Component gradient iridium tantalum coating anode and preparation method thereof

Abstract

The invention discloses a component gradient iridium tantalum coating anode and a preparation method thereof, the component gradient iridium tantalum coating anode comprises a titanium-based bottom layer, a middle layer and a surface active layer structure with component gradient, and the middle layer and the active layer are both prepared through a thermal decomposition method. And the intermediate layer is prepared on the titanium substrate and is composed of TiO2 / Ta2O5 mixed oxide. The surface active layer is prepared on the outer side of the middle layer and comprises a plurality of layers of IrO2 / Ta2O5 oxide coatings with different iridium-tantalum proportions. Compared with a traditional uniform coating anode, the prepared component gradient iridium tantalum coating anode can relieve the stress concentration phenomenon and reduce coating cracking, the service life of the anode is remarkably prolonged, and the catalytic activity of the anode is remarkably improved; the modified carbon nano tube is added into the active layer precursor solution, so that the conductivity change caused by component gradient is improved, and the cell voltage of the component gradient iridium tantalum coating anode is effectively reduced; and moreover, the iridium content is lower, and the preparation cost of the electrode is reduced.

Description

Technical Field

[0001] This invention relates to the field of electrode coating preparation technology, specifically to a composition gradient iridium-tantalum coated anode and its preparation method. Background Technology

[0002] Electrolytic copper foil is a crucial material in the manufacture of copper-clad laminates, printed circuit boards, and lithium-ion batteries. In recent years, the demand for electrolytic copper foil has experienced rapid growth. During the production process, the anode needs to undergo an oxidation reaction in a sulfuric acid system, thus requiring the anode material to possess strong corrosion resistance and a low polarization potential. Currently, titanium-based anodes are commonly used. These anodes primarily use valve-type titanium metal as a substrate, with a catalytically active oxide coating applied to its surface. Among these, Ti-based IrO2-Ta2O5 mixed oxide anodes are widely used as electrolytic copper foil anodes due to their excellent oxygen evolution characteristics and strong acid stability.

[0003] However, iridium-tantalum anodes still have certain shortcomings in application. Since TiO2 / Ta2O5 mixed oxide coated anodes are generally prepared using thermal decomposition methods, the compositional differences between the coating, substrate, and intermediate layer are significant. These differences in thermal expansion coefficients lead to substantial thermal stress between the coating and substrate during sintering, resulting in numerous cracks in the coating. Furthermore, the anode generates a large amount of gas during electrolysis, and the impact of this gas accelerates the peeling off of the anode coating at these cracks, leading to anode failure. Additionally, oxygen species generated during electrolysis can penetrate from the cracks into the titanium substrate, causing the formation of insulating titanium dioxide and resulting in anode failure. Therefore, reducing interlayer thermal stress and minimizing the number of surface cracks on the coated anode can effectively increase the anode's service life. Summary of the Invention

[0004] The purpose of this invention is to provide a composition-gradient iridium-tantalum coated anode and its preparation method, which can significantly reduce cracking of the iridium-tantalum anode coating, improve the anode service life, reduce the cell voltage, and at the same time reduce the iridium content of the anode, thereby achieving the goal of reducing production costs.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a composition-gradient iridium-tantalum coated anode, comprising a titanium substrate, an intermediate layer, and an iridium-tantalum oxide surface active layer having a composition gradient, arranged sequentially from the inside to the outside; the intermediate layer comprises titanium-tantalum oxide; the composition-gradient iridium-tantalum oxide surface active layer comprises multiple layers of IrO2 / Ta2O5 oxide coatings with different iridium-tantalum ratios, and the iridium content of the IrO2 / Ta2O5 oxide coatings increases sequentially from the inner layer to the outer layer.

[0006] This invention also discloses a method for preparing the above-mentioned composition gradient iridium-tantalum coated anode, comprising the following steps: Step 1: Pre-treat the titanium substrate, including sandblasting, etching, cleaning and drying; Step 2: Prepare an intermediate layer on the surface of the pretreated substrate. The intermediate layer is composed of titanium tantalum oxide. Titanium salt and tantalum salt are prepared into a solution and coated onto the pretreated titanium substrate. After drying, an oxidation treatment is performed, and this process is repeated at least 5 times to obtain the TiN and titanium tantalum oxide intermediate layer. Step 3: Prepare multiple (three or more) solutions with different iridium-tantalum molar ratios using the iridium and tantalum sources; Step 4: Modify the carbon nanotubes and add the modified carbon nanotubes to the iridium-tantalum precursor solution to obtain iridium-tantalum precursor solutions with different composition gradients.

[0007] Step 5: First, coat the iridium-tantalum precursor solution with the lowest iridium content prepared in Step 4 onto the intermediate layer, and perform sintering oxidation treatment, repeating at least 5 times; then, similarly, coat and sinter the iridium-tantalum precursor solutions in order of increasing iridium content, repeating the coating-sintering process multiple times for each iridium-tantalum precursor solution until the coating and sintering of the iridium-tantalum precursor solution with the highest iridium content is completed, forming an iridium-tantalum oxide surface active layer with a compositional gradient, thus obtaining a compositional gradient iridium-tantalum coated anode.

[0008] The intermediate layer is mainly composed of a TiO2 / Ta2O5 mixed oxide. As a transition layer between the titanium substrate and the active layer, it alleviates thermal stress caused by differences in composition and coefficient of thermal expansion between the two. Through multiple coating and oxidation treatments, the intermediate layer becomes denser and more uniform, enhancing its bonding strength with the substrate and active layer and reducing the possibility of cracking during sintering and use. The titanium-tantalum oxide intermediate layer also possesses a certain degree of corrosion resistance, protecting the titanium substrate from electrolyte erosion and extending the anode's service life.

[0009] Compositional gradient design can distribute thermal stress, which would otherwise be concentrated between layers, throughout the entire coating, reducing stress concentration, minimizing coating cracking, and improving the anode's lifespan and stability. Coatings with different iridium-tantalum ratios exhibit varying performance in terms of catalytic activity and stability. By rationally configuring the iridium-tantalum molar ratio, it is possible to reduce the amount of iridium used while ensuring good catalytic activity of the anode, thereby lowering production costs.

[0010] Carbon nanotubes possess excellent electrical properties, particularly superior axial conductivity. Adding modified carbon nanotubes to the active layer precursor solution effectively mitigates conductivity variations caused by compositional gradients, reduces the cell voltage of compositionally gradient iridium-tantalum coated anodes, and minimizes energy loss. The modified carbon nanotubes are loaded with various oxygen-containing functional groups, such as carboxyl (-COOH), hydroxyl (-OH), and carbonyl (C=O). These functional groups serve as catalytic sites to enhance the catalytic activity of the anode and also increase hydrophilicity, ensuring uniform dispersion in the solution system and further improving anode performance.

[0011] An active layer with a continuous compositional gradient is formed by sequentially coating and sintering solutions with different iridium-tantalum molar ratios. This compositional gradient structure enables uniform distribution of thermal stress, reduces coating cracking, and improves the service life of the anode.

[0012] Furthermore, in step one, the titanium substrate is first cut and sandblasted, then washed with NaOH solution to remove oil, and finally etched in boiling acid solution. After etching, it is rinsed with pure water to obtain the pretreated titanium substrate.

[0013] Specifically, the abrasive used for sandblasting is one or more of steel grit, brown fused alumina, and white fused alumina, with a grit size between 14 and 30 mesh. Sandblasting with steel grit increases the surface roughness of the titanium substrate, improving the adhesion between the subsequent coating and the substrate. The rough surface provides more adhesion points for the coating, allowing it to adhere more firmly to the substrate and reducing the likelihood of coating peeling.

[0014] Specifically, in step one, the etching acid used is boiling 10-25% hydrochloric acid, 4-10% oxalic acid, or 10-30% sulfuric acid, and the etching time is 0.5-2 hours. Etching with boiling oxalic acid further removes the oxide layer and impurities from the titanium substrate surface, while simultaneously creating a microporous structure on the substrate surface. This facilitates better penetration and adhesion of the coating solution, enhancing the mechanical bond between the coating and the substrate. Cleaning removes residual acid and impurities from the etching process, and drying ensures the substrate surface is dry, preventing moisture from adversely affecting subsequent coating preparation processes and guaranteeing the quality and stability of the coating.

[0015] Furthermore, in step two, one or more of the chloride, nitrate or acetate salts containing titanium or tantalum are dissolved in a solvent to obtain a titanium and tantalum salt solution, wherein the solvent is one or more of water, n-butanol, ethanol, ethylene glycol, isopropanol, and propanol.

[0016] Furthermore, in step two, titanium tetrachloride and tantalum pentachloride are dissolved in dilute hydrochloric acid to prepare a salt solution for use as a coating liquid. The coating liquid is applied to the surface of the titanium substrate and then dried in a forced-air drying oven. After drying, the substrate is placed in a muffle furnace and sintered at a temperature of 460-550°C for 15-60 minutes. The titanium substrate is then removed and allowed to cool naturally to room temperature.

[0017] Furthermore, in step three, the method for preparing solutions with different iridium-tantalum molar ratios is as follows: An iridium source and a tantalum source are dissolved in one or more of water, dilute hydrochloric acid, n-butanol, ethanol, ethylene glycol, and isopropanol to obtain an iridium-tantalum solution. The iridium source is one or more of iridium trichloride, potassium chloroiridate, or chloroiridic acid. The tantalum source is one or more of tantalum pentachloride, tantalum ethoxide, or tantalum n-butoxide. The total cation concentration in the iridium-tantalum coating solution is 0.1–0.4 mol / L, and the total cation concentration is equal in solutions with different iridium-tantalum molar ratios. The iridium content in the first to fourth gradient iridium-tantalum solutions is 10–30%, 30–50%, 40–60%, and 60%–80%, respectively.

[0018] Furthermore, in step four, the carbon nanotubes are modified with concentrated nitric acid. The specific modification method is as follows: the carbon nanotubes are added to a round-bottom flask containing concentrated nitric acid, the ratio of carbon nanotubes to concentrated nitric acid is 1:125 g / ml, and the mixture is sonicated for 30-60 min to ensure full dispersion. Then, the flask is placed in an oil bath at 110-160℃ and heated under reflux for 1-3 h. After the reaction is completed, the carbon nanotubes are washed with deionized water until neutral.

[0019] Furthermore, in step four, the amount of modified carbon nanotubes added to the iridium-tantalum precursor solution is 10–50 mg / ml.

[0020] Furthermore, in step five, the sintering temperature is 460–550℃, and the sintering time is 20–50 min. Sintering oxidation treatment at this temperature transforms the metal salts in the coating into stable oxide structures, enhancing the coating's chemical stability and mechanical properties.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. The composition-gradient iridium-tantalum coated anode provided by this invention has a continuous composition gradient, effectively reducing stress concentration caused by differences in interlayer thermal expansion coefficients. By uniformly dispersing the thermal stress originally concentrated between the intermediate layer and the active layer throughout the active layer, it effectively reduces cracks generated during sintering oxidation, slows down the oxidation of the titanium substrate, and thus effectively improves the service life of the titanium anode. Coatings with different iridium-tantalum ratios exhibit different performances in catalytic activity and stability. When the iridium content is ≤30%, the sintering product of the coating solution is mainly tantalum pentoxide, with iridium atoms dissolved in the lattice of tantalum pentoxide to form a solid solution. At this time, the coating has good corrosion resistance, and as the inner layer of the active layer, it can improve the service life of the coating. When the iridium content is ≥30%, iridium dioxide begins to appear in the sintering product of the coating solution, and its proportion gradually increases with the increase of iridium content. Iridium dioxide is the main component providing oxygen evolution activity for the coating. Using a coating with an iridium content ≥60% as the outer layer of the active layer can maintain high oxygen evolution activity of the anode and reduce the tank pressure. Using a coating with an iridium content of 30-60% as the intermediate layer of the active layer can reduce stress concentration caused by the difference in thermal expansion coefficients between layers and improve coating adhesion. Experiments show that the anode has good adhesion when the number of gradient layers in the active layer is 4. Further increasing the number of gradient layers has limited effect on improving the anode's service life and increases the anode manufacturing cost. This invention improves the anode's service life by rationally configuring the iridium-tantalum molar ratio of different gradient layers, and reduces the amount of iridium used while ensuring good catalytic activity of the anode, thereby reducing production costs.

[0022] 2. The method for preparing a composition-gradient iridium-tantalum coated anode provided by this invention incorporates modified carbon nanotubes with good conductivity into the active layer. Utilizing the excellent axial conductivity of carbon nanotubes, the composition-gradient iridium-tantalum coated anode exhibits a lower electrode potential while extending its service life; its cell voltage is lower than that of the currently optimal uniform iridium-tantalum coated anode with an iridium-tantalum molar ratio of 7:3. Furthermore, considering the poor dispersion of unmodified carbon nanotubes, this invention modifies the carbon nanotubes with concentrated nitric acid before adding them to the active layer coating solution. The carbon nanotubes are modified by heating in concentrated nitric acid. The strong oxidizing properties of concentrated nitric acid introduce various oxygen-containing functional groups, such as carboxyl groups (-COOH), hydroxyl groups (-OH), and carbonyl groups (C=O), onto the surface of the carbon nanotubes. These functional groups improve the hydrophilicity of the carbon nanotubes, enabling uniform dispersion in the coating solution and enhancing their bonding ability with the coating. In the active layer, the addition of modified carbon nanotubes improves the conductivity of the coating, particularly compensating for the poor conductivity caused by the low iridium content in the inner layer of the active layer. In the outer layer of the active layer, due to the high iridium content, iridium dioxide particles are prone to agglomeration during sintering, reducing the utilization rate of active sites. After adding modified carbon nanotubes, the oxygen-containing functional groups on the surface of the carbon nanotubes adsorb iridium ions from the coating solution through coordination, inhibiting iridium dioxide particle agglomeration during subsequent sintering and increasing the number of active sites. This invention, by adding modified carbon nanotubes to the active layer, not only improves the conductivity of the anode but also enhances its catalytic activity to a certain extent, further improving the anode's performance.

[0023] 3. The gradient iridium-tantalum coated anode provided by this invention has a lower iridium content than the uniform iridium-tantalum coated anode with an iridium-tantalum molar ratio of 7:3, thus reducing the electrode preparation cost. Attached Figure Description

[0024] Figure 1 This is a surface SEM image of the oxide active layer in Example 1 of this invention.

[0025] Figure 2 This is a surface SEM image of the oxide active layer in Comparative Example 1 of this invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1: The composition gradient iridium-tantalum coated anode of this example includes a titanium substrate, a titanium-tantalum oxide intermediate layer coated on the titanium substrate, and an iridium-tantalum oxide surface active layer with composition gradient coated on the titanium-tantalum oxide intermediate layer, wherein the iridium-tantalum oxide surface active layer is sequentially coated and sintered by coating solutions with iridium-tantalum molar ratios of 1:9, 3:7, 5:5 and 7:3.

[0028] The specific steps of the preparation method of the composition gradient iridium-tantalum coated anode in this embodiment are as follows: 1) Pretreatment of titanium substrate: The titanium substrate is cut and sandblasted with steel grit of 20 mesh. Then it is washed with 10% NaOH solution for 0.5 hours to remove oil. Finally, it is etched in boiling 6% oxalic acid solution for 1 hour. After etching, it is rinsed with pure water to obtain titanium substrate.

[0029] 2) Preparation of intermediate layer: Titanium tetrachloride and tantalum pentachloride are dissolved in dilute hydrochloric acid to prepare a salt solution for use as a coating solution. The coating solution is applied to the surface of the titanium substrate and then dried in a forced-air drying oven at 60°C for 10 min. After drying, it is placed in a muffle furnace and sintered at 520°C for 30 min. The titanium substrate is then removed and naturally cooled to room temperature. This process is repeated 5 times to obtain the titanium tantalum oxide intermediate layer on the titanium substrate.

