Question

Explain why it is generally more preferred to use a three-electrode system (composed of working, counter, and reference electrodes) than a two-electrode system in electrochemical analysis. Also explain the role of working, counter, and reference electrodes, respectively, in a three-electrode system.

Answer 1

# Three electrode system is preferred over Two electrode system, Why?

• In the three-electrode system, potential of the working electrode vs. reference electrode can be observed. It is used to control and measure both the potential and current through a cell.   Additionally, since the reference electrode passes negligible current, the iR drop between the reference and working electrode (iRU) is often very small.  Thus, with the three-electrode system, the reference potential is much more stable, and there is compensation for iR drop across the solution
• In the two-electrode system, potential difference between anode and cathode can be observed, which is considered as "voltage". Moreover, it not possible to observe where the interfacial potential difference occurs in this system.

The electrochemical reaction depends on its thermodynamic property, which is reflected by the electrode potential rather than the voltage according to Nernst equation. Therefore, the three-electrode system is preferable.

# Roles of the electrode:

The three-electrode system consists of a working electrode, counter electrode, and reference electrode.

• Reference electrode’s role is to act as a reference in measuring and controlling the working electrode potential, without passing any current.
• Counter electrode is to pass all the current needed to balance the current observed at the working electrode.
• Working electrode is used to study the electrochemical phenomena (reduction or oxidation) taking place.