Preparation method of sulfur-indium-copper-cadmium sulfide composite photoanode based on small molecule coordination interaction and application thereof in electrochemical corrosion prevention

Abstract

The application discloses a preparation method of a sulfur indium copper-cadmium sulfide composite photoanode based on small molecule coordination cooperation and application in electrochemical corrosion prevention, and belongs to the technical field of photoelectric materials and electrochemical corrosion prevention. The application takes FTO glass as a substrate, and prepares a CIS-EDTA-CdS composite material through a hydrothermal method, small molecule coordination and an ion adsorption reaction method, and constructs a CIS-EDTA-CdS photoanode. The CIS-EDTA-CdS has wide light absorption performance from ultraviolet to near infrared and high photoelectron-hole separation rate. The CIS-EDTA-CdS photoanode has good photoelectrochemical cathodic protection performance on 304 stainless steel. The photoanode constructed by the application generates photoelectrons under light, and the photoelectrons migrate and enrich to the surface of the protected metal, so that the metal cathode is polarized to reach a thermodynamic stable state, and then the metal corrosion is inhibited, and a photoelectrochemical cathodic protection metal corrosion prevention method is constructed.

Description

Technical Field

[0001] This invention belongs to the fields of optoelectronic materials and electrochemical corrosion protection technology, and particularly relates to a method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding and its application in electrochemical corrosion protection. Background Technology

[0002] Stainless steel, due to its excellent corrosion resistance and comprehensive performance, is widely used in construction, transportation, aerospace, energy, medical devices, and many other fields. However, metals are thermodynamically unstable and inevitably corrode during use. Corrosion not only significantly shortens the service life of stainless steel materials, leading to frequent equipment maintenance and replacement, causing serious resource consumption and economic losses, but may even trigger major safety accidents, endangering human life and property. Therefore, metal corrosion protection is of great significance for industrial development and reducing the economic losses and hazards caused by corrosion. Currently used anti-corrosion measures include coatings, sacrificial anode cathodic protection, and impressed current cathodic protection, but these methods have problems such as high energy consumption, environmental pollution, and failure or cracking of the protective layer. To address this, a new cathodic protection technology—photoelectrochemical (PEC) cathodic protection—has emerged. Its mechanism of action is: when light irradiates a semiconductor material, the material is excited to generate photoelectrons, which accumulate on the metal surface, putting it in a cathodic polarization protective state. This technology has been widely studied in recent years due to its advantages such as not consuming energy and being environmentally friendly.

[0003] The key to achieving efficient photocathode protection in photoelectric cathodes (PECs) lies in developing high-performance photoanode materials. Currently, the most studied materials include TiO2, BiVO4, CdS, and g-C3N4. Among them, CdS, an n-type semiconductor with a band gap of approximately 2.4 eV, can absorb visible light and achieve efficient photoelectric conversion, showing great application potential in the field of photocathode protection. Numerous studies have shown that combining CdS with other semiconductor materials to form heterojunctions can effectively improve the catalytic activity and photocathode protection performance of the composite material. However, the light absorption of CdS is mainly limited to the ultraviolet-visible region, with extremely low utilization efficiency in the near-infrared (NIR) region, which accounts for about 50% of the solar spectrum. This severely restricts the improvement of overall energy conversion efficiency. Ternary metal sulfides (CIS) have a narrow band gap (approximately 1.5 eV) and a high absorption coefficient (>10). 5 cm -1 With advantages such as low cost and tunable bandgap, it can extend the photoresponse range to the NIR region and form a band-matched heterojunction with CdS, thus it can be used as a near-infrared responsive photosensitizer for CdS.

[0004] However, constructing efficient CIS / CdS heterojunctions still faces significant challenges: ideal interface charge separation requires a tightly packed interface structure with low defects between semiconductors. However, due to lattice mismatch and differences in growth orientation, high-density defect states are often introduced at the interface between different semiconductor materials. These defect states become charge recombination centers, severely restricting the improvement of heterojunction performance. To address this issue, interface passivation has become a key strategy for improving charge separation efficiency. This strategy introduces an interface layer between materials to release lattice stress and reduce defect state density. The passivation layer not only acts as a tunneling barrier, effectively suppressing interface charge recombination, but also passivates surface states to reduce non-radiative recombination; some materials can even modulate the charge transport direction and efficiency.

[0005] Current interfacial passivation methods mainly fall into two categories. The first category involves inserting thin layers with good physical or chemical compatibility (such as Al2O3 and SnO2 prepared by atomic layer deposition) between heterojunction materials. For example, Ma et al. introduced an ultrathin Al2O3 layer between CdS and ZnO to construct a CdS@Al2O3@ZnO composite structure. This Al2O3 layer not only lowers the interfacial barrier and promotes charge transfer, but its fixed negative charge also optimizes the carrier transport path, thereby enhancing the photocatalytic activity of the system (Journal of Materials Chemistry A, 2020, 8: 11031-11042). However, these methods mainly rely on physical contact or weak interactions, and the lack of strong chemical bonding at the interface often forms a charge transport "barrier," which restricts further performance improvement.

[0006] The second type of approach focuses on achieving atomically close interfaces by constructing strong chemical bonds (such as coordination and covalent bonds). For example, Zheng et al. significantly enhanced the catalytic performance of the composite material by doping P atoms into g-C3N4 to form anchoring sites, thereby constructing Ni-PN bonds with Ni nanoparticles (ACS Applied Energy Materials, 2022, 5: 5756-5765). Although atomic-level interface construction strategies have shown significant advantages in the field of photocatalysis, related research is still in its early stages. Crucially, the application of this advanced atomic-level interface engineering strategy in PEC cathodic protection is almost nonexistent, and its potential in improving protection current, enhancing stability, and expanding spectral utilization needs to be further explored. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding and its application in electrochemical corrosion protection. This invention utilizes the coordination bonding of small molecule ligands to form an atomically close contact interface between copper indium sulfide (CuInS2, CIS) and cadmium sulfide (CdS), constructing a heterojunction composite material that can be applied in the field of electrochemical corrosion protection.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding. First, CuInS2 is prepared by hydrothermal method; then, CuInS2-EDTA photoanode is prepared by coordination with ethylenediaminetetraacetic acid; finally, the copper indium sulfide-cadmium sulfide composite photoanode (CuInS2-EDTA-CdS photoanode) is prepared by coordination bonding and ion adsorption reaction.

