BaTaO2N photoanode and preparation method thereof

Abstract

The application relates to the field of photoelectrocatalytic water decomposition hydrogen production technology, and particularly discloses a BaTaO2N photoanode and a preparation method thereof. Clean tantalum sheets are placed in a sealed container containing potassium hydroxide solution to react, and after repeatedly washing the alkaline solution adhered to the surfaces of the tantalum sheets with deionized water, the tantalum sheets are placed in a container containing a barium salt solution to react for a proper time, and after washing the excess barium ions adhered to the surfaces with deionized water, a matte color barium tantalate hydrate film is obtained. Finally, the barium tantalate hydrate film is sintered in an ammonia atmosphere for a certain time, and a metal luster sample is obtained again, which is the BaTaO2N photoanode. In the preparation process of the BaTaO2N photoanode, tantalum and barium atoms are uniformly arranged on the surfaces of the tantalum sheets in advance, the product crystal grains are uniform, the repeatability is good, and the cost is low. The method has the advantages of mild preparation conditions, high energy utilization rate, small equipment requirement, strong popularization, and extremely high application value in photoelectrocatalytic water decomposition hydrogen production and semiconductor thin film and device preparation.

Description

Technical Field

[0001] This invention relates to the field of photoelectrocatalytic water splitting for hydrogen production, specifically to a BaTaO2N photoanode and its preparation method. Background Technology

[0002] Photoelectrochemical (PEC) water splitting systems based on semiconductor electrodes can convert endless solar energy into stable hydrogen energy. They are considered the most efficient green hydrogen production method due to their advantages such as simple structure, high product purity and easy separation, strong continuous operation, and low operating cost. The water oxidation reaction occurring at the photoanode involves the transfer of four electrons at the solid-liquid interface, resulting in extremely high reaction barriers that limit the efficiency of the entire PEC system. Therefore, designing and fabricating high-efficiency water splitting photoanodes is a key scientific technology for improving the overall energy efficiency of PEC systems. BaTaO2N is derived from [TaON]. 2＋ Octahedron and Ba 2+ It constitutes a perovskite-type nitrogen oxide (AB(O,N)3), where site A is Ba and site B is Ta. BaTaO2N has the following characteristics: I) Suitable band structure: the conduction band is -0.4 V, higher than the reduction potential of water, and the valence band is 1.5 V, lower than the oxidation potential of water, meeting the basic thermodynamic requirements for photocatalytic water splitting. II) The band gap is between 1.8 and 1.9 eV, allowing it to absorb sunlight with wavelengths less than 660 nm, essentially covering the visible light range.

[0003] III) [TaON] within BaTaO2N crystal 2＋ The octahedron is a stable geometric structure that allows it to maintain structural stability during long-term catalysis. Moreover, tantalum-based materials have extremely strong acid and alkali resistance properties, enabling them to withstand long-term industrial photoelectrocatalytic water splitting processes.

[0004] Currently, the main methods for preparing BaTaO2N include the following: 1. Solid-state reaction method: This is a traditional method that requires sintering the raw materials at high temperatures to obtain the desired compound. However, the powder obtained by this method has uneven micro-mixing, resulting in component segregation and uneven microstructure. 2. Molten salt method: This method is more destructive to the substrate, affecting the stability of the electrode. However, it can provide more uniform BaTaO2N films, which helps to obtain high-quality materials. 3. Self-propagating combustion method: This can obtain lanthanum tantalate with high sintering activity, but the crystal structure may be incomplete. 4. Physicochemical deposition method: Such as epitaxial growth, electron beam deposition, magnetron sputtering, etc. This is a simple and feasible approach for the preparation and production of film materials. However, this type of scheme is only effective for certain components and structures, the equipment is expensive, the operation is cumbersome, and most of the equipment is imported.

[0005] Based on the above analysis, it is essential and urgently needed to develop a controllable method for preparing BaTaO2N photoanodes that does not require expensive equipment. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a BaTaO2N photoanode and its preparation method. This method features a mild reaction, simple process and equipment, easy process control, low cost, and safety and environmental friendliness, thus solving the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a BaTaO2N photoanode, wherein the BaTaO2N photoanode has a regular octahedral structure with an edge length of 400 nm to 800 nm; wherein the BaTaO2N layer and the substrate layer are bonded through Ta4N and TaN to form a heterostructure; the BaTaO2N layer uniformly covers the surface of the tantalum substrate and is a single-layer thin film structure, the thickness of the film being the same as the size of the BaTaO2N particles, and is composed of monodisperse and interpenetrating BaTaO2N particles.

