Preparation method of a BVO / CoPc+BN composite photoanode and its application in photoelectrochemical water splitting

Abstract

The present invention relates to the field of photoanode technology, and specifically to a preparation method of a BVO / CoPc+BN composite photoanode and its application in photoelectrochemical water decomposition. The preparation method of the BVO / CoPc+BN composite photoanode is as follows: after mixing boron nitride BN and cobalt phthalocyanine CoPc, acetonitrile is added, ultrasonicated, stirred, centrifuged, the supernatant is discarded, the product obtained by centrifugation is placed in a crucible, calcined, and ground to obtain a CoPc+BN composite material; N,N-dimethylformamide is added to the CoPc+BN composite material, ultrasonicated, deionized water is added, and ultrasonication is continued until no precipitate is generated, and then BVO is added to carry out a hydrothermal reaction. After the reaction is completed, washing is carried out, and drying is carried out to obtain a BVO / CoPc+BN composite photoanode. The BVO / CoPc+BN composite photoanode exhibits an excellent photocurrent density of 5.04 mA·cm ‑2 .

Description

Technical Field

[0001] The present invention relates to the technical field of photoanodes, and in particular to a preparation method of a BVO / CoPc+BN composite photoanode and its application in photoelectrochemical water decomposition. Background Art

[0002] In practical applications, bismuth vanadate (BVO) has poor electrical conductivity, severe charge recombination, and sluggish surface dynamics, and its PEC performance is still limited. Therefore, in the construction of bismuth vanadate-based composite photoanodes, the multi-layer multi-component assembly method has been explored by most researchers. In most cases, in a multi-component bismuth vanadate-based composite photoanode, one component assists in improving the transfer of photogenerated carriers, while the remaining components act as OECs to enhance the water oxidation activity of BVO. This shows that in order to assist BVO in completing an efficient oxygen evolution reaction, the synergistic effect between multiple components is crucial.

[0003] In this research context, the team considered selecting a layered material that promotes the separation of photogenerated carriers and a layered material with efficient water oxidation activity, and assembling them into a thin layered composite material. Furthermore, the layered composite material needs to be kept at a relatively thin thickness to ensure that each layered material can fully exert its function without increasing the hole transport distance, and to achieve a superposition effect of multiple effects. Subsequently, by loading it onto BVO through appropriate modification methods, the resulting BVO-based composite photoanode is theoretically expected to assist BVO in achieving an efficient oxygen evolution reaction.

[0004] Among various two-dimensional nanomaterials, boron nitride (BN) nanosheets, often referred to as "white graphene" due to their similarity to graphene, are characterized by a honeycomb structure composed of covalently bonded boron and nitrogen atoms. They possess exceptional properties, including extremely high oxidation resistance and good chemical inertness, high thermal conductivity, a high melting point, and a high specific surface area. This makes them a promising catalyst support material, particularly for preventing sintering of supported catalysts at hot spots under relatively harsh conditions. In addition to BN's inherent properties, its rich pores and large specific surface area have shown innovative applications in hydrogen storage and water purification. It is believed that BN can serve as a hole transport layer, suppressing the recombination of photogenerated electron-hole pairs.

[0005] As a versatile class of organic functional dyes, metal phthalocyanines (MPcs) have great potential as electrocatalysts due to their interesting and tunable optical and electronic properties. When these transition metal complexes are modified on the surface of semiconductors, their molecular orbitals will overlap with the electronic energy bands of the semiconductor, which will reduce the energy barrier of the OER reaction and improve the PEC performance. In addition, these molecular / semiconductor hybrid photoanodes can be manufactured and controlled using a much simpler preparation process. On the other hand, phthalocyanine is a planar macrocyclic structure with a large conjugated electron system. Due to the presence of four central nitrogen atoms, it is easy to coordinate with transition metal cations to form stable metal complexes. Therefore, cobalt phthalocyanine (CoPc) has great potential as OECs in theory. Summary of the Invention

[0006] The present invention prepared a BN+CoPc composite material and then loaded it onto BVO to form a BVO / BN+CoPc composite photoanode. Under the condition of a potential of 1.23V vs RHE, the BVO / CoPc+BN composite photoanode showed an excellent photocurrent density of 5.04mA·cm -2 A series of characterizations and tests demonstrated that the BN+CoPc composite not only facilitates the separation of photogenerated charge carriers but also achieves a water oxidation photocurrent density significantly higher than that of BVO alone during a 3-hour electrolysis process. This demonstrates its potential for practical applications in hydrogen and oxygen evolution reactions using light and electricity.

