Phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate and preparation method of phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode

Abstract

The invention discloses a nickel borate-loaded phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode and a preparation method thereof, and belongs to the technical field of electrode materials. The photoelectrode comprises the BiVO4 layer, the P-C3N4 layer and the nickel borate (NiBi) layer, the P-C3N4 layer serves as a hole transport layer, electrons and holes which are separated under illumination can be rapidly guided away, recombination of surface charges is reduced, BiVO4 interface defects are passivated, and the performance of the photoelectrode is greatly improved; the NiBi layer serves as a cocatalyst, photo-induced electrons can be effectively isolated, photo-induced electron hole pair compounding of the BiVO4 photoelectrode is reduced, meanwhile, the surface catalytic oxygen production efficiency of BiVO4 is improved, and finally the nickel borate loaded phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode with high light-induced carrier transport capacity and good stability is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of electrode materials, and in particular relates to a phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate and a preparation method thereof. Background Art

[0002] As a new and environmentally friendly renewable energy source, solar energy has attracted much attention in solving the energy crisis and energy shortage. In recent years, the efficiency of solar energy conversion has been low, so improving the utilization rate of solar energy has become an urgent problem that needs to be solved. Photoelectrochemical water splitting (PEC) can directly convert solar energy into hydrogen energy that is easy to store; photoelectrochemistry is the process of using light to drive electrochemistry, which refers to the redox reaction of photogenerated electron-hole pairs generated on the surface of a semiconductor in contact with an electrolyte after being separated by the electric field of the semiconductor / electrolyte junction and then undergoing redox reactions with ions in the solution.

[0003] Recently, BiVO 4 It has attracted extensive attention as a photoanode material for PECs because it has a suitable band structure with a band gap of 2.40-2.50 eV and a favorable conduction band edge position (≈0.1 eV) that is conducive to H 2 The maximum photocurrent density is estimated to be 7.5 mA cm -2 , the theoretical conversion efficiency of solar energy to hydrogen is 9.2%. However, pure BiVO 4 The actual performance of the photoanode is far lower than the theoretical value due to its inherent disadvantages such as weak light absorption, poor separation and transport performance of photogenerated carriers, and poor surface catalytic oxygen production kinetics. 4 Modification to enable it to have stronger photogenerated carrier transport capability and good stability has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate and a preparation method thereof.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate, comprising a conductive substrate and BiVO2 in turn loaded on the conductive substrate. 4 (bismuth vanadate) layer, PC 3 N 4 (phosphorus-doped carbon nitride) layer and a nickel borate (NiBi) layer;

[0007] The PC 3 N 4 Layer by PC 3N 4 The nickel borate layer is attached to the PC 3 N 4 Layer and BiVO 4 On the layer.

[0008] Technical principle: The present invention provides a 4 Layer, PC 3 N 4 layer and a nickel borate (NiBi) layer of the photoelectrode, wherein PC 3 N 4 The layer acts as a hole transport layer, which can quickly conduct away the electrons and holes separated under light, reduce the recombination of surface charges, and passivate BiVO 4 The interface defects greatly improve the catalytic performance and stability of the electrode; the NiBi layer, as a co-catalyst, can effectively isolate photogenerated electrons and reduce BiVO 4 The photogenerated electron-hole pairs of the photoelectrode recombine and improve the BiVO 4 The surface catalytic oxygen production efficiency was improved, and finally a phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate was obtained with strong photogenerated carrier transport ability and good stability.

[0009] The present invention also provides a method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate as described in the above technical solution, comprising the following steps:

[0010] (1) Deposition of BiVO on a conductive substrate 4 , forming BiVO 4 layer, and obtain BiVO 4 Photoelectrode;

[0011] (2) dissolving melamine and tetrabutylammonium hexafluorophosphate in anhydrous ethanol, heating and calcining to obtain a powder; mixing the powder with ethanol to obtain a spraying liquid; and 4 The spraying liquid is deposited on the photoelectrode to form PC 3 N 4 layer, get PC 3 N 4 / BiVO 4 Composite photoelectrode;

[0012] (3) mixing a potassium borate buffer solution and nickel sulfate hexahydrate to obtain a precursor solution A; and 3 N 4 / BiVO 4 The precursor liquid A is deposited on the composite photoelectrode to form a nickel borate layer to obtain the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode (NiBi / PC 3 N4 / BiVO 4 Composite photoelectrode).

