JP6661976B2 - Electrode catalyst, catalyst layer using the electrode catalyst, and fuel cell - Google Patents

Description

  The present invention relates to an electrode catalyst, particularly an electrode catalyst used for a fuel cell, a catalyst layer using the electrode catalyst, and a fuel cell.

  A polymer electrolyte fuel cell (PEFC) using a proton-conducting solid polymer membrane has a lower temperature than other types of fuel cells, such as a solid oxide fuel cell and a molten carbonate fuel cell. Operate. For this reason, polymer electrolyte fuel cells are expected as stationary power sources and power sources for mobile bodies such as automobiles, and their practical use has been started.

  The structure of a PEFC generally has a structure in which a membrane-electrode assembly (MEA) is sandwiched between separators. The MEA generally has a structure in which a gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and a gas diffusion layer are stacked.

  In the MEA, the following electrochemical reaction proceeds. First, hydrogen contained in the fuel gas supplied to the anode (fuel electrode) side is oxidized by the catalyst to become protons and electrons. Next, the generated protons reach the cathode (air electrode) side catalyst layer through the polymer electrolyte contained in the anode side catalyst layer and further through the solid polymer electrolyte membrane in contact with the anode side catalyst layer. The electrons generated in the anode-side catalyst layer are converted into a conductive carrier constituting the anode-side catalyst layer, a gas diffusion layer in contact with a different side of the anode-side catalyst layer from the solid polymer electrolyte membrane, and a gas separator. And an external circuit to reach the cathode-side catalyst layer. Then, the protons and electrons that have reached the cathode side catalyst layer react with oxygen contained in the oxidizing gas supplied to the cathode side catalyst layer to generate water. In a fuel cell, electricity can be extracted to the outside through the above-described electrochemical reaction. The catalyst used for the catalyst layer is generally formed by supporting a catalyst metal such as platinum or a platinum alloy on a carbon carrier.

The potentials of the anode and the cathode greatly change due to various causes such as long-time continuous operation and start / stop of the fuel cell. For example, in a start-stop state is a state in which both of the anode gas passage and the cathode gas passage contains air (O _2), is supplied with H ₂ to the anode at startup, H ₂ is supplied portion a potential difference is generated between the with H ₂ does not reach portions. Due to this potential difference, the cathode serving as the counter electrode is forced to supply H ⁺ , and the H ⁺ supply portion on the cathode side is exposed to a high potential. Such a change in potential causes corrosion of the catalyst carrier containing carbon as a main component. As a result, the electrode performance deteriorates with time, which is a main cause of deterioration of the performance of the fuel cell.

  Therefore, the catalyst carrier is required to be stable even when exposed to a high potential. In Patent Literature 1, conductive diamond has a wider potential window than graphite, so that carbon is hardly deteriorated even when the catalyst layer has a high potential, and can be used as a catalyst carrier for a fuel cell. And

Also, on the anode side, corrosion of the catalyst carrier containing carbon as a main component occurs due to hydrogen starvation in which fuel (H ₂ ) supplied during operation of the fuel cell is deficient.

JP 2010-199063 A

  Fuel cells have been studied as driving sources and stationary power sources for moving bodies as described above, but in order to be applied to these applications, high conductivity is required in addition to long-term durability. . However, Patent Document 1 only describes that conductive diamond refers to those having a conductivity of 1000 Ωcm or less, and when conductive diamond is used as a catalyst carrier for a fuel cell, sufficient conductivity is not obtained. No consideration has been given as to whether it will be secured.

  In view of the above circumstances, an object of the present invention is to provide an electrode catalyst that has long-term durability while ensuring conductivity.

  The electrode catalyst of the present invention is characterized in that conductive diamond is used as an electrode catalyst carrier, and the conductive diamond has a specific peak area ratio and / or peak intensity ratio.

  ADVANTAGE OF THE INVENTION According to this invention, the electrocatalyst which has ensured electroconductivity and the durability over a long period of time can be provided.

FIG. 1 is a schematic sectional view showing a basic configuration of a polymer electrolyte fuel cell according to one embodiment of the present invention. 3 is a transmission electron microscope (TEM) photograph of Example 1. It is a figure showing the result of the endurance test of an example.

  The electrode catalyst of the first embodiment (also referred to as “catalyst” in the present specification) uses conductive diamond as a catalyst carrier, and a catalyst metal is supported on the conductive diamond. Here, the conductive diamond satisfies at least one of the following (1) and (2). (1) The ratio of the peak area derived from the sp3 orbit to the peak area derived from the sp2 orbit measured in the Raman spectrum is more than 0 and not more than 0.2. (2) The ratio of the peak intensity derived from the sp3 orbit to the peak intensity derived from the sp2 orbit measured in the Raman spectrum is more than 0 and not more than 0.8.

  Hereinafter, the ratio of the peak area derived from the sp3 orbit to the peak area derived from the sp2 orbit measured by Raman spectroscopy (peak area derived from the sp3 orbit / peak area derived from the sp2 orbit) is also simply referred to as peak area ratio. The ratio of the peak intensity derived from the sp3 orbital to the peak intensity derived from the sp2 orbital measured in the Raman spectroscopy spectrum (peak intensity derived from the sp3 orbital / peak intensity derived from the sp2 orbital) is also simply referred to as peak intensity ratio.

  According to the catalyst having the above configuration, an electrode catalyst having excellent conductivity and durability can be provided.

