Preparation method of oxygen-vacancy-enriched BiVO4 photo-anode co-modified by hydroxyl ferric nickel oxide and carbon quantum dots

Abstract

The invention belongs to the technical field of photocatalysis and photoelectrochemistry, and discloses a preparation method of an oxygen-vacancy-enriched BiVO4 photo-anode co-modified by hydroxyl ferronickel oxide and carbon quantum dots and application of the oxygen-vacancy-enriched BiVO4 photo-anode in a urea photoelectrolysis reaction. According to the method, a BiVO4 photo-anode is prepared firstly, then NiFeOOH and CQDs modification is carried out in sequence, and a Bi2S3 thin film is converted into the BiVO4 photo-anode through a two-step annealing method. Experiments show that compared with an unmodified BiVO4 photo-anode, the modified photo-anode can effectively reduce the recombination rate of photon-generated carriers and improve the charge separation efficiency and the surface catalytic activity. Experimental data show that the photocurrent density Jph of the BiVO4 / NiFeOOH / CQDs photoanode under 1.23 VRHE reaches 5.4 mAcm <-2 >, which is nearly 11 times higher than that of a pure BiVO4 photoanode, and the charge separation efficiency is improved from 42% to 73.49%. The preparation method is simple in process and low in cost, and the prepared photo-anode is excellent in performance in a photoelectrolysis urea reaction and integrally shows good application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photoelectrochemical catalytic materials, and particularly relates to a preparation method of a hydroxyl nickel oxide iron and carbon quantum dot co-modified oxygen vacancy-rich BiVO4 photoanode and application thereof in photoelectrolysis of urea oxidation reaction. The technology significantly improves the photocurrent density of the BiVO4 photoanode by synergistically introducing oxygen vacancies, a hydroxyl nickel oxide iron and carbon quantum dot catalytic layer / photoredox, and provides a new electrode material for efficient photoelectrolysis of urea to produce hydrogen and degradation of urea-containing wastewater. BACKGROUND

[0002] In a photoelectrochemical system, the photoanode is the main source of photo-generated carriers, and its performance directly affects the efficiency of water splitting or pollutant degradation. Among numerous photoanode materials, bismuth vanadate (BiVO4) is of great concern due to its narrow band gap (2.4 eV), visible light response capability and environmental friendliness, and is considered as one of the ideal candidate materials for realizing efficient solar energy conversion. However, the actual performance of the pure BiVO4 photoanode is limited by two major problems: first, the rapid recombination of photo-generated electron-hole pairs in the bulk phase leads to low charge separation efficiency; second, the slow kinetics of surface oxygen evolution reaction requires high overpotential driving, further reducing energy conversion efficiency.

[0003] To improve the photoelectric performance of BiVO4, existing research mainly focuses on bulk defect engineering and surface catalytic modification. Oxygen vacancy-rich BiVO4 is synthesized by a two-step annealing method, and the positive effect of oxygen vacancies on inhibiting carrier recombination is verified. However, simple bulk defect regulation cannot effectively solve the problem of slow surface reaction kinetics. In terms of surface modification, the photoelectric current density is effectively improved by loading NiFeOOH cocatalyst on the surface of BiVO4. However, the modification of transition metal hydroxyl oxides still has defects such as limited catalytic active sites and large interface charge transport resistance, and the research on multi-element synergistic modification is still in the exploratory stage. In addition, the existing methods have not effectively solved the problems of accurate control of the thickness of the modified layer, interface stability with the substrate and large-scale preparation cost. Therefore, developing a composite modification strategy that can synergistically optimize the bulk charge separation and surface catalytic activity of BiVO4 has become the key to improving its photoelectrolysis performance. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a hydroxyl nickel oxide iron and carbon quantum dot co-modified oxygen vacancy-rich BiVO4 photoanode, which synergistically introduces oxygen vacancies, NiFeOOH and CQDs catalytic layer / photoredox to solve the problems of high photo-generated carrier recombination rate and insufficient surface catalytic activity of the existing BiVO4 photoanode, and to improve its photoelectrochemical performance in photoelectrolysis of urea wastewater to produce hydrogen.

