CNT-COOH / Sr-ZnIn2S4 Composite Photocathode Protection Material, Its Preparation Method and Application

Abstract

The application belongs to the field of photoelectrochemical cathodic protection, and discloses a CNT-COOH / Sr-ZnIn2S4 composite photoelectrode protection material, a preparation method and application thereof. The preparation method comprises the following steps: dissolving ZnCl2, InCl3 and Sr(CH3COO)2 in deionized water, adding C2H5NS to the mixed solution after uniform stirring, continuously stirring uniformly at room temperature to obtain a Sr-ZnIn2S4 precursor solution; adding carboxylated multi-walled carbon nanotubes MWCNTs-COOH to the precursor solution and stirring, pouring the solution into a reaction kettle for hydrothermal reaction; after reaction, centrifuging the solution, then washing and drying the precipitate to obtain the CNT-COOH / Sr-ZnIn2S4 composite material. The composite photoelectrode material prepared by the method can significantly improve the photo-generated carrier separation efficiency, improve the photo-generated electron transport capacity, and enhance the universal photo-generated cathodic protection performance in the simulated marine environment.

Description

Technical Field

[0001] This invention relates to the field of photoelectric cathodic protection, and in particular to a CNT-COOH / Sr-ZnIn2S4 composite photoelectric cathodic protection material, its preparation method, and its application. Background Technology

[0002] With the large-scale deployment of new energy equipment, marine engineering facilities, and offshore aquaculture platforms, marine engineering equipment operates for extended periods in harsh marine environments characterized by high salinity, high humidity, high oxygen levels, and strong sunlight radiation. Consequently, metal corrosion is becoming increasingly prominent, seriously threatening the safety, reliability, and service life of these equipment. Traditional metal corrosion prevention methods mainly include coating protection, sacrificial anode protection, and impressed current cathodic protection. However, these methods suffer from drawbacks such as high maintenance costs, high energy consumption, environmental unfriendliness, and limited protective effects.

[0003] Photoelectrochemical cathodic protection technology, as a novel green protection method powered by solar energy, has attracted widespread attention in recent years. This technology utilizes photogenerated electrons produced by semiconductor materials under illumination to cathodically polarize the metal, shifting the metal electrode potential negatively into the thermodynamic passivation region, thereby effectively inhibiting the corrosion reaction of the metal. Compared with traditional cathodic protection technologies, photoelectrochemical cathodic protection requires no external power source and has advantages such as being clean, sustainable, and having low operating costs, showing promising application prospects in the field of marine metal corrosion protection.

[0004] However, most semiconductor photoelectrode materials still face key technical bottlenecks such as high photogenerated carrier recombination rate, limited photogenerated electron migration capability, and large interfacial charge transport impedance, which make it difficult to fully realize their photoelectrochemical cathodic protection performance and leave a large gap from practical engineering applications.

[0005] ZnIn2S4, a ternary metal sulfide semiconductor material, possesses suitable band structure, good chemical stability, and visible light response, making it a highly sought-after material in photoelectrocatalysis and photoelectrochemistry. However, pure-phase ZnIn2S4 exhibits low electrical conductivity, and its crystal structure is prone to intrinsic defects such as sulfur vacancies. These defects become recombination centers for photogenerated carriers, leading to rapid recombination of photogenerated electron-hole pairs in both the bulk and surface phases. This severely restricts the improvement of its photoelectric conversion efficiency and cathodic protection performance.

[0006] Ion doping is an effective strategy for controlling the band structure and improving carrier transport properties of semiconductor materials. By introducing appropriate amounts of heterometallic ions into the ZnIn2S4 lattice, its electronic state density and band arrangement can be altered, thereby promoting the separation and migration of photogenerated carriers. Sr, as a typical alkaline earth metal, possesses stable valence states and a similar ionic radius to Zn. 2+It possesses characteristics such as being relatively similar to Zn and having mild chemical properties. Doping it into the ZnIn2S4 lattice holds promise for replacing some of the Zn content. 2+ Lattice sites introduce lattice distortion and modulate the local coordination environment, thereby optimizing the electronic structure of the material, promoting the migration of photogenerated electrons in the bulk phase, and reducing the recombination probability of charge carriers. However, the gain effect of Sr doping on the optoelectronic properties of ZnIn2S4 is closely related to its doping amount. When the doping amount is too low, the modulating effect is not significant, while when the doping amount is too high, it may introduce too many lattice defects or impurity phases, which may become carrier recombination centers. Therefore, the Sr doping amount needs to be precisely controlled. In addition, ion doping alone cannot fundamentally solve the loss problem in the long-distance transport of photogenerated electrons from the bulk phase of the material to the metal substrate. The limitation of the intrinsic conductivity of the material makes it difficult to efficiently output photogenerated electrons.

