JP2008077974A - Electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode having superior durability and superior catalytic performance. <P>SOLUTION: The electrode contains a compound 4 containing a nitrogen-containing six-membered ring, catalyst particles 3, catalyst carrying carbon 2 carrying the catalyst particles, and fibrous carbon 5. The compound containing the nitrogen-containing six-membered ring is a pyridine compound, and at least one compound selected from the group comprising a bipyridiene compound, a terpyridine compound, and a phenanthroline compound. The fibrous carbon is vapor phase growth carbon fibers, and 1-30 mass% is contained with respect to the total mass of the electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode, and more particularly to a fuel cell electrode having excellent durability.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature.

  In general, a polymer electrolyte fuel cell has a structure in which a membrane-electrode assembly (hereinafter, also simply referred to as “MEA”) is sandwiched between separators. The MEA is formed by sandwiching a solid polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusion layer. The electrode catalyst layer includes at least an electrode catalyst and a solid polymer electrolyte, and is also simply called an electrode.

  Catalysts used for fuel cell electrodes are required to maintain a desired catalytic activity for a long period from the beginning of power generation, and various research and developments are underway.

For example, Patent Document 1 discloses an electrode in which fibrous carbon is added to a catalyst layer. According to this method, since the porosity in the electrode catalyst layer is increased by adding fibrous carbon, the gas diffusibility and drainage of the electrode catalyst layer are improved, and high power generation performance can be obtained. . Further, it has been clarified that the addition of fibrous carbon forms a conductive network of the electrode catalyst layer, thereby improving the catalyst utilization rate and further contributing to the improvement of the durability of the catalyst layer.
JP 2003-115302 A

  However, in an actual operation mode, catalyst particles are eluted from the catalyst-carrying carbon or carbon is corroded due to a load fluctuation or a high potential state, and the water repellency of the surface of the fibrous carbon is further reduced. As a result, dissolved, precipitated, and free catalyst particles are likely to deposit and adhere to the fibrous carbon. Therefore, the oxidative corrosion of the fibrous carbon is promoted at high potentials, and the pores of the catalyst layer are reduced. There was a problem that the performance of the layer was lowered, and as a result, the performance of the fuel cell was lowered.

  Then, an object of this invention is to provide the electrode which has the performance outstanding in both durability and catalyst performance.

  As a result of accumulating intensive studies in view of the above problems, the present inventors can suppress elution and corrosion deterioration of the components of the electrode catalyst by adding a compound containing a nitrogen-containing six-membered ring to the electrode catalyst layer. The inventors have found that an electrode catalyst excellent in durability and catalytic performance can be obtained, and have completed the present invention.

  That is, the present invention is an electrode comprising a compound containing a nitrogen-containing 6-membered ring, catalyst particles, catalyst-supporting carbon formed by supporting the catalyst particles, and fibrous carbon.

  According to the present invention, an electrode having excellent performance in both durability and catalyst performance can be provided.

  Embodiments of the present invention will be described below.

  The present invention is an electrode comprising a compound containing a nitrogen-containing 6-membered ring, catalyst particles, catalyst-supporting carbon formed by supporting the catalyst particles, and fibrous carbon.

  First, the structure of the electrode of the present invention will be described with reference to the drawings. In the present invention, the drawings are exaggerated for convenience of explanation, and the technical scope of the present invention is not limited to the forms shown in the drawings. Also, embodiments other than the drawings may be employed.

  FIG. 1 is a cross-sectional view showing an embodiment of the electrode of the present invention. The electrode 1 having the form shown in FIG. 1 has a catalyst particle 3 supported on a conductive carrier 2 and a compound 4 containing a nitrogen-containing six-membered ring so as to cover the conductive carrier 2 and the catalyst particle 3. Has a structure. Conventionally, by adding fibrous carbon to the catalyst-supporting carbon, the porosity in the electrode catalyst layer is increased, so that gas diffusibility and drainage are improved, and high power generation performance can be obtained. It has been clarified that it contributes to the improvement of the durability. On the other hand, conventionally, in an actual operation mode, catalyst particle elution of the catalyst-supported carbon or carbon corrosion occurs due to battery load fluctuation or high potential state, and the water repellency of the surface of the fibrous carbon decreases. As a result, dissolved, precipitated, and liberated catalyst particles tend to adhere to the fibrous carbon, which promotes oxidative corrosion of the fibrous carbon at high potentials, reduces the pores of the catalyst layer, and lowers the performance of the electrode catalyst layer. Could cause. Therefore, by adding a compound containing a nitrogen-containing 6-membered ring having a metal coordination ability and having an elution resistance effect of the catalyst particles in the electrode catalyst layer, the adhesion of the catalyst particles on the fibrous carbon is suppressed, It becomes possible to suppress degradation of the added fibrous carbon itself. Moreover, corrosion of the fibrous carbon due to precipitation of platinum particles can be suppressed by supporting a compound containing a nitrogen-containing 6-membered ring in advance on the fibrous carbon. Furthermore, even if the fibrous carbon is entangled with the catalyst-carrying carbon evenly, the distance between the catalyst particles is increased, and even if a minute amount of the catalyst component is dissolved and precipitated, the particles can hardly be aggregated.