[0005] To solve the above technical problems, the application provides a preparation method of a hydroxyl nickel oxide iron and carbon quantum dot co-modified oxygen-rich vacancy BiVO4 photoanode, which comprises the following steps:

[0006] S1: preparing a BiVO4 photoanode

[0007] A bismuth sulfide precursor solution is configured, 1.16g of Bi(NO3)3.5H2O is dissolved into 2ml of (CH2OH)2 and 2ml of CH3OH solution, and 0.3g of CH4N2S is added. The bismuth sulfide precursor solution is spin-coated onto the treated FTO substrate by using a spin coating method, the spin coating rotation speed is 2500r / min, and the spin coating time is 25s. Then, the spin-coated FTO is heated and treated at a high temperature of 200 DEG C to obtain a black Bi2S3 film. The Bi2S3 film is treated by using a two-step annealing method, that is, the Bi2S3 film is first placed in a muffle furnace, heated to 500 DEG C and kept for 2h for constant temperature annealing treatment to obtain a white Bi2O3 film. Then, vanadium source (preferably vanadyl acetylacetonate) is drop-coated on the white film, and the film is heated and treated again at 500 DEG C for 50min. Finally, the obtained film is soaked in 1M NaOH solution for 15min to remove excess V2O5, and then washed with deionized water for several times to obtain a yellow BiVO4 photoanode.

[0008] S2: preparing a BiVO4 / NiFeOOH photoanode

[0009] A mixed solution is prepared, 1mmol of Fe(NO3)3.9H2O and 0.5mmol of Ni(NO3)2.6H2O are dissolved into 150ml of deionized water.

[0010] The BiVO4 photoanode prepared in step S1 is soaked in the above mixed solution for 5h, and then dried at room temperature after the soaking is completed to obtain a BiVO4 / NiFeOOH photoanode.

[0011] S3: preparing a BiVO4 / NiFeOOH / CQDs photoanode

[0012] First, a mixed solution of 25ml, 1M NaOH solution and 25ml, 1M C6H12O6 is configured, and then ultrasonic treatment is carried out at room temperature for 5h. Then, HCl is added dropwise to the solution after ultrasonic treatment, and adjusted to pH=7 to finally synthesize a CQDs solution. Then, 1mmol Fe(NO3)3·9H2O and 0.5mmol Ni(NO3)2·6H2O solutions are added to 150ml deionized water, and the BiVO4 photoanode is immersed in the mixed solution for 5h. After the end of the immersion, the BiVO4 / NiFeOOH photoanode is dried at room temperature. Finally, the synthesized CQDs solution with a concentration of 10-20mg / ml is spin-coated on the surface of the BiVO4 / NiFeOOH photoanode, the spin-coating speed is 2500r / min, the spin-coating time is 25s, and then the BiVO4 / NiFeOOH / CQDs photoanode is obtained after drying at room temperature.

[0013] Other photoanodes are immersed separately to obtain BiVO4 / NiFeOOH samples and spin-coated separately to obtain BiVO4 / CQDs samples.

[0014] Optionally, the concentration of the CQDs solution is 10-20mg / ml.

[0015] Optionally, in the spin-coating method, the spin-coating speed can be in the range of 2500-3500r / min, and the spin-coating time can be in the range of 20-40s.

[0016] Optionally, the heating treatment temperature can be adjusted in the range of 180-220℃.

[0017] Optionally, spin-coating can be performed twice to make the surface more uniform.

[0018] Optionally, in the bismuth sulfide precursor solution, the amount of Bi(NO3)3·5H2O can be adjusted in the range of 1.1-1.2g, the amount of (CH2OH)2 can be selected in the range of 1.5-2.5ml, the amount of CH3OH can be selected in the range of 1.5-2.5ml, and the amount of CH4N2S can be varied in the range of 0.2-0.4g.

[0019] Optionally, in the preparation of the mixed solution of the BiVO4 / NiFeOOH photoanode, the amount of Fe(NO3)3·9H2O can be in the range of 0.8-1.2mmol, the amount of Ni(NO3)2·6H2O can be in the range of 0.4-0.6mmol, and the amount of deionized water can be in the range of 100-200ml.

[0020] The photoanode prepared by the method of the hydroxyl nickel oxide-iron and carbon quantum dot co-modified oxygen-rich vacancy BiVO4 photoanode is used for photoelectrolysis of urea wastewater to prepare hydrogen. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 (a) and (b) are SEM images of BiVO4 photoanodes prepared by two-time annealing method in the present application and BiVO4 photoanodes prepared by electrodeposition and thermal annealing method;

[0022] Figure 2 Comparison of ηsep graphs of electrodeposited and thermally annealed BiVO4 and two-time annealed BiVO4;

[0023] Figure 3 is an XRD pattern of BiVO4 / NiFeOOH / CQDs photoanode prepared in the present application;

