Types of Reversible Electrodes

A reversible electrode is one in which the electrode reaction can proceed in both forward and reverse directions with a small change in potential.

Based on the species present at the electrode surface, reversible electrodes are classified into different types.

The metal–metal ion electrode forms when a metal, like copper, is placed in a solution of its ions. The metal can dissolve as ions. Simultaneously, metal ions in solution can gain electrons and deposit back onto the metal surface.

In an amalgam electrode, a reactive metal like sodium is dissolved in mercury. The resulting amalgam remains in equilibrium with its ions in solution.

A redox electrode involves a solution containing two oxidation states of the same species, such as Fe²⁺ and Fe³⁺. An inert electrode, often platinum, enables electron transfer between them.

In a metal–insoluble salt electrode, a metal is coated with a sparingly soluble salt and placed in a solution containing the same anion. A common example is the silver–silver chloride electrode immersed in potassium chloride solution.