Potential Screening at Electrode/Ionic Liquid Interfaces from In Situ X-ray Photoelectron Spectroscopy

Area of Science:

• Electrochemistry
• Materials Science
• Surface Science

Background:

• Understanding potential screening at electrode-ionic liquid interfaces is crucial for electrochemical applications.
• Existing methods often lack the resolution to differentiate screening at individual electrodes within a cell.

Purpose of the Study:

• To introduce and validate a novel in situ method for investigating potential screening at ionic liquid/electrode interfaces.
• To quantify and compare potential screening at working and counter electrodes in a two-electrode system.

Main Methods:

• Utilized in situ X-ray photoelectron spectroscopy (XPS) to monitor core level binding energy shifts in the bulk ionic liquid.
• Employed a two-electrode electrochemical cell with identical electrodes to deduce potential screening at each electrode.
• Analyzed various ionic liquid/electrode combinations, including imidazolium-based ILs with Pt and Au electrodes.

Main Results:

• Demonstrated asymmetric potential screening at anode and cathode interfaces for imidazolium-based ionic liquids on Pt electrodes, attributed to cation-Pt interactions.
• Observed asymmetric screening in imidazolium chloride on Au electrodes, linked to differences in cation and anion sizes and electrical double layer thicknesses, in the absence of specific ion-electrode interactions.
• Concluded that potential screening in ionic liquids is predominantly governed by a single layer of counterions.

Conclusions:

• The developed in situ XPS approach provides valuable insights into the complex potential screening mechanisms at ionic liquid/electrode interfaces.
• Specific ion-electrode interactions and differences in ion size significantly influence the asymmetry of potential screening.
• Potential screening in ionic liquids is primarily a surface phenomenon dominated by the arrangement of the first layer of counterions.