[0009] This invention provides a novel S-type heterojunction based on coordination bonds to construct an atomic-level interface and a method for using it for photoelectrochemical cathodic protection. Starting from the hydrothermal preparation of CIS, the surface defects of CIS are passivated through the coordination effect of the small molecule ligand ethylenediaminetetraacetic acid (EDTA). Then, a CIS-EDTA-CdS composite material is prepared through coordination bonding and ion adsorption reaction. Finally, a CIS-EDTA-CdS photoanode is constructed to establish a method for photoelectrochemical cathodic protection.

[0010] The principle of this invention is as follows: The corrosion protection of metals such as 304 stainless steel by the copper indium sulfide-cadmium sulfide (CIS-EDTA-CdS) composite photoanode is essentially a form of photoelectrochemical cathodic protection (PECCP). CIS (bandgap approximately 1.5 eV) and CdS (bandgap approximately 2.4 eV) form a broad-spectrum absorption system. Under illumination, both absorb photons simultaneously, and valence band (VB) electrons are transitioned to the conduction band (CB), generating photogenerated electrons (electrons). - ) and holes (h +Yes. CIS is responsible for extending the photoresponse range into the near-infrared region, while CdS is responsible for enhancing absorption in the visible light region. Their complementarity ensures that the photoanode can generate sufficient photogenerated carriers under the solar spectrum, providing a sufficient electron source for subsequent cathodic protection. The core corrosion suppression of the composite material lies in its charge separation efficiency. The band positions of CIS and CdS form an alternating arrangement (S-type heterojunction): the conduction band (CB) of CIS is higher than that of CdS, while the valence band (VB) of CdS is lower than that of CIS. After photoexcitation, photogenerated electrons on the CdS conduction band recombine with holes in the CIS valence band, while electrons on the CIS conduction band migrate to the 304 stainless steel surface (304SS) through the conductive substrate (FTO) and external circuitry. This spatial charge separation greatly suppresses the bulk recombination of electron-hole pairs within the material, significantly extending the lifetime of photogenerated electrons. This is the fundamental driving force behind the continuous current output of this photoanode to drive cathodic protection. EDTA's coordination effect can effectively chelate dangling bonds and unsaturated metal sites (such as Cu) on the CIS surface. + / In 3+ This significantly reduces the defect state density on the CIS surface. This reduces the probability of photogenerated electrons being trapped and recombine by defects when transported to the interface, ensuring that more effective electrons can be successfully conducted to the conductive substrate (FTO). After EDTA adsorbs on the CIS surface, it alters the interfacial charge distribution, facilitating subsequent Cd deposition. 2+ The ion adsorption provides specific coordination anchors, allowing CdS nanoparticles to uniformly and tightly coat the CIS surface, forming an atomically close heterogeneous interface. This close contact greatly shortens the distance electrons travel from CdS to CIS, reducing the interfacial resistance. After photogenerated electrons are efficiently separated within the CIS-EDTA-CdS and enriched in the CIS conduction band, they are rapidly injected into the connected 304SS via the FTO conductive glass substrate and external wires. This process causes a sharp increase in the electron density on the 304SS surface, shifting its electrode potential negatively and significantly deviating from its own natural corrosion potential (Ecorr), i.e., cathodic polarization occurs. Cathodic polarization puts the metal surface in a thermodynamically "electron-rich" state, forcibly inhibiting the anodic dissolution reaction. At this time, 304SS becomes the "cathode" in the cathodic protection system and is protected; simultaneously, the photogenerated holes (h) remaining on the CIS-EDTA-CdS photoanode surface... + The reducing substances in the oxidation solution are consumed, thus avoiding photocorrosion of the photoanode itself and maintaining a continuous and stable output of the protection current.

[0011] Furthermore, the specific process for preparing CuInS2 using the hydrothermal method is as follows: Cu2O, InCl3∙3H2O and thiourea are dissolved in ethylene glycol and ultrasonically mixed to obtain a mixed solution; FTO glass (fluorine-doped tin oxide conductive glass) is immersed in the mixed solution and reacted at 80~300℃ for 2~16h. After washing and calcination, CuInS2 is obtained.

[0012] Further, the mass ratio of Cu2O, InCl3∙3H2O and thiourea is (0.01~0.5):(0.01~1.1):(0.01~1.3).

[0013] Furthermore, the calcination temperature is 100~800℃, and the time is 1~8 h.

[0014] Furthermore, the process of preparing CuInS2-EDTA photoanode through the coordination effect of ethylenediaminetetraacetic acid is as follows: dissolve disodium ethylenediaminetetraacetate in ethanol, immerse CuInS2 in the resulting solution, and dry to obtain CuInS2-EDTA photoanode.

[0015] Furthermore, the soaking time is 0.5 to 6 hours.

[0016] Furthermore, the process of preparing the copper indium sulfide-cadmium sulfide composite photoanode by coordination bonding and ion adsorption reaction is as follows: first, the CuInS2-EDTA photoanode is immersed in a solution containing soluble cadmium salt, washed with ethanol, and then immersed in Na2S solution. This process is repeated 2 to 50 times, and the photoanode is obtained after drying.

[0017] Further, the soluble cadmium salt is Cd(NO3)2∙4H2O, and the mass ratio of Cd(NO3)2∙4H2O to Na2S∙9H2O is (0.04~1.1):(0.02~1).

[0018] The present invention also provides a copper indium sulfide-cadmium sulfide composite photoanode prepared according to the above method.

[0019] The present invention also provides an application of the above-mentioned copper indium sulfide-cadmium sulfide composite photoanode in electrochemical corrosion protection.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects: This invention prepares a CIS-EDTA-CdS composite material by hydrothermal method, combined with small molecule coordination bonding and ion adsorption reaction method. The photoanode constructed by the composite material is used for photoelectrochemical cathodic protection of metals. This invention provides a heterojunction composite optoelectronic material constructed by atomic-level interface formed by small molecule coordination bonding and its photoelectrochemical cathodic protection method for metal corrosion prevention.

[0021] This invention utilizes small molecule coordination bonding to passivate interface defects and achieve strong coupling between semiconductors, ensuring efficient charge separation. The constructed CIS-EDTA-CdS composite material can absorb a wide spectral range of light from ultraviolet to near-infrared.

