Transition metal-doped tungsten molybdic acid and method for producing the same, and heating apparatus, electric device, and hydrogen generation apparatus

Abstract

To provide a new transition metal-doped tungsten molybdic acid doped with one or more transition elements.SOLUTION: In the transition metal-doped tungsten molybdate, a compound represented by MoxW1 - xO3 - nH2O (0 ≤ x ≤ 1, 0 ≤ n) is doped with one or more elements selected from the group consisting of transition elements (excluding Mo and W).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transition metal-doped tungsto-molybdic acid and a method for producing the same, as well as a heating apparatus, an electric device, and a hydrogen generating apparatus. [Background technology]

[0002] Tungstate molybdic acid, which contains tungsten and molybdenum, is known to have special electrical and optical properties. It is expected that this tungstate molybdic acid will be used in a wide range of applications, including photoelectric conversion materials and photocatalysts. Various methods have been proposed for synthesizing tungstate molybdic acid. Non-Patent Document 1 describes the synthesis of ammonium metatungstate hydrate ((NH4)6H2W 12 O 40 ·XH2O) and ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O 24 4H2O) and heated to 180°C. x W 1-x A method for synthesizing O3·0.33H2O has been reported.

[0003] In addition, Non-Patent Document 2 discloses that powdered molybdenum and powdered tungsten are dissolved in hydrogen peroxide and heated to 200°C to obtain Mo x W 1-x A method for obtaining O3·0.33H2O is described.

[0004] Furthermore, Non-Patent Document 3 states that Na2WO4 -2 A method for synthesizing tungsten oxide is described, in which H2O is dissolved in an aqueous solution of H2SO4 and heated at 180°C. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] A. Arzola-Rubio, et al., "Enhanced optical properties of W1-xMoxO3·0.33H2O solid solutions with tunable band gaps", Superlattices and Microstructures, 81 (2015), 175-184 [Non-patent document 2] Liang Zhou, et al., "MoxW1-xO3·0.33H20 Solid Solutions with Tunable Band Gaps", J. Phys. Chem. C, 114 (2010), 20947-20954 [Non-patent document 3] Shobhnath P. Gupta, et al., "Highly ordered nano-tunnel structure of hydrated tungsten oxide nanorods for superior flexible quasi-solid-state hybrid supercapacitor", Applied Surface Science, 545 (2021), 149044 Summary of the Invention [Problem to be solved by the invention]

[0006] In all of the above methods, a high-temperature reaction is essential, and a simpler synthesis method is desired. Furthermore, in the methods of Non-Patent Document 1 and Non-Patent Document 2, elements other than the essential elements are present in the reaction system. Therefore, it is necessary to remove impurities from the obtained compound by calcination or the like. Furthermore, the tungstate molybdate obtained in any of the above documents does not contain transition elements other than W and Mo as dopants.

[0007] An object of the present invention is to provide a novel transition metal-doped tungsto-molybdic acid doped with one or more transition elements, a simple method for producing the transition metal-doped tungsto-molybdic acid, and a heating apparatus, electric device, and hydrogen generator that include the transition metal-doped tungsto-molybdic acid. [Means for solving the problem]

[0008] The present invention provides the following transition metal-doped tungsto-molybdic acid. [1]Mo x W 1-x Transition metal-doped tungstate molybdate, in which a compound represented by O3·nH2O (0≦x≦1, 0≦n) is doped with one or more elements selected from the group consisting of transition elements (excluding Mo and W). [2] The transition metal-doped tungsten molybdate according to [1], which is doped with two or more elements selected from the group consisting of Cu, Fe, Mn, Co, and Zn. [3] The transition metal-doped tungsto-molybdic acid according to [1] or [2], which contains oxygen vacancies in its structure.

