JP2009146760A - Electrode catalyst layer for fuel cell, and manufacturing method of electrode catalyst layer for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst layer for fuel cell which satisfies two mutually contradictory functions of a good drainage performance of generated water and a proper moisture retention function in both high levels respectively. <P>SOLUTION: This is a porous electrode catalyst layer and the electrode catalyst layer has first holes V1 of hole diameters in a range of 0.01-0.1 μm and a second holes V2 of hole diameters in a range of 0.1-1 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode catalyst layer for a fuel cell and a method for producing the same.

  As a fuel cell mounted on an automobile, a solid polymer electrolyte fuel cell using an ion exchange membrane has attracted attention. This solid polymer electrolyte fuel cell is configured by laminating a plurality of unit cells, which are basic units of power generation.

  Each unit cell includes a membrane electrode assembly (MEA) having a structure in which a positive electrode (anode) and a negative electrode (cathode) are sandwiched on both sides of a solid polymer electrolyte membrane, respectively. A separator having a gas flow path or a cooling water flow path is provided on the outside. Each of the positive electrode and the negative electrode is composed of an electrode catalyst layer provided on the side in contact with the solid polymer electrolyte membrane and a gas diffusion layer provided so as to overlap the electrode catalyst layer.

  The electrode catalyst layer of each electrode includes catalyst-supported conductor particles formed by supporting catalyst particles having catalytic action on conductor particles and a polymer electrolyte made of an ion exchange resin, and the catalyst-supported conductor particles are aggregated. It has become a porous body. In this method for producing an electrode catalyst layer, a conductive ink carrying catalyst particles, such as carbon particles, an electrolyte solution, and a catalyst ink containing a solvent are applied onto a solid polymer electrolyte membrane or a gas diffusion layer. There is a method of forming an electrode catalyst layer by drying.

The pores of the electrode catalyst layer serve as a passage for fuel gas and air, and serve as a discharge path for water generated by the reaction. For this reason, the pore shape and pore ratio of the electrode catalyst layer affect the breathability of the fuel gas and air and the drainage of the generated water, and consequently the performance of the fuel cell. Therefore, there is an electrode catalyst layer in which the pores of the electrode catalyst layer are formed in a crucible shape (Patent Document 1).
JP 2005-267972 A

  In the conventional electrode catalyst layer in which the shape of the pores and the pore ratio of the electrode catalyst layer are adjusted, when the electrode catalyst layer is incorporated as a fuel cell, good drainage of the generated water and an appropriate moisture retention function, It was difficult to satisfy two contradictory functions at a high level. For this reason, it has been difficult to improve both the power generation characteristics under both the high humidification operation condition and the low humidification operation condition. Since the fuel cell is still desired to further improve the power generation characteristics, further improvement of the characteristics of the electrode catalyst layer for fuel cells is desired.

  The electrode catalyst layer for a fuel cell of the present invention that solves the above problems is a porous electrode catalyst layer, and the electrode catalyst layer has first pores having a pore diameter in the range of 0.01 to 0.1 μm. And a hole structure having a hole diameter of 0.1 to 1 μm and a second hole.

  The electrode catalyst layer for a fuel cell of the present invention is a porous electrode catalyst layer provided, and the electrode catalyst layer has a pore distribution curve in the range of 0.01 to 0.1 μm in pore diameter range. The gist is to have a pore distribution having a peak and having a second peak in a pore diameter range of 0.1 to 1 μm.

  The method for producing an electrode catalyst layer for a fuel cell according to the present invention comprises preparing a catalyst slurry by stirring and mixing a catalyst-carrying conductor carrying catalyst particles, an electrolyte solution, and a solvent, and drying the catalyst slurry after coating. In forming the electrode catalyst layer, the gist is to add a nonionic polymer to the catalyst slurry.

  According to the electrode catalyst layer for a fuel cell of the present invention, it is possible to obtain a fuel cell in which drainage and moisture retention functions are compatible at a high level.

  Hereinafter, an electrode catalyst layer for a fuel cell according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing the structure of a fuel cell electrode catalyst layer according to an embodiment of the present invention. The illustrated electrode catalyst layer for a fuel cell includes catalyst-carrying conductor particles 1 including catalyst particles 11 having a catalytic action and conductor particles 12 that carry the catalyst particles 11. An electrolyte polymer 2 is formed around the catalyst-carrying conductive particles 1. These catalyst-carrying conductor particles 1 and electrolyte polymer 2 are also provided in a conventional electrode catalyst layer. The electrode catalyst layer of the present embodiment includes a nonionic polymer 3 in addition to the catalyst-supporting conductive particles 1 and the electrolyte polymer 2.

  In the electrode catalyst layer of this embodiment including these catalyst-carrying conductor particles 1, electrolyte polymer 2, and nonionic polymer, a large number of catalyst-carrying conductor particles 1 are aggregated together to form a primary aggregate A1. A large number of primary aggregates A1 are aggregated to form secondary aggregates A2.

