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

Electric Double Layer: The Good, the Bad, and the Beauty

The electric double layer (EDL) is the most important region for electrochemical and heterogeneous catalysis. Because of it, its modeling and investigation are something that can be found in the literature for a long time. However, nowadays, it is still a hot topic of investigation, mainly because of the improvement in simulation and experimental techniques. The present review aims to present the classical models for the EDL, as well as presenting how this region affects electrochemical data in everyday experimentation, how to obtain and interpret information about EDL, and, finally, how to obtain some molecular point of view insights on it.

High-Throughput Surface-Enhanced Raman Scattering for Screening Chemical Sensor Candidates Enabled by Bipolar Electrochemistry

A variety of hydrothermal or electrochemical methods have been explored to prepare noble metal nanostructures as surface-enhanced Raman scattering (SERS) substrates. However, most of those metallic nanoarrays are structurally homogeneous, which makes it laborious to select the high-performance substrates for particular Raman sensing purposes. Here, a high-throughput SERS imaging strategy is demonstrated for the first time for screening chemical sensors with sub-nanomolar sensitivities. Bipolar electrochemistry was applied to generate Au or Au-Ag gradient nanoarrays with diverse chemical compositions, morphologies, and particle dimensions ranging from several nanometers to micrometers. The selected "hot-spots" on the Au-Ag alloy nanoarray exhibited a 660-fold enhancement in SERS intensity compared to those on the pure Au gradient nanoarray. The SERS screening of 4-aminothiophenol, 4-nitrothiophenol, and 4-mercaptobenzoic acid was carried out that provided a limit of detection (LOD) between 1 and 5 pM. The distinctive LODs among three thiophenolic Raman probes are ascribed to the differences in the affinity of the probe to the alloy, orientation of the metal-ligand monolayer, or plasmonic environment of the nanoarray surface. As a continuous, rapid, and cost-effective manner to fabricate transitional nanostructures and screen out SERS responsive sites, this method not only facilitates controllable synthesis of noble metal nanoarrays but has the potential to provide an alternative tool for ultrasensitive chemical sensing on a wide range of bimetallic substrates.

Recent advances in spectroelectrochemistry

The integration of two quite different techniques, conventional electrochemistry and spectroscopy, into spectroelectrochemistry (SEC) provides a complete description of chemically driven electron transfer processes and redox events for different kinds of molecules and nanoparticles. SEC possesses interdisciplinary advantages and can further expand the scopes in the fields of analysis and other applications, emphasizing the hot issues of analytical chemistry, materials science, biophysics, chemical biology, and so on. Considering the past and future development of SEC, a review on the recent progress of SEC is presented and selected examples involving surface-enhanced Raman scattering (SERS), ultraviolet-visible (UV-Vis), near-infrared (NIR), Fourier transform infrared (FTIR), fluorescence, as well as other SEC are summarized to fully demonstrate these techniques. In addition, the optically transparent electrodes and SEC cell design, and the typical applications of SEC in mechanism study, electrochromic device fabrication, sensing and protein study are fully introduced. Finally, the key issues, future perspectives and trends in the development of SEC are also discussed.

SERS spectroelectrochemical study of electrode processes at copper hexacyanoferrate modified electrode

Electrochemical redox processes taking place at copper hexacyanoferrate (CuHCF) modified electrode have been investigated by near-infrared laser (785nm) induced surface-enhanced Raman spectroscopy (SERS). Raman bands observed within the spectral ranges of 2200-2000cm^-1 and 500-100cm^-1, as well as their dependence on electrode potential, have been analysed. The most characteristic Raman bands, related to triple CN bond vibrations and centered at 2187 and 2127cm^-1 were assigned to the oxidised and the reduced forms of CuHCF, respectively. Time-resolved Raman spectroelectrochemical study shows that the electrochemical redox interconversions between these two forms proceed relatively slow, thus resembling the behaviour of structurally related cobalt hexacyanoferrate, and differing essentially from that of Prussian blue layer studied previously. It has been shown by the time-resolved Raman spectroelectrochemistry that the rate of some redox processes of solute species like the anodic oxidation of ascorbate or cathodic reduction of hydrogen peroxide at CuHCF modified electrode appears to be limited by the slow electrochemical redox transformations within the modifier layer itself rather than by the redox interactions of a modifier with the solute species.