Probing Voltage- and Electrolyte-Dependent Monolayer Dynamics with 2D-IR Spectroscopy

Area of Science:

• Electrochemistry
• Surface Science
• Spectroscopy

Background:

• Understanding electrode surface dynamics under applied potential is crucial.
• Molecular-level insights into interfacial processes are limited.

Purpose of the Study:

• To investigate the structural dynamics of a 4-mercaptobenzonitrile monolayer on a gold electrode using 2D-IR spectroscopy.
• To determine how electrolyte composition and applied potential influence these dynamics.

Main Methods:

• Utilized 2D-IR spectroscopy to probe molecular dynamics.
• Employed molecular dynamics simulations to calculate radial distribution functions.
• Measured dynamics across different electrolytes (MgCl2, LiCl, KCl) and potentials (-200 mV and +300 mV vs Ag/AgCl).

Main Results:

• Observed chemical exchange between molecular subensembles on picosecond timescales.
• Electrolyte concentration, not ion charge, correlated with slower dynamics.
• Dynamics were modulated by solvation, electric double layer formation, and monolayer reorientation.

Conclusions:

• Electrolyte composition significantly impacts molecular reorientation and hydrogen bonding at functionalized electrode surfaces.
• Local ion densities play a key role in modulating interfacial dynamics.
• Provides a molecular-level understanding of electrochemical interfaces.