Nernstian waves

CYCLIC VOLTAMMETRY OF FAST ELECTRON TRANSFERS. NERNSTIAN WAVES... 

Two well-separated Nernstian waves are observed for large values of AE°. As AE° decreases, the two waves come closer to each other and tend to merge. Upon moving to negative values, the response tends asymptotically toward a limiting single two-electron wave, the equation of which is obtained from equation (1.57) by making AF° = —oo ... 

The peak height of the wave is four times the height of a one-electron Nernstian wave ... 

As with one-electron Nernstian waves, the entire current-potential curve is proportional to FSC y/D Fv/RT. The most salient features of the cyclic... 

Its main characteristics are as follows. The height of the wave is 2a/2 the height of a one-electron Nernstian wave rather than twice this height. Thus, the forward peak current is... 

Within the range of small values of Athat gives rise to a single two-electron wave, it is interesting to note that a wave twice the one-electron Nernstian wave is not obtained for A= 0 but rather for A ° = ( TZT/F)ln4 (see Section 5.1.3). As shown in the next section, this is precisely the value of A ° that corresponds to a molecule containing two identical and independent reducible or oxidizable groups. 

When Xe —> 0, we are back to the reversible Nernstian wave. When, conversely, Xe — oo (pure kinetic conditions),... 

The redox properties of tris(quinoxaline-2,3-dithiolato)molybdate(IV), [Mo(qdt)3]2, in the presence of protons provides a clear demonstration of the chemical versatility that is possible for a redox-active metal dithiolene center that involves a pyrazine ring linked to the dithiolene group. In an aprotic solvent, two reversible, Nernstian, waves are observed that (formally) correspond to the Mo(V)/Mo(IV) and Mo(IV)/Mo(III) couples. However, on addition of trifluoroacetic acid (Htfa), the Mo(V)/Mo(IV) couple slightly shifts to a higher potential and becomes non-Nernstian and a new three-electron, quasir-eversible, couple occurs some 900 mV less negative than the original Mo(IV)/ Mo(HI) couple. The latter is attributed to the addition of one electron and one... 

Two measured parameters of interest on these i-E curves cyclic voltammograms) are the ratio of peak currents, i Ji and the separation of peak potentials, jFpa — E. For a nernstian wave with stable product, /paApc = 1 regardless of scan rate, E (for E > 35ln mV past E c), and diffusion coefficients, when /pa is measured from the decaying cathodic current as a baseline (see Figures 6.5.1 and 6.5.2). This baseline can be determined by the methods described in Section 6.6. 

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