[0024] Figure 4 is an LSV curve of BiVO4-based photoanode prepared in the present application corresponding to urea decomposition response (solid line: containing urea; dotted line: not containing urea);

[0025] Figure 5 (a) is an LSV curve of BiVO4-based photoanode in the present application in an electrolyte containing urea; Figure 5 (b) is the ABPE efficiency of each photoanode calculated based on Figure 5 (a) data;

[0026] Figure 6 is an electrochemically active area graph of BiVO4-based photoanode in the present application;

[0027] Figure 7 is an LSV curve of BiVO4 / NiFeOOH / CQDs photoanode prepared in the present application before and after stability test;

[0028] Figure 8 is a chopped light it curve before and after stability test. DETAILED DESCRIPTION

[0029] A specific embodiment of a preparation method of a nickel oxyhydroxide and carbon quantum dot co-modified BiVO4 photoanode is described in further detail below in combination with the accompanying drawings and specific examples. The advantages and features of the present application will be more apparent according to the following description and claims, but the scope of protection of the present application is not limited to the described content. The present application provides a preparation method of a nickel oxyhydroxide and carbon quantum dot modified BiVO4 photoanode, and the steps are as follows:

[0030] S1: Preparation of BiVO4 photoanode substrate treatment: The conductive glass coated with fluorine-doped tin oxide (FTO) thin film was first placed in acetone, ethanol and deionized water for ultrasonic cleaning for 15 min, and then dried with nitrogen blowing, and then treated with ultraviolet ozone for 30 min to improve the hydrophilicity and activity of the substrate surface. Bismuth sulfide precursor preparation: 1.16 g of Bi(NO3)3·5H2O was accurately weighed and dissolved in a mixture of 2 ml of (CH2OH)2 and 2 ml of CH3OH, and stirred at a speed of 500 r / min on a magnetic stirrer for 30 min until completely dissolved. Then 0.3 g of CH4N2S was added and continued to stir for 60 min to obtain a uniform bismuth sulfide precursor solution. Bismuth sulfide film preparation: The bismuth sulfide precursor solution was spin-coated onto the treated FTO substrate using a spin coating method, with a spin coating speed of 2500 r / min and a spin coating time of 25 s. After spin coating, the substrate was heated on a heating table at 200℃ for 10 min to obtain a black Bi2S3 thin film. Two-step annealing method for preparing BiVO4 photoanode: The Bi2S3 thin film was placed in a muffle furnace and heated to 500℃ at a rate of 2℃ / min and kept at a constant temperature for 2h annealing treatment to obtain a white film. 0.2 mL of 0.2 mol / L vanadyl acetylacetonate dimethyl sulfoxide solution was dropped onto the white film, and then heated to 150℃ in a fume hood to volatilize the dimethyl sulfoxide solvent. The film was again placed in a muffle furnace and heated to 500℃ at a rate of 2℃ / min and annealed for 50 min. Finally, the obtained film was immersed in 1M NaOH solution for 15 min to remove excess V2O5, washed with deionized water several times, and dried in an oven at 60℃ for 30 min to obtain a yellow BiVO4 photoanode.

[0031] S2: Preparation of BiVO4 / NiFeOOH photoanode mixed solution preparation: 1 mmol of Fe(NO3)3·9H2O and 0.5 mmol of Ni(NO3)2·6H2O were dissolved in 150 ml of deionized water, and stirred at a speed of 400 r / min on a magnetic stirrer for 45 min to completely dissolve the two salts, to obtain a mixed solution containing NiFeOOH. Immersion treatment: The prepared BiVO4 photoanode was immersed in the above mixed solution for 5h, and during the immersion process, the solution was gently stirred every 1h to ensure uniform adsorption of metal ions on the surface of the BiVO4 photoanode. After the immersion was completed, the photoanode was taken out, the surface was gently washed with deionized water, and then naturally dried at room temperature to obtain a BiVO4 / NiFeOOH photoanode.

[0032] S3: Preparation of BiVO4 / NiFeOOH / CQDs photoanode CQDs solution synthesis: CQDs solution was synthesized by hydrothermal method. 0.5 g of citric acid and 0.2 g of urea were added to 20 ml of deionized water, and after ultrasonic dissolution for 15 min, it was transferred to a 50 ml reaction kettle and reacted at 200℃ for 4 h. After the reaction was completed, it was cooled to room temperature, centrifuged at 8000 r / min for 15 min, and the supernatant was filtered with a 0.22 μm filter membrane to obtain a CQDs solution with a concentration of 2 mg / ml. Spin coating treatment: The synthesized CQDs solution was spin-coated onto the surface of the BiVO4 / NiFeOOH photoanode, and the spin-coating speed was 2500 r / min, and the spin-coating time was 25 s. After spin coating, it was naturally dried at room temperature to obtain the final BiVO4 / NiFeOOH / CQDs photoanode.

