Membrane electrode assembly

Abstract

The present disclosure aims to provide a membrane electrode assembly having durability and performance. The membrane electrode assembly of the present embodiment contains a nitrogen-containing polydentate ligand capable of complexing metal ions, and a cathode catalyst layer containing an electrode catalyst and an ionomer, the electrode catalyst being a metal-supported catalyst in which metal particles having catalytic activity are supported on a support having fine pores, the peak pore diameter of the support being 2 nm to 9 nm, or the pore volume of mesopores of 2 nm to 30 nm of the support being 7.5 cc / g or more.

Description

Technical Field

[0001] This disclosure relates to a membrane electrode assembly. Background Technology

[0002] Solid polymer fuel cells typically consist of a membrane electrode assembly (MEA) comprising a solid polymer electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane. The anode catalyst layer functions as the fuel electrode, and the cathode catalyst layer functions as the air electrode. Sometimes, gas diffusion layers are further disposed on both sides of the MEA; this configuration is also known as a membrane electrode gas diffusion layer assembly (MEGA).

[0003] In solid polymer fuel cells, metal ions can be introduced during manufacturing or power generation, leading to electrolyte membrane degradation. To address this issue, Patent Document 1 discloses a method to improve the durability of the electrolyte membrane (MEA) by adding a complex of a specific metal and a nitrogen-containing aromatic compound ligand to the MEA.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: US Patent No. 9,172,107 Summary of the Invention

[0007] As described above, in Patent Document 1, a nitrogen-containing aromatic compound is used as a ligand to improve the durability of the MEA. However, it has been shown that the ligand can cause cathode catalyst poisoning in the technology disclosed in Patent Document 1, resulting in a decrease in fuel cell performance.

[0008] Therefore, the purpose of this disclosure is to provide a membrane electrode assembly that combines durability and performance.

[0009] To address the aforementioned issues, the inventors conducted in-depth research and found that the performance degradation was due to ligands contained in the anode catalyst layer and electrolyte membrane migrating to the cathode catalyst layer, leading to cathode catalyst poisoning via ionomers in the cathode catalyst layer. Therefore, the inventors conducted further research and discovered that by using a specified metal-supported catalyst as the electrode catalyst in the cathode catalyst layer, ligand-induced catalyst poisoning could be suppressed. As a result, a membrane electrode assembly with both durability and performance can be provided, thus completing the present invention.

[0010] Therefore, examples of this embodiment are described below.

[0011] (1) A membrane electrode assembly comprising: a solid polymer electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane.

[0012] The aforementioned membrane electrode assembly contains a nitrogen-containing polydentate ligand that can be coupled to metal ions.

[0013] The aforementioned cathode catalyst layer contains an electrode catalyst and an ionomer.

[0014] The aforementioned electrode catalyst is a metal-supported catalyst in which catalytically active metal particles are loaded onto a porous support.

[0015] The peak pore diameter of the above-mentioned carrier is 2nm to 9nm.

[0016] (2) A membrane electrode assembly comprising: a solid polymer electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane.

[0017] The aforementioned membrane electrode assembly contains a nitrogen-containing polydentate ligand that can be coupled to metal ions.

[0018] The aforementioned cathode catalyst layer contains an electrode catalyst and an ionomer.

[0019] The aforementioned electrode catalyst is a metal-supported catalyst in which catalytically active metal particles are loaded onto a porous support.

[0020] The micropore volume of the mesopores of the above-mentioned carrier, ranging from 2nm to 30nm, is above 7.5cc / g.

[0021] (3) The membrane electrode assembly according to (1) above, wherein the pore volume of the mesopores of the carrier with a diameter of 2 nm to 30 nm is 7.5 cc / g or more.

[0022] (4) The membrane electrode assembly according to any one of (1) to (3) above, wherein the nitrogen-containing polydentate ligand that can be coupled to the metal ion is at least one selected from compounds represented by the following general formulas (1) to (4) and their salts.

[0023]

[0024]

[0025]

[0026]

[0027] (where R)1 R 2 R 3 and R 4 The functional group is selected from the group consisting of hydrogen atom, halogen atom, nitrile group, amide group, imine group, amino group, thiol group, hydroxyl group, sulfonyl group, carboxylic acid group, phosphonic acid group, phosphate group, ketone group, aldehyde group, ester group, alkoxy group, haloalkoxy group, phenolic group, cyclopentyl group, cyclohexyl group, alkylamino group with 1 to 10 carbon atoms, alkylsulfonic acid group with 1 to 10 carbon atoms, haloalkyl group with 1 to 10 carbon atoms, alkyl group with 1 to 10 carbon atoms, alkenylamino group with 2 to 10 carbon atoms, alkenylsulfonic acid group with 2 to 10 carbon atoms, haloalkenyl group with 2 to 10 carbon atoms, and alkenyl group with 2 to 10 carbon atoms. The functional group may have at least one group selected from the group consisting of at least one functional group selected from the above functional group, aromatic ring, heterocycle, oxygen atom, sulfur atom, and nitrogen atom in its respective molecular chain.

[0028] (5) The membrane electrode assembly according to any one of (1) to (4) above, wherein the metal particles are selected from at least one of platinum particles, platinum alloy particles and platinum-containing composite particles.

[0029] According to this disclosure, a membrane electrode assembly that combines durability and performance can be provided. Attached Figure Description

[0030] Figure 1 This is a cross-sectional schematic diagram used to illustrate the configuration example of the membrane electrode assembly and solid polymer fuel cell of this embodiment, and is a cross-sectional view of the main part of the fuel cell 10 as an example.

[0031] Figure 2 This is a graph showing the relationship between the peak pore diameter of the support used for the electrode catalyst in the cathode catalyst layer of the membrane electrode conjugate with added ligands (Comparative Example 2, Examples 1-3) and the voltage reduction caused by the addition of ligands.

[0032] Figure 3 This is a graph showing the relationship between the pore volume of the 2nm to 30nm mesopores of the support used for the electrode catalyst in the cathode catalyst layer of the membrane electrode conjugate with added ligands (Comparative Example 2, Examples 1-3) and the voltage reduction caused by the addition of ligands.

[0033] Symbol Explanation

[0034] 1: Battery cell; 2: MEGA (Membrane Electrode Gas Diffusion Layer Assembly); 3: Separator (Separator for fuel cells); 4: Membrane Electrode Assembly (MEA); 5: Electrolyte membrane; 6: Electrode; 7: Gas diffusion layer; 10: Fuel cell; 21, 22: Gas flow paths Detailed Implementation

[0035] This disclosure relates to a membrane electrode assembly having a solid polymer electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane. The membrane electrode assembly contains a nitrogen-containing multidentate ligand that can be disposed on metal ions. The cathode catalyst layer contains an electrode catalyst and an ionomer. The electrode catalyst is a metal-supported catalyst in which catalytically active metal particles are supported in a porous support.

[0036] In the first embodiment, the peak pore diameter of the above-mentioned carrier is 2nm to 9nm.

[0037] In the second embodiment, the pore volume of the mesopores of the above-mentioned carrier, ranging from 2 nm to 30 nm, is 7.5 cc / g or more.

[0038] The configurations of the first embodiment and the second embodiment (hereinafter also referred to as "this embodiment") will be described below.

[0039] Solid polymer electrolyte membranes have the following functions: they prevent the flow of electrons and gases, while simultaneously absorbing protons (H+) generated at the anode. ＋ The catalyst is transferred from the anode-side catalyst layer to the cathode-side catalyst layer. As the solid polymer electrolyte membrane in this embodiment, a proton-conducting electrolyte membrane known in the art can be used. For example, a membrane formed from a fluoropolymer with sulfonic acid groups (such as Nafion (DuPont), Flemion (AGC), and Aciplex (Asahi Kasei)) can be used as the electrolyte.

[0040] There is no particular limitation on the thickness of the solid polymer electrolyte membrane; for example, from the viewpoint of improving proton conductivity, it can be 5 μm to 50 μm.

[0041] The cathode catalyst layer functions as an air electrode (oxygen electrode). The cathode catalyst layer contains at least an electrode catalyst and an ionomer. In this embodiment, a metal-supported catalyst, in which catalytically active metal particles are loaded onto a porous support, is used as the electrode catalyst in the cathode catalyst layer. In the metal-supported catalyst, particulate catalyst metal is supported on the support. In this disclosure, the state of having a catalyst loaded on a porous support refers to at least one of the states of having the catalyst loaded on the surface of the support and the state of having the catalyst loaded on the inner wall surface inside the pores of the support.

[0042] As a method for loading metal particles onto a support, conventional methods can be used. For example, a method can be employed where catalytically active metal particles are mixed into a support dispersion, filtered, washed, and then redispersed in ethanol or the like, followed by drying using a vacuum pump or similar method. After drying, heat treatment can be performed as needed.

[0043] In this embodiment, a pore-bearing carrier is used as the carrier; specifically, a mesoporous carrier with fine pores is used. A pore-bearing granular carrier can also be used as the carrier. In this embodiment, the carrier contains primary particles with pores. A primary particle refers to the smallest unit of the carrier particle that cannot be decomposed. If the carrier contains primary particles with pores, it may also contain secondary particles formed by the aggregation of primary particles with pores. The presence of pores in the primary particles of the carrier can be confirmed, for example, by observation using an electron microscope.

