Oxygen evolution catalyst and electrode for oxygen evolution reaction

Abstract

To provide an oxygen evolution catalyst that evolves oxygen from water, the catalyst capable of reducing the voltage required for oxygen evolution.SOLUTION: The present invention provides an oxygen evolution catalyst that is a Ni complex of a ligand of an imidazole derivative having a carbonyl group and a Ni salt, or an Fe complex of a ligand of an imidazole derivative having a carbonyl group and an Fe salt.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an oxygen generation catalyst for generating oxygen from water, and an electrode for an oxygen generation reaction including the oxygen generation catalyst.

Background Art

[0002] The oxygen generation reaction for generating oxygen from water is used as a counter electrode reaction such as a water electrolysis reaction for generating hydrogen in an alkaline solution or a carbon dioxide reduction reaction for synthesizing useful compounds such as carbon monoxide, formic acid, and ethanol from carbon dioxide (CO2). Various studies have been conducted on the oxygen generation catalyst used in this oxygen generation reaction.

[0003] For example, Non-Patent Document 1 describes an oxygen generation reaction using an oxygen generation catalyst synthesized based on both or one of Ni(NO3)2·6H2O and Co(NO3)2·6H2O and 2-methylimidazole. Even the catalyst containing both Ni and Co having the highest performance in Non-Patent Document 1 requires a high voltage of about 300 mV.

[0004] Non-Patent Document 2 describes an oxygen generation reaction using an oxygen generation catalyst synthesized based on both or one of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O and 2-methylimidazole. In the catalyst containing both Ni and Fe having the highest performance in Non-Patent Document 2, the required voltage is about 200 mV, and in the catalyst containing only Ni, the required voltage is as high as 300 mV.

[0005] Non-Patent Document 3 describes an oxygen generation reaction using an oxygen generation catalyst synthesized based on at least one of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O and 2-methylimidazole. Even the catalyst containing three types of Ni, Co, and Fe having the highest performance in Non-Patent Document 3 requires a high voltage of about 250 mV.

[0006] Non-Patent Document 4 describes an oxygen generation reaction using a metal oxide-based oxygen generation catalyst in which NiOOH / FeOOH is formed on a Ni foam. In the reaction of Non-Patent Document 4, an overvoltage of 250 mV is required to generate a current of 10 mA.

[0007] Non-Patent Document 5 describes an oxygen generation reaction using a metal oxide-based oxygen generation catalyst in which NiOOH / FeOOH is formed on a Ni foam. In the catalyst having the highest performance in Non-Patent Document 5, an overvoltage of 290 mV is required to generate a current of 10 mA.

[0008] Non-Patent Document 6 describes an oxygen generation reaction using a Ni-Fe-based metal complex type oxygen generation catalyst having a pyridine-based ligand. Since Non-Patent Document 6 uses a catalyst dissolved in a reaction solution and conducts an examination using a glassy carbon electrode, the generated current value is quite small, about 0.3 mA. In addition, the electrolytic solution requires 10% by mass of acetonitrile in a 0.1 M NaHCO3 aqueous solution with a pH of about 10.

[0009] Non-Patent Document 7 describes an oxygen generation reaction using a metal oxide-based oxidation generation catalyst in which a NiFeCu metal salt is added on a Ni foam and NiOOH is driven as a catalyst. In Non-Patent Document 7, the reaction is carried out in a 0.5 M KHCO3 aqueous solution that is not saturated with carbon dioxide. In the catalyst having the highest performance in Non-Patent Document 5, an overvoltage of 385 mV is required to generate a current of 10 mA.

[0010] Non-Patent Documents 1 to 5 are examples of using an alkaline electrolytic solution as a reaction solution for the oxygen generation reaction. It is known that an oxygen generation catalyst using imidazole, particularly 2-methylimidazole, as a ligand as in Non-Patent Documents 1 to 3 can generate oxygen at a lower voltage than an oxygen generation catalyst of a single metal such as Ni foam. In the prior art using 2-methylimidazole, it is known that it can be driven at a relatively low voltage only when using an oxygen generation catalyst combining a plurality of metal salts (such as Fe and Ni, Fe, Ni, and Co), and the voltage required for oxygen generation increases when using only a single metal species.

