Surface-enhanced Raman Spectroelectrochemistry Research Articles

Recent advances in Raman and surface enhanced Raman spectroelectrochemistry

Raman spectroscopy could supply the molecular vibrational process giving the detailed information of molecular structure. At the same time, electrochemistry could provide kinetic and thermodynamic processes. Integration of both technology with the general definition of using spectroscopic approaches for assaying the variations triggered through an electrochemistry-based system within an electrochemical cell induces a novel technique, spectroelectrochemistry (SEC). Raman-spectroelectrochemistry possesses interdisciplinary advantages and can further expand the scopes in the fields of analysis and other applications, emphasizing the cutting-edge issues of analytical chemistry, materials science, biophysics, chemical biology, and so on. This review emphasizes on the recent progress of integrated Raman/Surface enhanced Raman scattering-spectroelectrochemistry and aimed to summarize the spectroelectrochemistry device, electrode materials and applications of Raman/Surface enhanced Raman scattering-spectroelectrochemistry over the past several decades. Finally, the key issues, future perspectives and trends in the development of Raman/Surface enhanced Raman scattering-spectroelectrochemistry are discussed.

In situ surface-enhanced Raman spectroelectrochemistry reveals the molecular conformation of electrolyte additives in Li-ion batteries.

We report the mechanism of rhodamine B (RhB) acting as an electrolyte additive in Li/graphite cells. We show that the cycle performance and rate capability of graphite are enhanced in carbonate-based electrolytes containing 0.2 wt% RhB. By using silica-encapsulated Au nanoparticles, in situ surface-enhanced Raman spectroscopy (SERS) is applied to study the graphite/electrolyte interface. We find that the adsorption orientation of RhB molecules on the surface of graphite can be modulated by the applied potential: vertical adsorption at higher potentials while horizontal adsorption takes place at lower potentials. This behavior effectively suppresses the electrolyte solvent decomposition, as well as electrode corrosion while improving the Li+ diffusion. This work shows that SERS is a powerful tool for interfacial analysis of battery systems and provides new ideas for rational design of electrolyte additives.

Investigating the effects of pyridine and poly(4-vinylpyridine) on CO2 reduction electrocatalysis at gold electrodes using in situ surface-enhanced Raman spectroelectrochemistry.

The CO2 reduction reaction (CO2RR) at metal electrodes is altered in the presence of pyridine and related species. Thick films of poly(4-vinylpyridine) on Au electrodes result in large current enhancements at low applied potentials but do not enhance CO2RR at these potentials. Surface-enhanced Raman spectroelectrochemistry can probe CO2-surface interactions and reveals that desorption of CO2 as bicarbonate is retarded in the presence of 4-PVP, with implications for ion-transport limitations in thick film CO2RR.

Surface-Enhanced Raman Spectroelectrochemistry with Screen-Printed Electrodes for Quantitative Analysis

Electrochemically roughened silver surfaces have been widely employed for Surface-enhanced Raman scattering (SERS) assays. In most cases, the roughening process is usually performed ex situ with a specific electrolyte solution and, afterwards, the analyte is adsorbed on the substrate for the detection. This procedure has several possible issues: the final state of the substrate could not be the optimum for enhancing the SERS effect, the surface could become passivated between the roughening and the detection steps, decreasing the SERS activity, and the step for the analyte adsorption could take several minutes. Moreover, one of the main issues of SERS-based assays is the reproducibility between experiments and these substrates have been mainly used for qualitative studies. However, there is a strong scientific interest for increasing the applicability of SERS assays for quantitative studies with reproducible and simple methods. Screen-printed electrodes could be promising SERS substrates because they are mass-fabricated using the well-established thick-film technology leading to precise, disposable, low-cost and easy-to-use devices. In this work, the real-time in situ electrochemical roughening of readily-available metal screen-printed electrodes is proposed to obtain a quantitative and precise SERS detection of several species at low concentrations using a fast and cost-effective methodology. The roughening and the analytical detection are carried out simultaneously, solving the typical issues of the ex situ preparation. The time-resolved character of this method allows to get dynamic information about the processes leading to a SERS active substrate and correlate them with the microscopic electrode structure at various stages of the substrate preparation. Results show a good linearity between the SERS signals and low concentrations of several species with a good precision between measurements.

Surface enhanced resonance Raman spectroscopy of iron Hangman complexes on electrodes during electrocatalytic oxygen reduction: advantages and problems of common drycast methods.

Drycast methods have been used frequently in recent decades to adsorb a range of synthetic catalysts on electrodes. The uncoordinated multilayers that are formed via this immobilization method can however have a strong impact on the electrocatalytic reaction pathway as slow electron transfer and intermolecular interactions can alter the chemistry of the catalysts on the surface. To gain insight into the structure of Fe porphyrin Hangman catalysts during electrocatalytic oxygen reduction a combination of electrochemistry and surface enhanced resonance Raman spectroscopy (SERRS) was applied. The Hangman complexes were attached to the electrodes via different methods and the influence of the immobilisation technique on oxygen chemistry was studied. In multilayer systems, new intermediates could be identified via potential dependent SERRS that were not present in solution or in monolayer systems under catalytic conditions. A comparison of Raman spectra obtained either via Soret or Q-band excitation showed that the porphyrin symmetry is strongly distorted under reducing conditions, which was interpreted by the transient formation of dimer complexes during catalysis.

Surface enhanced Raman spectroelectrochemistry of a μ-oxo triruthenium acetate cluster: an experimental and theoretical approach.

