Electrochemical Voltammetry

BAS (Bioanalytical Systems) CV-27 Voltammograph, BAS C-1B Cell Stand, coupled with a BAS XYT Analog Recorder. The Cell Stand features magnetic stirring and selectable gas purge rate for the sample. The gas control provides for blanketing the sample when active purging is not occurring.

The magnetic stirrer controls mass transport to the electrode surface and mixing for titrations. The lift arm with detachable cell top allows removal and replacement of the cell vial. The cell is enclosed in a Faraday Cage to minimize electrical interference. The BAS Voltammetric Analyzer is an electrochemical instrument capable of performing a variety standard controlled-potential techniques. It is ideal for demonstrating basic electrochemistry and doing routine electroanalysis. It is capable of: digital smoothing, peak or wave height determination transformation (the Anson and Cottrell transforms, convolution, deconvolution. etc.), peak potential and current measurement, half-wave and limiting current measurement, and cyclic voltammetry.

BAS CV27 allows for cyclic voltammetric and bulk electrolysis experiments. Cyclic voltammetry is an electrolytic method that uses microelectrodes and an unstirred solution so that the measured current is limited by analyte diffusion at the electrode surface. The electrode potential is ramped linearly to a more negative potential, and then ramped in reverse back to the starting voltage. The forward scan produces a current peak for any analytes that can be reduced through the range of the potential scan. The current will increase as the potential reaches the reduction potential of the analyte, but then falls off as the concentration of the analyte is depleted close to the electrode surface. As the applied potential is reversed, it will reach a potential that will reoxidize the product formed in the first reduction reaction, and produce a current of reverse polarity from the forward scan. This oxidation peak will usually have a similar shape to the reduction peak.

Cyclic Voltammetry (CV)is a versatile electroanalytical technique for the study of electroactive species. CV consists of linearly cycling the potential of an electrode immersed in an unstirred solution while measuring the resulting current. Thus, a voltammogram is a display of current versus potential. The most useful aspect of this technique is its application to the qualitative diagnosis of electrode reactions. Such as voltammetry of a redox couple (e.g. ferro-/ferricyanide or Fe²⁺/Fe³⁺ in aqueous solution ) using a rotating disc electrode (Pt or Au) or cyclic voltammetry of a redox system. A simple potential wave form that is often used in electrochemical experiments is the linear wave form i.e., the potential is continuously changed as a linear function of time. The rate of change of potential with time is referred to as the scan rate. Cyclic voltammetry can be used as a technique to:

• Reveal surface contamination.
• Estimate relative surface area and roughness.
• Evaluate electrolyte leakage at electrode-insulator interfaces.
• "Fingerprint" electrochemical reactions for benchmarking and quality control
• Estimate potentials at which reduction-oxidation reactions occur.
• Determine charge storage capacity

The simplest technique that uses this wave form is linear sweep voltammetry. The potential range is scanned in one direction, starting at the initial potential and finishing at the final potential. A more commonly used variation of the technique is cyclic voltammetry, in which the direction of the potential is reversed at the end of the first scan. Thus, the waveform is usually of the form of an isoceles triangle. This has the advantage that the product of the electron transfer reaction that occurred in the forward scan can be probed again in the reverse scan. In addition, it is a powerful tool for the determination of formal redox potentials, detection of chemical reactions that precede or follow the electrochemical reaction and evaluation of electron transfer kinetics.

An example wave form that can be used in cyclic voltammetry is shown below (Reload to view the cycle). In this example it is assumed that only the reduced form of the species is initially present. Thus, a positive potential scan is chosen for the first half cycle during which an anodic current is observed. Because the solution is quiescent, the product generated during the forward scan is available at the surface of the electrode for the reverse scan resulting in a cathodic current.

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