Block copolymer, supported metal catalyst, battery electrode, and battery

Abstract

Provided is a block copolymer comprising a polymer block (A) that exhibits interaction with carbon or silica and a polymer block (B) that has a protic cation structure.

Description

Block copolymers, metal-supported catalysts, battery electrodes, and batteries

[0001] The present invention relates to a block copolymer that can be well immobilized on carbon or silica and exhibits excellent proton conductivity.

[0002] In recent years, fuel cells, which can operate at room temperature and achieve high power density, have attracted attention as power sources for electric vehicles and stationary power sources, in response to social demands and trends stemming from energy and environmental issues. Because fuel cells produce water as a byproduct of electrode reactions, they are a clean power generation system with virtually no adverse impact on the global environment. In particular, polymer electrolyte fuel cells (PEFCs) are expected to be used as power sources for electric vehicles because they operate at relatively low temperatures.

[0003] The structure of a polymer electrolyte fuel cell generally consists of an electrolyte membrane-electrode assembly (MEA) sandwiched between separators. The electrolyte membrane-electrode assembly comprises a polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers and a gas-diffusible electrode (gas diffusion layer; GDL).

[0004] In polymer electrolyte fuel cells, improving the activity of the electrode catalyst in the electrode catalyst layer has been studied from the viewpoint of power generation performance. For example, Patent Document 1 describes an electrode catalyst that contains platinum and metal components other than platinum, has mesopores with a radius of 1 nm or more, has a mode radius of the vacancy distribution of the mesopores of 1 nm or more and less than 2.5 nm, has alloy fine particles of platinum and metal components other than platinum supported in the mesopores, and has a molar ratio of platinum to metal components other than platinum in the alloy fine particles supported in the mesopores of 1.0 to 10.0. While catalysts with metal particles such as alloy fine particles supported in mesopores suppress deactivation due to contact with the electrolyte, they have the problem that the catalyst utilization rate is greatly reduced because they cannot sufficiently form a proton path under low humidity conditions.

[0005] In response to this challenge, it has recently been proposed to incorporate ionic liquids as electrolytes into catalysts. Ionic liquids not only improve the oxygen reduction activity of catalysts, but they can also be filled into mesopores where conventional electrolytes such as ionsomers cannot penetrate. Therefore, they are attracting attention as materials that improve the low-humidification performance of metal-supported catalysts with mesopores. Non-patent document 1 describes [MTBD][C] as an ionic liquid. ４ F ９ SO ３ It has been reported that adding [ ] to a metal-supported catalyst improves MEA performance. On the other hand, in the technology described in Non-Patent Literature 1, it has been confirmed that the ionic liquid elutes after the accelerated degradation test, which poses a challenge to practical application.

[0006] International Publication No. 2017 / 183475

[0007] Journal of The Electrochemical Society, 2022 169 044516

[0008] The object of the present invention is to provide a block copolymer that can be well immobilized on carbon or silica and exhibits excellent proton conductivity. The present invention also aims to provide a metal-supported catalyst, a battery electrode, and a battery obtained using such a block copolymer.

[0009] As a result of diligent research to achieve the above objective, the present inventors have found that the above objective can be achieved by a block copolymer comprising a polymer block that interacts with carbon or silica and a polymer block having a protic cationic structure, and have completed the present invention.

[0010] In other words, according to the present invention, [1] a block copolymer comprising a polymer block (A) that interacts with carbon or silica and a polymer block (B) having a protic cationic structure, [2] the block copolymer according to [1] represented by the following general formula (1), (In the above general formula (1), R １ , R ２is, independently of each other, a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, A is an organic group that shows an interaction with carbon or silica, X － is an anionic organic group, Z ＋ is a protic organic cation, m is 1 to 1000, and n is 1 to 1000. ) [3] The block copolymer according to [1] represented by the following general formula (2), (In the above general formula (2), R １ , R ２ is, independently of each other, a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, A is an organic group that shows an interaction with carbon or silica, Z' ＋ is a protic cationic organic group, X' － is an organic anion, p is 1 to 1000, and q is 1 to 1000. ) [4] The block copolymer according to any one of [1] to [3] above, wherein the polymer block (B) having the protic cation structure is a polymer block polymerized using an ionic liquid as a monomer. [5] A metal-supported catalyst comprising a carrier and catalyst metal particles supported on the carrier, wherein the block copolymer according to any one of [1] to [4] above is fixed. [6] A metal-supported catalyst comprising a carbon carrier having pores and catalyst metal particles supported on the carbon carrier, wherein the block copolymer according to any one of [1] to [4] above is fixed. [7] A battery electrode containing the metal-supported catalyst according to [5] or [6] above. [8] A battery containing the battery electrode according to [7] above is provided.

[0011] According to the present invention, a block copolymer that can be well fixed to carbon or silica and exhibits excellent proton conductivity can be provided. Further, according to the present invention, a metal-supported catalyst, a battery electrode, and a battery obtained by using such a block copolymer can also be provided.

[0012] <Block Copolymer> The block copolymer of the present invention is a block copolymer comprising a polymer block (A) that interacts with carbon or silica and a polymer block (B) having a protic cationic structure. The polymer block (A) that interacts with carbon or silica can be any structure that can interact with carbon or silica, and is not particularly limited. It can be any structure that can form a covalent bond with the carbon or silica surface, or a structure that can form intermolecular forces weaker than covalent bonds (for example, ion-dipole interactions, dipole-dipole interactions, hydrogen bonds, van der Waals forces, etc.).

