How to Clean and Polish a Glassy Carbon Electrode: Alumina Size and Figure Eights

Glassy carbon electrodes are often polished by moving them across the polishing cloth in a figure-eight pattern. It is a common practice in electrochemistry, but is a figure eight actually better than a circle?

Do we always need to start with the coarsest alumina? And how do we know that the electrode is clean beyond the fact that it looks shiny?

The short answer is that a figure eight is a useful technique, not an electrochemical law. The path does not replace control of pressure, flatness, abrasive sequence, or residue removal.

Cleaning, resurfacing, and activation are not the same

To avoid mixing different objectives, this article uses cleaning for the removal of residue, resurfacing for polishing that removes a surface layer, and activation for a treatment intended to modify the electrochemical response. This is a practical distinction, not a universal nomenclature: the terms can overlap in the literature, and polishing itself can modify the surface.

Using this convention:

Cleaning removes adsorbed species or residues without deliberately trying to alter the electrode chemistry.
Resurfacing removes a thin layer by polishing to expose carbon again.
Activation intentionally modifies the surface to change its response, for example through an electrochemical treatment.

Polishing a glassy carbon disk may clean and resurface it at the same time, but it does not necessarily return a chemically identical surface. Kamau et. al. shows that the response depends on the preparation method and the electrode's prior history. McCreery et. al. reports differences in kinetics, residue, and surface oxygen content between surfaces prepared using different procedures.

Consequently, visually similar finishes do not by themselves guarantee an identical electrochemical response. Shine is a visual criterion; it does not characterize the complete surface chemistry.

Which alumina particle size should you use?

Before choosing a particle size, decide whether polishing is actually needed. BASi notes that the need varies greatly with the application and recommends trying a lighter cleaning step first. When resurfacing is necessary, a classical full preparation proceeds from coarse to finer abrasives. For example, McCreery describes silicon carbide paper followed by successively smaller alumina particles, typically finishing at 0.05 µm. This does not mean that every maintenance polish must begin with the largest particles. For a surface without visible damage, the maintenance guides reviewed allow starting directly with the fine abrasive.

Surface condition	Suggested sequence	Objective
No visible damage; maintenance requiring polishing	0.05 µm	Remove light contamination and restore the finish
Dull surface or response not restored by the fine step	0.3 → 0.05 µm	Deeper resurfacing followed by final polishing
Scratches or persistent deposit	1.0 → 0.3 → 0.05 µm	Remove more material and progressively rebuild the finish
Severe damage or loss of flatness	Consult the manufacturer	Repair may be required; this is not routine maintenance

This table does not come from a scientific trial that validated a universal sequence. It combines manufacturer-recommended sequences with suggested selection criteria proposed in this guide. Pine recommends 0.05 µm for routine maintenance and 0.3 → 0.05 µm for periodic cleaning; redox.me reserves 1.0 → 0.3 → 0.05 µm for thorough cleaning and allows maintenance to be limited to 0.05 µm.

Pine states that its guidance comes from the experience of its electrochemists and electrode machinists. Redoxme includes general pretreatment references but does not tie every level to a specific comparative trial. The table should be used as a starting point and adapted to the electrode manual and the response that needs to be restored.

Figure eights, circles, or straight lines?

Commercial instructions are not unanimous, Pine describes the figure eight as a useful technique, while BASi calls the figure eight optimal in its general guidelines but prescribes smooth circular motion for glassy carbon, silver, and nickel on the same page. Two studies published in 2025 help put this tradition into context.

Swiderski and co-workers manually compared figure-eight, circular, and linear motions. Under their conditions, the authors obtained the best repeatability with 30 figure eights, completed in about 22 seconds. Both 10 and 50 figure eights were less reproducible than 30. The article identifies the manufacturer of the Al₂O₃ suspension but does not report its particle size.

Yoshikawa and co-workers used a robotic arm to hold the electrode under controlled vertical force while a station moved the polishing pad. Before the test, they damaged the electrodes by applying 5 V for 30 seconds and monitored recovery using the voltammogram integral, which the study used as an indicator of capacitance and surface condition. With 0.05 µm alumina, they found no significant difference between figure-eight, circular, linear, and more complex paths. This criterion allows recovery to be compared within that experiment, but does not establish equivalent cleanliness or kinetics for other applications.

The results do not show that the figure eight is universally superior. They support 30 figure eights only under Swiderski's manual conditions. Yoshikawa's authors proposed that the constant force applied by the robot regardless of pattern might explain the absence of significant differences. This is a plausible interpretation, not a mechanism demonstrated by the experiment.

In practice, circular motions appear in manufacturer protocols and can produce acceptable results, although they were less reproducible than figure eights in Swiderski's manual comparison. In Yoshikawa's robotic study, by contrast, the pattern produced no significant differences. With any path, manufacturer guides recommend keeping the face parallel, applying light and even pressure, and rotating the electrode periodically.

A short polishing procedure

For a solid, reusable glassy carbon disk, the following outline is a starting point. The manufacturer's instructions take priority.

