CN112538638A

CN112538638A - High-efficiency Bi2MoO6Coated BiVO4Preparation method of heterojunction photoelectrode system

Info

Publication number: CN112538638A
Application number: CN202011305018.4A
Authority: CN
Inventors: 陈卓元; 田景; 冯昌; 荆江平; 孙萌萌
Original assignee: Institute of Oceanology of CAS
Current assignee: Institute of Oceanology of CAS
Priority date: 2020-11-19
Filing date: 2020-11-19
Publication date: 2021-03-23
Anticipated expiration: 2040-11-19
Also published as: CN112538638B

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to high-efficiency Bi₂MoO₆Coated BiVO₄A preparation method of a heterojunction photoelectrode system. Soaking FTO conductive glass as a substrate into the deposition solution of the BiOI, forming a BiOI film on the substrate through electrochemical deposition, and then spot-coatingForming a pure BiVO4 film on the surface film of the substrate by an annealing method; and soaking the substrate into a deposition solution containing bismuth nitrate and sodium molybdate to prepare a Bi2MoO 6-coated BiVO4 heterojunction photoelectrode system by a hydrothermal method. Bi in the BMO @ BVO heterojunction photoelectrode system₂MoO₆Coating on BiVO₄Upper and BiVO₄The contact is good and a II heterojunction is formed. BMO @ BVO-2 at AM1.5G (100 mW. cm)^‑2) And λ>420nm(100mW·cm^‑2) The photo-generated current densities under light irradiation of (1) were 1.47mA · cm^‑2And 1.11mA · cm^‑2Are respectively pure BiVO₄4.9 times and 3.9 times; therefore, the high-efficiency photoelectrochemistry water splitting agent has high water splitting performance.

Description

High-efficiency Bi2MoO6Coated BiVO4Preparation method of heterojunction photoelectrode system

Technical Field

The invention belongs to the technical field of photocatalysis, and particularly relates to high-efficiency Bi₂MoO₆Coated BiVO₄A preparation method of a heterojunction photoelectrode system.

Background

Since the discovery of TiO₂Since solar energy can be utilized to crack water to generate hydrogen, the photoelectrochemical water cracking technology is increasingly considered as a potential technology for providing green energy and solving the problem of environmental pollution. Meanwhile, more and more photocatalysts are used in the fields of hydrogen production and oxygen production by photoelectrochemical decomposition of water, such as ZnO, WO₃And BiVO₄And the like. However, TiO₂And the wider band gap of ZnO, results in its ability to absorb less than 5% of the ultraviolet light in the solar spectrum. And BiVO₄Due to the fact that the material has a proper band gap width (2.4-2.6 eV), is non-toxic and high in stability, the material is considered to be one of the photoelectrode materials which have the most potential for realizing efficient photoelectrochemical water splitting performance. However BiVO₄Also has the inherent disadvantages of slow carrier migration, low photon-generated carrier separation efficiency and the like, which greatly limits BiVO₄The photoelectrode is applied to the field of photoelectrochemical water splitting. Thus, BiVO is improved by modification₄The carrier migration rate of the photoelectrode and the separation efficiency of the photogenerated carriers and the final improvement of the photoelectrochemical water splitting performance of the photoelectrode are that BiVO is used₄Push to the inevitable choice of practical application.

The heterojunction photoelectrode system is constructed, so that the separation efficiency of the photon-generated carriers can be improved, the migration rate of the photon-generated carriers is improved, and the purpose of improving the photoelectrochemistry cracking water performance is finally achieved. In recent years, Bi₂MoO₆Due to the proper forbidden band width (2.6-2.8eV) and the proper energy band position (E)_CB-0.32eV) andthe shape is easy to control, and the like, so that the composite material is used for forming a heterojunction by being compounded with other semiconductors, and the photocatalytic or photoelectrochemical water splitting performance of a composite photoelectrode system is improved. However, at present for Bi₂MoO₆/BiVO₄The system is less studied, in particular, for Bi₂MoO₆/BiVO₄The system is less studied for photoelectrochemical water splitting. BiVO is prepared by spin-coating₄Coating with Bi₂MoO₆Bi is prepared on the nanorod array₂MoO₆/BiVO₄Heterojunction photoelectrode, Bi found₂MoO₆/BiVO₄Has a ratio of Bi₂MoO₆And BiVO₄All have excellent photoelectrochemical properties, but the defect that after the heterojunction is formed, the photoproduced electrons are formed by Bi₂MoO₆The conduction band is transferred to the coating layer BiVO₄On the guide belt and coating a layer of BiVO₄The contact area with the conductive substrate is small, the transfer of photogenerated electrons from the material to the conductive substrate is relatively slow, and the photogenerated carriers cannot be timely and effectively transmitted to the conductive substrate, so that Bi is enabled to be in₂MoO₆/BiVO₄The photoelectrochemical properties of the photoelectrode are not outstanding.

Therefore, the design and preparation of simple and efficient energy band-matched Bi₂MoO₆/BiVO₄Heterojunction photoelectrode systems still have great challenges to achieve fast transport of photogenerated carriers.

Disclosure of Invention

The main purpose of the present invention is to provide a high-efficiency Bi₂MoO₆Coated BiVO₄A preparation method of a heterojunction photoelectrode system.

In order to achieve the purpose, the invention adopts the technical scheme that:

high-efficiency Bi₂MoO₆Coated BiVO₄A preparation method of a heterojunction photoelectrode system,

1) soaking FTO conductive glass serving as a substrate into the deposition solution of the BiOI, forming a BiOI film on the substrate through electrochemical deposition, and forming a pure BiVO on the surface film of the substrate through a spot coating and annealing method₄A film;

2) the substrate is soaked into a deposition solution containing bismuth nitrate and sodium molybdate to prepare Bi through a hydrothermal method₂MoO₆Coated BiVO₄Heterojunction photoelectrode systems.

The deposition solution of the BiOI in the step 1) is Bi (NO)₃)₃·5H₂Dissolving O in KI solution to obtain mixed solution A, wherein Bi (NO) in the mixed solution A₃)₃·5H₂The final concentration of O is 0.02-0.06mol/L, the final concentration of KI is 0.02-0.06mol/L, and the pH value of the mixed solution A is adjusted to 1.7-2.0; dissolving p-benzoquinone in ethanol to obtain a mixed solution B with the final concentration of the p-benzoquinone of 0.1-0.3 mol/L; and mixing the mixed solution A and the mixed solution B according to the volume ratio of 5:1-5: 3.

After the BiOI thin film is formed on the substrate in the step 1), the vanadium acetylacetonate is coated on the surface of the BiOI by a point coating method, dried at the temperature of 60-80 ℃, annealed at the temperature of 400-450 ℃ for 2-5h, washed and dried at room temperature, even if the pure BiVO is formed on the thin film on the surface of the substrate₄And (3) a membrane.

Said step 2) adding Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂Adding O into ethylene glycol respectively, mixing the two solutions in a volume ratio of 1:1 to obtain a mixed solution A, and adding ethanol to obtain a deposition solution; wherein, Bi (NO) in the ethylene glycol₃)₃·5H₂The final concentration of O is 2-8mol/L, Na₂MoO₄·2H₂The final concentration of O is 1-4 mol/L; the volume ratio of the mixed solution A to the ethanol is 1:5-1: 3.

It is further said that:

(1) preparation of BiVO₄Substrate: cleaning FTO conductive glass as a substrate, soaking the cleaned FTO conductive glass in the FTO conductive glass, depositing a layer of BiOI film on the FTO in a deposition solution of BiOI by an electrochemical deposition method, then coating vanadium acetylacetonate on the surface of the BiOI film of a substrate by a point coating method, drying the BiOI film at 60-80 ℃, placing the substrate in a tube furnace after drying, raising the temperature to 400-450 ℃ at the heating rate of 5-10 ℃/min, annealing for 2-5h, washing the substrate by NaOH solution and deionized water after annealing, and drying the substrate at room temperature, namely forming pure BiVO on the surface of the substrate₄A film;

(2) preparation of Bi₂MoO₆/BiVO₄: adding Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂And respectively dissolving O in ethylene glycol, mixing the two solutions after the O is completely dissolved, adding the mixture into ethanol to obtain a clear solution, immersing the substrate obtained in the step 1) into the clear solution, reacting for 8 hours at 160 ℃ under a drying condition, and washing and drying to obtain the product.

The electrodeposition condition is a three-electrode system, 300s of deposition is carried out under the constant potential of-0.1V, and a BiOI film is formed on the surface of the substrate, wherein the electrode system is FTO 1 x 5cm²Is a working electrode, Ag/AgCl is a reference electrode, and Pt is a counter electrode.

Pure BiVO is not formed on the substrate in the step 2)₄The surface of the membrane is immersed downwards in the deposition solution for reaction.

And cooling after the reaction, taking out, washing with water and ethanol for several times in sequence, and drying at 80 ℃ for 4 hours to obtain the product.

As can be seen from the above, Bi₂MoO₆Successfully coated on BiVO₄Photoelectrode surface and BiVO (BiVO) unchanged₄And Bi₂MoO₆@BiVO₄The photoelectrochemical property of the photoelectrode is obviously improved, and the Bi with the best photoelectrochemical property is obtained under the irradiation of simulated sunlight₂MoO₆@BiVO₄The photo-generated current density can reach 1.47mA cm^-2Is pure BiVO₄4.9 times of photoelectrode, and Bi₂MoO₆@BiVO₄The heterojunction photoelectrode also has excellent photoelectrochemical stability due to Bi₂MoO₆And BiVO₄A good II type heterojunction system is formed, photogenerated carriers can escape from the surface of the electrode more easily, the recombination efficiency of photogenerated electrons and holes is remarkably inhibited under the action of the heterojunction system, the electron transfer rate is remarkably improved, and further Bi is enabled to be₂MoO₆@BiVO₄The type II heterojunction photoelectrode has obvious high-efficiency stability.

The invention is high-efficiency Bi₂MoO₆Coated BiVO₄The heterojunction photoelectrode system has the maximum light in the scanning voltage range when the precursor solution concentration is 2mM, namely BMO @ BVO-2The current density is generated. At AM1.5G 100mW cm^-2Under the irradiation of light, the photoproduction current density of BMO @ BVO-2 can reach 1.47 mA-cm^-2Is pure BiVO₄4.9 times of photoelectrode.

Compared with the prior art, the invention has the beneficial effects that:

(1) bi in the BMO @ BVO heterojunction photoelectrode system₂MoO₆Coating on BiVO₄Upper and BiVO₄The contact is good and a II heterojunction is formed. BMO @ BVO-2 at AM1.5G (100 mW. cm)^-2) And λ>420nm(100mW·cm^-2) The photo-generated current densities under light irradiation of (1) were 1.47mA · cm^-2And 1.11mA · cm^-2Are respectively pure BiVO₄4.9 times and 3.9 times; therefore, the high-efficiency photoelectrochemistry water splitting agent has high water splitting performance.

(2) The BMO @ BVO-2 heterojunction photoelectrode system has high photoelectric conversion efficiency, can convert more light energy into electric energy, and is beneficial to improvement of photoelectrochemical cracking water performance of the BMO @ BVO-2 heterojunction photoelectrode. In addition, the BMO @ BVO-2 heterojunction photoelectrode system has a smaller work function, so electrons of the photoelectrode system can escape more easily, and the BMO @ BVO-2 heterojunction photoelectrode has better photoelectrochemistry cracking water performance.

(3) The photoelectrochemical cracking aqueous performance improvement of the BMO @ BVO-2 heterojunction photoelectrode system is also attributed to the fact that the heterojunction is constructed, so that the separation efficiency of photon-generated carriers is improved, and the migration of the carriers is accelerated. Bi₂MoO₆@BiVO₄The design and preparation of the II type heterojunction photoelectrode provide important theoretical basis for further developing the efficient and stable photoelectrode.

