A gradient microcrack composite coating titanium-based metal oxide electrode and a preparation method thereof

Abstract

The present application relates to the field of electrochemistry, and more particularly to a gradient micro-crack composite coating titanium-based metal oxide electrode and a preparation method thereof. The electrode comprises a titanium substrate and a gradient micro-crack composite coating, which comprises, in sequence, a dense low-crack bottom layer prepared by a thermal decomposition method and a high-crack density surface layer prepared by a sol-gel method. Experimental results show that the gradient micro-crack composite coating can effectively prevent the penetration of electrolyte into the titanium substrate through the dense structure of the bottom layer, avoid the passivation of the substrate, and prolong the service life; the high-crack structure of the surface layer significantly increases the electrochemical active surface area, ensuring high electrocatalytic activity. The electrode realizes the synergistic consideration of activity and life, and has simple preparation process and low cost, without the need to introduce additional intermediate layers or complex equipment, and is suitable for electrochemical engineering fields such as chlor-alkali industry, electrolytic seawater chlorination, cathodic protection and wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and more specifically, to a gradient microcrack composite coated titanium-based metal oxide electrode and its preparation method. Background Technology

[0002] Titanium-based metal oxide electrodes (DSA) are key materials in modern electrochemical industry. Due to their excellent electrocatalytic activity and dimensional stability, they are widely used in chlor-alkali industries, seawater electrolysis for chlorination, impressed current cathodic protection, and wastewater treatment. DSAs typically use industrially pure titanium as a substrate, coated and sintered with a mixed metal oxide coating of RuO2, IrO2, Ta2O5, TiO2, etc. Despite their widespread application, a long-standing and fundamental technical challenge has consistently hindered further performance improvements: achieving both high electrocatalytic activity and long service life is difficult.

[0003] The root of this contradiction lies in the inherent "microcrack" structure of the coating. Due to the difference in thermal expansion coefficients between the titanium substrate and the oxide coating, internal stress is generated within the coating after high-temperature sintering, leading to the formation of a network of microcracks (often referred to as "mud cracks"). While these microcracks increase the actual electrochemical active surface area of ​​the electrode and expose more active sites, thereby enhancing catalytic activity, they also constitute rapid channels for electrolyte penetration into the coating and the titanium substrate interface. Under harsh conditions such as strong oxygen evolution, the penetrating electrolyte causes the formation of a poorly conductive TiO2 passivation film on the titanium substrate surface. This passivation film not only increases interfacial resistance, leading to higher cell voltage, but also weakens the adhesion between the coating and the substrate, ultimately causing the coating to peel off and resulting in electrode failure.

[0004] To block electrolyte leakage and delay substrate passivation, introducing an "intermediate layer" between the titanium substrate and the active coating has become a common technical improvement approach in the industry. Existing technologies disclose various methods for constructing intermediate layers. For example, patent CN102174704A discloses a method for preparing a metal oxide electrode containing a tantalum intermediate layer using a thermal decomposition method. This method is relatively simple and can effectively improve electrode lifespan; however, the tantalum intermediate layer prepared by this thermal decomposition method is mainly mechanically bonded to the titanium substrate, resulting in limited bonding strength. This poses a risk of coating peeling during long-term service, and the method lacks precise control over the intermediate layer thickness, making it difficult to meet high stability requirements. Patent CN118480807B discloses a method for preparing a gradient alloy intermediate layer using a double-layer glow discharge plasma tantalum infiltration technique. The tantalum infiltrated layer formed by this method achieves a metallurgical bond with the titanium substrate, exhibiting strong bonding strength and significantly improving the protection of the substrate and electrode lifespan. However, this method requires specialized plasma alloying equipment and must be carried out under high temperature (800-900℃) and vacuum conditions. The process is complex, energy-intensive, and requires significant equipment investment, making it difficult to achieve low-cost, large-scale preparation of large-size electrodes or electrodes with complex structures.

