CN115094459B

CN115094459B - Nickel cobaltate/magnesium oxide/bismuth vanadate photo-anode and preparation method thereof

Info

Publication number: CN115094459B
Application number: CN202210666395.3A
Authority: CN
Inventors: 王其召; 王李娜; 陈凯怡; 梅琼; 丁飞; 黄静伟
Original assignee: Changan University
Current assignee: Changan University
Priority date: 2022-06-14
Filing date: 2022-06-14
Publication date: 2023-05-30
Anticipated expiration: 2042-06-14
Also published as: CN115094459A

Abstract

The invention discloses a NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode and the preparation method thereof comprises the following steps: deposition of BiVO on a substrate material ₄ The film is then deposited with an electrophoretic deposition method to form MgO film, and the MgO/BiVO is prepared by cleaning, drying and calcining in sequence ₄ An electrode; spin-coating NiCo ₂ O ₄ Drying the precursor solution, and calcining at 250-350deg.C for 3.5-4.5 hr to obtain NiCo ₂ O ₄ /MgO/BiVO ₄ A photo-anode. NiCo prepared by the invention ₂ O ₄ /MgO/BiVO ₄ The highest photocurrent density generated by the photoanode at 1.23V vs. RHE is 4.6mA.cm ^‑2 About NiCo ₂ O ₄ /BiVO ₄ 1.5 times of photo anode, mgO/BiVO ₄ 1.7 times photo anode and BiVO ₄ 2.8 times the photoanode.

Description

Nickel cobaltate/magnesium oxide/bismuth vanadate photo-anode and preparation method thereof

Technical Field

The present invention relates to photoelectrochemistryThe technical field of battery preparation, in particular to a NiCo ₂ O ₄ /MgO/BiVO ₄ A photoanode and a method for preparing the same.

Background

Photoelectrochemical cell technology (PEC) is a novel cell technology which directly utilizes light energy and converts the light energy into chemical energy, and generally consists of a photoelectrode with photoactivity, electrolyte and a circuit, has a simple structure, is widely applied to the field of solar energy conversion, and can directly generate H through solar energy conversion in a photoelectrochemical hydrogen production system ₂ Is considered one of the most attractive and cost-effective techniques for producing "green" fuels. BiVO (BiVO) ₄ The photo-anode material has the advantages of small band gap, good band edge position, low initial potential, high theoretical water decomposition efficiency and the like, is one of the photo-anode materials which are most attractive at present and are used for PEC water decomposition hydrogen production, and theoretically, biVO under AM1.5G simulated sunlight ₄ The density of the water oxidation photocurrent of the water oxidation reactor is 7.5 mA.cm when the density is 1.23Vvs. RHE ^-2 However, the experimental values are far lower than this result, mainly because of BiVO ₄ Is short, causes severe electron-hole recombination, and at the same time, biVO ₄ The surface water oxidation kinetics is also poor, and it is difficult to maintain high-efficiency water decomposition for a long time. Thus, biVO ₄ Having good hole conductivity and excellent charge transfer are critical for water oxidation of the photoanode. High efficiency oxygen evolution promoters (OECs), e.g. Co ₃ O ₄ 、FeCoO _X 、NiCo ₂ O ₄ 、MnCo ₂ O ₄ And ZnCo ₂ O ₄ For accelerating BiVO ₄ To achieve an impressive positive effect of efficient water splitting, loading OEC on BiVO by an electrophoretic deposition process ₄ After the surface, biVO is modified ₄ Photoanode has excellent PEC water splitting activity and excellent hydrogen production performance, however OEC and BiVO ₄ The interface of the catalyst has the problems of carrier recombination or trapping by interface defects, and the like, so that the water decomposition capacity is limited.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a NiCo ₂ O ₄ /MgO/BiVO ₄ The photoanode and the preparation method thereof are used for solving the problem of poor water splitting performance of the photoanode in the prior art.

The technical scheme for solving the technical problems is as follows: providing a NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photo-anode comprises the following steps:

(1) Deposition of BiVO on a substrate material ₄ Thin film, biVO is prepared ₄ An electrode;

(2) BiVO prepared in step (1) ₄ BiVO of electrode ₄ Depositing MgO film on the film by electrophoresis deposition, cleaning, drying and calcining to obtain MgO/BiVO ₄ An electrode;

(3) MgO/BiVO obtained in the step (2) ₄ Spin-coating NiCo on the electrode ₂ O ₄ Drying the precursor solution, calcining at 250-350deg.C for 3.5-4.5 hr to obtain NiCo ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

The beneficial effects of the invention are as follows: the invention successfully combines the MgO passivation layer and the NiCo by a simple over-electrophoretic deposition method and a spin-coating method ₂ O ₄ Oxygen evolution co-catalyst layer is supported on BiVO ₄ On the photo-anode, successfully prepare NiCo ₂ O ₄ /MgO/BiVO ₄ Photoanode (nickel cobaltate/magnesium oxide/bismuth vanadate photoanode). First, modified BiVO ₄ The light utilization rate can be improved, and the photoelectric utilization efficiency is further improved; second, niCo ₂ O ₄ The Ni/Co bimetallic active site accelerates the process of decomposing water by PEC, the high valence state of Ni (II)/Co (II) is oxidized into trivalent Co and trivalent Ni, and then is further oxidized into tetravalent Co and tetravalent Ni under the action of holes, and unstable Ni (IV) and Co (IV) are respectively reduced into Ni (II) and Co (II) in the water decomposition process; again, the addition of MgO passivation layer can promote BiVO ₄ The charge transfer on the surface accelerates the transfer of charge carriers and improves the charge injection and separation efficiency; finally, in BiVO ₄ MgO and NiCo ₂ O ₄ Under the synergistic effect of (2), not only the initial overpotential of the reaction can be reduced, but also the recombination efficiency of electrons and holes can be reduced, niCo ₂ O ₄ /MgO/BiVO ₄ The significant improvement in PEC water splitting performance of photoanode can be attributed to the catalytic/absorptive/synergistic triple function. The highest photocurrent density generated by the photoanode prepared by the invention at the time of 1.23V vs. RHE is 4.6 mA.cm ^-2 About NiCo ₂ O ₄ /BiVO ₄ 1.5 times of photo anode, mgO/BiVO ₄ 1.7 times photo anode and BiVO ₄ 2.8 times the photoanode.

Based on the technical scheme, the invention can also be improved as follows:

further, in the step (1), the substrate material is FTO glass.

Further, in step (1), biVO is deposited on the substrate material ₄ The specific method of the film is as follows: pretreating a substrate material, depositing a BiOI film on the substrate material by an electrophoretic deposition method, cleaning, drying, and then dripping V ⁵⁺ Source, calcination, and preparation of BiVO ₄ A film.

Further, the specific method for pretreatment is as follows: placing a base material in a volume ratio of 0.8-1.2:0.8-1.2:1, acetone and distilled water, ultrasonic treating for 25-35min, washing, and drying.

