The electrode potential of Hydrogen electrode depends upon the __________concentration, the pressure of ______________ and the temperature at which the electrode system is maintained. The electrode potential is independent of the surface area of the inert Platinum electrode.

$\left[{\mathrm{H}}_3{\mathrm{O}}^{+1}\right],$ diatomic Hydrogen gas $\left[{\mathrm{H}}^{+1}\right]$  ion has no independent existence. $\left[{\mathrm{H}}^{+1}\right]$ion combines with water to form $\left[{\mathrm{H}}_3{\mathrm{O}}^{+1}\right]$. Pure, dry diatomic Hydrogen gas has to be passed through the HCl aqueous solution to attain equilibrium. So, pressure of ${\mathrm{H}}_2$ gas decides the electrode potential. $\mathrm{E}={\mathrm{E}}^0-\frac{2.303\mathrm{RT}}{2\mathrm{F}}{\log }_{10}\frac{{\mathrm{P}}_{{\mathrm{H}}_2}}{{\left[{\mathrm{H}}_3{\mathrm{O}}^{+}\right]}^2}$ . The electrode potential is independent of the surface area of the electrodes.