Photo-anode material based on single-walled carbon nanotube composite structure as well as preparation method and application of photo-anode material

Abstract

The invention discloses a photo-anode material based on a single-walled carbon nanotube composite structure and a preparation method and application of the photo-anode material. The preparation method of the photo-anode material comprises the steps of SWCNT purification, WO3-ZnO precursor preparation, mixed slurry synthesis, Zn-Bi2S3 in-situ growth and the like. According to the invention, the SWCNT, the WO3-ZnO heterojunction and the Zn-Bi2S3 are subjected to ternary compounding, and the conductivity and electron storage characteristics of the SWCNT are utilized, so that the separation and transmission efficiency of photo-generated charges is remarkably improved, and continuous cathode protection in a dark environment is realized. According to the photo-anode material, the metal potential can be kept to be lower than-0.55 V for more than 10 hours in the dark in a 3.5% NaCl solution, and the photo-anode material is suitable for metal protection in a marine environment.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of metal corrosion protection and new energy materials, specifically relating to a photoanode material based on a single-walled carbon nanotube (SWCNT) composite structure and its preparation method. Background Technology

[0002] Metal corrosion, especially in harsh marine environments, causes enormous losses to the national economy and national defense. Cathodic protection technology is one of the most effective means of preventing metal corrosion, mainly including sacrificial anode method and impressed current method. However, these two traditional methods have drawbacks such as consuming sacrificial anode material, relying on a continuous external power supply, high maintenance costs, and the potential for overprotection. Photoelectric cathodic protection technology, as an emerging green protection technology, uses photogenerated electrons generated by a semiconductor photoanode under illumination to polarize the protected metal, shifting its potential negative to below the corrosion potential, thereby inhibiting corrosion. This technology directly utilizes solar energy, theoretically requiring no additional materials or electrical energy, and has broad application prospects.

[0003] Currently, commonly used photocathode protection materials mainly include wide bandgap semiconductors such as TiO2, ZnO, and WO3. However, these materials have the following inherent defects: (1) Narrow spectral response range: They mainly utilize ultraviolet light, and their utilization efficiency in the visible light region, which has the highest energy in sunlight, is low. (2) High recombination rate of photogenerated carriers: Photogenerated electron-hole pairs are very easy to recombine in the bulk or on the surface, resulting in low quantum efficiency. (3) "Dark state" protection failure: Once the light stops, the protection effect disappears immediately, which cannot meet the need for continuous protection around the clock, which seriously restricts its practical application.

[0004] To overcome these problems, researchers have attempted methods such as constructing heterojunctions, ion doping, and loading noble metals. While these methods have improved light absorption and charge separation efficiency to some extent, they have failed to fundamentally solve the challenge of continuous protection in dark environments. Furthermore, single photoelectrode materials have limited electron transport capabilities and lack effective electron storage mechanisms. Therefore, developing a novel photocathode protection system with broad spectral response, efficient charge separation and transport characteristics, and continuous dark protection capability has become an urgent technological breakthrough in this field. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a photoanode material based on a single-walled carbon nanotube composite structure and its preparation method. This photoanode material is loaded onto a conductive substrate as an anode to construct a photoelectric continuous cathodic protection system. This system broadens the photoresponse spectral range, improves the separation and transport efficiency of photogenerated charges, and enables the system to continuously provide cathodic protection for metals for a period of time after illumination ceases. This solves the problems of narrow spectral response range, low charge separation and transport efficiency, and poor dark continuous protection capability of existing photoelectrode materials.

[0006] To achieve the above objectives, the present invention first provides a method for preparing a photoanode material based on a single-walled carbon nanotube composite structure, comprising the following steps: (1) Purification and dispersion of SWCNT: The original SWCNT was placed in concentrated acid for reflux purification to remove amorphous carbon and metal catalyst impurities. The purified SWCNT was dispersed in an organic solvent by ultrasonic treatment to form a stable SWCNT dispersion. (2) Preparation of WO3-ZnO precursor: WO3-ZnO composite nanoparticles or precursor sol were prepared by hydrothermal method or sol-gel method using tungsten source and zinc source as raw materials; (3) Preparation of mixed slurry: The SWCNT dispersion obtained in step (1) is mixed with the WO3-ZnO composite nanoparticles or precursor sol obtained in step (2) to obtain SWCNT / WO3-ZnO mixed slurry; (4) Introduction and film formation of Zn-Bi2S3: Bismuth source, sulfur source and zinc source are added to the mixed slurry obtained in step (3), and Zn-Bi2S3 is grown in situ on the SWCNT / WO3-ZnO framework by chemical bath deposition or hydrothermal method to form SWCNT / WO3-ZnO / Zn-Bi2S3 ternary composite material.

