CN1328151C - Water photolysis system and process - Google Patents

Abstract

The present invention provides a water photolysis system comprising: a casing 1 into which incident sunlight L can enter from the outside and a photolytic layer 5 which is disposed inside the casing 1; wherein the photolytic layer 5 has a light-transmissive porous material 51 and photocatalyst particles 52 supported thereon; a water layer 4 containing water in its liquid state is disposed below the photolytic layer 5 with a first space 6 disposed between the water layer and the photolytic layer; a sealed second space 7 is formed above the photolytic layer 5 in the casing 1; vapor generated from the water layer 4 is introduced into the photolytic layer 5 via the first space 6; and the vapor is decomposed into hydrogen and oxygen by the photocatalyst particles 52, which are excited by the sunlight L.

Description

Water photodecomposition device and photodecomposition method

technical field

The invention relates to a photodecomposition device and a photodecomposition method for decomposing water to obtain hydrogen and oxygen by photocatalyst reaction.

technical background

Since the discovery of photo-splitting water with semiconductor photoelectrodes and the discovery of the so-called "Hondo-Fujishima effect", as an effective means of converting light into chemical energy, a large number of researches on water splitting using photocatalysts have been carried out. The mechanism of photo-splitting water using a semiconductor photocatalyst is known as follows. That is, for example, when an n-type semiconductor is used as a photocatalyst, when light with energy greater than the energy of the forbidden band is irradiated, electrons in the valence band are excited to the conduction band. hole. As long as these can induce reduction and oxidation reactions, respectively, photocatalytic reactions can be performed.

In order to photosplit water with a semiconductor photocatalyst, the bandwidth of the semiconductor must be greater than the electrolysis voltage of water (theoretical value is 1.23 V). Furthermore, it is also required that the electrons in the conduction band have the ability to reduce water, and the holes in the valence band have the ability to oxidize water. That is, the lower end of the conduction band must be located on the negative side of the hydrogen generation potential of water, and the upper end of the valence band must be located on the positive side of the oxygen generation potential.

Titanium dioxide, strontium titanate, barium titanate, sodium titanate, cadmium sulfide, zirconium dioxide, iron oxide and the like have been found so far as semiconductors satisfying such conditions. Furthermore, it is known that metals such as promoter platinum, palladium, rhodium, and ruthenium supported on these semiconductors are effective photocatalysts for photo-splitting water.

Examples of the above-mentioned photocatalysts are described in, for example, Document 1 (JP-A-11-188269) and Document 2 (JP-A-2000-126761). These documents also disclose that water is purified by floating a porous body carrying a photocatalyst on the water surface of a pond or the like, and irradiating the porous body with light to carry out a photocatalytic reaction.

Therefore, if sunlight is used for the above-mentioned photolysis reaction of water, and the generated hydrogen and oxygen are stored, the reaction can be performed to obtain heat and electricity when needed. That is, by converting sunlight energy into chemical energy and storing it, an extremely effective method of utilizing solar energy can be formed.

However, catalysts that exhibit activity for generating hydrogen, especially metal catalysts, also exhibit activity in the reaction of hydrogen and oxygen, which raises the problem of reverse reactions occurring when photo-splitting of water is performed. For example, when a platinum (Pt)-carrying photocatalyst is suspended in water and irradiated with light, hydrogen and oxygen generated by the photolysis reaction are mixed before detaching from the catalyst as individual bubbles. The hydrogen and oxygen thus mixed contact with Pt to react and return to form water, so that the amount of hydrogen and oxygen obtained is extremely small.

In order to solve this problem, for example, a method is disclosed in Document 3 (Surface, Volume 33, No. 2, Pages 45-58 (1995)), that is, a powdery semiconductor photocatalyst is dispersed in water, and the Shake the entire reaction device to increase the contact between sunlight and the catalyst. In addition, Document 4 (Japanese Patent No. 3096728) also discloses a method in which a photocatalyst is placed on a water-absorbing material, while the water-absorbing material is soaked in water to the extent that the surface is wetted, and sunlight is irradiated from above. method.

However, the method of Document 3 requires the input of mechanical energy, and there is a problem that the input energy for generating hydrogen is far greater than the obtained energy. In order to solve this problem, literature 4 uses water-absorbing materials to supply water to the surface of the photocatalyst, and at the same time allows sunlight to directly reach the interface between the photocatalyst and water, without mechanical mixing such as shaking. However, in this structure, the photocatalyst is dispersed only on the surface of the water-absorbing material, and it is difficult to obtain sufficient yield due to the low density.

In addition, there are also the following problems. That is, sunlight has a wide range of energy distribution from the ultraviolet region to the infrared region, but only light in the ultraviolet-visible region can be used for photocatalytic decomposition reactions. Therefore, the thermal energy of the sun in the infrared region has not been utilized for many years. Therefore, it cannot be said that the existing photodecomposition device effectively utilizes sunlight.

The present invention was made in view of the above-mentioned problems, and an object of the present invention is to provide a water photolysis device and photolysis method that can efficiently obtain hydrogen and oxygen by suppressing the reverse reaction, further utilize solar energy effectively, and promote the photolysis of water.

Contents of the invention

In order to solve the above-mentioned problems, the photodecomposition device of water of the present invention comprises a case into which light can enter from the outside, and a photodecomposition layer housed in the case. The above-mentioned photodecomposition layer has a translucent porous body, and the photocatalyst carried on the porous body, below the above-mentioned photodecomposition layer, a water layer containing liquid water is arranged through a first space, and in the above-mentioned box, A closed second space is formed above the photodecomposition layer, and water vapor generated from the water layer enters the photodecomposition layer through the first space, and the water vapor is decomposed into hydrogen by the photocatalyst excited by the light. and oxygen.

In addition, in order to solve the above-mentioned problems, the photodecomposition method of water according to the present invention includes the step of arranging a photodecomposition layer comprising a light-transmitting porous body and a photocatalyst carried on the porous body at predetermined intervals in a layer containing A step on the water layer of liquid water; a step of irradiating light to the above-mentioned photodecomposition layer; a step of introducing water vapor generated from the above-mentioned water layer into the above-mentioned photodecomposition layer, and decomposing the above-mentioned water vapor into hydrogen and oxygen by a photocatalyst excited by light .

Description of drawings

Fig. 1 is a cross-sectional view of a schematic structure of a water photolysis device according to a first embodiment of the present invention.

Fig. 2 is a schematic diagram of a photodecomposition layer according to the first embodiment of the present invention.

Fig. 3 is a cross-sectional view showing a schematic structure of a water photolysis device according to a second embodiment of the present invention.

Fig. 4 is a cross-sectional view showing a schematic structure of a water photolysis device according to a third embodiment of the present invention.

Fig. 5 is a schematic cross-sectional view of another water photolysis device according to the third embodiment of the present invention.

Reference signs: 1: box body, 11: body part, 111: outlet, 115: inlet, 116: first outlet, 117: second outlet, 118: opening, 12: transparent window, 3: Photothermal conversion layer, 4: Water layer, 5: Photodecomposition layer, 51: Porous body, 52: Photocatalyst particles, 6: First space, 7: Second space, 8: Hydrogen separation membrane, 9 : water layer.

Detailed ways

(first embodiment)

A water photolysis device according to a first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a cross-sectional view showing a schematic structure of a water photolysis device according to a first embodiment.

As shown in FIG. 1 , the photodecomposition device has a cylindrical body part 11 with an opening at the top, and a box 1 with an opening at the top of the body 11 sealed by a light-transmitting window 12 , and the whole is an airtight structure. The light-transmitting window 12 is made of a light-transmitting material such as quartz glass, and sunlight enters the inside of the housing 1 through the light-transmitting window 12 . A light-to-heat conversion layer 3 formed of a metal thin film is arranged on the bottom surface inside the box 1, and a water layer 4 formed of liquid pure water is formed on the light-to-heat conversion layer 3. A photodecomposition layer 5 for decomposing water is disposed above the water layer 4 , and a first space 6 is formed between the water layer 4 and the photodecomposition layer 5 . A sealed second space 7 is formed between the photodecomposing layer 5 and the light-transmitting window 12 . In addition, a discharge port 111 that communicates the second space 7 with the outside is formed on the side wall of the housing 1 , and a gas separator (not shown) is attached to the discharge port 111 . Although not shown, an introduction port may be formed on the side wall of the tank to introduce liquid water into the water layer 4 inside the tank.

Next, the photodecomposition layer 5 will be described with reference to FIG. 2 . Fig. 2 is a schematic diagram illustrating the structure of a photodecomposition layer. As shown in the figure, the photodecomposition layer 5 has a structure in which photocatalyst particles 52 are dispersed on the surface of a gas permeable membrane 51 having a porous structure. The air-permeable film 51 is transparent to at least the wavelength range in which the photocatalyst is active, is insoluble in water and inactive in water, and only needs to be permeable to water vapor. As such a gas permeable membrane, there is, for example, a porous body made of an organic material or an inorganic material. Hereinafter, an inorganic oxide porous body having a network structure skeleton will be described as an example of the porous body.

The material of the inorganic oxide porous body is preferably a transparent metal oxide, and it is preferably formed by a sol-gel method in order to form a network structure skeleton. Examples include silicon oxide (silicon dioxide), aluminum oxide (alumina), magnesium oxide, titanium oxide, and oxides containing several kinds of metals. Among them, silicon oxide and aluminum oxide are preferable because they easily form a wet gel by the sol-gel method. As raw materials for these inorganic oxides, those capable of forming a wet gel by sol-gel reaction may be used. For example, inorganic raw materials such as sodium silicate and aluminum hydroxide, and organic raw materials of organometallic alkoxides such as tetramethoxysilane, tetraethoxysilane, aluminum isopropoxide, and Sec-butoxyaluminum, and the like can be used. Using the sol-gel method, wet gels are formed by reacting these materials with a catalyst in a solvent.

The method for producing the silica wet gel will be described in detail below as an example. As a method of obtaining a wet gel, a silicon oxide raw material is synthesized by a sol-gel reaction in a solvent to form a wet gel. At this time, a catalyst is used as needed. In this formation process, the raw materials are reacted in a solvent to form silicon oxide fine particles, and the fine particles are aggregated to form a network structure skeleton to obtain a wet gel. Specifically, the composition of the raw material and the solvent as the specified solid content is determined. A catalyst, a viscosity modifier, and the like are added as necessary to the solution prepared to this composition, stirred, and the desired form of use is formed by casting, coating, or the like. After a certain period of time in this state, the solution turns into a gel, and a wet gel is obtained. In addition, if necessary, aging treatment may be performed in order to control aging and pores of the wet gel.

