Bismuth vanadate photoanode with high charge separation efficiency, its preparation method and application

Abstract

This invention provides a bismuth vanadate photoanode with high charge separation efficiency, its preparation method, and its applications. The photoanode comprises an FTO conductive glass, a bismuth vanadate (BiVO4) layer, and a NiFe(OH)X layer, arranged sequentially from bottom to top. The advantages of this invention are: it improves the crystallinity of bismuth vanadate by controlling the rapid heating rate and temperature during thermal annealing, while simultaneously inhibiting the growth of bismuth vanadate particles, overcoming the long-standing trade-off between high crystallinity and small particle size in traditional tube furnace heat-treated bismuth vanadate photoanodes; the heat treatment process of this invention has a low thermal budget, strong controllability and repeatability, and is economically feasible; furthermore, the bismuth vanadate photoanode of this invention exhibits excellent water-splitting performance, making it valuable for industrial scale-up.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water splitting for hydrogen production technology, specifically relating to a bismuth vanadate photoanode with high charge separation efficiency, its preparation method, and its application in the photocatalytic water splitting oxygen production reaction. Background Technology

[0002] With the increasing severity of global environmental pollution and the escalating energy crisis, finding clean and renewable energy sources to replace traditional fossil fuels and achieving energy structure transformation is imperative. Photocatalytic water splitting technology can directly convert solar energy into green hydrogen energy, providing an effective means to accelerate energy structure transformation. However, the high kinetic overpotential of the oxygen evolution reaction (OER) (0.25V) is a bottleneck limiting the photocatalytic water splitting process. Currently, various semiconductor materials have been developed for use as photoanodes in OERs, such as TiO2, WO3, Fe2O3, BiVO4, and Si. Among them, BiVO4 is currently the most promising photoanode material due to its suitable conduction band edge position, relatively wide band gap (2.4eV), good chemical stability, and low cost. However, BiVO4 has a low electron mobility (0.02-0.044cm). 2 V -1 s -1 Furthermore, the hole diffusion distance is short (~70nm), resulting in poor charge separation ability and severe photogenerated charge recombination, thus leading to low efficiency.

[0003] Over the past few decades, numerous strategies have been investigated to improve the charge separation properties of BiVO4, including nanostructure synthesis, external / internal defect doping, heterojunction formation, surface passivation, and substrate modification. Almost all of these strategies require high-temperature treatment (>400℃) to ensure the acquisition of highly active monoclinic scheelite BiVO4. Furthermore, high-temperature treatment is essential for promoting reactant decomposition and forming BiVO4 with high crystallinity and low defect state density. With increasing heat treatment temperature, the crystallinity of BiVO4 gradually increases, positively impacting charge separation. However, simultaneously, the particle size of BiVO4 gradually increases, even exceeding its hole diffusion length, which negatively affects charge separation. Synthesizing large, highly crystallinity BiVO4 particles at ultra-high temperatures (800℃) followed by ball milling to reduce particle size can effectively improve the charge separation efficiency of BiVO4. However, obtaining BiVO4 with high crystallinity while maintaining a small particle size directly during heat treatment to reduce defect state density, meet hole diffusion distance requirements, and improve photogenerated charge separation efficiency remains a challenge. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bismuth vanadate photoanode with high charge separation efficiency and its preparation method, thereby improving the performance of the bismuth vanadate photoanode in the photocatalytic water splitting oxygen production reaction.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] A bismuth vanadate photoanode with high charge separation efficiency includes an FTO conductive glass, a bismuth vanadate (BiVO4) layer, and a NiFe(OH)X layer, arranged sequentially from bottom to top. The bismuth vanadate (BiVO4) layer is composed of bismuth vanadate (BiVO4) particles with a particle size of 180-540 nm, preferably 250 nm. The crystallinity is determined by the relative intensity of the diffraction peaks in the X-ray diffraction pattern, with the peak intensity (i.e., high crystallinity) being preferred.

[0007] The FTO conductive glass has a light transmittance of 80% and a resistivity of 14Ω / □.