[0009] The present invention provides the following method for producing transition metal-doped tungsto-molybdic acid. [4] A method for producing a transition metal-doped tungsten molybdenum acid, comprising the steps of: preparing a solution in which tungsten oxide and / or molybdenum oxide is dissolved in hydrogen peroxide; irradiating the solution with light having a wavelength of 365 nm or less; adding one or more transition elements (excluding Mo and W) to the solution after light irradiation; and irradiating the solution after adding the transition elements with light having a wavelength of 365 nm.

[0010] The present invention provides the following heating apparatus, electric device, and hydrogen generation apparatus. [5] A heating device having a photothermal conversion part containing the transition metal-doped tungsto-molybdic acid according to any one of [1] to [3] above. [6] An electric device having a photocapacitor containing the transition metal-doped tungsto-molybdic acid according to any one of [1] to [3] above. [7] A hydrogen generator having an electrode containing the transition metal-doped tungsto-molybdic acid according to any one of [1] to [3] above. [Effects of the Invention]

[0011] According to the present invention, a novel transition metal-doped tungsto-molybdic acid is provided, which is doped with one or more transition elements. Furthermore, according to the method for producing the transition metal-doped tungsto-molybdic acid of the present invention, it is possible to produce the transition metal-doped tungsto-molybdic acid with an extremely low impurity content by a simple method. Furthermore, according to the present invention, a heating apparatus, an electric device, and a hydrogen generating apparatus having excellent properties are also provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1A is a schematic diagram of the arrangement of elements in a transition metal-doped tungsten molybdate according to one embodiment of the present invention. FIG. 1B is a HAADF-STEM image of Cu-doped MoxW1-xO3·nH2O. FIG. 1C is a HAADF-STEM image of Cu-, Fe-, and Mn-doped MoxW1-xO3·nH2O. [Figure 2] 2A to 2D are schematic diagrams illustrating a method for producing a transition metal-doped tungsto-molybdic acid according to one embodiment of the present invention. [Figure 3] 3A and 3B are photographs showing the state of crystals grown by a method for producing transition-metal-doped tungsto-molybdic acid according to one embodiment of the present invention. [Figure 4] FIG. 4 is a graph showing the light absorption characteristics of the transition metal-doped tungstate molybdate (Cu doping amount: 0% to 20%) synthesized in Example 1. [Figure 5]FIG. 5A is an image of a sample obtained by performing a photothermal conversion test on the transition metal-doped tungsto-molybdic acid synthesized in Example 1, and FIG. 5B is a thermography image of the sample when irradiated with simulated sunlight. [Figure 6] FIG. 6A is an SEM image of the transition metal-doped tungsto-molybdic acid synthesized in Example 2, and FIG. 6B is its XRD pattern. [Figure 7] FIG. 7A shows the measurement results of the visible-near infrared light absorptance of the transition metal-doped tungsto-molybdic acid synthesized in Example 2, and FIG. 7B is a graph showing the solar light absorption efficiency. [Figure 8] FIG. 8A is an image of a sample obtained by performing a photothermal conversion test on the transition metal-doped tungsto-molybdic acid synthesized in Example 2, and FIG. 8B is a thermography image of the sample when irradiated with simulated sunlight. [Figure 9] FIG. 9A is a graph showing the photoresponsive current characteristics of Cu / Fe / Mn-doped MoWOH, and FIG. 9B is a graph showing the photoresponsive current characteristics of Cu-doped MoWOH. [Figure 10] FIG. 10 is a graph showing the photogeneration capacity in the dark and under simulated solar light irradiation for undoped MoWOH, Cu-doped MoWOH, and Cu / Fe / Mn-doped MoWOH. DETAILED DESCRIPTION OF THE INVENTION

[0013] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages.

[0014] 1. Transition metal-doped tungsto-molybdic acid and its manufacturing method The present invention uses Mo as the base material. x W 1-xRelates to transition metal-doped tungsten molybdate in which a compound represented by O3·nH2O (0≦x≦1, 0≦n) is doped with one or more elements selected from the group consisting of transition elements (excluding Mo and W).