[0007] Carbon nanotubes, due to their excellent conductivity and unique one-dimensional tubular structure, are widely used as electron transport media and conductive frameworks in photoelectrochemistry. However, ordinary multi-walled carbon nanotubes lack active functional groups on their surface, resulting in poor dispersibility in aqueous systems and polar solvents, making them prone to aggregation and entanglement. When combined with semiconductor materials, they struggle to form uniform and compact heterogeneous interfaces, and localized aggregation may even reduce the effective active area of ​​the composite material, weakening its electron transport enhancement effect. Furthermore, the amount of carbon nanotubes introduced and the composite method directly affect the structure and properties of the composite material. Insufficient introduction makes it difficult to form a continuous conductive network, while excessive introduction may cover active sites on the semiconductor surface, reducing the material's light absorption capacity and photogenerated carrier generation efficiency.

[0008] In the study of Sr-doped ZnIn2S4 composites with carbon nanotubes, the key technical challenge to fully leverage their synergistic effect is how to accurately optimize the Sr doping amount, achieve uniform dispersion of carbon nanotubes, and ensure a tight interfacial bond between the two. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material, its preparation method, and its application, aiming to improve the separation efficiency of photogenerated carriers, enhance the photogenerated electron transport capability, and strengthen the photocathode protection performance under simulated marine environments.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material includes the following steps: Zinc salt, indium salt, and strontium source were dissolved in deionized water, stirred evenly, and then sulfur source was added. Stirring was continued to obtain Sr-ZnIn2S4 precursor solution. Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were added to the Sr-ZnIn2S4 precursor solution, stirred, and the mixed solution was transferred to a reaction vessel for hydrothermal reaction. After the reaction was completed, the resulting suspension was centrifuged, the precipitate was washed and dried to obtain the CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material.

[0011] In the above scheme, the zinc salt is ZnCl2, the indium salt is InCl3, the strontium source is Sr(CH3COO)2, and the sulfur source is C2H5NS; and the molar ratio of ZnCl2, InCl3, Sr(CH3COO)2, and C2H5NS is 1∶2∶1.5~3∶4.

[0012] Preferably, the molar ratio of ZnCl2, InCl3, Sr(CH3COO)2, and C2H5NS is 1:2:2:4.

[0013] In the above scheme, the amount of MWCNTs-COOH added is 5% to 7% of the mass of ZnCl2.

[0014] Preferably, the amount of MWCNTs-COOH added is 6.2% of the mass of ZnCl2.

[0015] In the above scheme, the hydrothermal reaction temperature is 160~180℃ and the reaction time is 10~12 hours.

[0016] Preferably, the hydrothermal reaction temperature is 180°C and the reaction time is 12 hours.

[0017] In the above scheme, the centrifugation rate is 8000 r / min; the drying is carried out in a 60℃ forced-air drying oven for 12 hours.

[0018] A CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material prepared by the preparation method described above.

[0019] Application of the CNT-COOH / Sr-ZnIn2S4 composite photoelectric cathodic protection material as described above in photoelectrochemical cathodic protection.

[0020] Through the above technical solution, the CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material, its preparation method, and its application provided by the present invention have the following beneficial effects: (1) Significantly improved separation and migration efficiency of photogenerated carriers. In this composite material, Sr-doped ZnIn2S4 serves as the main photoresponsive component, generating photogenerated electron-hole pairs under simulated sunlight irradiation. The introduction of Sr effectively modulates the electronic structure and photoresponsive behavior of ZnIn2S4, promoting the separation and migration of photogenerated carriers. Simultaneously, MWCNTs-COOH forms a continuous conductive network in the composite system, providing a fast transport channel for photogenerated electrons. After irradiation, the photogenerated electrons generated by ZnIn2S4 are rapidly transported to the protected metal surface via the MWCNTs-COOH conductive network, effectively reducing electron-hole recombination losses and improving the utilization efficiency of photogenerated electrons. Photoelectrochemical test results show that the photogenerated current density of the CNT-COOH / Sr ZnIn2S4 composite material is approximately 2.19 times that of Sr-doped ZnIn2S4, and the open-circuit potential shifts negatively by approximately 0.10 V, confirming a significant enhancement in carrier separation and transport capabilities.