Patent Literature 1 discloses that conductive diamond can be used as an electrode catalyst carrier for a fuel cell. Here, in Patent Document 1, “conductive diamond-like carbon is a mixture of both diamond bonds (SP ₃ hybrid orbital bonds between carbons) and graphite bonds (SP ₂ hybrid orbital bonds between carbons). Of carbon having an amorphous structure, which has a conductivity of 1000 Ωcm or less. ” For this reason, the conductive diamond referred to in Patent Document 1 defines a very wide range. In fact, Patent Document 1 does not discuss the details of the properties of conductive diamond, and only describes the conductive diamond used in the examples as diamond-like carbon powder having an average particle size of 0.03 μm. No specific properties are described. Further, in Patent Document 1, diamond-like carbon having a property intermediate between graphite and diamond is a ratio of SP ₂ hybrid orbital bond and SP ₃ hybrid orbital bond of carbon atoms constituting diamond-like carbon at “at the time of film formation”. It is described that the conductivity can be adjusted by adjusting. However, Patent Literature 1 does not disclose at all what specific ratio is preferable in the ratio of SP ₂ hybrid orbital coupling to SP ₃ hybrid orbital coupling of diamond-like carbon. There is no description of the specific ratio of the catalyst used.

  On the other hand, carbon materials such as Ketjen Black, which has been widely used as a conventional catalyst carrier (peak area derived from sp3 orbital = 0), have high conductivity, but the corrosion of the catalyst carrier due to long-time continuous operation or start / stop is caused. Can occur. The present inventor has inferred that, among conductive diamonds, the above problem can be solved by a structure having relatively weak diamond properties and relatively strong graphite properties. As a result of further studies based on the above inference, it has been found that if the peak area ratio of the conductive diamond is more than 0 and 0.2 or less and / or the peak intensity ratio is more than 0 and 0.8 or less, the conductivity and It was found that the characteristics could be balanced.

  According to the electrode catalyst of the present embodiment, it has high conductivity and durability. Therefore, the catalyst layer and the fuel cell using the catalyst of the present invention are excellent in power generation performance and have high durability.

  Hereinafter, an embodiment of a catalyst of the present invention, and a catalyst layer, a membrane electrode assembly (MEA) and a fuel cell using the same according to an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to only the following embodiments. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one. In addition, in the case where the embodiments of the present invention have been described with reference to the drawings, the same elements will be denoted by the same reference symbols in the description of the drawings, and redundant description will be omitted.

  In this specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise specified, the operation and measurement of physical properties are performed under the conditions of room temperature (20 to 25 ° C.) / Relative humidity of 40 to 50%.

[Electrode catalyst]
The electrode catalyst of the present embodiment uses conductive diamond as a catalyst carrier, and the conductive diamond satisfies at least one of the following (1) and (2); (1) the peak area ratio exceeds 0 to 0.1. (2) The peak intensity ratio is more than 0 and not more than 0.8. When the peak area ratio exceeds 0.2 or the peak intensity ratio exceeds 0.8, the conductivity of the electrode catalyst is significantly reduced. On the other hand, by using conductive diamond as a catalyst carrier, that is, by using a catalyst having an sp3 bond (the peak intensity ratio and the peak area ratio exceed 0), the durability is significantly improved. Preferably, the conductive diamond satisfies (1) and (2).

  The peak area ratio of the conductive diamond is preferably 0.01 or more from the viewpoint of durability. The peak area ratio of the conductive diamond is more preferably 0.02 or more and 0.15 or less. As described above, by making the peak area ratio of the conductive diamond into the structure having the diamond bond in the graphite bond in the above ratio, an electrode catalyst having more sufficient conductivity and higher durability can be obtained.

  The peak intensity ratio of the conductive diamond is preferably 0.01 or more from the viewpoint of durability. Further, the peak intensity ratio of the conductive diamond is more preferably 0.02 or more and 0.75 or less. By setting the peak intensity ratio of the conductive diamond to a structure having a slight diamond bond to the graphite bond as described above, an electrode catalyst having sufficient conductivity and high durability can be obtained.

The peak derived from the sp3 orbit is a sharp peak due to diamond bonding, which is observed around 1290 to 1350 cm ^{-1 by} Raman scattering analysis. The peak derived from the sp2 orbital is a peak due to a graphite bond (vibration in a hexagonal lattice of carbon atoms) observed near 1580 cm ^{-1 by} Raman scattering analysis.

  In the present specification, the peak area ratio and the peak intensity ratio are obtained by measuring the peak area / peak intensity derived from the sp3 orbit and the peak area / peak intensity derived from the sp2 orbit using the apparatus, conditions, and software described in the examples. I do. Then, a value obtained by calculating the peak area ratio and the peak intensity ratio based on this value is adopted. Further, the so-called D band and the peak derived from the sp3 orbit have an overlapping portion, but can be clearly separated by the software.

  The specific resistance of the conductive diamond of the present embodiment is preferably 1 Ω · cm or less. When the specific resistance of the conductive diamond is such a value, sufficient conductivity can be secured. The specific resistance of the conductive diamond is more preferably 0.8 Ω · cm or less, further preferably 0.6 Ω · cm or less. Note that the lower the specific resistance, the better. Therefore, the lower limit is 0 Ω · cm. As the specific resistance, a value measured by the method described in “Powder specific resistance” in Examples is adopted.

  Since the peak area ratio, peak intensity ratio and specific resistance of the conductive diamond as the catalyst carrier are substantially the same as the peak area ratio, peak intensity ratio and specific resistance of the conductive diamond before supporting the catalytic metal, the production is performed. If the peak area ratio, peak intensity ratio and specific resistance of the conductive diamond are known at the stage, the values are adopted. Alternatively, in the electrode catalyst, a catalyst metal such as platinum may be eluted with an acid such as aqua regia to obtain only the catalyst carrier, and the peak area ratio, peak intensity ratio and specific resistance of the catalyst carrier may be measured.

  The conductive diamond is also referred to as diamond-like carbon, and refers to carbon having electrical conductivity among carbons having an sp3 bond and an sp2 bond in a Raman spectroscopic spectrum described in Examples. Further, the conductive diamond preferably has an amorphous structure. Note that “having an amorphous structure” is not limited to an amorphous structure, but also includes a partially graphite structure in addition to the amorphous structure. Here, having conductivity means that the powder specific resistance measured by the method described in Examples described later is 1000 Ω · cm or less.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient to allow the catalyst component to be highly dispersed and supported, but is preferably 10 m ² / g or more, more preferably 20 to ²⁰⁰ m ² / g. The BET specific surface area of the catalyst carrier in the catalyst is the BET specific surface area of the catalyst carrier in the production stage or the BET specific surface area measured by removing the catalyst metal from the catalyst.

