JP5544689B2 - Water retention layer for fuel cell, production method thereof, and electrolyte membrane-electrode assembly - Google Patents

Description

  The present invention relates to a water retention layer for a fuel cell, a method for producing the same, and an electrolyte membrane-electrode assembly.

  In recent years, fuel cells have attracted attention as power sources for electric vehicles and stationary power sources in response to social demands and trends against the background of energy and environmental problems. Fuel cells are classified into various types according to the type of electrolyte, the type of electrode, and the like, and representative types include alkali type, phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer type. Among them, a polymer electrolyte fuel cell that can operate at a low temperature (usually 100 ° C. or less) has attracted attention, and in recent years, development and practical application as a low-pollution power source for automobiles is progressing.

  The polymer electrolyte fuel cell (PEFC) generally has a structure in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between separators. In MEA, an electrolyte membrane is sandwiched between a pair of electrodes, that is, an anode and a cathode. The electrode contains an electrode catalyst and an electrolyte typified by a solid polymer electrolyte, and has a porous structure for diffusing a reaction gas supplied from the outside.

  In the polymer electrolyte fuel cell, electricity can be taken out through the following electrochemical reaction or the like. First, hydrogen contained in the fuel gas supplied to the anode (fuel electrode) side is oxidized by the catalyst particles as shown in the following chemical formula (1) to become protons and electrons. Next, the generated protons pass through the solid polymer electrolyte contained in the anode-side electrode catalyst layer and the solid polymer electrolyte membrane in contact with the anode-side electrode catalyst layer, and enter the cathode (oxygen electrode) -side electrode catalyst layer. Reach. The electrons generated in the anode-side electrode catalyst layer include a conductive carrier constituting the anode-side electrode catalyst layer, and a gas diffusion layer in contact with a different side of the anode-side electrode catalyst layer from the solid polymer electrolyte membrane The cathode side electrode catalyst layer is reached through the separator and the external circuit. The protons and electrons that have reached the cathode electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water as shown in the following chemical formula (2).

In the polymer electrolyte fuel cell, the amount of water distributed to each member is important based on various factors. One method for controlling the amount of water or the amount of water distribution in the polymer electrolyte fuel cell is to provide a water retaining layer having a function of retaining water in addition to the members constituting the fuel cell. Accordingly, various forms of water retention layers have been proposed. For example, in Patent Document 1, a water retention layer containing a water retention material and an electrolyte is disposed on the anode gas diffusion layer, so that the anode gas diffusion layer usually has a high water retention property. A technique for supplying water from the gas diffusion layer to the anode-side electrode catalyst layer has been proposed. By adopting such a form, it is said that electrolysis of water at the anode, which occurs when fuel is insufficient, is promoted. In Patent Document 1, oxides such as zeolite, γ-alumina, and silica are used as water-retaining substances (Patent Document 1, paragraph “0015” and Examples). The water retention layer is specifically composed of a polymer electrolyte, carbon black powder as an electronic conductive material, zeolite as a water retention material, and optionally a mixture of crystalline carbon fibers (Patent Document 1, Examples). 1-6).
JP 2004-146305 A

  However, it has been difficult to say that the water retention capacity of the conventional water retention layer is sufficient. For example, since carbon black used as a conductive material in the water retention layer of Patent Document 1 also has a water retention function, a water retention material such as zeolite can be omitted. At that time, the conventional water retention layer does not have a structure that maximizes the water retention capability of carbon black, it is necessary to use an extra water retention material, and the transportability of hydrogen and water vapor is also poor. It was. Furthermore, water-repellent substances such as crystalline carbon fibers used in the water-retaining layer of Patent Document 1 are difficult to adsorb moisture, and such a material does not allow the water-retaining ability of the water-retaining substance to be fully utilized. It was. If the water-retaining capacity of the water-retaining layer is insufficient, there is a risk that a voltage drop due to reaction gas transport inhibition by liquid water may occur during startup (especially when the temperature is low, such as below freezing point). Accordingly, the present invention has been made paying attention to the above-described problems, and aims to improve the water retention capacity of the water retention layer.

  A water retention layer for a fuel cell having a structure in which the water retention material is partially covered in a state where the binder material is unevenly distributed and a water retention layer for a fuel cell manufactured using an ink containing a high-boiling solvent can solve the above problems. The headline and the present invention were completed.

  The water retention layer of the present invention has a structure in which the water retention ability is effectively exhibited. Therefore, by providing the electrolyte membrane-electrode assembly to which the water retention layer of the present invention is applied, it becomes possible to suppress the voltage drop due to the influence of liquid water, such as that seen at low temperature startup (particularly below freezing point). .

  The present invention relates to a water retention layer for a fuel cell, which includes a powder water retention material and a water permeable binder material, and partially covers the water retention material in a state where the binder material is unevenly distributed.

  The present inventors paid attention to the structure formed by the water-retaining material and the binder material constituting the water-retaining layer as a cause that the conventional water-retaining layer did not sufficiently exhibit the water-retaining ability. And it discovered that the water retention ability of a water retention layer improved by taking the structure which covers a water retention material partially in the state where the binder material was unevenly distributed. This reason is not limited, but the following reasons are conceivable. In the region where the relative pressure of water vapor is high, the water vapor is generally adsorbed over multiple layers on the surface of the water retaining material. However, when the surface of the water retention material is almost entirely covered with the binder material, the water vapor adsorption (water absorption) function as the water retention layer is reduced because the adsorption site of water vapor (water) that can be adsorbed on the surface of the water retention material is reduced. Will be weakened. As a result, the total amount of water absorption is determined by the balance between the reduction of the adsorption sites and the increase in the amount of water absorption to the binder material. On the contrary, when the binder material is unevenly distributed and covers only a part of the surface of the water retention material, more water vapor can be adsorbed as the water retention layer. In this case, the water vapor adsorption amount in the equilibrium state increases.

  In addition, when the surface of the water retaining material is almost entirely covered with the binder material, the water retaining function of the water retaining material is not fully exhibited, and therefore water that is not retained by the water retaining material is likely to exist. If there is water that cannot be retained by the water retention material in the water retention layer, gas diffusion from the gas diffusion layer to the electrode catalyst layer may be hindered when the water retention layer is applied to a fuel cell. On the other hand, when the binder material is unevenly distributed and partially covers the water retention material, the water retention layer appropriately retains water, so that the gas is likely to diffuse. Therefore, when the gas diffusibility of the water retention layer is important, for example, a configuration in which the water retention layer is disposed between the gas diffusion layer and the electrode catalyst layer (hereinafter also simply referred to as catalyst layer) as shown in FIG. Then, application of the water retention layer of the present invention is effective.

  Furthermore, the water retention layer of the present invention has the following effects. After the fuel cell system is stopped, the water retention layer adsorbs water (water vapor) remaining in the electrolyte membrane and gas. After the long-term stoppage, it is expected that the water content inside the MEA has reached equilibrium, and a part of the water inside the membrane moves to the water retaining layer and is retained. Therefore, since the water retention layer of the present invention is excellent in water retention capacity, the moisture content of the membrane is lowered and the water retention buffer is increased. Until now, the generated water generated at the start (particularly below freezing point) hindered the transport of the reaction gas and easily caused a voltage drop. However, the water retention layer of the present invention allows the generated water to move and hold smoothly on the membrane. Therefore, it is possible to suppress a voltage drop.