Further, an electrophoretic deposition solution for depositing a BiOI film is prepared by the following method: bi (NO) ₃ ) ₃ ·5H ₂ O is dissolved in KI solution, the pH value is regulated to be 1-2, then the ethanol solution of p-benzoquinone is added, and the mixture is mixed to prepare the electrophoretic deposition solution.

Further, the concentration of KI solution is 0.3-0.5mol/L, the concentration of p-benzoquinone in ethanol solution is 0.2-0.3mol/L, bi (NO) ₃ ) ₃ ·5H ₂ O, KI and p-benzoquinone in the weight-volume ratio of 0.8-1.1g:45-55mL:18-22mL.

Further, the electrophoretic deposition conditions for depositing the BiOI film are: the potential area is-0.13-0V, the scanning speed is 4-6mV/s, and the electrodeposition turns are 8-12.

Further, V ⁵⁺ The source is VO (acac) with the concentration of 0.1-0.3mol/L ₂ Is a solution of DMSO in (B).

Further, drop coating V ⁵⁺ The volume of the source is 80-120. Mu.L.

Further, the calcination conditions were: heating to 400-500 deg.C at a rate of 1-3 deg.C/min for 1.5-2.5 hr.

Further, after calcination, the substrate material with the film is immersed into NaOH solution with the concentration of 0.8-1.2mol/L, stirred for 1.5-2.5 hours, washed and dried to obtain BiVO ₄ A film.

Further, the electrophoretic deposition conditions in step (2) are: mgNO with deposition liquid of 0.8-1.2mol/L ₃ ·6H ₂ O solution, potential-0.6-0.8V, deposition time 10-60s.

Further, the calcining conditions in the step (2) are as follows: heating to 450-550deg.C at a rate of 1-3deg.C/min for 0.8-1.2 hr.

Further, niCo in step (3) ₂ O ₄ The precursor solution is prepared by the following method: niCo is prepared ₂ O ₄ Dispersing the precursor in a mixed solution of DMF and Nafion to prepare NiCo ₂ O ₄ A precursor solution; wherein NiCo ₂ O ₄ The mass volume ratio of DMF and Nafion is 0.08-0.12g:8-12mL:0.2-0.4mL.

Further, niCo ₂ O ₄ The precursor is prepared by the following steps: coCl is to be processed ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ Dissolving O and urea in deionized water to form a mixed solution, stirring, performing hydrothermal reaction at 100-150deg.C for 5-7h, soaking in water, and drying to obtain NiCo ₂ O ₄ A precursor.

Further, deionized water is used for soaking for 3-10min.

Further, coCl in the mixed solution ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ The concentrations of O and urea are 8-12mmol/L, 4-6mmol/L and 45-55mmol/L, respectively.

Further, the spin coating conditions in step (3) are: spin coating at 1800-2200r/min for 15-25s.

Further, spin-coating NiCo in step (3) ₂ O ₄ The volume of the precursor solution is 80-120. Mu.L.

Further, the drying temperature in the step (3) is 58-62 ℃.

The invention also provides the NiCo ₂ O ₄ /MgO/BiVO ₄ NiCo prepared by preparation method of photo-anode ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

The invention also provides the NiCo ₂ O ₄ /MgO/BiVO ₄ Use of a photoanode in the manufacture of a photoelectrochemical cell.

The invention also provides a photoelectrochemical cell comprising the NiCo ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

The invention has the following beneficial effects:

1. after the MgO passivation layer is introduced, biVO ₄ The separation and migration rate of photo-generated carriers on the surface of the photo-anode are improved, and NiCo ₂ O ₄ Can be used as an active site to accelerate the water oxidation of the photo-anode, and the two can synergistically improve the water decomposition performance of the photo-anode.

2. NiCo prepared by the invention ₂ O ₄ /MgO/BiVO ₄ The highest photocurrent density generated by the photoanode at 1.23V vs. RHE is 4.6mA.cm ^-2 About NiCo ₂ O ₄ /BiVO ₄ 1.5 times of photo anode, mgO/BiVO ₄ 1.7 times photo anode and BiVO ₄ 2.8 times the photoanode.

3. The preparation method provided by the invention is simple and answering, the raw materials are easy to obtain, and the operability is strong.

Drawings

FIG. 1 is an SEM image of the electrode and photoanode prepared according to example 1;

FIG. 2 is a TEM image and an HRTEM image of the photoanode obtained in example 1;

FIG. 3 is an XPS full spectrum of the photoanode prepared in example 1;

FIG. 4 is a chart of Bi 4f spectra in FIG. 2;

FIG. 5 is a V2p spectrum of FIG. 2;

FIG. 6 is a graph of the O1s spectrum of FIG. 2;

FIG. 7 is a graph of the Mg 1s spectrum of FIG. 2;

FIG. 8 is a graph of Ni 2p spectra in FIG. 2;

FIG. 9 is a graph of the Co 2p spectrum of FIG. 2;

FIG. 10 is an XRD pattern of the photo-anode prepared in example 1 and comparative examples 1-3;

FIG. 11 is an ultraviolet-visible diffuse reflectance spectrum of the photo-anode prepared in example 1 and comparative examples 1-3;

FIG. 12 is a graph of the Kubelka-Munk transformed reflectance spectrum of FIG. 11;

FIG. 13 is a graph of LSV under light conditions for the photoanode prepared in example 1 and comparative examples 1-3;

FIG. 14 is a LSV graph of the photo-anode non-illumination conditions produced in example 1 and comparative examples 1-3;

FIG. 15 is a graph of I-t at the ON/OFF cycle of light Yang Jiguang produced in example 1 and comparative examples 1-3;

FIG. 16 is an EIS graph of the photo-anode prepared in example 1 and comparative examples 1-3;

FIG. 17 is an IPCE spectrum of the photo-anode prepared in example 1 and comparative examples 1-3;

FIG. 18 is an ABPE graph of photoanodes prepared in example 1 and comparative examples 1-3;

FIG. 19 is a graph showing charge injection efficiency of the photoanode fabricated in example 1 and comparative examples 1-3;

FIG. 20 is a graph showing charge separation efficiency of the photoanodes fabricated in example 1 and comparative examples 1 to 3;

FIG. 21 is a graph of LSV under photo-anode illumination for the preparations of examples 1, 4-6 and comparative example 1;

FIG. 22 is a LSV graph of the photo-anode of examples 1, 4-6 and comparative example 1 without illumination;

FIG. 23 is an on/off cycle I-t graph of light Yang Jiguang produced in examples 1, 4-6 and comparative example 1;

FIG. 24 is a graph showing EIS curves of photoanodes obtained in examples 1, 4-6 and comparative example 1;

FIG. 25 is a graph showing LSV under light from the photo-anode of examples 1, 7-8 and comparative example 1;

FIG. 26 is a graph showing LSV curves for anodes prepared in examples 1, 7-8 and comparative example 1 without illumination;

FIG. 27 is an on/off cycle I-t graph of light Yang Jiguang produced in examples 1, 7-8 and comparative example 1;

FIG. 28 is a graph showing EIS curves of photoanodes obtained in examples 1, 7-8 and comparative example 1;

FIG. 29 is an OCPD test chart for photoanodes produced in example 1 and comparative examples 1-3;

FIG. 30 is an enlarged view of the exact moment of the light of FIG. 29;

FIG. 31 is a graph showing the retardation of the photo-anode-cathode photocurrent curves obtained in example 1 and comparative examples 1-3;

FIG. 32 is a graph showing the density of states of the photo-anode and MgO prepared in comparative example 1-2;

FIG. 33 is a view showing H of the photoanode obtained in comparative example 1 ₂ And O ₂ Yield;

FIG. 34 is a photograph of H of the photoanode prepared in example 1 ₂ And O ₂ Yield and faraday efficiency.