  Between the individual catalyst-carrying conductive particles 1 in the primary aggregate A1, first voids V1 are formed. The first hole V1 has a hole diameter in the range of 0.01 to 0.1 μm. In addition, between the individual primary aggregates A1 in the secondary aggregate A2, second holes V2 are formed by the action of the nonionic polymer. The second hole V2 has a hole diameter in the range of 0.1 to 1 μm.

  The inventors of the present invention, as a result of diligent research on the electrode catalyst layer for fuel cells, formed an electrode catalyst layer structure having two types of pores, large and small, so that the drainage property in the upper electrode catalyst layer was improved. It has been found that it is possible to achieve both a moderate moisturizing function and a high degree of compatibility.

  Based on such knowledge, the electrode catalyst layer of the present embodiment includes a first hole corresponding to the hole V1 of the primary aggregate A1 and a hole diameter of 0.01 to 0.1 μm, and a secondary aggregate. Since it has two types of large and small holes corresponding to the hole V2, the second hole having a hole diameter in the range of 0.1 to 1 μm, it is possible to achieve both high drainage and moisture retention functions. As a result, the power generation characteristics of the fuel cell can be improved.

  The reason why the electrode catalyst layer according to the present embodiment has a structure having the first hole and the second hole as described above, so that drainage and water retention function can be obtained at a high level. Although not necessarily clear, it is considered that the drainage can be enhanced by the second hole while the water retaining function is maintained by the first hole.

  In addition, according to the present invention, the electrode catalyst layer having the structure having the first hole and the second hole as described above has an effect of preventing flooding. More specifically, when the fuel cell is continuously operated, the pores of the catalyst layer are blocked due to the corrosion of the carbon material in the catalyst layer, and there is a possibility that the performance is deteriorated due to flooding. As a means for preventing this flooding, there is a method of adding crystalline carbon fiber to the electrode catalyst layer in order to enhance the water discharging property. However, when the water discharging property is increased by adding crystalline carbon fiber or the like, the performance degradation due to flooding can be prevented, but the performance degradation under dry conditions (low humidification) occurs.

  On the other hand, the electrode catalyst layer of the present embodiment has a structure having the first hole and the second hole described above, so that drainage can be performed while suppressing a decrease in performance under dry conditions (low humidification). Can increase the sex. Therefore, it is possible to prevent the pores of the catalyst layer from being blocked during the continuous operation. As a result, performance degradation due to flooding can be suppressed.

  FIG. 2 is a photomicrograph of the conventional electrode catalyst layer and the electrode catalyst layer according to this embodiment. The conventional electrode catalyst layer shown in FIG. 2 (a) is an example that does not contain a nonionic polymer as an additive, and the catalyst-carrying conductor particles shown in the photograph are formed only with primary aggregates. The pores shown as the dark portions have a pore diameter in the range of 0.01 to 0.1 μm. On the other hand, the electrode catalyst layer of this embodiment shown in FIG. 2B is an example containing a nonionic polymer as an additive, and the catalyst-supported conductor particles shown in the photograph are only primary aggregates. But the secondary agglomerates are formed and the pores shown as dark portions have a pore diameter in the range of 0.01 to 0.1 μm and a pore diameter in the range of 0.1 to 1 μm. There is something.

  FIG. 3 shows the results obtained by measuring the pore distribution with a Hg porosimeter when the nonionic polymer was added at a ratio of 0 wt%, 10 wt%, 20 wt% and 30 wt% with respect to the solid content of the catalyst slurry. In the pore distribution of FIG. 3, those having a pore diameter exceeding 1 μm are those in which noise, surface flaws and cracks have been detected, and do not indicate pores contained in the electrode catalyst layer.

  As shown in FIG. 3, the pore distribution curve when the addition amount of the nonionic polymer is 0 wt% is a single peak curve having a peak only in a range where the pore diameter is 0.01 to 0.1 μm. is there. The pore diameter at this peak value is about 0.03 μm.

  On the other hand, the pore distribution curve when 10 wt% of the nonionic polymer is added has a first peak in the pore diameter range of 0.01 to 0.1 μm and the pore diameter range of 0.1 to 1 μm. And has a second peak. The peak in the range where the pore diameter is 0.01 to 0.1 μm is shifted to the larger pore diameter side as compared with the case where the addition amount is 0 wt%. The pore diameter at this peak value is about 0.05 μm. Moreover, the pore peak newly seen in the range whose pore diameter is 0.1-1 micrometer is about 0.5 micrometer.

  The first peak with a pore size of 0.05 μm corresponds to the pores V1 of the primary aggregate A1 in FIG. 1, and the second peak with a pore size of 0.5 μm is the pores V2 of the secondary aggregate A2 in FIG. It is thought that it corresponds to.

