Bismuth vanadate large-area flat plate photo-anode material, preparation method thereof and application of bismuth vanadate large-area flat plate photo-anode material in decomposition of water

Abstract

The invention discloses a bismuth vanadate large-area flat plate photo-anode material, a preparation method thereof and application of the bismuth vanadate large-area flat plate photo-anode material in water decomposition. The catalyst comprises a transparent conductive oxide carrier and bismuth vanadate with a plane structure, the planar bismuth vanadate is prepared by a metal organic pyrolysis method and grows on the surface of the transparent conductive oxide carrier. The preparation method of the large-area plate bismuth vanadate is simple, easy to operate and low in cost, and the Bi / V content in the reaction precursor solution can be adjusted by changing reaction conditions. According to the method, the Bi / V content in the reaction precursor solution is adjusted, and the built-in electric field is constructed in the bulk phase whole domain, so that the energy band bending is adjusted, the separation efficiency of bismuth vanadate bulk phase electron holes is improved, the high charge separation efficiency is obtained, and a new thought is provided for preparing the efficient bismuth vanadate photoelectrode.

Description

Technical Field

[0001] The invention relates to the preparation of bismuth vanadate thin film electrode materials and large-area flat-plate photoelectrodes, which are used in the field of photoelectric catalysis. Background Art

[0002] Using solar energy to produce hydrogen from water is an effective technological approach to address the growing global energy demand and environmental problems caused by human activities. The large-scale application of photocatalysis (PC), photovoltaic-electrochemistry (PV-EC) and photoelectrocatalysis (PEC) has demonstrated the feasibility of these technological pathways for converting solar energy into chemical energy. Currently, the most promising of these technologies is PV-EC, which has an efficiency of up to 30%, but its equipment is complex. Considering the simplicity and scalability of equipment and operation as well as the lower cost, photoelectrocatalysis is more attractive than improving and controlling the large-scale preparation of photoanodes.

[0003] At present, among the many widely studied photoanode materials, such as TiO2, WO3, Fe2O3, and BiVO4, bismuth vanadate (BiVO4, BVO) with a monoclinic scheelite structure shows great prospects due to its excellent chemical stability, suitable light absorption coefficient, band gap size and band gap position. However, it also has some disadvantages, such as a short carrier diffusion distance (70nm) and low carrier mobility, which leads to serious bulk charge recombination. At present, there are two main methods for preparing BVO: two-step electrodeposition (ED) and metal organic decomposition (MOD). Since BVO prepared by electrodeposition has a nanoporous structure, it is conducive to charge transport, but this porous structure will cause serious light scattering, which is not conducive to its application in some tandem devices. In addition, this two-step electrodeposition method is complicated and not conducive to large-area preparation. The planar structure BVO prepared by MOD makes up for the above shortcomings, but this planar structure leads to serious bulk charge recombination. Various strategies have been adopted to improve its performance, such as improving the charge separation efficiency through metal ion doping, surface modification, heterostructure construction or defect engineering, but most of them are spatially confined to the surface or depletion layer region. The use of homogeneous structures to create global spatial electric fields has been well verified in semiconductor physics and has been applied to the fields of photovoltaics and optoelectronics. For example, the BVO photoanode achieves 80% carrier separation efficiency by introducing a gradient W doping concentration to form a distributed n+-n homojunction in the material body, and then forms a moderate depletion layer in the BVO body. However, the introduction of foreign elements may lead to uneven doping distribution. In addition, the current research on bismuth vanadate electrodes is mainly limited to the preparation of small areas. For the preparation of large-area flat bismuth vanadate, there are currently problems such as severe increase in defects and uneven films, as well as higher requirements for experimental methods and equipment.

[0004] Based on the above research status, it can be seen that seeking a relatively simple preparation method can control the preparation of high-performance bismuth vanadate electrodes and large-area flat photoelectrodes with the same structure and uniform thickness, and use them in the field of photoelectrocatalytic water decomposition. The present invention has important application value. Summary of the invention

[0005] In order to solve the above technical problems, one of the purposes of the present invention is to prepare a large-area flat bismuth vanadate thin film electrode with the same structure and uniform thickness through a simple, easy-to-operate and low-cost method for the study of photoelectrocatalytic water decomposition performance, and by regulating the Bi / V ratio in the preparation process, changing the energy band bending and increasing the width of the space charge layer region, thereby improving the bulk charge separation and obtaining excellent charge separation performance (95%).

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a bismuth vanadate large-area flat-plate photoanode material, which is a catalyst used in the direction of photoelectrocatalysis. The catalyst comprises a conductive substrate and a catalyst grown in situ on the surface thereof; the catalyst composition is bismuth vanadate; the catalyst morphology is a planar nanoparticle structure, and the phase structure is a monoclinic phase structure.

[0008] The conductive carrier is selected from transparent conductive oxides, such as fluorine-doped tin oxide (FTO) and indium tin oxide (ITO);

[0009] In the above technical solution, further, the thickness of the bismuth vanadate electrode is 150-300nm.

[0010] The molar ratio of bismuth vanadate Bi:V in the catalyst is 1:(1-1.1);

[0011] The bismuth vanadate in the catalyst is 1-4 layers (preferably 2-4 layers) from bottom to top, and the vanadium content in each layer of bismuth vanadate decreases layer by layer from bottom to top, thereby changing the energy band bending, increasing the width of the space charge layer region, and thus improving the bulk charge separation.

[0012] Another aspect of the present invention provides a method for preparing the above-mentioned large-area flat plate bismuth vanadate catalyst for photoelectrocatalytic water decomposition, the method comprising the following steps:

[0013] (1) cleaning the transparent conductive oxide support;

[0014] The transparent conductive oxide support was immersed in acetone, ethanol, and water for ultrasonic cleaning for 10 min, and then purged and dried in an Ar flow for later use.

[0015] (2) adding different proportions of soluble bismuth salt and vanadium salt into an organic solvent and mixing them evenly for later use;

[0016] (3) adding the precursor solution obtained in (2) dropwise onto the transparent conductive oxide support obtained in (1) to obtain precursors containing different Bi / V ratios;

[0017] (4) heating and calcining the sample obtained in (3) in a muffle furnace to obtain a bismuth vanadate photoelectrode catalyst;

[0018] Alternatively, there is a step (5) of changing the molar ratio of Bi:V in (2) to prepare a mixed solution, while other conditions remain unchanged, repeating the above operation process for multiple depositions, and the molar content of vanadium decreases layer by layer from bottom to top to obtain a large-area flat bismuth vanadate electrode.

[0019] In the above technical solution, further, the cleaning method in (1) is: immersing the transparent conductive oxide support in acetone, ethanol, and water for ultrasonic cleaning for 10 minutes, blowing and drying in an Ar flow for later use;

[0020] In the above technical scheme, further, the soluble vanadium salt includes any one of vanadium acetylacetonate and triisopropoxy vanadium (V) oxide, and the soluble bismuth salt is bismuth nitrate; the concentration molar ratio of the soluble bismuth salt to the vanadium salt is 1: (1 to 1.1).

[0021] In the above technical solution, further, the molar amount of the vanadium salt decreases layer by layer, and the ratio of the vanadium salt in each two adjacent layers ranges from 1.01 to 2.1.

[0022] In the above technical solution, further, the organic solvent includes one or two of DMSO, methanol, acetic acid, ethanol, or ethylene glycol.

[0023] In the above technical solution, further, the calcination temperature each time is 450-550°C, and the calcination time each time is 0.5-4h.

[0024] In the above technical solution, further, the number of depositions of the precursor solution is 1-4 times; the volume of the precursor solution is between 60ul and 1500ul. The area of ​​the transparent conductive oxide carrier is 4-100cm 2 ;

[0025] In the above technical solution, further, the transparent conductive oxide carrier is selected from one of FTO and ITO;

[0026] In the above technical solution, further, the precursor solution containing bismuth salt and vanadium salt is deposited on the transparent conductive oxide support by spin coating or spray coating, and the thickness of the film is controlled by controlling the conditions of spin coating or spray coating;

[0027] The spin coating speed is 1500-4000r, the time is 20-60s, and the number of spin coating is controlled at 1-4 times;

[0028] The spraying height is controlled at 15-20cm, and the number of spraying times is controlled between 100-300 times;

[0029] Another aspect of the present invention provides an application of the above-mentioned large-area flat-plate bismuth vanadate electrode material in the field of photoelectrocatalysis.