  The compound containing a nitrogen-containing 6-membered ring used in the present invention is not particularly limited as long as it is a compound containing a nitrogen-containing 6-membered ring structure that does not show a catalytic effect on the electrode reaction and has a metal coordination ability. Conventionally known compounds can be used, and among them, a pyridine compound is preferable, and at least one compound selected from the group consisting of a bipyridine compound, a terpyridine compound, and a phenanthroline compound is more preferable.

  This is because the bridge structure formed by a compound having a polycyclic structure (especially a polycyclic aromatic compound) secures a catalytic function site of a metal such as platinum and the above-described dissolution mechanism of platinum. It can be presumed that elution of selenium can be suppressed. Furthermore, the steric effect resulting from the structure of the polycyclic aromatic compound, that is, the atoms at the edges and corners of the catalyst component such as Pt having a polyhedral structure have a greater degree of freedom than the atoms on the surface. Because there are few steric hindrances when a relatively large polycyclic aromatic compound approaches the catalyst component, it is easy to selectively coordinate to the edge portion and corner portion of the catalyst component preferentially. It is considered that the ligand is stable.

  Specific examples of the bipyridine compound, terpyridine compound, and phenanthroline compound according to the present invention include 2,2′-bipyridine, 2,6-di (2-pyridyl) pyridine, 1,10-phenanthroline, 4,7-biphenyl- 1,10-phenanthroline, 1,7-phenanthroline, bathocuproin, bathocuproin sulfonic acid and the like are preferable, and 2,2′-bipyridine is particularly preferable.

The addition amount of the compound containing a nitrogen-containing 6-membered ring used in the present invention is preferably 0.1 to 1.5 nmol / cm ² per platinum electrode area in the platinum-supported carbon powder. May if the addition amount of the compound containing a nitrogen-containing 6-membered ring is less than 0.1 nmol / cm ² inhibitory effect of the platinum elution hardly cracks Table, lowering the power generation performance exceeds 1.5 nmol / cm ² There is a case.

  Since the compound containing a nitrogen-containing 6-membered ring according to the present invention coexists on the catalyst surface via a nitrogen atom having a metal coordination ability, Pt oxidation is suppressed, so that Pt elution can be suppressed or prevented. It is thought that. Assuming that Pt elution starts from the formation of Pt oxide species that occurs at this highly active site, these aromatic compounds selectively adsorb to the highly active site to suppress the formation of oxidants of platinum. As a result, it is considered that platinum elution is suppressed.

  Furthermore, when the compound containing a nitrogen-containing 6-membered ring according to the present invention is used in a conventional membrane-electrode assembly, it can be applied without changing the form of the conventional membrane-electrode assembly, and the amount of Pt elution is suppressed. can do. Moreover, since the compound containing a nitrogen-containing 6-membered ring according to the present invention can exert an effect with a very small amount of adsorption, it can suppress a decrease in catalyst performance accompanying adsorption of the adsorbent to the catalyst metal, Thereby, the battery life can be extended.

  The electrode catalyst layer used in the present invention includes a catalyst-supporting carbon on which a catalyst component is supported, an electrolyte (also referred to as an ion conductive material), fibrous carbon, and a compound containing the nitrogen-containing six-membered ring. . Hereinafter, the catalyst component, catalyst-supporting carbon, ion conductive material, fibrous carbon, and polymer electrolyte used in the present invention will be described. In addition, since the compound containing the nitrogen-containing 6-membered ring which concerns on this invention was demonstrated above, it abbreviate | omits here.

  The catalyst component used in the electrode of the present invention is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. Also, the catalyst component used for the fuel electrode side catalyst is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, gold, silver, cobalt, nickel, manganese, vanadium, molybdenum, gallium, or aluminum, and their It is selected from alloys and the like. Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like.