[0013] The present invention first deposits BiVO on a conductive substrate. 4 Formation of BiVO 4 layer, and then phosphorus-doped carbon nitride (PC 3 N 4 ) deposited on BiVO 4 Nanosheets are formed on the surface of the photoelectrode, and then NiBi is deposited to obtain a phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate. The operation is simple and safe, the materials are easily available, and large-scale production can be achieved.

[0014] Furthermore, step (1) is specifically as follows:

[0015] A. Nitric acid solution, potassium iodide (KI) and bismuth nitrate pentahydrate (Bi(NO 3 ) 3 ·5H 2 O) to obtain solution A; dissolving p-benzoquinone in ethanol and subjecting to ultrasound to obtain solution B; mixing the solution A and solution B to obtain a precursor liquid B; depositing the precursor liquid B on a conductive substrate to form a BiOI film, thereby obtaining a conductive substrate with a BiOI film deposited on the surface;

[0016] B. Mixing vanadium acetylacetonate and dimethyl sulfoxide to obtain solution C; dripping the solution C onto the conductive substrate with the surface-deposited BiOI film obtained in step A, and annealing, alkali washing, water washing and drying to form BiVO 4 layer, and obtain BiVO 4 Photoelectrode.

[0017] Furthermore, in step A, the usage ratio of the nitric acid solution, potassium iodide and bismuth nitrate pentahydrate is 25 mL: 0.4 mol: 0.04 mol; and the pH value of the nitric acid solution is 1.6-1.8.

[0018] Furthermore, in step A, the usage ratio of p-benzoquinone to ethanol is 0.23 mol:10 mL.

[0019] Furthermore, in step A, the ultrasonication time is 3 to 5 minutes.

[0020] Furthermore, in step A, the process conditions for depositing the precursor liquid B are: initial voltage of -0.1 V, sampling interval of 0.1 s, deposition time of 150-200 s, static time of 0 s, sensitivity of 1×10 -3 A. The static time indicates the waiting time before deposition. 0s means no waiting and direct deposition.

[0021] Furthermore, in step A, the deposition method of the deposition precursor liquid B is a time-current curve method; during deposition, the conductive substrate is the working electrode, the platinum mesh is the counter electrode, and Ag / AgCl is the reference electrode.

[0022] Furthermore, in step A, the conductive substrate is conductive glass doped fluorine tin oxide (FTO).

[0023] Furthermore, in step A, the conductive substrate also includes a pretreatment step before depositing the precursor liquid B; the pretreatment is: cutting the conductive substrate into a size of 2×3 cm using a glass cutting table, and then ultrasonically washing it with acetone, ethanol and grade tertiary water for 15 minutes each, and then placing it in an oven for drying after washing.

[0024] Furthermore, in step B, the usage ratio of the vanadium acetylacetonate and dimethyl sulfoxide is 0.2 mol:1 mL.

[0025] Furthermore, in step B, the dripping amount is 25 μL / cm 2 .

[0026] Furthermore, in step B, the annealing treatment is performed at a temperature of 440-460° C. and for a time of 2 hours.

[0027] Furthermore, in step B, the concentration of the alkali solution used for alkali washing is 1 mol / L; the alkali solution is a NaOH solution; the alkali washing method is soaking; and the soaking time is 15 to 25 minutes. 2 O 5 .

[0028] Furthermore, in step (2), the mass ratio of melamine to tetrabutylammonium hexafluorophosphate is 10:1. The present invention controls the mass ratio of melamine to tetrabutylammonium hexafluorophosphate to control PC 3 N 4 The doping amount of P in the layer; controlling the doping amount of P within the above range has the advantages of improving conductivity and photocatalytic performance.

[0029] Furthermore, in step (2), the calcination temperature is 240-260° C. and the time is 3 hours. In the present invention, melamine and tetrabutyl hexafluorophosphoric acid undergo deamination condensation by calcination, thereby obtaining phosphorus-doped carbon nitride.

[0030] Furthermore, in step (2), the ratio of the mass of the powder to the volume of ethanol is 1:1 (mg:mL).