[0030] The present invention provides an application of the above-mentioned large-area flat-plate bismuth vanadate electrode material in photoelectrocatalytic water decomposition.

[0031] The electrode is a large-area flat-plate bismuth vanadate electrode, which is a working electrode or a photoanode;

[0032] In the photoelectric test process, hydrogen peroxide or sodium sulfite is selected as the hole capture agent, preferably sodium sulfite solution.

[0033] The electrolyte for the photoelectric test of water decomposition or sodium sulfite oxidation is a potassium borate or potassium phosphate buffer solution, the electrolyte concentration is 0.5-1M, and the electrochemical potential range is 0-1.4V vs.RHE.

[0034] The scanning rate of the electrochemical linear sweep voltammetry is 20-100 mV s -1 , preferably 50mV s -1 ;

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention provides a large-area planar bismuth vanadate photoanode catalyst. Compared with the prior art, it has a specific and identical structure and uniform thin thickness. By changing the Bi / V ratio in the preparation process, the energy band structure and the position of the Fermi level of bismuth vanadate are adjusted, and a built-in electric field is formed in the entire bismuth vanadate bulk phase, thereby improving the separation of electrons and holes, and providing a new idea for realizing efficient bismuth vanadate photoelectrode synthesis.

[0037] 2. The preparation method of the large-area planar bismuth vanadate electrode catalyst provided by the present invention has the advantages of simple operation and low cost, and the Bi / V content in the bismuth vanadate can be adjusted by changing the reaction conditions, thereby achieving the adjustment of the catalytic performance.

[0038] 3. The large-area flat bismuth vanadate catalyst provided by the present invention can be used in the field of photoelectrocatalysis, such as photoelectrocatalytic water decomposition, oxidation of hydrogen peroxide, etc., while the existing technology for preparing large-area flat bismuth vanadate electrodes has serious defects and uneven films, resulting in bulk charge recombination and large-area performance degradation. In addition, the complex preparation method is more difficult to operate for the preparation of large-area electrodes.

[0039] Specifically, the large-area flat-plate bismuth vanadate catalyst provided by the present invention achieves a charge separation efficiency of 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0041] Figure 1 This is a scanning electron microscope image of a planar bismuth vanadate electrode using FTO as a conductive substrate in Example 1 of the present invention;

[0042] Figure 2 The area is 10*10cm in Example 1 of the present invention. 2 Optical image of bismuth vanadate electrode;

[0043] Figure 3 XRD and UV-visible absorption spectra of different positions of large-area flat bismuth vanadate in Example 1 of the present invention;

[0044] Figure 4 4cm in Example 2 of the present invention 2 The photocurrent density test and charge separation efficiency calculation results of bismuth vanadate electrode in the presence of hole capture agent;

[0045] Figure 5 The area is 10*10cm in Example 1 of the present invention. 2 The photocurrent density distribution test of bismuth vanadate electrode at different positions in the presence of hole capture agent;

[0046] Figure 6 For implementation case 3, the area is 10*10cm 2 Optical images of a single-layer bismuth vanadate electrode and test diagrams of the photocurrent density distribution at different positions in the presence of a hole scavenger. DETAILED DESCRIPTION

[0047] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0048] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0049] There is no particular limitation on the purity of all raw materials in the present invention, and analytically pure materials are preferably used in the present invention.

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] It should be noted that the terms used here are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope. Unless otherwise specified, all technical and scientific terms used herein have the same meanings commonly understood by conventional technicians in the field of the present invention. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. In addition, it should also be understood that "including", "including", "having", "containing" and the like used herein are all open terms, that is, it means including but not limited to.

[0052] Example 1

[0053] Preparation of large-area planar bismuth vanadate:

[0054] (1) The area is 10*10cm 2 The FTO was immersed in acetone, ethanol, and water for ultrasonic cleaning for 10 min, and then purged and dried in an Ar stream for later use.

[0055] (2) adding bismuth nitrate powder to 2 ml of DMSO solvent, dissolving by ultrasonication to obtain a 0.6 M bismuth nitrate solution, and then adding vanadium acetylacetonate powder to the above solution, wherein the concentration of vanadium acetylacetonate in the solution is 0.648 M, and mixing by ultrasonication to obtain a uniform solution for later use;

[0056] (3) The cleaned FTO obtained in (1) is placed on the chuck of the spin coater, 1.5 ml of the precursor solution obtained in (2) is measured and dripped onto the conductive substrate, and the spin coater is operated at 3000 r for 40 s to obtain a precursor sample containing bismuth and vanadium;

[0057] (4) The sample obtained in (3) was heated and calcined at 500° C. in a muffle furnace for 2 h to obtain a bismuth vanadate photoelectrode;

[0058] (5) Changing the molar ratio of Bi:V in the precursor (2), adding bismuth nitrate powder to 2 ml of DMSO solvent, dissolving by ultrasonication, obtaining a 0.3 M bismuth nitrate solution, and then adding vanadium acetylacetonate powder to the above solution, wherein the concentration of vanadium acetylacetonate in the solution is 0.318 M, and mixing by ultrasonication for 30 min to obtain a uniform solution for later use;

[0059] (6) placing the sample obtained in (4) on a spin coater chuck, dripping the solution obtained in (5) onto the sample obtained in (4), and operating the spin coater at 3000 r for 40 s to obtain a precursor sample containing bismuth and vanadium;

[0060] (7) The sample obtained in (6) was heated and calcined in a muffle furnace at 500° C. for 2 h to obtain a bismuth vanadate photoelectrode;

[0061] (8) Changing the molar ratio of Bi:V in the precursor (2), adding bismuth nitrate powder to 2 ml of DMSO solvent, dissolving by ultrasonication, obtaining a 0.3 M bismuth nitrate solution, and then adding vanadium acetylacetonate powder to the above solution, wherein the concentration of vanadium acetylacetonate in the solution is 0.312 M, and mixing by ultrasonication for 30 min to obtain a uniform solution for later use;

[0062] (9) placing the sample obtained in (7) on a spin coater chuck, dripping the solution obtained in (8) onto the sample obtained in (7), and operating the spin coater at 3000 r for 40 s to obtain a precursor sample containing bismuth and vanadium;

[0063] (10) The sample obtained in (9) was heated and calcined in a muffle furnace at 500° C. for 2 h to obtain a bismuth vanadate photoelectrode;

[0064] like Figure 1 As shown, the scanning electron microscope image and cross-sectional information of bismuth vanadate, the film thickness is ~160nm.

[0065] like Figure 2 As shown, the optical image of a large-area flat plate of bismuth vanadate indicates that bismuth vanadate has a uniform surface and high transmittance.

[0066] like Figure 3 As shown, the XRD and UV-visible absorption spectra of large-area flat bismuth vanadate have the same structure and absorption properties at different positions, indicating the uniformity of the film thickness.

[0067] like Figure 5 As shown, the area is 10*10cm 2 The photocurrent density of the bismuth vanadate electrode at different positions under the presence of hole traps has little difference, and the average photocurrent density reaches 5.87 mA cm-2 , indicating the uniformity of film thickness.

[0068] Example 2

[0069] The preparation method is the same as that in Example 1, except that the area of ​​FTO in step (1) is changed to 2×2 cm 2 .like Figure 4 As shown, 4cm 2 The photocurrent density of the bismuth vanadate electrode containing a hole trap reached 6.17 mA / cm 2 , and the charge separation efficiency reaches 99.7%.

[0070] Example 3

[0071] The preparation method is the same as that of Example 1, except that only one layer is deposited, namely, steps (1) to (4) of Example 1. Figure 6 As shown, the single layer area is 100cm 2 The photocurrent density of different parts of the bismuth vanadate electrode containing hole capture agents shows similar current density and uniformity of surface film properties. The average current density reaches 5.0 mA / cm 2 .

[0072] Example 4

[0073] The preparation method is the same as that of Example 1, except that: in step (1), the DMSO solution is replaced with a methanol solution.

[0074] Example 5

[0075] The preparation method is the same as that of Example 1, except that the secondary calcination temperature in step (4) is 450°C.

[0076] Example 6

[0077] The preparation method is the same as that of Example 1, except that the secondary calcination temperature in step (4) is 450°C.

[0078] Example 7

[0079] Photoelectric performance test of large-area planar bismuth vanadate photoelectrode.

[0080] The catalyst prepared in Example 1 or 2 of the present invention was used to test the photoelectrocatalytic water decomposition performance.