The temperature conditions at the time of production are usually at an operating temperature close to room temperature, but may be performed at a temperature below the boiling point of the solvent if necessary. As the silicon oxide raw material at this time, there are alkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, and their oligomers, silicon Water glass compounds such as sodium bicarbonate (sodium natron), potassium silicate, etc., colloidal silica, etc. may be used alone or in combination. As the solvent, it is preferable to dissolve the raw material to form silicon oxide. For example, there are general organic solvents such as water, methanol, ethanol, propanol, acetone, toluene, and hexane, which can be used alone or in combination. As the catalyst, water, acids such as hydrochloric acid, sulfuric acid, and acetic acid, and bases such as ammonia, pyridine, sodium hydroxide, and potassium hydroxide can be used. As the viscosity modifier, ethylene glycol, glycerin, polyvinyl alcohol, silicone oil, etc. can be used, and they are not limited to these as long as they can form a wet gel into a predetermined use form.

Next, the obtained wet gel of the inorganic oxide is dried to obtain a dried gel. For the drying treatment, common drying methods such as natural drying, heat drying, and reduced-pressure drying, supercritical drying methods, freeze-drying methods, and the like can be used. In general, reducing the amount of solids in a wet gel in order to increase the surface area of the dry gel and reduce the density will reduce the strength of the gel. In general, in the drying method where only drying is performed, most of the gel shrinks due to the stress generated when the solvent is evaporated. Therefore, in order to obtain a dry gel with excellent porous properties from a wet gel, supercritical drying is preferably used as a drying method And freeze-drying, which can prevent the shrinkage of the gel during drying, that is, prevent densification. In a general drying method of evaporating a solvent, shrinkage of the gel during drying can be suppressed by using a high-boiling-point solvent with a slow evaporation rate or by controlling the evaporation temperature. In addition, the shrinkage of the gel during drying can also be suppressed by controlling the surface tension by subjecting the surface of the solid component of the wet gel to hydrophobic treatment.

In the supercritical drying method and the freeze drying method, drying is performed by changing the solvent from a liquid state to a phase state. At this time, a gas-liquid interface is not formed, and there is no stress on the gel skeleton due to surface tension, so drying can be prevented. The shrinkage of the gel is a method suitable for obtaining a low-density dry gel porous body. In particular, a dry gel obtained by a supercritical drying method can be preferably used in the present invention.

As the solvent used in supercritical drying, a solvent that wets the gel can be used. It is preferable to replace with an easy-to-handle solvent in supercritical drying as needed. Alcohols such as methanol, ethanol, and isopropanol, carbon dioxide, and water are used as alternative solvents to directly form the solvent into a supercritical fluid. Or, replace it with acetone, isoamyl acetate, hexane and other general easy-to-handle organic solvents that are easy to dissolve with these supercritical fluids.

As supercritical drying conditions, it is carried out in a pressure vessel such as an autoclave. For example, when methanol is used, the critical conditions are formed at a critical pressure of 8.09MPa and a critical temperature of 239.4°C or higher. Under a constant temperature, slowly release the pressure and carry out dry. When carbon dioxide is used, the critical pressure is 7.38MPa, and the critical temperature is above 31.1°C. Also in the state of constant temperature, the pressure is released from the supercritical state, and the gas state is formed for drying. When water is used, the critical pressure is 22.04MPa and the critical temperature is above 374.2°C for drying. As the time required for drying, the time for replacing the solvent in the wet gel with the supercritical fluid one or more times may pass.

The method of drying the wet gel after hydrophobic treatment is to chemically react the hydrophobic treated surface treatment agent with the surface of the solid component in a solvent in the state of the wet gel. This reduces the surface tension generated in the fine mesh structure of the wet gel, reduces stress during drying, suppresses shrinkage during normal drying, and obtains a dry gel. As surface treatment agents, halogenated silane treatment agents such as trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, ethyltrichlorosilane, trimethylmethoxysilane, trimethylethylsilane, etc., can be used. Alkoxy-based silane treatment agents such as oxysilane, dimethyldimethoxysilane, and methyltriethoxysilane, and silicone-based agents such as hexamethyldisiloxane and dimethylsiloxane oligomer Silane treatment agents, amine-based silane treatment agents such as hexamethyldisilazane, alcohol-based treatment agents such as propanol, butanol, hexanol, octanol, and decyl alcohol, etc. These surface treatment agents are not limited as long as the wet gel can be obtained without shrinkage and a dry gel can be obtained by a normal drying method.

The inorganic oxide porous body structure obtained by the above method is schematically shown in FIG. 2 in order to aggregate fine particles to form a network structure. When observed with an electron microscope, it is a fine particle aggregate, and its voids form a porous structure. The inorganic oxide porous body 51 produced in this way is transparent to sunlight over a wide wavelength range, and has the property of only passing gas due to its hydrophobicity.

