An electrode and a method of manufacturing the same

Abstract

The application provides an electrode and a preparation method, the electrode comprises, from bottom to top, a substrate, an intermediate layer and a coating layer, the substrate is made of titanium, the intermediate layer is made of tantalum oxide, and the coating layer is made of metal oxide; the intermediate layer is obtained by calcining a tantalum-containing precursor solution coated on the substrate, and the tantalum-containing precursor solution is prepared by a polyvinylpyrrolidone-assisted sol-gel method. The preparation method of the electrode comprises the following steps: (1) performing surface pretreatment on the substrate; (2) preparing the intermediate layer by using the polyvinylpyrrolidone-assisted sol-gel method; and (3) preparing the coating layer by using a thermal decomposition method to obtain the target electrode. The polyvinylpyrrolidone-assisted sol-gel method is used to prepare the tantalum oxide intermediate layer, and the catalytic activity and service life of the electrode under harsh working conditions such as strong acid and high current density are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and more specifically, to an electrode and its preparation method. Background Technology

[0002] Titanium-based metal oxide electrodes are core electrode materials in the field of electrochemistry. They are prepared by creating a mixed metal oxide coating based on RuO2, IrO2, SnO2, Ta2O5, etc., on the surface of a titanium substrate. Depending on the coating composition, they can be widely used in electrochemical engineering applications such as electrolytic copper production, high-speed electroplating, electrolytic seawater chlorination, impressed current cathodic protection, electrochemical oxidation, wastewater treatment, and the chlor-alkali industry. They are among the most commercially mature electrode materials currently available. However, conventional titanium-based metal oxide electrodes are prone to rapid failure in actual operation, especially under harsh conditions such as strongly acidic environments and high current densities, resulting in a service life that fails to meet practical engineering requirements. Research has revealed that the core reason for electrode failure is the gradual dissolution of the active components in the coating during electrolysis, leading to the titanium substrate being exposed to the electrolyte solution and continuously oxidized to form a TiO2 passivation layer. The rupture of this passivation layer directly triggers electrode failure. To address this critical issue, adding an intermediate layer between the titanium substrate and the active coating has become an effective technical approach to extend the service life of titanium-based metal oxide electrodes.

[0003] Patent application number 201110044764.7 discloses a method for preparing a metal oxide electrode containing a tantalum interlayer. First, a tantalum-containing interlayer is prepared on a titanium substrate using a thermal decomposition method. Then, a mixed metal oxide electrocatalytic coating is prepared on the tantalum-containing interlayer. The tantalum-containing interlayer provides better protection for the titanium substrate, delaying passivation, improving the stability of the oxide electrode, and extending its service life. However, the thermal decomposition method easily generates a large number of surface cracks during the preparation process, affecting the growth and distribution of the surface electrocatalytic coating. Patent application number 201310153286.2 discloses a method for preparing a metal oxide anode containing a cold-sprayed tantalum interlayer. It uses a cold-spray method to prepare the tantalum interlayer on the surface of a pretreated titanium substrate. The prepared electrode has high current density, high breakdown potential, and good stability. However, its cold-spray process suffers from significant waste of tantalum powder raw materials, and the interfacial bonding between the prepared tantalum interlayer and the titanium substrate and surface electrocatalytic coating is insufficient, making it prone to interlayer delamination during long-term electrolysis and failing to achieve a sustained improvement in lifespan. These tantalum-containing intermediate metal oxide electrodes, prepared using different methods, have shown significant improvements in performance, especially in electrode lifespan. However, they have not yet solved the industry technical problem of existing titanium-based metal oxide electrodes being unable to achieve both longevity and catalytic activity under harsh operating conditions.

[0004] Therefore, there is an urgent need for an electrode that can simultaneously improve electrocatalytic activity and lifespan under harsh conditions such as strong acid and high current density. Summary of the Invention

[0005] In view of this, the present invention aims to provide an electrode that can simultaneously improve electrocatalytic activity and lifespan under harsh conditions such as strong acid and high current density, so as to solve the problems in the prior art.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] The present invention provides an electrode comprising a substrate, an intermediate layer, and a coating layer arranged sequentially from bottom to top. The substrate is made of titanium, the intermediate layer is tantalum oxide, and the coating layer is a metal oxide. The intermediate layer is obtained by calcining a tantalum-containing precursor solution coated on the substrate. The tantalum-containing precursor solution is prepared by a polyvinylpyrrolidone-assisted sol-gel method.