  Further, the pore distribution curve when 20 wt% of the nonionic polymer is added is the same as when the nonionic polymer is added by 10 wt%, and the pore diameter is in the range of 0.01 to 0.1 μm. And a second peak at 0.5 μm which is a pore diameter range of 0.1 to 1 μm. Therefore, it is thought that it has the hole V1 of the primary aggregate A1 of FIG. 1, and the hole V2 of the secondary aggregate A2.

  Furthermore, the pore distribution curve when 30 wt% of the nonionic polymer is added is a single peak curve having a first peak at a pore diameter of about 0.04 μm, which is in the range of 0.01 to 0.1 μm. ing. The second peak in the pore size range of 0.1 to 1 μm has disappeared. This is presumably because the nonionic polymer was excessive and closed the pores.

  The peak in the range of the pore diameter of 0.01 to 0.1 μm is preferably near the pore diameter of 0.05 μm, and the peak in the range of the pore diameter of 0.1 to 1 μm is preferably around the pore diameter of 0.5 μm. The effects of the present invention can be effectively obtained when the first holes and the second holes are in the vicinity of 0.05 μm and 0.5 μm, respectively, in terms of pore diameter.

  Such a structure having the first hole and the second hole can be obtained by including a nonionic polymer in the electrode catalyst layer. Although the action of the nonionic polymer is not necessarily clear, the nonionic polymer crosslinks between the primary aggregates of the catalyst-carrying conductive particles by adding the nonionic polymer to the electrode catalyst layer. As a result, it is considered that the electrode catalyst layer has a crosslinked structure, and voids of secondary aggregates are formed.

  The nonionic polymer can be appropriately selected from polyether, polyamide, polyurethane, polyacrylic acid and the like.

  The addition amount of the nonionic polymer is preferably in the range of 5 to 20 wt% with respect to the catalyst slurry solid content. If the addition amount is less than 5 wt%, it is difficult to form the second vacancy because the effect of adding the nonionic polymer is poor. On the other hand, when the addition amount exceeds 20 wt%, the pores are blocked by excess nonionic polymer, so that it is difficult to form the second pores, and the drainage of the catalyst layer is deteriorated.

  In the electrode catalyst layer of the present invention, the shape and size of the catalyst particles are not particularly limited, and those having the same shape and size as known catalyst components can be used. The smaller the average particle size of the catalyst particles, the higher the catalytic activity because the effective electrode area in which the electrochemical reaction proceeds increases. However, in practice, a phenomenon in which the catalytic activity decreases due to the fact that the average particle size is too small is seen. . Therefore, the average particle diameter of the catalyst particles is preferably 1.5 to 15 nm, more preferably 2 to 10 nm, and even more preferably 2 to 5 nm. The thickness is preferably 1.5 nm or more from the viewpoint of easy loading, and is preferably 15 nm or less from the viewpoint of catalyst utilization. The average particle size of the catalyst particles can be measured by the crystallite size obtained from the half-value width of the diffraction peak of the catalyst particles in X-ray diffraction or the average value of the particle size of the catalyst particles determined from a transmission electron microscope image. it can.

  The material of the catalyst particles may be any material as long as it has a catalytic action on the oxygen reduction reaction in the cathode catalyst layer, and may have any catalytic action on the hydrogen oxidation reaction in the anode catalyst layer. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like, and alloys thereof. Is done. 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. In the case of an alloy containing platinum, depending on the type of metal to be alloyed, platinum is preferably 30 to 90 atomic%, and the metal to be alloyed is preferably 10 to 70 atomic%.

The electroconductive particles of the electrode catalyst layer may have any specific surface area for supporting the catalyst particles in a desired dispersion state and have sufficient electronic conductivity as a current collector. The specific surface area of the conductive particles is preferably 20 to 1000 m ² / g, more preferably 80 to 800 m ² / g. When the specific surface area is 20 m ² / g or more, the dispersibility of the catalyst particles and the electrolyte polymer on the conductive support is not lowered, and sufficient power generation performance is obtained, and the specific surface area is 1000 m ² / g or less. Thus, a decrease in the effective utilization rate of the catalyst particles and the electrolyte polymer accompanying an increase in the specific surface area can be avoided.

  The conductive particles are preferably carbon or those whose main component is carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. In order to improve the characteristics of the fuel cell, the conductive particles may contain elements other than carbon atoms as necessary. Moreover, mixing of impurities of about 2 to 3% by mass or less is allowed.

  Further, the size of the conductive particles is not particularly limited, but the average particle diameter is 5 from the viewpoint of controlling the ease of loading of the catalyst particles, the catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range. It is preferable to set the thickness to about 200 nm, preferably about 10 to 100 nm.

