Doped carbon quantum dot modified photoelectrocatalytic photo-anode and preparation method and application thereof

Abstract

The invention discloses a preparation method of a doped carbon quantum dot modified photoelectrocatalysis photo-anode. The preparation method comprises the following steps: a, heating a citric acid aqueous solution in a high-pressure hydrothermal reaction kettle, cooling, dialyzing, and freeze-drying to obtain carbon quantum dot powder; and b, dissolving the carbon quantum dot powder prepared in the step a into deionized water to obtain a solution, adding bismuth vanadate into the solution for soaking, washing and drying to obtain the doped carbon quantum dot modified photoelectrocatalytic photo-anode. The prepared photo-anode material not only can accelerate transfer and separation of charges, but also can effectively inhibit recombination of holes, so that the material shows relatively high photocurrent density, meanwhile, the material has excellent electrochemical oxidation catalytic activity, the water oxidation reaction kinetics of a photo-anode is effectively improved, and the stability of an electrode material is improved.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalysis technology, specifically relating to a carbon quantum dot-modified photoelectrocatalytic photoanode and its preparation method, and further relating to the application of the carbon quantum dot-modified photoelectrocatalytic photoanode. Background Technology

[0002] Photoelectrochemical water splitting for hydrogen production is a clean energy technology. Its basic principle is to use light energy to activate a catalyst, which, under the influence of an external circuit, promotes the decomposition of water molecules to produce hydrogen and oxygen. This technology has the potential to convert solar energy into chemical energy and is considered a sustainable energy solution for the future. Therefore, developing efficient photoelectrochemical water splitting technology is of great significance for reducing dependence on fossil fuels and lowering greenhouse gas emissions. Among numerous photoanode materials, bismuth vanadate (BiVO4) has attracted widespread attention due to its high theoretical photocurrent density and conversion efficiency. However, due to the poor charge transport characteristics of the BiVO4 photoelectrode (carrier mobility of 0.044 cm⁻¹), it has been difficult to produce hydrogen. 2 V -1 s -1 The short hole diffusion length (<70 nm) leads to severe charge recombination and slow water oxidation kinetics, greatly limiting its potential for practical applications. Therefore, it is necessary to conduct in-depth research on photoelectrocatalytic materials. Summary of the Invention

[0003] This invention is based on the inventors' discoveries and understanding of the following facts and problems: heteroatom doping, structure construction, crystal plane engineering, heterostructure construction, defect engineering, and supported oxygen evolution catalysts (OECs) are considered effective strategies to improve the water oxidation activity of BiVO4 photoelectrodes in PEC. The oxygen evolution reaction (OER) is a complex four-electron transfer process, and modifying the BiVO4 surface with appropriate OECs is crucial for suppressing surface charge recombination. However, modifying the BiVO4 surface with some highly active OECs does not always achieve high photoelectrocatalytic performance because the driving force at the OEC / BiVO4 interface is relatively weak, failing to extract all photogenerated holes from BiVO4 for OER in a timely manner. Therefore, there is an urgent need to develop a highly efficient photoelectrocatalytic material that suppresses charge recombination at the OEC / BiVO4 interface for photoelectrochemical water splitting processes.

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a carbon quantum dot-modified photoelectrocatalytic photoanode and its preparation method. In the prepared photoanode material, quantum dots and BiVO4 form a heterojunction structure, which not only accelerates charge transfer and separation but also effectively suppresses hole recombination, resulting in a high photocurrent density. Simultaneously, the material exhibits excellent electrochemical oxidation catalytic activity, effectively improving the water oxidation reaction kinetics of the photoanode and enhancing the stability of the electrode material.

[0005] This invention provides a method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode, comprising the following steps: a. Carbon quantum dot powder was obtained by heating an aqueous solution of citric acid in a high-pressure hydrothermal reactor, cooling it, dialyzing, and freeze-drying. b. Dissolve the carbon quantum dot powder obtained in step a in deionized water to obtain a solution, add bismuth vanadate to the solution for soaking, and then wash and dry to obtain a carbon quantum dot modified photoelectrocatalytic photoanode.

[0006] The advantages and technical effects of the preparation method of the carbon quantum dot modified photoelectrocatalytic photoanode of the present invention are as follows: 1. In the method of the present invention, carbon quantum dot powder prepared by citric acid is combined with a bismuth vanadate electrode by immersion. The carbon quantum dots and BiVO4 form a heterostructure. Under sunlight irradiation, both carbon quantum dots and BiVO4 will generate electron-hole pairs. Photogenerated holes are transferred from the valence band of BiVO4 to the valence band of carbon quantum dots and participate in the water oxidation reaction. This not only accelerates charge transfer and separation, but also inhibits hole recombination, so that the modified photoanode exhibits a high photocurrent density; 2. The method of the present invention loads carbon quantum dot nanoparticles on the surface of the modified BiVO4 photoanode, giving the photoanode excellent electrochemical oxidation catalytic activity and effectively improving the water oxidation reaction kinetics on the surface of the BiVO4 photoanode; 3. The method of the present invention has widely available raw materials and a simple synthesis method, which is conducive to industrial application.

[0007] In some embodiments, step a involves heating citric acid and nickel chloride in a high-pressure hydrothermal reactor, cooling them, and then dialyzing and freeze-drying them to obtain Ni-doped carbon quantum dot powder.

[0008] In some embodiments, in step a, the concentration of citric acid is 1-5 mol / L, the heating temperature is 150-200°C, and the heating time is 4-8 hours.

[0009] In some embodiments, in step a, the molar ratio of citric acid to nickel chloride is 1:(0.01-0.1).

[0010] In some embodiments, in step b, the concentration of carbon quantum dot powder in the solution is 2-5 g / L, and the soaking time is 0.5-2 h.

[0011] In some embodiments, in step b, the carbon quantum dot powder in the obtained photoanode has a mass percentage content of 0.05-0.25 wt%.

[0012] In some embodiments, step c is further included, in which the photoelectrode obtained in step b is placed in a ferric sulfate solution and photoelectrode deposition is performed to obtain a composite photoelectrode.

[0013] In some embodiments, the concentration of the ferric sulfate solution is 0.1-0.2 mol / L, the deposition temperature is 20-30℃, the deposition voltage is 0.1-0.3V vs. Ag / AgCl, and the deposition time is 10-20s.

[0014] In some embodiments, step b, the method for preparing bismuth vanadate includes the following steps: S1. A three-electrode system was constructed using FTO conductive glass as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. An aqueous solution containing bismuth nitrate and potassium iodide was mixed with an ethanol solution containing p-benzoquinone as the electrolyte, and the electrode BiOI was obtained by constant potential deposition. Preferably, in the aqueous solution containing bismuth nitrate and potassium iodide, the concentration of bismuth nitrate is 0.01~0.1 mol / L and the concentration of potassium iodide is 0.4~0.6 mol / L; Preferably, in the ethanol solution containing p-benzoquinone, the concentration of the p-benzoquinone solution is 0.1~0.5 mol / L; Preferably, the volume ratio of the aqueous solution containing bismuth nitrate and potassium iodide to the ethanol solution containing p-benzoquinone is 5:(1-3), the deposition potential is -0.1±0.05 V vs. Ag / AgCl, and the deposition time is 100~600 s; S2. A dimethyl sulfoxide solution containing vanadium acetylacetonate is drop-coated onto the BiOI electrode prepared in step S1, calcined and cooled to room temperature, then immersed in NaOH solution for 20-30 min, and after cleaning and drying, the photoanode BiVO4 is obtained. Preferably, in the dimethyl sulfoxide solution containing vanadium acetylacetonate, the concentration of vanadium acetylacetonate is 0.1~0.3 mol / L, the calcination temperature is 400~600 ℃, the heating rate is 1~20 ℃ / min, and the calcination time is 0.2~2 h.

[0015] This invention also provides a carbon quantum dot-modified photoelectrocatalytic photoanode, prepared using the method described in this invention. The carbon quantum dot-modified photoelectrocatalytic photoanode of this invention exhibits high photocurrent density and excellent electrochemical oxidation catalytic activity, providing a novel photoelectrocatalytic material for hydrogen production through water splitting.