In this specification, the “BET specific surface area” is measured by a nitrogen adsorption method. Specifically, about 0.04 to 0.07 g of a sample is precisely weighed and sealed in a sample tube. This sample tube is pre-dried at 90 ° C. for several hours in a vacuum dryer to obtain a sample for measurement. An electronic balance (AW220) manufactured by Shimadzu Corporation is used for weighing. In the case of a coated sheet, the net weight of the coated layer obtained by subtracting the Teflon (registered trademark) (base material) weight of the same area from the total weight of the coated sheet is used as the sample weight. . Next, the BET specific surface area is measured under the following measurement conditions. On the adsorption side of the adsorption / desorption isotherm, a BET plot is created from the range of the relative pressure (P / P ₀ ) of about 0.00 to 0.45, and the BET specific surface area is calculated from its slope and intercept.

  The size of the catalyst carrier is not particularly limited. From the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst layer in an appropriate range, the average particle diameter (diameter) of the catalyst carrier is preferably 5 to 2000 nm, more preferably 10 to 200 nm, Particularly preferably, the thickness is about 20 to 100 nm. Unless otherwise specified, the value of the “average particle size of the catalyst carrier” is observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle diameters of the particles is adopted. Further, the “particle diameter (diameter)” means the maximum distance among any two points passing through the center of the particle and on the outline of the particle.

  The catalytic metal has a function of catalyzing an electrochemical reaction. The catalyst metal used for the anode catalyst layer is not particularly limited as long as it has a catalytic action on the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst metal used for the cathode catalyst layer is not particularly limited as long as it has a catalytic action on the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specific examples of the catalyst metal include metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. And alloys thereof.

  Among them, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. That is, the catalyst metal is preferably platinum or contains platinum and a metal component other than platinum, and more preferably platinum or a platinum-containing alloy. Such a catalytic metal can exhibit high activity. Although the composition of the alloy depends on the type of the metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. Note that an alloy is generally a metal element obtained by adding one or more metal elements or non-metal elements, and is a general term for an alloy having metallic properties. The alloy structure includes eutectic alloys, which are so-called mixtures in which the component elements are separate crystals, those in which the component elements are completely dissolved and in solid solution, and those in which the component elements are intermetallic compounds or compounds of metals and nonmetals. Some of them are formed, and any of them may be used in this specification. At this time, the catalyst metal used for the anode catalyst layer and the catalyst metal used for the cathode catalyst layer can be appropriately selected from the above. In this specification, unless otherwise specified, the description of the catalyst metal for the anode catalyst layer and the catalyst metal for the cathode catalyst layer has the same definition for both. However, the catalyst metal of the anode catalyst layer and the catalyst metal of the cathode catalyst layer do not need to be the same, and can be appropriately selected so as to exert the above-described desired action.

  The amount of the catalyst carried on the carrier (sometimes referred to as the carrying ratio) is preferably 5 to 80% by weight, more preferably 10 to 60% by weight, based on the total amount of the catalyst carrier (that is, the carrier and the catalyst). It is good to do. It is preferable that the loading amount is in the above-mentioned range since sufficient dispersion of the catalyst component on the carrier, improvement of power generation performance, economical advantage, and catalytic activity per unit weight can be achieved.

  The method for producing the electrode catalyst is not particularly limited, but the peak area ratio is more than 0 and 0.2 or less, and / or the peak area ratio is more than 0 and 0.8 or less. It is preferable that the metal catalyst precursor is supported on a crystalline diamond (catalyst carrier).

  The method for producing the catalyst carrier having a specific peak area ratio and / or peak intensity ratio is not particularly limited, but can be obtained by a so-called detonation method.

  The detonation method is a method of synthesizing an explosive composition as a carbon raw material by explosion in a closed container or in water or the like. Such a detonation method is known as a method for producing nanodiamond used for abrasives and the like, for example, in Japanese Patent Application Laid-Open No. 2005-289677. There may be carbon components that do not have a perfect diamond structure. In the present invention, a conductive diamond having the above-mentioned peak area ratio or peak intensity ratio can be selected from a carbon content not having a complete diamond structure. In addition, in the detonation method, the pressure at the time of detonation is reduced, sampling from a place in the container where shock waves are difficult to transmit, the energy of the detonation is reduced (reducing the amount of explosives), the shock wave is difficult to transmit The conductive diamond can be selectively formed by arranging a sample so as to be suitable.

  Although the size of the closed container is not particularly limited, for example, for explosives of 100 g to 200 g, the explosive is preferably about 5 to 50 liters, more preferably about 10 to 30 liters, for ease of recovery of synthetic diamond and the like. A tolerable container is preferred. Specifically, the closed container shown in FIG. 1 of JP-A-2005-289677 can be used as the closed container. In the case of using a closed container, when the atmosphere is substantially free of oxygen during the detonation, the oxidation reaction of carbon can be suppressed, so that the yield can be improved. In order to obtain such an atmosphere, for example, the atmosphere may be replaced with an inert gas such as a nitrogen gas, an argon gas, or a carbon dioxide gas.

  The explosion can be initiated using a detonator or detonating wire, just like a normal explosive. At this time, an explosive may be used.

  The explosive component in the explosive composition preferably has an explosion speed of 6,000 m / s or more, more preferably 7,000 m / s or more, and those currently used generally have an explosion speed of about 10,000 m / s or less. .