  In the catalyst-supported conductor particles in which the catalyst particles are supported on the conductive particles, the supported amount of the catalyst particles is preferably 10 to 75% by mass, more preferably based on the total amount of the electrode catalyst composed of the catalyst-supported conductor particles. It is good to set it as 20-50 mass%. When the supported amount of the catalyst particles is 75% by mass or less, sufficient dispersibility of the catalyst component on the conductive particles can be obtained, and high power generation performance can be obtained. When the loading amount is 10% by mass or more, a large amount of electrode catalyst is not required to obtain a desired power generation performance without reducing the catalytic activity per unit mass. The amount of catalyst particles supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  The electrolyte polymer (polymer electrolyte) contained in the electrode catalyst layer is not particularly limited, and a known one can be used, but preferably has at least proton conductivity. By using a polymer electrolyte having proton conductivity, an electrode catalyst layer having high power generation performance can be obtained. The polyelectrolyte that can be used is a fluorinated polymer in which all or part of the polymer skeleton is fluorinated and has an ion-exchange group, or a hydrocarbon polymer that does not contain fluorine in the polymer skeleton. And polymer electrolytes having ion exchange groups.

The ion-exchange groups of the polymer electrolyte is not specifically _{limited, -SO3H, -COOH, -PO (OH} ) 2, -POH (OH), - SO 2 NHSO 2 -, - Ph (OH) (Ph represents a phenyl A cation exchange group such as —NH ₂ , —NHR, —NRR ′, —NRR′R ″ +, —NH ₃ ^{+ and the} like (R, R ′, R ″ are alkyl groups, cyclo Anion exchange group such as an alkyl group and an aryl group).

  Specific examples of polymer electrolytes that are fluoropolymers and have ion exchange groups include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, Asahi Glass). Perfluorocarbon sulfonic acid polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylenetetrafluoroethylene-g-styrene sulfonic acid polymer, Suitable examples include ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene-g-polystyrene sulfonic acid polymer, and polyvinylidene fluoride-g-polystyrene sulfonic acid polymer.

  In addition, as a polymer electrolyte that is a hydrocarbon polymer and has an ion exchange group, specifically, a polysulfone sulfonic acid polymer, a polyether ether ketone sulfonic acid polymer, a polybenzimidazole alkyl sulfonic acid polymer, Preferred examples include benzimidazole alkylphosphonic acid polymers, cross-linked polystyrene sulfonic acid polymers, polyethersulfone sulfonic acid polymers, and the like.

  Among the polymer electrolytes listed above, polymer electrolytes that are fluorinated polymers and have ion exchange groups have high ion exchange ability, and are excellent in chemical durability and mechanical durability. Particularly preferred are fluorine-based electrolytes such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

  From the viewpoint of setting the electrolyte resistance value to a desired value, the content of the polymer electrolyte contained in the electrode catalyst layer is the total mass of the components constituting the electrode catalyst layer, that is, the mass of the electrode catalyst and the mass of the polymer electrolyte. Is preferably 0.15 to 0.45% by mass, and more preferably 0.25 to 0.40% by mass. If the content of the polymer electrolyte is 0.15% by mass or more, an effect of uniformly holding the polymer electrolyte in the catalyst layer is obtained, and if it is 0.45% by mass or less, sufficient diffusibility of the reaction gas is obtained. Can be obtained.

  The thickness of the electrode catalyst layer is preferably 1 to 25 μm, more preferably 2 to 20 μm, and particularly preferably 5 to 10 μm, considering the diffusibility of the gas supplied from the outside and the power generation performance of the membrane electrode assembly. It is good. If the thickness of the electrode catalyst layer is 1 μm or more, an electrode catalyst layer having a uniform thickness in both the surface direction and the thickness direction can be easily formed. If the thickness is 25 μm or less, moisture is contained in the electrode catalyst layer. A flooding phenomenon caused by stopping can be suppressed. In addition, the thickness of an electrode catalyst layer can be measured with the observation result of a transmission electron microscope.

  Next, a method for producing an electrode catalyst layer according to an embodiment of the present invention will be described. In the method for producing an electrode catalyst layer according to an embodiment of the present invention, a catalyst-carrying conductor powder carrying catalyst particles, an electrolyte solution, and a solvent are stirred and mixed to prepare a catalyst slurry. In forming an electrode catalyst layer by drying after coating, a nonionic polymer is added to the catalyst slurry.

  FIG. 4 is a flowchart for explaining an example of the method for producing the electrode catalyst layer of the present invention. 4, first, an electrode catalyst powder 21 made of catalyst-supporting conductive particles, a polymer electrolyte solution 22, a nonionic polymer 23, and n-propyl alcohol as a solvent 24, for example, are prepared. Next, the catalyst powder 21, the electrolyte solution 22 and the solvent 24 are mixed and dispersed by a disperser, for example, a bead mill (step S1). A catalyst ink is obtained by dispersing.

