Rotating disk electrode curves

Figure 7.70 Cathodic photocurrent-potential c-e) p-GaAs covered with 6,40, and 100 nm curves at p-GaAs in aqueous solutions (pH large Au particles, respectively (curve f) p-3) under illumination (curve a) bare p-GaAs GaAs covered with platinized Au particles rotating disk electrode (curve b) gold-plated (40 nm) rotation velocity, 200 rpm scan rate, p-GaAs covered with 0.7 monolayers (curves 10 mV s" (after [105]).

Theoretical treatment of polarographic curves for the calculation of values of jo has been described [65Hey, 66Hey], for an overview see [94Gal], a further evaluation procedure has been described [6801d]. Experimental details, in particular of solid electrodes in combination with a rotating disk electrode have been reported elsewhere [84Guy]. (Data obtained with this method are labelled PP.)... 

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. 

Figure 8.9 Polarization curves for a PtSn/C catalyst recorded by a rotating disk electrode in 0.5 M H2SO4 saturated with either pure hydrogen, a H2/2% CO mixture, and pure CO (the arrow points to the onset of CO oxidation) at 60 °C with 1 mV/s and 2500 rev/min the dashed curve is the cyclic voltammogram (in arbitrary units) in an argon-purged solution at 60 °C with 50 mV/s. (Reprinted with permission from Aienz etal. [2005]. Copyright 2005. Elsevier.)...

Fig. 2. Curve A Eleotropolymerization of ImH H2(o-NH2)TPP in 0.1M Et NClO /CH CN by sweeping potential at 200mV/s on Pt electrode. Numbers represent scan number. Curve B Cyclic voltammogram of an electropolymerized film of poly-[H2(o-NH2)TPP] on a Pt electrode, in 0.1M Et NClO /CH CN at 200 mV/s. Integration of the charge under the wave shows that coverage is 3.5X10 9 mol/cm of the porphyrin sites. Curve C Rotated disk electrode voltammetry of the Os(lII,Il) reaction for 0.2 mM...

Figure 3a is an illustration of the effect of surface overpotential on the limiting-current plateau, in the case of copper deposition from an acidified solution at a rotating-disk electrode. The solid curves are calculated limiting currents for various values of the exchange current density, expressed as ratios to the limiting-current density. Here the surface overpotential is related to the current density by the Erdey Gruz-Volmer-Butler equation (V4) ... 

Experimental results obtained at a rotating-disk electrode by Selman and Tobias (S10) indicate that this order-of-magnitude difference in the time of approach to the limiting current, between linear current increases, on the one hand, and the concentration-step method, on the other, is a general feature of forced-convection mass transfer. In these experiments the limiting current of ferricyanide reduction was generated by current ramps, as well as by potential scans. The apparent limiting current was taken to be the current value at the inflection point in the current-potential curve. 

FIGURE 1.10. Rotating disk electrode voltammetry. A + e B, with a concentration of A equal to C° and no B in the solution a Linearized concentration profiles —, at the plateau (vertical arrow in b), , at a less negative potential (horizontal arrow in b). b Current potential curve, c Concentrations of A and B at the electrode surface, d Logarithmic analysis of the current potential curve. 

Rose, potential energy curves, 1487 Rotating disk electrode, 1139... 

Assume that the reaction ox + c <=> red at the planar electrode is diffusion controlled. Sketch and correlate the concentration profiles Cox =f(x), where x is the distance from the electrode surface to the bulk of the solution, with the shape of the current-potential curve for electrolysis carried out at (a) a stationary disk electrode and (b) a rotating disk electrode. Support your explanation by the equations. (Skompska)... 

A rotating disk electrode (RDE) [7] is used to study electrode reactions, because the mass transfer to and from the electrode can be treated theoretically by hydrodynamics. At the RDE, the solution flows toward the electrode surface as shown in Fig. 5.22, bringing the substances dissolved in it. The current-potential curve at the RDE is S-shaped and has a potential-independent limiting current region, as in Fig. 5.6. The limiting current (A) is expressed by Eq. (5.33), if it is controlled by mass transfer ... 

