Photocatalyst fixation member for water splitting and producing method thereof

Abstract

To provide a photocatalyst fixation member for water splitting having high water splitting efficiency and excellent in durability and a producing method thereof.SOLUTION: A photocatalyst fixation member for water splitting includes a metallic porous body and a composite plating film fixed to the metallic porous body. The composite plating film is formed by plating treatment using a plating solution that contains metallic components and plating photocatalyst particles, comprising a film part containing the metal of the metallic component and water-splitting photocatalyst particles co-precipitated during the plating treatment. The producing method for the photocatalyst fixation member for water splitting includes a plating solution preparation step for preparing a plating solution that contains metallic components and plating photocatalyst particles, and a plating treatment step that co-precipitates the plating photocatalyst particles by subjecting the metallic porous body to electrolytic plating treatment or electroless plating treatment using the prepared plating solution.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a member in which water decomposition photocatalyst particles capable of decomposing water by sunlight are fixed to a substrate, and a method for manufacturing the same.

Background Art

[0002] From the viewpoints of suppressing global warming and eliminating dependence on fossil resources, it is essential to construct an energy system using renewable energy such as sunlight. Hydrogen is known as a clean fuel because it does not emit carbon dioxide even when burned. However, in order to realize a hydrogen energy system that also does not emit carbon dioxide during production, the practical application of hydrogen production technology using renewable energy is required.

[0003] As a hydrogen production technology using sunlight, there is a method of producing hydrogen and oxygen by decomposing water using a photocatalyst. For example, Patent Document 1 describes a substrate with photocatalyst particles in which hydrogen generation photocatalyst particles and oxygen generation photocatalyst particles are supported on a porous substrate containing a water-absorbing polymer as a member capable of generating hydrogen without requiring a water supply device. Patent Document 2 describes a water decomposition photocatalyst immobilized product in which a water decomposition photocatalyst is immobilized on nanofibers. Patent Document 3 describes a composite member in which a water decomposition photocatalyst is held on ceramic fibers. Patent Documents 4 and 5 describe a photocatalyst material having a substrate and a photocatalyst layer immobilized on the substrate. The photocatalyst layer in the photocatalyst material includes hydrogen generation photocatalyst particles, oxygen generation photocatalyst particles, and conductive particles, and the conductive particles are disposed between the hydrogen generation photocatalyst particles and the oxygen generation photocatalyst particles to connect the two.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] The first problem in the hydrogen production technology using photocatalysts is the low water decomposition efficiency. When using two or more types of photocatalysts, in order to increase the water decomposition efficiency, the formation of a conductive path through which holes and electrons can move between the photocatalyst particles is important. However, as described in Patent Documents 1 to 3, in the method of supporting the photocatalyst on cellulose fibers, ceramic fibers, etc., the formation of the conductive path is not sufficient. Further, in the photocatalyst materials described in Patent Documents 4 and 5, although the photocatalysts are connected to each other using conductive particles, conductive particles are required in addition to the photocatalyst, resulting in high costs. Further, when the photocatalyst is supported on a flat substrate, the contact area between water and the photocatalyst is small, so it is difficult to increase the water decomposition efficiency. The second problem is that when the photocatalyst is supported on a substrate and water decomposition is carried out, the durability is low. That is, conventionally, since the immobilization of the photocatalyst on the substrate is not sufficient, when water is passed through the member supporting the photocatalyst or the member is immersed in water for a long time, the photocatalyst particles may fall off from the substrate.

[0006] In view of such a situation, the present disclosure has been made, and an object thereof is to provide a photocatalyst fixing member for water decomposition having high water decomposition efficiency and excellent durability, and a method for manufacturing the same. [Means for Solving the Problems

[0007] (1) In order to solve the above problems, the photocatalyst fixing member for water splitting of the present disclosure includes a metal porous body and a composite plating film fixed to the metal porous body. The composite plating film is formed by a plating process using a plating solution containing a metal component and photocatalyst particles for plating. The composite plating film has a film portion containing the metal of the metal component and photocatalyst particles for water splitting having the photocatalyst particles for plating eutectic in the plating process.

[0008] In the photocatalyst fixing member for water splitting of the present disclosure, a metal porous body is used as a base material. According to the metal porous body, photocatalyst particles for water splitting (hereinafter, may be simply referred to as "photocatalyst particles") can be fixed not only on its surface but also in a large number of pores, so that the fixed amount of the photocatalyst particles increases. Further, when water is decomposed, water passes through the pores of the metal porous body, so that the contact area between the photocatalyst particles and water also increases. Thereby, the decomposition efficiency of water can be enhanced. Further, according to the metal porous body, film formation by plating treatment is easy, and a conductive path for connecting photocatalyst particles to each other is sufficiently formed in both the metal porous body itself and the formed composite plating film. Thereby, the decomposition efficiency of water can be enhanced.

[0009] In the plating process, the metal and the photocatalyst particles for plating are eutectic. In the formed composite plating film, the photocatalyst particles for plating are incorporated and fixed in the film portion containing the metal. The photocatalyst particles for plating may be used as they are as the photocatalyst particles for water splitting, or may further support a cocatalyst or the like to constitute the photocatalyst particles for water splitting. Thus, by adopting the immobilization method of plating, the dropout of the photocatalyst particles for water splitting can be suppressed and the durability can be improved.

