Rotating disc electrode studies

Whilst this may initially appear to be in opposition to the results of the optical rotating disc electrode study on colloidal CdS (Fig. 9.9), this may be readily explained by consideration of the relatively low illumination intensities used in the ORDE experiments, and the high surface state concentrations typical of the samples employed therein. The former precludes the generation of a Burstein shift while the latter, with a quantum yield of 0.77 for (S )surf generation from S2 ions at the CdS particle surface [115, 116], provides a highly efficient mechanism for positive charge accumulation at the particle surface. 

Boto KG, Williams LFG (1977) Rotating disc electrode studies of zinc corrosion , Jo rwa/... 

Platinum has also had its share of attention in recent years. The effect of phosphoric acid concentration on the oxygen evolution reaction kinetics at a platinum electrode using 0-7 m-17-5 m phosphoric acid at 25°C has been studied with a rotating disc electrode . The characteristics of the ORR are very dependent on phosphoric acid concentration and H2O2 is formed as an intermediate reaction. Also, platinum dissolution in concentrated phosphoric acid at 176 and 196°C at potentials up to 0-9 (SHE) has been reported . 

C60 has been used to produce solvent-cast and LB films with interesting photoelec-trochemical behavior. A study of solvent-cast films of C60 on Pt rotating disc electrodes (RDEs) under various illumination conditions was reported [284]. Iodide was used as the solution-phase rednctant. The open-circuit potential shifted by 74 mV per decade of illumination intensity from a continuous wave (cw) argon-ion laser. The photocurrent versus power was measured at -0.26 V under chopped illumination (14-Hz frequency, vs. SCE) up to 30 mW cm and was close to linear. The photoexcitation spectrum (photocurrent versus wavelength) was measured at 0.02 V (vs. SCE) from 400 to 800 mn and found to be... 

Zutic, V., and W. Stumm (1984), "Effect of Organic Acids and Fluoride on the Dissolution Kinetics of Hydrous Alumina. A Model Study Using the Rotation Disc Electrode", Geochim. Cosmochim. Acta 48, 1493-1503. 

None of the set-ups discussed so far provides stirring of the electrolyte for bubble removal or for enhancement of the reaction rates. A standard set-up developed to study kinetic electrode processes is the rotating disc electrode [11]. The electrode is a small flat disc set in a vertical axle. The hydrodynamic flow pattern at the disc depends on rotation speed and can be calculated. An additional ring electrode set at a different potential provides information about reaction products such as, for example, hydrogen. However, because this set-up is designed to study kinetic processes and is usually equipped with a platinum disc, it becomes inconvenient if silicon samples of different geometries have to be mounted. 

Recently, the mechanism of cathodic electrodeposition of ZnO thin films from aqueous Zn(N03)2 baths has been studied using a rotating disc electrode [165]. Non-electrochemical methods of preparation of ZnO were also described, but they are not covered in this review. 

The authors [373] have studied the effect of prolonged cathodic polarization at negative potentials (E < 0.00 V) using both gold wire and rotating disc electrodes. They have shown that Au electrode prepolarized at —0.60 V for 20 min reveals in... 

The mechanism of anodic dissolution of silver in cyanide solutions has been studied by Bek and coworkers [378-380]. For example, using [379] the rotating disc electrode and pulse potentiostatic method, it has been found that the limiting step involved the formation, at the electrode surface, of the adsorbed complex with two... 

Sun et al. [382] have studied the dissolution behavior of gold and silver from Au—Ag alloys in aerated cyanide solutions using rotating disc electrodes. 

A rotating disc electrode (RDE) is a conductive disc of the material of interest embedded in an inert non-conductive polymer or resin that can be attached to an electric motor which has very fine control of the electrode s rotation rate. During the experiment, the electrode rotates in the solution under study, thus inducing a flux of redox analyte to the electrode [75]. 

The method of resolution of (8.1) was indicated in Sections 5.7-5.9, showing as an example the calculation of the limiting current at the rotating disc electrode. In this chapter we discuss this and other hydrodynamic electrodes used in the study of electrode processes. The rotating disc electrode has probably been the hydrodynamic electrode... 

Another example of a similar rotating disc electrode with an EQCM has been reported by Ritchie et al. [22] for the study of gold and copper dissolution during the electroreduction of oxygen in alkaline cyanide solutions. 

Fortunately, the low enol content in simple ketone systems does not necessarily impose an obstacle to generating the corresponding enol radical cations in solution. As outlined in Sect. 2 the selective oxidation of the enol tautomer even in the presence of a vast excess of the ketone opens up an indirect, but quantitative access to enol radical cation intermediates for all systems, if an appropriate oxidant has been chosen. The first, albeit indirect evidence for this selective oxidation step stems from kinetic studies by Henry [109] and Littler [110-112] and will be discussed in more detail in Sect. 3.3. Direct evidence for a specific oxidation of enols was provided by Orliac-Le Moing and Simonet [108]. Using voltammetry at a rotating disc electrode they were able to establish a linear correlation between the anodic current and the enol content for various a-cyano ketones 11. In electrolysis experiments the corresponding 1,4-diketones 13 were obtained in high current yield (ca. 90%). 

Figure 4-1. Protein film voltammetry as a technique for studying redox enzyme mechanisms. The catalytic current-potential profile provides information on the rate-defining catalytic processes occurring within the enzyme. It is important that interfacial electron transfer is facile and information is not masked by limitations due to tlie transport of substrate and product for this reason the rotating disc electrode is an important tool in these studies.

Bartlett, P. N. Pratt, K. F. E. A study of the kinetics of the reaction between ferrocene monocarboxylic acid and glucose-oxidase using the rotating-disc electrode. J. Ekctroanal. Chem. 1995, 397, 53-60. 

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