[0011] In addition, as oxygen generation catalysts, metal oxide-based oxygen generation catalysts such as those in Non-Patent Documents 4 and 5 are well known. However, even for metal oxide-based catalysts (FeOOH + NiOOH) synthesized based on an alloy type into which a plurality of atoms have been introduced, the overvoltage required is as large as 250 mV or more as described above.

[0012] Non-Patent Documents 6 and 7 are examples of using a neutral electrolyte as the reaction solution for the oxygen generation reaction. There are very few examples of studies on metal complex-based oxygen generation catalysts in a neutral electrolyte. Non-Patent Document 6 is an example of a pyridine-based Ni-Fe-based metal complex type oxygen generation catalyst in 0.1 M NaHCO3 (containing 10% by mass of acetonitrile) at about pH 10. However, since a water-soluble catalyst is used, the generated current value is small and remains at about 0.3 mA as described above.

[0013] There are reports of using metal oxide-based oxygen generation catalysts even under neutral conditions as in Non-Patent Document 7. However, even for a catalyst of a metal oxide-based catalyst (NiOOH + Fe + Cu) synthesized based on an alloy type into which a plurality of atoms have been introduced, the overvoltage required is as large as 385 mV as described above.

[0014] When an oxygen generation catalyst is used in combination with a catalyst for carbon dioxide reduction, a two-chamber reaction cell in which the oxygen generation catalyst and the catalyst for carbon dioxide reduction are separated and operated by a membrane is common. However, some carbon dioxide (CO2) is HCO3 - or CO3 2-It is known that it will pass through the membrane in this state, and in the long term, the electrolyte used in the oxygen generation catalyst will also contain carbon dioxide. Therefore, over time, an alkaline solution such as 1M KOH undergoes a neutralization reaction, gradually causing a decrease in pH, leading to a decrease in catalytic activity and an increase in the voltage required to drive the reaction. Similarly, in other electrolytes, as carbon dioxide dissolves, the pH gradually decreases towards the neutral side. Considering long-term use, it is desirable to be able to react with a neutral electrolyte saturated with carbon dioxide. However, as known from Non-Patent Documents 3 and 4, in a carbon dioxide-saturated electrolyte, the voltage required for the oxygen generation reaction is higher than that in a carbon dioxide-unsaturated electrolyte. Most of the oxygen generation catalysts so far are inorganic metal / metal oxide catalysts, and these are known to have the highest catalytic performance in alkaline solutions and are particularly difficult to react in a carbon dioxide-saturated electrolyte.

Prior Art Documents

Non-Patent Documents

[0015]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0016] An object of the present invention is to provide an oxygen generation catalyst capable of reducing the voltage required for oxygen generation in a catalyst for generating oxygen from water, and an electrode for an oxygen generation reaction containing the oxygen generation catalyst.

Means for Solving the Problems

[0017] The present invention is an oxygen generation catalyst which is a Ni complex of an imidazole derivative having a carbonyl group and a Ni salt or an Fe complex of an Fe salt.

[0018] In the oxygen generation catalyst, the carbonyl group is preferably at least one of a ketone group and an ester group.

[0019] In the oxygen generation catalyst, the Ni salt or the Fe salt is preferably at least one of a nitrate and a chloride salt.

[0020] In the oxygen generation catalyst, the imidazole derivative is preferably at least one of carbonyldiimidazole and oxalyldiimidazole.

[0021] In the oxygen generation catalyst, the oxygen generation catalyst is preferably for an oxygen generation reaction in which oxygen is generated using an alkaline aqueous solution having a pH of 10 or more as a reaction solution.

[0022] In the oxygen generation catalyst, the imidazole derivative is oxalyldiimidazole, and the oxygen generation catalyst is preferably for an oxygen generation reaction in which oxygen is generated using a neutral aqueous solution having a pH of 6 to 8 as a reaction solution.

