Electrodes mainly refer to the positive and negative electrodes in the primary battery system and the cathode and anode materials in the electrolytic cell system. Distinguished according to the direction of current flow: one end of the input current is called the anode, and the end of the output current is called the cathode.
If distinguished by the type of reaction on the anode: the anode where the oxidation reaction occurs and the cathode where the reduction reaction occurs. As the core component in the electrochemical reaction system, the anode material has an important impact on the reaction rate, reaction mechanism and energy consumption during the reaction process. Therefore, in the context of energy shortage and difficult wastewater treatment, the development of new high-performance anode materials has important theoretical significance and economic value for industrial production.
In the electrochemical reaction system, the reduction reaction mainly occurs at the cathode, so the requirements for cathode materials are not too strict. The anode material mainly undergoes an oxidation reaction during the reaction process, causing the anode material to be easily lost and replaced more frequently than the cathode material. Anode materials with excellent performance need to meet requirements such as good electrical conductivity, high catalytic activity, good stability, and certain mechanical strength. How to develop anode materials with the above characteristics has become a hot topic of research by domestic and foreign scholars.
The continuous development of the electrolysis industry has promoted the progress and development of anode materials. E.G. Acheson successfully produced artificial graphite using the electrothermal crystallization method in 1896, and realized industrial production in the electrolytic salt industry.
As an anode material, graphite anode has been found to have the following shortcomings during its long-term industrial application: when the electrolyte is acidic, the electrocatalytic degradation process is accompanied by an oxygen evolution reaction, and the carbon material is easily oxidized, resulting in graphite The anode material expands, deforms, falls off and slag; another disadvantage is that the carbon material has poor high temperature resistance and poor mechanical strength, and may break during processing and transportation. Therefore, people are looking for metal anodes to replace graphite anodes to meet the needs of industrial development. The biggest problem with metal anodes is anode passivation. Passivation films are easy to form on the surface, causing the catalytic activity of metal anodes to decrease or even lose activity, such as iron anodes and copper anodes. Platinum anodes have high electrocatalytic activity and high current efficiency, but platinum metal is expensive, which limits its application scope. In 1948, a major breakthrough was made in the preparation of titanium metal and industrial production was achieved. This was mainly attributed to the invention of Dr. W. Claure of the United States by the magnesium thermal reduction method and the successful preparation of titanium sponge. It is possible to use titanium as the anode base material to prepare new anodes. In 1959, researchers proposed a new concept: using titanium metal as the base material and metal oxide as the active layer to develop a new metal anode. In 1968, Italian company DeNora took the lead in industrializing H.Beer's ruthenium-titanium coated anodes, and the development of titanium anodes entered a new chapter.
1. Preparation method of titanium anode
(1)Thermal decomposition method
Thermal decomposition method is to evenly apply the organic solution or aqueous solution of metal oxide on the surface of the pretreated substrate, and then undergo low-temperature drying, high-temperature oxidation and other processes to obtain the required oxide film. The advantages of this method are simple equipment and process, controllable coating thickness, and the formation of many cracks on the anode surface, which increases the specific surface area of the coating and improves the catalytic activity of the anode. The disadvantage is that deep cracks like mud cracks are easy to form on the surface of the coating, and the coating is easy to fall off.
(2)Sol-gel method
The sol-gel method is to prepare a sol with metal oxide or hydroxide particles dissolved in a solution of metal organic compounds through hydrolysis and polymerization of the compounds, and then generate a gel with a certain spatial structure through a series of physical or chemical reactions. , the required metal oxide nanofilm can be obtained through low-temperature drying and high-temperature sintering. The advantage is that nanoparticles are precipitated from the coating, the grains are small, and the coating is dense. The disadvantage is that the preparation process is complicated and time-consuming.
(3)Electrodeposition method
The electrodeposition method is to place the pretreated substrate as an anode in a metal salt electroplating solution, and use stainless steel as the cathode. After electrodeposition for a period of time under the action of a constant current, a metal oxide film is obtained on the surface of the substrate.
The electrodeposition method has mild preparation conditions, a stronger bonding force between the substrate and the coating, and is most promising for industrial production. However, the preparation process is complex, has many influencing factors, and consumes large amounts of energy.
(4)Magnetron sputtering method
The magnetron sputtering method is in an argon atmosphere, under the action of a high-frequency and high-voltage electric field, the high-energy gas ion flow formed bombards the target surface, and the atoms on the target surface are sputtered out and deposited on the substrate surface.
Preparation method of thin film material. The advantage of this method is that the resulting coating has a higher density, a stronger bonding force between the substrate and the coating, and the life of the anode is greatly improved. However, the equipment used is expensive and difficult to apply on a large scale.
In addition to the above four main preparation methods, the preparation methods of titanium-based metal oxide anodes also include CVD, PVD, spray thermal decomposition, etc. Thermal decomposition method is the most common method for preparing titanium-based tin-antimony anodes. The process is simple, the equipment is easy to operate, and the coating components are precise and controllable. It is especially suitable for general laboratory research.
2. Several commonly used titanium anode classifications
The choice of coating in the titanium anode determines the electrochemical reaction process, that is, whether the electrochemical reaction type is oxygen evolution reaction or chlorine evolution reaction, and the degradation principle is direct degradation or indirect degradation. The structure and chemical composition of the coating have a decisive influence on the electrochemical reaction. At present, research on several commonly used titanium anodes mainly includes Ir02/Ti series, Ru02/Ti series, Pb02/Ti series, Sn02/Ti series, etc.
Ir02 /Ti anode is an oxygen evolution anode. The active layer of unit lr02 coated titanium anode is easy to peel off during use, and the anode has a short service life. It is usually necessary to add some other components for modification research. Iridium is a precious metal element and is relatively expensive.
Ru02-Ti02/Ti anode is a chlorine evolution anode. Like iridium, ruthenium is also a precious metal element and is expensive. At present, Ru02/Ti series anodes are mainly used in the chlor-alkali industry.
The Pb02/Ti anode has a strong ability to degrade organic matter in wastewater, such as some organic wastewater that is difficult to biodegrade. The final degradation products of organic matter are C02 and H20]. Pb02/Ti anode is mainly used in chromium plating in strong acid solution, electrolytic smelting of zinc and copper, wastewater treatment, oil-water separation, etc.
Sn02/Ti anode refers to an anode material with tin oxide as the active component on a titanium matrix. It is a promising non-noble metal titanium-based metal oxide anode. SnO2 has a high resistivity at room temperature, so it cannot be used directly as an anode material. Doping Sb can effectively improve the conductive properties of Sn02. A continuous solid solution will be formed between Sb oxide and Sn02. Sb plays a role in supporting and improving the stability of Sn02. Therefore, SnO2 modified by Sb doping can be used as an anode coating. Research has proven that Sb-doped Sn02. Sb/Ti anode exhibits a high oxygen evolution potential and a strong ·OH generation ability, so it exhibits good electrocatalytic oxidation activity for organic matter and has been widely used in the field of wastewater treatment.
3.Related products in ehisen
