Effects of the dipolar double layer on elemental electrode processes at micro- and macro-interfaces

Area of Science:

• Electrochemistry
• Physical Chemistry

Background:

• Determining heterogeneous rate constants for redox reactions and charge transfer resistances is often ambiguous.
• This ambiguity stems from the interplay between double-layer (DL) capacitances and solution resistances.

Purpose of the Study:

• To investigate the controlling factors of DLs by analyzing the frequency-dependence of capacitance.
• To clarify the origins of discrepancies between steady-state and time-dependent voltammogram analyses.

Main Methods:

• Analysis of frequency-dependence of capacitance based on current and capacitance definitions.
• Examination of the power law relationship between capacitance and frequency.
• Investigation of redox species' impact on DL capacitance and impedance.

Main Results:

• DL capacitance follows a power law with frequency, influenced by solvent dipole orientation, independent of salt concentration.
• Oppositely oriented redox species reduce DL capacitance, potentially leading to negative values and increased real impedance.
• This phenomenon can manifest as a 'ghost' charge transfer resistance, distinct from true resistances observed in film-electrode systems.

Conclusions:

• Solvent dipole orientation is a key determinant of DL capacitance.
• Redox species can significantly alter DL capacitance and introduce apparent resistances.
• Distinguishing between true and apparent charge transfer resistances is crucial for accurate electrochemical analysis.