Catalyst and method for producing the same, electrode for metal-air secondary battery or electrode for water electrolysis system including the catalyst, and metal-air secondary battery or water electrolysis system including the electrode

Abstract

Provided are: a catalyst and a method for producing the same, the catalyst demonstrating both excellent oxygen reduction catalytic performance and excellent oxygen generation catalytic performance, and effectively utilizing a biomass; a catalyst-containing electrode for a metal-air secondary battery or for a water electrolysis system, and a metal-air secondary battery or a water electrolysis system including an electrode. The present invention provides: a catalyst and a method for producing the same, the catalyst including a baked substance of a mixture of biomass-derived cellulose nanofibers and a dry substance that contains proteins or amino acids; a catalyst-containing electrode for a metal-air secondary battery or for a water electrolysis system; and a metal-air secondary battery or a water electrolysis system including an electrode.

Description

Technical Field

[0001] The present invention relates to a catalyst and a method for producing the same, an electrode for a metal-air secondary battery or an electrode for a water electrolysis system including the catalyst, and a metal-air secondary battery or a water electrolysis system including the electrode.

Background Art

[0002] Among metal-air batteries having a high energy density by using oxygen present in the air as a positive electrode active material and a metal as a negative electrode active material, those that can be reversibly charged and discharged are called metal-air secondary batteries, and it is known that they have an energy density several times to more than 10 times higher than that of lithium-ion batteries. In the positive electrode (air electrode) of this battery, an oxygen reduction reaction occurs during discharge, and a catalyst is used to promote the reduction reaction. As a typical oxygen reduction catalyst, a carbon material supporting a rare metal such as platinum is known. On the other hand, during charging, an oxygen evolution reaction, which is the reverse reaction, occurs at the air electrode, and a rare metal such as iridium oxide or ruthenium oxide is generally used as a catalyst for promoting the oxygen evolution reaction.

[0003] However, since rare metals such as platinum, iridium, and ruthenium are expensive and their resource amounts are limited, the development of an electrode catalyst using materials that are cheaper and have abundant resource amounts without using these rare metals has become an issue.

[0004] In addition, in the air electrode of a metal-air secondary battery, a catalyst having activities for both an oxygen reduction reaction and an oxygen evolution reaction is required. Although platinum exhibits excellent catalytic performance in the oxygen reduction reaction, it has a problem of low catalytic activity in the oxygen evolution reaction. On the contrary, iridium, ruthenium, etc. exhibit high catalytic performance in the oxygen evolution reaction, but have a problem of low catalytic activity in the oxygen reduction reaction. Therefore, a binary catalyst having excellent activity in both the oxygen evolution reaction and the oxygen reduction reaction has been demanded.

[0005] One of the promising cathode catalyst materials that do not use rare metals such as platinum includes nitrogen-doped graphene, carbon nanotubes, and metal-containing carbon materials having an MN4 structure in which four nitrogen atoms (N) are coordinated in a plane around a central metal (M). For example, Patent Document 1 describes that an oxygen reduction electrode catalyst substituting for platinum was manufactured by thermally decomposing a metal complex having an MN4 structure and a carbon material. However, in the technique described in Patent Document 1, a process for synthesizing a metal complex having an MN4 structure as a raw material is required.

[0006] On the other hand, in recent years, as environmental problems have become more serious, the realization of a resource recycling-based society has become an important issue. Therefore, materials that effectively utilize biomass have attracted attention as cathode catalyst materials to replace rare metals such as platinum. For example, Patent Document 2 discloses manufacturing an oxygen reduction catalyst using metal-containing organic natural products such as hemoglobin as a raw material. Further, Patent Document 3 describes that a conductive material such as carbon black can be added to a metal-containing carbon material having an FeN4 structure using a metal-containing organic natural product as a raw material to manufacture an oxygen reduction electrode. Patent Documents 2 and 3 also describe that blood meal obtained from blood waste can also be used as a raw material containing a metal-containing natural product.

[0007] However, the performance of the cathode catalyst material as an oxygen reduction catalyst in the techniques described in Patent Documents 2 and 3 is still insufficient and there is room for improvement. In addition, in order to be utilized as a metal-air secondary battery, it is important to have oxygen evolution catalyst performance in addition to the oxygen reduction catalyst. Furthermore, in order to achieve a more complete resource cycle, in addition to not using rare metals, it is desirable to use biomass-derived carbon materials instead of expensive nanocarbons such as graphene and carbon nanotubes as the carbon material. Therefore, there has been a demand to develop a catalyst having better catalyst performance while effectively utilizing biomass.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made to solve the above problems of the prior art, and provides a high-performance catalyst using biomass, a method for producing the same, an electrode for a metal-air secondary battery or an electrode for a water electrolysis system, which replaces rare metals such as platinum, iridium, and ruthenium, and a metal-air secondary battery or a water electrolysis system including the electrode.

Means for Solving the Problems

[0010] As a result of intensive studies on the above problems, the present inventors unexpectedly found that the catalyst includes a fired product of a mixture containing cellulose nanofibers derived from biomass and a dried product containing a protein or an amino acid, and thus is excellent in both oxygen reduction catalyst performance and oxygen evolution catalyst performance, and at the same time is excellent in hydrogen evolution catalyst performance, and further has catalyst performance comparable to that of a carbon catalyst using rare metals such as platinum, iridium, and ruthenium, and thus reached the present invention.

[0011] In addition, as a result of intensive studies on the above problems, the present inventors unexpectedly found that the catalyst includes a fired product of a mixture containing cellulose nanofibers derived from biomass, a dried product containing a protein or an amino acid, and further a cobalt complex, and thus the oxygen evolution catalyst performance of the catalyst is remarkably improved, and it is excellent in both oxygen reduction catalyst performance and oxygen evolution catalyst performance, and further excellent in hydrogen evolution catalyst performance, and thus reached the present invention.

[0012] The object of the present invention is It is achieved by a catalyst, including a fired product of a mixture containing cellulose nanofibers derived from biomass and a dried product containing protein or amino acids.

[0013] The cellulose nanofibers are preferably derived from marine biomass.

[0014] The cellulose nanofibers are preferably derived from sea squirt shells or seaweeds.

[0015] The dried product containing the protein or amino acids is preferably a dried product of blood waste having an FeN4 structure.

[0016] The catalyst preferably contains 0.1 to 30% by mass of iron based on the total mass of the catalyst.

[0017] The catalyst preferably contains 0.1 to 40% by mass of phosphorus based on the total mass of the catalyst.

[0018] The mass ratio of the dried product containing the protein or amino acids to the cellulose nanofibers contained in the mixture is preferably 1:1 to 20:1.

[0019] The mixture preferably further contains a cobalt complex.

[0020] The cobalt complex is preferably a vitamin B 12 class.

[0021] The vitamin B 12 class is preferably derived from biomass.

[0022] The vitamin B 12 class is preferably derived from nori seaweed and / or oysters.

[0023] The catalyst preferably contains 0.1 to 30% by mass of cobalt based on the total mass of the catalyst.

[0024] It is preferable that the mass ratio of the cellulose nanofiber, the dry matter containing the protein or amino acid, and the cobalt complex contained in the mixture (cellulose nanofiber: dry matter containing protein or amino acid: cobalt complex) is 1:1 to 20:0.1 to 10.

[0025] The catalyst is preferably a catalyst for oxygen generation, oxygen reduction, or hydrogen generation.

