Transforms in Spectroelectrochemistry

OPTICAL DIFFRACTION BY ELECTRODES USE OF FOURIER TRANSFORMS IN SPECTROELECTROCHEMISTRY... 

Infrared spectroelectrochemical methods, particularly those based on Fourier transform infrared (FTIR) spectroscopy can provide structural information that UV-visible absorbance techniques do not. FTIR spectroelectrochemistry has thus been fruitful in the characterization of reactions occurring on electrode surfaces. The technique requires very thin cells to overcome solvent absorption problems. 

For the first reduction the IR shifts point to a porphyrin-centred electron transfer. This is supported by further spectroscopy on the anion radical complexes [(Por)Ru(CO)(L)]. The observed EPR lines are narrow, unstructured, with g values around 2. The UV-Vis-NIR spectra of the radical anions are characterised by redshifted Soret bands of reduced intensity, a weak structured band system around 600 nm and weak broad absorptions around 800 or 900 nm (see Figure 4.15). Further support comes from resonance Raman investigations on [(OEP)Ru(CO)(THF)] for which the observed Raman bands fit perfectly to those of the [(OEP)VO] radical anion. There is some evidence that if the spectroelectrochemistry is not carried out in very aprotic and unpolar solvents or traces of water are present, the radical anionic complexes are readily transformed. This has been investigated for the [(OEP)Ru(CO)(L)] system, where the use of solvents like MeOH or nitriles for the electrochemical reduction leads to altered species with unreduced porphyrin ligands (see Figure 4.15)." ... 

Although spectroelectrochemistry with transparent electrodes has been used extensively to obtain new information inaccessible to other methods, there remains room for significant improvement in the area of sensitivity. Consider reaction 1, in which R is a colorless reactant which is transformed electrochemically to some colored product P. 

Vis-NIR absorption spectroelectrochemistry is usually performed using specifically designed three-electrode cells adapted to transmission or reflection geometries. However, it should be noted that building a set-up for transmission Vis-NIR spectroelectrochemistry is a fairly simple task, at least to study the doping processes in thin films. Any optical cell can be transformed into a spectroelectrochemical cell by insertion of transparent indium tin oxide (ITO)-covered plates as electrodes. Therefore, basic in situ Vis-NIR spectroelectrochemistry can be performed in all laboratories where a spectrophotometer and an electrochemical setup are available. 

In situ subtractively normalized interfacial Fourier transform infrared reflectance spectroelectrochemistry (SNIFTIRS) studies confirm this prediction [37]. They also... 

Fang et al. have investigated the influence of pH on the mechanism of ethanol electrooxidation on a palladium electrode [80]. Cyclic voltammetry and in situ Fourier Transform Infrared (FTIR) spectroelectrochemistry were used for identification of the oxidation products at different NaOH concentrations. The activity for ethanol oxidation on Pd was largely affected by pH as well as by the resulting product. Sodium acetate was the main product for NaOH concentrations higher than 0.5 M. Nevertheless, CO2 was identified as the pH was lowered (below 13). 

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