Cyclic voltammetry reversibility criteria

As a general criterion one must bear in mind that, in cyclic voltammetry, the presence of a following chemical reaction has little influence on the forward peak, whereas it has a considerable effect on the reverse peak. 

Since a is usually between 0.3 and 0.7, both the wave slope and the Tomes criterion for a totally irreversible system are normally significantly larger than for a reversible system. These figures of merit are not without ambiguity, however. Consider the predicted wave slope of 63.8 mV for a = 0.85. Within the precision of normal measurements, one could diagnose the system as either reversible or irreversible. It is always a good idea to examine reversibility by a method, such as cyclic voltammetry, that allows a view of the electrode reaction in both directions. 

A necessary pre-requisite to such a study required accurate assessment of Ae formal potentials involved this in turn demanded careAl appraisal of adherence to a suitable mechanistic scheme. This criterion was satisfied by a combination of convolution techniques applied to cyclic voltammetry direct comparison wiA simulation results normally via Ae symmetrical deconvolution or dl /dE peaks produced when Ae time-scales are such Aat Ae system appeared electrochemically reversible. 

The first wave corresponds to a one-electron reversible process as suggested by the Tomes criterion, i.e., IE3/4-E1/4I = 60 mV. The diffusion coefficient, determined by the limiting current and for n=l, was 1.4x10 cm s in agreement with the value obtained in cyclic voltammetry for scan rates above 300 mV/s, when the process is reversible. Furthermore, the Ei/2 values were the same ( 5 mV) when different electrode radii were used (5, 12.5 and 25 xm) confirming the reversibility of the process (5). 

Uncomplicated quasi-reversible electrode processes in conditions of "usual" linear and cyclic voltammetry is defined by the following criterion [5] ... 

---