[0008] On the other hand, to achieve the above objectives, the present invention also provides the following technical solution: a method for preparing a BaTaO2N photoanode, comprising the following steps:

[0009] S1. Preparation of metastable K2Ta2O6 precursor: Potassium hydroxide KOH solution and clean, bright tantalum sheet are placed in a dissolving container, sealed, and placed in an oven for etching reaction. After removal, the surface is repeatedly rinsed with deionized water to remove the alkaline solution adhering to the surface, and a matte K2Ta2O6 / Ta sheet is obtained.

[0010] S2. Preparation of BaTa2(O,OH)7 / Ta tablets by ion exchange method: The K2Ta2O6 / Ta tablets obtained in step S1 are placed in a dissolving container containing Ba salt solution and the reaction is continued in a sealed container. After that, the tablets are taken out and repeatedly rinsed with deionized water to remove the ions attached to the surface, and then matte BaTa2(O,OH)7 / Ta tablets are obtained.

[0011] S3. Place the BaTa2(O,OH)7 / Ta sheet obtained in step S2 in a tube furnace and sinter it in an ammonia atmosphere. The sample that regains its metallic luster is the BaTaO2N photoanode.

[0012] Preferably, in step S1, before use, the tantalum sheet is polished off with 200-mesh, 400-mesh, 600-mesh and 800-mesh diamond abrasive in stages to remove the oxide layer on the surface of the tantalum sheet, so that the tantalum sheet can be etched by KOH solution, and the surface of the tantalum sheet is smooth and flat after polishing.

[0013] Preferably, in step S1, the concentration of potassium hydroxide (KOH) is 1-5M, the etching reaction temperature is 80-200℃, and the reaction time is 5-48h.

[0014] Preferably, in step S2, the concentration of the Ba salt solution is 10-100 mM, the Ba salt solution is neutral, and the type of Ba salt is soluble BaCl2 or Ba(NO3)3 or their hydrated salts.

[0015] Preferably, in step S2, the reaction time in the dissolving container is 10-24 h, and the reaction temperature is 100-220 °C.

[0016] Preferably, in step S3, the ammonia atmosphere is provided in the furnace cavity by high-purity liquid ammonia, which also serves as a nitrogen source and protective gas to prevent the Ta substrate from being further oxidized.

[0017] Preferably, the ammonia flow rate in the ammonia atmosphere is 20-200 sec, the sintering temperature is 600-1000℃, and the sintering time is 3-12 h.

[0018] The beneficial effects of this invention are:

[0019] This invention utilizes a mild preparation method. During the preparation process, tantalum and barium elements with poor migration capabilities are pre-arranged on the surface of a tantalum sheet. The size of the product is determined solely by the etching reaction conditions, and the product exhibits uniform size. The method employs ion exchange and crystal phase transformation to prepare BaTaO2N photoanodes, overcoming the challenge of low ion mobility in tantalum-based material preparation. The product is uniform and reproducible. Furthermore, it avoids the use of expensive scientific instruments and equipment required for methods such as electron beam deposition and magnetron sputtering. This invention offers advantages such as mild preparation conditions, high energy efficiency, and minimal equipment requirements. It is highly scalable, solving the problems of high-temperature conditions and expensive equipment required in the synthesis of tantalum-based materials, and produces no organic waste. It has significant application value in the preparation of new energy materials and devices. Attached Figure Description

[0020] Figure 1 XRD pattern of the BaTa2(O,OH)7 / Ta thin film precursor prepared in Example 1 of this invention;

[0021] Figure 2 The images show the XRD patterns of the BaTaO2N photoanodes obtained in Examples 1-4, where a, b, c, and d correspond to Examples 1, 2, 3, and 4, respectively.

[0022] Figure 3 This is a front scanning electron microscope image of the BaTaO2N photoanode prepared in Example 1 of the present invention;

[0023] Figure 4 The front X-ray dispersive energy spectrum of the BaTaO2N photoanode prepared in Example 1 of this invention;

[0024] Figure 5 This is a cross-sectional scanning electron microscope image of the BaTaO2N photoanode prepared in Example 1 of the present invention;

[0025] Figure 6 This is a scanning electron microscope image of the BaTaO2N photoanode prepared in Example 2 of the present invention;

[0026] Figure 7 The front X-ray dispersive energy spectrum of the BaTaO2N photoanode prepared in Example 2 of this invention;

[0027] Figure 8 A front scanning electron microscope image of the BaTaO2N photoanode prepared in Example 3 of this invention;

[0028] Figure 9 The front X-ray dispersive energy spectrum of the BaTaO2N photoanode prepared in Example 3 of this invention;

[0029] Figure 10 An optical photograph of the BaTaO2N photoanode prepared in Example 4 of this invention;

