Absolute Calibration for Cyclic Voltammetry from the Solution-Phase Ionisation of Ferrocene

Area of Science:

• Materials Science
• Electrochemistry
• Physical Chemistry

Background:

• Accurate material energy level determination is vital for electronics, catalysis, and energy technologies.
• Molecular orbital energy levels are often estimated using redox potentials measured against internal standards like the ferrocene/ferrocenium (Fc+/Fc) couple.
• Discrepancies up to 0.3 eV exist due to the use of multiple, conflicting reference electrode scales in the literature.

Purpose of the Study:

• To report an absolute energy level measurement for the Fc+/Fc redox couple in acetonitrile solution.
• To establish a benchmark value for the Fc+/Fc couple, enabling accurate conversion of voltammetry data to an absolute energy scale.

Main Methods:

• Ambient pressure photoemission spectroscopy was employed to measure the adiabatic ionization energy of ferrocene in acetonitrile.
• Photoemission data from varying solution concentrations were analyzed using a model to account for liquid surface barrier effects.

Main Results:

• The adiabatic ionization energy of ferrocene in acetonitrile solution was determined to be 4.94 ± 0.05 eV.
• The study confirmed the measurement of adiabatic ionization energy and found minimal liquid surface barrier effects.
• The determined value aligns with one of the existing, albeit conflicting, reference values in the literature.

Conclusions:

• This work provides a benchmark absolute energy level for the widely used Fc+/Fc internal reference in acetonitrile.
• The established value facilitates the accurate conversion of electrochemical data to an absolute energy scale, resolving literature discrepancies.
• The findings are critical for advancing fields reliant on precise energy level characterization of materials.