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

Voltammetric studies in the absence of added supporting electrolyte 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 migration-diffusion theory have been reported for the [Fe(CN)₆]^3-/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 technique at glassy carbon, gold, or platinum macrodisk electrodes and K₄[Fe(CN)₆] or K₃[Fe(CN)₆] concentrations of 50 mM or greater provides an approximately reversible response in the absence of added electrolyte. It is suggested that the use of very high [Fe(CN)₆]^3- and [Fe(CN)₆]^4- concentrations overcomes problems associated 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)₆]^3-/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 convection arising from density gradients under transient conditions at macrodisk electrodes also are considered.