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By convention ,E_cell = E_cathode  -E_anode 

From this for the cell with the standard hydrogen electrode we get

E_cell   =   E_right    -   0   =E_electrode 

Electrode potential is measured in volts (V)

Illustration:

There are two types of electrodes positively charged and negatively chargedTo understand this ,let us consider a metal -metal ion electrode .A metal -metal ion  electrode can be obtained by dipping a rod or strip of the metal into a solution containing its ions ,Example a metal M dipped into a solution containing Mⁿ⁺ ions .

When a strip of a metal M is placed in a solution of its ions Mⁿ⁺ ,either of the following three possibilities can occur .

1.   A metal ion Mⁿ⁺ collides with the electrode and undergoes no change .

2.  A metal ion Mⁿ⁺ collide with the electrode ,gains n electrons and get converted into a metal atom M that is metal ion is reduced )

3.A metal atom on the electrode M may lose n electrons to the electrode it gets oxidised to Mⁿ⁺ that is metal atom is oxidised .

M(s)   ______>    Mⁿ⁺ (aq)  +n e-

Let us take the three situations one by one .

1.When neither the metal atom nor the metal ion Mⁿ⁺undergo any change .In such a situation no charge is dveloped on the electrode reletive to the solution .

2.When the metal Mn+ undergoes reduction at the electrode surface by accepting electrons from the electrode ,then the lectrode develops a positive charge .

3.When the metal atom of the electrode loses n electrons to the elecrode ,it gets oxidised to Mⁿ⁺ .The Mⁿ⁺ ion so formed goes into the solution ,and the electrode develops a negative charge .Thus if the metal ion Mⁿ⁺ has a greater tendency towards reduction at the electrode ,then the electrode develops a positive charge and if the the metal has greater tendency towards oxidation then the electrode develops  negative charge due to the accumulation of electrons in the electrode .As a result ,the electrode develops a definite electrical potential  with respect to the solution .The potential difference between the electrode and the solution is termed as the electrode potential .