Second harmonic generation as a probe of structure and dynamics of ionic liquids at the electrode interface

22 August 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Electrochemical second harmonic generation (ESHG) has been applied as a probe of the slow dynamics in the electric double layer (EDL) at the ionic liquid (IL)/Au interface. When the electrode potential was stepped, the SHG signal from the interface was relaxed on the time scale of longer than tens of seconds, which is distinctively slower than the RC time constant of the cell. This ultraslow relaxation in ESHG was quantitatively analyzed and discussed for several ILs, revealing that the ultraslow relaxation itself is a common phenomenon for the EDL in the ILs studied but the asymmetry of the time constants to the potential-step directions depends on the IL ions, which is likely to reflect the structure ordering of the interfacial ionic layer in the EDL depending on both ILs and the potential. The EDL structure in equilibrium has also been investigated via SHG measurements with a potential scan at a sufficiently slow rate; the potential dependence of the SHG signal was found to deviate from a simple parabolic one, reflecting the camel-shaped static differential capacitance for the EDL in ILs.


ionic liquid
surface plasmon resonance
differential capacitance
ionic multilayers
camel-shaped capacitance

Supplementary materials

Supplementary Materials
Ionic structures; Experimental schematics; CV data; PS-ESHG data; LS-ESHG data


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