A metal-porphyrin polymer / bismuth vanadate composite photoanode, its preparation method and application

Abstract

This application belongs to the field of photoelectrochemical water splitting for hydrogen production, and more specifically, relates to a metal-porphyrin polymer / bismuth vanadate composite photoanode, its preparation method, and its application. This invention, through electropolymerization, successfully polymerized a polytransition metal-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin catalyst in situ on the surface of BiVO4 for the first time. This successfully achieved uniform dispersion of the transition metal-anchored molecular polymer catalyst on the BiVO4 composite photoanode, significantly improving the water oxidation kinetics and photogenerated charge transfer efficiency of BiVO4, enhancing the performance of photoelectrocatalysis, and exhibiting good stability.

Description

Technical Field

[0001] This application belongs to the field of photoelectrochemical water splitting for hydrogen production, and more specifically, relates to a metal-porphyrin polymer / bismuth vanadate composite photoanode, its preparation method, and its application. Background Technology

[0002] Photoelectrochemical water splitting offers a promising pathway to utilizing renewable solar energy by converting sunlight into chemical fuels. Its efficiency primarily depends on the oxygen evolution reaction (OER), a kinetically slow four-electron water oxidation process. However, the inefficient transport of photogenerated charges at the semiconductor / electrolyte interface leads to severe charge recombination, a major factor limiting the performance of solar-driven water splitting. Bismuth vanadate possesses a small band gap (2.4 eV) and suitable charge mobility (0.044 cm⁻¹). -2 V -1 S -1 Bismuth vanadate is a promising light-absorbing semiconductor material. However, the slow oxygen evolution reaction kinetics of bismuth vanadate lead to the accumulation of photogenerated holes on the semiconductor surface, resulting in severe photogenerated charge recombination.

[0003] Therefore, loading oxygen evolution co-catalysts onto the surface of bismuth vanadate is an effective method to improve surface charge transfer and suppress surface charge recombination. Common oxygen evolution co-catalysts mainly include oxides, sulfides, nitrides, and metal-anchored organic molecular catalysts. Among them, metal-anchored molecular polymer catalysts can be applied to high-performance photoelectrochemical systems because the electronic structure of their metal active centers can be tunable through coordination environment adjustment. Existing techniques typically load metal-anchored molecular polymer catalysts onto the surface of bismuth vanadate through spin coating, drop coating, or immersion adsorption. However, it is worth noting that due to the loose and porous structure of the bismuth vanadate surface, it is difficult for metal-anchored molecular polymer catalysts to completely cover the surface of bismuth vanadate, resulting in agglomeration and catalyst deactivation, which reduces the oxygen evolution reaction kinetics at the photoanode surface. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a metal-porphyrin polymer / bismuth vanadate composite photoanode, its preparation method, and its application. Through in-situ electrochemical polymerization, transition metal-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin is successfully and uniformly polymerized on the surface of bismuth vanadate, ultimately solving the technical problems of insufficient reaction kinetics, severe charge recombination, and uneven catalyst dispersion of bismuth vanadate.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for preparing a metal-porphyrin polymer / bismuth vanadate composite photoanode, comprising the following steps: (1) A BiVO4 thin film is deposited on a conductive substrate to obtain a BiVO4 photoanode; (2) Using 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin and metal salts of transition metals as raw materials, a coordination reaction is carried out in the presence of a solvent to obtain transition metal ion-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer; (3) The organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer is first mixed with an organic solvent used to promote electrolyte dissolution, and then the electrolyte is added. After mixing, a precursor solution is obtained. (4) Immerse the BiVO4 photoanode described in step (1) into the precursor solution described in step (3), and polymerize the monomer onto the BiVO4 surface through an electrochemical polymerization reaction to obtain the metal-porphyrin polymer / bismuth vanadate composite photoanode.

[0006] Secondly, a metal-porphyrin polymer / bismuth vanadate composite photoanode prepared by the aforementioned preparation method is provided.

[0007] Thirdly, the invention provides an application of the aforementioned metal-porphyrin polymer / bismuth vanadate composite photoanode in photoelectrocatalytic water splitting for hydrogen production.

