WO2015147311A1 - 電極用触媒、ガス拡散電極形成用組成物、ガス拡散電極、膜・電極接合体、燃料電池スタック - Google Patents
電極用触媒、ガス拡散電極形成用組成物、ガス拡散電極、膜・電極接合体、燃料電池スタック Download PDFInfo
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- WO2015147311A1 WO2015147311A1 PCT/JP2015/059813 JP2015059813W WO2015147311A1 WO 2015147311 A1 WO2015147311 A1 WO 2015147311A1 JP 2015059813 W JP2015059813 W JP 2015059813W WO 2015147311 A1 WO2015147311 A1 WO 2015147311A1
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- electrode
- electrode catalyst
- catalyst
- gas diffusion
- shell
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- Y02B90/10—Applications of fuel cells in buildings
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02T90/40—Application of hydrogen technology to transportation, e.g. using fuel cells
Definitions
- the present invention relates to an electrode catalyst.
- the present invention also relates to a gas diffusion electrode forming composition comprising the above electrode catalyst, a gas diffusion electrode, a membrane / electrode assembly, and a fuel cell stack.
- a so-called solid polymer fuel cell (Polymer Electrolyte Fuel Cell: hereinafter referred to as “PEFC” as necessary) has an operating temperature of about room temperature to about 80 ° C.
- PEFC can employ an inexpensive general-purpose plastic or the like as a member constituting the fuel cell main body, so that the weight can be reduced.
- PEFC can reduce the thickness of the solid polymer electrolyte membrane, can reduce electric resistance, and can reduce power generation loss relatively easily.
- PEFC has many advantages, it can be applied to fuel cell vehicles, household cogeneration systems, and the like.
- an electrode catalyst for PEFC an electrode catalyst in which platinum (Pt) or a platinum (Pt) alloy as an electrode catalyst component is supported on carbon as a carrier has been proposed (for example, Patent Document 1, Non-Patent Document 1). Reference 1).
- an electrode catalyst for PEFC is undesirable as an electrode catalyst when the chlorine content contained in the electrode catalyst is 100 ppm or more (for example, Patent Document 2). For that reason, if the chlorine content contained in the electrode catalyst is 100 ppm or more, sufficient catalytic activity as an electrode catalyst for a fuel cell cannot be obtained, corrosion of the catalyst layer occurs, It is disclosed that the lifetime is shortened.
- platinum (Pt) or platinum (Pt) alloy powder containing less than 100 ppm of chlorine is disclosed as a catalyst component of the electrode catalyst (for example, Patent Document 2).
- the following method is disclosed as a method for preparing the platinum (Pt) or platinum (Pt) alloy powder. That is, as a starting material, after forming a melt of a chlorine-free platinum compound and a chlorine-free alloying element, heat until it gives an oxide of this melt, cool the oxide, dissolve in water A preparation method through a process of reducing the oxide formed is disclosed.
- the electrode catalyst having a chlorine content of less than 100 ppm described above must be prepared through a complicated process for removing chlorine disclosed in Patent Document 2 and the like, and there is room for improvement. It was. Thus, when mass production of PEFC in the future is assumed, even if it contains a relatively high concentration of chlorine exceeding 100 ppm, sufficient performance can be obtained, and chlorine removal can be achieved. It is considered that an electrode catalyst suitable for mass production that can be prepared without a special and complicated process and for reduction of manufacturing cost is required.
- the present invention has been made in view of such technical circumstances, and provides an electrode catalyst that can exhibit sufficient catalytic performance even if it contains a relatively high concentration of chlorine exceeding 100 ppm.
- Another object of the present invention is to provide an electrode catalyst that is suitable for mass production in that it does not go through a special and complicated manufacturing process for removing chlorine, and that is also suitable for reducing manufacturing costs.
- an object of the present invention is to provide a composition for forming a gas diffusion electrode, a gas diffusion electrode, a membrane / electrode assembly (MEA), and a fuel cell stack including the electrode catalyst.
- MEA membrane / electrode assembly
- the present inventors have reduced the concentration of bromine (Br) species measured by the fluorescent X-ray (XRF) analysis method contained in the electrode catalyst, so that a high concentration exceeding 100 ppm can be obtained. It has been found that an electrode catalyst (a core-shell catalyst described later) that exhibits sufficient performance can be produced even if it contains chlorine, and the present invention has been completed. More specifically, the present invention includes the following technical matters.
- an electrode catalyst having a core / shell structure including a carrier, a core portion formed on the carrier, and a shell portion formed to cover at least a part of the surface of the core portion.
- M represents the amount (number of atoms) of the constituent metal elements of the shell portion calculated using an electrochemical surface area (ECSA) based on hydrogen desorption waves obtained by cyclic voltammetry
- X1 indicates the amount (number of atoms) of bromine (Br) calculated based on the content of bromine (Br) species measured by fluorescent X-ray (XRF) analysis.
- X2 indicates fluorescent X-ray (XRF)
- the substance amount (the number of atoms) of chlorine (Cl) calculated based on the content of chlorine (Cl) species measured by the analytical method is shown. ]
- the value of (X2 / M) (that is, the substance amount (atomic weight) of chlorine (Cl) per substance amount (number of atoms) of the constituent metal elements in the shell portion) exceeds 47.0. Even in this case, the value of (X1 / M) (that is, the substance amount (number of atoms) of bromine (Br) per substance amount (number of atoms)) of the constituent metal elements of the shell portion should be 1.2 or less.
- the electrode catalyst is suitable for mass production in that it does not go through a special and complicated manufacturing process for removing chlorine, and is also suitable for reducing manufacturing costs.
- the bromine (Br) species refers to a chemical species containing bromine as a constituent element.
- the chemical species containing bromine include bromine atoms (Br), bromine molecules (Br 2 ), bromide ions (Br ⁇ ), bromine radicals (Br ⁇ ), polyatomic bromine ions, bromine compounds (X -Br, etc., where X is a counter ion).
- a chlorine (Cl) species refers to a chemical species containing chlorine as a constituent element.
- the chemical species containing chlorine include chlorine atoms (Cl), chlorine molecules (Cl 2 ), chlorinated ions (Cl ⁇ ), chlorine radicals (Cl ⁇ ), polyatomic chlorine ions, chlorine compounds (X -Cl and the like, where X is a counter ion).
- the content of bromine (Br) species and the content of chlorine (Cl) species are measured by fluorescent X-ray (XRF) analysis.
- the bromine (Br) species contained in the electrode catalyst is measured by fluorescent X-ray (XRF) analysis, and the content of the bromine (Br) species is the content.
- the chlorine (Cl) species contained in the electrode catalyst measured by a fluorescent X-ray (XRF) analysis method is the content of chlorine (Cl) species.
- the bromine (Br) species content and the chlorine (Cl) species content are the bromine atom converted to the bromine element contained in the electrode catalyst and the chlorine atom content converted to the chlorine element, respectively. ing.
- the present invention also provides: (2) The shell portion contains at least one metal of platinum (Pt) and a platinum (Pt) alloy, and the core portion includes palladium (Pd), a palladium (Pd) alloy,
- the electrode catalyst according to (1) comprising at least one metal selected from the group consisting of platinum (Pt) alloy, gold (Au), nickel (Ni), and nickel (Ni) alloy. provide. Thereby, the effect of the present invention can be obtained more reliably. Moreover, by setting it as said structure, a higher catalyst activity and higher durability can be acquired.
- the present invention provides (3)
- the carrier contains conductive carbon, the shell part contains platinum (Pt), and the core part contains palladium (Pd).
- the electrode catalyst according to 1) or (2) is provided. Thereby, the effect of the present invention can be obtained more reliably. Moreover, by setting it as said structure, a higher catalyst activity and higher durability can be acquired. Furthermore, with the above configuration, the electrode catalyst of the present invention can reduce the content of platinum compared to the conventional electrode catalyst having a configuration in which platinum is supported on a carbon support, so that the raw material cost can be reduced. It can be easily reduced.
- the present invention also provides: (4) M is the amount of material (number of atoms) of platinum (Pt), which is a constituent metal element of the shell, calculated using an electrochemical surface area (ECSA) based on a hydrogen desorption wave obtained by cyclic voltammetry.
- the electrode catalyst according to (3) is provided. Thereby, the effect of the present invention can be obtained more reliably. Moreover, by setting it as said structure, a higher catalyst activity and higher durability can be acquired. Furthermore, with the above configuration, the electrode catalyst of the present invention can reduce the content of platinum compared to the conventional electrode catalyst having a configuration in which platinum is supported on a carbon support, so that the raw material cost can be reduced. It can be easily reduced.
- the present invention provides (5) The shell part is formed so as to cover at least part of the surface of the core part, and the second part is formed so as to cover at least part of the surface of the first shell part.
- the present invention also provides: (6)
- the first shell portion contains palladium (Pd),
- the second shell part contains platinum (Pt).
- the electrode catalyst according to (5) is provided. Thereby, the effect of the present invention can be obtained more reliably. With the above configuration, higher catalytic activity and higher durability can be obtained.
- the present invention provides (7) The electrode catalyst according to any one of (1) to (6), wherein (X2 / M) in the formula (2) is more than 4.5. Thereby, the effect of the present invention can be obtained more reliably.
- the present invention provides (8) A composition for forming a gas diffusion electrode, comprising the electrode catalyst according to any one of (1) to (7).
- a composition for forming a gas diffusion electrode of the present invention since the electrode catalyst of the present invention is included, a gas diffusion electrode having high catalytic activity (polarization characteristics) can be easily produced.
- the present invention also provides: (9) A gas diffusion electrode comprising the electrode catalyst according to any one of (1) to (7) is provided. According to the gas diffusion electrode of the present invention, since the electrode catalyst of the present invention is included, high catalytic activity (polarization characteristics) can be obtained.
- the present invention provides (10) A membrane / electrode assembly (MEA) including the gas diffusion electrode according to (9) is provided. According to the membrane-electrode assembly (MEA) of the present invention, since the gas diffusion electrode of the present invention is included, high battery characteristics can be obtained.
- the present invention also provides: (11) A fuel cell stack comprising the membrane / electrode assembly (MEA) according to (10) is provided. According to the fuel cell stack of the present invention, since the membrane-electrode assembly (MEA) of the present invention is included, high battery characteristics can be obtained.
- an electrode catalyst capable of exhibiting catalytic performance is provided.
- an electrode catalyst suitable for mass production of an electrode catalyst in that it does not go through a special and complicated manufacturing process for removing chlorine is provided, and an electrode catalyst suitable for reducing manufacturing cost is provided.
- a gas diffusion electrode forming composition, a gas diffusion electrode, a membrane / electrode assembly (MEA), and a fuel cell stack comprising such an electrode catalyst.
- FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of the electrode catalyst (core-shell catalyst) of the present invention.
- the electrode catalyst 1 of the present invention includes a support 2 and catalyst particles 3 having a so-called “core-shell structure” supported on the support 2.
- the catalyst particle 3 includes a core portion 4 and a shell portion 5 formed so as to cover at least a part of the surface of the core portion 4.
- the catalyst particle 3 has a so-called “core / shell structure” including a core portion 4 and a shell portion 5 formed on the core portion 4.
- the electrode catalyst 1 has catalyst particles 3 supported on a carrier 2, and the catalyst particles 3 have a core portion 4 as a core and a shell portion 4 as a shell.
- covers at least one part of this surface is provided. Further, the constituent element (chemical composition) of the core part 4 and the constituent element (chemical composition) of the shell part 5 are different.
- the electrode catalyst 1 is not particularly limited as long as the shell portion 5 is formed on at least a part of the surface of the core portion 4 of the catalyst particles 3.
- the electrode catalyst 1 is preferably in a state in which substantially the entire surface of the core portion 4 is covered by the shell portion 5.
- the electrode catalyst 1 is in a state where a part of the surface of the core part 4 is covered with the shell part 5 and the surface of the core part 4 is partially exposed.
- the electrode catalyst only needs to have a shell portion formed on at least a part of the surface of the core portion.
- FIG. 2 is a schematic cross-sectional view showing another preferred embodiment (electrode catalyst 1A) of the electrode catalyst (core-shell catalyst) of the present invention.
- the electrode catalyst 1 ⁇ / b> A of the present invention covers the core portion 4, the shell portion 5 a that covers a part of the surface of the core portion 4, and a part of the other surface of the core portion 4. It has the catalyst particle 3a comprised from the shell part 5b.