[0008] A bismuth vanadate (BiVO4) layer is formed on the surface of FTO conductive glass by a metal-organic decomposition method. The thickness of the bismuth vanadate (BiVO4) layer is 200-300 nm, preferably 200-250 nm.

[0009] The preparation method of a bismuth vanadate photoanode with high charge separation efficiency is carried out according to the following steps:

[0010] Step 1, Pretreatment of FTO conductive glass: After ultrasonic cleaning of FTO conductive glass for 20-40 minutes, it is dried with nitrogen gas and treated with ultraviolet ozone equipment at 50-60℃ for 10-20 minutes to obtain FTO conductive glass with hydrophilic surface.

[0011] Step 2, Preparation of bismuth vanadate (BiVO4): A precursor solution uniformly dispersed in bismuth nitrate and vanadium acetylacetonate is spin-coated onto the hydrophilic FTO conductive glass prepared in Step 1, preheated to 45-65℃. Calcination is carried out in air as the calcination atmosphere using a two-step heating method: In the first heating step, the temperature is increased from room temperature (20-25℃) to 180-320℃ at a heating rate of 4-12℃ / min, followed by a treatment of 8-24 min; in the second heating step, the temperature is increased at 5-5℃ / min. After heating from 180-320℃ to 360-850℃ at a heating rate of 5℃ / s and then processing for 8s-35min, the FTO / BiVO4 photoelectrode is obtained. In the precursor solution, bismuth nitrate pentahydrate is used, with an amount of 0.2390-0.2480g, vanadium acetylacetone is used, with an amount of 0.1290-0.1360g, and dimethyl sulfoxide is used as the solvent, with an amount of 450-550μL. The amount of the precursor solution used for spin coating is 60-80μL.

[0012] Step 3, Preparation of NiFe(OH)x: The FTO / BiVO4 photoelectrode prepared in Step 2 is immersed in the cocatalyst precursor solution for 5-10 seconds, dried at 50-60℃ for 0.5-1 h, and then immersed in 1M potassium hydroxide aqueous solution for 5-10 min. After removal, it is washed with deionized water and dried with nitrogen gas to obtain a bismuth vanadate photoanode (FTO / BiVO4 / NiFe(OH)x) with high charge separation efficiency. The cocatalyst precursor solution is an aqueous solution of 25-35 mM sodium citrate, 3-8 mM ferric nitrate and 3-8 mM nickel nitrate, and the amount of precursor solution used is 15-25 μL.

[0013] In step 1, the FTO conductive glass is ultrasonically cleaned for 30 minutes using acetone, ethanol, and deionized water respectively to remove organic matter and other contaminants from its surface.

[0014] In step 2, the amount of bismuth nitrate pentahydrate used is 0.2425 g, the amount of vanadium acetylacetonate used is 0.1325 g, the amount of dimethyl sulfoxide used is 500 μL, and the amount of precursor solution used is 75 μL.

[0015] In step 2, the precursor solution is spin-coated onto the hydrophilic FTO conductive glass prepared in step 1 by a spin coater and preheated to 50-60℃. The spin coating is divided into two stages. In the first stage, the spin coating speed is 1000-1200 r / min and the duration is 20-30 s. In the second stage, the spin coating speed is 1500, 2500 or 3000 r / min and the duration is 40 s.

[0016] In step 2, in the two-step heating method, the first heating process raises the temperature from room temperature (20-25℃) to 200-300℃ at a heating rate of 5-10℃ / min, followed by a treatment of 10-20min; the second heating process raises the temperature from 200-300℃ to 400-800℃ at a heating rate of 6-50℃ / s, followed by a treatment of 10s-30min.

[0017] In step 3, the catalyst precursor solution is an aqueous solution of 30 mM sodium citrate, 5 mM ferric nitrate and 5 mM nickel nitrate, and the amount of precursor solution used is 20 μL.