[0081] The photoelectrocatalytic performance test was carried out in a customized H-type electrolytic cell with bismuth vanadate loaded with the vanadate obtained in Example 1 or 2 of the present invention as the working electrode, a platinum electrode as the counter electrode, Ag / AgCl as the reference electrode, a 0.5M potassium borate buffer solution as the electrolyte, and 0.2M Na2SO3 as the hole trapping agent. The linear sweep voltammetry curve test was tested, and the applied potential range was 0-1.3V vs.RHE. The charge separation efficiency was calculated based on the current density of the electrode in the sodium sulfite solution and the integrated theoretical photocurrent density.

[0082] like Figure 4 As shown, the area is 2*2cm 2 Photocurrent density and charge separation efficiency of bismuth vanadate electrode;

[0083] like Figure 5 As shown, the area is 10*10cm 2 The photocurrent density at different positions of the bismuth vanadate electrode is shown in Figure 2. The photocurrent density of the films in different regions is similar, indicating that the film structure and thickness are uniform.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0085] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A bismuth vanadate large-area flat-plate photoanode material, characterized in that: The material is a catalyst used in photoelectrocatalysis; The catalyst comprises a transparent conductive oxide as a substrate and a catalyst in situ grown on the surface thereof; The catalyst composition is bismuth vanadate; The catalyst has a planar nanoparticle structure and a monoclinic phase structure.

2. The catalyst according to claim 1, characterized in that The transparent conductive oxide carrier is selected from one of FTO and ITO; The molar ratio of bismuth vanadate Bi:V in the catalyst is 1:(1-1.1); The bismuth vanadate in the catalyst is 1-4 layers from bottom to top, and the vanadium content in each layer of bismuth vanadate decreases layer by layer from bottom to top.

3. The catalyst according to claim 1, characterized in that The thickness of the bismuth vanadate is 150-300 nm.

4. A method for preparing a photoanode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) cleaning the transparent conductive oxide support; (2) adding different proportions of soluble bismuth salt and vanadium salt into an organic solvent and mixing them evenly for later use; (3) adding the precursor solution obtained in (2) dropwise onto the transparent conductive oxide support obtained in (1) to obtain precursors containing different Bi / V ratios; (4) calcining the sample obtained in (3) in a muffle furnace to obtain a bismuth vanadate photoelectrode catalyst; Alternatively, there is a step (5) of changing the molar ratio of Bi:V in (2) to prepare a mixed solution, while other conditions remain unchanged, repeating the above operation process for multiple depositions, and the molar content of vanadium decreases layer by layer from bottom to top to obtain a large-area flat bismuth vanadate electrode.

5. The preparation method according to claim 4, characterized in that: The soluble vanadium salt includes any one of vanadium acetylacetonate and triisopropoxyvanadium (V) oxide, The soluble bismuth salt is bismuth nitrate; The molar ratio of the soluble bismuth salt to the vanadium salt is 1:(1-1.1); The molar amount of the vanadium salt decreases layer by layer, and the ratio of the vanadium salt in each two adjacent layers ranges from 1.01 to 2.

1.

6. The preparation method according to claim 4, characterized in that: The organic solvent includes one or more of DMSO, methanol, acetic acid, ethanol, or ethylene glycol.

7. The preparation method according to claim 4, characterized in that: The number of depositions of the precursor solution is 1-4 times; the volume of the precursor solution is between 60ul and 1500ul; the area of ​​the transparent conductive oxide carrier is 4-100cm 2 .

8. The preparation method according to claim 4, characterized in that: The calcination temperature is 450-550° C. and the calcination time is 0.5-4 h.

9. The preparation method according to claim 4, characterized in that: The precursor solution containing bismuth salt and vanadium salt is deposited on the transparent conductive oxide support by spin coating or spray coating, and the thickness of the film is controlled by controlling the conditions of spin coating or spray coating; The spin coating speed is 1500-4000r, the time is 20-60s, and the number of spin coating is controlled at 1-4 times; The spraying height is controlled at 15-20cm, and the number of spraying times is controlled between 100-300 times; The transparent conductive oxide carrier is selected from one of FTO and ITO; The electrode is a working electrode or a photoanode.

10. Use of the photoanode material according to claims 1 to 3 or the photoanode material prepared by the preparation method according to claims 4 to 9 in photoelectrocatalytic water decomposition reaction.

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