Depolarizer


 * ''for other uses see Depolarization (disambiguation)

A depolarizer or depolariser is a substance used to depolarize an electrochemical cell.

Polarization
In an electrochemical cell hydrogen ions are converted into hydrogen atoms and bubbles of hydrogen gas appear at the positive plate. These bubbles interfere with the chemical action of the cell, causing the voltage and thus current to be reduced, and becoming severely polarized as the bubbles cover the entire plate. Many different substances have been used as depolarizers; the most notable are listed below.

Oxidizing agents
These oxidize the hydrogen to water. Examples include:


 * Nitric acid, used in the Grove cell and Bunsen cell
 * Chromic acid, used in the Chromic acid cell
 * Manganese dioxide, used in the Leclanché cell and Dry cell

Nitric and chromic acids are powerful oxidizing agents, and effective depolarizers, but their hazardous nature makes them unsuitable for general use. Manganese dioxide is, therefore, the most widely used depolarizer.

Salts of metals
The hydrogen ions displace metal from the salt so that metal, instead of hydrogen, is deposited on the positive plate. Examples:


 * Silver oxide, used in the Silver-oxide battery
 * Copper sulphate, used in the Daniell cell
 * Mercurous sulphate, used in the Weston and Clark standard cells