- the catalyst particle 3a included in the electrode catalyst 1A shown in FIG. 2 there is a core portion 4 that is not covered by the shell portion 5a or the shell portion 5b. Such a core part 4 becomes the core part exposed surface 4s. That is, as shown in FIG.
- the catalyst particles 3a included in the electrode catalyst 1A are in a state where the surface of the core part 4 is partially exposed (for example, a state where 4s which is a part of the surface of the core part 4 shown in FIG. 2 is exposed). It may be.
- a shell part 5a is partially formed on a part of the surface of the core part 4
- a shell part 5b is partially formed on a part of the other surface. May be.
- FIG. 3 is a schematic cross-sectional view showing another preferred embodiment (electrode catalyst 1B) of the electrode catalyst (core-shell catalyst) of the present invention.
- the electrode catalyst 1 ⁇ / b> B of the present invention includes a catalyst particle 3 including a core portion 4 and a shell portion 5 that covers substantially the entire surface of the core portion 4.
- the shell part 5 may have a two-layer structure including a first shell part 6 and a second shell part 7. That is, the catalyst particle 3 has a so-called “core / shell structure” including the core portion 4 and the shell portion 5 (the first shell portion 6 and the second shell portion 7) formed on the core portion 4.
- the electrode catalyst 1B has catalyst particles 3 supported on a carrier 2, the catalyst particles 3 have a core portion 4 as a core, and the first shell portion 6 and the second shell portion 7 become shell portions 5.
- the core portion 4 has a structure in which substantially the entire surface is covered.
- the constituent element (chemical composition) of the core part 4, the constituent element (chemical composition) of the first shell part 6, and the constituent element (chemical composition) of the second shell part 7 have different structures.
- the shell portion 5 included in the electrode catalyst 1 ⁇ / b> B of the present invention may further include another shell portion. From the viewpoint of obtaining the effect of the present invention more reliably, it is preferable that the electrode catalyst 1B is in a state in which substantially the entire surface of the core portion 4 is covered with the shell portion 5 as shown in FIG.
- FIG. 4 is a schematic cross-sectional view showing another preferred embodiment (electrode catalyst 1C) of the electrode catalyst (core-shell catalyst) of the present invention.
- the electrode catalyst 1 ⁇ / b> C of the present invention covers the core portion 4, the shell portion 5 a that covers a part of the surface of the core portion 4, and a part of the other surface of the core portion 4.
- the catalyst particle 3a is composed of a shell portion 5b.
- the shell part 5a may have a two-layer structure including a first shell part 6a and a second shell part 7a.
- the shell portion 5b may have a two-layer structure including a first shell portion 6b and a second shell portion 7b.
- the catalyst particle 3a includes a core part 4, a shell part 5a (a first shell part 6a and a second shell part 7a) formed on the core part 4, It has a so-called “core-shell structure” including a shell portion 5 b (first shell portion 6 b and second shell portion 7 b) formed on the core portion 4.
- core-shell structure including a shell portion 5 b (first shell portion 6 b and second shell portion 7 b) formed on the core portion 4.
- the shell portion 5b constituting the catalyst particle 3a shown in FIG. 4 there is a first shell portion 6b that is not covered by the second shell portion 7b.
- the first shell portion 6b that is not covered by the second shell portion 7b becomes the first shell portion exposed surface 6s.
- the shell part 5a constituting the catalyst particle 3a it is preferable that substantially the entire area of the first shell part 6a is covered with the second shell part 7a.
- a part of the surface of the first shell portion 6b is covered with the shell portion 5b constituting the catalyst particle 3a, and the first shell portion 6b
- the surface may be partially exposed (for example, a state where a part 6s of the surface of the first shell portion 6b shown in FIG. 4 is exposed).
- the electrode catalyst 1 is formed on the carrier 2 with the core portion 4 and the shell portion 5 in a state where substantially the entire surface of the core portion 4 is covered by the shell portion 5.
- a state in which a “composite” and a “composite of the core part 4 and the shell part 5 in a state where a part of the surface of the core part 4 is covered by the shell part 5” may be mixed.
- the electrode catalyst of the present invention includes the electrode catalyst 1 and 1A shown in FIGS. 1 and 2 and the electrode catalyst 1B shown in FIGS. 1C may be mixed.
- the electrode catalyst of the present invention is in a state where the shell portion 5a and the shell portion 5b are mixed with respect to the same core portion 4 as shown in FIG. Good. Furthermore, the electrode catalyst of the present invention may be in a state in which only the shell part 5a is present with respect to the same core part 4 within the range in which the effects of the present invention can be obtained. There may be a state in which only the shell portion 5b exists (none of the states is shown). In addition, within the range in which the effects of the present invention can be obtained, the electrode catalyst 1 includes, on the carrier 2, in addition to at least one of the electrode catalysts 1, 1A, 1B, 1C, “the core portion 4 is a shell portion.
- the electrode catalyst 1 includes “particles composed only of the constituent elements of the shell portion 5” in addition to at least one of the electrode catalysts 1, 1A, 1B, and 1C.
- carrier 2 in the state which does not contact the core part 4 may be contained (not shown).
- the electrode catalyst 1 includes, in addition to at least one of the electrode catalysts 1, 1A, 1B, 1C, “only the core portion 4 not covered with the shell portion 5”.
- “particles composed only of the constituent elements of the shell portion 5” may be included in a state where they are independently supported on the carrier 2.
- the average particle size of the core part 4 is preferably 2 to 40 nm, more preferably 4 to 20 nm, and particularly preferably 5 to 15 nm.
- a preferable range is suitably set by the design concept of the electrode catalyst.
- metal element for example, platinum
- it is preferably a layer composed of one atom (one atomic layer).
- the thickness of the shell portion 5 is equivalent to twice the diameter of one atom of the metal element (when approximating a sphere) when the metal element constituting the shell portion 5 is one kind.
- the thickness be When there are two or more kinds of metal elements constituting the shell part 5, a layer composed of one atom (one atom layer formed by juxtaposing two or more kinds of atoms on the surface of the core part 4). It is preferable that the thickness corresponds to.
- the thickness is preferably 1 to 10 nm, and more preferably 2 to 5 nm.
- the thickness of the first shell part 6 and the second shell part 7 depends on the electrode catalyst of the present invention.
- a preferable range is appropriately set according to the design concept.
- a noble metal such as platinum (Pt) which is a metal element contained in the second shell portion 7
- the second shell portion 7 is composed of one atom. It is preferable that it is a layer (one atomic layer).
- the thickness of the second shell portion 7 is one kind of metal element constituting the second shell portion 7, the diameter of one atom of the metal element (one atom is regarded as a sphere) A thickness equivalent to about twice the case).
- the second shell part 7 is a layer composed of one or more kinds of atoms (two or more kinds of atoms are the core part 4. It is preferable that the thickness corresponds to one atomic layer formed side by side in the surface direction.
- the thickness of the second shell portion 7 is set to 1.0 to 5.0 nm. It is preferable that In order to further improve the durability of the electrode catalyst, the thickness of the second shell portion 7 is preferably set to 2.0 to 10.0 nm.
- the “average particle diameter” refers to an average value of the diameters of particles composed of an arbitrary number of particle groups by observation with an electron micrograph.
- the support 2 is not particularly limited as long as it can support the catalyst particles 3 that are a composite body including the core portion 4 and the shell portion 5 and has a large surface area. Furthermore, it is preferable that the support
- Carrier 2 is glassy carbon (GC), fine carbon, carbon black, graphite, carbon fiber, activated carbon, pulverized product of activated carbon, carbon nanofiber, carbon nanotube, etc., or glass or ceramics material such as oxide. It can be adopted as appropriate.
- a carbon-based material is preferable from the viewpoint of the adsorptivity with the core portion 4 and the BET specific surface area of the carrier 2.
- conductive carbon is preferable, and as the conductive carbon, conductive carbon black is particularly preferable. Examples of the conductive carbon black include trade names “Ketjen Black EC300J”, “Ketjen Black EC600”, “Carbon EPC” and the like (manufactured by Lion Chemical Co., Ltd.).
- the component which comprises the core part 4 will not be specifically limited if it is a component coat
- FIG. As in the electrode catalysts 1 and 1A shown in FIGS. 1 and 2, when the shell portion 5 adopts a single layer structure instead of the above two-layer structure, a noble metal can be adopted for the core portion 4.
- the core part 4 constituting the catalyst particles 3 and 3a of the electrode catalyst 1 and 1A includes palladium (Pd), palladium (Pd) alloy, platinum (Pt) alloy, gold (Au), nickel ( Ni) and at least one metal selected from the group consisting of nickel (Ni) alloys are included.
- the palladium (Pd) alloy is not particularly limited as long as it is a combination of palladium (Pd) and another metal capable of forming an alloy.
- a two-component palladium (Pd) alloy that is a combination of palladium (Pd) and another metal, or a three-component or more palladium (Pd) that is a combination of palladium (Pd) and two or more other metals.
- Alloy examples of the two-component palladium (Pd) alloy include gold palladium (PdAu), silver palladium (PdAg), copper palladium (PdCu), and the like.
- the ternary palladium (Pd) alloy include gold and silver palladium (PdAuAg).
- the platinum (Pt) alloy is not particularly limited as long as it is a combination of platinum (Pt) and another metal capable of forming an alloy.
- a two-component platinum (Pt) alloy that is a combination of platinum (Pt) and another metal, or a three-component or more platinum (Pt) that is a combination of platinum (Pt) and two or more other metals.
- Alloy Specifically, nickel platinum (PtNi), cobalt platinum (PtCo), etc. can be illustrated as a binary platinum (Pt) alloy.
- the nickel (Ni) alloy is not particularly limited as long as it is an alloy that is a combination of nickel (Ni) and another metal capable of forming an alloy.
- a two-component nickel (Ni) alloy that is a combination of nickel (Ni) and another metal, or a three-component or more nickel (Ni) that is a combination of nickel (Ni) and two or more other metals ) Alloy.
- tungsten nickel (NiW) etc. can be illustrated as a binary nickel (Ni) alloy.
- the shell portion 5 contains at least one metal of platinum (Pt) and a platinum (Pt) alloy.
- the platinum (Pt) alloy is not particularly limited as long as it is an alloy that is a combination of platinum (Pt) and another metal capable of forming an alloy.
- a two-component platinum (Pt) alloy that is a combination of platinum (Pt) and another metal, or a three-component or more platinum (Pt) that is a combination of platinum (Pt) and two or more other metals.
- Alloy Specifically, nickel platinum (PtNi), cobalt platinum (PtCo), platinum ruthenium (PtRu), platinum molybdenum (PtMo), platinum titanium (PtTi), etc. are exemplified as the binary platinum (Pt) alloy. Can do.
- a platinum ruthenium (PtRu) alloy In order to give the shell portion 5 poisoning resistance to carbon monoxide (CO), it is preferable to use a platinum ruthenium (Pt
- the core portion 4 is preferably a metal containing a metal element other than platinum (Pt) or palladium (Pd), a metal compound, and a mixture of a metal and a metal compound, and a metal element other than a noble metal. More preferably, it is a metal, a metal compound, and a mixture of a metal and a metal compound.
- the supported amount of platinum (Pt) contained in the shell part 5 is 5 to 30% by weight, preferably 8 to 25% by weight with respect to the weight of the electrode catalyst 1. It is preferable that the supported amount of platinum (Pt) is 5% by weight or more, since the catalytic activity as the electrode catalyst can be sufficiently exhibited, and the supported amount of platinum (Pt) is 30% by weight or less. ) Is preferable from the viewpoint of manufacturing cost.
- the first shell part 6 is composed of palladium (Pd), palladium (Pd) alloy, platinum (Pt). It is preferable that at least one metal selected from the group consisting of an alloy, gold (Au), nickel (Ni), and nickel (Ni) alloy is included, and that palladium (Pd) alone is included. Is more preferable. From the viewpoint of obtaining higher and easier catalytic activity of the electrode catalysts 1B and 1C, the first shell portion 6 is more preferably composed of palladium (Pd) alone as a main component (50 wt% or more), More preferably, it is composed only of palladium (Pd) alone.
- the second shell portion 7 preferably contains at least one metal of platinum (Pt) and a platinum (Pt) alloy, and more preferably contains platinum (Pt) alone. From the viewpoint of obtaining higher and easier catalytic activity of the electrode catalysts 1B and 1C, the second shell portion 7 is more preferably composed of platinum (Pt) alone as a main component (50 wt% or more), More preferably, it is composed only of platinum (Pt) alone.
- the electrode catalyst 1 has the following formula (1) and the following formula (2).
- M represents the amount (number of atoms) of the constituent metal elements of the shell part 5 or the second shell part 7 calculated using an electrochemical surface area (ECSA) based on hydrogen desorption waves obtained by cyclic voltammetry.
- X1 indicates the amount (number of atoms) of bromine (Br) calculated based on the content of bromine (Br) species measured by fluorescent X-ray (XRF) analysis.
- X2 indicates fluorescent X-ray (XRF) The substance amount (the number of atoms) of chlorine (Cl) calculated based on the content of chlorine (Cl) species measured by the analytical method is shown.
- the electrode catalyst 1 has a value of (X2 / M) (that is, the substance amount (atomic weight) of chlorine (Cl) per substance amount (number of atoms) of the constituent metal elements of the shell part 5 or the second shell part 7). Even if it exceeds 47.0, the value of (X1 / M) (that is, the amount of bromine (Br) per amount (number of atoms) of the constituent metal elements of the shell part 5 or the second shell part 7) By setting the (number of atoms) to 1.2 or less, the catalytic activity as the electrode catalyst can be sufficiently exhibited.
- the electrode catalyst 1 is suitable for mass production in that it does not go through a special and complicated manufacturing process for removing chlorine, and is also suitable for reducing manufacturing costs.
- the amount (number of atoms) X1 of bromine (Br) in the electrode catalyst 1 and the amount (number of atoms) X2 of chlorine (Cl) are bromine (Br) species measured by X-ray fluorescence (XRF) analysis, respectively. And the chlorine species (Cl) species content.
- the value measured for the bromine (Br) species contained in the electrode catalyst 1 by a fluorescent X-ray (XRF) analysis method is the content of bromine (Br) species.
- the chlorine (Cl) species contained in the electrode catalyst 1 measured by a fluorescent X-ray (XRF) analysis method is the content of chlorine (Cl) species.
- the bromine (Br) species content and the chlorine (Cl) species content are the bromine atom converted to bromine element contained in the electrode catalyst 1 and the chlorine atom content converted to chlorine element, respectively. It has become.
- a fluorescent X-ray (XRF) analysis method irradiates a sample containing an element A with primary X-rays, generates fluorescent X-rays of the element A, and measures the intensity of the fluorescent X-rays relating to the element A, thereby Is a method for quantitative analysis of the element A contained in.
- XRF fluorescent X-ray
- FP method fundamental parameter method of theoretical calculation may be employed.
- the FP method utilizes the fact that the intensity of each fluorescent X-ray (XRF) can be theoretically calculated if the type and composition of the elements contained in the sample are all known.
- the FP method estimates a composition that matches the X-ray fluorescence (XRF) of each element obtained by measuring the sample.
- X-ray fluorescence (XRF) analysis methods include general-purpose fluorescence X such as energy dispersive X-ray fluorescence (XRF) analyzers, scanning X-ray fluorescence (XRF) analyzers, and multi-element simultaneous X-ray fluorescence (XRF) analyzers. This is done by using a line (XRF) analyzer.
- the X-ray fluorescence (XRF) analyzer includes software, and performs experimental data processing on the relationship between the intensity of the fluorescent X-ray (XRF) of the element A and the concentration of the element A by the software.
- the software is not particularly limited as long as it is generally adopted in a fluorescent X-ray (XRF) analysis method.
- fluorescent X-ray (XRF) analyzer examples include, for example, a wavelength dispersion type fully automatic fluorescent X-ray analyzer (trade name: Axios “Axios”) (manufactured by Spectris Co., Ltd.).
- the value of the above (X1 / M) of the electrode catalyst 1 is 1.2 or less. From the viewpoint of obtaining the effect of the present invention more reliably, the value of (X1 / M) is preferably 0.7 or less, more preferably 0.4 or less, and 0.2 or less. It is particularly preferred. When the value of (X1 / M) is 1.2 or less, even if the electrode catalyst 1 contains high-concentration chlorine (Cl) species, sufficient catalytic activity as an electrode catalyst is obtained. Since it can be exhibited, it is preferable.
- the electrode catalyst 1 has a value of (X2 / M) of 47.0 or less, preferably 40.0 or less, more preferably 35.0 or less, and more preferably 30.0. More preferably, it is more preferably 15.0 or less. Further, the value of (X2 / M) is particularly preferably 10.0 or less. It is preferable that the value of (X2 / M) is 47.0 or less because sufficient catalytic activity can be exhibited as the electrode catalyst 1 due to the influence of chlorine (Cl) species. Further, when the value of (X2 / M) is 47.0 or less, the electrode catalyst 1 is produced without going through the production process of removing chlorine (Cl) species in the production process of the electrode catalyst 1. This is preferable.
- the electrode catalyst 1 of the present invention can sufficiently exhibit the performance as an electrode catalyst even when the value of (X2 / M) is more than 4.5, more than 23. That is, the electrode catalyst of the present invention pays attention to the bromine (Br) species, and by defining the value of (X1 / M) to be 1.2 or less, the value of (X2 / M) is 4.5. Even if it exceeds (47.0 or less), it has a technical feature in that the performance as an electrode catalyst can be sufficiently exhibited.
- (X2 / M) In order to set the value of (X2 / M) to 47.0 or less, it is necessary to carefully select the metal compound that is the starting material of the electrode catalyst 1 and the reagents used in the production process of the electrode catalyst. It becomes. Specifically, a metal compound that does not generate chlorine (Cl) species is used as a metal compound that is a starting material of the electrode catalyst 1, and chlorine (Cl is used as a reagent used in the manufacturing process of the electrode catalyst 1. ) Adopting a compound that does not contain seeds. Furthermore, the chlorine (Cl) species can be greatly reduced by employing the chlorine reduction method described later.
- the method for producing the electrode catalyst 1 includes a step of producing an electrode catalyst precursor, and for this catalyst precursor, the value of (X1 / M) is 1.2 or less and the value of (X2 / M) is 47. Cleaning step so as to satisfy the condition of 0.0 or less.
- the electrode catalyst precursor of the electrode catalyst 1 is produced by supporting the catalyst components (core portion 4 and shell portion 5) of the electrode catalyst on the carrier 2.
- the method for producing the electrode catalyst precursor is not particularly limited as long as the catalyst component of the electrode catalyst 1 can be supported on the carrier 2.
- an impregnation method in which the carrier 2 is brought into contact with a solution containing the catalyst component of the electrode catalyst 1 and the carrier 2 is impregnated with the catalyst component, and a reducing agent is added to the solution containing the catalyst component of the electrode catalyst 1.
- Electrochemical deposition methods such as liquid phase reduction method, underpotential deposition (UPD) method, chemical reduction method, reduction deposition method using adsorbed hydrogen, surface leaching method of alloy catalyst, displacement plating method, sputtering method, vacuum deposition method, etc.
- the employed manufacturing method can be exemplified.
- the concentration of bromine (Br) species in the electrode catalyst precursor so as to satisfy the condition that the value of (X1 / M) is 1.2 or less and the value of (X2 / M) is 47.0 or less.
- adjusting the concentration of chlorine (Cl) species Specifically, the following chlorine reduction methods 1 to 3 are adopted.
- [Chlorine reduction method 1] First step: The catalyst precursor (I) for electrodes (I) (for example, the concentration of chlorine (Cl) species measured by fluorescent X-ray (XRF) analysis) in ultrapure water exceeds a preset chlorine concentration of 76000 ppm (for example, The electrode catalyst precursor (I) in which the preset chlorine concentration is 8500 ppm or 7600 ppm and exceeds these concentration values is added to disperse the electrode catalyst precursor (I) in ultrapure water.
- Washing is repeated until the electrical conductivity ⁇ measured by (1) is equal to or lower than a preset value (for example, equal to or lower than a preset value within a range of 10 to 100 ⁇ S / cm).
- a preset value for example, equal to or lower than a preset value within a range of 10 to 100 ⁇ S / cm.
- Electrode catalyst precursor for example, ultra-pure water, reducing agent, and chlorine (Cl) species concentration measured by fluorescent X-ray (XRF) analysis method exceeds a preset chlorine concentration of 6000 ppm (for example, And at least one step set in advance in the range of 20 ° C. to 90 ° C., the electrode catalyst precursor for the electrode having a chlorine concentration of 8500 ppm or 6000 ppm exceeding the concentration value.
- a method comprising a first step of holding at a temperature and for a preset holding time.
- [Chlorine reduction method 3] First step: manufactured using a material containing ultrapure water, a gas containing hydrogen, and a chlorine (Cl) species, and a chlorine (Cl) species measured by X-ray fluorescence (XRF) analysis An electrode catalyst precursor having a concentration of the first chlorine (Cl) species exceeding the preset concentration of the first chlorine (Cl) species, at a preset temperature of at least one step in the range of 20 to 40 ° C., And a first step of holding for a preset holding time.
- XRF X-ray fluorescence
- the “ultra pure water” used in the chlorine reduction methods 1 to 3 has a specific resistance R (electric conductivity measured by the JIS standard test method (JIS K0552) represented by the following general formula (3). Water whose reciprocal number is 3.0 M ⁇ ⁇ cm or more. Further, “ultra pure water” preferably has a water quality equivalent to “A3” defined in JIS K0557 “water used in water / drainage tests” or a clean water quality higher than that.
- R represents specific resistance
- ⁇ represents electrical conductivity measured by JIS standard test method (JIS K0552).
- the ultrapure water is not particularly limited as long as it has electrical conductivity satisfying the relationship represented by the general formula (3).
- ultrapure water produced using the ultrapure water production equipment “Milli-Q Series” (Merck Co., Ltd.) and “Elix UV Series” (Nihon Millipore Co., Ltd.) be able to.
- chlorine (Cl) species contained in the electrode catalyst precursor can be reduced.
- an electrode catalyst precursor for which the concentration of bromine (Br) species measured by fluorescent X-ray (XRF) analysis is 500 ppm or less and the concentration of chlorine (Cl) species is 8500 ppm or less is used for the electrode of the present invention. Use as a catalyst.
- the electrode catalyst has a chlorine (Cl) species concentration of 8500 ppm or less and a bromine (Br) species concentration of 500 ppm or less as measured by the fluorescent X-ray (XRF) analysis method.
- the required catalytic activity can be exhibited.
- the X-ray fluorescence (XRF) analysis method is performed as follows, for example. (1) Measuring device / Wavelength dispersive X-ray fluorescence analyzer Axios (manufactured by Spectris Co., Ltd.) (2) Measurement conditions and analysis software: “UniQuant5” (semi-quantitative software using FP (four peak method) method) -XRF measurement room atmosphere: helium (normal pressure) (3) Measurement procedure (i) The sample container containing the sample is placed in the XRF sample chamber. (ii) Replace the XRF sample chamber with helium gas.
- FIG. 5 shows a gas diffusion electrode forming composition containing the electrode catalyst of the present invention, a gas diffusion electrode produced using this gas diffusion electrode forming composition, and a membrane / electrode assembly comprising this gas diffusion electrode
- FIG. 1 is a schematic view showing a preferred embodiment of a fuel cell stack including MEA) and this membrane-electrode assembly (MEA).
- the fuel cell stack S shown in FIG. 5 has a configuration in which a membrane / electrode assembly (MEA) 400 is a unit cell and a plurality of the unit cells are stacked.
- MEA membrane / electrode assembly
- the fuel cell stack S has a membrane / electrode assembly (MEA) 400 including an anode 200a, a cathode 200b, and an electrolyte membrane 300 disposed between these electrodes.
- MEA membrane / electrode assembly
- the fuel cell stack S has a configuration in which the membrane / electrode assembly (MEA) 400 is sandwiched between the separator 100a and the separator 100b.
- the gas diffusion electrode forming composition, the gas diffusion electrode 200a and the gas diffusion electrode 200b, and the membrane / electrode assembly (MEA) 400, which are members of the fuel cell stack S including the electrode catalyst of the present invention, will be described.
- the electrode catalyst 1 can be used as a so-called catalyst ink component to form the gas diffusion electrode forming composition of the present invention.
