JP2011142009A - Catalyst layer for fuel cell, manufacturing method of catalyst layer for fuel cell, and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst layer for a fuel cell, and its manufacturing method, capable of attaining both reduction of a use volume of catalyst fine particles in the catalyst and enhancement of a power output, and that, to provide a membrane electrode assembly equipped with the catalyst layer for a fuel cell. <P>SOLUTION: A cathode catalyst layer 10 of an MEA 1 includes the innumerable number of catalyst made by carrying Pt fine particles on a carbon carrier and polymer electrolyte, and is jointed to one face of an electrolyte layer 11. At least a part of the carbon carrier is one with a low specific surface area with a pore diameter of 4 nm or more. Further, the cathode catalyst layer 10 includes a water-retaining material capable of retaining water, and the water-retaining material has the polymer electrolyte put under insolubilization treatment. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell catalyst layer, a method for producing a fuel cell catalyst layer, and a membrane electrode assembly.

  An electrode such as a cathode electrode or an anode electrode of a fuel cell includes a gas-permeable base material such as carbon cloth, carbon paper, or carbon felt, and a catalyst layer formed on one surface of the base material. The portion other than the catalyst layer is constituted by a base material, which is a diffusion layer that diffuses air and fuel into the catalyst layer on the non-electrolyte layer side. In addition, in each electrode, in order to control the diffusion of air and fuel and the drainage of generated water, an intermediate layer having pores is generally provided between the catalyst layer and the diffusion layer. Yes. The catalyst layer contains a catalyst and a polymer electrolyte. The catalyst is formed by supporting fine catalyst particles such as platinum (Pt) on a carbon support.

  In order to improve the performance of the fuel cell, it is considered necessary to improve the density at the active point of the reaction, and the specific surface area of the carbon support is increased, and more catalyst fine particles are supported on the carbon support at a high dispersion rate. I have been aiming for that.

For example, when a carbon support having a specific surface area of 800 m ² / g or more is used and 50 wt% or more of Pt fine particles are supported thereon, the specific surface area of the Pt fine particles can be 100 m ² / g-Pt or more. Examples of such carbon carriers include Ketjen Black EC (trade name (hereinafter, the same) manufactured by Ketjen Black International), Ketjen Black EC-600JD (hereinafter abbreviated as KB600JD), and the like. it can.

  By increasing the amount of catalyst fine particles supported in this way, the catalyst layer can be made thin, and a membrane electrode assembly (MEA) with high activity and low concentration overvoltage can be provided. Note that there is Non-Patent Document 1 as a document disclosing the technology related to the present case. This Non-Patent Document 1 discloses a carbon support having pores with diameters of 40 nm and 100 nm.

J. Electrochem. Soc., Vol. 142, No. 12, December 1995, P4146, right column.

  However, since the catalyst fine particles such as platinum are expensive, if they are dispersed at a high concentration and high, the production cost of the fuel cell catalyst layer and thus the MEA will be increased. For this reason, the inventors have intensively studied to reduce the amount of catalyst fine particles used. As a result, the following knowledge was found.

  FIG. 1 shows a 3D-TEM observation result of a catalyst in which Pt fine particles 92 are supported at a support density of 60 wt% on KB600JD as a carbon support 91. (A) shows a 2D-TEM image, and (B) shows a three-direction slice image. From the right figure, it is confirmed that Pt fine particles 92 are present inside the catalyst. Moreover, a catalyst layer is manufactured with this catalyst, and a part of MEA having this catalyst layer is schematically shown in an enlarged manner in FIG. In FIG. 2, the Pt fine particles 92a are indicated by black circles. As shown in FIGS. 1 and 2, in the catalyst 90 to be observed, about 60% of the Pt fine particles 92 are present in the carbon support 91, and as a result, about 50% of the surface of the Pt fine particles 92 serving as an active site. The area is within the carbon support 91.

  If the Pt fine particles 92 present in the carbon carrier 91 do not contribute to power generation, a considerable proportion of the supported Pt fine particles 92 exists in vain. If the amount of Pt fine particles 92 supported is sufficiently large, sufficient performance can be obtained with only the Pt fine particles 92 present on the outer surface of the carbon support 91. However, in order to reduce the amount of Pt fine particles 92 used, In order to reduce the loading amount and maintain the performance, it is necessary to reduce the ratio of the Pt fine particles 92 present in the carbon support 91 as much as possible and increase the utilization rate of the Pt fine particles 92.

FIG. 3 shows the measurement results of N ₂ adsorption in the catalyst layer. The catalyst layer is produced by changing the weight ratio (N / C ratio) between the polymer electrolyte functioning as an ionomer and the carbon support.

  According to FIG. 3, the pore volume of the carbon support that decreases when the N / C ratio is increased is mainly due to pores having a pore diameter of 4 nm or more. The pore volume due to pores having a pore diameter of less than about 4 nm in the carbon support hardly changes even when the N / C ratio is increased. This shows that the pores in the carbon support are hardly blocked by the polymer electrolyte.

  FIG. 4 is a graph showing the relationship between the N / C ratio and the pore volume of the carbon support based on the results of FIG. FIG. 4 shows that the pore volume that decreases when the N / C ratio is increased is mainly that having a pore diameter of 4 nm or more, and the pore volume due to pores having a pore diameter of less than 4 nm hardly changes.