Drawings

FIG. 1 is a sample XRD pattern of a series of BMO @ BVO-2 heterojunction photoelectrode systems provided by an example of the present invention;

FIG. 2 is a Raman spectrum of a series of samples of a BMO @ BVO-2 heterojunction photoelectrode system provided by an embodiment of the invention;

FIG. 3 is SEM and HRTEM images of a series of BMO @ BVO-2 heterojunction photoelectrode systems provided by an embodiment of the invention; wherein FIG. 3a is the SEM topography of the BVO, FIG. 3b is the SEM topography of BMO @ BVO-1 of example 3, FIG. 3c is the SEM topography of BMO @ BVO-2 of example 2, FIG. 3d is the SEM topography of BMO @ BVO-3 of example 3, FIG. 3e is the SEM topography of BMO @ BVO-4 of example 4, FIG. 3f is the SEM topography of the BMO, FIGS. 3g and h are TEM images of BMO @ BVO-2 of example 2, and FIG. 3i is the STEM Mapping graph of BMO @ BVO-2 of example 2;

FIG. 4 is an EDS plot of BMO @ BVO-2 of example 2 of the present invention;

FIG. 5 is a XPS total measurement spectrum of BMO @ BVO-2 of example 2 of the present invention;

FIG. 6 is an XPS spectrum of BMO @ BVO-2 of example 2 of the present invention; wherein fig. 6a is a Bi 4f XPS core spectrum, fig. 6b is a V2 p XPS core spectrum, fig. 6c is a Mo3d XPS core spectrum, and fig. 6d is an O1s XPS core spectrum;

FIG. 7 is a chart of the UV-VIS absorption spectra of a series of samples of a BMO @ BVO-2 heterojunction photoelectrode system provided by an example of the present invention;

FIG. 8 is an i-t curve and an i-V curve at 1V bias (vs Ag/AgCl) for a series of BMO @ BVO-2 heterojunction photoelectrode systems provided by an example of the present invention, all at 0.1M Na₂SO₄The measurement in solution of (a); wherein, FIG. 8a is the i-t curve of the series of samples under AM1.5G, FIG. 8b is the i-t curve of the series of samples under visible light, FIG. 8c is the i-V curve of the series of samples under AM1.5G, FIG. 8d is the i-V curve of the series of samples under visible light, FIG. 8e is the long-time photo-induced current density change curve of BMO @ BVO-2 of example 2 under AM1.5G, and FIG. 8f is the IPCE spectrogram of the series of samples under 1V bias (vs Ag/AgCl);

FIG. 9 is a surface charge distribution plot for a series of samples measured by SKP techniques provided by an embodiment of the present invention;

FIG. 10 is a graph of surface work function, PL and EIS for a series of samples provided by an embodiment of the present invention; wherein FIG. 10a is the surface work function converted from the measurements of FIG. 9, FIG. 10b is the PL test results for BVO, BMO and BMO @ BVO-2 of example 2, and FIG. 10c is the EIS plot for BVO, BMO and BMO @ BVO-2 of example 2;

FIG. 11 is a Mott-Schottky curve and linear fit plot of BVO and BMO prepared according to examples of the present invention;

fig. 12 shows the forbidden bandwidths of BVO and BMO obtained by the Tauc formula according to an embodiment of the present invention;

FIG. 13 is a schematic diagram of the mechanism of enhancement of photoelectrochemical properties of BMO @ BVO-2 of example 2 of the present invention under AM1.5G light.

Detailed Description

The following examples are given to facilitate a better understanding of the invention, but do not limit the invention. The experimental procedures in the following examples are conventional unless otherwise specified.

The invention provides a high-efficiency BMO @ BVO heterojunction photoelectrode system and photoelectrochemistry cracking water performance thereof. Bi₂MoO₆Coating on BiVO₄Upper and BiVO₄The contact is good and a II heterojunction is formed. BMO @ BVO-2 at AM1.5G (100 mW. cm)^-2) And λ>420nm(100mW·cm^-2) The photo-generated current densities under light irradiation of (1) were 1.47mA · cm^-2And 1.11mA · cm^-2Are respectively pure BiVO₄4.9 times and 3.9 times. The BMO @ BVO-2 heterojunction photoelectrode body has high photoelectric conversion efficiency, can convert more light energy into electric energy, and is favorable for improving the photoelectrochemical cracking water performance of the BMO @ BVO-2 heterojunction photoelectrode. In addition, the BMO @ BVO-2 heterojunction photoelectrode system has a smaller work function, so electrons of the photoelectrode system can escape more easily, and the BMO @ BVO-2 heterojunction photoelectrode has better photoelectrochemistry cracking water performance. The photoelectrochemical cracking aqueous performance improvement of the BMO @ BVO-2 heterojunction photoelectrode is also attributed to that the separation efficiency of a photon-generated carrier is improved and the migration of the carrier is accelerated by the construction of the heterojunction. Bi₂MoO₆@BiVO₄The design and preparation of the II type heterojunction photoelectrode provide important theoretical basis for further developing the efficient and stable photoelectrode.

Example 1

High efficiency of Bi₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system comprises the following steps of:

(1) preparation of BiVO₄Substrate: 1 x 5cm²The FTO conductive glass is used as BiVO₄And (4) growing a substrate. Placing FTO in a volume ratio of 1: 1:1 mixture of ethanol, acetone and waterUltrasonically cleaning the FTO substrate in a solution for 15min, then ultrasonically cleaning the FTO substrate in deionized water for 15min, airing to obtain a clean FTO substrate, soaking the FTO substrate in a deposition solution of the BiOI by an electrochemical deposition method, wherein the deposition conditions are as follows: three-electrode system (FTO 1 x 5 cm)²Is a working electrode, Ag/AgCl is a reference electrode, Pt is a counter electrode), and the BiOI thin film is obtained on the surface of an FTO substrate by depositing for 300s under the constant potential of 0.1V; then, 0.6mL of 0.02M vanadium acetylacetonate is taken to be coated on the surface of the BiOI film by a spot coating method, dried at 80 ℃, annealed at 450 ℃ for 2h (the temperature rise speed is 5 ℃/min) in a tube furnace, and finally cleaned in 1mol/L NaOH solution for 30min to remove redundant V₂O₅Washing with deionized water, and air drying at room temperature to obtain pure BiVO₄Sample, labeled BVO.