- the composition for forming a gas diffusion electrode of the present invention is characterized by containing the above-mentioned electrode catalyst.
- the composition for forming a gas diffusion electrode contains the electrode catalyst and an ionomer solution as main components.
- the ionomer solution contains water, alcohol, and a polymer electrolyte having hydrogen ion conductivity.
- the mixing ratio of water and alcohol in the ionomer solution may be any ratio that provides a viscosity suitable for applying the gas diffusion electrode forming composition to the electrode.
- alcohol is added to 100 parts by weight of water. It is preferable to contain 0.1 to 50.0 parts by weight.
- the alcohol contained in the ionomer solution is preferably a monohydric alcohol or a polyhydric alcohol. Examples of the monohydric alcohol include methanol, ethanol, propanol, butanol and the like. Examples of the polyhydric alcohol include dihydric alcohols and trihydric alcohols.
- Examples of the dihydric alcohol include ethylene glycol, diethylene glycol, tetraethylene glycol, propylene glycol, 1,3-butanediol, and 1,4-butanediol.
- Examples of the trihydric alcohol include glycerin.
- the alcohol contained in the ionomer solution may be a single type or a combination of two or more types of alcohol.
- an additive such as a surfactant can be appropriately contained in the ionomer solution as necessary.
- the ionomer solution contains a polymer electrolyte having hydrogen ion conductivity as a binder component in order to improve adhesion to the gas diffusion layer that is a member constituting the gas diffusion electrode.
- the polymer electrolyte is not particularly limited, and examples thereof include known perfluorocarbon resins having a sulfonic acid group and a carboxylic acid group.
- polymer electrolytes having hydrogen ion conductivity Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) It can be illustrated.
- the gas diffusion electrode forming composition can be prepared by mixing an electrode catalyst and an ionomer solution, crushing, and stirring.
- the composition for forming a gas diffusion electrode can be prepared using a pulverizing mixer such as a ball mill or an ultrasonic disperser.
- the pulverization conditions and the stirring conditions when operating the pulverization mixer can be appropriately set according to the mode of the gas diffusion electrode forming composition.
- Each composition of the electrode catalyst, water, alcohol, and polymer electrolyte having hydrogen ion conductivity contained in the gas diffusion electrode forming composition has a good dispersion state of the electrode catalyst, and the electrode catalyst is gas diffused. It is necessary to set so that the entire catalyst layer of the electrode can be widely spread and the power generation performance of the fuel cell can be improved.
- the coating film made of the gas diffusion electrode forming composition is preferable because it does not spread too much on the gas diffusion electrode, and the coating made of the gas diffusion electrode forming composition is also preferred. It is preferable because the film can form a coating film having an appropriate and uniform thickness.
- the weight of the polymer electrolyte is a weight in a dry state and does not include a solvent in the polymer electrolyte solution, and the weight of water is a weight including water contained in the polymer electrolyte solution.
- the gas diffusion electrodes (200a, 200b) of the present invention include a gas diffusion layer 220 and an electrode catalyst layer 240 laminated on at least one surface of the gas diffusion layer 220.
- the electrode catalyst layer 240 provided in the gas diffusion electrodes (200a, 200b) contains the electrode catalyst.
- the gas diffusion electrode 200 of the present invention can be used as an anode and also as a cathode. In FIG. 5, for convenience, the upper gas diffusion electrode 200 is referred to as an anode 200a, and the lower gas diffusion electrode 200 is referred to as a cathode 200b.
- the electrode catalyst layer 240 is a layer in which, in the anode 200a, a chemical reaction is performed in which the hydrogen gas sent from the gas diffusion layer 220 is dissociated into hydrogen ions by the action of the electrode catalyst 1 included in the electrode catalyst layer 240. It is. Further, the electrode catalyst layer 240 is an electrode in which the electrode catalyst layer 240 includes air (oxygen gas) sent from the gas diffusion layer 220 and hydrogen ions moving from the anode through the electrolyte membrane in the cathode 200b. It is a layer in which a chemical reaction is performed by the action of the catalyst 1 for use.
- the electrode catalyst layer 240 is formed using the gas diffusion electrode forming composition.
- the electrode catalyst layer 240 has a large surface area so that the reaction between the electrode catalyst 1 and the hydrogen gas or air (oxygen gas) sent from the gas diffusion layer 220 can be sufficiently performed.
- the electrode catalyst layer 240 is preferably formed so as to have a uniform thickness throughout. The thickness of the electrode catalyst layer 240 may be appropriately adjusted and is not limited, but is preferably 2 to 200 ⁇ m.
- the gas diffusion layer 220 provided in the gas diffusion electrode 200 includes hydrogen gas introduced from the outside of the fuel cell stack S into a gas flow path formed between the separator 100a and the gas diffusion layer 220a, the separator 100b, This is a layer provided for diffusing air (oxygen gas) introduced into the gas flow path formed between the gas diffusion layers 220b into each electrode catalyst layer 240.
- the gas diffusion layer 220 has a role of supporting the electrode catalyst layer 240 on the gas diffusion electrode 200 and immobilizing it on the surface of the gas diffusion electrode 200.
- the gas diffusion layer 220 has a role of increasing contact between the electrode catalyst 1 included in the electrode catalyst layer 240 and hydrogen gas or air (oxygen gas).
- the gas diffusion layer 220 has a function of allowing the hydrogen gas or air (oxygen gas) supplied from the gas diffusion layer 220 to pass through well and reaching the electrode catalyst layer 240. Therefore, the gas diffusion layer 220 has a water repellent property so that the pore structure, which is a microstructure in the gas diffusion layer 220, is not blocked by the water generated in the electrode catalyst 1 and the cathode 200b. It is preferable to have. For this reason, the gas diffusion layer 220 has a water repellent component such as polyethylene terephthalate (PTFE).
- PTFE polyethylene terephthalate
- the member that can be used for the gas diffusion layer 220 is not particularly limited, and a known member used for the gas diffusion layer of the fuel cell electrode can be used.
- a known member used for the gas diffusion layer of the fuel cell electrode can be used.
- carbon paper, carbon paper as a main raw material, and carbon powder, ion-exchanged water as optional components, and a secondary material made of polyethylene terephthalate dispersion as a binder are applied to carbon paper.
- the thickness of the gas diffusion layer can be appropriately set depending on the size of the fuel cell and the like, and is not particularly limited. However, in order to shorten the reaction gas diffusion distance, a thin one is preferable. On the other hand, since it is also required to have mechanical strength in the coating and assembling processes, for example, those having a thickness of about 50 to 300 ⁇ m are usually used.
- the gas diffusion electrode 200a and the gas diffusion electrode 200b may include an intermediate layer (not shown) between the gas diffusion layer 220 and the electrode catalyst layer 240.
- the gas diffusion electrode 200a and the gas diffusion electrode 200b have a three-layer structure including a gas diffusion layer, an intermediate layer, and a catalyst layer.
- the method for producing a gas diffusion electrode comprises a composition for forming a gas diffusion electrode comprising an electrode catalyst 1 having a catalyst component supported on a carrier, a polymer electrolyte having hydrogen ion conductivity, and an ionomer solution of water and alcohol. And a step of drying the gas diffusion layer 220 coated with the gas diffusion electrode forming composition to form an electrode catalyst layer 240.
- What is important in the process of applying the gas diffusion electrode forming composition onto the gas diffusion layer 220 is to uniformly apply the gas diffusion electrode forming composition onto the gas diffusion layer 220.
- a coating film made of the gas diffusion electrode forming composition having a uniform thickness is formed on the gas diffusion layer 220.
- the coating amount of the gas diffusion electrode forming composition can be appropriately set depending on the usage form of the fuel cell. From the viewpoint of the cell performance of the fuel cell equipped with the gas diffusion electrode, platinum contained in the electrode catalyst layer 240 is used.
- the amount of the active metal such as 0.1 to 0.5 (mg / cm 2 ) is preferable.
- the coating film of the gas diffusion electrode forming composition applied to the gas diffusion layer 220 is dried to obtain the gas diffusion layer 220.
- An electrode catalyst layer 240 is formed thereon.
- the coating film of the gas diffusion electrode forming composition present on the gas diffusion layer 220 is an electrode catalyst containing an electrode catalyst and a polymer electrolyte.
- Layer 240 is formed.
- the membrane-electrode assembly 400 (hereinafter referred to as MEA) of the present invention is an anode 200a and a cathode 200b that are gas diffusion electrodes 200 using the electrode catalyst 1 and an electrolyte that partitions these electrodes. 300.
- the membrane / electrode assembly (MEA) 400 can be manufactured by laminating the anode 200a, the electrolyte 300, and the cathode 200b in this order, and then pressing them.
- the separator 100a (anode side) is attached to the outside of the anode 200a of the obtained membrane-electrode assembly (MEA) 400, and the separator 100b (cathode side) is attached to the outside of the cathode 200b.
- One unit cell (single cell).
- the unit cell (unit cell) is integrated to form a fuel cell stack S.
- the fuel cell system is completed by attaching and assembling peripheral devices to the fuel cell stack S.
- Example 1 The electrode catalyst of the present invention was produced by the following process.
- the raw materials for the electrode catalyst used are as follows.
- Carbon black powder Trade name “Ketjen Black EC300” (Ketjen Black International) ⁇ Sodium tetrachloropalladium (II) ⁇ Palladium nitrate ⁇ Potassium chloroplatinate
- Platinum (Pt) coating on palladium (core) By dripping a potassium chloroplatinate aqueous solution containing platinum (Pt) equivalent to twice the substance amount ratio with respect to the coated copper into a solution containing copper-palladium-supported carbon coated with palladium on palladium. The copper (Cu) in the copper-palladium supported carbon was replaced with platinum (Pt).
- the supported amount (% by mass) of platinum and palladium was measured by the following method.
- the electrode catalyst of Example 1 was immersed in aqua regia to dissolve the metal.
- insoluble component carbon was removed from the aqua regia.
- aqua regia without carbon was analyzed by ICP.
- the amount of supported platinum was 19.3% by mass and the amount of supported palladium was 24.1% by mass.
- Examples 2 to 15 and Example 17 In the same manner as in Example 1, except that the supported amount of platinum (Pt) and palladium (Pd) contained in the electrode catalyst was the concentration (mass% concentration) described in Tables 1 and 2. 2 to 15 and Example 17 electrode catalysts were prepared.
- Example 16 Except for changing the palladium salt that is the raw material of the electrode catalyst so that the supported amount of platinum (Pt) and palladium (Pd) contained in the electrode catalyst is the concentration (mass% concentration) described in Table 1. In the same manner as in Example 1, the electrode catalyst of Example 16 was prepared.
- Example 18 An electrode catalyst was prepared in the same manner as in Example 1. This was further immersed in an aqueous sulfuric acid solution (1M) at room temperature for a predetermined time. Next, the electrode catalyst in the sulfuric acid aqueous solution was filtered and washed with ultrapure water. Next, the electrode catalyst was immersed in an oxalic acid aqueous solution (0.3 M) and kept at 90 ° C. for a predetermined time. Next, the electrode catalyst in the oxalic acid aqueous solution was filtered and washed with ultrapure water. Next, the electrode catalyst after washing with ultrapure water was dried at 70 ° C. As a result, an electrode catalyst of Example 18 was obtained. Further, ICP analysis was performed in the same manner as in Example 1 to measure the amount of platinum supported and the amount of palladium supported.
- Example 19 to 20 An electrode catalyst was prepared in the same manner as in Example 1. This was further immersed in an aqueous sodium formate solution (0.01 M) and kept at room temperature for a predetermined time. Next, the electrode catalyst in the sodium formate aqueous solution was filtered and washed with ultrapure water. Next, the electrode catalyst after washing with ultrapure water was dried at 70 ° C. This obtained the electrode catalyst of Examples 19-20. Further, ICP analysis was performed in the same manner as in Example 1 to measure the amount of platinum supported and the amount of palladium supported.
- Example 21 An electrode catalyst was prepared in the same manner as in Example 1. This was further immersed in an aqueous sodium formate solution (0.01 M) and kept at room temperature for a predetermined time. Next, the electrode catalyst in the sodium formate aqueous solution was filtered and washed with ultrapure water. This was further immersed in an aqueous sulfuric acid solution (1M) at room temperature for a predetermined time. Next, the electrode catalyst in the sulfuric acid aqueous solution was filtered and washed with ultrapure water. Next, the electrode catalyst was immersed in an oxalic acid aqueous solution (0.3 M) and kept at 90 ° C. for a predetermined time.