[0008] In this invention, the intermediate layer is a dense, crack-free tantalum oxide film layer, which can effectively block the diffusion of active oxygen, chloride ions, and electrolyte to the titanium substrate under harsh conditions such as strong acid and high current density, thus preventing the titanium substrate from being oxidized and causing electrode deactivation. In addition, the titanium surface is easy to form a micro-rough structure through chemical etching, and Ti-O-Ta chemical bonding is formed after calcination, which significantly improves the interlayer bonding force and prevents the coating from falling off.

[0009] Furthermore, the intermediate layer is amorphous tantalum oxide.

[0010] In this invention, the tantalum oxide includes one or more of TaO, Ta3O2, Ta2O, and Ta2O5.

[0011] In this invention, amorphous tantalum oxide exhibits good electrical conductivity and low resistivity (typically 10). 6 ~10 10 (Ω・cm), can be used as the intermediate layer of the electrode to conduct current without increasing the internal resistance of the electrode.

[0012] In this invention, the thickness of the intermediate layer is preferably 200 nm to 2 μm, and the surface is free of obvious cracks.

[0013] Furthermore, the metal oxide includes noble metal oxides and / or non-noble metal oxides.

[0014] In this invention, the metal oxide is an electrochemical oxygen evolution or chlorine evolution catalyst. This invention can significantly reduce the overpotential of the electrocatalytic reaction and improve the current efficiency by adjusting the coating composition, thereby adapting to the working conditions of different electrolysis systems such as chlor-alkali, electroplating, sewage treatment, and electrolytic hydrogen production.

[0015] Furthermore, the noble metal oxide is selected from one or more of iridium oxide, ruthenium oxide, and platinum oxide; the non-noble metal oxide is selected from one or more of tantalum oxide, tin oxide, silicon oxide, manganese oxide, and zirconium oxide.

[0016] In this invention, the metal oxide preferably includes noble metal oxide and non-noble metal oxide; the noble metal oxide is preferably iridium oxide, more preferably iridium dioxide, and the non-noble metal oxide is preferably tantalum oxide, more preferably tantalum pentoxide.

[0017] The present invention also provides a method for preparing the electrode described in the above technical solution, comprising the following steps:

[0018] Step (1): Pre-treat the substrate to remove oil and oxide film and form a rough surface;

[0019] Step (2): A tantalum precursor solution was prepared by polyvinylpyrrolidone-assisted sol-gel method. The tantalum precursor solution was coated onto a substrate that had undergone surface pretreatment and then calcined to obtain an intermediate layer.

[0020] Step (3): Prepare a metal oxide precursor solution and use a thermal decomposition method to generate a coating on the surface of the intermediate layer to obtain the electrode.

[0021] In this invention, the intermediate layer is tantalum oxide. On one hand, the physicochemical structure of the tantalum oxide intermediate layer can regulate the dispersion and crystallization behavior of active particles in the surface mixed metal oxide coating, providing uniform nucleation sites for the active components, inhibiting excessive growth of active grains, making the distribution of active components more uniform and the grain size smaller, thereby effectively increasing the number of electrocatalytic active sites and improving the electrocatalytic activity of the electrode. On the other hand, the dense tantalum oxide intermediate layer can serve as a highly efficient barrier layer, effectively preventing the diffusion of active oxygen generated during electrocatalysis to the titanium substrate, avoiding the oxidation of the titanium substrate to form a high-resistivity TiO2 passivation layer, delaying the passivation of the titanium substrate, and significantly extending the service life of the metal oxide anode.

[0022] Furthermore, the specific steps of step (2) are as follows:

[0023] Step S1: Preparation of tantalum precursor solution

[0024] First, polyvinylpyrrolidone is dissolved in an alcohol solvent and stirred to obtain solution A; then tantalum alkoxide and alcohol solvent are mixed to obtain solution B; solution B is slowly added dropwise to solution A, with continuous stirring and simultaneous heating during the dropwise addition. After the dropwise addition is completed, the temperature is kept constant. After the temperature is kept constant, glacial acetic acid is added to obtain the tantalum precursor solution.

