Probing double layer structures of Au (111)-BMIPF6 ionic liquid interfaces from potential-dependent AFM force curves.

High quality AFM force curves are presented with detailed potential dependent layering behaviors of the ionic liquid molecules, from which charged interior and neutral exterior layers are distinguished. The electric double layer is confined within the interior layers of one to two molecular size within the potential range of up to 1 V negative of the PZC.

The electrode/ionic liquid interface: electric double layer and metal electrodeposition.

The last decade has witnessed remarkable advances in interfacial electrochemistry in room-temperature ionic liquids. Although the wide electrochemical window of ionic liquids is of primary concern in this new type of solvent for electrochemistry, the unusual bulk and interfacial properties brought about by the intrinsic strong interactions in the ionic liquid system also substantially influence the structure and processes at electrode/ionic liquid interfaces. Theoretical modeling and experimental characterizations have been indispensable in reaching a microscopic understanding of electrode/ionic liquid interfaces and in elucidating the physics behind new phenomena in ionic liquids. This Minireview describes the status of some aspects of interfacial electrochemistry in ionic liquids. Emphasis is placed on high-resolution and molecular-level characterization by scanning tunneling microscopy and vibrational spectroscopies of interfacial structures, and the initial stage of metal electrodeposition with application in surface nanostructuring.

Supramolecular aggregation of inorganic molecules at Au(111) electrodes under a strong ionic atmosphere.

Neutral inorganic molecules are generally weak in surface adsorption and intermolecular interactions. Self-assembly of such types of molecule would provide valuable information about various interactions. At electrochemical interfaces, the relative strength of these interactions may be modified through control of electrode potential and electrolyte, which may lead to the discovery of new structures and new phenomena. However, studies of this nature are as yet lacking. In this work, we consider the covalent-bound semimetal compound molecules, XCl(3) (X = Sb, Bi), as model systems of neutral inorganic molecules to investigate their self-assembly at electrochemical interfaces under a high ionic atmosphere. To fulfill such investigations, in situ STM and cyclic voltammetry are employed, and comparative experiments are performed on Au(111) in ionic liquids as well as aqueous solutions with high ionic strength. In the room temperature ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF(4)), potential-dependent partial charge transfer between the Au surface and XCl(3) molecules creates a molecule-surface interaction and provides the driving force for adsorption of the molecules. Supramolecular aggregations of adsorbed XCl(3) are promoted through chlorine-based short-range intermolecular correlation under crystallographic constraint, while repulsive Coulombic interactions created between the partially charged aggregations facilitate their long-range ordering. For SbCl(3) molecules, hexagonally arranged 6- or 7-member clusters are formed at 0.08 to -0.2 V (vs Pt), which assemble into a secondary ( radical31 x radical31)R8.9 degrees structure. For BiCl(3) molecules, both the 6-membered hexagonal and 3-membered trigonal clusters are formed in the narrow potential range -0.3 to -0.35 V, and are also arranged into an ordered secondary structure. Comparative studies were performed with SbCl(3) in concentrated aqueous solutions containing 2 M HCl to simulate the strong ionic strength of the ionic liquid. Almost identical 6-/7-member clusters and long-range ( radical31 x radical31)R8.9 degrees structure are observed at -0.1 V, demonstrating the crucial role of strong ionic strength in such supramolecular aggregations. However, such supramolecular structures are modified and eventually destroyed as ionic strength is further increased by addition of NaClO(4) up to 6 M. The destructive changes of the supramolecular structures are attributed to the alteration of ion distribution in the double layer from cation-rich to anion-rich at increasing NaClO(4) concentration. This modifies and eventually breaks the balance of intermolecular and molecule-electrolyte interactions. Finally, the dynamic behavior of the SbCl(3) assembly is investigated down to molecular level. It has been demonstrated that the initial stage of assembly follows a two-dimensional nucleation and growth mechanism and has a potential-dependent rate that is closely related to the surface mobility of the SbCl(3) clusters. There is a probability that clusters can escape from an existing assembly domain or insert into a vacancy in such a domain while they can also relax with central or ring members in a dynamic fashion. These phenomena indirectly reflect the dynamic properties of cations from electrolytes at the interface. The rich information contained in the self-assembly behavior of SbCl(3) and BiCl(3) demonstrates that neutral inorganic molecules can be employed for fundamental studies of a variety of interesting issues, especially the interplay of various interfacial interactions.

Double layer of Au(100)/ionic liquid interface and its stability in imidazolium-based ionic liquids.

Ring any bells? The differential capacitance curve of Au(100) in neat [BMI]BF(4) (BMI = 1-butyl-3-methylimidazolium) ionic liquid has a bell-shaped feature (see picture). The adsorption of BMI(+) shows a disorder-order transition and depends on the structure of the surface. Ordered adsorption in a micelle-like structure stabilizes the underlying Au surface.