[0023] The present invention is an electrode for an oxygen generation reaction containing the above oxygen generation catalyst.

Effects of the Invention

[0024] According to the present invention, in a catalyst for generating oxygen from water, an oxygen generation catalyst capable of reducing the voltage required for oxygen generation, and an electrode for oxygen generation reaction including the oxygen generation catalyst can be provided.

Mode for Carrying Out the Invention

[0025] Embodiments of the present invention will be described below. This embodiment is an example of carrying out the present invention, and the present invention is not limited to this embodiment.

[0026] <Oxygen Generation Catalyst> The oxygen generation catalyst according to this embodiment is a Ni complex of an imidazole derivative having a carbonyl group and a Ni salt, or an Fe complex of an imidazole derivative having a carbonyl group and an Fe salt.

[0027] In the oxygen generation reaction, as an equilibrium potential for generating oxygen from water, it is necessary to perform an electrochemical reaction at a value higher than 1.23 V vs RHE (reversible hydrogen electrode level). In reality, almost no oxygen generation reaction occurs when a voltage of 1.23 V is applied, and the reaction does not proceed unless an extra voltage (overvoltage) corresponding to the activation energy is applied. Therefore, the larger the overvoltage, the more it becomes a factor of energy loss. The oxygen generation reaction is a reaction used as a counter electrode reaction such as a water electrolysis reaction for generating hydrogen in an alkaline solution or a carbon dioxide reduction reaction for synthesizing useful compounds such as carbon monoxide, formic acid, and ethanol from carbon dioxide. In order to reduce the energy (voltage) required for the entire reaction, it is also important to reduce the overvoltage of the oxygen generation reaction.

[0028] The present inventors considered that in an electrochemically driven oxygen generation catalyst, an approach such as bringing water close to the active center and facilitating the reception of electrons and protons contributes to a reduction in overvoltage.

[0029] In the oxygen generation catalyst according to this embodiment, imidazole, which is an organic compound with high electron conductivity and proton conductivity, and among them, an imidazole derivative having a carbonyl group is included as a ligand in the catalyst structure, so that the effect of enhancing the reception efficiency of electrons and protons can be expected. Further, by having an interaction such as a hydrogen bond between the carbonyl group and water, water molecules can be adjacent to the vicinity of the metal atom serving as the catalyst center, and an improvement in the catalyst reaction probability can also be expected. In the oxygen generation catalyst according to this embodiment, it is considered that these factors can reduce the voltage required for oxygen generation.

[0030] The oxygen generation catalyst according to this embodiment is formed by a combination of a ligand R, which is an imidazole derivative having a carbonyl group, and a salt of a metal M (Ni or Fe).

[0031]

Chemical formula

[0032] As the Ni salt or Fe salt, any one can be used as long as it can be used for catalyst synthesis as a Ni ion source or Fe ion source, and there is no particular limitation. Examples of the Ni salt or Fe salt include inorganic salts such as nitrates, sulfates, chloride salts, bromide salts, and organic salts such as citrate salts. From the viewpoint of catalyst performance and the like, nitrates and chloride salts are preferable. The Ni salt or Fe salt may be used alone or in combination of two or more.

[0033] Examples of R include diimidazole, triimidazole, etc. in which two or more imidazole rings are linked by a group having one or more carbonyl groups, imidazole having an alkyl ester group having a linear, branched or cyclic alkyl group with 1 to 6 carbon atoms, an aryl ester group having an aryl group with 6 to 12 carbon atoms, and the like.

[0034] Examples of the carbonyl group include a ketone group, an ester group, an aldehyde group, an amide group, a carboxylic acid group, etc. From the viewpoint of catalyst performance and the like, a ketone group and an ester group are preferable.

[0035] Examples of R include carbonyldiimidazoles such as 1,1-carbonyldiimidazole in which two imidazole rings are linked by one carbonyl group, and oxalyldiimidazoles such as 1,1-oxalyldiimidazole in which two imidazole rings are linked by two carbonyl groups.

[0036]

Chem.

[0037]

Chem.

[0038] Examples of R include alkyl 1-imidazolecarboxylates such as ethyl 1-imidazolecarboxylate which is an imidazole having an alkyl ester group, alkyl 2-imidazolecarboxylates such as ethyl 2-imidazolecarboxylate, and alkyl 4-imidazolecarboxylates such as ethyl 4-imidazolecarboxylate.

[0039]

Chem.

[0040]

Chem.

[0041] [Chemistry] Ethyl 4-imidazolecarboxylate (4COOEt)

[0042] The ligand R, which is an imidazole derivative having a carbonyl group, may be any imidazole derivative having a carbonyl group due to the factors described above, and there is no particular limitation. However, from the viewpoint of catalyst performance and the like, carbonyldiimidazole, oxalyldiimidazole, and imidazole having an alkyl ester group having a linear alkyl group with 1 to 6 carbon atoms (alkyl imidazole carboxylate) are preferable, and carbonyldiimidazole and oxalyldiimidazole are more preferable from the viewpoint of being able to reduce the voltage required for oxygen generation.

[0043] The oxygen generation catalyst according to this embodiment can be obtained by dissolving an imidazole derivative having a carbonyl group and a Ni salt or an Fe salt in a solvent at a predetermined molar ratio and reacting them at a predetermined temperature for a predetermined time.

[0044] The solvent may be any solvent that can dissolve or disperse the imidazole derivative having a carbonyl group and the Ni salt or the Fe salt, and there is no particular limitation. For example, acetonitrile, ethanol, methanol, etc. may be used.

[0045] The molar ratio may be, for example, in the range of imidazole derivative having a carbonyl group:Ni salt or Fe salt = 1:0.5 to 1:4.

[0046] The reaction temperature may be, for example, in the range of 0 to 60°C. The reaction time may be, for example, in the range of 0.5 to 24 hours.

[0047] During the reaction, the reaction solution may be stirred or ultrasonic treatment may be performed.

[0048] After the reaction, if necessary, the solvent may be removed to isolate, purify, and dry the oxygen generation catalyst, or the reaction solution may be directly used to coat a substrate or the like by a known coating method to produce an electrode or the like.

[0049] The electrode for oxygen generation reaction according to this embodiment is, for example, for an oxygen generation reaction that generates oxygen using an alkaline aqueous solution with a pH of 10 or more, for example, a pH of 10 to 14. The alkaline aqueous solution with a pH of 10 or more is not particularly limited, and examples include an aqueous potassium hydroxide (KOH) solution with a pH of 10 or more, a CO2-unsaturated KHCO3 + K2CO3 electrolyte, a CO2-unsaturated K2B4O7 + K2SO4 electrolyte, a phosphate electrolyte, and CO2-unsaturated sodium carbonate.

[0050] Also, when the imidazole derivative is oxalyldiimidazole, the electrode for oxygen generation reaction according to this embodiment is, for example, for an oxygen generation reaction that generates oxygen using a neutral aqueous solution with a pH of 6 to 8. The neutral aqueous solution with a pH of 6 to 8 is not particularly limited, and examples include a CO2-saturated KHCO3 + K2CO3 electrolyte, a CO2-saturated K2B4O7 + K2SO4 electrolyte, and a phosphate electrolyte with a pH of 6 to 8.

[0051] <Electrode for Oxygen Generation Reaction> The electrode for oxygen generation reaction according to this embodiment is an electrode containing the above oxygen generation catalyst. For example, it is an electrode with the above oxygen generation catalyst supported on a substrate.

[0052] The electrode for oxygen generation reaction can be obtained, for example, by using a solution containing the above oxygen generation catalyst and supporting the oxygen generation catalyst on a substrate using a coating method such as dip coating, spin coating, or spray coating.

[0053] As the substrate, Ni foam, carbon paper, Ti mesh, etc. can be used.

