Electric Double Layer of Au(100)/Imidazolium-Based Ionic Liquids Interface: Effect of Cation Size

Abstract

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.

Static Capacitance at the Electrochemical Liquid-liquid Interface Between Ionic Liquids and Eutectic Ga-In Alloy Measured Using the Pendant Drop Method

“…In contrast to the progress of the understanding of the EDL of ILs from the theoretical side, experimental confirmation of the predicted IL-peculiar behavior is not straightforward. It has been found, from studies using electrochemical impedance spectroscopy (EIS), that C for the EDL of ILs has strong frequency dependence [11][12][13][14][15][16][17][18] and shows potential hysteresis, 11,[19][20][21] both of which seem to result from the structural ordering of IL interface [22][23][24][25][26][27][28][29] and the ultraslow dynamics [29][30][31][32][33][34][35][36][37][38] of such ordered structure. These tendencies have hampered rigorous evaluation of C experimentally.…”

Electrochemical Behavior and Specific Adsorption of an Iodide-based Ionic Liquid on Au(111)

“…2 In addition, distinctive interfacial phenomena dependent on the orientation of IL cations in the double-layer region have been reported. [3][4][5] From the standpoint of electrochemical surface science, it is important to understand and to characterize the specific adsorption of ions and the dynamics of phase transitions. [6][7][8] In particular, the specific adsorption of anions such as halides, sulfate, and cyanide on metal electrode surfaces is well known.…”

The Electric Double Layer in an Ionic Liquid Incorporated with Water Molecules: Atomic Force Microscopy Force Curve Study

“…When ILs are used as an electrolyte for electrochemical research, the water present exists as an impurity and can reduce and oxidize on electrode surfaces, which then dramatically decreases electrochemical windows, particularly when the water concentration is higher . Some measures are usually taken to remove the absorbed water from ILs before experiments are conducted to eliminate the influence of water on the properties of the ILs . For example, ILs can be vacuum‐dried for several hours at 80 °C in a glovebox filled with ultra‐pure N 2 .…”