Detailed Description

The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Example 1:

NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps:

(1) Pretreatment of a substrate: placing FTO glass in a volume ratio of 1:1:1, in the mixed solution of isopropanol, acetone and distilled water, carrying out ultrasonic treatment for 30min, taking out, washing with distilled water, and then placing in an oven for drying for standby;

(2) Preparing an electrophoretic deposition solution: bi (NO) ₃ ) ₃ ·5H ₂ O is dissolved in KI solution, the pH value is regulated to 1.6, then ethanol solution of p-benzoquinone is added, and the mixture is mixed to prepare electrophoretic deposition solution; wherein the concentration of the KI solution is 0.4mol/L, the concentration of the ethanol solution of the p-benzoquinone is 0.23mol/L, and Bi (NO ₃ ) ₃ ·5H ₂ O, KI and p-benzoquinone in ethanol in a mass to volume ratio of 0.97g:50mL:20mL;

(3)BiVO ₄ electrode preparation: adopting a typical three-electrode system, taking a platinum electrode as a counter electrode, taking pretreated FTO conductive glass as a working electrode and Ag/AgCl as a reference electrode, immersing the three electrodes into the electrophoretic deposition liquid prepared in the step (2), depositing in a potential area of-0.08V by Cyclic Voltammetry (CV), electrodepositing for 10 circles at a scanning rate of 5mV/s to obtain a BiOI film, thoroughly cleaning with deionized water, drying the BiOI film in an oven, and dripping 100 mu L of V ⁵⁺ Heating to 450deg.C at a rate of 2deg.C/min, maintaining for 2 hr, soaking in 1mol/L NaOH solution, stirring for 2 hr, washing with distilled water completely, and air drying to obtain BiVO ₄ An electrode, wherein V ⁵⁺ The source is VO (acac) with the concentration of 0.2mol/L ₂ Is a DMSO solution;

(4)MgO/BiVO ₄ electrode preparation: biVO prepared in step (3) ₄ The electrode is a working electrode, the platinum sheet is a counter electrode, the Ag/AgCl is a reference electrode, and the three electrodes are immersed into the electrophoretic deposition solution (MgNO of 1mol/L ₃ ·6H ₂ O solution), depositing for 20s at-0.7V potential, washing the electrode with deionized water and drying, placing the electrode in a muffle furnace, heating to 500 ℃ at a speed of 2 ℃/min, and maintaining for 1h to obtain MgO/BiVO ₄ An electrode;

(5)NiCo ₂ O ₄ /MgO/BiVO ₄ preparation of photoanode

(5.1)NiCo ₂ O ₄ Precursor preparation: coCl is to be processed ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ Dissolving O and urea in deionized water to form a mixed solution, stirring until a bright powder color solution is formed, transferring into a stainless steel autoclave lined with Teflon, performing hydrothermal reaction for 6 hours at 120 ℃ to obtain powder, soaking the powder in deionized water for 5min, and drying to obtain NiCo ₂ O ₄ A precursor; wherein, coCl in the mixed solution ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ The concentrations of O and urea are 10mmol/L, 5mmol/L and 50mmol/L respectively;

(5.2)NiCo ₂ O ₄ precursor solution preparation: will beNiCo ₂ O ₄ Dispersing the precursor in a mixed solution of DMF and Nafion to prepare NiCo ₂ O ₄ A precursor solution; wherein NiCo ₂ O ₄ The mass-volume ratio of DMF and Nafion is 0.1g:10mL:0.3mL;

(5.3) MgO/BiVO obtained in the step (4) ₄ Spin-coating 100 μL of NiCo on the electrode at a rotation speed of 2000r/min ₂ O ₄ Spin-coating the precursor solution for 20s, drying at 60deg.C in a vacuum drying oven, and calcining at 300deg.C for 4 hr to obtain NiCo ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

Example 2:

(1) Pretreatment of a substrate: FTO glass was placed at a volume ratio of 0.8:0.8:1, in the mixed solution of isopropanol, acetone and distilled water, carrying out ultrasonic treatment for 25min, taking out, washing with distilled water, and then placing in an oven for drying for standby;

(2) Preparing an electrophoretic deposition solution: bi (NO) ₃ ) ₃ ·5H ₂ O is dissolved in KI solution, the pH value is regulated to 1, then the ethanol solution of p-benzoquinone is added, and the mixture is mixed to prepare electrophoretic deposition solution; wherein the concentration of the KI solution is 0.3mol/L, the concentration of the ethanol solution of the p-benzoquinone is 0.2mol/L, and Bi (NO ₃ ) ₃ ·5H ₂ O, KI solution and p-benzoquinone in ethanol solution in a mass-volume ratio of 0.8g:45mL:18mL;

(3)BiVO ₄ electrode preparation: adopting a typical three-electrode system, taking a platinum electrode as a counter electrode, taking pretreated FTO conductive glass as a working electrode and Ag/AgCl as a reference electrode, immersing the three electrodes into the electrophoretic deposition liquid prepared in the step (2), depositing in a potential area of-0.13V by Cyclic Voltammetry (CV), electrodepositing for 12 circles at a scanning rate of 4mV/s to obtain a BiOI film, thoroughly cleaning with deionized water, drying the BiOI film in an oven, and then dripping 80 mu L of V ⁵⁺ A source, heated to 400 ℃ at a rate of 1 ℃/min, kept for 2.5h, immersed in 0.8mol/L NaOH solution and stirred for 1.5h, finally completely treated with distilled waterWashing and drying in air to obtain BiVO ₄ An electrode, wherein V ⁵⁺ The source is VO (acac) with the concentration of 0.1mol/L ₂ Is a DMSO solution;

(4)MgO/BiVO ₄ electrode preparation: biVO prepared in step (3) ₄ The electrode is a working electrode, the platinum sheet is a counter electrode, the Ag/AgCl is a reference electrode, and the three electrodes are immersed into the electrophoretic deposition solution (MgNO of 0.8mol/L ₃ ·6H ₂ O solution), depositing for 60s at-0.6V potential, washing the electrode with deionized water and drying, placing the electrode in a muffle furnace, heating to 450 ℃ at a speed of 1 ℃/min, and maintaining for 0.8h to obtain MgO/BiVO ₄ An electrode;

(5)NiCo ₂ O ₄ /MgO/BiVO ₄ preparation of photoanode

(5.1)NiCo ₂ O ₄ Precursor preparation: coCl is to be processed ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ Dissolving O and urea in deionized water to form a mixed solution, stirring until a bright powder color solution is formed, transferring into a stainless steel autoclave lined with Teflon, performing hydrothermal reaction at 100 ℃ for 7h to obtain powder, soaking the powder in deionized water for 3min, and drying to obtain NiCo ₂ O ₄ A precursor; wherein, coCl in the mixed solution ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ The concentrations of O and urea are 8mmol/L, 4mmol/L and 45mmol/L respectively;

(5.2)NiCo ₂ O ₄ precursor solution preparation: niCo is prepared ₂ O ₄ Dispersing the precursor in a mixed solution of DMF and Nafion to prepare NiCo ₂ O ₄ A precursor solution; wherein NiCo ₂ O ₄ The mass-volume ratio of DMF and Nafion is 0.08g:8mL:0.2mL;

(5.3) MgO/BiVO obtained in the step (4) ₄ Spin-coating 80. Mu.L of NiCo on the electrode at 1800r/min ₂ O ₄ Spin-coating the precursor solution for 25s, drying at 58 ℃ in a vacuum drying oven, and calcining at 250 ℃ for 4.5h to obtain NiCo ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

Example 3:

(1) Pretreatment of a substrate: FTO glass was placed at a volume ratio of 1.2:1.2:1, in the mixed solution of isopropanol, acetone and distilled water, carrying out ultrasonic treatment for 35min, taking out, washing with distilled water, and then placing in an oven for drying for standby;

(2) Preparing an electrophoretic deposition solution: bi (NO) ₃ ) ₃ ·5H ₂ O is dissolved in KI solution, the pH value is regulated to 2, then the ethanol solution of p-benzoquinone is added, and the mixture is mixed to prepare electrophoretic deposition solution; wherein the concentration of the KI solution is 0.5mol/L, the concentration of the ethanol solution of the p-benzoquinone is 0.3mol/L, and Bi (NO ₃ ) ₃ ·5H ₂ O, KI the mass-volume ratio of the ethanol solution of the solution to the p-benzoquinone is 1.1g:55mL:22mL;

(3)BiVO ₄ electrode preparation: adopting a typical three-electrode system, taking a platinum electrode as a counter electrode, taking pretreated FTO conductive glass as a working electrode and Ag/AgCl as a reference electrode, immersing the three electrodes into the electrophoretic deposition liquid prepared in the step (2), depositing in a potential area of 0V by Cyclic Voltammetry (CV), electrodepositing for 12 circles at a scanning rate of 6mV/s to obtain a BiOI film, thoroughly cleaning with deionized water, drying the BiOI film in a baking oven, and then dripping 120 mu L of V ⁵⁺ Heating to 500deg.C at a rate of 3deg.C/min, maintaining for 1.5 hr, soaking in 1.2mol/L NaOH solution, stirring for 2.5 hr, washing with distilled water, and oven drying in air to obtain BiVO ₄ An electrode, wherein V ⁵⁺ The source is VO (acac) with the concentration of 0.3mol/L ₂ Is a DMSO solution;

(4)MgO/BiVO ₄ electrode preparation: biVO prepared in step (3) ₄ The electrode is a working electrode, the platinum sheet is a counter electrode, the Ag/AgCl is a reference electrode, and the three electrodes are immersed into the electrophoretic deposition solution (MgNO of 1.2mol/L ₃ ·6H ₂ O solution), depositing for 10s at-0.8V potential, washing the electrode with deionized water and drying, placing the electrode in a muffle furnace, heating to 550deg.C at a rate of 1-3deg.C/min, and maintaining for 0.8hObtaining MgO/BiVO ₄ An electrode;

(5)NiCo ₂ O ₄ /MgO/BiVO ₄ preparation of photoanode

(5.1)NiCo ₂ O ₄ Precursor preparation: coCl is to be processed ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ Dissolving O and urea in deionized water to form a mixed solution, stirring until a bright powder color solution is formed, transferring into a stainless steel autoclave lined with Teflon, performing hydrothermal reaction at 150 ℃ for 5 hours to obtain powder, soaking the powder in deionized water for 10min, and drying to obtain NiCo ₂ O ₄ A precursor; wherein, coCl in the mixed solution ₂ ·6H ₂ O、NiCl ₂ ·6H ₂ The concentrations of O and urea are 12mmol/L, 6mmol/L and 55mmol/L respectively;

(5.2)NiCo ₂ O ₄ precursor solution preparation: niCo is prepared ₂ O ₄ Dispersing the precursor in a mixed solution of DMF and Nafion to prepare NiCo ₂ O ₄ A precursor solution; wherein NiCo ₂ O ₄ The mass-volume ratio of DMF and Nafion is 0.12g:12mL:0.4mL;

(5.3) MgO/BiVO obtained in the step (4) ₄ Spin-coating 120 μL of NiCo on the electrode at 2200r/min ₂ O ₄ Spin-coating the precursor solution for 15s, drying in a vacuum drying oven at 62 ℃, and calcining for 3.5h at 350 ℃ to obtain NiCo ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

Example 4:

NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps: mgO/BiVO ₄ The electrode was prepared with a deposition time of 10s and the rest of the procedure was as in example 1.

Example 5:

NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps: mgO/BiVO ₄ The electrode was prepared with a deposition time of 40s and the rest of the procedure was as in example 1.

Example 6:

NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps: mgO/BiVO ₄ The electrode was prepared with a deposition time of 60s and the rest of the procedure was as in example 1.

Example 7:

NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps: mgO/BiVO ₄ The electrode was prepared with a deposition potential of-0.6V and the rest of the procedure was as in example 1.

Example 8:

NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps: mgO/BiVO ₄ The electrode was prepared with a deposition potential of-0.8V and the rest of the procedure was as in example 1.

Comparative example 1:

BiVO (binary organic acid) ₄ The preparation method of the photoanode comprises the following steps: the procedure was as in steps (1) - (3) of example 1. Comparative example 2:

MgO/BiVO ₄ The preparation method of the photoanode comprises the following steps: the procedure was as in steps (1) - (4) of example 1.

Comparative example 3:

NiCo ₂ O ₄ /BiVO ₄ The preparation method of the photo-anode comprises the following steps: the procedure is as in example 1, but without step (4).