[0031] Furthermore, in step (2), the deposition of the spray liquid is carried out by spraying; the process conditions for depositing the spray liquid are: the heating plate temperature is 200°C, the amount of the spray liquid is 0.5-1 mL / cm2 , the static time is 0s. The present invention deposits the spray liquid under the above conditions, which is conducive to the generation of nano carbon nitride.

[0032] Furthermore, in step (2), after the deposition of the spray liquid, the steps of re-firing, rinsing and heating are also included; the re-firing temperature is 230-280°C and the time is 30 minutes; the rinsing reagent is grade 3 water; the heating temperature is 60°C and the time is 10 minutes. 3 N 4 Tightly adhere to BiVO 4 On the photoelectrode.

[0033] Furthermore, in step (3), the potassium borate buffer solution and nickel sulfate hexahydrate (NiSO 4 6H 2 O) is used in an amount ratio of 0.5 mol: 1 mmol; the pH value of the potassium borate buffer solution is 9.5.

[0034] Furthermore, in step (3), the deposition method of the precursor liquid A is electrochemical deposition; the deposition conditions of the deposition precursor liquid A are: the deposition temperature is room temperature, the potential is 0 V, the running time is 10 s, the sampling interval is 0.1 s, the static time is 2 s, and the sensitivity is 1×10 -3 A, light intensity is 100mWcm -2 The present invention deposits the precursor liquid A under the above conditions, which has the advantages of low energy consumption and simple operation.

[0035] Furthermore, in step (3), the deposition method of the deposition precursor liquid A is a time-current curve method; during deposition, the conductive substrate is the working electrode, the platinum mesh is the counter electrode, and Ag / AgCl is the reference electrode.

[0036] Compared with the prior art, the present invention has the following advantages and technical effects:

[0037] The phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate provided by the present invention can improve the hole transmission rate and the oxygen evolution efficiency performance, reduce the composite, passivate BiVO 4 The interface defects can improve the photoelectric performance of the photoanode. The preparation method provided by the invention is simple and safe to operate, the materials are easily available, and large-scale production can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0039] Figure 1BiVO prepared in step (1) of Example 1 4 SEM image of the photoelectrode;

[0040] Figure 2 is the BiVO in step (1) of Example 1 4 Photoelectrode, C in Comparative Example 1 3 N 4 / BiVO 4 Composite photoelectrode, PC in step (2) of Example 1 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) of Example 1 3 N 4 / BiVO 4 XRD pattern of the composite photoelectrode;

[0041] Figure 3 NiBi / PC prepared in Example 1 3 N 4 / BiVO 4 TEM image of the composite photoelectrode;

[0042] Figure 4 is the BiVO in step (1) of Example 1 4 Photoelectrode, PC in step (2) 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) 3 N 4 / BiVO 4 The oxygen evolution efficiency of the composite photoelectrode changes with voltage

[0043] Figure 5 is the BiVO in step (1) of Example 1 4 Photoelectrode and PC in step (2) 3 N 4 / BiVO 4 Photoluminescence spectrum of the composite photoelectrode;

[0044] Figure 6 is the BiVO in step (1) of Example 1 in the presence of a hole trap 4 Photoelectrode, PC in step (2) 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) 3 N 4 / BiVO 4 Linear sweep voltammetry curve of the composite photoelectrode;

[0045] Figure 7 is the BiVO in step (1) of Example 1 without a hole trapping agent 4 Photoelectrode, PC in step (2) 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) 3 N 4 / BiVO 4 Linear sweep voltammogram of the composite photoelectrode. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0049] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0050] Example 1

[0051] A phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate, comprising FTO conductive glass and BiVO2 in turn loaded on the FTO conductive glass. 4 Layer, PC 3 N 4 layer and NiBi layer; PC 3 N 4 Layer by PC 3 N 4 Nanosheets, NiBi layer attached to PC 3 N 4 Layer and BiVO 4 on the layer;

[0052] The preparation process of phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate is as follows:

[0053] (1) Take a 20×15 cm piece of FTO conductive glass and cut it into 2×3 cm using a glass cutting table. Then, ultrasonically wash it with acetone, ethanol, and grade tertiary water for 15 min each. After washing, put it in an oven to dry to obtain the pretreated FTO conductive glass. Take 25 mL of nitric acid solution with a pH value of 1.7 and place it in a 100 mL beaker. Add 0.4 mol potassium iodide (KI) and 0.04 mol bismuth nitrate pentahydrate (Bi(NO 3 ) 3 ·5H 2 O), stir thoroughly until the solution is clear and transparent to obtain solution A. Take 10mL of anhydrous ethanol and place it in a beaker, add 0.23mol of p-benzoquinone, and ultrasonicate for 5min until the precipitate is completely dissolved to obtain solution B. The above solution A and solution B are mixed and stirred to make them fully miscible to obtain precursor liquid B. The obtained precursor liquid B is used as the electrolyte, the above pretreated FTO conductive glass is used as the working electrode, the platinum mesh is used as the counter electrode, and Ag / AgCl is used as the reference electrode. The electrodeposition is carried out by the time-current curve method. The electrodeposition conditions are: initial voltage -0.1V, sampling interval time 0.1s, deposition time 180s, static time 0s, sensitivity 1×10 -3 A, rinse with tertiary water after the electrodeposition, dry, obtain FTO conductive glass deposited with BiOI film, and then cut into 2×1cm specifications with a glass cutting table, and then place it on a corundum sheet, the distance between two adjacent cut FTO conductive glasses is 2mm. Take 1mL dimethyl sulfoxide (DMSO), add 0.2mol acetylacetonato vanadium, stir vigorously until there is no obvious precipitation, and obtain solution C. Use a 100μL pipette to take 50μL (the amount of each cut FTO conductive glass) solution C, drip it on the surface of the BiOI film, then place the corundum sheet in a muffle furnace, heat it to 450℃ at a heating rate of 2℃ / min, calcine for 2h, and cool it to room temperature to obtain the fired FTO conductive glass; place the fired FTO conductive glass in a watch glass, add 1mol / LNaOH solution, soak for 15min, rinse with tertiary water, and dry it to obtain BiVO 4 Photoelectrode.

[0054] (2) Melamine and tetrabutylammonium hexafluorophosphate were mixed in a mass ratio of 10:1 and dissolved in anhydrous ethanol. The mixture was heated with stirring at 80°C for 0.5 h, and then calcined at 240°C for 3 h. The mixture was ground and dissolved in water. The powder was crushed by ultrasonic and dried to obtain a powder. 50 mL of anhydrous ethanol was added to 50 mg of the above powder. The powder was crushed for 1 h and then centrifuged for 3 min to obtain a spray liquid. A heating plate was set to a temperature of 200°C, and 1 mL (the amount of the spray liquid was 0.5 mL / cm 2 ) The above-mentioned spraying liquid is applied to the BiVO obtained in step (1) 4The photoelectrode was sprayed by spraying, and after spraying, it was placed in a muffle furnace and fired at 230°C for 30 minutes, then rinsed with three-grade water, and heated on a heating plate at 60°C for 10 minutes to obtain PC 3 N 4 / BiVO 4 Composite photoelectrode.

[0055] (3) Take 0.5 mol potassium borate buffer solution with a pH value of 9.5 and add 1 mmol nickel sulfate hexahydrate (NiSO 4 6H 2 O), stirring until the solution is clear and transparent, to obtain precursor liquid A. The obtained precursor liquid A is used as the electrolyte, and the PC obtained in step (2) 3 N 4 / BiVO 4 The composite photoelectrode was used as the working electrode, the platinum mesh was used as the counter electrode, and the Ag / AgCl was used as the reference electrode. The electrodeposition was carried out using the time-current curve method. The electrodeposition conditions were as follows: the deposition temperature was room temperature, the potential was 0 V, the running time was 10 s, the sampling interval was 0.1 s, the static time was 2 s, and the sensitivity was 1 × 10 -3 A, light intensity is 100mWcm -2 After the electrodeposition, the working electrode was rinsed with three-grade water and dried to obtain a phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate (NiBi / PC 3 N 4 / BiVO 4 Composite photoelectrode).

