Phosphorized cobalt-carbon composite particles

Abstract

To provide phosphorized cobalt-carbon composite particles having supported CoP.SOLUTION: A method for producing phosphorized cobalt-carbon composite particles includes: a step of impregnating cells in a treatment solution containing a cobalt compound and an organic solvent, in a state where the cells coexist with a phosphorus source selected from the group consisting of oxoacids of phosphorus and salts thereof; and a step of calcining the cells after the impregnation treatment. The amount of phosphorus constituting the phosphorus source is greater than the amount of phosphorus contained in the wild type of the cells.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to transition metal phosphides (TMPs) useful as catalysts for hydrogen evolution reactions (HER), etc., and more specifically to cobalt phosphide-carbon composite particles.

Background Art

[0002] Effective and environmentally friendly catalysts for the hydrogen evolution reaction (HER) are important for new clean energy technologies. As catalysts having HER activity, typically platinum etc. have been used, but as an alternative to such expensive catalysts, it has been reported that cheaper transition metal phosphides (TMPs) such as Co2P and Ni2P are useful as HER catalysts.

[0003] Originally, since the synthesis of TMPs requires a chemical phosphorus source, there were problems to be addressed regarding the complexity of the synthesis procedure and the issue of toxicity. However, in recent years, there has been a groundbreaking report that cobalt phosphide nanoparticles (Co2P-C) covered with a carbon matrix, which is a conductor, can be produced by hydrothermally treating and firing yeast cells together with Co 2+ (Non-Patent Document 1).

[0004] On the other hand, it has also been reported that CoP is synthesized by using DNA as a phosphorus source and firing DNA extracted from yeast and cobalt (Non-Patent Document 2).

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] When the inventor examined the catalytic activity of CoP, it was found that excellent catalytic activity equal to or higher than that of Co2P could be expected. However, the technique of Non-Patent Document 2, which reports that CoP can be synthesized, has a complicated DNA extraction operation as a phosphorus source and is not practical. On the other hand, for a catalyst in which TMP is supported in carbonized cells as reported in Non-Patent Document 1, although the DNA extraction operation becomes unnecessary, the TMP that can be synthesized in Non-Patent Document 1 is Co2P. That is, cobalt phosphide carbon composite particles supported with CoP have not been reported so far.

[0007] Therefore, an object of the present invention is to provide cobalt phosphide carbon composite particles supported with CoP. [Means for Solving the Problems]

[0008] The inventors of the present invention have found that by impregnating cells containing accumulated phosphate in a treatment liquid containing a cobalt compound and an organic solvent, or impregnating normal cells in a treatment liquid containing a phosphate source, a cobalt compound, and an organic solvent, and then firing the treated cells, phosphorylated cobalt carbon composite particles carrying CoP can be obtained. The present invention has been completed by further studies based on these findings.

[0009] That is, the present invention provides an invention in the following aspects. Item 1. A step of impregnating cells in a treatment liquid containing a cobalt compound and an organic solvent in a state of coexisting with a phosphorus source selected from the group consisting of oxoacids of phosphorus and salts thereof; A step of firing the cells after the impregnation treatment, and A method for producing phosphorylated cobalt carbon composite particles, wherein the amount of phosphorus constituting the phosphorus source is larger than the amount of phosphorus contained in the wild type of the cells. Item 2. The production method according to Item 1, wherein the cells are phosphorus-enriched mutants, and the state is a state in which more phosphorus than the wild type is accumulated as the phosphorus source inside the cells. Item 3. The production method according to Item 1, wherein the state is a mixed state of the cells and the phosphorus source added outside the cells. Item 4. The production method according to any one of Items 1 to 3, wherein the organic solvent is selected from the group consisting of acetone, methanol, ethanol, and tetrahydrofuran. Item 5. The production method according to any one of Items 1 to 4, wherein the organic solvent is used together with water, and in the mixed solvent composed of the organic solvent and water, the content of the organic solvent is 10 to 90% by volume. Item 6. The production method according to any one of Items 1 to 5, wherein the amount of the phosphorus source contained in the cells after the impregnation treatment is 2.5 parts by weight or more in terms of the amount of phosphorus per 100 parts by weight of the dry weight of the cells after the impregnation treatment. Item 7. The production method according to Item 3, wherein the addition amount of the phosphorus source is 5 to 100 parts by weight in terms of the amount of phosphorus per 100 parts by weight of the cell dry weight. Item 8. The production method according to any one of Items 1 to 6, wherein the amount of the cobalt compound used is 0.36 to 70 millimoles per gram of the dry weight of the cells in terms of the amount of cobalt. Item 9. The production method according to any one of Items 1 to 8, wherein the firing time is 5 minutes to 2.5 hours. Item 10. The production method according to any one of Items 1 to 9, wherein the firing temperature is 800 °C or higher. Item 11. The production method according to any one of Items 1 to 10, wherein the firing is carried out under the condition of an inert gas flow rate of 10 to 1500 ml / min. Item 12. Cobalt phosphide carbon composite particles containing carbonized cells and CoP supported on the carbonized cells. Item 13. A catalyst for hydrogen generation reaction containing the cobalt phosphide carbon composite particles according to Item 12. Item 14. An electrode for hydrogen generation reaction comprising a conductive substrate and a coating layer provided on the surface of the conductive substrate and containing the catalyst for hydrogen generation reaction according to Item 13. Item 15. A catalyst for ammonia generation reaction containing the cobalt phosphide carbon composite particles according to Item 12. Item 16. An electrode for ammonia generation reaction comprising a conductive substrate and a coating layer provided on the surface of the conductive substrate and containing the catalyst for ammonia generation reaction according to Item 15.

Advantages of the Invention

[0010] According to the present invention, cobalt phosphide carbon composite particles supported with CoP are provided.

Brief Description of the Drawings

[0011]

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Mode for Carrying Out the Invention

[0012] 1. Method for manufacturing cobalt phosphide-carbon composite particles The method for producing cobalt phosphide-carbon composite particles of the present invention includes a step of impregnating cells in a treatment liquid containing a cobalt compound and an organic solvent in a state of coexisting with a phosphorus source selected from the group consisting of oxoacids of phosphorus and salts thereof, and a step of firing the cells after the impregnation treatment, wherein the amount of phosphorus constituting the phosphorus source is larger than the amount of phosphorus contained in the wild type of the cells. By the production method of the present invention, cobalt phosphide-carbon composite particles carrying CoP can be obtained. Hereinafter, the method for producing cobalt phosphide-carbon composite particles of the present invention will be described in detail.

[0013] 1-1. Cells As the cells serving as the material of the cobalt phosphide-carbon composite particles, any biological cells can be used, and it does not matter whether they are wild type or mutant type.

[0014] Specific examples of the cells include microbial cells. Examples of the microbial cells include single-celled organisms such as yeast and bacteria.

[0015] The yeast is not particularly limited as long as it is a yeast classified into Ascomycota or Basidiomycota.

[0016] Specific examples of yeasts classified in the Ascomycota phylum include Saccharomyces cerevisiae, Saccharomyces pastrianus, Saccharomyces bayanus, Saccharomyces carlsbergensis, Saccharomyces sake, Saccharomyces uvarum, Saccharomyces pastorianus (carlsbergenisis), Saccharomyces bayanus, Saccharomyces awamori, etc. of the genus Saccharomyces; Pichia pastoris, Pichia angusta, Pichia finlandica, Pichia trehalophila, Pichia koclamae, Pichia membranaefaciens, Pichia minuta, etc. of the genus Pichia; Schizosaccharomyces pombe of the genus Schizosaccharomyces; Dekkera bruxellensis, Dekkera anomala, etc. of the genus Dekkera; Kluyveromyces lactis, Kluyveromyces marxianus, Kluyveromyces fragilis, etc. of the genus Kluyveromyces; Aureobasidium pullulans, etc. of the genus Aureobasidium; Zygosacoharomyces rouxi, etc. of the genus Zygosacoharomyces;Yeasts belonging to the genus Candida, such as Candida utilis, Candida versatilis, and Candida etchellsii, etc., can be mentioned.;

[0017] Specific examples of yeasts classified in the phylum Basidiomycota include yeasts belonging to the genus Sporobolomyces; the genus Rhodotorula, such as Rhodotorula mucilaginosa, etc.

[0018] The above cells may be used alone or in combination of multiple types. Among the above cells, preferably microbial cells are mentioned, more preferably single-celled organisms are mentioned, still more preferably yeasts are mentioned, even more preferably yeasts belonging to the genus Saccharomyces are mentioned, and particularly preferably Saccharomyces cerevisiae is mentioned.

[0019] The cells that serve as the material for the phosphorus-doped cobalt-carbon composite particles contain phosphorus element P (hereinafter also simply referred to as "phosphorus" or "phosphorus atom") in the form of phosphate groups that constitute nucleic acids and phospholipids that constitute cell membranes, or in yet another form (for example, free phosphoric acid, polyphosphoric acid, etc.). When using wild-type cells as the cells, phosphorus is mainly contained in the form of phosphate groups that constitute nucleic acids and phospholipids that constitute cell membranes, and its content is the weight ratio of phosphorus atoms per 100 parts by weight of the cell dry weight, for example, about 2 parts by weight. When using mutant cells as the cells, as the mutant cells, phosphorus-enriched mutants that accumulate a larger amount of phosphorus than the amount of phosphorus contained in the corresponding wild-type cells can be used. In the phosphorus-enriched mutants, phosphorus is contained not only in the form of phosphate groups that constitute nucleic acids and phospholipids that constitute cell membranes but also in the form of polyphosphoric acid and the like, whereby more phosphorus is accumulated than in the wild type. The phosphorus content in the phosphorus-enriched mutants is the weight ratio of phosphorus atoms per 100 parts by weight of the cell dry weight, and examples thereof include 4 parts by weight or more, preferably 5 parts by weight or more, more preferably 6 parts by weight or more, still more preferably 7 parts by weight or more, and even more preferably 7.5 parts by weight or more. The upper limit of the phosphorus content in the phosphorus-enriched mutants is not particularly limited, but examples thereof include 15 parts by weight or less, 13 parts by weight or less, 10 parts by weight or less, or 9 parts by weight or less in terms of the weight ratio of phosphorus atoms per 100 parts by weight of the cell dry weight. Phosphorus-enriched mutants are known, and examples thereof include mutants of regulatory genes of the phosphate metabolism control system. Specifically, those disclosed in Archives of Microbiology (2023) 205:138 https: / / doi.org / 10.1007 / s00203-023-03488-x and the like can be used, and the Saccharomyces cerevisiae pho81 mutant strain (NBRP ID: BY8407) can also be purchased and used.

[0020] In the present invention, it is particularly preferable to use phosphorus-enriched mutants as the cells that serve as the material for the phosphorus-doped cobalt-carbon composite particles.

[0021] The amount of cells charged into the treatment liquid is not particularly limited. For example, in terms of the dry weight of cells per 100 mL of the treatment liquid, it may be, for example, 0.5 to 10 g, preferably 1 to 7 g, more preferably 2 to 4 g.

[0022] 1-2. Phosphorus source The phosphorus source serves as a raw material for CoP supported on cobalt carbon composite particles containing phosphorus. The phosphorus source is selected from the group consisting of phosphorus oxoacids and their salts.

[0023] Examples of phosphorus oxoacids include hypophosphorous acid (H3PO2), phosphonic acid (R-P(=O)(OH)2, where R represents an organic group), phosphorous acid (H3PO3), phosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7), triphosphoric acid (H5P3O 10 ), metaphosphoric acid (H3P3O9), and polyphosphoric acid represented by the following formula (1) (where n represents an integer of 4 or more).

Chemical formula

[0024] Examples of phosphorus oxoacid salts include alkali metal salts such as potassium salts and sodium salts, and ammonium salts.

[0025] As the phosphorus source, one kind may be used alone, or two or more kinds may be used in combination. Among the above phosphorus sources, preferably, dihydrogen phosphate salts, polyphosphate salts, and polyphosphoric acid are mentioned. More preferably, alkali metal dihydrogen phosphate salts, alkali metal polyphosphate salts, and polyphosphoric acid are mentioned. Even more preferably, potassium dihydrogen phosphate, sodium polyphosphate (preferably Na6P4O 13 ), and polyphosphoric acid are mentioned.

[0026] The phosphorus source may be a phosphorus compound contained in the cells used as a material for the cobalt carbon composite particles containing phosphorus, or may be a phosphorus compound added from outside the cells.

[0027] 1-3. Coexistence state of cells and phosphorus source The cells can coexist with a phosphorus source. More specifically, the cells can coexist with a phosphorus source in a treatment solution containing a cobalt compound and an organic solvent. In this coexisting state, the amount of phosphorus constituting the phosphorus source is conditioned to be greater than the amount of phosphorus contained in the wild type of the cells.

[0028] For example, when the cells are phosphorus-enriched mutants, the above coexisting state refers to a state in which more phosphorus than the wild type is accumulated as the phosphorus source inside the cells of the phosphorus-enriched mutants. That is, when the cells are phosphorus-enriched mutants, the phosphorus source is a phosphorus compound that is accumulated more in the cells of the phosphorus-enriched mutants than in the corresponding wild-type cells, preferably polyphosphoric acid. Thus, when the cells are phosphorus-enriched mutants, the phosphorus compound contained in the cells themselves of the phosphorus-enriched mutants can be used as the phosphorus source. In the present invention, when the cells are phosphorus-enriched mutants, a phosphorus source may or may not be further added from outside the cells. Further, when a phosphorus source is added from outside the cells, the added phosphorus source can be selected from the phosphorus sources added when the cells are not phosphorus-enriched mutants.

[0029] Also, when the cells are not phosphorus-enriched mutants, the above coexisting state refers to a mixed state of the cells and the phosphorus source added outside the cells. That is, when the cells are not phosphorus-enriched mutants, the phosphorus source is a phosphorus compound added outside the cells, preferably an oxoacid salt of phosphorus, more preferably a dihydrogen phosphate and / or a polyphosphate, still more preferably an alkali metal dihydrogen phosphate and / or an alkali metal polyphosphate, and even more preferably potassium dihydrogen phosphate and / or sodium polyphosphate (preferably Na6P4O 13 )

[0030] The amount of phosphorus source added is not particularly limited, but it is the amount of phosphorus per 100 parts by weight of the dry cell weight, for example, 5 to 100 parts by weight, preferably 10 to 95 parts by weight, more preferably 25 to 85 parts by weight, still more preferably 30 to 82 parts by weight, and even more preferably 57 to 65 parts by weight. Also, as the amount of phosphorus source added, it is the amount of phosphorus in the treatment liquid, for example, 0.05 to 1 M, preferably 0.1 to 0.95 M, more preferably 0.25 to 0.85 M, still more preferably 0.3 to 0.82 M, and even more preferably 0.57 to 0.65 M.

[0031] 1-4. Cobalt compound As the cobalt compound, any cobalt salt can be used. Specific examples of cobalt salts include divalent cobalt salts. More specifically, cobalt(II) chloride, cobalt(II) fluoride, cobalt(II) bromide, cobalt(II) iodide, cobalt(II) acetate, cobalt(II) nitrate, cobalt(II) sulfate, cobalt(II) carbonate, cobalt(II) phosphate, cobalt(II) perchlorate, cobalt(II) tetrafluoroborate, cobalt(II) thiocyanate, cobalt(II) oxalate, cobalt(II) phthalocyanine, cobalt(II) 2-ethylhexanoate, cobalt(II) acetylacetonate, cobalt(II) hexafluoroacetylacetonate, cobalt(II) cyanide, cobalt(II) hydroxide, etc. are included. The cobalt salt may be a hydrate of these.

[0032] The cobalt compound may be used alone as one of the above cobalt salts or in combination of two or more. Preferably, as the cobalt compound, divalent cobalt salts and / or their hydrates are included. More preferably, cobalt(II) nitrate and / or its hexahydrate are included. Particularly preferably, cobalt(II) nitrate hexahydrate is included.

[0033] The amount of the cobalt compound used is not particularly limited, but in terms of the amount of cobalt, per 1 g of the dry weight of the cells, for example, 0.36 to 70 millimoles, preferably 0.44 to 40 millimoles or 0.45 to 30 millimoles, more preferably 1 to 20 millimoles, 3 to 10 millimoles, or 3.5 to 7 millimoles can be mentioned.

[0034] 1-5. Organic solvent The organic solvent is not particularly limited, but preferably, acetone, methanol, ethanol, tetrahydrofuran, etc. can be mentioned. These organic solvents may be used alone or in combination of two or more.

[0035] Among these organic solvents, preferably ethanol and / or tetrahydrofuran can be mentioned.

[0036] In the present invention, water may be used together with the organic solvent. In a preferred embodiment, the organic solvent is used together with water. When the organic solvent is used as a mixed solvent with water, the content of the organic solvent in the mixed solvent is, for example, 10 to 90% by volume, preferably 27 to 80% by volume.

[0037] When ethanol is used together with water as the organic solvent, the content of ethanol in the mixed solvent (ethanol aqueous solution) is preferably 26 to 75% by volume, more preferably 28 to 50% by volume, still more preferably 29 to 38% by volume, and even more preferably 30 to 35% by volume.

[0038] When tetrahydrofuran is used together with water as the organic solvent, the content of tetrahydrofuran in the mixed solvent (tetrahydrofuran aqueous solution) is preferably 30 to 78% by volume, more preferably 50 to 76% by volume, still more preferably 60 to 74% by volume, and even more preferably 65 to 72% by volume.

[0039] 1-6. Impregnation treatment conditions The cells are subjected to an impregnation treatment in a treatment liquid containing a cobalt compound and an organic solvent while coexisting with a phosphorus source.

[0040] The conditions (temperature, time, operation, etc.) during the impregnation treatment are not particularly limited. For the treatment time, for example, normal temperature (15 - 25°C) can be mentioned. For the treatment time, 0. - 5 hours, preferably 1 - 3 hours, more preferably 1.5 - 2.5 hours can be mentioned. For the operation during the treatment, preferably stirring can be mentioned.

[0041] The cells after the impregnation treatment are subjected to solid-liquid separation (preferably centrifugation can be mentioned.) and drying (preferably freeze-drying can be mentioned.) to obtain the cells after the impregnation treatment (pre-firing cells).

[0042] The phosphorus source contained in the cells after the impregnation treatment (pre-firing cells) is not particularly limited, but in terms of the amount of phosphorus per 100 parts by weight of the dry weight of the cells after the impregnation treatment (pre-firing cells), for example, 2.5 parts by weight or more, preferably 2.8 parts by weight or more, more preferably 5 parts by weight or more, still more preferably 6 parts by weight or more, even more preferably 6.5 parts by weight or more can be mentioned. The amount of phosphorus per 100 parts by weight of the dry weight of the cells after the impregnation treatment (pre-firing cells) is not particularly limited even at its upper limit, but for example, 10 parts by weight or less, 9 parts by weight or less, 8 parts by weight or less, or 7.5 parts by weight or less can be mentioned.

[0043] 1-7. Firing conditions The cells after the impregnation treatment are subjected to firing. The firing conditions are not particularly limited as long as they are conditions under which the cells can be carbonized. By firing, the cells are carbonized, and at the same time, the phosphorus source and the cobalt compound incorporated into the cells react to form CoP.

[0044] Regarding the firing temperature, for example, it is 800 °C or higher, preferably 840 °C or higher or 850 °C or higher, more preferably 890 °C or higher or 900 °C or higher. The upper limit of the firing temperature is not particularly limited, but for example, it is 1050 °C or lower, preferably 1010 °C or lower or 1000 °C or lower, more preferably 940 °C or lower, still more preferably 920 °C or lower, 910 °C or lower, or 900 °C or lower.

[0045] Regarding the firing time, for example, it is 5 minutes to 2.5 hours, preferably 8 minutes to 2 hours, more preferably 10 minutes to 65 minutes or 10 minutes to 1 hour, still more preferably 13 minutes to 35 minutes or 0.25 hours to 0.5 hours.

[0046] The firing is preferably carried out in an inert gas atmosphere. The inert gas is not particularly limited and can be selected from the group consisting of noble gases and nitrogen gas, and preferably nitrogen gas.

[0047] The inert gas atmosphere is preferably maintained until the firing is completed. Therefore, it is preferable to constantly introduce the inert gas into the firing atmosphere. The inflow rate of the inert gas is not particularly limited, but for example, it is 10 to 1500 ml / min, preferably 15 to 1300 ml / min, more preferably 300 to 1300 ml / min, 400 to 1200 ml / min, 480 to 1100 ml / min, 500 to 1000 ml / min, 500 to 800 ml / min, 500 to 700 ml / min, or 500 to 600 ml / min.

[0048] After the firing is completed, the obtained fired product is allowed to cool to obtain cobalt phosphide carbon composite particles carrying CoP.

[0049] 2. Cobalt phosphide-carbon composite particles The cobalt phosphide carbon composite particles of the present invention include carbonized cells and CoP supported on the carbonized cells.

