RDE rotating disc electrode

Notes LSV linear sweep voltammetry. CV cyclic voltammetry, DCP direct current polarogra-phy, MEV steady-state voltammetry at microelectrodes, ChP chronopotentiometry, RDE rotating disc electrode, TEV voltammetry in tubular electrodes, kf and k, rate constants of irreversible follow-up and catalytic reactions, respectively cj, the bulk concentration of the catalyst Z k = kf + k, sum of the rate constants and drop time and transition time, respectively a radius of a hemispherical microelectrode, Xf length of the tubular electrode in the flow direction, co the angular rotation rate, Uf linear flow rate in a TE (7 = RT/(nFv) is the time required for the dimensionless potential shift nFdE/RT at the sweep rate v (Vs" ). 

C60 has been used to produce solvent-cast and LB films with interesting photoelec-trochemical behavior. A study of solvent-cast films of C60 on Pt rotating disc electrodes (RDEs) under various illumination conditions was reported [284]. Iodide was used as the solution-phase rednctant. The open-circuit potential shifted by 74 mV per decade of illumination intensity from a continuous wave (cw) argon-ion laser. The photocurrent versus power was measured at -0.26 V under chopped illumination (14-Hz frequency, vs. SCE) up to 30 mW cm and was close to linear. The photoexcitation spectrum (photocurrent versus wavelength) was measured at 0.02 V (vs. SCE) from 400 to 800 mn and found to be... 

Levich124 has given the relationships between the limiting current i) and the bulk concentration C of the metal ion for plate electrodes, conical electrodes and rotated disc electrodes (RDEs) under hydrodynamic conditions anticipating his well known equations treated in Section 3.3.2.2 on hydrodynamic electrodes, we may assume the relationships concerned using the more general equation... 

Here we have to deal with three types (see Fig. 3.68), viz. (a) the rotating disc electrode (RDE), and (b) the rotating ring electrode (RRE) and the rotating ring-disc electrode (RRDE). The construction of the latter types suits all purposes, i.e., if the disc or the ring is not included in the electric circuit, it yields an RRE or an RDE, respectively, and if not an RRDE, where either the disc forms the cathode and the ring the anode, or the reverse. 

There arc many controllcd-convection techniques available but we will restrict our discussion to the two most commonly employed by the electrochemist the rotating disc electrode (RDE) and the rotating ring disc electrode (RRDE). 

To find that the limiting current at a rotated disc electrode (RDE) is directly proportional to the concentration of analyte, according to the Levich equation. 

The rotated disc electrode (RDE) is one of the most commonly employed hydro-dynamic electrodes. Figure 7.1 shows a schematic representation of a typical RDE. The electrode itself is a flat, circular disc of metal, graphite or an other conductor, and has a radius of r its area A, therefore, is straightforwardly nr. The disc is embedded centrally into one flat end of a cylinder of an insulatory material such as Teflon or epoxy resin. Behind the face of the electrode is an... 

Related to the rotated disc electrode (RDE) is the rotated ring-disc electrfxle (RRDE). Such an electrode is illustrated in Figure 7.9 and is seen to be, in effect, a modified RDE, insofar as the central disc is surrounded with a concentric ring electrode. The gap between the ring and the disc is filled with an insulator such as Teflon or epoxy resin. The face of the RRDE is polished flat in order to prevent viscous drag, which is itself likely to cause the induction of eddy currents. 

Convection-based systems fall into two fundamental classes, namely those using a moving electrode in a fixed bulk solution (such as the rotated disc electrode (RDE)) and fixed electrodes with a moving solution (such as flow cells and channel electrodes, and the wall-jet electrode). These convective systems can only be usefully employed if the movement of the analyte solution is reproducible over the face of the electrode. In practice, we define reproducible by ensuring that the flow is laminar. Turbulent flow leads to irreproducible conditions such as the production of eddy currents and vortices and should be avoided whenever possible. 

Provided that the flow is laminar, and the counter electrode is larger than the working electrode, convective systems yield very reproducible currents. The limiting current at a rotated disc electrode (RDE) is directly proportional to the concentration of analyte, according to the Levich equation (equation (7.1)), where the latter also describes the proportionality between the limiting current and the square root of the angular frequency at which the RDE rotates. 

Albery, W. J. and Hitchman M. L., Ring-Disc Electrodes, Oxford University Press, Oxford, 1971. This now-classic book describes one of the most formidable tools in the arsenal of the electroanalyst, i.e. the rotated ring-disc electrode (RRDE). Its first two chapters are a clear and lucid introduction to the basic rotated disc electrode (RDE) and the multi-faceted problems of mass transport. Well worth a read, if only for the occasional dip into this field. 

As is thoroughly discussed in Chap. 2 of this volume, the convective diffusion conditions can be controlled under steady state conditions by use of hydrodynamic electrodes such as the rotating disc electrode (RDE), the wall-jet electrode, etc. In these cases, steady state convective diffusion is attained, becomes independent of time, and solution of the convective-diffusion differential equation for the particular electrochemical problem permits separation of transport and kinetics from the experimental data. 

A rotating disc electrode (RDE) is a conductive disc of the material of interest embedded in an inert non-conductive polymer or resin that can be attached to an electric motor which has very fine control of the electrode s rotation rate. During the experiment, the electrode rotates in the solution under study, thus inducing a flux of redox analyte to the electrode [75]. 

For a -> rotating disc electrode (RDE) the - convective-diffusion equations can be solved which gives the dependence of the diffusion layer thickness on the angular velocity of the rotation (on)... 

One of the best methods of obtaining efficient mass transport in a highly reproducible manner is by the use of the rotating disc electrode. The RDE consists of a cylindrical metal rod embedded in a larger cylindrical plastic (e.g.. Teflon) holder. The electrode is cut and polished Hush with its holder, so that only the bottom end of the metal cylinder is exposed to the solution. 

Figure 21. Schematic illustration of a rotating disc electrode (RDE). The stream arrows indicate the flow to the rotating disc.

Fig. 3.3 Surface modification with Pd thin films by UHV vapor deposition (Left) Gold surface modified with Pd thin film (a) Rotating disc electrode (RDE) polarization curves for electrochemical hydrogen oxidation reaction on pure Au(lll), Au(lll)-Pd (for different rpm ) and Pt(lll) surfaces [51] (b) and (c) LEIS spectra of Au(lll)-Pd surfaces after vapor deposition of Pd in the amount that corresponds to four atomic monolayers. (Right) Platinum surface modified with Pd thin film (d) LEIS spectra of the Pt(l 11)-Pd surface with 65% of Pd and (e) LEIS spectra of Pd monolayer on Pt(lll) (red line) and pure Pt(lll) (dashed line), (a) Reprinted with permission from [51], copyright 2002 Elsevier...

Both qualitative and quantitative insight can be garnered from transient X -i, i-t and r -t measurements in quiescent or stirred solutions, while measurements of steady-state behavior are best performed under well-defined hydrodynamic conditions. Typically, a rotating disc electrode (RDE), or a related method, is used to specify and/or modulate the hydrodynamic boundary layer thickness, 8. With an RDE the boundary layer is specified by... 

---