Rotating ring-disc

The addition of various Kolbe radicals generated from acetic acid, monochloro-acetic acid, trichloroacetic acid, oxalic acid, methyl adipate and methyl glutarate to acceptors such as ethylene, propylene, fluoroolefins and dimethyl maleate is reported in ref. [213]. Also the influence of reaction conditions (current density, olefin-type, olefin concentration) on the product yield and product ratios is individually discussed therein. The mechanism of the addition to ethylene is deduced from the results of adsorption and rotating ring disc studies. The findings demonstrate that the Kolbe radicals react in the surface layer with adsorbed ethylene [229]. In the oxidation of acetate in the presence of 1-octene at platinum and graphite anodes, products that originate from intermediate radicals and cations are observed [230]. 

Santos MC, Machado SAS (2004) Microgravimetric, rotating ring-disc and voltammetric studies of the underpotential deposition of selenium on polycrystalline platinum electrodes. J Electroanal Chem 567 203-210... 

Here we have to deal with three types (see Fig. 3.68), viz. (a) the rotating disc electrode (RDE), and (b) the rotating ring electrode (RRE) and the rotating ring-disc electrode (RRDE). The construction of the latter types suits all purposes, i.e., if the disc or the ring is not included in the electric circuit, it yields an RRE or an RDE, respectively, and if not an RRDE, where either the disc forms the cathode and the ring the anode, or the reverse. 

The Controlled-Convection Techniques The Rotating Disc and Rotating Ring-Disc Electrodes... 

The controlled-convection techniques the rotating disc and rotating ring-disc electrodes... 

There arc many controllcd-convection techniques available but we will restrict our discussion to the two most commonly employed by the electrochemist the rotating disc electrode (RDE) and the rotating ring disc electrode (RRDE). 

To learn that the rotated ring-disc electrode (RRDE) is one of the most powerful analytical tools for following the kinetics of fast homogeneous reactions. 

Related to the rotated disc electrode (RDE) is the rotated ring-disc electrfxle (RRDE). Such an electrode is illustrated in Figure 7.9 and is seen to be, in effect, a modified RDE, insofar as the central disc is surrounded with a concentric ring electrode. The gap between the ring and the disc is filled with an insulator such as Teflon or epoxy resin. The face of the RRDE is polished flat in order to prevent viscous drag, which is itself likely to cause the induction of eddy currents. 

Figure 7.9 Schematic representation of a rotated ring-disc electrode, defining the radii ri (the radius of the disc), and rj and rs (the inner and outer radii of the ring, respectively).

The rotated ring-disc electrode (RRDE) has been shown to be an ideal tool for measuring the rate constants of very fast homogeneous reactions. In this method, we start with one reagent in the solution while the other is electrogenerated at the disc electrode, with the proportion of the latter that remains after reaction being monitored at the ring electrode. 

Albery, W. J. and Hitchman M. L., Ring-Disc Electrodes, Oxford University Press, Oxford, 1971. This now-classic book describes one of the most formidable tools in the arsenal of the electroanalyst, i.e. the rotated ring-disc electrode (RRDE). Its first two chapters are a clear and lucid introduction to the basic rotated disc electrode (RDE) and the multi-faceted problems of mass transport. Well worth a read, if only for the occasional dip into this field. 

The article by Hitchman and Hill (above) is again useful here in that it also contains an introduction to the rotated ring-disc and wall-jet electrodes. 

Rotated ring-disc electrode (RRDE) Disc electrode within a concentric ring electrode. 

Considerable progress. However, has been achieved in the recent past due to the development of techniques for the detection of intermediates in low concentrations, such as the rotating ring—disc electrode and in situ spectroelectrochemical techniques such as electron spin resonance (ESR). 

Use of twin electrode cell [103] or rotating ring disc electrode [104] techniques permit the independent separation of the charge and amount... 

The electrosorption valency usually increases as the underpotential decreases to approach the ionic charge (total discharge of the cation) close to the Nernst potential, for instance in the case of lead and thallium upd on silver [114]. However, the co-adsorption of anions may contribute to the observed apparent electrosorption valence, as rotating ring disc electrode (RDE) experiments have shown [113]. 

W.J. Albery, Rotating Ring-Disc Electrodes, Oxford University Press, Oxford, 1971. 

The rotating ring—disc electrode (RRDE) is probably the most well-known and widely used double electrode. It was invented by Frumkin and Nekrasov [26] in 1959. The ring is concentric with the disc with an insulating gap between them. An approximate solution for the steady-state collection efficiency N0 was derived by Ivanov and Levich [27]. An exact analytical solution, making the assumption that radial diffusion can be neglected with respect to radial convection, was obtained by Albery and Bruckenstein [28, 29]. We follow a similar, but simplified, argument below. 

A. Rotating ring—disc electrode. Wall-tube electrode. 

It is more difficult to manufacture these electrodes than the simple disc electrode since the ring must be exactly concentric with the disc. Additionally, in many applications the insulation gap must be thin (0.25 mm or less) as must the ring. For rotating ring—disc electrodes, typical dimensions are a disc radius of 3—4 mm and an outer ring radius of 4—5 mm. For wall-jet ring—disc electrodes, these dimensions can be approximately halved. 

Fig. 7. Typical rotating ring—disc electrode cell. A, rotating ring—disc electrode B, reference electrode with Luggin capillary C, counter electrode D, teflon lid E, porous frit F, thermostatted water jacket.

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