  The nonionic polymer 23 is added to the obtained catalyst ink and mixed with stirring (step S2). The nonionic polymer can be appropriately selected from polyether, polyamide, polyurethane, polyacrylic acid and the like. Moreover, it is preferable to make the addition amount of a nonionic polymer into the range of 5-20 wt% with respect to catalyst slurry solid content. By adding 5 wt% or more, the second hole is reliably formed due to the addition effect of the nonionic polymer, and drainage performance is improved. Moreover, by adding at 20 wt% or less, the blockage | closure of the pore by an excess nonionic polymer can be avoided, a 2nd void | hole is formed reliably, and drainage property improves. A catalyst slurry is obtained by stirring and mixing after adding such a nonionic polymer to the catalyst ink.

  The obtained catalyst slurry is applied onto a solid polymer electrolyte membrane or gas diffusion layer, which is a member of a membrane electrode assembly constituting a fuel cell, and then dried. By this drying, the solvent in the catalyst slurry evaporates, and an electrode catalyst layer solidified in a state where desired pores according to the present invention are formed is obtained.

  The membrane electrode assembly using the electrode catalyst layer of the present invention described above has the effect of the electrode catalyst layer of the present invention, has a high level of drainage and water retention function, and is low under high humidification conditions. The power generation characteristics under both humidification conditions can be improved. In addition, there is little performance degradation due to flooding, and long-term repeated use is possible.

  In addition, a fuel cell comprising a membrane electrode assembly using the electrode catalyst layer of the present invention has a high level of drainage and water retention when used as a fuel cell, and is highly humidified under low humidification conditions. The power generation characteristics under both conditions can be improved. In addition, there is little performance degradation due to flooding, and long-term repeated use is possible.

  An example of a fuel cell provided with a membrane electrode assembly using the electrode catalyst layer of the present invention is shown in FIG. 5 in a perspective view of the fuel cell stack, and a developed view of the main part of the fuel cell stack is shown in FIG. As shown in FIG. 6, the fuel cell stack 30 shown in FIG. 5 has end flanges 51A and 51C disposed at both ends of a complex cell in which a plurality of unit cells 40 are stacked, and the outer peripheral portions of these end flanges 51A and 51C. The complex cell is fixed by fastening bolts 52 suspended between them.

  The unit cell 40 includes a membrane electrode assembly 41 and an anode side separator 401A and a cathode side separator 401C disposed on both sides of the membrane electrode assembly 41.

  A schematic cross-sectional view of the unit cell 40 is shown in FIG. The membrane electrode assembly 41 constituting the unit cell 40 is formed by disposing an anode 43A and a cathode 43C on both sides of a solid polymer electrolyte membrane. The anode 43A has a structure in which the electrode catalyst layer 44A and the gas diffusion layer 45A are adjacent to each other in order from the side closer to the solid polymer electrolyte membrane 42, and the cathode 43C is similarly from the side closer to the solid polymer electrolyte membrane 42. In this order, the electrode catalyst layer 44C and the gas diffusion layer 45C are adjacent to each other.

  In the membrane electrode assembly 41, the electrode catalyst layer of the present invention is used for the cathode-side electrode catalyst layer 44C among the anode-side electrode catalyst layer 44A and the cathode-side electrode catalyst layer 44C.

  The structure of the membrane electrode assembly of the present invention is not particularly limited except that the electrode catalyst layer of the present invention is used, and can be the same as that of a known membrane electrode assembly.

  For example, the solid polymer electrolyte membrane used in the membrane electrode assembly of the present invention is not particularly limited, and examples thereof include a membrane made of an electrolyte having proton conductivity. For example, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical Co., ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Fluoropolymer electrolyte membranes such as resin membranes based on styrene, hydrocarbon resin membranes having sulfonic acid groups, and other commercially available polymer electrolyte membranes, polytetrafluoroethylene (PTFE) Using a membrane made by impregnating a microporous polymer membrane made of polyvinylidene fluoride (PVDF) with a liquid electrolyte such as phosphoric acid or ionic liquid, or a membrane filled with a polymer electrolyte in a porous body May be. The electrolyte used for the solid polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same material or different.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained membrane / electrode assembly, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 100 μm. . From the viewpoint of strength during film formation and durability during operation, it is preferably 5 μm or more, and from the viewpoint of output characteristics during operation, it is preferably 300 μm or less.

  The gas diffusion layer is not particularly limited, and a known one can be used in the same manner. For example, a sheet-like gas diffusion base material having conductivity and porosity, such as carbon woven fabric, paper-like paper body, felt, and non-woven fabric. The thing which consists of.

  The thickness of the gas diffusion substrate adjacent to the electrode catalyst layer may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness is less than 30 μm, sufficient mechanical strength or the like may not be obtained. If the thickness exceeds 500 μm, the distance through which gas or water permeates is undesirably increased.