[0021] (2) The microstructure and interfacial charge transport pathway of the composite material were optimized. Sr doping modulated the lamellar growth behavior of ZnIn2S4, transforming the original complete flower-shaped structure into a more loose and dispersed nanosheet structure, significantly increasing the contact area between the material and the electrolyte, which is beneficial to the electrolyte penetration and mass transfer process, and exposing more interfacial reactive sites. MWCNTs-COOH plays a supporting and bridging role in the composite system, enabling Sr-doped ZnIn2S4 nanosheets to be uniformly attached to the surface of the carbon nanotube network, forming a lamellar conductive framework composite structure. This structure constructs a continuous electron migration pathway, reduces the interfacial charge transport resistance, and accelerates the directional migration of photogenerated electrons to the metal cathode.

[0022] (3) Enhanced visible light response and photoelectric conversion efficiency of composite optoelectronic materials. Sr doping red-shifted the absorption edge of ZnIn2S4 from approximately 550 nm to approximately 574 nm, expanding the material's light absorption wavelength range. Further composite with MWCNTs-COOH significantly enhanced the absorption intensity of the material throughout the visible light region, with the absorption edge shifting further towards longer wavelengths, thus broadening the light response range. The enhanced visible light absorption capability is beneficial for improving the generation efficiency of photogenerated carriers, providing more electron sources for photoelectrochemical reactions. The synergistic effect of Sr doping and the MWCNTs-COOH conductive network improves the light absorption, carrier separation, and electron output capabilities of the composite material, significantly increasing the overall photoelectric conversion efficiency.

[0023] (4) Excellent photoelectrochemical cathodic protection performance was achieved. This composite material, without an external power source, utilizes photogenerated electrons generated by illumination to cathodically polarize the coupled metal, achieving effective corrosion protection for the metal material. Compared to ordinary multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes, due to the introduction of surface carboxyl functional groups, improve the dispersion stability of carbon nanotubes in the aqueous system, enhance the interfacial bonding affinity with ZnIn2S4, and make the composite material more uniformly dispersed, avoiding performance degradation caused by agglomeration, thereby significantly improving electron transport efficiency. Compared with other strontium sources such as SrCl2·6H2O and Sr(NO3)2, doping with Sr(CH3COO)2 as a strontium source has a more significant gain effect on the photoelectrochemical cathodic protection performance of ZnIn2S4. When the photoelectrode made of this composite material is coupled with a 316L stainless steel electrode, the open circuit potential of the 316L stainless steel shifts significantly negatively under simulated sunlight irradiation, and the photocurrent response is greatly improved. This shows stronger photogenerated electron output capability and cathodic polarization capability, which can effectively suppress the corrosion reaction of metal in simulated marine environment.

[0024] (5) The preparation process is simple, the conditions are mild, and it is easy to control. The present invention can achieve the simultaneous completion of Sr doping and MWCNTs-COOH composite by a one-step hydrothermal method. It does not require complex equipment and cumbersome steps, the raw material cost is low, the reaction conditions are mild, and the operation is simple, which is conducive to large-scale preparation and practical application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0026] Figure 1 X-ray diffraction patterns of different optoelectronic materials are shown, where (a) is the X-ray diffraction pattern of ZnIn2S4 materials with different Sr doping amounts, and (b) is the X-ray diffraction pattern of CNT-COOH, 2-Sr-ZnIn2S4, and CNT-COOH / Sr-ZnIn2S4 materials. Figure 2 The images are scanning electron microscope (SEM) images of different optoelectronic materials magnified 15,000 times. Among them, (a) is ZnIn2S4, (b) is 2-Sr-ZnIn2S4, and (c) is CNT-COOH / Sr-ZnIn2S4. Figure 3 The ultraviolet-visible diffuse reflectance absorption spectra of different optoelectronic materials; Figure 4The graphs show the open-circuit potential changes of different photoelectrodes and 316L SS electrode coupling systems prepared in the embodiments and comparative examples of the present invention under intermittent simulated sunlight irradiation and simulated marine environment; wherein, (a) is the test result of ZnIn2S4 photoelectrodes with different Sr doping amounts, and (b) is the test result of photoelectrodes after composite carbon nanotubes. Figure 5 The graphs show the changes in photocurrent density of different photoelectrodes coupled with 316L SS electrodes prepared in the embodiments and comparative examples of the present invention under intermittent simulated sunlight irradiation and simulated marine environment; wherein, (a) is the test result of ZnIn2S4 photoelectrodes with different Sr doping amounts, and (b) is the test result of photoelectrodes after composite carbon nanotubes. Figure 6 The figures show the open-circuit potential variation curves and photocurrent density variation curves of photoelectrodes and 316L SS electrode coupling systems prepared for different strontium sources under intermittent illumination. Among them, (a) is the open-circuit potential variation curve, and (b) is the photocurrent density variation curve. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0028] This invention provides a CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material, its preparation method, and its application. Specific embodiments are as follows: I. Preparation of Optoelectronic Materials Example 1: Preparation of CNT-COOH / Sr-ZnIn2S4 composite optoelectronic materials 136.3 mg ZnCl2, 442.4 mg InCl3, and 411.4 mg Sr(CH3COO)2 were dissolved in 30 mL of deionized water and stirred at room temperature until completely dissolved. Then, 300.5 mg C2H5NS was added and stirring was continued for 30 min to obtain the Sr-ZnIn2S4 precursor solution. 8.5 mg MWCNTs-COOH (carboxylated multi-walled carbon nanotubes) was added to the Sr-ZnIn2S4 precursor solution and stirring was continued at room temperature for 30 min. The solution was transferred to a 50 mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 12 h. After the reaction, the resulting suspension was centrifuged at 8000 r / min for 5 min. The precipitate was washed three times with deionized water and anhydrous ethanol, and dried in a 60 °C oven for 12 h to obtain the CNT-COOH / Sr-ZnIn2S4 composite optoelectronic material.