[0008] This application utilizes a transition metal-porphyrin ring as an electron acceptor and a diphenylaminophenyl unit as an electron donor to rationally design a novel tetra-diphenylaminophenyl transition metal porphyrin molecular polymer catalyst, which is then dispersed and fixed on a BiVO4 (BVO) anode via in-situ electropolymerization deposition. The bismuth vanadate composite photoanode proposed in this invention, using tetra-diphenylaminophenyl-porphyrin as a ligand to modulate the catalytic activity of the transition metal site, can significantly improve the water oxidation kinetics of this composite photoanode, reduce photogenerated charge recombination at the photoanode / electrolyte interface, and enhance photoelectrochemical performance. Overall, compared with existing technologies, the above-described technical solution conceived in this application has the following beneficial effects: (1) This invention successfully polymerized polytetra-diphenylaminophenyl transition metal-porphyrin molecular catalysts on the surface of BiVO4 for the first time via electropolymerization, and successfully obtained a BiVO4 composite photoanode modified with a metal-anchored molecular polymer catalyst (taking Co as an example, this photoanode is represented as CoTDP-CP / BiVO4). The in-situ polymerization strategy gives the polytetra-diphenylaminophenyl transition metal-porphyrin molecular catalyst good dispersibility, avoids catalyst deactivation, significantly improves the water oxidation kinetics and photogenerated charge transfer efficiency of the BiVO4 composite photoanode, promotes the performance of photoelectrocatalysis, and exhibits good stability. In the preferred embodiment, the composite photoanode of this invention exhibits good stability at AM 1.5G (100mW / cm). 2 ) produces 4.78 mA / cm2 The photocurrent density is significantly better than that of existing photoanode systems using organic polymers as cocatalysts.

[0009] (2) In a preferred embodiment of the present invention, a Co-porphyrin polymer catalyst was deposited on the surface of bismuth vanadate by electropolymerization. After being rinsed with dichloromethane and ethanol and naturally dried, a Co-porphyrin polymer (Co-TDP) / bismuth vanadate composite photoanode was prepared. Using metal coordination chemistry, Co metal was anchored on the porphyrin molecule. The porphyrin molecule acted as a carrier to introduce Co sites onto the bismuth vanadate photoanode. At the same time, the introduction of porphyrin molecules improved conductivity and promoted the separation of photogenerated charges. The introduction of Co sites improved the surface water oxidation kinetics, improved the stability of bismuth vanadate, and promoted the improvement of photoelectrochemical performance.

[0010] (3) In a preferred embodiment of the present invention, Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin was used as the electropolymerization monomer. By adjusting the ratio of diphenylamine-4-benzaldehyde and pyrrole and performing a condensation reaction, 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin was successfully synthesized. Then, using 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin and CoCl2·6H2O as precursors, Co metal was coordinated to the porphyrin molecule. Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin was used as the electropolymerization monomer and anchored on the bismuth vanadate photoanode, significantly promoting the PEC performance of bismuth vanadate. The method of the present invention has the advantages of tunable coordination molecules, improved conductivity, and simple process. Compared with the pure-phase bismuth vanadate photoelectrode, the composite photoelectrode shows significantly improved water splitting activity.

[0011] (4) In the preferred embodiment of the present invention, a Co-porphyrin molecular polymer co-catalyst (CoTDP-CP) was prepared on bismuth vanadate by electropolymerization. This method is non-toxic, simple, produces uniformly dispersed catalytic sites, and significantly improves PEC (photoelectrochemical) performance. The Co-porphyrin molecular polymer co-catalyst has the advantages of strong catalytic kinetics, high conductivity, and corrosion resistance, thus enhancing charge separation efficiency, increasing photocurrent density, and promoting stability. Therefore, the CoTDP-CP / BiVO4 photoanode exhibits significantly enhanced photoelectrochemical performance. Under simulated sunlight, its oxygen evolution reaction photocurrent density reaches 4.72 mA cm⁻¹ at 1.23 V relative to the reversible hydrogen electrode (RHE). -2 The performance is 2.6 times that of the original BiVO4, and the photoanode also exhibits a charge injection efficiency of over 88%. This provides a new approach to solving the problems of insufficient reaction kinetics and severe charge recombination in bismuth vanadate, and also offers new insights into the design of organic polymer catalysts. Attached Figure Description