[0007] In one embodiment of the present invention, the concentrated acid in step (1) is a mixed solution of concentrated sulfuric acid and concentrated nitric acid, wherein the mass concentration of the concentrated sulfuric acid is 95-98%, the mass concentration of the concentrated nitric acid is 65-68%, and the volume ratio of the two is 2:1-4:1.

[0008] In one embodiment of the present invention, in step (1), the mass-to-volume ratio of the single-walled carbon nanotube to the concentrated acid is 2~5 g / L.

[0009] In one embodiment of the present invention, in step (1), the reflux purification refers to reflux under oil bath conditions, with a temperature of 60~80℃ and a time of 3~6h. After reflux, the reflux is diluted with deionized water and filtered until neutral to obtain acid-purified SWCNT.

[0010] In one embodiment of the present invention, the organic solvent in step (1) includes at least one of N-methylpyrrolidone (NMP), N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and the ultrasonic treatment is performed under ice bath conditions, with a power of 500~800W, an ultrasonic time of 0.5~2h, and an ultrasonic working period of 2~5s followed by an interval of 2~5s.

[0011] In one embodiment of the present invention, in step (1), the concentration of the SWCNT dispersion is 0.5~2.0 mg / mL.

[0012] In one embodiment of the present invention, in step (2), the tungsten source is sodium tungstate and the zinc source is zinc nitrate.

[0013] In one embodiment of the present invention, the specific steps of the hydrothermal synthesis of WO3-ZnO composite nanoparticles in step (2) are as follows: tungsten source and zinc source are dissolved in deionized water, and under magnetic stirring, the pH is adjusted to 2.0 with 2 M HCl to form a white suspension; the suspension is transferred to a high-pressure reactor for reaction and then naturally cooled, the precipitate is collected by centrifugation, washed, and dried to obtain WO3-ZnO composite nanoparticles.

[0014] In one embodiment of the present invention, the molar ratio of the tungsten source to the zinc source is 1:1 to 1:3, the reaction temperature is 100 to 150°C, the reaction time is 8 to 15 hours, the washing is performed by washing three times with water and three times with ethanol, and the washing is followed by drying at 60°C.

[0015] In one embodiment of the present invention, the specific steps for preparing the precursor sol using the sol-gel method in step (2) are as follows: dissolve the tungsten source and zinc source in an alcohol solvent (such as ethanol or isopropanol), add citric acid complexing agent, stir at 60-80°C to form a sol, and use after aging for 12-14 hours.

[0016] In one embodiment of the present invention, in step (3), the mass-to-volume ratio of the WO3-ZnO composite nanoparticles or precursor sol to the SWCNT dispersion is 5:1~2:1 mg / mL. After mixing, the mixture is first treated under ultrasonic conditions for 20~40 min, and then magnetically stirred for 4~8 h.

[0017] In one embodiment of the present invention, in step (4), the bismuth source is selected from at least one of bismuth nitrate, bismuth nitrate, and bismuth chloride; the sulfur source is selected from at least one of thioacetamide and thiourea; the zinc source is selected from at least one of zinc acetate, zinc nitrate, and zinc sulfate; the molar ratio of the bismuth source to the sulfur source is 1:2 to 1:4; and the molar ratio of the bismuth source to the zinc source is 2 to 4:1.

[0018] In one embodiment of the present invention, in step (4), the mass ratio of the bismuth source to the SWCNT / WO3-ZnO mixed slurry is 1:100 to 1:200.

