Surface-Enhanced Raman Scattering Based Vibrational Stark Effect as a Spatial Probe of Interfacial Electric Fields in the Diffuse Double Layer

Abstract

Potential-dependent surface-enhanced Raman scattering (SERS) spectra of the nitrile stretching mode were acquired from a series of monolayers composed of alkanethiols (HS(CH 2 ) x CH 3 , where 6 e x e 10) and mercaptododecanenitrile (HS(CH 2 ) 11 CN). These spectra were used to investigate the diffuse double layer at a silver electrode interface modified with mixed self-assembled monolayers (SAMs). The alkanethiol species acts to dilute the nitrile-terminated thiol to isolate the nitrile reporter group within the diffuse double-layer region. Nitrile groups co-immobilized with shorter diluent alkanethiol chains are placed more deeply into the diffuse double layer (relative to the methyl terminus of the surrounding alkanethiol). Interfacial electric fields, measured using observed Stark tuning rates of the nitrile stretching frequency, were examined as a function of SAM composition to map the structure of the diffuse double-layer region versus distance from the SAM/ solution interface. The trends in the experimental data are largely consistent with Gouy-Chapman theory, in which Stark tuning rates, and the interfacial electric fields from which they originate, depend on both distance of the probe from the electrode surface and the ionic strength of the aqueous phase. For measurements at the highest ionic strengths, the experimentally observed double layer appeared to extend further into solution than predicted by Guoy-Chapman theory, which is consistent with the finite size of hydrated ions and theoretical predictions of the effect of a hydrophobic interface on the structure of the adjacent water layer. The results demonstrate the ability of this spectroelectrochemical experiment to characterize diffuse double-layer structure at electrochemical interfaces on a subnanometer distance scale.

In Situ Characterization of Bipolar Electrodes by using Vibrational Stark Spectroscopy and Surface‐Enhanced Raman Spectroelectrochemistry

“…The experimental conditions used for this calculation represent the maximum Stark shift observed in this study, and the electric field is an upper limit for the magnitude of the electric field that exists at the BPE–solution interface in aqueous electrolytes. The value we calculated is consistent both with early measurements from Korzeniewski et al., as well as with more recent experiments reported by Harris and co‐workers …”

Intermediate stages of electrochemical oxidation of single-crystalline platinum revealed by in situ Raman spectroscopy

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Adsorption of 2‐amino‐5‐cyanopyridine on a gold surface as probed by surface‐enhanced Raman spectroscopy

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