Guide
How to Set Up a Three-Electrode Electrochemical Cell
A three-electrode cell uses a working electrode where the reaction happens, a reference electrode that fixes the potential scale, and a counter electrode that carries the current. Place the reference close to the working electrode, use a counter electrode larger than the working electrode, and clean everything first.
What each electrode does
| Electrode | Job | Common choices |
|---|---|---|
| Working | Where the reaction under study happens | Glassy carbon, gold, platinum disks; your own sample in a holder |
| Reference | Fixes the potential scale; carries almost no current | Ag/AgCl, SCE, Hg/HgO |
| Counter | Carries the current | Platinum wire or mesh; graphite rod |
Step by step
- Clean the cell and rinse it with deionised water.
- Polish the working electrode and rinse it well.
- Fill the cell with electrolyte, and purge with gas if oxygen would interfere.
- Place the reference electrode close to the working electrode, to reduce the resistance between them.
- Place the counter electrode so that the current reaches the working electrode evenly.
- Connect the potentiostat leads, then check the open-circuit potential before you start.
Mistakes that spoil a measurement
- A counter electrode smaller than the working electrode, which limits the current.
- A reference electrode far from the working electrode, which adds a voltage error at high current.
- Air bubbles on an electrode surface.
- Using platinum as the counter electrode in hydrogen evolution catalyst studies, where it can deposit on the sample.
- Forgetting to correct for solution resistance (iR compensation) at high current.
Frequently asked questions
Why use three electrodes instead of two?
In a two-electrode cell, the current flows through the same electrode that sets the reference, so the potential drifts. A third electrode separates the two jobs, which gives an accurate potential.
How close should the reference electrode be?
As close as practical to the working electrode without touching it or blocking the current. Many cells use a Luggin capillary for this.