Tech Team · Kintek Solution

The standard hydrogen electrode (SHE) is the most commonly used reference electrode for measuring half-cell potentials. It is arbitrarily assigned a potential of 0.000 V, making it a universal reference point in electrochemistry. However, practical applications often use other reference electrodes like the saturated calomel electrode (SCE) or silver/silver chloride electrode (Ag/AgCl) due to their stability and ease of use. These electrodes have known potentials relative to the SHE and are chosen based on compatibility with the sample and experimental conditions. For example, Ag/AgCl is widely used, but if the sample is incompatible with silver or chloride ions, SCE or other alternatives may be employed.

Key Points Explained:

1. Standard Hydrogen Electrode (SHE) as the Primary Reference:

   • The SHE is the fundamental reference electrode in electrochemistry, with a potential arbitrarily set to 0.000 V.
   • It serves as the baseline for measuring half-cell potentials, allowing for the comparison of different electrochemical systems.
   • However, the SHE is not always practical for routine measurements due to its complexity and the need for precise conditions (e.g., hydrogen gas at 1 atm and a platinum electrode).

2. Common Practical Reference Electrodes:

   • Saturated Calomel Electrode (SCE):
     • Composed of mercury and mercurous chloride in a saturated potassium chloride solution.
     • Has a potential of +0.241 V relative to the SHE.
     • Widely used but contains mercury, making it unsuitable for certain applications like food, beverage, or environmental studies.
   • Silver/Silver Chloride Electrode (Ag/AgCl):
     • Consists of a silver wire coated with silver chloride, immersed in a chloride solution.
     • Has a potential of +0.197 V to +0.222 V relative to the SHE, depending on the chloride concentration.
     • The most commonly used reference electrode due to its stability, reproducibility, and ease of use.
   • Other Reference Electrodes:
     • Copper-Copper(II) Sulfate Electrode (CSE): Used in specific applications like corrosion studies, with a potential of +0.314 V relative to the SHE.
     • Mercury-Mercurous Sulfate Electrode: Used in non-aqueous or acidic environments, with potentials ranging from +0.64 V to +0.68 V relative to the SHE.

3. Selection Criteria for Reference Electrodes:

   • Compatibility with the Sample:
     • The reference electrode must not react with or contaminate the sample.
     • For example, Ag/AgCl is unsuitable for samples sensitive to silver or chloride ions, necessitating the use of SCE or other alternatives.
   • Stability and Reproducibility:
     • The electrode must provide a stable and reproducible potential over time.
     • This ensures accurate and consistent measurements in electrochemical experiments.
   • Environmental and Safety Considerations:
     • Mercury-based electrodes like SCE are avoided in certain applications due to environmental and health concerns.
     • Non-toxic alternatives like Ag/AgCl are preferred in such cases.

4. Role of Reference Electrodes in Electrochemical Measurements:

   • Reference electrodes complete the electrical circuit in an electrochemical cell, providing a stable potential against which the working electrode's potential is measured.
   • They do not pass current, ensuring that their potential remains constant during measurements.
   • The liquid junction of the reference electrode allows contact with the sample, maintaining ionic conductivity without introducing significant errors.

5. Practical Considerations for Purchasers:

   • Cost and Availability:
     • Ag/AgCl electrodes are generally more cost-effective and widely available compared to SCE or other specialized electrodes.
   • Ease of Maintenance:
     • Some reference electrodes require regular maintenance, such as refilling electrolyte solutions or cleaning, which should be considered when selecting an electrode.
   • Application-Specific Requirements:
     • The choice of reference electrode should align with the specific needs of the application, such as pH range, temperature, and sample composition.

In summary, while the SHE is the theoretical standard for measuring half-cell potentials, practical applications often rely on reference electrodes like Ag/AgCl or SCE due to their stability, reproducibility, and ease of use. The choice of reference electrode depends on factors such as sample compatibility, environmental considerations, and experimental requirements.

Summary Table:

Reference Electrode	Potential (vs. SHE)	Key Features	Applications
Standard Hydrogen Electrode (SHE)	0.000 V	Universal reference, complex setup	Theoretical measurements
Silver/Silver Chloride (Ag/AgCl)	+0.197 V to +0.222 V	Stable, reproducible, easy to use	Widely used in labs
Saturated Calomel Electrode (SCE)	+0.241 V	Contains mercury, less environmentally friendly	Avoided in food/environmental studies
Copper-Copper(II) Sulfate (CSE)	+0.314 V	Used in corrosion studies	Specific industrial applications
Mercury-Mercurous Sulfate	+0.64 V to +0.68 V	Used in non-aqueous/acidic environments	Specialized electrochemical studies

Need help selecting the right reference electrode for your application? Contact our experts today for personalized advice!