How does a potentiostat control the potential and current of an electrochemical cell?

A short introduction video to potentiostats is available in our knowledge base. A very simplified description is that a potentiostat keeps the potential between two electrodes, the working electrode and the reference electrode, at a set potential. Current will flow between the working electrode and a third electrode, the counter electrode. This way the reference electrode has a constant electrochemical potential and can be used by the potentiostat as a fixed reference point.

From the electronic designer’s point of view, the situation must be described quite differently. The working electrode is connected to the ground. The potentiostat changes the potential of the counter electrode versus the ground until the measured potential difference between the reference electrode and the working electrode is the set potential.

If you want to dive deeper into the details of the circuits, the Wikipedia entry is a good point to start.