At this time, the porosity of the porous body is preferably 50-98%. The reason for this is as follows. When the porosity is less than 50%, the gas permeation amount tends to decrease, and when it exceeds 98%, the porosity becomes brittle, the strength becomes weak, and handling is difficult. However, this range cannot be limited because the preferred value differs depending on the material characteristics of the inorganic oxide. The porosity mentioned here is the value obtained by subtracting the apparent density of the porous body from 100% and dividing it by the percentage of the true density of the material forming the skeleton of the porous body. Calculated value.

In addition, as the pore size of the inorganic oxide having a network structure, the pore diameter is not more than 1 μm, preferably not more than 100 nm, more preferably not more than several tens of nm. When it is smaller or larger than this range, the specific surface area of the porous body becomes smaller, the amount of supported photocatalyst particles decreases, and the reaction efficiency tends to decrease. The specific surface area is preferably at least several tens of m ² /g, more preferably at least 100 m ² /g. The pore size and specific surface area mentioned here are determined by measuring the physical properties of the porous body with a mercury porosimeter, nitrogen adsorption method, and the like.

Next, the photocatalyst particles 52 supported on such a porous body 51 will be described. As the photocatalyst particle 52 used here, any one can be arbitrarily selected and used as long as it can induce the above-mentioned photocatalytic reaction. For example, titanium dioxide, strontium phthalate, barium phthalate, sodium phthalate, cadmium sulfide, zirconium dioxide, α-Fe ₂ O ₃ , K ₄ Nb ₆ O ₁₇ , Rb ₄ Nb ₆ O ₁₇ , K ₂ Rb ₂ Nb ₆ Semiconductors such as O ₁₇ , Pb _1-x K _2x NbO ₆ (0<x<1), metals such as platinum, palladium, ruthenium, and rhodium supported as co-catalysts, semiconductors such as _NiOx , _RuOx , and _RhOx , etc. The average particle diameter is preferably in the range of 0.01-10 µm. The supporting amount of the co-catalyst can be selected from the range of 0.1 to 20% by weight based on the total weight of the semiconductor and the co-catalyst in view of the photocatalyst activity. In addition, two or more photocatalysts may be used in combination. Similarly, two or more co-catalysts may be used in combination.

Next, a method for supporting the photocatalyst particles 52 on the porous inorganic oxide body 51 will be described. As a method of forming the photocatalyst particles 52 , there are the following: forming support with colloids, carrying precursors such as metal salts, reducing them with hydrogen or a reducing agent, and firing precursors such as metal salts. As a method of supporting a catalyst or a catalyst precursor, there are a method of adding it when forming an inorganic oxide wet gel, a method of forming an inorganic oxide wet gel and forming it on the surface, and the like. When the catalyst precursor is used for loading, the catalyst treatment is carried out after loading. These methods can be selected according to the materials used and the structure. For example, the above-mentioned photodecomposing layer 5 is fixed on the inner wall surface of the box body 1 through a gas gasket installed around the box body 1 .

Next, the working principle of the water photo-splitting device having the above-mentioned structure will be described. First, sunlight L is irradiated to the inside of the box body 1 through the light-transmitting window 12 , and the irradiated solar energy in the mid-infrared region (heat energy) is irradiated to the water layer 4 through the photodecomposition layer 5 . Part of the heat energy is absorbed by the water layer 4 , and the rest of the heat energy is absorbed by the light-to-heat conversion layer 3 through the water layer 4 . In this way, the heat energy absorbed by the light-to-heat conversion layer 3 indirectly heats the water layer 4, and part of the heated water forms water vapor. Here, the air-permeable membrane 51 constituting the photodecomposition layer 5 only permeates the above-mentioned gas, and the water layer 4 and the photodecomposition layer 5 are separated by the space 6, so only water vapor enters the photodecomposition layer 5.

On the other hand, light (ultraviolet-visible region) whose energy is higher than the forbidden band energy of the photocatalyst particles is absorbed by the photocatalyst particles 52 dispersed in the photodecomposition layer 5 . At this time, when the water vapor entering the photodecomposition layer 5 reaches the surface of the photocatalyst particle 52, the photodecomposition reaction of water proceeds to generate hydrogen and oxygen. The generated hydrogen and oxygen are diffused into the gas phase through the photodecomposition layer 5 , suppressing the reverse reaction on the surface of the photocatalyst particle, and efficiently gather in the second space 7 . In this way, when the pressure in the tank 1 increases, these gases, that is, hydrogen and oxygen, enter the gas separator through the discharge port 11, and are separated for their respective purposes.

When a depressurized environment is formed in the box body 1, the generated hydrogen and oxygen can quickly diffuse into the second space 7, and the reverse reaction can be further suppressed. Alternatively, it is preferable to make the gas phase in the box 1 an inert gas atmosphere such as argon. In this case, an introduction port may be formed on a wall surface opposite to the discharge port 111, thereby allowing the inert gas to flow.

According to the present embodiment described above, the water vapor generated in the water layer 4 is photo-decomposed to obtain hydrogen and oxygen. Therefore, since the diffusion in the gas phase is utilized, the mechanical energy such as stirring water shown in the conventional example is not required. The result is improved energy efficiency.