[0015] The base material may be WO3·H2O (in the above chemical formula, x = 0), or may be MoO3·H2O (in the above chemical formula, x = 1). Also, Mo x W 1-x O3·H2O (in the above chemical formula, 0 < x < 1) may also be used. Also, n = 0 may be used, but when 0 < n, the electrical and optical properties of the transition metal-doped tungsten molybdate tend to be better. The upper limit of n is not particularly limited, but usually n≦1 or n = 2 (dihydrate). Here, when 0 < x < 1, if the value of x is sufficiently small, it tends to be Mo-doped WO3·H2O having the crystal structure of WO3·H2O. Also, when the value of x is sufficiently large, it tends to be W-doped MoO3·H2O having the crystal structure of α-MoO3·H2O. Furthermore, when the value of x is an intermediate value, it has a crystal structure different from WO3·H2O or α-MoO3·H2O, and tends to be Mo x W 1-x O3·0.33H2O (hereinafter also referred to as "MoWOH"). However, other compositions may also be used.

[0016] The element (dopant) doped in the transition metal-doped tungsten molybdate of the present invention may be only one kind, or two or more kinds. Particularly, when two or more elements are doped, it is preferable from the viewpoint that it is easier to adjust the light absorption characteristics and the like according to requirements.

[0017] The dopant may be any transition element (excluding W and Mo). In this specification, the term "transition element" includes not only elements from Groups 3 to 11 but also elements from Group 12. Among these transition elements, Cu, Fe, Mn, Co, and Zn are particularly preferred from the viewpoints of ease of availability, ease of doping by the production method (underwater crystal photosynthesis) described below, and the tendency of the resulting transition metal-doped tungstate molybdate to have good optical absorption properties and electrical properties.

[0018] Figure 1A shows a schematic diagram of the arrangement of elements in MoWOH doped with multiple transition elements. Figure 1B shows a HAADF-STEM (high-angle annular dark-field scanning transmission microscopy) image of Cu-doped MoWOH, and Figure 1C shows a HAADF-STEM image of Fe-, Cu-, and Mn-doped MoWOH. For example, as shown in Figure 1B, when MoWOH is doped with a transition element (Cu in this case), oxygen vacancies (V) appear in a portion of the MoWOH. o ) occurs. Such oxygen vacancies (V o ) occurs, the light absorption rate of the transition metal-doped tungsten molybdate increases, and the light absorption rate in the infrared region also increases. o The presence of ) can be confirmed not only by HAADF-STEM image observation but also by analysis using, for example, XPS (X-ray photoelectron spectroscopy).

[0019] Also, W on the W site 6+ Fe, which has a larger ionic radius 2+ and Mn 2+ When a transition metal-doped tungsten molybdate is doped, planar defects occur, as shown in Figure 1C. The occurrence of these planar defects tends to increase the light absorption rate of the transition metal-doped tungsten molybdate in sunlight, increase the light absorption rate in the infrared region, and also increase the capacitance of the transition metal-doped tungsten molybdate.

[0020] The amount of dopant in the transition metal-doped tungsto-molybdic acid is not particularly limited, but is usually preferably 0.5 mol% to 40 mol% per mol of the base material. If the amount of dopant is above the lower limit, the optical and electrical properties of the hydrated transition metal tend to be good. If the amount of dopant is below the upper limit, it is unlikely to affect the crystalline structure of the base material.

[0021] (Manufacturing method) The transition metal-doped tungstate molybdate can be produced by the submerged photosynthesis of crystallites (SPsC) method. Specifically, the method includes the following steps: (i) preparing a solution in which tungsten oxide and / or molybdenum oxide is dissolved in an aqueous hydrogen peroxide solution (solution preparation step); (ii) irradiating the solution with light having a wavelength of 365 nm or less (nucleation step); (iii) adding one or more transition elements (excluding Mo and W) to the solution after light irradiation (dopant addition step); and (iv) irradiating the solution after adding the transition elements with light having a wavelength of 365 nm or less (crystal growth step). Note that the production of the transition metal-doped tungstate molybdate may include additional steps, if necessary. The production method will be described below using the schematic diagrams of FIGS. 2A to 2D. 2A to 2D are schematic illustrations of only the main components, and do not accurately represent the amount of each component or the ratio between components.

