1. What is iR Compensation?

2a. How do I activate and maintain my electrodes?

Simple Activation, of Glassy Carbon Electrodes

Explanation of the Process

Polishing on smooth ground glass plates allows the condition of the polishing material to be tightly controlled for optimum cleanliness. In addition, the use of deagglomerated aluminas with small particle size (0.05 µm) allows for a more scratch free highly active electrode surface. The use of particles of even smaller size (0.007 µm fumed silica) should enhance the smooth properties of the surface producing a highly active electrode with a scratch free surface. If this does not activate the surface polishing with larger particle size alumina and then silica should result in an active surface.

In addition, for applications where electrodes need to be kept active but it is not convenient to polish them, they can be kept in a stirred solution of alumina or fumed silica overnight. The resulting electrodes will be much more active than if left out exposed to the air.

Materials for Electrode Polishing

Cypress Systems 1 mm dia. GC disk electrodes
Cypress Systems Ag/AgCl reference electrode
NANOpure deionized water
Baikalox (Baikowski International, Charlotte, NC) agglomerate free alumina (0.05 µm)
Fumed Silica (Sigma) (0.007 µm)
Smooth ground glass plate (necessary to prevent scratches during polishing)

Methods

b. How to polish your electrodes

The degree of activation of the Cypress Systems GC disk electrode can be evaluated by the difference in peak potentials for the redox couple of ferri/Ferrocyanide, which is expected to be close to 60 mV. [3] First use a slurry of the 0.05 µm alumina to polish the electrode. You may add several scoops of alumina to a small wash bottle of deionized water and squirt it on a clean ground glass plate. For optimum cleanliness it is wise to use gloves when handling the electrodes. This precaution is necessary so that skin oils do not get onto the electrode. The gentlest method is to start with fine silica, test and if not sufficiently activated then gently polished in a figure 8 pattern in the slurry of alumina for approximately 30 seconds then follow with silica for smooth surface. The electrode should then be immediately rinsed with deionized water. It is suggested that the stream of water be directed directly against the surface of the electrode. In order to dry the electrode afterwards the body of the electrode can be gently touched with a Kimwipe.

In order to polish to an even smoother surface, the electrode can be polished in a slurry of 0.007 µm fumed silica. After thoroughly washing the polishing plate with deionized water and drying with a Kimwipe, silica can be added directly to the polishing plate. Deionized water can then be added to the silica to make a slurry. The silica should be visibly white on the plate. The electrode can be polished for 30 seconds in a figure 8 pattern and rinsed.

Now check the activation of the electrode with a solution 1 mM Ferrocyanide in 1 M KCl. Be sure to degass all solutions with argon before running the experiment. A typical result for an electrode scanned At 100 mV/s is shown in Figure 1. For this electrode Ep = 67 mV which is very close to the expected result.

If your electrode does not produce satisfactory results, repeat the process. Repolishing is expected particularly when the electrode is new.

c. How to keep your electrodes active

For applications where it is not convenient to repolish the electrodes, the electrodes can retain much of their activity by placing them in a stirred solution of alumina or silica. To do this, add 6 or 7 scoops of either alumina or silica to about 25 ml of deionized water and stir the solution with the electrode in it. Essentially, the electrode is being continuously polished. When you are ready to use the electrode again, rinse it with a stream of deionized water and it is ready to go. Results for storage in both alumina and silica are presented in Figures 2 and 3 respectively.

Table 1 shows that after storage overnight in alumina or silica the electrodes maintained a much higher degree of activation than if left out on the table in air.

Table 1: Results of Electrode Storage in Solutions of Alumina or Fumed Silica Storage in Alumina: