CN118786249A

CN118786249A - Additive for carbon dioxide reduction catalyst, catalyst layer, cathode, ion exchange membrane-electrode assembly, and solid electrolyte type electrolytic device

Info

Publication number: CN118786249A
Application number: CN202380023492.3A
Authority: CN
Inventors: 兼古宽之; 贾庆鑫
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2022-02-28
Filing date: 2023-02-22
Publication date: 2024-10-15
Also published as: JPWO2023163041A1; TW202340540A; AU2023223827A1; WO2023163041A1

Abstract

The invention provides an additive for a carbon dioxide reduction catalyst, an electrode, an ion exchange membrane-electrode assembly, and a solid electrolyte type electrolytic device, wherein the additive can inhibit the function from decreasing, and the conductivity of the electrode catalyst layer and the electrolytic efficiency of the carbon dioxide reduction reaction are excellent. The additive for carbon dioxide reduction catalysts comprises a carrier containing carbon and 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 type electrolytic device

Technical Field

The present invention relates to an additive for a carbon dioxide reduction catalyst, a catalyst layer, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte type electrolytic device.

Background

Carbon dioxide is discharged when energy is extracted from fossil fuel or the like. It can be said that an increase in the carbon dioxide concentration in the atmosphere is one of the causes of global warming. Since carbon dioxide is an extremely stable substance, there is currently little available route. However, there is also an epoch demand that global warming is becoming more and more serious, and a new technology for converting carbon dioxide into other substances to be recycled is demanded. For example, carbon dioxide reduction plants capable of directly reducing carbon dioxide in a gas phase have been developed.

For example, patent document 1 discloses that in order to obtain a catalyst layer for a carbon dioxide reduction electrode that exhibits a high partial current density by controlling wettability and can withstand long-term operation, a metal catalyst supported on a carbon material, an ion-conducting substance, and a hydrophilic polymer are contained in the catalyst layer so that the ratio (a _H2O/A_N2) of the BET specific surface area (a _N2) obtained by adsorbing nitrogen to the BET specific surface area (a _H20) obtained by adsorbing water vapor is 0.08 or less.

Patent document 2 discloses that an electrode body modified with a hydrophobic polymer is provided in a reduction reaction electrode used in a reduction reaction of a carbon compound in order to make it possible to suppress at least one of a production ratio of hydrogen by a side reaction and a production ratio of a reduction product by the reduction reaction of the carbon compound in the reduction reaction of the carbon compound.

Patent document 3 discloses a method in which molecules having hydrophobicity and/or hydrophilicity are grafted on carbon, so that the technical problem can be solved.

Further, non-patent document 1 discloses a method of adding Polytetrafluoroethylene (PTFE) fine particles to a catalyst layer for a carbon dioxide reduction electrode to control wettability of the electrode and prevent deterioration of the function.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2021-147677

Patent document 2: japanese patent laid-open No. 2021-21095

Patent document 3: japanese patent application laid-open No. 2021-2528

Non-patent literature

Non-patent document 1: xing, L Hu, D.S.Ripatti, X.Hu, X.Feng, nature Communications,2021, 12, 136.

Disclosure of Invention

Problems to be solved by the invention

In an electrolytic device having a catalyst layer for performing a carbon dioxide reduction reaction and an ion exchange membrane, if an electrolyte solution permeates the ion exchange membrane and oozes out to the catalyst layer, the function of the catalyst layer is reduced.

In patent documents 1 and 2 and non-patent document 1, although the hydrophobization of the catalyst layer is attempted by adding a hydrophobic polymer to the catalyst layer, the hydrophobic polymer is insulating, and increases the resistance of the catalyst layer. In patent document 3, the hydrophobic compound is supported on the gas diffusion layer or the intermediate layer between the gas diffusion layer and the catalyst layer to improve the hydrophobicity, but the improvement of the hydrophobicity of the catalyst layer itself has not been achieved, and the effect of the hydrophobization is limited.

The present invention has been made in view of the above circumstances, and 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 electrolytic device, which are capable of suppressing a decrease in function of a catalyst layer, and have excellent conductivity of an electrode catalyst layer and electrolytic efficiency of a carbon dioxide reduction reaction.

Solution for solving the problem

<1> An additive for a carbon dioxide reduction catalyst, which has a carrier containing carbon and having aryl groups on the surface.

<2> An additive for a carbon dioxide reduction catalyst, which has a carrier containing carbon and has a ratio of the amount of water vapor adsorption at 25 ℃ and a water vapor pressure of 2.2kPa to the amount of water vapor adsorption at the same temperature and a water vapor pressure of 3.1kPa of less than 0.5.

<3> The additive for carbon dioxide reduction catalysts according to <1>, wherein the aryl group contains 1 or more selected from phenyl groups and condensed ring groups having 2 to 6 benzene rings.

<4> The additive for carbon dioxide reduction catalysts according to <3>, wherein the condensed ring group having 2 to 6 benzene rings contains 1 or more selected from the group consisting of naphthyl group, anthryl group, phenanthryl group and pyrenyl group.

<5> The additive for a carbon dioxide reduction catalyst according to any one of <1>, <3> and <4>, wherein the aryl group has 1 or more substituents selected from the group consisting of alkyl groups, fluoroalkyl groups, phenyl groups, fluorophenyl groups and fluorine atoms.

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

[ chemical formula 1]

In (1) to (8), a bond to the surface of the support is represented.

<7> A catalyst layer comprising: an additive having a carrier containing carbon and having aryl groups on the surface, and

A catalyst comprising a carrier comprising carbon and carrying inorganic fine particles or a metal complex compound.

<8> A catalyst layer comprising:

an additive having a carrier containing carbon and having a ratio of the water vapor adsorption amount at 25 ℃ and a water vapor pressure of 2.2kPa to the water vapor adsorption amount at the same temperature and a water vapor pressure of 3.1kPa of less than 0.5, and

<9> The catalyst layer according to <7> or <8>, wherein the inorganic particles are 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 a metal complex in which a ligand is coordinated to a metal selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum or an ion of the metal.

<10> The catalyst layer according to <7>, wherein the aryl group contains 1 or more selected from phenyl groups and condensed ring groups 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 1 or more selected from the group consisting of naphthyl, anthryl, phenanthryl and pyrenyl.

<12> The catalyst layer according to <7>, wherein the aryl group has 1 or more substituents selected from the group consisting of alkyl groups, fluoroalkyl groups, phenyl groups, fluorophenyl groups, and fluorine atoms.

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

[ Chemical formula 2]

In (1) to (7), a bonding portion to the surface of the support is represented.

<14> Cathode, having: a catalyst layer according to <9>, and a gas diffusion layer.

<15> An ion exchange membrane-electrode assembly comprising: a cathode, a solid electrolyte, and an anode according to <14 >.

<16> The ion-exchange membrane-electrode assembly according to < 15>, wherein the solid electrolyte is an anion-exchange membrane.

<17> A solid electrolyte type electrolytic device comprising: a cathode according to < 14>, an anode forming a pair of electrodes with the cathode,

A solid electrolyte interposed between the cathode and the anode in a contact state, and

And a voltage applying section for applying a voltage between the cathode and the anode.

<18> The solid electrolyte type electrolytic device according to <17>, wherein the solid electrolyte is an anion exchange membrane.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the technology of the present invention, it is possible to provide an additive for a carbon dioxide reduction catalyst, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte type electrolytic device, which are capable of suppressing a decrease in function, and are excellent in the conductivity of the electrode catalyst layer and the electrolytic efficiency of the carbon dioxide electrolytic reduction reaction.

Brief description of the drawings

Fig. 1 is a schematic view of an ion exchange membrane-electrode assembly suitable for use in the present embodiment.

Fig. 2 is a schematic view of a solid electrolyte type electrolytic device suitable for use in the present embodiment.

Fig. 3 is a graph showing the relative water vapor adsorption amounts of examples and comparative examples.

Detailed Description

The upper limit and the lower limit of the numerical range described in the present specification may be arbitrarily combined. For example, when the numerical ranges are described as "a to B" and "C to D", the numerical ranges of "a to D" and "C to B" are also included in the technical scope of the present invention.

Unless otherwise specified, the numerical range from the "lower limit value to the" upper limit value "described in the present specification means not lower than the lower limit value but not higher than the upper limit value.

< Additive for carbon dioxide reduction catalyst >)

The additive for a carbon dioxide reduction catalyst according to the first embodiment includes a carrier containing carbon and having an aryl group on the surface.

The additive for a carbon dioxide reduction catalyst according to the second embodiment has a carrier containing carbon, and the ratio of the amount of water vapor adsorption at 25 ℃ and a water vapor pressure of 2.2kPa to the amount of water vapor adsorption at the same temperature and a water vapor pressure of 3.1kPa is less than 0.5.

The additive for a carbon dioxide reduction catalyst according to the first embodiment and the additive for a carbon dioxide reduction catalyst according to the second embodiment of the technology of the present invention are sometimes collectively and simply referred to as "additive for a carbon dioxide reduction catalyst according to the present embodiment".

In general, a carbon dioxide reduction electrolysis apparatus includes: a cathode having a gas diffusion layer and a catalyst layer for performing a carbon dioxide reduction reaction, an ion exchange membrane, an anode, and an electrolyte (electrolyte) supplied to the anode.

The ion exchange membrane has a property that an electrolyte is permeable to ions in addition to the structure. Oftentimes it is found that: the phenomenon that the electrolyte supplied to the anode permeates the ion exchange membrane in a trace amount and the water in the catalyst layer becomes excessive; the electrolyte dissolved in the electrolyte solution is precipitated in the form of salt near the cathode, and blocks the flow path of carbon dioxide. These phenomena adversely affect the supply of carbon dioxide or the like to the catalyst layer, and reduce the electrolytic performance such as current density and selectivity. In particular, the higher the reaction temperature, the more significantly the effect is produced.

As a method of controlling the moisture content of the catalyst layer, there is a method of controlling the hydrophobicity of the catalyst layer. In patent document 1, the hydrophobicity is controlled by the addition amount of polyvinyl alcohol, polyvinylpyrrolidone, or the like, in patent document 2, the hydrophobicity is controlled by the addition of polystyrene, and in non-patent document 1, the hydrophobicity is controlled by the addition of PTFE.

However, these hydrophobic polymers are insulators, and there are problems that the resistance of the catalyst layer increases, heat generation occurs, and the electrolytic efficiency decreases by adding the hydrophobic polymer.

In patent document 3, a hydrophobic polymer is not used, but a hydrophobic compound is supported on a gas diffusion layer or an intermediate layer between a gas diffusion layer and a catalyst layer to improve the hydrophobicity. However, an improvement in the hydrophobicity of the catalyst layer has not been achieved, and thus the effect based on the hydrophobization is limited.

In contrast, by using the additive for a carbon dioxide reduction catalyst according to the present embodiment as a constituent of the catalyst layer of the electrode including the catalyst layer, not only the surface of the catalyst layer but also the entire catalyst layer can be hydrophobized without impairing the conductivity of the catalyst layer. The reason for this is presumed to be as follows.

The additive for a carbon dioxide reduction catalyst according to the first embodiment is provided with a support containing carbon having excellent electrical conductivity and has an aryl group on the surface of the support, whereby the additive can impart hydrophobicity to the catalyst layer. Since the aryl group is fixed to the surface of the support by a chemical bond, the catalyst layer can be reliably hydrophobized, and can be hydrophobized not only at the surface of the catalyst layer but also throughout the inside of the catalyst layer.

The additive for a carbon dioxide reduction catalyst according to the second embodiment has a carrier containing carbon excellent in conductivity, and the specific water vapor adsorption amount ratio is less than 0.5, and the additive has conductivity and excellent in hydrophobicity. Therefore, by adding the additive to the catalyst layer, the catalyst layer can be hydrophobized not only on the surface of the catalyst layer but also throughout the inside of the catalyst layer without impairing the conductivity of the catalyst layer.

As a result, even if the electrolyte permeates the ion exchange membrane, the electrolyte can be inhibited from adhering to the catalyst layer containing the additive for a carbon dioxide reduction catalyst according to the present embodiment, and the supply of carbon dioxide to the catalyst layer is difficult to be inhibited. Accordingly, the electrolysis performance such as current density and selectivity is not impaired, and thus the electrolysis efficiency of the carbon dioxide electrolysis reduction reaction is excellent.

The first embodiment and the second embodiment will be described below in order with respect to the additive for a carbon dioxide reduction catalyst according to the present embodiment.

[ Additive for carbon dioxide reduction catalyst according to the first embodiment ]

The additive for a carbon dioxide reduction catalyst according to the first embodiment has a carrier containing carbon and having an aryl group on the surface.

As described above, the additive has conductivity and hydrophobicity by having aryl groups on the surface of the carbon-containing support, and by containing the additive in the catalyst layer, conductivity and hydrophobicity can be imparted to the entire catalyst layer.

(Aryl)

Aryl groups can be exemplified by: phenyl, a group (condensed ring group) obtained by removing 1 hydrogen atom from a condensed ring containing 2 or more benzene rings, and the like.

Among them, from the viewpoint of suppressing steric hindrance of aryl groups on the surface of the carrier and from the viewpoint of securing conductivity of the additive, the aryl groups preferably contain 1 or more selected from phenyl groups and condensed ring groups having 2 to 6 benzene rings. By setting the number of benzene rings in the aryl group to 6 or less, charge transfer between carriers is hardly inhibited, and conductivity is excellent.

Examples of the condensed ring group having 2 to 6 benzene rings include: from naphthalene, anthracene, phenanthrene, pyrene, triphenylene, and,And a group obtained by removing 1 hydrogen atom from a condensed ring such as perylene, pentacene, pentylphene, etc.

Among the above, the condensed ring group having 2 to 6 benzene rings preferably contains a group in which 1 hydrogen atom is removed from a condensed ring of 1 or more selected from naphthalene, anthracene, phenanthrene, and pyrene. In other words, the condensed ring group having 2 to 6 benzene rings preferably contains 1 or more selected from naphthyl, anthryl, phenanthryl and pyrenyl.

More preferably, the fused ring group having 2 to 6 benzene rings is a substituted pyrenyl group.

The aryl group bonded to the surface of the support according to this embodiment may be unsubstituted or may further have 1 or 2 or more substituents.

