Rotated disk electrode

Convection terms commonly crop up with the dropping mercury electrode, rotating disk electrodes and in what has become known as hydrodynamic voltammetry, where the electrolyte is made to flow past an electrode in some reproducible way (e.g. the impinging jet, channel and tubular flows, vibrating electrodes, etc). This is discussed in Chap. 13. 

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,... 

Tank Cells. A direct extension of laboratory beaker cells is represented in the use of plate electrodes immersed into a lined, rectangular tank, which may be fitted with a cover for gas collection or vapor control. The tank cell, which is usually undivided, is used in batch or semibatch operations. The tank cell has the attraction of being both simple to design and usually inexpensive. However, it is not the most suitable for large-scale operation or where forced convection is needed. Rotating cylinders or rotating disks have been used to overcome mass-transfer problems in tank cells. An example for electroorganic synthesis is available (46). 

FIGURE 4-9 (a) Rotating disk and (b) ring-disk electrodes. 

Derive the Levich equation for the limiting current at the rotating disk electrode [based on combining equations (4-4) and (1-12)]. 

Rigid film approximation, 53 Rotating disk electrode, 111 Rotating ring disk electrode, 113 Ruthenium dioxide, 121... 

In situ electron transport measurements on conducting polymers are commonly made by using a pair of parallel-band electrodes bridged by the polymer [Fig. 9(A)].141142 Other dual-electrode techniques in which the polymer film is sandwiched between two electrodes [Fig. 9(B)],139,140 rotating-disk voltammetry [Fig. 9(C)],60,143 impedance spectroscopy,144,145 chronoamperometry,146 and chronopotentiometry147 have also been used. 

Figure 9. Schematic diagrams of (A) parallel-band electrode,141 142 (B) sandwiched electrode,139 140 and (C) rotating-disk voltammetry60 143 methods for making in situ electron transport measurements on polymer films.

Figure 11. Cyclic votammetry (top) and in situ electronic conductivity from rotating-disk voltammetry [ , Fig. 9(C)] and sandwich electrode voltammetry [ , Fig. 9(B)] for poly(3-methylthiophene) in acetonitrile containing 0.1 M BU4CIO4.60 (Reprinted from J. Ochmanska and P. G. Pickup, In situ conductivity of poly-(3-methylthiophene) and (3-methylthiophene)x,-[Ru(2,2 -bipyridine)2 (3- pyrrol-l-ylmethyl pyridine)2]2+ copolymers, J. Electroanal. Chem. 297, 211-224, 1991, with kind permission from Elsevier Sciences S.A.)...

Rotating-disk voltammetry is the most appropriate and most commonly employed method for studying mediation. In most systems that have been studied, there has been little penetration of the substrate in solution into the polymer film. This can be demonstrated most easily if the polymer film is nonconductive at the formal potential of the substrate. Then the absence of a redox wave close to this potential for an electrode coated with a very thin film provides excellent evidence that the substrate does not penetrate the film significantly.143 For cases where the film is conductive at the formal potential of the substrate, more subtle argu-... 

Theoretical treatment of polarographic curves for the calculation of values of jo has been described [65Hey, 66Hey], for an overview see [94Gal], a further evaluation procedure has been described [6801d]. Experimental details, in particular of solid electrodes in combination with a rotating disk electrode have been reported elsewhere [84Guy]. (Data obtained with this method are labelled PP.)... 

The rqjroducibility of polymer film formation is greatly improved by the spin coating technique where the polymer solution is applied by a microsyringe onto the center of a rapidly rotated disk electrode Rather thick films can be produced by repeated application of small volumes of stock solution. A thorough discussion and detailed experimental description of a reliable spin coating procedure was given recently... 

For the in situ characterization of modified electrodes, the method of choice is electrochemical analysis by cyclic voltammetry, ac voltammetry, chronoamperometry or chronocoulometry, or rotating disk voltametry. Cyclic voltammograms are easy to interpret from a qualitative point of view (Fig, 1). The other methods are less direct but they can yield quantitative data more readily. 

Fig. 3. Steady state concentration profiles of catalyst and substrate species in the film and diffusion layer for for various cases of redox catalysis at polymer-modified electrodes. Explanation of layers see bottom case (S + E) f film d diffusion layer b bulk solution i, limiting current at the rotating disk electrode other symbols have the same meaning as in Fig. 2 (from ref.

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. 

Verbrugge MW, Tobias CW (1985) Triangular current-sweep chronopotentiometry at rotating disk and stationary, planar electrodes. J Electroanal Chem 196 243-259... 

In such systems the researcher can electrochemically clean and precondition the metal electrode before each run to provide an identical surface for the anodic and the cathodic half-reactions as well as for the catalytic reaction between them. Use of a rotating disk electrode/ckatalyst also allows surface- and diffusion-controlled processes to be easily distin-guished. ... 

Chronoamperometry Linear sweep Polarography Rotating disk electrode Faradaic impedance... 

FIGURE 4.6 Rotating-disk electrode (arrows in the space below the electrode indicate the directions of hqnid flow). 

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 constancy of the diffusion layer over the entire surface and thus the uniform current-density distribution are important features of rotating-disk electrodes. Electrodes of this kind are called electrodes with uniformly accessible surface. It is seen from the quantitative solution of the hydrodynamic problem (Levich, 1944) that for RDE to a first approximation... 

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