[0022] (i) Solution preparation process In the solution preparation step, a solution is prepared by dissolving raw material (W and / or Mo) 100 of the base compound in hydrogen peroxide 110 (FIG. 2A). In the solution, the hydrogen peroxide 110 reacts with the raw material 100 to generate oxide ions 101.

[0023] For example, if the base material is WO3·H2O, W is dissolved in hydrogen peroxide. This causes the reaction shown in the following formula (1), and WO4 2- is generated. [ka]

[0024] When the base material is MO3·H2O, Mo is dissolved in hydrogen peroxide. This causes the reaction shown in the following formula (2), and MoO4 2- is generated. [ka]

[0025] When the base material is MoWOH, W and Mo are dissolved in hydrogen peroxide. 2- and MoO4 2- The following is produced. Although W and Mo may be dissolved in hydrogen peroxide at the same time, a solution of W dissolved in hydrogen peroxide and a solution of Mo dissolved in hydrogen peroxide may be prepared separately and then mixed in a predetermined ratio. In this case, the ratio of W and Mo used as raw materials is adjusted appropriately to match the composition of the desired base material.

[0026] The shape of W or Mo to be dissolved in hydrogen peroxide is not particularly limited, and may be any of flake, particle, foil, wire, rod, plate, etc. Among these, a shape that has a large contact area with hydrogen peroxide is preferred because it allows for dissolution in a short time, and flake, particle, foil, etc. are preferred.

[0027] On the other hand, hydrogen peroxide is preferably used in the form of an aqueous solution. The concentration of hydrogen peroxide in the aqueous hydrogen peroxide solution is not particularly limited, but is preferably about 5 to 15% by mass. This concentration allows hydrogen peroxide to react efficiently with W and Mo. The amount (moles) of hydrogen peroxide (H2O2) used is preferably about 2 to 10 times the total amount (moles) of W and Mo. When the amount of hydrogen peroxide (H2O2) is within this range, not only does the above reaction occur more efficiently, but the nucleation step (ii) described below also proceeds more efficiently.

[0028] It is preferable that W and / or Mo are completely dissolved in the solution, and after adding W and / or Mo to the aqueous hydrogen peroxide solution, the solution is preferably left to stand for several hours to several days.

[0029] (ii) Nucleation process The solution prepared in the above (i) solution preparation step is irradiated with light 121 having a wavelength of 365 nm or less from light source 120 to generate base material nuclei 103 (FIGS. 2B and 2C). When the solution is irradiated with light 121 having a wavelength of 365 nm or less, hydrogen peroxide is photodecomposed to generate hydroxyl radicals 102 as shown in the following formula (3). Then, the hydroxyl radicals 102 react with the above-mentioned oxide ions 101 as shown in the following formulas (4a) to (4c) (FIG. 2B). As a result, base material nuclei 103 are generated in the solution (FIG. 2C). [ka]

[0030] For example, tungsten oxide ions (WO4 2- When only molybdenum oxide ions (MoO4 2- When only tungsten oxide ions (WO4 2- ) and molybdenum oxide ion (MoO4 2- When both MoWOH and MoWOH are present, the reaction of the above formula (4c) occurs. Then, MoWOH aggregates to form nuclei.

[0031] The light irradiated onto the solution may be light with a wavelength of 365 nm or less that can photodecompose hydrogen peroxide and generate hydroxyl radicals as described above. In this specification, light with a wavelength of 365 nm also includes electromagnetic waves such as X-rays and gamma rays. The light source is appropriately selected depending on the desired light, and examples include UV lamps, excimer lamps, halogen lamps, and mercury lamps.

[0032] The temperature of the solution during the (ii) nucleation step is preferably 20°C or higher and 50°C or lower. When the solution temperature is within this range, nucleation is likely to be promoted. The (ii) nucleation step may be carried out in a dark place, or may be carried out under normal conditions as long as the light irradiation intensity is sufficient. Stirring is preferably carried out during this step.