Examples of the substituent include: the substituent may further have a substituent, such as an alkyl group, an alkenyl group, a fluoroalkyl group, an aryl group, a fluoroaryl group, and a fluorine atom.

The alkyl group may be a C1-30 alkyl group, and may be linear, branched, or cyclic. Specifically, examples thereof include: methyl, benzyl (phenylmethyl), trityl (triphenylmethyl), ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl, cyclohexyl, n-octyl, n-dodecyl, and the like. The alkyl group may further have a substituent.

The upper limit 30 of the number of carbons of the alkyl group includes the number of carbons of the substituent which may be further included. The same applies to alkenyl, fluoroalkyl, aryl, and fluoroaryl groups described below.

The carbon number of the alkyl group is preferably 1 to 25, more preferably 2 to 20.

When the alkyl group is linear, the carbon number is preferably 10 to 14. When the alkyl group is branched, it is preferable that the alkyl group has 1 to 3 carbon atoms and further has 1 to 5 unsubstituted phenyl groups.

The alkenyl group may be a straight-chain alkenyl group having 2 to 30 carbon atoms, a branched alkenyl group, or a cyclic alkenyl group. Specifically, for example, vinyl groups and the like are cited.

The carbon number of the alkenyl group is preferably 2 to 25, more preferably 2 to 20.

The fluoroalkyl group may be a fluoroalkyl group having 1 to 30 carbon atoms, and may be linear, branched, or cyclic. Specifically, examples of the group in which 1 or more hydrogen atoms in the alkyl group are substituted with fluorine atoms include: fluoromethyl, fluoroethyl, and the like.

The fluoroalkyl group preferably has 1 to 25 carbon atoms, more preferably 2 to 20 carbon atoms.

When the fluoroalkyl group is linear, the carbon number is preferably 1 to 4.

The aryl group as a substituent may be the same as the aryl group bonded to the surface of the support according to the present embodiment, but the carbon number is preferably 6 to 12. Specifically, there may be mentioned: phenyl, naphthyl, and the like.

The fluorinated aryl group includes those in which 1 or more hydrogen atoms in the aryl group as a substituent are substituted with fluorine atoms, and examples thereof include a fluorinated phenyl group having 1 to 4 fluorine atoms, a fluorinated naphthyl group having 1 to 7 fluorine atoms, and the like.

Among the above, in the case where the surface-bonded aryl group of the support according to the present embodiment has a substitution value, the substituent preferably contains 1 or more selected from the group consisting of an alkyl group, a fluoroalkyl group, a phenyl group, a fluorophenyl group, and a fluorine atom.

The number of the substituents may be 1 to 2 or more, or 2 or more to 2 or more.

For example, in the case where the aryl group bonded to the surface of the support according to the present embodiment is a phenyl group, the phenyl group may have a structure having 2 fluoromethyl groups, or may have a structure in which 4 out of 5 hydrogen atoms of the phenyl group are substituted with fluorine atoms and the remaining 1 hydrogen atom is substituted with a fluorophenyl group.

Further, the aryl group bonded to the surface of the support according to the present embodiment is preferably a phenyl group having a substituent, a condensed ring group having 2 to 6 unsubstituted benzene rings, more preferably a phenyl group having any substituent selected from a triphenylmethyl group, a linear unsubstituted alkyl group having 10 to 14 carbon atoms, and a linear fluoroalkyl group having 1 to 4 carbon atoms, a condensed ring group having 4 to 5 unsubstituted benzene rings, still more preferably a phenyl group having any substituent selected from a linear unsubstituted alkyl group having 11 to 13 carbon atoms and a linear fluoroalkyl group having 2 to 3 carbon atoms, and a condensed ring group having 4 unsubstituted benzene rings.

More specifically, the aryl group bonded to the surface of the support according to the present embodiment is preferably any one or more of the groups represented by the following (1) to (8). In (1) to (8), the bonding portions to the surface of the support according to the present embodiment are shown. The aryl group is more preferably any one or more of the groups represented by the following (1) to (3) and (5), and still more preferably any one or more of the groups represented by the following (2), (3) and (5).

[ Chemical formula 3]

The aryl groups contained in the carrier according to this embodiment may be 1 or 2 or more.

The carrier according to the present embodiment may have 1 aryl group or may have 2 or more aryl groups. The presence of the aryl group in the carrier can be confirmed and quantified by infrared spectrometry.

(Method of introducing aryl group into surface of Carrier)

The method of introducing an aryl group (method of performing chemical modification) onto the surface of the support according to the present embodiment is not particularly limited.

For example, when carbon black is used as the carrier according to the present embodiment, an aromatic compound having 1 primary amino group is used as the precursor, and nucleophilic reaction is performed on an aromatic ring or the like on the surface of carbon black by diazotization reaction, whereby a chemical bond can be formed.

The aromatic compound includes, in addition to benzene, a condensed-ring compound having 2 or more benzene rings, and the condensed-ring compound having 2 or more benzene rings is preferably a condensed-ring compound having 2 to 6 benzene rings.

Specifically, there may be mentioned: aniline, aminonaphthalene, aminoanthracene, aminophenyl, aminopyrene, and the like.

The aromatic compound having 1 primary amino group may further have a substituent other than the primary amino group. Examples of the substituent include: the substituent may further have a substituent, such as an alkyl group, an alkenyl group, a fluoroalkyl group, an aryl group, a fluoroaryl group, and a fluorine atom. The details of the substituent that the aromatic compound having 1 primary amino group may have are the same as those of the substituent that the aryl group bonded to the surface of the support of the additive for a carbon dioxide reduction catalyst according to the first embodiment may have, and the preferable mode is the same.

More specifically, the aromatic compound having 1 primary amino group is preferably any one or more of the compounds represented by the following (11) to (18).

[ Chemical formula 4]

(Carrier)

The carrier according to the present embodiment contains carbon.

Since carbon is generally conductive, the carrier according to this embodiment is a conductive carrier.

Carbon is not limited as long as it can be used as a conductive material of a gas diffusion layer in an electrode provided in a device for reducing carbon dioxide, and examples thereof include: carbon black (furnace black, acetylene black, ketjen black, medium-particle thermal black, etc.), activated carbon, graphite, carbon nanotubes, carbon nanofibers, carbon nanohorns, graphene nanoplatelets (Graphene Nanoplatelet), nanoporous carbon, etc., among which carbon black is preferred. Further, a porous structure is preferable as the structure. As the carbon having a porous structure, a porous carbon material typified by graphene is exemplified.

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 500ml/100g, more preferably 100 to 300ml/100g, still more preferably 100 to 200ml/100g. The primary particle diameter is preferably 5 to 200nm, more preferably 10 to 100nm, and even more preferably 10 to 50nm.

DBP oil absorption of carbon black according to JIS K6217-4: 2001 (method for obtaining oil absorption amount), primary particle diameter is obtained by, for example, measuring a laser diffraction type particle size distribution.

Carbon black may be commercially available, and examples thereof include: vulcan (registered trademark) XC-72 (manufactured by Cabot corporation), denka BLACK HS-100 (manufactured by Denka corporation), ketjen BLACK EC-600JD (manufactured by Lion SPECIALTY CHEMICALS corporation), conducex-7055 Ultra (manufactured by Birla Carbon corporation), and the like.