  The uneven distribution state of the binder material covering the water retention material can be determined using the water vapor adsorption isothermal characteristic. For example, the water vapor adsorption isotherm can be determined by the water vapor adsorption amount of the water retention material in the region where the water vapor activity (relative pressure) is 0.9 to 1.0. When the activity of water vapor is high (for example, 0.9 or more and 1.0 or less), the surface of the water-retaining material increases drastically because water is adsorbed in multiple layers, but there is a binder material. Then, the adsorption site of water vapor (water) is limited. Therefore, by measuring the water vapor adsorption isotherm and evaluating the region where the activity of water vapor is, for example, 0.9 or more and 1.0 or less, the ratio that the binder material covers the surface area of the water retention material, that is, the uneven distribution state Can be determined.

  The water vapor adsorption amount of the water retention layer at a relative pressure of 1 is preferably 400 mg / g or more, and more preferably 600 mg / g or more per 1 g of the water retention material contained in the water retention layer. Below the freezing point, the water generated by power generation freezes, which inhibits oxygen transport, and it is considered that the startability at the start of the fuel cell is lowered. In the process in which the temperature decreases from room temperature to below freezing point, each member (electrolyte membrane, catalyst layer, gas diffusion layer) constituting the MEA has a higher relative pressure near 1 because it is exposed to a relative pressure near 1 for a long time. The higher the ability to adsorb more water, the higher the water retention capacity when starting below freezing. Therefore, when starting below the freezing point under the same environment and conditions, the form including the water retention layer whose water vapor adsorption amount at the relative pressure 1 is 400 mg / g or more can adsorb more water as a whole MEA. Therefore, the generated water at the time of start-up can be smoothly absorbed by each of the above members (particularly the cathode catalyst layer where the generated water is generated and the adjacent electrolyte membrane).

  The water vapor adsorption amount per gram of the water retention material in the water retention layer is preferably 110 to 140% with respect to the water vapor adsorption amount per gram of the water retention material (not coated with the binder material), and 130 to More preferably, it is 140%. If it is such a range, it is preferable from being excellent in water retention ability and holding a water retention material.

  The content of the binder material contained in the water retention layer is such that the water vapor adsorption amount of the water retention layer becomes a minimum value in the range of the water vapor activity from 0.9 to 1.0 in the water vapor adsorption isothermal characteristic. It is preferable to make it less than the content. As the binder amount is increased with respect to the water retention material, the water retention amount in the range of the water vapor activity of 0.9 or more and 1.0 or less decreases and increases after showing a minimum value. At the minimum value, it is considered that the binder coats the outer surface of the water retaining material relatively uniformly. By setting the content to be less than the binder content at that time, the surface of the water-retaining material is exposed and the water retention amount (water vapor adsorption amount) is increased. By setting the binder material in such a range, it is possible to provide a water retention layer that maintains the structure of the water retention material, has water retention and transport functions, and suppresses deterioration of other substance transport functions such as gas. . In addition, even when the content is higher than the binder content at that time, by creating a state in which the binder material is unevenly distributed as described above, the water vapor adsorption amount is increased, and water is retained and transported. It is possible to provide a water retention layer that has a function and suppresses a decrease in the function of transporting other substances such as gas.

  In the present invention, the water vapor adsorption amount employs a value measured by a water vapor desorption isotherm described in Examples described later.

  Moreover, the uneven distribution state of the binder material covering the water-retaining material can be determined from the nitrogen BET specific surface area. When the binder material is coated on the surface of the water retention material, the number of nitrogen adsorption sites decreases due to the interaction between the water retention material and the binder material. Therefore, when the ratio of the binder material covering the surface of the water retention material increases, the BET specific surface area calculated by nitrogen adsorption decreases. In other words, the ratio of the binder material covering the surface area of the water-retaining material, that is, the uneven distribution state can be determined by measuring the nitrogen BET specific surface area.

  Specifically, the nitrogen BET specific surface area of the water retention layer is preferably 30% or more and less than 100% with respect to the nitrogen BET specific surface area of the water retention material (not coated with the binder material). Further, it is more preferably 50% or more and less than 100%. Since the binder material is present in the water-retaining material or in the gaps between the materials, the presence of the binder material inhibits the transport of other substances (gas). Therefore, it is also important to suppress a decrease in gas transportability. Considering water retention performance and gas transportability, the nitrogen BET specific surface area of the water retention layer is preferably 50% or more with respect to the nitrogen BET specific surface area of the water retention material. Further, as described above, the larger the area that is not covered with the binder, the more preferable the water retaining material is. Therefore, it is sufficient that the water retaining material contains a binder that can retain the water retaining material. This means that the nitrogen BET specific surface area of the water retention layer is preferably as large as possible relative to the nitrogen BET specific surface area of the water retention material. However, considering the binding force of the binder, the nitrogen BET specific surface area of the water retaining layer is preferably 90% or less with respect to the nitrogen BET specific surface area of the water retaining material. As the nitrogen BET specific surface area, a value measured by the following method is adopted.

(Method for measuring nitrogen BET specific surface area)
1. Sampling, Weighing and Pre-drying About 0.04 to 0.07 g of powder is precisely weighed, and the coated sheet is cut out about 5 cm × 5 cm square, and further weighed into sections of about 5 mm width × 25 mm, and then weighed into each sample tube. Enclosed. This sample tube was pre-dried at 90 ° C. for several hours in a vacuum dryer and subjected to measurement. For weighing, an electronic balance (AW220) manufactured by Shimadzu Corporation was used. In addition, about the coating sheet, about 0.03-0.04g net weight of the coating layer which deducted the Teflon (base material) weight of the same area from the total weight of this was used as a sample weight.

  2. Measurement condition

3. Measurement method On the adsorption side of the adsorption / desorption isotherm, create a BET plot from the relative pressure (P / P ₀ ) range of approximately 0.00 to 0.45, and calculate the BET specific surface area from the slope and intercept. To do.

  As described above, by keeping the nitrogen BET specific surface area of the water-retaining material coated with the binder material in the water-retaining layer to be 50% or more and less than 100%, the structure of the water-retaining layer is maintained, and the water retention and transport function is achieved. It is possible to provide a water-retaining layer that suppresses a decrease in the function of transporting other substances such as gas.

  It is preferable that the binder material contained in the water retention layer is appropriately blended so as to satisfy the relative ratio condition of the nitrogen BET specific surface area. As described above, it is possible to reduce the nitrogen BET specific surface area by intentionally unevenly distributing the coating state of the binder, but at the same time, it is necessary to contain a predetermined amount of binder in order to maintain the water retention layer structure. is there. By appropriately adjusting the amount of the binder, it is possible to suppress a decrease in the gas transport function while maintaining the water retention and transport function as the water retention layer.

  The thickness of the water retaining layer is not particularly limited, but is preferably 5 to 200 μm, more preferably 10 to 100 μm, and particularly preferably 10 to 50 μm. If the thickness of the water retention layer is within the above range, it is preferable because it is possible to ensure both water retention and gas diffusibility. As will be described later, when the water retention layer functions as a catalyst layer, the thickness of the water retention layer (catalyst layer) is not particularly limited, but is preferably 5 to 50 μm, more preferably 5 to 30 μm. Particularly preferably, the thickness is 10 to 30 μm.

  The porosity of the water retaining layer is not particularly limited, but is preferably 20 to 80%, and more preferably 50 to 80%. A porosity within the above range is preferable because gas diffusibility can be secured. When the water retention layer functions as a catalyst layer, the porosity of the water retention layer (catalyst layer) is not particularly limited, but is preferably 30 to 70%, preferably 40 to 60 % Is more preferable.

