Rotating disk electrode techniques

The most appropriate experimental arrangement for the quantitative determination of the stationary curves for the reaction is the rotating disk electrode technique, in which the convective transport is controlled mechanically and thus a constant diffusion layer for each species is achieved [101-106]. Modifications of this technique, to primarily collect the intermediates of the reactions, such as ring-disk electrode techniques [93,94] and a hanging meniscus rotating disk electrode... 

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. 

Continue evaluation of Pt catalysts being synthesized using the colloidal sol, carbothermal and the electrodeposition techniques and compare results against catalyst screening specifications. Debug rotating disk electrode technique. 

UTCFC has modified the carbothermal synthesis process (U.S. Patent 4,677,092, US 4,806,515, US 5,013,618, US 4,880,711, US 4,373,014, etc.) to prepare 40 wt% ternary Pt alloy catalysts. Various high-concentration Pt catalyst systems were synthesized and the electrochemical surface area (EGA) and electrochemical activity values compared to commercially available catalysts (see Table 3). The UTCFC catalysts showed EGA and activity values comparable to the commercial catalysts. A rotating disk electrode technique for catalyst activity measurements has been developed and is currently being debugged at UTCFC. 

Proposed Spectrochemical Method of Test for Wear Metals in Used Diesel Lubricating Oils by a Rotating-Disk Electrode Technique Using a Direct-Reading Spectrometer, in Methods for Emission Spectrochemical Analysis, 6th ed., Philadelphia American Society for Testing and Materials, 1971, pp 375-82, ASTM D-2-... 

Electrochemical data (from cychc voltammetry and rotating disk electrode techniques, see Box 8.2) for the 2-electron reduction of tF to Tl in aqueous solution, are consistent with the formation of a transient intermediate T1(1I) species, p-j T1]4+ fonned near the electrode. 

In Eqn (2.82), Cm is normally treated as the solubility of the oxidant in the ionomer membrane. The diffusion layer thickness 5o can be obtained using a rotating disk electrode technique, which will be given in a very detailed discussion in Chapter 5. The equivalent thickness of the ionomer membrane can be calculated according to the amount of ionomer applied in the electrode layer using the following equation ... 

For non-noble metal ORR catalysts, the definition of catalytic activity is different from that of Pt-based catalysts. For a nonnoble metal catalyst, the similar preparation procedure for CL and ORR measurement steps using rotating disk electrode technique to that for Pt-based catalyst have been widely used in literature. However, due to both the ORR onset and half-wave potentials catalyzed by non-noble metal catalysts are much lower than those of Pt-based catalysts, it is difficult or impossible to observed ORR current density at 0.9 V vs RHE. A current density at other lower potentials may be used to define the catalyst activity for the purpose of comparison. In this case, Eqn (3.7) may still usable except the electrode potential is not 0.9 V, instead of... 

Table 3.1. Catalytic Activities of Some Typical Electrocatalysts for Oxygen Reduction Reaction, Measured Using Rotating Disk Electrode Technique...

Electrochemiluminescence quantum yields of 8—10% from 9,10-diphenylanthracene and 14—20% from the 9,10-diphenylanthracene anion—thianthrene cation combination have been reported using the rotating ring disk electrode technique (157,173). 

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... 

Recently significant advances have been made in the analytical solution of mass transfer to a sinusoidally modulated rotating disk electrode. The resulting expressions, confirmed by refined experimental techniques, allow deter-... 

Shuman and Michael [326,327] introduced a technique that has sufficient sensitivity for kinetic measurement at very dilute solutions. It combines anodic scanning voltammetry with the rotating-disk electrode and provides a method for measuring kinetic dissociation rates in situ, along with a method for distinguishing labile and non-labile complexes kinetically, consistent with the way they are defined. 

Shuman and Michael [10] applied a rotating disk electrode to the measurement of copper complex dissociation rate constants in marine coastal waters. An operational definition for labile and non-labile metal complexes was established on kinetic criteria. Samples collected off the mid-Atlantic coast of USA showed varying degrees of copper chelation. It is suggested that the technique should be useful for metal toxicity studies because of its ability to measure both equilibrium concentrations and kinetic availability of soluble metal. 

Although cyclic voltammetry could fruitfully be applied to the kinetic analysis of these catalytic systems, it has mostly been investigated by means of rotating disk electrode voltammetry (Section 1.3.2). The simplest case is that of an irreversible catalytic reaction at a monolayer coating. The next section is devoted to the analysis of these systems by the two techniques. 

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... 

The homogeneous catalysis method is suitable to measure rate constants over a very wide range, up to the diffusion limit. The lower limit is determined by interferences, such as convection, which occur at very slow scan rates. It is our experience that, unless special precautions are taken, scan rates below lOOmV/s result in significant deviations from a purely diffusion-controlled voltammetric wave. For small values of rate constants (down to 10 s ), other potentiostatic techniques are best suited, such as chronoamperometry at a rotating disk electrode UV dip probe and stopped-flow UV-vis techniques. ... 

Although new spectroscopic methods have reduced the need for some functions of the rotating disk electrode, there are a number of situations in which it remains the most effective technique. The detection of H202 as an intermediate in the reduction of 02, described above, is one example. Here are a few others. 

This can certainly be done, e.g., by using a rotating disk electrode, or by using ultramicroelectrodes (Section 7) one can increase iL several hundred times compared with its value at a flat plate in a still solution. However, every technique comes with a price tag, which may not only be a dollar one. Thus, if one uses ultramicroelectrodes to give a high iL, one has to recall that the currents there are tiny (picoamperes) and... 

Since the limiting current is proportional to concentration, a rotating-disk electrode can be used for analytical purposes (but almost never is in practice). In summary, the rotating disk electrode is one of the valuable techniques available for the fundamental study of electrode reactions as evidenced by its substantial popularity. 

The measurement of a molecular diffusion coefficient D by electrochemical techniques is generally done with a rotating disk electrode in the limiting diffusion current condition and application of the Levich s equation [8]. 

C. Deslouis and B. Tribollet present the theoretical basis and state of the art of a novel technique for kinetic analysis, in which the mass transfer rate to a rotating disk electrode is modulated. The capabilities and limitations of this technique are demonstrated along with illustrations of typical applications. 

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