[0030] 3) Preparation of iridium-tantalum coating solution: Dissolve chloroiridic acid and tantalum pentachloride in dilute hydrochloric acid to obtain iridium-tantalum solution. The total cation concentration of iridium-tantalum coating solution is 0.2 mol / L. Four coating solutions are prepared according to the iridium-tantalum atomic ratio Ir:Ta = 1:9, 3:7, 5:5 and 7:3 respectively. Then, the modified carbon nanotubes are added. The amount of modified carbon nanotubes added to the coating solution is 20 mg / ml.

[0031] 4) Preparation of the iridium-tantalum active layer: First, a 1:9 coating solution was applied to the surface of the titanium substrate, and then dried in a 60℃ forced-air drying oven for 10 min. The dried titanium substrate was then placed in a muffle furnace and sintered at 520℃ for 30 min. After that, the titanium substrate was removed and allowed to cool naturally to room temperature. This process was repeated 5 times to obtain the first gradient of iridium-tantalum oxide coating. Then, a 3:7 coating solution was used for coating and sintering to obtain the second gradient of iridium-tantalum oxide coating. After coating and sintering the four coating solutions in sequence, iridium-tantalum oxide active layers with four composition gradients of 1:9, 3:7, 5:5, and 7:3 were obtained. Each gradient was coated and sintered 5 times, with the same amount of solution used for each coating.

[0032] In step 3) above, carbon nanotubes are modified with concentrated nitric acid. The specific modification method is as follows: 2g of carbon nanotubes are added to a round-bottom flask containing 250ml of concentrated nitric acid, and ultrasonicated for 45min to disperse them fully. Then, the flask is placed in an oil bath at 130℃ and heated under reflux for 2h. After the reaction is completed, the carbon nanotubes are washed with deionized water until neutral.

[0033] Example 2: The difference between the preparation method of this example and that of Example 1 is that the surface active layer of iridium tantalum oxide is coated and sintered sequentially with coating solutions of iridium tantalum molar ratios of 3:7, 4:6, 6:4 and 7:3.

[0034] In step 1), the sand used for sandblasting is brown corundum with a mesh size of 14.

[0035] In step 1), the boiling acid used for etching can be 10% hydrochloric acid, 4% oxalic acid, or 10% sulfuric acid, and the etching time is 2 hours.

[0036] In step 2), titanium nitrate and tantalum nitrate are dissolved in n-butanol to prepare a salt solution for use as a coating solution; sintering is carried out at 460°C for 60 minutes; this process is repeated 5 times.

[0037] In step 3), iridium trichloride and tantalum ethoxide are dissolved in n-butanol to obtain an iridium-tantalum solution; the total cation concentration of the iridium-tantalum coating solution is 0.1 mol / L.

[0038] In step 3), the carbon nanotubes are modified with concentrated nitric acid and sonicated for 30 minutes to disperse them fully. Then, the flask is placed in an oil bath at 160°C and heated under reflux for 1 hour. After the reaction is completed, the carbon nanotubes are washed with deionized water until neutral. The amount of modified carbon nanotubes added to the coating solution is 10 mg / ml.

[0039] In step 4), the sintering temperature is 460℃ and the sintering time is 50 min. By sequentially coating and sintering solutions with different iridium-tantalum molar ratios, an active layer with a continuous compositional gradient is formed.

[0040] Example 3: The difference between the preparation method of this example and that of Example 1 is that the composition gradient iridium-tantalum coating is applied and sintered sequentially by coating solutions with iridium-tantalum molar ratios of 3:7, 5:5, 6:4 and 7:3.

[0041] In step 1), the sand used for sandblasting is white corundum with a mesh size of 30.

[0042] In step 1), the boiling acid used for etching can be 25% hydrochloric acid, 10% oxalic acid, or 30% sulfuric acid, and the etching time is 0.5 hours.

[0043] In step 2), titanium acetate and tantalum acetate are dissolved in ethylene glycol to prepare a salt solution for use as a coating solution; sintering is carried out at 550°C for 15 minutes; this process is repeated 6 times.

