An experimental evaluation of cyclic voltammetry of multicharged species at macrodisk electrodes in the absence of added supporting electrolyte

The reversible reduction of[S2Mo18O62](4-) to [S2Mo18 O-62](5-)and [S2Mo18O 62](6-) at a glassy carbon macrodisk electrode has been studied by cyclic v oltammetry in acetonitrile as a function of the concentration of [(C6H13)(4 )N](4)[S2Mo18O62] in the absence and presence of [(C6H13)(4)N]ClO4 as the a dded supporting electrolyte. Consideration is given to the influence of sca n rate, reference-working electrode distance, [(C6H13)(4)N](4)[S2Mo18O62], and electrolyte concentrations. Experimental data confirm theoretical predi ctions that cyclic voltammetry at a macrodisk electrode is a viable techniq ue for studies of multiply charged electroactive species without added elec trolyte, provided the influence of enhanced complexities associated with ef fects of increased solution resistance, the mass transport contribution fro m migration, and convection arising from enhanced density gradients are con sidered. Enhanced density gradients present in the absence of added support ing electrolyte give rise to a more marked dependence of voltammograms on t he angle of the electrode and hence lead to significant distortion of wave shapes at low scan rates. The summation of all these obstacles implies that quantitative evaluation of cyclic voltammograms of multiply charged specie s requires significantly greater care in the absence than in the presence o f added supporting electrolyte.