[0033] Example one

[0034] This example is used to convert Bi2S3 precursor film into a structurally dense BiVO4 photoanode by secondary annealing, to illustrate the method of preparing BiVO4 photoanode by secondary annealing and its charge separation performance advantages, including the following steps:

[0035] First step: configuration of bismuth sulfide precursor solution, 1.16 g of Bi(NO3)3·5H2O was dissolved in 2 ml of (CH2OH)2 and 2 ml of CH3OH solution, and 0.3 g of CH4N2S was added. The bismuth sulfide precursor solution was spin-coated onto the treated FTO substrate by spin coating method to obtain a black Bi2S3 thin film.

[0036] Second step: The Bi2S3 thin film was treated by two-step annealing method, first placed in a muffle furnace, heated to 500℃ and kept for 2h constant temperature annealing treatment, obtained Bi2O3 white film; then drop-coat vanadium source (preferably vanadium acetylacetone) on the white film, and heat to 500℃ again for 50 min; finally, the obtained film was immersed in 1M NaOH solution for 15 min to remove excess V2O5, and washed with deionized water several times to obtain a yellow BiVO4 photoanode.

[0037] Comparative example one:

[0038] This example uses electrodeposition and thermal annealing to synthesize BiVO4, including the following steps:

[0039] Step 1: Mix 0.1M Bi(NO₃)₃·5H₂O, 0.05M NH₄VO₃, 0.1M citric acid, and 50% C₂H₂O₂ with nitric acid, adjusting the pH to 1.5–2.0. Using a three-electrode system with FTO as the working electrode, platinum as the counter electrode, and Ag / AgCl as the reference electrode, potentiostatic deposition was performed at -0.6V vs. Ag / AgCl for 30 minutes at room temperature.

[0040] Step 2: Place the electrodeposited FTO substrate in a muffle furnace, heat it to 500°C at 5°C / min, and keep it at that temperature for 2 hours.

[0041] Step 3: Take it out after cooling to obtain a yellow BiVO4 photoanode.

[0042] like Figure 1 As shown in the SEM image, it can be seen that compared with BiVO4 obtained by electrodeposition and thermal annealing, the BiVO4 synthesized by double annealing has a tighter spatial structure and smaller gaps between grains. Using an X-ray diffractometer, the scanning range 2θ = 10°-80°, the step length 0.02°, and the scanning speed 2° / min, the XRD patterns of pure BiVO4, two-step annealed BiVO4, and BiVO4 / NiFeOOH / CQDs were tested simultaneously. It can be seen from the crystal structure of the sample by XRD characterization that Figure 3 As shown in the figure, except for the FTO (PDF#46-1088) peak, all other peaks are directly referred to as monoclinic BiVO4 (PDF#14-0688). It is worth mentioning that compared with the BiVO4 standard card, it can be observed that the (011) and (121) peaks are very strong, while the (040) peak is very weak, which indicates that the synthesized BiVO4 preferentially exposes the (011) and (121) crystal planes, which can promote the water oxidation reaction. The performance test of the photoanode was carried out, as shown in the figure. Figure 2 As shown, the η of the BiVO4 photoanode synthesized by double annealing is sep is 42%, while the BiVO4 photoanode synthesized by electrodeposition and annealing has an η sep The charge separation effect of the BiVO4 photoanode synthesized by double annealing is better, which proves that the preparation method of the present invention has good performance in improving the charge separation performance.

[0043] Example 2

[0044] This example is used to prepare a BiVO4 / NiFeOOH / CQDs photoanode to illustrate the synergistic effect of multi-component modification on the photoanode's photoelectric conversion efficiency, charge separation, and other properties, including the following steps:

[0045] The first step is to transform the Bi2S3 precursor film into a densely structured BiVO4 photoanode through a double annealing method.

[0046] Step 2: Using a solution impregnation method, 1 mmol of Fe(NO₃)₃·9H₂O and 0.5 mmol of Ni(NO₃)₂·6H₂O were added to 150 ml of deionized water. The BiVO₄ photoanode from step 1 was then immersed in the mixed solution for 5 hours. After immersion, the BiVO₄ / NiFeOOH photoanode was dried at room temperature to obtain the resulting product.