[0018] Application of bismuth vanadate photoanodes with high charge separation efficiency in photocatalytic water splitting for oxygen production, especially using the aforementioned bismuth vanadate photoanodes as the anode in the photocatalytic water splitting reaction.

[0019] Under illumination conditions of 1M potassium borate buffer solution and AM 1.5G (i.e., irradiance of 100mW / cm²), the bismuth vanadate photoanode can efficiently carry out water splitting and oxygen production reaction. Relative to the reversible hydrogen electrode potential, the charge separation efficiency and charge injection efficiency at 1.23V are 82% and 85%, respectively, and the stability at 0.6V exceeds 300h.

[0020] The beneficial effects of the present invention are as follows: The present invention utilizes the ultra-high heating rate of the rapid thermal annealing process to effectively control the nucleation and growth process of bismuth vanadate, so that the particle size of bismuth vanadate matches its hole diffusion distance, thereby improving the separation efficiency of photogenerated charge. Compared with the traditional tube furnace heat treatment process, the rapid thermal annealing used in the present invention can achieve a significant increase in the heating rate, promoting the formation of bismuth vanadate particles.

[0021] This invention utilizes the ultra-high temperature of the rapid thermal annealing process to achieve rapid crystallization of bismuth vanadate particles, reduce photogenerated charge recombination, and improve photogenerated charge separation efficiency. Compared with the traditional tube furnace heat treatment process, the rapid thermal annealing used in this invention can achieve a significant increase in heat treatment temperature, which greatly improves the crystallinity of bismuth vanadate.

[0022] This invention utilizes rapid thermal annealing heating rate and temperature control to improve the crystallinity of bismuth vanadate while inhibiting the growth of bismuth vanadate particles, breaking through the long-standing trade-off between high crystallinity and small particle size in traditional tube furnace heat-treated bismuth vanadate photoanodes.

[0023] The bismuth vanadate photoanode of the present invention has a low thermal budget, strong controllability and repeatability in the preparation process, and is economically feasible. At the same time, the bismuth vanadate photoelectrode of the present invention has excellent water decomposition performance and has certain industrial scale-up value. Attached Figure Description

[0024] Figure 1These are temperature-time diagrams of the heat treatment processes in Embodiments 1, 3, and 4 of this invention;

[0025] Figure 2 These are optical property diagrams of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4 of this invention;

[0026] Figure 3 These are scanning electron microscope images and particle size statistics of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4 of this invention.

[0027] Figure 4 These are grazing incidence X-ray diffraction patterns of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, 4, and 5 of this invention.

[0028] Figure 5 This is a scanning electron microscope image of the FTO / BiVO4 photoelectrode obtained in Example 5 of this invention;

[0029] Figure 6 These are sulfur oxidation photocurrent-voltage curves of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4 of this invention.

[0030] Figure 7 This is a charge separation efficiency diagram of the FTO / BiVO4 photoelectrode obtained in Examples 1, 3, and 4 of this invention;

[0031] Figure 8 This is the FTO / BiVO4 / NiFe(OH) obtained in Example 2 of this invention. x Photocurrent-voltage curve of the photoelectrode;

[0032] Figure 9 This is the FTO / BiVO4 / NiFe(OH) obtained in Example 2 of this invention. x Water splitting stability curve of photoelectrode;

[0033] Figure 10 This is a schematic diagram of the bulk charge separation of BiVO4 obtained in Examples 1, 3, and 4 of this invention. Detailed Implementation

[0034] The technical solution of the present invention will be further described below through specific embodiments.

[0035] Example 1

[0036] (1) Pretreatment of FTO conductive glass

[0037] The area of ​​the FTO conductive glass is 2×2cm. 2The FTO conductive glass was ultrasonically cleaned for 30 minutes each with acetone, ethanol, and deionized water, and then dried with nitrogen. It was then treated with ultraviolet ozone at 60°C for 15 minutes to obtain a hydrophilic FTO conductive glass surface.

