Reflectivity change potential scan

FIGURE 27.26 Cyclic voltammogram obtained on An electrode in O.IM NaCI04 (a) and reflectivity change-potential curves for O.IM NaC104 (b), O.IM LiCI04 (c), O.IM NaNOj (d), and 0.1 M NaOH (e). Scan rate 0.1 V/s. (From Aral et al., 1997, with permission from... 

A. Observation of Reflectivity Change During a Potential Scan... 

A. OBSERVATION OF REFLECTIVITY CHANGE DURING A POTENTIAL SCAN... 

The mode of reflectivity change observed with the scanning of applied potential E R/Rq - E curve) is schematically depicted in Fig. 4. Typical results for solutions with or without organic species are shown in Fig. 4, from which it is evident that R/Ro drops in value in the potential range where adsorption takes place. 

Fig. 2.8 Result of simultaneous measurement of current and change of reflectance during cyclic potential scan at 100 mV for a sub-monolayer of hemin on an HOPC electrode in 0.1 M Na2B407 aqueous solution. In part (a), potential, current, and dc reflectance change (ARjJ a a wavelength...

When the potential was scanned to 0 mV, a pair of waves due to the redox of the azobenzene moiety appeared, in addition to that of ferrocene in the first potential scan (sohd line in Fig. 13c). The wave due to the redox of azobenzene, however, disappeared, and the redox potential and the peak separation of the redox wave due to ferrocene became more negative and smaller, respectively, in the second scan (dotted line in Fig. 13c). The redox potential and the peak separation returned to the original values after UV irradiation. These changes in the electrochemical characteristics of the latter electrode were reversible. On the basis of the structural analysis results by in situ Fourier-transform infrared reflection absorption spectroscopy (FT-IRRAS), we concluded that the electrochemical properties, that is, the redox potential and the charge transfer rate, of the ferrocene group in the SAM-modified gold electrode can be reversibly controlled... 

As discussed later, this potential scan rate can be used to study electrode kinetics. For example, if the potential scan rate is too fast, the electrochemical reactions on the electrode may not be able follow the electrode potential change, which willbe reflected on the CVs (current-potential curves) recorded as a function of potential scan rate. From this potential scan rate dependence, the reaction kinetics can be deduced qualitatively and quantitatively. 

In the second case the potential can be modulated between two values (a reference and a sample potential) while the spectral frequencies are slowly scanned, or else the spectral data can first be collected at a reference potential, after which this is stepped to the sampling value where a second spectrum is obtained. The change in reflectivity AR/R is then computed,... 

Moreover, each of the chemical and electrochemical reactions can have different reaction rates and reversibilities. All of them are reflected in cyclic voltammograms. If we measure cyclic voltammograms of an electrode reaction, changing parameters such as potential range, voltage scan rate, temperature, electrode material and solution composition, and analyze the voltammograms appropriately, we can obtain information about the electrode reaction. However, except for cases where the electrode process is very simple, it is not easy to analyze the cyclic voltammograms appropriately. 

Fig. 28. Change with potential of the reflection absorption at constant wavenumbers from a platinum electrode under a fast cyclic voltammetric condition. 5M CH3OH + 1M HC104 sweep rate 8.5 V s 1, 256 scans.

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