Electrolyzer classification

According to different classifications of electrolytes
Aqueous solution electrolyzer
Aqueous solution electrolyzers can be divided into two types: diaphragm electrolyzers and diaphragm-less electrolyzers. Diaphragm electrolyzers can be divided into homotropic membranes (asbestos wool), ionic membranes and solid electrolyte membranes (such as β-Al2O3); diaphragm-free electrolyzers can be divided into mercury electrolyzers and oxidation electrolyzers.
When using different electrolytes, the structure of the electrolytic cell is also different.
Aqueous solution electrolyzers are divided into two types: diaphragm and non-diaphragm. Diaphragm electrolyzers are generally used. Diaphragmless electrolytic cells are used in chlorate production and mercury production of chlorine and caustic soda. Enlarging the electrode surface area per unit volume as much as possible can improve the production intensity of the electrolytic cell. Therefore, the electrodes in modern diaphragm electrolyzers are mostly upright. Electrolyzers show different performance and characteristics due to different materials, structures, installations, etc. of internal components [1].
Molten salt electrolyzer
It is mostly used to produce low melting point metals. It is characterized by operating at high temperatures and should try to prevent moisture from entering and avoid hydrogen ions from being reduced on the cathode. For example, when preparing metallic sodium, since the cathode reduction potential of sodium ions is very negative, reduction is very difficult. Anhydrous molten salt or molten hydroxide that does not contain hydrogen ions must be used to avoid hydrogen precipitation at the cathode. For this reason, the electrolysis process needs to be carried out at high temperatures. For example, when electrolyzing molten sodium hydroxide, it is 310°C. If it contains sodium chloride and becomes a mixed electrolyte, the electrolysis temperature is about 650°C.
The high temperature of the electrolytic cell can be achieved by changing the electrode spacing and converting the electrical energy consumed by the ohmic voltage drop into heat energy. When electrolyzing molten sodium hydroxide, the tank body can be made of iron or nickel. Electrolysis of molten electrolyte containing chloride often inevitably brings a small amount of moisture into the raw materials, which will cause the anode to generate moist chlorine gas, which has a strong corrosive effect on the electrolytic cell. Therefore The electrolytic tank for electrolyzing molten chloride generally uses ceramic or phosphate materials, and iron can be used in parts that are not affected by chlorine gas. The cathode and anode products in the molten salt electrolytic tank also need to be properly separated and should be led out of the tank as soon as possible to prevent the cathode product metal sodium from floating on the surface of the electrolyte for a long time and further interacting with the anode product or oxygen in the air. .
Non-aqueous solution electrolyzer
Since non-aqueous solution electrolyzers are often accompanied by various complex chemical reactions when producing organic products or electrolyzing organic matter, their applications are limited and few are industrialized. The commonly used organic electrolyte has low conductivity and low reaction speed. Therefore, a lower current density must be used and the pole spacing should be minimized. The electrode structure using fixed bed or fluidized bed has a larger electrode surface area, which can improve the production capacity of the electrolyzer.
Classified by electrode connection method
Electrolytic cells can be divided into two types: unipolar electrolytic cells and bipolar electrolytic cells according to the connection method of electrodes. In a unipolar electrolytic cell, electrodes of the same polarity are connected in parallel with the DC power supply, and the polarities on both sides of the electrodes are the same, that is, they are anodes or cathodes at the same time. The electrodes at both ends of the bipolar electrolyzer are connected to the positive and negative poles of the DC power supply, becoming anodes or cathodes. When current flows through the electrolytic cell through electrodes connected in series, one side of each electrode in the middle is the anode and the other side is the cathode, so it is bipolar. When the total electrode area is the same, the current of the bipolar electrolyzer is smaller and the voltage is higher, and the investment in DC power supply required is less than that of the unipolar electrolyzer. The multi-polar type generally adopts the structure of a filter press and is relatively compact. However, it is prone to leakage and short circuit, and the tank structure and operation management are more complicated than the unipolar type. The cross-section of monopolar electrolyzers is generally rectangular or square. The cylindrical shape occupies a large area, has low space utilization, and is rarely used.