Test examples

1. Characterization analysis

1. BiOI and BiVO obtained in example 1 ₄ 、MgO/BiVO ₄ And NiCo ₂ O ₄ /MgO/BiVO ₄ Scanning Electron Microscope (SEM) analysis was performed, and the results are shown in FIG. 1 (wherein a is BiOI and b is BiVO) ₄ C is MgO/BiVO ₄ D is NiCo ₂ O ₄ /MgO/BiVO ₄ ). As can be seen from FIG. 1, the BiOI film shows a typical two-dimensional plate structure placed vertically, with a thickness of 30-40nm; after being calcined, biOI is completely converted into BiVO with nano holes on the surface ₄ A film; many irregular platelets were observed on the surface as MgO was depositedThe contact surface between the shaped particles and the outside is large; interestingly, when MgO/BiVO ₄ With NiCo ₂ O ₄ When combined, niCo ₂ O ₄ The sample has a flower-like appearance of the superstructure, and can be seen from the flower-like NiCo ₂ O ₄ Firmly and densely fixed on the MgO of the intermediate layer, the structure reduces the possibility of falling off, and the PEC activity can be further improved.

2. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ The photo-anode was subjected to Transmission Electron Microscope (TEM) and High Resolution Transmission Electron Microscope (HRTEM) analyses, and the results are shown in fig. 2 (where e is a TEM image and f is an HRTEM image). As can be seen from FIG. 2, mgO and NiCo ₂ O ₄ And BiVO ₄ Close contact, at the same time, 0.30nm corresponds to BiVO ₄ (121) Lattice fringes of the facets, lattice spacing of 0.25nm, may be a good indication of NiCo ₂ O ₄ The lattice spacing of 0.34nm belongs to MgO.

3. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ The photo-anode was subjected to surface element composition and chemical valence analysis by X-ray photoelectron spectroscopy (XPS), and the results are shown in fig. 3 to 9. As can be seen from FIG. 3, niCo ₂ O ₄ /MgO/BiVO ₄ The film is composed of Ni, co, mg, bi, V and O. As can be seen from FIG. 4, for the Bi 4f spectrum, bi 4f _5/2 And Bi 4f _7/2 Peaks of (2) are observed at 164.5eV and 159.2eV, respectively. As can be seen from FIG. 5, for the V2p spectrum, the peaks at 516.9eV and 524.3eV are attributed to V2p, respectively _3/2 And V2p _1/2 . As can be seen from FIG. 6, two peaks are clearly seen in the O1s spectrum, including lattice oxygen (OL, 530.7 eV) and adsorbed oxygen (H ₂ O,532.9 eV). As can be seen from FIG. 7, the binding energy of Mg 1s is 1304.6eV, which is derived from Mg in MgO ²⁺ . As can be seen from FIG. 8, peaks centered on 873.8eV (satellite peak 880.24 eV) and 856.3eV (satellite peak 861.87 eV) correspond to Ni 2p, respectively _1/2 And Ni 2p _3/2 These four peaks are Ni ²⁺ Is a characteristic peak of (2). As can be seen from FIG. 9, co 2p _1/2 And Co 2p _3/2 The signals of (2) are located at 797.1eV and 781.2eV, respectively, indicating that Co is Co-to-Co ²⁺ Is present.

4. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ Photo anode, biVO prepared in comparative example 1 ₄ Photo-anode, mgO/BiVO prepared in comparative example 2 ₄ Photoanode and NiCo produced in comparative example 3 ₂ O ₄ /BiVO ₄ The photo-anode was subjected to a crystal structure analysis by X-ray diffraction (XRD), and the result is shown in fig. 10. As can be seen from fig. 10, in addition to the FTO substrate (SnO ₂ JCPDS No. 46-1088), all characteristic diffraction peaks are directed to monoclinic BiVO ₄ (JCPDS No. 14-0688), which illustrates the successful preparation of BiVO 4; in NiCo ₂ O ₄ /MgO/BiVO ₄ 、NiCo ₂ O ₄ /BiVO ₄ And MgO/BiVO ₄ In the XRD pattern of the composite, no NiCo was observed ₂ O ₄ And diffraction peaks of MgO, possibly due to its low content.

5. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ Photo anode, biVO prepared in comparative example 1 ₄ Photo-anode, mgO/BiVO prepared in comparative example 2 ₄ Photoanode and NiCo produced in comparative example 3 ₂ O ₄ /BiVO ₄ Photoanode, light absorption capacity assessment by ultraviolet-visible diffuse reflection (UV-vis DRS), results are shown in fig. 11-12. As can be seen from FIG. 11, biVO obtained in comparative example 1 ₄ The photoanode exhibits strong absorption edges around 500 nm; and BiVO ₄ In contrast, mgO/BiVO obtained in comparative example 2 ₄ The absorption edge of (2) does not change significantly, while the visible light region of 500-800nm shows a relatively high visible light absorption intensity; introduction of NiCo ₂ O ₄ After that, a clear red-shifted edge was observed, indicating that the NiCo prepared in comparative example 3 ₂ O ₄ /BiVO ₄ And NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ The light absorption of the composite is enhanced. As can be seen from fig. 12, biVO ₄ 、MgO/BiVO ₄ 、NiCo ₂ O ₄ /BiVO ₄ And NiCo ₂ O ₄ /MgO/BiVO ₄ Band gap energies of 2.43eV, 2.37eV and 2.35eV, respectively, illustrate further enhancement of absorption of light by the modified BiVO 4.

2. Photoelectrochemical property analysis

1. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ Photo anode, biVO prepared in comparative example 1 ₄ Photo-anode, mgO/BiVO prepared in comparative example 2 ₄ Photoanode and NiCo produced in comparative example 3 ₂ O ₄ /BiVO ₄ And (3) a photo-anode, and performing PEC performance analysis. The specific method comprises the following steps: the test is carried out by adopting a three-electrode system, wherein a Pt sheet is used as a counter electrode, an Ag/AgCl electrode is used as a reference electrode, a photo-anode is used as a working electrode, and an electrolyte is used as a reference electrode: contains 1mol/L potassium borate buffer solution (pH 9.5), light source: the AM1.5G sunlight is configured, a 300W xenon lamp (Beijing Porphy) of the optical filter is arranged, and the light intensity is 1 sun (namely 100mW/cm ² ) The test parameters were recorded using CM660E electrochemical workstation. Before testing, argon (purity 99.999%) was bubbled for half an hour to remove dissolved oxygen from the electrolyte, as oxygen is prone to interface reactions, ultimately affecting the actual photoelectric response. All measurements were made with Ag/AgCl as reference electrode and the final test potential was converted to a reversible standard hydrogen electrode (RHE) according to the formula: e (E) _RHE ＝E _Ag/AgCl +0.197+0.059pH。

1.1 by measuring J-V curves under AM1.5G illumination and no illumination, respectively, the scan rate was 5mV/s and the frequency was 1KHz under no illumination, the results are shown in FIGS. 13-14.