[0044] In the first embodiment, the peak pore diameter of the support used for the electrode catalyst in the cathode catalyst layer is 2 nm to 9 nm. As a countermeasure to the problem of nitrogen-containing polydentate ligands migrating from the anode catalyst layer to the cathode catalyst layer poisoning the cathode catalyst and reducing power generation performance via ionomers in the cathode catalyst layer, it is effective to load metal particles (catalyst metal) inside the pores of the support to avoid contact with the ionomers. If the peak pore diameter of the support is 2 nm or more, the metal particles can be sufficiently loaded inside the pores of the support. Furthermore, if the peak pore diameter of the support is 9 nm or less, the intrusion of ionomers into the pores of the support can be suppressed. Therefore, if the peak pore diameter of the support is 2 nm to 9 nm, catalyst poisoning caused by nitrogen-containing polydentate ligands is less likely to occur in the cathode catalyst layer, and the reduction in power generation performance caused by ligand addition is suppressed. The peak pore diameter of the support is preferably 2 nm to 5.4 nm. If the peak pore diameter of the support is within this range, the reduction in power generation performance caused by ligand addition is further suppressed. In this disclosure, pore diameter refers to the diameter of the pore. In addition, in this disclosure, the peak pore diameter refers to the pore diameter with the highest peak in the pore distribution curve obtained by the measurement method described below (also known as the mode diameter).

[0045] In the second embodiment, the mesopores (hereinafter also simply referred to as "mesopores") of the support used for the electrode catalyst in the cathode catalyst layer have a pore diameter of 2 nm to 30 nm and a pore volume of 7.5 cc / g or more. As a countermeasure to the problem of nitrogen-containing polydentate ligands transferring from the anode catalyst layer to the cathode catalyst layer causing cathode catalyst poisoning and reducing power generation performance via ionomers in the cathode catalyst layer, it is effective to load metal particles (catalyst metals) inside the pores of the support to avoid contact with the ionomers. If the pore volume of the mesopores of the support is 7.5 cc / g or more, metal particles can be sufficiently loaded inside the pores of the support. Therefore, catalyst poisoning caused by nitrogen-containing polydentate ligands is less likely to occur, and the reduction in power generation performance caused by ligand addition is suppressed. The pore volume of the mesopores of the support is preferably 10.5 cc / g or more. If the pore volume of the mesopores of the support is within this range, the reduction in power generation performance caused by ligand addition is further suppressed.

[0046] In one embodiment, the support used for the electrode catalyst in the cathode catalyst layer may possess both the peak pore diameter of the first embodiment and the pore volume of the second embodiment. Specifically, in one embodiment, the peak pore diameter of the support is 2 nm to 9 nm, and the pore volume of the mesopores (2 nm to 30 nm) is 7.5 cc / g or more. If the peak pore diameter and the pore volume of the mesopores of the support are within this range, the reduction in power generation performance caused by ligand addition is suppressed.

[0047] When a carrier comprises secondary particles formed by the aggregation of primary particles with fine pores, the peak pore diameter and mesopore volume of the primary particles with fine pores satisfy the aforementioned ranges. Therefore, carriers whose primary particles do not have fine pores are not included in the carriers of this disclosure. Furthermore, carriers comprising secondary particles formed by the aggregation of primary particles with fine pores, where the peak pore diameter and mesopore volume of the primary particles do not satisfy the aforementioned ranges, but the voids within the secondary particles formed by the aggregation of primary particles satisfy the aforementioned configuration, are also not included in the carriers of this disclosure.

[0048] The average particle size of the primary particles in the carrier can be, for example, 5 nm to 3000 nm. Preferably, the average particle size of the primary particles in the carrier is 50 nm to 2000 nm, more preferably 100 nm to 1500 nm. The particle size is calculated from the volume of the particles in a transmission electron microscope image in the form of an equivalent sphere diameter. For the average particle size, the particle size (equivalent sphere diameter) of 100 to 1000 carrier particles can be measured using a transmission electron microscope, and their average value can be taken as the average particle size of the carrier particles.

[0049] In this embodiment, the BET specific surface area of ​​the support used for the electrode catalyst in the cathode catalyst layer is typically 336 m². 2 / g or above, or 458m 2 / g or more. If the BET specific surface area of ​​the carrier is 336m² 2 At concentrations above / g, the reduction in power generation performance caused by ligand addition is suppressed.

[0050] The peak pore diameter, pore volume of mesopores (2 nm–30 nm), and specific surface area of ​​the support can all be determined using nitrogen (N2) adsorption-desorption. Specifically, these three parameters can be obtained based on the relative pressure dependence of the amount of N2 adsorbed in the sample. The BET theory is used to calculate the specific surface area. It should be noted that the evaluation methods are not limited to the above methods; mercury porosimetry, H2O adsorption, and the oil absorption of dibutyl phthalate (DBP) can also be used. Microscopic observation can also be employed. It should be noted that the physical properties of the support can be directly measured, or the mass of a metal-supported catalyst with metal particles loaded on the support can be measured and converted to the mass of the support.

[0051] There are no particular limitations on the support; for example, carbon or oxides can be used. The carbon used can be electrically conductive. One type of support can be used alone, or two or more types can be used in combination.