[0030] Figure 11 The front X-ray dispersive energy spectrum of the BaTaO2N photoanode prepared in Example 4 of this invention;

[0031] Figure 12 The LSV scan curves of the BaTaO2N photoanodes prepared in Examples 1-4 of this invention;

[0032] Figure 13 The time-current curve of the BaTaO2N photoanode prepared in Example 2 of this invention;

[0033] Figure 14 An optical photograph of the BaTaO2N photoanode prepared in Example 3 of this invention;

[0034] Figure 15 An optical photograph of the BaTaO2N photoanode prepared in Example 4 of this invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention provides a technical solution: a BaTaO2N photoanode, wherein a BaTaO2N layer is uniformly covered on the surface of a tantalum substrate, forming a single-layer thin film structure. The thickness of the film is the same as the size of the BaTaO2N particles, and it consists of monodisperse and interpenetrating BaTaO2N particles. The BaTaO2N layer and the substrate layer are bonded through Ta4N and TaN to form a heterostructure. The BaTaO2N has a regular octahedral geometry; the edge length of the octahedron is 400 nm to 800 nm.

[0037] A method for preparing a BaTaO2N photoanode includes the following steps:

[0038] 1. Prepare a clear potassium hydroxide (KOH) solution: Slowly add 561g of KOH to an appropriate amount of deionized water and stir thoroughly until dissolved to obtain a KOH solution with a concentration of 1-5 mol / L for later use.

[0039] 2. Apply 200, 400, 600, and 800 mesh diamond abrasive to a hand drill with a wool grinding head, and grind away the tantalum oxide layer on the surface of the tantalum sheet step by step. After grinding, the surface of the tantalum sheet is bright and smooth without obvious scratches. Then, wash away the esters, diamond abrasive, and wool fibers adhering to the surface of the tantalum sheet with soapy water, deionized water, and ethanol alternately to obtain crystalline tantalum sheet.

[0040] 3. Take 20-350mL of potassium hydroxide KOH solution (1-5M) and a clean and bright tantalum sheet of a certain size (1*1cm-10*10cm) and put it into a dissolving container (capacity of 25-500mL). After sealing, place it in an oven at 80-200℃ for 5-48h of etching reaction. After taking it out, rinse it repeatedly with deionized water to remove the alkaline solution adhering to the surface and obtain a matte K2Ta2O6 / Ta metastable precursor.

[0041] 4. Place the K2Ta2O6 / Ta sheet obtained in step 3 into a dissolving container (capacity 25-500mL, filling degree 70%) containing 1-100mM Ba salt solution and continue to react at 100-220℃ for 10-24h. After that, take it out and rinse it repeatedly with deionized water to remove excess ions adhering to the surface to obtain a matte BaTa2(O,OH)7 / Ta film precursor. The concentration of Ba salt solution is 10-100mM, the Ba salt solution is neutral, and the type of Ba salt is soluble BaCl2 or Ba(NO3)3 or their hydrated salt. Alkaline Ba(OH)2 cannot be used.

[0042] 5. Place the BaTa2(O,OH)7 / Ta precursor obtained in step 4 into a tube furnace, using ammonia as a protective gas and nitrogen source, controlling the flow rate between 20-200 sec, and the sintering temperature at 600-1000℃. After sintering for 3-12 hours, the sample regains its metallic luster, and the obtained product is the BaTaO2N photoanode. The tail gas from the tube furnace is connected to deionized water for treatment, and then the tail gas is dried by a calcium chloride column before being recycled to the inlet of the tube furnace to continue reacting with the sample. There is no tail gas emission during the sintering process.

[0043] Example 1

[0044] A method for preparing a BaTaO2N photoanode includes the following steps:

[0045] Step 1: Prepare a strong alkaline solution of potassium hydroxide (KOH). Slowly add 56.1g of KOH to 100 mL of deionized water and stir thoroughly until dissolved to obtain a KOH solution with a concentration of 1 mol / L.

[0046] Step 2: Take a 1*1*0.01cm tantalum sheet, and apply 200, 400, 600 and 800 mesh diamond abrasive to four wool grinding heads respectively. Use an electric hand drill to grind away the tantalum oxide layer on the surface step by step. After grinding, the surface of the tantalum sheet is bright and smooth without obvious scratches. Then, use soapy water, deionized water and ethanol alternately to wash away the esters, diamond abrasive and wool fibers attached to the surface of the tantalum sheet to obtain a crystalline tantalum sheet.

[0047] Step 3: Take 20 mL of the potassium hydroxide KOH solution prepared in Step 1 and the clean and bright tantalum sheet obtained in Step 2, put them into a 25 mL dissolving container, seal it, and place it in an oven. After etching at 160℃ for 6 hours, take it out and rinse it repeatedly with deionized water to remove the alkaline solution adhering to the surface to obtain a matte K2Ta2O6 / Ta metastable precursor.

