Rotating-disk voltammograms

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. 

Figure 5.71 Rotating-disk voltammograms showing the reduction of a 0.2 m/mM [Fe(H20)6]3+ solution in 0.1 M H2SO4 at an electrode modified with [Os(bpy)2(PVP)ioCl]+. The rotation rates, from top to bottom, are 500,1000,1500,2000,2500 and 3000 rpm, respectively the surface coverage is 5 x 10-9 mol cm 2. From R. J. Forster and J. G. Vos,. Chem. Soc., Faraday Trans., 87,1863-1867 (1991). Reproduced by permission of The Royal Society of Chemistry...

FIGURE 3.9 Linewaver-Burke plots of 1A vs. 1/c, from rotating disk voltammograms recorded for OC (squares) and p (rhombs) cobalt cordierite-modified glassy carbon electrodes (GCEs) in contact with a 1.25 mM mannitol plus 1.0 M NaOH aqueous solution. Potential scan rate. 50 mV/sec. 

Coupling reactions of the electrogenerated cation radicals can also occur. If the parent molecule is a good nucleophile, this can be considered as a nucleophilic attack by parent on its own cation radical. The nature of the electrochemical responses in CV and coulometry depend upon whether the coupled product can undergo further oxidation. For example, in the oxidation of aromatic aza-hydrocarbons such as acridine (AcH), studied by Marcoux and Adams (1974), the CV was characterized by an irreversible one-electron wave and coulometry showed an napp-value of one. An analysis of rotating disk voltammograms demonstrated that the reaction sequence (79)-(81) was more probable them that involving... 

Finite-difference techniques are useful in elucidating time-dependent behavior in such layers, for example the time-dependent rotating disk voltammogram in Fig. 6 10 (68,79) nonstationary behavior has also been observed elsewhere. " ... 

FIGURE 6.10. Nonstationary rotating disk voltammogram of a glassy carbon electrode coated with [Ru(bipy)2(PVP)5Cl]Cl in a solution of [Fe(CN)6] at various scan rates. Surface coverage of Ru is 7... 

A typical set of rotating disk voltammograms for the mediated reduction of [Fe(H20)6] in 0.1 M H2SO4 is shown in Fig. 8.24. These plots show that the mediating process occurs in the potential region of the Os(III/II) redox couple. Koutechy—Levich plots obtained from such curves are shown in Fig. 8.25 as a function of the layer surface coverage. These Koutechy—Levich plots are linear, and the catalytic reaction increases with increasing film thickness. Furthermore slopes obtained are the same as the one obtained at the bare electrode. Since the intercepts of these plots are equal to electrochemical rate constant clearly depends... 

Figure 7.24 (A) Rotating-disk voltammograms of 20 wt% CoSe2/C nanocatalyst in O2- saturated 0.1 M KOH at 25 °C with a sweep rate of 5 mV s at different rotating rates from 400 rpm to 2500 rpm from top to bottom. (B) The corresponding Koutecky—Levich plots as a function of at four different potentials 0.1,0.4,0.6 and 0.65 V vs RHE. Catalyst mass loading is c.

Figure 3. Background-corrected rotating-disk voltammograms with 7-DADMN-modified BPGE (full circles) and naked BPGE (open circles) in air-saturated phosphate buffer at pH 7.00, w = 1200 rpm, v =...

For the in situ characterization of modified electrodes, the method of choice is electrochemical analysis by cyclic voltammetry, ac voltammetry, chronoamperometry or chronocoulometry, or rotating disk voltametry. Cyclic voltammograms are easy to interpret from a qualitative point of view (Fig, 1). The other methods are less direct but they can yield quantitative data more readily. 

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 6 Steady state rotating ring-disk voltammograms of (A) compound (42) (B) compound (43) and (C) a Ru-bridged polymer of (43) each adsorbed to a graphite working electrode. Disk current shows reduction of 02 while ring current reveals the presence of H202 simultaneously reoxidised at the ring anode poised at +1.0 V (reproduced with permission of the American Chemical Society from Acc. Chem. Res., 1997, 30, 437-444).

Figure 3.13 Electrochemical oxidation of HOOH and reduction of its products at GC electrodes in MeCN (0.1 M TEAP) (a) linear-sweep anodic voltammograms for (A) 0, (B) 0.3, (C) 1.7, and (D) 3.3 mM HOOH (scan rate 2 V min-1 electrode area, 0.46 cm2) (b) rotated-ring electrode cathodic voltammogram (scan rate 10 mV s-1) of the product from the oxidation of 4 mM HOOH at the rotated-disk electrode (rotation rate 1600 rpm) for (A) ED disconnected, and (B) En = +2.6 V versus SCE (c) rotated-ring electrode cathodic voltammogram (scan rate 10 mV s-1) of the products from the oxidation of 1 mM HOOH at the rotated-disk electrode (rotation rate 4900 rpm) for (A) disconnected and (B) ED = +2.6 V versus SCE.

Figure 9.1 Electrochemical behavior of dioxygen (1 atm) in aqueous solutions (1 M NaC104) at a platinum electrode (area 0.458 cm2) A) the cyclic voltammogram was initiated at the rest potential with a scan rate of 0.1 V s-1 (B) the rotated-disk (400-rpm) voltammogram was obtained with a scan rate of 0.5 V min-1. 

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