Electric double layer contribution to sum frequency generation signal from Au electrode

Area of Science:

• Electrochemistry
• Surface Science
• Spectroscopy

Background:

• The electric double layer (EDL) at the metal electrode-electrolyte interface is crucial for electrochemical processes.
• Sum Frequency Generation (SFG) spectroscopy is a powerful technique for probing interfacial structures.

Purpose of the Study:

• To investigate the influence of specific adsorption on the EDL structure and its contribution to SFG signals at gold electrodes.
• To analyze potential-dependent SFG intensities in different electrolyte systems (HClO4 and H2SO4).

Main Methods:

• Electrochemical measurements, including differential capacity curves, to determine the potential of zero charges (PZC).
• Potential-dependent Sum Frequency Generation (SFG) spectroscopy of polycrystalline gold electrodes.
• Analysis of SFG intensities in HClO4 (non-specific adsorption) and H2SO4 (specific adsorption) electrolytes.

Main Results:

• The PZC of gold electrodes was determined to be -0.06 V in HClO4 and 0.38 V in H2SO4.
• In HClO4, SFG intensity was primarily from the gold surface, enhanced by proximity to double resonance.
• In H2SO4, the EDL contributed significantly (approx. 30%) to the SFG signal due to specific adsorption, especially above PZC.

Conclusions:

• Specific adsorption of ions, particularly in H2SO4, substantially influences the EDL structure and its SFG response.
• The EDL SFG contribution increases with potential in the presence of specific adsorption, highlighting its importance in electrochemical interfaces.
• SFG spectroscopy effectively distinguishes between EDL contributions with and without specific adsorption.