[0025] Step S2: Generate an intermediate layer on the pretreated substrate surface

[0026] The tantalum precursor solution is coated onto a pretreated substrate and calcined. After calcination, the substrate is kept at a temperature of 10-30 min. The coating and calcination operations are repeated multiple times. After the last calcination, the substrate is kept at a temperature of 1-2 h to obtain the intermediate layer.

[0027] In this invention, polyvinylpyrrolidone is present as a stabilizer.

[0028] During the calcination process in step S2, the tantalum-containing precursor undergoes solvent evaporation, condensation reaction, and decomposition of organometallic compounds in sequence. The condensation reaction is a key factor leading to crack formation in the film: during condensation, the interlayer shrinks towards the substrate, while the titanium substrate does not shrink accordingly, resulting in tensile stress within the interlayer. When this tensile stress exceeds the film's tolerance limit, cracks will initiate and propagate. This invention introduces polyvinylpyrrolidone (PVP) into the tantalum-containing precursor solution, utilizing its long-chain polymer structure to construct an organic-inorganic hybrid network during the sol-gel transformation process. This delays excessive condensation of the inorganic components and reduces the shrinkage rate. Simultaneously, PVP can completely decompose and volatilize at high temperatures without residue, providing structural relaxation space for the film and effectively dissipating internal stress, thereby fundamentally inhibiting the initiation and propagation of interlayer cracks.

[0029] Furthermore, in step S2, the tantalum precursor solution is coated onto the surface of the pretreated substrate and then calcined in an inert atmosphere.

[0030] In this invention, the inert atmosphere is preferably nitrogen, which can effectively isolate oxygen in the air and prevent the titanium substrate from being excessively oxidized at medium and high temperatures to form a TiO2 passivation layer.

[0031] In this invention, it is preferred to apply the tantalum precursor solution to the surface of the substrate after surface pretreatment by brushing or spraying.

[0032] Furthermore, in step S2, the calcination temperature is 400~600℃, and the heating rate to the calcination temperature is 5~7℃ / min.

[0033] In this invention, the calcination temperature is preferably 450~550℃, more preferably 500℃, the heating rate to the calcination temperature is preferably 5~6℃ / min, more preferably 5.5℃ / min, the holding time after calcination is preferably 15min, and the holding time after the last calcination is preferably 1h.

[0034] In step S2 of this invention, if the calcination temperature is too high, the amorphous tantalum oxide will undergo a crystallization transformation, forming a high-resistivity crystalline tantalum oxide, causing the intermediate layer to lose its conductivity. At the same time, the thermal stress caused by the high temperature increases, which can easily cause the film to crack and reduce its adhesion to the substrate. If the calcination temperature is too low, the precursor will not decompose completely and the organic residues cannot be fully removed, resulting in a decrease in the density of the intermediate layer and a decrease in conductivity, making it difficult to form a stable amorphous tantalum oxide structure. In addition, if the heating rate is too fast, the solvent evaporation and organic component decomposition will be too violent, which can easily cause the film to blister, pinhole, or even locally peel off, making it impossible to form a continuous and dense amorphous tantalum oxide intermediate layer. If the heating rate is too low, the solvent will evaporate too slowly and the organic matter will decompose for too long, making the film prone to excessive shrinkage.

[0035] The present invention employs a repeated coating-calcination operation, in which calcination is performed immediately after each coating of tantalum oxide precursor, and this process is repeated multiple times until the target film thickness is achieved. Compared with directly performing multiple coatings and then calcination (i.e., performing only one overall calcination after multiple coatings), this method can effectively avoid the film layer becoming too thick after multiple coatings, which would prevent the large amount of gas generated during subsequent calcination from being discharged in time, thus causing defects such as blistering, cracking, and peeling of the film layer.

[0036] Furthermore, in step S3, preferably after coating the metal oxide precursor solution onto the surface of the intermediate layer, the coating, drying, calcining, and cooling processes are repeated several times until the coating reaches the predetermined loading to obtain the target electrode.

[0037] The precursor solution is preferably a mixture of a metal salt and an alcohol solution. The metal salt is preferably one or more of iridium salt, ruthenium salt, platinum salt, tantalum salt, tin salt, manganese salt, and zirconium salt, with a concentration of 0.1~1 mol / L. The drying temperature is 80~120℃, the drying time is 8~15 min, the calcination temperature is 400~600℃, the calcination is followed by a holding time of 10~20 min, and the final calcination is followed by a holding time of 1~2 h.

[0038] Furthermore, in step S1, after heating to 80℃~100℃, the temperature is kept for 10~30 minutes. After the temperature is kept, 0.5~2 ml of glacial acetic acid is added.

[0039] In this invention, glacial acetic acid is added to inhibit the rapid hydrolysis and self-polymerization of tantalum alkoxide and prevent precipitation and stratification of the precursor solution.

[0040] Furthermore, in step S1, the ratio of polyvinylpyrrolidone to alcohol solvent in solution A is 0~5g:10~100ml, and the amount of polyvinylpyrrolidone used is not 0; the ratio of tantalum alkoxide to alcohol solvent in solution B is 1~5ml:2~10ml.

[0041] In this invention, the ratio of tantalum alkoxide to polyvinylpyrrolidone is preferably 5~40 ml: 1 g.

[0042] In this invention, the alcohol solvent is preferably ethanol, the tantalum alkoxide is preferably tantalum ethoxide, and the ratio of tantalum ethoxide to polyvinylpyrrolidone is preferably 15-30 ml: 1 g, more preferably 20 ml: 1 g.

[0043] In this invention, the molecular weight of the polyvinylpyrrolidone is preferably 1 × 10⁻⁶. 6 ~2×10 6 More preferably 1.3×10 6 .

[0044] In this invention, if the amount of polyvinylpyrrolidone is too low, it cannot effectively suppress the violent shrinkage caused by the condensation reaction, and it is difficult to avoid the formation of cracks in the film layer; if the amount is too high, it will lead to excessive viscosity of the tantalum precursor solution, resulting in excessive coating thickness and increased internal stress, which will also easily cause film layer cracking.

[0045] Furthermore, the specific steps for surface pretreatment of the substrate in step (1) are as follows: after removing oil stains from the substrate, mechanical grinding and polishing are performed, and then oxalic acid solution with a mass fraction of 10~20% is used to etch the substrate at 75℃~95℃ for 1~2 hours to remove the oxide film on the substrate surface and obtain a uniform and rough surface.

[0046] In this invention, after the titanium substrate is roughened by oxalic acid etching, a porous structure is formed on the surface. The coated tantalum oxide intermediate layer can be embedded in this porous structure. In addition, a small number of Ta-O-Ti chemical bonds can also be formed between the tantalum oxide intermediate layer and the titanium substrate, further strengthening the interfacial bonding strength.

[0047] The electrode described in this invention can be widely used in various electrochemical engineering fields, including but not limited to electrolytic chlorine production, chlor-alkali industry, electroplating (such as nickel / chromium plating), and wastewater treatment.

[0048] Compared with existing technologies, the electrode and its preparation method described in this invention have the following advantages:

[0049] (1) The present invention uses amorphous tantalum oxide as an intermediate layer, which has better conductivity than crystalline tantalum oxide. It can not only ensure the overall conductivity of the electrode, but also effectively block the diffusion of active oxygen generated during electrocatalysis to the titanium matrix, delay the passivation of the titanium matrix, and significantly extend the service life of the electrode. At the same time, the tantalum oxide intermediate layer can also optimize the dispersion and grain size of surface active components, increase the number of active sites and improve their utilization rate, thereby significantly improving the electrocatalytic activity and current efficiency of the electrode.

[0050] (2) By introducing polyvinylpyrrolidone as a film-forming stabilizer, the present invention constructs an organic-inorganic hybrid network during the sol-gel conversion process, which can delay the excessive condensation of inorganic components and effectively dissipate the internal stress of the film layer, thereby inhibiting the initiation and propagation of intermediate layer cracks from the root, and finally obtaining a continuous and dense amorphous tantalum oxide film.

[0051] (3) The present invention roughens the titanium substrate by oxalic acid etching, so that a porous structure is formed on the substrate surface. After the tantalum oxide intermediate layer is coated, it can be embedded in the porous structure and form a mechanical interlocking effect with the titanium substrate. At the same time, Ta-O-Ti chemical bonds can be formed between the two, which greatly improves the interfacial bonding strength, ensures that the intermediate layer is not easy to fall off, and further ensures the stability of the electrode structure. Attached Figure Description

[0052] 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:

[0053] Figure 1 Figure 1 shows the surface morphology of the intermediate layer prepared in Example 1 and Comparative Example 2 of the present invention. Figure 2(a) shows the intermediate layer obtained in Comparative Example 2 and Figure 2(b) shows the intermediate layer obtained in Example 1.

[0054] Figure 2 The cross-sectional morphology and elemental distribution diagram of the electrode prepared in Example 1 of this invention are shown below.

[0055] Figure 3 This is a comparison chart of the electrocatalytic performance of electrodes obtained in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0056] Figure 4 This is a comparison chart of the electrochemical stability of electrodes obtained in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention under a strongly acidic environment. Detailed Implementation

[0057] 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.

[0058] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0059] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0060] While there are reports in the prior art of preparing crack-free tantalum-based oxide films using the polyvinylpyrrolidone-assisted sol-gel method, these methods typically involve high-temperature calcination at 900℃, resulting in crystalline films with poor conductivity, large thickness, and difficulty in controlling the thickness. Furthermore, the high-temperature calcined films have a large difference in thermal expansion coefficients compared to the titanium substrate, leading to weak interlayer bonding. Consequently, they cannot be used as intermediate layers for titanium-based metal oxide electrodes in harsh conditions involving strong acids and high current densities. Therefore, there is an urgent need for a method to prepare crack-free tantalum-based intermediate layers suitable for titanium-based metal oxide electrodes.

[0061] It should be noted that in the following embodiments, the substrate is a pure titanium plate of type TA2, the coating is a mixed metal oxide composed of iridium oxide and tantalum oxide, the ratio of polyvinylpyrrolidone to tantalum ethoxide is 20 ml: 0.1 g, and the molecular weight of polyvinylpyrrolidone is 1.3 × 10⁻⁶. 6 It is also known as PVP.

[0062] Example 1

[0063] A method for preparing an electrode includes the following steps:

[0064] Step (1): Immerse the TA2 pure titanium plate in a 1M NaOH solution and treat it at 90℃ for 1h to remove surface oil stains; then place it in a 10wt% oxalic acid solution and etch it at 80℃ for 2h to form a micro-rough structure on the surface; finally, repeatedly clean the titanium plate with deionized water and anhydrous ethanol until the cleaning solution is neutral and free of obvious impurities, and place it in anhydrous ethanol for later use.

[0065] Step (2): Dissolve 0.1g PVP in 5mL anhydrous ethanol and stir continuously until homogeneous to obtain solution A; mix 2mL tantalum ethoxide with 3mL ethanol to obtain solution B. Under continuous stirring, slowly add solution B to solution A, heating simultaneously during the addition; after the addition is complete, keep warm at 90℃ for 15min, then add 1mL glacial acetic acid to stabilize the system to obtain a tantalum precursor solution; coat the above precursor solution onto the surface of the pretreated substrate with a brush, then place the sample in a tube furnace under a nitrogen atmosphere of 99.99wt% purity, heat from room temperature to 500℃ at a heating rate of 5℃ / min and keep warm for 15min; repeat the above coating-calcination operation three times, and keep warm for 1h after the last calcination to obtain an intermediate layer with a thickness of about 1μm.

[0066] Step (3): First, chloroiridic acid and tantalum pentachloride are dissolved in a mixed solution of n-butanol and hydrochloric acid at a molar ratio of 7:3 (hydrochloric acid mass fraction is 37%, and the volume ratio of n-butanol and hydrochloric acid is 90:1). The solution is stirred continuously for 3 minutes to prepare a metal oxide precursor solution with a concentration of 0.3 mol / L. Then, the above metal oxide precursor solution is brushed onto the surface of the intermediate layer, dried at 120℃ for 10 minutes, and then calcined at 500℃ for 15 minutes. After removal, it is naturally cooled to room temperature. The above brushing, drying, calcination and cooling operations are repeated 5-7 times. After the last calcination, the temperature is maintained for 1 hour to obtain an electrode with a thickness of about 3 μm, in which the metal oxide loading is 7 g / m. 2 .