  As the explosive component, a compound containing a nitro group, preferably a compound containing three or more nitro groups, for example, an aromatic nitro compound (preferably tri- or tetranitrobenzene optionally substituted with an amino group and / or a methyl group) , Nitroamines (preferably C3-C6 alkyl (3-6 nitro) amines), and nitrates. Specifically, trinitrotoluene (TNT), trinitrobenzene (TNB), trimethylenetrinitroamine (RDX), tetramethylenetetranitroamine (HMX), tetranitromethylaniline (tetrile), triaminotrinitrobenzene (TATB) , Diaminotrinitrobenzene (DATB), hexanitrostilbene (HNS), hexanitroazobenzene (HNAB), hexanitrodiphenylamine (HNDP), picric acid, ammonium picrate, benzotriazole (TACOT), ethylene dinitramine (EDNA), Examples include nitroguanidine (NQ), pentaerythritol tetranitrate (PETN), and mixed explosives such as pentolite, cyclotol, and octol. These may be used alone or in combination of two or more.

  Examples of the explosive component include compounds containing three or more nitro groups such as powdery trinitrotoluene (TNT), trimethylenetrinitroamine (RDX) and tetramethylenetetranitroamine (HMX), and pentaerythritol tetranitrate ( A nitrate ester such as a pen slit is preferred from the viewpoints of the easiness of obtaining the carrier (easiness of controlling the peak area ratio / peak intensity ratio), performance, and safety in handling. These explosives may be used alone or in combination of two or more. The particle size of the powder explosive component is in the range of 10 to 200 μm, preferably in the range of 30 to 120 μm. It is also possible to use a mixture of a plurality of explosive components having different particle sizes.

  Further, in the explosive composition, a polymer binder described in JP-A-2005-289677 may be used in addition to the explosive component. Examples of the polymer binder include polybutadiene (polybutadiene: density 0.91 g / cc, oxygen balance-3.23 g), polyurethane (polyurethane: density 1.50 g / cc, oxygen balance-2.13 g), polyether-based (Polyethylene glycol: density 1.12 g / cc, oxygen balance -1.78 g), etc., glycidyl azide polymer (GAP: density 1.29 g / cc, oxygen balance -1.21 g, explosion heat 2500 kJ / kg) Oxetane polymers such as azido polymer, polynitratomethylmethyloxetane (polyNIMMO: density 1.26 g / cc, oxygen balance -1.14 g, heat of explosion 818 kJ / kg) and polyglycidyl nitrate (polyGLYN: density 1.46 g / cc, oxygen balance -0.61g, explosion 2661kJ / kg) oxirane polymers, and the like can be given. The heat of explosion is defined as the difference between the energy generated by the reactant and the energy generated by the explosion.

  The explosive composition preferably has a density of at least 1.4 g / cc. The detonation pressure of the explosive composition is preferably relatively low, and more preferably 15 to 35 GPa.

  The debris obtained by the detonation method may include debris from containers and blast debris such as wires and wires. In such a case, it is preferable to provide a step of removing rubble from the residue obtained in the detonation step and collecting the conductive diamond. A catalyst carrier can be obtained by collecting several samples of the obtained residue, measuring the Raman spectrum of each sample, and selecting a conductive diamond having a desired peak area ratio / peak intensity ratio.

  The method for supporting the metal catalyst precursor on the catalyst carrier is not particularly limited, but specifically, it is preferable to deposit the catalyst metal on the surface of the catalyst carrier. For example, a method of immersing a catalyst carrier in a precursor solution of a catalyst metal and then reducing the catalyst carrier is preferably used.

  Here, the precursor of the catalytic metal is not particularly limited, and is appropriately selected depending on the type of the catalytic metal used. Specific examples include chlorides, nitrates, sulfates, chlorides, acetates and amine compounds of the above-mentioned catalyst metals such as platinum. More specifically, chlorides such as platinum chloride (hexachloroplatinic acid hexahydrate), palladium chloride, rhodium chloride, ruthenium chloride, nitrates such as palladium nitrate, rhodium nitrate and iridium nitrate, palladium sulfate, rhodium sulfate and the like Sulfates, acetates such as rhodium acetate and the like, and ammine compounds such as dinitrodiammineplatinum nitrate and dinitrodiamminepalladium are preferable and exemplified. The solvent used for preparing the catalyst metal precursor solution is not particularly limited as long as it can dissolve the catalyst metal precursor, and is appropriately selected depending on the type of the catalyst metal precursor to be used. Specifically, water, acid, alkali, organic solvent and the like can be mentioned. The concentration of the catalyst metal precursor in the catalyst metal precursor solution is not particularly limited, but is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight in terms of metal. . When the catalyst carrier is immersed in the catalyst metal precursor solution, it is preferable to perform a reduced pressure treatment so that the solution is easily immersed inside the carrier.

  Examples of the reducing agent include hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like. . Note that a gaseous substance at normal temperature such as hydrogen can be supplied by bubbling. The amount of the reducing agent is not particularly limited as long as the precursor of the catalyst metal can be reduced to the catalyst metal, and a known amount can be similarly applied.

  The precipitation conditions are not particularly limited as long as the catalyst metal can be deposited on the catalyst carrier. For example, the deposition temperature is preferably a temperature near the boiling point of the solvent, more preferably room temperature to 100 ° C. Further, the deposition time is preferably 1 to 10 hours, more preferably 2 to 8 hours. The precipitation step may be performed with stirring and mixing, if necessary.

  As a result, the precursor of the catalyst metal is reduced to the catalyst metal, and the catalyst metal is deposited (supported) on the catalyst carrier.

[Fuel cell]
Another embodiment of the present invention is a catalyst layer including the electrode catalyst of the first embodiment and a fuel cell. The electrocatalyst of the first embodiment has high conductivity and its performance does not decrease much even when used for a long time. For this reason, the catalyst layer and the fuel cell using the electrode catalyst of the first embodiment have excellent power generation performance and maintain high power generation performance.

