Metal-organic framework heterojunction photoelectrode material and preparation method and application thereof

Abstract

The application provides a metal organic framework heterojunction photoelectrode material and a preparation method and application thereof, and relates to the technical field of photoelectrocatalysis. The material is composed of a conductive substrate, BiVO4 nanorods and CoMOF loaded on the surface, and the two form a heterojunction structure. The preparation adopts electrochemical deposition combined with a hydrothermal method, BiVO4 nanorods are first prepared on the substrate, and then CoMOF is loaded through hydrothermal treatment to form a heterojunction. The application effectively improves the electron transport efficiency, increases the active sites of oxygen atoms, suppresses the carrier recombination, significantly improves the photoelectrocatalytic water splitting performance, and the photocurrent density is much higher than that of a pure BiVO4 electrode. The application has the advantages of high efficiency, stability, simple process and the like, and can be used in a photoelectrolysis hydrogen production system.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalysis technology, specifically relating to a metal-organic framework heterojunction photoelectrode material, its preparation method, and its application. Background Technology

[0002] With the continued advancement of global industrialization and rapid socio-economic development, energy shortages and environmental pollution have become core challenges restricting the sustainable development of human society. Currently, traditional fossil fuels such as coal, oil, and natural gas still dominate the global energy consumption structure, but their reserves are limited and non-renewable. Long-term large-scale extraction and consumption are accelerating resource depletion, making it difficult to meet long-term energy demands. At the same time, the combustion of fossil fuels releases large amounts of harmful gases such as carbon dioxide, sulfur oxides, and nitrogen oxides, not only triggering environmental crises such as the greenhouse effect and global warming, but also causing ecological problems such as acid rain and air pollution, severely disrupting the natural ecological balance and threatening human health and the living environment. Against this backdrop, developing clean, efficient, and renewable new energy sources and building a green and low-carbon energy system has become a key strategic direction for countries around the world to address the dual challenges of energy and the environment.

[0003] Hydrogen energy, as a clean energy source with high energy density, pollution-free combustion products, and wide availability, is considered an ideal alternative energy source for the future. Efficient and low-cost hydrogen production technology is a core prerequisite for the large-scale application of hydrogen energy. Photoelectrochemical water splitting technology, with its advantages of directly converting solar energy into chemical energy, mild reaction conditions, and environmental friendliness, has become one of the most promising hydrogen production pathways. This technology uses photoelectrode materials to absorb sunlight, exciting the generation of electron-hole pairs, thereby driving the oxidation and reduction reactions of water to achieve the efficient production of hydrogen and oxygen. Among these, the photoanode material, as the core component of the photoelectrochemical water splitting system, directly determines the system's photoelectric conversion efficiency, catalytic activity, and stability, and is a key carrier for improving hydrogen production performance.

[0004] Currently, bismuth vanadate (BiVO4) has become one of the most widely studied photoanode materials due to its suitable band gap, wide visible light response range, strong chemical stability, and simple preparation process. However, pure BiVO4 photoanodes have significant technical defects: their low carrier mobility and rapid recombination rate of photogenerated electrons and holes lead to low charge separation and transport efficiency; simultaneously, the surface water oxidation reaction kinetics are slow, and the number of active sites is insufficient, severely restricting the efficiency of photoelectrochemical water splitting. To improve these problems, existing technologies often employ element doping, morphology control, and composite modification to modify BiVO4, but most modification methods are complex, costly, and difficult to simultaneously achieve efficient charge transport and sufficient active site supply, resulting in limited improvement in the overall performance of the photoelectrode. Therefore, developing a BiVO4-based heterojunction photoelectrode material that can effectively improve electron transport dynamics, increase oxygen atom active sites, has a simple preparation process, and stable performance, and solve the technical problems of severe charge recombination, slow reaction kinetics, and low hydrogen production efficiency in existing photoanodes, is of great significance for promoting the practical development of photoelectrochemical water splitting hydrogen production technology. Summary of the Invention

[0005] This invention addresses the problems of low photogenerated carrier separation and transport efficiency, slow electron transport dynamics, severe surface hole recombination, and insufficient oxygen atom active sites in existing photoelectrochemical water splitting photoanode materials. It provides a metal-organic framework heterojunction photoelectrode material, which solves the technical pain points of slow water oxidation reaction kinetics and low photoelectrochemical hydrogen production efficiency caused by the inherent defects of pure BiVO4 photoanodes. By constructing a BiVO4 and Co-MOF heterojunction structure, the charge transport efficiency and the number of catalytic active sites are improved simultaneously, achieving efficient and stable photoelectrochemical water splitting hydrogen production.