[0005] Besides introducing a metal or alloy interlayer, another approach is to construct a protective layer on top of the catalytic layer. For example, existing patent US20200194770A1 discloses a method for preparing a titanium-based active electrode. This method uses a thermal decomposition method to prepare a multi-metal active catalytic layer, and then combines a sol-gel method with an electrochemical deposition method to form a dense oxide protective layer on the surface of the catalytic layer to fill cracks and block electrolyte penetration. However, the outer dense protective layer directly shields a large number of electrocatalytic active sites, significantly reducing the actual electrochemical active surface area of ​​the electrode, resulting in a significant decrease in the electrocatalytic performance of the electrode. Essentially, it still does not escape the constraints of existing technologies that "sacrifice activity for lifespan." Moreover, this method requires the introduction of an electrochemical deposition process, which is complex, requires high-end equipment, and increases preparation costs.

[0006] Therefore, there is an urgent need in this field to develop a novel titanium-based metal oxide electrode that is simple to process and can balance activity and lifespan, in order to solve the problems existing in the prior art. Summary of the Invention

[0007] In view of this, the present invention aims to propose a gradient microcrack composite coating titanium-based metal oxide electrode and its preparation method, so as to solve the problems of high electrocatalytic activity and long service life of titanium-based metal oxide electrodes in the prior art, as well as the complex preparation process and high production cost.

[0008] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0009] This invention discloses a method for preparing a gradient microcrack composite coated titanium-based metal oxide electrode, comprising the following steps:

[0010] S1: Pretreatment of the titanium matrix;

[0011] S2: Preparation of precursor solution; The first precursor solution is prepared by thermal decomposition, in which a compound containing the target metal element is dissolved in a solvent to obtain the first precursor solution; The second precursor solution is prepared by sol-gel method, in which a complexing agent and a crosslinking agent are reacted, and then a compound containing the target metal element is added. After reaction and dilution, the second precursor solution is obtained.

[0012] S3: The first precursor solution is coated onto the surface of the pretreated titanium substrate, and then dried and sintered in sequence to form the bottom layer of the gradient microcrack composite coating; the second precursor solution is coated onto the surface of the bottom layer, and then dried and sintered in sequence to form the top layer of the gradient microcrack composite coating; thus, a titanium-based metal oxide electrode with a gradient microcrack composite coating is obtained.

[0013] Furthermore, in step S3, both the bottom coating and the top coating have microcrack structures; and the density of microcrack structures on the bottom coating is lower than the density of microcrack structures on the top coating.

[0014] Furthermore, in step S2, the target metal element includes an active catalytic metal and a stable framework metal. The active catalytic metal is at least one of a compound containing ruthenium and iridium, and the stable framework metal is at least one of a compound containing titanium, tantalum, and tin.

[0015] Furthermore, the atomic ratio of the active catalytic metal to the stable framework metal is (30~70):(70~30).

[0016] Furthermore, in step S2, the total ion concentration of the target metal element in both the first precursor solution and the second precursor solution is 0.1~1.0 mol / L.

[0017] Furthermore, in step S2, when the second precursor solution is prepared using the sol-gel method, the complexing agent includes an organic acid, the crosslinking agent includes a polyol, and the molar ratio of the complexing agent to the crosslinking agent is 1:(1~5).

[0018] Furthermore, in step S3, the final sintering time for forming the surface coating is 1~2 hours.

[0019] Furthermore, in the titanium-based metal oxide electrode prepared by the method, the ratio of the total number of metal atoms in the bottom coating to the top coating is 1:(1~10).

[0020] Furthermore, in step S1, the surface pretreatment includes degreasing, polishing and acid etching; the acid etching includes immersing the titanium substrate in an 8-12 wt% oxalic acid solution at a solution temperature of 80-100°C for 1-2 hours.

[0021] This invention also discloses a gradient microcrack composite coated titanium-based metal oxide electrode, prepared by the method described above. The titanium-based metal oxide electrode comprises:

[0022] Titanium substrate, and gradient microcrack composite coating applied to the surface of titanium substrate;

[0023] Gradient microcrack composite coatings consist of a base layer and a top layer layer stacked together.

[0024] The bottom layer coating is applied directly to the surface of the titanium substrate, while the top layer coating is applied to the surface of the bottom layer coating.

[0025] Furthermore, the total thickness of the gradient microcrack composite coating is 5~50μm, the thickness of the bottom coating is 1~20μm, and the thickness of the top coating is 1~30μm.