[0019] In one embodiment of the present invention, in step (4), the specific steps for preparing the SWCNT / WO3-ZnO / Zn-Bi2S3 ternary composite material by chemical bath deposition are as follows: the SWCNT / WO3-ZnO mixed slurry is mixed with bismuth source and zinc source under weakly acidic conditions (pH 4~6), and in a water bath at 50-70°C, thioacetamide is slowly added as a sulfur source, and the reaction is carried out for 1-4 hours, so that sulfide ions are slowly hydrolyzed and uniformly deposited on the surface of the composite material. After the reaction, the SWCNT / WO3-ZnO / Zn-Bi2S3 composite material was finally obtained by centrifugation, washing with pure water 3-5 times, and vacuum drying. The bismuth salt was bismuth nitrate or bismuth chloride with a concentration of 0.02-0.1 mM, the zinc source was zinc sulfate or zinc acetate with a concentration of 0.01-0.05 mM, the sulfur source had a concentration of 0.1-0.5 mM, the centrifugation speed was 8000-12000 rpm, the time was 5-10 minutes, and the vacuum drying temperature was 60-80℃ for 6-12 hours.

[0020] In one embodiment of the present invention, in step (4), the specific steps for preparing the SWCNT / WO3-ZnO / Zn-Bi2S3 ternary composite material by hydrothermal method are as follows: Bismuth nitrate (Bi(NO3)3·5H2O), zinc acetate (Zn(CH3COO)2·2H2O), and thioacetamide (TAA) are added sequentially to the SWCNT / WO3-ZnO mixed slurry, and the mixture is stirred continuously for 1-3 hours; a pre-cleaned FTO conductive glass (2 cm × 3 cm) is then placed on the slurry. FTO (cm) is immersed in slurry, transferred to a reaction vessel, and hydrothermally reacted at 80-100℃ for 10-14 hours. After the reaction is complete, FTO is removed and gently rinsed with deionized water to obtain the film precursor. The FTO loaded with the film is placed in a tube furnace and annealed at 300-400℃ for 1-3 hours under N2 atmosphere protection at a heating rate of 2℃ / min. After natural cooling, the SWCNT / WO3-ZnO / Zn-Bi2S3 composite photoanode is obtained. The bismuth salt concentration is 0.4-0.8 mM, the zinc source concentration is 0.1-0.4 mM, and the sulfur source concentration is 1.0-2.0 mM. In one embodiment of the present invention, in step (4), after the material is synthesized, the conductive substrate of the SWCNT / WO3-ZnO / Zn-Bi2S3 ternary composite material is subjected to heat treatment, which is annealing under N2 atmosphere or argon atmosphere.

[0021] In one embodiment of the present invention, the annealing temperature is 300~400℃, the annealing time is 1~3h, the heating rate during annealing is 1~5℃ / min, and the annealing is naturally cooled to room temperature.

[0022] The present invention also provides a photoanode material prepared according to the above method.

[0023] The present invention also provides an application of the above-mentioned photoanode material in a photoelectric continuous cathodic protection system.

[0024] In one embodiment of the present invention, the application is to use a conductive substrate loaded with photoanode material as the anode and the protected metal as the cathode. After being connected to the photoanode through an external circuit wire, the substrate and the cathode are immersed together in an electrolyte to form a photoelectric continuous cathodic protection system. The electrolyte is a 3.5 wt% NaCl solution used to simulate a seawater environment.

[0025] In one embodiment of the present invention, the photoelectric continuous cathodic protection system may further include a counter electrode and / or a reference electrode, wherein the counter electrode may be a platinum sheet and the reference electrode may be a saturated calomel electrode.

[0026] Beneficial effects: (1) This invention forms a composite material by combining single-walled carbon nanotubes with WO3-ZnO heterostructures, and then grows Zn-Bi2S3 in situ on the SWCNT / WO3-ZnO framework to form a ternary composite material of SWCNT / WO3-ZnO / Zn-Bi2S3. The prepared ternary composite material has a wide spectral response and high light absorption efficiency, efficient photogenerated charge separation and transport performance, photochemical stability and corrosion resistance, and excellent continuous cathodic protection capability.

