Low-cost high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and preparation process

Abstract

The invention discloses a Ti / IrO2-SnO2-SbO2 gradient active coating anode with low cost and high stability and a preparation process of the Ti / IrO2-SnO2-SbO2 gradient active coating anode. The gradient active coating is characterized in that the gradient active coating is composed of 3-5 layers, the total thickness is 5-15 microns, the thickness of each layer is 1-5 microns, the molar percentage content of iridium in a bottom layer is 0-5%, the sum of the molar percentage content of tin and antimony is 95-100%, the molar percentage content of iridium in a surface layer is 10-20%, the sum of the molar percentage content of tin and antimony is 80-90%, and the thickness of each layer is 1-5 microns. The molar percentage content of iridium from the bottom layer to the surface layer is sequentially increased from 2% to 10%, the molar percentage content of tin and antimony is sequentially reduced from 2% to 10%, and the total iridium loading amount in the gradient active coating is 0.05-0.2 mg / cm < 2 >. The preparation method comprises the three steps of titanium substrate pretreatment, precursor salt alcohol solution preparation and gradient active coating preparation. By adopting a gradient coating mode, the thermal stress between the coating and the titanium substrate in the preparation process is remarkably reduced, the consumption of noble metal is reduced, the oxygen evolution activity of the anode is improved, and the service life of the anode is prolonged. The method is simple to operate and low in cost, and has remarkable industrialization advantages.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to a low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process, which can be applied to electrochemical descaling, water pollutant treatment and other fields. Background Technology

[0002] Compared to PbO2 anodes and carbon materials, titanium-based coated anodes exhibit superior conductivity, oxidation resistance, corrosion resistance, mechanical strength, and electrocatalytic performance, leading to their widespread application in water electrolysis for hydrogen production, water pollutant treatment, and electrochemical descaling. Titanium-based coated anodes typically require low oxygen evolution overpotentials to reduce energy consumption. Failure of titanium-based coated anodes is primarily attributed to three factors: electrochemical dissolution of the coating, mechanical wear of the coating, and passivation of the titanium substrate.

[0003] Electrochemical dissolution of coatings is directly related to the stability of the coating solid solution; a highly stable solid solution can effectively mitigate this process. Titanium-based coated anodes typically require doping with noble metals (such as iridium) to reduce the oxygen evolution overpotential. However, iridium is not only expensive but also prone to dissolution during electrolysis, leading to anode failure. Adding stabilizing components (such as Sn-Sb) to iridium-coated titanium-based anodes to form a stable IrO2-SnO2-SbO2 solid solution can significantly slow down the electrochemical dissolution of the coating, thereby improving the anode's service life. However, due to the significant difference in thermal expansion coefficients between the high-Ir-loading IrO2-SnO2-SbO2 solid solution and the titanium matrix, cracks are easily formed during coating heating. The oxygen evolution reaction at these cracks accelerates the mechanical wear of the coating. Furthermore, once the cracks extend into the titanium matrix, the matrix will be oxidized, leading to titanium matrix passivation. Therefore, reducing cracks on the coating surface can effectively mitigate coating mechanical wear and titanium matrix passivation. CN201110388952.1 discloses a method for preparing a titanium-based oxide-coated anode with low precious metal content. CN202110095255.0 discloses an anode, its preparation method and application, an ozone generation system, and a food purifier. However, both of the above patents prepare titanium-based coated anodes using a traditional uniform coating-thermal decomposition method, which easily leads to long and deep cracks forming on the surface of the anode catalyst layer.