[0033] The time for (ii) nucleation step may be any time long enough to generate nuclei, and may be about 24 to 72 hours. The generation of nuclei causes a change in the color of the solution. Therefore, the change in the color of the solution may be used as a guide for the completion of (ii) nucleation step.

[0034] (iii) Dopant addition step One or more transition elements (excluding Mo and W) 104 are added to the solution after the nucleation step (ii) and dissolved (FIG. 2C). The addition of the transition elements 104 is preferably carried out while irradiating the solution with light, similar to that used in the nucleation step (ii).

[0035] The transition element to be added may be in any shape, such as flakes, particles, foil, wire, rod, plate, etc. However, a shape that has a large contact area with hydrogen peroxide is preferred, such as flakes, particles, foil, etc.

[0036] The amount of the transition element to be added is appropriately selected depending on the desired doping amount. When two or more transition elements are added, the ratio between them is adjusted depending on the desired doping ratio.

[0037] Although transition elements are often insoluble in hydrogen peroxide under normal conditions, it is believed that these elements can be dissolved by photodecomposing hydrogen peroxide into hydroxyl radicals, as in the present invention.

[0038] (iv) Crystal growth process (iii) A step of irradiating the solution after the dopant addition step with light 121 having a wavelength of 365 nm or less from a light source 120 is carried out (FIG. 2D). As a result, transition elements 104 and oxide ions (WO4 2- and MoO4 2- ) 101 aggregate, and crystals grow around nuclei 103. In the (iv) crystal growth step, when the above-mentioned light irradiation is performed, photoelectrons generated within the aggregates hop to the nearest lattice point. As a result, the photoelectrons concentrate at the apex of the crystal (aggregate). Therefore, polarization occurs within the crystal (aggregate), and crystals grow at the apex, resulting in the desired transition metal-doped tungsto-molybdic acid. Electron microscope images of transition metal-doped tungsto-molybdic acid crystals grown using this method are shown in Figures 3A and 3B. In Figure 3A, crystals grow mainly at the apex of the crystal, while in Figure 3B, crystals grow around the crystal.

[0039] When irradiating with light in this step, infrared light irradiation or heating may be performed at the same time. Crystal growth can be further promoted by infrared light irradiation or heating. When performing these steps, it is preferable to adjust the temperature of the solution to 20°C or higher and 50°C or lower. The light source of the infrared light can be the same as a general light source. The heating means can be a known heater, oven, etc.

[0040] The time for applying energy is not particularly limited as long as it allows sufficient crystal growth, and is appropriately selected depending on the energy application method, the desired particle size of the transition metal-doped tungsten molybdate, etc. For example, when growing crystals by irradiation with ultraviolet light, it is preferable to perform the application for about 6 to 24 hours.

[0041] After the crystal growth step, the aqueous hydrogen peroxide solution and unreacted components are removed by centrifugation or the like to obtain transition metal-doped tungsten molybdic acid. If necessary, drying may be performed in a dry oven or the like at about 50°C. According to the above method, particulate transition metal-doped tungsten molybdic acid can be obtained, with an average particle size of about 200 nm to 400 nm when observed under an electron microscope. However, in the (ii) nucleation step, (iii) dopant addition step, and (iv) crystal growth step, a metal plate or the like may be placed in the solution and crystals of the transition metal-doped tungsten molybdic acid may be grown on the metal plate.

[0042] (Effect of manufacturing method) According to the above-described production method, it is difficult for components other than essential elements to enter the system. Therefore, it is easy to obtain a transition metal-doped tungsten molybdic acid with high purity, and furthermore, a step of removing impurities is not required. Furthermore, according to this method, it is possible to obtain the desired transition metal-doped tungsten molybdic acid under very mild conditions. Furthermore, it is possible to easily produce transition metal-doped tungsten molybdic acid doped with two or more transition elements, which was difficult to achieve using conventional methods.

