Detection of Short-Lived Electrogenerated Species by Raman Microspectrometry

Abstract

Raman microprobe spectrometry has been applied to the characterization of unstable species generated electrochemically at a microelectrode (radius in the 10 microm range). The ability of the spectroelectrochemical method to detect short-lived intermediates is directly related to its capability to probe small volumes. Raman microprobe spectrometry is appropriate for electrochemical applications because it allows the analysis of approximately 1 microm3 of solution. In spectroelectrochemical experiments, such a volume corresponds to a reaction layer of 1 microm thickness. Potentially, this technique can allow the observation of species with lifetimes of the order of 1 ms. To enhance the capabilities of this spectroscopic technique, we utilized it in combination with steady-state voltammetry at a microelectrode, to increase the concentration of unstable intermediates near the electrode surface. To determine the detection limit of this combined technique, we varied the base concentration as a means for varying the lifetime the radical cation electrogenerated from 9,10-dichloroanthracene. Well-resolved resonance Raman spectra were obtained for this radical cation when the lifetime was > or = 0.1 ms. This short time resolution achieved with micro-Raman spectroelectrochemistry makes this technique a powerful tool for the characterization of short-lived intermediates that are generated electrochemically in solution.

Linearly Moving Low-Volume Spectroelectrochemical Cell for Microliter-Scale Surface-Enhanced Resonance Raman Spectroscopy of Heme Proteins

“…Using a Raman microprobe with a high numerical aperture (NA) microscope objective greatly enhances the efficiency of light focusing and collection and allows very small sample sizes (thus an even lower amount of substance), though a spectroelectrochemical cell with the working electrode facing up is needed just below the objective. , …”

Selective Analysis of Redox Processes at the Electrode Interface with Time-Resolved Raman Spectroscopy

“…The current demands on electrochemical materials, sustainable energy, electrocatalysis, and synthetic applications of electrochemistry place increasing attention on the reactions that occur at electrode interfaces. − Heterogeneous electron transfer requires redox-active molecules to approach the Stern layer. Subsequent chemical reactions, for example, comproportionations and molecular rearrangements, take place further from the electrode, typically within the Nernst diffusion layer .…”

“…However, one-electron oxidized and reduced species are often open shell and show strong low-energy absorption bands that are resonant with NIR lasers. Hence, resonance Raman spectroscopy is useful, for example, in the study of redox polymers. ,, …”

“…Hence, resonance Raman spectroscopy is useful, for example, in the study of redox polymers. 3 , 15 , 16 …”

Time-Resolved Monitoring of Electrochemical Reactions Using In Situ Stimulated Raman Spectroscopy

“…A typical current density of 1 mA/cm 2 in 1 ms generates one-electron redox equivalent of 10 –11 mol/cm 2 or 0.1 mM (within a diffusion length of 1 μm), which is below the detection limit of traditional Raman techniques. Thus, to achieve a time-resolved Raman characterization of electrochemical reactions, resonance Raman effect − and surface-enhanced Raman spectroscopy (SERS) , have been employed to improve the SNR. However, both effects restrict the application to a limited number of electrochemical reactions.…”