Technical Insights into Electrolytic Cells:
Basic Structure 1: Tank: The outer shell of the electrolytic cell, designed to contain the electrolyte and electrodes, must have excellent corrosion resistance and sealing properties. Materials for the tank can include steel, concrete, ceramics, etc. For highly corrosive electrolytes, the interior of steel tanks is typically lined with lead, synthetic resin, or rubber.
Anode: The electrode where oxidation reactions occur. Anode materials are categorized into soluble and insoluble types. For example, in the electrolytic cells used for refining copper, the anode material is a soluble crude copper to be refined. During the electrolysis process, the crude copper dissolves into the solution, supplementing the copper that precipitates from the solution at the cathode. In electrolytic cells used for electrolyzing aqueous solutions (such as brine solutions), the anode is insoluble, and they undergo minimal change during the electrolysis process. However, they often have a catalytic effect on the anodic reactions occurring at the electrode surface. Common anode materials include graphite and metal oxide-coated electrodes, with metal oxide-coated electrodes offering excellent chemical stability and catalytic activity, resulting in a long service life.
The Cathode: It is the electrode where reduction reactions occur. When using metals or alloys as cathodes, due to their operation at relatively negative potentials, they often provide cathodic protection, have low corrosiveness, and thus, cathode materials are relatively easy to select. In aqueous electrolytic cells, the cathode typically produces hydrogen evolution reactions, with a high overpotential. Therefore, the main direction for improving cathode materials is to reduce the hydrogen evolution overpotential, such as using porous nickel plated cathodes, etc.
Diaphragms: Used to prevent the mixing of products from the anode and cathode, avoiding potentially harmful reactions. Diaphragms must have a certain porosity to allow ions to pass through while blocking molecules or bubbles. When an electric current flows, the diaphragm's ohmic voltage drop should be low. Common diaphragm materials include asbestos diaphragms and cation exchange membranes. Cation exchange membranes have selective ion permeability, allowing chloride ions to largely not enter the cathode chamber, thus enabling the production of alkali solutions with low sodium chloride content.
