Cleaning and Polishing Voltammetric Electrodes

These procedures are recommended for eDAQ voltammetric disk electrodes:

• ET074 Glassy Carbon Disk Electrode
• ET075 Platinum Disk Electrode
• ET076 Gold Disk Electrode
• ET079 Copper Disk Electrode

Safety

Polishing powders comprise submicron sized particles which can be dangerous, especially if inhaled. Please follow your local safety guidlines and especially work in a well ventilated environment.

Materials

Abrasive cleaning materials can be obtained from Buehler Incsuch as:

• Micropolish Alumina Suspension, 1 micron, Product Number: 406361006. Use for heavy duty abrasive cleaning.
• Micropolish Alumina Suspension, 0.3 micron, Product Number: 406363006. Use for abrasive cleaning.
• Nylon polishing pads, PSA backed, 73 mm diameter, Product Number: 407052

For routine or final polishing Buehler Inc supply:

• MasterPrep Alumina Suspension, 0.05 micron, Product Number: 636377006
• MicroCloth polishing pads, PSA backed, 73 mm diameter, Product Number: 407212

Local lapidary supply companies may have equivalent products. Diamond, silica, or silicon carbide powders of similar particle size can also be used. A polishing pad that has a pressure sensitive adhesive (PSA) backing can be affixed to a glass plate to ensure a flat polishing surface.

A dry cloth can scratch the electrode and can cause the cloth to tear, always wet a new cloth with abrasive powder suspension, or deionised water before use. Use each cloth only with a powder of single particle size. Rinse cloths with deionised water after each polishing cycle, but reserve them for use only with that particle size polish in the future. Rather than adding dry powder to a polishing pad, it is often better to use a prepared polishing suspension. If you have a source of dry powder suspend it in a wash bottle containing ethanol, and then add a small amount of the suspension (shake well before use) to the pad.

General Procedure

Resist the temptation to over-polish the electrodes. In most cases the electrode remains clean after the experiment, or could be washed clean with suitable organic solvent to remove greasy organic materials, or dilute acid or base (0.1 mol/L HCl, HNO3, NaOH) to remove inorganics. Protein deposits can be hydrolysed with an appropriate commercial enzyme-based cleaner.

Mercury films on platinum or glassy carbon substrates can be removed by gently wiping the electrode tip with lab tissue (dispose of tissue in mercury waste container) any residual mercury can be removed by holding the electrode at an oxidizing potential (eg +1 V) in dilute acid solution (0.1 mol/L).

Only if there is an intractable coating electrodeposited on the electrode, or after extended use, will the electrode need any polishing at all. Polishing should only be done if there is visually obvious surface contamination (use a magnifying glass) or where a trial cyclic voltammogram in clean solvent indicates that there has been surface contamination. Standard maintenance polishing should use a 0.05 micron polishing powder, only a badly scratched electrode, or one with an extremely intractable coating would need to use coarser (larger particle size) powders.

While automatic polishing machines might be useful if large numbers of electrode have to be polished on a regular basis, hand polishing is more usual in a research or teaching lab.

When hand polishing, grip the electrode low down (near its tip) and hold it in a vertical position while making figure-8 motions on the polishing pad which is moistened with deionized water and to which has been added a small amount of polishing powder suspension. After three or four of the figure-8 motions turn the electrode through 90 degrees in your grip and repeat the figure-8 movement. The aim is to ensure even wear on the electrode tip so that a flat surface is maintained.

If you have previously used glass body electrodes then be aware that PEEK or Teflon body electrodes need significantly less downwards pressure to be applied while polishing. Also note that coarse powders (more than 0.05 micron) will cause extensive abrasion of the electrode surface which then takes a lot more polishing with 0.05 micron alumina powder to obtain a mirror smooth finish.

After polishing, use the figure-8 motion on a clean moist MicroCloth polishing pad (no powder) to remove any adherent material.

Some users prefer immersion of the electrode tip in an ultrasonic bath for a few seconds to remove adherent polish. eDAQ PEEK body working electrodes will withstand sonication but only immerse the tips of the electrode. Do NOT immerse the electrical contacts.

Glassy Carbon Electrodes

Glassy carbon is a unique electrode material often used for electrochemical experiments. A variety of surface pretreatments have been reported to optimise electrode behaviour in specific instances. An IUPAC review article is available.

ET069 and ET072 Leakless Reference Electrodes

The tip of these reference electrodes can become fouled with use. The tip can be washed or lightly polished (like a working electrode) to remove intractable adhering material. In extreme cases you can even use a scalpel, or razor blade, to shave a thin slice from the tip, which exposes fresh polymer junction.

Summary

1. Only polish when necessary.
2. Use only light downwards pressure when polishing. When polishing, grip the electrode at its base, ie the end where it is being polished.
3. Only use 0.05 micron powder for routine polishing.
4. Only use coarser powders if absolutely necessary for very contaminated electrodes.