[0043] (Application) As shown in the examples below, the transition metal-doped tungsten molybdate exhibits excellent solar light absorption characteristics. Furthermore, its light absorption characteristics change depending on the amount, type, and combination of transition elements (dopants). Therefore, by combining transition metal-doped tungsten molybdates containing different dopants or transition metal-doped tungsten molybdates with different doping amounts, it is possible to achieve a solar light absorption efficiency approaching 100%.

[0044] Therefore, it is conceivable to use the transition metal-doped tungsten molybdate in the photothermal conversion section of a heating device that receives sunlight or other light to perform heating. Such a heating device is thought to be useful, for example, in a technology for separating water and salt from seawater.

[0045] Furthermore, the capacitance of the transition metal-doped tungsto-molybdic acid increases when irradiated with light, depending on the type and combination of dopants. Therefore, it is conceivable that the transition metal-doped tungsto-molybdic acid could be used as a material for photo-capacitors in various electrical devices.

[0046] Furthermore, the transition metal-doped tungstate molybdate is also useful as a photocatalyst and as an electrode material for a hydrogen generator that generates hydrogen by electrolyzing water. [Example]

[0047] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by these examples, and modifications of the embodiments are possible without departing from the spirit of the present invention.

[0048] [Example 1] (1) Synthesis of transition metal-doped tungsto-molybdic acid W flakes (purity 99.95%, manufactured by Nilaco) and Cu foil (purity 99.95%, manufactured by Nilaco) were ultrasonically bathed in acetone, ethanol, and purified water, respectively, for 10 minutes each. 0.5 g of the W flakes were mixed with 20 ml of a 10% by mass aqueous hydrogen peroxide solution, and the W was dissolved in the aqueous hydrogen peroxide solution over a period of 3 days.

[0049] The solution was irradiated with light of 365 nm wavelength at an illuminance of 28 mW / cm using a light source (UVP B-100AP, manufactured by Analytik Jena) in a dark room. 2 After irradiation with ultraviolet light, Cu foil was added to the solution. The amount of Cu added was adjusted so that the Cu doping amount was 0.5 mol% relative to the amount of base material (WO3·H2O). Furthermore, light with a wavelength of 365 nm was irradiated from the same light source as above at an illuminance of 28 mW / cm2. 2 The mixture was irradiated at 400 K for 72 hours. The resulting transition metal-doped tungsto-molybdic acid (Cu-doped WO3·H2O) was then separated by centrifugation and stored in a drying oven (50 °C) for 1 day.

[0050] Similarly to the above, transition metal-doped tungsten molybdates were synthesized with Cu doping amounts of 0 mol% (pure), 1.0 mol%, 2.0 mol%, 2.5 mol%, 3.0 mol%, 3.5 mol%, 4.0 mol%, 5.0 mol%, 5.5 mol%, 5.75 mol%, 9.5 mol%, 10.5 mol%, 12.5 mol%, 14.0 mol%, 15.0 mol%, 16.0 mol%, and 20.0 mol%.

[0051] (2) Evaluation and Results (Evaluation of light absorption characteristics) The results of measuring the UV-visible-NIR optical absorptance of the resulting transition metal-doped tungstate molybdate are shown in Figure 4. As shown in Figure 4, when Cu was doped, the optical absorption in the visible and infrared regions was significantly improved compared to the undoped (pure) case, regardless of the doping amount. Note that the peculiar peak at 1400 nm is the spectral background caused by the glass coating powder of the UV-Vis / NIR integrating sphere used for the measurements.

[0052] (Photothermal conversion test) The transition metal-doped tungsten molybdate obtained above (Cu doping amounts: 0 mol%, 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, and 5.8 mol%) was fixed to double-sided adhesive tape, as shown in Figure 5A. The transition metal-doped tungsten molybdate was irradiated with simulated sunlight using a solar simulator AM1.5G. Thermography images obtained at this time are shown in Figure 5B. As shown in Figure 5B, the temperature increased in all cases when Cu was doped compared to when no doping was performed (0 mol%). In particular, the temperature rose to 30.3°C when the doping amounts were 1% and 5%.

