JP6497276B2 - Coating agent and method for producing catalyst-carrying electrode - Google Patents

Description

  The present invention relates to a coating agent containing a carbon dioxide reduction electrode catalyst for carbon dioxide reduction reaction and an organic solvent, and a method for producing a catalyst-carrying electrode comprising a carbon dioxide reduction electrode catalyst supported on the surface.

  Many techniques related to the reduction reaction of carbon dioxide using metal complexes have been proposed. For example, a technique for electrochemically reducing carbon dioxide using a nickel cyclam complex, a rhenium complex, a ruthenium complex, a manganese complex, or the like has been proposed.

In Patent Document 1, when electrochemically reducing carbon dioxide, a nickel cyclam complex is used as a catalyst. By introducing an aliphatic hydrocarbon residue C _n H _{2n + 1} into a ligand structure, nickel is obtained. It describes that the function of the cyclam complex was improved.

  Patent Document 2 describes that a complex having a chelate-like ligand is dispersed in an organic solvent (acetonitrile) and carbon dioxide gas is electrolytically reduced in the organic solvent.

  In Patent Document 3, an electrodeposition coating body is manufactured by coating an object to be coated with a polymer using an electrodeposition coating material in which a polymer and an organic solvent contained in the electrodeposition coating material satisfy a specific Hansen solubility parameter relationship. Is described.

JP-A-4-013883 JP 2013-193056 A JP 2014-173110 A

  The reaction environment of electrolytic reduction in Patent Document 1 and Patent Document 2 is a solution dispersion type in which a catalyst is dispersed in a solution, and the catalyst is not fixed on the electrode surface. Depends on contact probability. For this reason, it is unlikely that the environment considering the reaction efficiency is the best, and even in an actual measurement example, the catalyst current value is about several tens of μA. Therefore, it can be considered that a catalyst is supported on the electrode surface to form a catalyst-supporting electrode.

  Since nickel cyclam complex is deactivated by high heat, it cannot be supported by a method involving heating such as vapor deposition. Therefore, it is conceivable to manufacture the catalyst-supporting electrode by liquid phase coating in which a liquid phase containing a nickel cyclam complex is coated and then the liquid phase is removed by drying. There is a need for a coating agent for producing a carbon dioxide reduction catalyst-carrying electrode with improved reaction efficiency of carbon dioxide reduction reaction by liquid phase coating, on which the electrode catalyst for carbon dioxide reduction is carried on the surface of the electrode substrate. Yes.

The present invention relates to a coating agent comprising an electrocatalyst comprising a nickel cyclam complex and a hydrophobic counteranion, and an organic solvent, the Hansen solubility parameter (HSP) of the electrocatalyst and the Hansen solubility parameter (HSP) of the organic solvent. ) To the following formula (1):
_{Ra = [4 × (δD S} -δD C) 2 + (δP S -δP C) 2 + (δH S -δH C) 2] 1/2 (1)
(Wherein, [delta] D _C, [delta] P _C and delta] H _C are dispersion term of the HSP of each of the electrode catalyst, it represents the polarization term and a hydrogen bond term, [delta] D _S, dispersion term of [delta] P _S and delta] H _S is HSP each said organic solvent Represents a polarization term and a hydrogen bond term), and Ra is 13.6 or less.

The organic solvent is represented by the following formula (2):
[4 × (δD _S −19.3) ² + (δP _S −20.3) ² + (δH _S −7.7) ² ] ^1/2 ≦ 13.6 (2)
(Wherein, [delta] D _S, [delta] P _S and delta] H _S is dispersion term of the HSP of each of the organic solvent,. Representing a polarization term and a hydrogen bond term) is preferable to have a HSP satisfying.

The organic solvent is represented by the following formula (3):
[4 × (δD _S −18.4) ² + (δP _S −17.5) ² + (δH _S −8.1) ² ] ^1/2 ≦ 10.2 (3)
(Wherein, [delta] D _S, [delta] P _S and delta] H _S is dispersion term of the HSP of each of the organic solvent,. Representing a polarization term and a hydrogen bond term) is preferable to have a HSP satisfying.

  The organic solvent preferably contains a compound having at least one of a carbonyl group and a nitrile group.