  From the above results, it can be seen that the polymer electrolyte does not enter the pores of less than 4 nm of the carbon support, and the catalyst fine particles existing in the pores of less than 4 nm cannot contact the electrolyte. It can also be seen that a three-phase interface is not formed around such catalyst fine particles and cannot contribute to power generation.

  As a measure for bringing the electrolyte into contact with the catalyst fine particles, it is conceivable that the polymer electrolyte is made fine or low molecular so that the polymer electrolyte can enter into pores having a pore diameter of less than 4 nm. In order to ensure proton conductivity, continuity of the polymer electrolyte is required, and it is difficult to control the structure of the polymer electrolyte in the pores. In addition, there is a question as to whether or not mass transfer such as sufficiently supplying oxygen to the catalyst fine particles and discharging the generated water in a very small pore of less than 4 nm is performed.

  Based on the above findings, the inventors have filed a patent application that a catalyst obtained by supporting catalyst fine particles on a carbon support having only pores having a pore diameter of 4 nm or more is suitable as a catalyst for a fuel cell. (Japanese Patent Application No. 2009-013219). According to this catalyst, catalyst fine particles can be prevented from entering pores into which the polymer electrolyte cannot enter. For this reason, the utilization rate of catalyst fine particles can be increased by using this carbon carrier, and as a result, the amount of platinum used can be reduced.

  And the inventors examined the catalyst layer using the carbon support | carrier which does not have the pore whose pore diameter is less than 4 nm aiming at the further improvement of an output. It has been found that in order to achieve further higher output (higher current density) for a fuel cell having such a catalyst layer, it is necessary to eliminate flooding in the catalyst layer.

  That is, the polymer electrolyte mixed with the catalyst has a function as a water retaining material that temporarily holds water in the catalyst layer. The water retention function of the polymer electrolyte is also considered to have an effect of buffering the increase and decrease of the amount of water in the catalyst layer during an electrochemical reaction in an overhumidified environment and a low humidified environment.

  However, when a low specific surface area carbon support is used for the purpose of reducing the amount of catalyst fine particles used, in order to sufficiently supply oxygen to the Pt fine particles 92, generally used pores such as KB600JD are used. Compared to the case of the carbon support 91 having a large specific surface area, it is necessary to reduce the polymer electrolysis mass in the catalyst layer, and the water retention function by the polymer electrolyte is reduced. As a result, flooding is likely to occur in the catalyst layer in a high current region, and smooth progress of the electrochemical reaction is hindered.

  Similarly, if the polymer electrolyte in the catalyst layer is reduced, the catalyst layer is likely to dry during an electrochemical reaction in a low humidified environment. For this reason, in this catalyst layer, it is thought that smooth progress of the electrochemical reaction under a low humidified environment is also hindered.

  Based on the above findings, the inventors can achieve both reduction in the amount of catalyst fine particles used in fuel cells and high output by providing a catalyst layer having a low specific surface area carbon support with the function of retaining water. I thought it was possible. A patent application was filed for a fuel cell catalyst layer containing a water retention material capable of retaining water (Japanese Patent Application No. 2009-253436).

  According to this catalyst layer, the problems of flooding in the high current region and drying of the catalyst layer in a low humidified environment can be solved, and high output of the fuel cell can be achieved.

  However, even with the fuel cell catalyst layer filed by the inventors, the smooth progress of the electrochemical reaction in the low current region is still not sufficient, and further improvement in output is required.

  The present invention has been made in view of the above circumstances, and provides a fuel cell catalyst layer capable of achieving both reduction in the amount of catalyst fine particles in the catalyst and high output, and a method for producing the same. This is a problem to be solved. Another object to be solved is to provide a membrane electrode assembly including the fuel cell catalyst layer.

  In the above catalyst layer, the inventors have inferred the problem that the smooth progress of the electrochemical reaction in the low current region becomes insufficient as follows. That is, this catalyst layer is composed of a mixed paste 52 in which a catalyst paste 50 and a water retaining material paste 51 are mixed as shown in FIG. The catalyst paste 50 includes a catalyst 90, water, and an ionomer solution (polymer electrolyte solution). The water retaining material paste 51 includes hydrophilic carbon (carbon black) 95 and a polymer electrolyte solution. In the mixed paste 52, the water retaining material paste 51 has a relationship including more polymer electrolyte solution than the catalyst paste 50. For this reason, in the mixed paste 52, the polymer electrolyte 93 of the water retention material paste 51 is solubilized, so that a part of the polymer electrolyte 93 moves to the catalyst 90 side. For this reason, the layer of the polymer electrolyte 93 formed around the catalyst 90 becomes thick. Thus, when the layer of the thick polymer electrolyte 93 is formed around the catalyst 90, in this catalyst layer, the supply of oxygen gas tends to be hindered during the electrochemical reaction. For this reason, it becomes difficult for the electrochemical reaction to proceed smoothly from the low current region, and as a result, further improvement in the output of the fuel cell cannot be expected.

Thus, the inventors have conducted intensive research and have invented the following fuel cell catalyst layer. That is, the fuel cell catalyst layer of the present invention can hold a myriad of catalysts in which catalyst fine particles are supported on a low specific surface area carbon support having a pore diameter of 4 nm or more, a polymer electrolyte, and water. A fuel cell catalyst layer that is bonded to one surface of the electrolyte layer,
The water retention material comprises a substance serving as a nucleus and the polymer electrolyte fixed to the substance (Claim 1).