[0038] (2) Preparation of BiVO4

[0039] 0.2425 g of bismuth nitrate pentahydrate and 0.1325 g of vanadium acetylacetonate were mixed in 500 μL of dimethyl sulfoxide and sonicated at room temperature for 30 min to obtain a 1 M precursor solution. 75 μL of the precursor solution was spin-coated onto FTO conductive glass preheated to 60 °C using a spin coater. The first stage of spin coating was performed at a speed of 1000 r / min for 20 s, and the second stage at a speed of 2500 r / min for 40 s. After spin coating, the sample was placed in a rapid thermal annealing furnace with air as the calcination atmosphere. The temperature was increased from room temperature to 200 °C at a rate of 10 °C / min and held for 10 min. Then, the temperature was increased from 200 °C to 800 °C at a rate of 50 °C / s and annealed for 20 s to obtain the FTO / BiVO4 photoelectrode.

[0040] Example 2

[0041] (1) Pretreatment of FTO conductive glass

[0042] The area of ​​the FTO conductive glass is 2×2cm. 2 The FTO conductive glass was ultrasonically cleaned for 30 minutes each with acetone, ethanol, and deionized water, and then dried with nitrogen. It was then treated with ultraviolet ozone at 60°C for 15 minutes to obtain a hydrophilic FTO conductive glass surface.

[0043] (2) Preparation of BiVO4

[0044] 0.2425 g of bismuth nitrate pentahydrate and 0.1325 g of vanadium acetylacetonate were mixed in 500 μL of dimethyl sulfoxide and sonicated at room temperature for 30 min to obtain a 1 M precursor solution. 75 μL of the precursor solution was spin-coated onto FTO conductive glass preheated to 60 °C using a spin coater. The first stage of spin coating was performed at a speed of 1000 r / min for 20 s, and the second stage at a speed of 2500 r / min for 40 s. After spin coating, the sample was placed in a rapid thermal annealing furnace with air as the calcination atmosphere. The temperature was increased from room temperature to 200 °C at a rate of 10 °C / min and held for 10 min. Then, the temperature was increased from 200 °C to 800 °C at a rate of 50 °C / s and annealed for 20 s to obtain the FTO / BiVO4 photoelectrode.

[0045] (3) NiFe(OH) xDeposition—References M. Li, T. Liu, Y. Yang, W. Qiu, C. Liang, Y. Tong and Y. Li, ACS Energy Lett., 2019, 4, 1983-1990

[0046] The FTO / BiVO4 photoelectrode was immersed in a 20 μL precursor solution containing 30 mM sodium citrate, 5 mM ferric nitrate, and 5 mM nickel nitrate for 5 s, and then dried at 60 °C for 1 h. The resulting electrode was then immersed in 1 M KOH for 5 minutes to convert the complex into hydroxide, followed by rinsing with deionized water and drying with N2 to remove excess hydroxide, forming NiFe(OH). x catalyst.

[0047] Example 3

[0048] (1) Pretreatment of FTO conductive glass

[0049] The area of ​​the FTO conductive glass is 2×2cm. 2 The FTO conductive glass was ultrasonically cleaned for 30 minutes each with acetone, ethanol, and deionized water, and then dried with nitrogen. It was then treated with ultraviolet ozone at 60°C for 15 minutes to obtain a hydrophilic FTO conductive glass surface.

[0050] (2) Preparation of BiVO4

[0051] 0.2425 g of bismuth nitrate pentahydrate and 0.1325 g of vanadium acetylacetonate were mixed in 500 μL of dimethyl sulfoxide and sonicated at room temperature for 30 min to obtain a 1 M precursor solution. 75 μL of the precursor solution was spin-coated onto FTO conductive glass preheated to 60 °C using a spin coater. The first stage of spin coating was performed at a speed of 1000 r / min for 20 s, and the second stage at a speed of 2500 r / min for 40 s. After spin coating, the sample was placed in a conventional tube furnace and calcined in air at a heating rate of 5 °C / min from room temperature to 500 °C and held for 1 h, followed by natural cooling.