[0006] This invention also provides a method for preparing a metal-organic framework heterojunction photoelectrode material.

[0007] This invention also provides an application of a metal-organic framework heterojunction photoelectrode material.

[0008] A first aspect of the present invention provides a metal-organic framework heterojunction photoelectrode material, comprising a conductive substrate, wherein BiVO4 nanorods are distributed on the surface of the conductive substrate, and Co-MOF is distributed on the surface of the BiVO4 nanorods, wherein the Co-MOF and BiVO4 nanorods form a heterojunction.

[0009] This invention constructs BiVO4 nanorods and Co on a conductive substrate. The tightly bound heterojunction structure of MOFs can significantly improve the photoelectrocatalytic performance of photoelectrode materials, with the following specific benefits: Efficient type II heterojunctions are formed on the surface of a conductive substrate using BiVO4 nanorods and Co-MOFs, which significantly accelerates the photogenerated electron transport dynamics, suppresses photogenerated carrier recombination, and improves charge separation and transport efficiency.

[0010] Co The uniform distribution of MOFs on the surface of BiVO4 nanorods can significantly increase the active sites of oxygen atoms, enhance the kinetics of water oxidation, and lower the reaction energy barrier.

[0011] With a stable overall structure and strong photoelectric response, it can efficiently realize photoelectrochemical water splitting to produce hydrogen, significantly improving the efficiency and catalytic stability of photoelectrochemical hydrogen production.

[0012] According to some embodiments of the present invention, the particle size of the BiVO4 nanorods is 150~400 nm.

[0013] The particle size of BiVO4 nanorods. This refers to the diameter / lateral characteristic size of a single BiVO4 nanorod as directly observed by SEM (scanning electron microscopy).

[0014] According to some embodiments of the present invention, the particle size of the heterojunction is 50~100nm.

[0015] The particle size of a heterojunction refers to the characteristic size of the Co-MOF heterojunction structure, which is the morphological size.

[0016] According to some embodiments of the present invention, the sheet resistance of the conductive substrate is ≤15Ω.

[0017] According to some embodiments of the present invention, the conductive substrate is selected from at least one of FTO conductive glass and Si substrate.

[0018] A second aspect of the present invention provides a method for preparing a metal-organic framework heterojunction photoelectrode material according to the first aspect of the present invention, comprising the following steps: S1. A mixed solution of bismuth salt solution, potassium iodide solution and benzoquinone solution is used as electrolyte I. The conductive substrate is used as the working electrode. After electrochemical deposition, the working electrode is mixed with vanadium acetylacetonate solution and then annealed to obtain BiVO4 nanorod electrode. S2. Using a mixed solution of cobalt nitrate chloride solution, terephthalic acid solution, ethanol solution, and N,N-dimethylformamide solution as a precursor solution, and with the BiVO4 nanorod electrode as the working electrode, the metal-organic framework heterojunction photoelectrode material is obtained after hydrothermal deposition.

[0019] The preparation method of the present invention can be obtained by a two-step electrochemical deposition method, which is relatively simple and can be used for large-scale preparation.

[0020] According to some embodiments of the present invention, in step S1, the concentration of the bismuth salt solution is 3~5 mmol / L.

[0021] According to some embodiments of the present invention, the concentration of the potassium iodide solution is 0.3~0.6 mol / L.

[0022] According to some embodiments of the present invention, the concentration of the benzoquinone solution is 0.1~0.4 mol / L.