  The fuel cell includes a membrane electrode assembly (MEA), and a pair of separators including an anode-side separator having a fuel gas flow path through which a fuel gas flows and a cathode-side separator having an oxidizing gas flow path through which an oxidizing gas flows. Have.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to one embodiment of the present invention. The PEFC 1 has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the solid polymer electrolyte membrane 2. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched by a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). In this manner, the solid polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c) and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

  In the PEFC 1, the MEA 10 is further sandwiched by a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5a, 5c) are shown as being located at both ends of the MEA 10 shown. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used also as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked with the separator interposed therebetween, thereby forming a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another PEFC adjacent thereto. 1, these descriptions are omitted.

  The separators (5a, 5c) are obtained, for example, by pressing a thin plate having a thickness of 0.5 mm or less to form an uneven shape as shown in FIG. The protrusions of the separators (5a, 5c) viewed from the MEA side are in contact with the MEA 10. As a result, an electrical connection with the MEA 10 is ensured. In addition, the concave portion (the space between the separator and the MEA generated due to the uneven shape of the separator) as viewed from the MEA side of the separator (5a, 5c) is used to allow gas to flow during operation of the PEFC 1. Functions as a gas flow path. Specifically, a fuel gas (for example, hydrogen) flows through the gas flow path 6a of the anode separator 5a, and an oxidizing gas (for example, air) flows through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the recesses viewed from the side opposite to the MEA side of the separators (5a, 5c) serve as a coolant flow path 7 for flowing a coolant (for example, water) for cooling the PEFC 1 during operation of the PEFC 1. You. Further, the separator is usually provided with a manifold (not shown). This manifold functions as connecting means for connecting the cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  Note that, in the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to only such a concavo-convex form, as long as the function of the gas flow path and the refrigerant flow path can be exhibited, a flat form, an arbitrary form such as a partially concavo-convex shape. Is also good.

  The fuel cell having the electrode catalyst of the first embodiment as described above exhibits excellent power generation performance and durability. Here, the type of the fuel cell is not particularly limited, and in the above description, the polymer electrolyte fuel cell has been described as an example. In addition, an alkaline fuel cell, a direct methanol fuel cell And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferred because it is compact and can achieve high density and high output. In addition, the fuel cell is useful as a stationary power supply in addition to a power supply for a mobile body such as a vehicle having a limited mounting space. Above all, it is particularly preferable to use it as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long operation stop.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Among them, hydrogen and methanol are preferably used because high output can be achieved.

  The application of the fuel cell is not particularly limited, but is preferably applied to a vehicle. The fuel cell of this embodiment is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of the present invention is particularly advantageous when the fuel cell is applied to a vehicle from the viewpoint of vehicle mounting. Therefore, another embodiment of the present invention is a vehicle having the above fuel cell.

  Hereinafter, members constituting the fuel cell of the present embodiment will be briefly described, but the technical scope of the present invention is not limited to only the following embodiments.

[Catalyst layer]
The catalyst layer contains the electrode catalyst of the above embodiment and a (polymer) electrolyte. The electrode catalyst of this embodiment has high durability and sufficient conductivity, and high durability and sufficient conductivity are ensured even when applied to the catalyst layer.

  Here, the catalyst layer may be either a cathode catalyst layer or an anode catalyst layer, but the electrode catalyst of the above embodiment is preferably used at least for the anode catalyst layer. Since the reaction speed of the catalyst is high on the anode side, the amount of the catalytic metal, particularly platinum, can be reduced. However, when a small amount of catalyst metal is used, if the amount of catalyst metal is reduced due to deterioration of the catalyst carrier, even a small decrease in the amount of catalyst metal significantly reduces the performance. Since the electrode catalyst of the first embodiment has high durability, by applying the electrode catalyst of the first embodiment to the anode catalyst layer, it is possible to suppress a significant decrease in performance due to catalyst deterioration in the anode catalyst layer.

In the present embodiment, the catalyst content (mg / cm ² ) per unit catalyst application area is not particularly limited as long as a sufficient degree of dispersion of the catalyst on the carrier and power generation performance can be obtained, and for example, 0.01 to 1 mg. / Cm ² . Further, the platinum content per unit catalyst application area is preferably 0.5 mg / cm ² or less. The use of expensive noble metal catalysts typified by platinum has become a factor of high cost of fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range to reduce costs. The lower limit of the platinum content is not particularly limited as long as power generation performance can be obtained, and is, for example, 0.01 mg / cm ² or more. More preferably, the platinum content is between 0.02 and 0.4 mg / cm ² .

In the present specification, inductively coupled plasma emission spectroscopy (ICP) is used to measure (confirm) the “catalyst (platinum) content per unit catalyst application area (mg / cm ² )”. A person skilled in the art can easily carry out a method of obtaining a desired “content of catalyst (platinum) per unit catalyst application area (mg / cm ² )” by controlling the composition of the slurry (catalyst concentration) and the application amount. By doing so, the content can be adjusted.

  The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material.

  Examples of the ion exchange resin constituting the fluoropolymer electrolyte include, for example, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-par Fluorocarbon sulfonic acid polymers and the like can be mentioned. From the viewpoint of excellent heat resistance, chemical stability, durability and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably a fluorine-based polymer electrolyte composed of a perfluorocarbonsulfonic acid-based polymer. Is used.

  Specific examples of the hydrocarbon-based electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole, phosphonated polybenzimidazole, sulfonated polystyrene, and sulfonated polyetherether. Ketone (SPEEK), sulfonated polyphenylene (S-PPP), and the like. From the viewpoint of production that the raw materials are inexpensive, the production process is simple, and the selectivity of the material is high, these hydrocarbon-based polymer electrolytes are preferably used.

  In addition, only one kind of the above-mentioned ion exchange resin may be used alone, or two or more kinds may be used in combination. Further, the present invention is not limited to only the above-described materials, and other materials may be used.