[0029] In this embodiment, the molar ratio of ZnCl2, InCl3, Sr(CH3COO)2, and C2H5NS is 1:2:2:4; the amount of MWCNTs-COOH added is 6.2% of the mass of ZnCl2. After composite carbon nanotubes, 2-Sr-ZnIn2S4 is abbreviated as Sr-ZnIn2S4.

[0030] Example 2: Preparation of CNT-COOH / Sr-ZnIn2S4 composite optoelectronic materials The only difference between this embodiment and Example 1 is the amount of MWCNTs-COOH used. Specifically, the amount of MWCNTs-COOH used is 6.8 mg (5.0% of the mass of ZnCl2). All other steps and conditions are the same as in Example 1.

[0031] Example 3: Preparation of CNT-COOH / Sr-ZnIn2S4 composite optoelectronic materials The only difference between this embodiment and Example 1 is the amount of MWCNTs-COOH used. Specifically, the amount of MWCNTs-COOH used is 9.5 mg (7.0% of the mass of ZnCl2). All other steps and conditions are the same as in Example 1.

[0032] Example 4: Preparation of CNT-COOH / Sr-ZnIn2S4 composite optoelectronic materials The only difference between this embodiment and Embodiment 1 is the hydrothermal reaction conditions. Specifically, the hydrothermal reaction temperature is 160°C and the reaction time is 10 h. All other steps and conditions are the same as in Embodiment 1.

[0033] Comparative Example 1: Preparation of pure-phase ZnIn2S4 optoelectronic materials This comparative example provides a method for preparing undoped ZnIn2S4 optoelectronic materials, including the following steps: 136.3 mg of ZnCl2 and 442.4 mg of InCl3 were dissolved in 30 mL of deionized water and stirred at room temperature until completely dissolved. Then, 300.5 mg of C2H5NS was added and stirring was continued for 30 min to obtain a ZnIn2S4 precursor solution. The solution was transferred to a 50 mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 12 h. After the reaction was completed, the resulting suspension was centrifuged at 8000 r / min for 5 min. The precipitate was washed three times successively with deionized water and anhydrous ethanol, and dried in a forced-air drying oven at 60 °C for 12 h to obtain pure phase ZnIn2S4 powder.

[0034] Comparative Example 2: Preparation of ZnIn2S4 optoelectronic materials with different Sr doping levels This comparative example used the same preparation steps as Comparative Example 1, the only difference being the addition of different amounts of Sr(CH3COO)2 to the precursor solution. The precursor solutions for each sample contained 136.3 mg ZnCl2, 442.4 mg InCl3, and 300.5 mg C2H5NS, with Sr(CH3COO)2 amounts set to 205.7 mg, 411.4 mg, and 822.8 mg, respectively. After stirring, the above precursor solutions were transferred to a reaction vessel and hydrothermally reacted at 180°C for 12 h. After centrifugation, washing and drying, three ZnIn2S4 powders with different Sr doping amounts were obtained, which were designated as 1-Sr-ZnIn2S4, 2-Sr-ZnIn2S4 and 4-Sr-ZnIn2S4, respectively. The corresponding molar ratios of ZnCl2, InCl3, Sr(CH3COO)2 and C2H5NS were 1∶2∶1∶4, 1∶2∶2∶4 and 1∶2∶4∶4, respectively.