[0027] (2) WO3, as a narrow bandgap semiconductor, has good visible light absorption capability; ZnO has good electron transport performance. When the two are combined, they can form a type II heterojunction, which can effectively promote the spatial separation of photogenerated electron-hole pairs, prolong the carrier lifetime, and thus improve the performance of photoanode materials.

[0028] (3) Single-walled carbon nanotubes (SWCNTs) have a three-dimensional conductive network. When combined with WO3-ZnO heterojunction, they can provide an ultra-high-speed transport path for photogenerated electrons, greatly reducing the electron transport resistance and recombination probability, so that more electrons can quickly reach the protected metal. On this basis, Zn-Bi2S3 can be generated in situ on the SWCNT / WO3-ZnO surface by chemical bath deposition or water bath method, which can form a tight heterojunction interface, which is beneficial to the separation and transport of photogenerated charges.

[0029] (4) In the composite system of the present invention, SWCNTs can serve as the conductive framework and high-speed electron channel for the entire composite system. Their three-dimensional network structure not only greatly improves the conductivity of the material and accelerates the transport of electrons from the semiconductor to the protected metal, but also reduces recombination. SWCNTs not only serve as conductive channels, but their unique tubular structure and sp... 2 Carbon networks have excellent double-layer capacitance characteristics and can act as a "nano-electron reservoir" to store a large number of photogenerated electrons. When illuminated, some electrons are stored in SWCNTs. When the illumination stops, the stored electrons can be slowly released to continue to provide protective current for the metal, thereby achieving continuous cathodic protection for several hours or even tens of hours, and completely solving the bottleneck problem of "dark-state failure" in traditional photoelectric cathodic protection.

[0030] (5) This invention achieves wide-spectrum, high-efficiency absorption of ultraviolet to visible light by introducing narrow-bandgap semiconductors such as WO3 and Bi2S3 and constructing multi-level heterojunctions with ZnO, significantly improving the utilization efficiency of solar energy. Furthermore, Bi2S3 is a narrow-bandgap semiconductor, which can further extend the spectral response range of the system, while ZnO... 2+ The introduction of ...

[0031] (6) SWCNT has high chemical stability. Metal oxides / sulfides such as WO3 and ZnO are relatively stable in the electrolyte, which enables the composite system to maintain long-term effectiveness in harsh corrosive environments. The preparation method of the present invention does not require expensive equipment, the process conditions are controllable, and the raw materials are widely available, laying the foundation for large-scale preparation and practical engineering applications. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the performance testing of photoanode materials in embodiments and comparative examples of the present invention; Figure 2 This is a comparison graph of the photocurrent density of the photoanode materials in Example 1 and Comparative Examples 1-3; Figure 3 This is a comparison graph of the photocurrent density of the photoanode materials in Example 1 and Comparative Examples 4-6; Figure 4 Electrochemical impedance spectroscopy of the photoanode materials in Examples 1 and Comparative Examples 1-3; Figure 5 Electrochemical impedance spectroscopy (EIS) spectra of the photoanode materials in Examples 1 and Comparative Examples 4-6; Figure 6 The curves showing the open-circuit potential versus time for the photoanode materials of Examples 1 and Comparative Examples 1-3 are shown. Figure 7The curves showing the open-circuit potential versus time for the photoanode materials of Examples 1 and Comparative Examples 4-6 are shown. Figure 8 Tafel curves for the photoanode materials of Examples 1 and Comparative Examples 1-3; Figure 9 Tafel curves for the photoanode materials of Examples 1 and Comparative Examples 4-6; Figure 10 This is a diagram showing the effect of the photoanode material in Example 1 providing continuous protection in a dark environment. Detailed Implementation

[0033] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Example 1 A method for preparing a photoanode material based on a single-walled carbon nanotube composite structure includes the following steps: (1) Purification and dispersion of SWCNT: Take 100 mg of raw SWCNT and add 40 mL of concentrated H2SO4 / HNO3 (3:1 v / v) mixed acid. Reflux in an oil bath at 70℃ for 4 hours. After cooling, dilute with deionized water and filter until neutral to obtain acid-purified SWCNT. Place the acid-purified SWCNT in 60 mL of N-methylpyrrolidone (NMP) and sonicate in an ice-water bath (600W power, 2s working, 2s intermittent) for 1 hour to obtain a black stable dispersion with a concentration of 1.5 mg / mL.