  Further, Pt, Pd, Ir, Rh, or Au is particularly preferable as a catalyst species that is excellent in electrocatalytic activity for each electrocatalytic reaction and that has an elution suppressing effect by adsorption of a compound containing a nitrogen-containing 6-membered ring. These catalytic metals can be used in the state where a metal alone or an alloy, or other noble metal, base metal, or metal composition is mixed. Pd, Ir, Rh, and Au are considered to be eluted by the generation of dissolved species in their own redox process, like Pt, and the same elution suppression effect as Pt is obtained.

  In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties.

  The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the oxidant electrode side electrode catalyst layer and the catalyst component used for the fuel electrode side electrode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the oxidant electrode side electrode catalyst layer and the fuel electrode side electrode catalyst layer have the same definition for both, and are collectively referred to as “catalyst components”. . However, the catalyst components for the oxidant electrode side electrode catalyst layer and the fuel electrode side electrode catalyst layer do not need to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. Under the present circumstances, it is preferable that the average particle diameter of the catalyst component used for an electrode catalyst is 0.1-100 nm, It is more preferable that it is 0.5-10 nm, It is further more preferable that it is 1-5 nm. If the average particle size is 0.1 nm or more, the specific surface area is not too large, high mass activity is obtained, and sufficient Pt elution resistance is also obtained. If it is 100 nm or less, elution resistance is obtained, and the specific surface area is not too small, and sufficient mass activity is obtained. In addition, the value computed from the transmission electron microscope (TEM) observation shall be employ | adopted for the average particle diameter of the catalyst component in this invention.

  In the catalyst-supported carbon, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 60% by mass with respect to the conductive support. Here, a value measured by inductively coupled plasma emission spectroscopy (ICP) is adopted as the loading amount of the catalyst component.

  In order to further suppress the elution of Pt, the supported amount of the catalyst component should be within a certain range. If it is 10 mass% or more, the catalyst layer does not become too thick, and high electrode performance can be obtained. Moreover, if it is 80 mass% or less, the elution of Pt is further suppressed, and the catalyst component becomes highly dispersed, so that the performance obtained with respect to the amount of the catalyst component becomes sufficient.

  The carbon material used for the catalyst-carrying carbon according to the present invention has a specific surface area for carrying the catalyst component in a desired dispersed state, and has sufficient electronic conductivity as a current collector. It can be used in the present invention, and the main component is preferably a conductive material. By using a conductive material, it is possible to obtain a high-performance fuel electrode side electrode with little electrical resistance loss and material diffusion loss. Specific examples of the carbon material preferably include carbon materials such as carbon black, activated carbon, coke, natural graphite, and artificial graphite. Further, as such carbon materials, more specifically, acetylene black, Vulcan, Ketjen black, black pearl, graphitized acetylene black, graphitized Vulcan, graphitized Ketjen black, graphitized carbon, graphitized black pearl And at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils.

  Further, the size of the carbon material is not particularly limited, but the primary particle diameter is preferably 2 to 2 from the viewpoint of easy loading, catalyst utilization, and control of the thickness of the electrode catalyst layer within an appropriate range. The thickness should be 100 nm, more preferably 10 to 80 nm, and still more preferably about 20 to 50 nm. If the primary particle diameter of the carbon material is 2 nm or more, it becomes easy to maintain highly dispersed support without being too small with respect to the catalyst component particle diameter. Since the surface area is obtained, sufficient electrode performance can be obtained without aggregation of catalyst components. In the present invention, a value calculated from observation with a transmission electron microscope or a scanning electron microscope is adopted as the primary particle diameter of the carbon material.

  In addition, a plurality of conductive materials, for example, carbon materials such as the above-described carbon black are generally aggregated, but individual particles constituting the aggregate are referred to as “primary particles” in the present specification.

  Furthermore, the porosity of the conductive material is preferably 5 to 80% by volume, and more preferably 10 to 70% by volume.

  The carbon material is preferably a powder or a porous structure composed of 85% by mass to 100% by mass of carbon, more preferably 90% by mass to 100% by mass, and further 95% by mass to 100% by mass. preferable. When the proportion of carbon in the conductive material is within the above range, a high-performance electrode having both a sufficient specific surface area and high electronic conductivity can be obtained.

The specific surface area of the carbon material is preferably 25 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. If the specific surface area is less than 25 m ² / g, the dispersibility of the supported catalyst particles is reduced, resulting in coarse particles, and the specific surface area of the catalyst is greatly reduced, making it difficult to obtain good battery performance. There is a case. On the other hand, if it exceeds 1600 m ² / g, the catalyst particles are easily supported in a highly dispersed state, but the utilization rate of the catalyst particles may be reduced. In addition, the value measured by BET method shall be employ | adopted for the said specific surface area.

