JP5601315B2 - Fuel cell and manufacturing method thereof - Google Patents

Description

  The present invention relates to a fuel cell having a membrane electrode assembly in which an electrode catalyst layer is bonded to a membrane surface of an electrolyte membrane having proton conductivity, and a method for manufacturing the same.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas has attracted attention as an energy source. As this fuel cell, there is a solid polymer fuel cell using a solid polymer membrane as an electrolyte membrane. Such a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which an electrode catalyst layer is bonded to both surfaces of an electrolyte membrane having proton conductivity, and this MEA has gas permeability such as carbon paper. It is sandwiched between conductive gas diffusion members. In providing a fuel cell having such a configuration, various techniques have been proposed (for example, Patent Document 1).

JP 2004-47453 A

  In this patent document, a solution coating method is adopted not only in an electrode catalyst layer but also in an electrolyte membrane, and a solution (catalyst ink) containing an ionomer as a binder and a catalyst carrier is applied to a gas diffusion member such as carbon paper. After applying, a solution for forming an electrolyte membrane is applied before drying. And after application | coating of these solutions, drying and solidification are aimed at, and a gas-diffusion member, an electrode catalyst layer, and an electrolyte membrane are joined and laminated | stacked. By doing so, the adhesion between the constituent members of the fuel cell is improved.

  By the way, since the gas permeability and proton conductivity in the electrode catalyst layer are affected by the coating state of the catalyst carrier with the ionomer, it is necessary to ensure the coating of the catalyst carrier with the ionomer. In the above-mentioned patent document, since the catalyst ink for forming the electrode catalyst layer is applied to the gas diffusion member, the ionomer contained therein enters the pores of the gas diffusion member. For this reason, in the electrode catalyst layer after ink drying, the amount of ionomer is reduced by the amount that has entered the pores of the gas diffusion member. The more the ionomer that has entered the pores of the gas diffusion member, the higher the adhesion strength between the gas diffusion member and the electrode catalyst layer. However, in the electrode catalyst layer, the coating of the catalyst carrier with the ionomer is hindered. There is a concern that the gas permeability and proton conductivity in the layer will decrease. In the above-mentioned patent document, since there is no consideration about the ionomer entering into the gas diffusion member, there is a demand for a technique for suppressing deterioration of gas permeability and proton conductivity in the electrode catalyst layer while ensuring adhesion strength. It came to be done. In addition, even if it is a method of applying a catalyst paste to a sheet-like electrolyte membrane and bonding a gas diffusion member to this applied catalyst paste, the above-mentioned problem can occur because the paste can enter the gas diffusion member Can occur.

  In view of the above-described problems, an object of the present invention is to suppress a decrease in gas permeability and proton conductivity in an electrode catalyst layer while ensuring adhesion strength.

  In order to achieve at least a part of the above object, the present invention can be implemented as the following application examples.

[Application Example 1: Fuel Cell]
A membrane electrode assembly in which an electrode catalyst layer is bonded to the membrane surface of an electrolyte membrane having proton conductivity, and a conductive gas diffusion member having pores and exhibiting gas permeability through the pores. A fuel cell in which the membrane electrode assembly is sandwiched between members,
The electrode catalyst layer comprises a conductive catalyst carrier carrying a catalyst and an ionomer having proton conductivity,
The ionomer penetrates into the pores of the gas diffusion member on the electrode catalyst layer and the interface side between the electrode catalyst layer and the gas diffusion member, and the gas diffusion member on the interface side. To form an ionomer area,
When the thickness of the ionomer existing region is expressed as S0 and the thickness of the electrode catalyst layer is expressed as S1, the thickness S0 of the ionomer existing region is 9 to 37% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer. It is the summary.

  In the fuel cell of this application example 1, in addition to the presence of the ionomer in the electrode catalyst layer formed of the catalyst ink, the ionomer also enters the pores of the gas diffusion member joined to the electrode catalyst layer through the interface. In the gas diffusion member on the interface side, an ionomer existing region is formed. Then, the thickness S0 of the ionomer existing region is within a range of 9 to 37% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer. That is, by making the thickness S0 of the ionomer existing region 9% or more of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer, the adhesion strength between the electrode catalyst layer and the gas diffusion member can be ensured to a practical level. . On the other hand, if the thickness S0 of the ionomer existing region is less than 9% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer, there is a concern that the adhesion strength is lowered and the durability is insufficient. In addition, by setting the thickness S0 of the ionomer existing region to 37% or less of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer, the ionomer is prevented from entering the pores of the gas diffusion member excessively. The coating is ensured by the ionomer of the catalyst carrier in the catalyst layer, and it is possible to suppress a decrease in gas permeability and proton conductivity in the electrode catalyst layer. On the other hand, if the thickness S0 of the ionomer existing region exceeds 37% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer, the coating of the catalyst carrier with the ionomer in the electrode catalyst layer is impaired, and gas permeability and proton conductivity are reduced. There is concern that gender decline will occur.

  In this case, the thickness S0 of the ionomer-existing region, the thickness S0 of the ionomer-existing region, and the thickness S1 of the electrode catalyst layer are determined from the specifications of the fuel cell and can be within a practical range.

  The fuel cell of Application Example 1 described above can be configured as follows. For example, the ionomer can have a glass transition temperature of 150 ° C. or higher. In general, when the gas permeability (oxygen permeability) of the ionomer itself increases, the glass transition temperature of the ionomer increases. In addition, since the temperature dependence of the gas permeability of the ionomer is low, the gas permeability is not greatly reduced in a low temperature range that is assumed in the fuel cell operation. Therefore, by using an ionomer having a glass transition temperature of 150 ° C. or higher, battery performance at low temperatures can be improved. Moreover, even if the catalyst amount in the electrode catalyst layer is reduced, the battery performance can be prevented from being lowered due to the high gas permeability of the ionomer.