Wherein the deposition solution of the BiOI is 4mmol of Bi (NO)₃)₃·5H₂O was dissolved in 100mL of a KI solution containing 4mmol, the pH was adjusted to 1.7 with dilute nitric acid, and then mixed with 40mL of ethanol containing 9mmol of p-benzoquinone.

(2) Preparation of Bi₂MoO₆/BiVO₄: 2mM of Bi (NO)₃)₃·5H₂O and 1mM Na₂MoO₄·2H₂Dissolving O in 12.5mL of ethylene glycol under stirring (ultrasonic) respectively, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of sample 1 x 5cm obtained in the step (1)²(FTO, conductive side down, i.e., pure BiVO is not formed on the substrate₄The surface of the film faces downwards), the mixture is placed in a drying box, the reaction is carried out for 8 hours at 160 ℃, the mixture is taken out after cooling, the mixture is washed by water and ethanol for a plurality of times and dried for 4 hours at 80 ℃, and the obtained sample is Bi₂MoO₆/BiVO₄According to the addition of Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂The amount of O marks the sample as BMO @ BVO-1 (see FIGS. 1, 2 and 3).

Example 2

High efficiency of Bi₂MoO₆Coated BiVO₄A preparation method of a heterojunction photoelectrode system, wherein the concentration of the precursor is 2 mM.

The method comprises the following specific steps:

(1) preparation of BiVO₄Substrate: 1 x 5cm²The FTO conductive glass is used as BiVO₄And (4) growing a substrate. Placing FTO in a volume ratio of 1: 1:1, ultrasonically cleaning for 15min in a mixed solution of ethanol, acetone and water, then ultrasonically cleaning for 15min in deionized water, drying to obtain a clean FTO substrate, soaking the FTO substrate in a deposition solution of the BiOI by an electrochemical deposition method, wherein the deposition conditions are as follows: three-electrode system (FTO 1 x 5 cm)²Is a working electrode, Ag/AgCl is a reference electrode, Pt is a counter electrode), depositing for 300s under the constant potential of 0.1V to obtain a BiOI film on the surface of an FTO substrate, then coating 0.6mL of 0.02M vanadium acetylacetonate on the surface of the BiOI film by a spot coating method, drying at 80 ℃, annealing for 2h at 450 ℃ in a tube furnace (the heating rate is 5 ℃/min), and finally cleaning for 30min in 1mol/L NaOH solution to remove the redundant V₂O₅Washing with deionized water, and air drying at room temperature to obtain pure BiVO₄Sample, labeled BVO. Wherein the deposition solution of the BiOI is 4mmol of Bi (NO)₃)₃·5H₂O was dissolved in 100mL of a KI solution containing 4mmol, the pH was adjusted to 1.7 with dilute nitric acid, and then mixed with 40mL of ethanol containing 9mmol of p-benzoquinone.

(2) Preparation of Bi₂MoO₆/BiVO₄: adding 4mM Bi (NO)₃)₃·5H₂O and 2mM Na₂MoO₄·2H₂Respectively stirring (ultrasonically) O to dissolve in 12.5mL of ethylene glycol, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of the sample (FTO, BiVO) obtained in the step (1)₄Face down), reacting for 8h at 160 ℃, cooling, taking out, washing with water and ethanol for several times, and drying for 4h at 80 ℃ to obtain a sample Bi₂MoO₆/BiVO₄According to the addition of Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂The amount of O marks the sample as BMO @ BVO-2 (see FIG. 1, FIG. 2, FIG. 3, and FIG. 4).

Example 3

The method comprises the following specific steps:

(2) Preparation of Bi₂MoO₆/BiVO₄: adding 6mM Bi (NO)₃)₃·5H₂O and 3mM Na₂MoO₄·2H₂Respectively stirring (ultrasonically) O to dissolve in 12.5mL of ethylene glycol, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of the sample (FTO, BiVO) obtained in the step (1)₄Face down), reacting for 8h at 160 ℃, cooling, taking out, washing with water and ethanol for several times, and drying for 4h at 80 ℃ to obtain a sample Bi₂MoO₆/BiVO₄According to the addition of Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂The amount of O marks the sample as BMO @ BVO-3 (see FIG. 1, FIG. 2, FIG. 3, and FIG. 4).

Example 4

The method comprises the following specific steps:

(2) Preparation of Bi₂MoO₆/BiVO₄: adding 8mM Bi (NO)₃)₃·5H₂O and 4mM Na₂MoO₄·2H₂Respectively stirring (ultrasonically) O to dissolve in 12.5mL of ethylene glycol, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of the sample (FTO, BiVO) obtained in the step (1)₄Face down), reacting at 160 deg.C for 8 hr, cooling, washing with water and ethanolDrying for 4 hours at 80 ℃ for several times to obtain a sample which is Bi₂MoO₆/BiVO₄According to the addition of Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂The amount of O marks the sample as BMO @ BVO-4 (see FIG. 1, FIG. 2, FIG. 3, and FIG. 4).

The experimental results are as follows:

as can be seen from FIG. 1, the series of sample XRD patterns, in which the diffraction peaks at 26.58 °, 37.77 °, 51.76 ° and 65.74 ° for 2 θ correspond to the (110), (200), (211) and (301) crystal planes (PDF #46-1088) of FTO; diffraction peaks at 18.67 °, 28.95 °, 30.55 °, 35.22 ° and 47.30 ° 2 θ correspond to monoclinic phase BiVO₄The (110), (121), (040), (002) and (042) planes (PDF # 14-0688); diffraction peaks at 28.31 °, 32.53 °, 46.74 °, 55.44 ° and 58.48 ° 2 θ correspond to orthorhombic Bi₂MoO₆The (131), (200), (202), (331) and (262) crystal planes (PDF # 21-0102). BiVO₄Photoelectrode hydrothermal coating Bi in different precursors₂MoO₆Thereafter, only significant BiVO was observed in the XRD patterns of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrodes₄Does not find Bi₂MoO₆May be due to Bi₂MoO₆Are relatively dispersed.