[0022] This invention is applicable to the preparation of composite optoelectronic materials and the application of composite photoanodes for photoelectrochemical cathodic protection of metals. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a scanning electron microscope image of the CIS photoanode prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the CIS-EDTA photoanode prepared in Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of the CIS-EDTA-CdS photoanode prepared in Example 1 of the present invention; Figure 4 The image shows the elemental distribution map and EDS diagram of the CIS-EDTA photoanode prepared in Example 1 of this invention. A is the elemental distribution map and B is the EDS diagram. Figure 5 The image shows the elemental distribution map and EDS diagram of the CIS-EDTA-CdS photoanode prepared in Example 1 of this invention. A is the elemental distribution map and B is the EDS diagram. Figure 6 XRD patterns of the CIS photoanode, CIS-EDTA photoanode, and CIS-EDTA-CdS photoanode prepared in Example 1 of the present invention; Figure 7 XPS spectra of the CIS-EDTA-CdS photoanode prepared in Example 1 of this invention: A is the full spectrum, B is the C 1s spectrum, C is the Cd 3d spectrum, D is the Cu 2p spectrum, E is the In 3d spectrum, F is the N 1s spectrum, G is the O 1s spectrum, and H is the S 2p spectrum. Figure 8 The images shown are TEM and HRTEM images of the CIS-EDTA-CdS photoanode prepared in Example 1 of this invention. A is the TEM image and B is the HRTEM image. Figure 9The ultraviolet-visible diffuse reflectance spectra and Tauc diagrams of CdS, the CIS photoanode, the CIS-EDTA photoanode, and the CIS-EDTA-CdS photoanode prepared in Example 1 of this invention are shown. A is the ultraviolet-visible diffuse reflectance spectrum, B is the Tauc diagram of the CIS photoanode, C is the Tauc diagram of the CdS photoanode, D is the Tauc diagram of the CIS-EDTA photoanode, and E is the Tauc diagram of the CIS-EDTA-CdS photoanode. Figure 10 Photocurrent response diagrams of CdS, the CIS photoanode prepared in Example 1 of this invention, the CIS-EDTA photoanode, and the CIS-EDTA-CdS photoanode; Figure 11 The open-circuit potential of 304SS coupled with CdS, the CIS photoanode prepared in Example 1 of this invention, the CIS-EDTA photoanode, and the CIS-EDTA-CdS photoanode; Figure 12 Polarization curves of 304SS coupled with CdS, the CIS photoanode prepared in Example 1 of this invention, the CIS-EDTA photoanode, and the CIS-EDTA-CdS photoanode; Figure 13 The images show the photocurrent response diagram and the open-circuit potential of the CIS-EDTA-CdS photoanode coupled with 304SS prepared in Example 2 of this invention. A is the photocurrent response diagram and B is the open-circuit potential diagram. Figure 14 The photocurrent response diagram of the CIS photoanode prepared in Comparative Example 2 of this invention is shown. Figure 15 The images show the Mott-Schottky curves of CdS, the CIS photoanode and the CIS-EDTA photoanode prepared in Example 1 of this invention, and the XPS spectra of Cd 3d, Cu 2p and In 3d of the CIS photoanode, CIS-EDTA photoanode and CIS-EDTA-CdS photoanode prepared in Example 1. A is the Mott-Schottky curve, B is the Cd 3d spectrum of the CIS photoanode, CIS-EDTA photoanode and CIS-EDTA-CdS photoanode prepared in Example 1, C is the Cu 2p spectrum of the CIS photoanode, CIS-EDTA photoanode and CIS-EDTA-CdS photoanode prepared in Example 1, and D is the In 3d spectrum of the CIS photoanode, CIS-EDTA photoanode and CIS-EDTA-CdS photoanode prepared in Example 1. Figure 16 This is a diagram illustrating the mechanism of the S-type heterojunction formed by CIS-EDTA-CdS. Detailed Implementation

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0028] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0029] The present invention provides a method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding. First, CuInS2 (CIS) is prepared by hydrothermal method; then, CuInS2-EDTA photoanode (CIS-EDTA photoanode) is prepared by coordination with ethylenediaminetetraacetic acid; finally, the copper indium sulfide-cadmium sulfide composite photoanode (CuInS2-EDTA-CdS photoanode, denoted as CIS-EDTA-CdS photoanode) is prepared by coordination bonding and ion adsorption reaction.

[0030] In a preferred embodiment of the present invention, a method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding includes the following steps: (1) Weigh 0.010~0.500 g Cu2O, 0.010~1.100 g InCl3∙3H2O and 0.010~1.300 g thiourea into a beaker, add 5~200 mL of ethylene glycol, sonicate the mixture and then place it in a magnetic stir bar and stir for 5~80 min until the solution is clear and transparent; place the cleaned and prepared FTO glass plate with the conductive side down at a 45° angle in a polytetrafluoroethylene liner, transfer the obtained mixture into the polytetrafluoroethylene liner, cover it with a stainless steel outer liner, and place it in an oven at a constant temperature of 80~300℃ for 2~16 h. After the reaction vessel cools down, rinse the FTO glass plate three times with ethylene glycol and ethanol alternately; then calcine at 100~800℃ for 1~8 h. After calcine, cool to room temperature to obtain the CIS photoanode. (2) Weigh 0.010~0.120 g of EDTA disodium salt into a beaker, add 1~30 mL of ethanol, and sonicate the solution until it is completely dissolved; place the CIS photoanode prepared in step (1) with the conductive surface facing down, tilt it at 45° in the beaker and soak for 0.5~6 h, and dry it at room temperature to obtain the CIS-EDTA photoanode; (3) Weigh 0.040~1.100 g Cd(NO3)2∙4H2O into beaker 1, then add 1~15 mL of ethanol and 0.5~10 mL of deionized water, and sonicate until completely dissolved to obtain Cd(NO3)2 solution; weigh 0.020~1.000 g Na2S∙9H2O into beaker 2, then add 1~15 mL of ethanol and 0.5~10 mL of deionized water, and sonicate until completely dissolved to obtain Na2S solution; immerse the CIS-EDTA photoanode obtained in step (2) into the Cd(NO3)2 solution in beaker 1 for 3~60 s, wash with ethanol, then immerse in the Na2S solution in beaker 2 for 3~60 s, repeat the operation 2~50 times, and then dry at 30~150 ℃ for 0.5~6 h to obtain copper indium sulfide-cadmium sulfide composite photoanode, denoted as CIS-EDTA-CdS photoanode.

[0031] An exemplary method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding includes the following specific steps: (1) Weigh 0.065 g Cu2O, 0.18 g InCl3·3H2O and 0.19 g thiourea into a beaker, add 20 mL of ethylene glycol, sonicate the mixture and then place it in a magnetic stir bar and stir for 30 min until the solution is clear and transparent to obtain a mixed solution; place the cleaned and prepared FTO glass plate with the conductive side down at a 45° angle in a polytetrafluoroethylene liner, transfer the obtained mixed solution to the above polytetrafluoroethylene liner, cover it with a stainless steel outer liner, place it in an oven at a constant temperature of 180℃ for 6 h and then take it out. After the reaction vessel cools down, rinse the FTO glass plate three times with ethylene glycol and ethanol alternately; then calcine at 300℃ for 2 h. After calcine, cool to room temperature to obtain CuInS2 photoanode, which is denoted as CIS photoanode.