[Application Example 2: Manufacturing method of fuel cell]
A fuel cell manufacturing method comprising:
A catalyst ink including an electrolyte membrane having proton conductivity, a conductive catalyst carrier carrying a catalyst, and an ionomer having proton conductivity, and a conductive gas having pores and exhibiting gas permeability through the pores A first step of preparing a diffusion member;
A second step of applying the catalyst ink to the membrane surface of the electrolyte membrane;
A third step of joining the gas diffusion member to the coated catalyst ink and then drying the catalyst ink to form an electrode catalyst layer between the electrolyte membrane and the gas diffusion member ;
In the third step,
The load at the time of joining the gas diffusion member is controlled, and then the ionomer contained in the catalyst ink is applied to the fine particle of the gas diffusion member on the interface side between the coated catalyst ink and the gas diffusion member. The ionomer enters the hole before drying the ink, and the ionomer forms an ionomer existing area existing in the gas diffusion member on the interface side, and the thickness of the ionomer existing area is set to S0 under the control of the load, When the thickness of the electrode catalyst layer is expressed as S1, the gist is that the thickness S0 of the ionomer existing region is 9 to 37% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer.

  According to the fuel cell manufacturing method of Application Example 2 described above, it is possible to suppress a decrease in gas permeability and proton conductivity in the electrode catalyst layer while ensuring the adhesion strength between the electrode catalyst layer and the gas diffusion member. A fuel cell can be manufactured.

It is explanatory drawing which shows roughly the fuel cell 40 as one Example of this invention by sectional view. 4 is an explanatory diagram showing an outline of a manufacturing process of the fuel cell 40. FIG. It is explanatory drawing for demonstrating the property of the ionomer which can be employ | adopted. It is explanatory drawing for demonstrating application | coating of a catalyst ink, joining of the anode side gas diffusion layer 54 following this, and ink drying. FIG. 6 is an explanatory diagram schematically showing the behavior of ionomers in catalyst ink by pressing of a cathode side gas diffusion layer 55. It is explanatory drawing which shows the mode of the presence of the ionomer existence area | region 56 and the ionomer whole area | region 58 using an electron micrograph. 5 is a graph showing the peel strength of an example product and a comparative product in relation to the thickness S0 of the cathode side gas diffusion layer 55. FIG. 6 is a graph showing the oxygen gas diffusion resistance of an example product and a comparative product in relation to the thickness S0 of the cathode-side gas diffusion layer 55. It is the graph which plotted the voltage and electric current characteristic which shows the electric power generation performance of an example product and a comparative example product.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view schematically showing a fuel cell 40 as an embodiment of the present invention in a sectional view.

  As shown in the drawing, the fuel cell 40 is configured as a battery cell unit that generates electricity by an electrochemical reaction between hydrogen and oxygen, and has a stack structure in which a plurality of the units are stacked between a pair of end plates (not shown). . In this case, the number of stacked battery cell units can be arbitrarily set according to the output required for the fuel cell 40.

  The fuel cell 40 sandwiches battery cells 50 serving as a power generation unit with opposing separators 41. As shown in FIG. 1, the battery cell 50 includes both electrodes (electrode catalyst layers) of an anode 52 and a cathode 53 on both sides of an electrolyte membrane 51. The electrolyte membrane 51 is a proton conductive ion exchange membrane formed of a solid polymer material such as a fluorine resin, and exhibits good proton conductivity in a wet state. The anode 52 and the cathode 53 are configured by coating conductive particles carrying a catalyst such as platinum or a platinum alloy, for example, carbon particles (hereinafter referred to as catalyst-carrying carbon particles) with an ionomer having proton conductivity. The electrode catalyst layer is joined to both membrane surfaces of the electrolyte membrane 51 to form a membrane electrode assembly (MEA) together with the electrolyte membrane 51. Usually, the ionomer is a polymer electrolyte resin (for example, a fluororesin) that is a solid polymer material of the same quality as the electrolyte membrane 51, and has proton conductivity due to its ion exchange group.

  In addition, the battery cell 50 sandwiches the electrolyte membrane 51 with electrodes formed between the anode gas diffusion layer 54 and the cathode gas diffusion layer 55 from both sides. Hereinafter, the battery cell 50 is also simply referred to as MEGA. The separator 41 is located outside both the gas diffusion layers, and sandwiches the battery cell 50 including the gas diffusion layers. The anode-side gas diffusion layer 54 and the cathode-side gas diffusion layer 55 are formed of a conductive member that has pores and exhibits gas permeability, such as carbon paper or carbon cloth.

  As will be described in detail later, the fuel cell 40 of the present embodiment has the cathode-side gas diffusion layer 55 bonded after the application of the catalyst ink for forming the cathode 53 and before the drying, and then the ink is dried. Plan. Therefore, as schematically shown in FIG. 1, the ionomer contained in the catalyst ink forming the cathode 53 is present in the cathode 53, and in addition to the cathode 53 bonded to the cathode 53 through the interface. An ionomer existing region 56 is formed in the cathode side gas diffusion layer 55 on the interface side, which also enters the pores of the gas diffusion layer 55. Hereinafter, all regions including the ionomer including the cathode 53 and the ionomer existing region 56 are referred to as an ionomer total region 58.

  The separator 41 is a member that forms a gas flow path through which a reaction gas (a fuel gas containing hydrogen gas or an oxidizing gas containing oxygen) flows for each battery cell 50, and has low hydrogen permeability and good conductivity. Formed of material. For example, a plate-shaped conductive composite material or metal steel plate formed by mixing a conductive material into resin is used for forming the separator 41. The separator 41 includes an in-cell hydrogen gas flow path 42 and an in-cell air flow path 43 on the front and back surfaces thereof in order to supply and discharge gas to and from each electrode of the battery cell 50. In this embodiment, the in-cell hydrogen gas flow path 42 and the in-cell air flow path 43 are flow paths that are orthogonally arranged in the cell plane (in the electrode plane). It is set as the multi-row linear flow path extended up and down. The battery cell 50 of the fuel cell 40 receives the supply of hydrogen gas and air to the anode 52 and the cathode 53 through these in-cell flow paths, and generates electricity by causing an electrochemical reaction between hydrogen and oxygen.