[0010] (2) In the above configuration, at least a part of the photocatalyst particles for water splitting may have a configuration having an exposed portion not covered by the film portion. According to this configuration, sufficient light can be irradiated to the photocatalyst particles for water splitting, and the contact area between the photocatalyst particles for water splitting and water also becomes large, so that the decomposition efficiency of water can be enhanced.

[0011] (3) In any of the above configurations, the photocatalyst particles for water decomposition may have hydrogen-generating photocatalyst particles and oxygen-generating photocatalyst particles, and the plating solution may have the plating photocatalyst particles that constitute each of the particles. According to this configuration, various combinations become possible by using two types of photocatalyst particles in combination, and water can be decomposed efficiently. Also, there is an advantage that even a photocatalyst that is difficult to use alone can decompose water by being combined.

[0012] (4) In the configuration of (3) above, the plating photocatalyst particles that constitute the hydrogen-generating photocatalyst particles are strontium titanate doped with rhodium (SrTiO 3 :Rh), strontium titanate doped with chromium and tantalum (SrTiO 3 :Cr,Ta), anatase-type titanium oxide doped with chromium and tantalum (TiO 2 :Cr,Ta), strontium titanate doped with lanthanum and rhodium (SrTiO 3 :La,Rh), carbon nitride (C 3 N 4 ), tantalum oxynitride modified with zirconia (ZrO 2 / TaON), tantalum oxynitride modified with MgTa 2 O 6-y N x (MgTa 2 O 6-y N x / TaON), gallium nitride (GaN), BaZrO 3 ―BaTaO 2 N solid solution, CuGaS 2 ―ZnS solid solution, CuLi 1 / 3 Ti 2 / 3 O 2 , Sm 2 Ti 2 S 2 O 5 , Y 2 Ti 2 S 2 O 5 , CuGaS 2 , and LaMg 1 / 3 Ta 2 / 3 O 2It may be configured to have one or more types selected from N. According to this configuration, water can be decomposed using visible light with a wavelength of 400 nm or more, which is abundant in sunlight.

[0013] (5) In the configuration of the above (3) or (4), the electroplating photocatalyst particles constituting the oxygen generation photocatalyst particles are bismuth vanadate (BiVO 4 ), molybdenum-doped bismuth vanadate (BiVO 4 :Mo), rutile-type titanium oxide (TiO 2 ), nitrogen and tantalum-doped rutile-type titanium oxide (TiO 2 :N,Ta), tungsten trioxide (WO 3 ), rhodium and antimony-doped strontium titanate (SrTiO 3 :Rh,Sb), tantalum oxynitride (TaON), tantalum nitride (Ta 3 N 5 ), AgNbO 3 , Bi 2 MoO 6 , H 2 WO 4 , Bi 4 NbO 8 Cl, Bi 6 NbWO 14 Cl, and may be configured to have one or more types selected therefrom. According to this configuration, water can be decomposed using visible light with a wavelength of 400 nm or more, which is abundant in sunlight.

[0014] (6) In any of the above configurations, the water decomposition photocatalyst particles may be configured to have the electroplating photocatalyst particles and co-catalyst particles supported on the electroplating photocatalyst particles. When co-catalyst particles are supported on the electroplating photocatalyst particles, the catalytic activity can be increased. Thereby, the decomposition efficiency of water can be enhanced, and the production amounts of hydrogen and oxygen can be increased.

[0015] (7) In any of the above configurations, the thickness of the composite plating film may be configured to be 0.5 μm or more and 2 μm or less. According to this configuration, eutectoid due to the plating process can proceed sufficiently, and the photocatalyst particles for water decomposition can be immobilized. Further, it is difficult to inhibit the catalytic activity of the photocatalyst particles for water decomposition, and the water decomposition efficiency can be improved.

[0016] (8) In any of the configurations (1) to (7) above, the content of the photocatalyst particles for water decomposition per unit area of the composite plating film is 10 g / m 2 or more and 100 g / m 2 or less. According to this configuration, since the fixed amount of the photocatalyst particles for water decomposition is large, it is suitable for improving the water decomposition efficiency.

[0017] (9) In any of the configurations (1) to (8) above, the average particle diameter of the plating photocatalyst particles may be configured to be 0.5 μm or more and 10 μm or less. According to this configuration, the surface area per unit mass of the photocatalyst particles for water decomposition that can come into contact with water can be increased, and the hydrogen production efficiency can be enhanced. Further, it is also effective in suppressing the detachment of the photocatalyst particles for water decomposition.

[0018] (10) A method for manufacturing a photocatalyst fixing member for water decomposition according to an aspect of the present disclosure, which is a method for manufacturing a photocatalyst fixing member for water decomposition according to the present disclosure, includes a plating solution preparation step of preparing the plating solution containing the metal component and the plating photocatalyst particles, and a plating step of subjecting the metal porous body to electrolytic plating or electroless plating using the prepared plating solution to eutectoid the plating photocatalyst particles.

