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.

Oberflächlich betrachtet: Die differenzielle Kapazität von Au(100) in der ionischen Flüssigkeit [BMI]BF4 (BMI=1‐Butyl‐3‐methylimidazolium) als Funktion des elektrostatischen Potentials nimmt einen glockenförmigen Verlauf (siehe Bild). Die Adsorption von BMI+ geht von einem ungeordneten in einen geordneten Prozess über und hängt von der Struktur der Oberfläche ab. Die geordnete Adsorption zu einer micellartigen Struktur stabilisiert die darunter befindliche Au‐Oberfläche.magnified image

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 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.

We have carried out differential capacitance measurements and in-situ scanning tunneling microscope (STM) characterizations to investigate the effect of the length of alkyl side chains on an electric double layer of Au(100)/imidazolium-based ionic liquids interface. In ionic liquids consisting of BMI+ cation (1-butyl-3-methylimidazolium), differential capacitance curves present an obvious bell-shaped feature. In ionic liquids with PMI+ (1-methyl-3-propylimidazolium) or OMI+ (1-methyl-3-octylimidazolium) cations, the rising of capacitance from about −0.5 V disturbs the bell-shaped feature. In-situ STM characterizations reveal the generality of surface etching and micelle-like adsorption of imidazolium cations on Au(100) at potential around the peaks of the bell-shaped feature, demonstrating that the potential of zero charge (PZC) should locate at the potential close to the peaks. Because of the longer side chain length and stronger interaction with Au(100) substrate, an extra capacitance peak appears at the potential as negative as −1.65 V in OMIPF6 and a corresponding order–disorder transformation of OMI+ cation adlayer is revealed by STM, indicating a correlation between differential capacitance curve and STM.