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

Abstract

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.

Characterization and Optimization of Interdigitated Ultramicroelectrode Arrays as Electrochemical Biosensor Transducers

“…Thus, a simple two-electrode system with interdigitated working electrodes was used to measure the current produced by the redox species. When ferro/ferrihexacyanide is used with the IDUA, the potential applied to one set of electrodes drives the reduction Fe 3 (CN) 6 e 3 Fe 2 (CN) 6 , while the potential applied to the other electrode drives the oxdation Fe 2 (CN) 6 3 Fe 3 (CN) 6 e. Species produced at one electrode can diffuse to the other electrode, where they are converted back to their original form, creating a redox cycling process. The Faradaic current is amplified by this redox cycling of reversible and quasi-reversible redox systems.…”

Electrochemical reactions where the variation of supporting electrolyte concentration is mechanistically revealing: ECE-DISP1 processes in which the chemical step is an isomerisation

“…Performing voltammetric experiments under conditions of weak support has been shown to be a useful tool in probing electrochemical mechanisms [1][2][3][4][5][6]. Electrolysis of a solution transfers charge from the electrode into the solution, and will result in an electric field extending away from the electrode.…”

Electron transfer across a conducting nanowire (nanotube)/electrolyte solution interface

“…Secondly, as electron is transferred to bonding molecular orbital of [Fe(CN) 6 ] 3− , the intramolecular reorganization of the hexacyaneferrate system is negligibly small; this facilitates a model treatment of this reaction on a quantum mechanical basis. Last, this reaction has been thoroughly examined by microelectrode techniques [26][27][28][29][30][31]. The current-voltage curves reported in these works demonstrate steady-state behaviour over a wide range of the effective radii of spherical or hemi-cylindrical microelectrodes.…”