[0016] This invention also provides an application of a carbon quantum dot-modified photoelectrocatalytic photoanode in photoelectrocatalytic water splitting. In this invention, using a carbon quantum dot-modified photoelectrocatalytic photoanode for photoelectrocatalytic water splitting is beneficial for achieving efficient photoelectrocatalytic water splitting to produce hydrogen. Attached Figure Description

[0017] Figure 1 X-ray diffraction patterns of BiVO4 and BiVO4 / CQD prepared in Examples 1 and 2, and the BiVO4 / Ni-CQD photoanode.

[0018] Figure 2 The image shows a scanning electron microscope (SEM) image of the BiVO4 / Ni-CQD photoanode prepared in Example 2.

[0019] Figure 3 Transmission electron microscopy (TEM) image of the BiVO4 / Ni-CQD photoanode prepared in Example 2.

[0020] Figure 4 The image is a transmission electron microscope (TEM) image of the Ni-CQD prepared in step (3) of Example 2.

[0021] Figure 5 Linear scanning voltammetric curves of the BiVO4, BiVO4 / CQD, BiVO4 / Ni-CQD, and BiVO4 / Ni-CQD / FeOOH photoanodes prepared in Examples 1, 2, and 3 under illumination.

[0022] Figure 6 ABPE curves of the BiVO4, BiVO4 / CQD, BiVO4 / Ni-CQD, and BiVO4 / Ni-CQD / FeOOH photoanodes prepared in Examples 1, 2, and 3.

[0023] Figure 7 Charge separation efficiency curves of BiVO4, BiVO4 / CQD, BiVO4 / Ni-CQD, and BiVO4 / Ni-CQD / FeOOH photoanodes prepared in Examples 1, 2, and 3.

[0024] Figure 8 Injection curves of the BiVO4, BiVO4 / CQD, BiVO4 / Ni-CQD, and BiVO4 / Ni-CQD / FeOOH photoanodes prepared in Examples 1, 2, and 3.

[0025] Figure 9 Linear sweep voltammetry curves of the BiVO4, BiVO4 / CQD, BiVO4 / Ni-CQD, and BiVO4 / Ni-CQD / FeOOH photoanodes prepared in Examples 1, 2, and 3 under no-light illumination. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] This invention provides a method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode, comprising the following steps: a. Carbon quantum dot powder was obtained by heating an aqueous solution of citric acid in a high-pressure hydrothermal reactor, cooling it, dialyzing, and freeze-drying. b. Dissolve the carbon quantum dot powder obtained in step a in deionized water to obtain a solution, add bismuth vanadate to the solution for soaking, and then wash and dry to obtain a carbon quantum dot modified photoelectrocatalytic photoanode.

[0028] In the preparation method of the carbon quantum dot modified photoelectrocatalytic photoanode of this invention, carbon quantum dot powder prepared by citric acid is combined with a bismuth vanadate electrode by immersion. The carbon quantum dots and BiVO4 form a heterostructure. Under sunlight irradiation, both carbon quantum dots and BiVO4 will generate electron-hole pairs. Photogenerated holes are transferred from the valence band of BiVO4 to the valence band of carbon quantum dots and participate in the water oxidation reaction. This can not only accelerate the transfer and separation of charges, but also suppress the recombination of holes, so that the modified photoanode exhibits a high photocurrent density.

[0029] The method of this invention produces a modified BiVO4 photoanode with carbon quantum dot nanoparticles loaded on its surface, which gives the photoanode excellent electrochemical oxidation catalytic activity and effectively improves the water oxidation reaction kinetics on the surface of the BiVO4 photoanode.

[0030] The method described in this invention uses widely available raw materials and has a simple synthesis method, which is beneficial for industrial application.

