Ring-disk electrode construction

Figure 3.12 Construction of rotated-disk and ring-disk electrodes (a) hydrodynamic disk electrode for high rotation speeds (b) side and bottom views of a ring-disk electrode with wells for carbon paste or press-fit noble metals.

The construction of these electrodes requires precise machining of the disk, the Teflon shroud, and the spacers. Ring-disk electrodes now are available commercially (Pine Instrument Co., Grove City, Penn.), and most workers will prefer to buy them rather than to attempt their fabrication. The expression for the limiting current at a disk electrode is shown in Table 5.9. 

S. Vesztergom and G.G. Lang, The construction of a novel eleetroehemical measuring system for enhanced rotating ring-disk electrode experiments. Journal of Instrumentation Science and Technology 4 (2013) 82-95. 

A special form of a rotating electrode is the ring-disk electrode, a schematic diagram of which is shown in Fig. 63. The electrode is constructed from a centre disk which is conducting and is connected to its own voltage source and recorder. The ring, which is also conducting, is separated from the disk... 

Notice that for given reaction conditions (Cq and m), a ring electrode will produce a larger current than a disk electrode of the same area. Thus, the analytical sensitivity of a ring electrode (i.e., the current caused by a mass-transfer-controlled reaction of an electroactive species divided by the residual current) is better than that of a disk electrode, and this is especially true of a thin ring electrode. However, it is usually more difficult to construct a rotating ring electrode than an RDE. 

One important application of amperometry is in the construction of chemical sensors. One of the first amperometric sensors to be developed was for dissolved O2 in blood, which was developed in 1956 by L. C. Clark. The design of the amperometric sensor is shown in Figure 11.38 and is similar to potentiometric membrane electrodes. A gas-permeable membrane is stretched across the end of the sensor and is separated from the working and counter electrodes by a thin solution of KCl. The working electrode is a Pt disk cathode, and an Ag ring anode is the... 

Techniques have been devised for constructing microelectrodes of various geometries, such as hemispheres, disks, cylinders, rings, and bands. In addition, because the electrodes themselves are smaller than their associated diffusion layers, arrays of closely spaced microelectrodes have also been of considerable practical and theoretical interest. In this section, construction of the more frequently employed microelectrode configurations is described. First, however, it should be pointed out that several commercial sources of microelectrodes now exist, and these may represent an economically viable alternative to the do-it-yourself approach for those who anticipate requiring only a few electrodes for... 

In addition to disks and cylinders, microelectrodes with the geometry of bands and rings have also been constructed and used. Bands, like cylinders, exhibit the properties of microelectrodes by virtue of their narrow width, yet pass large currents due to their length. Ring electrodes, on the other hand, have been of interest because they can be constructed with very small surface areas. 

Stirred-flow reactors retain all the advantages of flow methods in general and eliminate all the problems associated with the thin-disk method. They also retain many advantages of the batch method. Reaction products desorbed into solution are continually removed. Film or particle diffusion is reduced or eliminated by mixing within the reactor. Direct control with feedback of reactor conditions is possible. Although stirred-flow reactors normally have much smaller volumes than conventional batch reactors, it is possible to construct a pH-stat stirred-flow reactor by inserting a microcombination pH electrode and microburette tip into the reactor. The O-rings can provide leak-proof seals where the electrode and burette tip enter the reactor. The electrode and burette tip are connected to an autotitrator as in the conventional batch reactor. 

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