[0013] The block copolymer of the present invention comprises a polymer block (A) that interacts with carbon or silica (hereinafter also simply referred to as "polymer block (A)") and a polymer block (B) having a protic cationic structure (hereinafter also simply referred to as "polymer block (B)"). Its composition is not particularly limited, and it may be a diblock body consisting of polymer block (A) - polymer block (B), a triblock body consisting of polymer block (A) - polymer block (B) - polymer block (A), a triblock body consisting of polymer block (B) - polymer block (A) - polymer block (B), or a tetrablock body consisting of polymer block (A) - polymer block (B) - polymer block (A) - polymer block (B). However, from the viewpoint of fixation to carbon or silica and proton conductivity, a diblock body consisting of polymer block (A) - polymer block (B) is preferred.

[0014] Furthermore, the block copolymer of the present invention may contain polymer blocks other than polymer block (A) and polymer block (B), but it is preferable that it does not contain other polymer blocks.

[0015] As the block copolymer of the present invention, one represented by the following general formula (1) is preferred. (In the above general formula (1), R１ , R ２ Each is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, A is an organic group that interacts with carbon or silica, X － Z is an anionic organic group. ＋ (where m is a protic organic cation, and n is 1 to 1000.)

[0016] In the above general formula (1), R １ , R ２ This is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom or a methyl group, and more preferably a methyl group.

[0017] In the above general formula (1), A is an organic group that interacts with carbon or silica, and it is preferable that A is an organic group that interacts with carbon. The organic group that interacts with carbon or silica is not particularly limited, but examples include hydrocarbon groups having aromatic groups, silicon-containing groups, and alkyl groups containing fluorine atoms. When m is 2 or more, A in the above general formula (1) may all be the same group, or it may be a configuration that includes two or more types of groups.

[0018] Examples of hydrocarbon groups having aromatic groups include optionally substituted phenyl groups, optionally substituted benzyl groups, optionally substituted naphthyl groups, and optionally substituted biphenyl groups. Examples of substituents include alkyl groups having 1 to 6 carbon atoms, nitro groups, halogeno groups, or cyano groups.

[0019] Examples of silicon-containing groups include the group represented by the following general formula (3): -Si(R ３ ) ｒ (OR ４ ) ３－ｒ (3) In the above general formula (3), R ３ , R ４ Each of these is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a methyl group or an ethyl group. Also, r is 0 to 2, preferably 0.

[0020] The fluorine atom-containing alkyl group can be any alkyl group in which some of the hydrogen atoms are substituted with fluorine atoms, and a fluorine atom-containing alkyl group having 1 to 6 carbon atoms is preferred, and a fluorine atom-containing alkyl group having 2 to 5 carbon atoms is more preferred. Furthermore, the fluorine atom-containing alkyl group is preferably a perfluoroalkyl group, and more specifically, a group represented by the following general formula (4) is preferred. -(CF ２ ) ｓ CF ３ (4) In the above general formula (4), s is 0 to 5, preferably 1 to 4, and particularly preferably 2. That is, it is particularly preferably a heptafluoropropyl group.

[0021] In the above general formula (1), X － Z is an anionic organic group. ＋ X is a protic organic cation. － Z ＋ X is a group that constitutes a polymer block (B) having a protic cationic structure, － Z ＋ Preferably, the residue is derived from a monomer that is an ionic liquid. That is, in the present invention, the polymer block (B) having a protic cation structure is preferably a polymer block polymerized using an ionic liquid (a polymer block containing structural units derived from an ionic liquid) as the monomer. Examples of ionic liquids include organic salts that are liquid at temperatures below 100°C, and preferably organic salts that are liquid at temperatures below 50°C. When n is 2 or more, X in the above general formula (1) － For example, all of them may be the same group, or they may be in a configuration that includes two or more types of groups, Z ＋ These may all be the same cation, or they may be configured to include two or more types of cations.

[0022] As anions constituting the ionic liquid used as monomers to constitute the polymer block (B), those capable of forming a bonding structure as represented by the above general formula (1) can be used, and as such anions constituting the ionic liquid, the anions represented by the following general formulas (5a) and (5b) are preferred.

[0023] In the above general formulas (5a) and (5b), R ２ The same as in the above general formula (1), where t is 1 to 5, u is 0 to 3, and v is 0 to 2. Among these, the anion represented by the above general formula (5a) is preferred, and in the above general formula (5a), R ２ An anion in which is a methyl group, t is 3, u is 0, and v is 0, or R ２ A preferred anion is one in which R is a methyl group, t is 3, u is 1, and v is 1. ２ An anion in which is a methyl group, t is 3, u is 0, and v is 0 (i.e., an anion represented by the following formula (6)) is more preferred.

[0024] Furthermore, the protic cations that constitute the ionic liquid as monomers used to construct the polymer block (B) are not particularly limited, but cations represented by the following formulas (7a) and (7b) are preferred, and among these, the cation represented by the following formula (7a) is more preferred.

[0025] In the above general formula (1), m is 1 to 1000, preferably 1 to 100, more preferably 5 to 60, even more preferably 5 to 25, and particularly preferably 5 to 20, and n is 1 to 1000, preferably 1 to 110, more preferably 1 to 100, even more preferably 5 to 60, even more preferably 5 to 25, and particularly preferably 5 to 20. Also, the ratio of m:n is preferably 1:100 to 100:1, more preferably 1:50 to 50:1, even more preferably 1:20 to 20:1, even more preferably 1:3 to 3:1, and particularly preferably 1:1.2 to 1.2:1. m and n can be determined, for example, from nuclear magnetic resonance (NMR).

