Question

The potential value of a standard hydrogen electrode is ______________.

Answer 1

Hint: The electrode potential for standard hydrogen electrode is considered the basis to calculate the standard electrode potential of other elements. The standard electrode potential is the measure of how strong or weak is the electrode than the standard electrode potential.

Complete answer:
The standard hydrogen electrode (abbreviated SHE), is a redox electrode reaction which forms the basis for the thermodynamic scale of oxidation and reduction potentials.
This redox reaction occurs at inert platinum electrodes. The electrode is dipped in solution that is acidic in nature and hydrogen gas is bubbled through it.
 The concentration of the reduced form and oxidized form are maintained to the value 1. That implies that the pressure of hydrogen gas is 1 bar and the activity coefficient of hydrogen ions in the solution is 1.
 The activity of hydrogen ions is their effective concentration, which is the product of the formal concentration and the activity coefficient.
The choice of platinum for the hydrogen electrode is due to the:
-Inertness of platinum as it does not react with the solution.
-The capability of platinum to catalyze the reduction of proton
The surface of platinum is platinized i.e. covered with platinum black to:
-Increase the total surface area. This improves the kinetics of the reaction.
-Use a surface material that absorbs hydrogen at this interface. This also improves the reaction kinetics.
The absolute electrode potential is estimated to be 4.44 V at 298 K but to form a basis for comparison with all other electrode reactions the standard electrode potential is taken as 0 V at all temperatures.

Note:
Other than standard hydrogen electrode there are 2 more types of hydrogen electrode:
-Normal Hydrogen Electrode(NHE) : Potential of a platinum electrode in acid solution of strength 1M.
-Reversible Hydrogen Electrode(RHE) : A hydrogen electrode whose potential depends on the pH of the resultant solution.