In addition, since the photolysis reaction proceeds in the gas phase, it is possible to suppress the reverse reaction of generated hydrogen and oxygen. In this regard, the photodecomposition device of this embodiment can further suppress the reverse reaction due to the special structure of the first space 6 provided between the water layer 4 and the photodecomposition 5 . That is, water vapor and water molecules formed by volatilization from the water layer 4 enter the photodecomposition layer 14 through the first space 6 . However, as shown in the above-mentioned documents 1 and 2, when the water layer is in contact with the porous photodecomposition layer, liquid water will penetrate into the porous interior due to capillary phenomenon, and the liquid water and the photocatalyst will react. Therefore, in this state, the hydrogen and oxygen generated by sunlight irradiation undergo a reverse reaction and return to water, so the generation efficiency is significantly reduced. On the contrary, in this embodiment, unlike the conventional example described above, the first space 6 is formed between the water layer 4 and the photodecomposition layer 5 so that the water layer 4 and the photodecomposition layer 5 are not in contact with each other. Therefore, liquid water is not easy to enter, and only water molecules that volatilize from the water layer 4 to form water vapor can enter the photodecomposition layer 5, and as a result, the above-mentioned reverse reaction is difficult to occur. In addition, compared with liquid water, since water vapor has high energy, it can quickly react with a photocatalyst, so it has the advantage of being able to efficiently obtain hydrogen and oxygen.

In addition, since the light-to-heat conversion layer 3 is provided at the bottom of the water layer 4 , sunlight L in the infrared region passing through the water layer 4 is absorbed by the light-to-heat conversion layer 3 . Thereby, water vapor can be generated from the water layer 4 by utilizing the heat. Therefore, energy efficiency can be further improved since previously unutilized energy in the infrared region can be utilized. In this case, since a catalyst having a high temperature has a high activity, there is an effect of further promoting the photodecomposition reaction.

In addition, it has the following advantages. In this embodiment, since sunlight L and water vapor enter the thickness direction of the entire photodecomposition layer 5, the region where the photodecomposition reaction takes place is not limited to the interface between the photodecomposition layer 5 and the water layer 4 unlike the conventional example. . Thereby, depending on the thickness of the photodecomposition layer 5, the photodecomposition reaction is promoted.

The hydrogen and oxygen obtained by the above method can be used, for example, as an energy source for a fuel cell.

(the second embodiment)

Next, a second embodiment of the water photolysis device of the present invention will be described with reference to the drawings. Fig. 3 is a cross-sectional view showing a schematic configuration of the water photodecomposition device according to the present embodiment. The difference between this embodiment and the first embodiment is the second space and its surrounding box structure. Other structures are the same as the first embodiment, and the same symbols are used for the same structural parts, and detailed description is omitted.

As shown in FIG. 3 , in the present embodiment, the second space 7 formed between the photodecomposition layer 5 and the light transmission window 12 is divided into two upper and lower spaces by the hydrogen separation film 8 . That is, the first gas accumulation part 71 is formed between the photolysis layer 5 and the hydrogen separation film 8 , and the second gas accumulation part 72 is formed between the hydrogen separation film 8 and the light transmission window 12 . Three through holes communicating with the outside are formed on the wall surface of the box body 1 . That is, an inlet port 115 and a first discharge port 116 are respectively formed at positions facing the wall surface of the first gas accumulation portion 71 , and a second discharge port 117 is formed on the wall surface of the second gas accumulation portion 72 . The introduction port 115 and the first discharge port 116 are respectively formed on wall surfaces facing each other. The hydrogen separation membrane 8 is not particularly limited as long as it can permeate hydrogen. For example, a polyimide membrane (Toray DuPont Co., Ltd., trade name [Kapton (registered trademark)]) after heat treatment at 600-1000° C. Ready to use.

Next, the working principle of the water photo-splitting device having the above-mentioned structure will be described. First, the sunlight L is irradiated into the inside of the box body 1 through the light-transmitting window 12 , and as in the first embodiment, the infrared region (heat energy) passes through the photodecomposing layer 5 and irradiates the water layer 4 . Furthermore, the thermal energy absorbed by the light-to-heat conversion layer 3 through the water layer 4 heats the water layer 4, and part of it becomes water vapor. This water vapor enters the photodecomposition layer 5 through the first space 6 .

On the other hand, light in the ultraviolet-visible region is absorbed by the photocatalyst particles 52 dispersed in the photodecomposition layer 5 . At this time, when the water vapor entering the photodecomposition layer 5 reaches the surface of the photocatalyst particle 52, the water undergoes a photodecomposition reaction to generate hydrogen and oxygen. The generated hydrogen and oxygen easily diffuse into the gas phase through the photodecomposition layer 5 , so that the reverse reaction on the surface of the photocatalyst particles can be suppressed, and they can be effectively collected in the first gas accumulation part 71 . The hydrogen accumulated in the first gas accumulation part 71 is accumulated in the second gas accumulation part 72 through the hydrogen separation membrane 8 . In this way, the hydrogen is discharged out of the tank 1 through the second discharge port 117 and stored in a hydrogen storage part not shown. The oxygen that has not permeated through the hydrogen separation membrane 8 is discharged from the first discharge port 116 . The gas discharged from the first discharge port 116 may also be separated by a gas separator as in the first embodiment.