[0026] Compared with existing technologies, the gradient microcrack composite coated titanium-based metal oxide electrode and its preparation method described in this invention have the following advantages:

[0027] (1) This invention achieves a synergistic balance between electrocatalytic activity and service life through the structural design of a gradient microcrack composite coating. The high crack density structure on the surface can significantly increase the actual electrochemical active surface area of ​​the electrode, fully expose the active sites, and ensure excellent electrocatalytic performance; the dense low crack structure at the bottom layer can effectively block the electrolyte from penetrating into the titanium substrate interface, avoid substrate passivation, and greatly extend the service life of the electrode.

[0028] (2) This invention does not require the introduction of additional functional layers and special preparation equipment. It can be prepared by conventional thermal decomposition method and sol-gel method in a step-by-step coating and sintering process. The process flow is short and the process parameters are easy to control, which effectively reduces the preparation cost and production threshold of the electrode.

[0029] (3) The bottom layer and the top layer of the gradient microcrack composite coating, as well as the composite coating and the titanium substrate, are chemically bonded by high-temperature sintering. The entire gradient microcrack composite coating is an integral structure, which avoids the risk of weak interfacial bonding and easy peeling that may be caused by introducing a heterogeneous intermediate layer, and greatly improves the service reliability of the electrode.

[0030] (4) By precisely controlling the precursor formulation of the bottom layer and the surface layer, as well as the thickness ratio during coating, the present invention can flexibly adjust the density and crack density of the gradient microcrack composite coating structure, thereby achieving on-demand customization of electrode electrocatalytic activity and stability, meeting the differentiated application needs under different working conditions, and has wide adaptability. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 An exploded view of the titanium-based metal oxide electrode with a gradient microcrack composite coating prepared in Example 1.

[0033] Figure 2 The images show the morphology of the surface coatings on the titanium-based metal oxide electrodes prepared in the examples and comparative examples; wherein, Figure 2 (a) is a morphology diagram of the surface coating prepared by thermal decomposition method; Figure 2 (b) is a morphology diagram of the surface coating prepared by the sol-gel method; Figure 2 (c) is a surface morphology diagram of the bottom layer of the gradient microcrack composite coating in Embodiment 1 of the present invention; Figure 2 (d) is a surface morphology diagram of the gradient microcrack composite coating in Example 1 of the present invention.

[0034] Figure 3 Potentiodynamic polarization curves of titanium-based metal oxide electrodes prepared for the examples and comparative examples;

[0035] Figure 4 The graph shows the change of cell voltage over time during enhanced electrolysis of the titanium-based metal oxide electrodes prepared for the examples and comparative examples.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1. Titanium substrate; 2. Gradient microcrack composite coating; 21. Undercoat; 22. Topcoat. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments. First, it should be noted that the data in the following experimental examples were obtained by the inventors through numerous experiments. Due to space limitations, only a portion of these data is shown in the specification, and those skilled in the art can understand and implement the present invention based on this data. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various modifications or alterations to the invention, and these modifications or alterations also fall within the scope of protection of this application.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0040] This invention provides a method for preparing a gradient microcrack composite coated titanium-based metal oxide electrode, comprising the following steps:

[0041] S1: Pretreatment of titanium matrix 1;

[0042] S2: Preparation of precursor solution; The first precursor solution is prepared by thermal decomposition, in which a compound containing the target metal element is dissolved in a solvent to obtain the first precursor solution; The second precursor solution is prepared by sol-gel method, in which a complexing agent and a crosslinking agent are reacted, and then a compound containing the target metal element is added. After reaction and dilution, the second precursor solution is obtained.

[0043] S3: The first precursor solution is coated onto the surface of the pretreated titanium substrate 1, and then dried and sintered in sequence to form the bottom layer coating 21 of the gradient microcrack composite coating 2; the second precursor solution is coated onto the surface of the bottom layer coating 21, and then dried and sintered in sequence to form the top layer coating 22 of the gradient microcrack composite coating 2; thereby obtaining a titanium-based metal oxide electrode with gradient microcrack composite coating 2.

[0044] The preparation method of the present invention constructs a gradient microcrack composite coating 2 with a dense bottom layer and multiple surface cracks by stepwise coating of thermally decomposable precursor and sol-gel precursor, thereby achieving a synergistic balance between high electrocatalytic activity and long service life of the electrode. Moreover, the process is simple and does not require the introduction of an intermediate layer.

