Polyethyleneimine modified metal sulfide heterostructure photoanode and preparation method thereof

Abstract

The invention belongs to the technical field of photocatalytic materials, discloses a polyethyleneimine modified metal sulfide heterostructure photo-anode and a preparation method thereof, and aims to solve the problems of poor light corrosivity, poor stability and the like of a metal sulfide photo-anode. On the basis of an ion exchange method, the polyethyleneimine non-conjugated polymer modification layer is introduced for the first time, directional adsorption of metal cations is guided through electrostatic interaction, the interface charge transmission efficiency is effectively enhanced, and therefore the uniform and compact metal sulfide heterostructure photo-anode is formed. The design strategy is simple in preparation process, mild in condition, low in production cost, short in period and friendly to application environment, the prepared heterostructure photo-anode has excellent and stable photoelectrocatalysis water splitting performance, a new way is provided for efficient utilization of solar energy and development of a green manufacturing technology, and the heterostructure photo-anode can be suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a polyethyleneimine-modified metal sulfide heterostructure photoanode and a preparation method thereof. Background Art

[0002] Photoelectrochemical water splitting technology drives water splitting to produce hydrogen through solar energy, and is regarded as one of the ideal ways to solve energy crisis and environmental problems. As the core component of this photoelectrocatalysis, the performance of the photoanode directly determines the separation efficiency of photo-generated charges, the carrier migration rate and the surface reaction kinetics, thus affecting the overall energy conversion efficiency. In recent years, metal sulfides have become a research hotspot for photoanode materials due to their suitable band structure, high carrier mobility and good chemical stability. However, single-component metal sulfides still face the following key challenges: (1) high recombination rate of photo-generated electron-hole pairs, resulting in limited quantum efficiency; (2) insufficient surface active sites, slow catalytic reaction kinetics; (3) prone to photocorrosion, poor stability.

[0003] By constructing a semiconductor heterojunction, the spatial separation of photo-generated carriers can be promoted by using the built-in electric field at the interface, the spectral response can be broadened, and photocorrosion can be inhibited, thus significantly improving the performance of the photoanode for photoelectrochemical water splitting. However, traditional heterojunction preparation methods (such as co-precipitation method, physical sputtering, chemical vapor deposition, etc.) have problems such as interface lattice mismatch, difficult to effectively regulate the transport path, and complex preparation process, resulting in the charge separation efficiency being difficult to further improve and limiting large-scale application. In the preparation of functional materials, the ion exchange method is favored due to its atomic-level precision, tight interface binding and mild reaction conditions. However, this method is highly sensitive to the crystal structure and surface state of the substrate material. If directly applied to the construction of metal sulfide heterostructures, it is easy to cause interface defects due to uneven ion exchange rates. Therefore, developing a heterojunction photoanode preparation method with simple process and controllable interface, which has both high charge separation and long-term stability, has become the key to promoting the practical application of photoelectrochemical water splitting technology.

[0004] Non-conjugated polymers show significant advantages in the construction of heterostructure interfaces due to their unique physical and chemical properties (such as flexible chain segments, rich functional groups). Among them, positively charged polyethyleneimine (bPEI) can bind to the negatively charged semiconductor surface through electrostatic interaction to form a uniform interface modification layer. The generated modification layer can not only provide additional surface active sites, but also regulate the migration direction of electrons or holes at the heterojunction interface, improving the charge separation efficiency. At the same time, the modification layer can block the direct contact of water molecules with the semiconductor surface, inhibit the oxidative degradation of the material by photo-generated holes, and help protect the heterojunction surface from photocorrosion, electrolyte erosion or oxidative damage.