[0052] Examples of carbon supports include carbon black (acetylene black, Ketjen black, or furnace black, etc.), activated carbon, graphite, glassy carbon, graphene, carbon fibers, carbon nanotubes, carbon nitride, carbon sulfide, or carbon phosphide. A single carbon support can be used, or two or more can be used in combination.

[0053] Examples of oxide supports include titanium oxide, niobium oxide, tin oxide, tungsten oxide, and molybdenum oxide. A single oxide support can be used, or two or more can be used in combination.

[0054] There are no particular restrictions on catalyst metals as long as they exhibit catalytic activity in the electrode reaction.

[0055] Air electrode (cathode): O2 + 4H ＋ +4e － →2H2O

[0056] Hydrogen electrode (anode): 2H₂ → 4H ＋ +4e －

[0057] The metal particles can be any metal with redox catalytic ability, such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, etc., or two or more of these metals may be used. Preferably, the metal particles are selected from at least one of platinum particles, platinum alloy particles, and platinum-containing composite particles. For platinum alloys and platinum-containing composite particles containing metals other than platinum, examples include ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, etc. These metals may be used individually or in combination of two or more.

[0058] The average particle size of the metal particles is not particularly limited, but is preferably 1 nm to 10 nm, for example, 1 nm to 4 nm or 2 nm to 3 nm. The particle size is calculated from the volume of the particles in a transmission electron microscope image in the form of an equivalent sphere diameter. For the average particle size, the particle size (equivalent sphere diameter) of 100 to 1000 particles can be measured using a transmission electron microscope, and their average value can be taken as the average particle size of the metal particles.

[0059] The metal loading ratio of the metal particles loaded on the carrier is not particularly limited, but is, for example, 1 to 50% by mass, preferably 29 to 48% by mass.

[0060] There is no particular limitation on the content of electrode catalyst in the cathode catalyst layer, for example, it is 3 to 40% by mass relative to the total mass of the catalyst layer.

[0061] The ionomer used as the cathode catalyst layer is preferably an ionomer with sulfonic acid groups. Ionomers, also known as cation exchange resins, exist in the form of clusters formed by ionomer molecules. There are no particular limitations on the ionomer used; for example, ionomers known in the art can be used. Examples of ionomers include fluoropolymer-based ionomers such as perfluorosulfonic acid resins; sulfonated plastic-based ionomers such as sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polyether ether sulfones, sulfonated polysulfones, sulfonated polysulfides, and sulfonated polyphenylene; and sulfonated plastic-based ionomers such as sulfonated alkylated polyether ether ketones, sulfonated alkylated polyaryl ether sulfones, sulfonated alkylated polyether sulfones, sulfonated polysulfides, and sulfonated polyphenylene. One type of ionomer can be used alone, or two or more can be used in combination.

[0062] The anode catalyst layer functions as the fuel electrode, i.e., the hydrogen electrode.

[0063] The anode catalyst layer contains an electrolyte such as an electrode catalyst and an ionomer. The ionomer is preferably an ionomer containing sulfonic acid groups. Examples of ionomers containing sulfonic acid groups include the aforementioned ionomers. In one embodiment, in addition to the electrode catalyst and the ionomer, the anode catalyst layer may also contain a nitrogen-containing polydentate ligand capable of coordinating with metal ions.

[0064] There are no particular limitations on its use as an electrode catalyst; for example, the materials described above can be used.

[0065] There are no particular limitations on ionomers containing sulfonic acid groups; for example, ionomers containing perfluorosulfonic acid groups and other ion-conducting polymeric electrolyte resins can be cited. Specific examples of ionomers containing sulfonic acid groups include Nafion and Aquivion (Solvay).

[0066] The membrane electrode assembly of this embodiment contains a nitrogen-containing polydentate ligand capable of coordinating with metal ions. Metal ions can be introduced during the manufacturing of the membrane electrode assembly, the manufacturing of the fuel cell, or during power generation, causing degradation of the membrane electrode assembly. The nitrogen-containing polydentate ligand can suppress the adverse effects of metal ions by coordinating with them, thereby improving the durability of the membrane electrode assembly. The metal ions that can be coordinated with the nitrogen-containing polydentate ligand are not particularly limited; examples include manganese ions, cerium ions, cobalt ions, iron ions, copper ions, palladium ions, and platinum ions. In one embodiment, the metal ion is an iron ion.

[0067] Nitrogen-containing polydentate ligands are compounds containing nitrogen atoms and having two or more coordination sites. Here, "coordination site" refers to an atom or group of atoms that has non-covalent electron pairs capable of forming coordinate bonds with metal ions. Examples of coordination sites include heteroatoms (nitrogen, oxygen, sulfur, phosphorus, etc.) and groups of atoms containing such heteroatoms. Nitrogen-containing polydentate ligands are, for example, nitrogen-containing aromatic compounds having two or more nitrogen atoms, and can be compounds having two or more pyridine rings or their derivatives. Examples of compounds having two or more pyridine rings include bipyridine, phenanthroline, phenanthrolinedione, and terpyridine.