As can be seen from FIG. 13, the MgO/BiVO obtained in comparative example 2 ₄ Photoanode and NiCo produced in comparative example 3 ₂ O ₄ /BiVO ₄ When the photoanode is at 1.23V vs. RHE, the current density can be respectively increased to 2.7 mA.cm ^-2 And 3.1 mA.cm ^-2 This is BiVO obtained in comparative example 1, respectively ₄ 1.7 times and 1.9 times (1.23V vs. RHE 1.6mA.cm) ^-2 ) The method comprises the steps of carrying out a first treatment on the surface of the Whereas NiCo prepared in example 1 ₂ O ₄ /MgO/BiVO ₄ The photocurrent density of the photoanode at 1.23V vs. RHE was 4.6mA.cm ^-2 Ratio NiCo ₂ O ₄ /BiVO ₄ The photo anode is 1.5 times higher than BiVO ₄ The photo anode is 3.1 times higher; in addition, with naked BiVO ₄ In contrast, mgO-modified BiVO ₄ The photoanode causes a reduction in the overpotential required for water oxidation and a cathodic potential at the onsetPolar offset, a phenomenon that may be attributed to BiVO ₄ The above results clearly show that the passivation layer MgO is improving BiVO ₄ Plays an important role in PEC performance.

As can be seen from FIG. 14, niCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ Photo anode comparison NiCo prepared in comparative example 3 ₂ O ₄ /BiVO ₄ MgO/BiVO obtained in comparative example 2 ₄ And BiVO obtained in comparative example 1 ₄ Photoanode with lower overpotential and higher current density, in particular NiCo ₂ O ₄ /MgO/BiVO ₄ The initial potential of (2) is about 1.4V vs. RHE, which is much lower than MgO/BiVO ₄ 、NiCo ₂ O ₄ /BiVO ₄ And BiVO ₄ Indicating NiCo ₂ O ₄ The main function of (2) is to accelerate the surface reaction as an oxygen evolution co-catalyst.

1.2, photocurrent response analysis was performed by means of an instantaneous photocurrent (I-t) curve under the light on/off cycle, the results of which are shown in fig. 15.

As can be seen from FIG. 15, niCo ₂ O ₄ /MgO/BiVO ₄ Relative to NiCo over the entire potential window ₂ O ₄ /BiVO ₄ 、MgO/BiVO ₄ And BiVO ₄ Shows excellent optical switching characteristics, which is consistent with the LSV results in fig. 13.

1.3 measurement of charge transfer ability by Electrochemical Impedance Spectroscopy (EIS) curve, the results are shown in FIG. 16.

As can be seen from FIG. 16, biVO obtained in comparative example 1 ₄ Compared with the photo anode, niCo prepared in example 1 ₂ O ₄ /MgO/BiVO ₄ NiCo produced in comparative example 3 ₂ O ₄ /BiVO ₄ And MgO/BiVO obtained in comparative example 2 ₄ The radius of the arc of the film is much smaller, indicating the presence of MgO and NiCo ₂ O ₄ In the case of (C), the charge transfer efficiency at the photoanode/electrolyte interface is significantly improved due to the NiCo produced in example 1 ₂ O ₄ /MgO/BiVO ₄ Comparative example 3 NiCo preparation ₂ O ₄ /BiVO ₄ The smaller arc radius, the result clearly demonstrates the inventionThe prepared NiCo ₂ O ₄ /MgO/BiVO ₄ Is superior to NiCo in interfacial charge transfer ₂ O ₄ /BiVO ₄ And an electrode, further demonstrating the synergistic effect of the combination of the passivation layer and the OECs layer.

1.4 photoelectrochemical characterization measurements were made by measuring IPCE spectra, ABPE curves, charge injection efficiency and charge separation efficiency, the results are shown in fig. 17-20.

As can be seen from FIG. 17, the NiCo is present in the entire wavelength range of 400-500nm ₂ O ₄ And MgO loading, the IPCE (incident photon-current conversion efficiency) value of the photo-anode prepared in example 1 is greatly improved, compared with that of NiCo prepared in comparative example 3 ₂ O ₄ /BiVO ₄ MgO/BiVO obtained in comparative example 2 ₄ Electrode and BiVO obtained in comparative example 1 ₄ In comparison, niCo prepared in example 1 ₂ O ₄ /MgO/BiVO ₄ The photoanode exhibits the highest IPCE value at 400-520nm, reaching the highest IPCE value at 440nm (≡70%); however, niCo ₂ O ₄ /BiVO ₄ And MgO/BiVO ₄ IPCE values of the photo-anode were only 58% and 43%, respectively, reflecting NiCo prepared by the present invention ₂ O ₄ /MgO/BiVO ₄ The charge collection and handling transport capacity in the photoanode is improved.

As can be seen from FIG. 18, niCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ The ABPE value of the photoanode reached a maximum of 1.59% at 0.64V vs. RHE, in contrast to the NiCo prepared in comparative example 3 ₂ O ₄ /BiVO ₄ MgO/BiVO obtained in comparative example 2 ₄ And BiVO obtained in comparative example 1 ₄ The maximum ABPE values of (C) are respectively 1.18% at 0.6V vs. RHE, 0.53% at 0.9V vs. RHE and 0.26% at 0.9V vs. RHE, which are lower than those of NiCo prepared by the invention ₂ O ₄ /MgO/BiVO ₄ A photo-anode. This shows that the photocurrent of the final composite photoanode increases rapidly with a lower applied bias, and the starting potential shifts significantly to the negative.

As can be seen from FIG. 19, niCo obtained in comparative example 3 ₂ O ₄ /BiVO ₄ And MgO/BiVO obtained in comparative example 2 ₄ Charge injection for photoanodeThe efficiencies were 65% and 60% at 1.23v vs. rhe, respectively; whereas NiCo prepared in example 1 ₂ O ₄ /MgO/BiVO ₄ The improved injection efficiency of the photoanode was unexpected (71% at 1.23v vs. rhe), which is the BiVO prepared in comparative example 1 ₄ The result (32%) is 2 times that possible due to the effect of the MgO passivation layer on reducing surface recombination, compensating for the poor water oxidation capacity.

As can be seen from FIG. 20, niCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ The photoanode showed a higher separation rate of about 86% at a low applied potential of 1.23v vs. rhe, much higher than the BiVO prepared in comparative example 1 ₄ (60%) MgO/BiVO obtained in comparative example 2 ₄ (80%) and NiCo obtained in comparative example 3 ₂ O ₄ /BiVO ₄ (81%) thus NiCo ₂ O ₄ And the MgO passivation layer can synergistically promote charge separation between the photo-anode and the solution, which is consistent with the results of fig. 16.

2. NiCo prepared in examples 1 and 4 to 6 ₂ O ₄ /MgO/BiVO ₄ Photo-anode and BiVO prepared in comparative example 1 ₄ The photoanode was subjected to PEC activity analysis, the results of which are shown in fig. 21-24.