The method for producing a catalyst-carrying electrode according to the present invention includes a coating that forms a coating layer by bringing a coating agent containing an electrode catalyst containing a nickel cyclam complex and a hydrophobic counteranion and an organic solvent into contact with the surface of an electrode substrate. And a solvent removal step of removing the organic solvent from the coating layer and supporting the electrode catalyst on the surface, wherein the Hansen Solubility Parameter (HSP) of the electrode catalyst is provided. ) And the Hansen solubility parameter (HSP) of the organic solvent, the following formula (1):
_{Ra = [4 × (δD S} -δD C) 2 + (δP S -δP C) 2 + (δH S -δH C) 2] 1/2 (1)
(Wherein, [delta] D _C, [delta] P _C and delta] H _C are dispersion term of the HSP of each of the electrode catalyst, it represents the polarization term and a hydrogen bond term, [delta] D _S, dispersion term of [delta] P _S and delta] H _S is HSP each said organic solvent Represents a polarization term and a hydrogen bond term), and Ra is 13.6 or less.

  By using the coating agent according to the present invention, a carbon dioxide reduction catalyst-carrying electrode in which a carbon dioxide reduction electrode catalyst is carried on the surface of the electrode substrate is used, so that the carbon dioxide reduction reaction by the carbon dioxide reduction electrode catalyst is performed. Reaction efficiency can be improved.

It is a schematic diagram which shows schematic structure of a carbon dioxide reduction apparatus. It is a figure which shows an example of the manufacturing method of the catalyst carrying | support electrode for carbon dioxide reduction. Two BPh as hydrophobic counteranion ₄ ^- shows the chemical structure of nickel cycle ram complexes with. It is a figure which shows the three-dimensional structure based on the single-crystal structure-analysis result of a nickel cyclam complex. It is a figure which shows the solubility data of the nickel cyclam complex in HSP space, and various single organic solvents. It is a figure which shows the solubility data of the nickel cyclam complex in HSP space, and various mixed organic solvents. It is a figure which shows the Hansen solubility sphere based on the solubility data with various organic solvents of a nickel cyclam complex. It is a figure which shows the Hansen solubility sphere based on the solubility data with various mixed organic solvents of a nickel cyclam complex. It is a schematic diagram which shows schematic structure of the carbon dioxide reducing apparatus used for the electrochemical measurement. It is a graph which shows an electrochemical measurement result (cyclic voltammogram). It is a graph which shows an electrochemical measurement result (increase amount of a detection electric current value). It is a graph which shows an electrochemical measurement result (cyclic voltammogram). It is a graph which shows an electrochemical measurement result (increase amount of a detection electric current value). It is a graph which shows the relationship between the electrode catalyst density | concentration of a coating agent, and the electric current increase amount based on the carbon dioxide reduction reaction of a catalyst carrying | support electrode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described herein.

[Configuration of carbon dioxide reduction device]
FIG. 1 shows an electrolysis apparatus (carbon dioxide reduction apparatus) using an electrode (hereinafter also referred to as “catalyst carrying electrode”) on which a carbon dioxide reduction electrode catalyst (hereinafter also simply referred to as “electrode catalyst”) is supported. The schematic diagram of is shown. The electrolytic bath 10 stores an electrolytic solution (aqueous solution) in which an electrolyte and carbon dioxide gas are dissolved, and a pair of electrodes 12 (cathode) and an electrode 14 (anode) are immersed in the electrolytic solution. The electrodes 12 and 14 are connected via a DC power supply 16. A negative voltage is applied to the electrode 12 and a positive voltage is applied to the electrode 14. The electrode 12 includes an electrode substrate 20 and an electrode catalyst layer 18 made of an electrode catalyst supported on the surface of the electrode substrate 20. In the electrolytic cell 10, the chamber on the electrode 12 side and the chamber on the electrode 14 side may be partitioned by an ion exchange membrane or the like.

With such a configuration, a reduction reaction occurs in the electrode 12, and an oxidation reaction occurs in the electrode 14. For example, in the electrode 14, H ₂ O is oxidized and decomposed into O ₂ gas and H ⁺ . On the other hand, at the electrode 12, CO ₂ is reduced, and a reducing substance such as CO, HCOOH, and CH ₄ is obtained. In the carbon dioxide reduction apparatus of FIG. 1, the carbon dioxide reduction electrode catalyst is arranged on the surface of the electrode 12, thereby promoting the carbon dioxide reduction reaction at the electrode 12.

[Catalyst electrode for reducing carbon dioxide]
In FIG. 2, an example of the manufacturing method of the catalyst carrying electrode 12 which concerns on this embodiment is shown. The catalyst-supporting electrode 12 according to the present embodiment includes a coating process in which the coating agent according to the present embodiment is brought into contact with the surface of the electrode substrate 20 to form the coating layer 22, and the organic solvent is removed from the formed coating layer 22. And a solvent removing step for supporting the electrode catalyst on the surface.