The additive for a carbon dioxide reduction catalyst according to the first embodiment preferably contains a carrier containing carbon and having an aryl group on the surface.

[ Additive for carbon dioxide reduction catalyst according to the second embodiment ]

In other words, a/b is less than 0.5 when a is set to a represents the water vapor adsorption amount (unit: cm ³ (STP)/g) at 25℃and the water vapor pressure of 2.2kPa, and b represents the water vapor adsorption amount (unit: cm ³ (STP)/g) at 25℃and the water vapor pressure of 3.1 kPa.

The water vapor adsorption amount a at 25℃and a water vapor pressure of 2.2kPa is strongly influenced by the number of monolayer adsorption molecules corresponding to the interaction force between the outermost surface of the additive and the adsorbed water molecules, and therefore means the water adsorption capacity of the additive. The water vapor adsorption amount b at 25℃and a water vapor pressure of 3.1kPa is strongly influenced by the number of adsorption molecules corresponding to the adsorption capacity of the additive and corresponds to the surface area per unit mass of the additive, and therefore the ratio (a/b) of the water vapor adsorption amount a to the water vapor adsorption amount b indicates the surface hydrophilicity of the additive.

A/b <0.5 means that the additive for carbon dioxide reduction catalyst exhibits high hydrophobicity and high conductivity. The smaller a/b, the more preferred, but also 0, but generally greater than 0.01.

The ratio 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, still more preferably 0.2 or less, still more preferably 0.15 or less.

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

From the above, the additive for carbon dioxide reduction catalyst according to the first embodiment preferably has a ratio of the amount of water vapor adsorption at 25 ℃ and a water vapor pressure of 2.2kPa to the amount of water vapor adsorption at the same temperature and a water vapor pressure of 3.1kPa of less than 0.5.

In addition, the additive for a carbon dioxide reduction catalyst according to the second embodiment preferably has an aryl group on the surface of a carrier containing carbon.

The additive for carbon dioxide reduction catalyst in the technique of the present invention is preferably covered with an ionomer described later. By covering the additive for carbon dioxide reduction catalyst with the ionomer, the hydrophobization effect can be more effectively exerted on the catalyst also present in the ionomer, and the electrolytic efficiency can be improved.

< Catalyst layer >)

The catalyst layer according to the first embodiment includes: an additive having a carrier containing carbon and having aryl groups on the surface; and a catalyst comprising a carrier containing carbon and carrying inorganic fine particles or a metal complex compound.

The catalyst layer according to the second embodiment includes: an additive having a carrier containing carbon, and a ratio of a water vapor adsorption amount at 25 ℃ and a water vapor pressure of 2.2kPa to a water vapor adsorption amount at the same temperature and a water vapor pressure of 3.1kPa of less than 0.5; and a catalyst comprising a carrier containing carbon and carrying inorganic fine particles or a metal complex compound.

The catalyst layer according to the first embodiment and the catalyst layer according to the second embodiment are sometimes collectively referred to simply as "the catalyst layer according to the present embodiment".

The "additive having a carrier containing carbon and having an aryl group on the surface" contained in the catalyst layer according to the first embodiment is sometimes referred to as an additive according to the first embodiment. The "additive having a ratio of the water vapor adsorption amount at 25 ℃ and a water vapor pressure of 2.2kPa to the water vapor adsorption amount at the same temperature and a water vapor pressure of 3.1kPa of less than 0.5" contained in the catalyst layer according to the second embodiment 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 are sometimes collectively referred to simply as "additive according to the embodiment".

In the catalyst layer according to the present embodiment, the kind of catalyst contained in the catalyst layer is not particularly limited. The catalyst layer according to the present embodiment is suitable for use as a catalyst layer containing a carbon dioxide reduction catalyst, but may be suitably used for various catalyst layers in which it is desired to avoid drawbacks caused by flooding of the catalyst layer, contact with water vapor, precipitation of salts, and the like.

(Additive)

The additive according to the first embodiment is the same as the additive for a carbon dioxide reduction catalyst according to the first embodiment, and preferably the same is also used.

The additive having a support containing carbon and having an aryl group on the surface thereof can hydrophobize the catalyst layer not only on the surface but also throughout the entire catalyst layer from the inside of the catalyst layer without impairing the electrical conductivity of the catalyst layer containing the additive, and therefore can suppress the decline in the function 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 ℃ and the water vapor pressure of 2.2kPa to the water vapor adsorption amount at the same temperature and the water vapor pressure of 3.1 kPa" is the same as the "ratio (a/b) of the water vapor adsorption amount a at 25 ℃ and the water vapor pressure of 2.2kPa to the water vapor adsorption amount b at the same temperature and the water vapor pressure of 3.1 kPa" in the additive for a carbon dioxide reduction catalyst according to the second embodiment.

The smaller a/b is, the higher the hydrophobicity and the higher the conductivity are for the additive according to the second embodiment. The smaller a/b is, the more preferable, but may be 0, but is usually more than 0.01.

By including the additive according to the second embodiment in the catalyst layer, the catalyst layer can be rendered hydrophobic not only on the surface but also over the entire catalyst layer from the inside of the catalyst layer without impairing the conductivity of the catalyst layer, and therefore, the decline in 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 hydrophobize the catalyst layer containing these additives not only on the surface but also throughout the entire range from the inside, and can maintain conductivity. Therefore, the catalyst layer can be suitably used as an additive for various catalyst layers, which is intended to avoid drawbacks caused by flooding of the catalyst layer, contact with water vapor, precipitation of salts, and the like.

(Catalyst)

The catalyst layer according to the present embodiment contains a catalyst including a carrier containing carbon and supporting inorganic fine particles or a metal complex compound.

In the catalyst of the present invention, the component exhibiting the catalytic action is an inorganic fine particle or a metal complex compound supported on a carrier, but in the present invention, the inorganic fine particle and the metal complex compound are referred to as "catalyst source", and the carrier on which the catalyst source is supported is referred to as "catalyst".

[ Carrier ]

As the carrier, the carrier according to the present embodiment, which is contained in the additive for a carbon dioxide reduction catalyst according to the first embodiment, can be used, and preferably contains carbon black.

The preferred mode of carbon black is the same as that described in the description of the additive for carbon dioxide reduction catalyst according to the first embodiment.

[ Inorganic particles, metal coordination Compound ]

The carrier according to the present 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 that exhibit a catalytic action. In the technique of the present invention, the inorganic fine particles are metals and inorganic compounds having an average particle diameter of 1 to 100nm, as measured by observation of a photograph such as a scanning electron microscope.

For example, when the catalyst source is used for a catalyst layer for a fuel cell, platinum, gold, nickel, ruthenium, rhodium, or the like can be used as the inorganic fine particles, and a nickel complex, cobalt complex, iron complex, manganese complex, zinc complex, or the like can be used as the metal complex.

In addition, for example, when the catalyst source is used for a catalyst layer for a secondary battery electrode, platinum, gold, nickel, iridium, a metal oxide, or the like can be used as the inorganic fine particles, and a nickel complex, a cobalt complex, an iron complex, a manganese complex, a zinc complex, or the like can be used as the metal complex.

In the case where the catalyst layer is used as the catalyst layer for carbon dioxide reduction, the inorganic fine particles and the metal complex preferably use a catalyst source having an effect of generating at least carbon monoxide by a reduction reaction.

Specifically, the carbon dioxide reduction inorganic fine particles are preferably fine particles selected from gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride. The inorganic fine particles may be used in an amount of 1 or 2 or more kinds.

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, and even more preferably silver, gold, and copper.

The average particle diameter of the inorganic fine particles as a catalyst source for carbon dioxide reduction is preferably 65nm or less, more preferably 60nm or less, still more preferably 50nm or less, yet more preferably 40nm or less, yet more preferably 30nm or less, from the viewpoint of the reaction rate of the carbon dioxide reduction reaction. The lower limit of the average particle diameter is not limited, but is preferably 1nm or more, more preferably 5nm or more, in view of ease of production.

The average particle diameter can be measured by observation of a photograph with a scanning electron microscope or the like.

The metal complex as the 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 ion is preferably selected from 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 preferably nickel, cobalt, and iron. The metal complex may contain only 1 metal or an ion of the metal, or may contain 2 or more metals or ions of the metal.

The kind of the ligand is not particularly limited, and examples thereof include: phthalocyanine coordination compounds, porphyrin coordination compounds, pyridine coordination compounds, metal-supported covalent triazine structures, metal-organic structures, and the like. Among them, preferred are phthalocyanine complex, porphyrin complex, pyridine complex and metal-supported covalent triazine structure, more preferred are phthalocyanine complex, porphyrin complex and metal-supported covalent triazine structure, and still more preferred are porphyrin complex and metal-supported covalent triazine structure. The metal complex may contain only 1 kind of ligand or may contain 2 or more kinds of ligands.

As described above, the catalyst layer for carbon dioxide reduction according to the present embodiment is preferably a catalyst layer comprising:

The additive according to the present embodiment (additive for carbon dioxide reduction catalyst according to the present embodiment); and

A catalyst comprising a carrier containing carbon and carrying inorganic fine particles or a metal complex compound,

The inorganic particles are 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 a metal complex in which a metal selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum or an ion of the metal is coordinated.

The inorganic fine particles and the metal complex are carried on the carrier according to the present embodiment by performing a known method such as vapor deposition, precipitation, adsorption, deposition, adhesion, welding, physical mixing, or spraying.

The catalyst in the technique of the present invention is preferably covered with an ionomer described later. By coating the catalyst with an ionomer, ion-conducting channels between the coated catalyst and a solid electrolyte described later are easily formed, and movement of ions generated by the reaction is facilitated, so that the electrolytic efficiency can be improved.

[ Ionomer ]

The catalyst layer may also further comprise an ionomer.

The ionomer functions as a binder resin in the catalyst layer, and is a matrix resin (continuous phase) capable of dispersing and immobilizing the additive and the catalyst according to the present embodiment, and also has a function of transmitting ions generated by electrolysis and improving CO ₂ electrolysis efficiency. In addition, from the viewpoint of improving conductivity, the ionomer is preferably a polymer electrolyte. The polyelectrolyte is more preferably 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.

Particularly, when an anion exchange resin is used, the anion exchange resin itself has carbon dioxide adsorption capacity, and the easiness of ion transfer of the ion exchange resin and the electrolysis efficiency of carbon dioxide can be greatly improved.

Examples of the cation exchange resin include: fluorine resin having sulfone group, styrene-divinylbenzene copolymer having sulfone group. Further, commercially available products may be used, and examples thereof include: nafion (manufactured by Chemours), aquivion (manufactured by Solvay Specialty Polymers), DIAION (manufactured by mitsubishi chemical company), fumasep (manufactured by FUMATECH), and the like.

Examples of the anion exchange resin include: a resin having 1 or more ion exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. Commercial products may be used, and examples thereof include: sustainion (manufactured by Dioxide Materials), fumasep (manufactured by FUMATECH), PENTION (manufactured by Xergy), DURION (manufactured by Xergy), NEOSEPTA (manufactured by ASTOM), TOYOPEARL (manufactured by eastern corporation), and the like.

From the viewpoint of improving the conductivity, the alkali site density of the anion exchange resin is preferably 2.0 to 5.0mmol/cm ³ in a dry state, more preferably 2.5mmol/cm ³ or more and less than 4.5mmol/cm ³, still more preferably 2.9mmol/cm ³ or more and less than 4.5mmol/cm ³.

The alkali site density of the anion exchange resin can be obtained from the integral value of the signal when ¹ H NMR measurement is performed on the anion exchange resin.

In addition, the anion exchange resin in a dry state means a state in which the content of free moisture in the anion exchange resin is 0.01g or less per 1g of resin, and for example, the anion exchange resin can be brought into a dry state by heating in vacuum.

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, the ionomer preferably uses the same resin as the solid electrolyte (ion-exchange membrane) from the viewpoint of improving the conductivity.

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, and even more preferably 10 to 50% by mass, from the viewpoint of improving the hydrophobicity of the catalyst layer and suppressing the decline of the catalyst function.

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, and even more preferably 15 to 60% by mass, from the viewpoint of further improving the production efficiency of the synthesis gas containing CO.

< Cathode >

The cathode (cathode) according to the present embodiment includes: the catalyst layer for carbon dioxide reduction and the gas diffusion layer according to the present embodiment described above.

By providing the cathode (cathode) according to the present embodiment with the catalyst layer containing the additive according to the present embodiment, the synthesis gas containing CO can be stably produced without interfering with the reduction reaction of carbon dioxide in the catalyst layer. Therefore, the electrolytic efficiency of the carbon dioxide electrolytic reduction reaction is excellent.

[ Gas diffusion layer ]

The gas diffusion layer comprises, for example, carbon paper or nonwoven fabric, or a metal mesh. Examples include: graphite carbon, glassy carbon, titanium, SUS steel, and the like.

< Ion exchange Membrane-electrode Assembly >

The ion exchange membrane-electrode assembly according to the present embodiment includes: the cathode, the solid electrolyte, and the anode according to the present embodiment described above.

Since the ion exchange membrane-electrode assembly according to the present embodiment includes the cathode having the catalyst layer containing the additive according to the present embodiment, the synthesis gas containing CO can be stably produced without interfering with the reduction reaction of carbon dioxide in the catalyst layer. Therefore, the electrolytic efficiency of the carbon dioxide electrolytic reduction reaction is excellent.

Fig. 1 is a schematic view of an ion exchange membrane-electrode assembly suitable for use in the present 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. The catalyst layer 20 includes: ionomer 22, a plurality of catalysts 24 according to the present embodiment, and a plurality of additives (additives for 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 a cathode (cathode) according to the present 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 generated through a reduction reaction.

Hereinafter, reference numerals are omitted in fig. 1 for explanation.

[ Solid electrolyte ]

The ion exchange membrane-electrode assembly according to the present embodiment has a solid electrolyte.

The solid electrolyte may be a polymer film. The polymer may be any of various ionomers, and may be a cation exchange resin or an anion exchange resin, but is preferably an anion exchange resin. That is, the solid electrolyte is preferably an anion exchange membrane. In addition, it is more preferable to use the same anion exchange resin as the ionomer used in the catalyst layer.

The solid electrolyte may be a commercially available product as a cation exchange membrane or an anion exchange membrane.

In the case of using an anion exchange membrane for the solid electrolyte, the density of the alkali sites in the dry state is preferably 0.5 to 5.0mmol/cm ³, more preferably 2.5mmol/cm ³ or more and less than 4.5mmol/cm ³, and still more preferably 2.9mmol/cm ³ or more and less than 4.5mmol/cm ³.

As the cation exchange membrane, for example, there can be used: a strongly acidic cation exchange membrane obtained by introducing a sulfone group into a fluororesin matrix, nafion117, nafion115, nafion212, nafion350 (manufactured by Chemrous company), a strongly acidic cation exchange membrane obtained by introducing a sulfone group into a styrene-divinylbenzene copolymer matrix, neoseptaCSE (manufactured by ASTOM company), and the like.

Examples of the anion exchange membrane include: an anion exchange membrane having 1 or more ion exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. Specifically, examples thereof include: neosepta (registered trademark) ASE, AHA, ACS, AFX (manufactured by ASTOM company); SELEMION (registered trademark) AMVN, DSVN, AAV, ASVN, AHO (manufactured by Asahi glass Co., ltd.).

Regarding the reduction reaction of carbon dioxide, the reduction reaction at the cathode (cathode) according to the present embodiment differs depending on the kind of the solid electrolyte. In the case of using a cation exchange membrane as a solid electrolyte, the reduction reactions of the following equations (1) and (2) are generated, and in the case of using an anion exchange membrane as a solid electrolyte, the reduction reactions of the following equations (3) and (4) are generated.

CO₂+2H^-+2e^-→CO+H₂O (1)

2H⁺+2e^-→H₂ (2)

H₂O+CO₂+2e^-→CO+2OH^- (3)

2H₂O+2e^-→H₂+2OH^- (4)

[ Anode ]

The oxidation reaction at the anode varies depending on the kind of the solid electrolyte. When a cation exchange membrane is used as a solid electrolyte, an oxidation reaction of the following reaction formula (5) occurs, and when an anion exchange membrane is used as a solid electrolyte, an oxidation reaction of the following reaction formula (6) occurs.

2H₂O→O₂+4H⁺+4e^- (5)

4OH^-→O₂+2H₂O+4e^- (6)

The anode is a gas diffusion electrode comprising a gas diffusion layer.

The gas diffusion layer comprises, for example, a metal mesh. Examples of the electrode material of the anode include ：Ir、IrO₂、Ru、RuO₂、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 Electrolysis apparatus >)

The solid electrolyte type electrolytic device according to the present embodiment includes: the cathode according to the present embodiment, the anode forming a pair of electrodes with the cathode, the solid electrolyte interposed between the cathode and the anode in a contact state, and the voltage applying section for applying a voltage between the cathode and the anode are described above.

Since the solid electrolyte type electrolytic device according to the present embodiment includes the cathode (cathode) having the catalyst layer containing the additive according to the present embodiment, the synthesis gas containing CO can be stably produced without interfering with the reduction reaction of carbon dioxide in the catalyst layer. Therefore, the electrolytic efficiency of the carbon dioxide electrolytic reduction reaction is excellent.

Fig. 2 shows a solid electrolyte type electrolytic device 800 having: the cathode (cathode) 200 constituting the electrode according to the present embodiment, an anode (anode) 400 constituting a pair of electrodes with the cathode 200, a solid electrolyte 300 interposed between the cathode 200 and the anode 400 in a contact state, and a voltage applying section 700 applying a voltage between the cathode 200 and the anode 400.

The solid electrolyte type electrolytic device 800 shown in fig. 2 further includes a cathode collector plate 100, an anode collector plate 500, and an electrolyte 600.

The electrode according to the present embodiment described above may be used as the cathode 200. In addition, the solid electrolyte 300 is preferably an anion exchange membrane, as in the solid electrolyte 30 in fig. 1. Anode 400 is identical to anode 40 of fig. 1.

Details of the cathode 200, the solid electrolyte 300, and the anode 400 are as described above.

Hereinafter, the elements other than the cathode 200, the solid electrolyte 300, and the anode 400 will be omitted from the description.

[ Cathode collector plate ]

Examples of the cathode collector plate (cathode collector plate) include: among these, copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, brass, and other metal materials are preferable from the viewpoints of ease of processing and cost. In the case where the material is a metal material, examples of the shape of the cathode collector plate include: metal foil, metal plate, metal film, porous metal, perforated metal, foamed metal, etc.

The cathode collector plate may be provided with a gas supply hole for supplying a raw gas containing carbon dioxide to the cathode and a gas recovery hole for recovering a generated gas containing carbon monoxide. By providing the gas supply hole and the gas recovery hole, the raw material gas (including unreacted raw material gas) can be fed uniformly and efficiently to the cathode, and the generated gas can be discharged. The gas supply holes and the gas recovery holes may be provided independently of each other in only 1 or in at least 2. The shape, position, size, etc. of the gas supply hole and the gas recovery hole are not limited, and may be appropriately set. In addition, in the case where the cathode collector plate has gas permeability, the gas supply hole and the gas recovery hole are not necessarily required.

In the case where the cathode has an electron-transporting function, a cathode collector plate is not necessarily required.

[ Anode collector plate ]

The anode collector plate (anode collector plate) preferably has conductivity and rigidity for supporting the anode so as to receive electrons from the anode. From this viewpoint, for example, a metal material such as titanium (Ti), copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, or brass may be suitably used as the anode current collector.

The anode current collector may be provided with a gas flow path for feeding a raw material gas (H ₂ O, etc.) to the anode. By providing the anode current collector plate with a gas flow path, the raw material gas can be fed uniformly and efficiently to the anode. The number, shape, position, size, etc. of the gas flow passages are not limited, and may be appropriately set.

[ Voltage application section ]

The voltage application unit has a function of applying a voltage between the cathode and the anode by applying a voltage to the cathode collector plate and the anode collector plate. Here, since the two current collecting plates are conductors, electrons are supplied to the cathode on the one hand, and electrons from the anode are received on the other hand. In addition, the voltage applying section may be electrically connected to a control section, not shown, in order to apply an appropriate voltage.

[ Electrolyte ]

The electrolyte is preferably an aqueous solution having a pH of 5 or more.

Examples include: aqueous carbonate, aqueous bicarbonate (e.g., aqueous KHCO ₃), aqueous sulfate, aqueous borate, aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous sodium chloride, and the like.

(Reaction gas supply portion)

In the solid electrolyte type electrolytic device according to the present embodiment, a reaction gas supply unit, not shown, may be provided outside the solid electrolyte type electrolytic device. That is, CO ₂ as a reaction gas may be supplied to the catalyst layer provided in the cathode, and the reaction gas may be supplied from the reaction gas supply unit to the gas supply hole via a pipe or the like, not shown, or may be supplied by blowing the reaction gas to the surface of the cathode collector plate opposite to the surface contacting the cathode. In addition, from the environmental point of view, it is appropriate to use a plant exhaust gas discharged from a plant.

[ CO production method ]

Next, a CO production method using the solid electrolyte type electrolytic device according to the present embodiment will be described.

First, CO ₂, which is a reaction gas as a raw material, is supplied in a gas phase state to a solid electrolyte type electrolyzer by a reaction gas supply unit, not shown. At this time, CO ₂ is supplied to the cathode through a gas supply hole provided in the cathode collector plate, for example.

Next, CO ₂ supplied to the cathode is brought into contact with the catalyst layer provided in the cathode, whereby the reduction reaction of the above-described reaction formulae (1) and (2) is generated when a cation-exchange membrane is used as a solid electrolyte, and the reduction reaction of the above-described reaction formulae (3) and (4) is generated when an anion-exchange membrane is used as a solid electrolyte, whereby a synthesis gas containing at least CO and H ₂ is generated.

Next, the generated synthesis gas containing CO and H ₂ is sent to a gas recovery device, not shown, through gas recovery holes provided in the cathode collector plate, for example, and is recovered in accordance with various predetermined gases.

Examples

Next, the technique of the present invention will be specifically described by way of examples, but the technique of the present invention is not limited by any of these examples.

< Production of additive >

Example 1

After irradiating an ethanol dispersion containing 0.5g of carbon black having an average particle diameter of 30nm with ultrasonic waves for 10 minutes, the dispersion was allowed to stand in a vacuum chamber under a reduced pressure atmosphere of 10kPa (absolute pressure) for 10 minutes. Next, 8.3mL of an aqueous solution of sodium nitrite (0.5 mol/L) was added to the dispersion. After adding 4mmol of 4-tritylaniline [ compound represented by the formula (11) ] to the dispersion, 2mL of hydrochloric acid was further added, and the mixture was stirred at 15℃for 5 hours or more. After neutralizing the dispersion by adding a sodium hydroxide solution, the obtained slurry was washed with distilled water, and the solid was recovered by a centrifuge, and the solid was dried under vacuum at 60 ℃ overnight to prepare an additive of example 1.

The average particle diameter of the carbon black was obtained by measuring the laser diffraction particle size distribution.

Examples 2 to 8

The 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 were the compounds represented by the above-mentioned formulas (12) to (18).

Comparative example 1

In comparative example 1, carbon black having an average particle diameter of 30nm was used as an additive.

Comparative example 2

In comparative example 2, polytetrafluoroethylene (trade name "Polytetrafluoroethylene Nanopowder" manufactured by PTFE, nanoshel Co., ltd.) having an aerodynamic particle diameter (Aerodynamic Particle Size) of 30 to 50nm was used as an additive.

Comparative example 3, 4

In comparative examples 3 and 4, no additive was used.

< Manufacture of catalyst >

Examples 1 to 7 and comparative examples 1 to 3

The catalysts used in examples 1 to 7 and comparative examples 1 to 3 were the same. The production is performed as follows.

In a beaker, 0.1g of carbon black carrier (carrier according to the present embodiment) was mixed with 100mL of ethanol, and the obtained ethanol dispersion was irradiated with ultrasonic waves for 10 minutes. Thereafter, the dispersion was allowed to stand in a vacuum chamber under a reduced pressure atmosphere of 10kPa (absolute pressure) for 10 minutes. Thereafter, 11.7mL of a 0.1mol/L AgNO ₃ solution was mixed with 1mL of a 2.3mol/L sodium phosphinate solution, and stirring was performed at 15℃for 16 hours, thereby reducing silver nitrate. After the completion of the reaction, the obtained slurry was washed with distilled water, and the solid was collected by a centrifuge, and the solid was dried under vacuum at 60℃overnight to obtain catalyst powders of examples 1 to 7 and comparative examples 1 to 3. The catalyst obtained was carbon black having Ag particles supported as a catalyst source, and the mass of the Ag particles supported was 40 parts by mass per 100 parts by mass of the carbon black having no Ag particles supported.

Example 8 and comparative example 4

The catalysts used in example 8 and comparative example 4 were the same. The preparation was carried out as follows.

In a beaker, 0.4g of carbon black carrier (carrier according to the present embodiment), 1.1mmol of pentaethylenehexamine and 0.7mmol of nickel (II) chloride hexahydrate were mixed in 15mL of ethanol, and the obtained ethanol dispersion was irradiated with ultrasonic waves for 10 minutes. Thereafter, the ethanol dispersion was dried by heating to evaporate ethanol, and the obtained mixture was heated in an electric furnace at 900 ℃ for 30 seconds or longer in an inert gas, followed by calcination. Thereafter, the product was washed with an aqueous sulfuric acid solution, and the solid was recovered by suction filtration, and the solid was dried under vacuum at 60℃overnight to obtain a Ni complex-supported catalyst powder. The catalyst powder was used as the catalyst powder of example 8 and comparative example 4.

The mass of the supported Ni was 1 part by mass with respect to 100 parts by mass of the carbon black on which the Ni complex compound was not supported with respect to the obtained catalyst.

< Solid electrolyte type Electrolysis apparatus >)

Example 1

43Mg of the obtained catalyst powder was dispersed in ethanol, and 12mg of the anion exchange resin to which 5mg of the additive of example 1 was added was mixed as an ionomer in the dispersion. As a result of carrying out ¹ H NMR measurement in a dry state on the anion exchange resin, the density of the alkali sites was calculated to be 2.8mmol/cm ³ from the integral value of the signal. The anion exchange resin is a fluorine-based resin having an aromatic ring in the main chain and a quaternary ammonium group (quaternary alkylamino group) as a side chain bonded to the main chain as a base material.

After mixing, the dispersion was irradiated with ultrasonic waves for 10 minutes, and the mixture was allowed to stand in a vacuum chamber under a reduced pressure of 10kPa (absolute pressure) for 10 minutes. The dispersion was applied to carbon paper using a spray coater to prepare a cathode (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 (density of alkali sites: 2.8mmol/cm ³) having a film thickness of about 30 μm, a carbon anode (manufactured by DioxideMaterials Co.) having iridium oxide supported thereon, and the above cathode were bonded to each other to prepare an ion exchange membrane-electrode assembly.

The anode (anode) was connected to a tank of an electrolyte (0.5 mol/L KHCO ₃ aqueous solution).

Examples 2 to 7 and comparative examples 1 to 2

In the production of the solid electrolyte type electrolytic device of example 1, the solid electrolyte type electrolytic devices of examples 2 to 7 and comparative examples 1 to 2 were produced in the same manner except that the additive of example 1 was changed from the additive of example 1 to any additive of examples 2 to 7 and comparative examples 1 to 2.

Example 8

A solid electrolyte type electrolytic device of example 8 was produced in the same manner as in example 1 except that the additive of example 1 was changed to the additive of example 8 and the ionomer of example 1 was changed to Nafion (manufactured by Chemours).

Comparative example 3

A solid electrolyte type electrolytic device of comparative example 3 was produced in the same manner except that no additive was added in the production of the solid electrolyte type electrolytic device of example 1.

Comparative example 4

A solid electrolyte type electrolytic device of comparative example 4 was manufactured in the same manner except that no additive was added in the manufacture of the solid electrolyte type electrolytic device of example 8.

< Evaluation of solid electrolyte type Electrolysis apparatus >

Examples 1 to 7 and comparative examples 1 to 3

Using the solid electrolyte type electrolytic devices of examples 1 to 7 and comparative examples 1 to 3, pure CO ₂ was supplied to the cathode, and CO ₂ was electrolyzed by applying a constant current of-1A/cm ² or-2.6V to the anode under the condition that the solid electrolyte type electrolytic device was heated to 50℃to measure the CO generation current density [ mA/cm ² ] and CO selectivity [% ] at the time of CO generation. When a constant current is applied, a voltage [ V ] is measured instead of the measured current.

The results are shown in table 1.

TABLE 1

< Evaluation of solid electrolyte type Electrolysis apparatus >

Example 8 and comparative example 4

Using each of the solid electrolyte type electrolytic devices of example 8 and comparative example 4, pure CO ₂ was supplied to the cathode, CO ₂ was electrolyzed at a potential of-1.8V with respect to a silver/silver chloride reference electrode at room temperature, and the CO generation current density [ mA/cm ² ] at the time of CO generation was measured.

The results are shown in table 2.

TABLE 2

As is clear from tables 1 and 2, when additives obtained by chemically modifying the surface of a support with an aromatic amine compound were used (examples 1 to 7), they exhibited a low necessary voltage and a high CO selectivity when a high current of-1A/cm ² was applied. In addition, in example 8, a higher current density was shown.

On the other hand, in comparative example 1 using an additive in which the surface of the support was not chemically modified with an aryl group, comparative example 2 using a hydrophobic polymer having insulation as an additive, and comparative example 3 not using an additive, the required voltage was increased, and the CO selectivity was lowered. In comparative example 4, where no additive was used, a lower current density was exhibited.

< Water vapor adsorption amount of additive >

The amounts of water vapor adsorption (a) at 25℃and water vapor pressure of 2.2kPa and water vapor adsorption (b) at 25℃and water vapor pressure of 3.1kPa were measured by BELSORP-max (manufactured by Bel corporation, japan) for the additives of examples 1 to 4, 6 and 7 and comparative example 1, and the ratios (a/b) of both were shown in Table 3. In the measurement, 0.2 to 0.3g of the additive sample was heated at 120℃for 5 hours or more under vacuum to remove the adsorbed gas on the surface, and then water vapor was introduced at 25℃to determine the amount of adsorbed gas under each water vapor pressure.

Fig. 3 is a graph showing the relative amount of water vapor adsorbed with respect to the relative pressure. Here, in fig. 3, the relative pressure of the vertical axis means a value obtained by dividing each water vapor pressure by the saturated water vapor pressure (3.1 kPa) at 25 ℃. The relative water vapor adsorption amount on the horizontal axis means a 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 ℃. When expressed by the formula, the expression 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 of the horizontal axis is 0.7, it means that the relative pressure=2.2/3.1, and means that the relative water vapor adsorption amount of the corresponding vertical axis is the ratio (a/b).

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.

The details of each curve in fig. 3 are as follows.

- (Ex.1): example 1 (4-tritylaniline)

- ■ -Ex.2): example 2 (1-aminopyrene)

- (Ex.3): example 3 (3, 5-bis (trifluoromethyl) aniline)

- ≡ - (Ex.4): example 4 (4-Aminononafluorobiphenyl)

- × - (Ex.6): example 6 (2-aminoanthracene)

-O- (ex.7): example 7 (4-ethylaniline)

- (Co-ex.1): comparative example 1 (unmodified carbon black)

TABLE 3

TABLE 3 Table 3

	Ratio (a/b)
		Example 1	0.16
Example 2	0.10
		Example 3	0.35
Example 4	0.16
		Example 6	0.19
Example 7	0.46
		Comparative example 1	0.52

As is clear from table 3 and fig. 3, the ratio (a/b) of the water vapor adsorption amount (a) at 25 ℃ and water vapor pressure of 2.2kPa to the water vapor adsorption amount (b) at 25 ℃ and water vapor pressure of 3.1kPa was less than 0.5. This means that the additive of the examples shows high hydrophobicity and high conductivity.

As described above, it is assumed that the use of the conductive additive according to the present embodiment does not interfere with high conductivity and can exhibit a hydrophobizing effect.

Industrial applicability

According to the present embodiment, for example, by using CO ₂ gas discharged from a factory as a raw material and using renewable energy such as a solar cell for a voltage application unit, a synthesis gas containing at least CO and H ₂ at a desired production ratio can be produced in the solid electrolyte type electrolysis apparatus. The synthesis gas thus produced can be subjected to methods such as FT synthesis (Fischer-Tropsch synthesis) and methanation to produce fuel substrates, chemical raw materials, and the like.

Description of symbols

10: Gas diffusion layer

20: Catalyst layer

22: Ionomer compositions

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 collector plate

200: Cathode (cathod)

300: Solid electrolyte (ion exchange membrane)

400: Anode (anode)

500: Anode collector plate

600: Electrolyte solution

700: Voltage applying part

800: Solid electrolyte type electrolytic device

Claims

1. An additive for a carbon dioxide reduction catalyst, which has a carrier containing carbon and having an aryl group on the surface.

2. An additive for a carbon dioxide reduction catalyst, which comprises a carrier containing carbon and has a ratio of the amount of water vapor adsorption at 25 ℃ and a water vapor pressure of 2.2kPa to the amount of water vapor adsorption at the same temperature and a water vapor pressure of 3.1kPa of less than 0.5.

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

4. The additive for carbon dioxide reduction catalysts according to claim 3, wherein the condensed ring group having 2 to 6 benzene rings contains 1 or more selected from the group consisting of naphthyl group, anthryl group, phenanthryl group and pyrenyl group.

5. The additive for a carbon dioxide reduction catalyst according to any one of claims 1, 3 and 4, wherein the aryl group has 1 or more substituents selected from an alkyl group, a fluoroalkyl group, a phenyl group, a fluorophenyl group, and a fluorine atom.

6. The additive for a carbon dioxide reduction catalyst according to any one of claims 1 and 3 to 5, wherein the aryl group is any one or more of the groups represented by (1) to (8);

[ chemical formula 1]

In (1) to (8), a bond to the surface of the support is represented.

7.A catalyst layer comprising:

An additive having a carrier containing carbon and having aryl groups on the surface, and

8. A catalyst layer comprising:

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

10. The catalyst layer according to claim 7, wherein the aryl group contains 1 or more selected from a phenyl group and a condensed ring group having 2 to 6 benzene rings.

11. The catalyst layer according to claim 10, wherein the condensed ring group having 2 to 6 benzene rings contains 1 or more selected from the group consisting of naphthyl, anthryl, phenanthryl and pyrenyl.

12. The catalyst layer according to claim 7, wherein the aryl group has 1 or more substituents selected from the group consisting of an alkyl group, a fluoroalkyl group, a phenyl group, a fluorophenyl group, and a fluorine atom.

13. The catalyst layer according to claim 7, wherein the aryl group is any one or more of the groups shown in (1) to (8),

[ Chemical formula 2]

In (1) to (8), a bonding portion to the surface is represented.

14. A cathode, which has: the catalyst layer of claim 9, and a gas diffusion layer.

15. An ion exchange membrane-electrode assembly comprising: the cathode, solid electrolyte, and anode of claim 14.

16. The ion exchange membrane-electrode assembly of claim 15 wherein the solid electrolyte is an anion exchange membrane.

17. A solid electrolyte type electrolytic device comprising:

the cathode according to claim 14,

An anode forming a pair of electrodes with the cathode,

18. The solid electrolyte type electrolytic device according to claim 17, wherein the solid electrolyte is an anion exchange membrane.