Surface enhanced Raman spectroelectrochemistry (SERS) spectroelectrochemistry provides a very sensitive technique to investigate the vibrational characteristics of coordination compounds and their particular behavior under the influence of plasmonic surfaces, concomitant with the exploitation of their redox properties and electronic spectra. The results, however, depend upon the mechanisms involved in the intensification of Raman spectra associated with the electromagnetic, resonance Raman and charge-transfer excitation at the Fermi levels. By probing the model complex [(Ru3O)(CH3COO)6(4,4'-bipy)3](n) (n = 1, 0, -1) adsorbed onto rough gold electrode surfaces, contrasting SERS profiles were obtained at several successive redox potentials and oxidation states, which enables a critical discussion on the role of the complex interaction with the gold surface, and the influence of the specific electronic bands in the triruthenium acetate cluster. Density functional theory (DFT) and time-dependent DFT calculations were carried out for the complex bound to an Au20 cluster to show the participation of active lowest unoccupied molecular orbital levels centered on the gold atoms. The corresponding charge-transfer band was predicted around 1200 nm, which supports a charge-transfer interpretation for the SERS response observed at λexc = 1064 nm. The selective enhancement of the vibrational modes was discussed based on the Raman theoretical calculations.

Study of Adenine and Guanine Oxidation Mechanism by Surface-Enhanced Raman Spectroelectrochemistry

Metal nanoparticles are systems largely employed in surface-enhanced Raman spectroscopy (SERS). In particular, gold nanoparticles are one of the best substrates used in this field. In this work, the optimal conditions for gold nanoparticles electrodeposition on single-walled carbon nanotubes electrodes have been established to obtain the best SERS response. Using this substrate and analyzing the changes of in situ Raman spectra obtained at different potentials, we have been able to explain simultaneously the oxidation mechanism of purine bases, differentiating the oxidation intermediates and their orientation during the different oxidation steps. Adenine orientation hardly changes during the whole oxidation; the molecule maintains a parallel configuration and only shows a slightly tilted orientation after the first oxidation step. On the other hand, guanine orientation changes completely during its oxidation. Initially, guanine is perpendicular respect to gold nanoparticles, changing its orientation after...

In situ surface-enhanced Raman spectroelectrochemical analysis system with a hemin modified nanostructured gold surface.

An integrated surface-enhanced Raman scattering (SERS) spectroelectrochemical (SEC) analysis system is presented that combines a small volume microfluidic sample chamber (<100 μL) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochemistry. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochemical working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl reference electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the electronic absorption of the target molecule. The new SEC analysis system has the merits of wide applicability to target molecules, small sample volume, and a low detection limit. We demonstrate in situ SERS spectroelectrochemistry measurements of the metalloporphyrin hemin showing shifts of the iron oxidation marker band ν4 with the nanostructured Au working electrode under precise potential control.

Surface-Enhanced Raman Spectroelectrochemistry of TTF-Modified Self-Assembled Monolayers.

Surface-enhanced Raman spectroscopy (SERS) was used to monitor the response of a self-assembled monolayer (SAM) of a tetrathiafulvalene (TTF) derivative on a gold film-over-nanosphere electrode. The electrochemical response observed was rationalized in terms of the interactions between TTF moieties as the oxidation state was changed. Electrochemical oxidation to form the monocation caused the absorbance of the TTF unit to coincide with both the laser excitation wavelength and the localized surface plasmon resonance (LSPR), resulting in surface-enhanced resonance Raman scattering (SERRS). The vibrational frequency changes that accompany electron transfer afford a high-contrast mechanism that can be used to determine the oxidation state of the TTF unit in an unambiguous manner.

Variable thickness thin-layer cell for electrochemistry and in situ UV–VIS absorption, luminescence and surface-enhanced Raman spectroelectrochemistry

A variable thickness thin layer spectroelectrochemical cell for in situ UV–VIS absorption, luminescence and surface-enhanced Raman spectroscopy measurement is described. It is constructed of chemically resistant polytetrafluoroethylene (PTFE) materials. The cell windows, working electrode, reference and auxiliary electrode are all assembled by a mechanical method. The cell is leak-light, easily disassembled and reassembled, and suitable for the study of both aqueous and non-aqueous systems. The thickness of thin layer can be varied from 10 μm to the dimension of a conventional electrochemical cell by adjusting the copper barrel thumbscrew mounted with the working electrode. The working electrode can be easily replaced by another for different experimental conditions. Three working electrodes of Cu, Ag and Au are used for an in situ surface-enhanced Raman spectroelectrochemical study of pyridine. Potassium hexacyanoferrate(III) and ferrocene were used to test the electrochemical performance of the cell under various thin layer conditions (from 10 to 500 μm) in both aqueous and non-queous solutions. Values of E 0′ and n obtained from the in situ UV–VIS absorption and fluorescence spectroelectrochemical study of o-tolidine are 0.608 V (versus SCE) and 1.94 and 0.608 V (versus SCE) and 1.85, respectively. These results agree with the value of 0.605 V (versus SCE) obtained by cyclic voltammetry and values in the literature.

Temperature dependence of the surface enhanced raman spectroelectrochemistry of iron in aqueous solutions

The effect of temperature on the composition of the corrosion film on iron in aqueous sodium hydroxide and borate solutions was investigated using surface enhanced Raman spectroelectrochemistry (SERS). Fe(OH) 2 and Fe 3O 4 were observed in the prepassivation region, while Fe 3O 4 and FeOOH accounted for most of the passivated film at 25, 60 and 95 °C. Fe(OH) 2 was found to be a stable component of the corrosion film on iron at 95 °C, which is contrary to recently published theoretical calculations.