[0019] According to the manufacturing method of the present disclosure, the plating photocatalyst particles are fixed to the metal porous body by eutectoiding the plating photocatalyst particles using the plating process. According to the manufacturing method of the present disclosure, the plating photocatalyst particles (photocatalyst particles for water decomposition) can be immobilized at a relatively low cost without performing complicated processes. Further, since the plating process can be performed at a relatively low temperature as compared with a firing process or the like, the catalytic activity of the plating photocatalyst particles is less likely to decrease. [Effect of the Invention]

[0020] According to the water splitting photocatalyst fixing member of the present disclosure, since the water splitting photocatalyst particles are fixed to the metal porous body, the contact area between the water splitting photocatalyst particles and water increases. Further, since the water splitting photocatalyst particles are fixed in the form of a composite plating film, a sufficient conductive path for connecting the water splitting photocatalyst particles to each other is formed. As a result, the water decomposition efficiency is increased, the detachment of the water splitting photocatalyst particles is suppressed, and the durability is improved. According to the manufacturing method of the present disclosure, the water splitting photocatalyst fixing member of the present disclosure can be manufactured at low cost by a relatively simple process. [Brief Description of the Drawings]

[0021]

Figure 1

Figure 2

[0022] Hereinafter, embodiments of the water splitting photocatalyst fixing member and its manufacturing method of the present disclosure will be described. Note that the embodiments are not limited to the following forms, and various modified forms and improved forms that can be carried out by those skilled in the art can be implemented.

[0023] [Water Splitting Photocatalyst Fixing Member] The water splitting photocatalyst fixing member of the present disclosure includes a metal porous body and a composite plating film fixed to the metal porous body.

[0024] [Metal Porous Body] As the metal porous body, a porous body made of various metals or alloys can be used. Considering the environment during use, it is desirable to use a material with excellent corrosion resistance such as water resistance and acid resistance. For example, materials such as nickel, nickel alloy, aluminum, titanium, stainless steel, copper, and silver are suitable. The manufacturing method of the metal porous body is not particularly limited. For example, it can be manufactured by sintering metal or alloy powders, fibers, etc. Also, like the product "Cermet (registered trademark)" manufactured by Sumitomo Electric Industries, Ltd., after forming a plating film on the surface of a foam such as resin, the foam can be removed by heat treatment or the like for manufacturing.

[0025] The shape, size, etc. of the metal porous body are not particularly limited. For example, a sheet-like one is easy to perform plating treatment and water easily passes through it during use. The size of the pores in the metal porous body is not particularly limited, but considering the ease of water passage, etc., the average pore diameter is preferably 10 μm or more. On the other hand, if the pores are too large, the contact area with water becomes small and the strength may decrease, so the average pore diameter is preferably 3000 μm or less. The average pore diameter of the metal porous body can be calculated as follows. First, observe the metal porous body with an optical microscope and select 30 large pores in order from the obtained micrograph. Next, for each of the selected pores, measure the maximum length of the opening and obtain the arithmetic mean of the 30 maximum lengths. In the case of using a commercially available product, the catalog value may be adopted.

[0026] [Composite plating film] The composite plating film is formed by plating treatment. For the plating treatment, whether it is electrolytic plating or electroless plating may be used as long as a plating solution containing a metal component and photocatalyst particles for plating is used. The method of plating treatment will be described in <Manufacturing method of water decomposition photocatalyst fixing member> later.

[0027] The composite plating film has a film portion and photocatalyst particles for water decomposition. The film portion contains the metal of the metal components constituting the plating solution. The metal may be nickel, copper, cobalt, chromium, zinc, tin, silver, gold, palladium, platinum, etc., depending on the material of the metal porous body, and alloys containing one or more of these may also be mentioned. Among them, considering corrosion resistance such as water resistance and acid resistance, and conductivity, nickel or a nickel alloy is preferable. Note that the film portion also contains components other than the metal contained in the plating solution (excluding the photocatalyst particles for plating). Further, another metal film may be laminated on the surface of the composite plating film. That is, the photocatalyst fixing member for water decomposition of the present disclosure may be in a form including a metal porous body, a composite plating film fixed to the metal porous body, and a metal film laminated on the surface of the composite plating film. The metal film is preferably formed of a metal having corrosion resistance, and for example, it may be formed using the aforementioned metals for plating. Even in the form in which the metal film is formed, it is desirable that at least some of the photocatalyst particles for water decomposition have exposed portions that are not covered by the metal film.

[0028] The photocatalyst particles for water decomposition include the photocatalyst particles for plating constituting the plating solution. The photocatalyst particles for water decomposition may be the photocatalyst particles for plating itself that have eutectoid with the metal in the plating process, or those in which a cocatalyst or the like is supported on the eutectoid photocatalyst particles for plating. The types of the photocatalyst particles for plating and the cocatalyst particles will be described later.

[0029] It is desirable that at least some of the photocatalyst particles for water decomposition have exposed portions that are not covered by the film portion. In other words, it is desirable that at least some of the photocatalyst particles for water decomposition are not buried in the film portion. From the viewpoint of irradiating sufficient light to the photocatalyst particles for water decomposition to increase the decomposition efficiency of water, a form in which more of the photocatalyst particles for water decomposition have exposed portions is desirable. Focusing on one photocatalyst particle for water decomposition, a form in which a part of the particle is embedded in the film portion and the other part is exposed is desirable.

[0030] Although it depends on the particle size of the photocatalyst particles for plating, from the viewpoint of sufficiently advancing the eutectoid by the plating treatment and immobilizing the photocatalyst particles for water decomposition, the thickness of the composite plating film is desirably 0.5 μm or more. More preferably, it is 1 μm or more. On the other hand, from the viewpoint of reducing the particles that are not exposed on the surface of the film part among the photocatalyst particles for water decomposition and allowing light to reach the buried photocatalyst particles for water decomposition to enhance the water decomposition efficiency, the thickness of the composite plating film is desirably 2 μm or less.

[0031] Also, from the viewpoint of increasing the amount of immobilized photocatalyst particles for water decomposition to enhance the water decomposition efficiency, the content of the photocatalyst particles for water decomposition per unit area of the composite plating film is desirably 10 g / m 2 or more. On the other hand, considering the ease of contact with water, cost, etc., the content of the photocatalyst particles for water decomposition is desirably 100 g / m 2 or less. In this specification, the content of the photocatalyst particles for water decomposition is calculated as follows. First, the surface of the composite plating film is observed using a scanning electron microscope (SEM), and the number of photocatalyst particles for water decomposition per unit area of the obtained SEM photograph is counted. When there are multiple types of photocatalyst particles, such as when the photocatalyst particles for water decomposition have photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation, the number is counted for each type. For the photocatalyst particles for water decomposition, the volume is calculated by regarding them as true spheres with the median diameter (D 50 ) measured in advance as the diameter. Then, the mass is calculated from the volume and density of the photocatalyst particles for water decomposition, and the content is obtained by multiplying the number per unit area. The median diameter of the photocatalyst particles for hydrogen generation can be determined from the volume-based particle size distribution measured by the laser diffraction / scattering method.

[0032] The photocatalyst particles for water decomposition are semiconductor particles having a band structure suitable for the photocatalytic decomposition of water. For example, the lower potential of the conduction band is on the negative side of the proton reduction potential (E(H + / H 2 )) and the upper potential of the valence band is the oxidation potential of water (E(O 2 / H 2Examples of semiconductor particles located on the positive side relative to O)) include. In order to efficiently cause a water splitting reaction using sunlight, which is renewable energy, it is desirable to use semiconductor particles that can respond to visible light with a wavelength of 400 nm or more. In this case, the photocatalyst particles for water splitting may be composed of a combination of photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation. The "photocatalyst particles for hydrogen generation" are semiconductor particles in which the lower end potential of the conduction band is on the negative side relative to the proton reduction potential (E(H + / H 2 ))), and the "photocatalyst particles for oxygen generation" are semiconductor particles in which the upper end potential of the valence band is on the positive side relative to the oxidation potential of water (E(O 2 / H 2 O)). As the light including visible light, in addition to sunlight, artificial light sources such as xenon lamps, halogen lamps, sodium lamps, fluorescent lamps, and light emitting diodes can be used.

[0033] When combining photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation, the photocatalyst particles for plating constituting each particle may be used in the plating solution for forming the composite plating film.

[0034] Examples of the photocatalyst particles for plating constituting the photocatalyst particles for hydrogen generation include, for example, rhodium-doped strontium titanate (SrTiO 3 :Rh), chromium and tantalum-doped strontium titanate (SrTiO 3 :Cr,Ta), chromium and tantalum-doped anatase-type titanium oxide (TiO 2 :Cr,Ta), lanthanum and rhodium-doped strontium titanate (SrTiO 3 :La,Rh), carbonitride (C 3 N 4 ), tantalum oxynitride modified with zirconia (ZrO 2 / TaON), MgTa 2 O 6-y N x modified tantalum oxynitride (MgTa 2 O 6-y N x / TaON), gallium nitride (GaN), BaZrO3 - BaTaO 2 N solid solution, CuGaS 2 - ZnS solid solution, CuLi 1 / 3 Ti 2 / 3 O 2 , Sm 2 Ti 2 S 2 O 5 , Y 2 Ti 2 S 2 O 5 , CuGaS 2 , and LaMg 1 / 3 Ta 2 / 3 O 2 N etc. can be mentioned. As the electroplating photocatalyst particles constituting the oxygen generation photocatalyst particles, bismuth vanadate (BiVO 4 ), molybdenum-doped bismuth vanadate (BiVO 4 :Mo), rutile-type titanium oxide (TiO 2 ), nitrogen and tantalum-doped rutile-type titanium oxide (TiO 2 :N,Ta), tungsten trioxide (WO 3 ), rhodium and antimony-doped strontium titanate (SrTiO 3 :Rh,Sb), tantalum oxynitride (TaON), tantalum nitride (Ta 3 N 5 ), AgNbO 3 , Bi 2 MoO 6 , H 2 WO 4 , Bi 4 NbO 8 Cl, Bi 6 NbWO 14 Cl etc. can be mentioned.

[0035] The photocatalyst particles for plating are considered to be incorporated into the film portion in a form that adsorbs to the deposited metal. For example, from the viewpoint of reducing particles that do not expose on the surface of the film portion, the average particle diameter of the photocatalyst particles for plating is desirably 0.5 μm or more. Also, from the viewpoints of increasing the production efficiency of hydrogen by increasing the surface area in contact with water per unit mass and suppressing the detachment of the photocatalyst particles for water decomposition, it is desirably 10 μm or less. The photocatalyst particles for plating become the main body of the photocatalyst particles for water decomposition (the photocatalyst particle main body excluding the cocatalyst particles described later). In this specification, as the average particle diameter of the photocatalyst particles for plating (photocatalyst particles for water decomposition), the median diameter (D 50 ) obtained from the volume-based particle size distribution measured by the laser diffraction / scattering method is adopted.