- Example 21 an electrode catalyst of Example 21 was obtained. Further, ICP analysis was performed in the same manner as in Example 1 to measure the amount of platinum supported and the amount of palladium supported.
- Example 22 An electrode catalyst was prepared in the same manner as in Example 1. This was further immersed in an aqueous sodium formate solution (0.01 M) and kept at 90 ° C. for a predetermined time. Next, the electrode catalyst in the sodium formate aqueous solution was filtered and washed with ultrapure water. Next, the electrode catalyst after washing with ultrapure water was dried at 70 ° C. This obtained the electrode catalyst of Example 22. Further, ICP analysis was performed in the same manner as in Example 1 to measure the amount of platinum supported and the amount of palladium supported.
- Example 23 An electrode catalyst was prepared in the same manner as in Example 1. Next, the electrode catalyst was immersed in an oxalic acid aqueous solution (0.3 M) and kept at 90 ° C. for a predetermined time. Next, the electrode catalyst in the oxalic acid aqueous solution was filtered and washed with ultrapure water. Next, the electrode catalyst after washing with ultrapure water was dried at 70 ° C. As a result, an electrode catalyst of Example 23 was obtained. Further, ICP analysis was performed in the same manner as in Example 1 to measure the amount of platinum supported and the amount of palladium supported.
- Comparative Examples 1 to 7 The electrode catalysts of Comparative Examples 1 to 7 were produced in the same manner as in Example 1 except that potassium chloroplatinate having a bromine content of 10000 ppm to 13000 ppm was used as the raw material and the bromine species concentrations shown in Table 3 were used. did.
- the sample for measuring the electrode catalyst was placed in an XRF sample container attached to the wavelength dispersion type fluorescent X-ray measurement apparatus.
- An XRF sample container containing a measurement sample of the electrode catalyst is placed in the XRF sample chamber, and the XRF sample chamber is replaced with helium gas. Thereafter, fluorescent X-ray measurement was performed under a helium gas atmosphere (normal pressure).
- analysis software “UniQuant5” for wavelength dispersive X-ray fluorescence measurement apparatus was used.
- the measurement conditions are set to “UQ5 application” in accordance with the analysis software “UniQuant5”, the main component of the electrode catalyst measurement sample is “carbon (component element of electrode catalyst carrier)”, and the sample analysis result display
- the calculation mode is set so that the format is “element”.
- the measurement results were analyzed by analysis software “UniQuant5”, and the concentrations of bromine (Br) species and chlorine (Cl) species were calculated.
- bromine (Br) species and chlorine (Cl) species calculated by X-ray fluorescence (XRF) analysis, the amount of bromine (Br) (number of atoms) X1 and chlorine (Cl) The amount of substance (atomic weight X2 was calculated, respectively.
- This Nafion-pure aqueous solution (2.5 mL) is slowly put into a sample bottle containing an electrode catalyst slurry (suspension), irradiated with ultrasonic waves at room temperature for 15 minutes, stirred thoroughly, and gas diffused. It was set as the composition for electrode formation.
- FIG. 6 is a schematic diagram showing a schematic configuration of a rotating disk electrode measuring apparatus D used in the rotating disk electrode method (RDE method).
- the rotating disk electrode measuring device D mainly includes a measuring device cell 10, a reference electrode (RE) 20, a counter electrode (CE) 30, a rotating disk electrode 40, and an electrolytic solution 60. It is configured.
- An electrode catalyst layer X was formed on the surface of the rotating disk electrode 40 provided in the rotating disk electrode measuring apparatus D. Then, the catalyst in the electrode catalyst layer X was evaluated by the rotating disk electrode method.
- a rotating disk electrode measuring apparatus D (model manufactured by Hokuto Denko Co., Ltd.) equipped with 0.1M HClO 4 as the electrolyte 60, an Ag / AgCl saturated electrode as the reference electrode (RE) 20, and a Pt black Pt mesh as the counter electrode 30 HSV110) was used.
- the electrode catalyst layer X on the surface of the rotating disk electrode 40 10 ⁇ L of the prepared gas diffusion electrode forming composition was taken and dropped onto the surface of a clean rotating disk electrode (made of glassy carbon, diameter 5.0 mm ⁇ , area 19.6 mm 2 ). Thereafter, the composition for forming the gas diffusion electrode is spread over the entire surface of the rotating disk electrode so as to have a uniform and constant thickness, and a coating film made of the composition for forming the gas diffusion electrode is formed on the surface of the rotating disk electrode. I let you. The coating film made of this gas diffusion electrode forming composition was dried at a temperature of 23 ° C. and a humidity of 50% RH for 2.5 hours to form an electrode catalyst layer X on the surface of the rotating disk electrode 40.
- the measurement by the rotating disk electrode method includes cleaning in the rotating disk electrode measuring device, evaluation of electrochemical surface area (ECSA) before measurement, measurement of oxygen reduction (ORR) current, and evaluation of electrochemical surface (ECSA) after measurement. .
- the rotating disk electrode measuring device D the rotating disk electrode 40 was immersed in the HClO 4 electrolyte 60, and then the electrolyte 60 was purged with argon gas for 30 minutes or more. Thereafter, potential scanning was performed for 20 cycles under the conditions of a scanning potential of 85 to 1085 mV vs RHE and a scanning speed of 50 mV / sec.
- i represents a measured value of oxygen reduction current (ORR current)
- iL represents a measured value of limiting diffusion current
- ik represents catalytic activity.
- bromine substance amount (number of atoms) X1 calculated based on the bromine species content calculated above and the chlorine substance amount (number of atoms) X2 calculated based on the chlorine species content are M, respectively.
- the divided value was calculated.
- the calculation results are shown in Tables 1 to 3.
