A Short Note On Polarisation Effect

Polarisation is a phenomenon that reduces battery performance. This effect is characterised by a shift in electrode potential away from the equilibrium value. Polarisation is classified into two types: activation and concentration. All electrochemical processes take place in a series of steps at the electrode-electrolyte interface. The scenario in which the reaction rate is dictated by the slowest step is referred to as activation polarisation. The term activation is employed because this slowest, rate-limiting step is coupled with an activation energy barrier. The second type, concentration polarisation, happens when the reaction rate is slowed by diffusion in the solution (the electrolyte in typical batteries is a solution.

Polarisation

Polarisation is a mechanism that causes an electrode’s potential to alter during electrolysis when the anode’s potential becomes nobler than the cathode. It has the effect (depending on the conditions) of decreasing battery output voltage, increasing the voltage required for electrolysis cells, or lowering currents.

Polarisation is also known as a kinetic divergence from equilibrium caused by an electric current passing through a galvanic cell. Polarisation can occur at the cathode (cathodic polarisation) or at the anode (anodic polarisation) (anodic polarisation). The use of cathodic polarisation is more widespread.

Polarisation is an important electrochemical event in the corrosion process. Cathodic polarisation always reduces the corrosion rate of all metals and alloys in any aqueous environment. Cathodic protection is the process of applying cathodic polarisation to a corroding system.

There are three ways in which polarisation can occur:

1. Polarization based on concentration
2. Polarization of resistance
3. Polarisation of activation

Concentration polarisation of an electrode occurs as a result of the creation of a diffusion layer next to the electrode’s surface where there is an ion concentration gradient. Ion diffusion through the layers regulates the electrochemical reaction and is vital in activities such as electroplating and corrosion. Concentration polarisation can be minimised by increasing agitation or heating the electrolyte.

The potential decrease caused by the high resistivity of the electrolyte surrounding the electrode is referred to as resistance polarisation. It could possibly be due to the insulating effect of the reaction products’ coating on the electrode surface. The Ohm’s law expresses resistance polarisation.

When an electrochemical reaction is carried out in a series of steps, activation polarisation develops. The slowest stage of the process (known as the rate-determining step) determines the total reaction speed. In a hydrogen reduction reaction, for example, the reaction could go as follows:

1. The anode surface absorbs hydrogen ions from the solution.
2. Electrons are transferred from the anode to the hydrogen ions, resulting in the formation of hydrogen.
3. Hydrogen gas molecules are formed by hydrogen atoms.
4. The formation of hydrogen gas bubbles

Polarisation of Bonds

The polarisation of a covalent bond is determined by the electronegativity of the two atoms that formed the link. In the sigma bond, the electron cloud contains two atoms that are not uniform and are somewhat shifted towards more electronegative atoms. This results in a permanent state of bond polarisation, with more electronegative atoms having a negative fractional charge. As a result, there are fewer electronegative atoms with positive fractional charges.

Water molecules, for example, contain electronegative atom oxygen molecules that attract a negative charge. Two positive stigmas next to the hydrogen atoms attract the negative sigma in the water molecule near the oxygen atom. The net dipole moment in the molecules is the result of the individual bond dipole moment. A polar bond is a covalent link formed between two atoms in which the electrons are not distributed equally.

In layman’s terms, polar covalent bonds form when electronegative atoms share electrons. In HCI, for example, the hydrogen chloride and water bond in the hydrogen-oxygen bond is suitable.

Conclusion 

Polarisation is an important electrochemical event in the corrosion process. Cathodic polarisation always reduces the corrosion rate of all metals and alloys in any aqueous environment. Cathodic protection is the process of applying cathodic polarisation to a corroding system.