[0047] Step 3: Use the spin coating method with a spin coating speed of 2500r / min and a spin coating time of 25s to evenly anchor the CQDs solution on the surface of the BiVO4 / NiFeOOH photoanode, and finally obtain the BiVO4 / NiFeOOH / CQDs photoanode.

[0048] The photoanode was tested for performance, such as Figure 6 As shown, from the LSV curve ( Figure 5 a) It can be seen that at 1.23V RHE J ph The photocurrent density of the BiVO4 / NiFeOOH / CQDs photoanode is 5.4 mA cm -2 , the photoelectric conversion efficiency ABPE ( Figure 5 b), BiVO4 / NiFeOOH / CQDs, at 0.73V RHE The efficiency is 1.25%. These results show that the NiFeOOH / CQDs modified BiVO4 / NiFeOOH / CQDs photoanode has good performance in terms of photocurrent density, photoelectric conversion efficiency, and charge separation and recombination.

[0049] Comparative Example 2 (Pure BiVO4 Photoanode)

[0050] This comparative example is used to prepare a pure BiVO4 photoanode and compare the basic performance of a single-structure photoanode, including the following steps:

[0051] The first step is to transform the Bi2S3 precursor film into a densely structured BiVO4 photoanode through a double annealing method.

[0052] The photoanode was tested for performance, such as Figure 6 As shown, from the LSV curve ( Figure 5 a) It can be seen that at 1.23V RHE J ph , J of pure BiVO4 photoanode ph Only 0.5mAcm -2 , but the J of BiVO4 / NiFeOOH / CQDs photoanode is ph 5.4 mA cm -2 , we can see a significant improvement, and J phIt increased by nearly 11 times, and the photoelectric conversion efficiency ABPE ( Figure 5 b), BiVO4 / NiFeOOH / CQDs photoanode is the most efficient among them, at 0.73V RHE The efficiency is 1.25%, which is 25 times the maximum photoelectric conversion efficiency of BiVO4 photoanode of 0.05%, and the performance is significantly improved.

[0053] This comparative example is used to prepare a BiVO4 / NiFeOOH photoanode to illustrate the inhibitory effect of a single component of NiFeOOH on charge recombination, and includes the following steps:

[0054] Step 1: Prepare BiVO4 photoanode (same as the two-step annealing process for synthesizing BiVO4).

[0055] Step 2: NiFeOOH is loaded on the BiVO4 surface by solution impregnation to form a BiVO4 / NiFeOOH photoanode.

[0056] The photoanode was tested for performance, such as Figure 6 As shown, from the LSV curve ( Figure 5 a) It can be seen that at 1.23V RHE J ph , J of BiVO4 / NiFeOOH ph Only 1.90mAcm -2 , but the J of BiVO4 / NiFeOOH / CQDs photoanode is ph 5.4 mA cm -2 , J ph increased by nearly 3 times, and further calculations yielded the respective photoelectric conversion efficiencies ABPE ( Figure 5 b), BiVO4 / NiFeOOH / CQDs photoanode is the most efficient among them, at 0.73V RHE The efficiency under potential is 1.25%, which is 1.8 times the maximum photoelectric conversion efficiency of BiVO4 / NiFeOOH photoanode of 0.68%. The above data show that the inhibitory effect on charge recombination is obvious and the performance is significantly improved.

[0057] Comparative Example 4 (CQDs / NiFeOOH Photoanode)

[0058] This comparative example is used to prepare a BiVO4 / CQDs photoanode and compare the performance improvement effect of single-component CQDs modification, including the following steps:

[0059] Step 1: Prepare BiVO4 photoanode (same as the two-step annealing process for synthesizing BiVO4).

[0060] Step 2: The CQDs solution was loaded onto the surface of the BiVO4 photoanode by spin coating at a speed of 2500 r / min and a spin coating time of 25 s to form a BiVO4 / CQDs photoanode.

[0061] The photoanode was tested for performance, such as Figure 6 As shown, from the LSV curve ( Figure 5 a) It can be seen that at 1.23V RHE Jph of BiVO4 / CQDs ph Only 1.84 mA cm -2 , but the J of BiVO4 / NiFeOOH / CQDs photoanode is ph 5.4 mA cm -2 , J ph increased by nearly 3 times, and further calculations yielded the respective photoelectric conversion efficiencies ABPE ( Figure 5 b), BiVO4 / NiFeOOH / CQDs photoanode is the most efficient among them, at 0.73V RHE The efficiency at this potential is 1.25%, which is 3.8 times the maximum photoelectric conversion efficiency of 0.33% for the BiVO4 / CQDs photoanode. These results show that the performance of the BiVO4 / NiFeOOH / CQDs photoanode modified with CQDs is significantly improved in terms of photocurrent density and photoelectric conversion efficiency.