  Next, the manufacturing process of the fuel cell 40 described above will be described. FIG. 2 is an explanatory diagram showing an outline of the manufacturing process of the fuel cell 40.

  As shown in FIG. 2, in manufacturing the fuel cell 40, in this embodiment, the fuel cell 40 is obtained through the manufacture of MEGA (battery cell 50). In manufacturing MEGA, first, preparation of an electrolyte membrane 51 (see FIG. 1, the same applies hereinafter) as a solid polymer electrolyte membrane (step S100), catalyst ink for forming anode 52 and cathode 53 as electrode catalyst layers (Step S110) and preparation of both gas diffusion layers of the anode side gas diffusion layer 54 and the cathode side gas diffusion layer 55 (step S120). Each of these steps can be performed in the order described above, and can be performed in parallel.

  In step S100, the electrolyte membrane 51 that has been formed can be purchased or can be formed from a polymer electrolyte resin as a film forming material. In this embodiment, the electrolyte membrane 51 is a Nafion membrane having proton conductivity (Nafion is a registered trademark, the same applies hereinafter).

  In step S110, carbon particles (catalyst-carrying carbon particles / catalyst carrier) supporting the catalyst particles using platinum alloy as a catalyst, ionomers having proton conductivity, and a dispersion medium (pure water and organic solvent) thereof are used. Are mixed and stirred with an appropriate stirring device to prepare a catalyst ink. Various types of carbon particles can be selected. For example, carbon nanotubes, carbon nanohorns, carbon nanofibers and the like can be used in addition to carbon black and graphite.

  When the catalyst is supported, a generally employed method such as an impregnation method, a coprecipitation method, or an ion exchange method may be performed. Moreover, what is distribute | circulating as the carbon particle by which catalyst support was carried out can also be obtained. An ultrasonic homogenizer was used for dispersing the catalyst-supporting carbon particles. The mixing ratio of pure water and organic solvent in the above dispersion medium can be determined as appropriate.

  As the ionomer, a commonly selected resin, for example, a fluorine ionomer having proton conductivity can be used, and a hydrocarbon ionomer such as polyarylene ether sulfonic acid (BPSH) having a glass transition temperature of 150 ° C. or higher can also be used. You can also. In addition, in order to obtain an ionomer having a glass transition temperature of 150 ° C. or higher, it is easy to blend a resin having the same quality as the ionomer and having a high glass transition temperature. For example, an ionomer having a high glass transition temperature can be obtained by blending a fluorine resin having a high glass transition temperature with a fluorine ionomer having proton conductivity. For example, fluorine ionomers can be variously selected from commercially available products such as DuPont's trade name DE2020CS ionomer, so that this ionomer (hereinafter referred to as the first ionomer) has a high glass transition temperature. By blending the resin, an ionomer having a high glass transition temperature (hereinafter referred to as a second ionomer) can be obtained. As a fluorine resin to be blended, there is a product name Teflon AF2400 (Teflon is a registered trademark, hereinafter the same) manufactured by DuPont, and Teflon AF2400 (solution) is added to the first ionomer (DE2020CS) at a resin solid content ratio of 2: 1. In this case, the second ionomer having a high glass transition temperature can be obtained.

  FIG. 3 is an explanatory diagram for explaining the properties of the second ionomer in which the first ionomer and a resin having a high glass transition temperature are blended. FIG. 3 shows the storage elastic modulus and loss tangent (tan δ) measured by the dynamic viscoelasticity measurement method (DMA method) for the test sheet in which the first ionomer and the second ionomer are thinned, respectively. Has been. And as shown in FIG. 3, the glass transition temperature of the 1st ionomer of brand name DE2020CS is about 117 degreeC. On the other hand, since the loss tangent of the second ionomer blended with the fluorine-based resin having the trade name Teflon AF2400 is not measured even at 150 ° C., the glass transition temperature exceeds 150 ° C. That is, since the glass transition temperature of the fluorine-based resin of the trade name Teflon AF2400 is about 240 ° C., the second ionomer blended with the resin has a high glass transition temperature. In this example, the second ionomer described above having a glass transition temperature of 150 ° C. or higher was employed. An ionomer having proton conductivity has various glass transition temperatures depending on its raw materials, molecular chain structure, resin properties, production process settings, etc., and the upper limit of the temperature is an ionomer that can be produced, for example, as described above. Determined by the properties of the resin to be blended.

  In step S120, carbon paper or carbon cloth is prepared as the anode side gas diffusion layer 54 and the cathode side gas diffusion layer 55.

  Following these steps S100 to 120, the prepared catalyst ink is applied to the membrane surface of the electrolyte membrane 51 (step S130). Next, before the coated catalyst ink is dried, the anode side gas diffusion layer 54 (for example, carbon cloth) is pressed and joined to the coated catalyst ink, and the catalyst ink is managed under the condition where the load at that time is controlled. Is dried (step S140). When the catalyst ink is dried through step S140, the cathode 53 is bonded to the membrane surface of the electrolyte membrane 51, and the cathode-side gas diffusion layer 55 is in close contact with the cathode 53. And the battery cell 50 (MEGA) is manufactured by performing the process of step S130-140 also on the anode 52 side. FIG. 4 is an explanatory diagram for explaining the application of the catalyst ink, the subsequent joining of the anode side gas diffusion layer 54 and the ink drying.