[0053] [Example 2] (1) Synthesis of transition metal-doped tungsto-molybdic acid W flakes (purity 99.95%, manufactured by Nilaco) and Mo foil (purity 99.95%, manufactured by Nilaco) were subjected to ultrasonic bath treatment for 10 minutes each in acetone, ethanol, and purified water, respectively. 0.5 g of the W flakes and 0.5 g of Mo foil were mixed with 20 ml of aqueous hydrogen peroxide solution (10% by mass) and dissolved in the hydrogen peroxide solution over 3 days. The two solutions were then mixed so that the Mo:W ratio was 1:5.

[0054] The resulting solution was stirred at 100 rpm and irradiated with light of 365 nm wavelength from a light source (UVP B-100AP, manufactured by Analytik Jena) in a dark room at an illuminance of 30 to 50 mW / cm. 2 The solution was irradiated with 1000 kJ / cm² for 72 hours. This caused the color of the solution to change from yellow to blue, and the Mo x W 1-x It was confirmed that nuclei consisting of O3·nH2O (MoWOH) were formed.

[0055] Cu (99.8% purity, 200 mesh, Nilaco), Fe (99.9% purity, 3-5 μm particle size, Kojundo Chemical Laboratory), and Mn (99.9% purity, 10 μm particle size, Kojundo Chemical Laboratory) were added to the solution according to the desired doping amount. The solution was then irradiated with UV light for 24 hours while stirring at 100 rpm. The resulting transition metal-doped tungsten molybdate was then separated by centrifugation and stored in a drying oven (50°C) for 1 day. This method yielded undoped MoWOH, 5% Cu-doped MoWOH, 5% Cu / 1% Mn-doped MoWOH, 5% Cu / 2% Fe-doped MoWOH, and 5% Cu / 2% Fe / 1% Mn-doped MoWOH.

[0056] (2) Evaluation and Results (Confirmation of crystal structure) The images of the transition metal-doped tungsten molybdates obtained above (Cu-doped MoWOH, Cu / Mn-doped MoWOH, Cu / Fe-doped MoWOH, and Cu / Fe / Mn-doped MoWOH) observed with a scanning electron microscope (SEM) are shown in Figure 6A. Their XRD (X-ray diffraction) patterns are shown in Figure 6B. From these results, it is clear that all of the Mo x W 1-x It was confirmed to have a crystal structure of O3·0.33H2O.

[0057] (Confirmation of light absorption and solar utilization efficiency) The results of measuring the visible-near-infrared light absorptance of the transition metal-doped tungstate molybdate obtained above are shown in Figure 7A. Figure 7B is a graph showing the solar light absorption efficiency when irradiated with simulated sunlight using a solar simulator AM1.5G.

[0058] As shown in Figure 7A, all transition metal-doped tungsto-molybdates exhibited significantly improved optical absorption in the visible and infrared regions compared to undoped MoWOH. Furthermore, the absorption characteristics changed significantly depending on the type and combination of doped transition elements.

[0059] Furthermore, as shown in Figure 7B, the solar absorptance of undoped MoWOH was 54%, whereas that of Cu-doped MoWOH was 81.0%, and that of Cu / Fe / Mn-doped MoWOH was 80.9%. In other words, doping with transition elements achieved extremely high solar absorptance.

[0060] (Photothermal conversion test 1) The transition metal-doped tungsto-molybdic acid obtained above was fixed to double-sided adhesive tape, as shown in Figure 8A. The transition metal-doped tungsto-molybdic acid was irradiated with simulated sunlight from a solar simulator AM1.5G. Thermography images taken at this time are shown in Figure 8B. As shown in Figure 8B, the temperature rose in both cases. Furthermore, compared to undoped MoWOH, the Cu-doped MoWOH and Cu / Fe / Mn-doped MoWOH showed a tendency to increase in temperature, reaching 37.7°C.