  As shown in FIG. 7, a low specific surface area carbon support 91 is employed in at least a part of the catalyst constituting the catalyst layer of the present invention. The low specific surface area carbon support 91 is a carbon support having a pore diameter of 4 nm or more. For this reason, in the catalyst layer using the catalyst 90, the catalyst fine particles 92 can be prevented from entering the pores into which the polymer electrolyte 93 cannot enter. For this reason, in this catalyst layer, the utilization rate of the catalyst fine particles 92 can be increased during the electrochemical reaction, and the amount of the catalyst fine particles 92 made of platinum or the like can be reduced. Examples of the low specific surface area carbon carrier 91 include BLACKPEARL 880 (trade name, manufactured by CABOT, hereinafter abbreviated as BP880). It is also possible to employ a carbon support having a pore diameter of less than 4 nm for the catalyst 90.

  Furthermore, this catalyst layer contains a water retention material capable of retaining water. For this reason, in this catalyst layer, flooding is unlikely to occur in a high current region, and smooth progress of the electrochemical reaction is not easily prevented. Further, by containing a water retaining material, the catalyst layer is difficult to dry during an electrochemical reaction in a low humidified environment, and the smooth progress of the electrochemical reaction is hardly hindered even in a low humidified environment.

  In this water retention material, since the polymer electrolyte 93 is fixed to the core substance, that is, the polymer electrolyte is insolubilized, as shown in FIG. 6, the polymer electrolyte 93 included in the water retention material Becomes difficult to move to the catalyst 90 side. For this reason, in this catalyst layer, the thinly formed polymer electrolyte 93 layer is unlikely to be thick. For this reason, in this catalyst layer, oxygen is sufficiently supplied at the time of the electrochemical reaction, and the utilization rate of the catalyst fine particles 92 is high as described above. Therefore, the electrochemical reaction proceeds smoothly from the low current region, and the fuel cell. Increases performance.

  Therefore, according to the catalyst layer for a fuel cell of the present invention, it is possible to achieve both reduction in the amount of catalyst fine particles in the catalyst and high output.

  In addition to the water retention capacity, the water retention material is required to be a substance that does not elute or denature in the environment where the fuel cell operates. The water retention material is also preferably a substance that does not adversely affect the operation of the fuel cell and can be easily processed such as pulverization when the catalyst layer is manufactured. Furthermore, from the viewpoint of improving the efficiency of the electrochemical reaction in the catalyst layer, the water retention material preferably has electron conductivity and proton conductivity as well as water retention.

  Based on these, as a substance serving as the core of the water retention material, carbon materials such as carbon black, conductive resins, conductive ceramics, metal oxides imparted with conductivity, and the like can be employed. Moreover, as a polymer electrolyte fixed with respect to the substance used as this nucleus, Nafion (registered trademark, Nafion (made by Du Pont)) can be mentioned.

The method for producing a catalyst layer for a fuel cell according to the present invention comprises a myriad of catalysts in which catalyst fine particles are supported on a low specific surface area carbon support having a pore diameter of 4 nm or more, a polymer electrolyte, and water. A method for producing a catalyst layer for a fuel cell, which contains a possible water retention material and is bonded to one surface of an electrolyte layer,
A catalyst paste preparation step of mixing the catalyst and the polymer electrolyte together with a solvent to obtain a catalyst paste;
A water retention material pre-paste preparation step of mixing a substance serving as a nucleus and the polymer electrolyte together with a solvent to obtain a water retention material pre-paste;
An immobilization step of immobilizing the water retentive material pre-paste to obtain a solid water retentive material in which the polymer electrolyte is fixed to the substance;
A pulverizing step of pulverizing the solid water retaining material into the water retaining material;
And a mixed paste preparation step of mixing the catalyst paste and the water retention material to obtain a mixed paste (Claim 2).

  By the immobilization step in the production method of the present invention, the polymer electrolyte 93 included in the water retention material is immobilized on a substance serving as a nucleus, that is, the polymer electrolyte 93 is insolubilized. For this reason, a catalyst layer having the features of the catalyst layer of claim 1 can be obtained by manufacturing the catalyst layer by this manufacturing method. Furthermore, in this manufacturing method, the water retention material is obtained by pulverizing the solid water retention material in the pulverization step. For this reason, in the mixed paste prepared in the mixed paste preparation step, the water retention material is evenly dispersed. For this reason, in this catalyst layer, the effect by said water retention material can be heightened, and it becomes easy to produce the electrochemical reaction in a catalyst layer uniformly. In the mixed paste preparation step, a water retention material can be dispersed in a solvent to obtain a water retention material paste, and the water retention material paste and the catalyst paste can be mixed to prepare a mixed paste.

  Therefore, according to the method for producing a fuel cell catalyst layer of the present invention, it is possible to obtain a fuel cell catalyst layer capable of achieving both reduction in the amount of catalyst fine particles in the catalyst and higher output.