  A material composed of carbon supporting the catalyst component has sufficient electronic conductivity, and it is necessary to easily disperse the catalyst component easily. Therefore, a carbonaceous material is preferably used. Examples of elements included other than, for example, fluorine and silicon for imparting water repellency, boron for improving the corrosion resistance of carbon materials, hydrogen, oxygen, nitrogen contained in surface functional groups, In addition, metals that become impurities can be used.

  The catalyst component can be supported on the conductive material according to the present invention by a known method. For example, a known method such as an impregnation method, a liquid phase reduction support method, an evaporation to dryness method, a colloid adsorption method, a spray pyrolysis method, or a reverse micelle method (microemulsion method) can be used.

  For example, in order to support the catalyst component on the surface of the conductive material by the impregnation method, a step of adding the conductive material to a solution containing the catalyst component (hereinafter also referred to as catalyst solution), and the catalyst on the surface of the conductive material And a step of impregnating the solution with a catalyst component supporting step of supporting the catalyst component on the conductive material. As a result, the catalyst component can be highly dispersed and supported on the surface of the conductive material, and an electrode catalyst having sufficient initial performance and excellent durability can be obtained.

  The solution containing the catalyst component is a solution containing the element of the catalyst component supported on the conductive material. Since the catalyst component exhibits high catalytic activity, the electrode catalyst according to the present invention described above is used. The same elements as the catalyst component used for the layer can be mentioned.

  The ion conductive material that is an electrolyte in the electrode catalyst layer is not particularly limited and a known material can be used. Examples thereof include the same materials as those used for the polymer electrolyte membrane, and at least high proton conductivity. Any material that has The oxidant electrode side catalyst layer / fuel electrode side catalyst layer (hereinafter also simply referred to as “catalyst layer”) of the present invention includes a polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark; manufactured by DuPont), Aciplex (registered trademark; manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark; manufactured by Asahi Glass Co., Ltd.), and the like. Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene Polymers or polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers are preferred examples.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, and poly A suitable example is phenylsulfonic acid.

  Since the polymer electrolyte is excellent in heat resistance, chemical stability, etc., it preferably contains a fluorine atom. Among them, 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 are more preferable.

  Preferred examples of the fibrous carbon used in the present invention include PAN (Polyacrylonitrile) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube. However, pitch-based carbon fibers and PAN-based carbon fibers have a fiber length longer than 100 μm, and as such, are difficult to mix uniformly with the catalyst, and it may be difficult to form a catalyst layer having a uniform thickness. Therefore, in view of conductivity, it is more preferable to use nanotubes or vapor-grown carbon fibers (VGCF (registered trademark); manufactured by Showa Denko KK), and VGCF (heat conductivity is increased by heat treatment) Registered trademark) is particularly preferred. VGCF (registered trademark) is entangled with the catalyst material constituting the catalyst layer and the carbon particles supporting the catalyst material, so that a new conductive path is developed in addition to the conductive path due to the point contact of the carbon particles. The electron conductivity of the is improved. In addition, VGCF (registered trademark) is entangled and exists in the catalyst layer, so that voids are likely to be generated, and these voids may remain even if they are press-bonded to the electrolyte membrane. It functions as a road and power generation efficiency is improved. In the present invention, it is preferable that no catalyst component is supported on VGCF (registered trademark). If the catalyst component is supported in advance, the corrosion of the VGCF (registered trademark) by the catalyst component at a high potential is promoted, resulting in a decrease in durability. Therefore, as a means for adding VGCF (registered trademark), a catalyst formed by kneading a polymer electrolyte and a solvent together with a catalyst-carrying conductive material prepared using a precursor solution containing a conductive material and a catalyst component It is preferable to add it to the ink. Further, a pyridine compound may be previously supported on the fibrous carbon.

  In addition, the thickness of the electrode catalyst layer according to the present invention is preferably 1 to 50 μm, more preferably 5 to 20 μm.

  The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that functions as an adhesive. Thereby, while being able to maintain the structure of an electrode stably, the sufficient three-phase interface where an electrode reaction advances can be ensured, and high catalyst activity can be obtained. Although content of the said ion conductive material contained in an electrode is not specifically limited, It is preferable to set it as 20-60 mass% with respect to the whole quantity of a catalyst component.

  In the case where the electrode according to the present invention is used as a membrane-electrode assembly (MEA), the polymer electrolyte used in the polymer electrolyte membrane and the electrode layer may be different, but the contact resistance between the membrane and the electrode, etc. In consideration, it is preferable to use the same one.