[0068] Nitrogen-containing polydentate ligands can be in the form of salts. When nitrogen-containing polydentate ligands are in the form of salts, there are no particular limitations on what constitutes a salt; examples include halides, sulfates, nitrates, phosphates, borates, silicates, carbonates, bicarbonates, and organic acid salts. A single salt can be used, or two or more salts can be used in combination.

[0069] In one embodiment, the nitrogen-containing polydentate ligand is at least one selected from compounds represented by the following general formulas (1) to (4) and their salts.

[0070]

[0071]

[0072]

[0073]

[0074] (where R) 1 R 2 R 3 and R 4 The functional group is selected from the group consisting of hydrogen atom, halogen atom, nitrile group, amide group, imine group, amino group, thiol group, hydroxyl group, sulfonyl group, carboxylic acid group, phosphonic acid group, phosphate group, ketone group, aldehyde group, ester group, alkoxy group, haloalkoxy group, phenolic group, cyclopentyl group, cyclohexyl group, alkylamino group with 1 to 10 carbon atoms, alkylsulfonic acid group with 1 to 10 carbon atoms, haloalkyl group with 1 to 10 carbon atoms, alkyl group with 1 to 10 carbon atoms, alkenylamino group with 2 to 10 carbon atoms, alkenylsulfonic acid group with 2 to 10 carbon atoms, haloalkenyl group with 2 to 10 carbon atoms, and alkenyl group with 2 to 10 carbon atoms. The functional group may have at least one group selected from the following groups in its respective molecular chain: at least one functional group selected from the above functional group group, aromatic ring, heterocycle, oxygen atom, sulfur atom, and nitrogen atom.

[0075] In equations (1) to (4), R 1 R 2 R 3 and R 4 It is located at a position where it can form a covalent bond with the carbon atom of the pyridine ring. In equations (1) to (4), the nitrogen of the pyridine ring can be obtained from R 1 R 2 R 3 and R 4 replace.

[0076] In one implementation, R in equations (1) to (4) 1 R 2 R 3 and R 4 They are either hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, preferably hydrogen atoms.

[0077] In one embodiment, the nitrogen-containing polydentate ligand is 1,10-phenanthroline.

[0078] Nitrogen-containing polydentate ligands can be contained in the anode catalyst layer, the solid polymer electrolyte membrane, or both.

[0079] When the anode catalyst layer contains nitrogen-containing polydentate ligands, the anode catalyst layer contains at least an electrode catalyst, an electrolyte, and nitrogen-containing polydentate ligands.

[0080] The content of nitrogen-containing polydentate ligands in the anode catalyst layer relative to the total solid content of the anode catalyst layer is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass.

[0081] [Method for manufacturing membrane electrode assembly]

[0082] The catalyst layer is formed, for example, by a process of preparing a catalyst ink (e.g., about 10% solids concentration) containing an electrode catalyst, an ionomer, and a solvent; a process of forming a catalyst layer on the substrate surface by coating the catalyst ink onto the substrate surface and allowing the solvent in the coating to evaporate; and a process of transferring the catalyst layer on the substrate surface to the electrolyte membrane. Alternatively, the catalyst layer can also be formed by directly coating the catalyst ink onto a solid polymer electrolyte membrane instead of the substrate. By forming a cathode catalyst layer and an anode catalyst layer on the solid polymer electrolyte membrane, a membrane electrode assembly can be fabricated.

[0083] Examples of coating methods for catalyst inks include spraying, doctor blade coating using a doctor blade coater or applicator, die coating, reverse roller coating, and intermittent die coating.

[0084] In the formation of the anode catalyst layer, the catalyst ink used to form the anode catalyst layer may contain the aforementioned nitrogen-containing multidentate ligands. Specifically, the catalyst ink used to form the anode catalyst layer may contain an electrode catalyst, an ionomer (e.g., an ionomer with sulfonic acid groups), the aforementioned nitrogen-containing multidentate ligands, and a solvent.

[0085] [The specific composition of membrane electrode assembly and solid polymer fuel cell]

[0086] Solid polymer fuel cells use a membrane electrode assembly (MEA), consisting of a solid polymer electrolyte membrane with catalyst layers (electrodes) bonded to both sides, as the basic unit. Additionally, a gas diffusion layer is typically disposed outside the catalyst layer in solid polymer fuel cells. This gas diffusion layer supplies reactant gases and electrons to the catalyst layer and can be made of materials such as carbon paper or carbon cloth. Furthermore, the catalyst layer is the site of the electrode reactions.

