Potentiometry:

While the energy is supplied from an external source, a cell by that it flows is known as electrolytic cell. Irrespective of whether the cell is galvanic or electrolytic, we call the electrode while oxidation takes place as anode of the electrode, where reduction takes place as cathode. Within potentiometry, we have already learnt in which a cathode is assigned a positive sign and an anode a negative sign in a galvanic cell. Therefore, in an electrolytic cell, those electrodes obtain charges opposite to the above.  A capacity to do electrical work by a cell is known as the cell potential and is expressed in volt.

Let consider a cell of the kind where copper is deposited at the cathode and oxygen is evolved at the anode.

Cu | Cu²⁺   || 2H⁺, ½ O2 | Pt

Cu ²⁺ +   H₂O ? Cu + ½ O₂ (g) + 2H⁺

Cathode Cu⁺⁺ + 2e ? Cu°  

Anode              HgO ? 2H⁺ + ½ O₂ + Cu°

Cu⁺⁺ + HgO ? 2H⁺ + ½ O₂ + Cu° 

The potential of the electrochemical cell, (E_cell), is the difference among the electrode potential of the cathode and the electrode potential of the anode.  That is

E_cell    =   E_cathode   -   E_anode

while E_cathode and  E_anode are the half cell potentials of the cathode  and anode respectively.