The interface between HOPG and 1-butyl-3-methyl-imidazolium hexafluorophosphate

Area of Science:

• Electrochemistry
• Materials Science
• Surface Science

Background:

• Understanding electrode-electrolyte interfaces is crucial for electrochemical applications.
• Ionic liquids offer unique properties as electrolytes but their interfacial behavior requires detailed study.
• Highly oriented pyrolytic graphite (HOPG) and gold (Au(100)) present distinct surface characteristics for interfacial investigations.

Purpose of the Study:

• To investigate the electrochemical interface between HOPG and 1-butyl-3-metyl-imidazolium hexafluorophosphate (BMIPF6).
• To compare the interfacial properties of HOPG with Au(100) in the same ionic liquid.
• To elucidate the nature of slow interfacial processes affecting capacitance spectra.

Main Methods:

• Cyclic voltammetry
• Electrochemical impedance spectroscopy
• Immersion charge measurements
• In situ scanning tunneling microscopy (in situ STM)

Main Results:

• High-frequency capacitance spectra for HOPG and Au(100) in BMIPF6 are similar.
• Slow interfacial processes, absent in HOPG, appear as a second capacitance arc for Au(100) at low frequencies.
• These slow processes on Au(100) are attributed to surface rearrangement and ionic liquid adlayer formation.

Conclusions:

• HOPG exhibits a more stable and less dynamic interface with BMIPF6 compared to Au(100).
• The observed differences are linked to the distinct surface properties and reactivity of HOPG and Au(100).
• In situ STM successfully visualized the dynamic processes occurring at the Au(100)/BMIPF6 interface.