  As shown in FIG. 4, the coating ink 100 is applied to the electrolyte membrane 51 with a uniform thickness using the coating apparatus 100 (step S130). As this coating method, applicator coating for forming a film, die coating, spray coating, or the like can be employed as appropriate. The catalyst ink thus applied to the membrane surface of the electrolyte membrane 51 becomes the cathode 53 after drying. After the catalyst ink coating, the electrolyte membrane 51 that has been coated with the catalyst ink is transported to the press drying device 120 using a transport device (not shown).

  The press drying apparatus 120 includes a drying furnace 121, and includes a set table 122, a pressing plate 124, and a lifting device 126 in the furnace. The lifting device 126 has a built-in advance / retreat mechanism such as a ball screw or a linear rail, and moves the pressing plate 124 up and down with respect to the set table 122.

  The electrolyte membrane 51 that has been coated with the catalyst ink and has been transported to the pressure drying device 120 is placed on the set table 122 and set. Thereafter, the cathode-side gas diffusion layer 55 is superimposed on the catalyst ink before drying, and the cathode-side gas diffusion layer 55 is joined to the ink. In this state, the pressure drying device 120 lowers the pressure plate 124 toward the set table 122 and presses and bonds the cathode side gas diffusion layer 55 to the undried catalyst ink. The control device 128 of the press drying device 120 is configured as a microcomputer including a CPU, a ROM, and a RAM, and controls the lifting device 126 to manage the bonding load of the cathode side gas diffusion layer 55 by the press plate 124. Then, the control device 128 turns on a heater (not shown) of the drying furnace 121 to control the furnace temperature to the ink drying temperature in the situation under the load management, thereby drying the catalyst ink. The furnace temperature at this time can be lower than the glass transition temperature of the ionomer contained in the catalyst ink, and is a temperature at which the pure water and the solvent in the ink can be removed by drying. It should be noted that natural drying may be achieved at a furnace temperature slightly higher than room temperature.

  The control device 128 stores various parameters necessary for load management. For example, in addition to the viscosity of the catalyst ink prepared in step S110 and its temperature dependency, the load applied by the pressing plate 124, the thickness of the ionomer existing area 56 and the entire ionomer area 58 shown in FIG. The relationship with the porosity, pore diameter, etc. of the material (carbon paper, carbon cloth, etc.) used for the diffusion layer 55 is stored. Then, the control device 128 manages the load at the time of pressing the cathode side gas diffusion layer 55 against the undried catalyst ink in step S120 so that the thickness of the ionomer existing area 56 falls within the range described later, while the catalyst ink Is dried (step S140). The drying of the catalyst ink under such load management will be described later, including the behavior of the ionomer during that time.

  When the battery cell 50 (MEGA) is manufactured through step SS140 of FIG. 2, the separator 41 is bonded to the gas diffusion layers on both sides of the battery cell 50 (step S200), and these are arranged in a predetermined order (FIG. 1). A predetermined number of layers are stacked to assemble a stack structure (so that cells are repeatedly formed), and a predetermined pressing force is applied in the stacking direction to hold the entire structure (step S300). Thereby, the fuel cell 40 is completed.

  Next, drying of the catalyst ink under load management performed in step S140 will be described. FIG. 5 is an explanatory view schematically showing the behavior of the ionomer in the catalyst ink due to the pressing of the cathode side gas diffusion layer 55.

  In FIG. 5, the magnitude of the load is schematically distinguished by a white arrow in the downward view, and the cathode side gas diffusion layer 55 is moved by the pressing plate 124 as the load transitions from the upper view to the lower step side. The load when pressing is increased. As described above, the cathode-side gas diffusion layer 55 exhibiting gas permeability due to the pores is joined so as to overlap with the catalyst ink in an undried state, so that the cathode-side gas diffusion layer 55 is bonded to the pressing plate 124. When the load is applied, the ionomer contained in the undried catalyst ink enters the pores of the cathode-side gas diffusion layer 55 bonded to the catalyst ink through the interface. As a result, an ionomer existence region 56 is formed on the cathode side gas diffusion layer 55 on the interface side. Since the ionomer intrusion into the cathode gas diffusion layer 55 depends on the magnitude of the load applied by the pressing plate 124, the thickness of the ionomer existence area 56 is as shown in FIG. As the load (joining load) managed through the above control increases, the load increases.

  The pressure drying apparatus 120 (see FIG. 4) heats and dries the catalyst ink in the furnace of the drying furnace 121 under such load control. Thus, the electrode catalyst layer is subjected to evaporative removal of pure water and solvent during the drying. In the cathode 53, the carbon particles carrying the catalyst particles (catalyst support S) are covered with an ionomer, and a void K is also formed. Since the ionomer contained in the catalyst ink enters the cathode side gas diffusion layer 55 to form the ionomer existence region 56, the ionomer that covers the catalyst carrier S and remains on the cathode 53 enters the cathode side gas diffusion layer 55. It will decrease by the amount. Therefore, when the cathode side gas diffusion layer 55 is bonded to the undried catalyst ink with a large load as shown in FIG. 5C, the ionomer enters the cathode side gas diffusion layer 55 and the catalyst carrier by the ionomer is increased. It is assumed that the coating of S is damaged, and the ionomer-uncoated catalyst carrier S remains or collects. On the other hand, when the cathode side gas diffusion layer 55 is bonded to the undried catalyst ink with a small load as shown in FIG. 5A, the ionomer entry into the cathode side gas diffusion layer 55 is reduced. Although the coating of the catalyst carrier S with the ionomer is not impaired, the thickness of the ionomer existence region 56 is reduced. Although the ionomer existence region 56 is formed by the ionomer entering into the pores of the cathode side gas diffusion layer 55, the pure water and the solvent are removed by evaporation when the catalyst ink is dried. The gas permeability of the cathode side gas diffusion layer 55 is not impaired.