[0062] Other performance tests

[0063] The BiVO4-based photoanode samples prepared in this experiment were used for performance testing and characterization.

[0064] Figure 4 This is the response diagram of BiVO4-based photoanode to urea decomposition. It can be seen from the figure that only BiVO4 / NiFeOOH / CQDs photoanode responds to urea decomposition and at 1.23V RHE High photocurrent density J ph 5.4 mA cm -2 , which indicates that the BiVO4 / NiFeOOH / CQDs photoanode modified with NiFeOOH / CQDs can effectively catalyze the urea decomposition reaction and exhibit good photocatalytic performance.

[0065] Figure 6 is the double layer capacitance of BiVO4-based photoanode. From the double layer capacitance diagram ( Figure 5 a) It can be seen that the active area of ​​BiVO4 / NiFeOOH / CQDs is much larger than that of other photoanodes, reaching 1.21mFcm -2 , is the original BiVO4 (4.03×10 -2 mxDV-2 ) was 30 times, and the electrochemical active area of the photoanode modified by CQDs also increased to 0.4 mF cm -2 , indicating that there were abundant oxygen-containing functional groups on the surface of CQDs, which could provide more active sites for the reaction.

[0066] Figure 7 are LSV and chopped i-t curves of BiVO4 / NiFeOOH / CQDs photoanode before and after stability test, and the results of stability test show that the photoelectric current retention rate of the BiVO4 / NiFeOOH / CQDs photoanode is 75% after 12 h long-term stability test under AM1.5G illumination of 1.23 V RHE Figure 7

[0067] Figure 8 The chopped i-t curve does not show obvious sharp peaks at the moment of light irradiation, indicating that the carrier recombination is improved.

[0068] In summary, the BiVO4 photoanode is prepared by secondary annealing, and is modified by NiFeOOH / CQDs, so that the microstructure, optical property, surface chemical state and charge transport and separation performance of the BiVO4 photoanode are effectively improved, and the performance of the photoanode in the photoelectrolysis of urea is significantly improved, and the photoanode as a whole shows good application potential.

[0069] The above description is only the preferred embodiment of the present application, and does not limit the present application in any form, although the present application has been disclosed as above, however, it is not intended to limit the present application, any person skilled in the art, without departing from the technical solution of the present application, can make some changes or modifications to the above disclosed technical content for equivalent embodiments, but as long as it does not deviate from the technical solution of the present application, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application, all still belong to the scope of the technical solution of the present application.​​

Claims

1. A method for preparing an oxygen-vacancy-rich BiVO4 photoanode co-modified with nickel iron oxyhydroxide and carbon quantum dots, which shares the essential technical features with existing BiVO4 photoanode preparation methods, including the use of a precursor solution, a substrate, and conventional operations such as annealing, characterized in that The following steps are involved: S1: Synthesis of oxygen vacancy-rich BiVO4 photoanode by spin coating and two-step annealing method; S2: immersing the BiVO4 photoanode obtained in S1 in a solution containing nickel nitrate and iron nitrate to form a NiFeOOH modified layer; S3: Spin-coating a carbon quantum dot solution on the surface of the NiFeOOH modified layer to obtain a composite photoanode.

2. The preparation method according to claim 1, characterized in that The two-step annealing method in S1 specifically includes: S1: The Bi2S3 precursor film obtained by spin coating is annealed at 500℃ for about 2 hours to obtain the intermediate product Bi2O3 film; S2: After adding a vanadium source to the surface of the intermediate product film, annealing is performed again at 500°C for 50 minutes to form an oxygen vacancy-rich BiVO4 photoanode.

3. The preparation method according to claim 1, characterized in that The molar ratio of nickel nitrate to ferric nitrate in S2 is 1:

2.

4. The preparation method according to claim 1, wherein: The thickness of the NiFeOOH layer in S2 is 1.5-2.5 nm.

5. The preparation method according to claim 1, characterized in that The size distribution of the carbon quantum dots in S3 is 2-20 nm, and they are evenly anchored on the surface of the NiFeOOH modified layer.

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