  The immobilization step preferably includes a drying step of drying the water retentive material pre-paste to obtain a dry water retentive material, and a heating step of heating the dry water retentive material at a temperature equal to or higher than the glass transition temperature of the polymer electrolyte. 3). In this case, the polymer electrolyte 93 is insolubilized by the drying process and the heating process. At this time, it is considered that the degree of insolubilization of the polymer electrolyte 93 is increased by heating the polymer electrolyte at the glass transition temperature or higher in the heating step. For this reason, it is thought that the polymer electrolyte 93 is more suitably fixed to a substance serving as a nucleus, and the insolubilization treatment of the polymer electrolyte 93 is in a sufficient state. For this reason, it becomes possible to obtain a more suitable fuel cell catalyst layer.

  In the pulverization step, it is preferable to pulverize the solid water retaining material so that the water retaining material has substantially the same diameter as the aggregates of the catalyst (claim 4). In this case, since the water retaining material and the catalyst in the aggregate form have substantially the same diameter, the water retaining material can be more uniformly mixed in the mixed paste 52. For this reason, it becomes easy to produce the electrochemical reaction in a catalyst layer more homogeneously.

The membrane electrode assembly of the present invention is a membrane electrode assembly comprising an electrolyte layer, a cathode catalyst layer bonded to one surface of the electrolyte layer, and an anode catalyst layer bonded to the other surface of the electrolyte layer. ,
At least the cathode catalyst layer contains a myriad of catalysts, a polymer electrolyte, and a water retention material capable of holding water,
At least a part of each catalyst is formed by supporting catalyst fine particles on a low specific surface area carbon support having a pore diameter of 4 nm or more,
The water retention material comprises a substance serving as a nucleus and the polymer electrolyte fixed to the substance (claim 5).

  In the membrane electrode assembly of the present invention, at least the cathode catalyst layer has the characteristics of the fuel cell catalyst layer according to claim 1. For this reason, in this membrane electrode assembly, flooding is unlikely to occur in a high current region, and the catalyst layer is difficult to dry during an electrochemical reaction in a low humidified environment.

  In this membrane electrode assembly, the catalyst layer provided on the cathode catalyst layer side preferably has a N / C ratio of 0.5 or less in the catalyst paste in order to ensure a high voltage from the low current region. Thereby, as shown in FIG. 7 described above, it is considered that the layer made of the polymer electrolyte 93 formed around the catalyst 90 becomes thin. Further, since the polymer electrolyte 93 included in the water retention material is insolubilized, as shown in FIG. 6 above, a part of the polymer electrolyte 93 hardly moves to the catalyst 90 side and is formed around the catalyst 90. The layer made of the polymer electrolyte 93 is less likely to be thick. For this reason, oxygen is sufficiently supplied during the electrochemical reaction, and the utilization rate of the catalyst fine particles is high. Therefore, the electrochemical reaction proceeds more smoothly from the low current region, and the performance of the fuel cell is improved.

  Therefore, the membrane electrode assembly of the present invention can achieve both reduction in the amount of catalyst fine particles in the catalyst and high output.

  In this membrane electrode assembly, a binder layer made of a polymer electrolyte may be provided between the electrolyte layer and the cathode catalyst layer. As described above, in the catalyst layer using the low specific surface area carbon support, since the amount of the polymer electrolyte 93 in the catalyst layer is reduced, it is considered that the effect of the polymer electrolyte 93 as a binder is also reduced. . For this reason, when the cathode catalyst layer is formed of the catalyst layer as in the membrane electrode assembly of the present invention, there is a possibility that the electrolyte layer and the cathode catalyst layer are easily peeled off. At this time, it is considered that this problem can be solved by providing a binder layer between the electrolyte layer and the cathode catalyst layer.

It is a 3D-TEM image showing the distribution of Pt fine particles on a carbon support having pores of about 3.5 nm. The figure (A) shows a 2D-TEM image, and the figure (B) shows a three-direction slice image. It is an expansion schematic diagram which shows the electrochemical reaction in the catalyst layer which has a carbon support | carrier which has a pore of about 3.5 nm. It is a graph which shows distribution of the pore of a catalyst layer when a catalyst layer which has a catalyst which has a carbon support which has a pore of about 3.5 nm changes N / C ratio. It is a graph which shows the relationship between N / C ratio and the pore volume of a catalyst layer. It is a model diagram which shows the state of the mixed paste which has the polymer electrolyte which is not insolubilized. It is a model diagram which shows the state of the mixed paste which has the insolubilized polymer electrolyte. It is an expansion schematic diagram which shows the electrochemical reaction in the catalyst layer which has a carbon support | carrier which has a pore of about 4 nm or more. 2 is a partially enlarged schematic view showing a part of an MEA of Example 1. FIG. It is a graph which shows the specific surface area of BP880 and KB600JD. It is a graph which concerns on Example 1 and shows the change prediction of the cell current and cell voltage in a full humidification state. It is a graph which concerns on Example 1 and shows the change prediction of the cell current and cell voltage in a low humidification state. It is a partial expansion schematic diagram which shows a part of MEA of a modification.

  Embodiments 1 to 3 and modifications embodying the present invention will be described below with reference to the drawings.

Example 1
As shown in FIG. 8, the MEA 1 of Example 1 is joined to the electrolyte membrane 11 made of Nafion, the cathode electrode 3 joined to one surface of the electrolyte membrane 11 and supplied with air, and the other surface of the electrolyte membrane 11. And an anode 5 to which a fuel such as hydrogen is supplied.