[0048] Step 4: Place the K2Ta2O6 / Ta sheet obtained in Step 3 into a dissolution container (capacity 25 mL) containing 15 mL of 5 mM BaCl2 solution and continue to react at 140℃ for 10 h. After that, take it out and rinse it repeatedly with deionized water to remove excess ions attached to the surface to obtain a matte BaTa2(O,OH)7 / Ta film precursor.

[0049] Step 5: Place the BaTa2(O,OH)7 / Ta obtained in Step 4 into a tube furnace, using ammonia as a protective gas and nitrogen source, controlling the flow rate at 120 sec, the sintering temperature at 600℃, and sintering for 6 hours. After the sintering is completed, the sample regains its metallic luster, and the product obtained is the BaTaO2N photoanode. The tail gas from the tube furnace is connected to deionized water treatment, and then the tail gas is dried by a calcium chloride column. Finally, it is circulated to the inlet of the tube furnace to continue reacting with the sample. There is no tail gas emission during the sintering process.

[0050] like Figure 1 As shown, by Figure 1 The lower part shows that the polished tantalum sheet corresponds to the standard card library JCPDS: 04-0788, is cubic, has a sharp main peak, and no impurity peaks. Figure 1 The diffraction curves in the upper part show that the sample maintained the main diffraction peaks of tantalum. After the secondary hydrothermal reaction, the basic structure of the tantalum sheet did not change significantly. A series of weaker diffraction peaks appeared in the diffraction curves, corresponding to the standard card library JCPDS: 16-0616 (BaTa2(O,OH)7), which belongs to the cubic crystal system. This indicates that a BaTa2(O,OH)7 precursor was grown on the surface of the tantalum sheet after the hydrothermal reaction, and the tantalum atoms on the surface of the tantalum sheet participated in the hydrothermal reaction.

[0051] The XRD pattern of the BaTaO2N photoanode in this embodiment is as follows: Figure 2 As shown in Figure a, the XRD pattern of the sample simultaneously shows four diffraction peaks from four different crystal states: 04-0788, 32-1282, 39-1485, and 40-0566, according to the standard card JCPDS: 04-0788, 32-1282, 39-1485, and 40-0566. These peaks are attributed to cubic tantalum, orthorhombic Ta4N, hexagonal TaN, and cubic BaTaO2N, respectively. This indicates that the BaTaO2N photoanode sample is composed of a Ta sheet as the substrate, with Ta4N and TaN acting as photoelectron transport media between the substrate and the BaTaO2N layer. The morphology and composition of the BaTaO2N photoanode are shown below. Figure 3 , Figure 4 , Figure 5 As shown: Frontal scanning electron microscope (SEM) Figure 3 It can be seen that the BaTaO2N thin film is composed of regular octahedral particles with an edge length of about 600 nanometers. The particles are flat and uniform in size, and the X-ray dispersion energy (…) Figure 4 As shown, the characteristic peaks of tantalum, nitrogen, and barium are all reflected in the energy dispersive spectroscopy (Note: Oxygen is a common element; the oxygen contained in the sample surface, such as adsorbed carbon dioxide and water molecules, may interfere with the detection, therefore it is not marked in the energy dispersive spectroscopy, and will not be described again in the following examples); cross-sectional scanning electron microscopy ( Figure 5 It can be seen that the thickness of the photoanode is also around 600 nanometers, which is close to the edge length of the BaTaO2N particles, indicating that BaTaO2N is a single-layer structure. Figure 12 The LSV scan curve of the BaTaO2N photoanode prepared in Example 1 of this invention under standard simulated sunlight irradiation shows that the current increases significantly with the addition of light conditions, and the current intensity gradually increases with the increase of voltage, reaching 1.12mA at 1.23 V.

[0052] Example 2

[0053] A method for preparing a BaTaO2N photoanode includes the following steps:

[0054] Step 1: Prepare a strong alkaline solution of potassium hydroxide (KOH). Slowly add 56.1g of KOH to 100 mL of deionized water and stir thoroughly until dissolved to obtain a KOH solution with a concentration of 1 mol / L.

[0055] Step 2: Take a 3*3*0.01cm tantalum sheet, and apply 200, 400, 600 and 800 mesh diamond abrasive to four wool grinding heads respectively. Use an electric hand drill to grind away the tantalum oxide layer on the surface step by step. After grinding, the surface of the tantalum sheet is bright and smooth without obvious scratches. Then, use soapy water, deionized water and ethanol alternately to wash away the esters, diamond abrasive and wool fibers attached to the surface of the tantalum sheet to obtain a crystalline tantalum sheet.