  The water retention layer includes a water retention material and a binder material. In some cases, the water retention material may carry a catalyst. The water retention layer may contain conventionally known materials used for the water retention layer in addition to the water retention material and the binder. In the water-retaining layer, the content of the water-retaining material and / or the catalyst-supported water-retaining material and the binder material is preferably 80% by mass or more, and more preferably 90% by mass or more. More preferably, the water retention layer is composed of a water retention material and / or a water retention material on which a catalyst is supported and a binder material. Since the water retention material of the present invention has a high water retention capability, the mass ratio of materials other than the water retention material and the binder material can be reduced.

The mass ratio of the water-retaining material and the binder material is preferably water-retaining material: binder material = 1: 0.4 to 1.8, and preferably 1: 0.4 to 1.3. Is more preferable. If it exists in such a range, the water retention of a water retention layer is kept moderate, and a water retention material can be bound with a binder. The mass ratio of the water-retaining material and the binder material is determined by measuring the binder material and the water-retaining material mixed in advance when preparing the water-retaining layer ink (slurry). By adjusting, it can be calculated and controlled. In addition, the water retention layer is analyzed, the water retention material and the binder material are quantified, and the mass ratio of the water retention material and the binder material can be calculated. For example, when the water retention layer is composed of a water retention material carrying a catalyst and a polymer electrolyte, the mass of the catalyst component can be quantified by inductively coupled plasma emission spectroscopy (ICP). Further, the polymer electrolyte mass (I) can be quantified by combining two of the structure analysis of the polymer electrolyte by ¹⁹ F NMR and the quantification of S atoms by coulometric titration.

  In the present invention, the water retentive layer is a layer containing a water retentive material and a binder material, and may be in any form as long as it has a water retentive function. That is, regardless of the name, even if it is referred to as an electrode catalyst layer in view of the purpose of use used in a fuel cell, it may be included in the water retention layer in the present invention. For example, if the catalyst is supported on the water retention material, the catalyst layer can be used for MEA as the water retention layer.

  Hereinafter, each component which comprises the water retention layer of this invention is demonstrated.

(Water retentive material)
Examples of powder water retention materials include carbon materials such as natural graphite, artificial graphite, activated carbon, carbon black (oil furnace black, channel black, lamp black, thermal black, acetylene black, etc.); alumina, titania, silica, tin oxide And metal oxides such as zeolite; These water retention materials may be used alone or in combination of two or more. The water-retaining material is preferably a carbon material or a metal oxide from the viewpoint of the specific surface area, and more preferably a carbon material, particularly carbon black or activated carbon.

  Commercially available carbon black can be used, such as Cabot Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, Ketjen Black EC manufactured by Lion Corporation, Oil furnace black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical Corporation; acetylene black such as Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. and the like.

  The average particle size of the powdery water retaining material is preferably 10 to 500 nm, and more preferably 10 to 100 nm. Thereby, gas diffusibility can be ensured. In the present specification, “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the active material particles. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

The nitrogen BET specific surface area of the water retaining material is preferably 500 m ² / g or more. The water retention of the water retention material depends on the nitrogen BET specific surface area. By using a material having a specific surface area of 500 m ² / g or more, it is possible to provide a water retention layer in which the water retention performance is maintained even when the content (weight) of the water retention material is reduced. More preferably, the water retention material has a nitrogen BET specific surface area of 700 to 2000 m ² / g. Further, in the MEA, assuming that the water retention layer is disposed adjacent to the catalyst layer, in order to increase the corrosion resistance of the adjacent catalyst layer, the crystallinity of the support such as carbon is increased, but the crystallinity is increased. In some cases, the water absorption was lowered. By setting the BET specific surface area within the above range, the trade-off can be solved, and the water retention function can be ensured even if the catalyst layer has a high corrosion resistance specification.

  A catalyst component may be supported on the water retention material. A water retention layer containing a water retention material on which a catalyst component is supported may be used as a catalyst layer. In this case, a conductive carrier which will be described later in the column of the catalyst layer can be used as the water retention material. Moreover, as a binder, the polymer electrolyte demonstrated later in the column of a catalyst layer can be used. The constituent components, component content, and the like for the case where the water retention layer is used as the catalyst layer are the same as those of the catalyst layer, and thus the description thereof is omitted here.

  Further, when the water retention layer is not used as the catalyst layer, for example, even if the water retention layer is disposed between the anode side electrode catalyst layer and the anode side gas diffusion layer, the water retention material does not contain the catalyst component. You may carry. When a solid polymer electrolyte is used as a binder in the water retention layer, a three-phase interface can be formed by further containing catalyst particles, and the electrochemical reaction area at the anode can be expanded to a certain extent. The amount of the catalyst particles supported on the water retention material contained in the water retention layer is preferably 0.1 to 10% by weight, more preferably 0.1 to 5% by weight. Examples of the catalyst particles include those similar to the catalyst particles used in the catalyst layer described later. In the catalyst layer and the water retention layer, the same catalyst particles may be used, or different catalyst particles may be used.

(Binder material)
The water-permeable binder material (hereinafter also simply referred to as a binder) is not particularly limited as long as it is a material that can bind the water-retaining material. Examples thereof include polymers such as polyacrylamide, aqueous urethane resin, and silicon resin; polymer electrolytes and the like. A polymer electrolyte (hereinafter also referred to as ionomer) is preferable. By making the binder material an ionomer, it is possible to stably arrange a water retention layer adjacent to a MEA component (electrolyte membrane or catalyst layer) containing the same ionomer, and a catalyst layer or membrane, It is possible to reduce water transport resistance with the water retention material. As a result, the water transportability between the electrolyte membrane or the catalyst layer and the water retention material is improved, and the equilibrium can be reached in an earlier time. When the binder material is a polymer electrolyte, the electrolyte may be the same as or different from the polymer electrolyte used in the catalyst layer or the electrolyte membrane. Further, when an MEA including a water retention layer is manufactured, the material can be shared, and labor saving at the time of manufacturing can be achieved.

  The ionomer used is not particularly limited. Specifically, ionomers are broadly classified into fluorine-based electrolytes containing fluorine atoms in all or part of the polymer skeleton and hydrocarbon-based electrolytes not containing fluorine atoms in the polymer skeleton.

  Specific examples of fluorine-based electrolytes include perfluorocarbon sulfonates 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.), etc. Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene A preferred example is a fluoride-perfluorocarbon sulfonic acid-based polymer. The fluorine-based electrolyte is excellent in durability and mechanical strength.

  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, polyphenyl. A suitable example is sulfonic acid.

  The above ionomers may be used alone or in combination of two or more.

  The electrolyte used is appropriately selected depending on the role of the water retention layer when the water retention layer is disposed in the electrolyte membrane-electrode assembly. In the water retention layer, since the water moving speed is important, the EW is preferably low. Preferably, the EW is 1200 g / eq. Hereinafter, more preferably, 700 g / eq. It is as follows. If it is such a range, the water retention layer which can make a water retention amount a saturated state in a shorter time can be provided. The lower limit of EW is not particularly limited, but is usually 500 g / eq. The above is preferable. In addition, EW (Equivalent Weight) represents an ion exchange group equivalent weight.