As can be seen from fig. 21, the amount of MgO has a great influence on the current density, and the photocurrent density increases and decreases as the amount of MgO increases. The activity sequence is as follows: niCo ₂ O ₄ /MgO/BiVO ₄ -20s>NiCo ₂ O ₄ /MgO/BiVO ₄ -40s>NiCo ₂ O ₄ /MgO/BiVO ₄ -60s>NiCo ₂ O ₄ /MgO/BiVO ₄ 10s, which means that a suitable MgO passivation layer can effectively increase PEC activity, and saturation of the MgO passivation layer can lead to a decrease in light conversion efficiency, which may be due to MgO nanoplatelets at BiVO ₄ Saturation of the surface and therefore photon absorption and charge transfer at the interface between the photo-anode and the electrolyte is reduced.

As can be seen from FIG. 22, all electrodes loaded with different amounts of MgO have different initial potentials, indicating NiCo ₂ O ₄ /MgO/BiVO ₄ -20s allows to achieve a decomposition of water at a small external voltage.

As can be seen from FIG. 23, all photo-anodes have excellent rapid photo-response, especially when MgO is deposited for 20s, the photo-current density is highest, consistent with the results of FIG. 17, indicating NiCo ₂ O ₄ /MgO/BiVO ₄ The photogenerated electrons and holes in the 20s sample can be effectively separated.

As can be seen from fig. 24, as the MgO deposition time increases, the EIS value decreases and then increases, and particularly, when the deposition time is 20s, the EIS value is the lowest, which indicates that the strong electron transport ability is more advantageous for the water decomposition reaction.

In conclusion, the NiCo prepared by the invention ₂ O ₄ /MgO/BiVO ₄ The photo anode PEC performance is better, wherein, when the optimal time for MgO deposition is 20s, niCo ₂ O ₄ /MgO/BiVO ₄ PEC performance of the photoanode is optimal.

3. NiCo prepared in examples 1 and 7 to 8 ₂ O ₄ /MgO/BiVO ₄ Photo-anode and BiVO prepared in comparative example 1 ₄ The photo-anode was subjected to PEC water splitting activity analysis, the results are shown in fig. 25-28.

As can be seen from fig. 25, the photocurrent density increases and then decreases with increasing deposited MgO voltage. The NiCo2O4/MgO/BiVO4 photo-anode can respectively reach 2.5 mA.cm under the bias voltage of-0.6V vs. RHE and-0.8V vs. RHE ^-2 And 3.0 mA.cm ^-2 In contrast, a higher photocurrent density (4.6 mA cm) was obtained at-0.7V vs. RHE ^-2 ). This means that a suitable voltage can effectively increase PEC activity, while too high or too low can result in a decrease in light conversion efficiency.

As can be seen from FIG. 26, niCo under dark reaction conditions ₂ O ₄ And MgO and BiVO ₄ After compounding, biVO ₄ The photocurrent density of the base electrode is obviously enhanced, and the initial oxidation potential is also reduced. Wherein, when the deposition voltage is-0.7V vs. RHE, niCo ₂ O ₄ /MgO/BiVO ₄ Photoanodes exhibit the most excellent performance, which may benefit from efficient transport of photogenerated electrons and holes.

As can be seen from fig. 27, all photo-anodes have excellent fast photo-responses, especially at a deposition voltage of-0.7 v vs. rhe, the photocurrent density is highest, indicating that charge recombination is suppressed in the photo-anode.

As can be seen from fig. 28, niCo is loaded ₂ O ₄ After MgO, the EIS curve radius is obviously reduced, which means that the charge transfer resistance of the photoelectrode is smaller, and means that the transmission speed of interface charge under illumination is higher than that of pure BiVO ₄ Is faster. NiCo when the deposition voltage is-0.7V vs. RHE ₂ O ₄ /MgO/BiVO ₄ Photoanode has minimal charge transfer resistance, consistent with its optimal PEC performance, confirming NiCo ₂ O ₄ And the addition of MgO can reduce the charge transfer resistance and promote the separation and transport of charges, ultimately improving PEC performance of the photoanode.

3. Photoelectrocatalytic mechanism analysis

1. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ Photo anode, biVO prepared in comparative example 1 ₄ Photo-anode, mgO/BiVO prepared in comparative example 2 ₄ Photoanode and NiCo produced in comparative example 3 ₂ O ₄ /BiVO ₄ Photoanode, interface charge transfer analysis by measuring Open Circuit Potential Decay (OCPD), which describes the recovery time of a feature of photoanode when moving from an open-circuited illumination steady state to an equilibrated dark state, typically charge-separated electrons at BiVO when open ₄ The results are shown in FIGS. 29-31.

As can be seen from fig. 29, in BiVO ₄ After MgO is introduced into the surface, the open circuit voltage increases between 0 and 50s, reflecting the reverse electron transfer delay, FIG. 30 shows a larger version of the OCPD file under dark reaction conditions, as is known, the lower the slope, the longer the electron lifetime, and thus the MgO/BiVO produced in comparative example 2 ₄ And NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ The slope of the anode is significantly smaller than that of BiVO prepared in comparative example 1 ₄ Indicating that MgO acts as a passivation layer to inhibit surface electron-hole recombination. In addition, niCo obtained in comparative example 3 ₂ O ₄ /BiVO ₄ MgO/BiVO prepared in comparative example 2 ₄ And NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ For photo-anode, the inclinationThe rate increases, indicating difficulty in injecting electrons into the solution.

As can be seen from FIG. 31, the cathode current transient for all photo-anodes at 0.2V vs. RHE, where t ₁ The photocurrent corresponding to the instant off light quenches and gradually decays until the current reaches a steady value (t ₂ ). A cathodic spike in current was observed when the lamp was turned off, which may be due to surface state charging and discharging. In BiVO ₄ After the MgO passivation layer is loaded on the surface, more time is needed to reach a stable state, which is similar to BiVO ₄ The amount of charge trapped in the electrode surface state is related to, in addition, mgO/BiVO ₄ Introducing NiCo on the film ₂ O ₄ After this time to steady state increases further, indicating NiCo ₂ O ₄ The promoter inhibits electron-hole recombination at the semiconductor-electrolyte interface.

2. The anodes prepared in comparative examples 1-2 and MgO were studied for their electronic properties by DFT calculation, and the state density and projected state density were used to further reveal the effect of MgO loading on BiVO4 band gap, as shown in FIG. 32 (a-b are BiVO ₄ C-d is MgO, e-f is MgO/BiVO ₄ )。

As can be seen from FIG. 32, the estimated bandgap is smaller than the experimental value because the conventional PBE method underestimates the bandgap, mgO/BiVO ₄ The band gap of the composite material is not significantly different from that of the individual materials, which is consistent with the results of the analyses of FIGS. 11-12. PDOS shows that the Valence Band (VB) is mainly engaged by the O-2p state, while the Conduction Band (CB) is mainly engaged by the V-3d state. MgO/BiVO ₄ The lower CB of the composite also indicates enhanced PEC water splitting properties of the composite.