  The cathode electrode 3 includes a base material made of carbon paper and a cathode catalyst layer 10 formed on one surface of the base material. A portion other than the cathode catalyst layer 10 in the cathode electrode 3 is formed of a base material, which is a cathode diffusion layer 13 that diffuses air into the cathode catalyst layer 10 on the non-electrolyte layer side. An anode diffusion layer 14 is provided on the anode 5 side. The cathode catalyst layer 10 of the MEA 1 is formed of a catalyst paste and a water retention material paste as a water retention material.

  The catalyst paste is manufactured by the following manufacturing method. First, a commercially available BP880 was prepared as the low specific surface area carbon support 91 shown in FIG. This BP800 has a primary particle size of about 15 nm.

FIG. 9 shows the N ₂ adsorption measurement results of this BP800 and KB600JD conventionally used as a carbon support. In FIG. 9, the specific surface area of mesopores having a pore diameter of 1.7 nm to 300 nm and the specific surface area of pore diameters of 4 nm to 300 nm determined by the BJH method are respectively shown by bar graphs.

  As shown in FIG. 9, in BP880, the specific surface area of mesopores having a pore diameter of 1.7 nm to 300 nm and the specific surface area of pore diameters of 4 nm to 300 nm are substantially equal. That is, it can be seen that there are almost no pores of less than 4 nm. On the other hand, in KB600JD, it can be seen that pores of less than 4 nm account for more than half of the total specific surface area.

  Pt fine particles 92 (see FIG. 7) as catalyst fine particles were supported on this BP880 at a support density of 20 wt% to obtain catalyst 90. Water was added to this catalyst 90, defoamed and stirred with a rotation / revolution centrifugal stirrer (trade name “Hybrid Mixer HM-500” manufactured by Keyence Corporation), and the catalyst 90 and water were blended together. A paste was obtained.

  An ionomer solution (Nafion solution (5% by mass solution)) was added to the pre-paste. At this time, the ionomer solution was added to the catalyst 90 so that the weight ratio (N / C ratio) of the Nafion (polymer electrolyte 93) in the ionomer solution to the carbon support 91 was 0.15. Thereafter, these were further stirred by a rotation / revolution centrifugal stirrer to obtain catalyst paste 50 (see FIG. 6).

  On the other hand, the water-retaining material paste is manufactured by the following manufacturing method. First, Vulcan-XC72R (trade name, manufactured by CABOT) was adopted as a carbon black 95 as a core material. Then, isopropyl alcohol (IPA) as a solvent was added to the carbon black 95 and stirred for 4 minutes by a rotation / revolution centrifugal stirrer to obtain a carbon paste in which the carbon black 95 and IPA were blended. In addition to IPA, water, ethanol, or a mixture thereof can be used as the solvent.

  A Nafion solution was added to the carbon paste. At this time, the Nafion solution was added so that the weight ratio (N / C ratio) between the weight of Nafion in the Nafion solution and the carbon black 95 was 1.0. Then, these were stirred for 4 minutes with a rotation / revolution centrifugal stirrer to obtain a water retention material pre-paste.

  Next, this water retention material pre-paste was poured into a petri dish and left to stand in the air until the solvent in the water retention material pre-paste volatilized and dried naturally. As a result, a dry water retaining material, which is a water retaining material pre-paste in the form of a film, was obtained. And this dry water retention material was heated at the temperature more than a glass transition temperature for 1 hour or more. In this way, the polymer electrolyte 93 in the dried water retention material was fixed to the carbon black 95 to obtain a solid water retention material in which the polymer electrolyte 93 was insolubilized. In Example 1, about 160 ° C. is set as the temperature higher than the glass transition temperature.

  The solid water-retaining material was put into a ball mill pulverization container, and the lid of the ball mill pulverization container was sealed in a nitrogen atmosphere while adding an appropriate amount of zirconia balls having a diameter of 5 mm for pulverization. Then, this ball mill pulverizing vessel was placed in a planetary rotating ball mill pulverizing apparatus (trade name “Planet Rotating Pot Mill” manufactured by Ito Seisakusho) and rotated and revolved at a rotational speed of 240 rpm for 2 hours for dry pulverization. Thereby, this solid water retaining material is in the form of fine particles.

  This particulate solid water retaining material and IPA were mixed and further stirred by a rotation / revolution centrifugal stirrer to obtain a water retaining material paste 51. At this time, an appropriate amount of a surfactant can be mixed.

  The catalyst paste 50 and the water retention material paste 51 obtained as described above were mixed at a solid content weight ratio of 0.65: 0.35 to obtain a mixed paste 52. By mixing these at this ratio, the N / C ratio of the entire mixed paste 52 becomes 0.35.

  The mixed paste 52 was screen-printed on a substrate and then dried to obtain the cathode electrode 3 shown in FIG. The printed portion is the cathode catalyst layer 10. In addition, as a method of applying the mixed paste 52 to the substrate, it can be performed by means of a spray method, an ink jet method or the like in addition to screen printing. The anode catalyst layer 12 of the anode electrode 5 is obtained by screen printing the catalyst paste 50 on a substrate.