[0004] In this invention, the bottom layer of the coating achieves a thermal expansion coefficient that is essentially the same as that of the titanium substrate by adjusting the ratio of tin to antimony, thereby reducing the formation of cracks. The catalyst top layer improves oxygen evolution activity by increasing the iridium content. From the bottom layer to the top layer, the iridium content gradually increases, minimizing crack formation, extending service life, and reducing costs. Summary of the Invention

[0005] This invention aims to improve the oxygen evolution reaction activity and solve the problem of TiO2 inert insulating layer formation on the anode of titanium-based coatings by using a gradient coating method. To achieve the above objectives, this invention employs the following technical means: A low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process are disclosed. The gradient active coating consists of 3-5 layers with a total thickness of 5-15 μm and a thickness of 1-5 μm for each layer. In the bottom layer, the molar percentage of iridium is 0%-5%, and the sum of the molar percentages of tin and antimony is 95%-100%. In the top layer, the molar percentage of iridium is 10%-20%, and the sum of the molar percentages of tin and antimony is 80%-90%. The molar percentage of iridium increases by 2%-10% from the bottom layer to the top layer, while the sum of the molar percentages of tin and antimony decreases by 2%-10%. The total iridium loading in the gradient active coating is 0.05-0.2 mg / cm³. 2 .

[0006] Furthermore, the above preparation process includes the following steps: 1) Titanium substrate pretreatment: After grinding and sandblasting, the Ti substrate is placed in an oxalic acid aqueous solution for acid etching. Then, the Ti substrate is cleaned with deionized water and dried for later use. 2) Preparation of precursor salt alcohol solution: Chloroiridic acid, soluble tin salt and soluble antimony salt are added to alcohol solution in a certain molar ratio, and then concentrated hydrochloric acid is added in a certain volume ratio of alcohol solution to concentrated hydrochloric acid to obtain precursor salt alcohol solution. 3) Gradient active coating preparation: Precursor salt alcohol solutions with different molar ratios are uniformly coated on the surface of Ti substrate, dried and calcined. The coating-drying-calcining process is repeated several times to form a catalytic layer of 3-5 layers on the anode surface.

[0007] Preferably, the concentration of the oxalic acid aqueous solution in step 1) is 10%-20%, and the acid etching is carried out in a water bath at 95-100℃ for 1-3 hours.

[0008] Furthermore, the Ti matrix shape described in step 1) includes plate-like, tubular, mesh-like, and rod-like shapes.

[0009] Furthermore, in step 2), the soluble tin salt is one or more of stannous chloride, stannous tetrachloride, and stannous sulfate; the soluble antimony salt is one or more of antimony trichloride, antimony pentachloride, and antimony nitrate; and the alcohol solution is at least one of isopropanol, n-butanol, and n-pentanol.

[0010] Preferably, in the above technical solution, in step 2), the percentage content of the total precursor salt is 0-20%, the sum of the percentage content of soluble tin salt and soluble antimony salt is 80%-100%, and the molar ratio of soluble tin salt to soluble antimony salt is 6:1-8:1.

[0011] Preferably, the volume ratio of the alcohol solution to concentrated hydrochloric acid in step 2) is 15:1-30:1.

[0012] Preferably, the drying in step 3) is performed at 100-140°C for 5-15 minutes in air. The calcination is performed at 400-500°C for 5-15 minutes in air. The total number of coating-drying-calcination cycles for each layer is 10-15, and after the last drying, the layer is cured at 400-500°C in air for 1-2 hours.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The bottom layer of the coating consists of dense Sn and Sb oxides, which hinder the penetration of active oxygen generated during electrolysis into the titanium substrate, preventing the titanium substrate from oxidizing and forming non-conductive TiO2, thus avoiding anodic failure. The surface of the coating is composed of Ir-Sn-Sb oxides with a high Ir content, reducing the oxygen evolution overpotential and improving the oxygen evolution reaction activity. Simultaneously, gradient coating reduces the thermal stress between the coating and the titanium substrate, minimizing the formation of cracks in the coating, thereby improving the coating's corrosion resistance and extending its service life. This invention provides a simple and effective strategy for developing low-cost, high-activity, long-life oxygen evolution anodes for engineering production applications. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] Figure 1 This is a SEM image of a metal oxide coated anode.

[0016] Figure 2 This is the oxygen evolution polarization curve of the metal oxide coated anode.

[0017] Figure 3 This refers to the lifespan of the metal oxide coating anode.

[0018] Figure 4 This is a schematic diagram of the metal oxide coating anode structure of the present invention. Detailed Implementation

[0019] The embodiments of the present invention will now be described in detail and clearly with reference to the accompanying drawings.

[0020] Example 1 (1) Pretreatment of metal matrix The metal substrate is a titanium sheet with a length of 50 mm, a width of 12.5 mm, a thickness of 2 mm, and a purity of 99.9%. The titanium sheet is polished with 600-grit and 1200-grit sandpaper in sequence to make the surface of the substrate appear bright silver-white. Then, it is ultrasonically cleaned in deionized water for 5 min, ultrasonically vibrated in acetone solution for 20 min, and ultrasonically cleaned in deionized water for 5 min to remove surface oil. It is then acid etched in a 10% oxalic acid aqueous solution in a 98℃ water bath for 2 hours to make the surface of the metal substrate appear uniform, flat, and grayish-brown. Finally, the metal substrate is rinsed with deionized water, dried, and sealed for storage, completing the metal substrate pretreatment.

[0021] (2) Preparation of precursor salt alcohol solution First, a mixed isopropanol solution was prepared by mixing tin tetrachloride (SnCl4) and antimony trichloride (SbCl3) at a ratio of 7:1. Next, iridium chlorohydrate (H2IrCl6) and a mixed Sn & Sb solution were added to the isopropanol solution at the molar ratios shown in Table 1 to prepare the precursor solution. Then, concentrated hydrochloric acid was added at a volume ratio of 20:1 to prevent Sb hydrolysis. Furthermore, the total metal ion concentration in all precursor solutions must be 0.2 mol / L. The prepared precursor solutions were named according to their Ir content (#0, #2, #4, #6, #8, #10, #12, #20), as shown in Table 1.

[0022] Table 1. Composition of precursor solution (mol%)

[0023] (3) Preparation of surface-active coating: After the #0 precursor solution is prepared, it is first placed in an ultrasonic cleaner to mix thoroughly, and then the precursor solution is evenly brushed onto the titanium sheet according to the experimental plan. Then, it is first placed in an oven at 120°C to dry for 10 min. After drying, it is quickly placed in a muffle furnace at 450°C to calcine for 10 min. After calcine, it is taken out and placed to cool to room temperature before the next brushing. The above brushing-drying-calcine-cooling operation is repeated 15 times to complete the preparation of the bottom layer; the above brushing-drying-calcine-cooling operation is repeated 15 times respectively to brush the #10 precursor solution and the #20 precursor solution. Finally, the anode is calcined and cured in a muffle furnace at 450°C for 1 h to prepare the anode of Example 1.

[0024] (Examples 2-3 and Comparative Examples 1-4) Similar to Example 1, the precursor liquid composition described in Table 2 was used, and the brushing-drying-calcining-cooling operation was repeated, with each layer brushed 15 times, to produce the anodes of Examples 2-3 and Comparative Examples 1-4.

[0025] Table 2 Composition of the gradient active layer

[0026] a. Surface morphology of metal oxide coated anode The surface morphology of the catalyst was tested using field emission scanning electron microscopy, such as... Figure 1 As shown.

[0027] b. Electrocatalytic activity of metal oxide coated anodes Electrochemical tests were performed on the metal oxide coated anodes prepared in the examples and comparative examples. The tests were conducted in a three-electrode system, with the various prepared metal oxide coated anodes serving as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. Polarization curves were measured in a 0.5 mol / L H₂SO₄ solution, and the test results are as follows. Figure 2 As shown. Accelerated lifetime testing was performed in a 0.5 mol / L H₂SO₄ solution, with the anode being the experimental electrode and the cathode being a platinum sheet. The distance between the anode and cathode plates was approximately 2 cm, and the current density was approximately 800 mA / cm². 2 Between. Test results as follows Figure 3 As shown.