[0005] Based on this, the present invention for the first time introduces polyethyleneimine into the interface of metal sulfide heterojunctions, and constructs a dense heterostructure through an ion-exchange synergistic strategy. The polyethyleneimine modification layer guides the directional adsorption of metal cations through electrostatic interaction, realizing the uniform growth of the heterojunction. This method abandons harsh conditions such as high temperature and vacuum, and adopts an aqueous-phase reaction throughout the process, having the dual advantages of environmental friendliness and process simplification. Therefore, this simple, green and efficient method for preparing metal sulfide photoanodes promotes the development of green material preparation technology, and has important scientific value and industrialization potential. Summary of the Invention

[0006] The object of the present invention is to address the problems of poor stability and strong photo-corrosion of existing metal sulfide photoanodes. By improving the research scheme, a polyethyleneimine-modified metal sulfide heterostructure photoanode and its preparation method are disclosed. The present invention can achieve the stable and efficient synthesis of target products. Compared with single-component photoanodes and photoanodes constructed without polyethyleneimine, the prepared metal sulfide heterostructure photoanode has excellent photoelectrocatalytic water splitting activity, good cycling performance, low production cost, simple production process, can be macroscopically prepared, is environmentally friendly, and is easy to recycle.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing a polyethyleneimine-modified metal sulfide heterostructure photoanode, comprising the following steps: (1) Preparation of a metal sulfide photoanode substrate: After cleaning the FTO conductive glass, place it in a metal sulfide nanosheet precursor solution, carry out a hydrothermal reaction, cool after the reaction is completed, take out the substrate, rinse, and dry to obtain a metal sulfide photoanode substrate.

[0008] (2) Preparation of a metal sulfide@bPEI photoanode: After cutting the metal sulfide photoanode substrate prepared in step (1), immerse it in a polyethyleneimine solution for reaction, take it out after the reaction is completed, rinse, and dry to obtain a metal sulfide@bPEI photoanode.

[0009] (3) Preparation of a metal sulfide@bPEI / ternary metal sulfide heterostructure photoanode: Immerse the metal sulfide@bPEI photoanode prepared in step (2) in an aqueous solution of ACl2·nH2O for reaction, take it out after the reaction is completed, rinse, and dry to obtain a metal sulfide@bPEI / ternary metal sulfide heterostructure photoanode.

[0010] The metal in the metal sulfide is one or two of Cd and In, A in ACl2·nH2O represents metal Zn or Cd, n = 0 to 2.5, and preferably, n = 0 or 2.5. The metals in the ternary metal sulfide include In and A.

[0011] Preferably, in step (1), the metal sulfide is CdIn2S4 or In2S3.

[0012] The metal sulfide (CdIn2S4) nanosheet precursor solution includes: 10 - 30 mmol / L of CdCl2·2.5H2O, 20 - 60 mmol / L of InCl3·4H2O, and 40 - 240 mmol / L of thioacetamide, with a molar ratio of Cd:In:S = 1:2:(4 - 8). More preferably, the metal sulfide (CdIn2S4) nanosheet precursor solution includes: 15 - 25 mmol / L of CdCl2·2.5H2O, 30 - 50 mmol / L of InCl3·4H2O, and 90 - 200 mmol / L of thioacetamide, with a molar ratio of Cd:In:S = 1:2:(6 - 8). Even more preferably, the metal sulfide (CdIn2S4) nanosheet precursor solution includes: 20 mmol / L of CdCl2·2.5H2O, 40 mmol / L of InCl3·4H2O, and 150 mmol / L of thioacetamide, with a molar ratio of Cd:In:S = 1:2:7.5.

[0013] Or the metal sulfide (In2S3) nanosheet precursor solution includes: 30 - 70 mmol / L of InCl3 and 45 - 210 mmol / L of thioacetamide, with a molar ratio of In:S = 1:(1.5 - 3). More preferably, the metal sulfide (In2S3) nanosheet precursor solution includes: 40 - 60 mmol / L of InCl3 and 60 - 150 mmol / L of thioacetamide, with a molar ratio of In:S = 1:(2 - 3). Even more preferably, the metal sulfide (In2S3) nanosheet precursor solution includes: 40 mmol / L of InCl3 and 100 mmol / L of thioacetamide, with a molar ratio of In:S = 1:2.5.

[0014] Preferably, in step (1), the hydrothermal reaction temperature is 150 - 210 °C, the reaction time is 6 - 20 hours, and the dosage of the metal sulfide nanosheet precursor solution is 30 - 50 times the volume of the FTO conductive glass. More preferably, the reaction time is 10 - 15 hours, and the dosage of the metal sulfide nanosheet precursor solution is 35 - 40 times the volume of the FTO conductive glass. Even more preferably, the reaction time is 12 hours, and the dosage of the metal sulfide nanosheet precursor solution is 37.5 times the volume of the FTO conductive glass.