[0035] (2) Preparation of WO3-ZnO precursor: Weigh 1.0 mmol Na2WO4·2H2O and 1.5 mmol Zn(NO3)2·6H2O, and dissolve them in 30 mL of deionized water. Under magnetic stirring, adjust the pH to 2.0 with 2 M HCl to form a white suspension. Transfer the suspension to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and react at 120 °C for 12 hours. After natural cooling, collect the precipitate by centrifugation, wash three times with water and three times with ethanol, and dry at 60 °C to obtain WO3-ZnO composite powder.

[0036] (3) Primary compounding: Take 40 mL of the SWCNT dispersion from step (1), add 80 mg of the WO3-ZnO powder obtained in step (2), sonicate for 30 minutes, and then magnetically stir for 6 hours to obtain a uniform SWCNT / WO3-ZnO mixed slurry.

[0037] (4) Introduction and film formation of Zn-Bi2S3: 0.6 mmol Bi(NO3)3·5H2O, 0.2 mmol Zn(CH3COO)2·2H2O and 1.8 mmol thioacetamide (TAA) were added sequentially to the slurry obtained in step (3), and the mixture was stirred continuously for 2 hours. Subsequently, a pre-cleaned FTO conductive glass (2 cm × 3 cm) was immersed in the slurry, and the entire system was transferred to a reaction vessel for hydrothermal reaction at 90°C for 12 hours. After the reaction was completed, the FTO was removed, and a black film was deposited on it. It was gently rinsed with deionized water.

[0038] (5) Heat treatment: The FTO loaded with the thin film was placed in a tube furnace and annealed at 350°C for 2 hours under N2 atmosphere protection (heating rate 2°C / min). After natural cooling to room temperature, the final SWCNT / WO3-ZnO / Zn-Bi2S3 composite photoanode was obtained.

[0039] Example 2 The difference between Example 2 and Example 1 is that in step (4), the amount of Bi(NO3)3·5H2O and thioacetamide added is 0.4 mmol and 0.8 mmol, respectively.

[0040] Example 3 The difference between Example 3 and Example 1 is that in step (4), the amount of Bi(NO3)3·5H2O and thioacetamide added is 0.8 mmol and 3.2 mmol, respectively.

[0041] Comparative Example 1: Preparation of WO3 photoanode The difference between Comparative Example 1 and Example 1 is that only WO3 was prepared as the photoanode, and the specific preparation method is as follows: (1) Preparation of WO3 precursor: Weigh 1.0 mmol Na2WO4·2H2O and dissolve it in 30 mL of deionized water. Under magnetic stirring, adjust the pH to 2.0 with 2 M HCl to form a white suspension. Transfer the suspension to a 50 mL high-pressure reactor lined with polytetrafluoroethylene. Immerse the pretreated FTO glass (placed tilted with the conductive side down) in the solution and react in an oven at 120℃ for 12 hours. After natural cooling, wash three times with water and dry at 60℃.

[0042] (2) Heat treatment: The FTO loaded with the thin film was placed in a tube furnace and annealed at 450°C for 2 hours under N2 atmosphere protection (heating rate 2°C / min). It was then naturally cooled to room temperature to obtain the final WO3 photoanode.

[0043] Comparative Example 2: Preparation of WO3-ZnO photoanode The difference between Comparative Example 2 and Example 1 is that steps (1), (3) and (4) are omitted, and WO3-ZnO is deposited only on the FTO stripping as the photoanode. The specific steps are as follows: (1) Preparation of WO3-ZnO precursor: Weigh 1.0 mmol Na2WO4·2H2O and 1.5 mmol Zn(NO3)2·6H2O, and dissolve them in 30 mL of deionized water. Under magnetic stirring, adjust the pH to 2.0 with 2 M HCl to form a white suspension. Transfer the suspension to a 50 mL high-pressure reactor lined with polytetrafluoroethylene, immerse the pretreated FTO glass (placed tilted with the conductive side down) in the solution, and react in an oven at 120℃ for 12 hours. After natural cooling, wash three times with water and dry at 60℃.