[0035] Comparative Example 3: Preparation of CNT / Sr-ZnIn2S4 Composite Optoelectronic Materials The only difference between this comparative example and Example 1 is that the carbon nanotubes used are ordinary multi-walled carbon nanotubes (MWCNTs) (non-carboxylated), and the amount used is 8.5 mg. All other steps and conditions are the same as in Example 1, and CNT / Sr-ZnIn2S4 composite optoelectronic materials are obtained.

[0036] Comparative Example 4: Preparation of CNT-COOH / SrCl2-ZnIn2S4 Composite Optoelectronic Materials The only difference between this comparative example and Example 1 is the strontium source. In this comparative example, 533.2 mg SrCl2·6H2O was used instead of 411.4 mg Sr(CH3COO)2 as the strontium source, and the remaining steps and conditions were the same as in Example 1, resulting in CNT-COOH / SrCl2-ZnIn2S4 composite optoelectronic materials.

[0037] Comparative Example 5: Preparation of CNT-COOH / Sr(NO3)2-ZnIn2S4 composite optoelectronic materials The only difference between this comparative example and Example 1 is the strontium source. In this comparative example, 423.3 mg Sr(NO3)2 was used instead of 411.4 mg Sr(CH3COO)2 as the strontium source, and the remaining steps and conditions were the same as in Example 1, resulting in CNT-COOH / Sr(NO3)2-ZnIn2S4 composite optoelectronic material.

[0038] II. Preparation of Photoelectrodes The photoelectric materials prepared in the above embodiments and comparative examples were used to prepare photoelectrodes, and the specific methods are as follows: Take 5 mg of optoelectronic material powder, add 90 μL of isopropanol and 10 μL of Nafion solution, and ultrasonically disperse for 10 min to form a uniform dispersion. Take 15 μL of the dispersion and drop it onto a 1 cm × 2 cm FTO conductive glass surface (effective area 1 cm²). 2 The photoelectrode is obtained by drying at 60°C for 1 minute.

[0039] III. Performance Testing and Characterization 1. X-ray diffraction (XRD) phase analysis X-ray diffraction analysis was performed on the different photoelectric materials prepared. The test conditions were Cu Kα radiation (λ = 0.15406 nm), the scanning range was 10°~80°, and the scanning rate was 5° / min.

[0040] Figure 1 (a) shows the X-ray diffraction patterns of ZnIn2S4 materials with different Sr doping levels. As can be seen from the figure, the peaks at 21.59°, 27.69°, 47.18°, and 52.38° of undoped ZnIn2S4 belong to the (006), (102), (110), and (116) crystal planes of ZnIn2S4 (JCPDS No. 65-2023), which are hexagonal crystal structures. For ZnIn2S4 samples with different Sr doping ratios, the positions of the main diffraction peaks in their XRD patterns are basically consistent with those of undoped ZnIn2S4, and no obvious impurity phase diffraction peaks were observed, indicating that Sr doping did not change the crystal structure of ZnIn2S4, and the material still retains its original crystal phase.

[0041] Figure 1 (b) shows the X-ray diffraction patterns of CNT-COOH, 2-Sr-ZnIn2S4, and CNT-COOH / Sr-ZnIn2S4 materials, where 2-Sr-ZnIn2S4 is the sample from Comparative Example 2, and CNT-COOH / Sr-ZnIn2S4 are the samples from Examples 1-4. As can be seen from the figure, after composite MWCNTs-COOH, the main characteristic diffraction peaks of ZnIn2S4 are still retained in the XRD patterns, and the peak positions do not shift significantly, nor do any new impurity phase peaks appear. This indicates that the introduction of MWCNTs-COOH did not destroy the crystal structure of ZnIn2S4, and the material retains its original crystal phase. No obvious characteristic diffraction peaks of MWCNTs-COOH were observed in the composite samples. This may be related to the low crystallinity of MWCNTs-COOH and the weak diffraction peaks, or it may be due to the tight composite of MWCNTs-COOH with the ZnIn2S4 nanostructure, causing its characteristic peaks to be masked.

