Depolarization

Process that reduces or eliminates electrochemical polarization on an electrode. An electrode is depolarized when the concentration of the substance formed on it (depolarizer) is reduced or even removed. The depolarizers prevent the formation of a counter-voltage.

Example

The dry battery (sold as mono, baby, mignon or micro cells) consists of a cylinder made of zinc sheet which contains a concentrated electrolyte solution of ammonium chloride thickened by absorbent substances (negative pole, cathode). The counter-electrode consists of a mixture of manganese dioxide, graphite and slag which is compressed to a solid rod (positive pole, anode).

When the dry battery is in operation, the following rections take place:

Cathode

Zn + 2NH₄Cl ↔ [Zn(NH₃)₂Cl₂] + 2H⁺ + 2Θ

anode

2MnO₂ + 2H⁺ + 2Θ ↔ 2MnO(OH)

overall equation

Zn + 2NH₄Cl + 2MnO₂ ↔ [Zn(NH₃)₂Cl₂] + 2MnO(OH) + energy

The hydrogen 2H⁺ + 2Θ ↔ H₂ formed on the graphite by the way, which leads to the formation of a counter-voltage at the cathode, i.e. would weaken the current, is oxidized by the manganese dioxide:

2MnO₂ + H₂ ↔ 2MnO(OH)

Non-polarized nickel anodes made of pure nickel dissolve very well in nickel baths at pH values of < 2.0. The standard nickel baths, however, are rarely so strongly acidic. For this reason, depolarized nickel anodes are used for the electrolytic deposition of nickel due to their improved solubility in electroplating.