3. NiCo obtained in example 1 ₂ O ₄ /MgO/BiVO ₄ Photo-anode and BiVO prepared in comparative example 1 ₄ PEC water splitting performance analysis of photoanode by H for each photoanode in simulated sunlight ₂ And O ₂ And (3) testing precipitation reaction.

The specific method comprises the following steps: the electrocatalytic decomposition of the aqueous hydrogen is tested in a self-made Shan Chiguang reaction vessel, a photoreaction instrument is connected with an electrochemical system, and the aqueous hydrogen is decomposed to produce oxygen under constant voltage, and the operation steps are as follows:

(1) Preparing 1mol/L potassium borate buffer electrolyte, measuring 90mL, and putting into a hydrogen production test reaction tank;

(2) An electrochemical workstation (CHI 660D) is connected with the hydrogen-generating container for generating N ₂ Introducing air into the photoreaction tank for 30min to extrude air in the reaction vessel;

(3) Bias voltage set at 1.23v vs. rhe for 10800s;

(4) The area of the working electrode is 1cm ² Light is incident from the back surface of the conductive glass and the power of the light is 100mW/cm ² (calibration of the optical power meter);

(5) When all the components are ready, starting the light source, clicking the start of the computer system, and starting the photoelectrocatalysis water decomposition reaction;

(6) Then 1mL of gas was drawn into the reaction cell with a microinjector every 30min, and was injected into an online gas chromatograph (GC 9560), the start button in the control panel was clicked, and experimental data was recorded.

The results are shown in FIGS. 33-34.

As can be seen from FIG. 33, biVO obtained in comparative example 1 ₄ Exhibits a lower 12. Mu. Mol.h ^-1 ·cm ^-2 Hydrogen production rate and 6. Mu. Mol.h ^-1 ·cm ^-2 Mainly due to the lower water splitting reaction resulting from its poor charge transfer kinetics.

As can be seen from fig. 34, niCo ₂ O ₄ And the introduction of MgO significantly improves BiVO ₄ Hydrogen and oxygen are 201 mu mol.h respectively after 180min ^-1 ·cm ^-2 And 10. Mu. Mol.h ^-1 ·cm ^-2 About more than the BiVO prepared in comparative example 1 ₄ 5 times higher. In addition, H ₂ And O ₂ The Faraday efficiency of the precipitation reaction reaches about 90%.

Based on the above results, we propose a mechanism of photo-anode generation in the water splitting process, firstly, the UV-Vis diffuse reflection and IPCE results show that the modified bismuth vanadate can improve the light utilization rate, and further improve the photoelectric utilization efficiency; second, niCo ₂ O ₄ The Ni/Co bimetallic active sites of (2) accelerate the decomposition of water by PECIn the process, the high valence state of Ni (II)/Co (II) is oxidized into trivalent Co and trivalent Ni, and then the trivalent Co and the tetravalent Ni are further oxidized under the action of holes, and in the water splitting process, unstable Ni (IV) and Co (IV) are respectively reduced into Ni (II) and Co (II); finally, adding MgO passivation layer can promote BiVO ₄ The charge transfer on the surface accelerates the transfer of charge carriers and improves the charge injection and separation efficiency. Thus, in BiVO ₄ MgO and NiCo ₂ O ₄ Under the synergistic effect of the (2), not only the initial overpotential of the reaction can be reduced, but also the recombination efficiency of electrons and holes can be reduced, in a word, niCo ₂ O ₄ /MgO/BiVO ₄ The significant improvement in PEC water splitting performance in photoanode can be attributed to the catalytic/absorptive/synergistic triple function.

In conclusion, the NiCo prepared by the invention ₂ O ₄ /MgO/BiVO ₄ The photoanode realizes 4.6mA.cm on a 1.23V vs. RHE ^-2 For water oxidation and negative shift initiation potential. This performance improvement is due to MgO and NiCo ₂ O ₄ Synergistic effect between, specifically, biVO after introducing MgO passivation layer ₄ The separation and migration rate of photo-generated carriers on the surface of the photo-anode are improved, and furthermore, niCo ₂ O ₄ Can be used as active site to accelerate NiCo ₂ O ₄ /MgO/BiVO ₄ Water oxidation of the photoanode. Thus, the MgO passivation layer can be coupled with the photo-anode material to achieve efficient solar water splitting.

The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims

1. NiCo ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photo-anode is characterized by comprising the following steps:

2. The NiCo of claim 1 ₂ O ₄ /MgO/BiVO ₄ A method for producing a photoanode, characterized by depositing BiVO on a substrate material in step (1) ₄ The specific method of the film is as follows: pretreating a substrate material, depositing a BiOI film on the substrate material by an electrophoretic deposition method, cleaning, drying, and then dripping V ⁵⁺ Source, calcination, and preparation of BiVO ₄ A film.

3. NiCo according to claim 2 ₂ O ₄ /MgO/BiVO ₄ A method for preparing a photo-anode is characterized in that V ⁵⁺ The source is VO (acac) with the concentration of 0.1-0.3mol/L ₂ Is a solution of DMSO in (B).

4. The NiCo of claim 1 ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode is characterized in that the electrophoretic deposition conditions in the step (2) are as follows: mgNO with deposition liquid of 0.8-1.2mol/L ₃ ·6H ₂ O solution, potential-0.6-0.8V, deposition time 10-60s.

5. The NiCo of claim 1 ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photoanode is characterized in that the calcining conditions in the step (2) are as follows: heating to 450-550deg.C at a rate of 1-3deg.C/min for 0.8-1.2 hr.

6. The NiCo of claim 1 ₂ O ₄ /MgO/BiVO ₄ A method for producing a photoanode, characterized by comprising the step (3)Middle NiCo ₂ O ₄ The precursor solution is prepared by the following method: niCo is prepared ₂ O ₄ Dispersing the precursor in a mixed solution of DMF and Nafion to prepare NiCo ₂ O ₄ A precursor solution; wherein NiCo ₂ O ₄ The mass volume ratio of DMF and Nafion is 0.08-0.12g:8-12mL:0.2-0.4mL.

7. The NiCo of claim 1 ₂ O ₄ /MgO/BiVO ₄ The preparation method of the photo-anode is characterized in that the spin coating conditions in the step (3) are as follows: spin coating at 1800-2200r/min for 15-25s.

8. NiCo as claimed in any one of claims 1 to 7 ₂ O ₄ /MgO/BiVO ₄ NiCo prepared by preparation method of photo-anode ₂ O ₄ /MgO/BiVO ₄ A photo-anode.

9. The NiCo of claim 8 ₂ O ₄ /MgO/BiVO ₄ Use of a photoanode in the manufacture of a photoelectrochemical cell.

10. A photoelectrochemical cell comprising the NiCo of claim 8 ₂ O ₄ /MgO/BiVO ₄ A photo-anode.