  FIG. 6 is an explanatory view showing the existence of the ionomer existing area 56 and the entire ionomer area 58 using an electron micrograph. FIG. 6 shows a secondary electron image and a reflected electron image obtained by cutting the test piece obtained through step S140 of FIG. 2 in the thickness direction using the press drying apparatus 120 of FIG. It is shown in contrast to the schematic configuration of the test piece. In this case, the test piece is a test piece in which the cathode 53 is formed on the membrane surface of the electrolyte membrane 51 using the catalyst ink, and the cathode-side gas diffusion layer 55 is joined to the cathode 53. The cut surface obtained by cutting the test piece in the thickness direction reflects the situation where the region where the ionomer exists and the region where the ionomer does not exist are adjacent to each other and the distribution state of the elements.

  The secondary electron image shown on the left side of FIG. 6 shows a surface irregularity image of the cut surface of the test piece. The surface unevenness is a physical state of the cut surface, and is different between a region where the ionomer is present and a region where the ionomer is not present. Since the region where the ionomer exists and the region where the ionomer does not exist are adjacent to each other at the cut surface of the test piece, the secondary electron image shows the boundary on the side of the electrolyte film 51 in the entire ionomer region 58 and the cathode of the entire ionomer region 58. The boundary on the side of the side gas diffusion layer 55 is found. On the other hand, the backscattered electron image shown on the right side of FIG. 6 shows the distribution of elements on the cut surface of the test piece, and the larger the element, the more the atoms are shown as a white image. In this cut surface, the cathode 53 including the catalyst carrier S supporting high-mass platinum as a catalyst and the cathode-side gas diffusion layer 55 not including the catalyst carrier S are adjacent to each other. The boundary of the side gas diffusion layer 55 is found. Thereby, as shown in FIG. 6, the thickness of the ionomer existing area 56 and the thickness of the entire ionomer area 58 can be defined. In the present embodiment, the thicknesses of the two are made to correspond to the load at the time of the load management described above, the relationship is grasped in advance, and the result is stored in the control device 128 as, for example, map-like memory data. For this reason, in step S120, the ionomer presence area 56 and the entire ionomer area 58 can be in a desired relationship by drying the catalyst ink after managing the load when the pressing plate 124 is pressed. . This point will be described below.

  As described with reference to FIG. 5, the thickness of the ionomer existence region 56 (hereinafter, this thickness is expressed as S0) reflects the state of the ionomer entering the cathode gas diffusion layer 55, and the catalyst carrier S by the ionomer. Affects the coating situation. Further, the ionomer existence area 56 exists at the interface between the cathode 53 and the cathode-side gas diffusion layer 55, and the ionomer exists from the ionomer existence area 56 to the cathode 53, so that the cathode formed after drying the catalyst ink. The adhesion strength between the gas diffusion layer 53 and the cathode side gas diffusion layer 55 is also affected. This adhesion strength decreases as the thickness S0 of the ionomer existence region 56 decreases, and increases as the thickness S0 increases. On the other hand, if the coating of the catalyst carrier S with the ionomer on the cathode 53 is damaged and the catalyst carrier S not covered with the ionomer remains (see FIG. 5C), the ionomer is coated on the cathode 53 with the catalyst carrier S present. Therefore, the gas permeability and proton conductivity that are ensured are impaired, resulting in a decrease in power generation performance. The power generation performance depending on gas permeability and proton conductivity decreases as the thickness S0 of the ionomer existence region 56 increases, and the decrease is suppressed as the thickness S0 decreases.

  By the way, the ionomer existence region 56 is a partial region of the entire ionomer region 58 including the cathode 53, and it is difficult to always make the thickness of both of them uniform in the MEGA manufacturing process. For this reason, the thickness S0 of the ionomer existing region 56 is determined by considering the relationship with the thickness of the entire ionomer region 58 (hereinafter, this thickness is referred to as “SA”), and thereby the adhesion strength between the cathode 53 and the cathode-side gas diffusion layer 55. Alternatively, it can be an index for defining gas permeability and proton conductivity in the cathode 53. The lower limit value of the thickness S0 of the ionomer existence region 56 in consideration of the thickness SA of the entire ionomer region 58 defines the adhesion strength between the cathode 53 and the cathode side gas diffusion layer 55, and the upper limit value of the thickness S0. Defines the gas permeability and proton conductivity in the cathode 53. Based on these findings, the thickness S0 of the ionomer existence region 56 was determined as follows. In this case, since the ionomer total region 58 includes the cathode 53 and the ionomer existing region 56, the thickness SA of the ionomer total region 58 is the sum of the thickness S 0 of the ionomer existing region 56 and the thickness of the cathode 53.

  First, the relationship between the lower limit value of the thickness S0 of the ionomer existence region 56 in consideration of the thickness SA of the entire ionomer region 58 and the adhesion strength between the cathode 53 and the cathode side gas diffusion layer 55 will be described. The test piece to be used is MEGA obtained through step S140 of FIG. 2, and this MEGA test piece was cut into a width of 10 mm and subjected to a 90 ° peel test in an environment of normal temperature and normal humidity. Regarding MEGA test pieces, a plurality of types having different load management values in step S140 were prepared. In addition, the existing MEGA was also subjected to a peel test for comparison. Table 1 shows a list of test pieces subjected to the peel test.

  In Table 1, the comparative example product 1 is an existing MEGA, which is an MEA in which an anode 52 and a cathode 53 are bonded to a sheet-like electrolyte membrane 51 with a catalyst ink, and an anode side gas diffusion layer 54 and a cathode side. It is a MEGA obtained by sandwiching between gas diffusion layers 55 and hot-pressing them under a pressure condition of 130 ° C. × 1.2 MPa. The adhesion between the cathode 53 and the cathode-side gas diffusion layer 55 in the comparative product 1 depends on a hot press method at 130 ° C. The press temperature (130 ° C.) at this time is higher than the glass transition temperature of the ionomer contained in the catalyst ink, for example, the ionomer of the trade name DE2020CS described above. Adhesion of the cathode side gas diffusion layer 55 to 53 becomes possible.