[0042] 2. Morphological characterization using scanning electron microscopy (SEM) The microstructure of the optoelectronic material was characterized using scanning electron microscopy with an accelerating voltage of 5 kV.

[0043] like Figure 2 As shown in (a), ZnIn2S4 mainly exhibits a relatively regular flower-shaped structure with a diameter of approximately 18 μm. These flower-shaped structures are composed of numerous stacked and interlaced nanosheets that self-assemble. After Sr doping, the original complete flower-shaped structure is significantly disrupted, transforming into a more dispersed nanosheet structure. Figure 2 (2-Sr-ZnIn2S4 shown in Figure (b)). This structural change significantly increases the contact area between the material and the electrolyte, which is beneficial for electrolyte penetration and mass transfer processes, thereby exposing more active sites and providing more reaction interfaces for photoelectrochemical reactions. Figure 2 Image (c) shows SEM images of the CNT-COOH / Sr-ZnIn2S4 composite materials prepared in Examples 1-4. Numerous sheet-like ZnIn2S4 particles are uniformly attached to the surface of the MWCNTs-COOH network, forming a layered + conductive framework structure. In this structure, MWCNTs-COOH not only improves the material's dispersion but also constructs a continuous electron transport channel in space, which helps accelerate the migration of photogenerated electrons within the material and reduces interfacial charge transport resistance.

[0044] 3. Ultraviolet-Vis DRS Analysis The light absorption performance of the photoelectrode was determined using a UV-Vis diffuse reflectance spectrometer (U-3900H type), with BaSO4 as the reference, and the scanning range was 300~800 nm.

[0045] like Figure 3 As shown, ZnIn2S4 exhibits strong absorption in the visible light region, with its absorption edge located at approximately 550 nm. In contrast, the absorption edge of 2-Sr-ZnIn2S4 is slightly red-shifted to approximately 574 nm, indicating that Sr doping extends the light absorption wavelength range of ZnIn2S4, thus enhancing the material's response to light in the visible light region. In Examples 1-4, after compositing MWCNTs-COOH, the resulting CNT-COOH / Sr-ZnIn2S4 exhibited stronger absorption intensity throughout the visible light region, and the absorption edge shifted significantly towards longer wavelengths, indicating that the introduction of MWCNTs-COOH broadened the material's photoresponse range. This enhanced visible light absorption is beneficial for improving the generation efficiency of photogenerated carriers, thereby providing more electron sources for subsequent photoelectrochemical reactions.

[0046] 4. Photoelectrochemical cathodic protection performance test Photoelectrochemical performance was tested using a CHI660D electrochemical workstation. The electrolyte was a 3.5 wt% NaCl solution (simulating a marine environment). A 300 W xenon lamp was used as the light source, equipped with an AM 1.5G filter, and the light intensity was 100 mW·cm². -2 The light was switched on and off 3 times during the test.

[0047] The prepared photoelectrode was used as the working electrode, a 316L stainless steel electrode (316L SS) as the coupling electrode, a saturated Ag / AgCl electrode as the reference electrode, and a platinum sheet as the counter electrode. The cathodic protection performance of the material was evaluated by measuring the changes in open-circuit potential (OCP) and photogenerated current density (it) under intermittent illumination after the photoelectrode was coupled to the 316L SS. When the metal cathode is subjected to polarization protection, the measured potential should be more negative than its open-circuit potential.

[0048] (1) Open circuit potential (OCP) test Figure 4 The graph shows the open-circuit potential variation of photoelectrodes made of different materials coupled with 316L SS electrodes under simulated marine environment to simulate intermittent sunlight irradiation.

[0049] Figure 4 Figure (a) shows the test results of ZnIn2S4 photoelectrodes with different Sr doping amounts, where ZnIn2S4 is the sample of Comparative Example 1, and 1-Sr-ZnIn2S4, 2-Sr-ZnIn2S4, and 4-Sr-ZnIn2S4 are samples of Comparative Example 2. As can be seen from the figure, when the metal electrode is coupled with ZnIn2S4 photoelectrodes with different Sr doping amounts, the mixing potential shifts negatively. After three light-dark cycles, the stable open-circuit potential of 1-Sr-ZnIn2S4 is -0.347 V, 4-Sr-ZnIn2S4 is -0.405 V, pure-phase ZnIn2S4 is -0.304 V, while 2-Sr-ZnIn2S4 exhibits the most negative stable open-circuit potential value, -0.477 V (vs. Ag / AgCl). This indicates that under illumination, 2-Sr-ZnIn2S4 can provide more photogenerated electrons to the coupled metal, thereby enabling stronger cathodic polarization of the metal electrode.