As can be seen from FIG. 2, the Raman spectrum of the series of samples, BiVO₄815cm in Raman spectrum of photoelectrode^-1The peak at corresponds to VO₄Symmetrical stretching mode of 123cm^-1And 208cm^-1The peak at corresponds to VO₄Bending mode [21 ]]This also further illustrates BiVO₄The successful synthesis of the compound. Bi₂MoO₆715cm in Raman spectrum of photoelectrode^-1、796cm^-1And 844cm^-1Corresponds to octahedral MoO₆Stretching mode of Mo-O in [21 ]]This also further illustrates Bi₂MoO₆The successful preparation. In BiVO₄Loaded with different amounts of Bi₂MoO₆Then, the Raman spectra of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode are 815cm^-1Peak at (b) compared with pure BiVO₄Slightly widened, which may be byIn Bi₂MoO₆And BiVO₄The effect of heterojunction formation between them.

From FIG. 3, SEM and HRTEM images of series of samples, pure BiVO in FIG. 3a₄The nano-worm has an average particle size of about 80nm, and gaps exist among the nano-worm structures, so that the photoelectrode material can be in full contact with a solution. FIG. 3f is pure Bi₂MoO₆From the SEM image, it can be found that pure Bi is present₂MoO₆Is nanosphere of about 200 nm. BiVO (bismuth oxide) is added₄Are placed in different concentrations of Bi₂MoO₆After hydrothermal reaction in the precursor, the surface morphologies of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode are changed. The BMO @ BVO-1 nano-worm-like structure in FIG. 3b was not changed, but the nano-worms were significantly coarsened, which indicates that BiVO₄The surface of the photoelectrode is successfully coated with Bi₂MoO₆. With Bi₂MoO₆The BMO @ BVO-2 (figure 3c) still presents a nano-worm-like structure due to the increase of the concentration of the precursor solution, and the nano-worms become thicker, indicating that BiVO₄Bi coated on surface of photoelectrode₂MoO₆The amount of (a) increases. FIG. 3i is a STEM Mapping chart of a prepared BMO @ BVO-2 photoelectrode, and the uniform distribution of four elements of Bi, V, O and Mo can be found, which shows that Bi₂MoO₆In BiVO₄Are uniformly distributed. With Bi₂MoO₆The concentration of the precursor solution is further increased, BiVO₄Bi coated on surface of photoelectrode₂MoO₆The amount of (b) is further increased, the BMO @ BVO-3 (fig. 3d) is changed from a nano worm-like structure to irregular large particles, and the inter-particle voids are significantly reduced, which is not favorable for sufficient contact of the photoelectrode material with the electrolyte solution, and may cause deterioration of photoelectrochemical properties. Further increase of Bi₂MoO₆When the concentration of the precursor solution is high, BiVO₄Bi coated on surface of photoelectrode₂MoO₆The amount of (B) is further increased, and Bi₂MoO₆In BiVO₄A dense thin film is formed on the surface of the photoelectrode, and the gaps among the particles disappear, which may also result in the deterioration of the photoelectrochemical properties of the photoelectrode. Further prepared by HRTEM pairThe micro-topography of the BMO @ BVO-2 photoelectrode of (a) was characterized as shown in fig. 3g and fig. 3 h. FIG. 3g is an HRTEM image under a low power microscope, and the nano-worm-like BiVO can be clearly observed₄And BiVO₄The surface of the film is coated with a layer of irregular Bi₂MoO₆. FIG. 3h is an HRTEM image under a high power lens, in which BiVO can be seen₄And Bi₂MoO₆A distinct heterojunction interface, a lattice spacing of 0.308nm corresponding to BiVO₄The lattice spacings of 0.210nm and 0.326nm of (121) correspond to Bi₂MoO₆The (142) and (140) crystal planes of (1). The results of both SEM and HETEM indicate successful fabrication of BMO @ BVO heterojunction photoelectrodes.

As can be seen from the EDS chart of BMO @ BVO-2 in FIG. 4, the presence of Bi, V, O, Mo, etc. is observed, which is consistent with the elemental composition of BMO @ BVO.

As can be seen from the XPS summary plot of FIG. 5BMO @ BVO-2, the BMO @ BVO-2 photoelectrode prepared therefrom was found to have elements such as Bi, V, O, M and C, where the element C was from the background C of the XPS test, consistent with the elemental composition of BMO @ BVO-2.

It can be seen from the XPS spectrum of FIG. 6BMO @ BVO-2, where FIG. 6a is the XPS spectrum of Bi 4f, where the binding energies at 159.4eV and 164.6eV correspond to BiVO₄And Bi₂MoO₆Middle Bi³⁺Bi 4f of_7/2And Bi 4f_5/2. FIG. 6b is an XPS spectrum of V2 p, in which the binding energy at 516.4eV corresponds to BiVO₄Middle V⁵⁺. FIG. 6c is an XPS spectrum of Mo3d, in which the binding energies at 232.4eV and 235.6eV are attributed to Bi₂MoO₆Middle Mo⁶⁺Mo3d of_5/2And Mo3d_3/2. FIG. 6d is an XPS spectrum of O1s showing binding energies at 530.1eV and 531.6eV corresponding to BiVO₄And Bi₂MoO₆And adsorbed oxygen on the surface of the photoelectrode. The XPS results further demonstrate the successful fabrication of the BMO @ BVO heterojunction.

FIG. 7 is the UV-VIS absorption spectrum of a series of samples from which pure BiVO can be seen₄The light absorption threshold of the photoelectrode is about 500nm and is in BiVO₄Coating Bi by a hydrothermal method₂MoO₆Thereafter, the light absorption thresholds of BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 were not substantially changed.