  Example products 1 to 3 are MEGAs obtained through the manufacturing procedure of FIG. 2 described above, and the cathode side gas diffusion layer 55 is subjected to load management and bonded to undried catalyst ink at room temperature. The load is different as shown in the table. Although the comparative example product 2 is a MEGA obtained by the same procedure as the above-described example product, the load when the cathode side gas diffusion layer 55 is joined to the undried catalyst ink is excessive. The catalyst ink drying temperature when obtaining MEGAs of Examples 1 to 3 and Comparative Example 2 was lower than the glass transition temperature of the ionomer used. The drying temperature of the catalyst ink was set to a temperature at which pure water and the solvent in the ink could be removed by evaporation. The catalyst inks in Examples 1 to 3 and Comparative Example 2 are catalyst inks using the second ionomer described above.

  FIG. 7 is a graph showing the peel strength of the example product and the comparative product in relation to the thickness S0 of the cathode side gas diffusion layer 55. In the graph of FIG. 7, the vertical axis represents the peel strength, and the horizontal axis is plotted as a ratio (%) obtained by dividing the thickness S0 of the cathode-side gas diffusion layer 55 by the thickness SA of the entire ionomer region 58. The peel strength was measured by preparing a test piece having a width of 10 mm from each of the Example product and the Comparative product in Table 1, and subjecting the test piece to a 90 ° C. peel test at room temperature and normal humidity. Hereinafter, for convenience of explanation, a ratio obtained by dividing the thickness S0 of the cathode side gas diffusion layer 55 by the thickness SA of the entire ionomer region 58 is referred to as an ionomer interface ratio S0 / SA. The value (%) of the ionomer interface ratio S0 / SA of the example product / comparative example product was determined using the method described in FIG. 6 with the thickness S0 of the cathode side gas diffusion layer 55 of each of the example product and the comparative product and the ionomer. The thickness SA of the entire region 58 was obtained and calculated.

  As MEGA, it is desirable that the peel strength between the cathode 53 and the anode-side gas diffusion layer 54 is as high as possible. As shown in FIG. 7, the battery cell 50 and thus the fuel cell 40 have a strength of about 45 N / m. Is required for durability and practical use. Since the comparative example product 1 has the cathode gas diffusion layer 55 bonded to the cathode 53 formed by drying the catalyst ink by a hot press method, the bonding strength is low and can meet the above-described strength requirements. Absent. On the other hand, the product 1 of Example in which the bonding load of the cathode side gas diffusion layer 55 is controlled to 0.85 Pa can meet the above-described strength requirement although the ionomer interface ratio S0 / SA is 9%. The same applies to Example Products 2 to 3 and Comparative Example Product 2 that are managed with loads exceeding this. In this case, in Examples 1 to 3 and Comparative Example 2 in which catalyst ink was dried under load management, the management load and the ionomer interface ratio S0 / SA are not in a simple proportional relationship, but the management load As shown in FIG. 5, it can be seen that the thickness S0 of the cathode-side gas diffusion layer 55 increases and the ionomer interface ratio S0 / SA also increases. In this embodiment, the relationship between the load and the ionomer interface ratio S0 / SA is ascertained by the control device 128 of the press drying device 120 through experiments as described above, and various kinds of load management are necessary. The parameters are stored. Thereby, for example, the value of the ionomer interface ratio S0 / SA, that is, the thickness S0 of the ionomer existing region 56 and the thickness SA of the entire ionomer region 58 are controlled through a control load so that the peel strength is about 45 N / m or more. Can be defined. In this case, the thickness of the cathode-side gas diffusion layer 55 and the thickness of the cathode 53 affect the above-mentioned ionomer interface ratio S0 / SA, but these thicknesses are within a practical range that is usually adopted for the battery cell 50. That's fine.

  Next, the relationship between the upper limit value of the thickness S0 of the ionomer existence region 56 in consideration of the thickness SA of the entire ionomer region 58 and the gas permeability required for MEGA will be described. MEGA is required to have high gas permeability. This gas permeability is obtained together with proton conductivity because of the presence of an ionomer in the cathode 53, and affects power generation performance. Therefore, the example products 1-3 and the comparative products 1-2 shown in Table 1 were subjected to oxygen gas diffusion resistance evaluation. This gas diffusion resistance evaluation can be calculated from the limit current values when the MEGA power generation operation of each of Examples 1 to 3 and Comparative Examples 1 to 2 is performed. FIG. 8 is a graph showing the oxygen gas diffusion resistance of the example product and the comparative example product in relation to the thickness S0 of the cathode side gas diffusion layer 55. The graph of FIG. 8 was obtained as follows. First, each MEGA of Examples 1 to 3 and Comparative Examples 1 to 2 was used as a test cell, the cell temperature was set to 50 ° C., and both the anode and cathode electrodes were set to an excessively humidified state with a humidifying bubbler temperature of 60 ° C. After that, low concentration oxygen gas (2%) is supplied to the cathode 53 of each test cell, and hydrogen gas is supplied to the anode 52 to generate electric power, and a limit current value at that time is obtained. From the above, the oxygen gas diffusion resistance was determined using a predetermined conversion formula. Then, the obtained oxygen gas diffusion resistance values were plotted in association with the values of the ionomer interface ratio S0 / SA of each of Examples 1 to 3 and Comparative Examples 1 to 2.

  For MEGA, the higher the gas permeability, the better. Therefore, as shown in FIG. 8, it is preferable that the oxygen gas diffusion resistance value is as low as about 120 sec / m as shown in FIG. Therefore, it is requested after securing the power generation capability as the fuel cell 40. The oxygen gas diffusion resistance value of 120 sec / m is obtained by combining MEA in which the anode 52 and the cathode 53 are bonded to the sheet-like electrolyte membrane 51 with the catalyst ink, and the anode-side gas diffusion layer 54 and the cathode-side gas diffusion layer 55. It is comparable to the resistance value obtained by the existing MEGA (Comparative Example Product 1) obtained by hot pressing them.