[0044] In step 3), chloroiridic acid and n-butanol tantalum are dissolved in ethylene glycol to obtain an iridium-tantalum solution; the total cation concentration of the iridium-tantalum coating solution is 0.4 mol / L.

[0045] In step 3), the carbon nanotubes are modified with concentrated nitric acid and sonicated for 60 min to disperse them fully. Then, the flask is placed in an oil bath at 110°C and heated under reflux for 3 h. After the reaction is completed, the carbon nanotubes are washed with deionized water until neutral. The amount of modified carbon nanotubes added to the coating solution is 50 mg / ml.

[0046] In step 4), the sintering temperature is 550℃ and the sintering time is 20 min. By sequentially coating and sintering solutions with different iridium-tantalum molar ratios, an active layer with a continuous compositional gradient is formed.

[0047] Example 4: The difference between the preparation method of this example and that of Example 1 is that the composition gradient iridium-tantalum coating is applied and sintered sequentially by coating solutions with iridium-tantalum molar ratios of 1:9, 3:7, 4:6 and 6:4.

[0048] Example 5: The difference between the preparation method of this example and that of Example 1 is that the composition gradient iridium-tantalum coating is applied and sintered sequentially by coating solutions with iridium-tantalum molar ratios of 2:8, 4:6, 6:4 and 8:2.

[0049] Comparative Example 1: The difference between the preparation method of this comparative example and Example 1 is that the same coating and sintering process was performed multiple times using a coating solution with an iridium-tantalum molar ratio of 7:3, and carbon nanotubes were not added to the coating solution to prepare the surface active layer. Everything else is the same as in Example 1.

[0050] Comparative Example 2: The difference between the preparation method of this comparative example and Example 1 is that carbon nanotubes were not added to the surface active layer coating solution. Everything else is the same as in Example 1.

[0051] Comparative Example 3: The difference between the preparation method of this comparative example and Example 1 is that unmodified carbon nanotubes were added to the active layer coating solution. Everything else is the same as in Example 1.

[0052] Comparative Example 4: The difference between the preparation method of this comparative example and Example 1 is that the same coating and sintering process was performed multiple times using a coating solution with an iridium-tantalum molar ratio of 7:3, and modified carbon nanotubes were added to the coating solution to prepare the surface active layer. Everything else is the same as in Example 1.

[0053] Comparative Example 5: The difference between the preparation method of this comparative example and Example 1 is that the composition gradient iridium-tantalum coating is applied and sintered sequentially by coating solutions with iridium-tantalum molar ratios of 0.5:9.5, 5:5, 7:3, and 8:2. Everything else is the same as in Example 1.

[0054] Microscopic comparison of surface active layers: The scanning electron microscope image of the iridium tantalum oxide surface active layer in Example 1 is shown below. Figure 1 As shown, the scanning electron microscope image of the surface active layer in Comparative Example 1 is as follows: Figure 2As shown in the comparison, the surface active layer cracks of the composition gradient iridium-tantalum coated anode of the present invention are significantly reduced compared to those of the uniformly coated anode.

[0055] Performance testing: 1. Slot voltage test The coated titanium anodes prepared in Examples 1-5 and Comparative Examples 1-5 of this invention were subjected to cell voltage tests. The method was as follows: the prepared coated titanium anodes and titanium cathodes were placed in a simulated electrodeposition copper electrolyte (H₂SO₄ 180 g / L, CuSO₄ 45 g / L), and an electrolysis experiment was conducted using a DC power supply. The electrolyte temperature was 65°C, and the anode current density was 0.5 A / cm². 2 The electrode spacing is 3.3 cm, and the electrode area is 1 cm². 2 The cell pressure was monitored at the start of electrolysis.