[0036] From the viewpoint of increasing the catalytic activity of the photocatalyst particles for plating and increasing the production amounts of hydrogen and oxygen, the photocatalyst particles for water decomposition preferably have a form including the photocatalyst particles for plating and the cocatalyst particles supported on the photocatalyst particles for plating. For example, as the cocatalyst particles of the photocatalyst particles for hydrogen generation, metal particles such as ruthenium, platinum, iridium, rhodium, and chromium, and composite particles such as ruthenium / chromium oxide can be mentioned. As the cocatalyst particles of the photocatalyst particles for oxygen generation, metal oxide particles such as iridium oxide, cobalt oxide, and ruthenium oxide can be mentioned.

[0037] The photocatalyst fixing member for water decomposition of the present disclosure may be used in a form in which light is irradiated while in contact with water. Since the water decreases as the water decomposition reaction proceeds, it is advisable to provide a mechanism capable of supplying water. For example, the photocatalyst fixing member for water decomposition can be used in a state of being submerged in water. However, in water, the catalytic activity may decrease due to refraction of light, and gas may be less likely to be generated due to water pressure. Therefore, it is desirable to use the photocatalyst fixing member for water decomposition in a state of floating on water. Floating on water also has advantages such as facilitating the supply of water into the pores of the metal porous body. For example, it is also possible to use it floating in the sea.

[0038] <Manufacturing method of the photocatalyst fixing member for water decomposition> As a preferred manufacturing method of the photocatalyst fixing member for water splitting of the present disclosure, the manufacturing method of the present disclosure includes a plating solution preparation step and a plating treatment step. If necessary, a co-catalyst loading step may be added after the plating treatment step. Hereinafter, each step will be described.

[0039] [Plating Solution Preparation Step] This step is a step of preparing a plating solution containing a metal component and photocatalyst particles for plating. As the metal component, a metal compound that forms the film portion of the composite plating film is used. Examples of water-soluble metal compounds soluble in the plating solution include inorganic acid salts such as metal sulfates, hydrochlorides, pyrophosphates, and sulfamic acids, and organic acid salts such as cyanide salts. As the metal, as described above, in addition to nickel, copper, cobalt, chromium, zinc, tin, silver, gold, palladium, platinum, etc., alloys containing one or more of these may be mentioned. Since the photocatalyst particles for plating have been described above, the description thereof will be omitted here.

[0040] When performing electrolytic plating treatment, the plating solution may be prepared by adding a pH adjuster such as boric acid to the metal salt and the photocatalyst particles for plating. For example, in the case of electrolytic plating treatment of nickel or a nickel alloy, a plating solution such as a Watts bath or a nickel sulfamate bath can be used.

[0041] When performing electroless plating, the plating solution may be prepared by adding a reducing agent, a complexing agent, a pH buffer, a surfactant, etc. to a metal salt and photocatalyst particles for plating. Examples of the reducing agent include hypophosphorous acid, hypophosphite, dimethylamine borane, hydrazine, etc. From the perspective of the stability of the plating solution, hypophosphorous acid and hypophosphite are preferred. Examples of the complexing agent include carboxylic acids and amine compounds. Examples of the carboxylic acid include propionic acid, citric acid, malic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), etc. Examples of the amine compound include glycine, alanine, ethylenediamine, propanediamine, etc. Examples of the pH buffer include lactic acid, acetic acid, succinic acid, etc. Examples of the surfactant include cationic surfactants and amphoteric surfactants. Among these, from the perspective of enhancing the dispersibility of the photocatalyst particles for plating, cationic surfactants are preferred. Examples of the cationic surfactant include quaternary ammonium salt types such as lauryltrimethylammonium chloride and ethylene oxide-added ammonium chloride. Examples of the amphoteric surfactant include betaine types such as lauryl betaine, amidopropyl betaine, and dimethylalkyl betaine.

[0042] From the perspective of forming a film portion of a desired thickness in a practical time, the concentration of the metal component in the plating solution is preferably 20 g / L or more and 30 g / L or less. From the perspective of increasing the content of photocatalyst particles for water decomposition in the composite plating film and increasing the production amounts of hydrogen and oxygen, the concentration of the photocatalyst particles for plating is preferably 0.5 g / L or more. On the other hand, if a large amount of photocatalyst particles for plating is added, the deposition rate of the metal in the plating process may decrease. Therefore, the concentration of the photocatalyst particles for plating is preferably 5 g / L or less. The photocatalyst particles for plating exist in a dispersed state without dissolving in the plating solution.

[0043] [Plating process] This process is a process of codepositing photocatalyst particles for plating by subjecting a metal porous body to electrolytic plating or electroless plating using the prepared plating solution.

[0044] In the electrolytic plating process, in the plating solution, a metal plate made of the metal in the plating solution and a metal porous body may be immersed, and the metal plate may be connected to a direct current with the metal plate as the anode and the metal porous body as the cathode. In the electroless plating process, the metal porous body may be immersed in the plating solution. Regarding the metal porous body, it is desirable to remove the oxide film on the surface in advance to enhance the reactivity.