[0044] (2) Heat treatment: The FTO loaded with the thin film was placed in a tube furnace and annealed at 450°C for 2 hours under N2 atmosphere protection (heating rate 2°C / min). After natural cooling to room temperature, the final WO3-ZnO photoanode was obtained.

[0045] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step (4) is omitted, and the SWCNT / WO3-ZnO mixed slurry obtained in step (3) is directly spin-coated onto the FTO surface (2000 rpm, 30 s), and annealed at 400°C for 1 hour (heating rate 5°C / min) to obtain the SWCNT / WO3-ZnO photoanode.

[0046] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the amount of SWCNT added is different. In step (3) of Comparative Example 4, the amount of SWCNT dispersion added is 20 mL.

[0047] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the amount of SWCNT added is different. In step (3) of Comparative Example 5, the amount of SWCNT dispersion added is 60 mL.

[0048] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the method of introducing Bi2S3 is different, and no zinc source is added in step (4). The specific steps of steps (4) and (5) in Comparative Example 6 are as follows: Pre-synthesized Bi₂S₃ nanoparticles: 0.6 mmol Bi(NO₃)₃·5H₂O and 1.8 mmol thioacetamide (TAA) were weighed and dissolved in 30 mL of deionized water. After magnetic stirring for 30 minutes, the solution was transferred to a 50 mL high-pressure reactor and hydrothermally reacted at 120 °C for 6 hours. After natural cooling, the black Bi₂S₃ precipitate was collected by centrifugation and repeatedly washed with deionized water and ethanol. Finally, it was vacuum dried at 60 °C to obtain Bi₂S₃ nanoparticles.

[0049] Preparation of Bi2S3 dispersion: The Bi2S3 nanoparticles obtained above were dispersed in N-methylpyrrolidone (NMP) or ethanol at a concentration of 0.5 mg / mL, and ultrasonically treated (300W power, 2s working, 2s intermittent) for 1 hour to form a uniform Bi2S3 dispersion.

[0050] Adsorption and binding: Take 40 mL of the SWCNT / WO3-ZnO mixed slurry prepared in step (3), and slowly add 20 mL of the prepared Bi2S3 dispersion (controlling the mass ratio of Bi2S3 to WO3-ZnO to 1:10). Stir continuously with magnetic force at room temperature for 12 hours, and use physical interactions such as van der Waals forces between nanomaterials to adsorb Bi2S3 particles onto the SWCNT / WO3-ZnO framework to obtain the mixed slurry.

[0051] Film formation and post-treatment: A pre-cleaned FTO conductive glass sheet is immersed in the above mixed slurry and allowed to stand for 10 minutes. Then, a film is formed on the FTO using a spin coating method (e.g., 2000 rpm, 30 s). After film formation, the subsequent heat treatment steps (original step 5) remain unchanged, i.e., annealing at 350°C for 2 hours under a N2 atmosphere to obtain the SWCNT / WO3-ZnO / Bi2S3 composite photoanode.

[0052] The photoanodes prepared in the examples and comparative examples were used as the working electrode, a 316SS (1 cm × 1 cm) electrode was used as the cathode (protected metal), an SCE electrode was used as the reference electrode, and a platinum sheet was used as the counter electrode, forming a three-electrode system. The electrolyte was a 3.5 wt% NaCl solution. Performance tests were conducted using a 300 W xenon lamp (100 mW / cm²) to simulate sunlight. A schematic diagram of the performance test is shown below. Figure 1 As shown.

[0053] Figure 2 Photocurrent density diagrams are given using Example 1 and Comparative Examples 1-3 as photoanodes. Figure 2 It can be seen that when the material of Example 1 is used as the photoanode, its photocurrent density is significantly greater than that of Comparative Examples 1 to 3, and Comparative Example 1 is the lowest. This indicates that the introduction of ZnO heterojunction, single-walled carbon nanotubes and Zn-Bi2S3 can all increase the photoanode performance of WO3.