[0056] 2. Accelerated life test Accelerated life tests were conducted on the coated titanium anodes prepared in Examples 1-5 and Comparative Examples 1-5 of this invention. The method was as follows: the prepared coated titanium anodes and titanium cathodes were placed in a 0.5M sulfuric acid electrolyte. Electrolysis experiments were performed using a DC power supply, with the electrolyte temperature at 65°C and the anolyte current density at 5 A / cm². 2 The electrode spacing is 3.3 cm, and the electrode area is 1 cm². 2 The cell voltage is continuously monitored, and when the cell voltage exceeds 10V, the anode is considered to have failed and the accelerated life results are recorded.

[0057] 3. Film adhesion test The film adhesion test was conducted using an automatic scratch tester, and the test conditions were as follows: Detection mode: Acoustic emission Load applied: 100N Loading method: Unidirectional continuous loading Scratch length: 6mm Loading rate: 60 N / min The adhesion test results are the critical load values ​​at which the coating begins to fail, and the results are shown in the table below:

[0058] Comparing Examples 1-5 with Comparative Example 1, it can be seen that the cell voltage of the gradient iridium-tantalum coated anode is significantly lower than that of the uniformly coated anode with an iridium-tantalum molar ratio of 7:3, the anode service life is significantly improved, and the coating adhesion is not significantly reduced.

[0059] Comparing Examples 2-5 with Example 1, it can be seen that adjusting the gradient of the active layer composition has a certain impact on the cell voltage and service life of the anode, with Example 5 being the best.

[0060] Comparing Comparative Example 1 and Comparative Example 2, it can be seen that the gradient coating can improve the electrode's working life, but it will lead to an increase in cell voltage due to the increased resistance. Comparing Example 1 and Comparative Example 2, it can be seen that, based on the presence of the gradient coating, the addition of modified carbon nanotubes can effectively reduce the cell voltage, reduce power consumption, and extend the working life.

[0061] Comparing Example 1 and Comparative Example 3, the cell voltage of Comparative Example 3 is 4.15V, higher than that of Example 1 (3.82V). This indicates that unmodified carbon nanotubes are less effective than modified carbon nanotubes in improving anode conductivity. The oxygen-containing functional groups on the surface of modified carbon nanotubes help improve their dispersibility in solution and their bonding ability with the coating, thus more effectively reducing the cell voltage. The anode lifetime of Comparative Example 3 is 2200h, lower than that of Example 1 (2732h). This shows that modified carbon nanotubes not only improve conductivity but also enhance the stability and lifespan of the anode to a certain extent. Unmodified carbon nanotubes may not be able to fully exert their role in enhancing coating performance due to poor dispersibility, leading to anode failure during use. The coating adhesion strength of Comparative Example 3 is 55N, similar to 53N in Example 1. This indicates that the modification of carbon nanotubes has a relatively small impact on coating adhesion strength, which is mainly affected by factors such as intermediate layer preparation and coating sintering process.

[0062] Comparing Example 1 and Comparative Example 4, it can be seen that although the cell voltage of Comparative Example 4 is lower, its anode service life is significantly insufficient, while the cell voltage of Example 1 increases only slightly, but the anode service life is greatly improved. This indicates that a surface-active layer with a compositional gradient can significantly improve the stability and service life of the anode.

[0063] Comparing Example 1 and Comparative Example 5, it can be seen that the cell voltage of Example 1 is lower than that of Comparative Example 5, and the working life is also significantly higher than that of Comparative Example 5. Therefore, by reasonably configuring the iridium-tantalum molar ratio, the present invention can improve the performance of the anode and reduce the amount of iridium used while ensuring that the anode has good catalytic activity, thereby reducing production costs.

[0064] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method of making a compositionally graded iridium-tantalum coated anode, characterized by, The method comprises the following steps: Step 1: pretreating the titanium substrate, which comprises sand blasting, etching, cleaning and drying; Step 2: configuring titanium salt and tantalum salt into a solution and coating the pretreated titanium substrate, drying and then performing oxidation treatment, and repeating multiple times to obtain an intermediate layer; Step 3: configuring iridium source and tantalum source into solutions with different iridium-tantalum molar ratios; Step 4: modifying carbon nanotubes and adding the modified carbon nanotubes into the iridium-tantalum precursor solution prepared in step 3 to obtain iridium-tantalum precursor solutions with different compositions and gradients; Step 5: coating the iridium-tantalum precursor solution with the least iridium content prepared in step 4 onto the intermediate layer, performing sintering and oxidation treatment, and repeating multiple times; then coating and sintering the iridium-tantalum precursor solutions in order of increasing iridium content, each of the iridium-tantalum precursor solutions being repeated multiple times until the iridium-tantalum precursor solution with the most iridium content is coated and sintered to form an iridium-tantalum oxide surface active layer with a composition gradient, i.e. to obtain the composition gradient iridium-tantalum coated anode.