[0056] Comparative Example 1

[0057] A C 3 N 4 / BiVO 4 The specific preparation steps of the composite photoelectrode are as follows:

[0058] Step (1) is the same as in Example 1;

[0059] (2) Dissolve 50 mg of melamine in 50 mL of anhydrous ethanol, crush for 1 hour, and then centrifuge for 3 minutes to obtain a spray liquid; select a heating plate and set the temperature to 200° C., and use a spray gun to take 1 ml of the above spray liquid to spray the BiVO obtained in step (1) 4 The photoelectrode was sprayed by spraying, and after spraying, it was placed in a muffle furnace at 230°C for 30 minutes, then rinsed with three-grade water, and heated on a heating plate at 60°C for 10 minutes to obtain C 3 N 4 / BiVO 4 Composite photoelectrode.

[0060] Figure 1BiVO prepared in step (1) of Example 1 4 SEM image of the photoelectrode. Figure 1 It can be seen that BiVO 4 The microscopic morphology of the photoelectrode is worm-like nanoparticles.

[0061] Figure 2 is the BiVO in step (1) of Example 1 4 Photoelectrode, C in Comparative Example 1 3 N 4 / BiVO 4 Composite photoelectrode, PC in step (2) of Example 1 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) of Example 1 3 N 4 / BiVO 4 XRD pattern of composite photoelectrode. Figure 2 It can be seen that Example 1 successfully prepared NiBi / PC 3 N 4 / BiVO 4 Composite photoelectrode.

[0062] Figure 3 NiBi / PC prepared in Example 1 3 N 4 / BiVO 4 TEM image of the composite photoelectrode. Figure 3 It can be seen that BiVO 4 There is a layer of PC on the surface 3 N 4 Nanosheets, PC 3 N 4 layer is attached to the BiVO 4 On the layer, a layer of amorphous material NiBi can be seen, and it is attached to the PC 3 N 4 Layer and BiVO 4 On the layer.

[0063] Figure 4 is the BiVO in step (1) of Example 1 4 Photoelectrode, PC in step (2) 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) 3 N 4 / BiVO 4 The oxygen evolution efficiency of the composite photoelectrode changes with voltage from Figure 4 It can be seen that BiVO 4 Photoelectrode, PC 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC 3 N 4 / BiVO 4 The oxygen evolution efficiencies of the composite photoelectrodes were 34.81%, 33.18% and 93.79%, respectively, indicating that NiBi / PC 3 N 4 / BiVO 4 The composite photoelectrode has excellent oxygen evolution performance.

[0064] Figure 5 is the BiVO in step (1) of Example 1 4 Photoelectrode and PC in step (2) 3 N 4 / BiVO 4 Photoluminescence spectrum of the composite photoelectrode. Figure 5 It can be seen that compared with the unmodified BiVO 4 Compared with the photoelectrode, the load PC 3 N 4 After getting the PC 3 N 4 / BiVO 4 The emission intensity of the composite photoelectrode is reduced, thereby suppressing the recombination of carriers.

[0065] Figure 6 is the BiVO in step (1) of Example 1 in the presence of a hole trap 4 Photoelectrode, PC in step (2) 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) 3 N 4 / BiVO 4 Linear sweep voltammetry curve of the composite photoelectrode. Figure 6 It can be seen that under the test conditions with hole capture agent, compared with BiVO 4 Photoelectrodes and PC 3 N 4 / BiVO 4 Composite photoelectrode, NiBi / PC at the same external voltage 3 N 4 / BiVO 4 The composite photoelectrode can achieve higher photocurrent density.

[0066] Figure 7is the BiVO in step (1) of Example 1 without a hole trapping agent 4 Photoelectrode, PC in step (2) 3 N 4 / BiVO 4 Composite photoelectrode and NiBi / PC in step (3) 3 N 4 / BiVO 4 Linear sweep voltammetry curve of the composite photoelectrode. Figure 7 It can be seen that under the test conditions without hole capture agent, compared with BiVO 4 Photoelectrode, added PC 3 N 4 Layer PC 3 N 4 / BiVO 4 Composite photoelectrode and added PC 3 N 4 , NiBi / PC of NiBi layer 3 N 4 / BiVO 4 The composite photoelectrode and photocurrent are improved. At 1.23V (vs. RHE), PC 3 N 4 / BiVO 4 Composite photoelectrode compared to BiVO 4 Photoelectrode, photocurrent increased by 1.2 times, NiBi / PC 3 N 4 / BiVO 4 Composite photoelectrode compared to BiVO 4 Photoelectrode, photocurrent increased by 3.6 times.