  In FIG. 2, the coating agent of this embodiment is made to contact by dripping on the surface of the electrode substrate 20, and the coating layer 22 is formed (coating process). Next, the organic solvent contained in the coating layer 22 is removed by natural drying, and the electrode catalyst is supported (fixed) on the surface of the electrode substrate 20 (solvent removal step), and the electrode catalyst layer 18 composed of the electrode catalyst is formed. The catalyst carrying electrode provided is manufactured. The surface of the electrode substrate 20 where the electrode catalyst layer 18 is not formed is covered with a masking 24. The method for manufacturing the catalyst-carrying electrode 12 according to the present embodiment is not limited to the mode shown in FIG.

  In the carbon dioxide reduction reaction by the nickel cyclam complex, carbon dioxide is added to the activated Ni ion center, and the carbon dioxide is activated to enable the reduction reaction (Shengfa Ye et. Al., Inorg. Chem., 2014, 53, 7500).

However, if there is a gap such as a pinhole or crack in the electrode catalyst layer 18 of the catalyst-carrying electrode 12, the electrolyte enters the gap and directly contacts the electrode substrate 20 to decompose the electrolyte (H ₂ O). (H ₂ generation reaction) occurs. As a result, some electrons flow and compete in the H ₂ generation reaction, which may reduce the reaction efficiency of the carbon dioxide reduction reaction by the electrode catalyst. Such a gap in the electrode catalyst layer 18 may occur when the catalyst-carrying electrode 12 is manufactured using a dispersed slurry in which the electrode catalyst is not sufficiently dissolved and the electrode catalyst particles are dispersed in the liquid phase as a coating agent. is there. On the other hand, if the electrode catalyst layer 18 is formed thick so as not to generate a gap, the electrode catalyst may act as an insulator, hindering the movement of electrons, and an efficient reduction reaction may not be performed.

  Since the coating agent according to this embodiment has a high solubility in the electrode catalyst of the organic solvent, the electrode catalyst does not aggregate by using the coating agent according to this embodiment, and the electrode catalyst has a uniform and high concentration on the electrode surface. An electrode catalyst layer 18 that is distributed and substantially free of gaps can be formed. For this reason, the manufacturing method according to the present embodiment does not cause a gap that reduces the reaction efficiency of the carbon dioxide reduction reaction in the electrode catalyst layer 18 and suppresses the thickness of the electrode catalyst layer 18. Can be manufactured.

  The thickness of the electrode catalyst layer 18 formed on the surface of the electrode substrate 20 can be adjusted by the concentration of the electrode catalyst contained in the coating agent according to this embodiment. If the electrode catalyst layer 18 is too thin, pinholes, cracks, etc. may occur in the electrode catalyst layer 18 in the coating process or the solvent removal process. If the electrode catalyst layer 18 is too thick, the movement of electrons is hindered and there is a possibility that an efficient reduction reaction cannot be performed.

  Moreover, the manufacturing method of the catalyst carrying electrode 12 using the coating agent which concerns on this embodiment is very simple. Furthermore, in the method for manufacturing the catalyst-carrying electrode 12 according to the present embodiment, since the material and shape of the electrode substrate 20 are not selected, a wide range of applications are possible for the catalyst-carrying electrode 12 according to the present embodiment. As a material used for the electrode substrate 20, a material having a high hydrogen overvoltage such as tin, zinc, lead, mercury, and carbon (glassy carbon) is desirable from the viewpoint of a carbon dioxide reduction reaction.

  The coating process for forming the coating layer 22 on the surface of the electrode substrate 20 is performed by bringing it into contact with the surface of the electrode substrate 20 by a known method such as spin coating or dip method, in addition to the dropping method shown in FIG. be able to. The solvent removal step of removing the solvent from the coating layer 22 can be performed by a known drying method that does not involve heating, such as natural drying or vacuum drying.

  In the catalyst-supporting electrode 12 according to the present embodiment, as shown in FIG. 1, the electrode catalyst layer 18 may be formed on all surfaces immersed in the electrolytic solution, and as shown in FIG. The electrode catalyst layer 18 may be formed on a part of the surface, and the remaining surface may be formed with a masking 24 that prevents contact between the electrolytic solution and the electrode substrate 20.

[Coating agent]
The coating agent according to the present embodiment is used in the production of the catalyst-supporting electrode 12, and includes an electrode catalyst containing a nickel cyclam complex and a hydrophobic counter anion, an organic solvent, and a Hansen solubility parameter (HSP) of the organic solvent. ) And the Hansen parameter (HSP) of the electrode catalyst, the following formula (1):
_{Ra = [4 × (δD S} -δD C) 2 + (δP S -δP C) 2 + (δH S -δH C) 2] 1/2 (1)
(Wherein, [delta] D _C, [delta] P _C and delta] H _C are dispersion term of HSP each electrode catalyst, represents the polarization term and a hydrogen bond term, [delta] D _S, [delta] P _S and delta] H _S dispersion section HSP each organic solvent, polarization The term “Ra” represents a term and a hydrogen bond term.) Ra is calculated to be 13.6 or less.

