A method for preparing a titanium base-titanium dioxide nanosheet-rare metal coating electrode

Abstract

The application discloses a preparation method of a titanium base-titanium dioxide nanometer plate-rare metal coating electrode, relates to the technical field of titanium material pultruded profiles, and is characterized by the following steps: taking TA1 industrial pure titanium plate or titanium mesh as a base material, performing sand blasting, oxalic acid pickling, electroplating (partly), sintering, annealing pretreatment, and in-situ growing a TiO2 nanometer plate array transition layer on the surface of the titanium base body by adopting an anodic oxidation method; and then loading a Ru-Ir-Ti composite oxide active coating by adopting a thermal decomposition method. The application introduces the TiO2 nanometer plate intermediate layer, significantly enhances the bonding force between the coating and the base body, inhibits the passivation of the titanium base body, increases the electrochemical active area, makes the strengthening life of the electrode 1.5-3 times longer than that of a traditional rare metal coating electrode, reduces the rare metal consumption, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of electrochemical electrode material preparation technology, specifically a method for preparing a titanium dioxide nanoplate-rare metal coated electrode. The method involves in-situ growth of a titanium dioxide (TiO2) nanoplate array on the surface of a titanium substrate using an anodic oxidation method as a transition layer, followed by loading a rare metal active oxide coating onto the composite electrode, and the method for its preparation. This electrode can be widely used in fields such as electrolytic descaling and sterilization of circulating water, antifouling in seawater electrolysis, cathodic protection, industrial wastewater treatment, chlor-alkali industry, and electrochemical synthesis. Background Technology

[0002] Since their introduction in the 1960s, titanium-based rare metal oxide coated electrodes (Dimensionally Stable Anodes, DSAs) have gradually replaced traditional graphite and lead-based electrodes, becoming the core electrode material in the electrochemical industry due to their excellent electrocatalytic activity, corrosion resistance, and dimensional stability. Among them, ruthenium-titanium (RuO2-TiO2) coated electrodes and iridium-tantalum (IrO2-Ta2O5) coated electrodes are currently the two most widely used types of DSA electrodes.

[0003] However, traditional DSA electrodes suffer from the following technical bottlenecks during long-term use: Insufficient interfacial adhesion: Traditional coatings are directly applied to the smooth surface of the titanium substrate. The coating and the substrate are mainly physically adsorbed. During electrolysis, the coating is easily peeled off and detached due to the scouring of bubbles and the action of thermal stress cycles, which leads to premature electrode failure.

[0004] Passivation failure risk: Under anodic polarization conditions, the titanium substrate is prone to surface oxidation to form an insulating TiO2 passivation layer, which causes a sharp increase in electrode resistance and eventually leads to complete electrode failure.

[0005] Low utilization rate of active layer: Traditional planar coating structures have limited specific surface area and low dispersion of rare metal active components, resulting in insufficient electrocatalytic active sites and low current efficiency.

[0006] Coating cracking problem: The coating and the titanium substrate have a large difference in thermal expansion coefficients, which can easily cause microcracks during repeated heat treatment and use, accelerating electrolyte penetration and substrate corrosion.

[0007] In recent years, titanium dioxide nanotube arrays (TiO2 nanotube arrays, TNTs) have attracted widespread attention as a novel nanostructure material. Studies have shown that highly ordered, vertically aligned TiO2 nanotube arrays can be grown in situ on the surface of a titanium substrate via anodic oxidation, exhibiting a large specific surface area, excellent structural stability, and good semiconductor properties. Introducing TiO2 nanotube arrays as an intermediate transition layer into the DSA electrode system can effectively solve the aforementioned technical problems: the nanotube structure significantly increases the contact area between the coating and the substrate, enhancing mechanical interlocking; the nanotube walls can serve as conductive channels, suppressing passivation of the titanium substrate; and the internal space of the nanotubes can load more active components, improving the utilization rate of rare metals.

[0008] Existing technologies have included studies on the preparation of rare metal coated electrodes using TiO2 nanoplates as an intermediate layer (e.g., CN201711247665A), but these studies mainly focus on ruthenium-titanium binary systems, and there is still room for optimization in pretreatment processes, nanoplate preparation parameters, and coating loading processes. In particular, research on using TiO2 nanoplate arrays as transition layers in ruthenium-iridium (Ru-Ir) composite coating systems is insufficient. Ruthenium-iridium composite coatings combine the high chlorine evolution activity of RuO2 with the high oxygen evolution activity and stability of IrO2. The introduction of TiO2 nanoplates (as a transition layer) is expected to significantly improve the overall performance of the electrode. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for preparing a titanium-based titanium dioxide nanoplate-rare metal coated electrode. By optimizing the pretreatment process of the titanium substrate, controlling the microstructure of the TiO2 nanoplate array, and designing the composition and loading process of the rare metal composite active coating, the technical problems of weak coating adhesion, easy passivation of the substrate, low utilization rate of active components, and short electrode life in existing technologies are solved. A novel DSA electrode with high electrocatalytic activity, long enhanced life, and high stability is obtained, thus solving the problems mentioned in the background technology.

[0010] To achieve the above objectives, the present invention provides a method for preparing a titanium-based titanium dioxide nanoplate-rare metal coated electrode, comprising the following steps: Step 1: Titanium Substrate Pretreatment TA1 industrial pure titanium plate or titanium mesh is selected as the substrate, and sandblasting, stress-relieving annealing and pickling are performed in sequence: (1) Sandblasting treatment: The surface of the titanium substrate is sandblasted with 10-900 mesh diamond abrasive (preferably 60-320 mesh diamond abrasive), the compressed air pressure is controlled at 0.3-0.8 MPa, the spraying distance is 80-150 mm, the spraying angle is 45°-75°, until the surface roughness Ra reaches 1.6-6.3 μm (preferably 2.5-5.0 μm), and a uniformly rough activated surface is obtained; (2) Stress relief annealing: Place the sandblasted titanium substrate in a vacuum or argon or nitrogen inert atmosphere furnace, heat it to 500-600℃, hold it for 25-40 min, and then cool it to room temperature by furnace cooling or air cooling to eliminate the surface processing stress introduced by sandblasting and prevent the substrate from deforming during subsequent heat treatment. (3) Pickling treatment: Immerse the annealed titanium substrate in an oxalic acid (H2C2O4) solution with a concentration of 1-90% (mass fraction) (preferably 5-20%), and cook at 80-100℃ for 30-120 min (preferably at 85-95℃ for 45-90 min) to remove the surface oxide layer, oil stains and embedded diamond particles, exposing the fresh titanium metal surface; after pickling, ultrasonically clean with deionized water for 10-20 min, rinse with anhydrous ethanol, blow dry with nitrogen or dry with hot air at 60-80℃, and seal and store for later use.

[0011] (4) Repeat the coating and sintering process: brush or spray one layer, dry at 70-130℃ for 20-60 minutes, and sinter at high temperature: 500-650℃ for 20-60 minutes to form oxides through thermal decomposition; repeat the above steps 20-40 times.

[0012] Step 2: Preparation of the TiO2 nanoplate transition layer An in-situ TiO2 nanoplate array was grown on the surface of a pretreated titanium substrate using a two-electrode anodic oxidation method. (1) Electrolyte preparation: Using ethylene glycol or glycerol as solvent, add 0.25-1.5 wt.% ammonium fluoride (NH4F) and 1-10 vol.% deionized water (the concentration of NH4F in the electrolyte is preferably 0.5-1.0 wt.%, and the water content is preferably 2-5 vol.%), and stir magnetically until completely dissolved to form a uniform and transparent electrolyte; (2) Anodizing: The pretreated titanium substrate is used as the anode, and a large-area platinum mesh or platinum sheet is used as the cathode. The distance between the two electrodes is 1.5 to 3.0 cm, and the substrate is placed in the electrolyte. A DC constant voltage power supply is used to apply a voltage of 15 to 60 V (preferably 20 to 40 V), the electrolyte temperature is controlled at 15 to 35℃ (preferably 25℃), the magnetic stirring speed is 200 to 1000 rpm, and the anodizing time is 0.5 to 5.0 h (preferably 1.5 to 3.0 h). (3) Post-treatment: After anodizing, the sample is taken out and ultrasonically cleaned with deionized water and anhydrous ethanol alternately for 3 to 5 times, each time for 5 to 10 minutes, to remove residual electrolyte and loose oxides on the surface; then, in an air or oxygen atmosphere, it is heated to 400 to 600°C (preferably 450 to 500°C) at a heating rate of 1 to 3°C / min and kept at that temperature for 1 to 3 hours (preferably 2 hours) to convert amorphous TiO2 into anatase phase, thereby enhancing the structural stability and conductivity of the nanoplate. The sample is then cooled to room temperature in the furnace to obtain a "titanium-based / TiO2 nanoplate" composite matrix.

[0013] Step 3: Preparation and Loading of Rare Metal Coatings A rare metal composite oxide coating was loaded onto the surface of a TiO2 nanoplate / Ti composite substrate using a thermal decomposition method (brush coating-drying-sintering process). The rare metals were one or more combinations of ruthenium, iridium, tantalum, platinum, silver, lanthanum, cerium, neodymium, and tungsten. (1) Preparation of coating solution; (2) Coating and heat treatment: The coating solution was uniformly coated onto the surface of TiO2 nanoplate / Ti composite substrate using a brush coating method or a dip-coating method, and the rare metal loading in a single coating was controlled to be 0.5–2.0 g / m² (calculated as Ru+Ir). After coating, place the product in an infrared drying oven or hot air circulating oven and dry at 80–120°C for 5–15 min to allow the solvent to evaporate. Then transfer it to a muffle furnace and heat it to 400–500°C (preferably 350–450°C) at a heating rate of 5–10°C / min in an air or oxygen atmosphere, and hold it at that temperature for 5–15 min to thermally decompose the metal precursor into the corresponding oxide solid solution. Repeat the above "coating-drying-thermal decomposition" process 5–20 times until the designed total rare metal loading (total Ru+Ir coating amount of 5–20 g / m², preferably 8–12 g / m²) is achieved. In the final heat treatment, the temperature is raised to 400–500℃ (preferably 450℃) and held for 0.75–1.5 h (preferably 1 h) to allow the coating to crystallize completely and form a stable RuO2-IrO2-TiO2 ternary solid solution structure. The electrode is then cooled to room temperature in the furnace to obtain the "titanium-based / TiO2 nanoplate / ruthenium-iridium coating" composite electrode. The electrode comprises a TA1 titanium substrate, an in-situ grown TiO2 nanoplate transition layer, and a RuO2-IrO2-TiO2 ternary oxide active coating loaded on the surface of the nanoplate.

[0014] A further improvement of this invention lies in: coating the surface of the titanium dioxide nanoplate array with a tin-antimony composite sol-gel coating to fill the pores of the nanoplates and construct a conductive buffer layer. The specific process is as follows: (1) Preparation of tin-antimony sol: Using tin tetrachloride and antimony trichloride as precursors, anhydrous ethanol as solvent, and hydrochloric acid as stabilizer, a mixed solution was prepared according to the Sn:Sb molar ratio of 8:1 to 12:1. After stirring and dissolving, an appropriate amount of citric acid was added as a complexing agent. The mixture was stirred for 2 to 4 hours and allowed to stand for 12 to 24 hours to obtain a stable and transparent tin-antimony sol. (2) Coating process: The tin antimony sol is uniformly coated on the surface of the titanium dioxide nanoplate by dip-coating or brush coating. The thickness of a single coating is 5-15 μm. After coating, the nanoplate is dried at 80-120℃ for 10-20 min to remove the solvent. The coating-drying process is repeated 3-8 times to ensure that the sol fully fills the pores of the nanoplate and forms a uniform and continuous coating. (3) High-temperature sintering: After the last drying is completed, the substrate is placed in a muffle furnace at 450-550℃ for sintering for 30-60 minutes, and then cooled to room temperature with the furnace to solidify and form a dense and stable tin-antimony oxide coating, thus completing the preparation of the double-layer transition layer.

[0015] The electrode consists of a TA1 titanium matrix, a titanium dioxide nanoplate transition layer, a sol-gel tin-antimony intermediate layer, and a ruthenium-iridium catalytic top layer, forming a four-layer gradient composite structure from the inside out.

[0016] A further improvement of this invention is that a sub-titanium oxide (Ti4O7) transition layer is prepared on the surface of the pretreated titanium substrate using plasma spraying technology. (1) Preparation of spray powder: Titanium suboxide powder and titanium powder are mixed at a mass ratio of (80-95):(5-20), and the powder particle size range is 10-100μm, preferably 20-60μm. The mixed powder is dried in a vacuum drying oven at 80-120℃ for 2-4h.

[0017] (2) Plasma spraying process parameters: Plasma gas: Ar as the main gas, flow rate 30-60 L / min; H2 as the auxiliary gas, flow rate 2-10 L / min; Spraying current: 400-600 A; Spraying voltage: 30-50 V; Spraying distance: 80-150 mm; Powder feeding rate: 20-60 g / min; Spraying angle: 75°-90°; Substrate temperature control: Compressed air cooling is used to control the substrate temperature ≤200℃; Coating thickness: 50-300 μm, preferably 100-00 μm. (3) Post-treatment: After the coating is completed, the substrate with the titanium suboxide transition layer is heat-treated at 300-500℃ for 1-3 hours in a vacuum or inert atmosphere to eliminate residual stress in the coating and improve the density of the coating.

[0018] (4) Repeat the coating and sintering process: brush or spray one layer, dry at 70-130℃ for 20-60 minutes, and sinter at high temperature: 500-650℃ for 20-60 minutes to form oxides through thermal decomposition; repeat the above steps 20-40 times.

[0019] This invention provides a method for preparing a titanium-based titanium dioxide nanoplate-rare metal coated electrode, which has the following beneficial effects: 1. Significantly enhanced interfacial bonding: TiO2 nanoplate arrays grow directly on the titanium substrate in situ, forming a metallurgical bond with the substrate; the porous structure of the nanoplates allows the rare metal active coating to be embedded inside the cavity, forming a mechanical locking effect. The coating bonding force is 2 to 3 times higher than that of traditional planar coatings, effectively resisting the erosion of electrolytic bubbles.

[0020] 2. Suppressing substrate passivation failure: The TiO2 nanoplate array serves as a semiconductor transition layer, and its tube walls can provide electron transport channels, preventing the direct formation of an insulating TiO2 passivation film on the surface of the titanium substrate during anodic polarization. At the same time, the nanoplate structure increases the contact area between the coating and the substrate, reduces the interfacial current density, and slows down the passivation process.

[0021] 3. Significantly increased electrochemical active area: The highly ordered TiO2 nanoplate array increases the actual surface area of ​​the electrode by 10 to 50 times compared to the geometric area. The ruthenium-iridium active components are dispersed on the inner and outer surfaces of the nanoplates, exposing more catalytic active sites, and the overpotential of the chlorine evolution reaction and oxygen evolution reaction is significantly reduced.

[0022] 4. Significantly Extended Lifespan: The TiO2 nanoplate transition layer effectively buffers the thermal expansion stress between the coating and the substrate, reducing coating cracking; the nanoplate structure hinders electrolyte penetration, forming a "maze effect" that delays the corrosive medium from reaching the substrate. Accelerated life tests show that the enhanced lifespan of the electrode of this invention is 1.5 to 3 times longer than that of traditional rare metal coated electrodes without a nanoplate intermediate layer. 5. High utilization rate of rare metals and controllable cost: The high specific surface area of ​​the nanoplate reduces the amount of rare metal coating required per unit area electrode by 20-40%, significantly reducing raw material costs while ensuring performance.

[0023] 6. The sol-gel tin-antimony coating fills the pores of the nanoplate, forming a continuous conductive buffer layer that effectively blocks electrolyte erosion, inhibits passivation of the titanium substrate, and reduces interlayer contact resistance.

[0024] 7. The sub-titanium oxide transition layer possesses excellent electrical conductivity (>100 S / cm) and chemical stability, effectively preventing the formation of a high-resistivity TiO2 passivation layer on the titanium substrate surface during high-temperature thermal decomposition and electrolysis, thus reducing electrode contact resistance by 20-40%. The sub-titanium oxide transition layer forms a metallurgical bond with the titanium substrate and a chemical bond with the ruthenium-iridium active coating, resulting in a dual-strengthened interface bond. This enhances the electrode's electrolysis life by more than 50% compared to traditional titanium-based ruthenium-iridium electrodes. The high conductivity of the sub-titanium oxide transition layer allows for a reduction in the ruthenium-iridium coating thickness while maintaining electrocatalytic performance, resulting in a 15-25% reduction in rare metal loading and a significant decrease in preparation costs. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example

[0026] Step 1: Titanium Substrate Pretreatment A 1.0 mm thick TA1 industrial pure titanium plate was selected and cut into 20 mm × 20 mm samples. The samples were sandblasted with 180-mesh diamond abrasive at a compressed air pressure of 0.5 MPa, a spray distance of 100 mm, a spray angle of 60°, and a sandblasting time of 2 min, resulting in a surface roughness Ra of 3.2 μm. The samples were then placed in an argon-protected annealing furnace, heated to 550 °C, held for 30 min, and then cooled to room temperature. Next, the samples were immersed in a 10% oxalic acid solution and boiled at 90 °C for 60 min. After removal, they were ultrasonically cleaned with deionized water for 15 min, rinsed with anhydrous ethanol, and dried with nitrogen for later use.

[0027] Step 2: Preparation of the TiO2 nanoplate transition layer Electrolyte preparation: Ethylene glycol was used as the solvent, and 0.5 wt.% NH4F and 2 vol.% deionized water were added and stirred to dissolve. The pretreated titanium sample was used as the anode, and a platinum mesh as the cathode, with a distance of 2.0 cm between the electrodes. A constant DC voltage of 20 V was applied, the electrolyte temperature was 25℃, the magnetic stirring speed was 600 rpm, and the anodizing time was 2 h. After oxidation, the sample was ultrasonically cleaned four times alternately with deionized water and anhydrous ethanol, 5 min each time. Subsequently, the temperature was increased to 450℃ at 2℃ / min in a muffle furnace, held for 2 h, and cooled with the furnace to obtain a TiO2 nanoplate / Ti composite matrix. SEM characterization showed that the nanoplates had an average diameter of approximately 100 nm, a wall thickness of approximately 20 nm, and a length of approximately 1.5 μm, exhibiting a neat and uniform arrangement.

[0028] Step 3: Preparation of rare metal coatings. The preparation steps for active coatings using ruthenium and iridium as the rare metals are as follows: Preparation of coating solution: Ruthenium source: Ruthenium trichloride or tetrabutyl ruthenate, calculated based on Ru metal content; Iridium source: chloroiridic acid or iridium tetrachloride, based on Ir metal content; Titanium source: tetrabutyl titanate or tetraisopropyl titanate, as an inert component and binder; Solvent: n-Butanol, isopropanol, or a mixture of both; Additive: 36% concentrated hydrochloric acid, used at 1-5% of the solvent volume, to inhibit precursor hydrolysis; According to the molar ratio of Ru : Ir : Ti of (1-4): (1-4): (2-8), each precursor is dissolved in a solvent, ultrasonically dispersed or magnetically stirred until completely dissolved, and a homogeneous and stable coating solution is prepared; the total mass concentration of Ru metal and Ir metal in the coating solution is controlled to be 10-50 g / L. Weigh 0.5 g of RuCl3·xH2O (based on Ru), 0.5 g of H2IrCl6 (based on Ir), and 2.0 mL of tetrabutyl titanate. Add 8.0 mL of n-butanol and 0.3 mL of 36% concentrated hydrochloric acid, and ultrasonically stir for 30 min until completely dissolved. Coat the TiO2 nanoplate / Ti substrate surface using a brush coating method. Dry under an infrared lamp at 100℃ for 10 min, then heat to 450℃ in a muffle furnace at a rate of 10℃ / min and hold for 10 min. Repeat the coating-drying-thermal decomposition process 10 times, with the final heating at 450℃ for 1 h. The total Ru+Ir coating amount is approximately 10 g / m². A "titanium-based / TiO2 nanoplate / ruthenium-iridium coating" composite electrode is obtained. Example

[0029] The difference from Example 1 is as follows: in step two, the anodic oxidation voltage is 40 V, the oxidation time is 1 h, and the nanoplate length is approximately 4 μm; in step three, the Ru:Ir:Ti molar ratio is 3:3:4, and the total coating amount is 12 g / m². All other process parameters are the same as in Example 1. Example

[0030] The difference from Example 1 is as follows: in step one, 60-mesh diamond abrasive is used for sandblasting, achieving a surface roughness Ra of 5.0 μm; in step two, the electrolyte solvent is glycerol, with an NH4F concentration of 1.0 wt.%, a water content of 5 vol.%, a voltage of 60 V, and an oxidation time of 3 h; in step three, the coating solvent is a mixture of isopropanol and n-butanol (volume ratio 1:1), with a Ru:Ir:Ti molar ratio of 2:2:6. All other process parameters are the same as in Example 1.

[0031] The same TA1 titanium plate as in Example 1 was selected. After sandblasting, annealing and pickling pretreatment, without anodizing, the same coating solution and coating process as in Example 1 were used to prepare ruthenium-iridium coated electrodes (or rare metal coatings). The total Ru+Ir coating amount was 10 g / m². Example

[0032] Based on Example 1, a method for preparing the tin-antimony transition layer was added: a sol was prepared with a Sn:Sb molar ratio of 10:1, aged for 18 hours, dip-coated 5 times, dried at 100°C for 15 minutes each time, and sintered at 500°C for 40 minutes to obtain a dense tin-antimony coating. Example

[0033] A sub-titanium oxide transition layer was prepared on the surface of a pretreated titanium substrate using plasma spraying technology. The specific process is as follows: Spraying powder: Ti4O7 powder (particle size 25-45μm) and titanium powder (particle size 15-35μm) were mixed at a mass ratio of 85:15 and dried at 110℃ for 2.5h; Plasma spraying parameters: Ar 50L / min, H2 6L / min, current 550A, voltage 42V, distance 100mm, powder feed rate 35g / min, substrate temperature controlled ≤180℃, coating thickness 120μm; Post-treatment: vacuum heat treatment at 380℃ for 2.5h.

[0034] Performance testing and comparison: 1. Microscopic morphological characterization The surface and cross-sectional morphology of the electrodes were observed using field emission scanning electron microscopy (FE-SEM). In Example 1, the TiO2 nanoplate array was vertically grown on the surface of a titanium substrate, with uniform diameter and clearly defined open ends; a ruthenium-iridium coating uniformly covered the surface of the nanoplate array, with some active components filling the nanoplate cavities. In Comparative Example 1, the surface was a smooth rare metal coating with a few visible microcracks.

[0035] 2. Electrochemical performance testing (1) Cyclic voltammetry (CV): The electrolyte was 0.5 mol / L H2SO4 solution, the scan rate was 50 mV / s, and the potential range was 0.2–1.2 V (vs. SCE). The integral area of ​​the CV curve of the electrode in Example 1 was significantly larger than that in Comparative Example 1, indicating that it had a larger electrochemical active area.

[0036] (2) Linear sweep voltammetry (LSV): The electrolyte was a saturated NaCl solution, and the scan rate was 20 mV / s. The chlorine evolution potential of the electrode in Example 1 was 1.08 V (vs. SCE), which was about 40 mV lower than the 1.12 V of Comparative Example 1, indicating a significant improvement in chlorine evolution activity.

[0037] 3. Enhanced lifespan testing According to the GB / T 12176-2008 standard "Metal Oxide Coated Anodes", in a 15wt.% H2SO4 solution, at a current density of 40kA / m², the cell voltage change curve over time was recorded, and the failure criterion was that the cell voltage rose to 12V or increased by 5V from the initial value.

[0038] Test results: The electrode enhancement lifetime of Example 1 was 3.2h, and that of Comparative Example 1 was 1.5h, representing an increase of approximately 113%. The enhancement lifetimes of Examples 2 and 3 were 3.8h and 3.5h, respectively.

[0039] 4. Coating adhesion test The coating adhesion was tested using the cross-cut test (ASTM D3359) and the ultrasonic peel test. In Example 1, the electrode cross-cut grade was 0–1, and the ultrasonic peel weight loss rate was <2%; in Comparative Example 1, the electrode cross-cut grade was 2–3, and the ultrasonic peel weight loss rate was >8%.

[0040] This invention uses TA1 industrial pure titanium plates or titanium mesh as substrates. After pretreatment by sandblasting (roughness Ra 1.6–6.3 μm), annealing (500–600℃), and oxalic acid pickling, a TiO2 nanoplate array transition layer is grown in situ on the titanium substrate surface using anodizing. Then, a Ru-Ir-Ti composite oxide active coating is loaded via thermal decomposition. By introducing the TiO2 nanoplate intermediate layer, this invention significantly enhances the adhesion between the coating and the substrate, inhibits passivation of the titanium substrate, and increases the electrochemical active area. This results in an electrode lifetime that is 1.5–3 times longer than that of traditional rare metal coated electrodes, while simultaneously reducing the amount of rare metals used, demonstrating promising prospects for industrial applications.

Claims

1. A method for preparing a titanium-based titanium dioxide nanoplate-rare metal coated electrode, characterized in that: Includes the following steps: A. Titanium substrate pretreatment: TA1 industrial pure titanium plate or titanium mesh is selected as the substrate, and sandblasting, stress-relieving annealing and pickling are performed in sequence: a1. Sandblasting treatment: The surface of the titanium substrate is sandblasted with 10-900 mesh diamond abrasive. The compressed air pressure is controlled at 0.3-0.8 MPa, the spraying distance is 80-150 mm, and the spraying angle is 45°-75° until the surface roughness Ra reaches 1.6-6.3 μm, so as to obtain a uniformly rough activated surface. a2. Stress-relief annealing: Place the sandblasted titanium substrate in a vacuum or inert atmosphere furnace, heat it to 500-600℃, hold it for 25-40 min, and then cool it to room temperature by furnace cooling or air cooling to eliminate the surface processing stress introduced by sandblasting and prevent the substrate from deforming during subsequent heat treatment. a3. Pickling treatment: Immerse the annealed titanium substrate in an oxalic acid solution with a concentration of 1-90% and boil it at 80-100℃ for 30-120 minutes to remove the surface oxide layer, oil stains and embedded diamond particles, exposing the fresh titanium metal surface; after pickling, ultrasonically clean it with deionized water for 10-20 minutes, rinse it with anhydrous ethanol, blow it dry with nitrogen or dry it with hot air at 60-80℃, and seal it for later use. a4. Repeat the coating and sintering process multiple times: Brush or spray one layer, dry at 70-130℃ for 20-60 minutes, and sinter at high temperature: 500-650℃ for 20-60 minutes to form oxides through thermal decomposition; repeat the above steps 20-40 times. B. Preparation of the transition layer of titanium dioxide nanoplates: An in-situ growth of titanium dioxide nanoplate arrays on the surface of a pretreated titanium substrate was achieved using a two-electrode anodic oxidation method. b1. Electrolyte preparation: Using ethylene glycol or glycerol as solvent, add 0.25-1.5 wt.% ammonium fluoride and 1-10 vol.% deionized water, and stir magnetically until completely dissolved to form a uniform and transparent electrolyte. b2. Anodizing: Using a pretreated titanium substrate as the anode and a large-area platinum mesh or platinum sheet as the cathode, with a distance of 1.5 to 3.0 cm between the two electrodes, the substrate is placed in an electrolyte. A DC constant voltage power supply was used, with a voltage of 15–60 V applied, the electrolyte temperature controlled at 15–35 °C, the magnetic stirring speed at 200–1000 rpm, and the anodizing time at 0.5–5.0 h. b3. Post-processing: After anodizing, the sample is taken out and ultrasonically cleaned 3-5 times with deionized water and anhydrous ethanol alternately, each time for 5-10 minutes, to remove residual electrolyte and loose oxides on the surface; then, in an air or oxygen atmosphere, it is heated to 400-600℃ at a heating rate of 1-3℃ / min and held for 1-3 hours to transform amorphous titanium dioxide into anatase phase, which enhances the nanoplate, structural stability and conductivity; then, it is cooled to room temperature in the furnace to obtain titanium-based or titanium dioxide nanoplate composite matrix. C. Preparation and loading of rare metal coatings: A rare metal composite oxide coating is loaded onto the surface of a titanium-based or titanium dioxide nanoplate composite substrate using a thermal decomposition method. The rare metal is one or more combinations of ruthenium, iridium, tantalum, platinum, silver, lanthanum, cerium, neodymium, and tungsten. c1. Preparation of coating solution; c2. Coating and heat treatment: Coating: The coating liquid is uniformly coated onto the surface of the titanium-based or titanium dioxide nanoplate composite substrate by brushing or dip-coating method, and the rare metal loading of a single coating is controlled to be 0.5 to 2.0 g / m². Drying: After coating, place in an infrared drying oven or hot air circulating oven and dry at 80-120℃ for 5-15 minutes to allow the solvent to evaporate; Thermal decomposition: The metal precursor is then transferred to a muffle furnace and heated to 350-500°C at a heating rate of 5-10°C / min in an air or oxygen atmosphere, and held for 5-15 min to thermally decompose the metal precursor into the corresponding oxide solid solution. Repeat the coating, drying, and thermal decomposition process 5 to 20 times until the designed total rare metal loading is achieved. During the final heat treatment, the temperature is raised to 400 to 500°C and held for 0.75 to 1.5 h to allow the coating to crystallize completely and form a stable RuO2-IrO2-TiO2 ternary solid solution structure. The coating is then cooled to room temperature in the furnace to obtain a titanium-based titanium dioxide nanoplate-rare metal coating composite electrode.

2. The method for preparing a titanium-based titanium dioxide nanoplate-rare metal coated electrode according to claim 1, characterized in that: A sol-gel tin-antimony intermediate coating is provided between the transition layer of the titanium dioxide nanoplate and the rare metal coating. That is, a tin-antimony composite sol-gel coating is coated on the surface of the titanium dioxide nanoplate to fill the pores of the nanoplate and construct a conductive buffer layer. The specific process is as follows: A. Preparation of tin-antimony sol: Using tin tetrachloride and antimony trichloride as precursors, anhydrous ethanol as solvent, and hydrochloric acid as stabilizer, a mixed solution was prepared according to the Sn:Sb molar ratio of 8:1 to 12:

1. After stirring and dissolving, an appropriate amount of citric acid was added as a complexing agent. The mixture was stirred for 2 to 4 hours and allowed to stand for 12 to 24 hours to obtain a stable and transparent tin-antimony sol. B. Coating process: The tin-antimony sol is uniformly coated on the surface of the titanium dioxide nanoplate using the dip-coating method or brush coating method. The thickness of a single coating is 5-15 μm. After coating, the nanoplate is dried at 80-120℃ for 10-20 min to remove the solvent. The coating-drying process is repeated 3-8 times to ensure that the sol fully fills the pores of the nanoplate and forms a uniform and continuous coating. C. High-temperature sintering: After the final drying, the substrate is placed in a muffle furnace at 450-550℃ for sintering for 30-60 minutes, and then cooled to room temperature with the furnace to solidify and form a dense and stable tin-antimony oxide coating, thus completing the preparation of the double-layer transition layer.

3. The method for preparing a titanium-based titanium dioxide nanoplate-rare metal coated electrode according to claim 1, characterized in that: A sub-titanium oxide transition layer was prepared on the surface of a pretreated titanium substrate using plasma spraying technology. The specific process is as follows: A. Preparation of spray powder: Mix sub-titanium oxide powder and titanium powder at a mass ratio of (80-95):(5-20), with a powder particle size range of 10-100μm. Dry the mixed powder in a vacuum drying oven at 80-120℃ for 2-4 hours. B. Plasma spraying process parameters: Plasma gas: Ar as the main gas, flow rate 30-60 L / min; H2 as the auxiliary gas, flow rate 2-10 L / min; Spraying current: 400-600 A; Spraying voltage: 30-50 V; Spraying distance: 80-150 mm; Powder feeding rate: 20-60 g / min; Spraying angle: 75°-90°; Substrate temperature control: Compressed air cooling, controlling the substrate temperature ≤200℃; Coating thickness: 50-300 μm. C. Post-treatment: After the coating is completed, the substrate with the titanium suboxide transition layer is heat-treated at 300-500℃ for 1-3 hours in a vacuum or inert atmosphere to eliminate residual stress in the coating and improve the density of the coating. D. Repeat the coating and sintering process multiple times: Brush or spray one layer, dry at 70-130℃ for 20-60 minutes, and sinter at high temperature: 500-650℃ for 20-60 minutes to form oxides through thermal decomposition; repeat the above steps 20-40 times.