[0026] Alternatively, the block copolymer of the present invention may also be one represented by the following general formula (2). (In the above general formula (2), R １ , R ２ Each of these is independently a hydrogen atom or a C1-C4 alkyl group, A is an organic group that interacts with carbon or silica, and Z' ＋ X' is a protic cationic organic group. － (This refers to an organic anion, where p is between 1 and 1000, and q is between 1 and 1000.)

[0027] In the above general formula (2), R １ , R ２ This is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom or a methyl group, and more preferably a methyl group.

[0028] In the above general formula (2), A is an organic group that interacts with carbon or silica, and it is preferable that A is an organic group that interacts with carbon. Specific examples of organic groups that interact with carbon or silica are not particularly limited, but include those exemplified as A in the above general formula (1). When p is 2 or more, A in the above general formula (1) may all be the same group, or it may include two or more different groups.

[0029] In the above general formula (2), Z' ＋ X' is a protic cationic organic group. － Z' is an organic anion. ＋ , X' － Z' is a group that constitutes a polymer block (B) having a protic cationic structure. ＋ , X' －Preferably, the residue is derived from a monomer that is an ionic liquid. That is, the polymer block (B) having a protic cation structure is preferably a polymer block polymerized using an ionic liquid as the monomer (a polymer block containing structural units derived from an ionic liquid). Examples of ionic liquids include organic salts that are liquid at temperatures below 100°C, and preferably organic salts that are liquid at temperatures below 50°C. When q is 2 or more, Z' in the general formula (2) above. ＋ For example, all of them may be the same group, or they may be in a configuration that includes two or more types of groups, X' － These may all be the same anion, or they may be in a configuration that includes two or more types of anions.

[0030] As cations constituting the ionic liquid used as monomers to constitute the polymer block (B), those capable of forming a bond structure as represented by the above general formula (2) can be used, and as such cations constituting the ionic liquid, protic cations represented by the following general formulas (8a), (8b), and (8c) are preferred.

[0031] In the above general formulas (8a), (8b), and (8c), R ２ The same as in the above general formula (1), where w is 1 to 5. Among these, a protic cation represented by the above general formula (8a) is preferred, and in the above general formula (8a), R ２ An anion in which is a methyl group and w is 2 (i.e., an anion represented by the following formula (9)) is preferred.

[0032] Furthermore, the anions that constitute the ionic liquid used as monomers to form the polymer block (B) are not particularly limited, but anions represented by the following formulas (10a) and (10b) are preferred.

[0033] In the above general formulas (10a) and (10b), x is between 0 and 5, and y is between 0 and 5. Among these, the anion represented by the above general formula (10a) is preferred, and in the above general formula (10a), the anion where x is 0 and y is 0, the anion where x is 1 and y is 1, and the anion where x is 0 and y is 0 (i.e., the anion represented by the following formula (11)) is more preferred.

[0034] In the above general formula (2), p is 1 to 1000, preferably 1 to 100, more preferably 5 to 60, even more preferably 5 to 25, and particularly preferably 5 to 20, and q is 1 to 1000, preferably 1 to 110, more preferably 1 to 100, even more preferably 5 to 60, even more preferably 5 to 25, and particularly preferably 5 to 20. Also, the ratio of p:q is preferably 1:100 to 100:1, more preferably 1:50 to 50:1, even more preferably 1:20 to 20:1, even more preferably 1:3 to 3:1, and particularly preferably 1:1.2 to 1.2:1. p and q can be determined, for example, by nuclear magnetic resonance (NMR).

[0035] The overall weight-average molecular weight (Mw) of the block copolymer of the present invention is not particularly limited, but is preferably 200 to 200,000, more preferably 200 to 30,000, and even more preferably 3,000 to 30,000, from the viewpoint of further enhancing the fixation performance to carbon or silica and the proton conductivity. Furthermore, the molecular weight (weight-average molecular weight (Mw)) of the polymer block (A) portion of the block copolymer of the present invention is not particularly limited, but is preferably 100 to 100,000, more preferably 100 to 10,000, and the molecular weight (weight-average molecular weight (Mw)) of the polymer block (B) portion of the block copolymer of the present invention is not particularly limited, but is preferably 100 to 100,000, more preferably 100 to 10,000. The molecular weight distribution (Mw / Mn) of the block copolymer of the present invention is not particularly limited, but is preferably 1 to 2.0, more preferably 1 to 1.5. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) can be measured using gel permeation chromatography (GPC) and expressed in terms of polyethylene glycol.

[0036] The method for synthesizing the block copolymer of the present invention is not particularly limited, but for example, in the case of a diblock body consisting of polymer block (A) - polymer block (B), one method is to obtain polymer block (B) by polymerizing the monomer for forming polymer block (B), and then polymerize the monomer for forming polymer block (A) in the presence of polymer block (B). Alternatively, one can adopt a method in which polymer block (A) is obtained by polymerizing the monomer for forming polymer block (A), and then polymerize the monomer for forming polymer block (B) in the presence of polymer block (A). Furthermore, in the case of a triblock or tetrablock body, depending on the type of block copolymer to be obtained, the monomer for forming polymer block (A) or the monomer for forming polymer block (B) may be further polymerized.