[0061] (Photothermal conversion test 2) The Cu / Fe / Mn-doped MoWOH attached to double-sided adhesive tape (Example) was immersed in water and irradiated with simulated sunlight from the solar simulator. The water evaporation rate was measured. The results are shown in Table 1 below. The performance of the Cu / Fe / Mn-doped MoWOH was also compared with that of a TiO2 / CuO sheet (Comparative Example 1) and a carbon nanosheet (Comparative Example 2), both of which are described in a publicly known literature. The results of Comparative Example 2 are the values ​​described in the literature (L. Sun et al., "Highly efficient solar steam generation via mass-produced carbon nanosheet frameworks," Carbon, 145 (2019), 352-358).

[0062] [Table 1] As shown in Table 1 above, the Cu / Fe / Mn doped MoWOH of the present invention was superior to TiO2 / CuO and showed results close to those of the carbon nanosheet (Comparative Example 2).

[0063] (Confirmation of photocurrent response characteristics) The photoresponse current characteristics of the transition metal-doped tungsto-molybdic acid were examined using chronoamperometry (CA). Figure 9A shows the photoresponse current characteristics of Cu / Fe / Mn-doped MoWOH, and Figure 9B shows the photoresponse current characteristics of Cu-doped MoWOH. As shown in Figures 9A and 9B, it was confirmed that current was generated in all cases upon light irradiation. Furthermore, Figure 10 is a graph showing the photogenerated capacitance in the dark and under simulated solar light irradiation for undoped MoWOH, Cu-doped MoWOH, and Cu / Fe / Mn-doped MoWOH. These results clearly demonstrate that doping MoWOH with transition elements increases photocapacitance.

[0064] (Confirmation of optical capacitor performance) The photocapacitor performance of the Cu / Fe / Mn-doped MoWOH was compared with that of a Zn-ion battery and Re-doped WSe2, which are known photocapacitor materials, and the results are shown in Table 2 below. [Table 2] As shown in Table 2 above, it is clear that the photocapacitor performance of the Cu / Fe / Mn doped MoWOH of the present invention is significantly superior to that of known capacitor materials. [Industrial Applicability]

[0065] The present invention provides a novel transition metal-doped tungsto-molybdic acid, which is doped with one or more transition elements. The transition metal-doped tungsto-molybdic acid exhibits excellent light absorption properties and photocapacitor performance, making it suitable for use in a variety of industrial fields. [Explanation of symbols]

[0066] 100 raw materials 101 oxide ion 102 Hydroxy radical 103 Aggregates 104 Transition elements 110 Hydrogen Peroxide 120 light source 121 Light

Claims

1. Mo ｘ W １－ｘ O ３ ・nH ２ a compound represented by the formula (x, n) doped with one or more elements selected from the group consisting of transition elements (excluding Mo and W); Transition metal doped tungsten molybdate.

2. Doped with two or more elements selected from the group consisting of Cu, Fe, Mn, Co, and Zn; 2. The transition metal-doped tungsto-molybdic acid of claim 1.

3. Contains oxygen vacancies in the structure 2. The transition metal-doped tungsto-molybdic acid of claim 1.

4. preparing a solution of tungsten oxide and / or molybdenum oxide dissolved in hydrogen peroxide; irradiating the solution with light having a wavelength of 365 nm or less; adding one or more transition elements (excluding Mo and W) to the solution after light irradiation; irradiating the solution to which the transition element has been added with light having a wavelength of 365 nm; A method for producing a transition metal-doped tungsto-molybdic acid, comprising:

5. A photothermal conversion part comprising the transition metal-doped tungsto-molybdic acid according to any one of claims 1 to 3. heating device.

6. A photocapacitor comprising the transition metal-doped tungsten molybdate according to any one of claims 1 to 3. Electrical devices.

7. An electrode comprising the transition metal-doped tungsto-molybdic acid according to any one of claims 1 to 3. Hydrogen generator.

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