  The polymer electrolyte membrane used for the membrane-electrode assembly is not particularly limited, and examples thereof include a membrane made of the same polymer electrolyte as that used for the electrode catalyst layer. In addition, perfluorosulfonic acid membranes represented by Nafion (registered trademark; manufactured by DuPont), Aciplex (registered trademark; manufactured by Asahi Kasei Co., Ltd.), or Flemion (registered trademark; manufactured by Asahi Glass Co., Ltd.), manufactured by Dow Chemical Co., Ltd. Fluorine polymer electrolytes such as ion exchange resins, ethylene-tetrafluoroethylene copolymer resin membranes, resin membranes based on trifluorostyrene, and hydrocarbon resin membranes with sulfonic acid groups Alternatively, a commercially available polymer electrolyte membrane, a membrane in which a polymer microporous membrane is impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, and the like may be used. Further, a porous thin film formed of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like may be impregnated with an electrolyte component such as phosphoric acid or ionic liquid. The polymer electrolyte used for the polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same or different, but the adhesion between each electrode catalyst layer and the polymer electrolyte membrane From the viewpoint of improving the properties, it is preferable to use the same one.

  The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained membrane-electrode assembly, but is preferably 10 to 75 μm, more preferably 15 to 70 μm, and particularly preferably 20 to 60 μm. is there. The thickness is preferably 10 μm or more from the viewpoint of strength during film formation and durability during operation of the membrane electrode assembly, and is preferably 75 μm or less from the viewpoint of output characteristics during operation of the membrane electrode assembly.

  Next, the manufacturing method of the electrode of this invention is demonstrated. In addition, the following aspects show the preferable aspect of this invention, and the manufacturing method of the electrode of this invention is not limited to the following method.

  The electrode of the present invention is supported after a catalyst component solution such as platinum and a solution containing a compound containing a nitrogen-containing 6-membered ring are added to a conductive carrier such as carbon black, and dispersed by a homogenizer or the like. Next, the catalyst-carrying carbon carrying the catalyst component and the compound containing a nitrogen-containing 6-membered ring is dried. Thereafter, catalyst-carrying carbon and ion conductive materials such as Nafion are added to a solvent such as water or alcohol as necessary to prepare a catalyst slurry.

  If the solid content concentration of the catalyst component solution is preferably 5% to 20% or less than 5%, the viscosity of the catalyst slurry may be lowered and a good catalyst application state may not be obtained, and it exceeds 20%. In addition, the viscosity of the catalyst slurry is increased, and a good catalyst application state may not be obtained. Since the catalyst component is as described above, the description thereof is omitted here.

  The concentration of the solution containing the compound containing the nitrogen-containing 6-membered ring is preferably 1-1000 μM. Since the compound containing a nitrogen-containing 6-membered ring is as described above, the description thereof is omitted here.

  The catalyst slurry is applied onto a transfer mount and dried to form an electrode catalyst layer. In this case, as the transfer mount, a known sheet such as a PTFE (polytetrafluoroethylene) sheet, a PET (polyethylene terephthalate) sheet, or a polyester sheet can be used. The transfer mount is appropriately selected according to the type of catalyst slurry to be used (particularly, a conductive material such as carbon in ink). Further, in the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (fuel electrode side) and the oxygen reduction reaction (oxidant electrode side). Similar thicknesses can be used. Specifically, the thickness of the electrode catalyst layer is preferably 0.1 to 50 μm, more preferably 1 to 10 μm.

  The catalyst slurry on the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. The applied electrode catalyst layer drying conditions are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the coating layer (electrode catalyst layer) of the catalyst slurry is dried in a vacuum dryer, preferably at room temperature to 100 ° C, more preferably at 50 to 80 ° C, for 30 to 60 minutes. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, the process proceeds to the following steps.

  That is, after sandwiching the solid polymer electrolyte membrane thus produced, hot pressing is performed on the laminate. At this time, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the solid polymer electrolyte membrane can be joined sufficiently closely, but are 110 to 150 ° C., more preferably 120 to 140 ° C. Preferably, the press pressure is 1 to 5 MPa. Thereby, bondability with a solid polymer electrolyte membrane and an electrode catalyst layer can be improved.

  After performing the hot press, the composite of the electrode catalyst layer and the solid polymer electrolyte membrane (so-called CCM) can be obtained by peeling off the transfer mount.

  In the method for producing a fuel cell using the electrode according to the present invention, it is necessary to provide a pair of gas diffusion layers on both sides of the composite of the electrode catalyst layer and the solid polymer electrolyte membrane.