[0023] According to some embodiments of the present invention, in step S1, the deposition voltage of the electrochemical deposition is -0.12~-0.1V vs. Ag / AgCl.

[0024] According to some embodiments of the present invention, in step S1, the electrochemical deposition method further includes a counter electrode and a reference electrode.

[0025] According to some embodiments of the present invention, the counter electrode is selected from Pt wire electrodes.

[0026] According to some embodiments of the present invention, the reference electrode is selected from an Ag / AgCl electrode.

[0027] According to some embodiments of the present invention, in step S1, the annealing temperature is 400~700°C.

[0028] According to some embodiments of the present invention, the annealing time is 0.5 to 5 hours.

[0029] According to some embodiments of the present invention, in step S2, the concentration of the cobalt chloride nitrate solution is 12.5~37.5 mmol / L.

[0030] According to some embodiments of the present invention, the concentration of the terephthalic acid solution is 12.5~37.5 mmol / L.

[0031] The purity of ethanol is ≥99.7%, and the purity of N,N-dimethylformamide solution is ≥99.99%.

[0032] According to some embodiments of the present invention, in step S2, the temperature of the hydrothermal deposition is 100~200°C.

[0033] According to some embodiments of the present invention, in step S2, the hydrothermal deposition time is 8-14 hours.

[0034] A third aspect of the present invention provides a photoelectrochemical water splitting device, comprising a metal-organic framework heterojunction photoelectrode material as described in the first aspect of the present invention.

[0035] The photoelectrochemical water splitting device using the metal-organic framework heterojunction photoelectrode material of this invention can significantly improve the separation and transport efficiency of photogenerated carriers, increase the active sites of oxygen atoms, accelerate the kinetics of water oxidation reaction, and reduce charge recombination and reaction energy barriers, thereby greatly improving the photoelectric conversion efficiency and hydrogen production performance, and enabling the device to have higher catalytic activity, operational stability and energy utilization efficiency. Attached Figure Description

[0036] Figure 1 This is a SEM image of the BiVO4 nanorods in Example 1 of the present invention.

[0037] Figure 2 This is a SEM image of the heterojunction in Embodiment 1 of the present invention.

[0038] Figure 3 This is a linear scan curve of the metal-organic framework heterojunction photoelectrode material of Embodiment 1 of the present invention. Detailed Implementation

[0039] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0040] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0041] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0042] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0043] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0044] Example 1 A metal-organic framework heterojunction photoelectrode material was prepared, comprising a conductive substrate, BiVO4 nanorods, and Co-MOF, wherein the BiVO4 nanorods are located on the surface of the substrate; the Co-MOF and BiVO4 nanorods form a heterojunction, with the Co-MOF distributed on the BiVO4 nanorods. The preparation method is as follows: Substrate selection: FTO conductive glass (sheet resistance <15Ω) is used.

[0045] S1. Using an electrochemical deposition method, BiOI was deposited onto FTO using a 4 mM bismuth nitrate solution, a 0.4 M potassium iodide solution, and a 0.2 M benzoquinone solution as the electrolyte. FTO conductive glass, Pt wire, and Ag / AgCl were used as the working electrode, counter electrode, and reference electrode, respectively. BiOI was electrodeposited onto FTO for 400 s under a bias voltage of -0.12 V vs. Ag / AgCl. Then, it was immersed in a 0.2 M vanadium acetylacetonate solution for 1 min, followed by annealing at 450 °C in an oxygen atmosphere for 2 h. Finally, it was immersed in a 1 M NaOH solution for 30 min to remove V₂O₅, yielding BiVO₄ nanorods. S2. The prepared BiVO4 nanorods were ultrasonically cleaned sequentially with ethanol, acetone, and water. Then, a hydrothermal deposition method was used, with 37.5 mM cobalt chloride solution, 37.5 mM terephthalic acid solution, ≥99.7% ethanol solution, and ≥99.99% N,N-dimethylformamide solution as precursor solutions, and BiVO4 nanorods as conductive substrates. Co-MOF was deposited on the BiVO4 nanorods in a forced-air oven at 140℃ for 12 h to obtain BiVO4 / Co-MOF. Finally, the nanorods were rinsed in pure water to obtain the metal-organic framework heterojunction photoelectrode material.