[0015] More preferably, when the metal sulfide is CdIn2S4, the hydrothermal reaction temperature is 150 - 170 °C, and even more preferably 160 °C; when the metal sulfide is In2S3, the hydrothermal reaction temperature is 160 - 210 °C, and even more preferably 200 °C.

[0016] Preferably, in step (2), the reaction temperature is room temperature and the reaction time is 2 to 30 minutes. More preferably, the reaction time is 5 to 15 minutes. Even more preferably, the reaction time is 10 minutes.

[0017] Preferably, in step (2), the polyethyleneimine used is a commercial product with an average molecular weight not higher than 25,000.

[0018] Preferably, in step (2), the concentration of the polyethyleneimine solution is 1 to 10 mg / L, the pH of the polyethyleneimine solution is 6.0 to 6.5, and the dosage of the polyethyleneimine solution is 5 to 10 times the volume of the cut metal sulfide photoanode substrate. More preferably, the concentration of the polyethyleneimine solution is 1 to 3 mg / L, and the dosage of the polyethyleneimine solution is 7 to 9 times the volume of the cut metal sulfide photoanode substrate. Even more preferably, the concentration of the polyethyleneimine solution is 2 mg / L, and the dosage of the polyethyleneimine solution is 8.3 times the volume of the cut metal sulfide photoanode substrate.

[0019] Preferably, in step (1), the cleaned FTO conductive glass needs to be placed with the conductive surface facing down in the metal sulfide nanosheet precursor solution. More preferably, the cleaned FTO conductive glass needs to be placed with the conductive surface facing down and inclined in the metal sulfide nanosheet precursor solution at an inclined angle of 30 to 60°. Even more preferably, the cleaned FTO conductive glass needs to be placed with the conductive surface facing down and inclined at 45° in the metal sulfide nanosheet precursor solution.

[0020] Preferably, in step (3), the metal sulfide@bPEI photoanode needs to be placed with the conductive surface facing down in the ACl2·nH2O aqueous solution. More preferably, the metal sulfide@bPEI photoanode needs to be placed with the conductive surface facing down and inclined in the ACl2·nH2O aqueous solution at an inclined angle of 30 to 60°. Even more preferably, the metal sulfide@bPEI photoanode needs to be placed with the conductive surface facing down and inclined at 45° in the ACl2·nH2O aqueous solution.

[0021] Preferably, in step (1), the drying method is drying by purging with nitrogen.

[0022] Preferably, in steps (2) and (3), the drying temperature is 50 to 70°C and the drying condition is vacuum drying. More preferably, the drying temperature is 60°C.

[0023] Preferably, in step (3), ACl2·nH2O is ZnCl2 or CdCl2·2.5H2O, and the ternary metal sulfide is ZnIn2S4 or CdIn2S4.

[0024] Preferably, in step (3), the concentration of the ACl2·nH2O solution is 1 to 15 mmol / L, the reaction temperature is room temperature to 70 °C, the reaction time is 2 to 30 minutes, and the volume dosage of the ACl2·nH2O solution is equal to the volume dosage of the polyethyleneimine solution. More preferably, the reaction time is 5 to 15 minutes. Even more preferably, the reaction time is 10 minutes.

[0025] More preferably, when the metal sulfide is CdIn2S4, the ternary metal sulfide is ZnIn2S4. The reaction temperature of step (3) is room temperature to 30 °C, ACl2·nH2O is CdCl2·2.5H2O, and the concentration of the CdCl2·2.5H2O solution is 1 to 8 mmol / L. Even more preferably, the reaction temperature of step (3) is room temperature, and the concentration of the CdCl2·2.5H2O solution is 2 mmol / L.

[0026] When the metal sulfide is In2S3, the ternary metal sulfide is CdIn2S4. The reaction temperature of step (3) is 30 to 70 °C, ACl2·nH2O is ZnCl2, and the concentration of the ZnCl2 solution is 2 to 15 mmol / L. Even more preferably, the reaction temperature of step (3) is 50 °C, and the concentration of the ZnCl2 solution is 10 mmol / L.

[0027] The present invention also provides a polyethyleneimine-modified metal sulfide heterostructure photoanode prepared by the above preparation method.