  For example, when the water retention layer is disposed in a form sandwiched between the catalyst layer and the gas diffusion layer as shown in FIG. 1 described in detail later, the proton transport function of the ionomer as the binder does not matter. For this reason, a material having lower proton conductivity than the fluorine-based electrolyte material can also be used as the electrolyte used for the water retention layer. Therefore, a hydrocarbon-based electrolyte that is inexpensive and has a lower EW can be used as a binder for the water retention layer. By using such a hydrocarbon-based electrolyte, it is possible to provide a water retention layer capable of bringing the water retention amount to a saturated state in a shorter time. The EW of the hydrocarbon-based electrolyte is preferably 700 g / eq. Or less, more preferably 500 to 700 g / eq. It is.

  Moreover, when a water retention layer is used as a catalyst layer as shown in FIG. 2 described in detail later, the electrolyte is required to have a proton transport function. For this reason, the ionomer preferably has a sulfonic acid group from the viewpoint of improving proton conductivity. Therefore, perfluorocarbon sulfonic acid polymer 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.) are preferably used. The perfluorocarbon sulfonic acid polymer electrolyte is composed of a main chain part constituting a hydrophobic skeleton and a side chain part forming a hydrophilic cluster region, and the side chain part has a sulfonic acid as an ion exchange group. A group is present. In particular, when a perfluorocarbon sulfonic acid polymer electrolyte is used as the ionomer, the EW is 600 to 1500 g / eq. , More preferably 600-1100 g / eq. It is preferable to use one having a degree.

(Manufacturing method of water retention layer)
The method for producing the water retention layer is not particularly limited. For example, a water retention layer, a binder, and a solvent are mixed to prepare a water retention layer ink, which is applied to a substrate and then dried. A method or the like is used. In the case of using a water retention material on which a catalyst component is supported, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method), etc. The catalyst component is preferably supported on the water-retaining material in advance using the method.

  Preferably, the water retention layer ink is obtained by mixing a powdery water retention material and a water-permeable binder material in the presence of a solvent containing an organic solvent having a boiling point exceeding 100 ° C. It is preferable. When the solvent contains an organic solvent having a boiling point exceeding 100 ° C. (hereinafter also referred to as a high boiling point organic solvent), a water retaining layer having excellent water retaining ability can be obtained. Although the detailed mechanism is unknown, it is presumed that the fine structure between the ink state and the water-retaining layer after drying is deviated by containing an organic solvent having a boiling point exceeding 100 ° C. In the ink state, it is assumed that the water-retaining binder covers the water-retaining material more uniformly. However, if an organic solvent having a boiling point exceeding 100 ° C. is included, drying takes time and high temperature, so the binder becomes non-uniform. It is thought that the structure which increases the ratio of covering is taken.

  It does not specifically limit as a high boiling point organic solvent, Ethylene glycol (boiling point: 197.6 degreeC), propylene glycol (boiling point: 188.2 degreeC), 1, 2- butanediol (boiling point: 190.5 degreeC), 1 , 3-butanediol (boiling point: 207.5 ° C.), 1,4-butanediol (boiling point: 229.2 ° C.), 1-butanol (boiling point: 117.2 ° C.), 1-pentanol (boiling point: 138.degree. C.). 3 ° C), 2-pentanol (boiling point 119.9 ° C), 3-pentanol (boiling point: 116.1 ° C), glycerin (boiling point 290 ° C), and the like. These may be used alone or in combination of two or more. The high boiling point organic solvent is preferably mixed uniformly with water.

  The solvent in the water retention layer ink may be composed of only a high-boiling organic solvent. Moreover, you may use the mixture of a high boiling-point organic solvent and another solvent (For example, water, organic solvents (both methanol, ethanol, 1-propanol, 2-propanol etc.) with a boiling point of less than 100 degreeC). In the case of a mixture of a high boiling organic solvent and another solvent, the ratio of the high boiling organic solvent in the solvent is preferably 10% by mass or more, and more preferably 30% by mass or more. From the viewpoint of water retention, the higher the ratio of the high-boiling organic solvent, the better. Therefore, the upper limit of the ratio of the high-boiling organic solvent in the solvent is not particularly limited, but considering the dispersibility of the polymer electrolyte, 70% by mass The following is preferable. When using a mixture of a high-boiling organic solvent and another solvent, the solvent composition in the ink during the drying process changes due to the difference in boiling point between the solvents, so the contact state between the water retention material and the binder material changes. . Such a change is considered to make it easier to coat the water retention material when the binder material is unevenly distributed.

  The boiling point of the entire solvent in the water-retaining layer ink is preferably higher than 100 ° C. When the boiling point of the whole solvent exceeds 100 ° C., the water retention ability is improved, which is preferable. The detailed mechanism is unknown for this reason, but the higher the boiling point of the whole solvent, the longer it takes to dry, so a water-retaining material with a structure that partially covers the water-retaining material in a state where the binder is unevenly distributed is easier. It is thought that this is because Therefore, it is preferable to appropriately adjust the content ratio of the high boiling point solvent and the other solvent so that the boiling point of the whole solvent exceeds 100 ° C. The upper limit of the boiling point of the entire solvent in the water-retaining layer ink is not particularly limited, but it is preferably 200 ° C. or lower in consideration of the drying temperature and drying time after the ink application.

  In addition, the solvent and the solvent in the present specification include all of a dispersion medium in which solid components such as a binder and a water retention material are dispersed, that is, liquid components other than the solid components. Therefore, for example, when an ink for water retention layer is produced by mixing an ionomer dispersed in water and an organic solvent, the solvent in the present specification refers to both water and the organic solvent.

  The solid content ratio of the water retention layer ink (weight ratio of the solid content to the total weight of the water retention layer ink) is not particularly limited, but is preferably 20% by mass or less, and preferably 10% by mass or less. More preferably. This is because when the solid content is in such a range, it becomes easy to coat the water-retaining material in a form in which the binder is unevenly distributed. Although this detailed mechanism is unknown, it is considered that the lower the solid content ratio, the more time is required for drying, and the fine structure between the ink state and the water-retaining layer after drying tends to deviate. The lower limit of the solid content is not particularly limited, but is usually 1% by weight or more in consideration of ease of application to the substrate.

  The mass ratio of the water-retaining material and the binder material in the ink is preferably water-retaining material: binder material = 1: 0.4 to 1.8, preferably 1: 0.4 to 1.3. More preferably. According to the method using a high boiling point solvent, even when the ratio of the binder material is higher than that of the water-retaining material to some extent, the unevenly distributed state of the binder material can be easily formed.

  The method for preparing the water retaining layer ink is not particularly limited. Moreover, the mixing order of the binder, the water retention material, and the solvent is not particularly limited, and specific examples thereof include the following (i-1) to (i-3).

(I-1) A solution containing a binder is prepared, and the solution is mixed with a water retention material. Thereafter, a solvent containing a high-boiling organic solvent is further added to prepare a water-retaining layer ink;
(I-2) A solution containing a binder is prepared, and a solvent containing a high-boiling organic solvent is added. Thereafter, the water retention material is further mixed (added) to prepare a water retention layer ink; and (i-3) The water retention material and a solvent containing a high-boiling organic solvent are mixed. Next, a solution containing a binder is further added to prepare a water retention layer ink.

  Among the above methods, the methods (i-1) and (i-2) are preferable, and the method (i-1) is more preferable. Thereby, water and an organic solvent are mixed uniformly and a solvent compound is easy to form.