[0045] It should be noted that the first precursor solution of this invention is a dedicated precursor for the bottom coating 21, and the second precursor solution is a dedicated precursor for the top coating 22. The target metal elements of the two solutions can be the same or different, and can be flexibly adjusted according to the catalytic and corrosion resistance requirements of the target operating conditions. The solvents used to prepare the first and second precursor solutions are preferably alcohol solvents, including but not limited to n-butanol, anhydrous ethanol, and isopropanol, and can be flexibly selected according to the solubility characteristics of the metal compounds.

[0046] Specifically, in step S3, both the bottom coating 21 and the top coating 22 have microcrack structures; and the density of the microcrack structure on the bottom coating 21 is lower than the density of the microcrack structure on the top coating 22.

[0047] By employing a gradient structure design with low crack density at the bottom layer and high crack density at the surface layer, the electrode's actual electrochemical active surface area is significantly increased by utilizing the abundant microcracks on the surface layer, fully exposing active sites and ensuring excellent electrocatalytic performance. On the other hand, the dense, low-crack structure at the bottom layer effectively blocks the electrolyte from penetrating into the titanium matrix 1 interface, preventing passivation of the titanium matrix 1 and significantly extending the electrode's service life, thus achieving a synergistic balance between electrode activity and stability.

[0048] More specifically, microcrack density refers to the number of microcracks per unit area on the undercoat 21 and the topcoat 22. The microcrack density of the undercoat 21 can be controlled by adjusting the concentration of the precursor from the thermal decomposition method, the number of coatings, and the sintering process. The microcrack density of the topcoat 22 can be controlled by adjusting the ratio of complexing agent to crosslinking agent in the sol-gel method, the concentration of metal ions, and the sintering conditions. The difference in microcrack density between the undercoat and the topcoat can be characterized and compared using scanning electron microscopy.

[0049] Specifically, in step S2, the target metal element includes an active catalytic metal and a stable framework metal. The active catalytic metal is at least one of a compound containing ruthenium and iridium, and the stable framework metal is at least one of a compound containing titanium, tantalum, and tin.

[0050] By combining active catalytic metals with stable framework metals, the gradient microcrack composite coating 2 is guaranteed to have excellent electrocatalytic chlorine / oxygen evolution activity. At the same time, the stable framework metal matches the thermal expansion coefficient of the titanium substrate 1, reducing the internal stress during the coating sintering process, improving the bonding force between the gradient microcrack composite coating 2 and the titanium substrate 1, and further optimizing the long-term service stability of the electrode.

[0051] More specifically, the atomic ratio of the active catalytic metal to the stable framework metal is (30~70):(70~30).

[0052] Preferably, the atomic ratio of the active catalytic metal to the stable framework metal is 30:70.

[0053] It should be noted that compounds of noble metals such as ruthenium and iridium provide excellent electrocatalytic activity, while compounds of metals such as titanium, tantalum, and tin constitute a stable framework structure, improving the corrosion resistance and bonding strength of the coating, thus jointly ensuring the overall performance of the electrode. The ratio of the total number of atoms of the active catalytic metal to the total number of atoms of the stable framework metal is the molar ratio.

[0054] Specifically, in step S2, the total ion concentration of the target metal element in both the first precursor solution and the second precursor solution is 0.1~1.0 mol / L.

[0055] By controlling the total concentration of metal ions in the precursor solution within the range of 0.1~1.0 mol / L, it is possible to ensure that a uniform and continuous coating can be formed in a single coating, avoiding the problem of the coating being too thin due to excessively low concentration and requiring repeated coatings, while also avoiding the problem of excessive internal stress and uncontrolled cracking after sintering due to excessively high concentration. This ensures the controllability of the microstructure of the gradient microcrack composite coating 2 and the batch consistency.

[0056] Preferably, the total concentration of metal ions is 0.1~0.5 mol / L.

[0057] It should be noted that if the metal ion concentration is too low, the coating will be too thin, requiring more coating cycles; if the concentration is too high, the solution viscosity will be too high, resulting in uneven coating and easily causing localized excessive thickness or cracking.