[0032] (2) Weigh 0.038 g of disodium EDTA (disodium ethylenediaminetetraacetate) and place it in a beaker. Add 5 mL of ethanol to it and sonicate the solution until it is completely dissolved. Place the CIS photoanode prepared in step (1) with the conductive side facing down and tilted at 45° in the beaker above for 2 h. Dry it at room temperature to obtain CuInS2-EDTA photoanode, which is denoted as CIS-EDTA photoanode.

[0033] (3) Weigh 0.154 g Cd(NO3)2∙4H2O into beaker 1, then add 4 mL of ethanol and 1 mL of deionized water, and sonicate until completely dissolved to obtain Cd(NO3)2 solution; weigh 0.12 g Na2S∙9H2O into beaker 2, then add 4 mL of ethanol and 1 mL of deionized water, and sonicate until completely dissolved to obtain Na2S solution; immerse the CIS-EDTA photoanode obtained in step (2) into the Cd(NO3)2 solution in beaker 1 for 15 s, wash with ethanol, then immerse in the Na2S solution in beaker 2 for 15 s, repeat the operation 12 times, and then dry at 60 ℃ for 1 h to obtain CuInS2-EDTA-CdS photoanode, denoted as CIS-EDTA-CdS photoanode.

[0034] An embodiment of the present invention also provides a copper indium sulfide-cadmium sulfide composite photoanode prepared according to the above method.

[0035] The embodiments of the present invention also provide an application of the above-mentioned copper indium sulfide-cadmium sulfide composite photoanode in electrochemical corrosion prevention.

[0036] This invention utilizes fluorine-doped tin oxide conductive glass (FTO) as a substrate to prepare a CIS-EDTA-CdS composite material via a hydrothermal method, combined with small molecule coordination and ion adsorption reaction, thus constructing a CIS-EDTA-CdS photoanode. CIS-EDTA-CdS exhibits broad light absorption performance from the ultraviolet to near-infrared region and a high photogenerated electron-hole separation rate. The CIS-EDTA-CdS photoanode demonstrates excellent photoelectrochemical cathodic protection performance for 304 stainless steel (304SS). The photoanode constructed using the composite material, under illumination, generates photogenerated electrons that migrate and accumulate on the surface of the protected metal, forcing the metal cathode to polarize and reach a thermodynamically stable state, thereby inhibiting metal corrosion. This invention establishes a photoelectrochemical cathodic protection method for metal corrosion prevention.

[0037] The present invention relates to a photocurrent response and photoelectrochemical cathodic protection method for metal corrosion prevention based on a CIS-EDTA-CdS composite photoanode, as follows: The photocurrent response of the CIS-EDTA-CdS composite photoanode was tested using a three-electrode system in a single electrolytic cell, wherein the prepared photoanode (effective area 1×1 cm⁻¹) 2 The photoanode was used as the working electrode, Ag / AgCl as the reference electrode, and a Pt column as the counter electrode. A 500W xenon lamp was used to simulate visible light (λ≥400 nm, with filters used to remove light below 400 nm) and was perpendicularly irradiated onto the photoanode surface. A quartz electrolytic cell was used. The electrolytes were 0.1 mol / L Na₂S and 0.2 mol / L NaOH solutions. It was tested on different photoanodes at a bias voltage of 0 V (vs. Ag / AgCl).

[0038] The photoelectrochemical cathodic protection performance of the prepared photoanode was tested using an H-type dual electrolytic cell, including a photolysis cell and a corrosion cell. The electrolyte in the photolysis cell was a 0.1 mol / L Na₂S and a 0.2 mol / L NaOH solution, while the corrosion cell contained a 3.5 wt% NaCl solution to simulate a seawater environment. The two electrolytic cells were connected by a Nafion proton exchange membrane (N117). A 500 W xenon lamp was used to simulate visible light (λ ≥ 400 nm; light below 400 nm was filtered out). A traditional three-electrode system was employed, with the corrosion cell containing a 304 stainless steel electrode (electrode area 1 × 1 cm⁻¹). 2 The photoanode in the photolysis cell is coupled to the working electrode clamp of the electrochemical workstation via a copper wire. The Ag / AgCl electrode and Pt column electrode placed in the corrosion cell serve as the reference electrode and counter electrode, respectively.

[0039] Open-circuit potential testing is the most direct and effective method for evaluating the photoelectrochemical cathodic protection performance of the prepared material's photoanode. When light shines on the surface of the photoanode, the electron-hole pairs in the photoanode material are excited and transition due to the absorption of light energy, generating photoelectrons. If these photoelectrons can effectively migrate to and accumulate on the metal surface coupled to the photoanode, the open-circuit potential of the coupled metal shifts negative, resulting in cathodic polarization and entering a thermodynamically stable state, thus providing protection. The more photoelectrons generated, the more negative the open-circuit potential of the coupled metal, and the better the photoelectrochemical cathodic protection performance. The open-circuit potential of 304SS is -0.202 V (vs. Ag / AgCl), while the open-circuit potential of 304SS coupled with a CIS-EDTA-CdS composite photoanode shifts negatively to -1.15 V (vs. Ag / AgCl).

[0040] To further evaluate the photoelectrochemical cathodic protection performance of the CIS-EDTA-CdS composite photoanode for 304SS, Tafel polarization curves of the photoanode coupled with 304SS were measured under visible light irradiation. The self-corrosion potential of 304SS was -0.202 V (vs. Ag / AgCl), which shifted negatively to -1.16 V (vs. Ag / AgCl) after coupling with the CIS-EDTA-CdS composite photoanode. In conclusion, the CIS-EDTA-CdS composite photoanode exhibits excellent photoelectrochemical cathodic protection performance for 304SS.

[0041] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0042] All raw materials used in the embodiments of this invention were purchased commercially.

[0043] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0044] The technical solution of the present invention will be further illustrated by the following embodiments.

[0045] Example 1 A method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding, the specific steps of which are as follows: (1) Weigh 0.065 g Cu2O, 0.18 g InCl3·3H2O and 0.19 g thiourea into a beaker, add 20 mL of ethylene glycol, sonicate the mixture and then place it in a magnetic stir bar and stir for 30 min until the solution is clear and transparent to obtain a mixed solution; place the cleaned and prepared FTO glass plate with the conductive side down at a 45° angle in a polytetrafluoroethylene liner, transfer the obtained mixed solution to the above polytetrafluoroethylene liner, cover it with a stainless steel outer liner, place it in an oven at a constant temperature of 180℃ for 6 h and then take it out. After the reaction vessel cools down, rinse the FTO glass plate three times with ethylene glycol and ethanol alternately; then calcine at 300℃ for 2 h. After calcine, cool to room temperature to obtain CuInS2 photoanode, which is denoted as CIS photoanode.

