Rotating Disk Electrode Electrochemical Cell

FIGURE 7.9 Three-electrode RDE cell connected to potentiostat (1) electric motor, (2) RDE, (3) reference electrode, (4) counter electrode, and (5) thermometer. 

FIGURE 7.10 A schematic of the three-electrode RDE cell, a potentiostat to carry out measurements, and a computer to control the system with storing the obtained data. 

FIGURE 7.11 Platinum RDE (1) polished mirror smooth surface of platinum and (2) outer shaft made by nonconducting polytetrafluoroethylene (PTEE), which is called Teflon by DuPont Co., who discovered this compound. 

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Schmidt TJ, Gasteiger HA, Behm RJ. 1999b. Rotating disk electrode measurements on a high-surface area Pt/Vulcan carbon fuel cell catalyst. J Electrochem Soc 146 1296-1304. 

Two types of cell have been described. In Fig. 1 a cell with a rotating disk electrode is shown. Connections to a pH-stat and to the interface are indicated simultaneously with recording CMT measurements, the metal and reference electrode and a counter electrode (not shown in Fig. 1) can be connected to a potentiostat, so that electrochemical measurements can be recorded intermittently. The volume of solution in the cell is ca. 400 ml. What matters for safe and reliable conditions of measurement is that the disk electrode rotating at a speed of no less than 1000 rpm ensures efficient stirring, so that the effect of alkali formed at the corroding metal (or sometimes at the counter electrode located ca. 1 cm below and parallel to the metal electrode) is immediately sensed effectively by the glass electrode and also the effect of acid supplied from the autoburet is quickly detected. 

Several cell configurations are common in electrochemical research and in industrial practice. The rotating disk electrode is frequently used in electrode kinetics and in mass-transport studies. A cell with plane parallel electrodes imbedded in insulating walls is a configuration used in research as well as in chemical synthesis. These are two examples of cells for which the current and potential distributions have been calculated over a wide range of operating parameters. Many of the principles governing current distribution are illustrated by these model systems. 

Hydrodynamic boundary layer — is the region of fluid flow at or near a solid surface where the shear stresses are significantly different to those observed in bulk. The interaction between fluid and solid results in a retardation of the fluid flow which gives rise to a boundary layer of slower moving material. As the distance from the surface increases the fluid becomes less affected by these forces and the fluid velocity approaches the freestream velocity. The thickness of the boundary layer is commonly defined as the distance from the surface where the velocity is 99% of the freestream velocity. The hydrodynamic boundary layer is significant in electrochemical measurements whether the convection is forced or natural the effect of the size of the boundary layer has been studied using hydrodynamic measurements such as the rotating disk electrode [i] and - flow-cells [ii]. 

Installation of the catalyzed electrode into the electrochemical cell for measurement. This process is suitable for stationary electrode measurement, rotating disk electrode (RDE), and/or rotating ring-disk electrode (RRDE). 

J. Wang and B. A. Freiha, Thin-Layer Flow Cell with a Rotating Disk Electrode. J. Electroanal. Chem. Interfacial Electrochem., 164 (1984) 79. 

Figure 4,29 Electrochemical cell with a rotating disk electrode.

R. (1984) A rotating disk electrode apparatus for the study of fuel cell reactions at elevated temperatures and pressures. J. Electrochem. Soc., 131, 1215. 

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... 

A bipolar rotating disk electrode is shown in (c). Electrolyte impinges on both sides of a rotating electrode (shaded). Each side is a separate electrochemical ceU. The rotating disk is bipolar in that it serves as the positive electrode for the upper ceU (the electrolyte between the upper stator (+) and the rotor) and the negative electrode of the lower cell. A fluidized-bed reactor based on a shell and tube heat exchanger is shown in (d). Catholyte fluid enters the bottom of the reactor (tube side) and flows upward to fluidize the bed around the... 

The rotating disk electrode (RDE), although best known to the electrochemist as an analytical tool, has been considered as the basis for an electrochemical reactor. Apart from this, as will be seen in Section 3.2.2.2, it is the preferred experimental equipment for determining kinetic constants when setting up a reaction model. To do this, however, the value of for the particular RDE cell arrangement must be known. 

Figure 2.21 Gas-tight Pyrex glass electrochemical cell for use with (A) moderate-melting molten salts (35) and (B) gas-tight cell with a magnetically coupled drive for rotating-disk electrode voltammetry in moderate-melting salts (36).

All of the catalysts synthesized are listed in Table 2, and the performance in rotating disk electrode (RDE) in acid conditions are depicted in Fig. 6 [65, 67, 70-72]. In RDE tests (RRDE-3A ALS coupled with a Bio-Logic SP-150 multi-potentiostat), a conventional three-electrode electrochemical cell configuration, equipped with a glassy carbon disk working electrode (0.1256 cm geometric area), a Pt helical wire counter electrode, and a saturated calomel (SCE) reference electrode, was used. The activity of a commercial 40 % Pt/C (Hyspec 6000 from Johnson Matthey) catalyst was assessed as well, as reference catalyst toward ORR. 

Figure 3.6. Hydrogen oxidation current on rotating disk electrode at 20 mV in 0.1 M HCIO4 saturated with 100 ppm CO/H2 at room temperature [69]. (Reproduced by permission of ECS—The Electrochemical Society, from Holleck GL, Pasquarello DM, Clanson SL. Carbon monoxide tolerant anodes for proton exchange membrane fuel cells.)...

Since a fuel cell is an electrochemical device, electrochemical mefliods are deemed to play important roles in characterizing and evaluating the cell and its components such as the electrode, the membrane, and the catalyst. The most popular eleetroehemical characterization methods include potential step, potential sweep, potential cycling, rotating disk electrode, rotating ring-disk eleetrode, and impedance spectroscopy. Some techniques derived from these methods are also used for fuel cell characterization. 

Merzougui B, Swathirajan S. Rotating disk electrode investigation of fuel cell catalyst degradation due to potential cycling in acid electrolyte. J Electrochem Soc 2006 153 A2220-6. 

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