[0007] The technical solution of the present invention is as follows: a BVO / CoPc+BN composite photoanode, the preparation method of which comprises the following steps:

[0008] 1) Preparation of CoPc+BN composite material: Boron nitride (BN) and cobalt phthalocyanine (CoPc) were mixed, acetonitrile was added, ultrasonicated, stirred, and centrifuged. The supernatant was discarded, and the product obtained by centrifugation was placed in a crucible, calcined, and ground to obtain a CoPc+BN composite material;

[0009] 2) Preparation of BVO / CoPc+BN composite photoanode: N,N-dimethylformamide was added to the CoPc+BN composite material, and the mixture was sonicated. Deionized water was added and sonicated until no precipitate was produced. The mixed solution was poured into a hydrothermal reactor, and BVO was added to carry out a hydrothermal reaction. After the reaction, the mixture was washed and dried to obtain a BVO / CoPc+BN composite photoanode.

[0010] In the above-mentioned BVO / CoPc+BN composite photoanode, in step 1), the mass ratio of boron nitride BN to cobalt phthalocyanine CoPc is 4:1 to 8:1.

[0011] In the above-mentioned BVO / CoPc+BN composite photoanode, in step 1), the mass ratio of boron nitride BN to cobalt phthalocyanine CoPc is 6:1.

[0012] In the above-mentioned BVO / CoPc+BN composite photoanode, in step 1), the calcination is carried out by heating the temperature to 300°C at a heating rate of 5°C / min and calcining at 300°C for 2h.

[0013] In the above-mentioned BVO / CoPc+BN composite photoanode, in step 2), the hydrothermal reaction is carried out at 80° C. overnight.

[0014] The above-mentioned BVO / CoPc+BN composite photoanode is used in electrochemical water splitting.

[0015] The above application method is as follows: at 0.6V vs RHE, 100mW·cm -2 The simulated sunlight device is used as a light source to carry out photoelectrochemical water oxidation reaction, the BVO / CoPc+BN described in claim 1 is used as a working electrode, a platinum wire is used as a counter electrode, and Ag / AgCl is used as a reference electrode to carry out photoelectrochemical water splitting to produce hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the SEM image of CoPc+BN.

[0017] Figure 2 (a) is the SEM image of BVO, and (b) is the SEM image of BVO / CoPc+BN.

[0018] Figure 3 XPS of (a) Bi 4f, (b) V 2p, and (c) O 1s of BVO and BVO / CoPc+BN.

[0019] Figure 4 XRD patterns of BVO and BVO / CoPc+BN.

[0020] Figure 5 (a) XRD patterns of the CoPc+BN composite material in Example 1 and the uncalcined CoPc+BN material in Comparative Example 1; (b) XRD patterns of BN, CoPc, and a series of CoPc+BN materials prepared at different feed ratios.

[0021] Figure 6 (a) and (b) LSV plots of different BVO-based composite photoanodes.

[0022] Figure 7(a) ABPE diagram, (b) charge transfer efficiency diagram, and (c) EIS spectrum of four photoanodes: BVO, BVO / BN, BVO / CoPc, and BVO / CoPc+BN.

[0023] Figure 8 IT diagrams of BVO and BVO / CoPc+BN. DETAILED DESCRIPTION

[0024] This invention combines boron nitride with cobalt phthalocyanine (CPCN) organics using ultrasonic exfoliation followed by high-temperature sintering to form a thin layer composite material, namely CoPc+BN. Ultrasonic exfoliation of the layered two-dimensional material is achieved. The introduction of boron nitride ensures the stability of the CPCN during sintering and enhances the crystal structure integrity of the resulting CoPc+BN composite material. The CoPc+BN-loaded composite material is then coated onto a BVO (BVO) photoanode, forming a BVO / CoPc+BN composite photoanode.

[0025] Example 1 Preparation of BVO / CoPc+BN Photoanode

[0026] 1. Preparation of CoPc+BN composites

[0027] First, a mixture of BN and CoPc was added to a beaker in ratios of m(BN):m(CoPc) = 4:1, 6:1, and 8:1. Then, 60 mL of acetonitrile solvent was added to the beaker and ultrasonicated for 3 hours. A rotor was then added to the beaker and stirred overnight. The mixture was centrifuged at 8000 rpm for five minutes to separate the mixture from the solvent, and the supernatant was discarded. The resulting product was placed in a crucible and heated to 300°C in a muffle furnace at a heating rate of 5°C / min. It was then calcined at 300°C for 2 hours. The calcined product was then ground to obtain the CoPc+BN composite material.