[0056] Step 3: Take 30 mL of the potassium hydroxide KOH solution prepared in Step 1 and the clean and bright tantalum sheet obtained in Step 2, put them into a 50 mL dissolving container, seal it, and place it in an oven. After etching at 160℃ for 18 hours, take it out and rinse it repeatedly with deionized water to remove the alkaline solution adhering to the surface to obtain a matte K2Ta2O6 / Ta metastable precursor.

[0057] Step 4: Place the K2Ta2O6 / Ta sheet obtained in Step 3 into a dissolution container (capacity 50 mL) containing 30 mL of 20 mM BaCl2 solution and continue to react at 180℃ for 12 h. After that, take it out and rinse it repeatedly with deionized water to remove excess ions attached to the surface to obtain a matte BaTa2(O,OH)7 / Ta film precursor.

[0058] Step 5: Place the BaTa2(O,OH)7 / Ta obtained in Step 4 into a tube furnace, using ammonia as a protective gas and nitrogen source, controlling the flow rate at 120 sec, the sintering temperature at 700℃, and sintering for 6 hours. After the sintering is completed, the sample regains its metallic luster, and the product obtained is the BaTaO2N photoanode. The tail gas from the tube furnace is connected to deionized water treatment, and then the tail gas is dried by a calcium chloride column. Finally, it is circulated to the inlet of the tube furnace to continue reacting with the sample. There is no tail gas emission during the sintering process.

[0059] The XRD pattern of the BaTaO2N photoanode in this embodiment is shown below. Figure 2As shown in b, the XRD pattern of the sample simultaneously shows four diffraction peaks from four different crystal states: 04-0788, 32-1282, 39-1485, and 40-0566, according to the standard card JCPDS: 04-0788, 32-1282, 39-1485, and 40-0566. These peaks are attributed to cubic tantalum, orthorhombic Ta4N, hexagonal TaN, and cubic BaTaO2N, respectively. This indicates that the BaTaO2N photoanode sample is composed of a Ta sheet as the substrate, with Ta4N and TaN acting as photoelectron transport media between the substrate and the BaTaO2N layer. The morphology and composition of the BaTaO2N photoanode are shown below. Figure 6 , Figure 7 As shown: Frontal scanning electron microscope (SEM) Figure 6 It can be seen that the BaTaO2N thin film is composed of regular octahedral particles with an edge length of about 500 nanometers. The particles are flat and uniform in size, and the X-ray dispersion energy ( Figure 7 As shown, its constituent elements are tantalum, nitrogen, and barium; Figure 12 As shown, the LSV scan curve of the BaTaO2N photoanode prepared in Example 2 of this invention under standard simulated sunlight irradiation shows that the current increases significantly with the addition of light conditions, and the current intensity gradually increases with the increase of voltage, reaching 12 mA at 1.23 V. Figure 13 The time-current curve of the BaTaO2N photoanode prepared in Example 2 of this invention under standard simulated sunlight irradiation with a voltage of 1.23 V shows that the photoanode can maintain a stable current of 10 mA and the current hardly decays after 100 hours of continuous operation.

[0060] Example 3

[0061] A method for preparing a BaTaO2N photoanode includes the following steps:

[0062] Step 1: Prepare a strong alkaline solution of potassium hydroxide (KOH). Slowly add 280.5g of KOH to 1000mL of deionized water and stir thoroughly until dissolved to obtain a KOH solution with a concentration of 5 mol / L.

[0063] Step 2: Take a 10*10*0.01 cm tantalum sheet and apply 200, 400, 600 and 800 mesh diamond abrasive to four wool grinding heads respectively. Use an electric hand drill to grind away the tantalum oxide layer on the surface step by step. After grinding, the surface of the tantalum sheet is bright and smooth without obvious scratches. Then, use soapy water, deionized water and ethanol alternately to wash away the esters, diamond abrasive and wool fibers attached to the surface of the tantalum sheet to obtain a crystalline tantalum sheet.

[0064] Step 3: Take 350 mL of the potassium hydroxide KOH solution prepared in Step 1 and the clean and bright tantalum sheet obtained in Step 2, put them into a 500 mL dissolving container, seal it, and place it in an oven. After etching at 180℃ for 32 hours, take it out and rinse it repeatedly with deionized water to remove the alkaline solution adhering to the surface to obtain a matte K2Ta2O6 / Ta metastable precursor.

[0065] Step 4: Place the K2Ta2O6 / Ta sheet obtained in Step 3 into a dissolution container (capacity 500 mL) containing 350 mL of 50 mM BaCl2 solution and continue to react at 200℃ for 18 h. After that, take it out and rinse it repeatedly with deionized water to remove excess ions attached to the surface to obtain a matte BaTa2(O,OH)7 / Ta film precursor.