[0028] The specific steps of photoelectrocatalytic water splitting are as follows: The photoelectrochemical performance is tested by the three-electrode method, where the Pt electrode is the counter electrode, the Ag / AgCl is the reference electrode, a 100 mL mixed solution of 0.5 M Na2SO4 and 0.05 M Na2SO3 (pH = 8.5) is used as the electrolyte, and a 300 W xenon lamp is used as the light source. The potential of the electrode is calibrated using the reversible hydrogen electrode (RHE) according to the following formula: .

[0029] The beneficial effects of the present invention are as follows: (1) The preparation method of the present invention is environmentally friendly: short cycle, easy to recycle, and conducive to the sustainable development of the environment and energy; (2) The preparation method is simple and efficient: the present invention is synthesized by a simple ion exchange method, with simple process operation and is conducive to large-scale industrial production; (3) The prepared photoanode has excellent photoelectric performance: the synthesized polyethyleneimine-modified metal sulfide photoanode has high photoelectrocatalytic activity and good stability, solving the limitation problems that restrict the use of single-component metal sulfide photoanodes and metal sulfide heterostructure photoanodes constructed by conventional ion exchange. Description of the Drawings

[0030] Figure 1 Zeta potential diagrams measured for CdIn2S4, ZnIn2S4, and polyethylenimine (bPEI) dissolved in deionized water, respectively; Figure 2 Scanning electron microscope image of the CdIn2S4 photoanode prepared in Example 1 of the present invention; Figure 3 Scanning electron microscope image of the CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1 of the present invention; Figure 4 Transmission electron microscope image and elemental distribution map of the CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1 of the present invention; Figure 5 Linear sweep voltammograms of the CdIn2S4 photoanode, CdIn2S4@bPEI photoanode, and CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1 of the present invention under simulated sunlight illumination (AM 1.5G), respectively; Figure 6 Stability test diagrams of the CdIn2S4 photoanode, CdIn2S4@bPEI photoanode, and CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1 of the present invention under simulated sunlight illumination (AM 1.5G), respectively; Figure 7 Linear sweep voltammograms of the In2S3 photoanode and In2S3@bPEI / CdIn2S4 photoanode prepared in Example 2 of the present invention under simulated sunlight illumination (AM 1.5G), respectively. Detailed Description of the Invention

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Unless otherwise specified, the reagents involved in the embodiments of the present invention are all commercially available products and can be obtained through commercial channels. The methods involved in the embodiments of the present invention are all conventional methods and can be obtained through the corresponding implementation specifications, implementation standards or existing literature in this field.

[0033] Example 1 Preparation of CdIn2S4@bPEI / ZnIn2S4 Heterostructure Photoanode (1) Preparation of the CdIn2S4 Photoanode Substrate: The FTO conductive glass (50 mm × 10 mm × 1.6 mm) was cleaned with ethanol under ultrasonic for 30 minutes, and then cleaned with deionized water for 30 minutes. Then, a precursor solution of CdIn2S4 nanosheets was prepared: 137.0 mg of CdCl2·2.5H2O, 351.9 mg of InCl3·4H2O, and 337.5 mg of TAA were dissolved in 30 mL of deionized water and stirred continuously for 30 minutes; subsequently, the cleaned FTO glass with the conductive side facing down was placed in a 50 mL polytetrafluoroethylene-lined reaction kettle, and the prepared precursor solution of CdIn2S4 nanosheets was transferred into the reaction kettle, and hydrothermal reaction was carried out at 160 °C for 12 hours; after natural cooling, the substrate was taken out, the sample was rinsed with deionized water, and dried by N2 blowing to obtain an orange CdIn2S4 photoanode substrate.

[0034] (2)Preparation of CdIn2S4@bPEI photoanode: The obtained CdIn2S4 photoanode substrate was cut into 10 mm × 15 mm, and then immersed in 2 mL of polyethylenimine (bPEI, 2 mg / L, pH = 6.0 - 6.5) solution with a positive charge on the surface, and soaked and reacted at room temperature for 10 minutes. After the reaction was completed, it was taken out, the sample was rinsed with deionized water, and dried in vacuum at 60 °C to obtain a CdIn2S4@bPEI photoanode.