[0012] Figure 1 Scanning electron microscope (SEM) images (contents a and b) of Co-porphyrin polymer / bismuth vanadate, high-resolution transmission electron microscopy (HRTEM) images (contents c and d) and mapping elemental distribution map (content e); Figure 2 The XRD diffraction pattern of the prepared Co-porphyrin polymer / bismuth vanadate photoanode is shown. The vertical line at the bottom of the figure is the PDF card of monoclinic bismuth vanadate. Figure 3 JV test results for Co-porphyrin polymer deposited on the surface of bismuth vanadate photoanode at different times; Figure 4 JV test results for Co-porphyrin polymers deposited on the surface of a bismuth vanadate photoanode under different potential conditions; Figure 5 JV test diagrams for bismuth vanadate photoanode and Co-porphyrin polymer / bismuth vanadate composite photoanode; Figure 6 Photoimpedance (PEIS) test results for bismuth vanadate photoanode and Co-porphyrin polymer / bismuth vanadate composite photoanode. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0014] The present invention provides a method for preparing a metal-porphyrin polymer / bismuth vanadate composite photoanode, comprising the following steps: (1) A BiVO4 thin film is deposited on a conductive substrate to obtain a BiVO4 photoanode; (2) Using 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin and metal salts of transition metals as raw materials, a coordination reaction is carried out in the presence of a solvent to obtain transition metal ion-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer; (3) The organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer is first mixed with an organic solvent used to promote electrolyte dissolution, and then the electrolyte is added. After mixing, a precursor solution is obtained. (4) Immerse the BiVO4 photoanode described in step (1) into the precursor solution described in step (3), and polymerize the monomer onto the BiVO4 surface through an electrochemical polymerization reaction to obtain the metal-porphyrin polymer / bismuth vanadate composite photoanode.

[0015] In some embodiments, the conductive substrate is conductive glass, such as FTO conductive glass.

[0016] In some embodiments, the transition metal is Co, Fe, or Ni, and the metal salt of the transition metal is a chloride or nitrate of the transition metal.

[0017] In some embodiments, the solvent in step (2) is one or more of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

[0018] In some embodiments, the preparation method of the 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin includes the following steps: mixing diphenylamine-4-benzaldehyde and propionic acid and heating to reflux, then dissolving freshly distilled pyrrole in propionic acid and refluxing for 1-3 hours under stirring; after removing propionic acid by distillation, the product is purified by silica gel column chromatography to obtain 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin.

[0019] In some embodiments, during the preparation of the 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin, diphenylamine-4-benzaldehyde and pyrrole are in excess, and the reflux time during synthesis is greater than or equal to 2 hours.

[0020] In some embodiments, the molar ratio of the 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin to the metal salt of the transition metal is 1:1 to 10.

[0021] In some embodiments, the temperature of the coordination reaction in step (2) is 90°C to 150°C.

[0022] In some embodiments, the organic solvent in the organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer in step (3) is one or more of dichloromethane (DCM) and trichloromethane (TCM). The electrolyte in step (3) is tetrabutylammonium hexafluorophosphate and / or tetrabutylammonium tetrafluoroborate. The molar ratio of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer to the electrolyte is 1:(4-6). The organic solvent that promotes the dissolution of the electrolyte is acetonitrile and / or acetone; the volume ratio of the organic solvent in the organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin (CoTDP) monomer to the organic solvent used to promote the dissolution of the electrolyte is 5:1-1:5, more preferably (1-2):1.

[0023] In the following embodiment, the electrochemical polymerization reaction in step (4) is specifically as follows: using BiVO4 photoanode as working electrode, platinum sheet as counter electrode, and Ag / AgCl as reference electrode, constant potential deposition is performed on the photoanode surface for 15-120s at a potential of 0.8V~1.4V. Preferably, the electropolymerization deposition time is 30-90s and the potential is 1-1.4V. The bismuth vanadate photoanode film obtained under these conditions has good quality and the photoanode has excellent photoelectrochemical water oxidation performance.