  In the methods (i-1) to (i-3), in the solution containing the binder, the binder is dispersed in the solvent. The binder content in the solution containing the binder is not particularly limited, but the solid content is preferably 1 to 40% by mass, more preferably 5 to 20% by mass. With such a content, the polymer electrolyte can be appropriately dispersed in the solvent. The solution containing the binder may be adjusted by itself or a commercially available product may be used. Although the dispersion solvent of the binder in the solution containing the said binder is not specifically limited, Water, methanol, ethanol, 1-propanol, 2-propanol etc. are mentioned. In consideration of dispersibility, water, ethanol, and 1-propanol are preferable. These dispersion solvents may be used alone or in combination of two or more.

  In addition, in the water-retaining layer ink manufacturing process, after mixing the binder, the water-retaining material, and the solvent, a separate mixing process may be provided for good mixing. In such a mixing step, the catalyst ink is well dispersed with an ultrasonic homogenizer, or the mixed slurry is well pulverized with an apparatus such as a sand grinder, a circulating ball mill, or a circulating bead mill, and then a vacuum defoaming operation is performed. The addition etc. are mentioned preferably.

  Next, after applying the obtained water retention layer ink on the substrate, the substrate coated with the water retention layer ink is dried.

  The method for applying the water-retaining layer ink to the substrate surface is not particularly limited, and a known method can be used. Specifically, it can be performed using a known method such as a spray (spray coating) method, a gulliver printing method, a die coater method, a screen printing method, or a doctor blade method. Moreover, the apparatus used for application | coating to the base-material surface of a catalyst ink is also not restrict | limited in particular, A well-known apparatus can be used. Specifically, coating apparatuses such as a screen printer, a spray device, a bar coater, a die coater, a reverse coater, a comma coater, a gravure coater, a spray coater, and a doctor knife can be used. The application step may be performed once or repeated a plurality of times until the content (supported amount) of the water-retaining material (supported catalyst component) described in detail below is achieved. It is preferable to perform appropriately.

  The specific drying temperature is appropriately set depending on the solvent used. It is preferable to carry out the drying temperature below the boiling point of the solvent. Thus, the water retention performance of a water retention layer improves more by drying slowly over time below boiling point. When the drying temperature does not include the high-boiling solvent as described above, a water retention layer excellent in water retention performance can be obtained by setting the temperature to about 40 to 80 ° C. and drying slowly. On the other hand, when a high boiling point solvent is included, the drying temperature is often determined according to the heat resistance of the electrolyte material. Specifically, when a fluorine-based electrolyte material is included, about 100 to 170 ° C. is preferable, and when a hydrocarbon-based electrolyte material is included, about 100 to 200 ° C. is desirable. When a high boiling point solvent is included, the drying temperature when drying the substrate on which the water retention layer ink is applied is preferably higher than 100 ° C. Although the detailed mechanism is unknown, it is presumed that this is because the fine structure of the ink state and the dried water retention layer deviates by drying slowly. In the ink state, it is assumed that the water-retaining binder covers the water-retaining material more uniformly, but the longer the drying time, the greater the proportion of the non-uniform coating of the fine structure of the water-retaining layer. It is done.

  Although the drying time at the time of drying the base material with which the water retention layer ink is applied is not particularly limited, it is preferably 5 to 30 minutes. The atmosphere during drying is not particularly limited, but it is preferable to perform drying in an air atmosphere or an inert gas atmosphere.

  The substrate to which the water retention layer ink is applied may be appropriately selected depending on the form of the finally obtained water retention layer, such as an electrode catalyst layer, a gas diffusion layer, or a polymer sheet such as a polytetrafluoroethylene sheet (PTFE). Can be used. When the water retention layer is used as a catalyst layer, the water retention layer can be formed by applying the water retention layer ink to the electrolyte membrane using the electrolyte membrane as a base material.

  The amount of the water-retaining material present in the water-retaining layer formed in the above step is not particularly limited and is appropriately selected depending on the desired effect described above. Specifically, the volume ratio of the water retaining layer is preferably 0.1 to 0.7, more preferably about 0.3 to 0.5. With such an amount, sufficient power generation performance can be achieved.

  The water retention layer of the present invention has excellent water retention ability. Therefore, when applied to MEA, it is possible to suppress a voltage drop due to the influence of liquid water seen at the time of low-temperature startup. Therefore, the present invention also includes a water retention layer for a fuel cell, which includes a powder water retention material and a water permeable binder material, and partially covers the water retention material in a state where the binder material is unevenly distributed, or For a fuel cell obtained by a production method, comprising a step of obtaining a water retention layer ink by mixing a solvent containing an organic solvent having a boiling point exceeding 100 ° C., a powdery water retention material, and a water-permeable binder material. The present invention relates to an MEA including a water retention layer. Furthermore, the present invention relates to a fuel cell using the MEA.

  Hereinafter, preferred embodiments of an MEA including a water retention layer of the present invention will be described with reference to the drawings. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of a suitable MEA including a water retention layer of the present invention. Hereinafter, this embodiment is referred to as a first embodiment. In the MEA 10 of FIG. 1, an anode side electrode catalyst layer 13 and a cathode side electrode catalyst layer 15 are disposed opposite to each other on both sides of a solid polymer electrolyte membrane 12, and are sandwiched between an anode side gas diffusion layer 14 and a cathode side 16. It has the structure. Further, the water retention layer 17 of the present invention is disposed between the anode side electrode catalyst layer 13 and the anode side gas diffusion layer 14.

  Since the water retention layer of the present application has a structure that partially covers the water retention material in a state where the binder material is unevenly distributed, the gas retention property is excellent. Therefore, even when a water retention layer is disposed between the gas diffusion layer and the catalyst layer as in the above embodiment, the water retention function is exhibited without hindering gas diffusion from the gas diffusion layer to the catalyst layer. be able to.

  The embodiment shown in FIG. 1 is a form in which the water retention layer 17 of the present invention is disposed between the anode side electrode catalyst layer 13 and the anode side gas diffusion layer 14. You may arrange | position between cathode side gas diffusion layers. Moreover, you may provide a water retention layer in both poles. Preferably, a water retaining layer is provided at least on the anode side. As described above, when the fuel cell is started below the freezing point, it is considered that the transport of oxygen is inhibited due to freezing of water generated by power generation, which is one cause of the decrease in startability. Accordingly, it is important that the direction of water movement when absorbing the produced water is the anode side electrode catalyst layer from the cathode side electrode catalyst layer through the electrolyte membrane. By disposing the water retention layer on the anode side, more generated water returns to the anode catalyst layer side, so that the startability below freezing point can be increased.

  The manufacturing method of MEA of 1st embodiment is not specifically limited, It can manufacture with a conventionally well-known manufacturing method.

  For example, electrode catalyst layers are prepared on both sides of the solid polymer electrolyte membrane, and the water retention layer ink is applied to the electrode catalyst layer. Examples thereof include a method of drying this, followed by sandwiching with a gas diffusion layer and hot pressing.

  Other examples include the following methods. First, a water retention layer ink is applied on a gas diffusion layer or a substrate such as a PTFE sheet, dried, and then the anode-side electrode catalyst layer ink is applied and dried on the obtained water retention layer. Separately, a cathode-side electrode catalyst layer is formed on a base material such as a gas diffusion layer or a PTFE sheet. Next, the solid polymer electrolyte membrane is sandwiched between the water retention layer and anode side electrode catalyst layer on the substrate and the cathode side electrode catalyst layer on the substrate so that the catalyst layer is in contact with the solid polymer electrolyte membrane. Thereafter, the solid polymer electrolyte membrane and each electrode catalyst layer are joined by hot pressing or the like. When a PTFE sheet is used as the substrate, after hot pressing, only the PTFE sheet is peeled off, and then a gas diffusion layer is laminated. The step of drying the water retention layer ink described in the above method for producing a water retention layer may be performed at any stage of the MEA production process, and immediately after the water retention layer ink is applied on the substrate. In addition, the present invention is not limited to the form of drying the water retention layer ink.

