A WO3 / Nb2O5 / ZnIn2S4 composite film and its preparation method and application in photoelectrochemical cathodic protection

Abstract

The present invention discloses a method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite film, a preparation method thereof, and an application thereof in photoelectrochemical cathode protection. The preparation method comprises the following steps: cleaning conductive glass; preparing a WO3 film; preparing a WO3 / Nb2O5 composite film, placing the conductive glass with the WO3 / Nb2O5 composite film deposited on the surface with the conductive surface facing downward into a mixed solution of a zinc source, an indium source, and a sulfur source, performing a hydrothermal reaction, removing the solution, and drying to obtain the result. The preparation method of the present invention is simple and has high delayed energy storage characteristics, which is conducive to the large-scale production of photoanodes for energy storage-type photoelectrochemical cathode protection, while also laying the foundation for future industrialization.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectrochemical cathode protection, and specifically relates to a WO3 / Nb2O5 / ZnIn2S4 composite film and a preparation method thereof, and application in photoelectrochemical cathode protection. Background Art

[0002] Metal corrosion is an unavoidable phenomenon in nature. With the exception of gold, platinum, and other precious metals, most metals in nature tend to spontaneously transform into oxides or stable compounds due to corrosion, resulting in the near-extinction of pure metals. Currently, metal corrosion causes significant economic losses and safety incidents worldwide. Therefore, metal corrosion protection has become a critical research topic in basic science. Marine engineering projects, such as offshore drilling platforms and marine vessels, face even higher demands for metal corrosion protection due to the harsh marine environment. Therefore, selecting appropriate corrosion protection technologies is extremely urgent for metal materials serving in marine environments, and researchers are actively developing various new technologies to mitigate metal corrosion. In recent years, photoelectrochemical cathodic protection (PECCP) has been extensively studied, driven by the integration of cathodic protection with the rapidly developing photoelectrochemical technology. The photoelectric effect is a green and pollution-free form of protection. Its principle is that when a semiconductor material is exposed to sunlight, electrons spontaneously transition from the valence band to the conduction band. These electrons are then transferred to the protected metal surface via an external wire, causing the cathode polarization to drop below the self-corrosion potential of the protected metal, thereby providing protection.

[0003] WO3 is a promising narrow-bandgap semiconductor material with strong visible light absorption and, in particular, excellent electron storage capacity. In the dark state, the WO3 photoelectrode can release stored electrons, thereby achieving continuous cathodic protection under visible light, thereby enabling continuous photoelectrochemical cathodic protection in both the light and dark states. Therefore, the use of WO3 is expected to address the problem of metal materials being unable to provide continuous protection in the dark. However, single-phase WO3 photoanodes have relatively positive conduction bands and high recombination rates of photogenerated carriers, making them difficult to protect 304 stainless steel (304SS) and Q345 carbon steel (Q345CS), limiting their application in the field of photoinduced cathodic protection.

[0004] Research has found that rationally designing heterojunctions between two or more semiconductors is an effective strategy for accelerating charge separation and transfer. For example, optimized photoanodes such as BiVO4 / CdSe, WO3 / ZnIn2S4, and WO3 / CdS have been constructed, reducing the recombination rate of photogenerated carriers and enabling the protection of 304SS and Q345CS. These designs are being continuously optimized towards achieving high efficiency, environmental friendliness, and applicability to real-world marine applications. However, existing binary heterojunctions suffer from poor matching, making them incapable of protecting Q345CS under dark conditions.

[0005] The ternary heterojunction proposed a buffer layer strategy, which can alleviate the recombination of electrons and holes and achieve effective photoelectrochemical cathodic protection. The study found that Yang et al. (Yang Y, Sun M, Chen Z, et al. 3D nanothorn cluster-like Zn-Bi2S3 sensitized WO3 / ZnO multijunction with electron-storage characteristic and adjustable energy band for improving sustained photoinduced cathodic protection application[J]. Chemical Engineering Journal, 2023, 458: 141458) synthesized WO3 / ZnO / Zn-Bi2S3 structure by solvent method, electrochemical method, and precipitation method, which provided continuous cathodic protection for 316 stainless steel (316SS) for up to 5460 seconds after the light stopped; Jiang et al. (Jiang X, Sun M, Chen Z, et al. High-efficiency photoelectrochemical cathodic protection performance of the TiO2 / AgInSe2 / In2Se3 multijunction nanosheet array[J]. Corrosion Science, 2020, 176: 108901) A ternary heterojunction (TiO2 / AgInSe2 / In2Se3) was prepared by a hydrothermal method and a continuous ion layer adsorption reaction method to achieve effective photoelectrochemical cathodic protection for 316SS. However, it cannot achieve effective photoelectrochemical cathodic protection for Q235CS, and the preparation method is complicated and cannot have both the advantages of high performance and simplicity. The introduction of a suitable buffer layer between WO3 / ZnIn2S4 is conducive to the uniform distribution of the energy band gradient. The conduction band potential of TiO2 is only -0.28V (vsNHE), which is close to WO3. In contrast, Nb2O5 has the advantages of negative conduction band potential and high chemical stability and is expected to achieve the above goals.

[0006] The present invention solves the aforementioned problems by constructing a ternary heterojunction with a suitable buffer layer through a three-step in-situ growth process. First, compared to other electrochemical methods and continuous ion layer adsorption reaction methods, it is easier to control and scale up. Second, the ion system with a good energy band gradient allows photogenerated electrons to be transported along the energy band gradient. The synergistic effect between the different semiconductors generates a large number of photoinduced electrons, thereby greatly improving the photoelectrochemical cathodic protection performance of the heterojunction system. Third, the performance is stable, capable of providing stable protection for 304SS in both the light and dark states, and can also provide protection for Q345CS. Summary of the Invention

[0007] The present invention provides a WO3 / Nb2O5 / ZnIn2S4 composite film, a preparation method thereof, and an application in photoelectrochemical cathode protection. A WO3 / Nb2O5 / ZnIn2S4 composite film with a band gradient is prepared by an in-situ growth method and can be used as a photoanode in photoelectrochemical cathode protection. The composite photoanode has the two advantages of uniform energy band gradient distribution and a simple preparation method. It can not only alleviate the recombination of electrons and holes, but also realize efficient photoelectrochemical cathode protection.

[0008] In order to achieve the above technical objectives, the technical solution of the present invention is:

[0009] A method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite film comprises the following steps:

[0010] S1. Clean the conductive glass;

[0011] S2. Dissolve sodium tungstate in water or anhydrous ethanol, then add concentrated sulfuric acid to make a mixed solution. Place the cleaned conductive glass in the mixed solution and react at 70-90°C for 7-9 hours. Then transfer it to a muffle furnace and heat it to 400-600°C. Calcining it for 1-3 hours will produce a WO3 film.

[0012] S3, preparing a mixed solution of ethanol and niobium chloride, then placing the WO3 film in the mixed solution of ethanol and niobium chloride, hydrothermally reacting at 150-200° C. for 8-12 hours, and then transferring the film to a muffle furnace and calcining it at 400-600° C. for 2-3 hours to obtain a WO3 / Nb2O5 composite film;

[0013] S4. Place the conductive glass with the WO3 / Nb2O5 composite thin film deposited on the surface facing downward into a mixed solution of zinc source, indium source and sulfur source, and carry out hydrothermal reaction at 150-200°C for 8-12 hours. After the reactor is cooled, the solution is removed and the glass is dried at 80-100°C for 0-1 hour to obtain the WO3 / Nb2O5 / ZnIn2S4 composite thin film for photoelectrochemical cathode protection.

[0014] In S1, the conductive glass is placed in the first solution and the second solution in sequence, and ultrasonic cleaning is performed. The duration of each ultrasonic cleaning is 10-30 minutes, and the glass is dried at 50-70° C. after cleaning.

[0015] Wherein, the conductive glass is FTO conductive glass or ITO conductive glass, the first solution is ethanol or acetone, and the second solution is deionized water.

[0016] Among them, in S2, the heating rate of the muffle furnace is 2.5°C / min, the mass volume ratio of sodium tungstate to water or anhydrous ethanol is 1:(100-150)g / ml, and the mass volume ratio of sodium tungstate to concentrated sulfuric acid is 1:(8-12)g / ml.

[0017] In S3, the mass volume ratio of niobium chloride to ethanol is 1:(100-150) g / ml, and the mass ratio of niobium chloride to sodium tungstate is 1:1.

[0018] Among them, in S4, the zinc source is an inorganic salt or organic salt of zinc, the indium source is an inorganic salt or organic salt of indium, and the sulfur source is at least one of thiourea, thioacetamide and sodium sulfite; the mass ratio of the zinc source, the indium source and the sulfur source is (0.1-1.0):(0.1-1.0):(0.1:1.0); the mass ratio of sodium tungstate to the zinc source is (2-6):1.

[0019] Wherein, the zinc source is at least one of zinc nitrate, zinc sulfate, zinc chloride and zinc acetate; and the indium source is at least one of indium nitrate, indium sulfate, indium chloride and indium acetate.

[0020] A WO3 / Nb2O5 / ZnIn2S4 composite film is made by the above-mentioned preparation method.

[0021] The above-mentioned WO3 / Nb2O5 / ZnIn2S4 composite film is used in photoelectrochemical cathodic protection.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention adopts the continuous ion layer adsorption reaction method to prepare the ternary heterojunction (WO3 / Nb2O5 / ZnIn2S4), which is easier to control and mass-produce than other electrochemical methods and the continuous ion layer adsorption reaction method.

[0024] (2) The present invention adopts a buffer layer strategy and utilizes a heterojunction method with a good energy band gradient to construct a WO3 / Nb2O5 / ZnIn2S4 composite film, which can delay the irradiation recombination of electrons and holes, so that photogenerated electrons are transported along the energy band gradient, promote the consumption of photogenerated holes, and significantly improve the photoelectric conversion efficiency.

[0025] (3) The WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathodic protection of the present invention can absorb and utilize visible light. Compared with WO3 and WO3 / ZnIn2S4, the photoelectrochemical cathodic protection performance in 3.5% NaCl solution is significantly improved. Under light, the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathodic protection of the present invention can shift the corrosion potential of 304SS negatively by more than 360mV. It can continue to protect metal materials in the dark and can shift the corrosion potential of Q345 negatively by more than 150mV, achieving effective photoelectrochemical cathodic protection.

[0026] (4) When the photoanode thin film material with heterojunction of the present invention is applied to the photoelectrochemical cathode protection system in a seawater environment, in situ protection can be achieved without adding a hole capture agent, and the protection is long-lasting and stable, laying the foundation for future industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings in the specification, which constitute a part of this application, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 This is the XRD pattern of WO3 / Nb2O5 / ZnIn2S4 composite film;

[0029] Figure 2 Scanning electron microscope images of the thin films (a is WO3, b is WO3 / Nb2O5 / ZnIn2S4);

[0030] Figure 3 This is the photoinduced open circuit short-term potential change diagram of WO3 / Nb2O5 / ZnIn2S4 composite film in the absence of hole scavenger and intermittent light;

[0031] Figure 4 This is the photoinduced open circuit long-term potential change diagram of WO3 / Nb2O5 / ZnIn2S4 composite film in the absence of hole scavenger and intermittent light. DETAILED DESCRIPTION

[0032] The following will be combined with specific embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] Example 1

[0034] 1. This embodiment provides a method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite film, comprising the following steps:

[0035] S1. Cleaning the conductive glass: Place the FTO conductive glass in ethanol and perform ultrasonic cleaning for 20 minutes; then place it in deionized water and perform ultrasonic cleaning for 20 minutes, and then dry it at 60°C.

[0036] S2. Dissolve 0.4 g of sodium tungstate in 50 mL of water, then add 4 ml of concentrated sulfuric acid to make a mixed solution. Transfer the mixed solution to a hydrothermal reactor, then place the cleaned FTO conductive glass in the mixed solution, react at 70 ° C for 9 h, then transfer to a muffle furnace and heat to 500 ° C at a heating rate of 2.5 ° C / min, calcined for 2 h to obtain a WO3 film;

[0037] S3. Add 0.4 g of niobium chloride to 50 mL of anhydrous ethanol, stir the solution until it becomes clear, transfer the mixed solution to a hydrothermal kettle, place the WO3 film conductive side down in the hydrothermal kettle, and then place it in a constant temperature oven at 170° C. for 8 hours. Finally, place the obtained film in a muffle furnace and anneal it at 500° C. for 1.5 hours to obtain a WO3 / Nb2O5 composite film;

[0038] S4. Use a mixed solution of 0.2g of zinc chloride, 0.66g of indium chloride and 0.4g of thioacetamide, place the conductive surface of the FTO conductive glass with a WO3 / Nb2O5 composite thin film deposited on the surface face down, control the temperature of the hydrothermal reaction to 160°C, and the reaction time to 10h. After the reactor is cooled, remove the solution, and dry the obtained solid at 100°C for 1h to prepare the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathode protection of this embodiment.

[0039] 2. Preparation method of WO3 for photoelectrochemical cathode protection: add 0.4g of anhydrous sodium tungstate to 50mL of anhydrous ethanol, stir the solution until it is clear and transparent, use a pipette to take 4ml of concentrated sulfuric acid and add it to the sodium tungstate solution and stir evenly, transfer the mixed solution to a hydrothermal kettle, place the FTO conductive glass with the conductive side facing down in the hydrothermal kettle, and then place it in a constant temperature oven at 70℃ for 8 hours. Finally, place the obtained tungsten oxide film in a muffle furnace and anneal it at 500℃ for 1.5 hours to obtain a WO3 film.

[0040] 3. Preparation of WO3 / Nb2O5 for photoelectrochemical cathodic protection: A mixed solution of ethanol and niobium chloride is prepared, followed by placing a WO3 film in the mixed solution, hydrothermally reacting at 150-200°C for 8-12 hours, and finally calcining at 400-600°C for 2-3 hours to obtain a WO3 / Nb2O5 composite film.

[0041] 4. Preparation method of ZnIn2S4 film for photoelectrochemical cathode protection: take a mixed solution of 0.2g zinc chloride, 0.66g indium chloride and 0.4g thioacetamide, place the conductive surface of FTO conductive glass with WO3 / Nb2O5 composite film deposited on the surface face down, control the temperature of the hydrothermal reaction to 160°C, the reaction time to 18h, remove the solution after the reactor is cooled, and dry the obtained solid at 100°C for 1h to prepare the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathode protection of this embodiment.

[0042] The XRD test of the phase composition of the WO3 / Nb2O5 / ZnIn2S4 composite film was carried out by X-ray diffractometer. The target material used in the test was Cu target, the test angle range was 10-80°, and the grazing test mode was adopted. Figure 1 As shown in the XRD spectrum of the WO3 / Nb2O5 / ZnIn2S4 composite film, the peaks can be well matched to the standard card of WO3, proving the presence of tungsten oxide in the prepared material. The diffraction peaks at 23.13, 23.63, 24.31, 26.45, 28.82, 34.08, 41.85, and 49.85 correspond to (002), (020), (200), (120), (112), (202), (222), and (223) of cubic WO3 (J Photoelectrochemical Cathodic Protection DS 83-0947). It was found that there were no obvious diffraction peaks of Nb2O5 in the composite material, which may be due to the superposition of the diffraction peaks of WO3 and FTO glass. The diffraction peaks at 27.8° and 55.6° correspond to the (102) and (202) crystal planes of ZnIn2S4, respectively. XRD results show that WO3 / Nb2O5 / ZnIn2S4 composite film was successfully synthesized.

[0043] Example 2

[0044] This embodiment provides a method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite film, comprising the following steps:

[0045] S1. Cleaning the conductive glass: Place the ITO conductive glass in acetone and perform ultrasonic cleaning for 10 minutes; then place it in deionized water and perform ultrasonic cleaning for 30 minutes, and then dry it at 50°C.

[0046] S2. Dissolve 0.4 g of sodium tungstate in 40 mL of water, then add 3.2 ml of concentrated sulfuric acid to make a mixed solution, then place the cleaned ITO conductive glass in the mixed solution, transfer the mixed solution to a hydrothermal reactor, react at 80 ° C for 8 hours, then transfer to a muffle furnace and heat to 400 ° C at a heating rate of 2.5 ° C / min, and calcine for 3 hours to obtain a WO3 thin film;

[0047] S3. Add 0.4 g of niobium chloride to 40 mL of anhydrous ethanol, stir the solution until it becomes clear, transfer the mixed solution to a hydrothermal kettle, place the WO3 film conductive side down in the hydrothermal kettle, and then place it in a constant temperature oven at 150° C. for 12 hours. Finally, place the obtained film in a muffle furnace and anneal at 400° C. for 3 hours to obtain a WO3 / Nb2O5 composite film;

[0048] S4. Use a mixed solution of 0.1g of zinc chloride, 1.0g of indium chloride and 0.1g of thioacetamide, place the conductive surface of the ITO conductive glass with a WO3 / Nb2O5 composite thin film deposited on the surface face down, control the temperature of the hydrothermal reaction to 150°C, and the reaction time to 12h. After the reactor is cooled, remove the solution, and dry the obtained solid at 80°C for 0.5h to prepare the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathode protection of this embodiment.

[0049] 2. Preparation of WO3 for photoelectrochemical cathode protection: Add 0.4g of anhydrous sodium tungstate to 50mL of anhydrous ethanol and stir the solution until it is clear and transparent. Use a pipette to add 4ml of concentrated sulfuric acid to the sodium tungstate solution and stir evenly. Transfer the mixed solution to a hydrothermal reactor and place the ITO conductive glass with the conductive side facing down in the hydrothermal reactor. Then place the film in a constant temperature oven at 80°C for 8 hours. Finally, place the resulting tungsten oxide film in a muffle furnace and anneal at 500°C for 3 hours to obtain a WO3 film.

[0050] 3. Preparation of WO3 / Nb2O5 for photoelectrochemical cathodic protection: 0.4 g of niobium chloride was added to 50 mL of anhydrous ethanol, and the solution was stirred until clear and transparent. The mixed solution was transferred to a hydrothermal reactor, and a WO3 film was placed with the conductive side facing downward in the hydrothermal reactor. The film was then placed in a constant temperature oven at 160°C for 12 hours. Finally, the resulting film was annealed in a muffle furnace at 500°C for 1.5 hours to obtain a WO3 / Nb2O5 composite film.

[0051] 4. Preparation method of ZnIn2S4 film for photoelectrochemical cathode protection: use a mixed solution of 0.1g zinc chloride, 0.66g indium chloride and 0.3g thioacetamide, place the conductive surface of ITO conductive glass with WO3 / Nb2O5 composite film deposited on the surface face down, control the temperature of the hydrothermal reaction to 180°C, the reaction time to 10h, remove the solution after the reactor is cooled, and dry the obtained solid at 80°C for 0.5h to prepare the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathode protection of this embodiment.

[0052] The microstructure of the WO3 / Nb2O5 / ZnIn2S4 composite film was observed by scanning electron microscopy (with WO3 as a control). Figure 2 As shown, the WO3 film exhibits a nanosheet structure, while the Nb2O5 / ZnIn2S4 composite film exhibits a spherical structure with nanoflower-like structures nearby. The prepared WO3 / Nb2O5 / ZnIn2S4 composite film is primarily nanosheet-shaped, with a large number of nanospheres and nanoflower-like particles densely distributed on the nanosheets, indicating that the WO3 / Nb2O5 / ZnIn2S4 composite film was successfully prepared.

[0053] Example 3

[0054] This embodiment provides a method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite film, comprising the following steps:

[0055] S1. Cleaning the conductive glass: Place the FTO conductive glass in ethanol and perform ultrasonic cleaning for 30 minutes; then place it in deionized water and perform ultrasonic cleaning for 10 minutes, and then dry it at 70°C.

[0056] S2. Dissolve 0.6g of sodium tungstate in 90ml of water, then add 7.2ml of concentrated sulfuric acid to make a mixed solution, then place the cleaned FTO conductive glass in the mixed solution, transfer the mixed solution to a hydrothermal reactor, react at 90℃ for 7h, then transfer to a muffle furnace and heat to 600℃ at a heating rate of 2.5℃ / min, calcining for 1h to obtain a WO3 thin film;

[0057] S3. Add 0.6 g of niobium chloride to 900 mL of anhydrous ethanol, stir the solution until it becomes clear, transfer the mixed solution to a hydrothermal kettle, place the WO3 film conductive side downward in the hydrothermal kettle, and then place it in a constant temperature oven at 200° C. for 8 hours. Finally, place the obtained film in a muffle furnace and anneal it at 600° C. for 1 hour to obtain a WO3 / Nb2O5 composite film;

[0058] S4. Use a mixed solution of 0.1g of zinc chloride, 0.01g of indium chloride and 0.1g of thioacetamide, place the FTO conductive glass with WO3 / Nb2O5 deposited on the surface facing down, control the temperature of the hydrothermal reaction to 200°C, and the reaction time to 8h. After the reactor is cooled, remove the solution to prepare the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathode protection of this embodiment.

[0059] 2. Preparation of WO3 for photoelectrochemical cathode protection: Add 0.6g of anhydrous sodium tungstate to 60mL of water, stir the solution until it is clear and transparent, use a pipette to add 5ml of concentrated sulfuric acid to the sodium tungstate solution and stir evenly, transfer the mixed solution to a hydrothermal reactor, place the FTO conductive glass with the conductive side facing down in the hydrothermal reactor, and then place it in a constant temperature oven at 90°C for 8 hours. Finally, place the obtained tungsten oxide film in a muffle furnace and anneal at 500°C for 2 hours to obtain a WO3 film;

[0060] 3. Preparation of WO3 / Nb2O5 for photoelectrochemical cathodic protection: 0.6 g of niobium chloride was added to 600 mL of anhydrous ethanol. The solution was stirred until clear and transparent. The mixed solution was transferred to a hydrothermal reactor. The WO3 film was placed with the conductive side facing down in the hydrothermal reactor. The film was then placed in a constant temperature oven at 180°C for 12 hours. Finally, the resulting film was annealed in a muffle furnace at 500°C for 3 hours to obtain a WO3 / Nb2O5 composite film.

[0061] 4. Preparation method of ZnIn2S4 film for photoelectrochemical cathode protection: A mixed solution of 0.1g zinc chloride, 0.3g indium chloride and 0.44g thioacetamide is used, and the conductive surface of FTO conductive glass with WO3 / Nb2O5 deposited on the surface is placed face down. The temperature of the hydrothermal reaction is controlled to 140°C and the reaction time is 14h. After the reactor is cooled, the solution is removed and the obtained solid is dried at 60°C for 2h to prepare the WO3 / Nb2O5 / ZnIn2S4 composite film for photoelectrochemical cathode protection of this embodiment.

[0062] Experimental Example 1: Photoelectrochemical cathodic protection effect test of WO3 / Nb2O5 / ZnIn2S4 composite film

[0063] Electrochemical testing of the WO3 / Nb2O5 / ZnIn2S4 composite thin film was conducted using a three-electrode method with a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, and 304 stainless steel (304SS) or Q345 carbon steel (Q345CS) coupled to the WO3 / Nb2O5 / ZnIn2S4 composite film as the working electrode. Intermittent light irradiation was used to measure the photoinduced open-circuit potential change, demonstrating the photoelectrochemical cathodic protection performance of the material. The intermittent light was cycled 50 seconds on and 50 seconds off in a 3.5wt% NaCl solution without a hole scavenger. The light source system used during the tests was a PLS-SXE300E, simulating sunlight.

[0064] like Figure 3 As shown in the figure, in a 3.5wt% NaCl solution without a hole trap and under intermittent light irradiation, the WO3 / ZnIn2S4 composite film can polarize the potential of 304 to -0.4 (V vs. Ag / AgCl). Compared with the self-corrosion potential of 304SS of -0.16 (V vs. Ag / AgCl), the WO3 / Nb2O5 / ZnIn2S4 composite film can provide a photoelectrochemical cathodic protection effect of about 240mV for 304SS under light. The WO3 / Nb2O5 / ZnIn2S4 composite film polarizes the potential of Q345CS to -0.625 (V vs. Ag / AgCl). Compared to the self-corrosion potential of 304SS (-0.16 V vs. Ag / AgCl), the WO3 / Nb2O5 / ZnIn2S4 composite film provides a photoelectrochemical cathodic protection effect of approximately 460 mV for 304SS under light. This indicates that in a real marine environment, the WO3 / Nb2O5 / ZnIn2S4 composite film can act as a photoanode and provide a photoelectrochemical cathodic protection effect of approximately 460 mV for 304SS under light.

[0065] Electrochemical testing of the WO3 / Nb2O5 / ZnIn2S4 composite film was conducted using a three-electrode method using a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, and a 304SS or Q345CS electrode coupled to the WO3 / Nb2O5 / ZnIn2S4 composite film as the working electrode. Intermittent light irradiation was used to measure the photoinduced open-circuit potential change, demonstrating the photoelectrochemical cathodic protection performance of the material. The intermittent light was cycled 1800 seconds on and 1800 seconds off in a 3.5wt% NaCl solution without a hole trap. The light source system used during the tests was a PLS-SXE300E, simulating sunlight.

[0066] like Figure 4As shown, in a 3.5wt% NaCl solution without a hole trap and under intermittent light irradiation, the WO3 / Nb2O5 / ZnIn2S4 composite film polarizes the potential of Q345CS to -0.65 (V vs. Ag / AgCl). Compared to the natural corrosion potential of Q345CS stainless steel of -0.5 (V vs. Ag / AgCl), the WO3 / Nb2O5 / ZnIn2S4 composite film provides approximately 150mV of photoelectrochemical cathodic protection for Q345CS under light irradiation. The fact that the potential recovers to its initial position in the dark after 600s demonstrates the delayed energy storage effect of the WO3 / Nb2O5 / ZnIn2S4 composite film, enabling sustained protection in both light and dark conditions in a real marine environment.

