Standard Hydrogen Electrode is used as a reference electrode when calculating the standard electrode potential of a half cell.
What is a Standard Hydrogen Electrode?
The Standard Hydrogen Electrode is often abbreviated to SHE, and its standard electrode potential is declared to be 0 at a temperature of 298K. This is because it acts as a reference for comparison with any other electrode .
The redox half cell of the SHE is where the following reaction takes place:
2H+ (aq) + 2e– → H2 (g)
The reaction given above generally takes place on a platinum electrode. The pressure of the hydrogen gas present in this half cell equals 1 bar.
Use of Platinum in the Standard Hydrogen Electrode
Platinum is used in the Standard Hydrogen Electrode due to the following reasons:
- Platinum is a relatively inert metal which does not corrode easily.
- Platinum has catalytic qualities which promotes the proton reduction reaction.
- The surface of platinum can be covered with platinum black, a fine powder of platinum. This type of platinum electrode is called a platinized platinum electrode.
- Platinum also improves the reaction kinetics by adsorbing hydrogen at the interface.
Standard Hydrogen Electrode Construction
The parts that make up a Standard Hydrogen Electrode are listed below.
- A platinum electrode which is covered in finely powdered platinum black (platinized platinum electrode).
- A hydrogen Blow.
- A solution of acid having a H+ molarity of 1 mole per cubic decimeter.
- The SHE also contains a hydroseal which is used to prevent the interference of oxygen.
- The other half-cell of the entire Galvanic cell must be attached to the Standard Hydrogen Electrode through a reservoir in order to create an ionically conductive path. This can be done through a direct connection, through a narrow tube, or even through the use of a salt bridge.
Standard Hydrogen Electrode Diagram
A labelled diagram of a standard hydrogen electrode is provided below. In the SHE illustrated, a salt bridge is used to link the SHE with the other half cell.
The platinized platinum surface has a very high adsorption activity. Therefore, this surface must be protected from atmospheric oxygen as well as from organic substances. Substances such as arsenic and sulfur compounds can deactivate or poison the catalyst.