  FIG. 2 is a schematic cross-sectional view showing another preferred embodiment of the MEA including the water retention layer of the present invention. Hereinafter, this embodiment is referred to as a second embodiment. In the MEA 20 of FIG. 2, an anode side electrode catalyst layer 23 and a cathode side electrode catalyst layer 25 are arranged on both sides of a solid polymer electrolyte membrane 22 so as to face each other, and these are arranged as an anode side gas diffusion layer 24 and a cathode side gas diffusion layer. 26. Further, the water retention layer 27 of the present invention is disposed between the anode side electrode catalyst layer 23 and the solid polymer electrolyte membrane 22.

  The embodiment shown in FIG. 2 is a form in which the water retention layer 27 of the present invention is disposed between the anode side electrode catalyst layer 23 and the solid polymer electrolyte membrane 22. You may arrange | position between solid polymer electrolyte membranes. Moreover, you may provide a water retention layer in both poles. Preferably, a water retaining layer is provided at least on the anode side. As described above, when the fuel cell is started below the freezing point, it is considered that the transport of oxygen is inhibited due to freezing of water generated by power generation, which is one cause of the decrease in startability. Accordingly, it is important that the direction of water movement when absorbing the produced water is the anode side electrode catalyst layer from the cathode side electrode catalyst layer through the electrolyte membrane. By disposing the water retention layer on the anode side, more generated water returns to the anode catalyst layer side, so that the startability below freezing point can be increased.

  The manufacturing method of MEA of 2nd embodiment is not specifically limited, It can manufacture with a conventionally well-known manufacturing method. For example, the water retention layer ink is applied to both sides of the solid polymer electrolyte membrane and dried, and then the electrode catalyst layer slurry is applied and dried on the water retention layer. Then, the method of hot-pressing after pinching with a gas diffusion layer is mentioned.

  Other examples include the following methods. First, the anode side electrode catalyst layer ink is applied and dried on a gas diffusion layer or a substrate such as a PTFE sheet, and then the water retention layer ink is applied on the electrode catalyst layer and dried. Separately, a cathode-side electrode catalyst layer is formed on a base material such as a gas diffusion layer or a PTFE sheet. Next, the solid polymer electrolyte membrane so that the water retention layer and the cathode catalyst layer are in contact with the solid polymer electrolyte membrane by the water retention layer and the anode side electrode catalyst layer on the substrate and the cathode side electrode catalyst layer on the substrate. Pinch. Thereafter, the solid polymer electrolyte membrane and each electrode catalyst layer are joined by hot pressing or the like. When a PTFE sheet is used as the substrate, after hot pressing, only the PTFE sheet is peeled off, and then a gas diffusion layer is laminated. The step of drying the water retention layer ink described in the above method for producing a water retention layer may be performed at any stage of the MEA production process, and immediately after the water retention layer ink is applied on the substrate. In addition, the present invention is not limited to the form of drying the water retention layer ink.

  In the present invention, it is preferable to dispose a water retention layer adjacent to the catalyst layer, particularly the anode catalyst layer, as in the first embodiment and the second embodiment. At least the membrane and the catalyst layer have a water retention function inside the MEA. Since the catalyst layer (anode / cathode) is installed so as to sandwich the membrane, a water retention layer is provided adjacent to the catalyst layer, so that the liquid water existing inside the MEA (membrane, catalyst layer) can be smoothly retained. It is possible to provide an MEA that can be moved and held in a layer and can suppress a voltage drop.

  FIG. 3 is a schematic cross-sectional view showing another preferred embodiment of the MEA of the present invention. Hereinafter, this embodiment is referred to as a third embodiment. The MEA 30 in FIG. 3 has a configuration in which an anode-side electrode catalyst layer 33 and a cathode-side electrode catalyst layer 35 face each other on both sides of a solid polymer electrolyte membrane 32 and are sandwiched between gas diffusion layers 34 and 36. doing. In this embodiment, the anode side electrode catalyst layer 33 is a water retention layer. Therefore, the water retention material contained in the catalyst layer 33 carries the catalyst. Since the catalyst layer also serves as the water retention layer as in the present embodiment, it is not necessary to provide a separate member, which is preferable from the viewpoint of productivity.

  In the embodiment shown in FIG. 3, the anode side electrode catalyst layer 33 is a water retention layer, but the water retention layer may be a cathode side electrode catalyst layer. Moreover, you may provide a water retention layer in both poles. Preferably, at least the anode side electrode catalyst layer 33 is a water retention layer. As described above, when the fuel cell is started below the freezing point, it is considered that the transport of oxygen is inhibited due to freezing of water generated by power generation, which is one cause of the decrease in startability. Accordingly, it is important that the direction of water movement when absorbing the produced water is the anode side electrode catalyst layer from the cathode side electrode catalyst layer through the electrolyte membrane. By disposing the water retention layer on the anode side, more generated water returns to the anode catalyst layer side, so that the startability below freezing point can be increased.

  The MEA of the third embodiment can be manufactured by a conventionally known MEA manufacturing method.

  Next, a PEFC that is a preferred embodiment using the MEA of the present invention will be described with reference to the drawings.

  FIG. 4 is a schematic cross-sectional view showing a single PEFC cell in which the fuel cell MEA of the first embodiment is sandwiched between a pair of separators. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals.

  The PEFC 100 shown in FIG. 4 is configured by sandwiching the MEA 10 between the anode side separator 102 and the cathode side separator 101. Further, the fuel gas and the oxidant gas supplied to the MEA are supplied to the anode side separator 102 and the cathode side separator 101 through gas supply grooves 104 and 103 provided at a plurality of locations, respectively. Further, in the PEFC of FIG. 4, the gasket 105 is disposed so as to surround the outer periphery of the electrode located on the surface of the MEA 10. The gasket is a seal member, and may have a configuration that is fixed to the outer surface of the electrolyte membrane 12 of the MEA 10 via an adhesive layer (not shown). The gasket has a function of ensuring the sealing property between the separator and the MEA. Note that the adhesive layer used as necessary preferably corresponds to the shape of the gasket and is arranged in a frame shape on the entire peripheral edge of the electrolyte membrane in consideration of securing adhesiveness.

  Hereinafter, each component of MEA and PEFC will be described in detail in order.

  As described above, the MEA and PEFC of the present invention are characterized by a water retention layer. Therefore, as for other members constituting the MEA and PEFC, a conventionally known configuration in the field of the fuel cell can be used as it is or after being appropriately improved. Hereinafter, typical forms of members other than the water retention layer will be described for reference, but the technical scope of the present invention is not limited to the following forms.

[Polymer electrolyte membrane]
The polymer electrolyte membrane is made of an ion exchange resin and has a function of selectively permeating protons generated in the anode side catalyst layer during PEFC operation to the cathode side catalyst layer along the film thickness direction. The polymer electrolyte membrane also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The specific configuration of the polymer electrolyte membrane is not particularly limited, and conventionally known polymer electrolyte membranes can be appropriately employed in the field of fuel cells. Polymer electrolyte membranes are roughly classified into fluorine-based polymer electrolyte membranes and hydrocarbon-based polymer electrolyte membranes depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane include 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. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolyte membranes composed of perfluorocarbon sulfonic acid polymers are used. It is done.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated. Examples include polyetheretherketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolyte membranes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the material selectivity is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is needless to say that other materials may be used without being limited to the above-described materials.