FIG. 8 is an i-t curve and an i-V curve for a series of samples at 1V bias (vs Ag/AgCl), all at 0.1M Na₂SO₄Is measured in the solution of (1). From FIG. 8a, it can be seen that pure BiVO₄And Bi₂MoO₆Photoelectrode is AM1.5G 100mW cm^-2The photo-generated current density under irradiation is 0.3mA cm^-2And 0.16. mu.A. cm^-2. BiVO (bismuth oxide) is added₄Placing the precursor solution with different concentrations for hydrothermal coating of Bi₂MoO₆And then, the photo-generated current density of the BMO @ BVO series photoelectrode is improved to different degrees. And the photo-generated current density of the BMO @ BVO heterojunction photoelectrode is increased and then decreased along with the increase of the concentration of the precursor solution in the hydrothermal reaction, and the photo-generated current densities of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 are respectively 1.33 mA-cm^-2，1.47mA·cm^-2，1.35mA·cm^-2And 1.23mA · cm^-2. Wherein the BMO @ BVO-2 photoelectrode has the highest photo-generated current density and is pure BiVO₄4.9 times of that of pure Bi₂MoO₆Several thousand times higher, indicating that the precursor concentration is optimal at 2 mM. FIG. 8c is a graph of BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3, BMO @ BVO-4 and BMO at AM1.5G 100 mW. cm^-2Photoinduced i-V curve under irradiation, tested at 0.1M Na₂SO₄In solution. As can be seen from FIG. 8c, Bi₂MoO₆The photo-generated current density is very small and the change of the photo-generated current density along with the voltage cannot be seen. And the photo-generated current density of other prepared series photoelectrodes is continuously increased along with the increase of the applied bias voltage. BiVO₄Still has smaller photo-generated current density, and BiVO₄Placing the precursor solution with different concentrations for hydrothermal coating of Bi₂MoO₆Then, the photo-generated current density of the BMO @ BVO photoelectrode is improved to different degrees, and the BMO @ BVO-2 has the maximum photo-generated current density in the scanning voltage range, which also indicates that the precursor solution concentration is 2mM which is the most suitable concentration. FIGS. 8b and 8d are prepared BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3, BMO @ BVO-4And BMO in visible light (lambda)>420nm,100mW cm^-2) I-t and i-V curves under illumination. As can be seen in FIG. 8b, pure BiVO₄The photo-generated current density under the irradiation of visible light is only 0.28mA cm^-2Hydrothermal coating of Bi in precursor solutions of different concentrations₂MoO₆Then, the variation trend of the photo-generated current density of the BMO @ BVO photoelectrode is shown in FIG. 8a as AM1.5G 100mW cm^-2The change in photo-generated current density under illumination is substantially uniform. The photoproduction current densities of BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 were 1.07mA cm^-2，1.11mA·cm^-2，0.93mA·cm^-2And 0.85mA · cm^-2. Wherein the BMO @ BVO-2 photoelectrode has the highest photo-generated current density and is pure BiVO₄3.9 times of the photoelectrode is Bi₂MoO₆Thousands of times as many photoelectrodes as possible. Visible light (λ) in FIG. 8d>420nm,100mW·cm^-2) The trend of the photoinduced i-V curve under irradiation is compared with that at AM1.5G 100mW cm in FIG. 8c^-2The variation under illumination is substantially uniform.

I-t and i-V curves under simulated sunlight and visible light are combined to find that the photoelectrochemical performance of the BMO @ BVO-2 photoelectrode is compared with BiVO₄And Bi₂MoO₆Are greatly improved, which shows that the generation and separation efficiency of the photon-generated carriers are greatly improved. BiVO₄And Bi₂MoO₆Has good energy band matching degree, and proper amount of Bi₂MoO₆Coating to BiVO₄In the above process, a heterojunction electric field is formed at the contact interface of the two, and the photogenerated carriers are efficiently and orderly separated under the action of the heterojunction electric field; at the same time, a proper amount of Bi₂MoO₆Coating and reserving BiVO₄The porous structure of the photoelectrode thin film (shown in figure 3c) is beneficial to the full contact of the photoelectrode material and the electrolyte solution, so that the photo-generated holes can be rapidly transferred out to be consumed by reacting with the electrolyte solution, and therefore, the BMO @ BVO-2 has the best photoelectrochemical property. For BMO @ BVO-1, Bi₂MoO₆Has a small coating amount of BiVO₄And Bi₂MoO₆The heterojunction electric field formed between the two is not enough to effectively separate photon-generated carriers, so that the BMO @ BVO-1 is inferior to the BMO @ BVO-2 in terms of the BMO @ BVO-1 but superior to the BMO @ BVO-2BiVO₄And Bi₂MoO₆Photoelectrochemical properties of (a). And for BMO @ BVO-3 and BMO @ BVO-4 photoelectrodes, the coated Bi₂MoO₆In a large amount, and can form a heterojunction to accelerate the separation of photogenerated carriers, but the excess Bi₂MoO₆Block BiVO₄The porous structure of the photoelectrode film is not beneficial to the full contact of the photoelectrode material and the electrolyte solution, so that the photoproduction holes can not be timely and effectively reacted with the electrolyte solution to be consumed, and the BMO @ BVO-3 and BMO @ BVO-4 have the characteristics of being inferior to BMO @ BVO-2 but superior to BiVO₄And Bi₂MoO₆Photoelectrochemical properties of (a).

Next, the AM1.5G (100 mW. cm) was passed for a long time^-2) Testing of photoinduced i-t curves under illumination the stability of the prepared BMO @ BVO-2 heterojunction photoelectrode was investigated, as shown in FIG. 8e, tested at 0.1M Na₂SO₄In solution. FIG. 8e shows that after 1000s of intermittent on-off light testing, the photo-generated current density of the BMO @ BVO-2 photo-electrode remained at 1.35 mA-cm^–2The above shows that it has good stability.

The photoelectric conversion efficiency of the prepared series photoelectrode is further analyzed by testing the photo-generated current density under the irradiation of monochromatic light. Generally, IPCE is calculated by equation (1):

wherein Isc is the photo-generated current density (mA-cm) generated by the photoelectrode^-2) I is the wavelength (nm) and Pin is the intensity of monochromatic light (mW. cm)^-2). Therefore, the value of IPCE can be obtained by calculation by measuring the intensity of light at a single wavelength and the density of the photo-generated current generated by the photoelectrode. FIG. 8f shows Na concentration at 0.1M₂SO₄And calculating the photoelectric conversion efficiency of the prepared BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode according to the measured photo-generated current density. FIG. 8f shows that BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 all have strong light absorption within 500nmThis is consistent with the results of the uv-vis diffuse reflectance spectrum in fig. 7. Pure BiVO₄The IPCE value of the photoelectrode is small, being about 8.82% (380nm) at the maximum. Coated with Bi₂MoO₆The IPCE values of BMO @ BVO heterojunction photoelectrode series are improved to different degrees, the IPCE values of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode series are respectively 12.64-28.05%, 13.37-29.46%, 10.85-27.75% and 7.90-18.70% within 360-480 nm, and the IPCE values of the photoelectrode series are maximum at 380nm, and the result shows that the IPCE values of the Bi @ BVO heterojunction photoelectrode series are Bi @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @₂MoO₆The coating obviously enhances the photoelectric conversion efficiency of the BMO @ BVO photoelectrode. Meanwhile, BMO @ BVO-2 has the highest photoelectric conversion efficiency compared with pure BiVO₄The improvement is 20.64% (at 380 nm).

