WO2023163041A1

WO2023163041A1 - Additive for carbon dioxide reduction catalysts, catalyst layer, cathode, ion exchange membrane-electrode assembly and solid electrolyte electrolysis device

Info

Publication number: WO2023163041A1
Application number: PCT/JP2023/006460
Authority: WO
Inventors: 寛之兼古; チンシンジア
Original assignee: 出光興産株式会社
Priority date: 2022-02-28
Filing date: 2023-02-22
Publication date: 2023-08-31
Also published as: TW202340540A; JPWO2023163041A1; CN118786249A; AU2023223827A1

Abstract

The present invention provides: a catalyst layer which can be suppressed in functional deterioration; an additive for carbon dioxide reduction catalysts, the additive enabling the achievement of excellent electrical conductivity of an electrode catalyst layer and excellent electrolysis efficiency of a carbon dioxide electrolytic reduction reaction; an electrode; an ion exchange membrane-electrode assembly; and a solid electrolyte electrolysis device. The additive for carbon dioxide reduction catalysts comprises a carrier which contains carbon, while having an aryl group on the surface.

Description

Additive for carbon dioxide reduction catalyst, catalyst layer, cathode, ion-exchange membrane-electrode assembly, and solid electrolyte electrolysis device

The technology of the present disclosure relates to additives for carbon dioxide reduction catalysts, catalyst layers, cathodes, ion exchange membrane-electrode assemblies, and solid electrolyte electrolysis devices.

Carbon dioxide is emitted when energy is extracted from fossil fuels. An increase in the concentration of carbon dioxide in the atmosphere is said to be one of the causes of global warming. Since carbon dioxide is an extremely stable substance, there have been few ways to utilize it. However, due to the demands of the times that global warming is becoming more serious, there is a demand for a new technology for converting carbon dioxide into other substances and recycling it as a resource. For example, the development of a carbon dioxide reduction device capable of directly reducing gaseous carbon dioxide is underway.

For example, in Patent Document 1, in order to obtain a carbon dioxide reduction electrode catalyst layer that exhibits a high partial current density by controlling wettability and can withstand long-term operation, a catalyst layer is supported by a carbon material. The ratio of the BET specific surface area (A _N2 ) determined by nitrogen adsorption to the BET specific surface area (A _H2O ) determined by water vapor adsorption (A _H2O /A _N2 ) is set to 0.08 or less.
In Patent Document 2, in the reduction reaction of the carbon compound, at least one of suppressing the production ratio of hydrogen by side reaction and improving the production ratio of the reduction product by the reduction reaction of the carbon compound is possible. In order to achieve this, it is disclosed that the reduction reaction electrode used for the reduction reaction of the carbon compound is provided with an electrode body modified with a hydrophobic polymer.
US Pat. No. 6,300,000 discloses a method that makes it possible to solve technical problems by grafting hydrophobic and/or hydrophilic molecules onto carbon.
Furthermore, Non-Patent Document 1 discloses a method for controlling the wettability of the electrode and preventing functional deterioration by adding polytetrafluoroethylene (PTFE) fine particles to the carbon dioxide reduction electrode catalyst layer.

JP 2021-147677 A Japanese Patent Application Laid-Open No. 2021-21095 Japanese Patent Application Laid-Open No. 2021-2528

In an electrolytic device having a catalyst layer for promoting a carbon dioxide reduction reaction and an ion-exchange membrane, if an electrolytic solution permeates the ion-exchange membrane and seeps into the catalyst layer, the function of the catalyst layer is deteriorated.
Patent Documents 1 and 2 and Non-Patent Document 1 attempt to make the catalyst layer hydrophobic by adding a hydrophobic polymer to the catalyst layer. increased. Further, in Patent Document 3, a hydrophobic compound is supported on the gas diffusion layer or the intermediate layer between the gas diffusion layer and the catalyst layer to increase the hydrophobicity, but the catalyst layer itself has not been improved in hydrophobicity. The effect of hydrophobization was limited.

The present disclosure has been made in view of the above circumstances. An object of the present invention is to provide an additive for a carbon dioxide reduction catalyst, an electrode, an ion-exchange membrane-electrode assembly, and a solid electrolyte type electrolysis device that are excellent in electrolysis efficiency.

<1> An additive for a carbon dioxide reduction catalyst having an aryl group on its surface and a carrier containing carbon.

<2> A carbon dioxide reduction catalyst having a carrier containing carbon and having a ratio of the water vapor adsorption amount at 25°C and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa being less than 0.5. Additive for

<3> The carbon dioxide reduction catalyst additive according to <1>, wherein the aryl group contains one or more selected from the group consisting of a phenyl group and a condensed ring group having 2 to 6 benzene rings.

<4> The carbon dioxide reduction catalyst according to <3>, wherein the condensed ring group having 2 to 6 benzene rings contains one or more selected from the group consisting of naphthyl group, anthracenyl group, phenanthrenyl group and pyrenyl group. Additive for

<5> The aryl group has one or more substituents selected from the group consisting of an alkyl group, a fluorinated alkyl group, a phenyl group, a fluorinated phenyl group and a fluorine atom <1>, <3> and < 4> The additive for a carbon dioxide reduction catalyst according to any one of items 4>.

<6> Carbon dioxide reduction according to any one of <1> and <3> to <5>, wherein the aryl group is one or more of the groups represented by (1) to (8) Additives for catalysts.

In (1) to (8), * represents a binding site to the surface of the carrier.

<7> an additive having an aryl group on its surface and a carrier containing carbon;
and a catalyst comprising a support containing carbon and having inorganic fine particles or a metal complex supported thereon.

<8> an additive having a carrier containing carbon and having a ratio of less than 0.5 of the water vapor adsorption amount at 25° C. and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa;
and a catalyst comprising a support containing carbon and having inorganic fine particles or a metal complex supported thereon.

<9> The inorganic fine particles are fine particles selected from the group consisting of gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride. <7>, wherein the metal complex is a metal selected from the group consisting of copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum, or a metal complex in which a ligand is coordinated to an ion of the metal or The catalyst layer according to <8>.

<10> The catalyst layer according to <7>, wherein the aryl group contains one or more selected from the group consisting of a phenyl group and a condensed ring group having 2 to 6 benzene rings.

<11> The catalyst layer according to <10>, wherein the condensed ring group having 2 to 6 benzene rings contains one or more selected from the group consisting of naphthyl group, anthracenyl group, phenanthrenyl group and pyrenyl group.

<12> The catalyst layer according to <7>, wherein the aryl group has one or more substituents selected from the group consisting of an alkyl group, a fluorinated alkyl group, a phenyl group, a fluorinated phenyl group, and a fluorine atom.

<13> The catalyst layer according to <7>, wherein the aryl group is one or more of the groups represented by (1) to (8).

In (1) to (7), * represents a binding site to the surface of the carrier.

<14> A cathode having the catalyst layer according to <9> and a gas diffusion layer.

<15> An ion-exchange membrane-electrode assembly comprising the cathode according to <14>, a solid electrolyte, and an anode.
<16> The ion exchange membrane-electrode assembly according to <15>, wherein the solid electrolyte is an anion exchange membrane.

<17> The cathode according to <14>;
an anode that forms a pair of electrodes with the cathode;
a solid electrolyte interposed in contact between the cathode and the anode;
A solid electrolyte type electrolysis device having a voltage applying section for applying a voltage between the cathode and the anode.
<18> The solid electrolyte electrolytic device according to <17>, wherein the solid electrolyte is an anion exchange membrane.

According to the technology of the present disclosure, a catalyst layer capable of suppressing deterioration in function, an additive for a carbon dioxide reduction catalyst that has excellent electrical conductivity of the electrode catalyst layer, and an excellent electrolysis efficiency of the carbon dioxide electroreduction reaction, a cathode, An ion-exchange membrane-electrode assembly and a solid electrolyte type electrolytic device can be provided.