  The gas diffusion layer is produced by impregnating a known solvent such as ethanol and carbon paper or carbon non-woven fabric or carbon cloth into a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) as necessary. It is preferably carried out by drying in air or an inert gas such as nitrogen.

  In the catalyst slurry used in the present invention, the electrode catalyst should have an amount sufficient to exhibit the desired action, that is, the action of catalyzing the hydrogen oxidation reaction (fuel electrode side) and the oxygen reduction reaction (oxidant electrode side). Any amount may be used. The electrode catalyst is preferably present in the catalyst slurry in an amount such that it is 5 to 75% by mass, more preferably 10 to 60% by mass, based on the total mass of the catalyst slurry.

  In addition to the electrode catalyst, the ion conductive polymer, and the solvent, the catalyst slurry has water repellency such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, if necessary. Polymers, thickeners and the like may be included. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged.

  The use of a thickener is effective when the catalyst slurry or the like cannot be successfully applied onto the transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, EG (ethylene glycol), and PVA (polyvinyl alcohol). The amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 0 to 10 with respect to the total mass of the catalyst slurry. % By mass. Furthermore, the solvent constituting the catalyst slurry used in the present invention is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, cyclohexanol, lower alcohols such as ethanol and 2-propanol can be used.

  The amount of the solvent used in the present invention is not particularly limited as long as it is an amount capable of dissolving the electrolyte, but the electrolyte is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass in the solvent. The amount is such that the concentration is reached. At this time, if the concentration of the electrolyte is 20% by mass or less, it is unlikely that the electrolyte is completely dissolved and colloid is formed. On the other hand, when the content is 0.1% by mass or more, the electrolyte mass contained is an appropriate amount, and thus the molecular chains of the electrolyte polymer are entangled well. For this reason, the mechanical strength of the electrode catalyst layer formed is excellent. Further, in the catalyst slurry, the concentration of the solid content including the electrode catalyst and the solid polymer electrolyte is preferably 5 to 50% by mass, more preferably about 10 to 40% by mass in the catalyst slurry.

  The catalyst slurry used in the present invention may be used only for either the oxidant electrode side electrode catalyst layer or the fuel electrode side electrode catalyst layer, or may be used for both, but the oxidant electrode side is particularly There is a high risk that the porous structure of the electrode catalyst layer in the initial state will collapse due to changes in the amount of generated water due to output fluctuations, the porosity will decrease, and the amount of reactant gas supplied to the electrode catalyst layer will decrease Therefore, it is preferably used for at least the fuel electrode side electrode catalyst layer.

  In the above method, the diffusion layer is peeled off the transfer mount, and the obtained joined body is further sandwiched between gas diffusion layers, so that the electrode catalyst layer and the solid polymer electrolyte membrane are further bonded to each electrode catalyst layer. It is preferable to join. Alternatively, after an electrode catalyst layer is formed on the surface of the gas diffusion layer in advance to produce an electrode catalyst layer-gas diffusion layer assembly, the electrode catalyst layer-gas diffusion layer assembly is solid as described above. It is also preferable to sandwich and bond the polymer electrolyte membrane by hot pressing.

  In addition to the hot pressing method, a method of laminating an electrode catalyst layer, a polymer electrolyte membrane, an electrode catalyst layer, and a gas diffusion layer by sequential coating on the gas diffusion layer may be used.

  A second invention is a fuel cell using the electrode according to the present invention.

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a solid polymer electrolyte fuel cell is preferable because it is small in size and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, mobile objects such as automobiles that are susceptible to corrosion of carbon materials due to high output voltage requirements after a relatively long shutdown, and deterioration of polymer electrolytes due to high output voltage being extracted during operation. It is particularly preferred to be used as a power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be used as appropriate. Generally, the fuel cell has a structure in which a membrane electrode assembly is sandwiched between separators.

  The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Further, in order to prevent the gas supplied to each catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion where the catalyst layer is not formed on the gasket layer. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin or polyester. In addition, the thickness of the gas seal portion is preferably 50 μm to 2 mm, more preferably about 100 μm to 1 mm.

  Furthermore, a stack in which a plurality of membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  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.