  The gas diffusion base material may contain a water repellent for the purpose of further improving water repellency and preventing flooding. Although it does not specifically limit as a water repellent, Fluorine type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  Further, as the structure of the gas diffusion layer with improved water repellency, the gas diffusion layer may have a carbon particle layer made of an aggregate of carbon particles containing a water repellent on the gas diffusion substrate. . The carbon particles are not particularly limited, and may be conventional ones such as carbon black, graphite, and expanded graphite. Of these, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area. Examples of the water repellent used for the carbon particle layer include the same water repellents as those described above used for the gas diffusion base material. Of these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction. The mixing ratio between the carbon particles and the water repellent in the carbon particle layer may result in insufficient water repellency as expected if there are too many carbon particles. If there are too many water repellents, sufficient electron conductivity will be obtained. There is a fear that it is not possible. Considering these, the mixing ratio of the carbon particles and the water repellent in the carbon layer is preferably about 90:10 to 40:60 in terms of mass ratio. The thickness of the carbon particle layer may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer, but is preferably 10 to 1000 μm, more preferably 50 to 500 μm.

  The configuration of the fuel cell of the present invention provided with the membrane electrode assembly described above may have the same configuration as a conventionally known fuel cell except that the membrane electrode assembly of the present invention is used.

  Specifically, the anode-side separator and the cathode-side separator provided with the membrane electrode assembly interposed therebetween may be those conventionally known, such as those made of carbon such as dense carbon graphite and carbon plate, and those made of metal such as stainless steel. Can be used without limitation. The separator has a function of separating the fuel and the oxidant gas, and a gas flow path having a meandering shape or a linear shape for securing the flow paths may be formed. The thickness and size of the separator, the shape of the gas flow path, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Furthermore, the shape of the unit cell, the shape of the fuel cell stack, the number of stacks, and the like are not particularly limited, and may be determined as appropriate so as to obtain battery characteristics such as a desired voltage.

  Hereinafter, although it demonstrates using an Example more concretely, it is not limited to the illustrated Example.

(Evaluation of drainage and water retention function)
1. Preparation of Electrocatalyst Powder Carbon black (Ketjen Black EC manufactured by Ketjen Black International Co., Ltd.) was subjected to heat treatment to graphitize carbon black (graphitized Ketjen Black EC, BET surface area: 130 m ² / g ) To 4.0 g of this graphitized ketjen black, 400 g of a dinitrodiammine platinum aqueous solution (Pt concentration: 1.0%) was added and stirred for 1 hour. Further, 50 g of formic acid as a reducing agent was mixed and stirred for 1 hour. Then, it heated up to 40 degreeC in 30 minutes, and stirred at 40 degreeC for 6 hours. The mixture was heated to 60 ° C. in 30 minutes, further stirred at 60 ° C. for 6 hours, and then cooled to room temperature in 1 hour. After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours, pulverized in a mortar, and a powder of an electrode catalyst (average particle diameter of Pt particles 4.8 nm, Pt support concentration 50% by mass) Got.

2. Preparation of electrode catalyst layer 5 times the amount of purified water was added to the mass of the electrode catalyst, and a vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol is added, and further a solution containing a proton conductive polymer electrolyte (containing 20% Nafion (registered trademark) manufactured by DuPont) is added to form a mixed slurry (catalyst layer ink). Obtained. The content of the polymer electrolyte in the solution is such that the solid content mass ratio with respect to the carbon mass of the anode electrode catalyst is Carbon / Ionomer = 1.0 / 0.9.

After the obtained mixed slurry is well dispersed using a bead mill, nonionic polymer is added to the solid content of the slurry under three conditions of 0 wt%, 10 wt% and 30 wt%. After mixing, a catalyst slurry was prepared by adding a vacuum degassing operation. This was applied as a solid polymer electrolyte membrane to NafionNRE211 (film thickness 25 μm) using an applicator, and an amount of catalyst slurry corresponding to the desired thickness was applied and dried at 90 ° C. for 1 hour. The size of the electrode catalyst layer to be formed was 5 cm × 5 cm. The coating layer was adjusted so that the Pt amount was 0.4 mg / cm ² (the average thickness of the electrode catalyst layer was 10 μm).

3. Performance Evaluation of Membrane Electrode Assembly (MEA) E-TEK LT1200N is used as a gas diffusion electrode on both sides of the MEA obtained above (size: 6.0 cm × 5.5 cm), and gas separator with gas flow path Was further sandwiched between gold-plated stainless steel current collector plates to form single cells for evaluation.

