1. A rectangular platinum plate coated with platinum black is welded to a platinum wire and the wire is fused into a glass tube with the help of mercury.
2. This tube is sealed into a jacket having a side tube at the top. It acts as the hydrogen inlet.
3. Two holes are provided at the bottom of the outer jacket, which act as the hydrogen outlet.
4. The outer jacket is immersed in a glass vessel containing 1m HCl.
Working: Hydrogen gas is passed from the top inlet. The pressure inside the jacket increases. Due to this, acid level is pushed down and the platinum plate gets exposed to hydrogen gas. Platinum adsorbs hydrogen. As a result, pressure falls and acid level increases back. Now, the adsorbed film of hydrogen comes in contact with hydrogen ions of the solution and equilibrium is established and potential is developed. The potential developed is taken as
Representation of Hydrogen electrode:
H2(g) (1atm) Pt || H+ (1M)