[0046] The BiVO4 nanorods prepared in step S1 of this invention were subjected to SEM analysis, and the results are as follows: Figure 1 As shown, the BiVO4 nanorod particle size is approximately 200 nm. From... Figure 1 It can be clearly observed that BiVO4 exhibits a uniform and regular nanorod morphology on the conductive substrate surface. The nanorods are well dispersed, without obvious agglomeration, and have uniform size, providing a stable substrate structure with high specific surface area for subsequent loading of Co-MOF and formation of heterojunction.

[0047] Furthermore, the heterojunction formed in step S2 of the present invention was subjected to SEM detection, and the results are as follows: Figure 2 As shown, the surface of BiVO4 is coated with a thin film. (The text abruptly ends here.) Figure 2As can be seen, Co-MOF is uniformly coated and grown on the surface of BiVO4 nanorods. The two are tightly combined to form a distinct heterojunction structure with no shedding or accumulation and good interfacial contact. This proves that a composite structure of BiVO4 and Co-MOF has been successfully constructed, providing a structural basis for efficient charge transport and interfacial catalytic reactions.

[0048] Furthermore, the metal-organic framework heterojunction photoelectrode material prepared in Example 1 of this invention was used for photoelectrochemical water splitting. The prepared metal-organic framework heterojunction photoelectrode material was fabricated into a photoelectrode. Photoelectrochemical tests were performed using an electrochemical workstation, specifically as follows: a 0.5 mol / L Na₂B₄O₇ (pH≈9) solution was used as the electrolyte, the prepared photoelectrode was used as the anode, Ag / AgCl as the reference electrode, a Pt wire as the cathode, and a 300W Xe lamp (light intensity ~100mW / cm²) was used. 2 Using the photoelectrode as the light source, the photocurrent density-bias voltage curve was obtained. As shown in Figure 3, the linear scan curve shows that the photocurrent density is 1.89 mA / cm² when the photoelectrode is biased at 1.23 V vs. RHE. 2 . Figure 3 The comparison shows that the photocurrent density of the BiVO4 / Co-MOF heterojunction photoelectrode of the present invention is much higher than that of the pure BiVO4 photoelectrode; under a bias voltage of 1.23V vs. RHE, the heterojunction photoelectrode exhibits a significantly higher photocurrent response, and the photoelectrocatalytic activity is greatly improved.

[0049] Example 2 A metal-organic framework heterojunction photoelectrode material was prepared, comprising a conductive substrate, BiVO4 nanorods, and Co-MOF. The BiVO4 nanorods are located on the surface of the substrate, and the Co-MOF and BiVO4 nanorods form a heterojunction. The Co-MOF is distributed on the BiVO4 nanorods, wherein the BiVO4 nanorods have a particle size of approximately 200 nm, and the heterojunction has a particle size of approximately 100 nm. The preparation method includes the following steps: Substrate selection: FTO conductive glass (sheet resistance <15Ω) is used.

[0050] S1. Using electrochemical deposition, BiOI was deposited onto FTO using 4 mM bismuth nitrate solution, 0.4 M potassium iodide and 0.2 M benzoquinone solution as electrolytes. FTO, Pt wire and Ag / AgCl were used as working electrode, counter electrode and reference electrode, respectively. BiOI was deposited onto FTO for 400 s under a bias voltage of -0.12 V vs. Ag / AgCl. Then, the electrode sheets were immersed in 0.2 M vanadium acetylacetonate solution for 1 min and annealed at 450 °C in an oxygen atmosphere for 2 h. Finally, V2O5 was removed by immersion in 1 M NaOH solution for 30 min to obtain BiVO4 nanorods.