[0058] Specifically, in step S2, when the second precursor solution is prepared using the sol-gel method, the complexing agent includes organic acids, the crosslinking agent includes polyols, and the molar ratio of the complexing agent to the crosslinking agent is 1:(1~5).

[0059] A stable metal ion complex system is formed through the esterification complexation reaction of organic acid complexing agent and polyol crosslinking agent, which avoids the hydrolysis and aggregation of metal ions and ensures the long-term storage stability of the second precursor solution. At the same time, by adjusting the ratio of complexing agent to crosslinking agent, the viscosity of the sol system and the decomposition and shrinkage rate during the sintering process can be precisely controlled, thereby achieving precise control of the microcrack density of the surface coating.

[0060] Preferably, the complexing agent is citric acid, the crosslinking agent is ethylene glycol, and the molar ratio of citric acid to ethylene glycol is 1:5.

[0061] More specifically, when preparing the second precursor solution, citric acid and ethylene glycol are first mixed and heated to 60-80°C and reacted at a constant temperature for 20-40 minutes to form a homogeneous complex system. Then, a compound containing the target metal element is added, and the temperature is raised to 80-100°C to continue the reaction for 1-2 hours to ensure complete complexation of the metal ions.

[0062] It should be noted that the molar ratio of complexing agent to crosslinking agent affects the gelation rate and cleavage behavior of the second precursor solution. If the ratio is too high, the surface coating 22 will not be dense enough, while if the ratio is too low, there will be too few cracks, which is not conducive to the exposure of active sites.

[0063] Specifically, in step S3, the final sintering time for forming the surface coating 22 is 1~2 hours.

[0064] Extending the final sintering time allows the surface coating 22 to fully crystallize, enhancing its adhesion to the underlying coating 21. This also prevents the coating from becoming loose and peeling off due to insufficient sintering, thus improving the reliability of the electrode during service.

[0065] Specifically, in the titanium-based metal oxide electrode prepared by this method, the ratio of the total number of metal atoms in the bottom coating 21 to the top coating 22 is 1:(1~10).

[0066] By controlling the total atomic molar ratio of metals between the bottom coating 21 and the top coating 22 within the range of 1:(1~10), it is possible to ensure that the bottom coating 21 has sufficient thickness and density to achieve long-term barrier protection of the titanium substrate 1, and to ensure that the top coating 22 has sufficient active site loading to ensure the electrocatalytic performance of the electrode. The activity and lifespan of the electrode can be flexibly balanced by adjusting this ratio to adapt to the differentiated needs of different working conditions.

[0067] Preferably, the ratio of the total number of metal atoms in the bottom coating 21 to the top coating 22 is 1:(3~6).

[0068] Specifically, in step S1, the surface pretreatment includes degreasing, grinding and polishing, and acid etching. The acid etching includes immersing the titanium substrate 1 in an 8-12 wt% oxalic acid solution at a solution temperature of 80-100°C for 1-2 hours.

[0069] The three-step pretreatment process of "degreasing, grinding and polishing, and acid etching" can completely remove oil stains, processing defects and native oxide film from the surface of the titanium substrate 1. At the same time, it forms a uniform micro-rough morphology on the surface of the titanium substrate 1, which greatly improves the mechanical bonding force and chemical bonding force between the coating and the titanium substrate 1, avoids the coating from peeling off during sintering and service, and further extends the service life of the electrode.

[0070] This invention also provides a gradient microcrack composite coated titanium-based metal oxide electrode, prepared using the above-described method, comprising:

[0071] Titanium substrate 1, and gradient microcrack composite coating 2 coated on the surface of titanium substrate 1;

[0072] The gradient microcrack composite coating 2 includes a bottom coating 21 and a top coating 22 stacked together;

[0073] The bottom coating 21 is directly coated on the surface of the titanium substrate 1, and the top coating 22 is coated on the surface of the bottom coating 21.

[0074] The titanium-based metal oxide electrode of the present invention, through the structural design of gradient microcrack composite coating 2, can simultaneously possess excellent electrocatalytic activity and ultra-long service life without the introduction of an additional intermediate layer. It is suitable for a variety of electrochemical engineering scenarios such as chlor-alkali industry, seawater electrolysis to produce chlorine, impressed current cathodic protection, electrochemical oxidation, and sewage treatment, and has a wide range of applications.

