Cyclic Voltammetry Experiment

Goals

The goals of this experiment are to:

• Learn how to set up a screen-printed electrode
• Learn how to operate the Gamry potentiostat
• Determine the redox potential of potassium ferricyanide
• Calculate the diffusion coefficient of potassium ferricyanide

Experimental Apparatus

• Gamry Instruments Interface 1010T
• Gamry Instruments Framework™ software package installed on a host computer
• Screen-printed electrode (SPE) cell stand (Gamry part number 990-00420)
• Platinum working screen-printed electrode (Gamry part number 935-00122)

Reagents and Chemicals

• 0.1 M potassium chloride, pre-purged to remove dissolved O2
• 2 mM potassium ferricyanide in 0.1 M potassium chloride, pre-purged to remove dissolved O2

CAUTION: Cyanide-containing compounds can hydrolyze to form hydrogen cyanide gas, which is highly poisonous. Never pour potassium ferricyanide down the drain!

Background

Cyclic voltammetry is the most commonly used electroanalytical technique for obtaining rapid quantitative data about an electrochemical reaction. The importance of cyclic voltammetry is that it provides a quick result concerning the kinetics of a heterogeneous electron-transfer, diffusion coefficients, and thermodynamic information for a process. Cyclic voltammetry also can give data on subsequent chemical reactions or adsorption processes. Cyclic voltammetry is usually the first experiment performed on an electroactive analyte because of its ability to provide the redox potential of that analyte. This technique also allows fast evaluation of the effect that a particular matrix may have on a redox process. During a typical cyclic voltammetry experiment, a component of the solution is electrolyzed (oxidized or reduced) by placing the solution in contact with an electrode, and then applying a potential to that electrode that is sufficiently positive or negative with respect to a reference half-cell (e.g., calomel or Ag|AgCl). The electrode’s voltage is adjusted higher or lower linearly, and finally, the voltage is returned to the original value at the same linear rate. When the electrode becomes sufficiently negative or positive, a species in solution may gain electrons from the electrode’s surface, or transfer electrons to that surface. As the potential is swept back and forth past the formal potential, E°, of an analyte, a current flows through the electrode that either oxidizes or reduces the analyte. Electron-transfer is a measurable current in the electrode’s circuitry. The magnitude of this current is proportional to the concentration of the analyte in solution, which allows cyclic voltammetry to be used in an analytical determination of concentration. The result is a cyclic voltammogram (or CV), in the form of a cycle between current and potential, where potential is plotted on the x-axis, and current is plotted on the y-axis.

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