[0028] 2. Preparation of BVO / CoPc+BN Photoanode

[0029] Weigh 0.03g of the CoPc+BN composite material into a beaker. Then, add 5mL of N,N-dimethylformamide solvent and sonicate for 1 hour. Then, add 15mL of deionized water and continue sonicating for 1 hour until no precipitate forms at the bottom. The mixed solution is then poured into a hydrothermal reactor, followed by BVO, and allowed to react overnight at 80°C. After the reaction is complete, remove the BVO, rinse repeatedly with deionized water, and blow dry with N2 to obtain the BVO / CoPc+BN photoanode.

[0030] Comparative Example 1 CoPc+BN uncalcined material

[0031] First, a mixture of BN and CoPc was added to a beaker at a ratio of m(BN):m(CoPc) = 6:1. 60 mL of acetonitrile solvent was then added to the beaker and sonicated for 3 hours. A rotor was then added to the beaker and stirred overnight. The mixture was centrifuged at 8000 rpm for five minutes to separate the mixture from the solvent, and the supernatant was discarded. The centrifuged product was placed in a 60°C oven and finally dried and ground to obtain an uncalcined CoPc+BN composite.

[0032] Comparative Example 2 Preparation of BVO / CoPc Photoanode

[0033] Weigh 0.03g of the CoPc composite material into a beaker. Then, add 5mL of N,N-dimethylformamide solvent and sonicate for 1 hour. Then, add 15mL of deionized water and continue sonicating for 1 hour to obtain a uniform dispersion. The mixed solution is then poured into a hydrothermal reactor, followed by BVO, and allowed to react overnight at 80°C. After the reaction, remove the BVO, rinse repeatedly with deionized water, and blow dry with N2 to obtain the BVO / CoPc photoanode.

[0034] Comparative Example 3 Preparation of BVO / BN Photoanode

[0035] Weigh 0.03g of hexagonal boron nitride into a beaker. Then, add 5mL of N,N-dimethylformamide solvent and sonicate for 1 hour. Then, add 15mL of deionized water and continue sonicating for 1 hour to obtain a uniform dispersion. The mixed solution is then poured into a hydrothermal reactor, followed by BVO, and allowed to react overnight at 80°C. After the reaction is complete, remove the BVO, rinse repeatedly with deionized water, and blow dry with nitrogen to obtain the BVO / BN photoanode.

[0036] Example 2 Characterization of BVO / CoPc+BN Photoanode

[0037] 1. Material Characterization

[0038] By observation Figure 1 Scanning electron microscope (SEM) images of the CoPc+BN composite material show that the material exhibits an irregular morphology. This morphological feature may be due to the varying degrees of fragmentation of the material during the ultrasonic process, but this process also provides more active sites for the oxygen evolution reaction. When further observing the micromorphology of the BVO / CoPc+BN composite material ( Figure 2 ) and found that hydrothermal loading of CoPc+BN onto BVO did not affect the porous morphology of BVO, while maintaining a relatively thin thickness of CoPc+BN. This loading method provides a shorter transport path for hole transport, effectively promoting the oxygen evolution reaction.

[0039] In order to determine the chemical state of the samples, X-ray photoelectron spectroscopy (XPS) tests were performed on the BVO and BVO / CoPc+BN photoanodes. By analyzing the fine spectra of Bi 4f, V 2p and O1s, it was observed that Figure 3 It can be seen that when CoPc+BN is loaded onto BVO, the Bi 4f, V 2p, and O1s peaks all shift to a certain extent, indicating that CoPc+BN interacts with BVO, resulting in changes in the BVO surface.

[0040] In addition, by comparing the X-ray diffraction (XRD) patterns of BVO and BVO / CoPc+BN materials ( Figure 4 ) found that they had the same diffraction peaks, indicating that the loading of CoPc+BN did not affect the monoclinic crystal structure of BVO. No peaks representing BN or CoPc characteristics were observed in the XRD pattern of BVO / CoPc+BN, further demonstrating the thin nature of the CoPc+BN catalytic layer.

