Rotating ring disk experiments

According to the results obtained from rotating ring disk experiments and the determination of Tafel slopes, it was concluded that the mechanism of oxygen electroreduction on an Ag/C catalyst is similar to that on a Pt/C catalyst at high potentials, that is, interesting potentials for fuel cell applications. Lee et al. also showed that a 30 wt% Ag electrode displayed the same electroactivity towards the ORR as a 10 wt% electrode and that the activity could be enhanced by doping Ag with Mg [115],... 

A shift in the band edge position also explains the observed dependence of the hole injection rate on the electrode polarization. Fig. 11 exempliHes this by the total current-potential behavior of a (111) n-GaP electrode in alpine Fe(CN) solutions (pH = 13), together with the partial current due to the injection of holes (revealed by rotating ring-disk experiments, see ref. [73]). Also at p-GaP, it was shown that the hole injection rate is lower with anodic polarization than with cathodic polarization. The potential-dependent position of the band edges is ascribed to a potential-dependent accumulation of positive charges (holes, surface decomposition intermediates,. ..) at the semiconductor surface [62, 73]. 

These relative surface excess parameters can be determined experimentally using different methods /)(w) can be determined by radiotracer studies, o-measurements, electroanalytical techniques (twin-electrode thin-layer, flow-through thin layer, rotating ring-disk experiments) etc., whereas q can be determined by charging curves, capacitance measurements etc. Isotherm conversion q-Fiiyf) is obtained by the corresponding Maxwell relations ... 

Even though most authors agree that the M(II) state is the active site for O2 reduction for FePc (iron phthalocyanine) and FeNPc (iron naph-thalocyanine)" it has been proposed that Fe(I) could also play a role in the electrocatalytic process. This was based on electroreflectance experiments that indicated that Fe(I) interacts with O2 whereas Fe(II) does not. However, many authors have shown experimental evidence that O2 reduction commences at potentials much more positive that those corresponding to the Fe(II)/(I) couple . On the contrary, the reduction currents are observed at potentials close to the potential of the Fe(III)/(II) couple, so it seems unlikely that Fe(I) could be the active site. Worse, as shown from rotating ring-disk experiments, Fe(I) only favors the 2-electron reduction in contrast to Fe(II). ... 

Figure 6.43 Rotating ring-disk experiment of passive film breakdown on Fe after injection of chloride ions. Parameters observed to vary as a function of time the current density of the disk the reduction current density of Fe " on the ring and the current density of formation of Fe on the disk. Electrolyte is borate solution of pH 7.3. Concentration of NaCl added at time t = 0 is O.Olmol 1 Dashed line shows the time to reach a uniform NaCl concentration [41].

The iron complex (23) adsorbed on graphite electrode surfaces is an active catalyst for the electroreduction of both nitrite and nitric oxide to yield NH2OH and NH3, as demonstrated by rotating ring-disk electrode voltammetry experiments.341... 

The most interesting conclusion of the rotating ring-disk electrode experiment is the absence of a reduction wave due to any species other than Cul2" and Is". The implication is that no free Cus+ or any other reducible species with a lifetime beyond tens of milliseconds is produced when YBa2Cus07 dissolves. 

Dry boxes are especially advantageous for rotating ring-disk electrode (RRDE) experiments [6]. Because the motor can be placed in the dry box, one is saved the expense of a rather expensive RRDE cell and sealed motor and the attendant problems of working outside the dry box. 

In a rotated ring-disk electrode experiment where the disk is controlled at +2.6 V versus SCE for the oxidation of HOOH and the ring electrode is controlled at -1.4 V versus SCE for the reduction of the oxidation products from HOOH, the observed collection efficiency (N = /r//d) is 0.384. This is slightly less than the theoretical value of 0.418 for the electrode. The products from HOOH oxidation at the glassy-carbon disk electrode (ED, + 2.6 V vs. SCE) can be characterized at the ring by scanning its potential from +1.0 to... 

Closely spaced band electrodes (pairs or triples), with each electrode within the diffusion layer of the other, can be used for studying reactions, in a manner analogous to ring-disk generation-collection and redox recycling experiments (131,132). Unlike with rotating ring-disk electrodes, the product of the reaction at the collector electrode can diffuse back across the narrow gap to the... 

A rotating ring disk electrode has been manufactured at TNO and it was successfully tested. Preliminary experiments with some old complexes (Tinnemans et al., 1984) showed that these materials had deteriorated over time. The new complexes were either not yet available in the pure state or were intended for use in anhydrous solvent (2 in MeCN), where stability problems occur during electrochemical operation. 

Rotating Ring-Disk electrode (RRDE-) experiments... 

The Frumkin epoch in electrochemistry [i-iii] commemorates the interplay of electrochemical kinetics and equilibrium interfacial phenomena. The most famous findings are the - Frumkin adsorption isotherm (1925) Frumkin s slow discharge theory (1933, see also - Frumkin correction), the rotating ring disk electrode (1959), and various aspects of surface thermodynamics related to the notion of the point of zero charge. His contributions to the theory of polarographic maxima, kinetics of multi-step electrode reactions, and corrosion science are also well-known. An important feature of the Frumkin school was the development of numerous original experimental techniques for certain problems. The Frumkin school also pioneered the experimental style of ultra-pure conditions in electrochemical experiments [i]. A list of publications of Frumkin until 1965 is available in [iv], and later publications are listed in [ii]. 

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