[0031] In some embodiments, step a involves heating citric acid and nickel chloride in a high-pressure hydrothermal reactor, followed by cooling, dialysis, and freeze-drying to obtain Ni-doped carbon quantum dot powder. Preferably, the molar ratio of citric acid to nickel chloride is 1:(0.01-0.1), more preferably 1:(0.05-0.08). In this embodiment, introducing nickel salt during the hydrothermal reaction of citric acid to prepare carbon quantum dots to obtain Ni-doped carbon quantum dot powder is beneficial for further improving the photocurrent density and catalytic activity of the photoanode, thereby increasing the efficiency of photoelectrocatalytic water splitting for hydrogen production. This embodiment further optimizes the molar ratio of citric acid to nickel salt, which is beneficial for fully utilizing the synergistic doping effect of carbon quantum dots and nickel in the photoanode, improving the efficiency of photoelectrocatalytic water splitting for hydrogen production. If the Ni doping amount in the carbon quantum dots is too low, its effect is limited; if the Ni doping amount in the carbon quantum dots is too high, the carbon quantum dots cannot be formed, and the reaction yields a larger-sized Ni compound.

[0032] In some embodiments, in step a, the concentration of citric acid is 1-5 mol / L, the heating temperature is 150-200℃, and the heating time is 4-8 hours. In these embodiments, the raw material concentration and hydrothermal reaction parameters of the carbon quantum dot preparation process are further optimized, which is beneficial for synthesizing uniform carbon quantum dot nanoparticles.

[0033] In some embodiments, in step b, the concentration of carbon quantum dot powder in the solution is 2-5 g / L. In these embodiments, using a preferred carbon quantum dot concentration facilitates uniform doping of carbon quantum dots on the photoanode bismuth vanadate, thereby improving the performance of the modified photoanode material.

[0034] In some embodiments, the soaking time in step b is 0.5-2 hours. In these embodiments, the preferred soaking time facilitates the complete doping of carbon quantum dots onto bismuth vanadate.

[0035] In some embodiments, in step b, the carbon quantum dot powder in the prepared photoanode has a mass percentage content of 0.05-0.25 wt%. In this embodiment of the invention, by optimizing the doping amount of carbon quantum dots, it is beneficial for the carbon quantum dots to fully function in the photoanode, thereby improving the performance of the photoelectrocatalytic material. If the carbon quantum doping amount is too low, it cannot fully function; if the carbon quantum doping amount is too high, it will completely cover the BiVO4 photoanode voids, which is not conducive to the entry of charge carriers into the electrolyte and the reaction.

[0036] In some embodiments, the method further includes step c, placing the photoelectrode obtained in step b in a ferric sulfate solution for photoelectrode deposition to obtain a composite photoelectrode. Preferably, the concentration of the ferric sulfate solution is 0.1-0.2 mol / L, the deposition temperature is 20-30℃, the deposition voltage is 0.1-0.3V vs. Ag / AgCl, and the deposition time is 10-20s. In this embodiment of the invention, further photoelectrodeposition of the modified carbon quantum doped photoanode in a ferric sulfate solution is beneficial to improving the surface water oxidation catalytic activity.

[0037] In some embodiments, step b, the method for preparing bismuth vanadate includes the following steps: S1. A three-electrode system was constructed using FTO conductive glass as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. An aqueous solution containing bismuth nitrate and potassium iodide was mixed with an ethanol solution containing p-benzoquinone as the electrolyte, and the electrode BiOI was obtained by constant potential deposition. Preferably, in the aqueous solution containing bismuth nitrate and potassium iodide, the concentration of bismuth nitrate is 0.01~0.1 mol / L and the concentration of potassium iodide is 0.4~0.6 mol / L; Preferably, in the ethanol solution containing p-benzoquinone, the concentration of the p-benzoquinone solution is 0.1~0.5 mol / L; Preferably, the volume ratio of the aqueous solution containing bismuth nitrate and potassium iodide to the ethanol solution containing p-benzoquinone is 5:(1-3), the deposition potential is -0.1±0.05 V vs. Ag / AgCl, and the deposition time is 100~600 s; S2. A dimethyl sulfoxide solution containing vanadium acetylacetonate is drop-coated onto the BiOI electrode prepared in step S1, calcined and cooled to room temperature, then immersed in NaOH solution for 20-30 min, and after cleaning and drying, the photoanode BiVO4 is obtained. Preferably, in the dimethyl sulfoxide solution containing vanadium acetylacetonate, the concentration of vanadium acetylacetonate is 0.1~0.3 mol / L, the calcination temperature is 400~600 ℃, the heating rate is 1~20 ℃ / min, and the calcination time is 0.2~2 h.