[0087] The following is for reference Figure 1 The structure of the membrane electrode assembly and the solid polymer fuel cell is described. Figure 1 This is a cross-sectional schematic diagram used to explain an example of the structure of the solid polymer fuel cell of this embodiment, and is a cross-sectional view of the main part of the fuel cell 10 as an example. The solid polymer fuel cell has a stack of single cells consisting of a power generator and fuel cell separators disposed on both sides of the power generator. Multiple single cells are stacked in the stacking direction, and each single cell is electrically connected in series. Figure 1As shown, the fuel cell 10 has multiple single cells 1 stacked as basic units. Each single cell 1 is a solid polymer fuel cell that generates an electromotive force through the electrochemical reaction of an oxidant gas (e.g., air) and a fuel gas (e.g., hydrogen). Each single cell 1 includes: a membrane electrode and gas diffusion layer assembly (MEGA) 2 with gas diffusion layers (GDL) 7 disposed on both sides, and a separator 3 that contacts the MEGA 2 in a manner that divides the MEGA 2. It should be noted that in this embodiment, the MEGA 2 is held by a pair of separators 3, 3.

[0088] MEGA2 comprises a membrane electrode assembly (MEA) 4 and gas diffusion layers 7, 7 disposed on both sides thereof. The membrane electrode assembly 4 consists of an electrolyte membrane 5 and a pair of electrodes 6, 6 joined together to hold the electrolyte membrane 5. The electrolyte membrane 5 is, for example, a proton-conducting ion exchange membrane formed of a solid polymer material. The electrodes 6 contain, for example, porous carbon raw materials supported on catalysts such as platinum. The electrode 6 disposed on one side of the electrolyte membrane 5 functions as an anode, and the electrode 6 on the other side functions as a cathode. The gas diffusion layer 7 is formed of a permeable conductive component. Examples of permeable conductive components include porous carbon materials such as carbon paper or carbon cloth, or porous metal materials such as metal mesh or foamed metal. In this embodiment, the anode electrode is formed of an anode catalyst layer, and the cathode electrode is formed of a cathode catalyst layer.

[0089] Example

[0090] The following describes this implementation method using examples.

[0091] <Preparation of Electrode Catalysts>

[0092] (Electrode catalyst A)

[0093] Electrode catalyst A (metal loading ratio: 36% by mass) was prepared, comprising Pt particles as the catalytic metal and carbon black (VULCAN, Cabot Corporation) as the support for the Pt particles. For electrode catalyst A, the peak pore diameter of the support, determined by N2 adsorption-desorption, was 11.5 nm, the pore volume of the mesopores (2 nm–30 nm) was 1.9 cc / g, and the BET specific surface area of ​​the support was 159.0 m². 2 / g.

[0094] (Electrode catalyst B)

[0095] Electrode catalyst B (metal loading ratio 29% by mass) was prepared, comprising Pt particles (average particle size: 2 nm–3 nm) as the catalytic metal and carbon black as the support for the Pt particles. For electrode catalyst B, the peak pore diameter of the support, determined by N2 adsorption-desorption, was 8.6 nm, the pore volume of the mesopores (2 nm–30 nm) was 7.6 cc / g, and the BET specific surface area of ​​the support was 336.5 m². 2 / g.

[0096] (Electrode catalyst C)

[0097] Electrode catalyst C (metal loading ratio: 42% by mass) was prepared, comprising Pt particles as the catalytic metal and Ketjen Black (EC300J, manufactured by Lion Specialty Chemicals) as the support for the Pt particles. For electrode catalyst C, the peak pore diameter of the support, determined by N2 adsorption-desorption, was 5.4 nm, the pore volume of the mesopores (2 nm–30 nm) was 10.5 cc / g, and the BET specific surface area of ​​the support was 458.0 m². 2 / g.

[0098] (Electrode catalyst D)

[0099] Electrode catalyst D (metal loading ratio: 48% by mass) was prepared, comprising Pt particles as the catalytic metal and carbon black as the support for the Pt particles. For electrode catalyst D, the peak pore diameter of the support, determined by N2 adsorption-desorption, was 3.5 nm, the pore volume of the mesopores (2 nm–30 nm) of the support was 14.0 cc / g, and the BET specific surface area of ​​the support was 708.0 m². 2 / g.

[0100] <Fabrication of Membrane Electrode Connectors>

[0101] [Comparative Example 1]

[0102] (Formation of the cathode catalyst layer)

[0103] Electrode catalyst A was dispersed in an ionomer solution (DE2020) containing water, ethanol, and Nafion (registered trademark) to prepare a catalyst ink. The mass ratio of water to alcohol (water / alcohol) in the catalyst ink was approximately 1. The catalyst ink was coated onto a polytetrafluoroethylene sheet and dried to form a cathode catalyst layer.

[0104] The Pt unit area weight of the cathode catalyst layer is 0.3 mg / cm². 2 The mass ratio (I / C) of the ionomer to the carrier is 1.0.

[0105] (Formation of the anode catalyst layer)

[0106] An ionomer solution containing ferric nitrate and Nafion (registered trademark) is prepared by adding an aqueous solution of ferric nitrate to an ionomer solution (DE2020).

