Decomposition voltage

In electrochemistry, the decomposition voltage is understood to be the minimum difference between the electrode potentials of anode and cathode that is required to carry out an electrolysis . At this voltage begins decomposition of the electrolyte by electrical attractive forces between the electrodes and the one hand oppositely charged anions or cations affect the other.

The term was introduced by Max Le Blanc . He also called the measured voltages decomposition values . In 1891, Le Blanc initially examined various 1 normal (1 molar or 0.5 molar etc. depending on the valency of the positive cation and the reduced form) metal salt solutions for the minimum voltages required for metal deposits. The knowledge gained formed the basis for the establishment of the normal potentials for individual redox pairs. Le Blanc also investigated the decomposition voltages of acids and bases - oxygen and hydrogen usually form on the electrodes. Most of the inorganic acids (e.g. phosphoric acid, sulfuric acid) and inorganic bases (caustic soda, potassium hydroxide) showed decomposition values ​​of about 1.65 V, but hydrochloric acid had a decomposition voltage of only 1.26 V.

The electrode potentials can be calculated using the Nernst equation . In some cases, so-called overvoltages also occur, which must be taken into account in the calculations. The overvoltage depends on the electrode material, its surface and the substance used. It has to be determined experimentally, as no calculation method has been found so far. The process of overvoltage has not yet been precisely explained scientifically, but the majority of experts assume some kind of activation energy.