  The Hansen Solubility Parameter (HSP) is a parameter introduced to estimate the solubility of a solute in a solvent, and includes a dispersion term (δD), a polarization term (δP), and a hydrogen bond term (δH). It consists of the parameters of the term. Each of these three parameters is material specific. When the HSP of two substances (for example, a solute and a solvent) is plotted in a three-dimensional space (HSP space) in which the parameters of these three terms are regarded as xyz coordinates, the closer the distance between the two plotted points, the two substances Means that they are easy to dissolve each other.

  The electrode catalyst and the organic solvent contained in the coating agent according to this embodiment can be used regardless of whether the HSP is unknown or known. The HSP of a substance whose HSP is unknown can be determined by the method described later, and if the molecular structure is clear, it can be estimated from the molecular structure. HSPs of substances whose HSPs are known can be obtained from databases and literatures. For example, the HSP of the liquid solvent is registered in a database included in commercially available software (HSPiP 4th Edition ver.4.1.07).

  In order to determine the HSP of a substance whose HSP is unknown, first, it is confirmed whether or not the substance is dissolved using a solvent whose HSP is known. The HSP of the solvent that dissolves the material is then plotted in the HSP space. At this time, in the HSP space, plots of the solvent that dissolves the substance are collected in a certain region. Next, a sphere (called a Hansen solubility sphere (HS-Sphere)) that includes all of these solvent plots and has the smallest diameter in the HSP space is calculated. The center coordinates of the sphere calculated at this time are determined as the HSP of the substance. That is, it can be said that the spherical surface of the Hansen solubility sphere and the substance having HSP therein have solubility in a substance having HSP at the center coordinates of the Hansen solubility sphere.

[Electrocatalyst for carbon dioxide reduction]
The electrode catalyst for carbon dioxide reduction used in the coating agent according to the present embodiment includes 1,4,8,11-tetraazacyclotetradecane and nickel cyclam complex containing nickel as a central metal, and a counter anion. And is used for electrolytic reduction in an aqueous solution of carbon dioxide gas. As the hydrophobic anion, any anion exhibiting hydrophobicity due to delocalization of electrons in the molecule can be used. For example, tetraphenylborate ion (BPh ₄ ⁻ ), hexafluoro Examples thereof include phosphate ion (PF ₆ ⁻ ), hexafluoroantimonate ion (SbF ₆ ⁻ ), and the like. In addition, neutral molecules may be coordinated to the nickel cyclam complex. For example, two neutral molecules may be coordinated to each molecule of the nickel cyclam complex. Examples of the neutral molecule coordinated to the nickel cyclam complex include acetonitrile, tetrahydrofuran, water, and the like.

  When the electrode catalyst contains a combination of a nickel cyclam complex containing nickel as a base metal and a hydrophobic counter anion, the solubility of the nickel cyclam complex in an aqueous solvent can be suppressed. For this reason, even if the catalyst-supporting electrode is immersed in the electrolytic solution in the carbon dioxide reduction device, the electrode catalyst can be held without being substantially dissolved while being fixed to the surface of the electrode substrate. As a result, compared with a conventional solution dispersion type reaction system in which a carbon dioxide reduction catalyst is dispersed or dissolved in an aqueous solution, complex molecules that react with carbon dioxide can be arranged at a high density on the electrode surface. In addition, it is possible to express a reduction ability equal to or higher than that of the conventional solution dispersion type, and to achieve a significant improvement in reaction efficiency. Moreover, since a base metal is used, it is advantageous in terms of cost.

[Organic solvent]
As the organic solvent used in the coating agent according to the present embodiment, Ra calculated by the above formula (1) using the HSP of the organic solvent and the HSP of the electrode catalyst used in combination is 13.6 or less. Such an HSP. Even if the organic solvent according to the present embodiment is a single organic solvent containing only one type of organic compound as long as Ra calculated by the above formula (1) is 13.6 or less, two or more types of organic solvents may be used. A mixed organic solvent containing an organic compound may be used. Therefore, the organic compound contained in the mixed organic solvent may or may not satisfy the requirement that “Ra is 13.6 or less” when used alone.

  Examples of the organic compound used in the organic solvent according to this embodiment include acetonitrile, acrylonitrile, propionitrile, acetone, methyl ethyl ketone (MEK), propionaldehyde, N, N-dimethylformamide (DMF), cyclobutanone, and cyclopentanone. , Cyclohexanone and dimethyl sulfoxide (DMSO). For example, these may be used alone as the organic solvent according to the present embodiment.

  Examples of the organic compound used in the organic solvent according to this embodiment include tetrahydrofuran (THF), dichloromethane, chloroform (trichloromethane), chlorobenzene, methanol, ethanol, 2-butanol, benzyl alcohol, propylamine, formamide, Examples include diethyl ether and hexane. These can be used, for example, as at least one kind of compounds contained in the mixed organic solvent.

The organic solvent according to this embodiment has the following formula (2):
[4 × (δD _S −19.3) ² + (δP _S −20.3) ² + (δH _S −7.7) ² ] ^1/2 ≦ 13.6 (2)
It is preferable to have an HSP that satisfies the above. In the case where the organic solvent has HSP satisfying the formula (2), an electrode catalyst containing a nickel cyclohexane complex and a tetraphenylborate ion (BPh ₄ ⁻ ) as a hydrophobic counter anion is dissolved. It can be used as a coating agent.

  Examples of the organic compound having HSP that satisfies the above formula (2) include acetonitrile, acrylonitrile, propionitrile, acetone, MEK, propionaldehyde, DMF, cyclobutanone, cyclopentanone, cyclohexanone, DMSO, and the like.

Moreover, HSP of the organic solvent which concerns on this embodiment is following formula (3):
[4 × (δD _S −18.4) ² + (δP _S −17.5) ² + (δH _S −8.1) ² ] ^1/2 ≦ 10.2 (3)
It is preferable to satisfy. ΔD _S, δP _S and delta] H _S even in the formula (3) are as defined above. Since the organic solvent having HSP satisfying the formula (3) has higher solubility with respect to an electrode catalyst including a tetracyclborate ion (BPh ₄ ⁻ ) as a nickel cycle complex and a hydrophobic counter anion, It can be used more suitably in such a coating agent.

  The organic compound contained in the organic solvent according to this embodiment preferably has at least one of a carbonyl group and a nitrile group. This is because an organic compound having at least one of a carbonyl group and a nitrile group is excellent in the solubility of the hydrophobic counter anion possessed by the electrode catalyst.

  Since the organic solvent according to the present embodiment has sufficient quick drying properties, the time required for the solvent removal step can be shortened. The evaporation rate of the organic compound can be measured using a standard test method stipulated in ASTM standard D3539. The evaporation rate of the target substance measured at 25 ° C. is measured at butyl acetate (25 ° C.). It can be defined by the relative evaporation rate normalized by the evaporation rate of a reference material such as BuAc).

  The relative evaporation rate of the organic solvent according to the present embodiment is preferably 3.0 or more, preferably 4.5 or more, where the evaporation rate of the reference material BuAc is 1. Examples of the organic compound having an ER of 3.0 or more include acetonitrile (5.79), acrylonitrile (4.54), acetone (5.70), MEK (3.70), THF (4.80), and the like. (The ER value for BuAc is shown in parentheses). From the above viewpoint, a coating agent containing these organic compounds alone or in combination as an organic solvent is preferable.

  Preferred specific examples of the organic solvent according to the present embodiment include an organic solvent containing acetonitrile, acrylonitrile, acetone, methyl ethyl ketone, and a combination thereof, and a mixing ratio of acetonitrile and THF of 90:10 or more and 50:50 or less. Preferably, a mixed organic solvent having a mixing ratio of 70:30 to 50:50 is used. A mixed organic solvent formed by mixing the above acetonitrile and THF is particularly preferable because it is easy to handle.

  The concentration of the electrode catalyst in the coating agent according to the present embodiment varies depending on the combination of the electrode catalyst used and the organic solvent, but can be set to, for example, 1 mM to 100 mM. Since the electrode catalyst layer having an appropriate thickness is formed to improve the reaction efficiency of the carbon dioxide reduction reaction, the concentration of the electrode catalyst in the coating agent according to this embodiment is preferably 10 mM or more and 50 mM or less.

  Hereinafter, based on an Example, embodiment of this invention is described more concretely. In addition, this invention is not limited to a following example.

Example 1
[Structural analysis of nickel cyclam complex with hydrophobic counteranion]
A nickel cyclam complex (hereinafter also referred to as “complex A”) having two sodium tetraphenylborate (BPh ₄ ⁻ ) as a hydrophobic counter anion and two acetonitriles as ligands is used as a raw material. , 8,11-tetraazacyclotetradecane (manufactured by Tokyo Chemical Industry Co., Ltd., product code T1597) and sodium tetraphenylborate (manufactured by Dojin Chemical Laboratory, Kalibor (registered trademark)). FIG. 3 shows the chemical structure of the complex A, and Table 1 shows the comparison result between the elemental analysis results (actually measured values) of the actually produced complexes and the calculated values (theoretical values) obtained from the chemical structure shown in FIG. . As shown in Table 1, the measured value and the theoretical value showed good agreement.

The single crystal structure analysis of the complex A actually produced was performed, FIG. 4 shows the three-dimensional structure based on the result, and Table 2 shows the crystal data after the analysis. In FIG. 4, only one hydrophobic counter anion “BPh ₄ ⁻ ” is displayed because of symmetry. Single crystal structure analysis also confirmed the presence of hydrophobic counter anions in the nickel cyclam complex.

(Example 2)
[HSP determination of nickel cyclam complex]
In order to obtain solubility data of the complex A and various organic solvents, a dissolution test was performed. The dissolution test is performed using a single organic solvent containing only one organic compound or a mixed organic solvent containing two organic compounds, and 5 mg of complex A is dissolved in 20 μl of various organic solvents. After stirring, it was performed by visually confirming whether it was completely dissolved. In a dissolution test using a mixed organic solvent, two types of organic compounds that dissolve each other but have different HSP values are selected, and the mixed ratio is changed to prepare a mixed organic solvent. It was confirmed.

FIG. 5 and Table 3 show the results of plotting the solubility data of Complex A and various single organic solvents in the HSP space. FIG. 6 and Table 4 show the results of plotting solubility data of the complex A and various mixed organic solvents in the HSP space. In FIG. 5, FIG. 6, Table 3 and Table 4, the evaluation criteria for the solubility (Solubility) of Complex A when various organic solvents are used are as follows.
○: soluble (quickly and completely dissolved)
Δ: Soluble but requires more than 24 hours to dissolve □: Insoluble

FIG. 7 shows the Hansen solubility sphere calculated based on the solubility data obtained by combining the solubility data of a single organic solvent and the solubility data of a mixed organic solvent. Center coordinates of the Hansen solubility sphere, i.e., HSP value of complex A is, [delta] D _C = 19.3, a [delta] P _C = 20.3 and delta] H _C = 7.7, the radius _{R 0} Hansen sphere 13. 6. In addition, the Hansen solubility sphere described in FIG. 7 was calculated by regarding an organic solvent having a solubility evaluation of Δ as a soluble solvent. An organic solvent having HSP on and inside the Hansen solubility sphere shown in FIG. 7 can dissolve the complex A and is considered to be usable in the coating agent of this embodiment.

FIG. 8 shows a Hansen solubility sphere calculated based only on the solubility data of the mixed organic solvent containing two kinds of organic compounds and the complex A. Center coordinates of the Hansen solubility sphere, δD _C = 18.4, a [delta] P _C = 17.5 and delta] H _C = 8.1, the radius _{R 0} Hansen spheres was 10.2. The Hansen solubility sphere described in FIG. 8 was calculated by regarding an organic solvent whose solubility was evaluated as Δ as an insoluble solvent. Therefore, the organic solvent having HSP on and inside the Hansen solubility sphere shown in FIG. 8 is considered to have higher solubility in the complex A.

(Example 3)
[Production of catalyst-supported electrode for carbon dioxide reduction]
Complex A is dissolved in an organic solvent obtained by mixing acetonitrile and THF at a mixing ratio of 50% (v / v): 50% (v / v), and the concentration is adjusted to 50 mmol / L. A coating agent according to the form was prepared. The HSP of the organic solvent is δD _S = 16.1, δP _S = 11.9 and δH _S = 7.1, and Ra calculated by the above formula (1) using the HSP of the complex A is 10 .5.

  The coating agent was dropped onto the surface of the electrode substrate 20 made of a tin plate to form a coating layer. Then, the organic solvent contained in the coating layer was removed by natural drying at normal temperature in the atmosphere, and a catalyst-carrying electrode having an electrode catalyst supported on the surface was produced.

(Comparative Example 1)
In the same manner as in Example 1, except that THF was used alone instead of the organic solvent used in Example 3 and a dispersion slurry in which Complex A was dispersed in THF was used as a coating agent, Manufactured. The HSP of THF is δD _S = 16.8, δP _S = 5.7 and δH _S = 8.0, and Ra calculated by the above formula (1) using the HSP of the complex A is 15.4. Met.

Example 4
[Electrochemical measurement]
A carbon dioxide reduction device as shown in FIG. 9 was prepared, and each of the catalyst-carrying electrode of Example 3, the catalyst-carrying electrode of Comparative Example 1, and the tin plate electrode having no electrode catalyst on the surface for reference was used as a working electrode. 26 was used for electrochemical measurements. In the electrochemical measurement, the potential of the working electrode 26 was swept with respect to the potential of the reference electrode 30 by a potentiostat 32, and the amount of current at that time was measured. The electrolyte used was a 0.1 M aqueous KCl solution (pH 4.0), and was thoroughly deaerated with nitrogen before measurement. The reference electrode 30 used Ag / AgCl, and the counter electrode 28 used a platinum wire. The sweep speed was set to 100 mV / sec. Five cycles of cyclic voltammetry (CV), sweeping from natural potential to -1.6 V (counter reference electrode) and then to -0.5 V (counter reference electrode), were performed. Thereafter, carbon dioxide gas was introduced until saturation, and CV was performed again under the above conditions. The presence or absence of a carbon dioxide reduction reaction was confirmed by comparing the detected current value in a nitrogen atmosphere with the detected current value in a carbon dioxide atmosphere.

  FIGS. 10 and 11 show that the catalyst-supporting electrode (Catalyst) and the reference tin plate electrode (No catalyst) of Example 3 were used in a nitrogen atmosphere (N2) and a carbon dioxide atmosphere (CO2), respectively. The electrochemical measurement results are shown. 12 and 13 show the electrochemical measurement results in a carbon dioxide atmosphere (CO2) when the catalyst-carrying electrode (Solution) of Example 3 and the catalyst-carrying electrode (Slurry) of Comparative Example 1 are used, respectively. Show. 10 and 12 are diagrams (cyclic voltammograms) showing the detected current value (Current) with respect to the applied potential (Potential). In FIGS. 11 and 13, the increase in the detected current value with respect to the applied potential (Potential) is shown. The amount (Current gain) is shown.

As shown in FIG. 10, in a nitrogen atmosphere, a current due to hydrogen generation was observed from −1.1 V (vs SHE). On the other hand, in a carbon dioxide atmosphere, an increase in the current value derived from the carbon dioxide reduction reaction was observed from −0.93 V (vs SHE), and a peak due to the diffusion-controlled diffusion of carbon dioxide molecules was confirmed. The peak current value based on the carbon dioxide reduction catalytic reaction at this time was 2.5 mA · cm ⁻² . The catalyst-carrying electrode of Example 3 according to this embodiment is such that the electrode catalyst is fixed on the surface of the electrode substrate even in the electrolytic solution, and the electrode catalyst is uniformly and highly concentrated to such an extent that there is no gap for the electrolytic solution to enter. By providing the distributed catalyst electrode layer, it was possible to further improve the reaction efficiency of the carbon dioxide reduction reaction by the electrode catalyst.

  As shown in FIGS. 12 and 13, the catalyst-carrying electrode of Comparative Example 1 produced using the dispersed slurry is different from the catalyst-carrying electrode of Example 3 produced using the coating agent according to the present embodiment. An increase in the current value derived from the carbon dioxide reduction reaction was not detected even in a carbon dioxide atmosphere. Moreover, the electrochemical measurement result of Comparative Example 1 in FIGS. 12 and 13 has an appearance that is very similar to the electrochemical measurement result of the tin plate electrode having no catalyst in FIGS. 10 and 11. A common point is that a current value increases significantly after .1 V (vs SHE), a small current value peak appears at -0.75 V (vs SHE), and the like. Therefore, in the coating agent of Comparative Example 1, Ra calculated by the above formula (1) exceeded 13.6, and the hydrophobic nickel cyclam complex was not dissolved but became a dispersed slurry. As a result, a gap is formed in the electrode catalyst layer of the catalyst-supported electrode manufactured using the above coating agent, and the electrolytic solution is in direct contact with the electrode substrate. As a result, the reaction efficiency of the carbon dioxide reduction reaction by the electrode catalyst is improved. Is considered to have been hardly obtained.

(Example 5)
In the same manner as in Example 3, the concentration of the complex A in the coating agent is 1.0 mmol / L, 5.0 mmol / L, 10 mmol / L, 25 mmol / L, 50 mmol / L, or 100 mmol / L. Each such coating agent was prepared. Using the coating agent containing the complex A at each concentration, a catalyst-carrying electrode having an electrode catalyst supported on the surface was produced.

  Using each of the catalyst-supported electrodes obtained above as the working electrode 26, electrochemical measurement was performed in a carbon dioxide atmosphere in the same manner as in Example 4. From the result of electrochemical measurement, the area of the peak corresponding to the carbon dioxide reduction reaction existing in the vicinity of −1.1 V (vs SHE) in the graph showing the increase in the detected current value with respect to the applied potential was calculated. This peak area is considered to be proportional to the amount of electricity consumed by the carbon dioxide reduction catalytic reaction during the electrochemical measurement, that is, the amount of carbon dioxide reduced. The peak of the current increase corresponding to the carbon dioxide reduction reaction calculated from the electrode catalyst concentration (Concentration) of the coating agent according to the present embodiment and the electrochemical measurement result of the catalyst-supported electrode produced using each coating agent The relationship with the area (Peak area) is shown in FIG.

  As shown in FIG. 14, in the catalyst-supported electrode produced in Example 5, the carbon dioxide reduction reaction was performed when the coating agent having a concentration of complex A of 10 mmol / L, 25 mmol / L, and 50 mmol / L was used. The peak area of the amount of current increase corresponding to is maximized. As a result of adjusting the concentration of the electrode catalyst in the coating agent according to the present embodiment, the thickness of the electrode catalyst layer formed on the surface of the electrode substrate is optimized, and the reaction efficiency of the carbon dioxide reduction reaction is further improved. Conceivable.

  DESCRIPTION OF SYMBOLS 10 Electrolyzer, 12 electrodes (catalyst carrying electrode), 14 electrodes, 16 DC power supply, 18 carbon dioxide reduction electrode catalyst layer, 20 electrode substrate, 22 coating layer, 24 masking, 26 working electrode, 28 counter electrode, 30 reference electrode, 32 Potentiostat.

Claims (5)

A coating agent comprising an electrocatalyst comprising a nickel cyclam complex and a hydrophobic counteranion, and an organic solvent,
Using the Hansen solubility parameter (HSP) of the electrode catalyst and the Hansen solubility parameter (HSP) of the organic solvent, the following formula (1):
_{Ra = [4 × (δD S} -δD C) 2 + (δP S -δP C) 2 + (δH S -δH C) 2] 1/2 (1)
(Wherein, [delta] D _C, [delta] P _C and delta] H _C are dispersion term of the HSP of each of the electrode catalyst, it represents the polarization term and a hydrogen bond term, [delta] D _S, dispersion term of [delta] P _S and delta] H _S is HSP each said organic solvent Represents a polarization term and a hydrogen bond term.)
The coating agent, characterized in that Ra calculated by the formula is 13.6 or less. The organic solvent is represented by the following formula (2):
[4 × (δD _S −19.3) ² + (δP _S −20.3) ² + (δH _S −7.7) ² ] ^1/2 ≦ 13.6 (2)
(Represented in the formula, [delta] D _S, [delta] P _S and delta] H _S is dispersion term of the HSP of each of the organic solvent, a polarization term and a hydrogen bond term.)
The coating agent according to claim 1, wherein the coating agent has an HSP that satisfies the conditions. The organic solvent is represented by the following formula (3):
[4 × (δD _S −18.4) ² + (δP _S −17.5) ² + (δH _S −8.1) ² ] ^1/2 ≦ 10.2 (3)
(Represented in the formula, [delta] D _S, [delta] P _S and delta] H _S is dispersion term of the HSP of each of the organic solvent, a polarization term and a hydrogen bond term.)
The coating agent according to claim 1, wherein the coating agent has an HSP that satisfies the conditions.   The said organic solvent contains the compound which has at least one of a carbonyl group and a nitrile group, The coating agent as described in any one of Claims 1-3 characterized by the above-mentioned. A coating step of forming a coating layer by bringing a coating agent containing a nickel cyclam complex and a hydrophobic counter anion into contact with a surface of an electrode substrate with a coating agent containing an organic solvent;
Removing the organic solvent from the coating layer and supporting the electrode catalyst on the surface, a method for producing a catalyst-carrying electrode,
Using the Hansen solubility parameter (HSP) of the electrode catalyst and the Hansen solubility parameter (HSP) of the organic solvent, the following formula (1):
_{Ra = [4 × (δD S} -δD C) 2 + (δP S -δP C) 2 + (δH S -δH C) 2] 1/2 (1)
(Wherein, [delta] D _C, [delta] P _C and delta] H _C are dispersion term of the HSP of each of the electrode catalyst, it represents the polarization term and a hydrogen bond term, [delta] D _S, dispersion term of [delta] P _S and delta] H _S is HSP each said organic solvent Represents a polarization term and a hydrogen bond term.)
Ra calculated by the above is 13.6 or less.