[0024] The metal-porphyrin polymer / bismuth vanadate composite photoanode prepared by this invention can be used for photoelectrocatalytic water splitting to produce hydrogen.

[0025] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0026] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0027] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0028] In the examples, the BiVO4 photoanodes were prepared according to the method published in Science by Professors Tae Woo Kim and Kyung-Shin Choi in 2014 (Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar Water Splitting).

[0029] In a preferred embodiment of this invention, a BiVO4 photoanode is obtained by electrodeposition, followed by the synthesis of Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin (CoTDP) monomer molecules. An organic solution containing CoTDP monomer is then prepared to form a precursor solution for electropolymerization. The BiVO4 photoanode is immersed in this solution, and by controlling the electrochemical polymerization time and potential, the Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin conjugated polymer (CoTDP-CP) is successfully polymerized onto the BiVO4 surface. After rinsing with ethanol, the surface is dried in an oven to obtain a cobalt porphyrin polymer co-catalyst / bismuth vanadate (CoTDP-CP / BiVO4) composite photoanode. The method of this invention is simple to operate, uses readily available raw materials, is low in cost, and exhibits good stability. In the preferred embodiment prepared by this invention, the photocurrent density of the CoTDP-CP / BiVO4 composite photoanode is 2.6 times that of the pure-phase BiVO4 photoanode.

[0030] The embodiments of this application are described below with reference to the accompanying drawings.

[0031] Example 1 Preparation of Co-porphyrin polymer / bismuth vanadate composite photoanode.

[0032] Step 1: Prepare BiVO4 thin films by electrodeposition.

[0033] First, prepare 50 ml of solution containing 0.04 M Bi(NO3)3. A solution of 5H₂O (0.9701 g) and 0.4 M KI was prepared, and the pH was adjusted to 1.7 with nitric acid. This solution was then mixed with 20 mL of anhydrous ethanol (100%) containing 0.23 M p-benzoquinone, stirred vigorously for several minutes, and then electrodeposited. The mixture was transferred to a three-electrode system consisting of fluorine-doped tin oxide (FTO, 1 × 2 cm⁻¹). 2 The working electrode (WE), silver / silver chloride reference electrode (RE), and platinum counter electrode (CE) were used. A BiOI nanosheet array was formed by electrodeposition at a constant potential of -0.1 V (relative to silver / silver chloride) for 180 s at room temperature. Next, the BiOI film was uniformly coated with 200 μL of a dimethyl sulfoxide solution containing 0.2 M vanadium acetylacetonate (VO(acac)2). The coated film was calcined in a muffle furnace at 450°C for 2 hours. After cooling to room temperature, the film was gently stirred in a 1 M sodium hydroxide solution for 15 minutes to remove excess V2O5. The resulting BiVO4 film was rinsed with deionized water and air-dried to obtain the BiVO4 photoanode.

[0034] Step 2: Preparation of 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin.

[0035] Diphenylamine-4-benzaldehyde (2.00 g, 7.40 mmol) and 20 mL of propionic acid were added to a 100 mL two-necked flask and heated to reflux. Freshly distilled pyrrole (7.42 mmol, 515 μL) was dissolved in 3.0 mL of propionic acid, and the mixture was refluxed with stirring for 2 hours. After removing propionic acid by distillation, the product was purified by silica gel column chromatography using CHCl3 / hexane (2:1, v / v) as eluent. Recrystallization from dichloromethane / methanol gave a purple product (285 mg, 11% yield). The boiling point of propionic acid was 141°C. The purple product was 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin.

[0036] Step 3: Prepare Co(II)5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin (CoTDP) monomer.

[0037] 5,10,15,20-tetratetra(4-diphenylaminophenyl)porphyrin (200 mg, 0.157 mmol) and CoCl₂·6H₂O (374 mg, 1.57 mmol) were dissolved in 20 mL of dimethylformamide (DMF). The reaction mixture was heated at 120°C for 2 hours and then cooled. After dilution with dichloromethane (DCM), the mixture was washed with brine, the organic phase was collected, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography using CHCl₃ / hexane (1:1, v / v) as eluent, and then recrystallized in dichloromethane / methanol to give purple crystals (171 mg, 72%).