  In a polymer electrolyte responsible for proton transmission, proton conductivity is important. Here, if the EW of the polymer electrolyte is too large, the ionic conductivity of the entire catalyst layer decreases. Therefore, the catalyst layer preferably contains a polymer electrolyte having a low EW. Specifically, the catalyst layer preferably has an EW of 1500 g / eq. It contains the following polymer electrolyte, more preferably 1200 g / eq. Including the following polymer electrolytes.

  On the other hand, if the EW is too small, the hydrophilicity is too high, and it is difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. In addition, EW (Equivalent Weight) represents the equivalent weight of an exchange group having proton conductivity. The equivalent weight is a dry weight of the polymer electrolyte per equivalent of the ion exchange group, and is expressed in units of “g / eq”.

  The catalyst layer may include, between the catalyst and the polymer electrolyte, a liquid proton conductive material capable of connecting the catalyst and the polymer electrolyte in a state capable of conducting protons. The introduction of the liquid proton conducting material ensures a proton transport path between the catalyst and the polymer electrolyte via the liquid proton conducting material, and efficiently transports protons required for power generation to the catalyst surface. Becomes possible. As a result, the utilization efficiency of the catalyst is improved, so that the usage amount of the catalyst can be reduced while maintaining the power generation performance. The liquid proton conductive material only needs to be interposed between the catalyst and the polymer electrolyte. The pores (secondary pores) between the porous carriers in the catalyst layer and the pores (mesopores) in the porous carrier are required. Etc .: primary vacancies).

  The liquid proton conductive material is not particularly limited as long as it has ion conductivity and can exhibit a function of forming a proton transport path between the catalyst and the polymer electrolyte. Specific examples include water, protic ionic liquid, aqueous perchloric acid, aqueous nitric acid, aqueous formic acid, and aqueous acetic acid.

  If water is used as the liquid proton conducting material, introduce water as the liquid proton conducting material into the catalyst layer by wetting the catalyst layer with a small amount of liquid water or humidified gas before starting power generation. Can be. Further, water generated by an electrochemical reaction during the operation of the fuel cell can be used as a liquid proton conductive material. Therefore, it is not always necessary to hold the liquid proton conductive material when the fuel cell starts operating. For example, it is desirable that the surface distance between the catalyst and the electrolyte be 0.28 nm or more, which is the diameter of oxygen ions constituting water molecules. By maintaining such a distance, water (liquid proton conductive material) is interposed between the catalyst and the polymer electrolyte (liquid conductive material holding portion) while maintaining the non-contact state between the catalyst and the polymer electrolyte. Thus, a proton transport path by water between the two can be secured.

  When using a substance other than water, such as an ionic liquid, as the liquid proton conductive material, it is desirable to disperse the ionic liquid, the polymer electrolyte, and the catalyst in the solution when preparing the catalyst ink. An ionic liquid may be added when applying to the layer substrate.

  If necessary, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol (EG) ), Polyvinyl alcohol (PVA), propylene glycol (PG), and other thickening agents, and additives such as pore-forming agents.

  The thickness (dry thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, and still more preferably 2 to 15 μm. Note that the above applies to both the cathode catalyst layer and the anode catalyst layer. However, the cathode catalyst layer and the anode catalyst layer may be the same or different.

  Since the electrode catalyst of the present invention has excellent electric conductivity, the resistance of the entire catalyst layer can be reduced. Preferably, the specific resistance of the catalyst layer is 10 Ω · cm or less (the lower limit is 0 Ω · cm), and more preferably 0.05 to 10 Ω · cm.

[Electrolyte membrane-electrode assembly (MEA)]
The MEA includes an electrolyte membrane, an anode catalyst layer and an anode gas diffusion layer, and a cathode catalyst layer and a cathode gas diffusion layer which are sequentially formed on both surfaces of the electrolyte membrane.

  The electrolyte constituting the electrolyte membrane is not particularly limited, but is preferably an ion-conductive polymer electrolyte. The polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, and is therefore also called a proton conductive polymer.

(Electrolyte membrane)
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane. The solid polymer electrolyte membrane has, for example, a function of selectively transmitting protons generated in the anode catalyst layer to the cathode catalyst layer along the film thickness direction during operation of a fuel cell (PEFC or the like). Further, the solid polymer electrolyte membrane also has a function as a partition for preventing the fuel gas supplied to the anode side and the oxidizing gas supplied to the cathode side from being mixed.

  The electrolyte material constituting the solid polymer electrolyte membrane is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte described as a polymer electrolyte in the catalyst layer can be used in the same manner. At this time, it is not always necessary to use the same polymer electrolyte as that used for the catalyst layer.

  The thickness of the electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte membrane is usually about 5 to 300 μm. When the thickness of the electrolyte membrane is within such a range, the balance between the strength during film formation, the durability during use, and the output characteristics during use can be appropriately controlled.

(Gas diffusion layer)
The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are formed of catalyst layers (3a, 3c) of gas (fuel gas or oxidizing gas) supplied through gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

  The material constituting the base material of the gas diffusion layers (4a, 4c) is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a conductive and porous sheet material such as a carbon woven fabric, a paper-like paper body, a felt, and a nonwoven fabric may be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, and may be about 30 to 500 μm. When the thickness of the base material is within such a range, the balance between mechanical strength and diffusibility of gas, water, and the like can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further increasing the water repellency and preventing the flooding phenomenon and the like. Examples of the water repellent include, but are not particularly limited to, fluorine-based high-molecular materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples include a molecular material, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer is provided with a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent on the catalyst layer side of the substrate. You may have.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately used. Among them, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black can be preferably used because of their excellent electron conductivity and large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. As a result, a high drainage property can be obtained by the capillary force, and the contact with the catalyst layer can be improved.

  Examples of the water repellent used in the carbon particle layer include the same water repellents as described above. Among them, a fluorine-based polymer material can be preferably used because it is excellent in water repellency, corrosion resistance during an electrode reaction, and the like.

  The mixing ratio between the carbon particles and the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) by weight in consideration of the balance between water repellency and electron conductivity. Is good. The thickness of the carbon particle layer is not particularly limited, and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer.