In the evaluation unit cell, hydrogen was supplied as a fuel to the anode side, and air was supplied as an oxidant to the cathode side. The supply pressure of both gases was atmospheric pressure, hydrogen was set to 58.9 ° C. and relative humidity 40%, air was set to 71.4 ° C. and relative humidity 70%, and the cell temperature was set to 80 ° C. The hydrogen utilization rate was 67% and the air utilization rate was 67%. Under this condition, the cell voltage when power was generated at a current density of 1.0 A / cm ² was measured as the initial cell voltage.

Subsequently, in an environment where the relative humidity of hydrogen on the anode side is 100% (81 ° C.), the relative humidity of the supply air on the cathode side is variously changed in the range of 20 to 100%, and the current density is maintained at each relative humidity for 10 minutes. The cell voltage when power was generated at 1.0 A / cm ² was measured.

4). Power generation evaluation (1) IV characteristics:
As the humidification conditions, the relative humidity of hydrogen on the anode side is 40% (RHa40), the relative humidity of air on the cathode side is 70% (RHc70), and the stoichiometric ratio of hydrogen on the anode side (supply / consumption) as the reaction gas condition ) Is 1.5 (SRa1.5 (H ₂ )), the stoichiometric ratio of air on the cathode side is 1.5 (SRc1.5 (Air)), and the cell temperature is 80 ° C., the current density is 1. The amount of voltage drop in the case of 1.2 A / cm ² relative to the case of 0 A / cm ² was examined (%).

(2) Relative humidity (RH) sensitivity characteristics:
As high humidification conditions, the relative humidity of hydrogen on the anode side is 100% (RHa100), as the reaction gas conditions, the stoichiometric ratio of hydrogen on the anode side is 1.5 (SRa1.5 (H ₂ )), and the stoichiometry of air on the cathode side For the case where the relative humidity of air on the cathode side is 60% (RHc60) under the conditions of the ratio of 1.5 (SRc1.5 (Air)), the cell temperature of 80 ° C., and the current density of 1.0 A / cm ² The amount of voltage drop when the relative humidity was 90% (RHc90) was examined (%).

The relative humidity of hydrogen on the anode side is 40% (RHa40) as the low humidification condition, the stoichiometric ratio of hydrogen on the anode side is 1.5 (SRa1.5 (H ₂ )) as the reaction gas condition, and the stoichiometry of the air on the cathode side For the case where the relative humidity of air on the cathode side is 60% (RHc60) under the conditions of the ratio of 1.5 (SRc1.5 (Air)), the cell temperature of 80 ° C., and the current density of 1.0 A / cm ² The amount of voltage drop when the relative humidity was 30% (RHc30) was examined (%).

(3) Evaluation results These results are shown graphically in FIG. As can be seen from FIG. 8, regarding the IV characteristics, the voltage drop amount was the same in the example in which 10 wt% of the nonionic polymer was added compared to the conventional example in which the nonionic polymer was not included (addition amount 0%). In the example in which 30 wt% nonionic polymer was added, the voltage drop amount increased.

  Looking at the characteristics under highly humidified conditions, the non-ionic polymer was not included (added amount 0%), whereas the voltage drop amount of the conventional example was 11%, while the nonionic polymer was added at 10 wt%. The amount of voltage drop is 7%, and the voltage drop is suppressed. This shows that the drainage performance of the example in which 10 wt% of the nonionic polymer is added is improved as compared with the conventional example. The example in which 30 wt% nonionic polymer was added increased the voltage drop rather than the conventional example.

  Looking at the characteristics under low humidification conditions, the voltage drop amount was equal in the example in which 10 wt% of the nonionic polymer was added, compared to the conventional example in which the nonionic polymer was not included (added amount 0%). From this, it can be seen that the example in which 10 wt% of the nonionic polymer is added maintains the same moisture retention function as the conventional example. In the example in which 30 wt% of the nonionic polymer was added, the amount of voltage drop was suppressed. That is, the moisturizing function was improved as compared with the conventional example.

  There is generally a contradictory relationship between the drainage of the electrode catalyst layer represented by the characteristics under high humidification conditions and the appropriate moisture retention of the electrode catalyst layer represented by the characteristics under low humidification conditions. According to the present invention, an example in which 10 wt% of a nonionic polymer is added is a conventional product (addition amount of 0%) because the electrode catalyst layer has two large and small hole structures, ie, a first hole and a second hole. Compared to), the characteristics under high humidification conditions are maintained and the voltage drop is low due to the characteristics under high humidification conditions. I was able to balance two matters.

  FIG. 9 is a graph showing the results of measuring the electrolyte resistance, that is, the proton conductivity in the catalyst layer, for each of the electrode catalyst layers in which the addition amount of the nonionic polymer is 0 wt%, 10 wt%, and 30 wt%. The example in which the addition amount of the nonionic polymer is 10 wt% has almost no increase in the electrolyte resistance as compared with the conventional example in which the nonionic polymer is not added (addition amount: 0 wt%). Does not occur.

