Chemistry

Decomposition voltage

Decomposition voltage


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Area of ​​Expertise - Electrochemistry

In electrochemistry, the decomposition voltage or also the deposition potential is understood to be the difference between the electrode potentials of the anode and the cathode that is at least required to carry out an electrolysis. At this voltage, the electrolyte begins to decompose.

The electrode potentials can be calculated using the Nernst equation. In some cases, overvoltages also occur which must be taken into account.

Learning units in which the term is dealt with

Electrolysis I - Basics30 min.

ChemistryPhysical chemistryElectrochemistry

Electrolysis arises from the reversal of the Galvanic cell.

Electrolysis II - electrode properties30 min.

ChemistryPhysical chemistryElectrochemistry

In this learning unit, the various voltages on electrodes during electrolysis are discussed in greater detail.

Experiment on decomposition voltage: The PEM electrolyzer90 min.

ChemistryGeneral ChemistryElectrochemistry

The electrolyser breaks down water into the gases hydrogen and oxygen, which are each stored in the gas tanks. However, the decomposition of the water only begins above the decomposition voltage. The aim of the experiment is to find out that water in electrolysis is only broken down above a minimum voltage.

PEM electrolyzer performance90 min.

ChemistryGeneral ChemistryElectrochemistry

The electrolyser breaks down water into the gases hydrogen and oxygen, which can be stored in gas tanks. However, the decomposition of the water only begins above the decomposition voltage. In this experiment the decomposition voltage is determined, which is required to decompose water with a PEM electrolyzer.


Decomposition voltage

Under the Decomposition voltage In electrochemistry, one understands the difference between the electrode potentials of the anode and cathode that is at least required to carry out an electrolysis. With this tension begins the decomposition of the electrolyte through electrical attractive forces that act between the electrodes on the one hand and the oppositely charged anions or cations on the other.

The term was introduced by Max Le Blanc. He also named 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 tensions of acids and bases - in the process, oxygen and hydrogen are usually formed on the electrodes. The majority of the inorganic acids (e.g. phosphoric acid, sulfuric acid) and inorganic bases (caustic soda, potassium hydroxide) showed decomposition values ​​of approx. 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 up to now. The process of overvoltage has not yet been precisely clarified scientifically, but the majority of experts assume some kind of activation energy.


1 answer

H + are discharged at one, OH- or Cl- at the other, the different electrodes have different ones

As soon as there is a noticeable current. Before (slowly increasing) it is more like the diffusion of gas into the solution, without realizing the gas development.


Video: Electroplating polarization, Decomposition potential and Over Voltage (May 2022).