[0075] More specifically, the total thickness of the gradient microcrack composite coating 2 is 5~50μm, the thickness of the bottom coating 21 is 1~20μm, and the thickness of the top coating 22 is 1~30μm.

[0076] It should be noted that the bottom coating 21 and the titanium substrate 1, as well as the bottom coating 21 and the top coating 22, are chemically bonded through high-temperature sintering, with no obvious interface delamination. The coating structure has strong integrity and excellent adhesion. The total thickness and layer thickness distribution of the gradient microcrack composite coating 2 can be optimized according to the electrode's operating conditions.

[0077] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0078] Example 1

[0079] This embodiment provides a method for preparing a gradient microcrack composite coated titanium-based metal oxide electrode. For example... Figure 1 As shown, the titanium-based metal oxide (Ti / RuO2-IrO2-TiO2) electrode comprises: a titanium substrate 1 and a gradient microcrack composite coating 2 coated thereon; its preparation method includes:

[0080] S1: Pretreatment of titanium matrix 1

[0081] TA2 titanium was selected as the titanium substrate 1. First, the surface of the titanium substrate 1 was degreased by hot alkaline water cleaning or ultrasonic degreasing with organic solvent. Then, the surface of the degreased titanium substrate 1 was mechanically ground and polished to remove surface processing defects. Next, the polished titanium substrate 1 was immersed in an 8~12wt% oxalic acid solution at a temperature of 90℃ for 2 hours to further remove the surface oxide film and form a uniform and rough microstructure on the surface of the titanium substrate 1. After the etching was completed, the substrate was removed, rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0082] S2: Preparation of precursor solution

[0083] S21: Preparation of the underlying precursor solution

[0084] The bottom precursor solution was prepared by thermal decomposition. Ruthenium trichloride, chloroiridium acid, and tetrabutyl titanate were added to n-butanol solvent according to the atomic ratio of ruthenium (Ru):iridium (Ir):titanium (Ti) = 15:15:70. The mixture was stirred until completely dissolved, and then n-butanol solvent was added to prepare a bottom precursor solution with a total metal ion concentration of 0.1 mol / L. The solution was then allowed to stand before use.

[0085] S22: Preparation of surface precursor solution

[0086] The surface precursor solution was prepared using the sol-gel method. Citric acid and ethylene glycol were added to a reaction vessel at a molar ratio of 1:5, heated to 65°C, and stirred at a constant temperature for 30 min to obtain a homogeneous complex system. Subsequently, ruthenium trichloride, chloroiridic acid, and titanium tetrachloride were added to the system according to an atomic ratio of Ru:Ir:Ti = 15:15:70, and the ratio of ethylene glycol:citric acid:total metal atoms was controlled at 14:3:1. The temperature was then raised to 90°C, and the reaction was continued with stirring at a constant temperature for 1.5 h. After the reaction solution cooled naturally to room temperature, it was diluted with n-butanol to adjust the total metal ion concentration in the system to 0.50 mol / L, thus obtaining a stable surface precursor solution.

[0087] S3: Coating and sintering of gradient microcrack composite coating 2

[0088] The bottom precursor solution prepared in step S21 is uniformly coated onto the surface of the pretreated titanium substrate 1. The solvent is first removed by low-temperature drying, and then sintered in a high-temperature environment to form a bottom coating 21 on the surface of the titanium substrate 1. Based on the bottom coating 21, the surface precursor solution prepared in step S22 is uniformly coated onto the surface of the bottom coating 21. The solvent is first removed by low-temperature drying, and then sintered in a high-temperature environment to form a surface coating 22. The final sintering time is 1 hour, and the ratio of the total molar number of metal atoms in the bottom layer to the surface layer is 1:4. After sintering, the substrate is cooled to room temperature in the furnace to obtain a titanium-based metal oxide electrode with a gradient microcrack composite coating 2, namely a Ti / RuO2-IrO2-TiO2 electrode.

[0089] Comparative Example 1

[0090] This comparative example uses the same titanium substrate 1 pretreatment process, bottom precursor solution formulation and coating sintering process as Example 1. The only difference is that only the thermal decomposition method is used to prepare a titanium-based metal oxide electrode with a single coating structure, and no surface coating 22 is prepared. The total number of molar metal atoms in the final electrode coating is the same as the total number of molar metal atoms in Example 1.