[0067] Example 2

[0068] Except for the heating rates being set to 1℃ / min, 3℃ / min, 7℃ / min, and 10℃ / min respectively, the rest of the preparation process was the same as steps (1) and (2) in Example 1. The surface morphology of the intermediate layer of each sample was observed using a scanning electron microscope, and the density was statistically analyzed. The results are shown in Table 1 below:

[0069] Table 1 Effect of heating rate on the surface morphology of tantalum oxide interlayer

[0070] heating rate 1℃ / min 3℃ / min 5℃ / min 7℃ / min 10℃ / min Intermediate layer surface morphology characteristics There are obvious microcracks and the structure is loose. The number of cracks has decreased, but traces of shrinkage are still visible in some areas. The surface is smooth and dense, without cracks or pinholes. The surface is smooth and dense, without cracks or pinholes. Bubbling and hole defects appear

[0071] In existing sol-gel systems, since the precursor does not contain polymeric additives, the film density typically increases gradually with decreasing heating rate. However, this invention uses a polyvinylpyrrolidone (PVP)-assisted sol-gel method to prepare the tantalum oxide interlayer. There is a significant difference between the heating rate and the film density in this method: if the heating rate is too low, the polymeric components such as PVP remain in the film for too long, leading to excessive condensation of inorganic components, significantly increasing internal stress and generating microcracks, ultimately resulting in decreased density. If the heating rate is too high, the solvent and organic components rapidly volatilize and decompose, and a large amount of gas cannot be discharged in time, easily causing defects such as blistering and pinholes in the film, also reducing density. Therefore, only by selecting an appropriate heating rate can PVP fully exert its film-stabilizing effect, effectively dissipating internal stress, and thus obtaining an amorphous tantalum oxide interlayer with optimal density and no obvious defects.

[0072] Comparative Example 1

[0073] A method for fabricating a bilayer electrode without an intermediate layer includes the following steps:

[0074] Step (1): After sandblasting the TA2 titanium plate, treat it with 1M NaOH solution at 90℃ for 1h to remove surface oil stains; then immerse it in boiling 10wt% oxalic acid solution for 2h to remove the passivation film on the surface and obtain a uniform rough surface; finally, repeatedly clean the titanium plate with deionized water and anhydrous ethanol until the cleaning solution is neutral and free of obvious impurities, and place it in anhydrous ethanol for later use.

[0075] Step (2): First, chloroiridic acid and tantalum pentachloride are dissolved in a mixed solution of n-butanol and hydrochloric acid at a molar ratio of 7:3 (hydrochloric acid mass fraction is 37%, and the volume ratio of n-butanol to hydrochloric acid is 90:1). The solution is stirred continuously for 3 minutes to prepare a metal oxide precursor solution with a concentration of 0.3 mol / L. Then, the above metal oxide precursor solution is brushed onto the substrate surface, dried at 120℃ for 10 minutes, and then calcined at 500℃ for 15 minutes. After removal, it is naturally cooled to room temperature. The above brushing, drying, calcination and cooling operations are repeated 5-7 times. After the last calcination, the temperature is maintained for 1 hour to obtain an electrode with a thickness of about 3 μm, in which the metal oxide loading is 7 g / m. 2 .

[0076] Comparative Example 2

[0077] A method for preparing an electrode without PVP assistance includes the following steps:

[0078] Step (1): Immerse the TA2 pure titanium plate in a 1M NaOH solution and treat it at 90℃ for 1h to remove surface oil stains; then place it in a 10wt% oxalic acid solution and etch it at 80℃ for 2h to form a micro-rough structure on the surface; finally, repeatedly clean the titanium plate with deionized water and anhydrous ethanol until the cleaning solution is neutral and free of obvious impurities, and place it in anhydrous ethanol for later use.