[0054] <Oxygen Generation Reaction> The oxygen generation reaction in which the oxygen generation catalyst and the electrode for oxygen generation reaction according to this embodiment are used is a reaction used as a counter electrode reaction such as a water electrolysis reaction for generating hydrogen in an alkaline solution or a carbon dioxide reduction reaction for synthesizing useful compounds such as carbon monoxide, formic acid, and ethanol from carbon dioxide (CO2).

[0055] This specification includes the following embodiments. [1] An oxygen generation catalyst that is a Ni complex of an imidazole derivative having a carbonyl group and a Ni salt or an Fe complex of an Fe salt.

[0056] [2] The oxygen generation catalyst according to [1], wherein the carbonyl group is at least one of a ketone group and an ester group.

[0057] [3] The oxygen generation catalyst according to [1] or [2], wherein the Ni salt or the Fe salt is at least one of a nitrate and a chloride salt.

[0058] [4] The oxygen generation catalyst according to any one of [1] to [3], wherein the imidazole derivative is at least one of carbonyldiimidazole and oxalyldiimidazole.

[0059] [5] The oxygen generation catalyst according to any one of [1] to [4], wherein the oxygen generation catalyst is for an oxygen generation reaction that generates oxygen using an alkaline aqueous solution having a pH of 10 or more as a reaction solution.

[0060] [6] The oxygen generation catalyst according to any one of [1] to [4], wherein the imidazole derivative is oxalyldiimidazole, and the oxygen generation catalyst is for an oxygen generation reaction that generates oxygen using a neutral aqueous solution having a pH of 6 to 8 as a reaction solution.

[0061] An oxygen generation reaction electrode containing the oxygen generation catalyst according to any one of [7][1] to [6].

Example

[0062] Hereinafter, examples and comparative examples will be given to explain the present invention more specifically and in detail. However, the present invention is not limited to the following examples.

[0063] [Preparation of an oxygen generation catalyst using an imidazole ligand having a ketone group] As Examples 1 to 8, investigations on oxygen generation catalysts using imidazole ligands having a carbonyl group, particularly ketone-based ligands, are shown.

[0064] [Example 1: Preparation of Ni-ODI electrode] Ni(NO3)2·6H2O and 1,1-oxalyldiimidazole (ODI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-ODI was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out and dried at 60 °C to fabricate a Ni-ODI electrode.

[0065] [Example 2: Preparation of Ni-CDI electrode] Ni(NO3)2·6H2O and 1,1-carbonyldiimidazole (CDI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-CDI was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out and dried at 60 °C to fabricate a Ni-CDI electrode.

[0066] [Example 3: Preparation of Fe-ODI electrode] Fe(NO3)3·9H2O and 1,1-oxalyldiimidazole (ODI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:1, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Fe-ODI was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, an Fe-ODI electrode was fabricated.

[0067] <Example 4: Fabrication of Fe-CDI Electrode> Fe(NO3)3·9H2O and 1,1-carbonyl diimidazole (CDI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:1, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Fe-CDI was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, an Fe-CDI electrode was fabricated.

[0068] <Example 5: Fabrication of Ni-Cl-ODI Electrode> NiCl2·6H2O and 1,1-oxalyldiimidazole (ODI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-Cl-ODI was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, a Ni-Cl-ODI electrode was fabricated.

[0069] <Example 6: Fabrication of Ni-Cl-CDI Electrode> NiCl2·6H2O and 1,1-carbonyldiimidazole (CDI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-Cl-CDI was supported on the Ni foam using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out, and the Ni-Cl-CDI electrode was fabricated by drying at 60 °C.

[0070] <Example 7: Fabrication of Fe-Cl-ODI Electrode> FeCl2·4H2O and 1,1-oxalyldiimidazole (ODI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:1, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Fe-Cl-ODI was supported on the Ni foam using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out, and the Fe-Cl-ODI electrode was fabricated by drying at 60 °C.

[0071] <Example 8: Fabrication of Fe-Cl-CDI Electrode> FeCl2·4H2O and 1,1-carbonyldiimidazole (CDI) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:1, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Fe-Cl-CDI was supported on the Ni foam using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out, and the Fe-Cl-CDI electrode was fabricated by drying at 60 °C.

[0072] [Fabrication of Oxygen Generation Catalyst Using Imidazole Ligand with Ester Group] As Examples 9 to 11, the investigation of oxygen generation catalysts using imidazole ligands having a carbonyl group, particularly ester-based ligands, is shown.

[0073] <Example 9: Fabrication of Ni-1COOEt Electrode> Ni(NO3)2·6H2O and ethyl 1-imidazole carboxylate (1COOEt) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-1COOEt was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, a Ni-1COOEt electrode was fabricated.

[0074] <Example 10: Fabrication of Ni-2COOEt Electrode> Ni(NO3)2·6H2O and ethyl 2-imidazole carboxylate (1COOEt) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-2COOEt was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, a Ni-2COOEt electrode was fabricated.

[0075] <Example 11: Fabrication of Ni-4COOEt Electrode> Ni(NO3)2·6H2O and ethyl 4-imidazole carboxylate (4COOEt) were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Ni-4COOEt was supported on the Ni foam using a dip coating method with drying at 60 °C for 1 cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, a Ni-4COOEt electrode was fabricated.

[0076] [Fabrication of Ni Foam Electrode] Comparative Example 1 is an oxygen evolution catalyst composed only of Ni foam as a carrier without an imidazole ligand.

[0077] <Comparative Example 1: Fabrication of Ni Foam Electrode> In Comparative Example 1, a Ni form cut into the same size as those in Examples 1 to 11 was used as the Ni form electrode.

[0078] [Preparation of Oxygen Generation Catalyst Using Imidazole Ligand Having No Carbonyl Group] Comparative Examples 2 to 5 are oxygen generation catalysts using imidazole ligands having no carbonyl group.

[0079] <Comparative Example 2: Preparation of Ni-imi Electrode> Ni(NO3)2·6H2O and imidazole were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:4, and ultrasonic treatment was performed at 25 °C for 30 minutes. The Ni form was immersed in the obtained solution, and Ni-imi was supported on the Ni form using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out and dried at 60 °C to prepare a Ni-imi electrode.

[0080] <Comparative Example 3: Preparation of Ni-Cl-imi Electrode> NiCl2·6H2O and imidazole were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:4, and ultrasonic treatment was performed at 25 °C for 30 minutes. The Ni form was immersed in the obtained solution, and Ni-Cl-imi was supported on the Ni form using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out and dried at 60 °C to prepare a Ni-Cl-imi electrode.

[0081] <Comparative Example 4: Preparation of Fe-imi Electrode> Fe(NO3)2·9H2O and imidazole were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. The Ni form was immersed in the obtained solution, and Fe-imi was supported on the Ni form using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out and dried at 60 °C to prepare an Fe-imi electrode.

[0082] <Comparative Example 5: Preparation of Fe-Cl-imi Electrode> FeCl2·4H2O and imidazole were dissolved in 20 mL of acetonitrile so that the molar ratio was 1:2, and ultrasonic treatment was performed at 25 °C for 30 minutes. Ni foam was immersed in the obtained solution, and Fe-Cl-imi was supported on Ni foam using a dip coating method with drying at 60 °C as one cycle. At this time, a total of 10 cycles were carried out, and by drying at 60 °C, an Fe-Cl-imi electrode was prepared.

[0083] [Oxygen Evolution Reaction in Alkaline Solution] Using the electrodes prepared in Examples 1 to 11 and Comparative Examples 1 to 5, the oxygen evolution reaction was carried out under the following measurement conditions. The oxygen evolution reaction tests using the electrodes prepared in Examples 1 to 11 and Comparative Examples 1 to 5 are all results in an alkaline solution in 1 M KOH.

[0084] The oxygen evolution reaction was all carried out by an electrochemical reaction. An electrochemical measurement system (Bio-Logic Science Instruments, SP-150) was used for electrochemical measurement. While recording the potential at which a current of 15 mA / cm 2 was generated using the electrochemical measurement system, an oxygen evolution reaction test was carried out. In the oxygen evolution reaction test, the oxygen evolution catalysts of Examples 1 to 11 and Comparative Examples 1 to 5 were used for the working electrode, a Pt-foil was used for the counter electrode, and an Ag / AgCl electrode was used for the reference electrode. All measurements were carried out so that the same reaction area (1 cm 2 ) was obtained between samples. The measurement was carried out using a one-compartment cell made of peek without a diaphragm in the reaction cell. As the electrolyte, any one of an aqueous solution of 1.0 mol / L potassium hydroxide (1 M KOH) (alkaline solution, pH 14), an aqueous solution of 0.1 M K2B4O7 + 0.2 M K2SO4 (pH 10), and an aqueous solution of 0.5 M KHCO3 + 0.5 M K2CO3 (pH 10 when not saturated with CO2, pH 7 when saturated with CO2) was used.

[0085] [Oxygen Evolution Reaction Results (Alkaline Electrolyte)] The oxygen generation reaction test results of Examples 1 to 11 and Comparative Examples 1 to 5 are shown in Tables 1 to 7.

[0086] [Table 1]

[0087] [Table 2]

[0088] [Table 3]

[0089] [Table 4]

[0090] [Table 5]

[0091] [Table 6]

[0092] [Table 7]

[0093] Table 1 shows 15 mA / cm of Examples 1 to 4 and Comparative Example 1 2The potential for generating the current by the oxygen evolution reaction was examined over time in a 10-minute measurement, and the value at 10 minutes was shown. At this time, the voltage value is based on the reversible hydrogen electrode (RHE) value, and at pH 14 of 1 M KOH aqueous solution, based on the theoretical potential of 1.23 V for generating oxygen from water, it is further shown as the required voltage value (= overvoltage value). In the Ni foam shown in Comparative Example 1, the voltage value at 10 minutes shows a high value of 0.38. Example 1 is 0.15, and Example 2 can generate oxygen at a voltage 0.2 V or more lower, at 0.18. Example 3 is 0.23, and Example 4 can be driven at a lower voltage than Comparative Example 1 even when Fe is used, at 0.28.

[0094] When using the chloride Ni salts and Fe salts of Examples 5 to 8 shown in Table 2 as raw materials, Example 5 is 0.31, Example 6 is 0.21, Example 7 is 0.19, and Example 8 is 0.23, and all can be driven at a potential lower than that of Comparative Example 1.

[0095] Comparative Examples 2 to 5 can be compared with the Examples in which the metal salts of the raw materials are the same, respectively. Specifically, Comparative Example 2 is compared with Examples 1 and 2 (Table 3), Comparative Example 3 is compared with Examples 3 and 4 (Table 4), Comparative Example 4 is compared with Examples 5 and 6 (Table 5), and Comparative Example 5 is compared with Examples 7 and 8 (Table 6). In any case, since the Examples can be driven at a smaller value than Comparative Examples 2 to 5, the effect of the imidazole ligand having a carbonyl group is clear. This is presumably due to the effect of improving the acceptance efficiency of electrons and protons by having imidazole, an organic compound with high electron and proton conductivity, and among them, a ligand having a carbonyl group in the catalyst structure.

[0096] Table 7 shows the results of the oxygen evolution catalysts using imidazole ligands having a carbonyl group, particularly ester-based ligands, in Examples 9 to 11. In Example 9, it is 0.30, in Example 10 it is 0.29, and in Example 11 it is 0.33. Although all of them are weaker in effect than Examples 1 to 8, the oxygen evolution reaction can proceed at a lower voltage than Comparative Example 1. It is presumed that, similar to Examples 1 to 8, having a carbonyl group in the ligand skeleton improves the efficiency of electron and proton acceptance.

[0097] [Oxygen evolution reaction in neutral solution] Using the electrodes prepared in Examples 12 to 20 and Comparative Examples 6 to 11, the oxygen evolution reaction was carried out under the following measurement conditions in all cases. The oxygen evolution reaction tests in Examples 12 to 20 and Comparative Examples 6 to 11 are all results in neutral solutions.

[0098] [Preparation of Ni-ODI electrode in Examples 12 to 14] The Ni-ODI electrode was prepared in the same procedure as in Example 1.

[0099] [Preparation of Fe-ODI electrode in Examples 15 to 17] The Fe-ODI electrode was prepared in the same procedure as in Example 3.

[0100] [Preparation of Fe-Cl-ODI electrode in Examples 18 to 20] The Fe-Cl-ODI electrode was prepared in the same procedure as in Example 7.

[0101] [Preparation of Ni foam electrode in Comparative Examples 6 to 8] The Ni foam electrode was prepared in the same procedure as in Comparative Example 1.

[0102] [Preparation of Ni-imi electrode in Comparative Examples 9 to 11] The Ni-imi electrode was prepared in the same procedure as in Comparative Example 2.

[0103] [Oxygen evolution reaction results (neutral electrolyte)] The oxygen evolution reaction test results of Examples 12 to 20 and Comparative Examples 6 to 11 are shown in Tables 8 to 10.

[0104]

Table 8

[0105]

Table 9

[0106]

Table 10

[0107] Table 8 shows the potential for generating a current of 15 mA / cm 2 by the oxygen evolution reaction in a CO2-unsaturated 0.5 M KHCO3 + 0.5 M K2CO3 electrolyte (pH 10.2) over a 10-minute measurement period, showing the value at 10 minutes. Since any of the examples can drive the oxygen evolution reaction at a lower potential compared to Comparative Examples 6 and 9, the effect of the imidazole ligand having a carbonyl group is clear.

[0108] Table 9 shows the results when the electrolyte is changed to a CO2-unsaturated 0.1 M K2B4O7 + 0.2 M K2SO4 electrolyte (pH 10.2). Similar to Table 8, any of the examples can drive the oxygen evolution reaction at a lower voltage than Comparative Examples 7 and 10.

[0109] Table 10 shows the results when the electrolyte is changed to a CO2-saturated 0.5 M KHCO3 + 0.5 M K2CO3 electrolyte (pH 7.0). Similar to Tables 8 and 9, any of the examples can drive the oxygen evolution reaction at a lower voltage than Comparative Examples 8 and 11. In any case, since the examples can be driven at a smaller value than the comparative examples, the effect of the imidazole ligand having a carbonyl group is clear. Similar to the study of alkaline solutions, this is presumably due to the effect of having a carbonyl group in the ligand skeleton, which improves the electron and proton acceptance efficiency.

[0110] Thus, in the catalyst for generating oxygen from water using the oxygen generation catalyst of the example, it was possible to reduce the voltage required for oxygen generation.

Claims

1. An oxygen generation catalyst characterized by being a Ni complex of an imidazole derivative having a carbonyl group and a Ni salt or an Fe complex of an Fe salt.

2. The oxygen generation catalyst according to Claim 1, wherein the carbonyl group is at least one of a ketone group and an ester group.

3. The oxygen generation catalyst according to Claim 1, wherein the Ni salt or the Fe salt is at least one of a nitrate and a chloride salt.

4. The oxygen generation catalyst according to Claim 1, wherein the imidazole derivative is at least one of carbonyldiimidazole and oxalyldiimidazole.

5. The oxygen generation catalyst according to Claim 1, wherein the oxygen generation catalyst is for an oxygen generation reaction that generates oxygen using an alkaline aqueous solution with a pH of 10 or higher as a reaction solution.

6. The oxygen generation catalyst according to Claim 1, wherein the imidazole derivative is oxalyldiimidazole, and the oxygen generation catalyst is for an oxygen generation reaction that generates oxygen using a neutral aqueous solution with a pH of 6 to 8 as a reaction solution.

7. An electrode for an oxygen generation reaction, characterized by containing the oxygen generation catalyst according to any one of Claims 1 to 6.

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