(Flooding prevention evaluation)
1. Preparation of single cell for evaluation The single cell for evaluation was the same as that for evaluating the drainage and water retention functions described above, and the addition amount of the nonionic polymer in the electrode catalyst layer was 0 wt%, 10 wt%, and 30 wt%. Three types were created.

2. Performance Evaluation of Membrane Electrode Assembly (MEA) Hydrogen was supplied as fuel to the anode side of the evaluation single cell, and air was supplied as oxidant to the cathode side. The supply pressure for both gases was atmospheric pressure, hydrogen was set to 58.9 ° C. and relative humidity 40%, air was set to 71.4 ° C. and relative humidity 70%, and the cell temperature was set to 80 ° C. The hydrogen utilization rate was 67% and the air utilization rate was 67%. Under this condition, the cell voltage when power was generated at a current density of 1.0 A / cm ² was measured as the initial cell voltage.

Subsequently, the operating conditions were the same as above except that the potential was changed to 0.6V-0.95-0.6V for one cycle. After the 7500 cycle test, power was generated at a current density of 1.0 A / cm ^2. The cell voltage was measured as the cell voltage after the endurance test.

3. Power generation evaluation IV characteristics:
As the humidification conditions, the relative humidity of hydrogen on the anode side is 40% (RHa40), the relative humidity of air on the cathode side is 70% (RHc70), and the stoichiometric ratio of hydrogen on the anode side (supply / consumption) as the reaction gas condition ) Is 1.5 (SRa1.5 (H ₂ )), the stoichiometric ratio of air on the cathode side is 1.5 (SRc1.5 (Air)), and the cell temperature is 80 ° C., the current density is 1. The amount of voltage drop before and after the durability test in the case of 0 A / cm ² was examined (%).

  The results are shown graphically in FIG. As can be seen from FIG. 10, the voltage drop after the durability test was large in the conventional example that did not contain the nonionic polymer (addition amount 0%). This indicates that flooding has occurred. On the other hand, in all examples containing 10 wt% and 30 wt% nonionic polymer, the voltage drop after the endurance test was suppressed. This indicates that flooding is suppressed.

It is a schematic diagram which shows the structure of the electrode catalyst layer for fuel cells which concerns on embodiment of this invention. It is a microscope picture of an electrode catalyst layer. It is a graph which shows the pore distribution curve of an electrode catalyst layer. It is a flowchart explaining an example of the manufacturing method of the electrode catalyst layer of this invention. It is a perspective view of a fuel cell stack. It is an expanded view of the principal part of a fuel cell stack. It is typical sectional drawing of a unit cell. It is a graph which shows the relationship between nonionic polymer addition amount and voltage drop amount. It is a graph which shows the relationship between the addition amount of nonionic polymer, and the electrolyte resistance of a catalyst layer. It is a graph which shows the relationship between the nonionic polymer addition amount and the voltage drop amount before and after an endurance test.

Explanation of symbols

1 ... Catalyst-supported conductor particles,
2 ... electrolyte polymer,
3 ... Nonionic polymer,
11 ... catalyst particles 11,
12 ... Conductor particles 12,
V1 ... first hole,
V2 ... second hole,

Claims (8)

A porous electrocatalyst layer,
The electrode catalyst layer has a hole structure having a first hole having a hole diameter in the range of 0.01 to 0.1 μm and a second hole having a hole diameter in the range of 0.1 to 1 μm. An electrode catalyst layer for a fuel cell. A porous electrocatalyst layer,
This electrode catalyst layer has a pore distribution curve having a first peak in the pore diameter range of 0.01 to 0.1 μm and a second distribution in the pore diameter range of 0.1 to 1 μm. An electrode catalyst layer for a fuel cell, comprising:   The peak in the range of the pore diameter of 0.01 to 0.1 μm is near the pore diameter of 0.05 μm, and the peak in the range of the pore diameter of 0.1 to 1 μm is near the pore diameter of 0.5 μm. The electrode catalyst layer for fuel cells according to claim 2.   The said electrode catalyst layer contains a nonionic polymer, The electrode catalyst layer for fuel cells of Claim 1 or 2 characterized by the above-mentioned.   A membrane electrode assembly comprising the fuel cell electrode catalyst layer according to claim 1 on both sides of a solid polymer membrane.   A fuel cell comprising the membrane electrode assembly according to claim 5. In forming a catalyst slurry by stirring and mixing a catalyst-carrying conductor powder carrying catalyst particles, an electrolyte solution, and a solvent, and drying the catalyst slurry after coating,
A method for producing an electrode catalyst layer for a fuel cell, comprising adding a nonionic polymer to the catalyst slurry.   The method for producing an electrode catalyst layer for a fuel cell according to claim 7, wherein the nonionic polymer is added in a range of 5 to 20 wt% with respect to the solid content of the catalyst slurry.