Spectroelectrochemistry in Transmission Mode

A very simple spectroelectrochemical experiment based on a conventional cuvette for UV/Vis spectroscopy with electrodes immersed in the solution phase is shown in Fig. II.6.4. The optically transparent working electrode is located directly in the beam path and additionally a large surface area counter electrode 

In order to improve the detection of short-lived intermediates, the potential step or chronoamperometric experiment can be replaced by a cyclic voltam-metric experiment, which involves applying a triangular potential ramp. With a fast UV/Vis spectrometer, e.g. a diode array system, additional UVA/ is/NIR spectroscopic information as a function of the potential can be recorded simultaneously to the voltammetric data. However, recording cyclic voltammograms with the simple cell shown in Fig. II.6.4 is complicated by the presence of ohmic drop in the solution phase which is amplified by poor cell design. In this kind of cell, the peak-to-peak separation in cyclic voltammograms of a reversible redox couple may increase by several hundreds of millivolts. Voltammetric data (and simultaneously recorded spectroscopic data) are therefore very difficult to interpret quantitatively. 

As a further requirement, many electrochemical investigations have to be carried out under an inert atmosphere of argon or nitrogen, and sometimes in predried organic solvents. Therefore, a lid with gas inlet and gas outlet is used combined with a septum seal, which allows solvent to be introduced into the cell without it coming into contact with the ambient atmosphere. The insulation of the OTE requires a material resistant to commonly used organic solvents. Commercially available lamination foil, used for protecting documents, has been em- 

As a further practical tip, for an OTE based on a thin conductive optically transparent layer, the resistance of the working electrode can be reduced if an additional thicker metal layer is coated on the optically transparent film in the region not exposed to the light beam under the insulation layer. If the insulation is prepared via lamination, a thin metal foil can be simply inserted instead of the deposited metal layer. This new cell design (Fig. II.6.5) enables cyclic voltam-mograms as well as current time curves in the case of a potential step experiment (chronoamperograms) simultaneously with a series of time-resolved spectra to be recorded. This experimental approach allows absorbance-potential or absorbance-time curves to be recorded to analyse the reaction kinetics of the generation of intermediates and the final product up to a time scale of approximately 0.1 s life-time. 

Unfortunately, even when capillary slit cells are used in the experiment, the spectra of the different species are still superimposed. Therefore, it is necessary to separate or to deconvolute the superimposed spectra in order to obtain information about the reaction kinetics of individual species. In the literature, techniques have been proposed for the deconvolution of the superimposed spectra [60,61]. Data processing and deconvolution may be achieved with spreadsheet software on a suitable computer system. As soon as the time dependence of the 

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