Structure of Electrolyser
Electrolyser consists of a tank, anode and cathode, most of which are separated by a diaphragm from the anode chamber and the cathode chamber. According to the difference of electrolyte, it is divided into three types: aqueous Electrolyser, molten salt Electrolyser and non-aqueous Electrolyser. When the direct current passes through the electrolytic cell, an oxidation reaction occurs at the interface between the anode and the solution, and a reduction reaction occurs at the interface between the cathode and the solution to prepare the desired product.
In addition to meeting the basic requirements of general electrode materials (such as conductivity, catalytic activity strength, processing, source, price), the anode material also needs to be insoluble or passivated in strong anode polarization and higher temperature anolyte. , Has high stability. For a long time, graphite is the most widely used anode material. However, graphite is porous, has poor mechanical strength, and is easily oxidized to carbon dioxide. It is continuously corroded and peeled off during the electrolysis process, which gradually increases the electrode spacing and the cell voltage. When used for electrolysis of salt water solution, the overpotential of chlorine evolution on the graphite electrode is also higher.
When metal or alloy is used as the cathode, because it works at a relatively negative potential, it can often play a role of cathodic protection and is less corrosive, so the cathode material is easier to choose. In the aqueous Electrolyser, the cathode generally produces hydrogen evolution reaction, and the overpotential is relatively high. Therefore, the main improvement direction of the cathode material is to reduce the hydrogen evolution overpotential. Except that lead or graphite must be used as the cathode when sulfuric acid is used as the electrolyte, low carbon steel is a commonly used cathode material. In order to reduce power consumption, various methods are currently used to prepare cathodes with high specific surface area and catalytic activity, such as porous nickel-plated cathodes.
In order to prevent the cathode and anode products from mixing and avoid possible harmful reactions, in Electrolyser, the cathode and anode compartments are basically separated by a diaphragm. The diaphragm needs to have a certain porosity to allow ions to pass through, but not molecules or bubbles. When there is current flowing through, the ohmic voltage drop of the diaphragm should be low. These performance requirements remain basically unchanged during use, and require good chemical stability and mechanical strength under the action of the electrolyte in the anode and cathode compartments.
When electrolyzing water, the electrolytes in the cathode and anode compartments are the same. Electrolyser's diaphragm only needs to separate the cathode and anode compartments to ensure the purity of hydrogen and oxygen, and prevent the mixture of hydrogen and oxygen from exploding. A more common and more complicated situation is that the electrolyte composition of the cathode and anode compartments of the Electrolyser is different. At this time, the diaphragm also needs to prevent the mutual diffusion and interaction of the electrolysis products in the electrolyte of the cathode and anode compartments. For example, the diaphragm in the electrolyser of the diaphragm method in the production of chlor-alkali can increase the resistance to the diffusion and migration of hydroxide ions from the cathode compartment to the anode compartment.