Rotating disk electrode components

The characteristics of laminar flow can allow mathematical prediction of the solution velocity and this has led to a range of hydrodynamic devices which use forced convection as a transport component under laminar flow conditions, examples include, the -> rotating disk electrode [i],-> wall jet electrode [ii], and channel flow cell (see -> flow cell). 

Although a major advantage of rotating disk electrode techniques, compared to stationary electrode methods, is the ability to make measurements at steady state without the need to consider the time of electrolysis, the observation of current transients at the disk or ring following a potential step can sometimes be of use in understanding an electrochemical system. For example the adsorption of a component. 

C03M03N was, however, used as a precursor to C0M0N2 via reaction with NH3 at 400 °C. The actual formula reported was C006M02 4N2 with a small Co(M) component. Rotating disk electrode measurements in acidic media under H2 atmosphere demonstrated that currents for the HER reaction were achieved at overpotentials of around 0.2 V, which indicates promising catalytic activity in the C02M0N sample. 

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. 

As the field of electrochemical kinetics may be relatively unfamiliar to some readers, it is important to realize that the rate of an electrochemical process is the current. In transient techniques such as cyclic and pulse voltammetry, the current typically consists of a nonfaradaic component derived from capacitive charging of the ionic medium near the electrode and a faradaic component that corresponds to electron transfer between the electrode and the reactant. In a steady-state technique such as rotating-disk voltammetry the current is purely faradaic. The faradaic current is often limited by the rate of diffusion of the reactant to the electrode, but it is also possible that electron transfer between the electrode and the molecules at the surface is the slow step. In this latter case one can define the rate constant as ... 

Rotating ring disk electrode (RRDE) — This electrode consists of a thin metallic ring inlaid around the metallic disk that is situated in the center of the base of the insulating cylinder. Because of the radial component of the solution movement, which is caused by the rotating of the cylinder, the products of the electrode reaction formed on the disk electrode are carried over the... 

A regime of simultaneous dissolution has also been found for Cu—Ni alloys in acidic chloride solutions. Rotating ring-disk electrode studies revealed an apparent Tafel region of the alloy and component polarization curves with mixed mass transfer and kinetic rate control [44, 45]. For a CugoNiio alloy, the kinetic parameters again indicate a coupling of the copper and nickel partial currents under steady state conditions [44]. 

An exact solution of the macroscopic flow can be obtained for the rotating risk, often used as an electrode in various electrochemical studies [78] and in colloid particle or protein adsorption experiments [79]. Although the velocity components are, in general, expressed in terms of complicated series expansions, for small separations from the disk when h < (where m is... 

F(y), G(y), and H y) are shown in the figure. Around the center of the base of the cylinder, where the metal disk lies, the axial component of the solution velocity is most important, since the electroactive material is transported towards the surface in this direction only. Under chronoamperometric conditions, a diffusion layer develops at the electrode surface and extends as far into the solution as the flux at the surface is not equal to the rate of mass transport in the bulk of the solution. Under steady-state conditions and the laminar flow of the solution, the distance S depends on the electrode rotation rate 8 = where D is the diffu-... 

FIGURE 8. (a) Electrochemical cell and ancillary components for quasi in situ conversion electron Mossbauer measurements/The counter and reference electrodes are not shown in this figure, (b) Schematic diagram of rotating system. A. Motor, B. aluminum support, C. reduction gear, D. phenolic shaft, E. brass contact, F. Teflon bushing, G. aluminum support, H. electrochemical cell, I. working electrode (disk), J. conversion electron counter, K. Mossbauer source, L. Mossbauer Doppler velocity transducer, M. carbon brush assembly. 

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