[0046] (2) Weigh 0.038 g of disodium EDTA (disodium ethylenediaminetetraacetate) and place it in a beaker. Add 5 mL of ethanol to it and sonicate the solution until it is completely dissolved. Place the CIS photoanode prepared in step (1) with the conductive side facing down and tilted at 45° in the beaker above for 2 h. Dry it at room temperature to obtain CuInS2-EDTA photoanode, which is denoted as CIS-EDTA photoanode.

[0047] (3) Weigh 0.154 g Cd(NO3)2∙4H2O into beaker 1, then add 4 mL of ethanol and 1 mL of deionized water, and sonicate until completely dissolved to obtain Cd(NO3)2 solution; weigh 0.12 g Na2S∙9H2O into beaker 2, then add 4 mL of ethanol and 1 mL of deionized water, and sonicate until completely dissolved to obtain Na2S solution; immerse the CIS-EDTA photoanode obtained in step (2) into the Cd(NO3)2 solution in beaker 1 for 15 s, wash with ethanol, then immerse in the Na2S solution in beaker 2 for 15 s, repeat the operation 12 times, and then dry at 60 ℃ for 1 h to obtain CuInS2-EDTA-CdS photoanode, denoted as CIS-EDTA-CdS photoanode.

[0048] Comparative Example 1: Preparation of Pure CdS Photoanode The cleaned and prepared FTO glass slide was immersed in the Cd(NO3)2 solution in beaker 1 of step (3) of Example 1 for 15 s, washed with ethanol, and then immersed in the Na2S solution in beaker 2 of step (3) of Example 1 for 15 s. The cycle was repeated 12 times, and then dried at 60 °C for 1 h to obtain the CdS photoanode.

[0049] Example 2 A method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding, the specific steps of which are as follows: (1) Weigh 0.065 g Cu2O, 0.18 g InCl3·3H2O and 0.19 g thiourea into a beaker, add 20 mL of ethylene glycol, sonicate the mixture and then place it in a magnetic stir bar and stir for 30 min until the solution is clear and transparent to obtain a mixed solution; place the cleaned and prepared FTO glass plate with the conductive side down at a 45° angle in a polytetrafluoroethylene liner, transfer the obtained mixed solution to the above polytetrafluoroethylene liner, cover it with a stainless steel outer liner, place it in an oven at a constant temperature of 180℃ for 6 h and then take it out. After the reaction vessel cools down, rinse the FTO glass plate three times with ethylene glycol and ethanol alternately; then calcine at 300℃ for 2 h. After calcine, cool to room temperature to obtain CuInS2 photoanode, which is denoted as CIS photoanode.

[0050] (2) Weigh 0.038 g of disodium EDTA (disodium ethylenediaminetetraacetate) and place it in a beaker. Add 5 mL of ethanol to it and sonicate the solution until it is completely dissolved. Place the CIS photoanode prepared in step (1) with the conductive side facing down and tilted at 45° in the beaker above for 2 h. Dry it at room temperature to obtain CuInS2-EDTA photoanode, which is denoted as CIS-EDTA photoanode.

[0051] (3) Weigh 0.154 g Cd(NO3)2∙4H2O into beaker 1, then add 4 mL of ethanol and 1 mL of deionized water, and sonicate until completely dissolved to obtain Cd(NO3)2 solution; weigh 0.12 g Na2S∙9H2O into beaker 2, then add 4 mL of ethanol and 1 mL of deionized water, and sonicate until completely dissolved to obtain Na2S solution; immerse the CIS-EDTA photoanode obtained in step (2) into the Cd(NO3)2 solution in beaker 1 for 15 s, wash with ethanol, then immerse in the Na2S solution in beaker 2 for 15 s, repeat the operation 4 times, and then dry at 60 ℃ for 1 h to obtain CuInS2-EDTA-CdS photoanode, denoted as CIS-EDTA-CdS photoanode.

[0052] Comparative Example 2 A method for preparing copper indium sulfide photoanodes, the specific steps of which are as follows: Weigh 0.087 g Cu2O, 0.18 g InCl3·3H2O, and 0.19 g thiourea into a beaker, add 20 mL of ethylene glycol, sonicate the mixture, and then place it in a magnetic stir bar. Stir for 30 min until the solution becomes clear and transparent. Place a cleaned FTO glass slide with the conductive side down at a 45° angle in a polytetrafluoroethylene (PTFE) liner. Transfer the resulting mixture into the PTFE liner, cover it with a stainless steel outer liner, and place it in an oven at a constant temperature of 180°C for 6 h. After the reaction vessel cools, rinse the FTO glass slide three times with ethylene glycol and ethanol alternately. Then calcine at 300°C for 2 h. After calcine, cool to room temperature to obtain the CuInS2 photoanode, denoted as the CIS photoanode.

[0053] The CIS photoanode, CIS-EDTA photoanode, and CIS-EDTA-CdS photoanode obtained in Example 1 were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS): The scanning electron microscope image of the CIS photoanode obtained in Example 1 is shown below. Figure 1 As shown, the scanning electron microscope image of the CIS-EDTA photoanode is as follows: Figure 2 As shown, the scanning electron microscope image of the CIS-EDTA-CdS photoanode is as follows: Figure 3 As shown. From Figure 1 As can be seen, CIS exhibits an interwoven, irregular nanosheet structure, growing relatively uniformly on FTO glass. The EDTA-modified CIS framework remains an irregular sheet-like nanosheet, but the network structure transforms into a three-dimensionally interconnected porous "coral-like" morphology. Figure 2 After loading with CdS, small particle clusters are formed. A large number of nano-sized CdS particles grow uniformly on the CuInS2-EDTA network framework. The original "coral-like" structure is wrapped by particle clusters, forming a rougher and denser surface. Figure 3 ).

[0054] The elemental content and surface distribution of EDS in CIS-EDTA and CIS-EDTA-CdS photoanodes were analyzed using EDS characterization techniques. The results are shown in [Figure number missing]. Figure 4 and Figure 5 .from Figure 4 It can be seen that S, In, Cu, C, N, and O elements are all uniformly distributed, indicating that EDTA effectively modifies the surface of the CIS material, proving the successful preparation of the CIS-EDTA material. Figure 5 It can be seen that the sample contains S, In, Cu, C, N, O and Cd elements, and each element is uniformly distributed, indicating that CdS nanoclusters are uniformly distributed on the CIS-EDTA surface.

