A depolarizer or depolariser, in electrochemistry, according to an IUPAC definition, is a synonym of electroactive substance, i.e., a substance which changes its oxidation state, or partakes in a formation or breaking of chemical bonds, in a charge-transfer step of an electrochemical reaction.

In the battery industry, the term "depolarizer" has been used to denote a substance used in a primary cell to prevent buildup of hydrogen gas bubbles. A battery depolarizer takes up electrons during discharge of the cell; therefore, it is always an oxidizing agent. The term "depolarizer" can be considered as outdated or misleading, since it is based on the concept of "polarization" which is hardly realistic in many cases.

Read more about Depolarizer:  Polarization, Oxidizing Agents, Salts of Metals