(Method of manufacturing electrolyte membrane-electrode assembly)
The method for producing the electrolyte membrane-electrode assembly is not particularly limited, and a conventionally known method can be used. For example, the catalyst layer is transferred or applied to the electrolyte membrane by hot pressing and dried, and then the gas diffusion layer is joined to the electrolyte membrane, or the microporous layer side of the gas diffusion layer (when the microporous layer is not included, A method in which two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer in advance on one side of the base material layer and drying, and joining the gas diffusion electrodes to both surfaces of the solid polymer electrolyte membrane by hot pressing. Can be used. The application and bonding conditions of hot pressing or the like may be appropriately adjusted depending on the type of polymer electrolyte (perfluorosulfonic acid or hydrocarbon) in the solid polymer electrolyte membrane or the catalyst layer.

[Separator]
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. Further, the separator also has a function as a partition for separating the fuel gas, the oxidizing gas, and the coolant from each other. In order to secure these flow paths, as described above, it is preferable that each of the separators is provided with a gas flow path and a cooling flow path. As a material for forming the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately used without any limitation. The thickness and size of the separator, the shape and size of each flow path provided, and the like are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The method for manufacturing the fuel cell is not particularly limited, and conventionally known knowledge in the field of the fuel cell can be appropriately referred to.

  Further, a fuel cell stack having a structure in which a plurality of electrolyte membrane-electrode assemblies are stacked via a separator and connected in series so that the fuel cell can exhibit a desired voltage may be formed. The shape and the like of the fuel cell are not particularly limited, and may be appropriately determined so as to obtain desired cell characteristics such as a desired voltage.

  The above-described PEFC and the electrolyte membrane-electrode assembly use a catalyst layer excellent in power generation performance and durability. Therefore, the PEFC and the electrolyte membrane-electrode assembly are excellent in power generation performance and durability.

  The PEFC of this embodiment and the fuel cell stack using the same can be mounted, for example, as a drive power source in a vehicle.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. Unless otherwise specified, each operation is performed under the conditions of room temperature (25 ° C.) / Relative humidity of 40 to 50%.

(Measurement of Raman spectrum)
The measurement of the Raman spectroscopy spectrum was performed with the following apparatus and conditions.

Measuring device: Renishaw inVia Raman microscope Irradiation laser wavelength: 325 nm (He-Cd laser)
Objective lens: x40NU
Laser power: 5%
Integration: 1 time Spectral range: -432.53 cm ^{-1 to} 3203.72 cm ^-1
Grating: 2400 l / mm (UV)
Irradiation time: 40s
Software used for analysis: WiRE ver. 4.0 (inVia mounted).

  The curve fitting was automatically performed by arbitrarily specifying a peak position on the spectrum screen. When the error between the actually measured spectrum and the simulated spectrum was large by visual recognition, the number of peaks was added or the position was moved, and the process was repeated until the error became small.

Reference Examples 1-3
After detonating the explosive composition described in Example 1 of JP-A-2005-289677 as described in [0039] of JP-A-2005-289677, several detonation residues were sampled, and each sample was washed with water. And dried. Thereafter, metal impurities were dissolved in each sample with hydrochloric acid, and the precipitate was filtered. The sample remaining on the filter paper was washed with water and dried to obtain each sample.

  The spectrum of each of the samples thus obtained was measured according to the following Raman spectroscopy. From among these, conductive diamonds A to C were obtained.

The conductive diamond A had a peak area ratio of 0.02 and a peak intensity ratio of 0.07, an average particle diameter (diameter) of about 40 nm, and a BET specific surface area of about 50 m ² / g.

The conductive diamond B had a peak area ratio of 0.14 and a peak intensity ratio of 0.59, an average particle diameter (diameter) of about 65 nm, and a BET specific surface area of about 50 m ² / g.

  The conductive diamond C had a peak area ratio of 0.21 and a peak intensity ratio of 0.91.

Reference example 4
Ketjen Black EC300J (Ketjen Black International) (Carrier D) was baked in an electric furnace under a nitrogen atmosphere at 2000 ° C. for 1 hour to obtain a graphitized Ketjen Black (Carrier E).

Example 1
Using the conductive diamond A obtained above, platinum (Pt) having an average particle diameter of more than 3 nm and 5 nm or less as a catalyst metal was supported on the conductive diamond A at a loading of 30% by weight to obtain a catalyst powder. That is, 46 g of the carrier A was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammineplatinum nitric acid solution having a platinum concentration of 4.6% by mass, stirred, and then 100 ml of 100% ethanol as a reducing agent was added. This solution was stirred and mixed at the boiling point for 7 hours, and platinum was supported on the conductive diamond A. Then, by filtering and drying, a catalyst powder having a loading of 30% by weight was obtained.

  FIG. 2 is a transmission electron microscope (TEM) photograph of the catalyst obtained in Example 1. As shown in FIG. 1, a uniform lattice image of the conductive diamond was obtained, and a clear boundary between the graphite layer and the diamond layer could not be confirmed. The black image in the photograph of FIG. 2 is the catalyst (Pt).

(Evaluation method and results)
<Durability test>
The catalyst powder obtained in Example 1 was mixed with 10 mg of a carrier (about 14.29 mg as a catalyst), 19 ml of water and 6 ml of isopropyl alcohol, and 100 μl of an ionomer dispersion (Nafion (registered trademark) D521, manufactured by DuPont). Ultrasonic waves were irradiated for 60 minutes while cooling with ice water.

  10 μl of the ink obtained above was applied onto an Au electrode mirror-polished with alumina (φ0.05 μm) and dried to prepare an electrode.

A Pt line was used as a counter electrode, and a reversible hydrogen electrode (RHE) was used as a reference electrode. Electrolyte with 0.1M perchloric acid (HClO _4), was saturated with _{N 2.} The measurement was performed at 60 ° C.