[0079] Step (2): Mix 2 mL of tantalum ethoxide with 3 mL of ethanol and stir continuously until homogeneous and transparent to obtain a tantalum precursor solution without polyvinylpyrrolidone. Apply the above precursor solution to the surface of the pretreated substrate with a brush, and then place the sample in a tube furnace under a nitrogen atmosphere of 99.99 wt% purity. Heat the sample from room temperature to 500°C at a heating rate of 5°C / min and hold for 15 min. Repeat the above coating-calcination operation three times. After the last calcination, hold the sample at a temperature of 1 h to obtain an intermediate layer with a thickness of about 1 μm.

[0080] Step (3): First, chloroiridic acid and tantalum pentachloride are dissolved in a mixed solution of n-butanol and hydrochloric acid at a molar ratio of 7:3 (hydrochloric acid mass fraction is 37%, and the volume ratio of n-butanol to hydrochloric acid is 90:1). The solution is stirred continuously for 3 minutes to prepare a metal oxide precursor solution with a concentration of 0.3 mol / L. Then, the above metal oxide precursor solution is brushed onto the surface of the intermediate layer, dried at 120℃ for 10 minutes, and then calcined at 500℃ for 15 minutes. After removal, it is naturally cooled to room temperature. The above brushing, drying, calcination and cooling operations are repeated 5-7 times. After the last calcination, the temperature is maintained for 1 hour to obtain an electrode with a thickness of about 3 μm, in which the metal oxide loading is 7 g / m. 2 .

[0081] Test case

[0082] (1) The intermediate layers obtained in step (2) of Example 1 and Comparative Example 2 were observed by scanning electron microscopy, and the results are as follows: Figure 1 As shown.

[0083] from Figure 1 As can be seen, compared with the intermediate layer without PVP (Comparative Example 2), the intermediate layer prepared with PVP in Example 1 showed a significant reduction in the number of surface cracks, indicating that the introduction of PVP can effectively suppress TaO2. x The formation of surface cracks in the intermediate layer.

[0084] (2) The cross-sectional morphology and elemental distribution of the electrode obtained in Example 1 were observed and quantitatively analyzed using transmission electron microscopy combined with energy dispersive spectroscopy. The results are as follows: Figure 2 As shown.

[0085] from Figure 2 As can be seen, cracks are generated on the coating surface. This microcrack structure is beneficial for releasing the internal stress of the coating and increasing the contact area between the electrode and the electrolyte, thereby improving the catalytic activity and service life of the electrode. Meanwhile, the Ta and O elements in the intermediate layer are evenly distributed and have no obvious crack structure, which can effectively block the electrolyte and active oxygen from diffusing into the titanium substrate through the surface microcracks, and prevent the titanium substrate from being oxidized to form a TiO2 passivation layer.

[0086] (3) The electrocatalytic activity of the electrodes prepared in Examples 1 and 1-2 was tested using a three-electrode system. A platinum sheet was used as the auxiliary electrode, a saturated calomel electrode as the reference electrode, and 0.5 mol / L sulfuric acid solution as the test electrolyte. The anodic polarization curves of the electrodes were measured at a scan rate of 0.33 mV / s in the potential range of 1.0 V-1.5 V (vs. SCE). The results are as follows. Figure 3 As shown.

[0087] from Figure 3As can be seen, the electrode prepared with PVP assistance (Example 1) has a significantly higher current density under the same potential conditions than the electrode without an intermediate layer (Comparative Example 1) and the electrode without PVP assistance (Comparative Example 2). This indicates that the intermediate layer prepared by the PVP-assisted sol-gel method in this invention can effectively improve the catalytic activity of the electrode.

[0088] (4) The stability of the electrodes prepared in Example 1 and Comparative Examples 1-2 was tested. The test conditions were as follows: constant current electrolysis was performed in a 1 mol / L sulfuric acid solution at 40℃ with a current density of 3 A / cm². The electrode under test was used as the working electrode, and the titanium plate was used as the cathode. The electrode spacing between the working electrode and the cathode was 2 cm. An increase in cell voltage of 10 V was used as the criterion for electrode failure. The changes in cell voltage over time were recorded for different electrodes during the enhanced electrolysis process. The results are as follows: Figure 4 As shown.

