JP6974731B2 - Compounds, adsorbents and their manufacturing methods, carbon dioxide reducing electrodes, and carbon dioxide reducing devices - Google Patents

Description

The present invention relates to a compound, an adsorbent and a method for producing the same, a carbon dioxide reducing electrode, and a carbon dioxide reducing device.

Since the recognition of global warming, how to reduce the carbon dioxide emitted into the atmosphere due to industrial activities has become an important issue.

Artificial photosynthesis technology has been attracting attention in recent years as a method for reducing carbon dioxide in the atmosphere. Artificial photosynthesis technology is a technology that reduces carbon dioxide by the energy of sunlight and converts it into usable organic compounds. In artificial photosynthesis, electrons and protons are generated by irradiating a photoexcited material placed on an anode with sunlight in a tank containing an electrolytic solution. Then, the generated electrons and protons are sent to a reduction catalyst placed on the cathode and reacted with carbon dioxide to generate carbon monoxide and an organic compound. The reaction on the cathode side at this time is a kind of electrolytic reduction, and on the catalyst of the cathode, carbon dioxide reacts stepwise with two electrons and two protons to formmic acid or carbon monoxide, formaldehyde, and methanol. , Methan and is reduced to highly useful substances.

In a general method of electrolytic reduction, an electrochemical cell having a working electrode, a counter electrode, and a tank is used (see, for example, Patent Document 1).

International Publication No. 2011/132375 Pamphlet

In the electrolytic reduction of carbon dioxide, it is important to retain carbon dioxide on an electrode that also serves as a catalyst and to supply protons to the reaction field in order to improve the efficiency of the reaction.
However, the conventional technique is not sufficient in terms of retaining carbon dioxide on the electrode and supplying protons to the reaction field.

The present invention can efficiently reduce carbon dioxide by using a compound useful for electrolytic reduction of carbon dioxide, an adsorbent having excellent carbon dioxide retention and conductivity and a method for producing the same, and the adsorbent. It is an object of the present invention to provide a carbon dioxide reducing electrode and a carbon dioxide reducing device.

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。 The means for solving the above problems are as follows. That is,
In one embodiment, the compound is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).

Also, in one embodiment, the adsorbent is
A porous metal complex having a central metal and a ligand coordinated to the central metal.
The ligand is represented by the general formula (1).

Further, in one embodiment, the method for producing an adsorbent comprises heating a mixed solution obtained by mixing a metal salt, a ligand capable of binding to a metal of the metal salt, and water. , The ligand is represented by the general formula (1).

Further, in one embodiment, the carbon dioxide reducing electrode is
A metal-containing member having a metal capable of reducing carbon dioxide, and
Having an adsorbent on the surface of the metal-containing member,
The adsorbent is a porous metal complex having a central metal and a ligand coordinated to the central metal.
The ligand is represented by the general formula (1).

Also, in one embodiment, the carbon dioxide reduction device is
A carbon dioxide reducing device having a carbon dioxide reducing electrode as an electrode on the cathode side.
The carbon dioxide reducing electrode has a metal-containing member having a metal capable of reducing carbon dioxide, and an adsorbent on the surface of the metal-containing member.
The adsorbent is a porous metal complex having a central metal and a ligand coordinated to the central metal.
The ligand is represented by the general formula (1).

According to the compound of the present invention, the above-mentioned problems in the prior art can be solved, and a compound useful for electrolytic reduction of carbon dioxide can be provided.
According to the adsorbent of the present invention, it is possible to solve the above-mentioned problems in the past, and to provide an adsorbent having excellent carbon dioxide retention and conductivity.
According to the method for producing an adsorbent of the present invention, it is possible to solve the above-mentioned problems in the past, and to provide a method for producing an adsorbent having excellent carbon dioxide retention and conductivity.
According to the carbon dioxide reducing electrode of the present invention, the above-mentioned problems in the prior art can be solved, and a carbon dioxide reducing electrode capable of efficiently reducing carbon dioxide can be provided.
According to the carbon dioxide reducing device of the present invention, it is possible to solve the above-mentioned problems in the prior art and provide a carbon dioxide reducing device capable of efficiently reducing carbon dioxide.

FIG. 1 is a schematic cross-sectional view of an example of a carbon dioxide reducing electrode. FIG. 2 is a schematic cross-sectional view of an example of a carbon dioxide reducing device. FIG. 3 is a schematic cross-sectional view of another example of the carbon dioxide reduction device. FIG. 4 is a schematic cross-sectional view of another example of the carbon dioxide reduction device. FIG. 5 is a schematic cross-sectional view of another example of the carbon dioxide reduction device. FIG. 6 is an FT-IR spectrum of the adsorbent of Example 1 and its raw material. _{FIG. 7 is a CO 2} adsorption isotherm of the powder samples of Example 1, Comparative Example 1, and Comparative Example 2.

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。 (Compound)
The disclosed compound is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).