(Example 1)
<Preparation of catalyst ink for oxidant electrode side>
What was dissolved in a 1.0 M sulfuric acid aqueous solution so that the concentration of 2,2′-bipyridine was 10 μM was prepared. Next, a platinum-supported carbon powder (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) having a platinum-supported concentration of 50% by mass and a conductive carrier of ketjen black is mixed, and 2,2′-bipyridine is mixed onto the platinum catalyst. Adsorbed. 5 g of the obtained bipyridine-adsorbed platinum-supported carbon powder and 4.6 g of water were mixed and subjected to stirring and defoaming treatment. Vapor growth carbon fiber (VGCF (registered trademark), manufactured by Showa Denko Co., Ltd.) was added so as to be 10% by mass with respect to the total mass of the catalyst composition, and further diluted with NPA at a concentration of 5% by mass. An electrolyte polymer (Nafion (registered trademark)) dispersion (DE-520, manufactured by DuPont) was mixed so that the mass ratio of the electrolyte to the mass of carbon in the catalyst layer was 0.9, and the mixture was sufficiently stirred and removed. Foam treatment was performed. Thereafter, a catalyst ink was prepared by pulverizing and homogenizing at room temperature for 3 hours or more using a homogenizer.

<Preparation of fuel electrode catalyst ink>
5 g of platinum-supported carbon powder (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) whose platinum support concentration is 50% by mass and the conductive carrier is ketjen black is mixed with 4.6 g of water, followed by stirring and defoaming treatment. went. Further, an electrolyte polymer (Nafion (registered trademark)) dispersion (DE-520, manufactured by DuPont) diluted with NPA and having a concentration of 5% by mass has an electrolytic mass ratio of 0.9 relative to the amount of carbon in the catalyst layer. The mixture was thoroughly stirred and defoamed, and pulverized and homogenized at room temperature for 3 hours or more using a homogenizer to prepare a fuel electrode catalyst ink.

<Application of catalyst ink>
The catalyst ink for the oxidant electrode side produced by the above method was applied on a Teflon sheet (thickness 80 μm) using a screen printer. The application was repeated until the amount of platinum supported per unit area of the Teflon sheet was 0.35 mg / cm ² . The catalyst-coated sheet was sufficiently dried to obtain an oxidant electrode side sheet. Further, the fuel electrode side catalyst ink produced by the above method was applied onto a Teflon sheet (thickness 80 μm) using a screen printer in the same manner as in the case of the oxidant electrode side catalyst ink. The coating was performed so that the amount of platinum supported per unit area of the Teflon sheet was 0.05 mg / cm ² and sufficiently dried to obtain a fuel electrode side sheet.

<Formation of membrane-catalyst layer assembly>
Using the oxidant electrode side sheet and the fuel electrode side sheet prepared as described above, the catalyst layer was transferred onto the electrolyte membrane by a decal method. Ion exchange membrane (NR-211, film thickness 25 μm, EW (Equivalent Weight: dry film per mole of sulfonic acid group) is transferred under transfer conditions of temperature 130 ° C., pressure 2.0 MPa, time 10 min. The above-mentioned oxidant electrode sheet and fuel electrode sheet were disposed on both sides of the electrolyte membrane in the thickness direction, using an electrolyte membrane of 1100 (made by DuPont).

(Example 2)
A membrane-catalyst layer assembly was produced in the same manner as in Example 1 except that the oxidant electrode side catalyst ink was produced as follows.

<Preparation of catalyst ink for oxidant electrode side>
A solution prepared by dissolving 2,2′-bipyridine in a 1.0 M sulfuric acid aqueous solution to 10 μM was prepared.

  Next, platinum-supported carbon powder (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) having a platinum-supported concentration of 50% by mass and a conductive carrier of ketjen black is mixed, and 2,2′-bipyridine is mixed onto the platinum catalyst. Adsorbed. 5 g of the obtained bipyridine-adsorbed platinum-supported carbon powder and 4.6 g of water were mixed and subjected to stirring and defoaming treatment. An electrolyte polymer (Nafion (registered trademark)) dispersion (DE-520, manufactured by DuPont) having a concentration of 5% by mass diluted with NPA was added to an electrolysis mass ratio of 0.9 relative to the amount of carbon in the catalyst layer. The mixture was mixed and sufficiently stirred and defoamed. Thereafter, the mixture was pulverized and homogenized at room temperature for 3 hours or more using a homogenizer.

Next, vapor-grown carbon fiber (VGCF (registered trademark) manufactured by Showa Denko KK) in an amount of 10% by mass with respect to the total mass of the catalyst composition, and the platinum electrode area of the platinum-supported carbon powder produced above. 2,2′-bipyridine in an amount of 1.1 nmol / cm ² per unit was mixed to prepare 2,2′-bipyridine-carrying VGCF (registered trademark). This 2,2′-bipyridine-supported VGCF (registered trademark) is mixed with the ink containing the platinum-supported carbon powder prepared above, sufficiently stirred and degassed, and the resulting product is used for the oxidant electrode side. A catalyst ink was obtained.

(Comparative example)
A membrane-catalyst layer assembly was produced in the same manner as in Example 1 except that the oxidant electrode side catalyst ink was produced as follows.