FIG. 9 is a surface charge distribution plot of a series of samples measured by the SKP technique, from which BiVO can be seen₄Has a surface potential of 0 +/-49 mV and is loaded with Bi₂MoO₆Then, the surface potentials of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode all become negative, and the surface potential values thereof are respectively-114.5 +/-61.5 mV, -364 +/-56 mV, -199 +/-50 mV and-100.5 +/-50.5 mV, wherein the surface potential of the BMO @ BVO-2 is most negative and is more negative than that of pure Bi₂MoO₆The lower the 364 mV. The surface WFs of the prepared electrode has the following relationship with the surface voltage measured by SKP:

where wf (sample) is the work function for preparing the photoelectrode, wf (tungsten) is the surface potential (4.55eV) relative to the tungsten reference electrode, and aw (photoelectrode) is the surface potential of the photoelectrode obtained according to the SKP test.

FIG. 10 is a graph of surface work function, PL and EIS for a series of samples, showing the magnitude of the work function of the photoelectrode calculated by equation (2) as shown in FIG. 10a, where BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 electrodes have work functions of 4.55eV, 4.39eV, 4.19eV, 4.35eV and 4.45eV, respectively, with the BMO @ BVO-2 photoelectrode having the lowest work function, indicating that it has the least energy required to escape electronsThat is, electrons of BMO @ BVO-2 flow out of the electrode material and participate in the reaction more easily, and thus it has more excellent photoelectrochemical properties. FIG. 10b shows the PL test results for BVO, BMO @ BVO-2 and BMO photoelectrodes with an excitation wavelength of 325 nm. For semiconductors, when excited by light, electrons in the valence band are excited to transition to the conduction band, leaving photogenerated holes in the valence band. A part of photo-generated electrons and photo-generated holes can be separated to generate photo-generated current or generate oxidation-reduction reaction with other substances; another portion of the photogenerated electrons and holes recombine secondarily releasing energy, which can be detected by PL spectroscopy. Generally, the stronger the peak intensity of the PL spectrum, the stronger the recombination capability of photogenerated carriers and the poorer the photoelectrochemical properties. In FIG. 10b, compared to pure BiVO₄And pure Bi₂MoO₆The PL spectrum intensity of the photoelectrode, BMO @ BVO-2 photoelectrode, was greatly reduced, indicating that the separation capability of its photogenerated carriers was greatly improved, which was attributed to the construction of the heterojunction. Therefore, the BMO @ BVO-2 photoelectrode has better photoelectrochemical properties.

In addition to the separation capability of photogenerated carriers, the mobility of carriers is also one of the factors that affect the photoelectrochemical properties of the photoelectrode. The EIS test can be used for characterizing the migration capability of the current carrier of the photoelectrode material, and the smaller the impedance arc radius in the EIS is, the better the migration capability of the current carrier of the photoelectrode material is represented. FIG. 10c is an EIS plot of the prepared BVO, BMO @ BVO-2 and BMO electrodes, from which it can be seen that BMO @ BVO-2 has a greatly reduced arc radius of resistance compared to BVO and BMO, indicating better carrier mobility. The construction of the heterojunction reduces the charge transfer potential of the thin-film electrode, so that carriers can be transferred to the surface of the electrode material more quickly after being generated, thereby having better photoelectrochemical properties.

FIG. 11 is a Mott-Schottky curve and line fit plot of the prepared BVO and BMO from which BiVO can be found₄And Bi₂MoO₆The slopes of (a) and (b) are both positive values, indicating that both are n-type semiconductors. Meanwhile, the Mott-Schottky linear part is extended to the horizontal axis to obtain BiVO₄And Bi₂MoO₆Flatness of photoelectrodeThe charged sites were 0.64V (vs RHE) and 0.22V (vs RHE), respectively. The valence band potential, the forbidden band width and the conduction band potential of the semiconductor photoelectrode have the following relations:

E_g＝E_VB-E_CB (3)

wherein E is_VBIs the value of the valence band potential of the semiconductor photoelectrode, E_gIs the value of the forbidden band width of the semiconductor photoelectrode, E_CBIs the value of the conduction band potential of the semiconductor photoelectrode.

Fig. 12 shows the forbidden bandwidths of BVO and BMO obtained from the Tauc formula, and the straight line part of the graph obtained in the graph is extrapolated to the abscissa axis, and the intersection point is the forbidden bandwidth value for preparing the photoelectrode. As can be seen from the figure, BiVO is prepared₄And Bi₂MoO₆The band gaps of the photoelectrode are 2.48eV and 2.85eV respectively. Thus, BiVO is calculated by the formula (3)₄And Bi₂MoO₆The valence band potentials of the photoelectrode were 3.12V and 3.07V, respectively. Bi₂MoO₆The potential of the conduction band is negative to BiVO₄And BiVO₄Valence band potential of (B) is greater than Bi₂MoO₆This also confirms BiVO₄And Bi₂MoO₆The method has good energy band matching, is beneficial to the construction of II type heterojunction, accelerates the effective separation of photon-generated carriers, and improves the photoelectrochemical property.