[0028] like Figure 1 As shown, the number of surface cracks in Examples 1-3 was significantly reduced compared to Comparative Examples 1-4, indicating that gradient coating using a suitable method can reduce the effect of thermal stress between the active layer and the titanium substrate. Figure 2 As shown, the oxygen evolution activity of Examples 1-3 was significantly improved compared to Comparative Examples 1-4. This is because the increased Ir content on the coating surface helps to reduce the oxygen evolution overpotential and improve the oxygen evolution activity. Figure 3 As shown, Examples 1-3 exhibit a significantly improved accelerated lifespan compared to Comparative Examples 1-4. This is because the gradient coating method significantly reduces the number of surface cracks, hinders the generation of active oxygen in the titanium dioxide matrix during electrolysis, and delays the anode failure process. The gradient brush coating method can improve electrocatalytic activity and lifespan without increasing costs.

[0029] In summary, the metal oxide-coated anode prepared by this invention possesses excellent oxygen evolution electrocatalytic performance. The superior performance of the metal oxide-coated anode gives this invention significant practical value.

[0030] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Any modifications, alterations, and variations made by those skilled in the art based on the disclosed technical content are equivalent embodiments of the present invention; furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process, characterized in that, This gradient active coating consists of 3-5 layers with a total thickness of 5-15 μm and a thickness of 1-5 μm for each layer. In the bottom layer, the molar percentage of iridium is 0%-5%, and the combined molar percentage of tin and antimony is 95%-100%. In the top layer, the molar percentage of iridium is 10%-20%, and the combined molar percentage of tin and antimony is 80%-90%. The molar percentage of iridium increases by 2%-10% from the bottom layer to the top layer, while the molar percentage of tin and antimony decreases by 2%-10% in each subsequent layer. The total iridium loading in the gradient active coating is 0.05-0.2 mg / cm³. 2 .

2. A low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process as described in claim 1, comprising the following steps: 1) Titanium substrate pretreatment: After grinding and sandblasting, the Ti substrate is placed in an oxalic acid aqueous solution for acid etching. Then, the Ti substrate is cleaned with deionized water and dried for later use. 2) Preparation of precursor salt alcohol solution: Chloroiridic acid, soluble tin salt and soluble antimony salt are added to alcohol solution in a certain molar ratio. Then concentrated hydrochloric acid is added at a volume ratio of alcohol solution to concentrated hydrochloric acid of 15:1-30:1 to prepare precursor salt alcohol solution. 3) Gradient active coating preparation: Precursor salt alcohol solutions with different molar ratios are uniformly coated on the surface of Ti substrate, dried and calcined. The coating-drying-calcining process is repeated several times to form a catalytic layer of 3-5 layers on the anode surface.

3. The low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process as described in claim 2, characterized in that: Step 1) The concentration of the oxalic acid aqueous solution is 10%-20%, and the acid etching is carried out in a water bath at 95-100℃ for 1-3 hours.

4. The low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process as described in claim 2, characterized in that: Step 1) The Ti matrix shape includes plate-like, tubular, mesh-like, and rod-like shapes.

5. The low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process as described in claim 2, characterized in that: The soluble tin salt in step (2) is one or more of stannous chloride, stannous tetrachloride, and stannous sulfate; the soluble antimony salt is one or more of antimony trichloride, antimony pentachloride, and antimony nitrate; and the alcohol solution is at least one of isopropanol, n-butanol, and n-pentanol.

6. The low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process as described in claim 2, characterized in that: In step (2), the total precursor salt contains 0-20% chloroiridic acid, and the sum of the percentages of soluble tin salt and soluble antimony salt is 80%-100%, with a molar ratio of 6:1 to 8:

1.

7. The low-cost, high-stability Ti / IrO2-SnO2-SbO2 gradient active coating anode and its preparation process as described in claim 2, characterized in that: The drying in step (3) is to dry at 100-140℃ for 5-15 minutes in an air atmosphere; the calcination is to calcinate at 400-500℃ for 5-15 minutes in an air atmosphere; the coating-drying-calcination cycle for each layer is 10-20 times, and after the last drying is completed, it is cured at 400-500℃ in air for 1-2 hours.

Images