Ferrocene ferricenium redox couple

R. E. Malpas, The electrochemistry and photoelectrochemistry of an aqueous ferrocene/ferricenium redox couple atplatinum, n-silicon and n-indium phosphide electrodes, J. Electrochem. Soc. 129, 1987, 1982. 

At low scan rate, in the absence of a base, and as observed for compound 4, the voltammogram of 7 exhibited a reversible oxidation wave corresponding to the ferrocene/ferricenium redox couple. Upon addition of increasing amounts of imidazole, used as the base model, the intensity of the oxidation wave dramatically increased and progressively split, leading ultimately to two distinct peaks at large imidazole excesses (Fig. 47.4a). The determination of the absolute number of electrons involved at the second oxidation wave was circa 3, which was consistent with the bielectronic formation of the QM followed by a one-electron oxidation of its ferrocene group. 

Several of the reversible redox couples could, in fact be used in a cell for electricity generation. However, the output photovoltage, Ey, associated with these n-type Si/ferricenium/-ferrocene photoanodes is only in the 0.3-0.4 V range at open-circuit. Such is likely too low to be useful in practical schemes for solar energy conversion. The approach of derivatization, though, may be applied to other photoanode materials to realize improved efficiency and durability. 

Thus the SECM is useful in probing heterogeneous kinetics at electrode surfaces, as well as other surfaces, like enzyme-containing membranes. The largest values of that can be measured are of the order of Did. Obviously this limit depends experimentally upon d, which is the characteristic length in SECM. Analogous measurements at a UME in bulk solution are similarly limited and provide a maximum on the order of DIa. For example, the for the ferrocene/ferricenium couple in MeCN, often used as a reference redox couple, as measured by SECM was 3.7 cm/s (22). 

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