[0091] Comparative Example 2

[0092] This comparative example uses the same titanium substrate 1 pretreatment process, surface precursor solution formulation and coating sintering process as Example 1. The only difference is that only the sol-gel method is used to prepare a titanium-based metal oxide electrode with a single coating structure, and no bottom coating 21 is prepared. The total number of molar metal atoms in the final electrode coating is the same as the total number of molar metal atoms in Example 1.

[0093] The titanium-based metal oxide electrodes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were characterized in morphology and tested in electrochemical performance. The specific procedures are as follows:

[0094] 1. Surface morphology characterization

[0095] The surface morphology of the coatings on the three types of electrodes was observed using a scanning electron microscope, and the results are as follows: Figure 2 As shown.

[0096] in, Figure 2 (a) is a surface morphology diagram of a single coating prepared by thermal decomposition method in Comparative Example 1. The coating has few cracks and a dense structure. Figure 2 (b) is a surface morphology image of a single coating prepared by the sol-gel method in Comparative Example 2. It can be seen that the coating is relatively loose and has many cracks. Figure 2 (c) is a surface morphology diagram of the bottom layer of the gradient microcrack composite coating 2 in Example 1. It can be seen that the bottom coating 21 has a dense structure and low microcrack density. Figure 2 (d) is a surface morphology diagram of the gradient microcrack composite coating 2 in Example 2. It can be seen that the surface coating 22 forms a high-density network microcrack structure with many cracks and a relatively loose coating.

[0097] The above morphological characterization results demonstrate that the present invention has successfully constructed a gradient microcrack composite coating 2 with a dense, low-crack bottom layer and a high-crack-density surface layer.

[0098] 2. Electrocatalytic performance testing

[0099] The electrocatalytic chlorine evolution performance of the three electrodes was tested using potentiodynamic polarization curves. The test system was a three-electrode system, with the electrode under test as the working electrode, a platinum sheet as the auxiliary electrode, and a saturated calomel electrode (SCE) as the reference electrode. The test solution was 3.5% NaCl solution, the scan rate was 0.33 mV / s, and the scan potential range was 1.0 V–2.0 V (vs. SCE). The test results are as follows: Figure 3 As shown.

[0100] Depend on Figure 3 The potentiodynamic polarization curves show that the electrode prepared by the single thermal decomposition method in Comparative Example 1 has the lowest chlorine evolution catalytic activity. The electrode with gradient microcrack composite coating 2 prepared in Example 1 and the electrode prepared by the single sol-gel method in Comparative Example 2 have basically the same electrocatalytic performance, both showing excellent electrocatalytic activity. This indicates that the high-density microcrack network on the surface constructed by the sol-gel method in this invention successfully exposes a sufficient number of electrochemical active sites, so that the electrode with gradient microcrack composite coating 2 achieves the same excellent level of chlorine evolution catalytic activity as the pure sol-gel method electrode, without sacrificing its electrocatalytic performance due to the presence of the dense underlying structure.

[0101] 3. Enhanced electrolytic life test

[0102] Accelerated life testing was used to assess the service stability and lifespan of the three electrodes described above. The test conditions were as follows: 1 mol / L sulfuric acid solution as the electrolyte, and a current density of 0.5 A / cm². 2 The metal oxide electrode under test was used as the working electrode, and the titanium plate was used as the cathode. The distance between the working electrode and the cathode was 2 cm. The criterion for electrode failure was an increase of 10V in the cell voltage compared to the initial value. The cell voltage change curve over time during the test is shown in the figure below. Figure 4 As shown.

[0103] Depend on Figure 4 It can be seen that the electrode prepared by the single sol-gel method in Comparative Example 2 has the shortest enhanced electrolysis life and the worst service stability. The electrode with gradient microcrack composite coating 2 prepared in Example 1 and the electrode prepared by the single thermal decomposition method in Comparative Example 1 have basically the same enhanced electrolysis life, both showing excellent service stability and long service life. This indicates that the dense low-crack structure of the bottom layer constructed by the thermal decomposition method in this invention effectively blocks the penetration of electrolyte into the titanium substrate 1, so that the gradient microcrack composite coating electrode achieves the same excellent level of enhanced electrolysis life as the electrode prepared by the pure thermal decomposition method, and its service life is not shortened due to the presence of the high crack structure on the surface.