[0067] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate, characterized in that: It comprises a conductive substrate and a BiVO4 layer, a P-C3N4 layer and a nickel borate layer sequentially loaded on the conductive substrate; The P-C3N4 layer is composed of P-C3N4 nanosheets; and the nickel borate layer is attached to the P-C3N4 layer and the BiVO4 layer.

2. A method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 1, characterized in that: The following steps are involved: (1) Depositing BiVO4 on a conductive substrate to form a BiVO4 layer to obtain a BiVO4 photoelectrode; (2) dissolving melamine and tetrabutylammonium hexafluorophosphate in ethanol, heating and calcining to obtain a powder; mixing the powder with ethanol to obtain a spray liquid; depositing the spray liquid on the BiVO4 photoelectrode obtained in step (1) to form a P-C3N4 layer, thereby obtaining a P-C3N4 / BiVO4 composite photoelectrode; (3) Mixing a potassium borate buffer solution and nickel sulfate hexahydrate to obtain a precursor liquid A; depositing the precursor liquid A on the P-C3N4 / BiVO4 composite photoelectrode obtained in step (2) to form a nickel borate layer, thereby obtaining the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate.

3. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 2, characterized in that: Step (1) is specifically as follows: A. mixing a nitric acid solution, potassium iodide and bismuth nitrate pentahydrate to obtain a solution A; dissolving p-benzoquinone in ethanol and subjecting to ultrasound to obtain a solution B; mixing the solution A and the solution B to obtain a precursor liquid B; depositing the precursor liquid B on a conductive substrate to form a BiOI film, thereby obtaining a conductive substrate with a BiOI film deposited on the surface; B. mixing vanadyl acetylacetonate and dimethyl sulfoxide to obtain solution C; The solution C is dripped onto the conductive substrate with the BiOI film deposited on the surface obtained in step A, and subjected to annealing, alkali washing, water washing and drying to form a BiVO4 layer, thereby obtaining a BiVO4 photoelectrode.

4. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 3, characterized in that: In step A, the usage ratio of the nitric acid solution, potassium iodide and bismuth nitrate pentahydrate is 25 mL: 0.4 mol: 0.04 mol; the pH value of the nitric acid solution is 1.6 to 1.8; and / or, The dosage ratio of p-benzoquinone to ethanol is 0.23 mol: 10 mL; and / or, The process conditions of the deposition precursor liquid B are as follows: initial voltage of -0.1 V, sampling interval of 0.1 s, deposition time of 150-200 s, static time of 0 s, sensitivity of 1×10 -3 A.

5. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 3, characterized in that: In step B, the ratio of vanadyl acetylacetonate to dimethyl sulfoxide is 0.2 mol: 1 mL; and / or, The dripping volume of the dripping was 25 μL / cm 2 and / or, The annealing treatment is performed at a temperature of 430-480° C. and for a time of 2 hours.

6. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 2, characterized in that: In step (2), the mass ratio of melamine to tetrabutylammonium hexafluorophosphate is 10:1; and / or, The calcination temperature is 240-260° C. and the calcination time is 3 hours.

7. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 2, characterized in that: In step (2), the ratio of the mass of the powder to the volume of ethanol is 1:1 (mg:mL).

8. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 2, characterized in that: In step (2), the deposition method of the spraying liquid is spraying; the process conditions of the deposition of the spraying liquid are: the temperature of the heating plate is 200°C, the amount of the spraying liquid is 0.5-1 mL / cm 2 , the static time is 0s.

9. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 2, characterized in that: In step (3), the dosage ratio of the potassium borate buffer solution to nickel sulfate hexahydrate is 0.5 mol: 1 mmol; and the pH value of the potassium borate buffer solution is 9.

5.

10. The method for preparing the phosphorus-doped carbon nitride composite bismuth vanadate photoelectrode loaded with nickel borate according to claim 2, characterized in that: In step (3), the deposition method of the precursor liquid A is electrochemical deposition; the deposition conditions of the deposition precursor liquid A are: the deposition temperature is room temperature, the potential is 0 V, the running time is 10 s, the sampling interval is 0.1 s, the static time is 2 s, and the sensitivity is 1×10 -3 A, light intensity is 100mWcm -2 .

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