RRDE

The RRDE is very usefiil for the detection of short-lived intemiediates, in the investigation of reaction iiiechanisms, but also in the distinction of free and adsorbed intemiediates, as tiie latter are not transported to the ring. 

Data on the electrochemistry of the telluride ion in alkaline media are relatively limited. Mishra et al. [53] studied the oxidation of Te to Te° at solid electrodes, focusing on the intermediate step(s) of this process, and in particular, the possibility of detecting ditelluride Te via rotating ring disk electrode (RRDE) methodology. Oxidation beyond the elemental state to TeO and TeO was also studied using cyclic and hydrodynamic voltammetry. 

The electrochemical behavior of single-crystal (100) lead telluride, PbTe, has been studied in acetate buffer pH 4.9 or HCIO4 (pH 1.1) and KOH (pH 12.9) solutions by potentiodynamic techniques with an RRDE setup and compared to the properties of pure Pb and Te [203]. Preferential oxidation, reduction, growth, and dissolution processes were investigated. The composition of surface products was examined by XPS analysis. It was concluded that the use of electrochemical processes on PbTe for forming well-passivating or insulating surface layers is rather limited. 

The ORR has been studied with a rotating ring-disk electrode (RRDE), which can provide theand the H2O2 yield P(H202) at around room temperamre. However, for improving the ORR activity, PEFCs should be operated at high temperature (> 80 °C). In this section, we demonstrate the temperature dependencies of ORR activity and P(H202) at pure Pt (both bulk and supported catalyst) and bulk Pt alloys (Pt-Ni, Pt-Co, and Pt-Fe). 

Thin catalyst layers on a GC rotating disk electrode (RDE) or a rotating ring-disk electrode (RRDE) serve for studies of ORR kinetics. In order to separate the kinetic current from the measured current j, Schmidt and co-workers [Schmidt et al., 1998b] corrected the latter for the influence of oxygen diffusion in the aqueous electrolyte and in the polymer film using the foUowing equation ... 

Note that for metal nanoparticles supported on porous carbon materials, it is even more difficult to establish the mechanism of the ORR. Indeed, for the above-described thin layer or porous RRDE (Section 15.3), H2O2 has very little chance to escape from the CL and be detected at the ring. H2O2 can readsorb either on Pt particles or on the carbon support, and undergo chemical decomposition or further electrochemical reduction, while diffusing out of the CL. This implies great difficulties in establishing the detailed ORR mechanism on nanometer-sized metal nanoparticles. 

In the most common approach, a water-insoluble metaUoporphyrin is deposited on the surface of a rotating disk electrode (RDE) or on the disk of a rotating ring-disk electrode (RRDE Fig. 18.7a) as a film of poorly defined morphology, either by spontaneous adsorption from a solution of the catalyst in an organic solvent or by evaporation of an aliquot of such a solution onto the electrode. It is impossible to know the... 

Figure 18.7 (a) Rotating ring-disk electrode (RRDE left) and schematics of chemical... 

Most electrodes are stationary, such as a mercury pool electrode (SMDE) or the HMDE others are non-stationary, such as the DME, MFE, MTFE, RDE and RRDE. 

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. 

At the RRDE, however, so-called collection experiments, the actual purpose of its integrated construction, are often carried out, i.e., in a solution of, for instance, only ox of a reversible redox couple ox + ne red, a cathodic current at the disc iD produces red, which reaches the ring where it is completely reoxidized to ox, because the ring is maintained at a sufficiently positive potential ER an RE, generally an SCE, is used together with a bipotentiostat for precise adjustment of the potentials ED and ER required. 

Interesting fundamental studies and analytical applications of RRDEs have been published by Bruckenstein and co-workers the attraction of collecting experiments with the RRDE lies more especially in the fact that metals with different oxidation states are becoming more accessible to analysis, e.g., Cu(II) and Cu(I)127, U(VI) and U(V), Fe(III) and Fe(H). Shielding experiments were carried out for Bi(III) and Bi(0)128. Special use of stripping voltammetry with collection at a glassy carbon RRDE for the determination of tin in the presence of lead was proposed by Kiekens et al.129 after cathodic electrode-deposition... 

Manufacturer Model DMB(A) HMDB1 SMDK M(T)FE GCE CPE Dead RDE RRDE Three Advanced DC LSV pulse5 AC superimposed sv4... 

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). 

The essentials of RRDE operation are effectively as for the RDE with the addition of one extremely important parameter the collection efficiency, N, defined for the reversible reaction ... 

Figure 3.67 Typical disc potential and ring current behaviour during galvanoslatic reduction of the passive him on pure iron (area 0.5 cm2) at a rotation speed of 25 Hz. The Pt ring potential is maintained at 0.2 V to oxidise all Fc(II) to Fellll), and the collection efficiency is 0.28. Note that the residual current detected on the ring beyond 70s corresponds to re-oxidation of hydrogen generated galvanostatically on the disc. Reprinted from Corrosion Science, 28, P. Southworth, A. Hamnett. A.M. Riley and J.M. Sykes, An Ellipsometric and RRDE Study of iron Passivation and Depassivation in Carbonate Buffer , pp. 1139-1161 (1988), with kind permission from Pergamon Press Ltd.. Headington Hill Hall. Oxford 0X3 OBW. UK.

Fig. 12. Alloy composition as a function of potential as derived from the RDE voltammetric currents in Figure 11. The Co(II) concentrations were ( ) 5.0, ( ) 10.0, (A) 25.0, and ( ) 50.0 mmol L-1. Also shown are the results of ALSV-RRDE experiments (O) of deposits from 5.0 mmol L 1 Co(II) melt. Adapted from Mitchell et al. [44] by permission of The Electrochemical Society.

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