[0104] In summary, this invention, through the design of a gradient microcrack composite coating 2 with a dense, low-crack bottom layer and a high-crack-density surface layer, overcomes the technical constraint of the prior art that it is difficult to achieve both "high electrocatalytic activity" and "long service life" in titanium-based metal oxide electrodes. Without introducing an additional intermediate layer or adding complex preparation processes, it simultaneously achieves high electrocatalytic activity and long service life of the electrode.

[0105] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a gradient microcrack composite coated titanium-based metal oxide electrode, characterized in that, Includes the following steps: S1: Pretreatment of the titanium matrix (1); S2: Preparation of precursor solution; The first precursor solution is prepared by thermal decomposition method, in which a compound containing the target metal element is dissolved in a solvent to obtain the first precursor solution; The second precursor solution is prepared by sol-gel method, in which a complexing agent and a crosslinking agent are reacted, and a compound containing the target metal element is added, and the second precursor solution is obtained after reaction and dilution. S3: The first precursor solution is coated onto the surface of the pretreated titanium substrate (1), and then dried and sintered in sequence to form the bottom layer coating (21) of the gradient microcrack composite coating (2); the second precursor solution is coated onto the surface of the bottom layer coating (21), and then dried and sintered in sequence to form the top layer coating (22) of the gradient microcrack composite coating (2); thus, a titanium-based metal oxide electrode with gradient microcrack composite coating (2) is obtained.

2. The preparation method according to claim 1, characterized in that, In step S3, both the bottom coating (21) and the top coating (22) have microcrack structures; and the density of the microcrack structure on the bottom coating (21) is lower than the density of the microcrack structure on the top coating (22).

3. The preparation method according to claim 1, characterized in that, In step S2, the target metal element includes an active catalytic metal and a stable framework metal. The active catalytic metal is at least one of a compound containing ruthenium and iridium, and the stable framework metal is at least one of a compound containing titanium, tantalum, and tin.

4. The preparation method according to claim 3, characterized in that, The atomic ratio of the active catalytic metal to the stable framework metal is (30~70):(70~30).

5. The preparation method according to claim 1, characterized in that, In step S2, the total ion concentration of the target metal element in both the first precursor solution and the second precursor solution is 0.1~1.0 mol / L.

6. The preparation method according to claim 1, characterized in that, In step S2, when the second precursor solution is prepared using the sol-gel method, the complexing agent includes an organic acid, the crosslinking agent includes a polyol, and the molar ratio of the complexing agent to the crosslinking agent is 1:(1~5).

7. The preparation method according to claim 1, characterized in that, In step S3, the final sintering time for forming the surface coating (22) is 1-2 hours.

8. The preparation method according to claim 1, characterized in that, In the titanium-based metal oxide electrode prepared by the method, the ratio of the total number of metal atoms in the bottom coating (21) to the total number of metal atoms in the top coating (22) is 1:(1~10).

9. The preparation method according to claim 1, characterized in that, In step S1, the surface pretreatment includes degreasing, polishing and acid etching; the acid etching includes immersing the titanium substrate (1) in an 8-12 wt% oxalic acid solution at a solution temperature of 80-100°C for 1-2 hours.

10. A gradient microcrack composite coated titanium-based metal oxide electrode, characterized in that, The titanium-based metal oxide electrode, prepared by any one of claims 1 to 9, comprises: Titanium substrate (1), and gradient microcrack composite coating (2) coated on the surface of the titanium substrate (1). The gradient microcrack composite coating (2) includes a bottom coating (21) and a top coating (22) stacked together. The bottom coating (21) is directly coated on the surface of the titanium substrate (1), and the top coating (22) is coated on the surface of the bottom coating (21).

11. The titanium-based metal oxide electrode according to claim 10, characterized in that, The total thickness of the gradient microcrack composite coating (2) is 5~50μm, the thickness of the bottom coating (21) is 1~20μm, and the thickness of the top coating (22) is 1~30μm.

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