[0107] As the electrode catalyst, a platinum-supported carbon catalyst (TEC10E30E, 30% platinum-supported carbon, manufactured by Tanaka Precious Metals Industry Co., Ltd.) was used. The electrode catalyst was dispersed in a prepared ionomer solution to prepare the catalyst ink. This catalyst ink was coated onto a polytetrafluoroethylene sheet and dried, thereby forming the anode catalyst layer.

[0108] The Pt unit area weight of the anode catalyst layer is 0.1 mg / cm². 2 The amount of iron ions added was 1.0 μg / cm³. 2 The mass ratio of ionomer to carbon (I / C) is 1.0.

[0109] (Fabrication of membrane electrode assembly)

[0110] The obtained cathode catalyst layer and anode catalyst layer were thermally transferred to both sides of a Nafion (registered trademark) membrane (NR211) to fabricate the membrane electrode assembly C1. The thermal transfer conditions were 140℃ and 50 kgf / cm². 2 (4.90 MPa), 5 min. The electrode area of ​​the membrane electrode assembly used for initial performance testing and durability testing is 3.6 cm × 3.6 cm (12.96 cm²). 2 The experimental cell was fabricated by clamping the membrane electrode assembly with a paper diffusion layer (GDL) containing a water-repellent layer.

[0111] [Comparative Example 2]

[0112] In the formation of the anode catalyst layer, the ionomer solution containing ferric nitrate and Nafion (registered trademark) was changed to an ionomer solution containing 1,10-phenanthroline, ferric nitrate, and Nafion (registered trademark). Otherwise, the membrane electrode assembly C2 was prepared in the same manner as in Comparative Example 1. The amount of 1,10-phenanthroline added to the anode catalyst layer was 9 μg / cm³. 2 .

[0113] [Comparative Example 3]

[0114] Electrode catalyst B was used as the electrode catalyst for the cathode catalyst layer, and the membrane electrode assembly C3 was prepared in the same manner as in Comparative Example 1.

[0115] [Comparative Example 4]

[0116] Electrode catalyst C was used as the electrode catalyst for the cathode catalyst layer. Otherwise, the membrane electrode assembly C4 was prepared in the same manner as in Comparative Example 1.

[0117] [Comparative Example 5]

[0118] Electrode catalyst D was used as the electrode catalyst for the cathode catalyst layer. Otherwise, the membrane electrode assembly C5 was prepared in the same manner as in Comparative Example 1.

[0119] [Example 1]

[0120] Electrode catalyst B was used as the electrode catalyst for the cathode catalyst layer. Otherwise, the membrane electrode assembly E1 was fabricated in the same manner as in Comparative Example 2.

[0121] [Example 2]

[0122] Electrode catalyst C was used as the electrode catalyst for the cathode catalyst layer, and the membrane electrode assembly E2 was prepared in the same manner as in Comparative Example 2.

[0123] [Example 3]

[0124] Electrode catalyst D was used as the electrode catalyst for the cathode catalyst layer. Otherwise, the membrane electrode assembly E3 was fabricated in the same manner as in Comparative Example 2.

[0125] <Evaluation>

[0126] (Initial performance test)

[0127] The above-mentioned test battery cell (electrode area: 12.96 cm²) was used. 2 The battery cell evaluation was conducted using this method. Current / voltage characteristics were evaluated under low humidity conditions (cell temperature 95°C, humidity 30% RH), measuring 1.0 A / cm². 2 The performance (voltage) was evaluated at a scan rate of 20 mA / s under anodic scanning. Additionally, the cell pressure was 150 kPa, the anodic gas was hydrogen with a flow rate of 1.0 L / min, and the cathode gas was air with a flow rate of 2.0 L / min. The results are shown in Table 1.

[0128] In addition, when using 1,10-phenanthroline (ligand) (Comparative Example 2, Examples 1-3), the voltage drop caused by the addition of the ligand was calculated as the difference between the voltage drop and the initial voltage when no ligand was added. The results are shown in Table 1.

[0129] (Durability test)

[0130] The above-mentioned test battery cell (electrode area: 12.96 cm²) was used. 2In a low-humidity environment (cell temperature 95°C, humidity 30% RH) where electrolyte membrane degradation is likely to occur, and with a low current density (0.2 A / cm²), 2 A 144-hour durability test was conducted. The cell pressure was 150 kPa, the anode gas was hydrogen with a flow rate of 1.0 L / min, and the cathode gas was air with a flow rate of 2.0 L / min. After the durability test, hydrogen and air were supplied, and the current density was measured at 1.0 A / cm² under the conditions of the initial performance test described above. 2 The performance (voltage) under the condition was determined. The voltage retention rate of the battery cell voltage after the durability test relative to the initial battery cell voltage was calculated (voltage after durability test / initial voltage × 100 (%)). The results are shown in Table 1.