[0066] Step 5: Place the BaTa2(O,OH)7 / Ta obtained in Step 4 into a tube furnace, using ammonia as a protective gas and nitrogen source, controlling the flow rate at 200 sec, the sintering temperature at 900℃, and sintering for 12 h. After the sintering is completed, the sample regains its metallic luster, and the product obtained is the BaTaO2N photoanode. The tail gas from the tube furnace is connected to deionized water treatment, and then the tail gas is dried by a calcium chloride column. Finally, it is circulated to the inlet of the tube furnace to continue reacting with the sample. There is no tail gas emission during the sintering process.

[0067] The XRD pattern of the BaTaO2N photoanode in this embodiment is shown below. Figure 2 As shown in c, the XRD pattern of the sample simultaneously shows four diffraction peaks from four different crystal states: 04-0788, 32-1282, 39-1485, and 40-0566, according to the standard card JCPDS: 04-0788, 32-1282, 39-1485, and 40-0566. These peaks are attributed to cubic tantalum, orthorhombic Ta4N, hexagonal TaN, and cubic BaTaO2N, respectively. This indicates that the BaTaO2N photoanode sample is composed of a Ta sheet as the substrate, with Ta4N and TaN acting as photoelectron transport media between the substrate and the BaTaO2N layer. The morphology and composition of the BaTaO2N photoanode are as follows: Figure 8 , Figure 9 As shown: Frontal scanning electron microscope (SEM) Figure 8 It can be seen that the BaTaO2N thin film is composed of regular octahedral particles with an edge length of about 500 nanometers. The particles are flat and uniform in size, and the X-ray dispersion energy ( Figure 9 As shown, its constituent elements are tantalum, nitrogen, and barium; Figure 12 As shown, the LSV scan curve of the BaTaO2N photoanode prepared in Example 3 of this invention under standard simulated sunlight irradiation shows that the current intensity gradually increases with increasing voltage, reaching 13.2 mA at 1.23V. An optical photograph of the BaTaO2N photoanode is shown below. Figure 14 As shown.

[0068] Example 4

[0069] A method for preparing a BaTaO2N photoanode includes the following steps:

[0070] Step 1: Prepare a strong alkaline solution of potassium hydroxide (KOH). Slowly add 224.4g of KOH to 200 mL of deionized water and stir thoroughly until dissolved to obtain a KOH solution with a concentration of 2 mol / L.

[0071] Step 2: Take a 3.5*3.5*0.2 cm tantalum sheet, and apply 200, 400, 600 and 800 mesh diamond abrasive to four wool grinding heads respectively. Use an electric hand drill to grind away the tantalum oxide layer on the surface step by step. After grinding, the surface of the tantalum sheet is bright and smooth without obvious scratches. Then, use soapy water, deionized water and ethanol alternately to wash away the esters, diamond abrasive and wool fibers attached to the surface of the tantalum sheet to obtain a crystalline tantalum sheet.

[0072] Step 3: Take 140 mL of the potassium hydroxide KOH solution prepared in Step 1 and the clean and bright tantalum sheet obtained in Step 2, put them into a 200 mL dissolving container, seal it, and place it in an oven. After etching at 160℃ for 24 hours, take it out and rinse it repeatedly with deionized water to remove the alkaline solution adhering to the surface to obtain a matte K2Ta2O6 / Ta metastable precursor.

[0073] Step 4: Place the K2Ta2O6 / Ta sheet obtained in Step 3 into a dissolution container (capacity 500 mL) containing 350 mL of 20 mM BaCl2 solution and continue to react at 180℃ for 18 h. After that, take it out and rinse it repeatedly with deionized water to remove excess ions attached to the surface to obtain a matte BaTa2(O,OH)7 / Ta film precursor.

[0074] Step 5: Place the BaTa2(O,OH)7 / Ta obtained in Step 4 into a tube furnace, using ammonia as a protective gas and nitrogen source, controlling the flow rate at 140 sec, the sintering temperature at 950℃, and sintering for 8 hours. After the sintering is completed, the sample regains its metallic luster, and the product obtained is the BaTaO2N photoanode. The tail gas from the tube furnace is connected to deionized water treatment, and then the tail gas is dried by a calcium chloride column. Finally, it is circulated back to the inlet of the tube furnace to continue the reaction with the sample. There is no tail gas emission during the sintering process.