  Although the comparative example product 2 is MEGA obtained by the same method as the example products 1 to 3, since the management load of the bonding load of the cathode side gas diffusion layer 55 is large, as shown in FIG. It is assumed that the thickness S0 of the ionomer existence area 56 is large. Therefore, in the comparative product 2 as shown in FIG. 5C, as described above, the amount of ionomer in the cathode 53 is reduced and the gas permeability is lowered. This is because the oxygen gas of the comparative product 2 is reduced. This agrees with the result of FIG. 8 in which the diffusion resistance value is as large as 220 sec / m. That is, even if the bonding load is controlled, if the load is excessive, the oxygen gas diffusion resistance value is large as in the comparative product 2, so that the above-described request for ensuring gas permeability cannot be met. On the other hand, the example products 1 to 3 in which the bonding load of the cathode side gas diffusion layer 55 is controlled to 0.85 to 13.1 Pa and a load smaller than the comparative example product 2 have different ionomer interface ratios S0 / SA. However, the ionomer interface ratio S0 / SA of these example products is 37% or less of the interface ratio of the example product 3. In each of Examples 1 to 3 having an ionomer interface ratio S0 / SA of 37% or less, the above-described demand for ensuring gas permeability can be met. In this case, in Examples 1 to 3 and Comparative Example 2 in which the catalyst ink was dried under load management, as described above, the management load and the ionomer interface ratio S0 / SA have a simple proportional relationship. Although not provided, the ionomer interface ratio S0 / SA can be reduced by reducing the management load. In this embodiment, the relationship between the load and the ionomer interface ratio S0 / SA is ascertained by the control device 128 of the press drying device 120 through experiments as described above, and various kinds of load management are necessary. The parameters are stored. Thereby, for example, the value of the ionomer interface ratio S0 / SA, that is, the thickness S0 of the ionomer existence region 56 and the thickness of the ionomer total region 58 are obtained through a management load so that the oxygen gas diffusion resistance value is within a range of about 120 sec / m. SA can be defined.

  As described above, in this embodiment, the anode-side gas diffusion layer 54 is bonded while the catalyst ink applied to the electrolyte membrane 51 is not dried, and the bonding load at that time is managed. The catalyst ink is dried to produce MEGA. In addition, in the MEGA obtained by drying the catalyst ink under the control of the bonding load, the ionomer interface ratio S0 / SA, which is the ratio of the thickness S0 of the ionomer existing area 56 and the thickness SA of the entire ionomer area 58, is 9 to By setting it to 37%, it is possible to prevent the gas permeability and proton conductivity of the cathode 53 from being lowered while ensuring the adhesion strength between 55 and the cathode 53. The same applies to the anode 52 and the anode-side gas diffusion layer 54.

  In the present embodiment, since the thickness S0 of the cathode side gas diffusion layer 55 can be measured as described above, the thickness S0 of the ionomer existence region 56 can be set to 0.8 to 3.3 μm. By doing so, it is not necessary to increase the thickness SA of the entire ionomer region 58, and hence the thickness of the cathode 53, so that the fuel cell 40 can be thinned and further downsized.

  Next, the performance evaluation of the example products 1 to 3 and the comparative product 1 to 2 shown in Table 1 will be described. FIG. 9 is a graph plotting voltage / current characteristics showing the power generation performance of the example product and the comparative product. The voltage / current characteristics of FIG. 9 are the steady operation of the fuel cell 40 with the cell temperature, the relative humidity of both poles, and the gas supply to both poles, with the MEGAs of the example products 1 to 3 and the comparative example products 1 and 2 as test cells. Under the circumstances of time, power was generated and plotted.

  As shown in FIG. 9, the MEGA test cells of Examples 1 to 3 in which the bonding load of the anode-side gas diffusion layer 54 is controlled so that the ionomer interface ratio S0 / SA is 9 to 37% are almost the same. A level of power generation performance was obtained. Then, in the MEGA test cells of these Example products 1 to 3, from the MEGA test cell of the comparative example product 2 in which the management load was controlled so that the ionomer interface ratio S0 / SA was 47% exceeding 37%, A significant improvement in power generation performance was observed. This can be considered as follows, coupled with the difference in the oxygen gas diffusion resistance as described above.

  As described above with reference to FIG. 5, when the thickness S0 of the ionomer existence region 56 increases (see FIG. 5C), the oxygen gas diffusion resistance value increases (FIG. 8). Since the ionomer is present by coating the catalyst carrier S, the proton conductivity secured is impaired. That is, a large amount of ionomer enters the cathode-side gas diffusion layer 55, so that the ionomer that covers the catalyst carrier S contained in the cathode 53 decreases, and the so-called three-phase interface that is generated when the catalyst carrier S is coated with the ionomer. Less. In addition, since the ionomer often enters the cathode side gas diffusion layer 55, the voids in the cathode side gas diffusion layer 55 are reduced, and the drainage performance is assumed to be deteriorated. It is assumed that these factors overlap to cause a large difference in battery performance between the example products 1 to 3 and the comparative example product 2.

