Electrochemical techniques and atomic force microscopy based force curve measurements under potential control are combined to investigate the effect of small amounts of water on the structure of the electric double layer of an Au(111)/1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) interface. Three to five layering structures, including two charged layers, are observed at the Au(111)/BMPTFSA interface at potentials more negative than the point of zero charge. With an increase in the water concentration, the stiffness values for both the first and second layers decrease, which demonstrates that more water molecules adsorb on the Au(111) surface or interact with the ionic liquid, and thus weaken the interactions between cations, anions, and the electrode surface and lower the stability of the layering structures. The thicknesses of the charged interior layers (the first and second layers in this system) increase with an increase in the water concentration and the thicknesses of neutral exterior layers (the next one to three layers in this system) remain almost unchanged. The structure of the first layer of the interface varies dramatically with the change in the water concentration.
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.
The influences of the electrode/ionic liquids interfaces on the charge transfer kinetics are addressed with the example of the oxidation of chromocene at a single crystal Ag(111) electrode. We considered three different imidazolium‐based room temperature ionic liquids (RTILs) with alkyl chains of different lengths but with a common anion. The standard charge transfer rate constants k° are extracted from cyclic voltammograms (CVs) by analyzing the peak potential variations with the scan rate and/or performing semi‐integral electroanalysis with a careful treatment of the ohmic drop. Linear variations between the logarithms of k° and the longitudinal relaxation times τL or the dynamic viscosity η of the ionic liquids are obtained. However, the amplitude of the decrease is much larger than it could be expected from the sole bulk properties of the ionic liquid indicating a strong effect of the interface on the kinetics. These observations agree with a well‐organized electrode/RTIL interface that behaves as a sort of self‐assembled monolayer that controls the charge transfer kinetics with an exponential tunneling coefficient β of 5.51 nm−1.
Glovebox-AFM-based force curve measurements have been employed to investigate the effect of controlled small amounts of water on the interfacial structure of mica/a pyrrolidinium-based ionic liquid. A close examination reveals...
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