[0052] Example 4

[0053] (1) Pretreatment of FTO conductive glass

[0054] The area of ​​the FTO conductive glass is 2×2cm. 2 The FTO conductive glass was ultrasonically cleaned for 30 minutes each with acetone, ethanol, and deionized water, and then dried with nitrogen. It was then treated with ultraviolet ozone at 60°C for 15 minutes to obtain a hydrophilic FTO conductive glass surface.

[0055] (2) Preparation of BiVO4

[0056] 0.2425 g of bismuth nitrate pentahydrate and 0.1325 g of vanadium acetylacetonate were mixed in 500 μL of dimethyl sulfoxide and sonicated at room temperature for 30 min to obtain a 1 M precursor solution. 75 μL of the precursor solution was spin-coated onto FTO conductive glass preheated to 60 °C using a spin coater. The first stage of spin coating was performed at a speed of 1000 r / min for 20 s, and the second stage at a speed of 2500 r / min for 40 s. After spin coating, the sample was placed in a conventional tube furnace and calcined in air at a heating rate of 5 °C / min from room temperature to 500 °C and held for 2 h, followed by natural cooling.

[0057] Example 5

[0058] (1) Pretreatment of FTO conductive glass

[0059] The area of ​​the FTO conductive glass is 2×2cm. 2 The FTO conductive glass was ultrasonically cleaned for 30 minutes each with acetone, ethanol, and deionized water, and then dried with nitrogen. It was then treated with ultraviolet ozone at 60°C for 15 minutes to obtain a hydrophilic FTO conductive glass surface.

[0060] (2) Preparation of BiVO4

[0061] 0.2425 g of bismuth nitrate pentahydrate and 0.1325 g of vanadium acetylacetonate were mixed in 500 μL of dimethyl sulfoxide and sonicated at room temperature for 30 min to obtain a 1 M precursor solution. 75 μL of the precursor solution was spin-coated onto FTO conductive glass preheated to 60 °C using a spin coater. The first stage of spin coating was performed at a speed of 1000 r / min for 20 s, and the second stage at a speed of 2500 r / min for 40 s. After spin coating, the sample was placed in a rapid thermal annealing furnace with air as the calcination atmosphere. The temperature was increased from room temperature to 200 °C at a rate of 10 °C / min and held for 10 min. Then, the temperature was increased from 200 °C to 800 °C at rates of 12, 25, and 50 °C / s for annealing for 20 s.

[0062] As attached Figure 4 The image shows the grazing incidence X-ray diffraction pattern of the FTO / BiVO4 photoelectrode obtained in Example 5. A higher heating rate results in sharper X-ray diffraction peaks and higher crystallinity.

[0063] like Figure 5 The image shown is a scanning electron microscope (SEM) image of the FTO / BiVO4 photoelectrode obtained in Example 5. All samples exhibit a nanoporous structure; the higher the heating rate, the smaller the particle size and the greater the number of particles. Therefore, the optimized heating rate was 50 °C / s.

[0064] like Figure 1As shown, compared with the traditional furnace tube heating process in Examples 3 and 4, the rapid thermal annealing process of Example 1 for heat treatment of bismuth vanadate can shorten the heat treatment time by 80% and reduce the thermal budget.

[0065] like Figure 2 As shown, the transmittance, reflectance, absorptivity, and absorption spectra of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4 are compared with the solar spectrum. It can be seen from the spectra that the light absorptivity of BiVO4 in Examples 1, 3, and 4 is almost the same, indicating that the charge production efficiency is the same.

[0066] like Figure 3 The images shown are scanning electron microscope (SEM) images of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4, along with their particle size statistics. All samples exhibit a nanoporous structure. The average particle sizes of BiVO4 obtained in Examples 1, 3, and 4 are 256, 258, and 402 nm, respectively.

[0067] like Figure 4 The grazing incidence X-ray diffraction patterns of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4 are shown. X-ray diffraction peak sharpness: Example 1 > Example 4 > Example 3; crystallinity: Example 1 > Example 4 > Example 3.

