What is Standard Hydrogen Electrode?

Standard Hydrogen Electrode (SHE) is a reference electrode that is used as a standard for measuring the electrode potential of other electrodes.

It is widely used in electrochemical research and serves as a benchmark for determining the electrochemical behavior of other electrodes.

In this article, we will discuss in detail the working principle of Standard Hydrogen Electrode, its construction, and applications.

What is Standard Hydrogen Electrode?

The Standard Hydrogen Electrode (SHE) is a reference electrode that is used as a standard for measuring the electrode potential of other electrodes.

The SHE consists of a platinum electrode coated with a thin layer of platinum black and immersed in an acidic solution of 1 M HCl.

The hydrogen gas is passed over the platinum black surface at a pressure of 1 atm, and the hydrogen molecules dissociate on the platinum surface to form hydrogen ions and electrons.

The half-cell reaction of SHE is given as:

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

This half-cell reaction has a standard electrode potential of zero volts at 25°C and 1 atm pressure. 

Therefore, the SHE is considered as a reference electrode with a fixed electrode potential, which serves as a benchmark for measuring the electrode potential of other electrodes.

Construction of Standard Hydrogen Electrode

The construction of Standard Hydrogen Electrode is quite simple. It consists of a platinum electrode coated with a thin layer of platinum black, which is immersed in an acidic solution of 1 M HCl.

The platinum black layer provides a large surface area for hydrogen gas to dissociate and allows for the efficient transfer of electrons.

The SHE is connected to a voltmeter through a salt bridge, which is used to maintain the electrical neutrality of the solution.

The salt bridge is a tube filled with a solution of KCl or NaCl, which connects the SHE with the other half-cell.

The salt bridge allows the flow of ions between the two half-cells, while preventing the mixing of solutions, which may lead to unwanted chemical reactions.

Working principle of Standard Hydrogen Electrode

The working principle of Standard Hydrogen Electrode is based on the half-cell reaction of hydrogen gas.

When hydrogen gas is passed over the platinum black surface of the SHE, it dissociates to form hydrogen ions and electrons.

The hydrogen ions are absorbed by the acidic solution of 1 M HCl, while the electrons are transferred to the platinum electrode.

The half-cell reaction of SHE is reversible, which means that it can work as an electrode that can both oxidize and reduce species.

Therefore, the SHE can be used as a reference electrode to measure the electrode potential of other electrodes, which are connected to it through a salt bridge.

Applications of Standard Hydrogen Electrode

The Standard Hydrogen Electrode is widely used in electrochemical research as a reference electrode.

It is used as a benchmark for determining the electrode potential of other electrodes. The applications of Standard Hydrogen Electrode are discussed below:

1. Determination of standard electrode potential:

The Standard Hydrogen Electrode is used as a reference electrode to measure the electrode potential of other electrodes.

The electrode potential of other electrodes is determined by comparing it with the electrode potential of SHE, which is fixed at zero volts.

2. Corrosion studies:

The corrosion of metals is an electrochemical process that involves the oxidation of metal ions to form metal oxide or metal hydroxide.

The Standard Hydrogen Electrode is used as a reference electrode to measure the corrosion potential of a metal. The corrosion potential of a metal is the potential at which the metal starts to corrode.

By measuring the corrosion potential of a metal, the corrosive environment can be identified and appropriate measures can be taken to prevent corrosion.

3. Fuel cell studies:

Fuel cells are electrochemical devices that convert the chemical energy of fuel into electrical energy.

The Standard Hydrogen Electrode is used as a reference electrode to measure the electrode potential of the electrodes in a fuel cell.

By measuring the electrode potential of the electrodes, the efficiency of the fuel cell can be determined, and appropriate measures can be taken to improve its efficiency.

4. pH measurement:

The Standard Hydrogen Electrode is used as a reference electrode to measure the pH of a solution.

The pH of a solution is determined by measuring the difference in potential between the SHE and the other half-cell, which is connected to the solution to be tested.

The difference in potential is then converted into pH units using the Nernst equation.

5. Electrochemical synthesis:

Electrochemical synthesis is a process that involves the use of an electric current to drive a chemical reaction.

The Standard Hydrogen Electrode is used as a reference electrode to control the potential of the reaction.

By controlling the potential of the reaction, the selectivity and yield of the product can be improved.

Conclusion

The Standard Hydrogen Electrode is a reference electrode that is used as a benchmark for measuring the electrode potential of other electrodes.

It consists of a platinum electrode coated with a thin layer of platinum black and immersed in an acidic solution of 1 M HCl.

The hydrogen gas is passed over the platinum black surface, and the hydrogen molecules dissociate on the platinum surface to form hydrogen ions and electrons.

The SHE is widely used in electrochemical research for the determination of the standard electrode potential of other electrodes, corrosion studies, fuel cell studies, pH measurement, and electrochemical synthesis.

By using the Standard Hydrogen Electrode as a reference electrode, the electrochemical behavior of other electrodes can be studied and appropriate measures can be taken to improve their efficiency.