[0054] Table 1. Photocurrent density test results of the photoanode materials in Examples 1-3 and Comparative Examples 1-6

[0055] Figure 3 Photocurrent density diagrams are given for tests using Examples 1-3 and Comparative Examples 4-6 as photoanodes. Table 1 shows the photocurrent density test results for all examples and comparative examples using photoanodes. Figures 2-3 As can be seen from Table 1, the photoanode material prepared in Example 1 exhibits the best performance, with the highest photocurrent density reaching 2100 μA / cm² during testing as a photoanode material. 2 The results showed that the photocurrent density of the photoanode material was significantly higher than that of other examples and comparative examples, indicating that the introduction of single-walled carbon nanotubes and Zn-Bi2S3 can significantly improve the photocurrent density. The amount of single-walled carbon nanotubes added, the method of introducing Zn-Bi2S3, and the amounts of sulfur and bismuth sources all significantly affected the improvement in photocurrent density. Combining the experimental results of Example 1 and Comparative Example 6, it can be seen that simply adsorbing Bi2S3 into SWCNT / WO3-ZnO does not effectively construct a Zn-Bi2S3 interface, making it a potential electron "trap" or energy storage site to greatly improve the performance of the photoanode material. The photoanode of Comparative Example 6 only slightly improved the photocurrent density through a weak interface effect between Bi2S3 and ZnO. Single-walled carbon nanotubes (SCHNTs) serve as the conductive framework and high-speed electron channel of the entire composite system, and their addition directly affects the performance of the photoanode. Experiments in this invention revealed that when the mass ratio of SCHNTs to WO3-ZnO is controlled between 1:2 and 1:1, the photoanode material exhibits better performance; exceeding this range leads to a significant decrease in the photoanode material's performance. Example 1 demonstrates that the photogenerated electron separation efficiency and electronic conductivity efficiency of the SWCNT / WO3-ZnO / Zn-Bi2S3 composite photoelectrode are superior to others.

[0056] To investigate the charge transfer efficiency of the photoelectrode, the electrochemical impedance spectroscopy of the photoelectrode connected to a 316ss electrode was measured under illumination. Figure 4 and Figure 5 As shown, the impedance semicircular arc diameter of Example 1 is the smallest among all photoelectrodes, indicating that its interfacial charge transfer rate is the fastest, which is beneficial to the electrochemical processes involved.

[0057] Open circuit potential (OCP) test results of photoelectrode connection at 316ss Figure 6 and Figure 7 As shown in Table 2, upon exposure to light, the potential of the 316ss in Example 1 rapidly shifted negatively from an initial -0.14 V to -0.72 V, which is far below its self-corrosion potential, indicating that effective cathodic protection was provided.

[0058] Table 2. Open-circuit potential test results of the photoanode materials in Examples 1-3 and Comparative Examples 1-6

[0059] Figure 8 and Figure 9 Table 3 shows the Tafel curves of 316SS connected to the photoelectrode under illumination. The corrosion potential data for the 316SS connected to the photoelectrode prepared in the examples and comparative examples are presented in Table 3. Figures 8-9 As can be seen from Table 3, the corrosion potential of 316SS with photoelectrodes connected to the prepared examples and comparative examples is much more negative than that of 316SS without photoelectrodes connected. Under illumination, photogenerated electrons in the photoanode material are transferred to 316SS, which serves as the working electrode, to accelerate the electrochemical reaction. This process leads to a more negative corrosion potential, and the metal is effectively protected.

[0060] Table 3. Corrosion potential test results of photoanode materials in Examples 1-3 and Comparative Examples 1-6

[0061] After illumination, the potential of the 316ss connected in Example 1 remained stable. After the light source was turned off, the potential did not immediately rise, but instead slowly shifted positive, as shown in the image. Figure 10 As shown, this indicates that the electrons stored in the composite material continuously supply 316SS to achieve cathodic protection in the dark. After continuous monitoring in a dark environment for over 10 hours, the 316SS potential remained below -0.55V, fully demonstrating the excellent continuous cathodic protection capability, stability, and durability of SWCNT / WO3-ZnO / Zn-Bi2S3.