1 is a schematic diagram of an ion-exchange membrane-electrode assembly suitably used in the present embodiment. FIG. 1 is a schematic diagram of a solid electrolyte type electrolytic device that is preferably used in the present embodiment; FIG. 4 is a graph showing relative water vapor adsorption amounts of Examples and Comparative Examples.

The upper and lower limits of the numerical ranges described herein can be arbitrarily combined. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges of "A to D" and "C to B" are also included in the technical scope of the present disclosure.
In addition, the numerical range "lower limit to upper limit" described in this specification means from the lower limit to the upper limit, unless otherwise specified.

<Additive for carbon dioxide reduction catalyst>
The carbon dioxide reduction catalyst additive according to the first embodiment has an aryl group on its surface and a carrier containing carbon.
The carbon dioxide reduction catalyst additive according to the second embodiment has a carrier containing carbon, and has a water vapor adsorption amount at 25 ° C. and a water vapor pressure of 2.2 kPa at the same temperature and a water vapor pressure of 3.1 kPa. The ratio to volume is less than 0.5.
The carbon dioxide reduction catalyst additive according to the first embodiment and the carbon dioxide reduction catalyst additive according to the second embodiment of the technology of the present disclosure are collectively referred to simply as "carbon dioxide according to the present embodiment It is sometimes referred to as "reduction catalyst additive".

A carbon dioxide reduction electrolyzer generally has a cathode having a gas diffusion layer and a catalyst layer that promotes a carbon dioxide reduction reaction, an ion exchange membrane, an anode, and an electrolytic solution (electrolyte) supplied to the anode.
Due to its structure, the ion exchange membrane has the property of permeating not only ions but also an electrolytic solution. A small amount of the electrolyte supplied to the anode permeates through the ion exchange membrane, resulting in excessive moisture inside the catalyst layer. A phenomenon such as clogging of the flow path was often found. These phenomena had adverse effects such as obstruction of the supply of carbon dioxide to the catalyst layer, resulting in deterioration of electrolysis performance such as current density and selectivity. In particular, this effect is more pronounced as the reaction temperature is higher.

As a method of controlling the water content of the catalyst layer, there is a method of controlling the hydrophobicity of the catalyst layer. In the above-mentioned Patent Document 1, the hydrophobicity is controlled by the addition amount of polyvinyl alcohol, polyvinylpyrrolidone, etc. In Patent Document 2, polystyrene is added, and in Non-Patent Document 1, PTFE is added to control the hydrophobicity. .
However, these hydrophobic polymers are insulators, and the addition of the hydrophobic polymers increases the electrical resistance of the catalyst layer, causing a problem of heat generation, deterioration of electrolysis efficiency, and the like.
Moreover, in Patent Document 3, although a hydrophobic polymer is not used, a hydrophobic compound is supported in the gas diffusion layer or in the intermediate layer between the gas diffusion layer and the catalyst layer to increase the hydrophobicity. However, the hydrophobization of the catalyst layer has not yet been enhanced, and therefore the effect of the hydrophobization has been limited.

On the other hand, the carbon dioxide reduction catalyst additive according to the present embodiment is used as a constituent component of the catalyst layer of the electrode provided with the catalyst layer, so that the surface of the catalyst layer can be In addition, the entire catalyst layer can be made hydrophobic. This is presumed to be due to the following reasons.
In the additive for carbon dioxide reduction catalyst according to the first embodiment, the additive brings hydrophobicity to the catalyst layer by having a carrier containing carbon with excellent electrical conductivity and having an aryl group on the surface. be able to. Since the aryl group is fixed to the carrier surface by chemical bonding, the catalyst layer can be reliably hydrophobized, and not only the surface of the catalyst layer but also the interior of the catalyst layer can be hydrophobized.
The additive for a carbon dioxide reduction catalyst according to the second embodiment has a specific water vapor adsorption ratio of less than 0.5 while having a carrier containing carbon with excellent electrical conductivity, and the additive is electrically conductive. Excellent hydrophobicity while possessing properties. Therefore, by adding the additive to the catalyst layer, not only the surface of the catalyst layer but also the inside of the catalyst layer can be made hydrophobic without impairing the electrical conductivity of the catalyst layer.

As a result, even if the electrolytic solution permeates the ion exchange membrane, the adhesion of the electrolyte to the catalyst layer containing the additive for the carbon dioxide reduction catalyst according to the present embodiment can be suppressed, and carbon dioxide can be supplied to the catalyst layer. is less likely to be disturbed. Therefore, the electrolysis performance such as current density and selectivity is not impaired, so that the electrolysis efficiency of the carbon dioxide electroreduction reaction is excellent.
A first embodiment and a second embodiment of the carbon dioxide reduction catalyst additive according to the present embodiment will be sequentially described below.

[Additive for carbon dioxide reduction catalyst according to first embodiment]
The carbon dioxide reduction catalyst additive according to the first embodiment has an aryl group on its surface and a carrier containing carbon.
As described above, having aryl groups on the surface of the carbon-containing support provides the additive with electrical conductivity and hydrophobicity, and by being contained in the catalyst layer, it provides electrical conductivity and conductivity throughout the catalyst layer. Hydrophobicity can be provided.

(aryl group)
Examples of the aryl group include a phenyl group and a group obtained by removing one hydrogen atom from a condensed ring containing two or more benzene rings (condensed ring group).
Among them, from the viewpoint of suppressing steric hindrance between the aryl groups on the surface of the carrier and from the viewpoint of ensuring the electrical conductivity of the additive, the aryl group consists of a phenyl group and a condensed ring group having 2 to 6 benzene rings. It preferably includes one or more selected from the group. When the number of benzene rings in the aryl group is 6 or less, the charge transfer between carriers is less likely to be inhibited, resulting in excellent electrical conductivity.
Examples of condensed ring groups having 2 to 6 benzene rings include groups obtained by removing one hydrogen atom from condensed rings such as naphthalene, anthracene, phenanthrene, pyrene, triphenylene, chrysene, perylene, pentacene, and pentaphene.

Among the above, the condensed ring group having 2 to 6 benzene rings includes a group obtained by removing one hydrogen atom from one or more condensed rings selected from the group consisting of naphthalene, anthracene, phenanthrene, and pyrene. is preferred. In other words, the condensed ring group having 2 to 6 benzene rings preferably contains one or more selected from the group consisting of naphthyl group, anthracenyl group, phenanthrenyl group and pyrenyl group.
The condensed ring group having 2 to 6 benzene rings is more preferably a pyrenyl group as a substituent.

The aryl group bonded to the surface of the carrier according to this embodiment may be unsubstituted or may have one or more substituents.
Examples of substituents include alkyl groups, alkenyl groups, fluorinated alkyl groups, aryl groups, fluorinated aryl groups, and fluorine atoms, and the substituents may further have a substituent.

Alkyl groups include alkyl groups having 1 to 30 carbon atoms, and may be linear, branched, or cyclic. Specifically, for example, methyl group, benzyl group (phenylmethyl group), trityl group (triphenylmethyl group), ethyl group, n-propyl group, isopropyl group, n-butyl group, tert-butyl group, n- Examples include hexyl group, cyclohexyl group, n-octyl group, n-dodecyl group and the like. The alkyl group may further have a substituent.

In addition, the upper limit of 30 carbon atoms of the alkyl group includes carbon atoms of substituents that may be further included. Hereinafter, the same applies to alkenyl groups, fluorinated alkyl groups, aryl groups, and fluorinated aryl groups.
The number of carbon atoms in the alkyl group is preferably 1-25, more preferably 2-20.
When the alkyl group is linear, it preferably has 10 to 14 carbon atoms. When the alkyl group is branched, it preferably has 1 to 3 carbon atoms and 1 to 5 unsubstituted phenyl groups.

Examples of alkenyl groups include alkenyl groups having 2 to 30 carbon atoms, which may be linear, branched or cyclic. Specifically, a vinyl group etc. are mentioned, for example.
The alkenyl group preferably has 2 to 25 carbon atoms, more preferably 2 to 20 carbon atoms.

The fluorinated alkyl group includes a fluorinated alkyl group having 1 to 30 carbon atoms, and may be linear, branched, or cyclic. Specific examples include groups in which one or more hydrogen atoms in the aforementioned alkyl group are substituted with fluorine atoms, such as a methyl fluoride group and an ethyl fluoride group.
The number of carbon atoms in the fluorinated alkyl group is preferably 1-25, more preferably 2-20.
When the fluorinated alkyl group is linear, it preferably has 1 to 4 carbon atoms.

The aryl group as a substituent includes the same aryl group as the aryl group bonded to the surface of the carrier according to the present embodiment, but preferably has 6 to 12 carbon atoms. Specific examples include a phenyl group and a naphthyl group.
Examples of the fluorinated aryl group include groups in which one or more hydrogen atoms in the aryl group as a substituent are substituted with a fluorine atom. Examples include a fluorinated naphthyl group having 1 to 7 atoms.

Among the above, when the aryl group bonded to the surface of the carrier according to this embodiment has a substitution value, the substituent is an alkyl group, a fluorinated alkyl group, a phenyl group, a fluorinated phenyl group, and a group consisting of a fluorine atom. It is preferable to include one or more more selected.
Further, the substituents may be one kind and two or more, or two or more kinds and two or more.
For example, when the aryl group bonded to the surface of the carrier according to the present embodiment is a phenyl group, the phenyl group may have a structure having two fluorinated methyl groups, or the five hydrogen atoms of the phenyl group may be A structure in which four of them are substituted with fluorine atoms and the remaining one is substituted with a fluorinated phenyl group may be employed.
Furthermore, the aryl group bonded to the surface of the carrier according to the present embodiment is preferably a condensed ring group having 2 to 6 substituted phenyl groups and unsubstituted benzene rings; triphenylmethyl group, carbon A phenyl group having any one substituent selected from the group consisting of a linear unsubstituted alkyl group having a number of 10 to 14 and a linear fluorinated alkyl group having 1 to 4 carbon atoms and an unsubstituted It is more preferably a condensed ring group having 4 to 5 benzene rings; consisting of a linear unsubstituted alkyl group having 11 to 13 carbon atoms and a linear fluorinated alkyl group having 2 to 3 carbon atoms A condensed ring group having four unsubstituted benzene rings and a phenyl group having any one substituent selected from the group is even more preferable.

More specifically, the aryl group that binds to the surface of the carrier according to this embodiment is preferably one or more of the groups represented by (1) to (8) below. In (1) to (8), * represents a binding portion to the surface of the carrier according to this embodiment. The aryl group is more preferably one or more of the groups represented by (1) to (3) and (5) below, and represented by (2), (3) and (5) below. more preferably any one or more of the groups.

The aryl group possessed by the carrier according to this embodiment may be of one type, or may be of two or more types.
In addition, the carrier according to this embodiment may have one aryl group, or may have two or more aryl groups. The presence of an aryl group possessed by the carrier can be confirmed and quantified by infrared spectroscopy.

(Method for introducing aryl group to carrier surface)
The method of introducing an aryl group onto the surface of the carrier (method of chemical modification) according to this embodiment is not particularly limited.
For example, using carbon black as a carrier according to the present embodiment, using an aromatic compound having one primary amino group as a precursor, via a diazotization reaction, to an aromatic ring or the like on the surface of the carbon black through a nucleophilic reaction. can form a chemical bond.

Aromatic compounds include benzene and condensed ring compounds containing two or more benzene rings, and condensed ring compounds containing two or more benzene rings are condensed ring compounds having 2 to 6 benzene rings. is preferred.
Specific examples include aniline, aminonaphthalene, aminoanthracene, aminophenanthrene, aminopyrene and the like.

The aromatic compound having one primary amino group may further have a substituent other than the primary amino group. Examples of substituents include alkyl groups, alkenyl groups, fluorinated alkyl groups, aryl groups, fluorinated aryl groups, and fluorine atoms, and the substituents may further have a substituent. The details of the substituents that the aromatic compound having one primary amino group can have are as follows: It is the same as the substituent to be obtained, and the preferred embodiments are also the same.

More specifically, the aromatic compound having one primary amino group is preferably any one or more of the compounds represented by (11) to (18) below.

(Carrier)
The carrier according to this embodiment contains carbon.
Since carbon usually has conductivity, the carrier according to the present embodiment is a conductive carrier.
Carbon is not limited as long as it is a conductive material that can be used as a gas diffusion layer in an electrode provided in an apparatus for reducing carbon dioxide, and carbon black (furnace black, acetylene black, ketjen black, medium thermal carbon black, etc.), activated carbon, graphite, carbon nanotube, carbon nanofiber, carbon nanohorn, graphene nanoplatelet, nanoporous carbon, etc. Among them, carbon black is preferred. Furthermore, the structure is preferably a porous structure. Carbon with a porous structure includes porous carbon materials typified by graphene.

The shape, size, grade, etc. of the carbon black are not limited, but the DBP oil absorption (dibutyl phthalate oil absorption) is preferably 50 to 500 ml/100 g, more preferably 100 to 300 ml/100 g. , 100 to 200 ml/100 g. Also, the primary particle size is preferably 5 to 200 nm, more preferably 10 to 100 nm, even more preferably 10 to 50 nm.
The DBP oil absorption of carbon black can be determined according to JIS K 6217-4:2001 (Determination of oil absorption), and the primary particle size can be determined, for example, by laser diffraction particle size distribution measurement.
Carbon black may be a commercial product, for example, Vulcan (registered trademark) XC-72 (manufactured by Cabot), Denka Black HS-100 (manufactured by Denka), Ketjen Black EC-600JD (manufactured by Lion Specialty Chemicals). , Conductex-7055 Ultra (manufactured by Birla Carbon) and the like.

The carbon dioxide reduction catalyst additive according to the first embodiment preferably has an aryl group on its surface and is composed of a carrier containing carbon.

[Additive for carbon dioxide reduction catalyst according to the second embodiment]
The carbon dioxide reduction catalyst additive according to the second embodiment has a carrier containing carbon, and has a water vapor adsorption amount at 25 ° C. and a water vapor pressure of 2.2 kPa at the same temperature and a water vapor pressure of 3.1 kPa. The ratio to volume is less than 0.5.
In other words, the water vapor adsorption amount at 25° C. and water vapor pressure of 2.2 kPa (unit: cm ³ (STP)/g) is a, and the water vapor adsorption amount at 25° C. and water vapor pressure of 3.1 kPa (unit: cm ³ (STP)/ When g) is defined as b, a/b is less than 0.5.
The water vapor adsorption amount a at 25°C and a water vapor pressure of 2.2 kPa is strongly affected by the number of adsorbed molecules in the monomolecular layer, which corresponds to the interaction force between the outermost surface of the additive and the adsorbed water molecules. means adsorption capacity. The water vapor adsorption amount b at 25° C. and water vapor pressure of 3.1 kPa is strongly affected by the number of adsorbed molecules corresponding to the adsorption capacity of the additive, and therefore corresponds to the surface area per unit mass of the additive. The ratio (a/b) of the water vapor adsorption amount a to the adsorption amount b represents the surface hydrophilicity of the additive.
a/b<0.5 means that the additive for carbon dioxide reduction catalyst exhibits high hydrophobicity and high electrical conductivity. A/b is preferably as small as possible and may be 0, but is usually greater than 0.01.
a/b is preferably 0.5 or less, more preferably 0.4 or less, still more preferably 0.35 or less, still more preferably 0.3 or less, and 0.4 or less. It is more preferably 2 or less, and even more preferably 0.15 or less.

The ratio (a/b) of the water vapor adsorption amount a of the carbon dioxide reduction catalyst additive at 25° C. and water vapor pressure of 2.2 kPa to the water vapor adsorption amount b at the same temperature and water vapor pressure of 3.1 kPa is less than 0.5. The method is not particularly limited. For example, a/b<0.5 can be achieved by chemically modifying the surface of a carbon-containing carrier with aryl groups.

From the above, the carbon dioxide reduction catalyst additive according to the first embodiment has a ratio of the water vapor adsorption amount at 25 ° C. and a water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa. is preferably less than 0.5.
In addition, in the carbon dioxide reduction catalyst additive according to the second embodiment, the carrier containing carbon preferably has an aryl group on the surface of the carrier.

In addition, the carbon dioxide reduction catalyst additive in the technology of the present disclosure is preferably coated with an ionomer, which will be described later. By coating the carbon dioxide reduction catalyst additive with the ionomer, it becomes possible to more effectively exert the hydrophobizing action on the catalyst also present in the ionomer, and the electrolysis efficiency can be improved.

<Catalyst layer>
The catalyst layer according to the first embodiment includes an additive having an aryl group on the surface and a carrier containing carbon, and a catalyst comprising a carrier containing carbon and supporting inorganic fine particles or a metal complex. .
The catalyst layer according to the second embodiment has a carrier containing carbon, and the ratio of the water vapor adsorption amount at 25° C. and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa is 0. less than 0.5, and a catalyst comprising a carrier containing carbon and supporting inorganic fine particles or a metal complex.

The catalyst layer according to the first embodiment and the catalyst layer according to the second embodiment may be collectively referred to simply as "the catalyst layer according to this embodiment".
Further, the "additive having an aryl group on the surface and a carrier containing carbon" contained in the catalyst layer according to the first embodiment may be referred to as the additive according to the first embodiment. . "The ratio of the water vapor adsorption amount at 25°C and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa is less than 0.5, which is contained in the catalyst layer according to the second embodiment. "agent" may be referred to as an additive according to the second embodiment.
Further, the additive according to the first embodiment and the additive according to the second embodiment may be collectively referred to simply as "the additive according to this embodiment".

In the catalyst layer according to this embodiment, the catalyst species contained in the catalyst layer is not particularly limited. Although the catalyst layer according to the present embodiment is preferably used as a catalyst layer containing a carbon dioxide reduction catalyst, it is also suitable for various catalyst layers where it is desired to avoid adverse effects caused by the catalyst layer being submerged in water, coming into contact with water vapor, depositing salts, and the like. can be used for

(Additive)
The additive according to the first embodiment is the same as the additive for the carbon dioxide reduction catalyst according to the first embodiment, and preferred aspects are also the same.
The additive having an aryl group on the surface and a carrier containing carbon can spread not only on the surface but also from the inside of the catalyst layer to the entire catalyst layer without impairing the electrical conductivity of the catalyst layer containing the additive, Since the catalyst layer can be hydrophobized, it is possible to suppress functional deterioration of the catalyst contained in the catalyst layer.

In the additive according to the second embodiment, "the ratio of the water vapor adsorption amount at 25°C and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa" is the second embodiment. It is the same as "ratio (a/b) of water vapor adsorption amount a at 25 ° C. and water vapor pressure 2.2 kPa to water vapor adsorption amount b at the same temperature and water vapor pressure 3.1 kPa" in the carbon dioxide reduction catalyst additive according to be.
Also in the additive according to the second embodiment, the smaller the a/b, the higher the hydrophobicity and the higher the electrical conductivity. A/b is preferably as small as possible and may be 0, but is usually greater than 0.01.
a/b is preferably 0.5 or less, more preferably 0.4 or less, still more preferably 0.35 or less, still more preferably 0.3 or less, and 0.4 or less. It is more preferably 2 or less, and even more preferably 0.15 or less.
By including the additive according to the second embodiment in the catalyst layer, the catalyst layer is hydrophobized not only on the surface but also from the inside of the catalyst layer to the entire catalyst layer without impairing the electrical conductivity of the catalyst layer. Therefore, deterioration of the function of the catalyst contained in the catalyst layer can be suppressed.

The additive according to the first embodiment and the additive according to the second embodiment can make the catalyst layer containing these additives hydrophobic not only on the surface but also from the inside to the whole. and maintain electrical conductivity. Therefore, it can be suitably used as an additive for various catalyst layers in which it is desired to avoid the harmful effects of the catalyst layer being inundated with water, contact with water vapor, salt deposition, and the like.

(catalyst)
The catalyst layer according to the present embodiment contains a catalyst that contains carbon and is made of a carrier on which inorganic fine particles or a metal complex is supported.
In the catalyst of the technology of the present disclosure, the component that exhibits catalytic action is an inorganic fine particle or a metal complex supported on a carrier. A carrier on which a catalyst source is supported is referred to as a "catalyst".

[Carrier]
As the carrier, the carrier according to the present embodiment contained in the additive for carbon dioxide reduction catalyst according to the first embodiment can be used, and carbon black is preferably included.
Preferred aspects of carbon black are the same as the preferred aspects of carbon black described in the description of the carbon dioxide reduction catalyst additive according to the first embodiment.

[Inorganic fine particles, metal complexes]
The carrier according to this embodiment supports inorganic fine particles or a metal complex as a catalyst source.
The inorganic fine particles and the metal complex are not particularly limited as long as they are components exhibiting catalytic activity. In the technology of the present disclosure, inorganic fine particles mean metals and inorganic compounds having an average particle size of 1 to 100 nm as measured by photographic observation using a scanning electron microscope or the like.
For example, when the catalyst source is used in the fuel cell catalyst layer, platinum, gold, nickel, ruthenium, rhodium, etc. can be used as the inorganic fine particles, and the metal complexes include nickel complexes, cobalt complexes, iron complexes, Manganese complexes, zinc complexes, and the like can be used.
Further, for example, when the catalyst source is used in the catalyst layer for secondary battery electrodes, platinum, gold, nickel, iridium, metal oxides, etc. can be used as the inorganic fine particles, and the metal complexes include nickel complexes, Cobalt complexes, iron complexes, manganese complexes, zinc complexes, and the like can be used.

When the catalyst layer is used as a catalyst layer for carbon dioxide reduction, the inorganic fine particles and the metal complex preferably use a catalyst source that has the action of generating at least carbon monoxide through a reduction reaction.
Specifically, the inorganic fine particles for carbon dioxide reduction are the group consisting of gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride. It is preferable that the fine particles are more selected. Only one inorganic fine particle may be used, or two or more may be used in combination.
Among the above, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the material of the inorganic fine particles is preferably silver, gold, zinc, tin, copper and bismuth, more preferably silver, gold, copper and tin. Copper is more preferred.

The average particle size of the inorganic fine particles as a catalyst source for carbon dioxide reduction is preferably 65 nm or less, preferably 60 nm or less, and preferably 50 nm or less from the viewpoint of the reaction rate of the carbon dioxide reduction reaction. It is preferably 40 nm or less, preferably 30 nm or less. The lower limit of the average particle diameter is not limited, but it is preferably 1 nm or more, more preferably 5 nm or more, from the standpoint of ease of production.
The average particle diameter can be measured by photographic observation using a scanning electron microscope or the like.

A metal complex as a catalyst source for carbon dioxide reduction is a metal complex in which a ligand is coordinated to a metal or an ion of the metal, and the metal ions include copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum.
Among the above, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the metal is preferably nickel, cobalt, iron, copper, zinc and manganese, more preferably nickel, cobalt, iron and copper, and further nickel, cobalt and iron. preferable. The metal complex may contain only one kind of metal or ions of the metal, or may contain two or more kinds thereof.
The type of ligand is not particularly limited, and examples thereof include phthalocyanine complexes, porphyrin complexes, pyridine complexes, metal-supporting covalent triazine structures, and metal organic structures. Among them, preferred are phthalocyanine complexes, porphyrin complexes, pyridine complexes and metal-supported covalent triazine structures, more preferred are phthalocyanine complexes, porphyrin complexes and metal-supported covalent triazine structures, and porphyrin complexes and metal-supported covalent triazine structures. Body is more preferred. The metal complex may contain only one ligand, or may contain two or more ligands.

As described above, the catalyst layer for carbon dioxide reduction according to the present embodiment is
an additive according to the present embodiment (additive for a carbon dioxide reduction catalyst according to the present embodiment);
A catalyst containing carbon and made of a carrier on which inorganic fine particles or a metal complex is supported,
The inorganic fine particles are fine particles selected from the group consisting of gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride; the metal complex; is preferably a catalyst layer composed of a metal selected from the group consisting of copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum, or a metal complex in which ions of the metal are coordinated.

The inorganic fine particles and metal complexes are supported on the carrier according to the present embodiment by carrying out known methods such as vapor deposition, deposition, adsorption, deposition, adhesion, welding, physical mixing, and spraying.

Also, the catalyst in the technology of the present disclosure is preferably coated with an ionomer, which will be described later. By coating the catalyst with an ionomer, an ion-conducting channel is easily formed between the coated catalyst and the solid electrolyte described later, ions generated by the reaction are easily transferred, and the electrolysis efficiency can be improved.

[Ionomer]
The catalyst layer may further contain an ionomer.
The ionomer functions as a binder resin in the catalyst layer, is a matrix resin (continuous phase) capable of dispersing and immobilizing the additive and the catalyst according to the present embodiment, and transfers ions generated by electrolysis to transfer CO ₂ It also has the function of improving electrolysis efficiency. Moreover, the ionomer is preferably a polymer electrolyte from the viewpoint of improving conductivity. More preferably, the polymer electrolyte is an ion exchange resin. The ion exchange resin may be a cation exchange resin or an anion exchange resin, but is preferably an anion exchange resin.
In particular, when an anion exchange resin is used, the anion exchange resin itself has a carbon dioxide adsorption capacity, and the electrolysis efficiency of carbon dioxide can be greatly improved together with the ease of ion transfer of the ion exchange resin. It becomes possible.

Examples of the cation exchange resin include a fluororesin having a sulfone group and a styrene-divinylbenzene copolymer having a sulfone group. Commercially available products can also be used, and examples thereof include Nafion (manufactured by Chemours), Aquivion (manufactured by Solvay Specialty Polymers), DIAION (manufactured by Mitsubishi Chemical), Fumasep (manufactured by FUMATECH) and the like.
Anion exchange resins include, for example, resins having one or more ion exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. Commercially available products can also be used. made) and the like.

From the viewpoint of improving electrical conductivity, the anion exchange resin preferably has a base point density of 2.0 to 5.0 mmol/cm ³ in a dry state, preferably 2.5 mmol/cm 3 or more, 4.5 mmol/cm ³ or more. /cm ³ , more preferably 2.9 mmol/cm ³ or more and less than 4.5 mmol/cm ³ .
The base point density of the anion exchange resin can be obtained from the integrated value of the signal when performing ¹ H NMR measurement on the anion exchange resin.
Regarding the anion exchange resin, the dry state means that the content of free water in the anion exchange resin is 0.01 g or less per 1 g of the resin. The ion exchange resin can be brought to a dry state.

When the cathode (cathode) according to the present embodiment is used in an ion-exchange membrane-electrode assembly and a solid electrolyte type electrolytic device described later, from the viewpoint of improving conductivity, the ionomer is the same as the solid electrolyte (ion-exchange membrane). It is preferable to use a resin.

The content of the additive according to the present embodiment in the catalyst layer is preferably 1 to 90% by mass, more preferably 5 to 70% by mass, from the viewpoint of improving the hydrophobicity of the catalyst layer and suppressing deterioration of the catalytic function. %, more preferably 10 to 50% by mass.
The content of the catalyst according to the present embodiment in the catalyst layer is preferably 5 to 90% by mass, more preferably 10 to 80% by mass, from the viewpoint of further improving the production efficiency of synthesis gas containing CO. More preferably, 15 to 60% by mass is even more preferable.

<Cathode>
The cathode (cathode) according to this embodiment has the catalyst layer for carbon dioxide reduction according to this embodiment described above and a gas diffusion layer.
The cathode (cathode) according to the present embodiment is provided with a catalyst layer containing the additive according to the present embodiment, so that the carbon dioxide reduction reaction in the catalyst layer is not hindered, and the synthesis gas containing CO is stably produced. be able to. Therefore, the electrolysis efficiency of the carbon dioxide electrolytic reduction reaction is excellent.

[Gas diffusion layer]
Gas diffusion layers include, for example, carbon paper or non-woven fabrics, or metal mesh. Examples thereof include graphite carbon, vitreous carbon, titanium, and SUS steel.

<Ion exchange membrane-electrode assembly>
The ion exchange membrane-electrode assembly according to this embodiment has the cathode according to this embodiment, a solid electrolyte, and an anode.
Since the ion exchange membrane-electrode assembly according to the present embodiment includes a cathode having a catalyst layer containing the additive according to the present embodiment, the carbon dioxide reduction reaction in the catalyst layer is not hindered, and CO can be stably can produce synthesis gas containing Therefore, the electrolysis efficiency of the carbon dioxide electrolytic reduction reaction is excellent.

FIG. 1 is a schematic diagram of an ion-exchange membrane-electrode assembly preferably used in this embodiment. FIG. 1 shows an ion exchange membrane-electrode assembly 50 having a gas diffusion layer 10, a catalyst layer 20, a solid electrolyte 30, and an anode 40. FIG. The catalyst layer 20 includes an ionomer 22, a plurality of catalysts 24 according to the present embodiment, and a plurality of additives (additives for a carbon dioxide reduction catalyst according to the present embodiment) 26 according to the present embodiment. The combination of the gas diffusion layer 10 and the catalyst layer 20 constitutes the cathode according to this embodiment.
As shown in FIG. 1, carbon dioxide (CO ₂ ) is supplied to the catalyst layer 20 through the gas diffusion layer 10, and carbon monoxide (CO) is produced by a reduction reaction.
Hereinafter, description will be made while omitting reference numerals in FIG.

[Solid electrolyte]
The ion exchange membrane-electrode assembly according to this embodiment has a solid electrolyte.
A polymer membrane can be used as the solid electrolyte. Various ionomers can be used as the polymer, and it may be a cation exchange resin or an anion exchange resin, but an anion exchange resin is preferred. That is, the solid electrolyte is preferably an anion exchange membrane. Further, it is more preferable to use the same anion exchange resin as the ionomer used in the catalyst layer described above.
As the solid electrolyte, a product commercially available as a cation exchange membrane or an anion exchange membrane may be used.
Further, when an anion exchange membrane is used as the solid electrolyte, the base point density in a dry state is preferably 0.5 to 5.0 mmol/cm ³ , 2.5 mmol/cm ³ or more, 4 It is more preferably less than 0.5 mmol/cm ³ , and even more preferably 2.9 mmol/cm ³ or more and less than 4.5 mmol/cm ³ .

Examples of the cation exchange membrane include strongly acidic cation exchange membranes in which sulfone groups are introduced into a fluororesin matrix, Nafion 117, Nafion 115, Nafion 212, Nafion 350 (manufactured by Chemrous), and styrene-divinylbenzene copolymer matrix with sulfone groups. The introduced strongly acidic cation exchange membrane, Neosepta CSE (manufactured by Astom) and the like can be used.
Examples of the anion-exchange membrane include anion-exchange membranes having one or more ion-exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. mentioned. Specific examples include Neocepta (registered trademark) ASE, AHA, ACS, AFX (manufactured by Astom), Celemion (registered trademark) AMVN, DSVN, AAV, ASVN, and AHO (manufactured by Asahi Glass Co., Ltd.).

The reduction reaction of carbon dioxide at the cathode (cathode) according to this embodiment differs depending on the type of solid electrolyte. When a cation exchange membrane is used as the solid electrolyte, reduction reactions of the following reaction formulas (1) and (2) occur, and when an anion exchange membrane is used as the solid electrolyte, the following reaction formula (3) and the reduction reaction of (4) occurs.

CO ₂ +2H ⁻ +2e ⁻ →CO+H ₂ O (1)
2H ⁺ +2e ⁻ →H ₂ (2)
H ₂ O+CO ₂ +2e ⁻ →CO+2OH ⁻ (3)
2H ₂ O+2e ⁻ →H ₂ +2OH ⁻ (4)

〔anode〕
The oxidation reaction at the anode differs depending on the type of solid electrolyte. When the cation exchange membrane is used as the solid electrolyte, the oxidation reaction of the following reaction formula (5) occurs, and when the anion exchange membrane is used as the solid electrolyte, the oxidation reaction of the following reaction formula (6) occurs. get up.

2H ₂ O→O ₂ +4H ⁺ +4e ⁻ (5)
4OH ⁻ →O ₂ +2H ₂ O+4e ⁻ (6)

An anode is a gas diffusion electrode that includes a gas diffusion layer.
The gas diffusion layer includes, for example, metal mesh. Electrode materials for the anode include, for example, Ir, IrO ₂ , Ru, RuO ₂ , Co, CoOx, Cu, CuOx, Fe, FeOx, FeOOH, FeMn, Ni, NiOx, NiOOH, NiCo, NiCe, NiC, NiFe, NiCeCoCe , NiLa, NiMoFe, NiSn, NiZn, SUS, Au, Pt.

<Solid electrolyte type electrolytic device>
The solid electrolyte type electrolysis device according to this embodiment includes the cathode according to the above-described embodiment, an anode forming a pair of electrodes with the cathode, and a solid electrolyte interposed between the cathode and the anode in a contact state. , and a voltage application unit that applies a voltage between the cathode and the anode.
Since the solid electrolyte type electrolysis device according to the present embodiment includes a cathode (cathode) having a catalyst layer containing the additive according to the present embodiment, the carbon dioxide reduction reaction in the catalyst layer is not hindered and is stable. Syngas containing CO can be produced. Therefore, the electrolysis efficiency of the carbon dioxide electrolytic reduction reaction is excellent.

FIG. 2 is a schematic diagram of a solid electrolyte type electrolytic device that is preferably used in this embodiment.
FIG. 2 shows a cathode (cathode) 200 constituting an electrode according to this embodiment, an anode (anode) 400 constituting a pair of electrodes with the cathode 200, and a contact state between the cathode 200 and the anode 400. A solid electrolyte electrolyzer 800 is shown having an intervening solid electrolyte 300 and a voltage application section 700 that applies a voltage between cathode 200 and anode 400 .
The solid electrolyte type electrolytic device 800 shown in FIG. 2 further has a cathode collector plate 100 , an anode collector plate 500 and an electrolytic solution 600 .
The electrode according to the present embodiment described above is used as the cathode 200 . Moreover, the solid electrolyte 300 is the same as the solid electrolyte 30 in FIG. 1, and the solid electrolyte 300 is preferably an anion exchange membrane. Anode 400 is the same as anode 40 in FIG.
The details of the cathode 200, the solid electrolyte 300, and the anode 400 are as described above.
Hereinafter, each element other than the cathode 200, the solid electrolyte 300, and the anode 400 will be described without reference numerals.

[Cathode current collector]
Examples of cathode current collectors (cathode current collectors) include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass. Copper is preferred from the viewpoint of As for the shape of the cathode current collector plate, when the material is a metal material, for example, metal foil, metal plate, metal thin film, expanded metal, punched metal, foamed metal, and the like can be mentioned.

The cathode current collector plate may be provided with a gas supply hole for supplying a raw material gas containing carbon dioxide to the cathode and a gas recovery hole for collecting a produced gas containing carbon monoxide. By having the gas supply hole and the gas recovery hole, it is possible to uniformly and efficiently feed the raw material gas into the cathode and discharge the generated gas (including the unreacted raw material gas). Only one or two or more gas supply holes and gas recovery holes may be provided independently. Further, the shape, location, size, etc. of the gas supply hole and the gas recovery hole are not limited and can be set as appropriate. In addition, if the cathode current collector plate is permeable, gas supply holes and gas recovery holes are not necessarily required.
If the cathode has a role of transferring electrons, the cathode current collector plate is not necessarily required.

[Anode current collector]
The anode current collector (anode current collector) is preferably electrically conductive to receive electrons from the anode and rigid to support the anode. From this point of view, metal materials such as titanium (Ti), copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass can be suitably used for the anode current collector plate.

The anode current collector plate may be provided with a gas flow path for sending a raw material gas (such as H ₂ O) to the anode. Since the anode current collector plate has the gas flow path, the raw material gas can be fed to the anode uniformly and efficiently. Note that the number, shape, location, size, etc. of the gas flow paths are not limited and can be set as appropriate.

[Voltage application part]
The voltage applying unit applies voltage between the cathode and the anode by applying voltage to the cathode current collector and the anode current collector. Here, since both current collector plates are conductors, they supply electrons to the cathode and receive electrons from the anode. In addition, a control section (not shown) may be electrically connected to the voltage application section in order to apply an appropriate voltage.

[Electrolyte]
The electrolytic solution is preferably an aqueous solution having a pH of 5 or higher.
For example, carbonate aqueous solution, bicarbonate aqueous solution (e.g., _KHCO3 aqueous solution), sulfate aqueous solution, borate aqueous solution, sodium hydroxide, potassium hydroxide aqueous solution, sodium chloride aqueous solution, and the like.

(Reactive gas supply unit)
The solid electrolyte type electrolytic device according to this embodiment may be provided with a reaction gas supply section (not shown) outside the solid electrolyte type electrolytic device. That is, the reaction gas CO ₂ may be supplied to the catalyst layer provided in the cathode, or the reaction gas may be supplied to the gas supply hole from the reaction gas supply unit through a pipe (not shown) or the like, or the cathode current collector may be supplied. The plate may be provided so that the reaction gas is sprayed onto the surface opposite to the contact surface with the cathode. Moreover, it is preferable from an environmental point of view to use the factory exhaust gas discharged from the factory as the reaction gas.

[CO generation method]
Next, a CO production method using the solid electrolyte type electrolysis device according to this embodiment will be described.
First, CO ₂ , which is a reaction gas as a raw material, is supplied in a gaseous state to the solid electrolyte type electrolysis device by a reaction gas supply unit (not shown). At this time, CO ₂ is supplied to the cathode through, for example, gas supply holes provided in the cathode current collector plate.
Next, the CO ₂ supplied to the cathode comes into contact with the catalyst layer of the cathode, and when a cation exchange membrane is used as the solid electrolyte, the above reaction formula (1) and reaction formula (2) ) occurs, and when an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the above-described reaction formulas (3) and (4) occur, so that at least CO and H ₂ are included. Only syngas is produced.
Next, the generated synthesis gas containing CO and H ₂ is sent to a gas recovery device (not shown) through, for example, a gas recovery hole provided in the cathode current collector plate, and recovered for each predetermined gas. It will happen.

The technology of the present disclosure will be specifically described below with reference to examples, but the technology of the present disclosure is not limited to these examples.

<Production of additives>
[Example 1]
An ethanol dispersion containing 0.5 g of carbon black having an average particle size of 30 nm was irradiated with ultrasonic waves for 10 minutes, and then the dispersion was allowed to stand in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Subsequently, 8.3 mL of 0.5 mol/L sodium nitrite aqueous solution was added to the dispersion. After adding 4 mmol of 4-tritylaniline [compound represented by formula (11)] to the dispersion, 2 mL of hydrochloric acid was further added and the mixture was stirred at 15° C. for 5 hours or more. After neutralizing the dispersion by adding a sodium hydroxide solution, the resulting slurry was washed with distilled water, the solid matter was recovered by a centrifuge, and the solid matter was vacuum-dried at 60°C overnight. The additive of Example 1 was used.
The average particle size of carbon black was determined by laser diffraction particle size distribution measurement.

[Examples 2 to 8]
Additives of Examples 2 to 8 were produced in the same manner, except that the basic organic compounds shown in Tables 1 and 2 were used instead of 4-tritylaniline in the production of the additive of Example 1. .
The basic organic compounds used in the production of the additives of Examples 2 to 8 are the compounds represented by formulas (12) to (18) described above.

[Comparative Example 1]
In Comparative Example 1, carbon black with an average particle size of 30 nm was used as an additive.

[Comparative Example 2]
In Comparative Example 2, polytetrafluoroethylene (PTFE, manufactured by Nanoshel, trade name “Polytetrafluoroethylene Nanopowder”) having an aerodynamic particle size of 30 to 50 nm was used as an additive.

[Comparative Examples 3 and 4]
In Comparative Examples 3 and 4, no additive was used.

<Production of catalyst>
[Examples 1 to 7 and Comparative Examples 1 to 3]
The catalyst used in Examples 1-7 and Comparative Examples 1-3 is the same. It was manufactured as follows.
In a beaker, 0.1 g of carbon black carrier (carrier according to the present embodiment) was mixed with 100 mL of ethanol, and the obtained ethanol dispersion was irradiated with ultrasonic waves for 10 minutes. After that, the dispersion was allowed to stand in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Thereafter, 11.7 mL of 0.1 mol/L AgNO ₃ solution and 1 mL of 2.3 mol/L sodium phosphinate solution were mixed and stirred at 15° C. for 16 hours to reduce silver nitrate. After completion of the reaction, the resulting slurry was washed with distilled water, the solid matter was recovered using a centrifuge, and the solid matter was vacuum-dried overnight at 60 ° C., and the catalysts of Examples 1 to 7 and Comparative Examples 1 to 3 A powder was obtained. The obtained catalyst was carbon black carrying Ag particles as a catalyst source, and the mass of Ag particles carried was 40 parts by mass with respect to 100 parts by mass of carbon black not carrying Ag particles.

[Example 8 and Comparative Example 4]
The catalyst used in Example 8 and Comparative Example 4 is the same. It was manufactured as follows.
In a beaker, 0.4 g of carbon black support (support according to the present embodiment), 1.1 mmol of pentaethylenehexamine and 0.7 mmol of nickel (II) chloride hexahydrate were mixed in 15 mL of ethanol, and the resulting ethanol The dispersion was irradiated with ultrasonic waves for 10 minutes. Thereafter, the ethanol dispersion was dried by heating to evaporate the ethanol, and the obtained mixture was heated at 900° C. for 30 seconds or more in an inert gas using an electric furnace to bake it. Thereafter, the product was washed with an aqueous solution of sulfuric acid, the solid matter was recovered by a suction filter, and the solid matter was vacuum-dried at 60° C. overnight to obtain a catalyst powder supporting a Ni complex. This catalyst powder was used as the catalyst powder of Example 8 and Comparative Example 4.
In the obtained catalyst, the mass of Ni supported was 1 part by mass with respect to 100 parts by mass of carbon black on which no Ni complex was supported.

<Solid electrolyte type electrolytic device>
[Example 1]
43 mg of the obtained catalyst powder was dispersed in ethanol, and 12 mg of an ionomer as an ionomer containing 5 mg of the additive of Example 1 was added to the dispersion. When the anion exchange resin was subjected to ¹ H NMR measurement in a dry state, the base point density was calculated to be 2.8 mmol/cm ³ from the integral value of the signal. The anion exchange resin is a fluorine-based resin having an aromatic ring as a base material and a quaternary ammonium group (quaternary alkylamine group) as a side chain attached to the main chain. .

After mixing, the dispersion was irradiated with ultrasonic waves for 10 minutes, and left standing in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. A carbon paper was coated with the dispersion using a spray coater to form a cathode. The cathode has a coating film of the dispersion liquid as a catalyst layer and carbon paper as a gas diffusion layer.
An anion exchange membrane with a film thickness of about 30 μm (basic point density 2.8 mmol/cm ³ ), a carbon anode supporting iridium oxide (manufactured by Dioxide Materials), and the cathode are bonded together to form an ion exchange membrane-electrode assembly. and
The anode (positive electrode) was structured to be in contact with the electrolytic solution (0.5 mol/L KHCO ₃ aqueous solution) bath.

[Examples 2 to 7 and Comparative Examples 1 to 2]
In the production of the solid electrolyte type electrolytic device of Example 1, the additive was changed from the additive of Example 1 to one of the additives of Examples 2 to 7 and Comparative Examples 1 and 2 in the same manner. , Examples 2 to 7 and Comparative Examples 1 to 2 were manufactured.

[Example 8]
In the production of the solid electrolyte type electrolytic device of Example 1, the additive was changed from the additive of Example 1 to the additive of Example 8, and the ionomer was changed from the ionomer of Example 1 to Nafion (manufactured by Chemours ), a solid electrolyte type electrolytic device of Example 8 was manufactured in the same manner as above.

[Comparative Example 3]
A solid electrolyte type electrolytic device of Comparative Example 3 was manufactured in the same manner as in the manufacturing of the solid electrolyte type electrolytic device of Example 1, except that no additive was added.

[Comparative Example 4]
A solid electrolyte type electrolytic device of Comparative Example 4 was manufactured in the same manner as in the manufacturing of the solid electrolyte type electrolytic device of Example 8, except that no additive was added.

<Evaluation of Solid Electrolyte Type Electrolytic Device>
[Examples 1 to 7 and Comparative Examples 1 to 3]
Using the solid electrolyte type electrolyzers of Examples 1 to 7 and Comparative Examples 1 to 3, pure CO ₂ was supplied to the cathode, and the solid electrolyte type electrolyzer was heated to 50°C. is −2.6 V with respect to the anode, or a constant current of −1 A/cm ² is applied to electrolyze CO ₂ to generate CO. CO generation current density [mA/cm ² ] and CO selectivity [%] were measured. Voltage [V] was measured instead of current when a constant current was applied.
Table 1 shows the results.

<Evaluation of Solid Electrolyte Type Electrolytic Device>
[Example 8 and Comparative Example 4]
Using each of the solid electrolyte electrolysis devices of Example 8 and Comparative Example 4, pure CO ₂ was supplied to the cathode, and the potential applied to the cathode was −1.8 V with respect to the silver/silver chloride reference electrode under room temperature conditions. , CO ₂ was electrolyzed to measure the CO generation current density [mA/cm ² ] when generating CO.
Table 2 shows the results.

As can be seen from Tables 1 and 2, when using various aromatic amine compounds as raw materials and using additives obtained by chemically modifying the carrier surface with aryl groups (Examples 1 to 7), -1A/ It showed a relatively low required voltage and high CO selectivity at high current application of cm ² . Moreover, Example 8 showed a relatively high current density.
On the other hand, Comparative Example 1 using an additive whose carrier surface is not chemically modified with an aryl group, Comparative Example 2 using an insulating hydrophobic polymer as an additive, and Comparative Example 3 using no additive. In , the required voltage increased and the CO selectivity decreased. Comparative Example 4, in which no additive was used, showed a relatively low current density.

<Water vapor adsorption amount of additive>
For the additives of Examples 1 to 4, 6, 7 and Comparative Example 1, water vapor adsorption amount (a) at 25 ° C. and water vapor pressure of 2.2 kPa, and water vapor adsorption amount (b) at 25 ° C. and water vapor pressure of 3.1 kPa. was measured by BELSORP-max (manufactured by Bell Japan Co., Ltd.), and the ratio (a/b) of the two is shown in Table 3. In the measurement, 0.2 to 0.3 g of the additive sample was heated at 120° C. for 5 hours or more under vacuum conditions to remove the adsorbed gas on the surface in advance, and then water vapor was introduced under the conditions of 25° C. to obtain each water vapor. The amount of adsorption at pressure was determined.

Also, FIG. 3 shows a graph in which the relative water vapor adsorption amount is plotted against the relative pressure. Here, in FIG. 3, the relative pressure on the vertical axis means the value obtained by dividing each water vapor pressure by the saturated water vapor pressure (3.1 kPa) at 25.degree. The relative water vapor adsorption amount on the horizontal axis means the value (a/b) obtained by dividing the water vapor adsorption amount (a) at each relative pressure by the water vapor adsorption amount (b) at the saturated water vapor pressure at 25°C. Expressed as a formula, it is as follows.
Relative pressure = (water vapor pressure at each measurement point) / (saturated water vapor pressure [= 3.1 kPa])
Relative water vapor adsorption amount = (water vapor adsorption amount at each measurement point) / (water vapor adsorption amount at saturated water vapor pressure)
In FIG. 3, when the relative pressure on the horizontal axis is 0.7, it means that the relative pressure = 2.2/3.1, and the corresponding relative water vapor adsorption amount on the vertical axis is the ratio (a/b) It means that there is
The "ratio (a/b)" shown in Table 3 is the relative water vapor adsorption amount on the vertical axis when the relative pressure on the horizontal axis is 0.7.

Details of each curve in FIG. 3 are as follows.
-▲- (Ex.1): Example 1 (4-tritylaniline)
-■- (Ex. 2): Example 2 (1-aminopyrene)
-Δ- (Ex.3): Example 3 (3,5-bis(trifluoromethyl)aniline)
-□- (Ex.4): Example 4 (4-aminononafluorobiphenyl)
-×- (Ex.6): Example 6 (2-aminoanthracene)
-○- (Ex.7): Example 7 (4-ethylaniline)
-●-(Co-Ex.1): Comparative Example 1 (unmodified carbon black)

As can be seen from Table 3 and FIG. 3, the ratio (a/b) of the water vapor adsorption amount (a) at 25° C. and water vapor pressure of 2.2 kPa to the water vapor adsorption amount (b) at 25° C. and water vapor pressure of 3.1 kPa is was less than 0.5. This means that the additives of the examples exhibit high hydrophobicity and high electrical conductivity.

As described above, it is presumed that the use of the conductive additive according to the present embodiment exerted a hydrophobic effect without hindering high electrical conductivity.

According to the present embodiment, for the solid electrolyte type electrolysis device, for example, CO ₂ gas discharged from a factory is used as a raw material, and renewable energy such as a solar battery is applied to the voltage application unit, so that the desired generation can be achieved. Syngas can be produced containing at least CO and H ₂ in proportion. The synthesis gas thus produced can be used to produce fuel base materials, raw materials for chemical products, and the like by methods such as FT synthesis (Fischer-Tropsch synthesis) and methanation.

REFERENCE SIGNS LIST 10 gas diffusion layer 20 catalyst layer 22 ionomer 24 catalyst 26 additive (additive for carbon dioxide reduction catalyst)
30 solid electrolyte (ion exchange membrane)
40 anode (anode)
50 ion exchange membrane-electrode assembly 100 cathode current collector plate 200 cathode (cathode)
300 solid electrolyte (ion exchange membrane)
400 anode (anode)
500 anode collector plate 600 electrolyte solution 700 voltage application unit 800 solid electrolyte type electrolytic device

Claims

An additive for a carbon dioxide reduction catalyst that has an aryl group on its surface and a carrier containing carbon.
An additive for a carbon dioxide reduction catalyst having a carrier containing carbon, wherein the ratio of the water vapor adsorption amount at 25°C and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa is less than 0.5. .
The carbon dioxide reduction catalyst additive according to claim 1, wherein the aryl group includes one or more selected from the group consisting of a phenyl group and a condensed ring group having 2 to 6 benzene rings.
The carbon dioxide reduction catalyst additive according to claim 3, wherein the condensed ring group having 2 to 6 benzene rings contains one or more selected from the group consisting of a naphthyl group, an anthracenyl group, a phenanthrenyl group and a pyrenyl group. .
5. Any one of claims 1, 3 and 4, wherein said aryl group has one or more substituents selected from the group consisting of an alkyl group, a fluorinated alkyl group, a phenyl group, a fluorinated phenyl group and a fluorine atom. The additive for the carbon dioxide reduction catalyst according to .
The additive for a carbon dioxide reduction catalyst according to any one of claims 1 and 3 to 5, wherein the aryl group is one or more of groups represented by (1) to (8).

[In (1) to (8), * represents a binding site to the surface of the carrier. ]
an additive having an aryl group on its surface and a carrier containing carbon;
and a catalyst comprising a support containing carbon and having inorganic fine particles or a metal complex supported thereon.
an additive having a carrier containing carbon and having a ratio of less than 0.5 of the water vapor adsorption amount at 25° C. and water vapor pressure of 2.2 kPa to the water vapor adsorption amount at the same temperature and water vapor pressure of 3.1 kPa;
and a catalyst comprising a support containing carbon and having inorganic fine particles or a metal complex supported thereon.
The inorganic fine particles are fine particles selected from the group consisting of gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride; 9. The metal complex according to claim 7 or 8, wherein the complex is a metal selected from the group consisting of copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum, or a metal complex in which a ligand is coordinated to an ion of the metal. catalyst layer.
The catalyst layer according to claim 7, wherein the aryl group includes one or more selected from the group consisting of a phenyl group and a condensed ring group having 2 to 6 benzene rings.
The catalyst layer according to claim 10, wherein the condensed ring group having 2 to 6 benzene rings contains one or more selected from the group consisting of naphthyl group, anthracenyl group, phenanthrenyl group and pyrenyl group.
The catalyst layer according to claim 7, wherein the aryl group has one or more substituents selected from the group consisting of an alkyl group, a fluorinated alkyl group, a phenyl group, a fluorinated phenyl group and a fluorine atom.
8. The catalyst layer according to claim 7, wherein the aryl group is any one or more of groups represented by (1) to (8).

[In (1) to (8), * represents a bond to the surface. ]
A cathode comprising the catalyst layer according to claim 9 and a gas diffusion layer.
An ion exchange membrane-electrode assembly comprising the cathode according to claim 14, a solid electrolyte, and an anode.
The ion exchange membrane-electrode assembly according to claim 15, wherein the solid electrolyte is an anion exchange membrane.
a cathode according to claim 14;
an anode that forms a pair of electrodes with the cathode;
a solid electrolyte interposed in contact between the cathode and the anode;
A solid electrolyte type electrolysis device having a voltage applying section for applying a voltage between the cathode and the anode.
The solid electrolyte type electrolytic device according to claim 17, wherein the solid electrolyte is an anion exchange membrane.