  The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained MEA and PEFC, and is not particularly limited. However, the thickness of the polymer electrolyte membrane is preferably 5 to 300 μm, more preferably 10 to 200 μm, and still more preferably 15 to 150 μm. When the thickness is within such a range, the balance between strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[Catalyst layer]
The catalyst layer is a layer where the reaction actually proceeds. Specifically, a hydrogen oxidation reaction proceeds in the anode side catalyst layer, and an oxygen reduction reaction proceeds in the cathode side catalyst layer. The catalyst layer includes a catalyst component, a conductive carrier that supports the catalyst component, and a proton-conductive polymer electrolyte.

  The catalyst component used in the anode side catalyst layer is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Further, the catalyst component used in the cathode side catalyst layer 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. 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. However, it goes without saying that other materials may be used. 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. The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. The composition of the alloy when the alloy is used as the cathode-side catalyst varies depending on the type of metal to be alloyed and the like and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 to It is preferable to set it as 70 atomic%. 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 anode catalyst layer and the catalyst component used for the cathode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both, and are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer and the cathode catalyst layer do not have 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. At this time, the average particle diameter of the catalyst particles is preferably 1 to 30 nm, more preferably 1.5 to 20 nm, still more preferably 2 to 10 nm, and particularly preferably 2 to 5 nm. When the average particle diameter of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. The “average particle diameter of catalyst particles” in the present invention is the average of the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction or the average particle diameter of the catalyst component determined from a transmission electron microscope image. It can be measured as a value.

  The conductive carrier functions as a carrier for supporting the above-described catalyst component and an electron conduction path involved in the exchange of electrons with the catalyst component.

  Any conductive carrier may be used as long as it has a specific surface area for supporting the catalyst component in a desired dispersed state and sufficient electron conductivity, and the main component is preferably carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Note that “substantially consisting of carbon atoms” means that contamination of about 2 to 3 mass% or less of impurities can be allowed.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. When the specific surface area of the conductive support is in such a range, the balance between the dispersibility of the catalyst component on the conductive support and the effective utilization rate of the catalyst component can be appropriately controlled.

  The size of the conductive carrier is not particularly limited, but from the viewpoint of easy loading, catalyst utilization, and control of the electrode catalyst layer thickness within an appropriate range, the average particle size is 5 to 200 nm, preferably 10 It is good to be about ~ 100 nm.

  When the catalyst layer is a water retention layer, a conductive water retention material as a conductive carrier, preferably graphite, activated carbon, carbon black (oil furnace black, channel black, lamp black, thermal black, acetylene black, etc. ) Or the like is used.

  In a composite in which a catalyst component is supported on a conductive carrier (hereinafter also referred to as “electrode catalyst”), the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably based on the total amount of the electrode catalyst. Is 30-70 mass%. When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the conductive support and the catalyst performance can be appropriately controlled. The supported amount of the catalyst component can be measured by inductively coupled plasma emission spectroscopy (ICP).

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

  Alternatively, in the present invention, a commercially available electrode catalyst may be used. As such commercially available products, for example, electrode catalysts such as those manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., N.E. Chemcat, E-TEK, and Johnson Matthey can be used. These electrode catalysts are obtained by supporting platinum or a platinum alloy on a carbon carrier (supporting concentration of catalyst species: 20 to 70% by mass). In the above, as the carbon carrier, ketjen black, vulcan, acetylene black, black pearl, graphitized carbon carrier (for example, graphitized ketjen black) previously heat treated at high temperature, carbon nanotube, carbon nanohorn, carbon fiber, There is mesoporous carbon.

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, the above-described ion exchange resin constituting the polymer electrolyte membrane can be added to the catalyst layer as the polymer electrolyte. When the catalyst layer is a water retention layer, the polymer electrolyte is used as a binder material.

[Gas diffusion layer]
The gas diffusion layer has a function of promoting the diffusion of the gas (fuel gas or oxidant gas) supplied through the separator channel to the catalyst layer and a function as an electron conduction path.

  The material which comprises the base material of a gas diffusion layer is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate 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 of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. 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.

  In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer: MLP) composed of an aggregate of carbon particles containing a water repellent on the catalyst layer side of the base material. May be.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include the same water repellent as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles to the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in terms of mass ratio in consideration of the balance between water repellency and electron conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

[gasket]
The gasket is disposed so as to surround the catalyst layer or the gas diffusion layer (that is, the gas diffusion electrode), and has a function of preventing leakage of supplied gas (fuel gas or oxidant gas) from the gas diffusion electrode.

  The material which comprises a gasket should just be impermeable with respect to gas, especially oxygen and hydrogen, and is not restrict | limited in particular. Examples of the material constituting the gasket include rubber materials such as fluorine rubber, silicon rubber, ethylene propylene rubber (EPDM), and polyisobutylene rubber, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE). And polymer materials such as polyvinylidene fluoride (PVdF). However, it goes without saying that other materials may be used.

  There is no restriction | limiting in particular also about the size of a gasket, What is necessary is just to determine suitably considering the relationship with the desired gas-sealing property, the size of another member, etc.

[Separator]
The MEA is sandwiched between separators to form a single PEFC cell. The PEFC generally has a stack structure in which a plurality of single cells are connected in series. At this time, in addition to the function of electrically connecting each MEA in series, the separator includes a flow path and a manifold through which different fluids such as a fuel gas, an oxidant gas, and a refrigerant flow, and further maintains the mechanical strength of the stack. It also has the function.

  The material constituting the separator is not particularly limited, and conventionally known knowledge can be referred to as appropriate, and examples thereof include carbon materials such as dense carbon graphite and carbon plate, and metal materials such as stainless steel. The size of the separator, the shape of the flow path, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of PEFC.

  The method for producing MEA or PEFC of the present invention is not particularly limited, and can be produced by appropriately referring to conventionally known knowledge in the field of fuel cells.

  As described above, the polymer electrolyte fuel cell has been described as an example, but other fuel cells include alkaline fuel cells, direct methanol fuel cells, micro fuel cells, etc. May be. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small 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. In particular, a vehicle in which system start / stop and output fluctuation frequently occur, Preferably, it can be used particularly suitably for automobile applications.

  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
A platinum-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E, Ketjen black support (BET specific surface area 560 m ² / g carbon) with Pt particles supported at a Pt support concentration of 46% by mass was used. A solution containing 20 wt% Nafion (registered trademark) (EW = 1000) serving as an electrolyte was added (DuPont Co., Ltd., solvent composition: 50 parts by mass of water and 50 parts by mass of 1-propanol). .

  The electrolyte in the solution had a solid content mass ratio (carbon / electrolyte) of 1.0 / 0.9 with respect to the mass of the carbon carrier of platinum-supported carbon. A 50 wt% aqueous propylene glycol solution was added thereto, and the solid content ratio of the ink (platinum-supported carbon + electrolyte) was 19% by mass with respect to the total weight of the ink.