[0075] The XRD pattern of the BaTaO2N photoanode in this embodiment is as follows: Figure 2As shown in d, the XRD pattern of the sample simultaneously shows four diffraction peaks from four different crystal states: 04-0788, 32-1282, 39-1485, and 40-0566, according to the standard card JCPDS: 04-0788, 32-1282, 39-1485, and 40-0566. These peaks are attributed to cubic tantalum, orthorhombic Ta4N, hexagonal TaN, and cubic BaTaO2N, respectively. This indicates that the BaTaO2N photoanode sample is composed of a Ta sheet as the substrate, with Ta4N and TaN acting as photoelectron transport media between the substrate and the BaTaO2N layer. The morphology and composition of the BaTaO2N photoanode are shown below. Figure 10 , Figure 11 As shown: Frontal scanning electron microscope (SEM) Figure 10 It can be seen that the BaTaO2N thin film is composed of regular octahedral particles with an edge length of about 500 nanometers. The particles are flat and uniform in size, and the X-ray dispersion energy ( Figure 11 As shown, its constituent elements are tantalum, nitrogen, and barium; Figure 12 As shown, the LSV scan curve of the BaTaO2N photoanode prepared in Example 4 of this invention under standard simulated sunlight irradiation shows that the current increases significantly with the addition of light, and the current intensity gradually increases with the increase of voltage. Its current intensity at 1.23V can reach 12 mA. The optical photograph of the BaTaO2N photoanode is shown below. Figure 15 As shown.

[0076] Comparative argument

[0077] Chinese patent CN 114657594 B discloses a method for directly depositing Ba and Ta sources onto a conductive substrate using dual-source electron beam deposition, followed by high-temperature reaction at nitrogen and ammonia atmospheres for a certain time to obtain a BaTaO2N photoanode. However, this method requires a dual-source electron beam device operating under extremely high vacuum, making it expensive and difficult to widely implement. The area of ​​the photoanode is limited by the cavity of the dual-source deposition device, hindering large-area fabrication. Furthermore, the photoanode absorber layer produced by this method exhibits loose particle arrangement, irregular morphology, and uneven size. This is due to insufficient mixing of the pre-deposited Ba and Ta atoms on the substrate; their extremely poor migration ability restricts the contact between Ba and Ta atoms, resulting in irregular morphology of the BaTaO2N absorber layer particles. In contrast, this method employs a very mild two-part liquid-phase method with low equipment requirements, enabling high-cost fabrication.

[0078] Chinese patent CN 109928762 A discloses a dual-nitrogen source preparation method for BaTaO2N oxynitride powder. The method involves ball milling and drying an alkaline earth metal and a nitrogen source tantalum salt to prepare a precursor, which is then calcined together with the nitrogen source in a protective atmosphere to produce BaTaO2N oxynitride powder. However, the precursor in this method contains alkaline earth metal and melamine. Alkaline earth metal salts exhibit strong corrosive properties at high temperatures, potentially damaging high-temperature equipment. Furthermore, melamine is a carbon-containing organic compound; its oxidation and decomposition at high temperatures produces carbonaceous waste, making it unsuitable for large-scale application. Additionally, the product of this method is an irregular BaTaO2N powder, which cannot be used to prepare photoanodes, thus limiting its application.

[0079] Chinese patent CN 103611556 B discloses a ZnO-BaTaO2N composite photocatalyst, which involves BaTaO2N powder. Specifically, BaTaO2N powder is prepared by grinding tantalum pentoxide, barium carbonate, and acetone in an agate mortar and then calcining them under an ammonia atmosphere. This method cannot avoid the influence of barium carbonate in the high-temperature molten state on the equipment. Moreover, acetone is a readily available toxic reagent and is itself a moderately toxic reagent, requiring additional protective devices during operation. This method avoids the damage to the equipment caused by high-temperature molten salt and does not involve excessive organic solvents, thus requiring no additional protection.

[0080] Most importantly, the synthesis methods used in the aforementioned existing technologies are all solid-phase synthesis methods. The contact density between solids is less than that between solids and liquids, resulting in non-uniform reaction centers, which in turn affects the morphology and size uniformity of the reaction products. In contrast, the tantalum and barium sources in this patent undergo mild liquid-phase synthesis and ion exchange processes in steps S1 and S2, causing the reaction of Ta and Ba atoms to occur on the substrate surface. Particularly important is the reaction between KOH and the tantalum sheet in step S1, which transforms the free Ta on its surface into a metastable K2Ta2O6 layer. The subsequent step S2 exchanges Ba ions with K ions in the K2Ta2O6 layer lattice to prepare a BaTa2(O,OH)7 precursor with regularly arranged Ba and Ta atoms, as well as a regular morphology and uniform size. Then, through subsequent nitriding, it is transformed into a BaTaO2N photoanode with a similar morphology and size to the precursor.