[0131] [Table 1]

[0132]

[0133] exist Figure 2 The diagram shows the relationship between the peak pore diameter of the support used in the cathode catalyst layer of the membrane electrode conjugate with added ligands (Comparative Example 2, Examples 1-3) and the voltage reduction caused by the addition of ligands. Additionally, in Figure 3 The diagram shows the relationship between the pore volume of the 2 nm to 30 nm mesopores of the support used in the cathode catalyst layer of the membrane electrode junction with added ligands (Comparative Example 2, Examples 1-3) and the voltage reduction caused by the addition of ligands.

[0134] As shown in Table 1, the addition of the ligand (1,10-phenanthroline) improved the voltage retention rate and durability after the durability test compared to the absence of the ligand. However, on the other hand, the initial voltage decreased with the addition of the ligand compared to the absence of the ligand.

[0135] As shown in Table 1 and Figure 2 As shown, in membrane electrode conjugates with added ligands, the smaller the peak pore diameter of the carrier, the smaller the decrease in initial voltage due to ligand addition. Moreover, compared with the membrane electrode conjugate of Comparative Example 2, where the peak pore diameter of the carrier is outside this range, the decrease in initial voltage due to ligand addition is significantly suppressed in the membrane electrode conjugates of Examples 1-3, where the peak pore diameter of the carrier is 2nm to 9nm.

[0136] Additionally, as shown in Table 1 and Figure 3As shown, in the membrane electrode conjugates with added ligands, the larger the pore volume of the 2nm to 30nm mesopores of the carrier, the smaller the decrease in initial voltage due to ligand addition. Moreover, compared with the membrane electrode conjugate of Comparative Example 2, whose pore volume of the 2nm to 30nm mesopores of the carrier is 7.5cc / g or more, the decrease in initial voltage due to ligand addition is significantly suppressed in the membrane electrode conjugates of Examples 1 to 3, which have a pore volume outside the aforementioned range.

[0137] The upper and / or lower limits of the numerical ranges described in this specification can be arbitrarily combined to define the preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define the preferred range, the upper limits of the numerical ranges can be arbitrarily combined with each other to define the preferred range, and the lower limits of the numerical ranges can be arbitrarily combined with each other to define the preferred range.

[0138] The above describes the embodiment in detail, but the specific configuration is not limited to this embodiment. Design changes may be added without departing from the scope of this disclosure, and these are all included in this disclosure.

Claims

1. A membrane electrode assembly comprising: a solid polymer electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane. The membrane electrode assembly contains a nitrogen-containing polydentate ligand that can be coupled to metal ions. The cathode catalyst layer contains an electrode catalyst and an ionomer. The electrode catalyst is a metal-supported catalyst in which catalytically active metal particles are loaded onto a porous support. The peak pore diameter of the carrier is 2nm to 9nm.

2. A membrane electrode assembly comprising: a solid polymer electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane. The membrane electrode assembly contains a nitrogen-containing polydentate ligand that can be coupled to metal ions. The cathode catalyst layer contains an electrode catalyst and an ionomer. The electrode catalyst is a metal-supported catalyst in which catalytically active metal particles are loaded onto a porous support. The carrier has a mesopore volume of 2nm to 30nm with a fine pore volume of 7.5cc / g or more.

3. The membrane electrode assembly according to claim 1, wherein, The carrier has a mesopore volume of 2nm to 30nm with a fine pore volume of 7.5cc / g or more.

4. The membrane electrode assembly according to claim 1 or 2, wherein, The nitrogen-containing polydentate ligand that can coordinate with metal ions is selected from at least one of the compounds represented by the following general formulas (1) to (4) and their salts. In the formula, R 1 R 2 R 3 and R 4 Each functional group is selected from the group consisting of hydrogen atom, halogen atom, nitrile group, amide group, imine group, amino group, thiol group, hydroxyl group, sulfonyl group, carboxylic acid group, phosphonic acid group, phosphate group, ketone group, aldehyde group, ester group, alkoxy group, haloalkoxy group, phenolic group, cyclopentyl group, cyclohexyl group, alkylamino group with 1 to 10 carbon atoms, alkylsulfonic acid group with 1 to 10 carbon atoms, haloalkyl group with 1 to 10 carbon atoms, alkyl group with 1 to 10 carbon atoms, alkenylamino group with 2 to 10 carbon atoms, alkenylsulfonic acid group with 2 to 10 carbon atoms, haloalkenyl group with 2 to 10 carbon atoms, and alkenyl group with 2 to 10 carbon atoms. The functional group may have at least one of the following groups selected in its respective molecular chain: at least one functional group selected from the group of said functional groups, aromatic ring, heterocycle, oxygen atom, sulfur atom and nitrogen atom.

5. The membrane electrode assembly according to claim 1 or 2, wherein, The metal particles are selected from at least one of platinum particles, platinum alloy particles, and platinum-containing composite particles.

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