Electrocapillarity and zero-frequency differential capacitance at the interface between mercury and ionic liquids...

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Understanding the structure of ionic liquids (ILs) at electrode interfaces is crucial for electrochemical applications.
• The electrical double layer (EDL) at the IL|electrode interface exhibits complex behavior influenced by IL properties.

Purpose of the Study:

• To investigate the structure of ionic liquids at the electrochemical IL|Hg interface.
• To evaluate the static differential capacitance (Cd) and its potential dependence.

Main Methods:

• Utilized the pendant drop method to study electrocapillarity (interfacial tension vs. potential).
• Calculated zero-frequency differential capacitance (Cd) from electrocapillarity data.

Main Results:

• The potential dependence of Cd at the IL|Hg interface showed one or two local maxima near the potential of zero charge (Epzc).
• ILs with short alkyl chain cations (e.g., 1-ethyl-3-methylimidazolium tetrafluoroborate) exhibited one maximum, while those with long alkyl chains (e.g., 1-octyl-3-methylimidazolium tetrafluoroborate) showed two maxima.
• Cd increased at potentials far from Epzc, attributed to densification of ionic layers in the EDL.

Conclusions:

• The observed Cd behavior aligns with theoretical and simulation predictions for EDLs in ILs.
• The cation's alkyl chain length significantly influences the EDL structure and capacitance at the IL|Hg interface.
• Ionic layer densification contributes to increased capacitance away from the potential of zero charge.