[0068] like Figure 6 The figure shows the sulfur oxidation photocurrent-voltage curves of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4. Compared with the bismuth vanadate photoanodes treated with tube furnace heat treatment in Examples 3 and 4, the FTO / BiVO4 photoanode treated with rapid thermal annealing in Example 1 can improve photoelectrochemical performance.

[0069] like Figure 7 The diagram shows the charge separation efficiency of the FTO / BiVO4 photoelectrodes obtained in Examples 1, 3, and 4. Compared to the bismuth vanadate photoanodes treated with tube furnace heat treatment in Examples 3 and 4, the FTO / BiVO4 photoanode treated with rapid thermal annealing in Example 1 can effectively improve the charge separation efficiency.

[0070] like Figure 8 As shown, FTO / BiVO4 / NiFe(OH) x The photocurrent-voltage curve of the photoelectrode shows that the rapid annealing process for BiVO4 involved a heating rate of 50℃ / s, a thermal annealing temperature of 800℃, and a time of 20s. Water oxidation performance was demonstrated in the FTO / BiVO4 / NiFe(OH) group. x The photoelectrode has an initial potential of 0.25V (relative to RHE), and the photocurrent density at 1.23V (relative to RHE) is approximately 2.7 mA / cm². 2 The charge injection efficiency is as high as 85%.

[0071] Figure 9 This is the FTO / BiVO4 / NiFe(OH) obtained in Example 2 of this invention. x Water decomposition stability curve of photoelectrode.

[0072] The bismuth vanadate photoanode with high charge separation efficiency of the present invention was used in the photocatalytic water splitting process, and the prepared FTO / BiVO4 / NiFe(OH) was used. x The photoanode was used as the working electrode, the Pt sheet as the counter electrode, and the Hg / HgO electrode as the reference electrode. The photocatalytic water splitting activity was tested in 1 MkBi electrolyte. (See attached image.) Figure 9 As shown, FTO / BiVO4 / NiFe(OH) x The water oxidation stability curve of the photoanode shows that the rapid annealing process for BiVO4 involved a heating rate of 50℃ / s, a thermal annealing temperature of 800℃, and a time of 20s. After 350 hours of water decomposition testing, the current density of the photoanode decreased by only 20%, indicating that the photoanode has high stability.

[0073] like Figure 10 The diagram shows the bulk charge separation of BiVO4 obtained in Examples 1, 3, and 4. In Example 1, the FTO / BiVO4 photoanode treated with rapid thermal annealing maintains a small particle size while avoiding defect states, effectively improving charge separation efficiency. However, in Examples 3 and 4, the bismuth vanadate heat-treated in a tube furnace exhibits severe bulk charge recombination.

[0074] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a bismuth vanadate photoanode with high charge separation efficiency, characterized in that: Follow these steps: Step 1, Pretreatment of FTO conductive glass: After ultrasonic cleaning of FTO conductive glass for 20-40 minutes, it is dried with nitrogen gas and treated with ultraviolet ozone equipment at 50-60℃ for 10-20 minutes to obtain FTO conductive glass with hydrophilic surface. Step 2, Preparation of bismuth vanadate: A precursor solution uniformly dispersed in bismuth nitrate and vanadium acetylacetonate is spin-coated onto the hydrophilic FTO conductive glass prepared in Step 1, preheated to 45-65℃. Calcination is performed in air as the calcination atmosphere, using a two-step heating method: In the first heating step, the temperature is increased from room temperature (20-25℃) to 180-320℃ at a rate of 4-12℃ / min, followed by a post-treatment of 8-24 min; in the second heating step… The FTO / BiVO4 photoelectrode was obtained by heating from 200℃ to 800℃ for 20s at a heating rate of 50℃ / s. In the precursor solution, bismuth nitrate pentahydrate was used, with an amount of 0.2390-0.2480 g, vanadium acetylacetone was used, with an amount of 0.1290-0.1360 g, and dimethyl sulfoxide was used as the solvent, with an amount of 450-550 μL. The amount of the precursor solution used for spin coating was 60-80 μL. Step 3, Preparation of NiFe(OH)x: The FTO / BiVO4 photoelectrode prepared in Step 2 is immersed in the co-catalyst precursor solution for 5-10 seconds, dried at 50-60℃ for 0.5-1 h, and then immersed in 1M potassium hydroxide aqueous solution for 5-10 min. After removal, it is washed with deionized water and dried with nitrogen gas to obtain a bismuth vanadate photoanode with high charge separation efficiency. The co-catalyst precursor solution is an aqueous solution of 25-35 mM sodium citrate, 3-8 mM ferric nitrate and 3-8 mM nickel nitrate, and the amount of precursor solution used is 15-25 μL.

