Porous rotating disk electrode

Rotating Disk Electrode Coated by a Porous Film... 

W. Ryan, R. E. White, and S. L. Kelly, A mathematical model for the initial corrosion rate of a porous layer on a rotating disk electrode, J. Electrochem. Soc. 134, 2154, 1987. 

The anodic dissolution experiments of zinc rotating disk electrode were carried out in alkaline electrolyte [278] and in solution at pH 5.5 containing NH4CI and NH4CI +- ZnCb [279], NH4CI -I- NiCb, and NH4CI - NiCh-h ZnCb [280, 281]. The zinc electrode was covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide [279]. In Ni-containing solutions, the passivation of Zn was a result of Zn-Ni alloy formation and Zn(OH)2 precipitation [280]. 

Samples of biological origin, plant or animal, are best handled by ashing to remove organic matter, followed by placing the sample in solution. The sample can then be excited as a solution by use of a porous cup electrode or a rotating disk electrode. Another approach is to place a known amount of the sample in the cup of a carbon electrode, dry it, and excite the solid residue. If this procedure is followed, it is best to render the electrode impervious to the solution by pretreating the electrode. One method is to fill the electrode cup with a saturated solution of carnauba wax in carbon tetrachloride and dry the electrode at about 100°C for 30 min. A liquid sample then will not penetrate the pores of the electrode. 

Silicon. The snrface of silicon immersed in fluoride media is of interest for semiconductor processing and production of porous silicon (Section 5.7) [541, 542, 549, 550]. A typical current-potential curve of p-Si in a flnoride electrolyte (0.975 MNH4CI + 0.025 MNH4F + 0.025 MHF, pH 2.8) measured at a rotating disk electrode at rotation rate of 3000 rpm and potential scanning speed of 5 mV s is shown in Fig. 7.29. The steep rise of the current density near... 

The question of the frequency dependence of the current distribution and its effect on the measured impedance of a solid state electrochanical system has been hardly considered, although it is important in discussing the impedance of, for example, porous gas electrodes on anion conductors, of rough electrodes (discussed below), and also perhaps of polycrystalline materials. In aqueous electrochemical situations the effects has been considered with respect to the rotating disk electrode, where there may be severe current distribution problems. 

Several basic flow configurations in electrochemical reactors are depicted in Fig. 1. Flow through a porous layer, as would occur in a fuel cell, is shown in (a). Flow along a single plate and through two parallel plates is shown in (b) and (c). A rotating disk electrode is shown in (d). This ccaifiguration reduces mass transfer... 

Figure 11.4. Some standard forms of graphite sample and counter electrodes. Counter electrodes represented by C , sample electrodes by S rotating disk by D , and porous cup by PC." Adapted from Methods for Emission Spectrochemical Analysis, 6th ed., Philadelphia American Society for Testing and Materials, 1971, pp 105-10, by permission of the publisher. Copyright 1971 by the American Society for Testing and Materials.

Electrodes of many shapes and sizes have been used and almost any shape of electrode can be made if desired. Figure 5-20 shows some of the basic electrode types and shapes. A simple cup, such as shown in Figure 5-20a, is often used for powder samples. The sample is placed in the cup and an arc struck between the cup and a counter electrode. The sample is vaporized and excited in the arc. In Figure 5-20b the cup is undercut. The temperature of the cup rises more rapidly in this case. Often the sample and cup are both volatilized into the arc. A porous cup electrode is shown in Figure 5-20c. The cup is filled with liquid and passes slowly through the porous bottom end of the electrode. An arc or spark is struck to a lower counter electrode to excite the sample. Another technique useful for liquids uses a disk electrode, as shown in Figure 5-20d. The disk rotates and feeds liquid into the arc or spark gap for excitation. Another method to introduce a liquid sample into the arc or spark is to use a cored electrode as shown in Figure 5-20e. The solution enters the electrode gap by capillary action in the core. 

One result of utilizing the rotating disk, porous cup, or spray technique for introducing the liquid sample into the analytical gap is that fractional distillation of the sample is not a problem. If the sample is dried on an electrode, fractional distillation of the sample into the arc or spark may occur as with any solid sample. This effect is most evident with dc arc excitations. 

Appleby, A. and Savy, M. (1978). Kinetics of Oxygen Reduction Reactions Involving Catalytic Decomposition of Hydrogen Peroxide Application to Porous and Rotating Ring-disk Electrodes, J. Electroanal. Chem., 92, pp. 15-30. 

Lima FHB, Ticianelli EA (2004) Oxygen electrocatalysis on ultra-thin porous coating rotating ring/disk platinum and platinum-cobalt electrodes in alkaline media. Electrochim Acta 49 4091-4099... 

Lima, B. Ticianelli, A. (2004). Oxygen Electrocatalysis on Ultra-thin Porous Coating Rotating Ring/Disk Platinum and Platinum-Cobalt Electrodes in Alkaline Media. Electrochimica Acta, Vol.49, No.24, (September 2004), pp. 4091-4099, ISSN 00134686 Kotz, R Yeager, E. (1980). Raman Studies of the Silver/Silver Oxide Electrode. Journal of Electroanalytical Chemistry, Vol.lll, No.l, (July 1980), pp. 105-110, ISSN 00220728 Demarcormay, L., Coutanceau, C. Leger, M. (2004). Electroreduction of Dioxygen (ORR) in Alkaline Medium on Ag/C and Pt/C Nanostructured Catalysts - Effect of the Presence of Methanol. Electrochimica Acta, Vol.49, No.25, (October 2004), pp. 4513-4521, ISSN 00134686... 

---