[0038] Step 4: Preparation of Co-porphyrin polymer / bismuth vanadate composite photoanode 1 mM Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin (CoTDP) monomer was dissolved in 30 mL dichloromethane (DCM), then 20 mL acetonitrile was added (acetonitrile was used to promote electrolyte dissolution), and finally 5 mM tetrabutylammonium hexafluorophosphate was added as electrolyte to obtain a precursor solution. BiVO4 photoanode was immersed in the above precursor solution, with BiVO4 photoanode as working electrode, platinum sheet as counter electrode, and Ag / AgCl as reference electrode. In the above precursor solution, a constant potential deposition was performed on the surface of BiVO4 photoanode at a potential of 0.8 V (relative to Ag / AgCl) for 60 s, and the molecular polymer CoTDP-CP catalyst was successfully polymerized to obtain the catalyst. After washing with dichloromethane and ethanol, the catalyst was naturally dried to obtain the Co metal-anchored tetra(diphenylaminophenyl)-porphyrin-based molecular polymer / bismuth vanadate (CoTDP-CP / BiVO4) composite photoanode.

[0039] Example 2 The rest is the same as in Example 1, except that the electrochemical deposition potential in step 4 is 1.2V.

[0040] Example 3 The rest is the same as in Example 1, except that the electrochemical deposition potential in step 4 is 1.4V.

[0041] Example 4 The rest is the same as in Example 2, except that the electrochemical deposition time in step 4 is 15s.

[0042] Example 5 The rest is the same as in Example 2, except that the electrochemical deposition time in step 4 is 30s.

[0043] Example 6 The rest is the same as in Example 2, except that the electrochemical deposition time in step 4 is 90s.

[0044] Example 7 The rest is the same as in Example 2, except that the electrochemical deposition time in step 4 is 120s.

[0045] This invention successfully synthesized diphenylaminophenylporphyrin using a condensation reaction, and further bound a metal to the diphenylaminophenylporphyrin through a coordination chemical reaction. Then, a Co-porphyrin polymer catalyst was generated in situ on the surface of bismuth vanadate by electrochemical polymerization. The constructed Co-porphyrin polymer / bismuth vanadate photoanode promotes photogenerated charge separation, enhances surface water oxidation kinetics, slows down the photocorrosion of bismuth vanadate, and promotes the improvement of photoelectrochemical performance.

[0046] Phase testing: As shown in Figure 1, the sample from Example 2 was taken, and the sample on the electrode surface was scraped off with a blade and the powder was collected for high-power transmission electron microscopy (HRTEM) testing; at the same time, scanning electron microscopy (SEM) testing was carried out directly on the photoanode thin film. Figure 1 Contents a and b are scanning electron microscope (SEM) images of the Co-porphyrin polymer / bismuth vanadate synthesized in Example 2; contents c, d, and e are its high-resolution transmission electron microscopy (HRTEM) images, and the remaining contents are the elemental distribution maps of the mapping corresponding to content e. Figure 1 shows that bismuth vanadate (BiVO4) exhibits excellent crystallinity on the 040 crystal plane with a lattice fringe spacing of 0.292 nm, while the cobalt-porphyrin polymer (CoTDP-CP) exhibits amorphous characteristics; furthermore, the cross-sectional elemental distribution maps clearly show that CoTDP-CP is uniformly coated on the BiVO4 surface. SEM test results indicate that the BiVO4 film has a creep-like porous structure, which can effectively promote the adsorption of water molecules and provide favorable conditions for related reactions.

[0047] As shown in Figure 2, grazing incidence small-angle X-ray diffraction (XRD) was performed on the sample prepared in Example 2. The figure shows that the diffraction peak positions of the sample perfectly match those of the monoclinic bismuth vanadate standard card (PDF#14-0688), confirming that BiVO4 in the sample has a typical monoclinic phase structure. Notably, the characteristic diffraction peaks of the cobalt-porphyrin polymer (CoTDP-CP) were not detected in this XRD pattern. This is presumably due to the combined effects of the low content of CoTDP-CP and its amorphous state.