[0037] The polymerization method is not particularly limited, but one example is a method in which radical polymerization is carried out in a solvent in the presence of a RAFT agent by a reversible addition-cleavage chain transfer type radical polymerization (RAFT polymerization). The polymerization initiator is not particularly limited, but examples include 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), and 2,2'-azobis[(2-carboxyethyl)-2-(methylpropionamidine) (V-057). Examples of RAFT agents, though not particularly limited, include 1-phenylethyl dithiobenzoate, 2-phenylpropane-2-yl dithiobenzoate, 2-(ethoxycarbonyl)propane-2-yl dithiobenzoate, 4-cyanopentanoic acid dithiobenzoate, 1-phenylethyl dithioacetate, 2-phenylpropane-2-yl dithioacetate, 2-(ethoxycarbonyl)propane-2-yl dithioacetate, 4-cyanopentanoic acid dithioacetate, 1-phenylethyl N,N-diethylaminodithioformate, 2-phenylpropane-2-yl N,N-diethylaminodithioformate, 2-(ethoxycarbonyl)propane-2-yl N,N-diethylaminodithioformate, and 4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid.

[0038] The solvent used for polymerization is not particularly limited and can be any solvent that does not inhibit the polymerization reaction, but examples include acetonitrile, hexane, cyclohexane, benzene, toluene, 1,4-dioxane, tetrahydrofuran (THF), and dimethylformaldehyde (DMF).

[0039] <Metal-supported catalyst> The metal-supported catalyst of the present invention is a metal-supported catalyst comprising a carrier and catalyst metal particles supported on the carrier, wherein the block copolymer described above is immobilized.

[0040] Carbon or silica can be used as the support material, with carbon support materials being preferred. The support preferably contains pores, and more preferably contains pores with high interconnectivity. That is, the support is preferably a carbon material having pores, and more preferably a carbon material having many interconnected pores. Furthermore, when a carbon material having pores is used as the support, it is preferable that at least a portion of the block copolymer is fixed in the pores of the carbon material.

[0041] The particle size of the carrier is not particularly limited, but for example, the median diameter of the carrier is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, and particularly preferably 0.5 μm or less. The lower limit of the median diameter of the carrier is not particularly limited, but is preferably 0.05 μm or more. The particle size of the carrier can be measured by laser diffraction.

[0042] The specific surface area of ​​the carrier is not particularly limited, but is preferably 400 m². ２ / g or more, more preferably 700m ２ / g or more, more preferably 1000m ２ / g or more, particularly preferably 1300m ２ / g or more, preferably 3000m ２ / g or less, more preferably 2500m ２ / g or less, more preferably 2000m ２ / g or less, particularly preferably 1800m ２ It is less than / g. The BET specific surface area can be determined by the BET method from the nitrogen adsorption isotherm at a temperature of 77K.

[0043] The carrier preferably has pores, and its average pore diameter is preferably 1 to 5 nm, more preferably 1.2 to 4 nm, even more preferably 1.4 to 3.5 nm, even more preferably 1.6 to 3 nm, and particularly preferably 1.8 to 2.5 nm. The average pore diameter can be determined from the nitrogen adsorption isotherm at a temperature of 77 K by the BJH method.

[0044] The catalytic metal particles can be any metal particles exhibiting catalytic activity and are not particularly limited, but for example, they are preferably metal particles exhibiting reducing activity and / or oxidizing activity, more preferably metal particles exhibiting oxygen reducing activity and / or hydrogen oxidizing activity, and particularly preferably metal particles exhibiting at least oxygen reducing activity.

[0045] Specifically, the catalyst metal particles are preferably metal particles containing precious metals (hereinafter referred to as "precious metal particles"). The precious metal particles include pure precious metals (precious metals that do not form alloys) and / or precious metal alloys.

[0046] The precious metal constituting the precious metal particles is preferably one or more selected from the group consisting of Ru, Pd, Rh, Ag, Os, Ir, Pt, and Au, more preferably one or more selected from the group consisting of Ru, Pd, Rh, Ir, and Pt, and particularly preferably Pt. In other words, the precious metal particles are particularly preferably Pt particles. The Pt particles include pure Pt and / or Pt alloys.

[0047] A noble metal alloy is an alloy of one or more noble metals and one or more non-noble metals. The non-noble metal is any metal other than a noble metal that forms an alloy with a noble metal, and is not particularly limited, but it is preferably a transition metal. The non-noble metal included in the noble metal alloy is preferably one or more selected from the group consisting of Cu, Mn, Ce, Nb, Ti, Fe, Co, and Ni, more preferably one or more selected from the group consisting of Fe, Co, and Ni, and particularly preferably one or more selected from the group consisting of Co and Ni.

[0048] The crystallite size of the catalyst metal particles is preferably 1.5 to 5 nm, more preferably 1.9 to 4 nm, even more preferably 2.1 to 3.8 nm, even more preferably 2.1 to 3.5 nm, and particularly preferably 2.1 to 3.4 nm. The crystallite size of the catalyst metal particles can be measured by X-ray diffraction.

[0049] The method for supporting catalyst metal particles on a support is not particularly limited as long as it is a known method, and liquid-phase reduction or gas-phase reduction can be used, with gas-phase reduction being preferred. In gas-phase reduction, catalyst metal particles can be formed on the support by subjecting a support on which a metal compound, which is a precursor of catalyst metal particles, is supported to a gas-phase reduction treatment.

[0050] As a metal particle precursor, any material that forms a catalytic metal constituting the catalytic metal particles upon reduction is acceptable. For example, when supporting Pt particles as catalytic metal particles on a support, the precursor Pt compound can be a platinumate (for example, chloroplatinic acid (H)). ２ PtCl ６ ) and dinitrodiammineplatinate (Pt(NH ３ ) ２ (NO ２ ) ２ Preferably, one or more selected from the group consisting of ) and one or more selected from the group consisting of bis(acetylacetonato)platinum are used.