[0055] X-ray diffraction (XRD) characterization tests were performed on the CIS photoanode, CIS-EDTA photoanode, and CIS-EDTA-CdS photoanode obtained in Example 1: The XRD patterns of CIS photoanode, CIS-EDTA photoanode, and CIS-EDTA-CdS photoanode are shown below. Figure 6 As shown. From Figure 6 It can be seen that the diffraction peak positions of CIS basically correspond to the standard diffraction pattern of chalcopyrite-structured CIS (PDF#97-016-3489). In the XRD pattern of the CIS photoanode, excluding the substrate FTO, the diffraction peaks at 26.62°, 27.68°, 54.9°, and 61.9° correspond to the (100), (200), (112), and (202) crystal planes of CIS. The possible reason for the indistinct diffraction peaks of the characteristic crystal plane of CIS (200) in the sample is that the diffraction peak of CIS at 50.36° overlaps with the diffraction peak of FTO. The XRD pattern of the CIS-EDTA photoanode modified with EDTA is basically consistent with that of pure CIS, with no new diffraction peaks or obvious peak position shifts, indicating that the EDTA modification did not destroy the crystal structure of CIS. The slight decrease in diffraction peak intensity of the CIS-EDTA photoanode is attributed to the covering and scattering effect of amorphous EDTA on the surface, proving that EDTA mainly exists in the form of surface adsorption and has not been doped into the crystal lattice or formed a new crystal phase. Comparing the XRD patterns of the CIS-EDTA photoanode and the CIS-EDTA-CdS photoanode, the newly added diffraction peaks at 24.8° and 28.1° belong to the (100) and (101) crystal planes of CdS (PDF#00-041-1049). The diffraction peak at 26.5° belongs to the (002) characteristic crystal plane of CdS, and the peak intensity at this point is slightly enhanced. The reason for this is that the diffraction peak overlaps with the diffraction peaks of FTO and CIS. The other diffraction peaks are the same as the CIS diffraction peaks, indicating that the successful preparation of the CIS-EDTA-CdS composite material has not damaged the crystal structure of each individual material.

[0056] XPS and TEM characterization tests were performed on the CIS-EDTA-CdS photoanode obtained in Example 1: To further investigate the elemental composition and chemical state of the prepared CIS-EDTA-CdS composite material, XPS analysis was performed on the CIS-EDTA-CdS photoanode obtained in Example 1. The results are as follows: Figure 7 As shown. Figure 7 Figure A shows the XPS full spectrum of the CIS-EDTA-CdS composite material. It can be seen that the spectrum contains obvious characteristic peaks of C, Cd, Cu, In, N, O and S elements, indicating that the surface of the CuInS2-EDTA-CdS composite material contains the above elements. Figure 7B, C, D, E, F, G, and H represent the high-resolution spectra of C, Cd, Cu, In, N, O, and S in the CIS-EDTA-CdS composite material, respectively. In the C 1s spectrum (… Figure 7 In the high-resolution spectrum of Cu 2p (B), the peaks at 284.8 eV, 286.7 eV, and 288.8 eV are attributed to the CC, CN / CO, and OC=O bonds in EDTA, respectively. Figure 7 From D), we can obtain Cu 2p at 932.4 eV and 952.3 eV. 3 / 2 and Cu 2p 1 / 2 Peak indications: The Cu in the CIS-EDTA-CdS photoanode is Cu. + In In 3d high-resolution spectra ( Figure 7 The peaks at 444.7 eV and 452.2 eV (in the middle E) are attributed to In 3d. 5 / 2 and In 3d 3 / 2 This corresponds to the In of the composite photoanode. 3+ In the N 1s high-resolution spectrum ( Figure 7 In the (F) spectrum, the peak at 399.89 eV corresponds to the N atom on the tertiary amine (CN(C)-C) group. Meanwhile, in the O 1s high-resolution spectrum ( Figure 7 In the CIS-EDTA-CdS matrix, the peaks at 533.3 eV and 530.9 eV correspond to oxygen atoms in COH and Cu-O / In-O / Cd-O bonds oxidized on the CIS-EDTA-CdS surface, respectively, while the peak at 531.9 eV corresponds to the deprotonated carboxylate group (-COO) in EDTA. - The presence of this peak in the conjugated system of oxygen atoms proves the interaction between the carboxylate group in EDTA and CuInS2, as well as the Cu in CdS. + In 3+ Cd 2+ Coordinate bonds were formed. This is shown in the high-resolution S 2p spectrum. Figure 7 From H), we can obtain S 2p 2p 3 / 2 and 2p 1 / 2 The two characteristic peaks are located at 161.3 eV and 162.6 eV, respectively. The XPS spectrum further verifies the successful preparation of the CIS-EDTA-CdS photoanode.

[0057] Figure 8 Image A is a TEM image of the CIS-EDTA-CdS photoanode, which characterizes the heterojunction morphology and detailed structure of CIS-EDTA-CdS. The composite material exhibits a particle cluster structure, consistent with the SEM characterization. Figure 8Image B shows the HRTEM image of the CIS-EDTA-CdS photoanode, further revealing the close contact between the CIS-EDTA-CdS surfaces and the clear lattice fringes. The interplanar spacings of the (100) and (112) crystal planes of CIS were determined to be 0.335 nm and 0.171 nm, respectively (PDF#97-016-3489), while the interplanar spacing of the (101) crystal plane of CdS was 0.314 nm (PDF#00-041-1049). The clearly visible lattice spacings of both materials demonstrate the successful preparation of the CIS-EDTA-CdS composite material.

[0058] To investigate the light absorption properties of CIS photoanodes, CdS, CIS-EDTA photoanodes, and CIS-EDTA-CdS photoanodes, the UV-Vis diffuse reflectance spectra of the samples in the wavelength range of 200–1200 nm were measured. Figure 9 As shown in Figure A, CIS exhibits strong absorption in the ultraviolet-visible to near-infrared regions. The absorption performance of the CIS-EDTA photoanode modified with EDTA is similar to that of CIS, indicating that EDTA modification has virtually no effect on the light absorption performance of CIS. Pure CdS only shows significant absorption in the ultraviolet and short-wavelength visible light regions. The CIS-EDTA-CdS photoanode has a higher absorbance in the visible light region than pure CdS, while retaining the broad-spectrum light response of CIS. This achieves complementary advantages in light absorption between the two materials, exhibiting strong absorption performance from the ultraviolet-visible to near-infrared regions.

[0059] To obtain the bandgap values ​​of CIS photoanodes, CdS, CIS-EDTA photoanodes, and CIS-EDTA-CdS photoanodes, the bandgap of the materials was analyzed by UV-Vis diffuse reflectance spectroscopy using Kubelka-Munk theory and the linear fitting Tauc-plot method. The results are as follows: Figure 9 As shown in B~E.

