Question

Describe the construction and working of Standard Hydrogen Electrode.

Answer 1

Construction:

1. SHE consists of a platinum plate coated with platinum black used as electrodes.
2. This plate is connected to the external circuit through a sealed narrow glass tube containing mercury. It is surrounded by an outer jacket.
3. The platinum electrode is immersed in \[\ce{1 M H^\oplus}\] ion solution.
4. The solution is kept saturated with dissolved H₂ by bubbling hydrogen gas under 1 atm pressure through the side tube of the jacket, as shown in Fig.
5. Platinum does not take part in the electrode reaction. It is an inert electrode and serves as the site for electron transfer.

Formulation: Standard hydrogen electrode is represented as

\[\ce{H^\oplus (1 M) | H2 (g, 1 atm) | Pt}\]

Electrode reaction: The platinum black, capable of adsorbing large quantities of H₂ gas, allows the change from gaseous to ionic form and the reverse process to occur.

The reduction half reaction at the electrode is

\[\ce{2H^\oplus(1 M) + 2e^\ominus -> H2 (\text{g}, 1\text{atm}); E^0_{H_2} = 0.000 V}\]