[0051] In the gas-phase reduction treatment, the support on which the precursor compound is attached is heated in a reducing atmosphere. The reducing atmosphere in the gas-phase reduction treatment is an atmosphere containing a reducing gas. The reducing gas is not particularly limited, but one or more selected from the group consisting of hydrogen gas, ammonia gas, and hydrocarbon gases (for example, one or more hydrocarbon gases selected from the group consisting of methane gas, propane gas, and butane gas) is preferably used.

[0052] In the gas-phase reduction treatment, the temperature at which the support bearing the precursor compound is heated is not particularly limited, but is preferably 250 to 1200°C, more preferably 300 to 1100°C, and even more preferably 700 to 1000°C. In the gas-phase reduction treatment, the time at which the support bearing the precursor compound is heated is not particularly limited, but is preferably 1 to 180 minutes, more preferably 5 to 60 minutes, and even more preferably 10 to 40 minutes.

[0053] Alternatively, after supporting catalyst metal particles on a carrier, the carrier may be heated in an inert atmosphere. The inert atmosphere is mainly composed of an inert gas, and while the inert gas is not particularly limited, it is preferably one or more selected from the group consisting of nitrogen gas, argon gas, and helium gas.

[0054] Then, the block copolymer of the present invention described above is immobilized on the carrier on which the catalyst metal particles obtained as described above are supported. Specifically, the block copolymer of the present invention described above is dissolved in a solvent to form a solution, the carrier on which the catalyst metal particles are supported is added to this solution, mixed, and then dried to obtain a metal-supported catalyst in which the block copolymer is immobilized on the carrier on which the catalyst metal particles are supported.

[0055] <Battery Electrode> The battery electrode of the present invention contains the metal-supported catalyst of the present invention as described above. The battery electrode of the present invention can be used, for example, as an electrode for a fuel cell (e.g., polymer electrolyte fuel cell), an air battery, a water electrolytic cell (e.g., polymer electrolyte water electrolytic cell), a redox flow battery, or a halogen battery.

[0056] Furthermore, the battery electrode of the present invention may be a cathode or an anode, but it is preferably a cathode. That is, the battery electrode of the present invention can be used as a cathode or anode of a fuel cell, air battery, water electrolytic cell, redox flow battery, or halogen battery, and is preferably a fuel cell cathode, air battery cathode, water electrolytic cell cathode, redox flow battery cathode, or halogen battery cathode, more preferably a fuel cell cathode or air battery cathode, and particularly preferably a fuel cell cathode.

[0057] <Battery> The battery of the present invention includes the battery electrode of the present invention as described above. Examples of the battery of the present invention include fuel cells (e.g., polymer electrolyte fuel cells), air batteries, redox flow batteries, or halogen batteries. The battery of the present invention may also have a membrane / electrode assembly (MEA) including the battery electrode of the present invention.

[0058] The battery of the present invention is a battery having the battery electrode of the present invention described above as the cathode or anode, preferably a battery having the battery electrode of the present invention as the cathode. That is, the battery of the present invention is a fuel cell, air battery, redox flow battery, or halogen battery having the battery electrode of the present invention as the cathode or anode, preferably a fuel cell, air battery, redox flow battery, or halogen battery having the battery electrode of the present invention as the cathode, more preferably a fuel cell or air battery having the battery electrode of the present invention as the cathode, and particularly preferably a fuel cell having the battery electrode of the present invention as the cathode.

[0059] The block copolymer of the present invention comprises a polymer block (A) that interacts with carbon or silica and a polymer block (B) having a protic cationic structure. Therefore, it can be well immobilized on carbon or silica and exhibits excellent proton conductivity, and as described above, it can be suitably used in a state immobilized on a metal-supported catalyst. Furthermore, the metal-supported catalyst obtained in this manner can be made to have excellent various electrical properties required for metal-supported catalysts, such as mass activity and specific activity, due to the excellent proton conductivity of the block copolymer of the present invention. In addition, because the block copolymer of the present invention exhibits excellent proton conductivity, it can be expected to improve low-humidity performance, and furthermore, because it can be well immobilized on carbon or silica, it does not cause elution problems like those that occur when using ionic liquids.

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In each example, "parts" refers to weight unless otherwise specified.

[0061] <Manufacturing Example 1> (Manufacturing of Carbon Carrier) 1.0 g of polyacrylonitrile (PAN), 1.0 g of 2-methylimidazole, and 6.0 g of zinc chloride (ZnCl ２) and 30 g of dimethylformamide were mixed. The solvent was removed from the resulting mixture by drying. The dried mixture was heated in an air atmosphere and infusible at 250°C.

[0062] The mixture, after being rendered infusible, was carbonized by heating it at 1500°C under a nitrogen atmosphere and a gauge pressure of 0.90 MPa. Dilute hydrochloric acid was added to the carbonized material obtained by carbonization and the mixture was stirred. Subsequently, the suspension containing the carbonized material was filtered using a filtration membrane, and the carbonized material was washed with distilled water until the filtrate became neutral. Thus, metal removal treatment was performed by acid washing.

[0063] The carbonized material, after metal removal treatment, was pulverized using a fine grinder until its median particle size was 0.4 μm or less. The pulverized carbonized material was then vacuum-dried to remove moisture. Subsequently, the carbonized material was heat-treated at 300°C in a nitrogen atmosphere to produce a carbon carrier with pores. The average pore size of the obtained carbon carrier (determined by the BJH method from the nitrogen adsorption isotherm at 77 K) was 1.9 nm, and the BET specific surface area (determined by the BET method from the nitrogen adsorption isotherm at 77 K) was 1620 m². ２ It was / g.

[0064] (Production of carbon carriers supporting catalyst metal particles) The porous carbon carrier obtained above and the platinum precursor chloroplatinic acid (H ２ PtCl ６ The mixture was mixed with an aqueous solution containing ) for 18 hours. The resulting mixture was then dried in air at 100°C and further maintained in nitrogen at 150°C to volatilize the solvent components.

[0065] The obtained solid was first subjected to a heat treatment at 825°C for 20 minutes in a hydrogen atmosphere (100% hydrogen gas by volume). Subsequently, while maintaining the atmosphere temperature within the range of 820°C to 830°C, the hydrogen atmosphere was replaced with a nitrogen atmosphere (100% nitrogen gas by volume), and the solid was subjected to a heat treatment at 825°C for 40 minutes in the nitrogen atmosphere. In this way, a carbon support on which catalyst metal particles were supported was obtained, and this was used as a metal-supported catalyst. The amount of platinum supported in the obtained metal-supported catalyst (the ratio of the weight of platinum contained in the metal-supported catalyst to the weight of the metal-supported catalyst) was 50% by weight.

[0066] <Example 1> (Synthesis of block copolymer) 90 parts of acetonitrile as a solvent and 10 parts of the ionic liquid monomer shown in formula (12) below were charged into a reactor. Then, 0.01 parts of 2,2'-azobis(isobutyronitrile) (AIBN) as a polymerization initiator and 0.006 parts of 4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid as a RAFT agent were added, and the polymerization reaction was started at a temperature of 60°C. After the polymerization reaction was carried out for 24 hours, 5 parts of the monomer shown in formula (13) below were added, and the polymerization reaction was continued for 24 hours to obtain a block copolymer in the form of an acetonitrile solution. The solvent was then removed using an evaporator to obtain a block copolymer (shown in formula (14) below) having a polymer block (A) formed by the monomer shown in formula (13) and a polymer block (B) formed by the ionic liquid monomer shown in formula (12).

[0067] The resulting block copolymer was treated with 0.1 M LiNO ３The polymer was dissolved in dimethylformaldehyde (DMF) containing the compound, and GPC measurements were performed to determine the number-average molecular weight (Mn) and weight-average molecular weight (Mw) in terms of polyethylene glycol. The results were Mn = 2990 and Mw = 3710. The obtained block copolymer had 10 repeating units for polymer block (A) formed by the monomer shown in formula (13) (m = 10 in formula (14)), and 10 repeating units for polymer block (B) formed by the ionic liquid monomer shown in formula (12) (n = 10 in formula (14)). The number of repeating units for each polymer block was calculated by determining the molecular weight of polymer block (B) formed by the ionic liquid monomer shown in formula (12) using the same GPC measurement as above, and then calculating the number of repeating units for the entire block copolymer from this result.

[0068] (Preparation of Block Copolymer Immobilized Metal-Supported Catalyst) The block copolymer obtained above was dissolved in a solvent (isopropyl alcohol (IPA):water = 6:4) to obtain a solution with a solid content of 10% by weight. Next, the metal-supported catalyst obtained in Production Example 1 was added to the obtained block copolymer solution in an amount 10 times the weight of the block copolymer, and the mixture was stirred with a magnetic stirrer for 15 hours. Then, the solvent was removed with an evaporator, and the mixture was dried in a vacuum dryer at 60°C for 15 hours to obtain a metal-supported catalyst in which the block copolymer was immobilized in the pores (block copolymer immobilized metal-supported catalyst).

[0069] (Electrochemical properties) The catalytic activity of the block copolymer immobilized metal-supported catalyst obtained above was evaluated using a rotating ring disk electrode device (RRDE-3A rotating ring disk electrode device ver. 1.2, manufactured by BAS Corporation) and a dual electrochemical analyzer (CHI700C, manufactured by ALS Corporation).

[0070] Specifically, a triode rotating ring disk electrode device was first fabricated, having a working electrode containing the block copolymer immobilized metal-supported catalyst obtained above. Specifically, a slurry was prepared by mixing 5.5 mg of block copolymer immobilized metal-supported catalyst (equivalent to 5 mg of carbon carrier (metal-supported catalyst) on which the catalyst metal particles were supported), 50 μL of 5% by weight of Nafion® (manufactured by Sigma-Aldrich, Nafion perfluorinated ion exchange resin, 5% solution (product number: 510211)), 400 μL of water, and 100 μL of isopropyl alcohol. Next, this slurry was subjected to sonication for 10 minutes, followed by homogenization for 2 minutes. The resulting slurry was then coated with a block copolymer immobilized metal-supported catalyst at a rate of 0.1 mg / cm². ２ To achieve this, the block copolymer immobilized metal-supported catalyst according to Example 1 was applied to a working electrode (RRDE-3A ring disk electrode platinum ring - gold disk electrode disk diameter 4 mm, manufactured by BAS Corporation) and dried, thereby producing a working electrode on which the block copolymer immobilized metal-supported catalyst according to Example 1 was supported.

[0071] Furthermore, a platinum electrode (Pt counter electrode 23 cm, manufactured by BAS Corporation) was used as the counter electrode, and a reversible hydrogen electrode (RHE) (accumulation-type reversible hydrogen electrode, manufactured by EC Frontier Corporation) was used as the reference electrode. In this way, a rotating ring disk electrode device was obtained having a working electrode containing a block copolymer immobilized metal-supported catalyst according to Example 1, a platinum electrode as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. In addition, a 0.1 M perchloric acid aqueous solution was used as the electrolyte.

[0072] Then, the electrochemical properties were evaluated using the above-described rotating ring disk electrode device. First, cyclic voltammetry (N) was performed in a nitrogen atmosphere using a three-electrode rotating ring disk electrode device having a working electrode containing a block copolymer immobilized metal-supported catalyst. ２ The effective electrochemical surface area (ECSA) was determined by -CV.

[0073] N ２- In CV, first, nitrogen bubbling was performed for 10 minutes to remove oxygen in the electrolyte. Then, the current density when performing potential sweep at a sweep rate of 50 mV / sec was recorded as a function of potential (N ２ - CV).

[0074] From the cyclic voltammogram thus obtained, ECSA (m ２ / g Ｐｔ ) was obtained. Specifically, in the cyclic voltammogram of the third cycle, the hydrogen adsorption charge amount (Q Ｈｕｐｄ ) (mC / cm ２ ) from 0.0 V (vs. NHE) to 0.4 V (vs. NHE) during the negative scan was used, together with the charge amount in terms of area (210 μC / cm ２ ) and the platinum coating amount (L Ｐｔ ) (mg-Pt / cm ２ ) to calculate ECSA (m ２ / g) using the following formula. The results are shown in Table 1. The measurement results of ECSA were obtained with an index taking the value of Comparative Example 1 described later as "1.00" (the same applies to Examples 2 to 6 described later). ECSA = Q Ｈｕｐｄ / (210 × L Ｐｔ ) × 10 ２

[0075] Next, the catalytic activity was determined by linear sweep voltammogram (LSV). Specifically, first, LSV in a nitrogen atmosphere was measured. That is, after holding at 1.00 V (vs. NHE) for 10 minutes, the current value when performing potential sweep in the potential range from 1.00 V (vs. NHE) to 0.00 V (vs. NHE) at a sweep rate of 20 mV / sec was recorded as a function of potential (N ２ - LSV). Then, oxygen gas was bubbled at 0.35 L / min for 15 minutes to saturate oxygen in the electrolyte, and then held at 1.00 V (vs. NHE) for 10 minutes, and the current value when performing potential sweep in the negative direction in the potential range from 1.00 V (vs. NHE) to 0.00 V (vs. NHE) at a sweep rate of 20 mV / sec was recorded as a function of potential (O ２ - LSV). The current value obtained by O ２ - LSV includes the current due to the oxygen reduction reaction and the charging current due to the electric double layer, so O ２- The current value obtained by LSV was subtracted from N ２ - By subtracting the current value obtained by LSV, only the current value due to the oxygen reduction reaction was determined.

[0076] Next, the mass activity (A / g Ｐｔ ) at 0.9 V (vs. NHE) was determined from the oxygen reduction current thus obtained. To remove the influence of diffusion, the following equation was used to obtain the activation-controlled current i ｋ (A). i ｋ = i·i Ｌ / (i Ｌ - i) Here, i (A) is the oxygen reduction current obtained at 0.9 V (vs. NHE), and i Ｌ is the diffusion-limited current. The diffusion-limited current i Ｌ (A) is the maximum value of the obtained absolute current value. The activation-controlled current i ｋ (A) obtained from the above equation was divided by the platinum loading amount (g Ｐｔ ) to calculate the mass activity. Here, the platinum loading amount was determined by the product of the platinum coating amount (mg / cm ２ ), the electrode area (cm ２ ), and the platinum loading density (wt%) of the catalyst. Furthermore, the mass activity was divided by the value of ECSA (m ２ / g Ｐｔ ) to obtain the area-specific activity (μA / cm 2 <> Ｐｔ ). The results are shown in Table 1. The measurement results of the mass activity and the area-specific activity were obtained with an index in which the value of Comparative Example 1 described later was set to "1.00" (the same applies to Examples 2 to 6 described later). [[ID=3S]]

[0077] <Example 2> Except for using 0.003 parts of the RAFT agent (4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid), the same procedure as in Example 1 was used to obtain a block copolymer (shown by formula (14)) having a polymer block (A) formed from the monomer shown in formula (13) and a polymer block (B) formed from the ionic liquid monomer shown in formula (12). The obtained block copolymer was measured in the same manner as in Example 1, and the values ​​were Mn = 4990 and Mw = 6110. The number of repeating units of the polymer block (A) formed from the monomer shown in formula (13) was 22, and the number of repeating units of the polymer block (B) formed from the ionic liquid monomer shown in formula (12) was 21. Using the obtained block copolymer, a block copolymer-immobilized metal-supported catalyst was obtained in the same manner as in Example 1, and its electrical properties were evaluated in the same manner. The results are shown in Table 1.

[0078] <Example 3> Except for using 0.0012 parts of the RAFT agent (4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid, the same procedure as in Example 1 was used to obtain a block copolymer (shown by formula (14)) having a polymer block (A) formed from the monomer shown in formula (13) and a polymer block (B) formed from the ionic liquid monomer shown in formula (12). The obtained block copolymer was measured in the same manner as in Example 1, and the results were Mn = 13100, Mw = 14800, the number of repeating units of polymer block (A) formed from the monomer shown in formula (13) was 51, and the number of repeating units of polymer block (B) formed from the ionic liquid monomer shown in formula (12) was 52. Using the obtained block copolymer, a block copolymer-immobilized metal-supported catalyst was obtained in the same manner as in Example 1, and its electrical properties were evaluated in the same manner. The results are shown in Table 1.

[0079] <Example 4> Except for using 0.0006 parts of the RAFT agent (4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid), a block copolymer (a block copolymer shown in formula (14)) was obtained in the same manner as in Example 1, having a polymer block (A) formed from the monomer shown in formula (13) and a polymer block (B) formed from the ionic liquid monomer shown in formula (12). When the obtained block copolymer was measured in the same manner as in Example 1, Mn = 23300 and Mw = 27600, the number of repeating units of the polymer block (A) formed from the monomer shown in formula (13) was 96, and the number of repeating units of the polymer block (B) formed from the ionic liquid monomer shown in formula (12) was 105. Then, using the obtained block copolymer, a block copolymer-immobilized metal-supported catalyst was obtained in the same manner as in Example 1, and its electrical properties were evaluated in the same manner. The results are shown in Table 1.

[0080] <Example 5> A block copolymer (shown by formula (14)) was obtained in the same manner as in Example 1, except that the amount of RAFT agent (4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid) used was 0.006 parts and the amount of monomer shown in formula (13) used was 2.5 parts. The block copolymer had a polymer block (A) formed by the monomer shown in formula (13) and a polymer block (B) formed by the ionic liquid monomer shown in formula (12). The obtained block copolymer was measured in the same manner as in Example 1, and the results were Mn = 4760, Mw = 5980, the number of repeating units of polymer block (A) formed by the monomer shown in formula (13) was 10, and the number of repeating units of polymer block (B) formed by the ionic liquid monomer shown in formula (12) was 21. Using the obtained block copolymer, a block copolymer-immobilized metal-supported catalyst was obtained in the same manner as in Example 1, and its electrical properties were evaluated in the same manner. The results are shown in Table 1.

[0081] <Example 6> Except for using 0.0012 parts of the RAFT agent (4-((((2-carboxyethyl)thio)carbonothio)thio)-4-cyanopentanoic acid and 12.5 parts of the monomer shown in formula (13), a block copolymer (shown as the block copolymer shown in formula (14)) was obtained in the same manner as in Example 1, having a polymer block (A) formed from the monomer shown in formula (13) and a polymer block (B) formed from the ionic liquid monomer shown in formula (12). When the obtained block copolymer was measured in the same manner as in Example 1, Mn = 12280 and Mw = 13540, the number of repeating units of the polymer block (A) formed from the monomer shown in formula (13) was 49, and the number of repeating units of the polymer block (B) formed from the ionic liquid monomer shown in formula (12) was 21. Then, using the obtained block copolymer, a block copolymer-immobilized metal-supported catalyst was obtained in the same manner as in Example 1, and its electrical properties were evaluated in the same manner. The results are shown in Table 1.

[0082] <Comparative Example 1> The carbon support on which the catalyst metal particles obtained in Production Example 1 were supported was used as the metal-supported catalyst, and its electrical properties were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0083] In Table 1, the measurement results for effective electrochemical surface area (ECSA), mass activity, and specific activity are shown as indices with the value for Comparative Example 1 set to "1.00". Note that higher values ​​for effective electrochemical surface area (ECSA), mass activity, and specific activity indicate better performance.

[0084] As shown in Table 1, a block copolymer comprising a polymer block (A) that interacts with carbon or silica and a polymer block (B) having a protic cationic structure can be well immobilized on carbon (carbon support), and due to its excellent proton conductivity, it is possible to obtain excellent mass activity and specific activity while suppressing a decrease in the effective electrochemical surface area (ECSA) in electrochemical properties. The number of repeating units m of the monomer shown in formula (13) and the number of repeating units n of the ionic liquid monomer shown in formula (12) were determined by NMR measurement, and this was used to evaluate whether the block copolymer was synthesized as designed. On the other hand, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) were determined by GPC measurement. GPC measurement provides values ​​corresponding to the measured molecular size (hydrodynamic radius) of the block copolymer in the developing solvent, and it can be said that the penetration of the block copolymer into the pores of the carbon support can be evaluated from the relationship between the number of repeating units m, the number of repeating units n, and Mn and Mw.

Claims

1. A block copolymer comprising a polymer block (A) that interacts with carbon or silica, and a polymer block (B) having a protic cationic structure.

2. The block copolymer according to claim 1, represented by the following general formula (1). (In the above general formula (1), R １ , R ２ Each is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, A is an organic group that interacts with carbon or silica, X － Z is an anionic organic group. ＋ (where m is a protic organic cation, and n is 1 to 1000.) 3. The block copolymer according to claim 1, represented by the following general formula (2). (In the above general formula (2), R １ , R ２ Each of these is independently a hydrogen atom or a C1-C4 alkyl group, A is an organic group that interacts with carbon or silica, and Z' ＋ X' is a protic cationic organic group. － (This refers to an organic anion, where p is between 1 and 1000, and q is between 1 and 1000.) 4. The block copolymer according to any one of claims 1 to 3, wherein the polymer block (B) having a protic cationic structure is a polymer block polymerized using an ionic liquid as a monomer.

5. A metal-supported catalyst comprising a carrier and catalyst metal particles supported on the carrier, wherein the block copolymer according to any one of claims 1 to 3 is immobilized.

6. A metal-supported catalyst comprising a carbon carrier having pores and catalyst metal particles supported on the carbon carrier, wherein the block copolymer according to any one of claims 1 to 3 is immobilized.

7. A battery electrode comprising the metal-supported catalyst described in claim 5.

8. A battery comprising the battery electrode described in claim 7.

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