Achievement of Near-Reversible Behavior for the [Fe(CN)_6]~(3-/4-) Redox Couple Using Cyclic Voltammetry at Glassy Carbon, Gold, and Platinum Macrodisk Electrodes in the Absence of Added Supporting Electrolyte

摘要

Voltammetric studies in the absence of added supporting elecirolyte are presently dominated by the use of near-steady-state microelectrode techniques and millimolar or lower depolarizer concentrations. However, with this methodology, large departures from conventional migra-tion—diffusionlheooybavebeenoWortedforthe[Fe(CN)613-/4-process at both carbon fiber and platinum microdisk electrodes. In contrast, data obtained in the present study reveal that use of the transient cyclic voltammetric tech-nique at glassy carbon, gold, or platinum macrodisk electrodes and KdFe(CN)aJ or Ka[Fe(CN)6J concentra-tions of 50 mM or greater provides an approximately reversible response in the absence of added electrolyte. It is suggested that the use of veiy high [Fe(CN)6P and [Fe(CN)6J4 concentrations overcomes problems associ-ated with a diffuse double layer and that large electrode surface areas and faster potential sweep rates minimize electrode blockage and passivating phenomena that can plague~voltammetric studies at microelectrodes. The cyclic voltammetry of the [Fe(CN)613-’4- couple at a range of concentrations at macroelectrodes in the absence of added inert electrolyte is compared with that obtained in the presence of 1 M KCl. The enhanced influences of uncompensated resistance, migration, and natural con-vection arising from density gradients under transient conditions at macrodisk electrodes also are considered.