[0035] (3)Preparation of CdIn2S4@bPEI / ZnIn2S4 heterostructure photoanode: The obtained CdIn2S4@bPEI photoanode was immersed in 2 mL of ZnCl2 (2 mmol / L) aqueous solution, and reacted at room temperature for 10 minutes. After the reaction was completed, it was taken out, the sample was rinsed with deionized water, and dried in vacuum at 60 °C to obtain a CdIn2S4@bPEI / ZnIn2S4 heterostructure photoanode.

[0036] CdIn2S4, ZnIn2S4 and polyethylenimine (bPEI) were respectively dissolved in deionized water, and the Zeta potential results of CdIn2S4, bPEI and ZnIn2S4 are as Figure 1 shown, which confirmed that they can be tightly combined by electrostatic force due to the opposite charges on the surface.

[0037] The scanning electron microscope images of the CdIn2S4 photoanode and the CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1 are respectively as Figure 2 、 Figure 3 shown. The photoanode has a uniform nanosheet array, and the larger specific surface area provides more active sites. From Figure 4From the transmission electron microscope and elemental distribution maps of the CdIn2S4@bPEI / ZnIn2S4 photoanode, it can be seen that the modified polyethyleneimine and ion-exchanged ZnIn2S4 were successfully deposited on the surface of CdIn2S4.

[0038] Figure 5 Figure 4 shows the linear sweep voltammetry (LSV) curves of the CdIn2S4 photoanode, CdIn2S4@bPEI photoanode, and CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1. Under simulated sunlight (AM1.5G) irradiation, the photocurrent density of the single CdIn2S4 photoanode is much lower than that of the CdIn2S4@bPEI / ZnIn2S4 photoanode, indicating that partial cation exchange is beneficial to improving the PEC water oxidation performance of the heterostructure photoanode.

[0039] The stability tests of the CdIn2S4 photoanode, CdIn2S4@bPEI photoanode, and CdIn2S4@bPEI / ZnIn2S4 photoanode prepared in Example 1 under illumination for 1 hour are as Figure 6 shown. Due to the hole accumulation on the surface of the CdIn2S4 photoanode causing photocorrosion, more than 85% of the photocurrent decays significantly. After introducing polyethyleneimine, the stability of the CdIn2S4@bPEI photoanode and CdIn2S4@bPEI / ZnIn2S4 photoanode has been significantly improved, effectively inhibiting the photocorrosion of metal sulfides.

[0040] Example 2 Preparation of In2S3@bPEI / CdIn2S4 Heterostructure Photoanode (1) Preparation of In2S3 Photoanode Substrate: The FTO conductive glass (50 mm × 10 mm × 1.6 mm) was ultrasonically cleaned with ethanol for 30 min, and then rinsed with deionized water for 30 minutes. Then, a precursor solution of In2S3 nanosheets was prepared: 265.4 mg of InCl3 and 225 mg of TAA were dissolved in 30 mL of deionized water and stirred continuously for 30 minutes; subsequently, the cleaned FTO glass was placed with the conductive side down in a 50 mL Teflon-lined reaction kettle, and the prepared precursor solution of In2S3 nanosheets was transferred into the reaction kettle, and hydrothermal reaction was carried out at 200 °C for 12 hours; after natural cooling, the substrate was taken out, rinsed with deionized water, and dried by N2 blowing to obtain the In2S3 photoanode substrate.

[0041] (2) Preparation of In2S3@bPEI Photoanode: The prepared In2S3 photoanode substrate was cut into 10 mm × 15 mm, and then immersed in a 2 mL solution of polyethylenimine (bPEI, 2 mg / L, pH = 6.0 - 6.5) with a positive charge on the surface. The immersion reaction was carried out at room temperature for 10 minutes. After the reaction was completed, the sample was taken out, rinsed with deionized water, and dried in vacuum at 60 °C to obtain the In2S3@bPEI photoanode.

[0042] (3)Preparation of In2S3@bPEI / CdIn2S4 heterostructure photoanode: The prepared In2S3@bPEI photoanode was immersed in a 2 mL aqueous solution of CdCl2·2.5H2O (0.01 M). The reaction was carried out at 50 °C for 10 minutes. After the reaction was completed, the sample was taken out, rinsed with deionized water, and dried in vacuum at 60 °C to obtain the In2S3@bPEI / CdIn2S4 heterostructure photoanode.

