Standard Hydrogen Electrode

Electrode potential is a measure of reducing power of any element. It is also called standard reduction potential. Standard Hydrogen Electrode is used as a reference electrode when calculating the standard electrode potential of a half cell.

Table of Contents

• What is a Standard Hydrogen Electrode?
• Recommended Videos
• Uses
• Standard Hydrogen Electrode Construction
• Standard Hydrogen Electrode Diagrams
• Solved Example
• Frequently Asked Questions – FAQs

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 half cell reaction of SHE can be written as follows:

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.

Recommended Videos

Uses 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 promote 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 is covered in finely powdered platinum black (platinized platinum electrode).
• A hydrogen blow.
• A solution of acid having an H⁺ molarity of 1 mole per cubic decimeter.
• 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 SHE, a salt bridge is used to link 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 sulphur compounds can deactivate or poison the catalyst.

Solved Example

Question:

The pressure of H₂ required to make the potential of H₂-electrode zero in pure water at 298 K is

Solution: