In-situ constructed VCN / ED-BiVO4 heterojunction as well as preparation method and application thereof
By generating oxygen vacant positions in situ on the BiVO4 photoelectrode and modifying synchronously with vanadium doping g-C3N4, VCN/ED-BiVO4 heterojunction is constructed, and the problem of low charge separation and transfer efficiency in the process of photoelectrocatalytic decomposition of water in BiVO4 photoelectrode is solved, and more efficient photoelectrocatalytic performance is achieved.
Patent Information
- Application Number
- CN202411447490.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-16
- Publication Date
- 2025-03-04
AI Technical Summary
During the photoelectrode photoelectrode photoelectrode has problems such as slow surface oxygen evolution reaction kinetics, small hole diffusion length, low carrier mobility and serious photogenerated carrier recombination, which limits its photoelectrocatalytic performance.
Oxygen vacancies were generated in situ on BiVO4 and modified synchronously with vanadium doped g-C3N4 (VCN) to construct a VCN/ED-BiVO4 heterojunction, and the energy band structure of the material was regulated to improve charge separation and transfer efficiency.
The synchronous generation of oxygen vacancy on BiVO4 photoelectrode and the construction of VCN heterojunctions are achieved, which significantly improves the separation and transfer efficiency of photogenerated carriers and improves the performance of photoelectrocatalytic decomposition of water.
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Figure CN119553305A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of photoelectrolytic water catalysis, and in particular to an in-situ constructed VCN / ED-BiVO 4 Heterojunction and its preparation method and application. Background Art
[0002] Hydrogen energy has the advantages of high energy density, carbon-free combustion, and abundant natural resources. It is an ideal primary clean energy. Many technologies have been developed to decompose water to generate hydrogen, such as electrocatalysis, photocatalysis, and photoelectrocatalysis (PEC). Among them, photoelectrocatalytic technology combines the advantages of electrocatalysis and photocatalysis, which can not only give full play to the synergistic effect of solar energy and electrical energy, but also solve the problem that powdered photocatalysts are difficult to recycle and reuse. Therefore, photoelectrocatalytic water decomposition is considered to be a very promising solar energy utilization technology. Since Fujishima and Honda first discovered TiO 2 Since it can be used for photocatalytic hydrogen production, researchers have developed many materials for photoelectrochemical water splitting, including oxides (such as TiO 2 、BiVO 4 , Fe 2 O 3 ), nitrides (such as TaON, Ta 3 N 5 , C 3 N 4 ) and sulfides (such as MoS 2 、CuInS 2 ) etc. Among them, BiVO 4 Due to its narrow bandgap (2.4eV, the maximum theoretical photocurrent is 7.6mA / cm 2 , the theoretical maximum photohydrogen conversion efficiency is 9.1%), with the advantages of suitable energy band position and low cost, it has become one of the most promising photoanode materials for PEC water splitting. 4 It also has the disadvantages of slow surface oxygen evolution reaction kinetics, small hole diffusion length (100nm), low carrier mobility, and serious photogenerated carrier recombination, which limits the development of BiVO 4 Application of photoelectrodes. In order to overcome these shortcomings and improve their photoelectrocatalytic performance, researchers have developed various modification methods, such as doping, surface / interface engineering, and vacancy defect engineering.
[0003] The use of two-dimensional materials to prepare heterojunctions for interface engineering is beneficial to promote hole extraction and inhibit surface recombination, which is one of the effective ways to improve the efficiency of photogenerated charge separation and transfer. 3 N 4Due to its unique structure, good stability, suitable bandgap width, non-toxicity, harmlessness, and low cost, it has been widely studied in the fields of photocatalysis and photoelectrocatalysis. 3 N 4 and doped gC 3 N 4 With BiVO 4 Constructing heterojunctions has received extensive attention. However, in order to achieve high PEC efficiency, the band structures of the two must be carefully adjusted to optimize charge separation. For example, Ye et al. prepared B-doped gC 3 N 4 Mo-doped BiVO 4 (BCN / Mo-BVO) coupling leads to significant improvement in photogenerated charge separation and optical performance. BiVO is tuned by selecting Mo and B dopants respectively 4 and gC 3 N 4 After the work function of each component is modulated, a favorable heterojunction is generated to promote charge transfer. Finally, the photocurrent density of the BCN / Mo-BVO composite photoelectrode is 3.85 mA cm -2 (0.54V vs. RHE). Xia et al. doped gC with Co 3 N 4 and F-doped BiVO 4 (CoVN / F-BVO) heterojunction is constructed to optimize the band structure. Theoretical calculations show that F doping does not change BiVO 4 Band gap. Co doping makes gC 3 N 4 The CBM and VBM of gC are shifted upward, and its band gap is narrowed. 3 N 4 and BiVO 4 In comparison, the VBM of F-BVO is lower and the CBM of CoCN is upward, so the CoVN / F-BVO heterojunction has better charge separation ability. Finally, under the synergistic effect of the two, the starting potential of CoVN / F-BVO is reduced and the photocurrent density reaches 5.89mAcm -2 The above studies show that by using appropriate dopants to 3 N 4 With BiVO 4 Coupling heterojunctions will help improve their PEC performance, but fully realizing their potential still requires the synergistic integration of multiple strategies. In recent years, vacancy defect engineering has been used as a self-dopant to adjust the conductivity, band edge position, and surface molecular adsorption properties of BiVO. 4 Currently, in BiVO4 Different vacancy defects have been generated in BiVO, including oxygen vacancies, vanadium vacancies, and bismuth vacancies. In particular, the introduction of oxygen vacancies is a key factor in improving the BiVO 4 The preferred method for improving the PEC performance of oxygen vacancies plays an important role in improving the PEC performance. Oxygen vacancies can not only act as shallow donors to improve charge conductivity and promote charge separation and transfer processes, but also act as electron capture centers to reduce recombination processes. In addition, oxygen vacancies can act as surface active sites to promote surface OER kinetics. Therefore, many methods for preparing oxygen vacancies have been explored, such as: chemical reduction, electrochemical reduction, photo / PEC treatment, and heteroatom doping. Among them, electrochemical reduction is a simple electrochemical reduction technique that can significantly reduce surface energy, passivate composite surface states, and increase carrier mobility. Although oxygen vacancies can promote PEC activity, it still suffers from photocorrosion due to the dissolution of vanadium ions. Therefore, coating a protective layer on the surface of the oxygen vacancy photoanode is crucial to stabilize the photoelectrode. For example, Peng et al. designed MoS by electrochemical reduction and drop coating. 2 Modified electrochemical treatment of BiVO 4 Heterojunction (E-BVO / MoS 2 ), at 1.23 V vs. RHE, E-BVO / MoS 2 The photocurrent density is higher than that of BiVO 4 The oxygen vacancies generated by electrochemical treatment increase the carrier concentration and accelerate the charge separation process. 2 The heterojunction establishes a unidirectional charge transfer channel, which further promotes the extraction of surface holes and OER kinetics. Therefore, the synergistic effect of oxygen vacancies and heterojunction improves PEC activity and photostability. Zhang et al. developed a novel and simple zero-valent iron (ZVI) reduction method to achieve the 4 In situ generation of oxygen vacancies and FeO x Synchronous modification of co-catalysts (BVO-Ov / FeO x The results show that oxygen vacancies can significantly prolong light absorption, increase electron lifetime (115.3 ms), and improve electron mobility (8.6×10 -7 cm 2 s -1 ).FeO x The layer accelerates the kinetics of the oxygen evolution reaction and significantly reduces the overpotential. x The optical flux density is higher than that of BiVO 4 These findings suggest that combining vacancy defect engineering with other state-of-the-art strategies (e.g., heterojunctions, co-catalysts) can lead to a more efficient and stable BiVO 4 Photoanode. Summary of the invention
[0004] The present invention uses a one-step electrochemical deposition method to achieve BiVO 4 In situ generation of oxygen vacancies and vanadium doping of gC 3 N 4 Synchronous modification (VCN / ED-BiVO 4 ), through the regulation of the band gap, a structure that is conducive to charge separation and transfer is formed inside the material, thereby improving the efficiency of carrier transfer. The present invention provides a novel method for in-situ construction of heterojunctions combined with vacancy defect engineering, which provides an important guiding direction for the construction of efficient photoanodes.
[0005] To achieve the above purpose, the technical solution adopted by the present invention is: an in-situ construction of VCN / ED-BiVO 4 A method for preparing a heterojunction comprises the following steps: ①Using conductive glass as substrate, BiVO is prepared 4 Photoelectrode; ② Grind the urea and ammonium metavanadate, transfer to a covered crucible and keep at 400-500℃ for 2-4h at a heating rate of 1-3℃ / min to obtain vanadium-doped gC 3 N 4 (VCN) powder; ③ Prepare a boric acid solution with a concentration of 0.1-5 mg / mL VCN (the concentration of boric acid is 0.5-1 mol / L), perform ultrasonic peeling, and take the supernatant (H 3 BO 3 +VCN) as the electrolyte, in the three-electrode system, BiVO 4 As the working electrode, Pt as the counter electrode, SCE as the reference electrode, the deposition was carried out at a voltage of -0.05V to -1.2V vs. RHE for 60s to 600s by constant potential method, and VCN / ED-BiVO was obtained after washing and drying. 4 Composite photoanode.
[0006] Preferably, the molar amount of vanadium doping in the VCN powder in step ② is 0.1% to 0.5%.
[0007] Preferably, in step ①, BiVO 4 The preparation method of the photoelectrode is as follows: A BiOI photoelectrode was prepared by electrodeposition in an electrodeposition solution containing bismuth nitrate, potassium iodide and p-benzoquinone using a conductive glass substrate; a 0.1-0.5 mol / L dimethyl sulfoxide solution of acetylacetonatovanadium was added dropwise to the obtained BiOI electrode, and then the temperature was raised to 450-500°C at a rate of 1-5°C / min, and the temperature was maintained for 2-4 hours, and then the electrode was cooled to room temperature, and the excess V was removed by washing with a 0.1-1 mol / L NaOH aqueous solution. 2 O 5 , dried with nitrogen to obtain yellow BiVO 4 Photoelectrode.
[0008] The beneficial effects of the present invention are as follows: 4 In a one-step electrochemical treatment, the generation of oxygen vacancies and VCN modification can be achieved simultaneously to construct a heterojunction, obtaining VCN / ED-BiVO 4 The composite photoanode, under the synergistic effect of oxygen vacancies generated by electrochemical reduction and heterojunction, effectively promotes the separation and transfer of photogenerated carriers, improving the VCN / ED-BiVO 4 Performance of photoelectrocatalytic water splitting. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 is the BiVO in Example 1 4 SEM images of Figure 2 VCN / ED-BiVO in Example 1 4 SEM image of the composite photoanode; Figure 3 VCN / ED-BiVO in Example 1 4 EDX-mapping of the composite photoanode Figure 4 BiVO obtained in Example 1 4 and VCN / ED-BiVO 4 , CN / ED-BiVO obtained in Example 2 4 and ED-BiVO obtained in Example 3 4 High-resolution XPS spectrum of surface O1s; Figure 5 BiVO obtained in Example 1 4 and VCN / ED-BiVO 4 , CN / ED-BiVO obtained in Example 2 4 and ED-BiVO obtained in Example 3 4 LSV curve of Figure 6 BiVO obtained in Example 1 4 and VCN / ED-BiVO4 Electron lifetime diagram of the composite photoanode. DETAILED DESCRIPTION
[0010] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.
[0011] Example 1 (1) BiVO 4 Preparation Weigh 3.3200g potassium iodide and 0.9701g bismuth nitrate pentahydrate into 25mL ultrapure water and fully dissolve to obtain solution A. Mix 70μL concentrated nitric acid (68wt%) and 25mL ultrapure water to obtain solution B; weigh 0.4928g p-benzoquinone, add 20mL anhydrous ethanol, and mix evenly to obtain solution C. After mixing the above solutions A and B evenly, mix solution C with the (A+B) mixed solution to obtain the required electrolyte. FTO was used as the working electrode, Pt as the counter electrode, and SCE as the reference electrode, and FTO / BiOI was obtained by deposition at a voltage of -0.14V vs.SCE for 100s. 50μL of DMSO solution of acetylacetone oxyvanadium (concentration: 0.2mol / L) was evenly added to the BiOI film, and then the temperature was raised to 450℃ (heating rate was 2℃ / min), and kept at 450℃ for 2h. After cooling to room temperature, the FTO electrode was placed in 0.1 mol / L NaOH, stirred for 20 min, and dried with nitrogen to obtain BiVO 4 Photoelectrode.
[0012] (2) Preparation of VCN 10 g of urea and 0.0584 g of ammonium metavanadate were weighed, mixed and ground, placed in a crucible with a lid, transferred to a muffle furnace, and kept at 450° C. for 2.5 h (heating rate of 2° C. / min). VCN powder was obtained after natural cooling.
[0013] (3) VCN / ED-BiVO 4 Preparation of composite photoanode Prepare a boric acid solution with a concentration of 1 mg / mL VCN (boric acid concentration: 0.5 mol / L), perform ultrasonic stripping, and take the supernatant (H 3 BO 3 +VCN) as the electrolyte. 4 As the working electrode, Pt as the counter electrode, SCE as the reference electrode, the VCN / ED-BiVO was obtained by deposition at -0.1 V vs. RHE for 210 s. 4 Photoelectrode.
[0014] Example 2 (1) BiVO 4 Preparation Weigh 3.3200g potassium iodide and 0.9701g bismuth nitrate pentahydrate into 25mL ultrapure water and mix them evenly to obtain solution A. Weigh 70μL concentrated nitric acid (68wt%) and 25mL ultrapure water respectively to obtain solution B; weigh 0.4928g p-benzoquinone, add 20mL anhydrous ethanol, and mix evenly to obtain solution C. After mixing the above solutions A and B evenly, mix solution C with the (A+B) mixed solution to obtain the required electrolyte. FTO was used as the working electrode, Pt as the counter electrode, and SCE as the reference electrode, and FTO / BiOI was obtained by deposition at a voltage of -0.14V vs.SCE for 100s. 50μL of DMSO solution of acetylacetone oxyvanadium (concentration: 0.2mol / L) was evenly added to the BiOI film, and then the temperature was raised to 450℃ (heating rate was 2℃ / min), and kept at 450℃ for 2h. After cooling to room temperature, the FTO electrode was placed in 0.1 mol / L NaOH, stirred for 20 min, and dried with nitrogen to obtain BiVO 4 Photoelectrode.
[0015] (2) Preparation of CN 10 g of urea was weighed and ground, then placed in a crucible with a lid, transferred to a muffle furnace, and maintained at 450° C. for 2.5 h (heating rate of 2° C. / min). CN powder was obtained by natural cooling.
[0016] (3) VCN / ED-BiVO 4 Preparation of composite photoanode Prepare a boric acid solution with a concentration of 1 mg / mL CN (boric acid concentration: 0.5 mol / L) for ultrasonic stripping, and take the supernatant (H 3 BO 3 +CN) as the electrolyte. In the three-electrode system, BiVO 4 , Pt and SCE were used as working electrode, counter electrode and reference electrode, and the deposition was carried out at -0.1 V vs. RHE for 210 s. 4 The process of BiVO 4 At the same time, immersion in CN solution can achieve simultaneous chemical impregnation and electrochemical reduction, and finally obtain CN / ED-BiVO 4 Photoelectrode.
[0017] Example 3 (1) BiVO 4 Preparation Weigh 3.3200g potassium iodide and 0.9701g bismuth nitrate pentahydrate into 25mL ultrapure water and mix well to obtain solution A. Weigh 70μL concentrated nitric acid (68wt%) and 25mL ultrapure water to obtain solution B; weigh 0.4928g p-benzoquinone, add 20mL anhydrous ethanol, and mix well to obtain solution C. After mixing the above solutions A and B, mix solution C with solution A+B to obtain the required electrolyte. FTO was used as the working electrode, Pt as the counter electrode, and SCE as the reference electrode, and FTO / BiOI was obtained by deposition at a voltage of -0.14Vvs.SCE for 100s. 50μL of DMSO solution of acetylacetone oxyvanadium (concentration: 0.2mol / L) was evenly added to the BiOI film, and then the temperature was raised to 450℃ (heating rate was 2℃ / min), and kept at 450℃ for 2h. After cooling to room temperature, the FTO electrode was placed in 0.1 mol / L NaOH, stirred for 20 min, and dried with nitrogen to obtain BiVO 4 Photoelectrode.
[0018] (2) ED-BiVO 4 Preparation of composite photoanode Prepare 0.5 mol / L boric acid solution as electrolyte. 4 As the working electrode, Pt as the counter electrode, SCE as the reference electrode, the deposition was carried out at -0.1 V vs. RHE for 210 s to obtain ED-BiVO 4 Photoelectrode.
[0019] Figure 1 is the BiVO in Example 1 4 SEM image of Figure 1 It can be seen that the BiVO prepared by electrodeposition 4 It is a uniform porous structure, and its pores can provide an appropriate location for the loading of VCN, which will be beneficial to the penetration of the electrolyte, provide more reaction active sites, and help improve the photoelectrocatalytic performance.
[0020] Figure 2 VCN / ED-BiVO in Example 1 4 SEM image of the composite photoanode. Figure 2 It can be seen that after the simultaneous electrochemical reduction treatment and chemical impregnation experiments, the VCN particles are uniformly loaded on the porous BiVO 4 The surface of the electrochemical reduction of BiVO 4 At the same time, VCN modification can be achieved, and finally VCN / ED-BiVO 4 Composite materials.
[0021] Figure 3 VCN / ED-BiVO in Example 1 4EDX-mapping diagram of the composite photoanode. Figure 3 It can be seen that after the simultaneous treatment of electrochemical reduction and chemical impregnation, the element distribution of the composite photoanode includes five elements: C, N, Bi, O and V, indicating that VCN is successfully modified on BiVO 4 The surface of the photoanode.