- the electrode catalyst of the present invention is suitable for mass production, which can exhibit sufficient catalytic performance even if it has a high chlorine content, and can simplify the manufacturing process and reduce the manufacturing cost.
- Catalyst. Accordingly, the present invention is an electrode catalyst that can be applied not only to the electric equipment industry such as fuel cells, fuel cell vehicles, and portable mobiles, but also to energy farms, cogeneration systems, etc. Contribute to development.
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Abstract
Description
従来、PEFC用の電極用触媒について、当該電極用触媒に含まれる塩素含有量が100ppm以上であると、電極用触媒として望ましくないことが開示されている(例えば、特許文献2)。その理由について、電極用触媒に含まれる塩素含有量が100ppm以上であると、燃料電池用の電極用触媒として十分な触媒活性を得ることができないこと、触媒層の腐食が発生し、燃料電池の寿命が短縮してしまうことが開示されている。
上記白金(Pt)又は白金(Pt)合金の粉末の調製法としては以下の方法が開示されている。すなわち、出発物質として、塩素を含まない白金化合物と塩素を含まない合金化元素の溶融物を形成した後、この溶融物の酸化物を与えるまで加熱し、当該酸化物を冷却後、水に溶解して形成される酸化物を還元するプロセスを経る調製方法が開示されている。
しかしながら、PEFCの実用化に向けて製造プロセスの簡略化や製造コストの低減を図る観点からは、上述の従来技術においても改善の余地があった。
すなわち、上述の100ppm未満の塩素含有量を有する電極用触媒は、特許文献2等に開示された塩素を除去するための複雑なプロセスを経由して調製しなければならず、改善の余地があった。
このように、将来のPEFCの量産化を想定した場合、100ppmを超える比較的高濃度の塩素を含有している場合であっても、十分な性能を得ることができるとともに、塩素除去のための特別で複雑なプロセスを経ずに調製できる量産化及び製造コストの低減にも適した電極用触媒が必要となると考えられる。
また、本発明は、塩素除去の特別で複雑な製造プロセスを経ないという点で量産化に適しており、製造コストの低減にも適した電極用触媒を提供することを目的とする。
さらに、本発明は、上記電極用触媒を含む、ガス拡散電極形成用組成物、ガス拡散電極、膜・電極接合体(MEA)、及び、燃料電池スタックを提供することを目的とする。
より具体的には、本発明は、以下の技術的事項から構成される。
(1) 担体と、前記担体上に形成されるコア部と、前記コア部の表面の少なくとも一部を覆うように形成されるシェル部とを含むコア・シェル構造を有する電極用触媒であって、
下記式(1)及び下記式(2)
(X1/M)≦1.2 ・・・(1)
(X2/M)≦47.0 ・・・(2)
で表される条件を同時に満たしている、電極用触媒
[前記式(1)及び前記式(2)中、
Mは、サイクリックボルタンメトリーにより得られる水素脱着波に基づく電気化学的表面積(ECSA)を用いて算出される前記シェル部の構成金属元素の物質量(原子数)を示し、
X1は、蛍光X線(XRF)分析法により測定される臭素(Br)種の含有量に基づき算出される臭素(Br)の物質量(原子数)を示し
X2は、蛍光X線(XRF)分析法により測定される塩素(Cl)種の含有量に基づき算出される塩素(Cl)の物質量(原子数)を示す。]
を提供する。
(2) 前記シェル部には、白金(Pt)及び白金(Pt)合金のうちの少なくとも1種の金属が含有されており、前記コア部には、パラジウム(Pd)、パラジウム(Pd)合金、白金(Pt)合金、金(Au)、ニッケル(Ni)、及び、ニッケル(Ni)合金からなる群より選択される少なくとも1種の金属が含まれている、(1)記載の電極用触媒を提供する。
これにより、本発明の効果がより確実に得られるようになる。また、上記の構成とすることにより、より高い触媒活性とより高い耐久性を得ることができる。
(3) 前記担体には、導電性カーボンが含有されており、前記シェル部には、白金(Pt)が含有されており、前記コア部には、パラジウム(Pd)が含有されている、(1)又は(2)に記載の電極用触媒を提供する。
これにより、本発明の効果がより確実に得られるようになる。また、上記の構成とすることにより、より高い触媒活性とより高い耐久性を得ることができる。更に、上記構成とすることにより、本発明の電極用触媒は、カーボン担体上に白金が担持された構成の従来の電極用触媒に比較して、白金の含有量を低減できるので、原料コストを削減することが容易にできる。
(4) 前記Mは、サイクリックボルタンメトリーにより得られる水素脱着波に基づく電気化学的表面積(ECSA)を用いて算出される前記シェル部の構成金属元素である白金(Pt)の物質量(原子数)を示す、(3)に記載の電極用触媒を提供する。
これにより、本発明の効果がより確実に得られるようになる。また、上記の構成とすることにより、より高い触媒活性とより高い耐久性を得ることができる。更に、上記構成とすることにより、本発明の電極用触媒は、カーボン担体上に白金が担持された構成の従来の電極用触媒に比較して、白金の含有量を低減できるので、原料コストを削減することが容易にできる。
(5) 前記シェル部が、前記コア部の表面の少なくとも一部を覆うように形成される第1シェル部と、当該第1シェル部の表面の少なくとも一部を覆うように形成される第2シェル部と、を有しており、
前記式(1)及び前記式(2)における前記Mは前記第2シェル部の構成金属元素の物質量(原子数)を示す、(1)に記載の電極用触媒を提供する。
これにより、本発明の効果がより確実に得られるようになる。上記の構成とすることにより、本発明の電極用触媒は、コア部に使用される白金等の貴金属の含有量を低減できるので、原料コストを削減することが容易にできる。
(6) 前記第1シェル部には、パラジウム(Pd)が含有されており、
前記第2シェル部には白金(Pt)が含有されている、
(5)に記載の電極用触媒を提供する。
これにより、本発明の効果がより確実に得られるようになる。上記の構成とすることにより、より高い触媒活性とより高い耐久性を得ることができる。
(7) 前記式(2)中の(X2/M)が4.5超である、(1)~(6)のいずれか1に記載の電極用触媒を提供する。
これにより、本発明の効果がより確実に得られるようになる。
(8) (1)~(7)いずれか1に記載の電極用触媒が含有されている、ガス拡散電極形成用組成物を提供する。
本発明のガス拡散電極形成用組成物によれば、本発明の電極用触媒を含んでいるため、高い触媒活性(分極特性)を有するガス拡散電極を容易に製造することができる。
(9) (1)~(7)いずれか1に記載の電極用触媒が含有されている、ガス拡散電極を提供する。
本発明のガス拡散電極によれば、本発明の電極用触媒を含んでいるため、高い触媒活性(分極特性)を得ることができる。
(10) (9)記載のガス拡散電極が含まれている、膜・電極接合体(MEA)を提供する。
本発明の膜・電極接合体(MEA)によれば、本発明のガス拡散電極を含んでいるため、高い電池特性を得ることができる。
(11) (10)記載の膜・電極接合体(MEA)が含まれていることを特徴とする燃料電池スタックを提供する。
本発明の燃料電池スタックによれば、本発明の膜・電極接合体(MEA)を含んでいるため、高い電池特性を得ることができる。
また、本発明によれば、塩素除去の特別で複雑な製造プロセスを経ないという点で電極用触媒の量産化に適しており、製造コストの低減に適した電極用触媒が提供される。
更に、本発明によれば、かかる電極用触媒を含む、ガス拡散電極形成用組成物、ガス拡散電極、膜・電極接合体(MEA)、燃料電池スタックが提供される。
<電極用触媒>
図1は、本発明の電極用触媒(コア・シェル触媒)の好適な一形態を示す模式断面図である。
図1に示されるように、本発明の電極用触媒1は、担体2と、担体2上に担持された、いわゆる「コア・シェル構造」を有する触媒粒子3を含んでいる。触媒粒子3は、コア部4と、コア部4の表面の少なくとも一部を被覆するように形成されたシェル部5とを備えている。触媒粒子3はコア部4と、コア部4上に形成されるシェル部5とを含む、いわゆる「コア・シェル構造」を有する。
すなわち、電極用触媒1は、担体2に担持された触媒粒子3を有しており、この触媒粒子3は、コア部4を核(コア)とし、シェル部4がシェルとなってコア部4の表面の少なくとも一部を被覆している構造を備えている。
また、コア部4の構成元素(化学組成)と、シェル部5の構成元素(化学組成)は異なる構成となっている。
例えば、本発明の効果をより確実に得る観点からは、図1に示すように、電極用触媒1は、シェル部5によってコア部4の表面の略全域が被覆された状態であることが好ましい。
また、本発明の効果を得られる範囲において、電極用触媒1は、シェル部5によってコア部4の表面の一部が被覆され、コア部4の表面が部分的に露出した状態であってもよい。
すなわち、本発明において、電極用触媒は、コア部の表面の少なくとも一部にシェル部が形成されていればよい。
図2に示されるように、本発明の電極用触媒1Aは、コア部4と、コア部4の表面の一部を被覆するシェル部5a及びコア部4の他の表面の一部を被覆するシェル部5bから構成されている触媒粒子3aを有している。
図2に示された電極用触媒1Aが含んでいる触媒粒子3aにおいて、シェル部5aによっても、シェル部5bによっても被覆されていないコア部4が存在する。このようなコア部4が、コア部露出面4sとなる。
すなわち、図2に示されるように、本発明の効果を得ることができる範囲において、
電極用触媒1Aが含んでいる触媒粒子3aは、コア部4の表面が部分的に露出した状態(例えば、図2に示されたコア部4の表面の一部である4sが露出した状態)であってもよい。
別の表現をすれば、図2に示された電極用触媒1Aのように、コア部4の表面の一部にシェル部5a、他の表面の一部にシェル部5bがそれぞれ部分的に形成されていてもよい。
図3に示されるように、本発明の電極用触媒1Bは、コア部4と、コア部4の表面の略全域を被覆するシェル部5から構成されている触媒粒子3を有している。
シェル部5は、第1シェル部6と第2シェル部7とを備えた二層構造であってもよい。すなわち、触媒粒子3は、コア部4とコア部4上に形成されるシェル部5(第1シェル部6及び第2シェル部7)とを含む、いわゆる「コア・シェル構造」を有する。
電極用触媒1Bは、担体2に担持された触媒粒子3を有し、触媒粒子3がコア部4を核(コア)とし、第1シェル部6及び第2シェル部7がシェル部5となってコア部4の表面の略全域が被覆されている構造を有している。
なお、コア部4の構成元素(化学組成)と、第1シェル部6の構成元素(化学組成)と、第2シェル部7の構成元素(化学組成)とは、それぞれ異なる構成となっている。
また、本発明の電極用触媒1Bが備えているシェル部5は、第1シェル部6、第2シェル部7に加えて、さらに別のシェル部を備えているものであってもよい。
本発明の効果をより確実に得る観点からは、図3に示すように、電極用触媒1Bは、シェル部5によってコア部4の表面の略全域が被覆された状態であることが好ましい。
図4に示されるように、本発明の電極用触媒1Cは、コア部4と、コア部4の表面の一部を被覆するシェル部5a、及びコア部4の他の表面の一部を被覆するシェル部5bから構成されている触媒粒子3aを有している。
シェル部5aは、第1シェル部6aと第2シェル部7aとを備えた二層構造であってもよい。
また、シェル部5bは、第1シェル部6bと第2シェル部7bとを備えた二層構造であってもよい。
すなわち、触媒粒子3aは、コア部4と、コア部4上に形成されるシェル部5a(第1シェル部6a及び第2シェル部7a)と、
コア部4上に形成されるシェル部5b(第1シェル部6b及び第2シェル部7b)と、を含む、いわゆる「コア・シェル構造」を有する。
図4に示された触媒粒子3aを構成するシェル部5bにおいて、第2シェル部7bよって被覆されていない第1シェル部6bが存在する。第2シェル部7bよって被覆されていない第1シェル部6bが第1シェル部露出面6sとなる。
図4に示されるように触媒粒子3aを構成するシェル部5aにおいて、第1シェル部6aの略全域が第2シェル部7aによって被覆された状態であることが好ましい。
また、図4に示されるように本発明の効果を得られる範囲において、触媒粒子3aを構成するシェル部5bにおいて、第1シェル部6bの表面の一部が被覆され、第1シェル部6bの表面が部分的に露出した状態(例えば、図4に示された第1シェル部6bの表面の一部6sが露出した状態)であってもよい。
具体的には、本発明の電極用触媒は、本発明の効果を得られる範囲において、図1及び2に示した電極用触媒1、1Aと、図3及び4に示した電極用触媒1B、1Cとが混在した状態であってもよい。
更に、本発明の電極用触媒は、本発明の効果を得られる範囲において、図4に示されるように同一のコア部4に対し、シェル部5aとシェル部5bとか混在した状態であってもよい。
更に、本発明の電極用触媒は、本発明の効果を得られる範囲において、同一のコア部4に対し、シェル部5aのみが存在する状態であってもよく、同一のコア部4に対し、シェル部5bのみが存在する状態であってもよい(いずれの状態も図示せず)。
また、本発明の効果を得られる範囲において、電極用触媒1には、担体2上に、上記電極用触媒1、1A、1B、1Cの少なくとも1種に加えて、「コア部4がシェル部5によって被覆されていないコア部のみからなる粒子」が担持された状態が含まれていてもよい(図示せず)。
更に、本発明の効果を得られる範囲において、電極用触媒1には、上記電極用触媒1、1A、1B、1Cの少なくとも1種に加えて「シェル部5の構成元素のみからなる粒子」がコア部4に接触しない状態で担体2に担持された状態が含まれていてもよい(図示せず)。
また、本発明の効果を得られる範囲において、電極用触媒1には、上記電極用触媒1、1A、1B、1Cの少なくとも1種に加えて「シェル部5に被覆されていないコア部4のみの粒子」と、「シェル部5の構成元素のみからなる粒子」とが、それぞれ独立に担体2に担持された状態が含まれていてもよい。
