Specific Half-Cells and Reference Electrodes

This class of electrodes is generally categorized as reversible or non-polarizable. By this, we mean simply that the electrode passes electric current without changing the chemical environment in the region of the electrode. The basic thermodynamic consideration for electrochemical reversibility is expressed by the Gibbs free-energy-loss relation 

This relation expresses valence changes and accompanying electron transfers which occur in oxidation-reduction systems. The basic property of such systems is the conversion of chemical energy into electrical energy. 

---