Electrochemical Measurements of Supported Catalysts Using a Potentiostat/Galvanostat

1. Catalyst Ink and Working Electrode Preparation

Safety Precautions: Metals supported on carbon black must be handled in a fume hood or balance enclosure until it is in suspension form as these powders are inhalation hazards.

1. Using an enclosed balance, weigh out 5–10 mg of metal/carbon black catalyst and add to a glass vial with a cap.
2. Using a micropipette, dilute the catalyst with water such that the final concentration is 7.5 mg of catalyst per mL of water.
3. While sonicating, 100 µL of Nafion 117 solution per mL of water is added to the suspension.
4. The ink should be sonicated for at least 10 min to ensure uniform dispersion and complete mixing of the carbon black support with the binding agent.
5. While the ink is sonicating, a 3 mm glassy carbon disk electrode should be cleaned and polished by rubbing it in a swirling circular motion on a soft alumina pad covered with 0.05 µm alumina solution. It should then be rinsed copiously with water to remove the alumina.
6. Next, 7 µL of ink is dripped onto a polished, vertically-oriented 3 mm glassy carbon disk electrode. The working electrode is then dried at 80 ˚C for 1 h if the catalyst is air-stable or evaporated under a weak vacuum for 30 min if the catalyst is air-sensitive.

2. Electrochemical Cell Preparation

Safety Precautions: Gloves, labcoat, and safety glasses must always be worn but is especially paramount for working with the sulfuric acid solution. Should any drops of solution spill onto the wrists, it must be washed with soap and water for 15 min. For major spills, removal of contaminated garments and use of the eyewash or showers should be used for 15 min followed by a medical consultation. The electrical leads should not be touched once placed onto the electrochemical cell.

1. A glass cell is filled with 10 mL of 0.5 M H₂SO₄ and degassed for at least 30 min with an ultra high purity nitrogen stream
2. The Teflon caps of the electrochemical cells have 3 ports for the working electrode, counter electrode, and the reference electrode
3. The Ag/AgCl reference electrode is removed from its 1 M KCl solution, rinsed thoroughly with DI water, and then placed into the cell.
4. The platinized platinum wire counter electrode is rinsed thoroughly with DI water and then placed into the cell.
5. The dried working electrode is rinsed with DI water and then placed into the cell.
6. The potentiostat is turned on.
7. The white electrode lead is connected first and connected to the reference electrode.
8. The red electrode lead is then connected to the Pt wire counter electrode.
9. The green electrode lead is then connected to the metal/carbon black working electrode.
10. A small N₂ purge stream is left continuously bubbling in the electrolyte.
11. Ensure no leads are touching and that there is no direct electrical contact between the 3 electrodes other than with the 0.5 M H₂SO₄ electrolyte.

3. Electrochemical Analysis

1. After turning on the potentiostat, perform at least 20 conditioning cycles between 0 and 0.4 V vs. RHE at 50 mV/s using CV. This is performed by choosing CV as a technique and entering the upper and lower potential limits as well as the scan rate.
2. Linear Sweep Voltammetry (LSV) can then be performed by choosing LSV as a technique and specifying a starting potential, a final potential, and a scan rate. The scan rate for LSV is typically much less than CV, usually 1 – 2 mV/s so that capacitive currents become much lower than currents arising from faradaic surface reactions
3. Chronoamperometry (CA) is performed by choosing CA or "Amperometric i-t curve" as a technique and specifying the fixed potential as well as the length of time the instrument should hold the working electrode as this fixed potential.
4. Chronopotentiometry (CP) is performed by choosing CP as a technique. CP can be performed in a series of current steps where one current is specified for a certain length of time followed by a new current for a specified length of time. These applied currents can span both anodic and cathodic currents within the same CP measurement.
5. When the electrochemical analysis is finished, turn off the potentiostat.
6. Disconnect the electrode leads and store them in a dry place away from any liquids to prevent corrosion.
7. Remove the reference electrode and rinse with copious amounts of DI water. Then return the reference electrode directly to its 1 M KCl storage solution. The tip of this electrode should never be allowed to become dry.
8. Remove the Pt wire counter electrode and rinse thoroughly with DI water
9. Remove the working electrode and rinse thoroughly with DI water and then use a Kimwipe with acetone to easily remove the dried catalyst ink from the working electrode surface. It is recommended to polish electrodes immediately after use.
10. Turn off the N₂ purge.
11. Empty the used electrolyte into an acidic waste container. Rinse the glass cell and Teflon cap with copious amounts of DI water.