2. The method of claim 1, wherein the method further comprises: In step 1, the titanium substrate is first cut and subjected to sand blasting treatment, then washed with NaOH solution to remove oil, and finally etched in a boiling acid solution, washed with pure water after etching to obtain the pretreated titanium substrate.

3. The method of claim 1, wherein the method further comprises: depositing a layer of iridium on the substrate; and annealing the layer of iridium at a temperature of about 600 °C to about 800 °C in an atmosphere comprising oxygen. In step 2, the titanium salt and the tantalum salt are dissolved in a solvent to obtain a salt solution of titanium and tantalum; The titanium salt and the tantalum salt are one or more of chloride, nitrate and acetate; The solvent is one or more of water, dilute hydrochloric acid, n-butanol, ethanol, ethylene glycol, isopropyl alcohol and propanol.

4. The method according to claim 3, wherein in step 2, titanium tetrachloride and pentachloride are dissolved in dilute hydrochloric acid to prepare a salt solution as a coating liquid, the coating liquid is coated on the surface of the titanium substrate, and then dried in a forced air drying oven, and after drying, the titanium substrate is placed in a muffle furnace and sintered at a temperature of 460-550℃ for 15-60min, and then naturally cooled to room temperature. In step 3, the solution with different iridium-tantalum molar ratios is prepared by:

5. The method of claim 1, wherein: The iridium source and the tantalum source are dissolved in one or more of water, dilute hydrochloric acid, n-butanol, ethanol, ethylene glycol and isopropyl alcohol to obtain an iridium-tantalum solution, the iridium source is one or more of iridium trichloride, potassium chloroiridate and chloroiridate, and the tantalum source is one or more of pentachloride, ethanolic tantalum and n-butanol tantalum. In step 3, the total cation concentration in the iridium-tantalum solution is 0.1-0.4 mol / L, and the iridium content in the first to fourth gradient iridium-tantalum solutions is 10-30%, 30-50%, 40-60% and 60%-80%, respectively.

6. The method of claim 5, wherein:

7. The method according to claim 1, wherein in step 4, the carbon nanotubes are modified using concentrated nitric acid, and the modification method is: ​ ​ The carbon nanotubes are added to a round bottom flask containing concentrated nitric acid, the ratio of carbon nanotubes to concentrated nitric acid is 1:125 g / ml, and the carbon nanotubes are ultrasonically dispersed for 30-60 min, and then the flask is placed in an oil bath at 110-160°C and heated to reflux for 1-3 h, and after the reaction is completed, the carbon nanotubes are washed with deionized water until neutral.

8. The method of claim 7, wherein the method further comprises: In the fourth step, the modified carbon nanotubes are added to the iridium-tantalum precursor solution in an amount of 10-50 mg / ml.

9. The method of claim 1, wherein: In the fifth step, the sintering temperature is 460-550°C, and the sintering time is 20-50 min.

10. A compositionally graded iridium-tantalum coated anode characterized by: The component-gradient iridium-tantalum coating anode is prepared by the preparation method of any one of claims 1-9, and comprises a titanium substrate, an intermediate layer, and a surface active layer of iridium-tantalum oxide with a component gradient arranged in sequence; the intermediate layer comprises titanium-tantalum oxide; and the surface active layer of iridium-tantalum oxide with a component gradient comprises multiple layers of IrO2 / Ta2O5 oxide coatings with different iridium-tantalum ratios, and the iridium content of the IrO2 / Ta2O5 oxide coatings gradually increases from the inner layer to the outer layer.

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