Consider a reversible redox reaction at the surface of an electrode. “Reversible” means that the reaction is fast enough so that reactants and products maintain equilibrium at the electrode surface consistent with the Nernst equation.
a. Why are there peaks (not plateaus) in cyclic voltammetry at a macroscopic planar electrode in Figure 17-19? Electrode size is millimeters.
b. Why are there plateaus (not peaks) in cyclic voltammetry at a microscopic electrode in Figure 17-35? Electrode size is micrometers.
c. Why are there plateaus instead of peaks in cyclic voltammetry at a macroscopic rotating disk electrode in Figure 17-16?

Figure 17-19

Figure 17-35

Figure 17-16

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— เ NO Current becomes more negative to 12 (a) Ipa (b) -1.00 8 0₂ + e- 0₂ Superoxide -1.75 -1.25 E1/27 Epc JLE Epa -E₁/12 Anodic peak -2.00 -1.50 100 μA t₁ Cathodic peak 50 μA -2.25 FIGURE 17-19 Cyclic voltammograms of (a) 1 mM 021 mM 02 in acetonitrile with 0.10 M (C2H5)4N+C104 0.10 M (C₂H5) NCIO with 0.10 M (n-C7H15)4N+C104- electrolyte and (b) 0.060 mM 0.060 mM 22-nitropropane in acetonitrile 0.10 M (n-C7H15),NCIO4 electrolyte. The reaction in curve a is 4- 02+e--02-Superoxide Working electrode, Hgg drop; reference electrode, Ag0.001 M AgNO3(aq) | 0.10 M Ag|0.001 M AgNO3(aq) | 0.10 M(C2H5)4N+C104-(C₂H5)4N+ C1O4 in acetonitrile; scan rate-100 V/s, scan rate = 100 V/S. 1papa is the peak anodic current and Ipe pc is the peak Ерс cathodic current. Epapa and Epc are the potentials at which these currents are observed. Curves (a) and (b) are displaced vertically. The current is near zero at time toto for each curve.