Here, by using an exhaust system connected to the second discharge port 117, the inside of the second gas accumulation part 72 is made into a depressurized environment, and hydrogen can rapidly diffuse into the gas accumulation part 72. As a result, the reverse reaction can be further suppressed, and hydrogen can be efficiently separated and recovered. Or, it is also possible to pass inert gas such as argon from the introduction port 115 located at the first gas accumulation part 71, so that the pressure in the first gas accumulation part 71 is greater than that of the second gas accumulation part 72. A pressure difference is formed between 71 and 72 . The pressure difference at this time is preferably not less than about 1.3×10 ⁴ Pa (about 100 Torr) and not more than about 1×10 ⁶ Pa (about 7600 Torr, that is, about 10 atmospheres). This is because when the pressure difference is less than about 1.3×10 ⁴ Pa, the pressure difference between the two gas accumulation parts 71, 72 is not large enough to effectively separate and recover hydrogen. On the other hand, when the pressure difference exceeds about 1×10 ⁶ Pa, the hydrogen separation membrane 8 may be damaged due to the excessive pressure difference.

The above structure can obtain the following effects in addition to the same effects as those of the first embodiment. That is, since the hydrogen separation membrane 8 is provided in the second space 7, the hydrogen separated by the photodecomposition layer 5 can be efficiently separated. Therefore, hydrogen can be obtained without using a gas separator, and the cost of the apparatus can be reduced.

However, in each of the above-mentioned embodiments, liquid water is supplied into the tank 1 to form a water layer, but it is also possible to perform photolysis without supplying water into the tank 1 and to use external water. A device of this form will be described below.

(the third embodiment)

Next, a third embodiment of the present invention will be described with reference to the drawings. Fig. 4 is a cross-sectional view of a water photolysis device according to a third embodiment. The difference between this embodiment and the above-mentioned embodiments is the structure of the box body, and the other structures are the same as those of the first embodiment.

As shown in FIG. 4 , in the water photolysis device of this embodiment, an opening 118 is formed at the bottom of the box 1 , and the main body 11 is formed into a square tube as a whole. The casing 1 is supported on the water layer 9 by a support device not shown, and can be arranged in water storage areas such as a water layer storing liquid water, indoor and outdoor swimming pools (preferably indoor swimming rooms), pools, lakes, and seas. More specifically, the lower part of the box body 1 is inserted into the water layer 9 and placed on the water layer 9 in a floating state. At this time, a distance is formed between the water surface of the water layer 9 and the photodecomposition layer 5, and when the housing 1 is arranged, the space 6 (first space) must be formed in the distance.

In the light splitting device with the above structure, the working principle is the same as that of the above-mentioned embodiments. That is, water vapor in the water layer 9 is evaporated by irradiating sunlight L or the like, and the water vapor enters the photodecomposition layer 5 through the first space 6 . At this time, in the photodecomposition layer 5 , the photocatalyst particles 52 are excited by the sunlight L, and decompose the entered water vapor into hydrogen and oxygen.

According to the present embodiment described above, in addition to obtaining the same effects as those of the above-described embodiments, the following effects can also be obtained. That is, the above-mentioned photodecomposition device has an opening 118 at the bottom of the box 1 , and water vapor can enter the box 1 through the opening 118 . Thus, unlike the devices of the first and second embodiments, it is not necessary to supply and contain water into the tank 1, and the water splitting can be carried out as long as the device is placed in a place where water exists. Therefore, no water supply work is required, and the work procedure is simplified.

In this embodiment, the tank body 1 is floated on the water layer 4, but it is not limited to this, and the structure as shown in FIG. 5 is also possible. As shown in the figure, in this example, the shallower water layer and the above-mentioned swimming pool are taken as examples, and when the box body 1 is arranged, the bottom of the box body 1 is in contact with the bottom surface of the water layer 9 . At this time, the water surface of the water layer 9 and the photodecomposition layer 5 cannot be in contact, and a space 6 (first space) needs to be formed therebetween. For this reason, when the box body 1 is set in a shallow water place, the above-mentioned space 6 is ensured by adjusting the distance between the bottom of the box body 1 and the photodecomposition layer 5 . In addition, a water inlet 114 is formed on the lower side wall of the box body 1 , and water enters the box body from the water layer 9 through the inlet port 114 . Also in the above configuration, the same effects as those of the above-described embodiments can be obtained, and furthermore, the housing 1 can be easily installed.

In addition, in the example of FIG. 5 , an opening 118 is formed at the bottom of the box body 1, but a box body with a closed bottom as shown in FIG. Just mouth.

The embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various changes can be made as long as they do not deviate from the spirit of the invention. For example, as the porous body used in the present invention, structures other than those described in the first embodiment can be used. For example, porous glass, sintered body and bonded body of inorganic oxide particles, etc. can be used. At this time, since the structure of the porous body is different from that described in the first embodiment, the porosity, pore size, and the like are not limited to the particularly preferable predetermined ranges of the structure. Further, in the first and second embodiments, the light-to-heat conversion layer 3 formed of a metal thin film is formed under the water layer 4, but the light-to-heat conversion layer 3 is not limited to this, as long as it is in contact with the water layer 4, it can be formed by A light-to-heat conversion layer 3 is formed of a black board that is easy to absorb heat energy, for example. In addition, the light-to-heat conversion layer 3 does not necessarily have to be provided. For example, when it is arranged on a heat-absorbing roof, the water layer is heated by the heat from the roof, that is, the heat from the outside, so it is not necessary to provide a light-to-heat conversion layer. Moreover, when the sunlight is strong, water vapor can be generated only by heating the water layer with sunlight, so there is no need to install a light-to-heat conversion layer.

In addition, although pure water is used for the water layer in each of the above-mentioned embodiments, in addition, aqueous solutions such as NaHCO ₃ aqueous solution, Na ₂ SO ₄ aqueous solution, and NaOH aqueous solution, or seawater, etc., can also be used to photodecompose them. .

In addition, the box body 1 is not limited to the above-mentioned structure, for example, the light-transmitting window 12 may not be provided, and the entire box body 1 is made of light-transmitting materials, that is, the box body is made of transparent components. In addition, the term "transparent" may be either colored or transparent, but colorless and transparent is preferred in order to obtain good light transmission.

Example

Specific examples of the water photolysis device of the present invention are shown below. However, the scope of the present invention is not limited to these examples.

(Example 1)

TiO ₂ photocatalyst particles carrying 1.0% by weight of co-catalyst RuO ₂ were dispersed in a porous silica body to form a photodecomposition layer. Photocatalyst particles are produced by the following method. First, 50 ml of an aqueous ruthenium chloride solution was added to 2.0 g of titanium dioxide, evaporated to dryness, and solidified. Then, it was dried at 110°C, and the resultant dried product was heat-treated in air at 400°C for 8 hours to obtain powdery 1.0 wt% RuO ₂ /TiO ₂ with an average particle diameter of about 0.5 µm. Then prepare tetramethoxysilane, ethanol and ammonia solution (0.1 equivalent) in a molar ratio of 1:3:4, suspend the obtained photocatalyst particles in the silicon oxide raw material solution, put them in a container, and perform gelation. to obtain a solidified composite wet gel layer. Next, the solvent inside the wet gel was replaced with acetone, and dried by a supercritical drying method to obtain a dry gel. The condition of supercritical drying is to use carbon dioxide as the drying medium, under the conditions of pressure 12MPa and temperature 50°C, after 4 hours, release the pressure slowly, and start to cool down after reaching atmospheric pressure. Through the above procedure, a silicon oxide porous body (average film thickness: 0.5 mm) in which photocatalyst particles were dispersed was obtained. The supported amount of photocatalyst particles was about 0.23 mg/cm ³ .

The photodecomposition layer produced by the above method was installed in the photodecomposition device shown in Fig. 1, and the discharge port was connected to a gas chromatograph. Next, supply 50ml of pure water into the box to form a water layer, use a rotary pump to exhaust to form a vacuum of 0.133Pa (that is, about 10 ^-3 Torr) in the box, and then pass in argon gas to form a vacuum of 1.3×10 ⁴ Pa (about 100Torr). ). Thereafter, the device was irradiated with sunlight from above, and the amount of hydrogen gas produced was measured with a gas chromatograph. As a result, the amount of hydrogen produced was 210 μmol/kW·h in terms of the amount of sunlight.

For comparison, the photodecomposition layer in the above device was taken out, and a device in which photocatalyst particles were dispersed in pure water was produced instead. After vacuum evacuation, argon gas was introduced to form 1.3×10 ⁴ Pa (about 100 Torr), and the same as the above case, the sunlight was irradiated. As a result, the amount of hydrogen produced was 20 μmol/kW·h.

(Example 2)

A photodecomposition layer was produced in the same manner as in Example 1. That is, TiO ₂ photocatalyst particles (average particle diameter: about 0.5 μm) carrying 1.0% by weight of cocatalyst RuO ₂ were dispersed in a silica porous body (average film thickness: 0.5 mm) to form a photodecomposition layer. This photodecomposition layer was installed in the device shown in FIG. 3 . An aqueous NaHCO ₃ solution (0.1 mol/l) was used as the aqueous layer. After exhausting with a rotary pump to form a vacuum in the box, argon gas of 1.3×10 ⁴ Pa (about 100 Torr) was introduced from the inlet to irradiate with sunlight. The amount of hydrogen separated and recovered by the hydrogen separation membrane, that is, the amount of hydrogen discharged from the second discharge port was measured, and the generated amount was 190 μmol/kW·h in terms of the amount of sunlight. The recovered gas was analyzed by a gas chromatograph, and it was found that high-purity hydrogen with a purity of 95% or higher was obtained.

For comparison, the photodecomposition layer in the above device was taken out, and a device in which photocatalyst particles were dispersed in NaHCO ₃ aqueous solution was used instead. After vacuum evacuation, argon gas of 1.3×10 ⁴ Pa (about 100 Torr) was introduced, and sunlight irradiation was carried out in the same manner as above. As a result, the amount of hydrogen produced was 30 μmol/kW·h.

From the results of the above examples, it can be confirmed that in the existing method, the hydrogen and oxygen generated by irradiation of sunlight return to water due to the reverse reaction, and the generation efficiency is very low. On the contrary, according to the present invention, hydrogen can be effectively generated and oxygen. In addition, it was also confirmed from Example 2 that hydrogen can be separated efficiently and independently, and high-purity hydrogen can be recovered.

Industrial applicability

The present invention provides a photodecomposition device capable of promoting the photodecomposition reaction of water by effectively utilizing solar energy, and efficiently obtaining hydrogen and oxygen water by suppressing the reverse reaction.

Claims (29)

1. the photolysis device of a water is characterized in that:

Possess and can and be contained in the intravital photolysis layer of described case from the casing of outside incident light,

Described photolysis layer contains the porous insert and the photocatalyst that is supported on this porous insert of light transmission,

Below described photolysis layer, dispose the water layer that contains liquid water across the 1st space,

In described casing, the top of described photolysis layer is formed with the 2nd airtight space,

The water vapour that described water layer produces imports to described photolysis layer by described the 1st space, and the described photocatalyst by the excitation that is subjected to described light resolves into hydrogen and oxygen with described water vapour,

The hydrogen of described generation and oxygen are diffused into described the 2nd space.

2. the photolysis device of the water of claim 1 record wherein is provided with described water layer in the inside of described casing.

3. the photolysis device of the water of claim 1 record wherein is provided with the photothermal transformation layer that joins with water layer and can absorb described light in the inside of described casing.

4. the photolysis device of the water of claim 3 record, wherein said photothermal transformation layer is made of the metallic film that is configured in below the described water layer.

5. the photolysis device of the water of claim 3 record, wherein said photothermal transformation layer is made of the black plate body that is configured in below the described water layer.

6. the photolysis device of the water of claim 1 record wherein forms opening at described bottom half.

7. the photolysis device of the water of claim 6 record, wherein said casing is provided with the state that swims on the described water layer.

8. the photolysis device of the water of claim 7 record, wherein said water layer is formed by the water in indoor and outdoor swimming pool, sea, pond or lake.

9. the photolysis device of the water of claim 1 record is characterized in that:

On the wall of described casing, form the introducing port that liquid water is imported to the water layer of this box house.

10. the photolysis device of the water of claim 9 record wherein is formed with opening at described bottom half.

11. the photolysis device of the water of claim 1 record when described casing wherein is set, makes this bottom half contact with the end of described water layer.

12. the photolysis device of the water of claim 1 record, wherein said casing is made of water white parts.

13. the photolysis device of the water of claim 1 record, wherein said light is sunlight.

14. the photolysis device of the water of claim 1 record, wherein said porous insert has eyed structure, and supports emboliform photocatalyst.

15. the photolysis device of the water of claim 14 record, the porosity of wherein said porous insert is 50%-98%.

16. the photolysis device of the water of claim 14 record, the hydrophobization processing has been carried out on the surface of wherein said porous insert.

17. right is wanted the photolysis device of the water of 1 record, wherein is formed with the gas in described the 2nd space is discharged to outside venting port on the inner-wall surface of described casing.

18. the photolysis device of the water of claim 17 record, wherein said the 2nd space is a reduced pressure atmosphere.

19. the photolysis device of the water of claim 17 record is formed with on the wall of wherein said casing rare gas element is passed into introducing port in described the 2nd space.

20. the photolysis device of the water of claim 1 record is characterized in that:

Described the 2nd space is separated into above-below direction 2 gas accumulation parts arranged side by side by hydrogen separation membrane,

The wall of described casing and on be formed with, be positioned at described hydrogen separation membrane top, from the relief outlet of gas accumulation part to outside vent gas body.

21. the photolysis device of the water of claim 20 record is characterized in that:

On the wall of described casing, be formed with, be positioned at introducing port described hydrogen separation membrane below, partly feed rare gas element to gas accumulation.

22. the photolysis device of the water of claim 20 record is characterized in that:

Be positioned at the pressure of the gas accumulation pressure partly of described hydrogen separation membrane top less than the opposing party's gas accumulation part, the pressure difference of two gas accumulations parts is 1.3 * 10 ⁴Pa-1 * 10 ⁶Pa.

23. the photolysis method of a water, the photolysis device of the water of use claim 1 record is characterized in that comprising:

To possess light transmission porous insert and the photolysis layer that is supported on the photocatalyst on this porous insert, be configured in the step on the water layer that contains liquid water across the 1st space,

To the step of described photolysis layer irradiates light and

The water vapour that described water layer produces imports on the described photolysis layer by the 1st space, by being subjected to photocatalyst that described light obtains encouraging described water vapour is resolved into the step of hydrogen and oxygen,

And, described photolysis layer is configured in the casing that can inject light, in described casing, above described photolysis layer, be formed with the 2nd airtight space, capture described hydrogen and oxygen by the 2nd space.

24. the photolysis method of the water of claim 23 record, the photothermal transformation layer that the below configuration of wherein said photolysis layer contacts with described water layer.

25. the photolysis method of the water of claim 23 record, wherein said light is sunlight.

26. the photolysis method of the water of claim 23 record, wherein said porous insert has eyed structure, and supports emboliform photocatalyst.

27. the photolysis method of the water of claim 26 record, the porosity of wherein said porous insert is 50%-98%.

28. the photolysis method of the water of claim 26 record, the hydrophobization processing has been carried out on the surface of wherein said porous insert.

29. the photolysis method of the water of claim 23 record, wherein said water layer is formed by the water in indoor and outdoor swimming pool, sea, pond or lake.

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