Cathode and Anode - Definition & Examples

What is Cathode and Anode?

Cathode and Anode are both defined by the flow of current. Therefore, a cathode is an electrode from which the current exits a polarized electrical device. Likewise, an anode is an electrode from which a current enters into a polarized electrical device.

Anode and cathode are the two types of electrodes

• An anode is an electrode from which polarized current enters the outer circuit.
•  A cathode is an electrode from which a conventional current leaves a polarized electrical device. 
• The anode and cathode charge are positive and negative respectively. 
• The anode cathode symbol respectively are A and K.

What is an Anode?

An anode is a place from where electricity passes through in a cell. It is a point where oxidation takes place. Anodes react and give off the electrons by which they can go into the driving circuit.

In the most basic form, an anode in electrochemistry is the point where an oxidation reaction occurs. Generally, at an anode, negative ions or anions due to its electrical potential tend to react and give off electrons. These electrons then move up and into the driving circuit.

• If we take a galvanic cell, the anode is negative in nature and the electrons mostly move towards the external part of the circuit.
• In an electrolytic cell, it is again positive. Additionally, an anode can be a plate or wire having an excess positive charge.

Examples of Anode

A simple example is electrolysis of water. A positively charged platinum electrode where H2 gas is oxidized to H+ ions is the anode.

The anode is the positive terminal that receives current from an external generator in a recharging battery. The current through a battery flows in an opposite direction of the current during discharge in the recharging battery.

What is Cathode?

 A cathode is a place from where electricity leaves through a cell. It is a point where reduction takes place. This is common in an electrochemical cell.

Generally, the cathode is the electrode where reduction reaction takes place. This means the cathode gains electrons from the external circuit and gets reduced. 

• The sign of cathode is ‘-'.
• In galvanic cells, copper is a cathode which is dipped in CuSO4 solution. 

There are two types of cathodes:

Cold cathodes: Cathodes that are not electrically heated by a filament. Which emits more electrons than can be supplied by thermionic emission are called cold cathodes. 

Hot cathodes: Cathodes are heated by electric current passing through the filament. 

Examples of Cathode

Electrolytic Cell

In an electrolytic cell, the cathode is where the negative polarity is applied. Some results of reduction at the cathode are pure metal or hydrogen gas from metal ions.

Galvanic Cell

In a galvanic cell, the cathode is the positive pole. This positive pole is connected to allow the circuit to be completed. The anode of the galvanic cell gives off electrons and return from the circuit into the cell through the cathode.

Electroplating Metal Cathode (Electrolysis)

When metal ions are reduced, they form a pure metal surface on the cathode. Items to be plated with pure metal are attached and become part of the cathode in the solution.

Anode and Cathode in Electrolysis

During electrolysis a chemical reaction or change takes place by the passage of electricity through the circuit and an electrolytic cell is the device which converts electrical energy to chemical energy. The charge of anion and cation is positive and negative respectively in an electrolytic cell. Consider the electrolysis of molten NaCl.

The anode of the wire or plate is having excessive positive charge because it is connected to the positive terminal of the battery. Hence anions will tend to move towards the anode and give off the electrons to the anode and get oxidized. These electrons are given by anion pass to the external circuit. In the electrolysis of molten NaCl, two inert electrodes are dipped in molten NaCl solution. When the electricity passes, the anode develops an excess positive charge and Cl- ions from the solution move towards the anode, where they become oxidized to sodium metal.

The cathode connects to the negative terminal of the battery, and it contains an excess negative charge. Cations from the solution move towards it and get reduced by accepting the electrons from the external circuit. Conversely, in galvanic cells, the cation is a positive electrode. When molten NaCl is subjected to electrolysis when electricity is passed, Na+ Ions start moving towards the cathode, where it is reduced to become sodium metal.

Difference Between Anode And Cathode

Here are some key differences between cathode and anode.