<Preparation of catalyst ink for oxidant electrode side>
A platinum-carrying carbon powder (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) having a platinum-carrying concentration of 50% by mass and a conductive carrier of ketjen black is mixed with 4.6 g of water, and sufficiently stirred and degassed. Processed. Thereafter, a catalyst ink was prepared by pulverizing and homogenizing at room temperature for 3 hours or more using a homogenizer.

(Evaluation test)
<Power generation test>
A gas separator with a gas flow path was disposed on both surfaces of the membrane electrode assembly, and a single cell for tightening evaluation was formed so as to have a predetermined surface pressure. The obtained polymer electrolyte fuel cell single cell was subjected to a power generation test using an evaluation apparatus under the following conditions.

In the single cell for evaluation, hydrogen was supplied as a fuel to the fuel electrode side, and air was supplied as an oxidant to the oxidant electrode side. For both gases, the cell outlet pressure was atmospheric pressure, hydrogen was 58.6 ° C., R.V. H60% and 0.261 L / min, air is 55.0 ° C., R.V. H. 50% and 1.041 L / min, the cell temperature was set to 70 ° C., the hydrogen utilization rate was 60%, and the air utilization rate was 40%. Under this condition, the cell voltage was measured at a current density of 1 A / cm ² to determine the power generation performance of the cell.

<Start / stop durability test>
About the polymer electrolyte fuel cell single cell obtained by Examples 1-2 and the comparative example, the start-stop durability test was done on the following conditions with the single cell evaluation apparatus.

In the single cell for evaluation, hydrogen was supplied as a fuel to the fuel electrode side, and air was supplied as an oxidant to the oxidant electrode side. For both gases, the cell outlet pressure was atmospheric pressure, hydrogen was 58.6 ° C., R.V. H60% and 0.261 L / min, air is 55.0 ° C., R.V. H. 50% and 1.041 L / min, the cell temperature was set to 70 ° C., the hydrogen utilization rate was 60%, and the air utilization rate was 40%. Under this condition, power was generated at a current density of 1 A / cm ^{2 for} 1 minute, and then power generation was stopped. After stopping, the supply of hydrogen and air was stopped, dry air was supplied to the single cell, the inside of the cell was replaced for 1 minute, and then hydrogen gas was supplied to the fuel electrode side at the above utilization rate for 1 minute. Thereafter, air was supplied to the oxidant electrode side at the same utilization rate as above, and power was generated again. This power generation / stop operation is repeated, and 1 A / cm ² _-geo. The cell voltage at the time was measured, and the evaluation was completed when the number of start / stop times reached 1500 times. The results are shown in FIGS.

  As can be seen from FIGS. 2 to 4, it can be seen that the electrodes of Examples 1 and 2 are superior in durability compared to the electrode of the comparative example.

It is sectional drawing which shows one Embodiment of the electrode of this invention. 4 is a graph showing the results of an electrode start / stop durability test according to Example 1; It is a graph which shows the result of the start-stop durability test of the electrode by Example 2. FIG. It is a graph which shows the result of the start-stop durability test of the electrode by the comparative example 1.

Explanation of symbols

1 electrode,
2 conductive carrier,
3 catalyst particles,
4 a compound containing a nitrogen-containing 6-membered ring,
5 Fibrous carbon.

Claims (9)

A compound containing a nitrogen-containing 6-membered ring;
Catalyst particles,
Catalyst-supporting carbon formed by supporting the catalyst particles;
Fibrous carbon,
An electrode comprising:   The electrode according to claim 1, wherein the compound is a pyridine compound.   The electrode according to claim 2, wherein the pyridine compound is at least one compound selected from the group consisting of a bipyridine compound, a terpyridine compound, and a phenanthroline compound.   The electrode according to claim 3, wherein the bipyridine compound is 2,2-bipyridine.   The electrode according to any one of claims 1 to 4, wherein the catalyst particles on the catalyst-supporting carbon are platinum particles or particles of an alloy containing platinum.   The electrode according to claim 1, wherein the fibrous carbon is a vapor-grown carbon fiber.   The said fibrous carbon is contained 1-30 mass% with respect to the gross mass of an electrode, The electrode of any one of Claims 1-6 characterized by the above-mentioned. A compound containing a nitrogen-containing 6-membered ring;
Catalyst particles,
A conductive carrier;
A vapor-grown carbon fiber on which no catalyst component is supported;
The manufacturing method of the electrode characterized by including the process of preparing the catalyst ink containing this.   A fuel cell using the electrode according to claim 1.

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