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Electric Fields at Metal-Surfactant Interfaces: A Combined Vibrational Spectroscopy and Capacitance Study
Sohini Sarkar1, Anwesha Maitra1, Soumyodip Banerjee2
1Department of Chemistry , University of Southern California , Los Angeles , California 90007 , United States.
The Journal of Physical Chemistry. B
|January 28, 2020
Summary
Cationic surfactants create strong interfacial electric fields, enhancing CO2 reduction and suppressing hydrogen evolution. This study quantifies these fields, aiding surfactant design for electrochemical applications.
Area of Science:
- Electrochemistry
- Surface Science
- Materials Science
Background:
- Surfactants influence interfacial processes in electrochemical reactions.
- Cationic surfactants are known to promote carbon product formation and suppress hydrogen evolution in CO2 reduction.
- Understanding the interfacial electric fields generated by surfactants is crucial for optimizing electrochemical CO2 reduction.
Purpose of the Study:
- To quantify the electric fields at metal-surfactant interfaces using complementary spectroscopic and electrochemical techniques.
- To investigate the effect of surfactant type (cationic vs. anionic) and concentration on interfacial fields.
- To propose a model explaining the observed interfacial field effects.
Main Methods:
- Vibrational Stark shift spectroscopy to probe molecular-level interfacial fields.
- Electrochemical impedance spectroscopy (EIS) to analyze the electrical double layer.
- Utilizing a nitrile molecule as a probe for interfacial field measurements.
Main Results:
- Cationic surfactants generate significantly larger effective interfacial fields (~-1.25 V/nm) compared to anionic surfactants (~0.4 V/nm) at open-circuit potentials.
- Surface electric fields reach a terminal value at high surfactant concentrations, indicating full layer formation, supported by EIS data.
- An electrostatic model was developed to explain the experimental observations.
Conclusions:
- The study quantifies the strong interfacial electric fields generated by cationic surfactants.
- These findings provide insights into designing tailored surfactants for controlling electrochemical reactions.
- The interfacial field effect is a key factor in optimizing electrochemical CO2 reduction and other interfacial processes.
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