Standard hydrogen electrode

Standard Hydrogen Electrode (SHE) is a reference electrode that is used in electrochemistry to measure the electrode potential of other electrode materials. It serves as a baseline or standard for the electrode potential scale. The SHE consists of a platinum electrode that is in contact with 1 molar acid solution and hydrogen gas at a pressure of 1 atmosphere (atm). The hydrogen gas bubbles over the platinum electrode, which acts as a catalyst for the redox reaction between hydrogen ions in the solution and hydrogen gas. The electrode potential of the SHE is defined as 0 volts at all temperatures.

Principle

The operation of the Standard Hydrogen Electrode is based on the half-cell reaction: \[2H^+(aq) + 2e^- \rightarrow H_2(g)\] This reaction involves the reduction of hydrogen ions (protons) to hydrogen gas. The SHE serves as a reference against which the potential of other electrodes is measured. Since the electrode potential of the SHE is assigned a value of 0 volts, it provides a fixed point on the electrochemical scale.

Construction

The construction of a Standard Hydrogen Electrode involves a platinum electrode that is coated with platinum black to increase its surface area and enhance the adsorption of hydrogen gas. The electrode is immersed in an acidic solution, typically 1 M sulfuric acid (H2SO4), and hydrogen gas is bubbled through the solution at a pressure of 1 atm. The entire setup is maintained at a constant temperature, usually 25°C (298 K), to ensure consistent measurements.

Applications

The Standard Hydrogen Electrode is widely used in electrochemistry for various purposes:

• Determining the standard electrode potential of other electrodes
• Calibrating pH meters and other electrochemical devices
• Studying the kinetics of redox reactions
• Investigating the thermodynamics of electrochemical cells

Advantages and Limitations

The SHE offers several advantages, including a well-defined and reproducible reference point and the ability to measure electrode potentials under standard conditions. However, it also has limitations, such as the requirement for a constant supply of pure hydrogen gas and the need for careful maintenance to prevent contamination of the platinum electrode.

Comparison with Other Reference Electrodes

Other reference electrodes, such as the Saturated Calomel Electrode (SCE) and the Silver/Silver Chloride Electrode (Ag/AgCl), are also used in electrochemistry. Each of these electrodes has its own advantages and specific applications. The choice of reference electrode depends on factors such as the experimental conditions, the required accuracy, and the nature of the electrochemical system being studied.

See Also

• Electrochemistry
• Redox
• Electrode potential
• Nernst equation