Phase-Sensitive Second-Harmonic Generation of Electrochemical Interfaces.

Area of Science:

• Electrochemistry
• Surface Science
• Spectroscopy

Background:

• Interactions between molecular species and charged interfaces are vital for electrochemical devices.
• The nature of these interfacial interactions, especially the electric field, remains poorly understood.
• Second-order nonlinear spectroscopy, like second-harmonic generation (SHG), offers chemical insights but often neglects phase information.

Purpose of the Study:

• To demonstrate the critical role of phase information in electrochemical second-harmonic generation (SHG) for measuring interfacial electric fields.
• To investigate the electrode-electrolyte interface using in situ SHG.
• To validate the parabolic model using complex nonlinear susceptibilities.

Main Methods:

• Utilizing in situ second-harmonic generation (SHG) spectroscopy.
• Analyzing the phase of the SHG signal.
• Applying nonlinear spectroscopy to probe electrode-electrolyte interfaces.

Main Results:

• The phase of the SHG signal is essential for accurately measuring the electric field at the electrode-electrolyte interface.
• Experimental results provide strong support for the parabolic model incorporating complex nonlinear susceptibilities.
• The study highlights the significance of both second-order (χ(2)) and third-order (χ(3)) nonlinear susceptibility contributions.

Conclusions:

• The absolute phase of the total SHG signal is key to understanding interfacial electric fields.
• Obtaining the absolute phase of SHG signals enables the measurement of the potential of zero charge for any electrochemical material.
• This research advances the application of nonlinear spectroscopy in electrochemistry.