FIG. 13 is a schematic diagram of the enhanced photoelectrochemical properties of the BMO @ BVO-2 of example 2 under AM1.5G light, the BMO @ BVO heterojunction photoelectrode system having a higher than pure BiVO₄And Bi₂MoO₆The photogenerated current density is obviously enhanced, which shows that the two have better energy band matching and form a II type heterojunction system with better energy band matching. BiVO prepared according to FIG. 12₄And Bi₂MoO₆The forbidden band widths of the photoelectrode are respectively 2.48eV and 2.85eV, and BiVO can be obtained through Figure S9₄And Bi₂MoO₆Relation of conduction band potential of photoelectrode E_Bi2MoO6(0.22V(vs RHE))＜E_BiVO4(0.64V (vs RHE)), and the relationship E between the valence band potentials_BiVO4(3.12V(vs RHE))＞E_Bi2MoO6(3.07V (vs RHE)). After being excited by illumination, Bi₂MoO₆The photo-generated electrons on the conduction band can be transferred to BiVO₄Further transferred to an FTO conductive substrate and finally transferred to a Pt electrode to remove H⁺Reducing to hydrogen; at the same time, BiVO₄Bi to which photogenerated holes in the valence band can be transferred₂MoO₆The valence band is eventually consumed by the oxidation reaction associated with the electrolyte solution. Therefore, a large amount of photo-generated electrons can be transferred to the Pt electrode, so that the BMO @ BVO heterojunction photoelectrode has better photoelectrochemistry water splitting performance.

And as can be seen from the above examples, the obtained high-efficiency Bi₂MoO₆Coated BiVO₄The heterojunction photoelectrode system is prepared by experiments on 4 samples with different precursor concentrations, and when the precursor concentration is 2mM, BMO @ BVO-2 has the maximum photoproduction current density in a scanning voltage range. Due to BiVO₄And Bi₂MoO₆Has good energy band matching degree, and proper amount of Bi₂MoO₆Coating to BiVO₄In the above process, a heterojunction electric field is formed at the contact interface of the two, and the photogenerated carriers are efficiently and orderly separated under the action of the heterojunction electric field; at the same time, a proper amount of Bi₂MoO₆Coating and reserving BiVO₄The porous structure of the photoelectrode film is beneficial to full contact between a photoelectrode material and an electrolyte solution, so that a photoproduction hole can be quickly transferred out to react with the electrolyte solution to be consumed, and therefore, the BMO @ BVO-2 has the best photoelectrochemical property. For BMO @ BVO-1, Bi₂MoO₆Has a small coating amount of BiVO₄And Bi₂MoO₆The heterojunction electric field formed between the two is not enough to efficiently separate photon-generated carriers, so that the BMO @ BVO-1 is second to the BMO @ BVO-2 but is better than the BiVO₄And Bi₂MoO₆Photoelectrochemical properties of (a). And for BMO @ BVO-3 and BMO @ BVO-4 photoelectrodes, the coated Bi₂MoO₆In a large amount, and can form a heterojunction to accelerate the separation of photogenerated carriers, but the excess Bi₂MoO₆Block BiVO₄The porous structure of the photoelectrode film is not beneficial to the full contact of the photoelectrode material and the electrolyte solution, so as to cause photoproduction holesCan not be timely and effectively reacted with an electrolyte solution to be consumed, so that BMO @ BVO-3 and BMO @ BVO-4 have the same BMO @ BVO-2 but are better than BiVO₄And Bi₂MoO₆Photoelectrochemical properties of (a).

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications can be made without departing from the principles of the invention and these modifications are to be considered within the scope of the invention.

Claims

1. High-efficiency Bi₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: 1) soaking FTO conductive glass serving as a substrate into the deposition solution of the BiOI, forming a BiOI film on the substrate through electrochemical deposition, and forming a pure BiVO on the surface film of the substrate through a spot coating and annealing method₄A film;

2. Highly potent Bi as claimed in claim 1₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: the deposition solution of the BiOI in the step 1) is Bi (NO)₃)₃·5H₂Dissolving O in KI solution to obtain mixed solution A, wherein Bi (NO) in the mixed solution A₃)₃·5H₂The final concentration of O is 0.02-0.06mol/L, the final concentration of KI is 0.02-0.06mol/L, and the pH value of the mixed solution A is adjusted to 1.7-2.0; dissolving p-benzoquinone in ethanol to obtain a mixed solution B with the final concentration of the p-benzoquinone of 0.1-0.3 mol/L; and mixing the mixed solution A and the mixed solution B according to the volume ratio of 5:1-5: 3.

3. Highly potent Bi as claimed in claim 1₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: after the substrate forms the BiOI film in the step 1), vanadium acetylacetonate passes throughPoint coating on the surface of BiOI, drying at 60-80 ℃, annealing at 400-450 ℃ for 2-5h, washing, and drying at room temperature, even if the film on the surface of the substrate forms pure BiVO₄And (3) a membrane.

4. Highly potent Bi as claimed in claim 1₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: said step 2) adding Bi (NO)₃)₃·5H₂O and Na₂MoO₄·2H₂Adding O into ethylene glycol respectively, mixing the two solutions in a volume ratio of 1:1 to obtain a mixed solution A, and adding ethanol to obtain a deposition solution; wherein, Bi (NO) in the ethylene glycol₃)₃·5H₂The final concentration of O is 2-8mol/L, Na₂MoO₄·2H₂The final concentration of O is 1-4 mol/L; the volume ratio of the mixed solution A to the ethanol is 1:5-1: 3.

5. Bi of high efficiency according to any of claims 1 to 4₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps:

6. Highly potent Bi as claimed in claim 5₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: the electrodeposition condition is a three-electrode system, 300s of deposition is carried out under the constant potential of-0.1V, and a BiOI film is formed on the surface of the substrate, wherein the electrode system is FTO 1 x 5cm²Is a working electrode, Ag/AgCl is a reference electrode, and Pt is a counter electrode.

7. Highly potent Bi as claimed in claim 5₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: pure BiVO is not formed on the substrate in the step 2)₄The surface of the membrane is immersed downwards in the deposition solution for reaction.

8. Highly potent Bi as claimed in claim 5₂MoO₆Coated BiVO₄The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: and cooling after the reaction, taking out, washing with water and ethanol for several times in sequence, and drying at 80 ℃ for 4 hours to obtain the product.