[0048] Photoelectric performance testing: All photoelectrochemical tests were performed using an electrochemical workstation (CHI 760) with a three-electrode system: the prepared sample as the working electrode (WE), an Ag / AgCl electrode as the reference electrode (RE), and a platinum wire as the counter electrode (CE). Unless otherwise specified, 0.5 M phosphate buffered saline (PBS) at pH 9.3 was used as the electrolyte; and a 300 W xenon lamp was used to simulate standard sunlight (100 mW / cm²). 2 All tests were conducted using backlighting.

[0049] Examples 1 and 3 are the same as Example 2 under the same conditions, except that the voltage of electropolymerization during the preparation of the Co-porphyrin polymer (CoTDP-CP) is changed. Examples 4 to 7 are the same as Example 2 under the same conditions, except that the electropolymerization time during the preparation of the Co-porphyrin polymer (CoTDP-CP) is changed, thus obtaining Co-porphyrin polymer catalysts with different film thicknesses. The photocurrent density of the obtained Co-porphyrin polymer / bismuth vanadate composite photoanodes with different polymer film thicknesses was measured, such as... Figure 3 , Figure 4 As shown in Table 1, it can be seen that the Co-porphyrin polymer with different deposition times significantly affects the photoelectrochemical water oxidation performance of bismuth vanadate.

[0050] Table 1. Photocurrent density of Co-porphyrin polymer / bismuth vanadate photoanodes prepared at different electropolymerization times

[0051] As shown in Figure 3 and Figure 4 As shown, the JV test of samples from Examples 1-7 was performed using linear voltammetry (LSV) with a test voltage range of 0.15-1.35 V (vs. RHE) and a scan rate of 25 mV / s. The comparison shows that the photocurrent density of the modified bismuth vanadate is significantly higher than that of the unmodified bismuth vanadate sample. Furthermore, the electropolymerization time and potential have a significant impact on the photocurrent density of the nickel-iron oxide / bismuth vanadate composite photoanode—the highest photocurrent density is achieved when the electropolymerization time is 60 s and the potential is 1.2 V (corresponding to Example 2). Photocurrent density is a key indicator for evaluating the performance of photoelectrochemical water splitting for hydrogen production. Its value is positively correlated with the hydrogen production rate; a higher photocurrent density indicates better hydrogen production efficiency. This demonstrates that the photoelectrode prepared in this invention has significant performance advantages in the field of photoelectrochemical catalytic water splitting for hydrogen production.

[0052] The electropolymerization time directly regulates the loading of cobalt porphyrin polymer cocatalyst on the bismuth vanadate surface, thus affecting the catalytic performance of the composite photoanode. It is speculated that when the polymerization potential is too low or the polymerization time is less than 30 s, the loading of cobalt (Co) active sites is low, making it difficult to fully utilize the auxiliary catalytic effect of the nickel-iron oxide layer. Conversely, when the polymerization potential is too high or the polymerization time is extended to 90 s, the excessively deposited cobalt porphyrin polymer cocatalyst forms a thick capping layer, hindering efficient charge transport and ultimately causing a decrease in the photoelectrocatalytic performance of the material. Therefore, the optimal polymerization time is 30-90 s, and the optimal polymerization potential is 1-1.4 V.

[0053] As shown in Figure 5, the JV test was performed on the pure bismuth vanadate (BiVO4) photoanode and the optimized sample from Example 2 using linear voltammetry (LSV). The test voltage range was 0.15–1.35 V (vs. RHE), and the scan rate was 25 mV / s. Under a bias voltage of 1.2 V (vs. RHE), the photocurrent density of the BiVO4 sample modified with the cobalt porphyrin polymer cocatalyst reached 4.85 mA / cm². 2 This is significantly higher than the 1.82 mA / cm² of a pure BiVO₄ photoanode. 2The performance improvement reached 2.66 times. This result confirms that the strategy of modifying BiVO4 with cobalt porphyrin polymer cocatalyst can effectively improve the photoelectrochemical performance of the material, and is an excellent solution to enhance the catalytic efficiency of BiVO4-based photoanodes.