  By joining the cathode electrode 3 and the anode electrode 5 thus obtained to the electrolyte layer 11, the MEA 1 is obtained.

  In this MEA 1, the cathode catalyst layer 10 constituting the cathode electrode 3 is formed by a mixed paste 52 in which a catalyst paste 50 and a water retention material paste 51 are mixed. As shown in FIG. 7, in the catalyst paste 50, since the low specific surface area carbon support 91 is employed for the catalyst 90, Nafion, which is the polymer electrolyte 93 in the ionomer solution, cannot enter the cathode catalyst layer 10. It is possible to prevent the Pt fine particles 92 from entering the pores. For this reason, in the cathode electrode 3 having the cathode catalyst layer 10, the utilization rate of the Pt fine particles 92 can be increased during the electrochemical reaction, and the amount of the Pt fine particles 92 can be reduced.

  Further, in the cathode electrode 3 obtained by the catalyst paste 50, the N / C ratio of the catalyst paste 50 is as small as 0.15, that is, the amount of the polymer electrolyte 93 is small, so that the conventional cathode electrode shown in FIG. In comparison with this, in the cathode electrode 3 (cathode catalyst layer 10), the layer made of the polymer electrolyte 93 formed around the catalyst 90 becomes thin (see FIG. 7).

  Furthermore, since the cathode catalyst layer 10 contains a water retention material, the cathode electrode 3 is less likely to be flooded in a high current region. Moreover, since the water retaining material paste is a mixture of carbon black 95 and polymer electrolyte 93 based on the above N / C ratio, a network for proton and electron paths is secured in the water retaining material portion. Has been. As a result, the smooth progress of the electrochemical reaction is hardly hindered. Further, since the cathode catalyst layer 10 contains a water retention material, it is difficult to dry during the electrochemical reaction in a low humidified environment, and the smooth progress of the electrochemical reaction is difficult to be hindered. Furthermore, in this MEA1, the particulate solid water retaining material is in a highly dispersed state in the water retaining material paste 51 constituting the water retaining material. For this reason, the solid water-retaining material is evenly dispersed in the mixed paste 52, so that the water-retaining material is evenly dispersed in the cathode catalyst layer 10. For this reason, while the effect by said water retention material becomes high, it becomes easy to produce the electrochemical reaction in the cathode catalyst layer 10 uniformly.

  Further, in this water retention material paste 51, the polymer electrolyte 93 in the water retention material paste 51 is insolubilized. In particular, in this water-retaining material paste 51, the polymer electrolyte 93 is more suitably fixed to the carbon black 95 by performing natural drying when the water-retaining material paste 51 is manufactured and then heating. That is, it is considered that the insolubilization treatment of the polymer electrolyte 93 is in a sufficient state. For this reason, in the cathode catalyst layer 10, as shown in FIG. 6, a part of the polymer electrolyte 93 in the water retention material paste 51 is difficult to move to the catalyst 90 side, and the polymer electrolyte 93 formed around the catalyst 90. Due to the layer is difficult to thicken.

  For this reason, in MEA1 of an Example, oxygen is fully supplied at the time of an electrochemical reaction, and a voltage can be made high from a low electric current area | region. Moreover, in this MEA1, since the utilization factor of the Pt fine particles 92 is high as described above, the electrochemical reaction proceeds more smoothly from the low current region, and the performance of the fuel cell can be improved.

  Therefore, the MEA 1 of Example 1 can achieve both reduction in the amount of Pt fine particles 92 in the catalyst 90 and high output.

  Next, assuming a cell including the MEA 1 of Example 1, the voltage characteristics of the MEA 1 of Example 1 were considered based on an assumed experiment. In this verification, as a comparative example, a cathode catalyst layer was formed only by the catalyst paste 50 obtained in Example 1, and a cell having an MEA similar to MEA 1 of Example 1 was assumed for the other configurations. In addition, the structure and manufacturing method of each assumed cell are the same as a well-known method.

(Expected experiment example 1)
In the assumed experimental example 1, the cell temperature of each of the cell including the MEA 1 and the cell including the MEA of the comparative example is set to 50 ° C., and the humidity is 100% RH (hereinafter referred to as a fully humidified state). The change in current and voltage of each cell when hydrogen was passed through the anode 5 and air was passed through the cathode 3 was predicted. The prediction result is shown in FIG.

  In FIG. 10, the horizontal axis represents the cell current (A), and the vertical axis represents the cell voltage (V). As shown in FIG. 10, in a fully humidified state, it can be predicted that the cell provided with MEA 1 can exhibit a higher voltage in the high current region than the cell provided with the MEA of the comparative example. In addition, it can be predicted that the cell including the MEA 1 has a small degree of voltage change with respect to current change.

(Expected experiment example 2)
In the assumed experimental example 2, the cell temperature of each of the cell including the MEA 1 and the cell including the MEA of the comparative example is set to 70 ° C., and the humidity is 40% RH (hereinafter referred to as a low humidified state). The change in current and voltage of each cell when hydrogen was passed through the anode 5 and air was passed through the cathode 3 was predicted. The prediction result is shown in FIG.