[0038] In this embodiment of the invention, there are no particular restrictions on the preparation of the electrode material bismuth vanadate, and all commonly used methods in the prior art are applicable to this invention.

[0039] This invention also provides a carbon quantum dot-modified photoelectrocatalytic photoanode, prepared using the method described in this invention. The carbon quantum dot-modified photoelectrocatalytic photoanode of this invention exhibits high photocurrent density and excellent electrochemical oxidation catalytic activity, providing a novel photoelectrocatalytic material for hydrogen production through water splitting.

[0040] This invention also provides an application of a carbon quantum dot-modified photoelectrocatalytic photoanode in photoelectrocatalytic water splitting. In this invention, using a carbon quantum dot-modified photoelectrocatalytic photoanode for photoelectrocatalytic water splitting is beneficial for achieving efficient photoelectrocatalytic water splitting to produce hydrogen.

[0041] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0042] I. Preparation of photoelectrodes Example 1: Preparation of BiVO4 / CQD photoanode (1) A three-electrode system was constructed using FTO conductive glass as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl (saturated KCl solution) as the reference electrode. 50 mL of an aqueous solution containing 0.5 g bismuth nitrate and 3 g potassium iodide with a pH of about 1.7 (i.e., the concentration of bismuth nitrate in the aqueous solution is 0.02 mol / L and the concentration of potassium iodide is 0.4 mol / L) was mixed with 20 mL of an ethanol solution of 0.23 mol / L p-benzoquinone and stirred to form an electrolyte. The BiOI electrode was obtained by depositing a potential of -0.1 V vs. Ag / AgCl for 400 s. (2) Prepare a solution by mixing 0.16 g of vanadium acetylacetonate and 3 mL of dimethyl sulfoxide solution (i.e., the concentration of vanadium acetylacetonate in the solution is 0.2 mol / L). Take 60 μL of this solution and drop it onto the surface of the BiOI electrode prepared in step (1) above, so that the vanadium acetylacetonate solution is uniformly covered on the surface of the BiOI material. Then put it into a muffle furnace for calcination treatment, raise the temperature to 450 ℃ at a rate of 2 ℃ / min, calcine for 1 h, and cool it naturally to room temperature. Place the BiVO4 electrode taken out into a 1 mol / L NaOH aqueous solution for 25 min to remove the residual V2O5 on the surface of the BiVO4 electrode. Then wash it repeatedly with deionized water to obtain the BiVO4 photoanode. (3) Mix 0.1 mol of citric acid with 30 ml of water (i.e., citric acid concentration of 3.3 mol / L), transfer to a 100 mL Teflon-lined stainless steel high-pressure hydrothermal reactor, and heat at 180 °C for 6 hours. After cooling to room temperature, dialyze using a dialysis bag with a molecular weight cutoff (MW) of 1000 for 24 hours. Then freeze-dry the dialyzed solution to obtain carbon quantum dot (CQD) powder.

[0043] (4) Dissolve 15 mg of CQD powder in 4 ml of water (i.e., the concentration of CQD powder in the aqueous solution is 3.75 g / L), and then put the bismuth vanadate obtained in step (2) above into the aqueous solution and soak for 1 hour. After soaking, remove the bismuth vanadate from the aqueous solution and rinse its surface with water; after rinsing, put the bismuth vanadate into an oven at 60°C and dry it for 30 minutes to obtain a carbon quantum dot modified photoelectrocatalytic photoanode, denoted as BiVO4 / CQD photoanode.

[0044] In this embodiment, the photoanode contains 0.2 wt% carbon quantum dots.

[0045] Example 2: Preparation of BiVO4 / Ni-CQD photoanode The method is the same as in Example 1, except that step (3) involves preparing nickel-doped carbon quantum dots. Steps (3) and (4) are as follows: Step (3): Citric acid and nickel chloride were mixed at a molar ratio of 1:0.05, stirred thoroughly, and then transferred to a 100 mL Teflon-lined stainless steel high-pressure reactor. The mixture was heated at 180 °C for 6 hours. After cooling to room temperature, the mixture was dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff (MW) of 1000. The dialyzed solution was then freeze-dried to obtain nickel-doped carbon quantum dot (Ni-CQD) powder.

