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Chemistry LibreTexts

Experiment

Equipment

  • A high sensitivity potentiostat with a wide range of scan rates is recommended. Please see your laboratory instructor for directions.
  • Electrochemical cell and electrodes
    • 10 μm microelectrode, Pt or GC
    • Pt auxiliary electrode
    • Ag/AgCl reference electrode
    • Small volume electrochemical cell
    • Polishing kit

Chemical Solutions

  1. 100 ml stock solution of 10 mM K3Fe(CN)6 in 0.1 M KNO3

    * An alternative is to use water-soluble ferrocene carboxylic acid (FCA) in pH 7 buffer.

  2. 100 ml of 1.0 M KNO3

    * Use high purity water throughout.

Procedure

  1. Prepare 50 ml each of 1, 2, 5 and 10 mM ferricyanide in 0.1 M KNO3 by appropriate dilution of solutions A and B.
  2. Please see laboratory instructor for set-up and operational direction of the potentiostat.
  3. Run scan rate (50, 100, 200 and 500 mV/s) dependence of iss with a 10 μm glassy carbon or Pt microelectrode. Scan from +600 mV to 0. 0 mV and back to +600 mV with the 2 mM ferricyanide solution. The electrode surface may need to be cleaned by lightly polishing the tip on 0.05 μm alumina particles (slightly wet) on smooth glass surface. Use only light pressure and polish carefully since it is easy to crack or chip and destroy the tip of the electrode. Wash the tip with high purity water and touch the edges with KimwipeTM or soft tissue paper to remove the excess water.

    * There may be a small hysteresis between the forward and reverse CV wave. The waves should track each other within a few millivolts. If they are unsymmetrical with > 20 mV differences try polishing the tip with the directions given above and rescan. With larger electrodes, the polishing directions often end with an ultrasonication step. Do not ultrasonicate microelectrodes since the tip will be seriously damaged.

  4. Run concentration dependence of iss with the 1, 2, 5 and 10 mM ferricyanide, scanning from +600 to 0.0 mV at a scan rate of 100 mV/s.

    Record and save your data files.