[0089] from Figure 4 As can be seen, the enhanced electrolysis life of the electrode without the intermediate layer (Comparative Example 1) is only 60h, the enhanced electrolysis life of the electrode without PVP assistance (Comparative Example 2) is 178h, while the electrode containing a dense tantalum oxide intermediate layer (Example 1) can achieve an enhanced electrolysis life of 246h, which is about 0.3 to 3 times longer. This shows that the intermediate layer prepared by the PVP-assisted sol-gel method in this invention can significantly extend the service life of titanium-based metal oxide electrodes and effectively improve the stability of the electrodes.

[0090] 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. An electrode comprising a substrate, an intermediate layer, and a coating layer disposed sequentially from bottom to top, characterized in that, The substrate is made of titanium, the intermediate layer is tantalum oxide, and the coating is a metal oxide. The intermediate layer is obtained by calcining a tantalum-containing precursor solution coated on the substrate. The tantalum-containing precursor solution is prepared by a polyvinylpyrrolidone-assisted sol-gel method.

2. The electrode according to claim 1, characterized in that, The intermediate layer is amorphous tantalum oxide.

3. The electrode according to claim 1, characterized in that, The metal oxides include noble metal oxides and / or non-noble metal oxides.

4. The electrode according to claim 3, characterized in that, The noble metal oxide is selected from one or more of iridium oxide, ruthenium oxide, and platinum oxide; the non-noble metal oxide is selected from one or more of tantalum oxide, tin oxide, silicon oxide, manganese oxide, and zirconium oxide.

5. A method for preparing the electrode according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step (1): Pre-treat the substrate to remove oil and oxide film and form a rough surface; Step (2): A tantalum precursor solution was prepared by polyvinylpyrrolidone-assisted sol-gel method. The tantalum precursor solution was coated onto a substrate that had undergone surface pretreatment and then calcined to obtain an intermediate layer. Step (3): Prepare a metal oxide precursor solution and use a thermal decomposition method to generate a coating on the surface of the intermediate layer to obtain the electrode.

6. The method for preparing the electrode according to claim 5, characterized in that, The specific steps of step (2) are as follows: Step S1: Preparation of tantalum precursor solution First, polyvinylpyrrolidone is dissolved in an alcohol solvent and stirred to obtain solution A; then tantalum alkoxide and alcohol solvent are mixed to obtain solution B; solution B is slowly added dropwise to solution A, with continuous stirring and simultaneous heating during the dropwise addition. After the dropwise addition is completed, the temperature is kept constant. After the temperature is kept constant, glacial acetic acid is added to obtain the tantalum precursor solution. Step S2: Generate an intermediate layer on the pretreated substrate surface The tantalum precursor solution is coated onto a pretreated substrate and calcined. After calcination, the substrate is kept at a temperature of 10-30 min. The coating and calcination operations are repeated multiple times. After the last calcination, the substrate is kept at a temperature of 1-2 h to obtain the intermediate layer.

7. The method for preparing the electrode according to claim 6, characterized in that, In step S2, the tantalum precursor solution is coated onto the surface of the pretreated substrate and then calcined in an inert atmosphere.

8. The method for preparing the electrode according to claim 6, characterized in that, In step S2, the calcination temperature is 400~600℃, and the heating rate to the calcination temperature is 5~7℃ / min.

9. The method for preparing the electrode according to claim 6, characterized in that, In step S1, the ratio of polyvinylpyrrolidone to alcohol solvent in solution A is 0~5g:10~100ml, and the amount of polyvinylpyrrolidone used is not 0; the ratio of tantalum alkoxide to alcohol solvent in solution B is 1~5ml:2~10ml.

10. The method for preparing the electrode according to claim 5, characterized in that, The specific steps for surface pretreatment of the substrate in step (1) are as follows: after removing oil stains from the substrate, mechanical grinding and polishing are performed, and then oxalic acid solution with a mass fraction of 10~20% is used to etch the substrate at 75℃~95℃ for 1~2 hours to remove the oxide film on the substrate surface and obtain a uniform and rough surface.

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