[0046] Step (4): Dissolve 10 mg of Ni-CQD powder in 3 ml of water (i.e., the concentration of Ni-CQD powder in the aqueous solution is 3.33 g / L). Then, place the bismuth vanadate obtained in step (2) into the aqueous solution and soak for 1 hour. After soaking, remove the bismuth vanadate from the aqueous solution and rinse its surface with water. After rinsing, place the bismuth vanadate in an oven at 60°C and dry for 30 minutes to obtain a carbon quantum dot modified photoelectrocatalytic photoanode, denoted as BiVO4 / Ni-CQD photoanode.

[0047] Example 3: Preparation of BiVO4 / Ni-CQD / FeOOH photoanode The method is the same as in Example 2, except that it also includes step (5): the BiVO4 / Ni-CQD photoanode obtained in step (4) is placed in a 0.15 mol / L ferric sulfate solution and photoelectrodeposited at 25°C. The deposition voltage is 0.2 V vs. Ag / AgCl and the deposition time is 15 s to obtain the BiVO4 / Ni-CQD / FeOOH photoanode.

[0048] Example 4: Preparation of BiVO4 / Ni-CQD photoanode The method is the same as in Example 2, except that the molar ratio of citric acid and nickel chloride in step (3) is 1:0.08.

[0049] Example 5: Preparation of BiVO4 / Ni-CQD photoanode The method is the same as in Example 2, except that the molar ratio of citric acid and nickel chloride in step (3) is 1:0.01.

[0050] Comparative Example 1 The method is the same as in Example 2, except that step (3) is omitted. Step (4) involves immersing the bismuth vanadate obtained in step (2) in an aqueous solution of nickel chloride (the mass content of nickel in the aqueous solution is the same as in Example 2) for 1 hour. After immersion, the bismuth vanadate is removed from the aqueous solution and its surface is rinsed with water. After rinsing, the bismuth vanadate is placed in an oven at 60°C and dried for 30 minutes to obtain a Ni-doped modified photoelectrocatalytic photoanode, denoted as BiVO4 / Ni photoanode.

[0051] II. The photoanodes prepared in Examples 1-5 and Comparative Example 1 were subjected to performance testing and characterization. The results are shown in Table 1 and... Figure 1-9 .

[0052] 1. Characterization Figure 1 The X-ray diffraction patterns of BiVO4 / CQD and BiVO4 / Ni-CQD photoanodes prepared in Examples 1 and 2 are shown. It can be seen that the main diffraction peaks in the patterns are consistent with the characteristic peaks of BiVO4 (JCPDS No. 14-0688) and SnO2 (FTO substrate) (JCPDS No. 46-1088).

[0053] Figure 2 The image shows a scanning electron microscope (SEM) image of the BiVO4 / Ni-CQD photoelectrode prepared in Example 2. After loading Ni-CQD nanoparticles, the surface of BiVO4 is covered by the accumulated tiny particles.

[0054] Figure 3 The transmission electron microscope image of the BiVO4 / Ni-CQD photoanode prepared in Example 2 clearly shows a distinct lattice. The crystal plane with a lattice spacing of 1.23 nm belongs to the (112) crystal plane of BiVO4.

[0055] Figure 4 This is a transmission electron microscope image of Ni-CQD prepared in step (3) of Example 2. Through transmission electron microscopy analysis, it can be seen that Ni-CQD is a tiny nanoparticle with a size of less than 10 nm and has good dispersibility, which is beneficial for dispersion and adhesion on the BiVO4 surface.

[0056] 2. Performance Testing In the photoelectrochemical water splitting test system, photocurrent density is a test method to measure the efficiency of semiconductor light energy absorption and conversion. The performance of the photoelectrochemical water splitting test was measured using an electrochemical analyzer (CHI660E) equipped with a standard three-electrode system, where a platinum sheet was used as the counter electrode, the photoanode prepared in each example was used as the working electrode, and the Ag / AgCl electrode was used as the reference electrode. The light source was simulated sunlight AM 1.5 G (100 mW cm⁻¹). -2 The electrolyte was a 0.5 M potassium borate (KBi) solution (pH=9.5), and the optical power was calibrated to 100 mW / cm² using a power meter. -2 The potential range for linear sweep spectroscopy (LSV) testing of photoelectrocatalytic performance was 0 V to 1.5 V vs. RHE, with a scan rate of 20 mV / s. -1 .