  Further, as shown in FIG. 9, the MEGA test cells of Examples 1 to 3 in which the bonding load of the anode side gas diffusion layer 54 is controlled so that the ionomer interface ratio S0 / SA is 9 to 37%, and the catalyst The oxygen gas diffusion resistance value is almost the same as that of the test cell of the comparative example product 1 which is an existing MEGA in which the cathode-side gas diffusion layer 55 is joined to the cathode 53 that has been formed through drying of the ink by a hot press method. Nevertheless, the MEGA test cells of Example products 1 to 3 showed higher power generation performance improvement than Comparative Example product 1. Therefore, according to the manufacturing method of the present embodiment in which the catalyst ink is dried while managing the bonding load of the anode-side gas diffusion layer 54, the fuel cell 40 that is superior to the existing fuel cell that employs the hot press method is manufactured. It will be possible. Further, the fuel cell 40 obtained by the manufacturing method of the present embodiment is a fuel cell that can be used in place of an existing fuel cell that employs a hot press method. Note that the difference in power generation performance described above between the test cells of the MEGA of the example products 1 to 3 of the present example and the comparative example product 1 that is an existing MEGA employing a hot press method is not yet known. It is considered that the ionomer contained in the dried catalyst ink enters the pores of the anode-side gas diffusion layer 54 so that the coating of the catalyst carrier S does not become excessive and the gap K is also suitably formed in the cathode 53. The In addition to this, in this example (example products 1 to 3), the gap between the cathode 53 and the cathode side gas diffusion layer 55 disappears due to the ionomer entering the cathode side gas diffusion layer 55, so that the drainage performance is improved. It is also assumed that this is because

  In addition to the improvement in battery performance as shown in FIG. 9, in this example, the ionomer included in the catalyst ink was the second ionomer described above (see FIG. 3) having a glass transition temperature of 150 ° C. or higher. . For this reason, the fuel cell 40 obtained by the manufacturing method of the present embodiment has a high glass transition temperature and a high gas permeability, and the temperature dependency of the gas permeability is low. Therefore, in the fuel cell 40 of the present embodiment, the gas permeability is not greatly reduced in the low temperature range assumed when the fuel cell 40 is operated, and the cell performance at low temperature can be improved. . Moreover, even if the blending amount of the catalyst carrier S in the cathode 53 is reduced, the battery performance can be prevented from being lowered due to the high gas permeability of the ionomer.

  In an existing MEGA employing a hot pressing method, hot pressing is performed at a temperature higher than the glass transition temperature of the ionomer used. For this reason, when using an ionomer having a glass transition temperature of 150 ° C. or higher as described above, hot pressing at a temperature higher than this temperature is required. Therefore, an ionomer having a high gas permeability and a high glass transition temperature should be used. It was not possible, and versatility was low. However, in this embodiment, hot press is not required in the first place, and it is only necessary to dry the catalyst ink under the control of the bonding load of the anode side gas diffusion layer 54. Rise. In addition, since no equipment such as a hot press machine is required, the cost can be reduced.

  Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, in the above-described embodiment, the catalyst ink is dried under the control of the bonding load in the electrode catalyst layers of the anode 52 and the cathode 53, but the gas permeability improvement treatment is performed for either one of the electrode catalyst layers. It can also be done. As the ionomer to be used, an ionomer having a relatively low glass transition temperature, which has been conventionally employed, can also be used.

  Further, both the anode-side gas diffusion layer 54 and the cathode-side gas diffusion layer 55, or at least the cathode-side gas diffusion layer 55, have a water-repellent layer (MPL: Micro) on the side of the electrode catalyst layer to which they are bonded. Porous Layer) can also be provided. In this case, as for the water repellent layer, the gas diffusion member in the present invention may include this water repellent layer.

DESCRIPTION OF SYMBOLS 40 ... Fuel cell 41 ... Separator 42 ... In-cell hydrogen gas flow path 43 ... In-cell air flow path 50 ... Battery cell 51 ... Electrolyte membrane 52 ... Anode 53 ... Cathode 54 ... Anode side gas diffusion layer 55 ... Cathode side gas diffusion layer 56 ... Ionomer existence area 58 ... Ionomer whole area 100 ... Coating equipment 120 ... Pressing dryer 121 ... Drying furnace 122 ... Set table 124 ... Pressing plate 126 ... Elevating equipment 128 ... Control device S ... Catalyst carrier K ... Gap

Claims (4)

A membrane electrode assembly in which an electrode catalyst layer is bonded to the membrane surface of an electrolyte membrane having proton conductivity, and a conductive gas diffusion member having pores and exhibiting gas permeability through the pores. A fuel cell in which the membrane electrode assembly is sandwiched between members,
The electrode catalyst layer comprises a conductive catalyst carrier carrying a catalyst and an ionomer having proton conductivity,
The ionomer penetrates into the pores of the gas diffusion member on the electrode catalyst layer and the interface side between the electrode catalyst layer and the gas diffusion member, and the gas diffusion member on the interface side. To form an ionomer area,
When the thickness of the ionomer existing region is expressed as S0 and the thickness of the electrode catalyst layer is expressed as S1, the thickness S0 of the ionomer existing region is 9 to 37% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer. Has been a fuel cell.   The fuel cell according to claim 1, wherein the ionomer has a glass transition temperature of 150 ° C. or higher. A fuel cell manufacturing method comprising:
A catalyst ink including an electrolyte membrane having proton conductivity, a conductive catalyst carrier carrying a catalyst, and an ionomer having proton conductivity, and a conductive gas having pores and exhibiting gas permeability through the pores A first step of preparing a diffusion member;
A second step of applying the catalyst ink to the membrane surface of the electrolyte membrane;
A third step of joining the gas diffusion member to the coated catalyst ink and then drying the catalyst ink to form an electrode catalyst layer between the electrolyte membrane and the gas diffusion member ;
In the third step,
The load at the time of joining the gas diffusion member is controlled, and then the ionomer contained in the catalyst ink is applied to the fine particle of the gas diffusion member on the interface side between the coated catalyst ink and the gas diffusion member. The ionomer enters the hole before drying the ink, and the ionomer forms an ionomer existing area existing in the gas diffusion member on the interface side, and the thickness of the ionomer existing area is set to S0 under the control of the load, When the thickness of the electrode catalyst layer is expressed as S1, the thickness S0 of the ionomer existing region is 9 to 37% of the sum of the thickness S0 and the thickness S1 of the electrode catalyst layer. The method of manufacturing a fuel cell according to claim 3, wherein in the first step, the catalyst ink containing an ionomer having a glass transition temperature of 150 ° C or higher is prepared.