Assessing Local Electrical Properties of Ionic Liquid/Metal Interfaces with Operando-XPS and by Incorporating...

Area of Science:

• Surface Science
• Electrochemistry
• Materials Science

Background:

• Ionic liquids (ILs) are crucial electrolytes in advanced devices.
• Understanding charge dynamics at electrode-electrolyte interfaces is key.
• X-ray photoelectron spectroscopy (XPS) offers surface sensitivity but its application in dynamic electrochemical studies is limited.

Purpose of the Study:

• To investigate the localized electrical potential changes within an ionic liquid film under applied DC and AC bias using XPS.
• To explore the influence of different frequencies and series resistors on charging/discharging processes and electrical double layer (EDL) formation.
• To establish XPS as a powerful tool for non-invasively extracting localized electrochemical properties.

Main Methods:

• Utilized XPS to measure binding energy shifts in response to applied DC and AC (square-wave) bias on a coplanar capacitor with an IL electrolyte.
• Employed electrochemical measurements alongside XPS to analyze local information before and after adding series resistors.
• Modulated the AC bias at different frequencies (10 kHz and 0.1 Hz) to distinguish fast electronic and slow migratory currents.

Main Results:

• Observed distinct electrical potential developments across the device, correlated with binding energy shifts.
• Demonstrated that AC modulation at different frequencies allows disentangling of complex charging/discharging processes.
• Quantified AC currents and system impedance by adding series resistors, revealing frequency-dependent voltage differences.

Conclusions:

• XPS can be effectively used as an electrical and surface-sensitive tool to probe localized electrochemical properties.
• The study provides insights into EDL formation and charge transport mechanisms in IL electrolytes.
• This approach is expected to facilitate the development of next-generation sensing, energy storage, and iontronic devices.