[0050] The cobalt phosphide supported on the cobalt phosphide-carbon composite particles of the present invention contains at least CoP. In the present invention, it is allowed that, in addition to CoP, other compounds containing phosphorus and cobalt (for example, Co2P, Co3(PO4)2, etc.) are further supported on the cobalt phosphide-carbon composite particles, but the smaller the amount of the other compounds relative to the amount of CoP, the more preferable. In the most preferable form of the cobalt phosphide-carbon composite particles of the present invention, the other compounds are substantially not contained (specifically, the peaks of the other compounds cannot be visually recognized in the X-ray diffraction spectrum).

[0051] The cobalt phosphide-carbon composite particles of the present invention can be produced by the production method described in the above "1. Production method of cobalt phosphide-carbon composite particles".

[0052] 3. Use of cobalt phosphide-carbon composite particles 3-1. Catalyst for hydrogen generation reaction CoP supported on the cobalt phosphide-carbon composite particles can act as a catalyst for the hydrogen evolution reaction (HER) as a kind of transition metal phosphide (TMP). The hydrogen evolution reaction (HER) is a technology for producing hydrogen by electrolyzing water, and when combined with renewable energy, it becomes green energy that can be produced without emitting CO2. Furthermore, since the cobalt phosphide-carbon composite particles are in the form of fine particles containing carbide of cells, they can be used as a highly active catalyst. Therefore, the present invention also provides a catalyst for hydrogen evolution reaction, which includes cobalt phosphide-carbon composite particles containing carbonized cells and CoP supported on the carbonized cells.

[0053] The catalyst for hydrogen evolution reaction of the present invention can reduce the overvoltage of the hydrogen evolution reaction. Therefore, the catalyst for hydrogen evolution reaction of the present invention can be used as an active ingredient of the coating layer of the electrode for hydrogen evolution reaction. Accordingly, the present invention also provides an electrode for hydrogen evolution reaction, which includes a conductive substrate and a coating layer provided on the surface of the conductive substrate and containing the above catalyst for hydrogen evolution reaction.

[0054] In the electrode for hydrogen generation reaction of the present invention, examples of the conductive base material include carbon, platinum, gold, etc. From the viewpoints of cost and scarcity, carbon is preferably used. Also, the content of the active ingredient (i.e., the catalyst for hydrogen generation reaction) contained in the coating layer is not particularly limited. For example, it is 0.1 to 0.6 mg / cm 2 , preferably 0.2 to 0.5 mg / cm 2 , more preferably 0.3 to 0.45 mg / cm 2 .

[0055] The electrode for hydrogen generation reaction of the present invention can be used as an electrode for electrolysis of water, more specifically as a cathode. Therefore, the present invention also provides a method for producing hydrogen, which includes a step of performing electrolysis treatment in an aqueous solution using the above electrode for hydrogen generation reaction as a cathode.

[0056] 3-2. Catalyst for ammonia generation reaction CoP supported on cobalt phosphide carbon composite particles can act as a catalyst for ammonia generation reaction for synthesizing ammonia, which is one of the most important chemical substances as a raw material for fertilizers, etc. Different from the conventional Haber-Bosch method that requires high temperature and high pressure conditions, CoP supported on cobalt phosphide carbon composite particles can be used as a catalyst showing ammonia synthesis activity under mild conditions suitable for the use of renewable energy. Therefore, the present invention also provides a catalyst for ammonia generation reaction, which includes cobalt phosphide carbon composite particles containing carbonized cells and CoP supported on the carbonized cells. It is particularly preferable that the cobalt phosphide carbon composite particles used as the catalyst for ammonia generation reaction are prepared using a phosphorus-enriched mutant.

[0057] The catalyst for ammonia generation reaction of the present invention can be used as an active ingredient of the coating layer of the electrode for ammonia generation reaction. Therefore, the present invention also provides an electrode for ammonia generation reaction, which includes a conductive base material and a coating layer provided on the surface of the conductive base material and containing the above catalyst for ammonia generation reaction.

[0058] In the electrode for ammonia generation reaction of the present invention, examples of the conductive substrate include carbon, platinum, gold, etc. From the viewpoints of cost and scarcity, carbon is preferably used. Also, the content of the active ingredient contained in the coating layer (that is, the catalyst for ammonia generation reaction) is not particularly limited. For example, it is 0.05 to 0.6 mg / cm 2 , preferably 0.1 to 0.4 mg / cm 2 , more preferably 0.2 to 0.3 mg / cm 2 is mentioned.

[0059] The electrode for ammonia generation reaction of the present invention is an electrode that reduces nitrate ions to generate ammonia, and more specifically, it can be used as an anode. Therefore, the present invention also provides a method for producing ammonia, which includes a step of performing a nitrate reduction reaction in an aqueous solution containing nitrate ions (specifically, an alkaline aqueous solution) using the above-mentioned electrode for ammonia generation reaction as an anode.

Example

[0060] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0061] <Test Example 1> (1) Preparation of raw material cells (1-1) Preparation of freeze-dried product of phosphorus-accumulating yeast Adenine-containing high-phosphate YPD medium [1 w / v% yeast extract (Oriental Yeast Co., Ltd.), 2 w / v% polypeptone (Nihon Seiyaku Co., Ltd.), 2 w / v% glucose (Wako, special grade reagent), 0.4 w / v% potassium dihydrogen phosphate (Wako, special grade reagent), 0.004 w / v% adenine sulfate dihydrate (Kanto Chemical Co., Inc., separately filter-sterilized before use)] 100 mL was inoculated with phosphorus-accumulating yeast (phosphorus-enriched mutant) Saccharomyces cerevisiae pho81 mutant (NBRP ID: BY8407). This phosphorus-accumulating yeast is a mutant of the regulatory gene of the phosphate metabolism control system and contains a large amount of polyphosphate in the cells. After shaking culture of the phosphorus-accumulating yeast at 30 °C for 24 hours with a baffle, it was scaled up to a 2 L jar fermenter. Batch culture was carried out at 250 rpm and 30 °C for 24 hours. Then, it was washed three times with pure water and freeze-dried for 2 - 3 days.

[0062] (1-2) Preparation of freeze-dried product of baker's yeast 15 g of dry yeast (Super Camellia, Nissin) was suspended in 400 mL of pure water, washed five times (3000×g, 5 minutes), and then freeze-dried.

[0063] (2) Preparation of cobalt phosphide-carbon composite particles The raw material cells obtained in the above (1) and cobalt(II) nitrate hexahydrate were suspended in a solvent and stirred at room temperature for 2 hours to obtain cells after impregnation treatment. Then, the suspension was centrifuged (3000×g, 5 minutes) and freeze-dried for 1 day to obtain cells after impregnation treatment (pre-firing cells). Next, the pre-firing sample was placed on a combustion board and set in the center of a ceramic furnace tube (AS ONE). Both ends of the furnace tube were sealed with a gas replacement unit (AS ONE), filled with nitrogen at 200 mL / min for 20 minutes, and then nitrogen was continuously flowed to maintain an inert atmosphere. Also, the furnace tube was heated by a ceramic electric tubular furnace (ARF50K, AS ONE) controlled by a temperature controller (AGC-S, AS ONE) to perform a firing treatment. After cooling, cobalt phosphide-carbon composite particles as the fired product were obtained.