[0050] Figure 4Figure (b) shows the test results after compositing with carbon nanotubes, where 2-Sr-ZnIn2S4 is the sample of Comparative Example 2, CNT / Sr-ZnIn2S4 is the sample of Comparative Example 3, and CNT-COOH / Sr-ZnIn2S4 is the sample of Example 1. As can be seen from the figure, the open-circuit potential of CNT-COOH / Sr-ZnIn2S4 shifts negatively by approximately 0.10V compared to 2-Sr-ZnIn2S4, reaching approximately -0.58V. This indicates that the introduction of MWCNTs-COOH significantly enhances the transport capability of photogenerated electrons to the metal electrode, thereby producing a stronger cathodic polarization effect. However, the open-circuit potential of CNT / Sr-ZnIn2S4 prepared using ordinary multi-walled carbon nanotubes is significantly weaker than that of CNT-COOH / Sr-ZnIn2S4, and even weaker than that of 2-Sr-ZnIn2S4. This suggests that ordinary carbon nanotubes, due to poor dispersibility and weak interfacial bonding, fail to effectively enhance electron transport.

[0051] (2) Photocurrent density (it) test Figure 5 The graph shows the variation of photocurrent density in a simulated marine environment for photoelectrodes made of different materials coupled with 316L SS electrodes under intermittent simulated sunlight irradiation.

[0052] Figure 5 (a) shows the test results of ZnIn2S4 photoelectrodes with different Sr doping levels. ZnIn2S4 is the sample in Comparative Example 1, and 1-Sr-ZnIn2S4, 2-Sr-ZnIn2S4, and 4-Sr-ZnIn2S4 are the samples in Comparative Example 2. As can be seen from the figure, the photocurrent values ​​of pure-phase ZnIn2S4, 1-Sr-ZnIn2S4, 2-Sr-ZnIn2S4, and 4-Sr-ZnIn2S4 after stabilization under illumination are 3.73, 4.45, 16.52, and 13.41 μA·cm, respectively. -2 Among them, 2-Sr-ZnIn2S4 showed the highest photogenerated current density, indicating that appropriate Sr doping can effectively improve the photoelectric conversion efficiency of ZnIn2S4 and promote the separation and migration of photogenerated carriers. When the Sr doping amount is too low (1-Sr-ZnIn2S4), the modulation effect is not significant, while when the doping amount is too high (4-Sr-ZnIn2S4), it may introduce too many lattice defects, which may lead to a decrease in performance.

[0053] Figure 5Figure (b) shows the test results after compositing with carbon nanotubes, where 2-Sr-ZnIn2S4 is the sample of Comparative Example 2, CNT / Sr-ZnIn2S4 is the sample of Comparative Example 3, and CNT-COOH / Sr-ZnIn2S4 is the sample of Example 1. As can be seen from the figure, the photocurrent density of CNT-COOH / Sr-ZnIn2S4 is approximately 36.2 μA·cm⁻¹. -2 Approximately 2-Sr-ZnIn2S4 (16.52 μA·cm⁻¹) -2 The photocurrent density of MWCNTs-COOH is 2.19 times that of CNTs-ZnIn2S4, indicating that MWCNTs-COOH can effectively promote the separation and migration of photogenerated carriers and enhance the continuous output of electrons to the metal cathode, thereby improving the photocathode protection effect. The photocurrent density of CNT / Sr-ZnIn2S4 is weaker than that of CNT-COOH / Sr-ZnIn2S4, and even weaker than that of 2-Sr-ZnIn2S4, further confirming the necessity of carboxylation modification.

[0054] (3) Comparative tests of different strontium sources Figure 6 The graph shows the changes in open-circuit potential and current density of optoelectronic materials prepared with different strontium sources coupled to metal electrodes under intermittent illumination. CNT-COOH / Sr-ZnIn2S4 is the sample from Example 1 (strontium source: Sr(CH3COO)2), CNT-COOH / SrCl2-ZnIn2S4 is the sample from Comparative Example 4 (strontium source: SrCl2·6H2O), and CNT-COOH / Sr(NO3)2-ZnIn2S4 is the sample from Comparative Example 5 (strontium source: Sr(NO3)2). Figure 6 In (a), it is evident that the open-circuit potential drop of the optoelectronic materials prepared with SrCl2·6H2O and Sr(NO3)2 as the Sr source is significantly weaker than that of the CNT-COOH / Sr-ZnIn2S4 material prepared with Sr(CH3COO)2 as the Sr source. The photogenerated current density also exhibits the same trend. Figure 6 (As shown in (b)). The above results indicate that different strontium sources have a significant impact on the Sr doping effect. Only by using Sr(CH3COO)2 as the strontium source for doping can the photocathode protection capability of ZnIn2S4 be significantly improved.