[0060] The specific calculation formula is as follows: Where α is the absorption coefficient (cm²) measured in the ultraviolet-visible diffuse reflectance spectrum. -1 h is Planck's constant. ν Frequency (s) -1 ), h ν Let A be the photon energy (eV), and A be a material-related constant (the bandgap is determined by the intercept on the X-axis, 0 = A(h)). ν -Eg), A will be eliminated). E g denoted as the bandgap width (eV) of the semiconductor; n is related to the semiconductor type, taking 1 / 2 for direct bandgap semiconductors and 2 for indirect bandgap semiconductors.

[0061] According to Formula 1, h ν As the x-axis, with (αh) ν ) 1 / n Plot a Tauc plot with the ordinate as the vertical axis, perform a linear fit on the near-straight portion of the curve, and the intercept on the X-axis represents the bandgap width of the semiconductor. Calculations show that the bandgap widths of CIS, CdS, CIS-EDTA, and CIS-EDTA-CdS... E g The band gaps were 1.87 eV, 2.17 eV, 1.67 eV, and 1.75 eV, respectively. This band gap variation indicates that an effective heterojunction interface was formed between CIS-EDTA and CdS, which effectively promoted the separation and migration of photogenerated carriers, suppressed electron-hole recombination, broadened the spectral absorption range, and improved the photoelectric response capability of the material, thereby enhancing the photocathode protection performance.

[0062] Photocurrent response and photoelectrochemical cathodic protection performance of CIS-EDTA-CdS composite photoanode: Figure 10 The photocurrent response diagrams for CdS, CIS-EDTA, CIS-CdS, and CIS-EDTA-CdS photoanodes are shown. The test results indicate that all samples exhibit n-type semiconductor photocurrent characteristics, rapidly generating current upon illumination and reaching a steady state. The photocurrent decays to zero upon illumination termination, and the photocurrent tends to be consistent across three consecutive cycles. Among them, the CuInS2-EDTA photoanode exhibits the lowest photocurrent value, at 223 μA / cm². 2 The photocurrent of the pure CdS photoanode is 0.42 mA / cm². 2 When CuInS2 is combined with CdS, the photocurrent density of the CuInS2-CdS photoanode increases to 0.59 mA / cm². 2 Compared to pure CdS, the photocurrent density improved by 38%, indicating that the formation of the heterojunction can promote the separation of photogenerated carriers to a certain extent and improve the photocathode protection performance. However, compared with the CuInS2-EDTA-CdS photoanode, this composite photoanode exhibits the best photoelectric performance, with a photocurrent density reaching up to 1.3 mA / cm². 2 The photocurrents are 3.1 times that of pure CdS and 2.2 times that of CuInS2-CdS, respectively, and are far higher than the simple sum of the photocurrents of the two single-component materials (0.64 mA / cm²). 2 This effectively demonstrates that the composite of CdS and EDTA-modified CuInS2 significantly improves the photocathode protection performance.

[0063] Figure 11This diagram shows the open-circuit potentials of CIS, CdS, CIS-EDTA, and CIS-EDTA-CdS photoanodes coupled to 304SS under intermittent visible light irradiation. Compared to CdS, CIS, and CIS-EDTA, as... Figure 11 As shown, the CIS-EDTA-CdS composite photoanode exhibits the most negative open-circuit potential, indicating that the formation of the heterojunction effectively improves visible light utilization and enhances the separation efficiency of photogenerated electron-hole pairs, thereby improving the photocathode protection performance of 304SS. After the illumination is turned off, photogenerated electrons recombine with holes, rapidly reducing the electron concentration near the semiconductor conduction band. The open-circuit potential then shifts towards a more positive direction, and even after stabilization, the open-circuit potential remains lower than the self-corrosion potential of 304SS, providing highly efficient photocathode protection. After three intermittent light cycle tests, the open-circuit potential showed a consistent trend with the switching on and off of the light, indicating that the prepared photoanode has good stability, which was further confirmed in subsequent stability tests.

[0064] To further evaluate the photoelectrochemical cathodic protection performance of the CIS-EDTA-CdS photoanode for 304SS, Tafel polarization curves of different photoanodes coupled with 304SS were tested under visible light irradiation. The results are as follows: Figure 12 As shown, the corrosion potential of 304SS is -0.202 V (vs. Ag / AgCl). Compared with 304SS coupled with CdS, CIS-EDTA, and CIS-CdS photoanodes, the corrosion potential of 304SS coupled with the CIS-EDTA-CdS composite photoanode is the most negative.

[0065] The photocurrent response and photoelectrochemical cathodic protection performance of the photoanode obtained in Example 2: Figure 13 Figure A shows the photocurrent response of the CIS-EDTA-CdS photoanode obtained in Example 2. During illumination, current is rapidly generated and reaches a steady state. At the end of illumination, the photocurrent decays to zero, and the photocurrents in three consecutive cycles tend to be consistent, with a photocurrent density of approximately 0.65 mA / cm². 2 . Figure 13 Figure B shows the open-circuit potential diagram of the CIS-EDTA-CdS photoanode obtained in Example 2 coupled with 304SS under intermittent visible light irradiation. Under visible light irradiation, the open-circuit potential shifts negatively to -1.01V.

[0066] Photocurrent response performance of the photoanode obtained in Comparative Example 2: Figure 14 The image shows the photocurrent response of the CIS photoanode obtained in Comparative Example 2. During illumination, current is rapidly generated and reaches a steady state. At the end of illumination, the photocurrent decays to zero, and the photocurrent tends to be consistent across three consecutive cycles, with a photocurrent density of approximately 0.60 mA / cm². 2 .

[0067] Photoelectrochemical cathodic protection mechanism of CIS-EDTA-CdS composite photoanode: Figure 15 Figure A shows the Mott-Schottky (MS) spectra of CIS, CdS, and CIS-EDTA with different photoanodes. It can be seen that all samples exhibit a positive slope, indicating that they are all n-type semiconductor materials, and photogenerated carriers are mainly transported by electrons. The flat-band potentials of CIS, CdS, and CIS-EDTA were obtained from the MS measurements. E fb The values ​​are -0.66 V, -0.7 V, and -0.85 V (vs. Ag / AgCl), respectively. CIS-EDTA is superior to CIS... E fb The significant negative shift indicates that the Fermi level of the photoanode shifts upward after EDTA modification, enhancing the semiconductor's reduction capability and thus improving the photocathode protection performance. Typically, semiconductors... E fb Its Fermi level ( E f Correspondingly. Based on the results obtained from MS testing. E fb This allows for further derivation of the sample's conduction band potential (E). CB ) and valence band potential (E) VB The conduction band of an n-type semiconductor ( E CB ) Usually located in E fb Nearly -0.2 V, the calculated values ​​of CIS, CdS, and CIS-EDTA are... E CB The band gaps were -0.66 V, -0.7 V, and -0.85 V (vs. NHE), respectively. The valence band positions of CIS, CdS, and CIS-EDTA were calculated using the band gaps measured by UV-Vis absorption spectroscopy. E VB The values ​​were 1.21 V, 1.47 V, and 0.82 V, respectively (vs. NHE).