[0045] The temperature of the plating process may be appropriately determined in consideration of the formation rate of the composite plating film, productivity, etc. For the electrolytic plating process, it may be carried out at a temperature of 20°C or higher and 60°C or lower. For the electroless plating process, it may be carried out at a temperature of 60°C or higher and 95°C or lower. The time of the plating process should be set to a time when the eutectic of the metal and the photocatalyst particles for plating proceeds sufficiently according to the concentration of the plating solution, the processing temperature, etc., so that a film portion with a desired thickness can be obtained. For example, the time of the plating process can be set to 1 minute or more and 10 minutes or less. According to electroless plating, it is easy to form a film portion with a uniform thickness on a metal porous body having a complex shape such as a three-dimensional network structure. In this step, the photocatalyst particles for plating are incorporated into the film portion in a form adsorbed to the deposited metal and fixed to the metal porous body.

[0046] [Promoter-supporting step] When promoter particles are supported on the surface of the photocatalyst particles for plating, a promoter-supporting step may be added after the plating process. By this step, a composite plating film having a film portion and photocatalyst particles for water decomposition having the photocatalyst particles for plating on which the promoter particles are supported is formed.

[0047] The co-catalyst supporting step may be carried out using an electrodeposition method, an impregnation method, or the like. In the case of the electrodeposition method, first, the metal porous body after the plating treatment is immersed in a co-catalyst-containing solution in which a precursor of co-catalyst particles is dispersed or dissolved, and visible light is irradiated thereto, whereby a metal or metal oxide serving as a co-catalyst is supported on the surface of the photocatalyst particles for plating. In the case of the impregnation method, the metal porous body after the plating treatment is immersed in a co-catalyst-containing solution in which a precursor of co-catalyst particles is dispersed or dissolved, and after adsorbing the precursor on the surface of the photocatalyst particles for plating by stirring or the like, water is evaporated and calcined. Examples of the co-catalyst particles include metal particles such as ruthenium, platinum, iridium, rhodium, and chromium, metal oxide particles such as iridium oxide, cobalt oxide, and ruthenium oxide, and composite particles such as ruthenium / chromium oxide. Examples of the precursor of the co-catalyst particles include oxides, chlorides, nitrates, and ammine salts of the metals used as the co-catalyst.

Example

[0048] Next, the present disclosure will be described more specifically with reference to examples. <Manufacture of Samples of Photocatalyst Fixing Member for Water Splitting> [Example 1] (1) Manufacture of First Photocatalyst Particles for Plating as Photocatalyst Particles for Hydrogen Generation Powder composed of rhodium-doped strontium titanate (SrTiO 3 :Rh) particles was manufactured as follows. First, 1.0013 g of SrCO 3 (manufactured by Kanto Chemical Co., Inc., 99.9%) was placed in an alumina crucible and heat-treated at 200 °C for 2 hours. Here, 0.5305 g of TiO 2 (manufactured by the same company, 99.0%) and 0.0083 g of Rh 2 O 3 (manufactured by Fujifilm Wako Pure Chemical Corporation, 98.0 - 102.0%) were added and stirred, and further 1 mL of methanol was added in two portions and stirred. Next, the obtained mixture was placed in an alumina crucible, heated at 200 °C for 2 hours, then heated at a rate of 10 °C / min, and calcined at 1050 °C for 10 hours. After calcination, it was allowed to cool to room temperature and crushed to obtain SrTiO 3: Rh powder was obtained. The average particle diameter (D 50 ) of the obtained powder was measured using a laser diffraction / scattering particle size distribution analyzer ("Microtrac MT3300EXII" manufactured by Microtrac Bell Corporation), and it was 3.4 μm.

[0049] (2) Production of the second photocatalyst particles for plating as oxygen-generating photocatalyst particles Powder composed of molybdenum-doped bismuth vanadate (BiVO 4 :Mo) particles was produced as follows. First, potassium molybdenum-doped layered vanadate (K 3 V 5 O 14 :Mo), which is one of the raw materials, was produced. 50 μL of a 0.25 M K 2 MoO 4 aqueous solution, 1.0469 g of K 2 CO 3 (manufactured by Kanto Chemical Co., Inc., 99.0%), and 2.2724 g of V 2 O 5 (manufactured by Fujifilm Wako Pure Chemical Corporation, 99.0%) were placed in a mortar, ground while adding ethanol, and then calcined at 450 °C for 5 hours in a double crucible. After calcination, it was allowed to cool to room temperature, and the calcined product was ground in a mortar to obtain K 3 V 5 O 14 :Mo powder. Next, 9.7014 g of bismuth nitrate pentahydrate (Bi(NO 3 ) 3 ·5H 2 O) was dispersed in 80 mL of distilled water, and ultrasonic treatment was performed for 5 minutes. 2.3849 g of the produced K 3 V 5 O 14 :Mo and 20 mL of distilled water were added thereto, and ultrasonic treatment was further performed for 1 minute. Then, this mixed solution was stirred at a stirring speed of 1200 rpm in an oil bath at 70 °C for 10 hours, and the precipitate after standing was taken out and filtered to obtain BiVO 4 :Mo powder, which is the second photocatalyst particles for plating. The average particle diameter (D 50 ) of the obtained powder was 8.5 μm (the measuring device was the same as in (1)).