  The calculation of the current value (Idl (μA)) of the electric double layer was performed as follows. Before performing the measurement, the voltage was maintained at 0.5 V for 10 seconds, and then the cycle between 0.02 and 1.2 V was performed at 100 mV / s for 5 cycles. Thereafter, the potential range of 1.0 to 1.5 V is raised (1 second) and lowered (1 second) at a potential sweep rate of 0.5 V / s, and this is taken as one cycle (2 seconds / cycle) to perform a potential cycle test. went. The CV evaluation was performed by performing three cycles between 0.02 and 1.2 V at a scanning speed of 50 mV / s. CV evaluation was performed when the cycle was 0, 100, 200, 500, 1000, 2000, 3000 and 4000 cycles. The electric current value (Idl (μA)) of the electric double layer was obtained from the sum of the oxidation and reduction currents at 0.2 V for those not containing a catalyst, and the minimum value (oxidation current) at 0.35 to 0.6 V for those containing a catalyst. ) And the maximum value (reduction current).

The conductive diamond A obtained in Reference Example 1, the conductive diamond B obtained in Reference Example 2, Ketjen Black EC300J (Ketjen Black International) as the support D, and the support E obtained in Reference Example 4 Was similarly subjected to a durability test. The change in the electric double layer current (Normalized I _dl ) with respect to the number of potential cycles was summarized by normalizing the electric double layer current in each of the 0 cycles.

  The results are shown in FIG.

  From the results shown in FIG. 3, it can be said that the catalyst of Example 1 and the conductive diamonds A and B hardly change their reaction area for as long as 4000 cycles, and therefore have excellent long-term durability. Therefore, it can be seen that the present invention is very advantageous in an application in which battery performance needs to be maintained for a long time, such as for a vehicle. In particular, when applied to an anode catalyst layer in which a reduction in the reaction area can cause a significant decrease in performance, it can be seen that the effect is remarkably exhibited. Further, since the results of the catalyst of Example 1 and the conductive diamond A were similar, it can be seen that the deterioration of the catalyst was substantially caused by the deterioration of the catalyst carrier.

(Evaluation method and results)
<Evaluation of conductivity (catalyst layer)>
Conductive diamond A or conductive diamond B obtained in Reference Example, and an ionomer dispersion liquid (Nafion (registered trademark) D2020, EW = 1100 g / eq, manufactured by DuPont) as a polymer electrolyte were used as a catalyst carrier and ionomer. Were mixed so that the weight ratio became 0.9. Furthermore, a catalyst ink was prepared by adding a normal propyl alcohol solution (40% by weight) as a solvent so that the solid content (Pt + catalyst carrier + ionomer) became 7% by weight.

  The catalyst ink was applied to the PTFE sheet to a thickness of 1.7 μm by a spray coating method. The catalyst ink was dried by maintaining the stage for performing the spray coating at 60 ° C. for 1 minute to obtain an electrode catalyst layer. Four equilibrium Pt wires having a distance of two centers of 1 cm were brought into contact with the catalyst layer, and the resistance of the catalyst layer was measured by an electrochemical impedance method (EIS) under the following conditions.

Temperature: 25 ° C
Humidity: dry (under dry Air atmosphere)
Frequency range: 10-0.1kHz
Superimposed voltage: 5 mV
Bias voltage: 0V.

  As a result, the specific resistance of the catalyst layer using the conductive diamond A was 1.6 Ω · cm, and the specific resistance of the catalyst layer using the conductive diamond B was 8.2 Ω · cm.

<Conductivity evaluation (powder specific resistance)>
The specific resistance of the conductive diamond obtained above was measured according to the electrical resistivity of JIS K1469: 2003.

  As a result, the specific resistance of the conductive diamond A was less than 0.1 Ω · cm, and the specific resistance of the conductive diamond B was 0.6 Ω · cm. The specific resistance of the conductive diamond C was 760 Ω · cm. Therefore, the specific resistance of the conductive diamonds A and B was significantly smaller than the specific resistance of the conductive diamond C.

  Since the conductivity of the electrode catalyst depends on the conductivity of the conductive carrier, the conductivity of the conductive diamond (carrier) was measured in the above.

1: Solid polymer fuel cell (PEFC),
2. Solid polymer electrolyte membrane,
3 ... catalyst layer,
3a: anode catalyst layer,
3c: cathode catalyst layer,
4a: anode gas diffusion layer,
4c: cathode gas diffusion layer,
5a: anode separator,
5c: cathode separator,
6a: anode gas flow path,
6c: cathode gas flow path,
7 ... refrigerant channel,
10. Electrolyte membrane-electrode assembly (MEA).

Claims (8)

  The conductive diamond has a ratio of the peak area derived from the sp3 orbital to the peak area derived from the sp2 orbital measured by Raman spectroscopy, which is more than 0 and 0.2 or less, and a catalytic metal supported on the conductive diamond. , Electrocatalyst.   The conductive diamond has a ratio of the peak intensity derived from the sp3 orbital to the peak intensity derived from the sp2 orbital measured by Raman spectroscopy, being more than 0 and not more than 0.8, and a catalytic metal supported on the conductive diamond. , Electrocatalyst.   The conductive diamond having a ratio of a peak intensity derived from an sp3 orbital to a peak intensity derived from an sp2 orbital measured by a Raman spectroscopy spectrum being more than 0 and 0.8 or less, and a catalyst metal are supported. Electrocatalyst.   The electrode catalyst according to any one of claims 1 to 3, wherein the specific resistance of the conductive diamond is 1 Ω · cm or less.   The electrode catalyst according to any one of claims 1 to 4, wherein the catalyst metal is platinum or contains platinum and a metal component other than platinum.   A catalyst layer comprising the electrode catalyst according to claim 1 and an electrolyte.   A fuel cell comprising the catalyst layer according to claim 6.   The fuel cell according to claim 7, wherein the catalyst layer is used on an anode catalyst layer side.