シェル部5の厚さ(コア部4との接触面から当該シェル部5の外表面までの厚さ)については、電極用触媒の設計思想によって好ましい範囲が適宜設定される。
例えば、シェル部5を構成する金属元素(例えば白金など)の使用量を最小限にすることを意図している場合には、1原子で構成される層(1原子層)であることが好ましく、この場合には、シェル部5の厚さは、当該シェル部5を構成する金属元素が1種類の場合には、この金属元素の1原子の直径(球形近似した場合)の2倍に相当する厚さであることが好ましい。また、当該シェル部5を構成する金属元素が2種類以上の場合には、1原子で構成される層(2種類以上の原子がコア部4の表面に並置されて形成される1原子層)に相当する厚さであることが好ましい。
また、例えば、シェル部5の厚さをより大きくすることにより耐久性の向上を図る場合には、1~10nmが好ましく、2~5nmがより好ましい。
例えば、第2シェル部7に含まれる金属元素である白金(Pt)等の貴金属の使用量を最小限にすることを意図している場合には、第2シェル部7は、1原子で構成される層(1原子層)であることが好ましい。この場合には、第2シェル部7の厚さは、当該第2シェル部7を構成する金属元素が1種類の場合には、当該金属元素の1原子の直径(1原子を球形とみなした場合)の約2倍に相当する厚さであることが好ましい。
また、第2シェル部7に含まれる金属元素が2種類以上である場合には、当該第2シェル部7は、1種類以上の原子で構成される層(2種類以上の原子がコア部4の表面方向に並置されて形成される1原子層)に相当する厚さであることが好ましい。例えば、第2シェル部7の厚さをより大きくすることにより、電極用触媒の耐久性を向上させることを図る場合には、当該第2シェル部7の厚さを1.0~5.0nmとすることが好ましい。電極用触媒の耐久性をさらに向上させることを図る場合には、当該第2シェル部7の厚さを2.0~10.0nmとすることが好ましい。
なお、本発明において「平均粒子径」とは、電子顕微鏡写真観察による、任意の数の粒子群からなる粒子の直径の平均値のことをいう。
さらに、担体2は、電極用触媒1を含んだガス拡散電極形成用組成物中で良好な分散性を有し、優れた導電性を有するものであることが好ましい。
これらの中で、コア部4との吸着性及び担体2が有するBET比表面積の観点から、炭素系材料が好ましい。
更に、炭素系材料としては、導電性カーボンが好ましく、特に、導電性カーボンとしては、導電性カーボンブラックが好ましい。導電性カーボンブラックとしては、商品名「ケッチェンブラックEC300J」、「ケッチェンブラックEC600」、「カーボンEPC」等(ライオン化学株式会社製)を例示することができる。
図1、2に示された電極用触媒1、1Aのように、シェル部5が上記二層構造ではなく、一層構造を採用する場合には、コア部4に貴金属を採用することもできる。上記電極用触媒1、1Aが有している触媒粒子3、3aを構成する
コア部4には、パラジウム(Pd)、パラジウム(Pd)合金、白金(Pt)合金、金(Au)、ニッケル(Ni)、及びニッケル(Ni)合金からなる群より選択される少なくとも1種の金属が含まれている。
具体的には、コア部4には、白金(Pt)、パラジウム(Pd)以外の金属元素を含む金属、金属化合物、及び金属と金属化合物との混合物であることが好ましく、貴金属以外の金属元素を含む金属、金属化合物、及び金属と金属化合物との混合物であることがより好ましい。
電極用触媒1B、1Cの触媒活性をより高く、容易に得る観点からは、第1シェル部6は、パラジウム(Pd)単体を主成分(50wt%以上)として構成されていることがより好ましく、パラジウム(Pd)単体のみから構成されていることがより好ましい。
第2シェル部7は、白金(Pt)及び白金(Pt)合金のうちの少なくとも1種の金属が含まれていることが好ましく、白金(Pt)単体が含まれていることがより好ましい。
電極用触媒1B、1Cの触媒活性をより高く、容易に得る観点からは、第2シェル部7は、白金(Pt)単体を主成分(50wt%以上)として構成されていることがより好ましく、白金(Pt)単体のみから構成されていることがより好ましい。
(X1/M)≦1.2 ・・・(1)
(X2/M)≦47.0 ・・・(2)
で表される条件を同時に満たしている。
前記式(1)及び前記式(2)中、
Mは、サイクリックボルタンメトリーにより得られる水素脱着波に基づく電気化学的表面積(ECSA)を用いて算出される前記シェル部5又は第2シェル部7の構成金属元素の物質量(原子数)を示し、
X1は、蛍光X線(XRF)分析法により測定される臭素(Br)種の含有量に基づき算出される臭素(Br)の物質量(原子数)を示し
X2は、蛍光X線(XRF)分析法により測定される塩素(Cl)種の含有量に基づき算出される塩素(Cl)の物質量(原子数)を示す。
なお、臭素(Br)種の含有量及び塩素(Cl)種の含有量は、それぞれ電極用触媒1に含まれる臭素元素に換算された臭素原子及び塩素元素に換算された塩素原子の含有量となっている。
FP法は、試料に含まれる元素の種類とその組成がすべて判れば、それぞれの蛍光X線(XRF)の強度を理論的に計算することができるということを利用している。そして、FP法は試料を測定して得られた各元素の蛍光X線(XRF)に一致するような組成を推定する。
ソフトウエアは、蛍光X線(XRF)分析法において一般的に採用されているものであれば特に制限されるものではない。
例えば、ソフトウエアとして、FP法を採用した汎用蛍光X線(XRF)分析装置用ソフトウエア「解析ソフト:「UniQuant5」」等を採用することができる。なお、蛍光X線(XRF)分析装置としては、例えば、波長分散型全自動蛍光X線分析装置(商品名:Axios「アクシオス」)(スペクトリス株式会社製)を例示することができる。
(X2/M)の値が47.0以下であると、塩素(Cl)種の影響により、電極用触媒1として、十分な触媒活性を発揮することができるため好ましい。さらに、(X2/M)の値が47.0以下であると、電極用触媒1の製造プロセスにおいて、塩素(Cl)種を除去する製造プロセスを経由することなく、電極用触媒1を製造することができるため好ましい。
すなわち、本発明の電極用触媒は、臭素(Br)種に着目し、上記(X1/M)の値を1.2以下に規定することによって、上記(X2/M)の値が4.5(47.0以下)を超えていても電極用触媒としての性能を十分に発揮することができる点に技術的特徴を有する。
さらに、後述する塩素低減法を採用することにより、塩素(Cl)種をきわめて低減することができる。
電極用触媒1の製造方法は、電極用触媒前駆体を製造する工程と、この触媒前駆体について、(X1/M)の値が1.2以下であり、(X2/M)の値が47.0以下である条件を満たすように洗浄する工程とを備えている。
電極用触媒1の電極用触媒前駆体は、電極用触媒の触媒成分(コア部4、シェル部5)を担体2に担持させることより製造される。
電極用触媒前駆体の製造方法は、担体2に電極用触媒1の触媒成分を担持させることができる方法であれば、特に制限されるものではない。
例えば、担体2に電極用触媒1の触媒成分を含有する溶液を接触させ、担体2に触媒成分を含浸させる含浸法、電極用触媒1の触媒成分を含有する溶液に還元剤を投入して行う液相還元法、アンダーポテンシャル析出(UPD)法等の電気化学的析出法、化学還元法、吸着水素による還元析出法、合金触媒の表面浸出法、置換めっき法、スパッタリング法、真空蒸着法等を採用した製造方法を例示することができる。
第1の工程:超純水に、蛍光X線(XRF)分析法により測定される塩素(Cl)種の濃度が予め設定された塩素濃度76000ppmを超える電極用触媒前駆体(I)(例えば、当該予め設定された塩素濃度が8500ppm、又は7600ppmでありこれらの濃度値を超える電極用触媒前駆体)を添加して、前記電極用触媒前駆体(I)を超純水に分散させた第1の液を調製する第1の工程と、
第2の工程:超純水を用いて、前記第1の液に含まれる前記電極用触媒前駆体(I)をろ過洗浄して、洗浄した後に得られるろ液のJIS規格試験法(JIS K0552)により測定される電気伝導率ρが予め設定された設定値以下(例えば、10~100μS/cmの範囲で予め設定される設定値以下)となるまで洗浄を繰り返し、得られた電極用触媒前駆体(II)を超純水に分散させて第2の液を調製する第2の工程と、を含む方法。
第1の工程:超純水と、還元剤と、蛍光X線(XRF)分析法により測定される塩素(Cl)種の濃度が予め設定された塩素濃度6000ppmを超える電極用触媒前駆体(例えば、当該予め設定された塩素濃度が8500ppm、又は6000ppmでありこれらの濃度値を超える電極用触媒前駆体)とを含む液を、20℃~90℃の範囲で予め設定された少なくとも1段階の設定温度でかつ予め設定された保持時間で保持する第1の工程を含む方法。
第1の工程:超純水と、水素を含む気体と、塩素(Cl)種を含む材料を使用して製造されており、蛍光X線(XRF)分析法により測定される塩素(Cl)種の濃度が予め設定された第1の塩素(Cl)種の濃度を超える電極用触媒前駆体と、を含む液を、20~40℃の範囲で予め設定された少なくとも1段階の設定温度で、かつ予め設定された保持時間で保持する第1の工程を含む方法。
蛍光X線(XRF)分析法は、例えば以下のように実行される。
(1)測定装置
・波長分散型全自動蛍光X線分析装置Axios(アクシオス)(スペクトリス株式会社製)
(2)測定条件
・解析ソフト:「UniQuant5」(FP(four peak method)法を用いた半定量ソフト)
・XRF測定室雰囲気:ヘリウム(常圧)
(3)測定手順
(i)試料を入れた試料容器をXRF試料室に入れる。
(ii)XRF試料室内をヘリウムガスで置換する。
(iii)ヘリウムガス雰囲気(常圧)下、測定条件を、解析ソフト「UniQuant5」を使用するための条件である、「UQ5アプリケーション」に設定し、サンプルの主成分が「カーボン(担体の構成元素)」、サンプルの分析結果の表示形式が「元素」となるよう計算するモードに設定する。
図5は本発明の電極用触媒を含むガス拡散電極形成用組成物、このガス拡散電極形成用組成物を用いて製造されたガス拡散電極、このガス拡散電極を備えた膜・電極接合体(MEA)、及びこの膜・電極接合体(MEA)を備えた燃料電池スタックの好適な一実施形態を示す模式図である。
図5に示された燃料電池スタックSは、膜・電極接合体(MEA)400を一単位セルとし、この一単位セルを複数積み重ねた構成を有している。
また、燃料電池スタックSは、この膜・電極接合体(MEA)400がセパレータ100a及びセパレータ100bにより挟持された構成を有している。
上記電極用触媒1をいわゆる触媒インク成分として用い、本発明のガス拡散電極形成用組成物とすることができる。本発明のガス拡散電極形成用組成物は、上記電極用触媒が含有されていることを特徴とする。ガス拡散電極形成用組成物は上記電極用触媒とイオノマー溶液を主要成分とする。イオノマー溶液は、水とアルコールと水素イオン伝導性を有する高分子電解質とを含有する。
本発明のガス拡散電極(200a、200b)は、ガス拡散層220とガス拡散層220の少なくとも一面に積層された電極用触媒層240とを備えている。ガス拡散電極(200a、200b)が備えている電極用触媒層240には、上記電極用触媒が含まれている。なお、本発明のガス拡散電極200は、アノードとして用いることができ、カソードとしても用いることができる。
なお、図5においては、便宜上、上側のガス拡散電極200をアノード200aとし、下側のガス拡散電極200をカソード200bとする。
電極用触媒層240は、アノード200aにおいて、ガス拡散層220から送られた水素ガスが電極用触媒層240に含まれている電極用触媒1の作用により水素イオンに解離する化学反応が行われる層である。また、電極用触媒層240は、カソード200bにおいて、ガス拡散層220から送られた空気(酸素ガス)とアノードから電解質膜中を移動してきた水素イオンが電極用触媒層240に含まれている電極用触媒1の作用により結合する化学反応が行われる層である。
ガス拡散電極200が備えているガス拡散層220は、燃料電池スタックSの外部より、セパレータ100aとガス拡散層220aとの間に形成されているガス流路に導入される水素ガス、セパレータ100bとガス拡散層220bとの間に形成されているガス流路に導入される空気(酸素ガス)をそれぞれの電極用触媒層240に拡散するために設けられている層である。また、ガス拡散層220は、電極用触媒層240をガス拡散電極200に支持して、ガス拡散電極200表面に固定化する役割を有している。ガス拡散層220は、電極用触媒層240に含まれる電極用触媒1と水素ガス、空気(酸素ガス)との接触を高める役割を有している。
ガス拡散電極の製造方法について説明する。
ガス拡散電極の製造方法は、触媒成分が担体に担持されてなる電極用触媒1と水素イオン伝導性を有する高分子電解質と、水とアルコールとのイオノマー溶液を含有するガス拡散電極形成用組成物をガス拡散層220に塗布する工程と、このガス拡散電極形成用組成物が塗布されたガス拡散層220を乾燥させ、電極用触媒層240を形成させる工程とを備える。
本発明の膜・電極接合体400(Membrane Electrode Assembly:以下、MEAと略する。)は、上記電極用触媒1を用いたガス拡散電極200であるアノード200aとカソード200bとこれらの電極を仕切る電解質300とを備えている。膜・電極接合体(MEA)400は、アノード200a、電解質300及びカソード200bをこの順序により積層した後、圧着することにより製造することができる。
本発明の燃料電池スタックSは、得られた膜・電極接合体(MEA)400のアノード200aの外側にセパレータ100a(アノード側)を取り付け、カソード200bの外側にそれぞれセパレータ100b(カソード側)を取り付け、一単位セル(単電池)とする。そして、この一単位セル(単電池)を集積させて燃料電池スタックSとする。なお、燃料電池スタックSに周辺機器を取り付け、組み立てることにより、燃料電池システムが完成する。
なお、本発明者らは、実施例及び比較例に示す触媒について、蛍光X線(XRF)分析法ではヨウ素(I)種が検出されないことを確認した。
また、以下の製造方法の各工程の説明において特にことわりない場合には、その工程は室温、空気中で実施した。
(実施例1)
本発明の電極用触媒を以下のプロセスにより製造した。なお、実施例において、使用した電極用触媒の原料は、以下の通りである。
・カーボンブラック粉末:商品名「Ketjen Black EC300」(ケッチェンブラックインターナショナル社製)
・テトラクロロパラジウム(II)酸ナトリウム
・硝酸パラジウム
・塩化白金酸カリウム