[0043] Figure 7 It is the linear sweep voltammogram of the In2S3@bPEI / CdIn2S4 heterostructure photoanode prepared in Example 2. It can be seen that under simulated sunlight conditions, the photocurrent density of In2S3@bPEI / CdIn2S4 is increased by about 3 times compared with In2S3.

[0044] Taking this as an example, a variety of polyethyleneimine-modified metal sulfide heterostructure photoanodes can be synthesized.

[0045] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a polyethyleneimine-modified metal sulfide heterostructure photoanode, characterized in that: It includes the following steps: (1) Preparation of a metal sulfide photoanode substrate: After cleaning the FTO conductive glass, place it in a metal sulfide nanosheet precursor solution for hydrothermal reaction. After the reaction is completed, cool it, take out the substrate, rinse it, and dry it to obtain a metal sulfide photoanode substrate; (2) Preparation of a metal sulfide@bPEI photoanode: After cutting the metal sulfide photoanode substrate prepared in step (1), immerse it in a polyethyleneimine solution for reaction. After the reaction is completed, take it out, rinse it, and dry it to obtain a metal sulfide@bPEI photoanode; (3) Preparation of a metal sulfide@bPEI / ternary metal sulfide heterostructure photoanode: Immerse the metal sulfide@bPEI photoanode prepared in step (2) in an aqueous solution of ACl2·nH2O for reaction. After the reaction is completed, take it out, rinse it, and dry it to obtain a metal sulfide@bPEI / ternary metal sulfide heterostructure photoanode; The metal in the metal sulfide is one or both of Cd and In. A in ACl2·nH2O represents metal Zn or Cd, n = 0 to 2.5, and the metals in the ternary metal sulfide include In and A.

2. The preparation method according to claim 1, characterized in that: In step (1), the metal sulfide is CdIn2S4 or In2S3; The metal sulfide nanosheet precursor solution includes: 10 to 30 mmol / L of CdCl2·2.5H2O, 20 to 60 mmol / L of InCl3·4H2O, and 40 to 240 mmol / L of thioacetamide, with a molar ratio of Cd:In:S = 1:2:(4 to 8); Or the metal sulfide nanosheet precursor solution includes: 30 to 70 mmol / L of InCl3 and 45 to 210 mmol / L of thioacetamide, with a molar ratio of In:S = 1:(1.5 to 3).

3. The preparation method according to claim 1, wherein: In step (1), the hydrothermal reaction temperature is 150 to 210 °C, the reaction time is 6 to 20 hours, and the dosage of the metal sulfide nanosheet precursor solution is 30 to 50 times the volume of the FTO conductive glass.

4. The preparation method according to claim 1, wherein: In step (2), the reaction temperature is room temperature, and the reaction time is 2 to 30 minutes.

5. The preparation method according to claim 1, characterized in that: In step (2), the concentration of the polyethyleneimine solution is 1 to 10 mg / L, the pH of the polyethyleneimine solution is 6.0 to 6.5, and the dosage of the polyethyleneimine solution is 5 to 10 times the volume of the cut metal sulfide photoanode substrate.

6. The preparation method according to claim 1, characterized in that: In step (1), the cleaned FTO conductive glass needs to be placed in the metal sulfide nanosheet precursor solution with the conductive surface facing down; In step (3), the metal sulfide@bPEI photoanode needs to be placed in the aqueous solution of ACl2·nH2O with the conductive surface facing down.

7. The preparation method according to claim 1, wherein: In steps (2) and (3), the drying temperature is 50 to 70 °C, and the drying condition is vacuum drying.

8. The preparation method according to claim 1, characterized in that: In step (3), ACl2·nH2O is ZnCl2 or CdCl2·2.5H2O, and the ternary metal sulfide is ZnIn2S4 or CdIn2S4.

9. The preparation method according to claim 1, characterized in that: In step (3), the concentration of the ACl2·nH2O solution is 1 to 15 mmol / L, the reaction temperature is from room temperature to 70 °C, the reaction time is 2 to 30 minutes, and the amount of the ACl2·nH2O solution used is equal to the amount of the polyethyleneimine solution used.

10. A polyethyleneimine-modified metal sulfide heterostructure photoanode, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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