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Standard Hydrogen Electrode (SHE)

Standard Hydrogen Electrode consists of a platinum wire sealed into a glass tube  and carrying a platinum foil at one end. The platinum foil is coated with finely divided platinum. The electrode is place in beaker containing an aqueous solution of some acid having one molar concentration of H+ions. Hydrogen gas at 1 bar pressure is continuously bubbled through the solution at a temperature of 298K. the oxidation or reduction in the SHE takes place at platinum foil. Hence, it can act as anode as well as cathode and may be represented as :

Pt, 1/2 H2 (1 bar)/ H+ (1M) or

H+ (1M) 1/2 H2(1 bar), Pt respectively.

If SHE acts as anode then oxidation will take place at it as

H2(g) --> H+ (aq) + 2e-

If SHE acts as cathode then reduction will take place at it as

2H+ (aq) + 2e->H2 (g)

The electrode potentials of other electrodes are determined by coupling them with SHE.The electrode potential of an electrode determined relative to the standard hydrogen electrode under standard conditions is called standard electrode potential. It is represented as E-. The standard conditions are 1M concentration of ions at 298K temperature and 1 bar pressure.

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