The rotating disk electrode rde

For theoretical references on the rde, see Levich (1962) and Albery and Hitchman (1971). Digital simulation studies include the classical work of Prater and Bard (1970), Clarenbach et al (1973) and, more recently, Feldberg (1980), to name but a few. These all used the box method, while Hoyer and Kryger (1985) used the point method. 

Some useful quantities with the rde (see Levich 1962) are hydrodynamic layer thickness 

In these equations, v is the hydrodynamic viscosity of the solution, w the angular rotation rate. The Prandtl number is usually of the order of 1000 - that is, the diffusion layer at a rde is only about 1/5 the thickness of the hydrodynamic layer. An excellent work on the significance of Pr in electrochemistry is that of Vielstich (1953). 

The coordinate system used is shown in Fig. 8.1. Levich (1962) showed that, to a good approximation, the velocity of fluid away from the disk, v.  

It is this equation whose solution gives the quantities in Eqs. 8.17 and 8.19. There is also radial convection but it is of secondary importance. If the disk is small, that is, r is comparable with S, edge effects become important the system then becomes two-dimensional, as transport in the radial direction cannot be ignored. This is also the case when a ring is present. We confine ourselves to one dimension for the moment. 

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Volt mmetiy. Diffusional effects, as embodied in equation 1, can be avoided by simply stirring the solution or rotating the electrode, eg, using the rotating disk electrode (RDE) at high rpm (3,7). The resultant concentration profiles then appear as shown in Figure 5. A time-independent Nernst diffusion layer having a thickness dictated by the laws of hydrodynamics is estabUshed. For the RDE,... 

At the rotating-disk electrode (RDE Fig. 4.6), it is the solid electrode and not the liqnid that is driven bnt from a hydrodynamic point of view this difference is nnim-portant. Liquid flows, which in the figure are shown by arrows, are generated in the solution when the electrode is rotated around its vertical axis. The liquid flow impinges on the electrode in the center of the rotating disk, then is diverted by centrifugal forces to the periphery. 

The rotating hemispherical electrode (RHSE) was originally proposed by the author in 1971 as an analytical tool for studying high-rate corrosion and dissolution reactions [13]. Since then, much work has been published in the literature. The RHSE has a uniform primary current distribution, and its surface geometry is not easily deformed by metal deposition and dissolution reactions. These features have made the RHSE a complementary tool to the rotating disk electrode (RDE). 

The most well-known hydrodynamic technique is the Rotating Disk Electrode (RDE) voltammetry, which, however, needs proper equipment. For information on this technique the reader is referred to specialized treatments.2"4 We prefer here to mention a simpler technique which can be carried out on the same equipment used for cyclic voltammetry. This technique is referred to as voltammetry at an... 

Rotating-Disk Electrode, Study of the kinetics and mechanism of electrode processes under well-defined mass transport conditions is possible through use of methods of the rotating-disk electrode (RDE). The RDE consists of a disk of metal embedded in a cylindrical insulator (e.g., Teflon) holder (see Fig. 6.24). It is rotated about its center. Only the bottom end of the metal disk is exposed to the solution. 

The rotating disk electrode (RDE) is an important system in electrochemistry. Axial followed by radial flow across the disk brings fresh solution to all points across the disk (Fig. 6). The surface is therefore uniformly accessible to reacting species. The RDE operates under laminar flow for Re < 1.7 X 105. Flow is turbulent above 3.5 X 105 and is transitional in between (4). Thus the system is less practical for the study of corrosion under turbulent conditions but enjoys widespread use in research electrochemistry. For the rotating disk electrode, the laminar mass transport correlation obtained in the literature is given by Levich (10) ... 

These methods constitute the frame on which any particular method can be elaborated. Yet in practice, the experimental difficulty is that with standard apparatus, 5 /D cannot be varied over an extremely wide range. For example, with the rotating disk electrode (RDE), which is the most convenient steady-state method (with the exception of ultramicroelectrodes [109]), 8 depends on the rotation frequency w of the electrode (see Chapter 2). Yet to maintain correct hydrodynamic conditions w cannot be varied, with... 

Another means of determining D, provided n is known, relies on the use of the rotating disk electrode (RDE). Based on the pioneering work of Levich [39], the steady state diffusion limiting current, measured at an RDE is given by ... 

The hydrodynamic flow in convective solutions is difficult to treat theoretically to develop quantitative expressions for expected plateau-current values. An exception is the rotated-disk electrode (RDE). The RDE is a flat disk sealed onto an inert shaft that is rotated with minimum wobble in an otherwise quiet solution. From the hydrodynamics is derived the expression of the limiting plateau current, i ... 

Investigation was made into the transport characteristics of ascorbic acid (AA). Cyclic voltammo-grams of 10 mM A A at different scan rates were recorded at platinum (Figure 21.8) without stirring the solution with the rotating disk electrode (RDE). 