[0064] The details of the amounts of dried phosphorus-accumulating yeast cells, baker's yeast, and cobalt nitrate hexahydrate used in the preparation of cobalt phosphide carbon composite particles, the composition and amount of solvent used, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) are shown in Table 1.

[0065] [Table 1]

[0066] (3) Crystal structure analysis of cobalt phosphide carbon composite particles by XRD The cobalt phosphide-carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD. A Cu-Kα (λ = 1.54178 Å) was used as the XRD source, and a curved imaging plate single crystal automatic X-ray structure analyzer (RIGAKU, R-AXIS RAPID II) was used as the XRD detector. The results are shown in Figure 1A.

[0067] As shown in Figure 1A, it was confirmed that CoP was supported on all of the cobalt phosphide carbon composite particles of Examples 1-1 to 1-6. Note that, as shown in Figure 2A (described later), only CoP was supported on the cobalt phosphide carbon composite particles of Comparative Example 1.

[0068] (4) Evaluation of catalytic activity of cobalt phosphide-carbon composite particles for water electrolysis 2 mg of the cobalt phosphide carbon composite particles (catalyst) of Examples 1-2, 1-3, 1-5, and 1-6 obtained in (2) above and 20 μL of Nafion solution were added to 0.8 mL of ethanol. After suspension, the catalyst was dispersed by ultrasonic treatment using an ultrasonic cleaner (BRANSON 1510, Yamato) for 1 hour. A three-electrode method was used for electrochemical measurements. The reference electrode was an Ag / AgCl electrode (RE-1BP, BAS) with a 3 M NaCl internal solution, and the counter electrode was a Pt electrode (Pt counter electrode 5.7 cm, BSA). The reference potential of the reference electrode is shown in Equation 1-1 below. The working electrode was a glassy carbon electrode (Teflon ring type) (GCEt10×5, BSA) with a Teflon ring width (outer diameter) of 10 mm and a glassy carbon width (inner diameter) of 5 mm. The working electrode was polished with 0.05 μm of Al2O3 before each measurement.

[0069] 30 μL of the dispersed catalyst solution was applied to the glass carbon bottom of the working electrode in six separate applications (catalyst application amount: 0.382 mg / cm 2 ) and dried in a dryer (SLI-600N, EYELA) at 70 °C for at least 1 hour. 15 mL of 0.5 M H2SO4 was placed in a voltammetry cell (SVC-2, BSA) as an electrolyte, and a working electrode coated with a catalyst, a reference electrode, and a counter electrode were set in place. Linear sweep voltammetry (LSV) was performed at a rate of 5 mV / s using an electrochemical measurement system (HSV-110, Hokuto Denko).

[0070] The measurement results were obtained from the measured values of the potential of the working electrode relative to the Ag / AgCl electrode (V vs. Ag / AgCl) and the current. Using Equations 1-2 and 1-3, the potential was calibrated to the potential relative to the reversible hydrogen electrode (RHE) (V vs. RHE), and the current density was calculated from the current. -2 The overvoltage η (mV) of the battery to achieve this was derived, and the results are shown in Figure 1B.

[0071]

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[0072]

number

[0073] As shown in FIG. 1B, the absolute value of the overvoltage required for the electrode reaction was 252 to 342. Considering that the absolute value of the overvoltage for the cobalt phosphide carbon composite particles carrying only CoP (Comparative Example 1) was 520 as shown in FIG. 2B (described later), it was confirmed that the CoP-loaded cobalt phosphide carbon composite particles of Examples 1-2, 1-3, 1-5, and 1-6 had significantly lower absolute values of overvoltage during operation than the CoP-loaded cobalt phosphide carbon composite particles. In other words, compared to the CoP-loaded cobalt phosphide carbon composite particles of Examples 1-2, 1-3, 1-5, and 1-6, the CoP-loaded cobalt phosphide carbon composite particles of Examples 1-2, 1-3, 1-5, and 1-6 have superior hydrogen generation reaction performance and can reduce the voltage required for water electrolysis. Therefore, the cobalt phosphide carbon composite particles of Examples 1-2, 1-3, 1-5, and 1-6 realize a highly efficient electrolysis reaction even at a low electrolysis voltage, making it possible to produce hydrogen at low cost.

[0074] (5) Measurement of the amount of cobalt and phosphorus in the cells after impregnation (before firing) 20 mg of the pre-calcined cells in Examples 1-3 was suspended in 25 mL of pure water and placed in an Erlenmeyer flask. 2 mL of concentrated nitric acid was added and the suspension was heated to 10 mL. 2 mL of nitric acid and 13 mL of pure water were added, and the suspension was again heated to 10 mL. The suspension was cooled to approximately room temperature, 3 mL of perchloric acid was added, and the suspension was heated to 3 mL. The pH was adjusted to 1-2 with NaOH, and the diluted solution was used as a sample for ICP measurement. The phosphorus and cobalt concentrations of the sample were measured using a Vista MPX Simultaneous ICP-OES (Varian Inc.), and the phosphorus and cobalt contents were calculated from the intensity. The results are shown in Figure 1C.

[0075] As shown in Figure 1C, in the cells after the impregnation treatment in Comparative Example 1, only a small amount of phosphorus and a trace amount of cobalt, which were originally present in the cells, were observed, whereas in the cells after the impregnation treatment in Example 1-3, it was observed that in addition to the phosphorus that the cells had originally accumulated in large amounts in the cells, a large amount of cobalt had been taken up.

[0076] (6) TEM observation of cobalt phosphide carbon composite particles The cobalt phosphide carbon composite particles of Example 1-3 obtained in (2) above were suspended in 1 mL of ethanol. The suspension was ultrasonically dispersed for 1 hour using an ultrasonic cleaner (BRANSON 1510, Yamato). 10 μL of the suspension was dropped onto high-resolution carbon (HRC-C10, Oken Shoji) and dried overnight in a dryer (SLI-600N, EYELA) at 70°C. Then, the suspension was observed using a TEM (JEM-2100, JEOL). The results are shown in Figure 1D.

[0077] <Test Example 2> (1) Preparation of baker's yeast A freeze-dried product of baker's yeast was prepared in the same manner as in Test Example 1 (1-2).

[0078] (2) Preparation of cobalt phosphide carbon composite particles The dry yeast obtained in (1) above and cobalt nitrate hexahydrate were suspended in a solvent, and potassium dihydrogen phosphate was added so that the final concentration of phosphorus reached a predetermined value. The mixture was then stirred for 2 hours to obtain cells after the impregnation treatment (cells before calcination). The subsequent treatment was carried out in the same manner as in (2) of Test Example 1, and calcined cobalt phosphide carbon composite particles were obtained.

[0079] The details of the amounts of dry yeast, cobalt nitrate hexahydrate, and potassium dihydrogen phosphate used (specified final concentrations), the composition and amount of solvent used, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) used in the preparation of cobalt phosphide carbon composite particles are as shown in Table 2.

[0080] [Table 2]

[0081] (3) Crystal structure analysis of cobalt phosphide carbon composite particles by XRD The cobalt phosphide carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD in the same manner as in (3) of Test Example 1. The results are shown in Figure 2A.

[0082] As shown in FIG. 2A, it was found that only Co2P was supported on the cobalt phosphide carbon composite particles of Comparative Example 1, whereas CoP was supported on all of the cobalt phosphide carbon composite particles of Examples 2-1 to 2-4.

[0083] (4) Evaluation of catalytic activity of cobalt phosphide-carbon composite particles for water electrolysis The cobalt phosphide carbon composite particles of Comparative Example 1 and Examples 2-1 to 2-4 obtained in (2) above were used as catalysts to evaluate their activity as catalysts for water electrolysis in the same manner as in (4) of Test Example 1. The results are shown in Fig. 2B.

[0084] As shown in Figure 2B, the absolute value of the overvoltage during operation was significantly lower for the cobalt phosphide carbon composite particles supporting CoP in Examples 2-1 to 2-4, which are cobalt phosphide carbon composite particles supporting CoP, compared to the absolute value of the overvoltage for the cobalt phosphide carbon composite particles supporting only CoP (Comparative Example 1). In other words, compared to the cobalt phosphide carbon composite particles supporting only CoP, the cobalt phosphide carbon composite particles supporting CoP in Examples 2-1 to 2-4 have superior hydrogen generation reaction performance and can reduce the voltage required for water electrolysis. Therefore, the cobalt phosphide carbon composite particles of Examples 2-1 to 2-4 can achieve highly efficient electrolysis reactions even at low electrolysis voltages, enabling hydrogen production at low cost.

[0085] (5) Measurement of the amount of cobalt and phosphorus in the cells after impregnation (before firing) The phosphorus content and cobalt content in the cells before firing were calculated in the same manner as in (5) of Test Example 1. The results are shown in Figure 2C.

[0086] As shown in FIG. 2C, in the cells after the impregnation treatment in Comparative Example 1, only a small amount of phosphorus and a trace amount of cobalt, which were originally present in the bacterial cells, were observed, whereas in the cells after the impregnation treatment in Examples 2-3 and 2-4, it was observed that large amounts of phosphorus and cobalt had been taken up.

[0087] <Test Example 3> (1) Preparation of baker's yeast A freeze-dried product of baker's yeast was prepared in the same manner as in Test Example 1 (1-2).

[0088] (2) Preparation of cobalt phosphide carbon composite particles The dry yeast obtained in (1) above and cobalt nitrate hexahydrate were suspended in a solvent, and sodium tetrapolyphosphate was added so that the final concentration of phosphorus reached a predetermined value. The mixture was then stirred for 2 hours to obtain cells after the impregnation treatment (cells before calcination). The subsequent treatment was carried out in the same manner as in (2) of Test Example 1 to obtain calcined cobalt phosphide carbon composite particles.

[0089] In the preparation of the cobalt phosphide carbon composite particles, the details of the amounts of dry yeast, cobalt nitrate hexahydrate, and sodium tetrapolyphosphate used (specified final concentrations), the composition and amount of solvent used, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) are as shown in Table 3.

[0090] [Table 3]

[0091] (3) Crystal structure analysis of cobalt phosphide carbon composite particles by XRD The cobalt phosphide carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD in the same manner as in (3) of Test Example 1. The results are shown in Figure 3A.

[0092] As shown in FIG. 3A, only Co2P was supported on the cobalt phosphide carbon composite particles of Comparative Example 1, whereas CoP was found to be supported on all of the cobalt phosphide carbon composite particles of Examples 3-1 to 3-4.

[0093] (4) Activity evaluation of cobalt phosphide carbon composite particles as an electrolysis catalyst for water Using the cobalt phosphide carbon composite particles of Comparative Example 1 and Example 3-1 obtained in (2) above as catalysts, the activity as an electrolysis catalyst for water was evaluated in the same manner as in (4) of Test Example 1. The results are shown in FIG. 3B.

[0094] As shown in FIG. 3B, compared with the absolute value of the overvoltage in the case of the cobalt phosphide carbon composite particles (Comparative Example 1) on which only Co2P was supported, Example 3-1, which is a cobalt phosphide carbon composite particle on which CoP was supported, was found to have a significantly lower absolute value of the overvoltage during operation in terms of electrode characteristics. That is, compared with the cobalt phosphide carbon composite particles on which only Co2P was supported, the cobalt phosphide carbon composite particles on which CoP was supported in Example 3-1 are excellent in hydrogen generation reaction performance and can reduce the required voltage for water electrolysis. Therefore, the cobalt phosphide carbon composite particles of Example 3-1 can realize a highly efficient electrolysis reaction even at a low electrolysis voltage and can produce hydrogen at low cost.

[0095] <Test Example 4> (1) Preparation of phosphorus-accumulating yeast In the same manner as in (1-1) of Test Example 1, a freeze-dried product of phosphorus-accumulating yeast was prepared.

[0096] (2) Preparation of cobalt phosphide carbon composite particles Using the dried yeast obtained in (1) above, cobalt phosphide carbon composite particles were obtained in the same manner as in (2) of Test Example 1.

[0097] In the preparation of the cobalt phosphide carbon composite particles, the details of the usage amounts of the dried phosphorus-accumulating yeast cells and cobalt(II) nitrate hexahydrate, the composition and usage amount of the solvent, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) are as shown in Table 4.

[0098] [Table 4]

[0099] (3) Crystal structure analysis of cobalt phosphide carbon composite particles by XRD The cobalt phosphide carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD in the same manner as in (3) of Test Example 1. The results are shown in Figure 4A.

[0100] As shown in FIG. 4A, it was found that only CoP was supported on the cobalt phosphide carbon composite particles of Comparative Example 2, whereas CoP was supported on all of the cobalt phosphide carbon composite particles of Examples 1-3 and 4-1 to 4-3.

[0101] (4) Evaluation of catalytic activity of cobalt phosphide-carbon composite particles for water electrolysis The cobalt phosphide carbon composite particles of Examples 1-3 and 4-1 to 4-3 obtained in (2) above were used as catalysts to evaluate their activity as catalysts for water electrolysis in the same manner as in (4) of Test Example 1. The results are shown in Fig. 4B.

[0102] As shown in FIG. 4B, the absolute value of the overvoltage required for the electrode reaction was 223 to 336. Considering that the absolute value of the overvoltage for the cobalt phosphide carbon composite particles carrying only CoP (Comparative Example 1) was 520 as shown in FIG. 2B, the absolute value of the overvoltage for the cobalt phosphide carbon composite particles carrying only CoP obtained in this test example (Comparative Example 2) can be inferred to be approximately 520. In contrast, the electrode characteristics of Examples 1-3 and 4-1 to 4-3, which are cobalt phosphide carbon composite particles carrying CoP, showed significantly lower absolute values of overvoltage during operation than the cobalt phosphide carbon composite particles carrying CoP. In other words, compared to the cobalt phosphide carbon composite particles carrying only CoP, the cobalt phosphide carbon composite particles of Examples 1-3 and 4-1 to 4-3 carrying CoP have superior hydrogen generation reaction performance and can reduce the voltage required for water electrolysis. Therefore, the cobalt phosphide carbon composite particles of Examples 1-3 and 4-1 to 4-3 realize a highly efficient electrolysis reaction even at a low electrolysis voltage, making it possible to produce hydrogen at low cost.

[0103] <Test Example 5> (1) Preparation of phosphorus-accumulating yeast A freeze-dried product of phosphorus-accumulating yeast was prepared in the same manner as in Test Example 1 (1-1).

[0104] (2) Preparation of cobalt phosphide carbon composite particles Cobalt phosphide carbon composite particles were obtained in the same manner as in Test Example 1 (2) using the dry yeast obtained in (1) above.

[0105] The details of the amounts of dried phosphorus-accumulating yeast cells and cobalt nitrate hexahydrate used, the composition and amount of solvent used, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) used in the preparation of cobalt phosphide carbon composite particles are as shown in Table 5.

[0106] [Table 5]

[0107] (3) Crystal Structure Analysis of Cobalt Phosphide Carbon Composite Particles by XRD The cobalt phosphide carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD in the same manner as in (3) of Test Example 1. The results are shown in Fig. 5.

[0108] As shown in Fig. 5, it was confirmed that CoP was supported on all of the cobalt phosphide carbon composite particles of Examples 1-3 and 5-1 to 5-4.

[0109] <Test Example 6> (1) Preparation of Phosphorus-Accumulating Yeast In the same manner as in (1-1) of Test Example 1, a freeze-dried product of phosphorus-accumulating yeast was prepared.

[0110] (2) Preparation of Cobalt Phosphide Carbon Composite Particles Using the dried yeast obtained in (1) above, cobalt phosphide carbon composite particles were obtained in the same manner as in (2) of Test Example 1.

[0111] In the preparation of cobalt phosphide carbon composite particles, the details of the usage amounts of dried phosphorus-accumulating yeast cells and cobalt nitrate hexahydrate, the composition and usage amount of the solvent, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) are as shown in Table 6.

[0112]

Table 6

[0113] (3) Crystal Structure Analysis of Cobalt Phosphide Carbon Composite Particles by XRD The cobalt phosphide carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD in the same manner as in (3) of Test Example 1. The results are shown in Fig. 6A.

[0114] As shown in Fig. 6A, it was confirmed that CoP was supported on all of the cobalt phosphide carbon composite particles of Examples 4-1, 6-1, and 6-2.

[0115] (4) Activity evaluation of the cobalt phosphide-carbon composite particles as an electrolysis catalyst for water Using the cobalt phosphide-carbon composite particles of Examples 4-1, 6-1, and 6-2 obtained in (2) above as catalysts, the activity as an electrolysis catalyst for water was evaluated in the same manner as in (4) of Test Example 1. The results are shown in Fig. 6B.

[0116] As shown in Fig. 6B, the absolute value of the overvoltage required for the electrode reaction was 246 to 293. Considering that the absolute value of the overvoltage in the cobalt phosphide-carbon composite particles (Comparative Example 1) supporting only Co2P was 520 as shown in Fig. 2B above, it was found that in Examples 4-1, 6-1, and 6-2 which are cobalt phosphide-carbon composite particles supporting CoP, the absolute value of the overvoltage during operation was significantly lower than that of the cobalt phosphide-carbon composite particles supporting Co2P in terms of electrode characteristics. That is, compared with the cobalt phosphide-carbon composite particles supporting only Co2P, the cobalt phosphide-carbon composite particles supporting CoP in Examples 4-1, 6-1, and 6-2 are excellent in hydrogen generation reaction performance and can reduce the required voltage for water electrolysis. Therefore, the cobalt phosphide-carbon composite particles of Examples 4-1, 6-1, and 6-2 can realize a highly efficient electrolysis reaction even at a low electrolysis voltage and can produce hydrogen at a low cost.

[0117] <Test Example 7> (1) Preparation of phosphorus-accumulating yeast In the same manner as in (1-1) of Test Example 1, a freeze-dried product of phosphorus-accumulating yeast was prepared.

[0118] (2) Preparation of cobalt phosphide-carbon composite particles Using the dried yeast obtained in (1) above, cobalt phosphide-carbon composite particles were obtained in the same manner as in (2) of Test Example 1.

[0119] In the preparation of the cobalt phosphide-carbon composite particles, the details of the usage amounts of the dried phosphorus-accumulating yeast cells and cobalt(II) nitrate hexahydrate, the composition and usage amount of the solvent, and the firing conditions (firing temperature, nitrogen flow rate, and firing time) are as shown in Table 7.

[0120] [Table 7]

[0121] (3) Crystal structure analysis of cobalt phosphide carbon composite particles by XRD The cobalt phosphide carbon composite particles obtained in (2) above were subjected to crystal structure analysis by XRD in the same manner as in (3) of Test Example 1. The results are shown in Figure 7A.

[0122] As shown in FIG. 7A, it was confirmed that CoP was supported on all of the cobalt phosphide carbon composite particles of Examples 4-1 and 7-1 to 7-8.

[0123] (4) Evaluation of catalytic activity of cobalt phosphide-carbon composite particles for water electrolysis The cobalt phosphide carbon composite particles of Examples 4-1 and 7-1 to 7-7 obtained in (2) above were used as catalysts to evaluate their activity as catalysts for water electrolysis in the same manner as in (4) of Test Example 1. The results are shown in Fig. 7B.

[0124] As shown in Figure 7B, the absolute value of the overpotential required for the electrode reaction was 180 to 317. As shown in Figure 2B above, the cobalt phosphide carbon composite particles carrying only Co2P (relatively Considering that the absolute value of the overvoltage in Comparative Example 1) was 520, it was confirmed that the CoP-supported cobalt phosphide carbon composite particles of Examples 4-1 and 7-1 to 7-7 had significantly lower absolute values of overvoltage during operation than the CoP-supported cobalt phosphide carbon composite particles. In other words, compared to the CoP-supported cobalt phosphide carbon composite particles of Examples 4-1 and 7-1 to 7-7, the CoP-supported cobalt phosphide carbon composite particles of Examples 4-1 and 7-1 to 7-7 have superior hydrogen generation reaction performance and can reduce the voltage required for water electrolysis. Therefore, the cobalt phosphide carbon composite particles of Examples 4-1 and 7-1 to 7-7 can achieve highly efficient electrolysis reactions even at low electrolysis voltages, enabling hydrogen production at low cost.

[0125] <Test Example 8> The catalysts used in this test example are as follows. · Cobalt phosphide-carbon composite particles of Examples 1-3 (prepared using phosphorus-accumulating yeast and a cobalt compound) · Cobalt phosphide-carbon composite particles of Example 2-2 (prepared using baker's yeast, an externally added 0.6 M phosphorus source, and a cobalt compound) · Cobalt phosphide-carbon composite particles of Comparative Example 1 (prepared using baker's yeast and a cobalt compound) · Pt-C (platinum supported on graphitized carbon; a catalyst in which 20 wt% platinum particles are supported on graphitized carbon)

[0126] (1) Chronoamperometry test For the electrochemical measurement, the three-electrode method was adopted. As the reference electrode, a Hg / HgO electrode (RE-61AP, BAS) with an internal solution of 1 M NaOH was used, and as the counter electrode, a graphite electrode was used. The reference potential of the reference electrode is shown in Equation 2-1. The catalyst and the Nafion solution were added to ethanol. After suspension, ultrasonic treatment was performed for 1 hour using an ultrasonic cleaner (BRANSON1510, yamato) to disperse the catalyst. The catalyst dispersion was applied to the bottom surface of the glassy carbon of the working electrode and dried. The catalyst coating amount was 0.22 mg / cm 2 It was.

[0127] In the chronoamperometry test, the reaction was carried out in an H-type electrolytic cell (VB8-1, Eicom Frontier), and an activated 3.0 cm × 3.0 cm Nafion N117 membrane was used as the separator between the cathode chamber and the anode chamber. The counter electrode was set in the anode chamber, and the working electrode and the reference electrode were set in the cathode chamber. As the electrolytic solution, 50 mL each of 1 M NaOH and 1 M NaNO3 were put into the cathode chamber and the anode chamber. While stirring the electrolytic solution in the cathode chamber with a magnetic stirrer so that the catalyst and the electrolytic solution could be sufficiently contacted, chronoamperometry (CA) measurement was performed at a voltage of -0.25 V using an electrochemical measurement device (HSV-110, Hokuto Denko).

[0128] The measurement results were obtained from the measured values of current at a constant voltage over time. Using Equation 2-1, the potential was calibrated to the potential versus the reversible hydrogen electrode (RHE) considering the influence of pH, and the current density was calculated from the current using Equation 2-2. The results are shown in Figure 8A.

[0129] As shown in Figure 8A, the cobalt phosphide-carbon composite particles of Examples 1-3 and Example 2-2 showed higher activity and stability compared to other catalysts. Among them, the cobalt phosphide-carbon composite particles of Example 1-3 showed particularly high activity and stability.

[0130]

Number

[0131] (2) Quantification of ammonia (Indophenol blue spectrophotometry) After the reaction in (1) above was completed, the electrolyte in the cathode chamber was collected as a sample solution. 5 mL of pure water was added to each of the sample solution arbitrarily diluted with the electrolyte (1M NaOH + 1M NaNO3) and 1 mL of the calibration curve solution. After adding 1 mL of the phenol nitroprusside sodium solution, 1 mL of the sodium hypochlorite solution was quickly added and mixed. The resulting mixed solution was allowed to stand at room temperature for 45 minutes, and then 200 μL of the mixed solution was transferred to a 96-well microplate, and the absorbance (A 630 ) at 630 nm was measured with a microplate reader. Using the calibration curve, the ammonia concentration in the sample solution was calculated, and the ammonia production rate per amount of catalyst (Equation 2-3) was calculated. The results are shown in Figure 8B.

[0132]

Number

[0133] As shown in Figure 8B, the cobalt phosphide-carbon composite particles of Examples 1-3 and Example 2-2 showed a higher ammonia production rate compared to other catalysts. Among them, the cobalt phosphide-carbon composite particles of Example 1-3 showed a particularly high ammonia production rate.

[0134] <Test Example 9> The catalyst surfaces of the cobalt phosphide carbon composite particles of Examples 1-3 and 2-2 were observed using a field emission scanning electron microscope (FE-SEM) (JSM-6500FS, JEOL). The results are shown in FIG. 9A. As shown in FIG. 9A, the presence of cobalt phosphide microparticles (microparticles indicated by arrows in the figure) was confirmed in these cobalt phosphide carbon composite particles. In particular, it was confirmed that the cobalt phosphide microparticles on the surface of the cobalt phosphide carbon composite particles of Example 1-3 were larger.

[0135] Furthermore, elemental analysis, spectral analysis, and mapping analysis were performed using EDS (Energy Dispersive X-ray Spectroscopy), an accessory function of the FE-SEM. The results are shown in Figure 9B. Figure 9B shows an SEM image and a mapping image of Co atoms corresponding to the SEM image. As shown in Figure 9B, the presence of cobalt phosphide microparticles was confirmed on the surface of these cobalt phosphide carbon composite particles. In particular, it was confirmed that the cobalt phosphide microparticles on the surface of the cobalt phosphide carbon composite particles of Example 1-3 were larger and more numerous.

Claims

1. A step of impregnating cells in a treatment liquid containing a cobalt compound and an organic solvent in a state of coexisting with a phosphorus source selected from the group consisting of oxo acids of phosphorus and salts thereof; A step of firing the cells after the impregnation treatment; and A method for producing cobalt phosphide carbon composite particles, wherein the amount of phosphorus constituting the phosphorus source is larger than the amount of phosphorus contained in the wild type of the cells.

2. The cells are phosphorus-enriched mutants, The method according to claim 1, wherein the state is a state in which more phosphorus than the wild type is accumulated as the phosphorus source inside the cells.

3. The method according to claim 1, wherein the state is a mixed state of the cells and the phosphorus source added outside the cells.

4. The method according to claim 1, wherein the organic solvent is selected from the group consisting of acetone, methanol, ethanol, and tetrahydrofuran.

5. The method according to claim 1, wherein the organic solvent is used together with water, and the content of the organic solvent in the mixed solvent composed of the organic solvent and water is 10 to 90% by volume.

6. The method according to claim 1, wherein the amount of the phosphorus source contained in the cells after the impregnation treatment is 2.5 parts by weight or more per 100 parts by weight of the dry weight of the cells in terms of the amount of phosphorus.

7. The method according to claim 3, wherein the addition amount of the phosphorus source is 5 to 100 parts by weight per 100 parts by weight of the cell dry weight in terms of the amount of phosphorus.

8. The method according to claim 1, wherein the usage amount of the cobalt compound is 0.36 to 70 mmol per 1 g of the dry weight of the cells in terms of the amount of cobalt.

9. The method according to claim 1, wherein the firing time is 5 minutes to 2.5 hours.

10. The method according to claim 1, wherein the firing temperature is 800 °C or higher.

11. The method according to claim 1, wherein the firing is performed under the condition of an inert gas flow rate of 10 to 1500 ml / min.

12. Cobalt phosphide carbon composite particles containing carbonized cells and CoP supported on the carbonized cells.

13. A catalyst for hydrogen generation reaction containing the cobalt phosphide carbon composite particles according to claim 12.

14. An electrode for hydrogen generation reaction, comprising a conductive substrate and a coating layer provided on the surface of the conductive substrate and containing the catalyst for hydrogen generation reaction according to claim 13.

15. A catalyst for ammonia generation reaction containing the cobalt phosphide carbon composite particles according to claim 12.

16. An electrode for ammonia generation reaction, comprising a conductive substrate and a coating layer provided on the surface of the conductive substrate and containing the catalyst for ammonia generation reaction according to claim 15.

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