Rotating ring disc electrodes

THE POTENTIOSTAT AND CORROSION STUDIES Rotating Disc-ring Electrodes... 

In reactions involving gas evolution, the RRDE can be problematic in that bubbles may become trapped at the centre of the disc electrode. To obviate this, a rotating double ring electrode was suggested [34], The collection efficiency, N0, is given by eqn. (41) if we define... 

Figure 15. Rotating disk-ring electrode measurements for O2 reduction on Ru(1010) in 0.1 M HCIO4. Sweep rate 20 mV s ring potential E = 1.2 V disc area 0.282 cm rotation rates are indicated in the graph. The insert shows the logy Kjd-j) vs. E plot obtained for 1600 rpm. Reprinted from Copyright (2002) with permission from Elsevier.

Most electrochemical cells consist of three electrodes working electrode, counter electrode, and reference electrode. In some applications, however, the working electrode is split into several separate electrodes, e.g., in rotating disc/ring systems (Rotating Disc Electrode). This requires an independent potential control of the working electrodes. 

Sakashita M, Lochel B, Strehblow HH (1982) An examination of the electrode reactions of Te, HgTe and Cdo.iHgo.sTe with rotating-split-ring-disc electrodes. J Electroanal Chem 140 75-89... 

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. 

Fig. 3.68 shows the longitudinal section and the bottom view of the electrode and also a section of the streamlines of flows in the solution near the bottom and symmetrical to. the axis of rotation of the electrode the electric circuit is provided for instance by brush contacts at the top of the brass shaft of the disc and/or at the brass collar of the ring it is essential for the proper functioning of the electrode that its rotation is kept rigidly centralized by means of bearings in order to exclude swinging as far as possible. 

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). 

In contrast to the rotating disc electrode, mass transport to the ring is nonuniform. Nevertheless, the thickness of the diffusion layer Spj, which depends on the coordinate x in the direction of flow, and the rate of mass transport can be calculated. We consider a simple redox reaction, and rewrite Eq. (14.5) in the form ... 

We note in passing that the same equation holds for the rotating disc electrode. Though the mass transport on the ring is nonuniform, the ratio ared/a0x) and hence also, turns out to be constant, so Eq. 

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. 

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. 

At heart, this titration method can be summarized as following the concentration of a reagent as a function of time Analyses with the RRDE are identical in concept. Analyte is formed at the central disc electrode, and because the disc rotates, such analyte is swept outward, past the ring electrode, and hence returned to the bulk solution. However, because the... 

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. 

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

Oxidation of ketone phenylhydrazones generates a radical-cation centre on the nitrogen atom adjacent to the benzene ring. The radical-cation is delocalised by both the hydrazone group and the phenyl ring. Reactions of 1,3,5-triphenyl-A -pyazolines illustrate the properties of these radical-cations. Two one-electron waves are seen at a rotating disc electrode in acetonitrile and for 1,3.5-triphenyl-pyrazoline, Ey. = 0.82 and 1.68 V vs. see [33]. The delocalised radical-cation is... 

In this section, we consider mass transport-controlled currents to disc and concentric ring electrodes on a planar spinning disc surface. For other less common rotating electrodes, e.g. rotating hemisphere, see Table 3. 

When p = 1 (disc electrode), 5N is independent of r. This shows us immediately that the rotating disc electrode is a uniformly accessible surface, whereas the rotating ring electrode is not. Substitution of eqn. (24) into eqn. (22) and evaluation gives the well-known... 

A variant of the RRDE in which the ring is split into two parts (the rotating split ring-disk electrode) was invented to enable the detection of different intermediates produced at the disc electrode [32]. It was shown that the current at the ring segments is proportional to the length and that there is no interference between the segments [9, 33]. 

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