[0050] (3) Preparation of plating solution To the basic plating solution for electroless nickel plating with the following composition, powders of the two types of photocatalyst particles for plating produced (SrTiO 3 :Rh, BiVO 4 :Mo) were added and stirred to prepare the plating solution. The concentrations of SrTiO 3 :Rh and BiVO 4 :Mo in the plating solution were both set to 1.5 g / L. · Composition of the basic plating solution Metal component: Nickel sulfate hexahydrate 20 g / L Reducing agent: Sodium hypophosphite monohydrate 25 g / L pH buffer: Lactic acid 27 g / L Complexing agent: Propionic acid 2.5 g / L Surfactant: Lauryl trimethyl ammonium chloride 0.1 g / L

[0051] (4) Plating treatment 200 mL of the prepared plating solution was heated to 90 °C, and a porous nickel sheet (Sumitomo Electric Industries, Ltd.'s "Cermet (registered trademark)", a square plate with a length of 50 mm, a width of 50 mm, and a thickness of 1.2 mm, and an average pore diameter of 450 μm) was immersed for 5 minutes for plating treatment. In this way, nickel and two types of photocatalyst particles for plating were co-precipitated on the surface of the porous nickel sheet to form a composite plating film with a thickness of 1 μm.

[0052] Thereafter, co-catalyst particles were supported on each of the first photocatalyst particles for plating and the second photocatalyst particles for plating contained in the composite plating film as follows. First, the porous nickel sheet subjected to the plating treatment was immersed in an RuCl 3 aqueous solution and irradiated with a xenon lamp. After the porous nickel sheet was taken out from the RuCl 3 aqueous solution, it was immersed in a K 2 CrO 4 aqueous solution and irradiated with a xenon lamp. As a result, ruthenium (Ru) / chromium oxide (Cr 2 O 3)Hydrogen generation photocatalytic particles supporting composite particles were produced. Also, ruthenium oxide (RuO 2 ) particles supporting oxygen generation photocatalytic particles were produced. In this way, a sample of a water splitting photocatalyst fixing member including a porous nickel sheet and a composite plating film was manufactured. The manufactured sample was referred to as the sample of Example 1. In the sample of Example 1, most of the water splitting photocatalytic particles were exposed on the surface of the film portion. The content of the water splitting photocatalytic particles per unit area of the composite plating film was 40 g / m 2 .

[0053] Fig. 1 shows an SEM photograph (magnification: 1000 times) of the surface of the composite plating film in the sample of Example 1. Fig. 2 shows an SEM photograph (magnification: 5000 times) of the surface of the same composite plating film. In Figs. 1 and 2, the large-sized oxygen generation photocatalytic particles (main body BiVO 4 :Mo) are shown brightly white, and the small-sized hydrogen generation photocatalytic particles (main body SrTiO 3 :Rh) are shown darkly gray.

[0054] [Example 2] In the manufacturing method of the sample of Example 1, the sample of Example 2 was manufactured in the same manner as in Example 1, except that the plating time (the time for immersing the porous nickel sheet in the plating solution) was changed to 10 minutes to form a composite plating film with a thickness of 2 μm. Also in the sample of Example 2, most of the water splitting photocatalytic particles were exposed on the surface of the film portion, but the exposed portion was less than that in the sample of Example 1. The content of the water splitting photocatalytic particles per unit area of the composite plating film was 21 g / m 2 .

[0055] [Comparative Example 1] Without performing plating treatment, two types of plating photocatalytic particles were fixed to a porous nickel sheet to manufacture a water splitting photocatalyst fixing member. First, 60 mg of powder of the first photocatalytic particle for plating (SrTiO 3 :Rh) and the second photocatalytic particle for plating (BiVO 4: 60 mg of the powder of (Mo) and were added to 3 mL of pure water, and ultrasonic dispersion was carried out for 15 minutes to prepare a dispersion. Next, after dropping the entire amount of the prepared dispersion onto the surface of the porous nickel sheet (the same as above), it was dried at 100 °C for 30 minutes to produce a photocatalyst-fixed member for water decomposition in which a photocatalyst layer was formed on the surface of the porous nickel sheet. Then, in the same manner as in Example 1, cocatalyst particles were supported on each of the first photocatalyst particles for plating and the second photocatalyst particles for plating contained in the photocatalyst layer. The produced sample was designated as the sample of Comparative Example 1. The content of the photocatalyst particles for water decomposition per unit area of the photocatalyst layer in the sample of Comparative Example 1 was 65 g / m 2 It was.

[0056] <Evaluation method> [Hydrogen generation amount] 40 mL of ultrapure water was placed in a reaction vessel made of Pyrex (registered trademark), and the produced sample was held in water using a glass plate. The reaction vessel was attached to a closed gas circulation reaction system (manufactured by Makuhari Riken Glass Co., Ltd.), and the atmosphere inside the measurement system was replaced with argon gas. Visible light was irradiated from above the reaction vessel using a xenon lamp (manufactured by Excelitas Technologies, CERMAX (registered trademark) "PE-300BFA") equipped with a UV (ultraviolet) cut filter (λ> 420 nm, "L42" manufactured by HOYA) to start the water decomposition reaction. The gas generated every time a predetermined time elapsed from the start of the reaction was sampled, and the amount of hydrogen was measured using a gas chromatography apparatus ("GC-8A" manufactured by Shimadzu Corporation, MS-5A column, TCD detector).

