Rotating ring-disk electrode current-potential curves

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 disk electrode (RRDE) assembly consisting of a semiconductor disk and a Pt ring is usually applied, that is, a technique which makes it possible to determine separately the current corresponding to the oxidation of a redox system [63, 64]. 

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 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%.

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 7.16 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.

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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