[0062] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a photoanode material based on a single-walled carbon nanotube composite structure, characterized in that, Includes the following steps: (1) Purification and dispersion of SWCNT: The original SWCNT was placed in concentrated acid for reflux purification to remove amorphous carbon and metal catalyst impurities. The purified SWCNT was dispersed in an organic solvent by ultrasonic treatment to form a stable SWCNT dispersion. (2) Preparation of WO3-ZnO precursor: WO3-ZnO composite nanoparticles or precursor sol were prepared by hydrothermal method or sol-gel method using tungsten source and zinc source as raw materials; (3) Preparation of mixed slurry: The SWCNT dispersion obtained in step (1) is mixed with the WO3-ZnO composite nanoparticles or precursor sol obtained in step (2) to obtain SWCNT / WO3-ZnO mixed slurry; (4) Introduction and film formation of Zn-Bi2S3: Bismuth source, sulfur source and zinc source are added to the mixed slurry obtained in step (3), and Zn-Bi2S3 is grown in situ on the SWCNT / WO3-ZnO framework by chemical bath deposition or hydrothermal method to form SWCNT / WO3-ZnO / Zn-Bi2S3 ternary composite material.

2. The preparation method according to claim 1, characterized in that, The concentrated acid in step (1) is a mixed solution of concentrated sulfuric acid and concentrated nitric acid. The mass concentration of the concentrated sulfuric acid is 95-98%, the mass concentration of the concentrated nitric acid is 65-68%, the volume ratio of the two is 2:1-4:1, and the mass-volume ratio of the single-walled carbon nanotube to the concentrated acid is 2-5 g:1 L.

3. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) includes at least one of N-methylpyrrolidone (NMP), N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). The ultrasonic treatment is performed under ice bath conditions. The ultrasonic power is 500~800W, the ultrasonic time is 0.5~2h, the ultrasonic operation is 2~5s, and the interval is 2~5s. The concentration of the SWCNT dispersion is 0.5~2.0 mg / mL.

4. The preparation method according to claim 1, characterized in that, In step (2), the tungsten source is sodium tungstate, the zinc source is zinc nitrate, the molar ratio of the tungsten source to the zinc source is 1:1 to 1:3, the reaction temperature is 100 to 150°C, and the reaction time is 8 to 15 hours.

5. The preparation method according to claim 1, characterized in that, In step (3), the mass-to-volume ratio of the WO3-ZnO composite nanoparticles or precursor sol to the SWCNT dispersion is 5:1~2:1 mg / mL. After mixing, the mixture is first treated under ultrasonic conditions for 20~40 min, and then magnetically stirred for 4~8 h.

6. The preparation method according to claim 1, characterized in that, In step (4), the bismuth source is selected from at least one of bismuth nitrate, bismuth nitrate, and bismuth chloride; the sulfur source is selected from at least one of thioacetamide and thiourea; the zinc source is selected from at least one of zinc acetate, zinc nitrate, and zinc sulfate; the molar ratio of the bismuth source to the sulfur source is 1:2 to 1:4; the molar ratio of the bismuth source to the zinc source is 2 to 4:1; and the mass ratio of the bismuth source to the SWCNT / WO3-ZnO mixed slurry is 1:100 to 1:

200.

7. The preparation method according to claim 1, characterized in that, In step (4), after the material is synthesized, the conductive substrate of the SWCNT / WO3-ZnO / Zn-Bi2S3 ternary composite material needs to be heat-treated. The heat treatment is annealing in an N2 atmosphere or an argon atmosphere. The annealing temperature is 300~400℃, the annealing time is 1~3h, the heating rate during annealing is 1~5℃ / min, and the substrate is naturally cooled to room temperature after annealing.

8. The photoanode material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the photoanode material according to claim 8 in a photoelectric continuous cathodic protection system.

10. The application according to claim 9, characterized in that, The application involves using a conductive substrate loaded with photoanode material as the anode and the metal to be protected as the cathode. The substrate and the metal are connected to the photoanode via external circuit wires and then immersed together in the electrolyte to form a photoelectric continuous cathodic protection system.

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