[0057] [Durability] During the water decomposition reaction, the presence or absence of the dropout of the photocatalyst particles from the sample was visually observed.

[0058] <Evaluation results> Table 1 shows the evaluation results of the hydrogen generation amount and durability in each sample. Regarding the hydrogen generation amount, it was compared by the amount per unit area of the porous nickel sheet (metal porous body), and evaluated by the value 10 minutes after the start of the water decomposition reaction.

Table 1

[0059] As shown in Table 1, according to the samples of Examples 1 and 2 in which photocatalyst particles were fixed by plating treatment, the amount of hydrogen generation was large and no detachment of photocatalyst particles was observed. Also, in Example 1 where the thickness of the composite plating film was thin, the amount of hydrogen generation was larger. This is presumably because the amount of photocatalyst particles exposed on the surface without being covered in the film part was larger in the sample of Example 1. On the other hand, in the sample of Comparative Example 1 where no plating treatment was used, although the amount of photocatalyst particles was large, the immobilization to the metal porous body was not sufficient and the conductive path was not connected, so the amount of hydrogen generation was small and detachment of photocatalyst particles was also observed. Thus, it was confirmed that the photocatalyst fixing member for water decomposition of the present disclosure in which photocatalyst particles are fixed in the form of a composite plating film has high water decomposition efficiency and excellent durability.

Claims

1. A water decomposition photocatalyst fixing member comprising a porous metal body and a composite plating film fixed to the porous metal body, wherein the composite plating film is formed by a plating process using a plating solution containing a metal component and photocatalyst particles for plating, and has a film portion containing the metal of the metal component and water decomposition photocatalyst particles having the photocatalyst particles for plating eutectic in the plating process.

2. The water decomposition photocatalyst fixing member according to claim 1, wherein at least some of the water decomposition photocatalyst particles have an exposed portion not covered by the film portion.

3. The water decomposition photocatalyst fixing member according to claim 1, wherein the water decomposition photocatalyst particles have hydrogen generation photocatalyst particles and oxygen generation photocatalyst particles, and the plating solution has the photocatalyst particles for plating constituting each particle.

4. The electroplating photocatalyst particles constituting the hydrogen generation photocatalyst particles are strontium titanate doped with rhodium (SrTiO ３ : Rh), strontium titanate doped with chromium and tantalum (SrTiO ３ : Cr, Ta), anatase-type titanium oxide doped with chromium and tantalum (TiO ２ : Cr, Ta), strontium titanate doped with lanthanum and rhodium (SrTiO ３ : La, Rh), carbonitride (C ３ N ４ ), tantalum oxynitride modified with zirconia (ZrO ２ / TaON), MgTa ２ O ６－ｙ N ｘ -modified tantalum oxynitride (MgTa ２ O ６－ｙ N ｘ / TaON), gallium nitride (GaN), BaZrO ３ -BaTaO ２ N solid solution, CuGaS ２ -ZnS solid solution, CuLi １／３ Ti ２／３ O ２ 、Sm ２ Ti ２ S ２ O ５ 、Y ２ Ti ２ S ２ O ５ 、CuGaS ２ 、およびLaMg １／３ Ta ２／３ O ２ N, and the water splitting photocatalyst fixing member according to claim 3 having one or more selected therefrom.

5. The electroplating photocatalyst particles constituting the oxygen-generating photocatalyst particles are bismuth vanadate (BiVO ４ ), molybdenum-doped bismuth vanadate (BiVO ４ :Mo), rutile-type titanium oxide (TiO ２ ), nitrogen and tantalum-doped rutile-type titanium oxide (TiO ２ :N,Ta), tungsten trioxide (WO ３ ), rhodium and antimony-doped strontium titanate (SrTiO ３ :Rh,Sb), tantalum oxynitride (TaON), tantalum nitride (Ta ３ N ５ ), AgNbO ３ ), Bi ２ MoO ６ ), H ２ WO ４ ), Bi ４ NbO ８ Cl, Bi 6 NbWO １４ Cl, and the photocatalyst fixing member for water decomposition according to claim 3, having one or more selected therefrom.

6. The water decomposition photocatalyst fixing member according to claim 1, wherein the water decomposition photocatalyst particles have the photocatalyst particles for plating and cocatalyst particles supported on the photocatalyst particles for plating.

7. The water decomposition photocatalyst fixing member according to claim 1, wherein the thickness of the composite plating film is 0.5 μm or more and 2 μm or less.

8. The content of the photocatalyst particles for water decomposition per unit area of the composite plating film is 10 g / m ２ or more and 100 g / m ２ or less. The photocatalyst fixing member for water decomposition according to claim 1.

9. The water decomposition photocatalyst fixing member according to claim 1, wherein the average particle diameter of the photocatalyst particles for plating is 0.5 μm or more and 10 μm or less.

10. A method for manufacturing the water decomposition photocatalyst fixing member according to claim 1, comprising a plating solution preparation step of preparing the plating solution containing the metal component and the photocatalyst particles for plating, and a plating step of subjecting the porous metal body to electrolytic plating or electroless plating using the prepared plating solution to eutectically deposit the photocatalyst particles for plating. The method for manufacturing a water decomposition photocatalyst fixing member is characterized by having the above steps.

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