[0057] Table 1

[0058] Note: BiVO4 was prepared by steps (1) and (2) of Example 1.

[0059] Through Table 1 and Figure 5 As can be seen, compared with the undoped BiVO4 photoanode, the photocurrent density of the BiVO4 / CQD photoanode prepared in Example 1 is 2 mA cm⁻¹ at 1.23 V vs. RHE. -2 The photocurrent density of the BiVO4 / Ni-CQD photoanode prepared in Example 2 is approximately 1.5 times that of the BiVO4 photoanode, and is 3.4 mA cm⁻¹ at 1.23 V vs. RHE. -2 This is approximately 2.6 times that of the BiVO photoanode. Example 3 further describes a FeOOH-loaded photoanode with an A / C ratio of 4.4 mA at 1.23 V vs. RHE. -2 .

[0060] Combination Figure 6The photocurrent conversion efficiency (ABPE) of the BiVO4 photoanode at a bias voltage of 0.9 V was only 0.26%, while the ABPE of the BiVO4 / CQD photoanode prepared in Example 1 could be increased to 0.4% at a bias voltage of 0.9 V. The BiVO4 / Ni-CQD photoanode prepared in Example 2 achieved an ABPE of 1.15% at a bias voltage of 0.63 V, which is 4.4 times higher than that of the BiVO4 photoanode. This improvement highlights the significant enhancement effect of Ni-CQD loading on the photoelectrochemical performance of BiVO4, indicating that the PEC performance is greatly improved after incorporating Ni-CQD nanoparticles. Furthermore, the BiVO4 / Ni-CQD / FeOOH photoanode prepared in Example 3 achieved an ABPE of 1.62% at a bias voltage of 0.63 V, and the FeOOH loading further improved the photocurrent conversion efficiency of the photoanode.

[0061] Comparative Example 1 shows a BiVO4 / Ni photoanode prepared by immersion doping with Ni on a BiVO4 photoanode. Compared with an undoped BiVO4 photoanode, the photocurrent density and photocurrent conversion efficiency only show a slight improvement. However, in Example 2 of this application, Ni is introduced during the preparation of carbon quantum dots, and then the Ni-doped carbon quantum dots are loaded onto the BiVO4 photoanode by immersion. Compared with Comparative Example 1, the BiVO4 / Ni-CQD photoanode prepared in Example 2 shows a significant improvement in photocurrent density and photocurrent conversion efficiency. The photocurrent density of Example 2 is increased by approximately 89% compared to Comparative Example 1, and the photocurrent conversion efficiency is increased by approximately 248%. This demonstrates that loading Ni-doped carbon quantum dots onto the BiVO4 photoanode significantly enhances the electrochemical oxidation catalytic activity of the photoanode.

[0062] To demonstrate that loading Ni-CQD nanoparticles onto a BiVO4 photoanode can improve carrier separation and suppress carrier recombination, this invention further tested the charge separation efficiency of the photoanodes prepared in Examples 1-3. Figure 7 As shown, the charge separation efficiency of the BiVO4 / Ni-CQD photoelectrode is 75%, which is much higher than that of the BiVO4 photoanode (56.5%), proving that the loading of Ni-CQD nanoparticles accelerates charge separation.

[0063] The embodiments of the present invention further tested the charge injection efficiency of the photoanodes prepared in Examples 1-3. For example... Figure 8 As shown, the charge injection efficiency is significantly improved after Ni-CQD nanoparticles are loaded onto BiVO4. This improved efficiency indicates that more photogenerated holes generated in the carbon quantum dot-modified photoelectrode prepared in this embodiment of the invention successfully participate in the water oxidation reaction, thereby accelerating the overall reaction kinetics.