  The obtained ink was dispersed with an ultrasonic homogenizer and vacuum degassing was performed to prepare a catalyst slurry (water retaining layer ink). The solvent composition in the catalyst slurry is water: propylene glycol: 1-propanol = 4: 1: 3, and the boiling point (average value) of the solvent is about 110 ° C. Here, the boiling point (average value) of the solvent is a value obtained by approximating the boiling point of the solvent by interpolating (averaging) the boiling point of each solvent together with the composition.

The catalyst slurry was placed on one side of a polytetrafluoroethylene sheet (7.5 cm × 7.5 cm, thickness 0.08 mm) by screen printing, with a platinum loading of 0.35 mg_Pt / cm ² and a carbon loading of 0.41 mg_c / It was printed to a thickness of cm ² equivalent. The obtained coated sheet was dried at 130 ° C. for 30 minutes.

Since the BET specific surface area of the water retention layer of Example 1 was 280 m ² / g_carbon, the ratio of the BET specific surface area to the water retention material was 50%.

(Example 2)
A ketjen black carrier used for the platinum-supported carbon used in Example 1 and not carrying platinum (Ketjen black simple substance (BET specific surface area 718 m ² / g_c)) was applied. By the same production method as in Example 1, a coated sheet having a carbon carrying amount equivalent to 0.35 mg_c / cm ² was produced. The solid content of the water retention layer ink is 19% by mass. The solvent composition in the water retention layer ink is water: propylene glycol: 1-propanol = 4: 1: 3, and the boiling point (average value) of the solvent is about 110 ° C.

Since the BET specific surface area of the water retention layer of Example 2 was 230 m ² / g_carbon, the ratio of the BET specific surface area to the water retention material was 32%.

(Comparative Example 1)
Platinum-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E, Ketjen Black support) on which Pt particles were supported at a Pt support concentration of 46% by mass was used. A solution containing 20 wt% Nafion (registered trademark) serving as an electrolyte (manufactured by DuPont) was added to the mass of the platinum-supporting carbon. As the electrolyte in the solution, a platinum-supported carbon solid mass ratio (carbon / electrolyte) with respect to the mass of the carbon support of 1.0 / 0.9 was used. Pure water was added thereto, and the solid content of the ink (platinum-supported carbon + electrolyte) was 19% by mass with respect to the total weight of the ink.

The obtained ink was dispersed with an ultrasonic homogenizer, and vacuum degassing was performed to prepare a catalyst slurry. The solvent composition in the slurry is water: 1-propanol = 5: 3, and the boiling point (average value) of the solvent is about 99 ° C. The produced catalyst slurry was screen-printed on one side of a polytetrafluoroethylene sheet (7.5 cm × 7.5 cm, thickness 0.08 mm), with a platinum loading of 0.35 mg_Pt / cm ² and a carbon loading of 0.1. It printed so that it might become thickness equivalent to 41 mg_c / cm < ² >. The obtained coated sheet was dried at 80 ° C. for 30 minutes.

Since the BET specific surface area of the water retention layer of Comparative Example 1 was 232 m ² / g_carbon, the ratio of the BET specific surface area to the water retention material was 41%.

[Evaluation]
Method for measuring water vapor adsorption isotherm Pretreatment / Sampling The coated sheet-like water-retaining layer was scraped off, an appropriate amount (about 0.03 to 0.05 g) was put in a glass cell, dried under reduced pressure at 90 ° C. for about 5 hours, and subjected to measurement.

2. Method: Water Vapor Adsorption / Desorption Measurement Method In this method, the amount of water vapor adsorption at a predetermined temperature and pressure can be determined by measuring a water vapor adsorption / desorption isotherm at a predetermined temperature. The amount of water vapor adsorption is calculated based on the gas state equation PV = nRT. That is, among the parameters, the volume V, the gas constant R, and the temperature T are always constant during the measurement. Therefore, by following the change in the pressure P, the number of moles of water molecules adsorbed on the sample n ). Since it takes tens of minutes to several hours to reach the equilibrium pressure, it takes about 1 to 3 days to measure one sample (several tens of measurement points).

  3. Measurement condition

  The results of the water vapor adsorption isotherm measured as described above are shown in FIGS. 5 and 6 (FIG. 5: adsorption side (water vapor relative pressure 0 → 1 direction), and FIG. 6: desorption side (water vapor relative pressure 1 → 0 direction). )). The amount of water vapor adsorption at relative pressure 1 on the water vapor desorption isotherm was Example 1: 432 mg / g_c, Example 2: 517 mg / g_c, and Comparative Example 1: 393 mg / g_c. The water retention layer of Example 1 carries an appropriate amount of catalyst and can function as a catalyst layer.

  As in this example, even in the water retaining layer containing the same weight ratio of carbon / electrolyte, when prepared by a method containing a high boiling point solvent (Examples 1 and 2), when not containing a high boiling point solvent (Comparative Example) On the other hand, it was shown that more water can be adsorbed particularly near the relative pressure of 1.

The cross-sectional schematic diagram of suitable MEA of this invention is shown. The cross-sectional schematic diagram of the other suitable MEA of this invention is shown. The cross-sectional schematic diagram of the other suitable MEA of this invention is shown. The schematic cross section of PEFC containing MEA of 1st embodiment of this invention is shown. It is a figure which shows the result of the water vapor adsorption isotherm of the adsorption side of an Example and a comparative example. It is a figure which shows the result of the water vapor | steam adsorption isotherm of the desorption side of an Example and a comparative example.

Explanation of symbols

10, 20, 30 MEA,
12, 22, 32 solid polymer electrolyte membrane,
13, 23 Anode-side electrode catalyst layer,
33 Anode-side electrode catalyst layer (water retention layer for fuel cells),
14, 24, 34 Anode-side gas diffusion layer,
15, 25, 35 cathode side electrode catalyst layer,
16, 26, 36 Cathode side gas diffusion layer,
17, 27 Water retention layer for fuel cell,
100 solid polymer electrolyte fuel cell,
101 cathode side separator,
102 anode separator,
103, 104 Gas supply groove.

Claims (8)

A step of obtaining a water-retaining layer ink by mixing a solvent containing an organic solvent having a boiling point exceeding 100 ° C., a powdery water-retaining material, and a water-permeable binder material, the solid content of the water-retaining layer ink rate is Ri der than 20 wt%,
The manufacturing method of the water retention layer for fuel cells including the process of apply | coating the said water retention layer ink on a base material, and drying at the temperature of 100 degreeC or more . Exceeding 100 ° C. boiling point of the solvent, method for manufacturing a fuel cell water retaining layer according to claim 1. An electrolyte membrane-electrode assembly comprising a water retention layer obtained by the production method according to claim 1 . A powdery water-retaining material and a water-permeable binder material, and the mass ratio of the water-retaining material and the binder material is water-retaining material: binder material = 1: 0.4 to 1.8, A water retention layer for a fuel cell that partially covers the water retention material in a state where the binder material is unevenly distributed ;
An electrolyte membrane-electrode assembly, wherein the water retention layer is provided adjacent to the electrode catalyst layer . The electrolyte membrane-electrode assembly according to claim 4 , wherein the binder material is a polymer electrolyte. The water vapor adsorption amount at a relative pressure of 1 water retention layer is 400 mg / g or more based on per unit weight of the water retaining material, an electrolyte membrane according to claim 4 or 5 - electrode assembly. The electrolyte membrane-electrode assembly according to any one of claims 4 to 6 , wherein the water retention material includes carbon powder having a nitrogen BET specific surface area of 500 m ² / g or more. A fuel cell using the electrolyte membrane-electrode assembly according to any one of claims 3 to 7 .

Images