  In FIG. 11, as in FIG. 9, the horizontal axis indicates the cell current (A), and the vertical axis indicates the cell voltage (V). As shown in FIG. 11, even in a low humidified state, it can be predicted that the cell provided with MEA 1 can exhibit a higher voltage in the high current region than the cell provided with the MEA of the comparative example. . Further, even in this environment, it can be predicted that the cell including the MEA 1 has a smaller degree of voltage change with respect to the current change than the cell including the comparative example MEA.

  From these assumption experiments, it can be predicted that the cell including the MEA 1 exhibits higher voltage characteristics with respect to the current in both the fully humidified state and the low humidified state as compared with the cell including the MEA of the comparative example. That is, the MEA 1 is predicted to have higher power generation stability, that is, robustness against changes in the environment and current than the MEA of the comparative example.

  This reason is considered to be the effect of the water retention material that the cathode catalyst layer 10 has. That is, it is considered that the water retaining material has improved MEA1 resistance to flooding in a high current region and dry-up during low humidification.

(Example 2)
The MEA of Example 2 employs a water retention material paste manufactured in the following steps in place of the water retention material paste 51 used in the MEA 1 of Example 1.

  This water-retaining material paste is manufactured by the following manufacturing method. First, in the same manner as in Example 1, carbon black 95 (Vulcan-XC72R) was adopted as a material serving as a nucleus. Then, water as a solvent was added to the carbon black 95 and stirred for 4 minutes with a rotation / revolution centrifugal stirrer to obtain a carbon paste in which the carbon black 95 and water were blended. The amount of water added at this time is such that the water-retaining material pre-paste freezes at about minus 30 ° C. to minus 40 ° C. in the process described later, and more than 50% of the water is present in the water-retaining material pre-paste. Is the amount possible. The same applies when IPA, ethanol, or a mixture thereof is used in addition to water.

  An amount of Nafion solution having the same N / C ratio as in Example 1 was added to the carbon paste, and then the mixture was stirred for 4 minutes by a rotation / revolution centrifugal stirrer to obtain a water retention material pre-paste.

  Next, this water retention material pre-paste was poured into a petri dish and placed in a thermostatic oven set to minus 30 ° C. to minus 40 ° C. to freeze the water retention material pre-paste. Thereafter, the inside of the thermostatic chamber was depressurized using a vacuum pump, and the water retention material pre-paste was freeze-dried to obtain a dry water retention material. And this dry water retention material was heated on the same conditions as Example 1. FIG. Thus, a solid water retaining material obtained by insolubilizing the polymer electrolyte 93 in the dried water retaining material was obtained.

  Next, this solid water retaining material was pulverized by a blade mill. At this time, if necessary, classification is performed by removing a solid water retaining material having a particle size larger than a predetermined value by a filtration method. And this solid water retention material and IPA were mixed, and also it stirred with the autorotation / revolution type | formula centrifugal stirrer, and obtained the water retention material paste. As in Example 1, an appropriate amount of a surfactant can be mixed at this time. Other steps in the production of the MEA of Example 2 are the same as those of Example 1.

(Example 3)
The MEA of Example 3 employs a water retention material paste manufactured in the following steps in place of the water retention material paste used in MEA 1 of Example 1.

  This water-retaining material paste is manufactured by the following manufacturing method. First, a carbon paste having the same configuration as in Example 1 was prepared, and an amount of Nafion solution having the same N / C ratio as in Example 1 was added to this carbon paste. Then, these were stirred for 4 minutes with a rotation / revolution centrifugal stirrer to obtain a water retention material pre-paste.

  Next, as in Example 1, this water-retaining material pre-paste was poured into a petri dish and left in the air to dry naturally to obtain a dry water-retaining material. And this dry water retention material was heated on the same conditions as Example 1. FIG. In this way, a solid water retaining material obtained by insolubilizing the polymer electrolyte 93 in the dried water retaining material was obtained. Thereafter, this solid water retaining material was placed in a freeze pulverizer and cooled at a liquid nitrogen temperature to perform freeze pulverization. At this time, as in Example 2, classification is performed by removing a solid water retaining material having a particle size larger than a predetermined value by a filtration method as necessary. And this solid water retention material and IPA were mixed, and also it stirred with the autorotation / revolution type | formula centrifugal stirrer, and obtained the water retention material paste. As in Example 1, an appropriate amount of a surfactant can be mixed at this time. Other steps in the production of the MEA of Example 3 are the same as those of Example 1.

  The water retention material paste employed in the manufacture of the MEAs of Examples 2 and 3 is also subjected to insolubilization treatment of the polymer electrolyte 93 in the same manner as the water retention material paste 52 of Example 1. For this reason, it is considered that the MEAs of Examples 2 and 3 can obtain the same effects as the MEA 1 of Example 1.

(Modification)
The MEA 20 of the modification shown in FIG. 12 includes binder layers 15a and 15b between the electrolyte membrane 11 and the cathode electrode 3 and between the electrolyte membrane 11 and the anode electrode 5, respectively, in addition to the configuration of the MEA 1 of Example 1. Is provided.

  The binder layer 15a is provided by screen-printing the mixed paste 52 on a base material to obtain the cathode catalyst layer 10, and then further applying a Nafion solution to the surface side of the cathode catalyst layer 10 and drying it. Yes. The binder layer 15b is provided by screen-printing the catalyst paste 50 on a base material to obtain the anode catalyst layer 12, and then applying a Nafion solution to the surface side of the anode catalyst layer 12 and drying it. It has been. In addition, as a method for applying the Nafion solution to the cathode catalyst layer 10 and the anode catalyst layer 12, in addition to screen printing, a spray method, an ink jet method, or the like can be used. Other configurations and manufacturing methods are the same as those of the MEA of the first embodiment.