[0026] The present invention also relates to a method for producing a catalyst comprising a fired product of a mixture containing a cellulose nanofiber derived from biomass and a dry matter containing a protein or amino acid, The production method includes a step of preparing and firing a mixture containing the dry matter containing the protein or amino acid and the cellulose nanofiber.

[0027] The mixture preferably further contains a cobalt complex.

[0028] The production method preferably includes a step of extracting the cellulose nanofiber from biomass.

[0029] The production method preferably includes a step of obtaining a dry matter of the blood waste by concentrating and drying the blood waste.

[0030] The present invention also relates to an electrode of a metal-air secondary battery or a water electrolysis system including the catalyst of the present invention.

[0031] The present invention also relates to a metal-air secondary battery or a water electrolysis system including the electrode of the present invention.

[0032] Examples of the aspects of the present invention are as follows.

[0033] (Aspect 1) A catalyst comprising a fired product of a mixture containing a cellulose nanofiber derived from biomass and a dry matter containing a protein or amino acid.

[0034] (Aspect 2) The catalyst according to Aspect 1, wherein the cellulose nanofiber is derived from marine biomass.

[0035] (Aspect 3) The catalyst according to Aspect 1 or 2, wherein the cellulose nanofiber is derived from sea urchin shells or seaweed.

[0036] (Aspect 4) The catalyst according to any one of Aspects 1 to 3, wherein the dried product containing the protein or amino acid has an FeN4 structure and is a dried product of blood waste.

[0037] (Aspect 5) The catalyst according to any one of Aspects 1 to 4, containing 0.1 to 30% by mass of iron based on the total mass of the catalyst.

[0038] (Aspect 6) The catalyst according to any one of Aspects 1 to 5, containing 0.1 to 40% by mass of phosphorus based on the total mass of the catalyst.

[0039] (Aspect 7) The catalyst according to any one of Aspects 1 to 6, wherein the mass ratio of the dried product containing the protein or amino acid contained in the mixture to the cellulose nanofiber is 1:1 to 20:1.

[0040] (Aspect 8) The catalyst according to any one of Aspects 1 to 7, wherein the mixture further contains a cobalt complex.

[0041] (Aspect 9) The cobalt complex is vitamin B 12 The catalyst according to Aspect 8, which is a class.

[0042] (Aspect 10) The vitamin B 12 The catalyst according to Aspect 9, wherein the class is derived from biomass.

[0043] (Aspect 11) The vitamin B 12 The catalyst according to aspect 9 or 10, wherein the class is derived from nori and / or oysters.

[0044] (Aspect 12) The catalyst according to any one of aspects 8 to 11, comprising 0.1 to 30% by mass of cobalt based on the total mass of the catalyst.

[0045] (Aspect 13) The catalyst according to any one of aspects 8 to 12, wherein the mass ratio of the cellulose nanofiber, the dried product containing the protein or amino acid, and the cobalt complex contained in the mixture (cellulose nanofiber: dried product containing protein or amino acid: cobalt complex) is 1:1 to 20:0.1 to 10.

[0046] (Aspect 14) The catalyst according to any one of aspects 1 to 13, which is for oxygen generation, oxygen reduction, or hydrogen generation.

[0047] (Aspect 15) A method for producing a catalyst comprising a fired product of a mixture containing a biomass-derived cellulose nanofiber and a dried product containing a protein or amino acid, The production method comprising the steps of preparing and firing a mixture containing the biomass-derived cellulose nanofiber and the dried product containing the protein or amino acid.

[0048] (Aspect 16) The production method according to aspect 15, wherein the mixture further contains a cobalt complex.

[0049] (Aspect 17) The production method according to aspect 15 or 16, comprising the step of extracting the cellulose nanofiber from biomass.

[0050] (Aspect 18) The production method according to any one of aspects 15 to 17, comprising the step of obtaining the dried product containing the protein or amino acid by concentrating and drying blood waste.

[0051] (Aspect 19) The manufacturing method according to any one of Aspects 15 to 18, wherein the cellulose nanofiber is derived from marine biomass.

[0052] (Aspect 20) The manufacturing method according to any one of Aspects 15 to 19, wherein the cellulose nanofiber is derived from sea squirt shells or seaweed.

[0053] (Aspect 21) The cobalt complex is a vitamin B 12 class, and the manufacturing method according to any one of Aspects 16 to 20.

[0054] (Aspect 22) The vitamin B 12 class is derived from biomass, and the manufacturing method according to Aspect 21.

[0055] (Aspect 23) The vitamin B 12 class is derived from nori and / or oysters, and the manufacturing method according to Aspect 21 or 22.

[0056] (Aspect 24) An electrode for a metal-air secondary battery or a water electrolysis system, comprising the catalyst according to any one of Aspects 1 to 14.

[0057] (Aspect 25) A metal-air secondary battery or a water electrolysis system, comprising the electrode according to Aspect 24. [Advantages of the Invention]

[0058] According to the present invention, it is possible to provide a catalyst that effectively utilizes biomass and has excellent catalyst performance in both oxygen reduction catalyst performance and oxygen evolution catalyst performance, and further has excellent catalyst performance in hydrogen evolution catalyst performance. [Brief Description of the Drawings]

[0059]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0060] [Catalyst] The catalyst of the present invention includes a fired product of a mixture containing a cellulose nanofiber derived from biomass and a dry matter containing a protein or an amino acid. By including a fired product of a mixture containing a cellulose nanofiber derived from biomass and a dry matter containing a protein or an amino acid, a catalyst can be obtained that has excellent catalytic abilities for both oxygen reduction and oxygen generation, and further has a catalytic performance for hydrogen generation.

[0061] [Cellulose Nanofiber Derived from Biomass] The cellulose nanofiber of the present invention is obtained from biomass. Preferably, the cellulose nanofiber is not derived from wood. More preferably, the cellulose nanofiber is derived from marine biomass. Even more preferably, the cellulose nanofiber is derived from tunicates or seaweeds.

[0062] In a preferred embodiment, the cellulose nanofibers of the present invention are derived from urochordates. In a more preferred embodiment, the cellulose nanofibers of the present invention are derived from ascidian shells. Ascidians are known as the only animals capable of producing cellulose. On the other hand, ascidian shells, which are inedible parts, have become a large amount of industrial waste. Therefore, if the cellulose nanofibers of the present invention are derived from ascidian shells, a catalyst that more effectively utilizes waste biomass can be produced. In addition, cellulose derived from ascidian shells has higher tensile strength and better crystallinity than cellulose derived from wood. Therefore, when the cellulose nanofibers of the present invention are derived from ascidian shells, a highly conductive carbon material can be obtained by firing.

[0063] In one embodiment, the cellulose nanofibers of the present invention are derived from seaweeds. Examples of seaweeds include wakame, kombu, agar, and sea lettuce. Among these, the cellulose nanofibers are preferably derived from wakame, and more preferably from the core and stem parts of wakame.

[0064] The cellulose nanofibers of the present invention may be a combination of one or more cellulose nanofibers. The cellulose nanofibers of the present invention may use only cellulose nanofibers derived from ascidian shells. Also, the cellulose nanofibers of the present invention may use only cellulose nanofibers derived from seaweeds. The cellulose nanofibers of the present invention may be used in combination with cellulose nanofibers derived from ascidian shells and cellulose nanofibers derived from seaweeds. In one embodiment, it is preferable to use only cellulose nanofibers derived from ascidian shells for the cellulose nanofibers of the present invention.

[0065] The cellulose nanofibers of the present invention preferably have a diameter of less than 200 nm, more preferably less than 100 nm, and even more preferably less than 50 nm. When the diameter of the cellulose nanofibers is less than the above upper limit value, the specific surface area can be increased and high conductivity can be achieved. In one embodiment, since the cellulose nanofibers of the present invention are derived from sea urchin shells, the fiber diameter is smaller than that of cellulose nanofibers derived from wood. Therefore, since the surface area of the cellulose nanofibers is increased, a carbon material having more excellent catalytic activity can be obtained.

[0066] The cellulose nanofibers of the present invention preferably have a fiber length of more than 4 μm, more preferably more than 4.5 μm, and even more preferably more than 5 μm. When the fiber length of the cellulose nanofibers exceeds the above upper limit value, excellent tensile strength can be achieved.

[0067] The cellulose nanofibers of the present invention preferably have a crystal size of 7 to 14 nm, more preferably 8 to 12 nm, and even more preferably 8.5 to 11.5 nm. In one embodiment, since the cellulose nanofibers are derived from marine biomass, they can have higher crystallinity than cellulose nanofibers derived from wood.

[0068] The cellulose nanofibers of the present invention preferably have a tensile strength of 2.5 to 7.5 GPa, more preferably 2.8 to 7.0 GPa, and even more preferably 3.0 to 6.4 GPa. In one embodiment, since the cellulose nanofibers are derived from marine biomass, they can have higher tensile strength than cellulose nanofibers derived from wood.

[0069] The cellulose nanofibers of the present invention preferably have a crystallinity of 80% or more, more preferably 90% or more, and even more preferably 95% or more. In one embodiment, since the cellulose nanofibers are derived from marine biomass, they can have higher crystallinity than cellulose nanofibers derived from wood.

[0070] [Dried product containing protein or amino acid] The dried product containing the protein or amino acid of the present invention includes, for example, dried products derived from raw materials derived from livestock meat, seafood, beans, milk, yeast, etc. Preferably, the dried product containing the protein or amino acid of the present invention is of animal origin or plant origin. In one embodiment, the dried product containing the protein or amino acid of the present invention is preferably derived from waste, more preferably animal waste, plant waste, or a mixture of animal waste and plant waste. In one embodiment, the dried product containing the protein or amino acid of the present invention is most preferably derived from blood waste.

[0071] In one embodiment, the protein or amino acid of the present invention can contain a metal. When the protein or amino acid contains a metal, examples of the type of metal include iron, copper, manganese, cobalt, nickel, vanadium, etc. In one embodiment, the protein or amino acid of the present invention contains iron. In one embodiment, the dried product containing the protein or amino acid of the present invention is a dried product of blood waste having an FeN4 structure.

[0072] For the dried product of blood waste having an FeN4 structure, for example, blood waste generated in a meat processing factory, a seafood processing factory, etc. can be used. As the blood waste, preferably, dried blood powder obtained by drying the waste blood generated in a meat processing factory can be used. As the blood waste, for example, dried blood powder obtained by drying waste blood derived from pigs, poultry, rabbits, sheep, cows, etc. may also be used. Preferably, dried blood powder obtained by drying waste blood derived from cows or pigs is used.

[0073] The dried product of blood waste having an FeN4 structure may contain a metal-containing organic compound having an FeN4 structure. As the metal-containing organic compound having an FeN4 structure, iron protein is preferred. Examples of iron protein include hemoglobin, catalase, peroxidase, cytochrome, etc. Among these, the iron protein is preferably hemoglobin.

[0074] When the dried product of blood waste having an FeN4 structure contains iron protein, the content of the iron protein is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more based on the total amount of the dried product of blood waste. When the content of the iron protein is at or above the lower limit value, the FeN4 structure source is abundant relative to the total amount of the catalyst, and the performance of the catalyst is further excellent.

[0075] The dried product of blood waste having an FeN4 structure may further contain one or more selected from proteins other than iron protein, lysine, and sulfur-containing amino acids in addition to the iron protein. The protein other than iron protein is not particularly limited, and examples thereof include copper protein. Examples of the copper protein include bilirubin oxidase, tyrosinase, laccase, and the like.

[0076] The dried product of blood waste having an FeN4 structure may further contain moisture and fat. The dried product of blood waste having an FeN4 structure preferably contains moisture of less than 12% by mass, more preferably less than 10% by mass, and still more preferably less than 8% by mass. When the dried product of blood waste having an FeN4 structure contains moisture below the upper limit value, the performance of the catalyst is further excellent. Further, the dried product of blood waste having an FeN4 structure preferably contains fat of less than 5% by mass, more preferably less than 2% by mass, and still more preferably less than 1% by mass. When the dried product of blood waste having an FeN4 structure contains fat below the upper limit value, the performance of the catalyst is further excellent.

[0077] [Fired product of a mixture containing a biomass-derived cellulose nanofiber and a dried product containing a protein or an amino acid] The fired product of the mixture containing the biomass-derived cellulose nanofiber of the present invention and the dried product containing a protein or an amino acid of the present invention is obtained by preparing a mixture containing the biomass-derived cellulose nanofiber of the present invention and the dried product containing the protein or an amino acid of the present invention, and firing the obtained mixture.

[0078] In addition to the fired product of a mixture containing cellulose nanofibers derived from biomass and a dried product containing a protein or an amino acid, the catalyst of the present invention may contain further components. As the further components, preferably a solvent is mentioned. The solvent may be a solvent in which the catalyst is easily soluble (i.e., has a high solubility), or may be a solvent in which the catalyst is hardly soluble (i.e., has a low solubility).

[0079] The solvent is not particularly limited, and may be an inorganic solvent such as water, or may be an organic solvent. Specific examples of the organic solvent include alcohols such as methanol, ethanol, propanol, isopropanol (2-propanol), and 1-hexanol; dimethyl sulfoxide; tetrahydrofuran; aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide, and acetone; and nonpolar solvents such as chloroform, dichloromethane, 1,4-dioxane, benzene, and toluene. The solvent may be used alone or in combination of two or more.

[0080] The catalyst of the present invention is preferably a catalyst for oxygen generation, a catalyst for oxygen reduction or a catalyst for hydrogen generation. In one embodiment, the catalyst of the present invention has the properties of oxygen generation catalyst performance, oxygen reduction catalyst performance and hydrogen generation catalyst performance. Therefore, in one embodiment, the catalyst of the present invention is a catalyst for oxygen generation, a catalyst for oxygen reduction and a catalyst for hydrogen generation.

[0081] The catalyst of the present invention is preferably a catalyst for oxygen generation or oxygen reduction in the positive electrode of a battery. The catalyst of the present invention is more preferably a catalyst for oxygen generation or oxygen reduction in the positive electrode (air electrode) of a metal-air secondary battery. Alternatively, the catalyst of the present invention is preferably a catalyst for oxygen generation in a water electrolysis system. The catalyst of the present invention is more preferably a catalyst for oxygen generation at the anode of a water electrolysis system.

[0082] In addition, the catalyst of the present invention can preferably also be used as a catalyst for hydrogen generation in a water electrolysis system. The catalyst of the present invention can more preferably also be used as a catalyst for hydrogen generation at the cathode of a water electrolysis system.

[0083] The catalyst of the present invention preferably contains 0.1 to 30% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 10% by mass of iron based on the total mass of the catalyst. By the catalyst of the present invention containing iron within the above range, it can have more excellent catalytic activity.

[0084] The catalyst of the present invention preferably contains 0.1 to 40% by mass, more preferably 0.2 to 20% by mass, and even more preferably 0.5 to 10% by mass of phosphorus based on the total mass of the catalyst. By the catalyst of the present invention containing phosphorus within the above range, it can have more excellent catalytic activity.

[0085] The catalyst of the present invention preferably contains 0.1 to 40% by mass, more preferably 0.2 to 20% by mass, and even more preferably 0.5 to 10% by mass of nitrogen based on the total mass of the catalyst. By the catalyst of the present invention containing nitrogen within the above range, it can have more excellent catalytic activity.

[0086] In the catalyst of the present invention, the mass ratio of the dried product containing the protein or amino acid contained in the mixture to the cellulose nanofiber is preferably 0.1:1 to 50:1, more preferably 1:1 to 30:1, and even more preferably 1:1 to 20:1. When the mass ratio of the dried product containing the protein or amino acid of the present invention to the cellulose nanofiber is within the above range, it can have better conductivity and catalytic activity. When the dried product containing the protein or amino acid of the present invention includes the dried product of blood waste, the mass ratio of the dried product of blood waste contained in the mixture of the present invention to the cellulose nanofiber is preferably 0.1:1 to 50:1, more preferably 1:1 to 30:1, and even more preferably 1:1 to 20:1. When the mass ratio of the dried product of blood waste of the present invention to the cellulose nanofiber is within the above range, it can have better conductivity and catalytic activity.

[0087] The oxygen evolution (OER) catalyst of the present invention preferably has a starting potential E of 1.5 V [vsRHE] or less, more preferably 1.45 V [vsRHE] or less, and even more preferably 1.4 V [vsRHE] or less. on-set / OER By having a starting potential below the above upper limit value, the oxygen evolution (OER) catalyst of the present invention can have an oxygen evolution catalytic activity comparable to that of a rare metal such as iridium.

[0088] The oxygen evolution catalyst of the present invention has a potential E 2 when the current density reaches 10 mA / cm j-10(OER) which is preferably 2.0 V [vsRHE] or less, more preferably 1.9 V [vsRHE] or less, and even more preferably 1.8 V [vsRHE] or less. j-10(OER) By having an E j-10(OER) above the above upper limit value, the oxygen evolution catalyst of the present invention can have an oxygen evolution catalytic activity comparable to that of a rare metal such as iridium.

[0089] The oxygen reduction (ORR) catalyst of the present invention preferably has a starting potential E of 0.8 V [vsRHE] or higher, more preferably 0.9 V [vsRHE] or higher, even more preferably 0.98 V [vsRHE] or higher, and particularly preferably 1.0 V [vsRHE] or higher. on-set / ORR By having a starting potential equal to or higher than the lower limit value, the oxygen reduction catalyst of the present invention can have an oxygen reduction catalytic activity comparable to that of noble metals such as platinum.

[0090] The oxygen reduction catalyst of the present invention preferably has a half-wave potential E of 0.75 V [vsRHE] or higher, more preferably 0.80 or higher, even more preferably 0.82 or higher, and particularly preferably 0.85 V [vsRHE]. half(ORR) By having a half-wave potential equal to or higher than the lower limit value, the oxygen reduction catalyst of the present invention can have an oxygen reduction catalytic activity comparable to that of noble metals such as platinum.

[0091] [A catalyst comprising a fired product of cellulose nanofibers derived from biomass, a dried product containing a protein or an amino acid, and a cobalt complex] In one embodiment, the mixture prepared to obtain the fired product contained in the catalyst of the present invention contains a cobalt complex in addition to the cellulose nanofibers derived from biomass and the dried product containing a protein or an amino acid. By including a fired product of a mixture containing cellulose nanofibers derived from biomass, a dried product containing a protein or an amino acid, and a cobalt complex, the activity of the oxygen evolution reaction is significantly improved, and the catalyst is excellent in both oxygen reduction catalyst performance and oxygen evolution catalyst performance. Furthermore, a catalyst with even better hydrogen evolution catalyst performance can be obtained.

[0092] [Cobalt complex] In one embodiment, the cobalt complex of the present invention is vitamin B 12 classes. Vitamin B 12 classes refer to vitamin B 12 (cyanocobalamin), its derivatives, and their salts. Vitamin B 12Examples of the derivatives include compounds in which the ligands on cobalt in cyanocobalamin are substituted, compounds in which the functional groups in cyanocobalamin are substituted, etc. More specifically, examples include methylcobalamin, hydroxocobalamin, adenosylcobalamin, aquacobalamin, etc. Also, vitamin B 12 Examples of salts of and its derivatives include carboxylates such as acetate, trifluoroacetate, butyrate, palmitate, stearate, fumarate, maleate, succinate, malonate, lactate, tartrate, citrate, etc.; organic sulfonates such as methanesulfonate, toluenesulfonate, tosylate, etc.; inorganic acid salts such as hydrochloride, sulfate, nitrate, phosphate, etc.; organic amine salts such as methylamine, triethylamine, triethanolamine, etc.; alkali metal salts such as sodium salt, potassium salt, etc.; alkaline earth metal salts such as calcium, magnesium, etc.; ammonium salts, etc. These vitamin B 12 classes may be used alone or in combination of two or more. Preferably, the cobalt complex of the present invention is vitamin B 12 (cyanocobalamin).

[0093] In one embodiment, the vitamin B 12 classes of the present invention are derived from biomass. By using vitamin B 12 classes derived from biomass, a catalyst that more effectively utilizes biomass can be produced. Examples of vitamin B 12 classes derived from biomass include, for example, vitamin B 12 classes derived from seafood, seaweeds, or meats. More preferably, the vitamin B 12 classes of the present invention are derived from seafood and / or seaweeds. Examples of seafood include, for example, oysters, clams, salmon roe, saury, and herring. Examples of seaweeds include, for example, nori, wakame, kombu, agar, and sea lettuce. Among these, the vitamin B 12 classes of the present invention are preferably derived from oysters and / or nori. The vitamin B 12 classes of the present invention may use only vitamin B 12 classes derived from oysters, or vitamin B derived from nori12 It may be used only with the class, vitamin B derived from oyster 12 class and vitamin B derived from nori seaweed 12 class may be used in combination. The vitamin B of the present invention 12 class, vitamin B derived from oyster and / or nori seaweed 12 By using the class, the activity of the oxygen generation reaction is further improved, and a catalyst excellent in both oxygen reduction catalyst performance and oxygen generation catalyst performance and having further improved hydrogen generation catalyst performance can be obtained. Preferably, the cobalt complex of the present invention is vitamin B derived from oyster and / or nori seaweed 12 (cyanocobalamin).

[0094] In one embodiment, the catalyst of the present invention preferably contains 0.1 to 30% by mass, more preferably 0.1 to 20% by mass, and even more preferably 0.5 to 10% by mass of cobalt based on the total mass of the catalyst. By the catalyst of the present invention containing cobalt within the above range, it can have more excellent oxygen generation catalyst performance and more excellent hydrogen generation catalyst performance.

[0095] In one embodiment, the mass ratio (cellulose nanofiber: dried product containing protein or amino acid: cobalt complex) of the cellulose nanofiber, protein or amino acid-containing dried product and cobalt complex contained in the mixture for the fired product contained in the catalyst of the present invention is preferably 1:1 to 20:0.1 to 10, more preferably 1:1 to 15:0.1 to 5, and even more preferably 1:1 to 12:0.5 to 3. By the mass ratio of the cellulose nanofiber, protein or amino acid-containing dried product and cobalt complex of the present invention being within the above range, it can have more excellent conductivity and catalytic activity.

[0096] In one embodiment, when the catalyst of the present invention contains a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or amino acid-containing dried product and a cobalt complex, the current density of the oxygen generation (OER) catalyst of the present invention is 10 mA / cm 2 when reaching the potential E j-10(OER)is preferably 1.8 V [vsRHE] or less, more preferably 1.75 V [vsRHE] or less, and even more preferably 1.73 V [vsRHE] or less, E j-10(OER) can have. When the catalyst of the present invention has an E j-10(OER) equal to or higher than the above upper limit value, it can have an oxygen generation catalyst activity comparable to that of a noble metal such as iridium.

[0097] The hydrogen evolution (HER) catalyst of the present invention preferably has a starting potential E of -0.7 V [vsRHE] or more, more preferably -0.5 V [vsRHE] or more, even more preferably -0.4 V [vsRHE] or more, and particularly preferably -0.3 V [vsRHE] or more. on-set / HER has. When the hydrogen generation catalyst of the present invention has a starting potential equal to or higher than the above lower limit value, it can have a hydrogen catalyst activity comparable to that of a noble metal such as platinum.

[0098] [Method for Producing Catalyst] In one embodiment, the present invention relates to a method for producing the catalyst of the present invention. The method for producing the catalyst includes a step of preparing a mixture containing a dried product containing a protein or an amino acid and cellulose nanofibers derived from biomass, and firing the mixture.

[0099] To produce the catalyst of the present invention, for example, a mixture containing a dried product containing a protein or an amino acid and cellulose nanofibers derived from biomass as a carbon source is prepared, and then the mixture is heat-treated and carbonized at a predetermined temperature in an inert atmosphere such as nitrogen or helium. The heat treatment temperature is not particularly limited as long as it is a temperature at which carbonization is possible, but a preferred temperature is 350 to 1600 °C, a more preferred temperature is 500 to 1200 °C, an even more preferred temperature is 600 to 1000 °C, and a particularly preferred temperature is 750 °C to 950 °C (around 900 °C). Also, the time required for this heat treatment is not particularly limited as long as it is a time at which carbonization is possible, but it is preferably 30 minutes to 6 hours, more preferably 1 to 5 hours, and even more preferably 1 to 3 hours. Subsequently, the obtained carbide is finely pulverized, for example, with a ball mill or the like, to obtain a fired product of a mixture containing a dried product containing a protein or an amino acid and cellulose nanofibers derived from biomass. In one embodiment, the dried product containing a protein or an amino acid can be a dried product of blood waste as a nitrogen-iron complex source.

[0100] The method for producing the catalyst of the present invention preferably further includes a step of extracting cellulose nanofibers from biomass. In the method for producing the catalyst of the present invention, preferably the cellulose nanofibers are not derived from wood. In the method for producing the catalyst of the present invention, more preferably, the cellulose nanofibers are derived from marine biomass. In the method for producing the catalyst of the present invention, even more preferably the cellulose nanofibers are derived from tunicates or seaweeds. In the method for producing the catalyst of the present invention, it is preferable that the cellulose nanofibers are derived from ascidian shells or seaweeds, and particularly preferably they are derived from ascidian shells. When the cellulose nanofibers of the present invention are derived from ascidian shells, they can be decomposed more easily compared to the case of using wood-derived cellulose containing a large amount of lignin, and the energy and cost required for production can be suppressed.

[0101] The method for extracting cellulose nanofibers from biomass is optional. When the cellulose nanofibers are derived from sea urchin shells, the method for extracting cellulose nanofibers may include, for example, a step of treating the sea urchin shells with an alkaline solution to decompose proteins and extract cellulose. The alkaline solution is not particularly limited, and examples include a 10% potassium hydroxide solution and a sodium hydroxide solution. When the cellulose nanofibers are derived from seaweeds such as wakame, a step of removing alginic acid by centrifugation or the like may be included. Subsequently, the method for extracting cellulose from biomass may include a step of pulverizing the obtained cellulose into a nano size.

[0102] When using the dried product of blood waste as the dried product containing the protein or amino acid of the present invention, the method for producing the catalyst of the present invention preferably further includes a step of obtaining the dried product of blood waste by concentrating and drying the blood waste. The method for concentrating and drying the blood waste is optional. For example, the blood obtained from meat can be concentrated and the moisture can be removed by low-temperature vacuum drying to obtain the dried product of blood waste. In one embodiment, there is no need to remove components other than iron protein from the blood waste in the method for producing the catalyst of the present invention. When the method for producing the catalyst of the present invention does not include a step of removing components other than iron protein from the blood waste, the production of the catalyst becomes simpler and the production cost can be suppressed.

[0103] In one embodiment, when the catalyst of the present invention includes a fired product of a mixture containing cellulose nanofibers, a dried product containing a protein or an amino acid derived from biomass, and a cobalt complex, the method for producing the catalyst of the present invention includes a step of preparing a mixture containing cellulose nanofibers, a dried product containing a protein or an amino acid derived from biomass, and a cobalt complex, and firing the mixture.

[0104] In one embodiment, when the catalyst of the present invention includes a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid-containing dry matter, and a cobalt complex, to produce the catalyst of the present invention, for example, a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid-containing dry matter, and a cobalt complex is prepared, and then heat-treated at a predetermined temperature in an inert atmosphere such as nitrogen or helium to carbonize it. This heat treatment temperature is not particularly limited as long as it is a temperature at which carbonization is possible, but a preferred temperature is 350 to 1600 °C, a more preferred temperature is 500 to 1200 °C, an even more preferred temperature is 600 to 1000 °C, and a particularly preferred temperature is 750 °C to 950 °C (around 900 °C). Also, the time required for this heat treatment is not particularly limited as long as it is a time at which carbonization is possible, but it is preferably 30 minutes to 6 hours, more preferably 1 to 5 hours, and even more preferably 1 to 3 hours. Subsequently, the obtained carbide is finely pulverized, for example, with a ball mill or the like, to obtain a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid-containing dry matter, and a cobalt complex.

[0105] When the catalyst of the present invention includes a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid-containing dry matter, and a cobalt complex, the method for producing the catalyst of the present invention preferably further includes a step of obtaining a cobalt complex from biomass. The method for obtaining a cobalt complex from biomass is arbitrary.

[0106] In one embodiment, the cobalt complex of the present invention is a vitamin B 12 class. Preferably, the cobalt complex of the present invention is vitamin B 12 (cyanocobalamin).

[0107] In one embodiment, the vitamin B 12 class of the present invention is derived from biomass, preferably the vitamin B 12 class is derived from fish and shellfish and / or seaweeds, and more preferably the vitamin B 12The class is derived from oysters and / or nori. In one embodiment, the method for manufacturing the catalyst of the present invention is to obtain vitamin B from biomass 12 a step of obtaining a cobalt complex, for example, by homogenizing a biomass raw material (such as oysters, nori, etc.) with a food processor and heating and extracting it in an acetate buffer solution containing a potassium cyanide solution.

[0108] [Electrode] In one embodiment, the present invention relates to an electrode containing the catalyst of the present invention. The electrode can be provided with a layer containing the catalyst of the present invention (i.e., a catalyst layer) on a substrate, and can be used as a catalyst for an oxygen evolution reaction or a catalyst for an oxygen reduction reaction. Also, in one embodiment, it can also be used as a catalyst for a hydrogen evolution reaction. The catalyst layer may be in direct contact with the substrate, or another layer may exist between the substrate and the catalyst.

[0109] The substrate is not particularly limited, but examples include aluminum foil, electrolytic aluminum foil, aluminum mesh (expanded metal), foamed aluminum, punched aluminum, aluminum alloys such as duralumin, copper foil, electrolytic copper foil, copper mesh (expanded metal), foamed copper, punched copper, copper alloys such as brass, brass foil, brass mesh (expanded metal), foamed brass, punched brass, nickel foil, nickel mesh, corrosion-resistant nickel, nickel mesh (expanded metal), punched nickel, foamed nickel, sponge nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), steel plate, punched steel plate, silver, titanium, etc. Also, a substrate-like substrate such as a silicon substrate; a metal substrate such as gold, iron, stainless steel, copper, aluminum, and lithium; an alloy substrate containing any combination of these metals; an oxide substrate such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO); and a carbon substrate such as glassy carbon, pyrolytic graphite, and carbon felt can also be used.

[0110] The method for manufacturing the electrode is not particularly limited. For example, it may be manufactured by applying a catalyst to the surface of a substrate. When removing components other than the catalyst, heat drying may be performed, or pressing may be performed after drying. Further, the catalyst layer may be provided on the surface of the substrate by vacuum evaporation or the like. The electrode may have the catalyst layer on only one side of the substrate, or may have it on both sides of the substrate.

[0111] The thickness of the catalyst layer is not particularly limited. For example, it can be set to 0.01 to 300 μm. When the thickness is equal to or greater than the lower limit value, the durability of the electrode is excellent. When the thickness is equal to or less than the upper limit value, the performance of the electrode is less likely to deteriorate.

[0112] The electrode has a function as a catalyst for oxygen generation reaction or oxygen reduction reaction, and has a function as a catalyst for the reduction reaction shown below. (Oxygen generation reaction) 2H2O→O2+4H + +4e - (Oxygen reduction reaction) O2+4H + +4e - →2H2O O2+2H2O+4e - →4OH -

[0113] [Metal-air secondary battery] In one embodiment, the present invention relates to a metal-air secondary battery including the electrode of the present invention. The electrode of the present invention can be used as a positive electrode (air electrode) of a metal-air secondary battery. The metal-air secondary battery can include a positive electrode (air electrode), a negative electrode (metal electrode), an electrolyte, and a separator. In the present invention, the positive electrode (air electrode) is an electrode using gaseous oxygen as an electrode active material.

[0114] The negative electrode (metal electrode) is not particularly limited, and examples thereof include simple metals such as aluminum, magnesium, calcium, lithium, zinc, and iron, and metal oxides thereof.

[0115] The electrolyte is preferably an aqueous electrolyte. Although not particularly limited, examples thereof include alkaline aqueous solutions such as potassium hydroxide aqueous solution and sodium hydroxide aqueous solution, neutral aqueous solutions such as sodium chloride and ammonium chloride, and acidic aqueous solutions such as sulfuric acid aqueous solution. The electrolyte may be used alone or in combination of two or more. Also, an inorganic solid electrolyte can be used.

[0116] The separator is a member that separates the positive electrode (air electrode) and the negative electrode (metal electrode), holds the electrolyte, and ensures ionic conductivity between the positive electrode (air electrode) and the negative electrode (metal electrode). The separator is not particularly limited, but examples thereof include polymers having micropores such as polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, cellulose, cellulose acetate, hydroxyalkyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, cellophane, polystyrene, polyacrylonitrile, polyacrylamide, polyvinyl chloride, polyimide, polyamide, vinylon, poly(meth)acrylic acid, gel compounds, ion exchange membranes, cyclized polymers, poly(meth)acrylate-containing polymers, sulfonate-containing polymers, quaternary ammonium salt-containing polymers, and quaternary phosphonium salt-containing polymers. The separator may be a non-porous membrane or a porous membrane. In the case of a porous membrane, the pore diameter is preferably 10 μm or less.

[0117] [Water electrolysis system] In one embodiment, since the catalyst of the present invention has excellent catalytic activity for the oxygen evolution reaction, it is also useful as an oxygen evolution catalyst for a water electrolysis system.

[0118] Currently practical water electrolysis systems are roughly divided into two types. One is alkaline water electrolysis in which an alkaline aqueous solution is used as the electrolyte, and the other is polymer electrolyte water electrolysis (also called PEM electrolysis) in which a solid polymer membrane is used as the electrolyte. In one embodiment, the electrode of the present invention can be used in an alkaline water electrolysis system or a polymer electrolyte water electrolysis system.

[0119] [Alkaline water electrolysis] An alkaline water electrolysis system can include, for example, an anode, a cathode, and an alkaline electrolysis diaphragm disposed between the anode and the cathode.

[0120] The anode can include a conductive substrate and a catalyst layer covering the surface of the substrate. Preferably, the catalyst of the present invention is included in the catalyst layer of the anode. The conductive substrate is not particularly limited, and examples include nickel, nickel alloy, nickel iron, vanadium, molybdenum, copper, silver, manganese, platinum group elements, graphite, or chromium, or combinations thereof.

[0121] The cathode can be used without particular limitation as a cathode that can be used in an electrolytic cell for alkaline water electrolysis. The cathode can include a conductive substrate and a catalyst layer covering the surface of the substrate. The catalyst layer is not particularly limited, and can include, for example, noble metal oxides, nickel, cobalt, molybdenum, or manganese, or oxides thereof, or noble metal oxides. The conductive substrate is not particularly limited, and examples include nickel, nickel alloy, stainless steel, mild steel, nickel alloy, or nickel-plated stainless steel or mild steel.

[0122] The alkaline electrolysis diaphragm can be used without particular limitation as a diaphragm that can be used in an electrolytic cell for alkaline water electrolysis. The diaphragm is not particularly limited, and examples include porous membranes made of asbestos or modified asbestos, porous diaphragms using polysulfone-based polymers, cloths using polyphenylene sulfide fibers, fluorine-based porous membranes, porous membranes such as those using hybrid materials containing both inorganic and organic materials, and ion exchange membranes such as fluorine-based ion exchange membranes.

[0123] As the alkaline water as an electrolytic solution used for electrolysis of water, those with a pH of 10 or more are preferably used from the viewpoint of electrolysis efficiency. Examples of this alkaline water include potassium hydroxide aqueous solution and sodium hydroxide aqueous solution.

[0124] [Proton Exchange Membrane (PEM) Water Electrolysis] A solid polymer type water electrolysis system can include, for example, two electrodes on both sides of a solid polymer electrolyte membrane.

[0125] In one embodiment, the anode of the solid polymer type water electrolysis system can include a conductive substrate and a catalyst layer covering the surface of the substrate. Preferably, the catalyst of the present invention is included in the catalyst layer of the anode.

[0126] The cathode can include a conductive substrate and a catalyst layer covering the surface of the substrate. The catalyst layer preferably has high hydrogen generation ability, and nickel, cobalt, iron, platinum group elements, etc. can be used. Also, the conductive substrate is not particularly limited, and examples include nickel, nickel alloy, stainless steel, mild steel, nickel alloy, or stainless steel, etc.

[0127] As the electrolytic membrane, water electrolysis can be performed using a solid polymer ion exchange membrane. The electrolyte membrane is not limited as long as the effects of the present invention can be obtained, and examples include fluorine-based sulfonic acid ion exchange membranes.

Examples

[0128] Hereinafter, the present invention will be described more specifically using examples and comparative examples, but the scope of the present invention is not limited to the examples.

[0129] [Preparation of Catalyst] (Example 1) Cellulose nanofibers derived from squid shell (CNF) as biomass-derived cellulose nanofibers and a dried product of blood waste (BM) having an FeN4 structure as a dried product containing protein or amino acid were mixed at a weight ratio of 1:10 and fired at 900 °C in a nitrogen atmosphere to prepare a fired product. The obtained fired product was used as the catalyst of Example 1.

[0130] (Example 2) Cellulose nanofibers derived from biomass, specifically cellulose nanofibers derived from oyster shells, and a dried product of blood waste having an FeN4 structure as a dried product containing protein or amino acids were mixed at a weight ratio of 1:5 and fired at 900 °C in a nitrogen atmosphere to prepare a fired product. The obtained fired product was used as the catalyst in Example 2.

[0131] (Example 3) Cellulose nanofibers derived from biomass, specifically cellulose nanofibers derived from oyster shells, and a dried product of blood waste having an FeN4 structure as a dried product containing protein or amino acids were mixed at a weight ratio of 1:2 and fired at 900 °C in a nitrogen atmosphere to prepare a fired product. The obtained fired product was used as the catalyst in Example 3.

[0132] (Comparative Example 1) Only the cellulose nanofibers derived from oyster shells were fired at 900 °C in a nitrogen atmosphere to prepare a fired product. The obtained fired product was used as the catalyst in Comparative Example 1.

[0133] [Fabrication of Electrodes] (Electrode of Example 1) 2 mg of the catalyst of Example 1 and 1 mg of Milli-Q water were kneaded with an ultrasonic stirrer, applied to a glassy carbon electrode, and further 5 μL of a 0.5 mass% Nafion aqueous solution was applied to the glassy carbon electrode to obtain the electrode of Example 1.

[0134] (Electrode of Example 2) The electrode of Example 2 was obtained in the same manner as the electrode of Example 1, except that the catalyst of Example 2 was used instead of the catalyst of Example 1.

[0135] (Electrode of Example 3) The electrode of Example 3 was obtained in the same manner as the electrode of Example 1, except that the catalyst of Example 3 was used instead of the catalyst of Example 1.

[0136] (Electrode of Comparative Example 1) The electrode of Comparative Example 1 was obtained in the same manner as the electrode of Example 1, except that the catalyst of Comparative Example 1 was used instead of the catalyst of Example 1.

[0137] (Electrode of Comparative Example 2) The electrode of Comparative Example 2 was obtained in the same manner as the electrode of Example 1, except that Pt / C was used instead of the catalyst of Example 1.

[0138] (LSV measurement) The LSV (Linear Sweep Voltammetry) curve was obtained using an oxygen-saturated 0.1 M potassium hydroxide aqueous solution as the electrolyte, under the condition of a sweep rate of 5 mV / s with a rotating ring-disk electrode (manufactured by BAS Inc., RRDE-3A). The rotation speed of the rotating disk was 1600 rpm, a Pt wire was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The LSV measurement by RRDE was performed using an oxygen-saturated 0.1 M potassium hydroxide aqueous solution as the electrolyte with a rotating ring-disk electrode (manufactured by BAS Inc., RRDE-3A) under the condition of a sweep rate of 5 mV / s. The LSV was measured for each case where the rotation speed of the rotating disk was set to 0 rpm, 400 rpm, 800 rpm, 1200 rpm, 1600 rpm, 2000 rpm, and 2400 rpm. Pt was used as the counter electrode and Ag / AgCl was used as the reference electrode.

[0139] (Initial potential) In the LSV curve, the potential at which the generation of current starts (extrapolating the portion where the oxidation / reduction current rapidly increases in the voltammogram and leading to the intersection with the residual current, and the potential at that intersection) is defined as the initial potential. The initial potential of the oxygen evolution reaction is denoted as E on-set / OER and the initial potential of the oxygen reduction reaction is denoted as E on-set / ORR .

[0140] (Half-wave potential) In the LSV curve of the oxygen reduction reaction, the potential corresponding to half of the limiting current value is defined as the half-wave potential in the oxygen reduction reaction. The half-wave potential of the oxygen reduction reaction is denoted as E half(ORR) .

[0141] (Comparison of Oxygen Generation Catalyst Performance) Using the electrodes of Examples 1 to 3 and the electrodes of Comparative Examples 1 and 2, the onset potential E of the oxygen generation reaction on-set / OER was measured. The respective results are shown in Table 1.

[0142]

Table 1

[0143] As shown in Table 1, the electrodes of Examples 1 to 3 using a catalyst containing a fired product of a mixture containing biomass-derived cellulose nanofibers and a dried product containing a protein or an amino acid had a lower onset potential than the electrode of Comparative Example 1 using a catalyst containing only a fired product of cellulose nanofibers, and it was found that they had excellent oxygen generation catalytic ability. Also, the electrodes of Examples 1 and 2 were found to have excellent oxygen reduction catalytic ability compared to the Pt / C electrode, and the electrode of Example 3 was found to have an oxygen reduction catalytic ability comparable to that of the Pt / C electrode.

[0144] (Comparison of Oxygen Reduction Catalyst Performance) Using the electrodes of Examples 1 to 3 and the electrode of Comparative Example 1, the onset potential E of the oxygen reduction reaction on-set / ORR and the half-wave potential E half(ORR) were measured. The respective results are shown in Table 2.

[0145]

Table 2

[0146] As shown in Table 2, the electrodes of Examples 1 to 3 using a catalyst containing a fired product of a mixture containing biomass-derived cellulose nanofibers and a dried product containing a protein or an amino acid had higher onset potential and half-wave potential than the electrode of Comparative Example 1 using a catalyst containing only a fired product of cellulose nanofibers, and it was found that they had excellent oxygen reduction catalytic ability.

[0147] Next, in addition to the dried product containing cellulose nanofibers, proteins, or amino acids derived from biomass, a mixture further containing a cobalt complex was calcined, and an electrochemical performance evaluation was performed on the catalyst containing the obtained calcined product.

[0148] [Preparation of Catalyst] (Example 4) As the cellulose nanofibers derived from biomass, cellulose nanofibers (CNF) derived from squid pen, as the dried product containing proteins or amino acids, the dried product of blood waste (BM) having an FeN4 structure, and as the cobalt complex, vitamin B 12 (VB12) were mixed at a weight ratio of 1:9:1, purified water was added, and a dispersion was prepared. Next, this dispersion was dried little by little on a hot plate maintained at 60 °C, and then calcined at 900 °C in a nitrogen atmosphere to obtain a calcined product. The obtained calcined product was used as the catalyst of Example 4.

[0149] (Example 5) As the cellulose nanofibers derived from biomass, cellulose nanofibers derived from squid pen, as the dried product containing proteins or amino acids, the dried product of blood waste having an FeN4 structure, and as the cobalt complex, vitamin B 12 A calcined product was obtained in the same manner as in Example 4, except that they were mixed at a weight ratio of 1:9:0. The obtained calcined product was used as the catalyst of Example 5.

[0150] [Preparation of Electrode] (Electrode of Example 4) 2 mg of the catalyst of Example 4 and 1 mg of Milli-Q water were kneaded with an ultrasonic stirrer, applied to a glassy carbon electrode, and further 5 μL of a 0.5 mass% Nafion aqueous solution was applied to the glassy carbon electrode to obtain the electrode of Example 4.

[0151] (Electrode of Example 5) The electrode of Example 5 was obtained in the same manner as the electrode of Example 4, except that the catalyst of Example 5 was used instead of the catalyst of Example 4.

[0152] (Electrode of Comparative Example 2) An electrode of Comparative Example 2 was obtained in the same manner as the electrode of Example 4, except that Pt / C was used instead of the catalyst of Example 4.

[0153] (Electrode of Comparative Example 3) An electrode of Comparative Example 3 was obtained in the same manner as the electrode of Example 4, except that GC was used instead of the catalyst of Example 4.

[0154] (LSV measurement by RRDE) The LSV curve was obtained under the following conditions using a rotating ring-disk electrode (RRDE-3A, manufactured by BAS Inc.) with an oxygen-saturated 0.1 M potassium hydroxide aqueous solution as the electrolyte. Rotation speed of the rotating disk: 1600 rpm Voltage range: 0.2 - 2.0 [V vs NHE] The results of the LSV measurement are shown in FIGS. 1 and 2.

[0155] As shown in FIG. 1, the electrode of Example 4 using a catalyst containing a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid, and a cobalt complex was found to have better oxygen evolution catalytic ability compared to the electrode of Example 5 using a catalyst containing a fired product obtained without adding a cobalt complex.

[0156] Also, as shown in FIG. 1, the electrode of Example 4 using a catalyst containing a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid, and a cobalt complex was found to be excellent in both oxygen reduction catalytic performance and oxygen evolution catalytic performance.

[0157] Furthermore, as shown in FIG. 1, the electrode of Example 4 using a catalyst containing a fired product of a mixture containing a biomass-derived cellulose nanofiber, a protein or an amino acid, and a cobalt complex was found to show performance equivalent to or better than that of a Pt / C electrode (Comparative Example 2) in terms of the difference between the oxygen reduction reaction potential and the oxygen evolution reaction potential.

[0158] As shown in Fig. 2, the electrode of Example 4 using a catalyst containing a fired product of a mixture containing biomass-derived cellulose nanofibers, a dried product containing protein or amino acid, and a cobalt complex was found to have better hydrogen generation catalytic ability compared to the electrode of Example 5 using a catalyst containing a fired product obtained without adding a cobalt complex.

[0159] (I-V Characteristic Evaluation) An air-zinc battery was fabricated using the catalyst of Example 4 containing a fired product of a mixture containing biomass-derived cellulose nanofibers, a dried product containing protein or amino acid, and a cobalt complex as the positive electrode catalyst of the air-zinc battery, and I-V characteristic evaluation was performed. The results of the I-V characteristic evaluation are shown in Fig. 3.

[0160] As shown in Fig. 3, in the battery using the catalyst of Example 4 containing a fired product of a mixture containing biomass-derived cellulose nanofibers, a dried product containing protein or amino acid, and a cobalt complex as the positive electrode catalyst, a maximum output density of 189 mW / cm 2 was obtained. Therefore, it was found that by using a catalyst containing a fired product of a mixture containing biomass-derived cellulose nanofibers, a dried product containing protein or amino acid, and a cobalt complex, a high-performance battery with a high output density can be obtained.

[0161] (Example 6) A fired product was obtained in the same manner as in Example 4, except that cellulose nanofibers derived from wakame, a seaweed, as the biomass-derived cellulose nanofibers, a dried product of blood waste having an FeN4 structure as the dried product containing protein or amino acid, and vitamin B 12 as the cobalt complex were mixed at a weight ratio of 1:9:0. The obtained fired product was used as the catalyst of Example 6. As a result, it was found that the onset potential E on-set / OER of the oxygen generation catalyst was 1.40 V vs RHE, and the onset potential E on-set / ORR of the oxygen reduction reaction catalyst was 0.965 V vs RHE, having excellent oxygen generation catalytic ability and oxygen reduction catalytic ability.

Industrial Applicability

[0162] When the catalyst of the present invention is used as a catalyst for promoting the oxygen evolution reaction and the oxygen reduction reaction at the positive electrode of a metal-air secondary battery or a water electrolysis system, it is useful because it has excellent catalytic performance. Further, the catalyst of the present invention can also have excellent catalytic performance when used as a catalyst for promoting the hydrogen generation reaction. Further, since the catalyst of the present invention does not use platinum, iridium, and ruthenium, the manufacturing cost can be suppressed, and a manufacturing process suitable for mass production can be designed. Furthermore, since the catalyst of the present invention uses biomass-derived cellulose nanofibers, it can greatly contribute to the resource recovery and resource circulation of waste.

Claims

1. It includes a fired product of a mixture containing a cellulose nanofiber derived from biomass and a dried product containing a protein or an amino acid, wherein the dried product containing the protein or the amino acid is a dried product of blood waste having an FeN4 structure, a catalyst for use in an electrode for a metal-air secondary battery or an electrode for a water electrolysis system.

2. The catalyst according to claim 1, wherein the cellulose nanofiber is derived from marine biomass.

3. The catalyst according to claim 1, wherein the cellulose nanofiber is derived from sea squirt shells or seaweed.

4. The catalyst according to claim 1, which contains 0.1 to 30% by mass of iron based on the total mass of the catalyst.

5. The catalyst according to claim 1, which contains 0.1 to 40% by mass of phosphorus based on the total mass of the catalyst.

6. The catalyst according to claim 1, wherein the mass ratio of the dried product containing the protein or the amino acid contained in the mixture to the cellulose nanofiber is 1:1 to 20:

1.

7. The catalyst according to claim 1, wherein the mixture further contains a cobalt complex.

8. The cobalt complex is a vitamin B １２ type, and the catalyst according to claim 7.

9. The vitamin B １２ The catalyst according to claim 8, wherein the class is derived from biomass.

10. The vitamin B １２ The catalyst according to claim 8, wherein the class is derived from laver and / or oysters.

11. The catalyst according to claim 7, which contains 0.1 to 30% by mass of cobalt based on the total mass of the catalyst.

12. The catalyst according to claim 7, wherein the mass ratio of the cellulose nanofiber, the dried product containing the protein or the amino acid, and the cobalt complex contained in the mixture is 1:1 to 20:0.1 to 10.

13. The catalyst according to claim 1, which is for oxygen generation, oxygen reduction, or hydrogen generation.

14. A method for producing a catalyst including a fired product of a mixture containing a cellulose nanofiber derived from biomass and a dried product containing a protein or an amino acid, the method including the steps of preparing a mixture containing the dried product containing the protein or the amino acid and the cellulose nanofiber, and firing the mixture, wherein the catalyst is a catalyst for use in an electrode for a metal-air secondary battery or an electrode for a water electrolysis system, and the dried product containing the protein or the amino acid is a dried product of blood waste having an FeN4 structure. Production method.

15. The production method according to claim 14, wherein the mixture further contains a cobalt complex.

16. The production method according to claim 14, including the step of extracting the cellulose nanofiber from biomass.

17. The manufacturing method according to claim 14, comprising the step of obtaining the dried product by concentrating and drying the blood waste.

18. The manufacturing method according to claim 14, wherein the cellulose nanofiber is derived from marine biomass.

19. The manufacturing method according to claim 14, wherein the cellulose nanofiber is derived from sea squirt shells or seaweed.

20. The cobalt complex is a vitamin B １２ class, and the production method according to claim 15.

21. The vitamin B １２ class is derived from biomass, the production method according to claim 20.

22. The vitamin B １２ class is derived from laver and / or oysters, and the production method according to claim 20.

23. An electrode for a metal-air secondary battery or a water electrolysis system, comprising the catalyst according to any one of claims 1 to 13.

24. A metal-air secondary battery or a water electrolysis system, comprising the electrode according to claim 23.

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