The calculated impedance I/Q is represented in Fig. 5-3. The curves in solid line correspond to the behaviour previously calculated for the rotating disk electrode (see Section 3.1) and in reference [57], for the isolated microelectrode. The different curves in dots and dashes were obtained for the microelectrode in the wake of the large electrode. The first two curves (solid line) show only a monotonic decrease with increasing frequency. The controlled microelectrode curves display, at variance, nonmonotonic evolutions with two characteristic frequency domains ... 

Figure 9.1 illustrates the electrochemical reduction of 02 at platinum electrodes in aqueous media (1.0 M NaC104). The top curve represents the cyclic voltammogram (0.1 V s-1) for 02 at 1 atm ( 1 mM), and the lower curve is the voltammogram with a rotated-disk electrode (900 rpm, 0.5 V min-1). Both processes are totally irreversible with two-electron stoichiometries and half-wave potentials (EU2) that are independent of pH. The mean of the Em values for the forward and reverse scans of the rotated-disk voltammograms for 02 is 0.0 V versus NHE. If the experiment is repeated in media at pH 12, the mean Em value also occurs at 0.0 V. 

The reduction of GcC.14 also proceeds easily. The polarizating curve for the reduction of GeCU (0.1 N BU4NCIO4 in absolute CH3CN, Pt rotating disk electrode) has a single two-electron cathodic wave with 1/2 = —0.35 V. The electron number was determined... 

The objective of the mass transport lab is to explore the effect of controlled hydrodynamics on the rate at which a mass transport controlled electrochemical reaction occurs on a steel electrode in aqueous sodium chloride solution. The experimental results will be compared to those predicted from the Levich equation. The system chosen for this experiment is the cathodic reduction of oxygen at a steel electrode in neutral 0.6 M NaCl solution. The diffusion-limited cathodic current density will be calculated at various rotating disk electrode rotation rates and compared to the cathodic polarization curve generated at the same rotation rate. 

Fig. 18. Steady-state log j-E curves for H202 reduction and oxidation at a LaNi03 (1.2m2g 1) rotating disk electrode in 0.1 M KOH at 25°C after correction for mass transport in solution. H202 concentration = ImM [48],...

The reactions of DPAt and radical cations of other aromatic hydrocarbons with pyridine and substituted pyridines are among the most intensively studied electrode reactions of positive ions. The first definitive study of the mechanism of the reaction employed the rotating disk electrode (Manning et al 1969). Data were found to fit ECE working curves (Fig. 21) for the reactions of DPA7 with 4-cyanopyridine, 4-acetoxypyridine, pyridine and 4-methylpyridine. Pseudo first order rate constants of about 3, 10, 30, 300... 

Figure 36. Current-voltage curves for a rotating disk electrode (1) without and (2) with substrate added. The regions indicated are a, control by electron transfer b, mixed control by electron and mass transfer c. control by mass transfer.

Figure 37. Rotating disk electrode working curves for the eCeh mechanism at different values of the rate constant k for the chemical step.

Curve (b) of Figure 4 shows the same silent system as curve (a) but now upon a contracted current scale, while curve (c) shows the effect of ultrasonic irradiation upon curve (b), scanned at the same rate and in the oxidation direction only. Note that curves (b) and (c) are on the same current scale, both taken from ref. 31. Ultrasound has produced a 10-fold increase in maximum current. The plateau shape shows a limiting current at the extreme of oxidation potential reflecting hydrodynamic control independent of the voltammetric sweep rate. (This shape is also seen in other voltammetric procedures, e.g. when using rotating disk electrodes or microelectrodes.) In Figure 4 curve (c) this limiting current is found to be inde-... 

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... 

Figure 1.5.1 Effect of an irreversible following homogeneous chemical reaction on nemstian i-E curves at a rotating disk electrode. (7) Unperturbed curve. (2) and (J) Curves with following reaction at two rotation rates, where the rotation rate for (3) is greater than for (2).

Figure 2. (top) Current-potential curve for a rotating disk electrode (1600 rpm) under 1 bar H2 in... 

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