  Since the MEA 20 of the modified example is provided with the binder layers 15a and 15b in addition to the effects of the MEA 1 of the first embodiment, it is considered that the following effects can also be obtained. That is, in the cathode catalyst layer 10 and the anode catalyst layer 12 using the low specific surface area carbon support 91, the amount of the polymer electrolyte 93 in the catalyst layer is reduced, so that the effect of the polymer electrolyte 93 as a binder is also reduced. Conceivable. For this reason, there is a possibility that the electrolyte membrane 11, the cathode catalyst layer 10, and the anode catalyst layer 12 are easily peeled off. In that case, it is thought that the electrolyte layer 11, the cathode catalyst layer 10, and the anode catalyst layer 12 can be made difficult to peel off by these binder layers 15a and 15b.

  In the above, the present invention has been described according to the first to third embodiments and the modified examples. However, the present invention is not limited to the first to third embodiments and the modified examples, and may be appropriately selected without departing from the spirit of the present invention. Needless to say, it can be changed and applied.

  For example, the binder layers 15a and 15b can be provided on the MEAs of the second and third embodiments.

Moreover, the modified example includes the following invention in addition to the present invention.
A membrane electrode assembly comprising an electrolyte layer, a cathode catalyst layer bonded to one surface of the electrolyte layer, and an anode catalyst layer bonded to the other surface of the electrolyte layer,
At least the cathode catalyst layer contains a myriad of catalysts, a polymer electrolyte, and a water retention material capable of holding water,
At least a part of each catalyst is formed by supporting catalyst fine particles on a low specific surface area carbon support having a pore diameter of 4 nm or more,
A membrane electrode assembly, wherein a binder layer made of the polymer electrolyte is provided between the electrolyte layer and the cathode catalyst layer.

  INDUSTRIAL APPLICABILITY The present invention can be used for a fuel cell system such as a moving power source for an electric vehicle, an outdoor stationary power source, and a portable power source.

91 ... Carbon carrier (low specific surface area carbon carrier)
92 ... Pt fine particles (catalyst fine particles)
90 ... Catalyst 51 ... Water retention paste (water retention material)
50 ... Catalyst paste 52 ... Mixed paste 11 ... Nafion membrane (electrolyte layer)
DESCRIPTION OF SYMBOLS 10 ... Cathode catalyst layer 12 ... Anode catalyst layer 1 ... MEA (membrane electrode assembly)
15a, 15b ... Binder layer

Claims (6)

One surface of an electrolyte layer containing at least a part of a catalyst having fine particles supported on a low specific surface area carbon support having a pore diameter of 4 nm or more, a polymer electrolyte, and a water retaining material capable of holding water. A fuel cell catalyst layer bonded to
The catalyst layer for a fuel cell, wherein the water retention material comprises a substance serving as a nucleus and the polymer electrolyte fixed to the substance. One surface of an electrolyte layer containing at least a part of a catalyst having fine particles supported on a low specific surface area carbon support having a pore diameter of 4 nm or more, a polymer electrolyte, and a water retaining material capable of holding water. A method for producing a fuel cell catalyst layer bonded to a fuel cell,
A catalyst paste preparation step of mixing the catalyst and the polymer electrolyte together with a solvent to obtain a catalyst paste;
A water retention material pre-paste preparation step of mixing a substance serving as a nucleus and the polymer electrolyte together with a solvent to obtain a water retention material pre-paste;
An immobilization step of immobilizing the water retentive material pre-paste to obtain a solid water retentive material in which the polymer electrolyte is fixed to the substance;
A pulverizing step of pulverizing the solid water retaining material into the water retaining material;
A method for producing a catalyst layer for a fuel cell, comprising a mixed paste preparation step of mixing the catalyst paste and the water retention material to obtain a mixed paste. The immobilization step is a drying step of drying the water retention material pre-paste to obtain a dry water retention material;
The method for producing a catalyst layer for a fuel cell according to claim 2, comprising a heating step of heating the dry water retaining material at a temperature equal to or higher than the vitrification temperature of the polymer electrolyte.   The method for producing a fuel cell catalyst layer according to claim 2 or 3, wherein, in the pulverization step, the solid water retention material is pulverized so that the water retention material has substantially the same diameter as the aggregate of the catalyst. A membrane electrode assembly comprising an electrolyte layer, a cathode catalyst layer bonded to one surface of the electrolyte layer, and an anode catalyst layer bonded to the other surface of the electrolyte layer,
At least the cathode catalyst layer contains a myriad of catalysts, a polymer electrolyte, and a water retention material capable of holding water,
At least a part of each catalyst is formed by supporting catalyst fine particles on a low specific surface area carbon support having a pore diameter of 4 nm or more,
The membrane electrode assembly, wherein the water retention material comprises a core substance and the polymer electrolyte fixed to the substance.   The membrane electrode assembly according to claim 5, wherein a binder layer made of the polymer electrolyte is provided between the electrolyte layer and the cathode catalyst layer.

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