Electrochemical TERS Elucidates Potential‐Induced Molecular Reorientation of Adenine/Au(111)

Abstract

Electrochemical surface activity arises from the interaction and geometric arrangement of molecules at electrified interfaces. We present a novel electrochemical tip‐enhanced Raman spectroscope that can access the vibrational fingerprint of less than 100 small, non‐resonant molecules adsorbed at atomically flat Au electrodes to study their adsorption geometry and chemical reactivity as a function of the applied potential. Combining experimental and simulation data for adenine/Au(111), we conclude that protonated physisorbed adenine adopts a tilted orientation at low potentials, whereas it is vertically adsorbed around the potential of zero charge. Further potential increase induces adenine deprotonation and reorientation to a planar configuration. The extension of EC‐TERS to the study of adsorbate reorientation significantly broadens the applicability of this advanced spectroelectrochemical tool for the nanoscale characterization of a full range of electrochemical interfaces.

A Happy Get‐Together – Probing Electrochemical Interfaces by Non‐Linear Vibrational Spectroscopy

“…VSFG is not only capable of monitoring molecular adsorption on electrodes, it rather also provides information on the orientation and reorientation of the adsorbates in response to external stimuli. Due to the importance of the molecular orientation on any specific surface chemistry, [76] this parameter has been studied not only by VSFG but also by, for example, surface enhanced [77] and tip‐enhanced Raman spectroscopy (SERS and TERS) [78] . However, application of SERS is mostly limited to the electrochemistry on roughened gold, copper, and silver electrodes while In case of TERS, reproducibility of the tips imposes some major constraints [79] .…”

“…Due to the importance of the molecular orientation on any specific surface chemistry, [76] this parameter has been studied not only by VSFG but also by, for example, surface enhanced [77] and tip‐enhanced Raman spectroscopy (SERS and TERS). [78] However, application of SERS is mostly limited to the electrochemistry on roughened gold, copper, and silver electrodes while In case of TERS, reproducibility of the tips imposes some major constraints. [79] Also, applying these techniques in liquid interface still requires substantial instrumental development.…”

In Situ/Operando Insights into the Stability and Degradation Mechanisms of Heterogeneous Electrocatalysts

“…By combining a tip with the confocal arrangement of an existing Raman spectroscopy setup, the tip‐enhanced Raman spectroscopy technique offers the improved intensity and spatial resolution of Raman spectroscopy, enabling potential active sites to be revealed, while identifying the induced molecular reorientation and nanoscale redox behavior via electrochemistry. [ 60–62 ]…”

Electrochemical Tip-Enhanced Raman Spectroscopy for the Elucidation of Complex Electrochemical Reactions

“…The potential-dependent response of 4′-(4-pyryl)­biphenyl-4-methanethiol (4-PBT) molecules, the spatially dependent redox behavior of sparse Nile Blue (NB) molecules, − the irreversible reduction of anthraquinone molecules, the reactivity mapping of nanoscale defect chemistry on gold surfaces, iron and cobalt phthalocyanine deactivation during oxygen reduction reaction, , and also the reversible transformation (oxidation) of a polyaniline on gold are successful examples of EC-TERS implementation. − Such redox-active systems were selected based on either (i) their strong Raman scattering cross-section at selected excitations (Raman-resonant compounds, at plasmonic junctions), (ii) their simple/unequivocal redox reaction scheme (one step, mostly reversible), and/or their well-established Raman signatures. For more complex electroactive systems involved in multistep reactions (electrochemical/chemical) such as those often implicated in electrocatalytic processes, the mechanism of operation can be difficult to decipher.…”