In the electrolytic reduction of carbon dioxide, it is important to retain carbon dioxide on an electrode that also serves as a catalyst and to supply protons to the reaction field in order to improve the efficiency of the reaction.
The present inventors considered that it is effective to retain carbon dioxide using an adsorbent and use the inside of the pores or the vicinity of the pores as a reaction field. This is because if an adsorbent having a large adsorption amount is placed on the electrode, carbon dioxide can be electrolyzed in a state where carbon dioxide is adsorbed or retained, and high efficiency of the reduction reaction can be expected.
The present inventors have focused on a porous metal complex having high adsorption performance. Representative as the porous metal complex, _M 2 for the 2,5-dihydroxy terephthalic acid as a ligand (dobdc) (M = Ni, Mg, Co , etc.), carbon dioxide mass, selectively adsorbs, Further, it is expected to be suitable because it has an open metal site that can be a catalytic activity point. However, in many porous metal complexes such as this, it is difficult to transfer electrons and protons into the pores.

Therefore, the present inventors have conducted repeated studies in order to obtain a porous metal complex having excellent carbon dioxide adsorption ability, electron conduction, and proton conduction, and have found a compound represented by the general formula (1).
The compound represented by the general formula (1) has a carboxy group and a hydroxy group, and can be coordinated to a metal. The compound represented by the general formula (1) has two pairs of carboxy groups and hydroxy groups bonded to an aromatic hydrocarbon ring on three sides of the terminal of the compound, similar to 2,5-dihydroxyterephthalic acid. , They are attached to two adjacent carbon atoms in the aromatic hydrocarbon ring, respectively. Therefore, the compound represented by the general formula (1) can form a porous structure in the same manner as _{M 2 (dobdc) when coordinated to the central metal.}

Further, the compound represented by the general formula (1) has a basic imidazole ring in the molecule of this compound. The basic imidazole ring has a high affinity for carbon dioxide, and the nitrogen atom site of the imidazole ring easily forms a hydrogen bond, which contributes to the improvement of proton conduction.
Therefore, since the porous metal complex having the compound represented by the general formula (1) as a ligand has a basic group in the pores, it is easy to retain carbon dioxide in the pores and a large amount of carbon dioxide is retained. The transfer of protons required for electron reduction can be performed more efficiently.

Further, the compound represented by the general formula (1) has a triphenylene skeleton in which a π-conjugated system is spread in a plane at the center of the compound. The triphenylene skeleton in which the π-conjugated system spreads in a plane contributes to the improvement of conductivity because the π electrons are delocalized.
Therefore, in the porous metal complex using the compound represented by the general formula (1) as a ligand, the π electrons existing in the triphenylene skeleton portion interact (π-π stacking) between the triphenylene skeleton molecules. Form an electron conduction path in the pores. As a result, conductivity can be enhanced and electron transfer can be performed more efficiently.

Examples of the alkyl group having 1 to 4 carbon atoms that can be substituted for the aromatic hydrocarbon ring in Ar ¹ , Ar ² , and Ar ³ include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and n-butyl. Groups, i-butyl groups, t-butyl groups and the like can be mentioned.

Examples of the aromatic hydrocarbon ring include a benzene ring, a naphthalene ring, an anthracene ring and the like.

前記一般式（１１）中、Ａｒは、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。なお、Ａｒは、上述したＡｒ^１、Ａｒ^２、Ａｒ^３と同様である。 <Compound manufacturing method>
The method for producing the compound represented by the general formula (1) is not particularly limited and may be appropriately selected depending on the intended purpose. For example, hexaaminotriphenylene (HATP) and the following general formula (11) are used. Examples thereof include a method of reacting with the compound to be produced. In the reaction between hexaaminotriphenylene and the compound represented by the following general formula (11), two adjacent amino groups of hexaaminotriphenylene and the aldehyde group of the general formula (11) are dehydrated and condensed in the presence of oxygen. It is a reaction to form an imidazole ring.

In the general formula (11), Ar represents an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, a carboxy group and a hydroxy group bonded to the aromatic hydrocarbon ring). Is bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring, respectively). Ar is the same as Ar ¹ , Ar ² , and Ar ³ described above.

(Adsorbent)
The disclosed adsorbent contains a central metal, a ligand, and, if necessary, other components.
The adsorbent is porous.
The adsorbent is a so-called porous metal complex.
The porous metal complex is a porous material containing a metal ion and an anionic ligand. The porous metal complex (MOF) may also be referred to as a porous coordination polymer (PCP).

<Central metal>
Examples of the central metal include titanium, manganese, iron, cobalt, nickel, magnesium, copper, zinc, aluminum, zirconium and the like. These may be used alone or in combination of two or more.

<Ligand>
The ligand coordinates to the central metal.
The ligand is a compound represented by the general formula (1).

<Other ingredients>
The other components are not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include proton conductive substances.
The proton conductive substance is a substance that is inserted into the pores of the formed porous metal complex and forms a hydrogen bond with the imidazole ring of the ligand. Since the proton conductive substance forms a hydrogen bond path by forming a hydrogen bond with the imidazole ring of the ligand in the pores, the proton conductivity of the adsorbent can be improved.
Examples of the proton conductive substance include an imidazole derivative, a low molecular weight or polymer having a hydroxy group, a carboxyl group, a sulfo group, or an amino group as a functional group, an ionic liquid, a Nafion® dispersion liquid, and the like.

(Manufacturing method of adsorbent)
The method for producing the adsorbent is not particularly limited and may be appropriately selected depending on the intended purpose, and a general method for producing a porous metal complex can be referred to. Examples of a general method for producing a porous metal complex include a method of heating a mixed solution containing a metal salt of a central metal, a ligand, and water.
As a method for heating the mixed solution, a hydrothermal synthesis method, which is a kind of solvothermal method in which the mixed solution is placed in a closed container and heated, is preferable.

The mixed solution contains a metal salt of the central metal, a ligand, water, and if necessary, other components such as an organic solvent.
The metal salt of the central metal is a metal salt of the central metal of the porous metal complex, and the central metal is the above-mentioned one. The counterion of the metal salt is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include nitrate ion and acetate ion.
The ligand is coordinated to the central metal and is represented by the general formula (1).
The organic solvent is not particularly limited as long as it can dissolve the ligand, and can be appropriately selected depending on the intended purpose. Examples thereof include dimethylformamide (DMF) and ethanol.
The ratio of the metal salt to the ligand in the mixed solution is not particularly limited and may be appropriately selected depending on the intended purpose, but the metal salt: ligand = 1: 3 is preferable in terms of the amount of substance ratio.

The heating temperature of the mixed solution is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 100 ° C to 110 ° C.
The heating time of the mixed solution is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 3 to 4 days.

(Electrode for carbon dioxide reduction)
The disclosed carbon dioxide reducing electrode has at least a metal-containing member and an adsorbent, and further has other members as needed.

<Metal-containing material>
The metal-containing member is not particularly limited in its material, shape, size, and structure as long as it has a metal capable of reducing carbon dioxide on its surface, and may be appropriately selected according to the purpose. can.
The reduction of carbon dioxide using the metal-containing member usually occurs when the metal-containing member is energized. By the reduction, carbon dioxide is transformed into formic acid or carbon monoxide, formaldehyde, methanol, and methane, which are highly useful substances.

The metal is not particularly limited and may be appropriately selected depending on the intended purpose, but copper, silver, gold, zinc and indium are preferable in terms of the ability to reduce carbon dioxide with multiple electrons.

The shape of the metal-containing member is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a flat plate shape.

The structure of the metal-containing member is not particularly limited and may be appropriately selected depending on the intended purpose. It may be composed of a metal capable of reducing carbon dioxide itself, or carbon dioxide may be formed on the surface of the core material. It may have a structure in which a thin film of a metal capable of reducing carbon is arranged.
The core material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a metal core material, a resin core material, and a glass core material. The metal core material may be a metal capable of reducing carbon dioxide, or may not be a metal capable of reducing carbon dioxide.
Examples of the thin film include a plating film and a sputter film.

<Adsorbent>
The adsorbent is the disclosed adsorbent.
The adsorbent is arranged on the surface of the metal-containing member.

Here, an example of the carbon dioxide reducing electrode will be described with reference to the figure.
FIG. 1 is a schematic cross-sectional view of the carbon dioxide reducing electrode 1. In the carbon dioxide reducing electrode 1 of FIG. 1, the adsorbent 3 is arranged in a layer on the surface of the metal-containing member 2.

The adsorbent has excellent proton conductivity. By arranging such an adsorbent on the surface of the metal-containing member, protons (for example, protons generated by decomposition of water) are transmitted into or near the pores, which are the reaction fields of the adsorbent. Will be done.
In addition, the adsorbent is excellent in carbon dioxide adsorbability. Therefore, the carbon dioxide reducing electrode can adsorb and retain a large amount of carbon dioxide in the pores and the like.

The method of arranging the adsorbent on the surface of the metal-containing member is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a coating material containing the adsorbent may be applied to the metal-containing member. Examples thereof include a method of applying the adsorbent and a method of spraying the adsorbent itself onto the metal-containing member.

The coating material used in the coating method contains at least the adsorbent and an adhesive component, and further contains other components, if necessary.
The adhesive component preferably has conductivity. Examples of such a component include carbon paste, conductive resin and the like.
The ratio of the adsorbent to the adhesive component in the coated material is not particularly limited and may be appropriately selected depending on the intended purpose.

Examples of the spraying method include aerosol deposition and the like.

(Carbon dioxide reduction device)
The disclosed carbon dioxide reducing device has a carbon dioxide reducing electrode as an electrode on the cathode side.

An example of the reaction of the carbon dioxide reduction device is shown below.
On the anode side of the carbon dioxide reduction device, for example, the light energy applied to the anode electrode is used to cause the following decomposition of water.
H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻
On the other hand, on the cathode side of the carbon dioxide reducing device, for example, the following carbon dioxide reduction occurs.
^{_{CO 2 + 2H + + 2e -}} → HCOOH
The total reaction formula is, for example, as follows.
H ₂ O + CO ₂ → HCOOH + 1 / 2O ₂
The formic acid produced is, for example, concentrated and recovered.

<First aspect>
The first aspect of the disclosed carbon dioxide reduction apparatus has a carbon dioxide reduction electrode as a cathode side electrode, and further has other members such as a cathode tank, an anode tank, and a proton permeable film, if necessary.
The carbon dioxide reduction electrode is the disclosed carbon dioxide reduction electrode.

<< Cathode tank >>
The cathode tank includes the carbon dioxide reducing electrode.

<< Anode tank >>
The anode tank has an anode electrode and, if necessary, other parts.
Examples of the material of the anode electrode in the normal electrolytic reduction performed by energizing the anode electrode and the cathode electrode using an external power source include Pt and the like.
On the other hand, examples of the material of the anode electrode in the electrolytic reduction of carbon dioxide (so-called artificial photosynthesis) performed by irradiating the anode electrode with light include a photoexcited material capable of oxidative decomposition of water and a multi-junction semiconductor. Examples of the photoexcited material include an anode electrode provided with a nitride semiconductor layer.

<< Proton Permeation Membrane >>
The proton permeable membrane is sandwiched between the cathode tank and the anode tank.
The proton permeable membrane prevents the electrolytic solution in the cathode tank from mixing with the electrolytic solution in the anode tank.

The proton permeable membrane is not particularly limited as long as only protons pass through the proton permeable membrane and other substances cannot pass through the proton permeable membrane, and can be appropriately selected depending on the intended purpose, for example. , Nafion (registered trademark) and the like.
Nafion is a perfluorocarbon material composed of a hydrophobic Teflon (registered trademark) skeleton composed of carbon-fluorine and a perfluoro side chain having a sulfonic acid group. Specifically, it is a copolymer of tetrafluoroethylene and perfluoro [2- (fluorosulfonylethoxy) propyl vinyl ether].

<< Other parts >>
Examples of the other members include a first electrolytic solution, a second electrolytic solution, a carbon dioxide supply member, a power source, a light source, and the like.

-First electrolytic solution-
The first electrolytic solution is housed in the cathode tank.
Examples of the first electrolytic solution include an aqueous solution of potassium hydrogen carbonate, an aqueous solution of sodium hydrogen carbonate, an aqueous solution of sodium sulfate, an aqueous solution of potassium chloride, and an aqueous solution of sodium chloride.

The concentration of the electrolyte in the first electrolytic solution is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.2 mol / L or more, and more preferably 1 mol / L or more.

-Second electrolyte-
The second electrolytic solution is housed in the anode tank.
Examples of the second electrolytic solution include an aqueous solution of potassium hydrogen carbonate, an aqueous solution of sodium hydrogen carbonate, an aqueous solution of sodium sulfate, and an aqueous solution of sodium hydroxide.

The concentration of the electrolyte in the second electrolytic solution is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.2 mol / L or more, more preferably 1 mol / L or more.

-Carbon dioxide supply member-
The carbon dioxide supply member is not particularly limited as long as it is a member that supplies carbon dioxide to the cathode tank, and can be appropriately selected depending on the intended purpose.

-Power supply-
The power source is not particularly limited as long as it is a member to which a direct current can be applied, and can be appropriately selected depending on the intended purpose.

-Light source-
The light source is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a xenon lamp.
The light source is used to irradiate the anode electrode with light in electrolytic reduction of carbon dioxide (so-called artificial photosynthesis) performed by irradiating the anode electrode with light.

Here, an example of the first aspect of the disclosed carbon dioxide reduction apparatus will be described with reference to the drawings.
FIG. 2 is a schematic cross-sectional view of the carbon dioxide reduction device 100A.
The carbon dioxide reduction device 100A of FIG. 2 has a cathode tank 110, an anode tank 120, a proton permeable membrane 130, a carbon dioxide supply member 140, a constant voltage power supply device 150, and a reference electrode 160.
A proton permeable membrane 130 is sandwiched between the cathode tank 110 and the anode tank 120.
The cathode tank 110 contains the first electrolytic solution 112. Then, in the cathode tank 110, the carbon dioxide reducing electrode 1 and the reference electrode 160 are immersed in the first electrolytic solution 112.
The second electrolytic solution 122 is housed in the anode tank 120. Then, in the anode tank 120, the anode electrode 121 is immersed in the second electrolytic solution 122.

The carbon dioxide supply member 140 is, for example, a hollow rod-shaped member, the tip of which is immersed in the first electrolytic solution 112, and carbon dioxide is supplied to the first electrolytic solution 112.
Therefore, carbon dioxide is dissolved in the first electrolytic solution 112.

In the carbon dioxide reduction device 100A, a voltage is applied between the carbon dioxide reduction electrode 1 which is a cathode electrode and the anode electrode 121 by the constant voltage power supply device 150. Then, oxidative decomposition of water occurs on the anode side, while carbon dioxide is reduced on the cathode side. On the cathode side, carbon dioxide can be retained on the surface of the metal-containing member 2 by the action of the adsorbent 3. Further, the proton conductivity of the adsorbent 3 is enhanced. Therefore, carbon dioxide can be efficiently reduced.

FIG. 3 is a schematic cross-sectional view of the carbon dioxide reduction device 100B.
The carbon dioxide reduction device 100B of FIG. 3 has a cathode tank 110, an anode tank 120, a proton permeable membrane 130, a carbon dioxide supply member 140, and a light source 170.
A proton permeable membrane 130 is sandwiched between the cathode tank 110 and the anode tank 120.
The cathode tank 110 contains the first electrolytic solution 112. Then, in the cathode tank 110, the carbon dioxide reducing electrode 1 is immersed in the first electrolytic solution 112.
The second electrolytic solution 122 is housed in the anode tank 120. Then, in the anode tank 120, the anode electrode 121 is immersed in the second electrolytic solution 122. The anode electrode 121 is a photochemical electrode for reducing carbon dioxide.

The carbon dioxide supply member 140 is, for example, a hollow rod-shaped member, the tip of which is immersed in the first electrolytic solution 112, and carbon dioxide is supplied to the first electrolytic solution 112.
Therefore, carbon dioxide is dissolved in the first electrolytic solution 112.

In the carbon dioxide reduction device 100B, water is oxidatively decomposed in the anode tank 120 in which the light from the light source 170 is applied to the anode electrode 121. As a result of the reaction, an electromotive force is generated between the anode electrode 121 connected by the conducting wire 180 and the carbon dioxide reduction electrode 1 which is the cathode electrode. Due to the electromotive force, carbon dioxide is reduced on the cathode side. On the cathode side, carbon dioxide can be retained on the surface of the metal-containing member 2 by the action of the adsorbent 3. Further, the proton conductivity of the adsorbent 3 is enhanced. Therefore, carbon dioxide can be efficiently reduced.

<Second aspect>
A second aspect of the disclosed carbon dioxide reduction apparatus has an anode electrode, a liquid retention membrane, a proton permeable membrane, a cathode electrode, and, if necessary, other members.

<< Anode electrode >>
The anode electrode is not particularly limited and may be appropriately selected depending on the intended purpose.
Examples of the material of the anode electrode in the normal electrolytic reduction performed by energizing the anode electrode and the cathode electrode using an external power source include Pt and the like.
On the other hand, examples of the material of the anode electrode in the electrolytic reduction of carbon dioxide (so-called artificial photosynthesis) performed by irradiating the anode electrode with light include a photoexcited material capable of oxidative decomposition of water and a multi-junction semiconductor. Examples of the photoexcited material include an anode electrode provided with a nitride semiconductor layer.

<< Liquid retention membrane >>
The liquid-retaining film is not particularly limited as long as it can hold the electrolytic solution, and can be appropriately selected depending on the intended purpose. Examples thereof include a layered water-absorbing material. The layered water-absorbing material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a layered porous body.
As the liquid-retaining film, a commercially available product can be used. Examples of the commercially available product include a high-performance perforated plate "Univex SB" manufactured by Unitika Ltd. The perforated plate is a water-absorbent perforated plate made of polyester fiber.

The shape and size of the liquid-retaining film are not particularly limited and may be appropriately selected depending on the intended purpose.

<< Proton Permeation Membrane >>
The proton permeable membrane is sandwiched between, for example, the liquid retention membrane and the cathode electrode.
The proton permeable membrane prevents the electrolytic solution held by the liquid retaining membrane from coming into contact with the cathode electrode.

The proton permeable membrane is not particularly limited as long as only protons pass through the proton permeable membrane and other substances cannot pass through the proton permeable membrane, and can be appropriately selected depending on the intended purpose, for example. , Nafion (registered trademark) and the like.
Nafion is a perfluorocarbon material composed of a hydrophobic Teflon (registered trademark) skeleton composed of carbon-fluorine and a perfluoro side chain having a sulfonic acid group. Specifically, it is a copolymer of tetrafluoroethylene and perfluoro [2- (fluorosulfonylethoxy) propyl vinyl ether].

<< Cathode electrode >>
The cathode electrode is the disclosed carbon dioxide reduction electrode.
In the cathode electrode, the adsorbent is preferably disposed at least on the surface of the metal-containing member on the proton permeable membrane side.

<< Other parts >>
Examples of the other member include an electrolytic solution, a power source, a light source, and the like.

-Electrolytic solution-
The electrolytic solution is held by the liquid retaining film.
Examples of the electrolytic solution include an aqueous solution of potassium hydrogen carbonate, an aqueous solution of sodium hydrogen carbonate, an aqueous solution of sodium sulfate, an aqueous solution of potassium chloride, an aqueous solution of sodium chloride, and an aqueous solution of sodium hydroxide.

The concentration of the electrolyte in the electrolytic solution is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.2 mol / L or more, more preferably 1 mol / L or more, and particularly preferably 2 mol / L or more. preferable.

-Power supply-
The power source is not particularly limited as long as it is a member to which a direct current can be applied, and can be appropriately selected depending on the intended purpose.

-Light source-
The light source is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a xenon lamp.
The light source is used to irradiate the anode electrode with light in electrolytic reduction of carbon dioxide (so-called artificial photosynthesis) performed by irradiating the anode electrode with light.

Here, an example of the second aspect of the disclosed carbon dioxide reduction device will be described with reference to the drawings.
FIG. 4 is a schematic cross-sectional view of the carbon dioxide reducing device 10A.
The carbon dioxide reduction device 10A has an anode electrode 12, a liquid retention film 13, a proton permeation film 14, and a carbon dioxide reduction electrode 1 which is a cathode electrode in this order. Further, it has a constant voltage power supply device 15.
In the carbon dioxide reducing electrode 1, the adsorbent 3 is arranged in a layer on the surface (one side) of the metal-containing member 2.
The anode electrode 12 is in contact with the liquid-retaining membrane 13, the liquid-retaining membrane 13 is in contact with the proton permeable membrane 14, and the proton permeable membrane 14 is in contact with the adsorbent 3 of the carbon dioxide reducing electrode 1.
The electrolytic solution is held in the liquid retaining film 13.

In the carbon dioxide reduction device 10A, a voltage is applied between the carbon dioxide reduction electrode 1 and the anode electrode 12 by the constant voltage power supply device 15. Then, oxidative decomposition of water occurs on the anode side, while carbon dioxide is reduced on the cathode side. On the cathode side, carbon dioxide can be retained on the surface of the metal-containing member 2 by the action of the adsorbent 3. Further, the proton conductivity of the adsorbent 3 is enhanced. Therefore, carbon dioxide can be efficiently reduced.
Further, since the electrolytic solution is held in the liquid retaining membrane 13, the dissolution of carbon dioxide in the electrolytic solution and the dissolution of the product in the electrolytic solution are small. In addition, since the proton permeable membrane 14 prevents the electrolytic solution from coming into contact with the adsorbent, it is possible to prevent the electrolytic solution from entering the pores of the adsorbent. Therefore, it is possible to efficiently supply carbon dioxide to the reaction field and recover the product from the reaction field.

FIG. 5 is a schematic cross-sectional view of the carbon dioxide reduction device 10B.
The carbon dioxide reduction device 10B has an anode electrode 12, a liquid retention film 13, a proton permeation film 14, and a carbon dioxide reduction electrode 1 which is a cathode electrode in this order. Further, it has a light source 16.
In the carbon dioxide reducing electrode 1, the adsorbent 3 is arranged in a layer on the surface (one side) of the metal-containing member 2.
The anode electrode 12 is in contact with the liquid-retaining membrane 13, the liquid-retaining membrane 13 is in contact with the proton permeable membrane 14, and the proton permeable membrane 14 is in contact with the adsorbent 3 of the carbon dioxide reducing electrode 1.
The electrolytic solution is held in the liquid retaining film 13.
The anode electrode 12 is a photochemical electrode for reducing carbon dioxide.

In the carbon dioxide reduction device 10B, the light from the light source 16 irradiates the anode electrode 12, so that water is oxidatively decomposed on the surface of the anode electrode 12. By the reaction, an electromotive force is generated between the anode electrode 12 connected by the conducting wire 17 and the carbon dioxide reducing electrode 1. Due to the electromotive force, carbon dioxide is reduced on the cathode side. On the cathode side, carbon dioxide can be retained on the surface of the metal-containing member 2 by the action of the adsorbent 3. Further, the proton conductivity of the adsorbent 3 is enhanced. Therefore, carbon dioxide can be efficiently reduced.
Further, since the electrolytic solution is held in the liquid retaining membrane 13, the dissolution of carbon dioxide in the electrolytic solution and the dissolution of the product in the electrolytic solution are small. In addition, since the proton permeable membrane 14 prevents the electrolytic solution from coming into contact with the adsorbent, it is possible to prevent the electrolytic solution from entering the pores of the adsorbent. Therefore, it is possible to efficiently supply carbon dioxide to the reaction field and recover the product from the reaction field.

Hereinafter, the disclosed technology will be described, but the disclosed technology is not limited to the following examples.

(Comparative Example 1)
A _{Ni 2} (dobdc) complex was synthesized and evaluated as a porous metal complex having _{CO 2 adsorption performance.} The Ni ₂ (dobdc) complex is a complex having a compound having the following structure as a ligand.
A THF (tetrahydrogen) solution of 2,5-dihydroxyterephthalic acid (structural formula below) and an aqueous solution of nickel acetate tetrahydrate were mixed at 1: 2 (2,5-dihydroxyterephthalic acid: nickel acetate tetrahydrate). _{A Ni 2} (dobdc) complex, which is a yellow powder, was obtained by a sorbothermal method in which the mixture was mixed at a molar ratio of 1 and heated at 110 ° C. for 3 days using a pressure resistant container. The synthesis was carried out with reference to the following documents.
<Reference>
Liu, J.M. Tian, J.M. Thallapally, P.M. K. McGrail, B.I. P. J. Phys. Chem. C 2012, 116, 9575-9581.

_{As a result of measuring the CO 2} adsorption characteristics of the obtained powder sample using a gas / steam adsorption amount measuring device (manufactured by Microtrac Bell Co., Ltd.), the adsorption isotherm of FIG. 7 was obtained.
Further, the obtained powder sample was formed into pellets having a diameter of 5 mm and a thickness of 0.3 mm, and the electrical resistivity was measured using an IV measuring device (manufactured by Keysight Co., Ltd., B2901A). Got

(Comparative Example 2)
Porous metal complex Cu (mipt) complex was synthesized by the solvothermal method according to the method of the following literature. The Cu (mipt) complex is a complex having a compound having the following structure as a ligand. Specifically, 5-methylisophthalic acid represented by the following structural formula and copper nitrate hexahydrate were heated in DMF + MeOH at 100 ° C. for 4 days to obtain a bluish-white complex powder.
<Reference>
N. L. Roshi, J.M. Kim, M.M. Eddaoodi, B. Chen, M. O'Keffe, O. M. Yaghi, J.M. Am. Chem. Soc. 2005, 127, 1504-1518

_{As a result of measuring the CO 2} adsorption characteristics of the obtained powder sample using a gas / steam adsorption amount measuring device (manufactured by Microtrac Bell Co., Ltd.), the adsorption isotherm of FIG. 7 was obtained.
Further, the obtained powder sample was formed into pellets having a diameter of 5 mm and a thickness of 0.3 mm, and the electrical resistivity was measured using an IV measuring device (manufactured by Keysight Co., Ltd., B2901A). Got

(Example 1)
Using 2,3,6,7,10,11-hexabromotriphenylene (manufactured by Wako Pure Chemical Industries, Ltd.) as a raw material, 2,3,6,7,10,11-hexaaminotriphenylene 6 hydrochloride by the method described in the following document. (HATP) was synthesized. The obtained HATP and 5-formylsalicylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed in dimethylformamide (DMF) at a molar ratio of 1: 3, under a nitrogen atmosphere at -30 ° C, and stirred for 3 hours. After returning to room temperature, air was aerated and heated at 130 ° C. for 24 hours to obtain a compound (ligand) having the following structure. When the IR spectrum of the obtained ligand was measured with an infrared spectrophotometer, ν (NH) observed at around ^{3000 cm -1} in HATP disappeared, and around ^{1650 cm -1 in formyl salicylic acid.} Since the ν (C = O) observed in the above disappeared partially, it was confirmed that the condensation reaction between the amino group and the aldehyde occurred (Fig. 6).
The obtained ligand and nickel acetate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed in DMF / water (DMF: water = 1: 1) at a molar ratio of 1: 3, and hydrothermal synthesis is performed at 110 ° C. By doing so, a porous metal complex was obtained.
<Reference>
L. Chen, J.M. Kim, T.M. Ishizuka, Y.M. Honsho, A. Saeki, S.A. Seki, H. Ihee, D.I. Jiang, J.M. Am. Chem. Soc. 2009, 131, 7287-7292

_{As a result of measuring the CO 2} adsorption characteristics of the obtained powder sample using a gas / steam adsorption amount measuring device (manufactured by Microtrac Bell Co., Ltd.), the adsorption isotherm of FIG. 7 was obtained, and about 20 cm at 1 atm. ^{It was confirmed that it has the ability to adsorb 3} g ^-3 and carbon dioxide larger than that of Comparative Example 2.
Further, as a result of molding this powder sample into pellets having a diameter of 5 mm and a thickness of 0.3 mm and measuring the electrical resistivity using an IV measuring device (manufactured by Keysight Co., Ltd., B2901A), the values shown in Table 1 were obtained. It was confirmed that the conductivity was higher than that of Comparative Example 1.

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。
（付記２）
Ａｒ^１における前記芳香族炭化水素環が、ベンゼン環、ナフタレン環、又はアントラセン環であり、
Ａｒ^２における前記芳香族炭化水素環が、ベンゼン環、ナフタレン環、又はアントラセン環であり、
Ａｒ^３における前記芳香族炭化水素環が、ベンゼン環、ナフタレン環、又はアントラセン環である、
付記１に記載の吸着剤。
（付記３）
前記中心金属が、ニッケル、銅、亜鉛、マグネシウム、鉄、及びコバルトから選択される少なくともいずれかである付記１から２のいずれかに記載の吸着剤。
（付記４）
金属塩と、前記金属塩の金属と結合可能な配位子と、水と、を含有する混合液を加熱することを含む吸着剤の製造方法であって、
前記配位子が、下記一般式（１）で表されることを特徴とする吸着剤の製造方法。

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。
（付記５）
下記一般式（１）で表されることを特徴とする化合物。

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。
（付記６）
二酸化炭素を還元可能な金属を有する金属含有部材と、
前記金属含有部材の表面に、吸着剤と、を有し、
前記吸着剤が、中心金属と、前記中心金属に配位する配位子と、を有する多孔性金属錯体であり、
前記配位子が、下記一般式（１）で表されることを特徴とする二酸化炭素還元用電極。

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。
（付記７）
前記金属含有部材の材質が、銅、銀、金、亜鉛、及びインジウムの少なくともいずれかである付記６に記載の二酸化炭素還元用電極。
（付記８）
二酸化炭素還元用電極をカソード側の電極として有する二酸化炭素還元装置であって、
前記二酸化炭素還元用電極が、二酸化炭素を還元可能な金属を有する金属含有部材と、前記金属含有部材の表面に吸着剤と、を有し、
前記吸着剤が、中心金属と、前記中心金属に配位する配位子とを有する多孔性金属錯体であり、
前記配位子が、下記一般式（１）で表されることを特徴とする二酸化炭素還元装置。

前記一般式（１）中、Ａｒ^１〜Ａｒ^３は、それぞれ独立して、非置換、又は炭素数１〜４のアルキル基による置換の芳香族炭化水素環を表す（ただし、前記芳香族炭化水素環に結合するカルボキシ基及びヒドロキシ基は、前記芳香族炭化水素環における隣接する２つの炭素原子にそれぞれ結合している）。 Further, the following additional notes will be disclosed.
(Appendix 1)
A porous metal complex having a central metal and a ligand coordinated to the central metal.
An adsorbent characterized in that the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).
(Appendix 2)
The ^{aromatic hydrocarbon ring in Ar 1} is a benzene ring, a naphthalene ring, or an anthracene ring.
The ^{aromatic hydrocarbon ring in Ar 2} is a benzene ring, a naphthalene ring, or an anthracene ring.
The ^{aromatic hydrocarbon ring in Ar 3} is a benzene ring, a naphthalene ring, or an anthracene ring.
The adsorbent according to Appendix 1.
(Appendix 3)
The adsorbent according to any one of Supplementary note 1 to 2, wherein the central metal is at least one selected from nickel, copper, zinc, magnesium, iron, and cobalt.
(Appendix 4)
A method for producing an adsorbent, which comprises heating a mixed solution containing a metal salt, a ligand capable of binding to a metal of the metal salt, and water.
A method for producing an adsorbent, wherein the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).
(Appendix 5)
A compound characterized by being represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).
(Appendix 6)
A metal-containing member having a metal capable of reducing carbon dioxide, and
On the surface of the metal-containing member, an adsorbent is provided.
The adsorbent is a porous metal complex having a central metal and a ligand coordinated to the central metal.
A carbon dioxide reducing electrode, wherein the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).
(Appendix 7)
The carbon dioxide reducing electrode according to Appendix 6, wherein the material of the metal-containing member is at least one of copper, silver, gold, zinc, and indium.
(Appendix 8)
A carbon dioxide reducing device having a carbon dioxide reducing electrode as an electrode on the cathode side.
The carbon dioxide reducing electrode has a metal-containing member having a metal capable of reducing carbon dioxide, and an adsorbent on the surface of the metal-containing member.
The adsorbent is a porous metal complex having a central metal and a ligand coordinated to the central metal.
A carbon dioxide reducing device, wherein the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).

1 Electrode for carbon dioxide reduction 2 Metal-containing member 3 Adsorbent 10A Carbon dioxide reduction device 10B Anode electrode 13 Retaining film 14 Proton permeable film 15 Constant voltage power supply device 16 Light source 17 Lead wire 100A Carbon dioxide reduction device 100B Carbon dioxide Carbon reduction device 110 Cathode tank 112 1st electrolytic solution 120 Anode tank 121 Anode electrode 122 2nd electrolytic solution 130 Proton permeable film 140 Carbon dioxide supply member 150 Constant voltage power supply device 160 Reference electrode 170 Light source 180 Lead wire

Claims (7)

A porous metal complex having a central metal and a ligand coordinated to the central metal.
An adsorbent characterized in that the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring). The ^{aromatic hydrocarbon ring in Ar 1} is a benzene ring, a naphthalene ring, or an anthracene ring.
The ^{aromatic hydrocarbon ring in Ar 2} is a benzene ring, a naphthalene ring, or an anthracene ring.
The ^{aromatic hydrocarbon ring in Ar 3} is a benzene ring, a naphthalene ring, or an anthracene ring.
The adsorbent according to claim 1. The adsorbent according to any one of claims 1 to 2, wherein the central metal is at least one selected from nickel, copper, zinc, magnesium, iron, and cobalt. A method for producing an adsorbent, which comprises heating a mixed solution containing a metal salt, a ligand capable of binding to a metal of the metal salt, and water.
A method for producing an adsorbent, wherein the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring). A compound characterized by being represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring). A metal-containing member having a metal capable of reducing carbon dioxide, and
On the surface of the metal-containing member, an adsorbent is provided.
The adsorbent is a porous metal complex having a central metal and a ligand coordinated to the central metal.
A carbon dioxide reducing electrode, wherein the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring). A carbon dioxide reducing device having a carbon dioxide reducing electrode as an electrode on the cathode side.
The carbon dioxide reducing electrode has a metal-containing member having a metal capable of reducing carbon dioxide, and an adsorbent on the surface of the metal-containing member.
The adsorbent is a porous metal complex having a central metal and a ligand coordinated to the central metal.
A carbon dioxide reducing device, wherein the ligand is represented by the following general formula (1).

In the general formula (1), Ar ^{1 to} Ar ³ each independently represent an aromatic hydrocarbon ring that is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms (however, the aromatic hydrocarbon). The carboxy group and the hydroxy group bonded to the ring are respectively bonded to two adjacent carbon atoms in the aromatic hydrocarbon ring).

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