JPH08290052A - Membrane photocatalytic chemical conversion device - Google Patents

Abstract

PURPOSE: To form hydrogen at room temp. from water, seawater or an electrolyte aq. soln. by utilizing a light source containing ultraviolet rays or solar rays and to further chemically convert CO2 at room temp. to use the same as resources. CONSTITUTION: In an apparatus having a TiO2 membrane photocatalyst 2, a proton separation membrane 8 and an electrochemical catalyst 9 successively arranged in a soln., a light source 1 irradiating the membrane photocatalyst with light and the circuit connecting the membrane photocatalyst 2 and the electrochemical catalyst 9 as main constitutional elements, the following process is performed at room temp. Electrons and holes are generated by irradiating the membrane photocatalyst 2 with light and the soln. brought into contact with the membrane photocatalyst 2 is reacted with the holes to generate protons and oxygen and the proton separation membrane 8 separates protons from oxygen to permit them to transmit and protons are electrochemically bonded to the surface of the electrochemical catalyst 9 to form hydrogen. When CO2 is supplied, the reduction reaction of CO2 is generated on the surface of the electrochemical catalyst 9 by protons and electrons to form CO and hydrocarbon.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film photocatalyst for water,
The present invention relates to a thin film photocatalytic chemical conversion device that generates a proton from seawater or an aqueous solution containing an electrolyte and combines the proton to generate hydrogen, or reacts the proton with carbon dioxide to generate a chemically compatible raw material.

[0002]

2. Description of the Related Art At present, it is desired to solve the problem of global environment conservation as well as energy conservation. First of all, it is necessary to pursue new energy sources in the long run in view of future depletion of fossil fuels. In that case, a clean fuel that does not emit any substances polluting the environment by combustion (for example, nitrogen oxides, sulfur oxides, hydrocarbons, carbon monoxide) and carbon dioxide that promotes global warming is preferable. For example, hydrogen attracts attention as the cleanest fuel because it produces only water by combustion.

Next, there is an urgent need to reduce atmospheric release of carbon dioxide, which is considered to be the main cause of global warming, and the recycling of carbon dioxide can be considered as one way of reducing it. This is, so to speak, based on the concept of chemical recycling, in which chemically stable carbon dioxide gas generated as a result of combustion of fossil fuels and many chemical reactions is recycled to be used as fuel again or as a raw material for chemical synthesis. It is intended to be converted into a reusable substance.

Hydrogen is currently industrially used to modify water gas,
It is manufactured by a method that requires the assistance of thermal energy such as natural gas modification, coal gasification, or a method that requires electric energy obtained by combustion of fossil fuels such as electrolysis of water. It can be said that the production cost is relatively high among the gas production methods. In order to use hydrogen widely as a fuel source, it is necessary to reduce the price and simplify the equipment.

Generally, a chemical conversion of a substance uses a catalyst as an industrial means, and it is widely used for pollution control such as denitration in addition to the chemical industry. However, the characteristic point common to these is that a considerable amount of external heat energy needs to be supplied, that is, the chemical reaction must be performed at a temperature of room temperature or higher. Even in the current hydrogen production and chemical conversion of carbon dioxide, it is a reaction at a temperature above room temperature and it is necessary to supply heat energy.

[0006]

The method of utilizing abundant energy sources and resources in the natural world is costly in the process of hydrogen generation and environmental conservation measures, and the process is not subject to secondary pollution (new energy source or It is preferable that it does not generate a negative effect on the environment because it is generated to create resources. Further, from a system perspective, a simpler one is needed if a widespread penetration rate is considered.

On the other hand, chemical recycling, that is, chemical recycling of substances can be considered as a basic principle of the ultimate global environment control method. Therefore, it is an important issue in the future to pursue a global optimum chemical balance on a small scale or a global scale by releasing unnecessary or harmful substances to the outside and recycling or utilizing them by utilizing chemical conversion. It is supposed to come.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thin film photocatalytic chemical conversion device for producing hydrogen as an energy source.

Another object of the present invention is to provide a thin film photocatalytic chemical conversion device for reducing carbon dioxide and recycling it.

[0010]

The thin film photocatalytic chemical conversion device of the present invention generally uses a light source including an ultraviolet wavelength region as a light energy source, water, seawater or an aqueous solution containing an electrolyte as a hydrogen source, and a thin film photocatalyst and an electrolyzer. As a system to which a chemical catalyst is added, it is a device that enables hydrogen generation and chemical conversion of carbon dioxide at room temperature without requiring external heat energy supply.

In order to achieve one of the above objects, the first thin film photocatalytic chemical conversion device of the present invention is filled with room temperature water, seawater or an aqueous solution containing an electrolyte (water, seawater or an aqueous solution is referred to as a solution). A container, a light source for irradiating light including an ultraviolet wavelength region from the outside to the inside of the container, and a photocatalyst, a proton separation membrane and an electrochemical catalyst which are respectively installed in a solution in the container. As a photocatalyst for receiving light, titanium oxide (TiO 2) with an anatase type crystal structure
₂ ) A photocatalyst formed by forming a thin film on one surface of a conductive substrate, a hole (h) generated by a solution in a titanium oxide (TiO ₂ ) thin film.
+) Is decomposed to generate a proton (H +) that is separated from the oxygen that is simultaneously generated, and a platinum (Pt) plate that captures the separated proton (H +) as an electrochemical catalyst) And a bias circuit connecting the substrate of the electrochemical catalyst and the photocatalyst body, the electrochemical catalyst body trapped with the electrons (e ~) generated from the titanium oxide (TiO ₂ ) thin film and flowing through the bias circuit. It is a device that combines with protons (H +) to generate hydrogen.

In the first thin film photocatalytic chemical conversion device, the conductive substrate of the photocatalyst is composed of a titanium plate, or stannic oxide (SnSn) is formed between the titanium oxide (TiO ₂ ) thin film and the conductive substrate.
It is preferable to use a glass plate with an O ₂ ) coating interposed.
Further, the bias circuit preferably applies a positive bias voltage to the titanium oxide (TiO ₂ ) thin film, or alternately applies a positive voltage and a negative voltage periodically.

In order to achieve the above-mentioned one object, the second thin film photocatalytic chemical conversion device of the present invention is such that in the first thin film photocatalytic chemical conversion device, one photocatalyst is the first photocatalyst Is added as a second photocatalyst, and the second photocatalyst is a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure as a photocatalyst for receiving light transmitted through the first photocatalyst. The electrochemical catalyst is formed on one surface of the first and second photocatalysts are titanium oxide.
The electrons (e) generated from the (TiO) thin film and flowing through the bias circuit are combined with the captured protons (H +) to generate hydrogen.

In the second thin film photocatalytic chemical conversion device, the conductive substrate of the second photocatalyst may be made of titanium. Further, instead of the second photocatalyst, a photocatalyst formed by forming a ferric trioxide (Fe ₂ O ₃ ) thin film on an iron substrate as a photocatalyst may be installed. The bias circuit preferably applies a positive bias voltage to the titanium oxide (TiO ₂ ) thin film, or alternately applies a positive voltage and a negative voltage periodically.

In the above first and second thin film photocatalytic chemical conversion devices, instead of the electrochemical catalyst body made of platinum,
An electrochemical catalyst body made of any one of palladium, gold, silver, copper, copper oxide, and silver oxide, or an electrochemical catalyst body made of copper coated with zinc oxide or silver oxide entirely or partially may be installed. Furthermore, the titanium oxide (TiO ₂ ) thin film has a thickness of 50
~ 2000nm is good, and ferric trioxide as a photocatalyst
When using a (Fe ₂ O ₃ ) thin film, the thickness is preferably 5 to 200 nm.

In order to achieve the above-mentioned another object, a third thin film photocatalytic chemical conversion device of the present invention comprises a container, a light source, a photocatalyst, which constitutes the first thin film photocatalytic chemical conversion device, and which is filled with a solution at room temperature. In addition to the body, the proton separation membrane, the electrochemical catalyst body, and the bias circuit, carbon dioxide gas supply means for supplying carbon dioxide gas to the surface of the electrochemical catalyst body is provided.
The electrochemical catalyst is a device that reduces carbon dioxide by trapped protons (H +).

In order to achieve the above-mentioned another object, a fourth thin film photocatalytic chemical conversion device of the present invention comprises a container filled with a solution at room temperature and a light source, which constitutes the second thin film photocatalytic chemical conversion device. In addition to the first and second photocatalyst bodies, the proton separation membrane, the electrochemical catalyst body, and the bias circuit, a carbon dioxide gas supply means for supplying carbon dioxide gas to the surface of the electrochemical catalyst body is provided. Is the captured proton
It is a device that reduces carbon dioxide by (H +).

In order to achieve the first object again, the fifth thin-film photocatalytic chemical conversion device of the present invention comprises a container filled with a solution at room temperature, and a light including an ultraviolet wavelength region inside and outside the container. A perforated photocatalyst, a proton separation membrane and a perforated electrochemical catalyzer (that is, anatase type as a photocatalyst for receiving irradiation light) are integrally connected so as to shield the light source for irradiation and the middle part of the container. Crystal structure of titanium oxide (T
iO ₂ ) A thin film is formed on one surface of a conductive substrate, and a perforated photocatalyst having holes penetrating this thin film and the substrate is used to form holes (h +) generated in the titanium oxide (TiO ₂ ) thin film by the solution. It consists of a proton separation membrane that separates protons (H +) that are generated by contact decomposition and move through the pores of the perforated photocatalyst from oxygen that is simultaneously generated, and a platinum plate that traps the separated protons (H +). , A perforated electrochemical catalyst body having a hole penetrating in the plate direction, and a bias circuit connecting the substrate of the perforated electrochemical catalyst body and the perforated photocatalyst body to the perforated electrochemical catalyst body. Is an apparatus for generating hydrogen by combining electrons (e) generated from a titanium oxide (TiO ₂ ) thin film and flowing through a bias circuit with protons (H +) that have moved through their own holes.

In order to achieve another object, the sixth thin-film photocatalytic chemical conversion device of the present invention comprises a solution-filled container, a light source, and a perforated type, which constitutes a fifth thin-film photocatalytic chemical conversion device. In addition to the photocatalyst, the proton separation membrane, the perforated electrochemical catalyst and the bias circuit, the perforated electrochemical catalyst is provided with carbon dioxide gas supply means for supplying carbon dioxide to the plate surface in contact with the solution. The electrochemical catalyst is a device that reduces carbon dioxide by protons (H +) that have moved through its own pores.

In order to achieve the above-mentioned one object,
A seventh thin film photocatalytic chemical conversion device of the present invention is installed integrally with a container filled with a solution, a light source for irradiating the inside of the container with light including an ultraviolet wavelength region, and the latter half of the container. A porous photocatalyst and a hydrogen storage alloy member (that is, a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure as a photocatalyst for receiving irradiation light is formed on one surface of a conductive substrate, and titanium oxide (TiO 2 ₂ ) A perforated photocatalyst having pores that penetrate the thin film and the substrate, and the solution is titanium oxide (TiO 2).
₂ ) Protons (H +) that are generated by being decomposed in contact with the holes (h +) generated in the thin film and moved through the holes of the perforated photocatalyst
And a bias circuit for connecting the hydrogen storage alloy member with the substrate of the perforated photocatalyst. The hydrogen storage alloy member is a bias circuit generated from a titanium oxide (TiO ₂ ) thin film. The device is a device that occludes hydrogen as hydrogen by combining with the electrons (e) that have flowed through and the captured protons.

In the seventh thin film photocatalytic chemical conversion device, a proton separation membrane may be provided between the perforated photocatalyst and the hydrogen storage alloy member.

[0022]

When the thin film photocatalyst is irradiated with light, it decomposes water in contact with the catalyst at room temperature to generate hydrogen and oxygen. By chemically reacting this hydrogen with carbon dioxide, carbon dioxide is chemically converted into various useful substances.

First, the principle of activation of the photocatalyst by light irradiation by the photocatalyst will be described with reference to FIG. When a substance absorbs light, the electrons in the substance (e ~) are excited by the energy of the light from the valence band to the conduction band across the band gap, and at the same time holes (holes) that are electron defects are generated. To do. The band gap energy differs depending on the type of photocatalyst. For example, in the case of titanium oxide (TiO ₂ ), it is 3.0 to 3.2 e.
V. This is 415 to 390 nm in terms of wavelength. Therefore, excitation of electrons occurs by irradiation with light having a shorter wavelength region having energy higher than this or lower than this.

FIG. 2 is a diagram for explaining the principle of decomposition of water (or seawater or an aqueous solution containing an electrolyte) by a thin film photocatalyst. In the photocatalyst irradiated with light, the holes (h +) generated by photoexcitation move to the surface of the thin-film photocatalyst and oxidize water molecules in contact with the surface to generate the reaction formula: H ₂
O + 2h + → 2H + + 1/2 · O ₂ causes a chemical conversion to produce protons (H +) and oxygen at the same time. Hydrogen can be obtained by synthesizing this proton (H +), and a hydrocarbon compound can be obtained by reacting this proton (H +) with carbon dioxide gas.

In the first thin film photocatalytic chemical conversion device of the present invention, titanium oxide (TiO ₂ ) of anatase type crystal structure which is a photocatalyst irradiated with light including an ultraviolet wavelength region in a solution.
The thin film generates holes (h +) and electrons (e), and the solution decomposes in contact with the holes (h +) on the surface of the titanium oxide (TiO ₂ ) thin film to generate protons (H +). The proton separation membrane separates protons (H +) migrating in the solution from oxygen generated together with the protons, and the electrochemical catalyst body separates the separated protons (H +).
+) Is trapped, and this proton (H +) and titanium oxide (TiO ₂ )
Hydrogen is generated by combining with the electrons (e) flowing from the thin film through the bias circuit. When a positive bias voltage is applied to the titanium oxide (TiO ₂ ) thin film by the bias circuit, the quantum efficiency of the titanium oxide (TiO ₂ ) thin film or the amount of photocurrent generated can be improved, and positive and negative voltages can be applied. By alternately and cyclically applying, the quantum efficiency or the amount of photocurrent generated can be further improved. The quantum efficiency and photocurrent will be described in detail in Examples 1 and 2 described later.

In the second thin film photocatalytic chemical conversion device of the present invention, by using the two photocatalysts of the first and second photocatalysts, the solution contacting the titanium oxide (TiO ₂ ) thin film of the first photocatalyst Protons (H +) are generated from the solution, and protons (H +) are also generated from the solution in contact with the titanium oxide (TiO ₂ ) thin film of the _second photocatalyst that receives the light transmitted through the first photocatalyst. A larger amount of protons (H +) can be generated as compared with the case of using one photocatalyst.
As a second photocatalyst, a ferric trioxide (Fe ₂ O ₃ ) thin film was used as iron (F 2
A larger amount of protons (H +) can be similarly generated by using the one formed on the substrate of e). This will be described later in Example 4.

The thickness of the titanium oxide (TiO ₂ ) thin film is 50 nm.
If less than 20, the photocurrent showing the activity of the photocatalyst becomes small,
Even if it exceeds 00 nm, it becomes small as well, so 50 to 200
0 nm is suitable. Further, the thickness of the ferric trioxide (Fe ₂ O ₃ ) thin film is 5 nm to 200 nm because the photocurrent becomes smaller when the thickness is less than 5 nm or exceeds 200 nm.

In the third and fourth thin film photocatalytic chemical conversion devices of the present invention, carbon dioxide gas is reduced by protons (H +) on the surface of the electrochemical catalyst to be converted into carbon monoxide or a hydrocarbon compound.

Fifth Thin Film Photocatalytic Chemical Conversion Device of the Present Invention
In (integrated type), the proton (H +) generated from the solution on the titanium oxide (TiO ₂ ) thin film moves through the solution that has entered the pores of the perforated photocatalyst, and is separated from oxygen by the proton separation membrane, The solution penetrates the pores of the perforated electrochemical catalyst to reach the back surface of the electrochemical catalyst. Where the proton
(H +) is converted to hydrogen by combining with the electrons (e ~) flowing through the bias circuit.

The sixth thin film photocatalytic chemical conversion device of the present invention
In the (integrated type), as in the fifth thin film photocatalytic chemical conversion device, the protons (H +) that reach the back surface of the chemical catalyst reduce the carbon dioxide gas supplied here, and the carbon monoxide and hydrocarbon compounds are reduced. To generate.

In the seventh thin film photocatalytic chemical conversion device of the present invention, the protons (H +) generated from the solution on the titanium oxide (TiO ₂ ) thin film penetrate into the holes provided in the thin film and the substrate, and the hydrogen storage alloy is passed through the solution. It reaches the member and is converted into hydrogen by combining with the electrons (e) flowing through the bias circuit here, and this hydrogen is sucked and stored in the hydrogen storage alloy member.

As described above, according to each apparatus of the present invention, hydrogen can be produced from water or carbon dioxide can be chemically converted into a useful substance. This device does not cause secondary pollution.

[0033]

【Example】

[Example 1] The experimental results of measuring the quantum efficiency of the thin film photocatalyst will be described below. As shown in FIG. 3, the thin-film photocatalyst device used in this experiment includes a photocatalyst body 4 in which a titanium oxide (TiO ₂ ) thin-film photocatalyst 2 containing anatase type crystal structure is formed on the surface of a substrate 3 made of titanium metal, and a proton separation membrane. 8 and an electrochemical catalyst body 9 of a platinum plate are arranged in order, and they are placed in a container filled with seawater or an aqueous solution containing an electrolyte of potassium bicarbonate (KHCO ₃ ), and the photocatalyst body 4 and the electrochemical catalyst body 4 are placed. Bias circuit E is connected to medium 9, and titanium oxide
The light source 1 for irradiating the (TiO ₂ ) thin film photocatalyst 2 with light (energy hν) is installed outside the container. In this thin film photocatalyst device, the protons (H +) generated by the decomposition of water on the surface of the thin film photocatalyst 2 diffuse in the solution, pass through the proton separation membrane 8, and move to the surface of the electrochemical catalyst 9.
The proton separation membrane 8 prevents recombination of protons and oxygen. On the other hand, the electrons e ~ generated along with holes (h +) in the thin film photocatalyst 2 upon receiving light move from the thin film photocatalyst 2 to the electrochemical catalyst 9 through the bias circuit.

In the experiment, the quantum efficiency of the photocatalyst was measured while irradiating the surface of the titanium oxide thin film photocatalyst 2 with light having a constant amount of photons emitted from the light source 1 and changing the wavelength at equal intervals. The bias voltage E was not applied in this experiment.

FIG. 4 is a diagram showing the results of the experiment, which is the curve (a).
Is the quantum efficiency when seawater is used as the solution, and curve (b) is the quantum efficiency when the potassium bicarbonate (KHCO ₃ ) solution is used as the solution.
(%) Is shown. Regarding the quantum efficiency of the photocatalyst composed of the titanium oxide (TiO ₂ ) thin film photocatalyst 2, in any solution, the quantum efficiency rises from a wavelength corresponding to the band gap of anatase of about 3.0 eV, that is, about 410 nm, and the wavelength is short. It rises and reaches about 55-60%. Quantum efficiency indicates how many valence band electrons are excited by one photon into the conduction band when the emitted light is captured as photons, as shown in the principle of Fig. 1. Represents the potential physical property of the photocatalyst. 55-60% is a fairly high quantum efficiency. This experimental data is important for evaluation of basic physical properties of titanium oxide thin film photocatalyst. By another experiment, the same result was obtained without the proton separation membrane 8, and it was found that the quantum efficiency of the thin film photocatalyst was irrelevant to the existence of the proton separation membrane.

Example 2 Next, the photocurrent characteristics of the titanium oxide thin film photocatalyst 2 under the bias voltage E were examined by the same apparatus as that used in Example 1. As shown in FIG.
A photocatalyst 4 having a titanium oxide thin film photocatalyst 2 and a platinum plate electrochemical catalyst 9 are connected via a battery, the surface of the titanium oxide thin film photocatalyst 2 is irradiated with light from a light source 1, and the titanium oxide thin film photocatalyst 2 is biased. The photocurrent was measured while the voltage E was changed stepwise and applied.

As shown in FIG. 5, the photocurrent generated in the titanium oxide thin film was +0.5 from the bias voltage of about -0.5V in both cases of seawater and potassium bicarbonate aqueous solution.
It rises over 5V and approaches a certain value at about + 0.5V,
It settled down to about 6 mA / cm ² . Curve (a) shows the photocurrent when seawater was used as the solution, and curve (b) shows the photocurrent when the aqueous potassium bicarbonate solution was used as the solution. Thus, the bias is effective in extracting more electrons generated in the photocatalyst, and in this result, too, a considerably high photocurrent is obtained. The results of this experiment are important together with Example 1 for evaluating the basic physical properties of the titanium oxide thin film catalyst.

[Embodiment 3] FIG. 6 shows a multistage thin film photocatalyst device in which two photocatalysts are arranged in two stages and combined with a proton separation membrane, an electrochemical catalyst, etc. in the same manner as the device shown in FIG. Show. No CO ₂ was supplied in this example.

The first photocatalyst body 4 uses a titanium oxide (TiO ₂ ) thin film photocatalyst 2 having an anatase type crystal structure as a photocatalyst, and a light-transmitting stannic oxide (SnO ₂ ) film as a substrate 3. It is configured by forming a titanium oxide (TiO ₂ ) thin film photocatalyst 2 on a stannic oxide (SnO ₂ ) film using a transparent glass. The second photocatalyst 7 is, like the first photocatalyst 4, a titanium oxide (TiO ₂ ) thin film 5 and a light-transmissive glass substrate 6 coated with light-transmissive stannic oxide (SnO ₂ ). It consists of and. First photocatalyst 4, second photocatalyst 7, proton separation membrane 8 and platinum plate electrochemical catalyst 9
Are sequentially installed in a container filled with KHCO ₃ solution,
The multistage thin film photocatalyst device was assembled by installing the light source 1 outside the container so that the second photocatalyst body was irradiated with light through the photocatalyst body 4.

The following results were obtained from the experiment using this apparatus. First, it was confirmed that a photocurrent was obtained by electrically connecting the thin film catalyst 2 and the electrochemical catalyst 9 and irradiating the thin film photocatalyst 1 with light using either a xenon lamp or a mercury lamp as the light source 1. For example, a current of 3 mA / cm ² was obtained under a bias voltage of 1 V with a 500 W mercury lamp. This means that the thin-film photocatalyst 1 has a light-transmitting property, and the thin-film photocatalyst 2 is electronically excited by light to obtain a photocurrent even by light that is transmitted without being absorbed by the thin-film photocatalyst 1. It shows that.

Next, the thin film photocatalyst 1 and the thin film photocatalyst 2 were electrically connected in parallel, and they were connected in series to the electrochemical catalyst 9. The photocurrent density in this case is 500 W mercury lamp,
It was 9 mA / cm ² under a bias voltage of 1V. This value was 3 mA / cm ² or more under the same conditions as in the case of using the photocatalyst 4 alone. From the above results, the effect of combining the thin film photocatalysts having the same band gap in multiple stages was shown.

[Embodiment 4] In the apparatus of this embodiment, FIG.
In the multi-stage thin film photocatalyst device shown in (1), the second catalyst body 7 made of a material different from that of the third embodiment was used. That is, the first photocatalyst body 4 is a titanium oxide (TiO ₂ ) thin film photocatalyst 2 having an anatase type crystal structure and a light-transmitting glass coated with light-transmitting stannic oxide (SnO ₂ ) as its substrate 4. On the other hand, the second photocatalyst 7 is composed of a thin film photocatalyst 5 of ferric trioxide (Fe ₂ O ₃ ) as a photocatalyst and metallic iron as its substrate 6. As described above, two photocatalysts having different photocatalysts, the proton separation membrane 8 and the electrochemical catalyst 9 of a platinum plate were installed to construct a multi-stage apparatus, and the following experimental results were obtained.

First, the second photocatalyst 7 and the electrochemical catalyst 9 are connected in series, and a photocurrent is generated by irradiating 1 of the first photocatalyst 4 with 1 of the xenon lamp or the mercury lamp as the light source 1. It was confirmed that it was obtained. For example, with a 500 W mercury lamp, under a bias voltage of 1 V, 2
A photocurrent of mA / cm ² was obtained. This means that the first photocatalyst body 4 has a light-transmitting property, and
It is shown that the second photocatalyst body 7 also electronically excites the light by the light that is transmitted without being absorbed by the second photocatalyst body 7, and a photocurrent is obtained.

Next, the first photocatalyst body 4 was irradiated with a 500 W xenon lamp with the first and second photocatalyst bodies 4 and 7 connected in parallel and connected in series to the electrochemical catalyst 9. In comparison with the case where the first photocatalyst body 4 and the second photocatalyst body 7 are independent of each other, when two photocatalysts are arranged in two stages, a significant improvement in photocurrent was observed. In particular, as compared to the first photocatalyst 4 alone, 50% in the bias voltage of V = 1V [first 12 mA / cm ² by 2-step sequence to the photocatalyst 4 alone 8 mA / cm ^2], also V = 1.
183% at 5 V [9 mA of the first photocatalyst body 4 alone
The two-stage arrangement with respect / cm ² 25.5mA / cm ^2]
Of each improvement rate. The above shows the effect of combining two thin film photocatalysts having different band gaps in a multi-stage manner.

[Embodiment 5] FIG. 7 shows a thin film photocatalytic chemical conversion device for producing a hydrocarbon compound or the like by using a proton obtained by a photocatalyst and a raw material CO ₂ . In this device, the thin-film photocatalyst 2 has a titanium oxide (TiO 2) containing anatase type crystal structure.
_{In 2} ), metallic titanium was used for the substrate 3 on which the thin film 2 was formed, and ZnO / Cu (a copper plate to which an appropriate amount of zinc oxide was attached) was used as the electrochemical catalyst 9. And this device is 0.1 at room temperature.
A photocatalyst body 4 comprising a thin film photocatalyst 2 and a substrate 3 and a proton separation membrane 8 in a mol / l concentration aqueous solution of KHCO ₃ electrolyte.
And the electrochemical catalyst 9 are sequentially arranged, the photocatalyst 4 and the electrochemical catalyst 9 are connected by the bias circuit E, and the 500 W xenon lamp 1 for irradiating the thin film photocatalyst 2 with light is installed.
Configured. In this device, protons (H +) generated by the decomposition of water on the surface of the thin film photocatalyst 2 diffuse in the solution, pass through the proton separation membrane 8, and move to the surface of the electrochemical catalyst 9. The proton separation membrane 8 prevents recombination of protons and oxygen. Then, the reaction product which comes into contact with the electrochemical catalyst 9 is reduced by protons and electrons by an electrochemical reaction represented by the following formula to generate various products.

ACO ₂ + bH + ce ~ → dCxHyOz + eH ₂ O In this device, the bias voltage is set to 1 V, and carbon dioxide (CO ₂ ) is caused to flow into the electrochemical catalyst 9 side. The current efficiency of the product was obtained. Methane 15.8%,
Ethylene 10.4%, carbon monoxide 23.4%, hydrogen 41.
It was 9%. Therefore, it was confirmed that this device, which is a combination of a thin film photocatalyst and an electrochemical catalyst, functions for hydrogen production and chemical conversion of carbon dioxide. The carbon dioxide conversion rate in this case was 58.1%.

Example 6 In the same experiment as in Example 5, the bias voltage is alternately changed between plus and minus at a constant time period to generate hydrocarbons produced by chemical conversion of carbon dioxide gas. I saw an improvement. That is,
With current efficiency, 44% of methane and 24% of ethylene were obtained. The conversion rate of carbon dioxide was considerably high at 86%. Also, by this bias voltage addition method, at least 30 hours or more,
It was also found that these current efficiencies were maintained and therefore the catalytic reaction was not degraded.

[Embodiment 7] FIG. 8 is a diagram showing the structure of a chemical conversion device in which a thin film photocatalyst, a proton separation membrane and an electrochemical catalyst are integrated. In this integrated device, the inside of the thin film photocatalyst layer and the electrochemical catalyst are made porous, and a proton separation membrane is sandwiched between them to integrate them so that protons (H +) generated on the side of the thin film photocatalyst can pass through. Is configured. A bias voltage may be applied between the thin film photocatalyst layer and the electrochemical catalyst.

In FIG. 8, titanium oxide (TiO ₂ ) containing an anatase type crystal structure is used as the perforated thin film photocatalyst 12, and stannic oxide (SnO ₂ ) coated glass is used as the perforated substrate 13, and the perforated type is shown. A platinum plate or the like as the electrochemical catalyst 19 is integrated with the proton separation membrane 8 at room temperature, an aqueous solution containing an electrolyte of KHCO _{3 at} a concentration of 0.1 mol / l, and 5 as the light source 1.
Under conditions such as a 00 W mercury lamp, 100% hydrogen generation current efficiency was obtained. The hydrogen generation rate was 20 1 / hr per 1 m ² of thin film photocatalyst area. Furthermore, when carbon dioxide gas was made to flow into the porous electrochemical catalyst 19 side, generation of carbon dioxide gas recycle such as methane and ethylene was confirmed. These experimental results show that this device functions as a hydrogen generator and a carbon dioxide chemical converter. Next, when the same experiment as described above was performed using sunlight as a light source, production of hydrogen and methane was confirmed. Therefore, the device works in sunlight.

Example 8 A method for producing a titanium oxide (TiO ₂ ) thin film photocatalyst will be described. Created a 0.5 mol / l concentration of titanium isopropoxide _{[Ti (i-OC 3 H 7} ) 4 ] sol solution obtained by adding an appropriate amount of hydrochloric acid in ethanol solution of. A transparent titanium oxide (TiO ₂ ) film was obtained by repeating the operation of applying this sol solution to a glass substrate coated with stannic oxide (SnO ₂ ) and air-baking and gelling at 500 ° C. This film had a thickness of 500 nm as measured by a scanning electron microscope, and was found to have almost 100% anatase type crystal structure by bulk structure analysis by X-ray analysis. Furthermore, it was confirmed by laser Raman spectroscopy that 100% anatase was present even near the surface.
The above results were the same when the substrate was made of metallic titanium.

The results of this experiment show that a photocatalyst of thin film titanium oxide having an anatase type crystal structure can be obtained by the above-mentioned method for preparing a titanium oxide (TiO ₂ ) film by the sol-gel method. This thin film titanium oxide was used in all the above examples.

Example 9 Next, a method for producing a ferric trioxide (Fe ₂ O ₃ ) thin film photocatalyst will be described. Iron nitrate nonahydrate (Fe ₉
(NO _{3) 3} · 9H to ₂ O] sol solution can be added an appropriate amount of nitric acid in ethylene glycol solution, air oxidized at to 500 ° C. is applied to a glass substrate coated with stannic oxide (SnO ₂₎ It was found by X-ray analysis that an alpha-type ferric trioxide (α-Fe ₂ O ₃ ) film was formed by repeating the gelling. It was also found that the photocurrent density was maximized in the case of a 500 W mercury lamp or a xenon lamp having a film thickness of about 40 nm. Similar results were also obtained with a substrate made of metallic titanium or metallic iron. These ferric trioxide (Fe ₂ O ₃ ) thin film photocatalysts were used in Example 4 above.

[Embodiment 10] FIGS. 9 and 10 show the structure of a thin film photocatalytic chemical conversion device in which a thin film photocatalyst and a hydrogen storage alloy are combined. In the apparatus shown in FIG. 9, the perforated thin film photocatalyst 12, the perforated substrate 13 and the hydrogen storage alloy 20 are sequentially arranged and integrated into one and placed in an aqueous solution, and then the perforated substrate 13 (conductive) and the hydrogen storage alloy are arranged. 20 is a bias circuit E
It is configured by connecting with. In this device, the hydrogen storage alloy 20 selectively stores protons. Figure 10
In the apparatus shown in FIG. 9, the proton separation membrane 6 is added to the apparatus shown in FIG. 9, and the perforated thin film photocatalyst 12, the perforated substrate 13, the proton separation membrane 6 and the hydrogen storage alloy 20 are sequentially arranged and integrated in an aqueous solution. It was installed and configured. 9 and 10, when storing protons, the bias circuit E is cut off. On the other hand, in the case of storing hydrogen, the bias circuit E is connected to take in the electrons generated at the time of light irradiation by the thin film photocatalyst to cause the reaction of 2H + + 2e ~ → H ₂ .

In FIG. 10, titanium oxide (TiO ₂ ) containing anatase type crystal structure is used as the perforated thin film photocatalyst 12, metallic titanium is used as the perforated substrate 13, a proton separation membrane 8 and a lanthanum-nickel hydrogen storage alloy 20. Installed in an aqueous solution containing an electrolyte of potassium bicarbonate (KHCO ₃ ) and integrated with a bias voltage of 1 V and a 500 W mercury lamp to 5
A hydrogen storage capacity of × 10 ²² pieces / cm ³ was obtained.

In the above embodiments, the xenon lamp and the mercury lamp were used as the light source, but it goes without saying that sunlight can be used. As the bias voltage power source, a solar cell, a dry cell, or another DC power source can be used.

[0056]

According to the present invention, a thin film photocatalyst chemical conversion device is sequentially installed in room temperature water, seawater or an aqueous solution containing an electrolyte (each solution is collectively referred to as a solution), and a titanium oxide thin film photocatalyst and proton separation are provided. Since the film, the electrochemical catalyst, the light source that irradiates the thin film photocatalyst with light, and the circuit that connects the thin film photocatalyst and the electrochemical catalyst are configured as basic elements, the following process at room temperature, that is, (1) light source Electrons and holes are generated by the thin film photocatalyst irradiated with light from (2), the solution in contact with the thin film photocatalyst is decomposed by reacting with holes to generate protons and oxygen, and (3) the proton separation membrane is Protons are separated from oxygen and permeated, and (4) protons are electrochemically bound on the surface of the electrochemical catalyst to generate hydrogen, and (5) if carbon dioxide is supplied to the surface of the electrochemical catalyst, the protons Reaction of carbon dioxide gas with electrons and electrons It is possible to wake up and generate CO and hydrocarbons, and thus decompose water to produce hydrogen at room temperature using a light source containing the ultraviolet region or sunlight and water or seawater or an aqueous solution containing an electrolyte as a raw material, and It makes it possible to recycle carbon dioxide into useful substances at room temperature.

As a modification of the above basic type device, (a) a device in which a thin film photocatalyst is installed in two stages, or (b) a thin film photocatalyst, a substrate for the thin film, and a hole for allowing a solution to pass through the electrochemical catalyst, The photocatalyst, the proton separation membrane, and the electrochemical catalyst body 9 are integrally connected to each other to reduce the size, or (c) a device having a hydrogen storage alloy installed therein, which enables recycling in the same manner as described above.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of photocatalytic activation by light irradiation.

FIG. 2 is a diagram illustrating the principle of water decomposition by titanium oxide, which is a photocatalyst.

FIG. 3 is a diagram showing a configuration of a thin film photocatalyst / proton separation membrane / electrochemical catalyst thin film photocatalyst device.

FIG. 4 is a diagram showing quantum efficiency characteristics of a titanium oxide thin film photocatalyst.

FIG. 5 is a diagram showing bias voltage-photocurrent characteristics of a titanium oxide thin film photocatalyst.

FIG. 6 is a diagram showing a configuration of a thin film photocatalyst device of two-stage array thin film photocatalyst / proton separation membrane / electrochemical catalyst.

FIG. 7 is a diagram showing the configuration of a thin film photocatalyst / proton separation membrane / electrochemical catalyst thin film photocatalytic chemical conversion device.

FIG. 8 is a diagram showing the configuration of a thin film photocatalyst / proton separation membrane / electrochemical catalyst integrated thin film photocatalyst chemical conversion device.

FIG. 9 is a diagram showing a configuration of a thin film photocatalyst / hydrogen storage alloy integrated thin film photocatalytic chemical conversion device.

FIG. 10 is a diagram showing the configuration of a thin film photocatalyst / proton separation membrane / hydrogen storage alloy integrated thin film photocatalyst chemical conversion device.

[Explanation of symbols]

 1 Light Source 2 Thin Film Photocatalyst 3 Substrate 4 Photocatalyst 5 Thin Film Photocatalyst 6 Substrate 7 Photocatalyst 8 Proton Separation Membrane 9 Electrochemical Catalyst 12 Porous Thin Film Photocatalyst 13 Porous Substrate 19 Porous Electrochemical Catalyst 20 Hydrogen Storage Alloy E Bias voltage

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hiroshi Tobita, 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Hiroshi Miyadera 1-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd. Hitachi Research Laboratory

Claims (18)

[Claims] 1. A container filled with room temperature water, seawater or an aqueous solution containing an electrolyte, a light source for irradiating the inside of the container with light including an ultraviolet wavelength region, and water, seawater or an aqueous solution in the container, respectively. As a photocatalyst that receives the irradiation light, a photocatalyst body formed by forming an anatase type crystal structure titanium oxide (TiO ₂ ) thin film on one surface of a conductive substrate, water, seawater or an aqueous solution is titanium oxide (TiO 2). ₂ ) It consists of a proton separation membrane that separates the generated protons (H +) from oxygen that simultaneously decomposes in contact with the holes (h +) generated in the thin film, and a platinum plate that traps the separated protons (H +). An electrochemical catalyst body and a bias circuit connecting the substrate of the electrochemical catalyst body and the photocatalyst body are provided, and the electrochemical catalyst body is titanium oxide.
A thin film photocatalytic chemical conversion device for producing hydrogen by combining an electron (e) generated from a (TiO ₂ ) thin film and flowing through a bias circuit with a captured proton (H +). 2. The conductive substrate is a titanium plate or a glass plate in which a stannic oxide film is interposed between a titanium oxide (TiO ₂ ) thin film and the conductive plate. Thin film photocatalytic chemical conversion device. 3. The titanium oxide (TiO 2) is used as the bias circuit.
₂ ) A thin film photocatalytic chemical conversion device according to claim 1 or 2, wherein a positive bias voltage is applied to the thin film. 4. The titanium oxide (TiO 2) is used as the bias circuit.
₂ ) The thin film photocatalytic chemical conversion device according to claim 1 or 2, wherein positive and negative voltages are alternately and periodically applied to the thin film. 5. A container filled with room temperature water, seawater or an aqueous solution containing an electrolyte, a light source for irradiating light including an ultraviolet wavelength region from the outside to the inside of the container, and water, seawater or an aqueous solution in the container, respectively. First, a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure is formed as a photocatalyst for receiving irradiation light on one surface of a conductive and light transmissive substrate.
And a second photocatalyst formed by forming a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure as a photocatalyst for receiving light transmitted through the first photocatalyst, on one surface of a conductive substrate, Water, seawater or aqueous solution decomposes in contact with holes (h +) generated in each titanium oxide (TiO ₂ ) thin film, and protons (H +) generated are separated from oxygen simultaneously generated proton separation membrane, and separated Equipped with an electrochemical catalyst body consisting of a platinum plate that captures protons (H +), and a bias circuit that connects the substrates of each photocatalyst body in parallel to the electrochemical catalyst body, the electrochemical catalyst body is made from each titanium oxide (TiO) thin film. Electrons (e ~) generated and flowing through the bias circuit and captured protons
A thin film photocatalytic chemical conversion device that combines with (H +) to generate hydrogen. 6. The thin film photocatalytic chemical conversion device according to claim 5, wherein the conductive substrate of the second photocatalyst body is made of titanium. 7. A photocatalyst formed by forming a ferric trioxide (Fe ₂ O ₃ ) thin film as a photocatalyst on an iron substrate instead of the second photocatalyst. 5. The thin film photocatalytic chemical conversion device described in 5. 8. The titanium oxide (TiO 2) is used as the bias circuit.
₂ ) A thin film photocatalytic chemical conversion device according to claim 5, 6 or 7, wherein a positive bias voltage is applied to the thin film. 9. The titanium oxide (TiO 2) is used as the bias circuit.
₂ ) A thin film photocatalytic chemical conversion device according to claim 5, 6 or 7, wherein positive and negative voltages are alternately and periodically applied to the thin film. 10. An electrochemical catalyst body made of any of palladium, gold, silver, copper, copper oxide and silver oxide, or zinc oxide or silver oxide in whole or part instead of the electrochemical catalyst body made of platinum. 10. The thin film photocatalytic chemical conversion device according to claim 1, further comprising an electrochemical catalyst body made of coated copper. 11. The titanium oxide (TiO ₂ ) thin film has a thickness of 50.
The thin film photocatalytic chemical conversion device according to claim 1, wherein the thin film photocatalytic conversion device has a thickness of ˜2000 nm. 12. The thin film photocatalytic chemical conversion device according to claim 7, wherein the ferric trioxide (Fe ₂ O ₃ ) thin film has a thickness of 5 to 200 nm. 13. A container filled with room temperature water, seawater or an aqueous solution containing an electrolyte, a light source for irradiating light having an ultraviolet wavelength region from the outside to the inside of the container, and water, seawater or an aqueous solution in the container, respectively. A photocatalyst body which is provided with a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure as a photocatalyst for receiving irradiation light, formed on one surface of a conductive substrate,
Protons (H +) generated when water, seawater or aqueous solution decomposes in contact with holes (h +) generated in titanium oxide (TiO ₂ ) thin film
A proton separation membrane that separates the oxygen from the oxygen that is simultaneously generated, and an electrochemical catalyst comprising a platinum plate that captures the separated protons (H +), and carbon dioxide supply means for supplying carbon dioxide to the surface of the electrochemical catalyst. And a bias circuit connecting the substrate of the electrochemical catalyst and the substrate of the photocatalyst, and the electrochemical catalyst is a thin film photocatalytic chemical conversion device for reducing carbon dioxide gas by the captured protons (H +). 14. A container filled with room temperature water, seawater or an aqueous solution containing an electrolyte, a light source for irradiating the inside of the container with light having an ultraviolet wavelength region, and water, seawater or an aqueous solution in the container, respectively. A first photocatalyst body, which is formed by forming a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure as a photocatalyst for receiving irradiation light on one surface of a conductive and light transmissive substrate, As a photocatalyst for receiving light transmitted through the photocatalyst, a second photocatalyst formed by forming a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure on one surface of a conductive substrate, water, seawater or an aqueous solution is used. Protons (H) generated by decomposition in contact with holes (h +) generated in the titanium oxide (TiO ₂ ) thin film
+), A proton separation membrane that separates oxygen generated simultaneously.
Also, an electrochemical catalyst body made of platinum that captures the separated protons (H +), a carbon dioxide gas supply means for supplying carbon dioxide gas to the surface of the electrochemical catalyst body, and a substrate for each photocatalyst body on the electrochemical catalyst body are provided. A thin film photocatalytic chemical conversion device that has a bias circuit connected in parallel, and whose electrochemical catalyst body reduces carbon dioxide by the captured protons (H +). 15. A container filled with room temperature water, seawater, or an aqueous solution containing an electrolyte, a light source for irradiating the inside of the container with light including an ultraviolet wavelength region, and a container integrally coupled so as to block the middle part of the container. A titanium oxide (TiO ₂ ) thin film with an anatase type crystal structure is formed on one surface of the conductive substrate as a photocatalyst that receives irradiation light, and a hole penetrating the titanium oxide (TiO ₂ ) thin film and the substrate. The photocatalyst having pores, water, seawater, or an aqueous solution decomposes in contact with the holes (h +) generated in the titanium oxide (TiO ₂ ) thin film, and the protons (H +) moving through the pores of the photocatalyst having pores (H +) are generated. ) Is simultaneously separated from oxygen that is generated simultaneously, and a platinum plate that captures the separated protons (H +), and a perforated electrochemical catalyst having pores penetrating in the plate direction, and a perforated system Substrate for electrochemical catalyst and perforated photocatalyst With a bias circuit connecting the, the porous electrochemical catalyst body is an electron (e ~) generated from the titanium oxide (TiO ₂ ) thin film and flowing through the bias circuit,
A thin film photocatalytic chemical conversion device that produces hydrogen by combining with protons (H +) that have moved through its own pores. 16. A container filled with room temperature water, seawater or an aqueous solution containing an electrolyte, a light source for irradiating the inside of the container with light including an ultraviolet wavelength region, and a container integrally coupled so as to block the middle part of the container. A titanium oxide (TiO ₂ ) thin film with an anatase type crystal structure is formed on one surface of the conductive substrate as a photocatalyst that receives irradiation light, and a hole penetrating the titanium oxide (TiO ₂ ) thin film and the substrate. The photocatalyst having pores, water, seawater, or an aqueous solution decomposes in contact with the holes (h +) generated in the titanium oxide (TiO ₂ ) thin film, and the protons (H +) moving through the pores of the photocatalyst having pores (H +) are generated. ) Is simultaneously separated from oxygen that is generated simultaneously, and a platinum plate that captures the separated protons (H +), and a perforated electrochemical catalyst having pores penetrating in the plate direction, and a perforated system Electrochemical catalyst with water, seawater or aqueous solution A carbon dioxide gas supply means for supplying carbon dioxide gas to the plate surface in contact with the plate surface; and a bias circuit connecting the substrate of the perforated electrochemical catalyst and the perforated photocatalyst,
The perforated electrochemical catalyst is a proton that has moved through its own pores.
Thin film photocatalytic chemical conversion device that reduces carbon dioxide by (H +). 17. A container filled with room temperature water, seawater or an aqueous solution containing an electrolyte, a light source for irradiating the inside of the container with light including an ultraviolet wavelength region, and the container are integrally connected to the latter half of the container. In addition, a titanium oxide (TiO ₂ ) thin film having an anatase type crystal structure is formed on one surface of the conductive substrate as a photocatalyst for receiving irradiation light, and the titanium oxide (TiO ₂ ) thin film and holes having holes penetrating the substrate are formed. The photocatalyst with pores and water, seawater or aqueous solution decomposes in contact with the holes (h +) generated in the titanium oxide (TiO ₂ ) thin film to generate protons (H +) that move through the pores of the photocatalyst with pores. A hydrogen storage alloy member to be captured and a bias circuit connecting the hydrogen storage alloy member and the substrate of the perforated photocatalyst body are provided, and the hydrogen storage alloy member is generated from a titanium oxide (TiO ₂ ) thin film and flows through the bias circuit. Electrons (e ~) and captured Ton is coupled with the thin film optical catalytic chemical conversion device for storing the hydrogen. 18. The thin film photocatalytic chemical conversion device according to claim 17, wherein a proton separation membrane is provided between the perforated photocatalyst body and the hydrogen storage alloy member.