Consider the reduction of a species O at a cathode O + nc R. In an actual case, the oxidized form, O, might be Fe(CN) and R might be t(CN)l, with only Fe(CN)6 daily present at the millimolar level in a solution of 0.1 M K2SO4. We envision a three-electrode cell having a platinum cathode, platinum anode, and SCE reference electrode. In addition, we furnish provision for agitation of the solution, such as by a stirrer. A particularly reproducible way to realize these conditions is to make the cathode in the form of a disk embedded in an insulator and to rotate the assembly at a known rate this is called the rotating disk electrode (RDE) and is discussed in Section 9.3. 

The advantages of controlled mass transport have long been recognized in electrochemistry, as discussed in Chapter 2.4. In the present context, the elegant combination of the rotating disk electrode (RDE) [48-50] and wall-jet electrode (WJE) [51, 52] solution hydrodynamics with EQCM interfacial detection has proved to be very effective. 

For a research on the electrode reaction mechanism and kinetics, particularly those of oxygen reduction reaction (ORR) (O2 + 4H+ + 4e -> 2H2O in acidic solution, or 02 + 2H20 + 4e -> 40H in alkaline solution), it is necessary to design some tools that could control and determine the reactant transportation near the electrode surface and its effect on the electron-transfer kinetics. A popular method, called the rotating disk electrode (RDE) technique has heen widely used for this purpose, particularly for the ORR. 

Figure 5.3 (A) Schematic of the rotating disk electrode (RDE) (B) solution flow pattern near the disk electrode surface (xis the coordinate direction perpendicular to the disk electrode surface, r is the coordinate direction parallel to the disk surface, and 0 is the coordinate direction of the electrode rotation, respectively).

The electrocatalytic activity of ORR on chalcogenides has been performed under hydrodynamic and temperature conditions using the rotating disk electrode (RDE) technique. We recall that dispersed catalysts either as non-supported or as supported on carbon have been prior prepared in form of inks, which are ahqnoted onto a well geometrically defined substrate, such as glassy caibon and/or gold disks. ... 

During the HER, hydrogen is produced at the electrode surface, Eqs. (7.9), and (7.10), and diffuses toward the bulk of the solution. At the electrode surface at the rotating disk electrode (RDE), oversaturation may appear without bubble formation [180, 270, 271]. In such cases, reactions (7.12) and (7.13) should be rearranged to... 

In the Rotating Disk Electrode (RDE) technique, the current-potential curves on smooth platinum exhibit an anodic limiting current density, which depends on rotation rate in both acidic and alkaline media [46]. These plots are well described by equation (19), which holds for a diffusion overpotential alone. Similar relationships have been observed in acidic solutions for Ir, Rh, and Pd, and well-characterized Pt-Ru, Pt-Rh, Pt-Sn [53], and Pt-Au [51] alloys, and also for Ni in alkaline solutions. In the case of platinum, a evolution of the limiting diffusion current density to a limiting reaction current density ( x) independent of rotation rate, is observed as a consequence of the rate-determining H2 adsorption. 

The rotating disk electrode (RDE) was used in LiCl-KCl melts by Delimarskii et al. (34) as early as 1960. The RDE, although more complex mechanically than stationary electrodes, is an "absolute" method which offers an approach to evaluating diffusion... 

The reaction rates of electrocatalytic reactions often are measured by polarization curves using the rotating disk electrode (RDE) method. As Fig. 2 shows, the HER and HOR currents (blue lines) on Pt, respectively, rise sharply with... 

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. 

To estimate ko or Xo quantitatively we must resort to an electrochemical technique that operates under steady-state conditions and for which the diffusion layer thickness is well-defined and quantifiable. The technique of choice is the rotating disk electrode (RDE) method. " Both of the aforementioned criteria are valid for the RDE. The solution hydrodynamics are well-defined, and the diffusion layer thickness can be estimated quantitatively in terms of the rotation speed... 

Two types of electrodes with convection are common the dropping mercury electrode (dme) and the rotating disk electrode (rde). Both are usually idealised to one-dimensional systems for convenience. 

Figure 14 Schematic of the experimental setup for the rotating disk electrode (RDE) detection in a bead-based immunoassay using the ALP-PAPP enzyme-substrate pair.

Polarographic methods have been applied to corrosion problems for several decades. The rotating-ring-disk electrode (RRDE) is a special modification of this technique, which is well suited for examining the formation of corrosion products, qualitatively and quantitatively, with a time resolution in the range of a second or less (Albery and Bruckenstein, 1966 Albery and Hitchman, 1991). The rotating-disk-electrode (RDE) works with a laminar flow... 

Sheng et al. [34] recently compared the rotating disk electrode (RDE) studies of the HOR in acid and alkaline and those for the carbon-supported Pt (Pt/C) for the first time. RDE studies are used to separate the current into its kinetic- and diffusion-based constituents, as shown by the Levich-Koutecky equation ... 

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