[0041] In order to further explore the changes in the crystal structure of CoPc+BN after calcination or without calcination, the materials were fed according to the mass ratio of m(BN):m(CoPc)=6:1 and were processed in two parts during the synthesis process. One part did not undergo high-temperature calcination and only required centrifugation and room-temperature drying, while the other part was calcined. Subsequently, the two parts of the material were ground to the same degree. By comparing the XRD patterns before and after calcination, as shown in Figure 2, the XRD patterns before and after calcination were significantly different from those before calcination. Figure 5 As shown in (a), it was found that the crystallinity of the CoPc+BN composite material calcined at 300°C was significantly better than that of the uncalcined material, indicating that the CoPc+BN formed by calcination has a more uniform lattice structure and provides a more unified catalytic environment.

[0042] In addition, a series of powder composite catalysts CoPc+BN were obtained under the same preparation conditions by feeding materials at different mass ratios (m(BN):m(CoPc)=4:1, 6:1, 8:1). Figure 5 The XRD pattern in (b) shows that the crystallinity of the composite material is highest when the mass ratio of m(BN):m(CoPc)=6:1. Therefore, it is theoretically speculated that this composite material is more effective in photoelectrochemical water splitting.

[0043] Example 3 Photoelectrochemical water splitting performance test

[0044] At 0.6 V vs RHE, 100 mW·cm -2A simulated sunlight device was used as the light source to conduct a photoelectrochemical water oxidation reaction, using the composite photoanode prepared in Example 1 as the working electrode, a platinum wire as the counter electrode, and an Ag / AgCl reference electrode. After half an hour of electrolysis, 100 microliters of gas was drawn with a gas injection needle and injected into a gas chromatograph. The analysis results were awaited. The cumulative hydrogen production within half an hour was 25.6 μmol.

[0045] To verify the above theory, separate BN and CoPc as well as different CoPc+BN materials were loaded onto bismuth vanadate to form different BVO-based composite photoanodes, and linear sweep voltammetry cycling tests were performed under AM1.5G illumination. Figure 6 The linear sweep voltammetry (LSV) curve in (a) found that loading BN or CoPc onto BVO alone did not effectively assist BVO in achieving efficient water oxidation reaction, but when BN and CoPc were combined and then loaded onto bismuth vanadate, the oxygen evolution reaction effect was significantly increased. This result further verifies the excellence of multi-components in photoelectrolyte water splitting applications. According to previous inferences, when the initial feed m(BN): m(CoPc) = 6:1, the obtained CoPc+BN composite material loaded onto BVO to form a BVO / CoPc+BN composite photoanode should exhibit the best water oxidation activity. Figure 6 The test results in (b) confirm the aforementioned inferences and further demonstrate the superiority of the structural uniformity of the CoPc+BN composite material for the multi-component synergistic assistance of BVO in the oxygen evolution reaction.

[0046] According to formula (1), the applied bias photoelectric conversion efficiency (ABPE) curves of different bismuth vanadate-based composite photoanodes were drawn. Figure 7 (a) clearly shows the electrochemical performance of each sample. After analyzing the data, it can be seen that BVO reaches a maximum ABPE value of 0.34% at 0.88V vs RHE. In contrast, BVO / BN shows a maximum ABPE value of 0.63% at 0.83V vs RHE, while BVO / CoPc achieves a maximum ABPE value of 1.41% at 0.72V vs RHE. Remarkably, the maximum ABPE value of BVO / CoPc+BN far exceeds that of previous samples, reaching an ABPE value of 1.83% at only 0.67V vs RHE. This discovery reveals the advantage of multi-component oxygen co-catalysts, which is the ability to achieve higher solar energy conversion efficiency at lower bias voltages.

[0047]

[0048] In order to explore the effect of multiple components on the charge transfer efficiency of bismuth vanadate, 0.2M sodium sulfite was added to the electrolyte to ensure that the photogenerated holes reacted with Na2SO3 as much as possible in the LSV test, thereby obtaining the J(Na2SO3) value. According to the derived formula (2), the charge transfer efficiency curve was drawn. Figure 7 It is clearly seen in (b) that the charge transfer efficiency of the composite photoanode formed by loading BN or CoPc onto BVO alone is significantly lower than that of the multi-component composite photoanode formed by CoPc+BN and BVO in the range of 0.4 V–1.23 V vs RHE (η trans =76%, 1.23 V vs RHE). This result demonstrates the importance of multi-component composite materials in improving charge transfer efficiency.

[0049]

[0050] The excellent performance of the multi-component composite photoanode BVO / CoPc+BN in promoting charge transfer was further demonstrated by conducting impedance spectroscopy (EIS) tests. Figure 7 (c) shows that the order of the impedance semicircle diameters is: BVO > BVO / BN > BVO / CoPc > BVO / CoPc+BN. A smaller impedance semicircle radius indicates faster charge transfer at the material interface, thereby improving charge transfer efficiency. Therefore, it can be concluded that both CoPc and BN can enhance charge transfer rates, and their combination further accelerates charge transfer at the material interface. This result further confirms the superiority of multi-component materials in promoting charge transfer.