電極用触媒の担体として、カーボンブラック粉末を用い、水に分散させて、5.0g/Lの分散液を調製した。この分散液に、テトラクロロパラジウム(II)酸ナトリウム水溶液(濃度20質量%)5mLを滴下して混合した。得られた分散液に、ぎ酸ナトリウム水溶液(100g/L)100mLを滴下した後、不溶成分を濾別し、濾別された不溶成分を純水で洗浄し、乾燥することにより、カーボンブラック上にパラジウムが担持されたパラジウム(コア)担持カーボンを得た。
50mMの硫酸銅水溶液を、三電極系電解セルに入れた。この三電極系電解セルに上記で調製したパラジウム担持カーボンを適量加え、攪拌後静置した。静止状態で450mV(対 可逆水素電極)を作用電極に印加し、パラジウム担持カーボンのパラジウム上に銅(Cu)を一様に被覆した。これを銅-パラジウム担持カーボンとする。
銅がパラジウム上に被覆された銅-パラジウム担持カーボンを含む液に、被覆された銅に対して、物質量比で2倍相当の白金(Pt)を含む塩化白金酸カリウム水溶液を滴下することにより、上記銅-パラジウム担持カーボンの銅(Cu)を白金(Pt)に置換した。
こうして得られる銅-パラジウム担持カーボンの銅(Cu)が白金(Pt)に置換された白金パラジウム担持カーボンの粒子の粉体をろ過後、乾燥させずにろ液により湿潤した状態で超純水を用いて洗浄し、70℃で乾燥させた。これにより、実施例1の電極用触媒{白金(Pt)-パラジウム(Pd)担持カーボン(コア部:パラジウム、シェル部:白金)}を得た。
得られた実施例1の電極用触媒について、白金と、パラジウムの担持量(質量%)を以下の方法で測定した。
実施例1の電極用触媒を王水に浸し、金属を溶解させた。次に、王水から不溶成分のカーボンを除去した。次に、カーボンを除いた王水をICP分析した。
ICP分析の結果は、白金担持量が19.3質量%、パラジウム担持量が24.1質量%であった。
電極用触媒に含まれる白金(Pt)及びパラジウム(Pd)の担持量が表1~2に記載された濃度(質量%濃度)となったこと以外は、実施例1と同様にして、実施例2~15、実施例17の電極用触媒を調製した。
電極用触媒に含まれる白金(Pt)及びパラジウム(Pd)の担持量が表1に記載された濃度(質量%濃度)となるように電極用触媒の原料であるパラジウム塩を変更させた以外は、実施例1と同様にして、実施例16の電極用触媒を調製した。
実施例1と同様にして電極用触媒を調製した。これを、さらに硫酸水溶液(1M)に常温で所定時間浸した。次に、硫酸水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、電極用触媒をシュウ酸水溶液(0.3M)に浸し、90℃で所定時間保持した。次に、シュウ酸水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、超純水で洗浄後の電極用触媒を70℃で乾燥させた。これにより、実施例18の電極用触媒を得た。
また、実施例1と同様にICP分析を行い、白金担持量とパラジウム担持量を測定した。
実施例1と同様にして電極用触媒を調製した。これを、さらにぎ酸ナトリウム水溶液(0.01M)に浸し、室温で所定時間保持した。次に、ぎ酸ナトリウム水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、超純水で洗浄後の電極用触媒を70℃で乾燥させた。これにより、実施例19~20の電極用触媒を得た。
また、実施例1と同様にICP分析を行い、白金担持量とパラジウム担持量を測定した。
実施例1と同様にして電極用触媒を調製した。
これを、さらにぎ酸ナトリウム水溶液(0.01M)に浸し、室温で所定時間保持した。次に、ぎ酸ナトリウム水溶液中の電極用触媒を超純水でろ過・洗浄した。
これを、さらに硫酸水溶液(1M)に常温で所定時間浸した。次に、硫酸水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、電極用触媒をシュウ酸水溶液(0.3M)に浸し、90℃で所定時間保持した。次に、シュウ酸水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、超純水で洗浄後の電極用触媒を70℃で乾燥させた。これにより、実施例21の電極用触媒を得た。
また、実施例1と同様にICP分析を行い、白金担持量とパラジウム担持量を測定した。
実施例1と同様にして電極用触媒を調製した。これを、さらにぎ酸ナトリウム水溶液(0.01M)に浸し、90℃で所定時間保持した。次に、ぎ酸ナトリウム水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、超純水で洗浄後の電極用触媒を70℃で乾燥させた。これにより、実施例22の電極用触媒を得た。
また、実施例1と同様にICP分析を行い、白金担持量とパラジウム担持量を測定した。
実施例1と同様にして電極用触媒を調製した。次に、電極用触媒をシュウ酸水溶液(0.3M)に浸し、90℃で所定時間保持した。次に、シュウ酸水溶液中の電極用触媒を超純水でろ過・洗浄した。次に、超純水で洗浄後の電極用触媒を70℃で乾燥させた。これにより、実施例23の電極用触媒を得た。
また、実施例1と同様にICP分析を行い、白金担持量とパラジウム担持量を測定した。
原料として臭素の含有濃度が10000ppm~13000ppmの塩化白金酸カリウムを使用して、表3に示す臭素種濃度としたこと以外は実施例1と同様にして比較例1~7の電極用触媒を製造した。
実施例1~23、及び比較例1~7で得られた電極用触媒の臭素(Br)種及び塩素(Cl)種の濃度を蛍光X線(XRF)分析法により測定した。電極用触媒中の臭素種及び塩素種濃度の測定は、波長分散型蛍光X線測定装置Axios(スペクトリス株式会社製)により測定した。具体的には、以下の手順により行った。
さらに、蛍光X線(XRF)分析法により算出された臭素(Br)種及び塩素(Cl)種の含有量に基づいて、臭素(Br)の物質量(原子数)X1及び塩素(Cl)の物質量(原子量X2をそれぞれ算出した。
実施例1~23、比較例1~7で製造した電極用触媒の触媒活性を回転ディスク電極法(RDE法)により評価した。電極用触媒の触媒活性の測定は回転ディスク電極法(RDE法)により、以下のように行った。
実施例1~23、比較例1~7で製造した電極用触媒の粉末を約8.0mg秤取り、超純水2.5mLとともにサンプル瓶に入れて超音波を照射しながら混合して電極用触媒のスラリー(懸濁液)を作製した。次に、別の容器に超純水10.0mLと10wt%ナフィオン(登録商標)分散水溶液((株)ワコーケミカル製、商品名「DE1020CS」)20μLを混合して、ナフィオン-超純水溶液を作製した。このナフィオン-超純水溶液2.5mLを電極用触媒のスラリー(懸濁液)が入ったサンプル瓶にゆっくり投入し、室温にて15分間、超音波を照射し、十分に撹拌して、ガス拡散電極形成用組成物とした。
図6は、回転ディスク電極法(RDE法)に用いる回転ディスク電極測定装置Dの概略構成を示す模式図である。
図6に示すように、回転ディスク電極測定装置Dは、主として、測定装置用セル10と、参照電極(RE)20と、対極(CE)30と、回転ディスク電極40と、電解液60とから構成されている。
この回転ディスク電極測定装置Dに備えられている回転ディスク電極40の表面に電極用触媒層Xを形成した。そして、回転ディスク電極法により電極用触媒層X中の触媒を評価した。
なお、電解液60として0.1MのHClO4、参照電極(RE)20としてAg/AgCl飽和電極、対極30としてPt黒付Ptメッシュを備えた回転ディスク電極測定装置D(北斗電工株式会社製 モデルHSV110)を用いた。
上記作製したガス拡散電極形成用組成物を10μL分取して、清浄な回転ディスク電極(グラッシーカーボン製、径5.0mmφ、面積19.6mm2)表面に滴下した。その後、回転ディスク電極の表面全体に、ガス拡散電極形成用組成物を均一、かつ一定の厚みとなるように行き渡らせ、回転ディスク電極の表面にガス拡散電極形成用組成物からなる塗布膜を形成させた。このガス拡散電極形成用組成物からなる塗布膜を温度23℃、湿度50%RHにて、2.5時間乾燥させ、回転ディスク電極40の表面に電極用触媒層Xを形成した。
回転ディスク電極法による測定は、回転ディスク電極測定装置内のクリーニング、測定前の電気化学表面積(ECSA)の評価、酸素還元(ORR)電流測定及び測定後の電気化学表面(ECSA)の評価からなる。
上記回転ディスク電極測定装置D内において、HClO4電解液60に上記回転ディスク電極40を浸した後、電解液60をアルゴンガスで30分以上パージした。その後、走査電位を85~1085mV vsRHE、走査速度50mv/secの条件にて20サイクル、電位走査を行った。
その後、走査電位を50~1085mV vsRHE、走査速度20mV/secの条件にて3サイクル、電位走査を行った。
電解液60を酸素ガスで15分以上パージした後、走査電位を135~1085mV vsRHE、走査速度10mV/secの条件にて10サイクル、回転ディスク電極40の回転速度を1600rpmの条件でサイクリックボルタグラム(CV)測定を行った。電位900mV vsRHEにおける電流値を記録した。さらに、回転ディスク電極40の回転速度をそれぞれ400rpm、625rpm、900rpm、1225rpm、2025rpm、2500rpm、3025rpmに設定して、1サイクルごとに酸素還元(ORR)電流測定を行った。電流測定値を酸素還元電流値(i)とした。
最後に、走査電位を50~1085mV vsRHE、走査速度20mV/secの条件にて、3サイクル、サイクリックボルタグラム(CV)測定を行った。
上記で得られた酸素還元電流値(i)及びサイクリックボルタグラム(CV)から測定された限界電流値(iL)と、下記一般式(4)で表されるNernstの拡散層モデルに基づく物質移動の補正式に基づいて、電極用触媒の触媒活性を算出した。実施例1~17の算出結果を表1に示し、実施例18~23の算出結果を表2に示す。併せて、比較例1~7の算出結果を表3に示す。
上述した[測定前の電気化学表面積(ECSA)の評価]及び[測定後の電気化学表面(ECSA)の評価]で測定したサイクリックボルタグラム(CV)より得られる水素脱着波に基づく電気化学的表面積(ECSA)と、下記一般式(5)に基づいて、測定に供した電極用触媒の白金元素の物質量(原子数)Mを算出した。
特に、表1に示された電極用触媒は、すべて(X2/M)の値が23を超えている。しかしながら、上記電極用触媒は、(X1/M)の値が1.0以下に制御されているため良好な触媒活性を示している。
一方、表3によれば、(X1/M)の値が1.2を超えた電極用触媒は、その触媒活性が低下していることが理解される。すなわち、高濃度の塩素(Cl)種を含有していても、臭素(Br)種の含有量が緻密に制御された電極用触媒は、きわめて良好な触媒活性を示し、量産化に適しており、製造コストの低減に適したものであることが明らかとなった。
1A 電極用触媒
1B 電極用触媒
1C 電極用触媒
2 担体
3 触媒粒子
3a 触媒粒子
4 コア部
4s コア部露出面
5 シェル部
6 第1シェル部
6s 第1シェル部露出面
7 第2シェル部
S 燃料電池スタック
100 セパレータ
100a セパレータ(アノード側)
100b セパレータ(カソード側)
200 ガス拡散電極
200a ガス拡散電極(アノード)
200b ガス拡散電極(カソード)
220 ガス拡散層
240 電極用触媒層
300 電解質
400 膜・電極接合体(MEA)
X 電極用触媒層
D 回転ディスク電極法(RDE法)測定装置
10 測定装置用セル
12 ガス導入口
20 参照電極(RE)
22 参照電極(RE)用セル
30 対極(CE)
40 回転ディスク電極
42 電極基材
50 固体台
52 支持部
54 オイルシール
60 電解液
Claims (11)
- 担体と、前記担体上に形成されるコア部と、前記コア部の表面の少なくとも一部を覆うように形成されるシェル部と、を含むコア・シェル構造を有する電極用触媒であって、
下記式(1)及び下記式(2)
(X1/M)≦1.2 ・・・(1)
(X2/M)≦47.0 ・・・(2)
で表される条件を同時に満たしている、
電極用触媒。
[前記式(1)及び前記式(2)中、
Mは、サイクリックボルタンメトリーにより得られる水素脱着波に基づく電気化学的表面積(ECSA)を用いて算出される前記シェル部の構成金属元素の物質量(原子数)を示し、
X1は、蛍光X線(XRF)分析法により測定される臭素(Br)種の含有量に基づき算出される臭素(Br)の物質量(原子数)を示し
X2は、蛍光X線(XRF)分析法により測定される塩素(Cl)種の含有量に基づき算出される塩素(Cl)の物質量(原子数)を示す。] - 前記シェル部には、白金(Pt)及び白金(Pt)合金のうちの少なくとも1種の金属が含有されており、
前記コア部には、パラジウム(Pd)、パラジウム(Pd)合金、白金(Pt)合金、金(Au)、ニッケル(Ni)、及び、ニッケル(Ni)合金からなる群より選択される少なくとも1種の金属が含まれている、
請求項1記載の電極用触媒。 - 前記担体には、導電性カーボンが含有されており、
前記シェル部には、白金(Pt)が含有されており、
前記コア部には、パラジウム(Pd)が含有されている、
請求項1又は2に記載の電極用触媒。 - 前記Mは、サイクリックボルタンメトリーにより得られる水素脱着波に基づく電気化学的表面積(ECSA)を用いて算出される前記シェル部の構成金属元素である白金(Pt)の物質量(原子数)を示す、
請求項3に記載の電極用触媒。 - 前記シェル部が、前記コア部の表面の少なくとも一部を覆うように形成される第1シェル部と、当該第1シェル部の表面の少なくとも一部を覆うように形成される第2シェル部と、を有しており、
前記式(1)及び前記(2)における前記Mは前記第2シェル部の構成金属元素の物質量(原子数)を示す、
請求項1に記載の電極用触媒。 - 前記第1シェル部には、パラジウム(Pd)が含有されており、
前記第2シェル部には、白金(Pt)が含有されている、
請求項5に記載の電極用触媒。 - 前記式(2)中の(X2/M)が4.5超である、請求項1~6のうちのいずれか1項に記載の電極用触媒。
- 請求項1~7のうちのいずれか1項に記載の電極用触媒が含有されている、
ガス拡散電極形成用組成物。 - 請求項1~7のうちのいずれか1項に記載の電極用触媒が含有されている、
ガス拡散電極。 - 請求項9記載のガス拡散電極が含まれている、
膜・電極接合体(MEA)。 - 請求項10記載の膜・電極接合体(MEA)が含まれている、
燃料電池スタック。
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