[0022] Figure 4 BiVO obtained in Example 1 4 and VCN / ED-BiVO 4 , CN / ED-BiVO obtained in Example 2 4 and ED-BiVO obtained in Example 3 4 High-resolution XPS spectrum of surface O1s. Figure 4 It can be seen that, compared with BiVO 4 In comparison, after one-step electrochemical treatment, ED-BiVO 4 、CN / ED-BiVO 4 and VCN / ED-BiVO 4 The O1s binding energy shifts positively. New peaks appear at 531.2eV, 530.8eV and 530.5eV, which belong to BiVO 4 The results show that oxygen vacancies can be generated after a one-step electrochemical reduction treatment. Figure 1-4 It can be seen that the present invention successfully achieves the BiVO 4 In situ generation of oxygen vacancies and vanadium doping of gC 3 N 4 Synchronous modification of VCN / ED-BiVO 4 Composite photoanode.
[0023] Figure 5 BiVO obtained in Example 1 4 and VCN / ED-BiVO 4 ED-BiVO obtained in Example 3 4 , CN / ED-BiVO obtained in Example 2 4 In Na 2 SO 4 The LSV result of Figure 5 It can be seen that, compared with BiVO 4 ,ED-BiVO 4 and CN / ED-BiVO 4 Compared with VCN / ED-BiVO 4 The photocurrent density of VCN / ED-BiVO is the largest in the entire electrochemical window. 4 The photocurrent density is 0.52 mA cm-2 , respectively BiVO 4 ,ED-BiVO 4 and CN / ED-BiVO 4 The electrochemical reduction treatment and the construction of VCN heterojunction can synergistically improve the performance of photoelectrocatalytic water splitting.
[0024] Figure 6 BiVO obtained in Example 1 4 and VCN / ED-BiVO 4 Composite photoanode in Na 2 SO 4 The electron lifetime results in . Figure 6 It can be seen that under the synergistic effect of electrochemical treatment and VCN, VCN / ED-BiVO 4 The electron lifetime of the composite photoanode is significantly longer than that of BiVO 4 This indirectly shows that electrochemical reduction treatment and the construction of VCN heterojunction can synergistically promote the effective separation of photogenerated electrons and holes, and ultimately promote the improvement of photoelectrocatalytic performance.
Claims
1. A method for preparing an in-situ VCN / ED-BiVO4 heterojunction, characterized in that The following steps are involved: ①Using conductive glass as substrate, BiVO4 photoelectrode was prepared; ② Mix urea and ammonium metavanadate and grind them, transfer them to a covered crucible and keep them at 400-500°C for 2-4 hours at a heating rate of 1-3°C / min to obtain VCN powder; ③ Prepare a boric acid solution with a concentration of 0.1-5 mg / mL VCN, perform ultrasonic stripping, take the supernatant as the electrolyte, and in a three-electrode system, use BiVO4 as the working electrode, Pt as the counter electrode, and SCE as the reference electrode. Use a one-step constant potential deposition method to deposit at a potential of -0.05V to -1.2V vs. RHE for 60s to 600s. After washing and drying, the VCN / ED-BiVO4 composite photoanode is obtained.
2. The method for preparing an in-situ VCN / ED-BiVO4 heterojunction as claimed in claim 1, characterized in that: The concentration of boric acid in the boric acid solution of VCN in step ③ is 0.5-1 mol / L.
3. The method for preparing an in-situ VCN / ED-BiVO4 heterojunction as claimed in claim 1, characterized in that: In the step ②, the molar amount of vanadium doped in the VCN powder is 0.1% to 0.5%.
4. The method for preparing an in-situ VCN / ED-BiVO4 heterojunction as claimed in claim 1, characterized in that: The preparation method of the BiVO4 photoelectrode in step ① is as follows: A BiOI electrode is prepared by electrodeposition in a mixed electrolyte containing bismuth nitrate, potassium iodide and p-benzoquinone using conductive glass as a substrate; a 0.1-0.5 mol / L dimethyl sulfoxide solution of acetylacetonatovanadium is drop-coated on the surface of the obtained BiOI electrode, and then the temperature is raised to 450-500°C at a heating rate of 1-5°C / min, and the temperature is maintained for 2-4 hours, and then the electrode is cooled to room temperature, and excess V2O5 is removed by washing with a 0.1-1 mol / L NaOH aqueous solution to obtain a yellow BiVO4 photoelectrode.
5. The VCN / ED-BiVO4 composite photoanode prepared by any method of claims 1-4.
6. Use of the VCN / ED-BiVO4 composite photoanode as claimed in claim 5 in photoelectrocatalytic water decomposition.