JP2002216776A - Photo-electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo-electrochemical device as a clean energy device having high energy conversion efficiency permitting charging with light energy. SOLUTION: The photo-electrochemical device comprises a hydrogen pole 1 as a first pole, an oxygen pole 2 as a second pole out of which electrochemical energy is picked in a space to the hydrogen pole 1 and a photoelectric pole 6 as a third pole, the photoelectric pole 6 as the third pole being formed of an organic material having photoelectron exciting ability such as a ruthenium complex (tris(2,2'-bipyridine) ruthenium (II)) for accelerating the pick-out of the electrochemical energy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a photoelectrochemical device.

[0002]

2. Description of the Related Art For example, a fuel cell as an electrochemical device is a device for extracting electric energy from the reaction between hydrogen and oxygen. In addition to the advantage of high energy conversion efficiency, the only product produced by the reaction is water. As a result, it is drawing attention as a completely clean energy device.

An important point here is how to obtain hydrogen used for a fuel cell. Currently, hydrogen is chemically reformed and produced industrially from natural gas and other fuels. Also, aiming for practical use in the near future,
Hydrogen supplied to the fuel cell system for automobiles, which is being actively developed, has a fuel tank such as methanol or gasoline inside the automobile, and reforms the fuel when used inside the automobile to supply hydrogen. Is being considered.

[0004]

However, the production of hydrogen by the above-described method produces carbon dioxide during reforming of the fuel, and so the fuel cell itself can be said to be clean.
It is not always clean when considering the system as a whole. Of course, when compared to a system that obtains (thermal) energy directly from these fuels and obtains power and electric power based on it, the above-mentioned system is an energy conversion with improved efficiency. Emissions are lower. However, it has not solved the fundamental problem anyway.

[0005] A method for obtaining hydrogen by a clean system without generating carbon dioxide or the like, and most preferable is a method for producing hydrogen from water. Water is a stable substance with low energy, as can be seen from reaction products of fuel cells and the like. Accordingly, it is technically difficult to extract a high-energy substance called hydrogen from water, which requires a relatively large amount of energy compared to the amount of energy required when producing hydrogen using a fuel such as natural gas or methanol. However, in order to create the ultimate clean energy system, a series of techniques for extracting hydrogen from water and extracting electrochemical energy from the hydrogen using an electrochemical device such as a fuel cell is considered to be most preferable.

[0006] Production of hydrogen from water can be achieved, for example, by using the same device as a fuel cell and externally applying electric energy to the device. It is preferable that the electric energy applied to the device from the outside is also manufactured by a clean method. One of the candidates is a solar cell. A solar cell is a device that converts light energy from the sun that falls infinitely into electric energy, and is also one of the clean energy devices.However, there is a variability over time such that electricity cannot be obtained without light. One of the drawbacks. If these fuel cells and solar cells are simply connected, light charging of the fuel cells becomes possible. However, with only such a simple connection, the energy conversion efficiency reflects the efficiencies of the fuel cell and the solar cell, respectively.
Since the energy conversion efficiency as a whole is lower than the respective efficiencies, it cannot be said that there is always a merit in combination.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a clean energy device and a photoelectrochemical device having a high energy conversion efficiency capable of being charged by light energy. To provide a device.

[0008]

That is, the present invention comprises a first pole, a second pole from which electrochemical energy is extracted between the first pole, and a third pole. The present invention relates to a photoelectrochemical device, which is constituted by an organic material having photoelectron excitation ability so as to promote the extraction of the electrochemical energy.

According to the present invention, the organic material having the photoelectron excitation ability constituting the third pole is easy to synthesize, has many peaks in visible light, and has excellent quantum efficiency. Extraction of electrochemical energy between the first electrode and the second electrode is greatly promoted, and highly efficient light energy conversion becomes possible.

In extracting electrochemical energy between the first electrode and the second electrode, water is applied by the light energy to the third electrode made of the organic material having photoelectron excitation ability. Decompose to produce hydrogen,
Since the electrochemical energy can be extracted by using the generated hydrogen, a clean system can be constructed as a whole.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically based on embodiments.

The photoelectrochemical device according to the present invention is preferably configured as a fuel cell or an air cell as described later.

The third pole is made of the organic material having photoelectron excitation ability. However, if the organic material itself does not have sufficient electron conductivity, the third pole may be made of a conductive material. (For example, carbon), it is also possible to secure sufficient electron conductivity throughout the third pole.

Further, the third pole is constituted by a composite of the organic material having photoelectron excitation ability and the conductive material and / or the proton conductive material, and the third pole itself has an electron conductive property. And / or have proton conductivity. Thereby, the extraction of electrochemical energy between the first electrode and the second electrode is more greatly promoted, and light energy conversion with higher efficiency becomes possible.

As the organic material having photoelectron excitation ability, HOMO (highest occupied molec) of the organic material can be used.
energy orbital (highest occupied molecular orbital) is higher than the energy level of oxygen generation in electrolysis of water, and LUMO (lowest unoccupied molecular orbita)
l: lowest empty molecular orbital) is preferably used as a material having a lower energy level than the Fermi level when the material constituting the first pole is used.

As shown in FIG. 1, the Fermi level of the material constituting the first pole generally varies depending on the amount of absorbed hydrogen. As the amount of absorbed hydrogen increases, the Fermi level increases. Will be higher. Then, charging is completed in a range where the Fermi level of the material forming the first pole is higher than the LUMO energy level of the organic material, and this becomes a factor for determining the capacity of the battery. Therefore,
Before charging, it is advantageous that the LUMO energy level of the organic material and the Fermi level of the material forming the first pole are as far apart as possible, or as a material forming the first pole, A material whose Fermi level does not change much due to charging (hydrogen absorption) is suitable.

It is preferable to use a ruthenium complex having a HOMO or LUMO energy level as shown in FIG. 1 as the organic material having the photoelectron excitation ability satisfying the above-mentioned conditions. The ligand structure is represented by the following structural formulas (1), (2),
It is preferably at least one of (3), (4), (5) and (6).

Embedded image Structural formula (1): Structural formula (2): Structural formula (3): Structural formula (4): Structural formula (5): Structural formula (6):

More specific examples of the ruthenium complex include tris (2,2'-bipyridine) ruthenium (II) represented by the following structural formula (7).

Embedded image Structural formula (7):

When the ruthenium complex is used as the organic material having photoelectron excitation ability, the ruthenium complex can greatly adjust the energy levels of HOMO and LUMO by selecting the ligand structure. It is preferable that the ligand of the ruthenium complex is appropriately selected in accordance with the Fermi level of the material constituting one pole. For example, in the case where porphyrins or the like as materials having energy levels of HOMO and LUMO as shown by dashes in FIG. 1 are used instead of the ruthenium complex, light energy conversion efficiency may be deteriorated, May not function as an energy device. Also,
For example, when the third electrode is made of titanium dioxide, titanium dioxide has many peaks on the short wavelength side, so that quantum efficiency is deteriorated and light energy conversion efficiency may be reduced. As described above, the energy levels of HOMO and LUMO can be greatly adjusted by selecting the ligand structure, the synthesis is easy, the peaks are large in visible light, and the quantum efficiency is excellent. Therefore, the extraction of electrochemical energy between the first electrode and the second electrode is more significantly promoted,
It enables more highly efficient light energy conversion.

FIG. 2 is a schematic sectional view showing an example of a configuration in which the photoelectrochemical device according to the present invention is configured as a fuel cell.

As shown in FIG. 2, the photoelectrochemical device according to the present invention comprises a hydrogen electrode 1 as the first electrode containing a material for oxidizing hydrogen or a hydrogen-containing gas, and a device for reducing oxygen or an oxygen-containing gas. And an oxygen electrode 2 as a second electrode containing a material that generates water and one proton conductor 3 sandwiched between these two electrodes, and is in contact with the proton conductor 3 of the hydrogen electrode 1. A hydrogen gas part 4 is provided on the side not provided, and a hydrogen generating catalyst electrode 5 disposed on the side facing the hydrogen electrode 1 in contact with the hydrogen gas part 4; And the other proton conductor 3 'sandwiched between these two electrodes is preferably provided. Also,
The hydrogen generation catalyst electrode 5 and the photoelectrode 6 are short-circuited, and electron transfer between the photoelectrode 6 and the hydrogen generation catalyst electrode 5 is enabled.

The principle of operation of the photoelectrochemical device according to the present invention according to FIG. 2 is that a proton (H ⁺ ) is generated from water vapor or a water vapor-containing gas by light energy at the photoelectrode 6 and the generated proton is converted into the other proton. The proton is moved to the hydrogen generation catalyst electrode 5 side through the proton conductor 3 ′, and the generated proton is converted into hydrogen gas at the hydrogen generation catalyst electrode 5.
This hydrogen gas is stored in the hydrogen gas part 4 or in an external hydrogen gas tank 7 connected to the hydrogen gas part 4 via a gas path 8, or is converted into protons again at the hydrogen electrode 1,
The generated protons are transferred to the oxygen electrode 2 through one proton conductor 3 and are converted into water at the oxygen electrode 2, and electrochemical energy can be extracted between the hydrogen electrode 1 and the oxygen electrode 2. .

As described above, the photoelectrode 6 is formed of, for example, tris (2,
It is preferably constituted by a ruthenium complex such as 2′-bipyridine) ruthenium (II). Although the photoelectrode 6 is made of the organic material having the photoelectron excitation ability, if the organic material itself does not have sufficient electron conductivity, a conductive material (for example, carbon or the like) is used for the photoelectrode 6. It is also possible to ensure sufficient electron conductivity throughout the photoelectrode 6 by containing it. Further, the photoelectrode 6 is composed of a composite of the organic material having photoelectron excitation ability and the conductive material and / or proton conductive material, and the photoelectrode 6 itself has electron conductivity and / or proton conductivity. It is also possible to have the nature. When the conductive material has a capability of transmitting protons or hydrogen atoms, the conductive material itself functions as the proton conductor. Thereby, the hydrogen electrode 1
In this case, the extraction of electrochemical energy between the oxygen electrode 2 and the oxygen electrode 2 is further greatly promoted, and light energy conversion with higher efficiency becomes possible.

As described above, protons generated at the photoelectrode 6 are transferred to the hydrogen generation catalyst electrode 5 through the proton conductor 3 ', and the protons are converted into hydrogen at the hydrogen generation catalyst electrode 5. The generated hydrogen can be stored in a gaseous state in the hydrogen gas part 4 or the external hydrogen gas tank 7, and according to the structure as shown in FIG. 2, instantaneous charging becomes possible. In addition, when using the fuel cell, if the amount of hydrogen gas produced by light is insufficient, hydrogen gas can be supplied from the external hydrogen gas tank 7 via the gas passage 8.

Hydrogen electrode 1, oxygen electrode 2 and hydrogen generation catalyst electrode 5
Can be produced by, for example, using carbon fiber, porous carbon, or the like as a material, forming these into a sheet shape, and supporting an active catalyst. By supporting the catalyst, hydrogen generation efficiency and energy conversion efficiency can be further improved. Can be improved. Further, such a sheet-like electrode material may be a net-like material made by knitting a metal wire as a core material, or may be attached. By inserting or attaching a metal core, the conductivity of the electrode itself is improved.

Examples of the catalyst include fine particles such as platinum, ruthenium, and iridium oxide. The catalyst may be supported on the hydrogen electrode 1, the oxygen electrode 2 and the hydrogen generation catalyst electrode 5 by a usual method. For example, a catalyst or a precursor thereof is supported on the surface of carbon powder, and a treatment such as heating is performed. Alternatively, a method may be used in which catalyst particles are formed and baked together with a fluororesin on the electrode surface, or an electrode body not carrying a catalyst is prepared, and then a precursor of the catalyst, for example, a mixture of chloroplatinic acid and ruthenic acid is mixed. An aqueous solution or a butyl alcohol solution was used as a coating solution, and the solution was applied to the electrode surface.
By firing at ℃, an alloy of platinum and ruthenium can be formed on the electrode surface.

According to the fuel cell as a photoelectrochemical device according to the present invention as shown in FIG. 2, the organic material having photoelectron excitation ability constituting the photoelectrode 6 is easy to synthesize, and visible light is , And the quantum efficiency is excellent, so the extraction of electrochemical energy between the hydrogen electrode 1 and the oxygen electrode 2 is greatly promoted, and more efficient light energy conversion is possible. Becomes

In extracting electrochemical energy between the hydrogen electrode 1 and the oxygen electrode 2, the photoelectrode 6 made of the organic material having photoelectron excitation ability is used.
Water can be decomposed by light energy to produce hydrogen, and the generated hydrogen can be used to extract the electrochemical energy, so that a clean system can be constructed as a whole.

FIG. 3 is a diagram showing an example of a configuration in which the photoelectrochemical device according to the present invention is configured as a fuel cell.
The fuel cell according to FIG. 3 is an example in which the oxygen electrode 2 and the photoelectrode 6 are arranged on the opposite sides, similarly to the fuel cell according to FIG. 2, and the structure in this case is simple and portable. It is possible.

As shown in FIG. 3, the photoelectrochemical device according to the present invention has an oxygen electrode 2, a negative electrode 9, and a proton conductor 3 sandwiched between these two electrodes. It is preferable that the photoelectrode 6 is further provided on the surface side where the pole 2 does not exist via the proton conductor 3 '. In addition, the photoelectrode 6 and the negative electrode 9 are short-circuited, and electrons can be transferred between the photoelectrode 6 and the negative electrode 9.

The photoelectrode 6 is made of the organic material having photoelectron excitation ability, and the negative electrode 9 is preferably provided with an active material electrode capable of absorbing hydrogen. For example, LaNi ₅ ),
It is preferable to use a carbonaceous material or the like having a high hydrogen storage capacity and contain a catalyst capable of protonating hydrogen gas. Further, the proton conductors 3 and 3 ′ may be the conductive material.

In the photoelectrochemical device according to the present invention shown in FIG. 3, the photoelectrode 6 generates protons from water vapor or a water vapor-containing gas by light energy, and the generated protons pass through the proton conductor 3 'to the negative electrode 9 side. And electrochemical energy can be extracted between the negative electrode 9 and the oxygen electrode 2.

FIGS. 4 to 8 show an example of a photoelectrochemical device according to the present invention configured as an air battery. Here, FIGS. 4 and 7 are perspective views of the air battery. Also,
FIG. 5 is a sectional view taken along line X ₁ -X ₂ in FIG. 4, and FIG. 6 is a sectional view taken along line X ₃ -X ₄ in FIG. Further, FIG. 8 is a sectional view taken along X ₅ -X ₆ lines in FIG.

The air battery 10 has a substantially rectangular battery can 1.
1 has a negative electrode 9 disposed on the bottom, a proton conductor 3 disposed on the negative electrode 9, an oxygen electrode 2 and a photoelectrode 6 disposed on the proton conductor 3. The photoelectrode 6 is made of the organic material having the photoelectron excitation ability. As the organic material, as described above, for example, tris (2,
It is preferable to use a ruthenium complex such as 2′-bipyridine) ruthenium (II).

The negative electrode 9 contains a compound that absorbs hydrogen and is filled over the entire bottom of the battery can 11.
As the compound for storing hydrogen, a known hydrogen storage alloy (for example, LaNi ₅ ) or the like can be used. In the air battery 10, the proton conductor 3 is disposed over the entire surface of the negative electrode 9, and the negative electrode 9 is sealed and shut off from the outside air. There is no restriction below atmospheric pressure. Therefore, a high capacity hydrogen storage alloy can be used for the negative electrode 9 even if the hydrogenation equilibrium pressure is high.

As the proton conductor 3, an electrolyte in which protons can move is used, and one having a withstand voltage of 1.5 V or more is preferable. This is because when the water in the air is electrolyzed by the photoelectrode 6, the proton conductor 3 itself is prevented from being decomposed. Therefore, as the proton conductor 3, it is preferable to use an organic electrolyte, a polymer electrolyte, an inorganic electrolyte, or the like instead of an electrolyte containing water.

The oxygen electrode 2 has a plurality of rectangular oxygen electrode pieces 2a.
However, they are arranged at predetermined intervals so that their longer sides are shorter sides of the battery can 11. These oxygen electrode pieces 2a are connected at one end in the short side direction of the battery can 11 to be integrated.

The oxygen electrode 2 contains a catalyst capable of reducing oxygen in the air and an electrolyte component capable of moving protons. As a catalyst capable of reducing oxygen in the air, for example, a Pt catalyst or the like is used.
The oxygen electrode 2 has gas permeability, and has a structure in which the entire oxygen electrode 2 can come into contact with air and an electrolyte.

The photoelectrode 6 includes a plurality of rectangular photoelectrode pieces 6a.
Are arranged between the oxygen electrode pieces 2a such that their long sides are substantially parallel to the short sides of the battery can. That is, the oxygen electrode pieces 2a and the photo electrode pieces 6a are alternately arranged on substantially the same plane. Here, the oxygen electrode piece 2a and the photo electrode piece 6
a are insulated from each other by an insulator 13 interposed therebetween. These photoelectrode pieces 6a are connected to the battery can 11
Are connected together at the other end in the short side direction to form an integral unit.

The photoelectrode 6 is made of the organic material having photoelectron excitation ability. As the organic material, for example, tris (2, 2)
It is preferable to use a ruthenium complex such as 2′-bipyridine) ruthenium (II), whereby the extraction of electrochemical energy between the negative electrode 9 and the oxygen electrode 2 is further greatly promoted, and a higher efficiency is obtained. Light energy conversion becomes possible. Further, as described above, the photoelectrode 6 may be formed of a composite of the organic material having the photoelectron excitation ability and the conductive material and / or the proton conductive material. The photoelectrode 6 has gas permeability, and has a structure in which the photocatalyst can contact the electrolyte and air in the entire photoelectrode.

As is clear from FIG. 4 or FIG. 7, the air battery 10 as a photoelectrochemical device according to the present invention
The oxygen electrode 2 and the photoelectrode 6 are arranged on the same plane. As described above, by arranging the positive electrode 5 and the photoelectrode 6 on the same surface, it is possible to very easily satisfy the structural condition that they both need to come into contact with air, and the entire battery can be satisfied. The structure can be simplified. However, oxygen electrode 2
The photoelectrode 6 and the photoelectrode 6 are both in contact with the same proton conductor 3, but are arranged so as not to directly contact each other, and are electrically insulated.

As shown in FIGS. 7 and 8, on the side surface of the battery can 11, an oxygen electrode terminal 14 connected to the oxygen electrode 2 by a lead 16 and a negative electrode connected to the negative electrode 9 by a lead 17. A terminal 15 is provided. These oxygen electrode terminal 14 and negative electrode terminal 15 serve as external electrodes of the air battery 10. As shown in FIGS. 4 and 5, the photoelectrode 6 and the negative electrode 9 are connected by a lead 12 inside the air battery 10 so that electrons can be transferred between the photoelectrode 6 and the negative electrode 9. ing.

Next, the operation principle of the air battery 10 having the above-described configuration will be described. 9 to 1
FIG. 1 is a diagram schematically showing the operation principle of the air battery 10. 9 to 11, the configuration of the air battery 10 is shown in a simplified manner for easy understanding.

First, in FIG. 9, the air battery 1 in the dark
0 indicates a discharge reaction. This is similar to the operation principle of a normal air battery.

Next, in FIG. 10, the external load is removed,
The principle of charging the air battery 10 by irradiating light is shown. When light is applied to the photoelectrode 6 made of the organic material having photoelectron excitation capability, a photoexcitation reaction occurs, and the generated holes oxidize water molecules in the air, generating oxygen and generating protons. Is supplied to the proton conductor 3. The photoexcited electrons generated during this reaction are
Is lowered to take in protons in the proton conductor 3. By this series of operations, hydrogen is occluded again in the negative electrode 9 and discharge is performed.

FIG. 11 shows a discharge reaction during light irradiation. In the air battery 10, since the oxygen electrode 2 and the photoelectrode 6 are arranged on the same surface, oxygen and protons generated at the photoelectrode 6 during light irradiation are easily supplied to the oxygen electrode 2, and the light irradiation is performed during discharge. This can further promote the discharge reaction. This not only promotes the reaction speed, but also enables the discharge reaction to be performed without using a load capacity, which leads to a dramatic improvement in capacity.

As described above, the air battery 10 as a photoelectrochemical device according to the present invention can be charged by using a clean energy source called light, and can be charged with hydride or hydrogen gas. It is possible to make full use of the property of high energy storage. Since the air battery 10 does not require an external charger,
This is particularly effective when applied to a portable battery.

Further, in the photoelectrochemical device according to the present invention, since the negative electrode portion is sealed by the proton conductor and is shielded from the outside air, it can be applied to a fuel cell. FIG. 12 shows an example of a configuration in which the photoelectrochemical device according to the present invention is applied to a fuel cell,
The case where the oxygen electrode and the photoelectrode are arranged on the same plane will be described.

The fuel cell 18 is a substantially rectangular battery can 1
9, a waterproof membrane 20, a negative electrode 21 disposed on the waterproof membrane 20, a proton conductor 22 disposed on the negative electrode 21, and an oxygen electrode 23 disposed on the proton conductor 22.
And a photoelectrode 24 made of, for example, a ruthenium complex as the organic material having photoelectron excitation ability. In the fuel cell 18, a supply pipe 25 is provided at the bottom of the battery can 19, and a hydrogen supply unit 26 is connected through the supply pipe 25. In this fuel cell, hydrogen generated at the photoelectrode 24 is supplied to the negative electrode 21, and hydrogen is further supplied from the hydrogen supply unit 26 to the negative electrode 21 via the supply pipe 25, and the hydrogen and the oxygen electrode 23 are supplied.
Reacts with oxygen taken from the reactor to generate electrochemical energy.

Also in this case, as described above, the photoelectrode 24
The organic material having photoelectron excitation ability, such as the ruthenium complex, is easy to synthesize, has many peaks in visible light, and has excellent quantum efficiency.
In addition, the extraction of electrochemical energy between the oxygen electrode 23 and the oxygen electrode 23 is further greatly promoted, and light energy conversion with higher efficiency becomes possible.

In extracting electrochemical energy between the negative electrode 21 and the oxygen electrode 23, the photoelectrode 24
Water can be decomposed by light energy to produce hydrogen, and the generated hydrogen can be used to extract the electrochemical energy, so that a clean system can be constructed as a whole.

The fuel cell shown in FIG. 12 as a photoelectrochemical device according to the present invention has been described by taking as an example the case where the oxygen electrode 23 and the photoelectrode 24 are insulated. The insulation may be achieved by providing a gap between the electrode and the photoelectrode 6.

One of the proton conductors sandwiched between the first electrode and the second electrode constituting the photoelectrochemical device according to the present invention, or the hydrogen generation catalyst electrode, and the third electrode As the other proton conductor sandwiched between the two electrodes, or the proton conductive material that can be contained in the third electrode, general Nafion (perfluorosulfonic acid resin: Nafion manufactured by Du Pont)
In addition to (R) and the like, a carbonaceous material derivative having a carbonaceous material whose main component is carbon as a base material and a proton dissociable group introduced into the carbon atom constituting the carbonaceous material may be used. Here, the “proton dissociable group” means a functional group from which a proton can be eliminated by ionization, and the “proton dissociation” means that a proton is separated from the functional group by ionization.

As the carbonaceous material serving as a base of the carbonaceous material derivative, any material can be used as long as it contains carbon as a main component, but a proton-dissociable group is introduced. Later, it is desirable that the ionic conductivity be greater than the electronic conductivity.

Here, as the carbonaceous material to be a base, specifically, a carbon cluster which is an aggregate of carbon atoms, a carbonaceous material including tubular carbonaceous material, and the like can be mentioned. It is preferable that it is composed mainly of carbon clusters. Further, the carbonaceous material may be one in which the carbon clusters are bonded.

The cluster is usually an aggregate formed by bonding or collecting several to hundreds of atoms. The cluster (aggregate) improves the proton conductivity. At the same time, the chemical properties can be stably maintained. The “cluster mainly composed of carbon” refers to an aggregate formed by bonding several to several hundred carbon atoms regardless of the type of carbon-carbon bond. However,
It is not always composed of only 100% carbon atoms, and other atoms may be mixed. An aggregate including a large number of carbon atoms including such a case is referred to as a carbon cluster.

When the proton conductor is composed of the carbonaceous derivative obtained by introducing a proton dissociable group into the carbon cluster as the carbonaceous material, protons are easily dissociated even in a dry state, and the proton It has excellent conductivity, its proton conductivity does not decrease even in a dry atmosphere, and its film conductivity and processability are further improved while maintaining high conductivity. In addition, since the carbon cluster contains various types of carbonaceous materials as described later, it is possible to provide an effect that the range of selection of the carbonaceous material is wide.

In this case, the use of the carbon cluster for the matrix is necessary in order to provide good proton conductivity.
It is necessary to introduce large amounts of proton dissociable groups, since this is made possible by the carbon clusters. However, while doing so significantly increases the acidity of the proton conductor on the solid, the carbon clusters are unlikely to be oxidized and degraded unlike ordinary carbonaceous materials outside, have excellent durability, and have close bonds between constituent atoms. As a result, even if the acidity is high, the bonds between the atoms are not broken (that is, the bond is hardly changed chemically), and the film structure can be maintained.

FIGS. 13 to 17 show the carbon clusters.
There are various types as shown in the following, and the range of choice as a raw material of the carbonaceous material derivative constituting the proton conductor is wide. The carbon cluster is preferably a substance made of at least one selected from the group consisting of a fullerene molecule, a structure having an open end in at least a part of the fullerene structure, and a structure having a diamond structure.

The fullerene molecule as the carbon cluster is not particularly limited as long as it is a spherical cluster molecule, but is usually C ₃₆ , C ₆₀ (see FIG. 14), C ₇₀ (see FIG. 14), C ₇₆ , C _78. , C ₈₀ , C ₈₂ , C _{84 and the} like, or a mixture of two or more of these fullerene molecules is preferably used.

These fullerene molecules were discovered in 1985 in a mass spectrometry spectrum of a cluster beam obtained by laser ablation of carbon (Kyoto, HW; Heath,
JR; O'Brien, SC; Curl, RF; Smalley, RENature 198
5.318,162.). It is only five years after the production method is actually established. In 1990, a method for producing a carbon electrode by an arc discharge method was found. Since then, fullerene has been attracting attention as a carbon-based semiconductor material and the like. Was.

The present inventors have conducted various studies on the proton conductivity of this derivative of the fullerene molecule. As a result, the polyhydroxylated fullerene obtained by introducing a hydrogen group into a carbon atom constituting the fullerene molecule can be dried at room temperature even in a dry state. Was found to exhibit high proton conductivity in a wide temperature range sandwiching, that is, a temperature range exceeding the freezing point of water and the boiling point (at least 160 ° C to -40 ° C). Then, it was found that this proton conductivity becomes more remarkable when a hydrogen sulfate ester group is introduced into a carbon atom constituting fullerene instead of a hydroxyl group.

More specifically, as shown in FIG. 13, polyhydroxylated fullerene is a generic term for a substance having a structure in which a plurality of hydroxyl groups are added to fullerene, and is generally called "fullerenol". Naturally,
Some variations are possible for the number of hydroxyl groups and the arrangement in the molecule. Fullerenol was Chia in 1992
ng et al. first reported a synthetic example (Chiang, LY; S
wirczewski, JW; Hsu, CS; Chowdhury, SK; Cameron,
S .; Creegan, K., J. Chem. Soc, Commun. 1992, 1791). Since then
Fullerenol having a certain amount of hydroxyl groups introduced therein has been particularly noted for its water-solubility, and has been studied mainly in the field of biotechnology.

FIG. 14 shows various carbon clusters having a closed surface structure similar to a sphere or a long sphere or a similar sphere formed by a large number of carbon atoms (however,
Molecular fullerenes are also shown).

On the other hand, FIG. 15 shows various carbon clusters in which a part of the sphere structure is deleted. In this case, it is characterized by having an open end in the structure, and such a structure is often seen as a by-product in the process of producing fullerene by arc discharge, and has the reactivity of fullerene, In addition, the defect or open part has a higher reactivity. Accordingly, the introduction of an acid (proton) dissociable substituent is promoted by an acid treatment or the like, so that a higher substituent introduction rate is obtained and a higher proton conductivity is obtained. Further, it can be synthesized in a larger amount than fullerene, and can be produced at very low cost.

When most of the carbon atoms of the carbon cluster are SP3 bonded, various clusters having a diamond structure as shown in FIG. 16 are obtained.

The carbon cluster in which most of the carbon atoms are bonded by SP2 has a planar structure of graphite, or has the structure of fullerenes or nanotubes in whole or in part. Among them, those having the graphite structure are not preferable as the carbonaceous material constituting the proton conductor because many of them have electron conductivity in clusters.

On the other hand, since the SP2 bond of fullerene or nanotube partially contains an element of SP3 bond, many of them do not have electron conductivity, and are preferable as the carbonaceous material constituting the proton conductor. Can be used.

FIG. 17 shows various cases in which clusters are bonded to each other. Such a structure can be applied to the present invention.

The carbonaceous material may be a tubular carbonaceous material. This tubular carbonaceous material has a diameter of about several nanometers or less, typically 1 nm or less.
To 2 nanometer carbon nanotubes (CNT)
There is a so-called carbon nanofiber (CNF) having a diameter of several nanometers or more, and a huge one having a diameter of even one micron. Also especially CN
As T, two types of single-walled carbon nanotubes (SWCNT) formed of a single-walled tube and multi-walled carbon nanotubes (MWCNT) in which two or more layers are concentrically overlapped are known.

Of course, the present invention is not limited to these, and may be any as long as it meets the above requirements (the ion conductivity is greater than the electron conductivity after the introduction of proton dissociation).

In the present invention, it is necessary to introduce the above-mentioned proton-dissociable group into the carbon atoms constituting the carbon cluster. As a means for introducing this proton dissociable group, the following production method is preferable.

That is, first, a carbon cluster made of carbon powder is produced by arc discharge of a carbon-based electrode.
Subsequently, the carbon cluster as the target product is obtained by subjecting the carbon cluster to an acid treatment (using sulfuric acid or the like), further performing a treatment such as hydrolysis, or further appropriately performing sulfonation or phosphoric esterification. The material derivative can be easily obtained.

The proton dissociable group is represented by the formula —XH, and X may be any atom or atomic group having a divalent bond. Furthermore, this group has the formula -OH or -YO
It is represented by H, and Y may be any atom or atomic group having a divalent bond.

Specifically, the group capable of dissociating the proton includes -COO in addition to -OH and -OSO ₃ H.
H, -SO ₃ H, either -OPO (OH) ₂ is preferred.

The inventor of the present invention has made fullerenol, for example, as the carbonaceous material derivative into an aggregate as schematically shown in FIG. 18 (A), and the adjacent fullerenol molecules (in the figure, full circles indicate fullerene molecules). )), The aggregates exhibit high proton conductivity as macroscopic aggregates (in other words, the dissociation of H ⁺ from the phenolic hydroxyl group of the fullerenol molecule). Could be found.

For example, an aggregate of fullerene having a plurality of —OSO ₃ H groups other than the fullerenol may be used as the proton conductor. FIG. 18 (B) in which OH groups are replaced with OSO ₃ H groups
Polyhydroxylated fullerenes, ie, fullerenol hydrogensulfate, are also shown by Chiang et al.
Reported in 994 (Chiang, LY; Wang, LY; Swi
rczewski, JW; Soled, S .; Cameron, S., J. Org. Chem. 1994,
59,3936). Hydrogen sulfate esterified fullerenes include:
Some contain only the OSO ₃ H group in one molecule,
Alternatively, it is possible to have a plurality of these groups and a plurality of hydrogen groups.

When a large number of the above-mentioned carbonaceous material derivatives are agglomerated, the proton conductivity as a bulk shows that a large amount of hydroxyl groups originally contained in the molecule and protons derived from OSO ₃ H groups are directly involved in the transfer. There is no need to take in hydrogen and protons originating from water vapor molecules and the like from the atmosphere, and there is no need to replenish moisture from the outside, in particular, to absorb moisture from the outside air, and there is no restriction on the atmosphere. Therefore, it can be used continuously even in a dry atmosphere.

The carbonaceous material has an electrophilic property, which greatly contributes to the promotion of ionization of hydrogen ions not only in a highly acidic OSO ₃ H group but also in a hydroxyl group. It shows excellent proton conductivity.

Further, since a large number of hydroxyl groups, OSO ₃ H groups, etc. can be introduced into one fullerene molecule as the carbonaceous material derivative, for example, protons involved in conduction are reduced per unit volume of the conductor. Has an extremely high number density, so that an effective conductivity is exhibited.

Since the above-mentioned carbonaceous material derivative is mostly composed of carbon atoms, it is light in weight, hardly deteriorates, and is relatively clean, and is free from contaminants which adversely affect the proton conductivity. Not included.

Further, in the carbonaceous material derivative, the number of carbon atoms exposed at the front is larger than that of the bulk carbon species material, so that the number of sites into which the proton-dissociable groups can be introduced is increased. The result can have a large number of said proton dissociable groups on the surface.

The carbonaceous material derivative having any of the above structures has high proton conductivity in a dry state and contributes to increasing the proton conductivity of the proton conductor.

Here, the proton conductor is left as it is.
Although it can be pressure-formed into a shape such as a film or a pellet without a binder, a binder may be used. In this case, the proton conductor having more sufficient strength can be formed.

Here, as the polymer material that can be used as the binder, one or more known polymers having film-forming properties are used, and the compounding amount in the proton conductor is usually Reduce to 20% by weight or less. If it exceeds 20% by weight, the conductivity of hydrogen ions may be reduced.

When the binder is used, the same proton conductivity as when the binder is not used can be exhibited because the binder contains the carbonaceous material derivative. Moreover, unlike the case of using the carbonaceous material derivative alone, a film-forming property derived from the polymer material is provided, and the strength is higher and the gas permeation is prevented as compared with the powder compression molded product of the carbonaceous material derivative. It can be used as a flexible ion-conductive thin film having a function (the thickness is usually 300 μm or less).

The polymer material is not particularly limited as long as it does not inhibit the conductivity of hydrogen ions as much as possible (for example, by reaction with a fullerene derivative) and has a film-forming property. Usually, it does not have electronic conductivity, and one having good stability is used, and specific examples thereof include polyfluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, and the like. It is a preferred polymer material.

First, polyfluoroethylene is preferable because a thin film having higher strength can be easily formed with a smaller amount of compounding than other polymer materials. In this case, the compounding amount may be as small as 3% by weight or less, preferably 0.5 to 1.5% by weight, and the thickness of the thin film is usually 100 μm to 1%.
It can be as thin as μm.

The reason why polyvinylidene fluoride or polyvinyl alcohol is preferable is that an ion conductive thin film having more excellent gas permeation preventing ability can be obtained. In this case, the amount is preferably in the range of 5 to 15% by weight.

When the amount of polyfluoroethylene, polyvinylidene fluoride or polyvinyl alcohol falls below the lower limit of each of the above ranges, film formation may be adversely affected.

In order to obtain a thin film of the ion conductive portion in which each carbonaceous material derivative of the present embodiment is bound by a binder, a known film forming method such as pressure molding and extrusion molding may be used. .

In the photoelectrochemical device according to the present invention, the proton conductor is not particularly limited, and any proton conductor can be used as long as it has ionic (hydrogen ion) conductivity. Examples thereof include fullerene hydroxide, sulfated fullerenol, and Nafion.

[0093]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Example 1 A proton conductor film containing fullerenol was formed to a thickness of 50 μm on both sides of a 100 μm thick foil of a LaNi ₅ hydrogen storage alloy by a printing method. Next, Tris (2,2'-
0.1 g of bipyridine) ruthenium (II) powder is dissolved in 100 ml of acetonitrile solvent, and this solvent is spin-coated on the proton conductor membrane on one side of the foil, and the solvent is evaporated to a thickness of about A photoelectrode was formed by forming a film having a thickness of 5 μm. After a while, tris of foil (2, 2'-
A carbon layer supporting a platinum catalyst having a thickness of about 100 μm as an oxygen electrode is in contact with the surface opposite to the bipyridine) ruthenium (II) film, and the photoelectrochemical device of Example 1 as shown in FIG. Was prepared.

Comparative Example 1 A device was prepared in the same manner as in Example 1 except that a photoelectrode was formed using porphyrin instead of tris (2,2′-bipyridine) ruthenium (II). 1
Photoelectrochemical device.

The photoelectrochemical devices of Example 1 and Comparative Example 1 were each irradiated with light for 30 minutes, and thereafter, the change with time of the potential of the hydrogen storage alloy when the light irradiation was stopped was examined. The energy density of the irradiation light was 75 mJ / cm ² . The result is shown in FIG.

As is apparent from FIG. 19, in the photoelectrochemical device of Example 1 according to the present invention, the photoelectrode as the third electrode is made of, for example, tris (2,2) as the organic material having photoelectron excitation ability. '-Bipyridine) ruthenium (I
Since the potential of the hydrogen storage alloy rises during light irradiation due to the configuration according to I), the potential of the hydrogen storage alloy decreases with the passage of time after the end of irradiation, and the hydrogen storage alloy operates as an energy source for the fuel cell. On the other hand, in Comparative Example 1, for example, porphyrin was used in place of tris (2,2′-bipyridine) ruthenium (II), so that the potential hardly changed even during light irradiation, and it might not function as an energy device. Was.

[0098]

According to the present invention, the organic material having the photoelectron excitation ability constituting the third pole is easy to synthesize, has many peaks in visible light, and has excellent quantum efficiency. Therefore, the extraction of electrochemical energy between the first electrode and the second electrode is greatly promoted, and highly efficient light energy conversion becomes possible.

In extracting electrochemical energy between the first electrode and the second electrode, water is applied to the third electrode made of the organic material having photoelectron excitation power by light energy. Decompose to produce hydrogen,
Since this electrochemical energy can be extracted using this hydrogen as a raw material, a clean system as a whole can be constructed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an energy level of an organic material having photoelectron excitation ability which can be suitably used for a photoelectrochemical device according to the present invention.

FIG. 2 is a schematic sectional view showing a configuration example of a fuel cell according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing one configuration example of a fuel cell according to an embodiment of the present invention.

FIG. 4 is a perspective view showing one configuration example of an air battery according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view of the air battery of FIG. 4 taken along line X ₁ -X ₂ .

6 is a cross-sectional view in X ₃ -X ₄ lines of the air battery of Fig.

FIG. 7 is a perspective view showing one configuration example of an air battery according to an embodiment of the present invention.

8 is a sectional view of X ₅ -X ₆ lines of the air battery of Fig.

FIG. 9 is a diagram schematically showing the operation principle of an air battery;
It is sectional drawing which showed the discharge reaction in the dark.

FIG. 10 is a diagram schematically showing the operation principle of the air battery, and a cross-sectional view showing a charging reaction in light irradiation.

FIG. 11 is a diagram schematically illustrating the operation principle of the air battery, and is a cross-sectional view illustrating a discharge reaction during light irradiation.

FIG. 12 is a cross-sectional view illustrating a configuration example of a fuel cell according to an embodiment of the present invention.

FIG. 13 is a structural diagram of polyhydroxy fullerene hydroxide, which is an example of a carbonaceous material derivative that can be used in the present embodiment.

FIG. 14 is a schematic view showing various examples of a carbon cluster serving as a base in a proton conductor according to the present embodiment.

FIG. 15 is a schematic diagram showing another example (partial fullerene structure) of the same carbon cluster.

FIG. 16 is a schematic view showing another example (diamond structure) of the carbon cluster.

FIG. 17 is a schematic diagram showing still another example of a carbon cluster (in which clusters are bonded to each other).

FIG. 18 is a schematic diagram showing an example of a fullerene derivative.

FIG. 19 is a diagram showing a comparison of changes with time of the potential of the hydrogen storage alloy according to an example of the present invention.

[Explanation of symbols]

1 ... hydrogen electrode, 2, 23 ... oxygen electrode, 3, 3 ', 22 ...
Proton conductor, 4 ... Hydrogen gas part, 5 ... Hydrogen generating catalyst electrode, 6, 24 ... Photoelectrode, 7 ... External hydrogen gas tank, 8
... gas path, 9, 21 ... negative electrode (hydrogen storage), 10 ...
Air battery, 11, 19 ... Battery can, 12, 16, 17 ...
Lead, 13 ... insulator, 14 ... oxygen electrode terminal, 15 ...
Negative electrode terminal, 18 ... fuel cell, 20 ... waterproof membrane, 25 ...
Supply pipe, 26 ... hydrogen supply section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/06 H01M 8/06 R 5H032 8/10 8/10 5H050 12/08 12/08 SF term ( (Reference) 4G040 AA11 4G140 AA11 5H018 AA02 AA10 AS02 AS03 EE03 HH00 5H026 AA02 CC03 CV10 EE05 5H027 AA02 BA14 5H032 AA06 AS12 AS16 EE01 EE17 5H050 AA01 AA17 BA20 CA12 CB07 FA02 FA03 FA17 FA17

Claims (23)

[Claims] 1. A first pole, a second pole from which electrochemical energy is extracted between the first pole and a third pole, wherein the third pole is made of an organic material having photoelectron excitation ability. A photoelectrochemical device configured to facilitate extraction of said electrochemical energy. 2. The photoelectrochemical device according to claim 1, configured as a fuel cell or an air cell. 3. The photovoltaic device according to claim 1, wherein the third pole is formed of a composite of the organic material having photoelectron excitation ability and a conductive material and / or a proton conductive material. Chemical device. 4. The method according to claim 1, wherein said organic material having photoelectron excitation ability is H.
The energy level of OMO (highest occupied molecular orbital) is higher than the energy level of oxygen generation in the electrolysis of water, and the LUMO (lowest occupied molecular orbital) is lower.
2. The photoelectrochemical device according to claim 1, wherein the energy level of noccupied molecular orbital (lowest unoccupied molecular orbital) is lower than the Fermi level when the material constituting the first pole is used. 5. The photoelectrochemical device according to claim 4, wherein the organic material having photoelectron excitation ability is a ruthenium complex. 6. The ligand structure of the ruthenium complex is at least one of the following structural formulas (1), (2), (3), (4), (5) and (6). Item 6. A photoelectrochemical device according to Item 5. Embedded image Structural formula (1): Structural formula (2): Structural formula (3): Structural formula (4): Structural formula (5): Structural formula (6): 7. The photoelectrode as the third pole, the photoelectrode as the third pole,
The photoelectrochemical device according to claim 1, wherein the photoelectrochemical device is arranged on the same plane as an oxygen electrode as a pole. 8. The photoelectrode as the third pole, wherein the first electrode is
The photoelectrochemical device according to claim 1, wherein the photoelectrochemical device is short-circuited with a hydrogen electrode as an electrode. 9. The first electrode containing a material that oxidizes hydrogen or a hydrogen-containing gas, the second electrode containing a material that reduces oxygen or a gas that reduces an oxygen-containing gas to produce water, and between the two electrodes. One proton conductor sandwiched between the first electrode and a hydrogen gas portion is provided on a surface side of the first electrode that is not in contact with the proton conductor. 2. The photoelectrochemical device according to claim 1, further comprising: a hydrogen generating catalyst electrode disposed on an opposite surface side; the third electrode; and the other proton conductor sandwiched between the two electrodes. 3. . 10. A proton (H ⁺ ) is generated from water vapor or a water vapor-containing gas by light energy at the photoelectrode serving as the third electrode, and the generated proton is passed through the other proton conductor to the hydrogen generation catalyst. Moved to the electrode side, the generated protons are converted to hydrogen gas at the hydrogen generation catalyst electrode, and the hydrogen gas is stored in the hydrogen gas portion or an external hydrogen gas tank connected to the hydrogen gas portion. Alternatively, at the hydrogen electrode as the first electrode, the proton is converted again into protons, and the generated protons are transferred to the oxygen electrode as the second electrode through the one proton conductor. 10. The photoelectrochemical device according to claim 9, wherein electrochemical energy is extracted between the hydrogen electrode and the oxygen electrode. 11. The photoelectrochemical device according to claim 10, wherein hydrogen gas is supplied from said external hydrogen gas tank. 12. A proton conductor is disposed between the first pole and the second pole. The proton conductor is composed of a carbonaceous material containing carbon as a main component and a carbon atom constituting the carbonaceous material. 2. The photoelectrochemical device according to claim 1, wherein the photoelectrochemical device is a carbonaceous material derivative obtained by introducing a proton-dissociable group into the device. 13. The one or other proton conductor is a carbonaceous material derivative comprising a carbonaceous material having carbon as a main component and a proton-dissociable group introduced into carbon atoms constituting the matrix. The photoelectrochemical device according to claim 9. 14. The carbonaceous material according to claim 12, wherein the main component is a carbon cluster which is an aggregate of carbon atoms.
Or the photoelectrochemical device according to 13. 15. The carbon cluster is a substance comprising at least one selected from the group consisting of a fullerene molecule, a structure having an open end in at least a part of the fullerene structure, and a structure having a diamond structure. is there,
A photoelectrochemical device according to claim 14. 16. The photoelectrochemical device according to claim 14, wherein the carbonaceous material is a combination of the carbon clusters. 17. The photoelectrochemical device according to claim 12, wherein the carbonaceous material is a carbon nanotube. 18. The method according to claim 18, wherein the proton-dissociable group is -XH
(X is an arbitrary atom or atomic group having a divalent bond, and H is a hydrogen atom).
3. The photoelectrochemical device according to 3. 19. The light according to claim 12, wherein the proton dissociable group is —OH or —YOH (Y is any atom or atomic group having a divalent bond). Electrochemical device. 20. The proton-dissociable group is -OH,
_{-OSO 3 H, -COOH, -SO 3} H, -OPO (O
20. The photoelectrochemical device according to claim 19, which is a group selected from any of H) ₂ . 21. The fullerene molecule is a spherical carbon cluster molecule C _m (m = 36, 60, 70, 76, 78,
80, 82, 84, etc.). 22. The photoelectrochemical device according to claim 1, wherein the first electrode contains a hydrogen storage alloy. 23. The photoelectrochemical device according to claim 1, wherein the first electrode contains a catalyst capable of protonating hydrogen gas.