[0067] As can be seen, the present invention utilizes a method with a suitable band structure heterojunction to construct a WO3 / Nb2O5 / ZnIn2S4 composite film. A gradient band structure is formed between WO3, Nb2O5, and ZnIn2S4. Under light excitation, the material generates photogenerated electron-hole pairs due to the photovoltaic effect. Due to the suitable band structure, the photogenerated electrons located in the conduction band of ZnIn2S4 transfer to the conduction band of Nb2O5, and then from the conduction band of Nb2O5 to the conduction band of WO3, and then transfer to the 304 stainless steel, providing it with a cathodic protection effect. On the other hand, the photogenerated holes located in WO3 transfer to the valence band of Nb2O5, and then from the valence band of Nb2O5 to the valence band of ZnIn2S4. The entire process exhibits excellent photogenerated cathodic protection performance due to the effective separation of the photogenerated electron-hole pairs. Therefore, the present invention constructs a ternary heterojunction with a reasonable buffer layer. The method is simple and has the dual advantages of high performance and simple preparation. When the photoanode thin film material with a heterojunction of the present invention is used in a photoelectrochemical cathode protection system under a seawater environment, there is no need to add a hole capture agent, and in-situ protection can be achieved with long-term stability, laying the foundation for future industrialization.

[0068] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite film, characterized in that The following steps are involved: S1. Clean the conductive glass; S2. Dissolve sodium tungstate in water or anhydrous ethanol, then add concentrated sulfuric acid to make a mixed solution. Place the cleaned conductive glass in the mixed solution and react at 70-90°C for 7-9 hours. Then transfer it to a muffle furnace and heat it to 400-600°C. Calcining it for 1-3 hours will produce a WO3 film. S3, preparing a mixed solution of ethanol and niobium chloride, then placing the WO3 film in the mixed solution of ethanol and niobium chloride, hydrothermally reacting at 150-200° C. for 8-12 hours, and then transferring the film to a muffle furnace and calcining it at 400-600° C. for 2-3 hours to obtain a WO3 / Nb2O5 composite film; S4. Place the conductive glass with the WO3 / Nb2O5 composite thin film deposited on the surface facing downward into a mixed solution of zinc source, indium source and sulfur source, and carry out hydrothermal reaction at 150-200°C for 8-12 hours. After the reactor is cooled, the solution is removed and the glass is dried at 80-100°C for 0-1 hour to obtain the WO3 / Nb2O5 / ZnIn2S4 composite thin film for photoelectrochemical cathode protection.

2. The method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite thin film according to claim 1, characterized in that: In S1, the conductive glass is placed in the first solution and the second solution in sequence, and ultrasonic cleaning is performed. The time of each ultrasonic cleaning is 10-30 minutes, and the glass is dried at 50-70° C. after cleaning.

3. The method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite thin film according to claim 2, characterized in that: The conductive glass is FTO conductive glass or ITO conductive glass, the first solution is ethanol or acetone, and the second solution is deionized water.

4. The method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite thin film according to claim 1, characterized in that: In S2, the heating rate of the muffle furnace is 2.5°C / min, the mass volume ratio of sodium tungstate to water or anhydrous ethanol is 1:(100-150)g / ml, and the mass volume ratio of sodium tungstate to concentrated sulfuric acid is 1:(8-12)g / ml.

5. The method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite thin film according to claim 1, characterized in that: In S3, the mass volume ratio of niobium chloride to ethanol is 1:(100-150) g / ml, and the mass ratio of niobium chloride to sodium tungstate is 1:

1.

6. The method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite thin film according to claim 1, characterized in that: In S4, the zinc source is an inorganic salt or organic salt of zinc, the indium source is an inorganic salt or organic salt of indium, and the sulfur source is at least one of thiourea, thioacetamide and sodium sulfite; the mass ratio of the zinc source, the indium source and the sulfur source is (0.1-1.0):(0.1-1.0):(0.1:1.0), and the mass ratio of sodium tungstate to the zinc source is (2-6):

1.

7. The method for preparing a WO3 / Nb2O5 / ZnIn2S4 composite thin film according to claim 6, characterized in that: The zinc source is at least one of zinc nitrate, zinc sulfate, zinc chloride, and zinc acetate; and the indium source is at least one of indium nitrate, indium sulfate, indium chloride, and indium acetate.

8. A WO3 / Nb2O5 / ZnIn2S4 composite film, prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the WO3 / Nb2O5 / ZnIn2S4 composite film according to claim 8 in photoelectrochemical cathodic protection.

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