[0051] According to the previous analysis, BVO achieved the maximum ABPE value at 0.88V vs RHE, while BVO / CoPc+BN showed the highest external bias photoelectric conversion efficiency at 0.67V vs RHE. Therefore, BVO was electrolyzed at 0.8V vs RHE and BVO / CoPc+BN was electrolyzed at 0.6V vs RHE for 3 hours. The chronoamperometric (it) curves were as follows: Figure 8 As shown in the figure, BVO modified with CoPc+BN can maintain water oxidation performance far superior to that of BVO for a long period of time, confirming its potential for application in photoelectric water oxidation.

[0052] The above experimental observations and analysis indicate that the loading of the CoPc+BN composite significantly enhances the water oxidation activity of the bismuth vanadate (BVO) photoanode. Scanning electron microscopy revealed that the CoPc+BN composite exhibited an irregular morphology, but its loading onto BVO did not affect the porous morphology of BVO. Furthermore, it provided a shorter transport path, effectively promoting the oxygen evolution reaction (OER). X-ray diffraction patterns revealed that the loading of CoPc+BN did not affect the monoclinic crystal structure of BVO. Furthermore, the calcined CoPc+BN composite exhibited a more uniform lattice structure, providing a more uniform catalytic environment. Furthermore, the highest crystallinity was achieved when the mass ratio of CoPc to BN was 6:1, consistent with theoretical predictions for superior performance in photoelectrochemical water splitting. LSV measurements revealed that the BVO / CoPc+BN composite exhibited the best water oxidation activity, further confirming the superiority of the structural homogeneity of the CoPc+BN composite in the synergistic support of BVO for the OER. Subsequent electrochemical performance tests further confirmed the excellent performance of BVO / CoPc+BN in promoting charge transfer.

[0053] In summary, the CoPc+BN composite, as a cocatalyst, effectively enhances the water oxidation activity and electrolytic stability of bismuth vanadate-based composite photoanodes, providing new research ideas and approaches for practical applications in solar energy conversion and water splitting. However, further optimization of the synthesis and preparation of this composite material is needed to improve its performance in practical applications and contribute further to the development of sustainable energy.

Claims

1. A BVO / CoPc+BN composite photoanode, characterized in that: The preparation method comprises the following steps: 1) Preparation of CoPc+BN composite material: Boron nitride (BN) and cobalt phthalocyanine (CoPc) were mixed in a mass ratio of 4:1 to 8:1, and then acetonitrile was added. The mixture was ultrasonicated, stirred, and centrifuged. The supernatant was discarded, and the product obtained by centrifugation was placed in a crucible, calcined, and ground to obtain the CoPc+BN composite material. 2) Preparation of BVO / CoPc+BN composite photoanode: N,N-dimethylformamide was added to the CoPc+BN composite material, and the mixture was sonicated. Deionized water was added and sonicated until no precipitate was produced. The mixed solution was poured into a hydrothermal reactor, and BVO was added to carry out a hydrothermal reaction. After the reaction, the mixture was washed and dried to obtain a BVO / CoPc+BN composite photoanode.

2. The BVO / CoPc+BN composite photoanode according to claim 1, characterized in that: In step 1), the mass ratio of boron nitride BN to cobalt phthalocyanine CoPc is 6:

1.

3. The BVO / CoPc+BN composite photoanode according to claim 1, wherein: In step 1), the calcination is carried out by heating the temperature to 300°C at a heating rate of 5°C / min and calcining at 300°C for 2 h.

4. The BVO / CoPc+BN composite photoanode according to claim 1, wherein: In step 2), the hydrothermal reaction is carried out at 80°C overnight.

5. Use of the BVO / CoPc+BN composite photoanode according to claim 1 in electrochemical water splitting.

6. The use according to claim 5, characterized in that The method is as follows: at 0.6 V vs RHE, 100 mW·cm -2 The simulated sunlight device is used as a light source to carry out photoelectrochemical water oxidation reaction, the BVO / CoPc+BN described in claim 1 is used as a working electrode, a platinum wire is used as a counter electrode, and Ag / AgCl is used as a reference electrode to carry out photoelectrochemical water splitting to produce hydrogen.

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