertion into graphite

“…25 Several interesting recent studies on graphite/graphene electrodes indicate a decrease in the contact angle upon cation or anion insertion in both aqueous and non-aqueous electrolytes akin to our observations. 25–30 EIS measurements (Fig. S15, ESI†) also show that the charge transfer resistance for the natural graphite electrode is much lower in comparison to the pyrolytic graphite electrode.…”