Electrodes

Introduction

The name electrode was first put forward by the scientist William Whewell. And is obtained from the Greek word 'Elektron' and 'hodos' which means 'amber' and 'way'. The highly conducting nature of electrodes leads to the use of electrodes in many fields. Electrophore is the early version of an electrode that was discovered by the scientist Johan Wilcke that is used for the study of static electricity. And is also used as a term where the electricity enters or leaves the system. They have become an essential part of batteries and cells after their discovery. Later different types of electrodes depending on their uses were introduced. The first battery discovered was a Daniel cell in the year 1839 by John Frederic Daniell.

What is an Electrode?

The point at which oxidation takes place or electrons leaves the cell is the anode. While the point where reduction takes place or electron enters the cell is the cathode. Any metal electrode cannot be permanently taken as anode or cathode. The nature of the electrode whether it is a cathode or anode varies with the direction of the flow of electrons. It will depend on the oxidation and reduction potentials of metals. There is another type of electrode called the bipolar which can simultaneously change its nature as a cathode and anode.

Cathode and Anode in Electrochemical Cells

Anode and cathode are important terms derived from the Greek words that have an important role in electrochemical applications. The anode is the negative electrode that can release electrons in the electrochemical circuit. So, this electrode undergoes oxidation during the process. Electrons enter a particular system through this electrode. While the cathode is a positive electrode that can accept electrons in the electrochemical circuit. So, it is an electrode where reduction takes place during the process. Electrons leave a particular system through this electrode.

Emanuele Oddo, Electro-oxidation apparatus, CC BY-SA 4.0

Some of the points associated with cathode and anode are tabulated below.

Anode	Cathode
Electron donor.	Electron acceptor.
Negative electrode.	Positive electrode.
Oxidation is taking place.	Reduction is taking place.
Electricity will enter through this.	Electricity leaves through it.

Types of Electrodes

Based on the way current enters electrodes are classified into two types. They are positive and negative electrodes. Based on the nature of electrodes, electrodes are generally classified into five different types.

• Metal-metal ion electrode − It is a type of electrode in which the metal electrode is dependent on a solution or the electrolyte that contains the same ions as that of the metal. The cathode in this electrode is the electrode that has a lower oxidation potential, and it is the one that undergoes reduction. While the anode in this electrode is the electrode that contains a higher oxidation potential and so it undergoes oxidation. The exchange of a current in this electrode takes place between the metal electrode and the ions of metals in the electrolyte. An example of this is a copper electrode dipped in a copper sulphate solution.

• Metal-Insoluble salt electrode − In this electrode, the insoluble salt is coated with the metal electrode. Then the coated one is dipped in a solution that contains the anions of the salt. And is reversible with the anions present in the insoluble salt. The mercury-calomel electrode is an example of this category.

• Metal-Amalgam electrode − Because of the high reactivity of metals such as sodium and potassium metal amalgam electrodes are introduced. Since the reactivity of such metals gets lowered by the introduction of their amalgamated form that is by the dilution with Mercury. The electrolyte used in this type of electron is the solution of the metal ions themselves.

• Gas-ion electrode − In this type of electrode the gas is continuously bubbled through the solution where it contains inert metals such as platinum and gold- dipped in a solution that contains the anions or the cations of the gas. Most commonly the gas used is hydrogen but also some other gases such as chlorine and oxygen are also used. The inert electrode used in this type of electrode helps it maintain an electrical contact only, it does not react in this electrode. In between the gas and ions, electron transfer will occur. An example of this is a standard hydrogen electrode.

• Redox electrode − In this type of electrode where the oxidation and reduction reaction will take place. For this electrode, the solution contains ions of the metal that is going to be dipped in the two different oxidation states. The inert metal used in the electrode acts as a source of electrons and as an acceptor of electrons. For example, this electrode contains ferric and ferrous ions of the metal iron.

Uses of Electrodes

Electrodes are very important in electrochemistry. So, the uses of electrodes are,

• It is present in electrochemical cells and batteries. And is necessary for the flow of current.

• For the measurement of pH glass electrodes are used.

• Electrical conductivity can be measured with the help of electrodes during the process of electrolysis.

• It is present in electrophysiology in biochemical applications.

• It is present in the welding device.

• It is present in the ECG.

• They are used in fuel cells.

• Electrodes are used for electroplating purposes.

• It is used for cathodic protection.

• In the field of Nano-electrochemistry Nano-electrodes are used.

• It is used for grounding purposes.

Conclusion

Electrodes are good conductors of electricity that are found in the application in the electrochemical cell. It acts as a conductor of electricity in non-metallic materials. They are mainly of two types that are negative and positive electrodes. And the classification is based on the flow of electricity. Anode and cathode electrodes are always present in all electrochemical applications. But depending on the nature of the electrode and its application there are some other classifications for electrodes too. Metal-metal ion electrodes, redox electrodes, etc. are some of them. The use of electrodes is also wide. Electrodes are present in batteries, cells, welding applications, ECG, grounding purposes, pH measurements, etc.

FAQs

1. What is a Clark oxygen electrode?

In this electrode platinum is used as the cathode and silver is used as the anode. An oxygen porous film is used for the separation of electrodes from the solution of saturated potassium chloride.

2. What is cathodic protection?

It is a type of protection given to metals that can corrode easily. Where in which the metals act as a cathode of the electrochemical cell. It uses a sacrificial metal or metal that can corrode easily as the anode for the protection of this cathode.

3. Why is grounding done?

For the protection of home and home appliances from damage from high electric voltage, grounding is done. An electrode that has high electrical conductivity is used for this process. The metal copper is most used for this purpose.

4. What are ion-selective electrodes?

The ion-selective electrode is an electroanalytic technique in which the measurement of the activity of ions present in a solution is done. It is an analytical technique, but it is measuring activity instead of measuring the concentration of ions. It involves the measurement of electrical potential.

5. What is a calomel electrode in chemistry?

It is a type of reference electrode that contains elemental mercury and mercury chloride. It is commonly present in pH meters and voltmeters. As it measures the pH and electrical voltages.