[0051] S2. The prepared BiVO4 nanorods were ultrasonically cleaned sequentially with ethanol, acetone, and water. Then, using an electrochemical deposition method, with 37.5 mM cobalt chloride solution, 37.5 mM terephthalic acid solution, ≥99.7% ethanol solution, and ≥99.99% N,N-dimethylformamide solution as precursor solutions, and BiVO4 nanorods as conductive substrates, Co-MOF was deposited on the BiVO4 nanorods by hydrothermal deposition in a forced-air oven at 140℃ for 12 h to obtain BiVO4 / Co-MOF; finally, the nanorods were rinsed in pure water to obtain the metal-organic framework heterojunction photoelectrode material.

[0052] The metal-organic framework heterojunction photoelectrode material of Example 2 was used for photoelectrochemical water splitting. The prepared metal-organic framework heterojunction photoelectrode material was fabricated into a photoelectrode. Photoelectrochemical tests were performed using an electrochemical workstation, specifically as follows: a 0.5 mol / L Na₂B₄O₇ solution (pH≈9) was used as the electrolyte; the prepared photoelectrode was used as the anode; Ag / AgCl was used as the reference electrode; Pt wire was used as the cathode; and a 300W Xe lamp (light intensity ~100mW / cm²) was used. 2 Using this as a light source, the photocurrent density-bias voltage curve was obtained. The linear scanning curve of the metal-organic framework heterojunction photoelectrode material shows that the photocurrent density is 2.07 mA / cm² at a bias voltage of 1.23 V vs. RHE. 2 .

[0053] Example 3 A metal-organic framework heterojunction photoelectrode material was prepared. The structure includes a conductive substrate, BiVO4 nanorods, and Co-MOF. The BiVO4 nanorods are located on the surface of the substrate, and the Co-MOF and BiVO4 nanorods form a heterojunction. The Co-MOF is distributed on the BiVO4 nanorods. The BiVO4 nanorods have a particle size of approximately 200 nm, and the heterojunction has a particle size of approximately 300 nm. The preparation method includes the following steps: Substrate selection: FTO conductive glass (sheet resistance <15Ω) is used.

[0054] S1. Using electrochemical deposition, BiOI was deposited onto FTO using 4 mM bismuth nitrate solution, 0.4 M potassium iodide and 0.2 M benzoquinone solution as electrolytes. FTO, Pt wire and Ag / AgCl were used as working electrode, counter electrode and reference electrode, respectively. BiOI was deposited onto FTO for 400 s under a bias voltage of -0.12 V vs. Ag / AgCl. Then, the electrode sheets were immersed in 0.2 M vanadium acetylacetonate solution for 1 min and annealed at 450 °C in an oxygen atmosphere for 2 h. Finally, V2O5 was removed by immersion in 1 M NaOH solution for 30 min to obtain BiVO4 nanorods.

[0055] S2. The prepared BiVO4 nanorods were ultrasonically cleaned sequentially with ethanol, acetone, and water. Then, using an electrochemical deposition method, with 37.5 mM cobalt nitrate solution, 37.5 mM terephthalic acid solution, ≥99.7% ethanol solution, and ≥99.99% N,N-dimethylformamide solution as precursor solutions, and BiVO4 nanorods as conductive substrates, Co-MOF was deposited on the BiVO4 nanorods by hydrothermal deposition in a forced-air oven at 140℃ for 12 h to obtain BiVO4 / Co-MOF; finally, the nanorods were rinsed in pure water to obtain the metal-organic framework heterojunction photoelectrode material.

[0056] The metal-organic framework heterojunction photoelectrode material prepared in Example 3 was used for photoelectrochemical water splitting. The prepared metal-organic framework heterojunction photoelectrode material was fabricated into a photoelectrode. Photoelectrochemical tests were performed using an electrochemical workstation, specifically as follows: a 0.5 mol / L Na₂PO₄ solution (pH≈9) was used as the electrolyte, the prepared photoelectrode was used as the anode, Ag / AgCl as the reference electrode, Pt wire as the cathode, and a 300W Xe lamp (light intensity ~100mW / cm²) was used. 2 Using the photoelectrode as a light source, the photocurrent density-bias voltage curve was obtained. With a photoelectrode biased at 1.23V vs. RHE, the photocurrent density was 2.44 mA / cm². 2 .