[0054] As shown in Figure 6, photoelectrochemical impedance spectroscopy (PEIS) tests were performed on the pure bismuth vanadate (BiVO4) photoanode and the sample from Example 2. The spectra show that the impedance arc radius of the sample from Example 2 is significantly smaller than that of pure BiVO4, indicating a faster carrier transfer rate. This result confirms that the cobalt porphyrin polymer cocatalyst modified on the BiVO4 surface can effectively promote the separation of photogenerated carriers, suppress electron-hole pair recombination, and thus improve the overall performance of photoelectrochemical (PEC) water splitting.

[0055] Comparative Example 1 The rest is the same as in Example 2, except that step 4, the preparation of the precursor solution, is specifically as follows: First, add 30 mL of dichloromethane (DCM) and 20 mL of acetonitrile, then add 1 mM Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin (CoTDP) monomer, and finally add 5 mM tetrabutylhexafluorophosphate as electrolyte to obtain the precursor solution.

[0056] Comparative Example 2 The rest is the same as in Example 2, except that step 4, the preparation of the precursor solution, is specifically as follows: 30 mL of dichloromethane (DCM), 20 mL of acetonitrile, 1 mM Co(II)-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin (CoTDP) monomer and 5 mM tetrabutylammonium hexafluorophosphate were added simultaneously and mixed thoroughly to obtain a precursor solution.

[0057] Comparative Examples 1 and 2 were performed under the same conditions as Example 2, except that acetonitrile was added before the monomer. Experiments showed that the introduction of acetonitrile may have affected the dissolution of the monomer, resulting in the inability to polymerize the tetra(tetraphenylaminophenyl)porphyrin cobalt monomer onto the photoelectrode surface, thus deteriorating its photoelectrochemical performance.

[0058] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a metal-porphyrin polymer / bismuth vanadate composite photoanode, characterized in that, Includes the following steps: (1) A BiVO4 thin film is deposited on a conductive substrate to obtain a BiVO4 photoanode; (2) Using 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin and a metal salt of a transition metal as raw materials, a coordination reaction is carried out in the presence of a solvent to obtain a transition metal ion-5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer; the transition metal is Co, Fe or Ni; the solvent is N,N-dimethylformamide and / or dimethyl sulfoxide; (3) The organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer is mixed with an organic solvent for promoting electrolyte dissolution, and then an electrolyte is added. After mixing, a precursor solution is obtained; the electrolyte is tetrabutylammonium hexafluorophosphate and / or tetrabutylammonium tetrafluoroborate; the organic solvent for promoting electrolyte dissolution is acetonitrile and / or acetone; the volume ratio of the organic solvent in the organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer to the organic solvent for promoting electrolyte dissolution is 5:1-1:5; (4) Immerse the BiVO4 photoanode described in step (1) into the precursor solution described in step (3), and polymerize the monomer onto the BiVO4 surface through an electrochemical polymerization reaction to obtain the metal-porphyrin polymer / bismuth vanadate composite photoanode; the electrochemical polymerization reaction is specifically as follows: using the BiVO4 photoanode as the working electrode, the platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, perform constant potential deposition on the photoanode surface for 15-120s at a potential of 0.8V~1.4V.

2. The preparation method according to claim 1, characterized in that, The metal salt of the transition metal is a chloride or nitrate of the transition metal.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin to the metal salt of the transition metal is 1:1~10; and / or, the temperature of the coordination reaction in step (2) is 90℃~150℃.

4. The preparation method according to claim 1, characterized in that, The organic solvent in the organic solution of the transition metal ion -5,10,15,20-tetra(4-diphenylaminophenyl)porphyrin monomer in step (3) is dichloromethane and / or trichloromethane.

5. The preparation method according to claim 1, characterized in that, Step (4) Electrochemical polymerization deposition time is 30-90s, and potential is 1-1.4V.

6. The metal-porphyrin polymer / bismuth vanadate composite photoanode prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the metal-porphyrin polymer / bismuth vanadate composite photoanode as described in claim 6 in photoelectrocatalytic water splitting for hydrogen production.

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