[0055] IV. Summary of Results Based on the above test results, the CNT-COOH / Sr-ZnIn2S4 composite optoelectronic material prepared in this invention (Example 1) has the following excellent properties: (1) Sr doping optimized the band structure and microstructure of ZnIn2S4 (Comparative Example 2), transforming it from a dense flower-like structure to a loose and dispersed nanosheet structure, increasing the reactive area and promoting the separation and migration of photogenerated carriers. The optimal Sr doping amount corresponds to a molar ratio of ZnCl2, InCl3, Sr(CH3COO)2, and C2H5NS of 1:2:2:4. (2) The introduction of MWCNTs-COOH forms a continuous conductive network (Example 1), providing a fast transport channel for photogenerated electrons and significantly reducing the interfacial charge transport impedance. The optimal amount of MWCNTs-COOH added is 5%~7% of the mass of ZnCl2, preferably 6.2%; (3) The synergistic effect of Sr doping and MWCNTs-COOH conductive network (Example 1) significantly enhances the absorption intensity of the composite material in the visible light region, with a significant red shift of the absorption edge, a widened light response range, and a significant improvement in the overall photoelectric conversion efficiency; (4) In a simulated marine environment (3.5 wt% NaCl solution), after the CNT-COOH / Sr-ZnIn2S4 composite photoelectrode (Example 1) was coupled with 316L SS, the open-circuit potential shifted significantly negatively to approximately -0.58 V, and the photogenerated current density reached approximately 36.2 μA·cm. -2 It exhibits excellent photogenerated electron output capability and cathode polarization capability, and can be used for photoelectrochemical cathodic protection under conditions without external power supply. (5) The doping effect of Sr(CH3COO)2 as strontium source (Example 1) is significantly better than that of SrCl2·6H2O (Comparative Example 4) and Sr(NO3)2 (Comparative Example 5), and the composite effect of carboxylated multi-walled carbon nanotubes (Example 1) is significantly better than that of ordinary multi-walled carbon nanotubes (Comparative Example 3).

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a CNTCOOH / Sr-ZnIn2S4 composite photocathode protection material, characterized in that, Includes the following steps: Zinc salt, indium salt, and strontium source were dissolved in deionized water, stirred evenly, and then sulfur source was added. Stirring was continued to obtain Sr-ZnIn2S4 precursor solution. Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were added to the Sr-ZnIn2S4 precursor solution, stirred, and the mixed solution was transferred to a reaction vessel for hydrothermal reaction. After the reaction was completed, the resulting suspension was centrifuged, the precipitate was washed and dried to obtain the CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material.

2. The preparation method according to claim 1, characterized in that, The zinc salt is ZnCl2, the indium salt is InCl3, the strontium source is Sr(CH3COO)2, and the sulfur source is C2H5NS; and the molar ratio of ZnCl2, InCl3, Sr(CH3COO)2, and C2H5NS is 1:2:1.5 to 3:

4.

3. The preparation method according to claim 2, characterized in that, The molar ratio of ZnCl2, InCl3, Sr(CH3COO)2, and C2H5NS is 1:2:2:

4.

4. The preparation method according to claim 2, characterized in that, The amount of MWCNTs-COOH added is 5% to 7% of the mass of ZnCl2.

5. The preparation method according to claim 4, characterized in that, The amount of MWCNTs-COOH added is 6.2% of the mass of ZnCl2.

6. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature is 160~180℃, and the reaction time is 10~12 hours.

7. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature is 180℃, and the reaction time is 12 hours.

8. The preparation method according to claim 1, characterized in that, The centrifugation rate is 8000 r / min; the drying is carried out in a 60°C forced-air drying oven for 12 hours.

9. A CNT-COOH / Sr-ZnIn2S4 composite photocathode protection material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the CNT-COOH / Sr-ZnIn2S4 composite photoelectric cathodic protection material as described in claim 9 in photoelectrochemical cathodic protection.

Images