[0057] Comparative Example 1 Comparative Example 1 provides a photoelectrode material, the preparation method of which is as follows: Substrate selection: FTO conductive glass (sheet resistance <15Ω) is used.

[0058] BiOI was deposited onto FTO using an electrochemical deposition method with 4 mM bismuth nitrate solution, 0.4 M potassium iodide and 0.2 M benzoquinone solution as electrolytes. FTO conductive glass, Pt wire and Ag / AgCl were used as working electrode, counter electrode and reference electrode, respectively. BiOI was electrodeposited onto FTO for 400 s under a bias voltage of -0.12 V vs. Ag / AgCl. Then, it was immersed in 0.2 M vanadium acetylacetonate solution for 1 min and annealed at 450 °C in an oxygen atmosphere for 2 h. Finally, it was immersed in 1 M NaOH solution for 30 min to remove V2O5, and BiVO4 nanorods were obtained.

[0059] BiVO4 nanorods from Comparative Example 1 were used for photoelectrochemical water splitting. The prepared metal-organic framework heterojunction photoelectrode material was fabricated into a photoelectrode. Photoelectrochemical tests were performed using an electrochemical workstation, specifically as follows: 0.5 mol / L Na2PO4 solution (pH≈9) was used as the electrolyte, the prepared photoelectrode was used as the anode, Ag / AgCl as the reference electrode, Pt wire as the cathode, and a 300W Xe lamp (light intensity ~100mW / cm²) was used. 2Using the photoelectrode as a light source, the photocurrent density-bias voltage curve was obtained. With a photoelectrode biased at 1.23V vs. RHE, the photocurrent density was 0.49 mA / cm². 2 .

[0060] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A metal-organic framework heterojunction photoelectrode material, characterized in that, The invention includes a conductive substrate, on the surface of which BiVO4 nanorods are distributed, and on the surface of which Co-MOF is distributed, wherein the Co-MOF and BiVO4 nanorods form a heterojunction.

2. The metal-organic framework heterojunction photoelectrode material according to claim 1, characterized in that, The BiVO4 nanorods have a particle size of 150~400 nm.

3. The metal-organic framework heterojunction photoelectrode material according to claim 1, characterized in that, The heterojunction has a particle size of 50~100nm.

4. A method for preparing a metal-organic framework heterojunction photoelectrode material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. A mixed solution of bismuth salt solution, potassium iodide solution and benzoquinone solution is used as electrolyte I. The conductive substrate is used as the working electrode. After electrochemical deposition, the working electrode is mixed with vanadium acetylacetonate solution and then annealed to obtain BiVO4 nanorod electrode. S2. Using a mixed solution of cobalt nitrate chloride solution, terephthalic acid solution, ethanol solution, and N,N-dimethylformamide solution as a precursor solution, and with the BiVO4 nanorod electrode as the working electrode, the metal-organic framework heterojunction photoelectrode material is obtained after hydrothermal deposition.

5. The method according to claim 4, characterized in that, In step S1, the concentration of the bismuth salt solution is 3-5 mmol / L; and / or, the concentration of the potassium iodide solution is 0.3-0.6 mol / L; and / or, the concentration of the benzoquinone solution is 0.1-0.4 mol / L.

6. The method according to claim 4, characterized in that, In step S1, the deposition voltage of the electrochemical deposition is -0.12~-0.1V vs. Ag / AgCl.

7. The method according to claim 4, characterized in that, In step S1, the annealing temperature is 400~700℃; and / or, the annealing time is 0.5~5h.

8. The method according to claim 4, characterized in that, In step S2, the concentration of the cobalt chloride nitrate solution is 12.5~37.5 mmol / L; and / or, the concentration of the terephthalic acid solution is 12.5~37.5 mmol / L.

9. The method according to claim 4, characterized in that, In step S2, the temperature of the hydrothermal deposition is 100~200℃.

10. A photoelectrocatalytic water splitting device, characterized in that, Including the metal-organic framework heterojunction photoelectrode material as described in any one of claims 1 to 3.

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