[0064] To demonstrate that carbon quantum dot nanoparticles can improve the water oxidation kinetics of BiVO4 photoanodes, dark-state LSV tests were performed on the photoanodes prepared in Examples 1-3. This test can directly reflect the catalytic OER activity; at the same potential, a higher current indicates higher catalytic activity and better water oxidation kinetics. Figure 9 As can be seen, compared with the undoped BiVO4 photoelectrode, the modified photoanode doped with carbon quantum dots prepared in the embodiments of the present invention has a higher current at the same potential, proving that the loading of carbon quantum dot nanoparticles can significantly improve the water oxidation kinetics of BiVO4 photoanode.

[0065] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0066] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode, characterized in that, Includes the following steps: a. Carbon quantum dot powder was obtained by heating an aqueous solution of citric acid in a high-pressure hydrothermal reactor, cooling it, dialyzing, and freeze-drying. b. Dissolve the carbon quantum dot powder obtained in step a in deionized water to obtain a solution, add bismuth vanadate to the solution for soaking, and then wash and dry to obtain a carbon quantum dot modified photoelectrocatalytic photoanode.

2. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 1, characterized in that, Step a involves heating citric acid and nickel chloride in a high-pressure hydrothermal reactor, followed by cooling, dialysis, and freeze-drying to obtain Ni-doped carbon quantum dot powder.

3. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 1 or 2, characterized in that, In step a, the concentration of citric acid is 1-5 mol / L, the heating temperature is 150-200℃, and the heating time is 4-8 hours.

4. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 2, characterized in that, In step a, the molar ratio of citric acid to nickel chloride is 1:(0.01-0.1).

5. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 1 or 2, characterized in that, In step b, the concentration of carbon quantum dot powder in the solution is 2-5 g / L; and / or, the soaking time is 0.5-2 h.

6. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 1 or 2, characterized in that, In step b, the carbon quantum dot powder in the obtained photoanode has a mass percentage content of 0.05-0.25 wt%.

7. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 1 or 2, characterized in that, The method also includes step c, which involves placing the photoelectrode obtained in step b in a ferric sulfate solution and performing photoelectrodeposition to obtain a composite photoelectrode. Preferably, the concentration of the ferric sulfate solution is 0.1-0.2 mol / L, the deposition temperature is 20-30℃, the deposition voltage is 0.1-0.3V vs. Ag / AgCl, and the deposition time is 10-20s.

8. The method for preparing a carbon quantum dot-modified photoelectrocatalytic photoanode according to claim 1 or 2, characterized in that, In step b, the method for preparing bismuth vanadate includes the following steps: S1. A three-electrode system was constructed using FTO conductive glass as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. An aqueous solution containing bismuth nitrate and potassium iodide was mixed with an ethanol solution containing p-benzoquinone as the electrolyte, and the electrode BiOI was obtained by constant potential deposition. Preferably, in the aqueous solution containing bismuth nitrate and potassium iodide, the concentration of bismuth nitrate is 0.01~0.1 mol / L and the concentration of potassium iodide is 0.4~0.6 mol / L; Preferably, in the ethanol solution containing p-benzoquinone, the concentration of the p-benzoquinone solution is 0.1~0.5 mol / L; Preferably, the volume ratio of the aqueous solution containing bismuth nitrate and potassium iodide to the ethanol solution containing p-benzoquinone is 5:(1-3), the deposition potential is -0.1±0.05 V vs. Ag / AgCl, and the deposition time is 100~600 s; S2. A dimethyl sulfoxide solution containing vanadium acetylacetonate is drop-coated onto the BiOI electrode prepared in step S1, calcined and cooled to room temperature, then immersed in NaOH solution for 20-30 min, and after cleaning and drying, the photoanode BiVO4 is obtained. Preferably, in the dimethyl sulfoxide solution containing vanadium acetylacetonate, the concentration of vanadium acetylacetonate is 0.1~0.3 mol / L, the calcination temperature is 400~600 ℃, the heating rate is 1~20 ℃ / min, and the calcination time is 0.2~2 h.

9. A carbon quantum dot-modified photoelectrocatalytic photoanode, characterized in that, It is prepared by any one of claims 1-8.

10. The application of a carbon-doped quantum dot modified photoelectrocatalytic photoanode prepared by any one of claims 1-8 or the carbon-doped quantum dot modified photoelectrocatalytic photoanode of claim 9 in photoelectrocatalytic water splitting.

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