Decide whether polishing is needed. If the response remains acceptable and there is no damage or persistent contamination, cleaning compatible with the manual may be enough. If maintenance requires polishing, start with 0.05 µm and move to a larger grade only if the fine step does not restore the response defined as acceptable. Before increasing the particle size, check the solution, reference electrode, connections, and residue removal: a poor response does not by itself show that more carbon needs to be removed.
Dedicate one pad to each particle size. Place it on a flat support and do not mix abrasives. A coarse particle transferred to the fine pad can prevent the expected finish.
Use a small amount of suspension and do not let it dry. McCreery warns that some commercial products contain dispersants that can adsorb on carbon. When maximum control is required, he recommends pure, dry alumina suspended in ultrapure water.
Keep the face parallel and apply light pressure. Use broad figure eights or circles, cover different parts of the pad, and rotate the electrode periodically.
Rinse thoroughly between grades and after polishing. Brief ultrasonication may help remove particles, but it is neither mandatory nor compatible with every assembly. Pine suggests one to five minutes with only the active end immersed, while a Metrohm guide prohibits ultrasonic treatment for its electrodes in one specific application.

Ultrasonication does not guarantee complete removal either. Under the conditions used by Kiema and co-workers, XPS detected approximately 1.8% surface aluminum after 10 minutes of ultrasonication, compared with 5.8% on freshly polished, non-sonicated carbon. The authors described this as about 30% of the polishing alumina still present. This is a result for that specific procedure, not a universal percentage. McCreery also warns that impurities from the bath may adsorb on the surface.

More intensive chemical or electrochemical treatments exist, but they can activate or oxidize the surface. They should not be added automatically to a polishing procedure without a validated protocol for the application.

When should you change the alumina or pad?

Move from coarse to fine alumina once the marks or contamination that justified the previous stage have disappeared. If the surface is in good condition, the complete sequence is unnecessary.

The guides reviewed do not establish a universal number of uses per pad. BASi allows its microcloth disks to be reused with the same abrasive, but specifies single use for a different abrasive pad. As a practical criterion, replace a pad if it is damaged, causes scratches, or accumulates residues that compromise the experiment. Use with another sample does not by itself require disposal: reuse depends on the manual, the pad's condition, and residues not interfering with the measurement. Keep abrasive particle sizes separate.

Elgrishi and co-workers recommend ideally using separate pads before and after experiments. Another practical example is reserving one set for glassy carbon disks and another for ring-disk electrodes containing platinum when platinum carryover to carbon must be avoided. This precaution draws on Pine's warning: polishing the disk and ring together can transfer platinum debris to the disk and affect an oxygen reduction experiment. Separate pad sets do not prevent transfer within the ring-disk electrode itself; where the design allows it, Pine recommends polishing the disk separately.

Choosing polishing materials

Working with several particle sizes requires a flat support and enough pads to keep the abrasives separate. On ElectroSeek, you can compare glassy carbon electrodes and different polishing kits.

The Corrtest CS942 contains three alumina grades but only one nylon and one microcloth pad, so additional pads are needed to dedicate one to every abrasive. The Ionode kit contains three pads, while the redox.me kit contains five microcloth pads, five nylon pads, and 1.0, 0.3, and 0.05 µm suspensions.

If you are unsure which abrasives are compatible with your electrode, tell us about your surface and application and we can help you compare the available options.

Scientific articles

Kamau, G. N. “Surface Preparation of Glassy Carbon Electrodes”. Analytica Chimica Acta 207 (1988), 1–16.
Kiema, G. K.; Aktay, M.; McDermott, M. T. “Preparation of Reproducible Glassy Carbon Electrodes by Removal of Polishing Impurities”. Journal of Electroanalytical Chemistry 540 (2003), 7–15.
McCreery, R. L. “Advanced Carbon Electrode Materials for Molecular Electrochemistry”. Chemical Reviews 108 (2008), 2646–2687.
Elgrishi, N. et al. “A Practical Beginner’s Guide to Cyclic Voltammetry”. Journal of Chemical Education 95 (2018), 197–206.
Yoshikawa, N. et al. “Does One Need to Polish Electrodes in an Eight Pattern? Automation Provides the Answer”. Digital Discovery 4 (2025), 326–330.
Świderski, M. et al. “Influence of Electrode Polishing Protocols, Potentiostat Models, and LOD Calculation Methods on the Electroanalytical Performance of SWV Measurements at Glassy Carbon Electrodes”. Molecules 30 (2025), 4651.

Technical guides consulted

Pine Research, “Probing Fuel Cell Electrocatalyst Properties with Rotating Disk and Rotating Ring-Disk Electrodes”, section 4.1
Pine Research, “Electrode Polishing Guide”.
BASi Manual: “Working Electrodes” and “EC FAQs: Electrodes”.
redox.me, “Methods for Cleaning Substrates and Glass Chambers for Electrochemical Measurements”.
Metrohm, “Hg-free Determination of Heavy Metals / Daily Routine for Best Performance”.