[0068] Cu 2p of CIS after EDTA modification 1 / 2 Cu 2p 3 / 2 The binding energy shifted negatively from 952.78 eV and 933.08 eV to 951.68 eV and 931.78 eV. Figure 15 (C) Meanwhile In 3d 3 / 2 In 3d 5 / 2The binding energy shifted negatively from 452.58 eV and 445.08 eV to 452.08 eV and 444.58 eV. Figure 15 (D), which is attributed to the effect of EDTA on the CuInS2 surface. + / In 3+ Coordination occurs, and the lone pair electrons of the amino and carboxyl groups in EDTA flow to CuInS2 through coordinate bonds, leading to Cu... + and In 3+ Electron cloud density increases, and binding energy decreases significantly. When a CIS-EDTA-CdS heterojunction is formed, the typical semiconductor... E fb Its Fermi level ( E f Correspondingly, due to CIS-EDTA E f (-0.85 V vs. Ag / AgCl) is higher than that of CdS. E f (-0.7 V vs. Ag / AgCl) In the dark state, electrons spontaneously flow from CIS-EDTA to CdS, resulting in electron enrichment on the CdS side. This creates a built-in electric field pointing from CIS-EDTA towards CdS, causing the energy bands of CIS-EDTA to bend upwards and those of CdS to bend downwards, promoting S-type electron transfer. This S-type mechanism enhances charge and carrier separation within both materials. On the other hand, the amino and carboxyl groups in EDTA interact with the CdS surface... 2+ Coordination activities also lead to an increase in the electron cloud density around the Cd nucleus. From Figure 15 As can be seen from B, compared with CdS, in the dark state, Cd 3d 3 / 2 Cd 3d 5 / 2 The binding energy shifted negatively from 411.94 eV and 405.16 eV to 411.72 eV and 404.96 eV, confirming an increase in the electron cloud density around the Cd nucleus; from Figure 15 As can be seen in C and D, compared with CIS-EDTA, CuInS2-EDTA photoanode Cu 2p 1 / 2 Cu 2p 3 / 2 The binding energy shifts positively from 951.68 eV and 931.78 eV to 952.18 eV and 932.43 eV in 3d 3 / 2 In 3d 5 / 2The binding energies shifted positively from 452.08 eV and 444.58 eV to 452.28 eV and 444.75 eV, confirming a decrease in electron cloud density around Cu and In nuclei. After illumination, the binding energies of Cu 2p and In 3d shifted to lower values, indicating an increase in electron cloud density of Cu and In nuclei in CuInS2-EDTA, while the binding energy of Cd 3d shifted to higher values, indicating a decrease in electron cloud density of Cd nuclei on the CdS side. In summary, the S-type heterojunction mechanism leads to the interaction of photogenerated electrons in the CB of CdS and the h electrons in the VB of CuInS2-EDTA. + The composite structure effectively enhances the separation of charge carriers within the two materials (e.g., ...). Figure 16 (As shown). Simultaneously, photogenerated electrons generated by CB located in CuInS2-EDTA migrate to the 304 SS surface via an external circuit, and h in VB of CdS... + S in the cavitation agent 2- Restore, and S 2- It is oxidized to elemental sulfur. Meanwhile, the Na in the hole scavenger... + The charge balance of the system is maintained by the directional migration of proton exchange membranes into the corrosion pool. In summary, the CIS-EDTA-CdS composite material prepared by hydrothermal method, combined with small molecule coordination bonding and ion adsorption reaction method can expand its light absorption range, promote the separation of photogenerated electron-hole pairs, and improve the photoelectrochemical cathodic protection performance of CIS-EDTA-CdS.

[0069] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding, characterized in that, First, CuInS2 was prepared by a hydrothermal method; then, CuInS2-EDTA photoanode was prepared by coordination with ethylenediaminetetraacetic acid; finally, the copper indium sulfide-cadmium sulfide composite photoanode was prepared by coordination bonding and ion adsorption reaction.

2. The method for preparing the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 1, characterized in that, The specific process for preparing CuInS2 using the hydrothermal method is as follows: Cu2O, InCl3∙3H2O and thiourea are dissolved in ethylene glycol and ultrasonically mixed to obtain a mixed solution. The FTO glass was immersed in the mixed solution and reacted at 80~300℃ for 2~16 h. After washing and calcination, CuInS2 was obtained.

3. The preparation method of the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 2, characterized in that, The mass ratio of Cu2O, InCl3∙3H2O and thiourea is (0.01~0.5):(0.01~1.1):(0.01~1.3).

4. The preparation method of the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 2, characterized in that, The calcination temperature is 100~800℃, and the time is 1~8 h.

5. The method for preparing the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 1, characterized in that, The specific process for preparing CuInS2-EDTA photoanode through the coordination of ethylenediaminetetraacetic acid is as follows: dissolve disodium ethylenediaminetetraacetate in ethanol, immerse CuInS2 in the resulting solution, and dry to obtain CuInS2-EDTA photoanode.

6. The method for preparing the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 5, characterized in that, The soaking time is 0.5 to 6 hours.

7. The method for preparing the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 1, characterized in that, The specific process for preparing the copper indium sulfide-cadmium sulfide composite photoanode by coordination bonding and ion adsorption reaction is as follows: First, the CuInS2-EDTA photoanode is immersed in a solution containing soluble cadmium salt, washed with ethanol, and then immersed in Na2S solution. This process is repeated 2 to 50 times. After drying, the copper indium sulfide-cadmium sulfide composite photoanode is obtained.

8. The method for preparing the copper indium sulfide-cadmium sulfide composite photoanode based on small molecule coordination bonding according to claim 7, characterized in that, The soluble cadmium salt is Cd(NO3)2∙4H2O, and the mass ratio of Cd(NO3)2∙4H2O to Na2S∙9H2O is (0.04~1.1):(0.02~1).

9. A copper indium sulfide-cadmium sulfide composite photoanode, characterized in that, It is prepared according to any one of claims 1 to 8.

10. The application of the copper indium sulfide-cadmium sulfide composite photoanode as described in claim 9 in electrochemical corrosion protection.

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