2. The method for preparing a bismuth vanadate photoanode with high charge separation efficiency according to claim 1, characterized in that: In step 1, the FTO conductive glass is ultrasonically cleaned for 30 minutes each using acetone, ethanol, and deionized water.

3. The method for preparing a bismuth vanadate photoanode with high charge separation efficiency according to claim 1, characterized in that: In step 2, the amount of bismuth nitrate pentahydrate used is 0.2425 g, the amount of vanadium acetylacetonate used is 0.1325 g, the amount of dimethyl sulfoxide used is 500 μL, and the amount of precursor solution used is 75 μL.

4. The method for preparing a bismuth vanadate photoanode with high charge separation efficiency according to claim 1, characterized in that: In step 2, the precursor solution is spin-coated onto the hydrophilic FTO conductive glass prepared in step 1 by a spin coater and preheated to 50-60℃. The spin coating is divided into two stages. In the first stage, the spin coating speed is 1000-1200 r / min and the duration is 20-30 s. In the second stage, the spin coating speed is 1500, 2500 or 3000 r / min and the duration is 40 s.

5. The method for preparing a bismuth vanadate photoanode with high charge separation efficiency according to claim 1, characterized in that: In step 2, in the two-step heating method, the first heating process involves heating from room temperature (20-25℃) to 200-300℃ at a heating rate of 5-10℃ / min, followed by a 10-20 min post-treatment.

6. The method for preparing a bismuth vanadate photoanode with high charge separation efficiency according to claim 1, characterized in that: In step 3, the catalyst precursor solution is an aqueous solution of 30 mM sodium citrate, 5 mM ferric nitrate and 5 mM nickel nitrate, and the amount of precursor solution used is 20 μL.

7. A bismuth vanadate photoanode with high charge separation efficiency prepared by the method according to any one of claims 1-6, characterized in that: It includes FTO conductive glass, a bismuth vanadate layer, and a NiFe(OH)X layer, which are arranged sequentially from bottom to top. The bismuth vanadate layer is composed of bismuth vanadate particles with a particle size of 180-540 nm.

8. The bismuth vanadate photoanode with high charge separation efficiency according to claim 7, characterized in that: The particle size of the bismuth vanadate particles is 250 nm.

9. The bismuth vanadate photoanode with high charge separation efficiency according to claim 7, characterized in that: The thickness of the bismuth vanadate layer is 200-300 nm.

10. The bismuth vanadate photoanode with high charge separation efficiency according to claim 7, characterized in that: The thickness of the bismuth vanadate layer is 200-250 nm.

11. The application of the bismuth vanadate photoanode with high charge separation efficiency as described in any one of claims 7-10 in the photocatalytic water splitting oxygen production reaction, characterized in that: Bismuth vanadate photoanodes with high charge separation efficiency are used as the anodes for the photocatalytic water splitting reaction.

12. The application according to claim 11, characterized in that, Bismuth vanadate photoanodes with high charge separation efficiency in 1M potassium borate buffer solution, AM 1.5G (i.e., irradiance of 100 mW / cm²) 2 Under illumination, the bismuth vanadate photoanode can efficiently carry out water splitting and oxygen production reaction. Compared with the reversible hydrogen electrode potential, the charge separation efficiency and charge injection efficiency at 1.23V are 82% and 85%, respectively, and the stability at 0.6V exceeds 300h.

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