[0081] The method of this invention has the advantages of mild preparation conditions, high energy utilization, and small equipment requirements. It is highly scalable and solves the problem of high temperature conditions and expensive equipment required in the preparation and synthesis of tantalum-based materials. It also has the characteristics of no organic waste emission and has extremely high application value in the preparation of optoelectronic semiconductor thin films and devices.

[0082] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A BaTaO2N photoanode, characterized in that, The BaTaO2N photoanode has an octahedral structure with an edge length of 400 nm to 800 nm. The BaTaO2N layer is bonded to the substrate layer via Ta4N and TaN, forming a heterostructure. The BaTaO2N layer uniformly covers the surface of the tantalum substrate, forming a single-layer thin film structure. The thickness of the film is the same as the size of the BaTaO2N particles, and it consists of monodisperse and interpenetrating BaTaO2N particles. The preparation of the BaTaO2N photoanode includes the following steps: S1. Preparation of metastable K2Ta2O6 precursor: Potassium hydroxide KOH solution and clean, bright tantalum sheet are placed in a dissolving container, sealed, and placed in an oven for etching reaction. After removal, the surface is repeatedly rinsed with deionized water to remove the alkaline solution adhering to the surface, and a matte K2Ta2O6 / Ta sheet is obtained. S2. Preparation of BaTa2(O,OH)7 / Ta tablets by ion exchange method: The K2Ta2O6 / Ta tablets obtained in step S1 are placed in a dissolving container containing Ba salt solution and the reaction is continued in a sealed container. After that, the tablets are taken out and repeatedly rinsed with deionized water to remove the ions attached to the surface, so as to obtain matte BaTa2(O,OH)7 / Ta tablets. The concentration of the Ba salt solution is 10-100mM, the Ba salt solution is neutral, and the type of Ba salt is soluble BaCl2 or Ba(NO3)3 or their hydrated salts. S3. Place the BaTa2(O,OH)7 / Ta sheet obtained in step S2 in a tube furnace and sinter it in an ammonia atmosphere. The sample that regains its metallic luster is the BaTaO2N photoanode.

2. A method for preparing a BaTaO2N photoanode according to claim 1, characterized in that: Includes the following steps: S1. Preparation of metastable K2Ta2O6 precursor: Potassium hydroxide KOH solution and clean, bright tantalum sheet are placed in a dissolving container, sealed, and placed in an oven for etching reaction. After removal, the surface is repeatedly rinsed with deionized water to remove the alkaline solution adhering to the surface, and a matte K2Ta2O6 / Ta sheet is obtained. S2. Preparation of BaTa2(O,OH)7 / Ta tablets by ion exchange method: The K2Ta2O6 / Ta tablets obtained in step S1 are placed in a dissolving container containing Ba salt solution and the reaction is continued in a sealed container. After that, the tablets are taken out and repeatedly rinsed with deionized water to remove the ions attached to the surface, so as to obtain matte BaTa2(O,OH)7 / Ta tablets. The concentration of the Ba salt solution is 10-100mM, the Ba salt solution is neutral, and the type of Ba salt is soluble BaCl2 or Ba(NO3)3 or their hydrated salts. S3. Place the BaTa2(O,OH)7 / Ta sheet obtained in step S2 in a tube furnace and sinter it in an ammonia atmosphere. The sample that regains its metallic luster is the BaTaO2N photoanode.

3. The method for preparing the BaTaO2N photoanode according to claim 2, characterized in that: In step S1, before use, the tantalum sheet is polished off with diamond abrasive of 200 mesh, 400 mesh, 600 mesh and 800 mesh in stages to remove the oxide layer on the surface of the tantalum sheet, so that the tantalum sheet can be etched by KOH solution. After polishing, the surface of the tantalum sheet is smooth and flat.

4. The method for preparing the BaTaO2N photoanode according to claim 2, characterized in that: In step S1, the concentration of potassium hydroxide (KOH) is 1-5M, the etching reaction temperature is 80-200℃, and the reaction time is 5-48h.

5. The method for preparing the BaTaO2N photoanode according to claim 2, characterized in that: In step S2, the reaction time in the dissolving container is 10-24 h, and the reaction temperature is 100-220 °C.

6. The method for preparing the BaTaO2N photoanode according to claim 2, characterized in that: In step S3, the ammonia atmosphere is provided in the furnace cavity by high-purity liquid ammonia, which also serves as a nitrogen source and protective gas to prevent the Ta substrate from being further oxidized.

7. The method for preparing the BaTaO2N photoanode according to claim 6, characterized in that: The ammonia flow rate in the ammonia atmosphere is 20-200 sec, the sintering temperature is 600-1000℃, and the sintering time is 3-12 h.

Images