Ring electrodes current-potential curves

Figure 1.16. Cyclic voltammograms under N2 (A,C) and rotating ring-disk current-potential curves in aqueous air-saturated pH 7 buffers (B,D) of 2FeCu and 2Fe-only directly adsorbed on a graphite electrode (A,B) and as a 0.7% (mol) suspension in a 1-/rm-thick phosphadytilcholine film on the electrode surface (C.D). The rapid charge transfer within the films of adsorbed catalysts is supported by the linear dependence of the peak currents on the scan rate. The non-ideal shape of the peaks is due to cooperative behavior of the catalytic films as a whole. The Fe / and Cu / potentials are the same in the adsorbed catalysts (A) but separate when the catalysts are in the lipid film (C). Autooxidation of the catalyst-02 complex is the major source of ring-detectable byproducts (see below) and accounts for the potential-dependent selectivity of electrode-adsorbed catalysts (B). The measured collection efficiency of the ring electrode toward H2O2 in these experiments was 15%.

Fig. 62. Snapshots and space-time current densities measured with ring-arrays of Fe electrodes in the oscillatory region on the transport-limited plateau of the current-potential curve. (Reproduced with permission from Z. Fei, J. Green and J. L. Hudson, J. Phys. Chem. B103 (1999) 2178, (1999) American Chemical Society.)...

Fig. 18. Current-potential curve for a rotating (1000 rpm) n-GaAs-electrode in the dark in 6 M HCl with 0.76 mM Cu ". Dashed curves are the partial currents of anodic decomposition (] ) and of Cu -reduction (jrea), as determined by a rotating ring-disk electrode [93]...

The competition between redox reaction and anodic dissolution became very important in the development of stable regenerative solar cells on the basis of semiconductor-liquid junctions. As shown in the previous section, it is determined by the thermodynamic and kinetic properties of the processes involved. Information on the competitions between these reactions cannot be obtained entirely from current-potential curves, because in many cases they do not look very different upon addition of a redox system, especially if the current is controlled by the light intensity. Therefore, a rotating ring disc electrode (RRDE) assembly consisting of a semiconductor disc and a Pt ring is usually applied, i.e. a technique which makes it possible to determine separately the current corresponding to the oxidation of a redox system [62, 63]. 

Figure 30. Current-potential curves of a ring-shaped Rh/YSZ cell at different polarization modes. O direct cathodic (DC) A direct anodic (DA) O DC + DA indirect bipolar (IB). I4eii. cell potential between the two feeder electrodes. Feed composition C3H6 NO/75 500 Pa, T= 375°C.

As an example. Figure 6.10 shows the ORR current—potential curves at the disk electrode and their corresponding currents at the ring electrode, recorded at different electrode rotating rates, where the horizontal abscissa is the disk potential, and the upper vertical ordinate is the ring current and the lower vertical ordinate is the disk current. 

Figure 6.10 Current—potential curves at the disk electrode (below the x-axis in each figure) and the current at the ring electrode (Pt) (above the x-axis in each figure), recorded in Oa-saturated 1.0 mol dm KOH aqueous solution at different electrode-rotating rates. Disk electrode surface coated with a layer of (A) W2C/C, (B) Ag/C, (C) Ag-W2C/C, or (D) Pt/C. Potential scan rate 5 mV s ring potential fixed at 0.474 V vs Hg/HgO, and ring collection efficiency 20%. The insets present the Koutecky—Levich p ols of the disk electrode at different potentials. (For color version of this figure, the reader is referred to the online version of this book.)...

Figure 7.15 Current—potential curves on (A) glassy carbon disk for O2 reduction and (B) Pt ring electrode for H2O2 oxidation obtained in an RRDE study. The disk electrode was coated by PtA/ulcan with a Pt loading of 0.014 mg cm T = 60 °C 02-saturated 0.5 M H2SO4 scan rate = 5 mV s Ring potential = 1.2 V. Reprinted with permission from Ref. 48.

Figure 7.16 Current—potential curves (bottom) of the carbon-supported nanosized Pt and PtNi alloy catalysts coated on a glassy carbon disk electrode in Oa-satu-rated 0.5 M HCIO4 solution (scan rate of 5 mV s and rotating speed of 2000 rpm) and the corresponding ring currents (Pt at 1.2 V vs RHE) data for the hydrogen peroxide production (upper) on Pt/C, Pt Ni(2 1)/C and Pt Ni(1 1)/C systems. Reprinted with permission from Ref. 55.

In this particular case, the stability of the Cu(I) intermediate depends strongly on the nature of the electrolyte. In the presence of chloride the reaction gives rise to two distinct waves in a current/potential curve, whereas in the absence of complexing ions a single two-electron process appears to occur. Studies with the ring-disc electrode [29] have established, however, that Cu(I) is formed as an intermediate with a measurable lifetime. The existence of lower valent intermediates in other metal ion electrode processes is more controversial, but it seems improbable, for example, that the reduction of Zv involves simultaneous transfer of two electrons. 

Figures 3a and b show the current-potential curves for p-type (100) GaAs electrodes in 0.05 and 0.5 M K3Fe(CN)g, respectively, at pH 13. It is obviousfrom the figures that the total current-potential curves (1) show three distinct plateaus. The partial cathode current due to Fe(CN)g + reduction (curve 2) (obtained by using a ring-disk electrode) and the partial anodic current due to GaAs reduction (curve 3) (obtained by subtracting the cathodic current from the total current) reveal a num ber of...

Fig. 20. Experimental I/U curve obtained during the H2 electrooxidation on Pt in H2-saturated 0.1 M H2SC>4 electrolyte solution in the presence of 10-3 M HC1 (curve a) and after addition of 10-4 M CUSO4 (curves b and c). The Pt ring-electrode (area 0.911 cm2) was rotated (rotation rate 20Hz). Curves a and b were obtained during a potential sweep (sweep rate lOmV s-1), curve c during a current scan with 7 pA s-1.

A point electrode resembles a spot. It adopts a spherical-shaped concentration profile and potential distribution in the solution. As a result, such electrodes easily achieve a steady state and yield a steady-state current. This current is expected to be proportional to the characteristic length (radius) of the electrode. A typical point electrode is a disk electrode inlaid on an insulating plane. On the other hand, an ultrathin ring electrode shares characteristics of the point electrode and the line electrode. It appears as a point from a position distal from the electrode, but it resembles a curved line upon closer inspection. It exhibits a steady-state current because of the feature of the point electrode. Next, a plane electrode of interest is a microarray electrode, which is composed of point electrodes and line electrodes on a planar insulator. It is versatile in functionality by designing the geometrical arrangement. A mode of mass transport depends on whether elementary electrodes are a point or a line electrode. 

In order to determine the kinetic parameters of the reaction corrected from diffusion phenomenon, a voltammetric investigation was pursued with a rotating platinum ring disk electrode. Figure 21.10 represents current density-potential curves obtained for different rotation speeds and for the positive variations of potential. It appears that the current density of the rotating disk increases with the rotation rate. 

Figure 4.8 RRDE current—voltage curves for O2 reduction at the PDDA (Phthalic acid Diethylene glycol Diacrylate)/MWCNTs/GC (curve 1) and hare GC (curve 2) disk electrodes in 02-saturated 0.10 M KOH solution. Curves V and l represent the current for the oxidation of HOa produced at the corresponding disk electrodes. Potential scan rate, 10 mV s electrode rotating rate, 400 rpm. The Pt ring electrode was polarized at +0.50 V for the oxidation of...

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