JP3896664B2 - Manufacturing method of fuel cell separator and fuel cell separator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a fuel cell separator and a fuel cell separator, and more specifically, in a fuel cell configured by stacking a plurality of single cells, the fuel gas is provided between adjacent single cells and between the electrodes. The present invention relates to a fuel cell separator that forms a flow path and an oxidizing gas flow path and separates the fuel gas from the oxidizing gas, and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, as this type of fuel cell separator, a carbon powder is used as a raw material, and a material obtained by adding a predetermined binder to the carbon powder is molded, and then fired, carbonized, and graphitized (for example, Japanese Patent Laid-Open No. Hei. No. 8-222241). In the case of firing and carbonizing and graphitizing a molded carbon material in this way, the phenol resin added as a binder to the carbon material generates water in the firing process, so the generated water is contained in the separator. There is a possibility that bubbles are generated and the gas impermeability of the fired separator is impaired. Therefore, normally, in order to ensure the gas impermeability of the separator, the fired separator is further impregnated with a thermosetting resin such as a phenol resin to block the generated bubbles.
[0003]
Alternatively, as another method for manufacturing a separator, a method in which a graphite material mixed with a predetermined amount of a phenol resin as a binder is subjected to hot press molding at a temperature at which the resin does not graphitize (for example, a special method). Kaihei 60-246568). With such a configuration, since the carbonization and graphitization steps are not required, the manufacturing process can be simplified, and a separator that realizes sufficient conductivity and gas impermeability can be easily manufactured. it can.
[0004]
[Problems to be solved by the invention]
However, in the above-described two methods, when the fuel cell separator is manufactured by firing, carbonizing and graphitizing the molded carbon, the firing process causes shrinkage of the entire carbon member. . Therefore, usually, a raw material added with a binder is formed into a block shape, fired, cut out from the fired block-shaped carbon material to obtain a plate-like member, and a predetermined machine is attached to the plate-like member. Processing was performed to obtain a desired separator shape. When the above-described resin impregnation operation is performed on the member that has been machined into the desired shape, the separator is completed. As described above, when a manufacturing method including a firing process is used, there is a disadvantage that the entire manufacturing process becomes complicated, for example, a machining process is required, thereby causing an increase in manufacturing cost.
[0005]
On the other hand, when a fuel cell separator is manufactured by adding a binder made of a thermosetting resin to a graphite material and performing heat press molding at a temperature at which the resin does not graphitize, the separator has a desired shape because of heat press molding. However, since a binder is added to the graphite material, the conductivity of the separator may be impaired due to the influence of the binder, and the resistance may increase. That is, as the amount of binder having no conductivity increases, the conductivity of the entire separator also decreases. In addition, during hot press molding, a binder may be deposited on the separator surface. When a fuel cell is assembled using such a separator, the contact resistance between the separator and the electrode increases. In order to prevent such inconvenience, a configuration in which the surface of the separator is shaved after hot press molding to remove the binder deposited on the surface is conceivable. However, in this configuration, the surface is shaved for each separator. Therefore, the manufacturing process becomes complicated and the advantages of simple hot press molding are impaired.
[0006]
The present invention has been made to solve such problems and to produce a separator having sufficient conductivity and gas impermeability by a simple production method. Therefore, the method for producing a fuel cell separator of the present invention is provided. The fuel cell separator has the following configuration.
[0007]
[Means for solving the problems and their functions and effects]
  The method for producing a fuel cell separator of the present invention comprises:
  (A)carbonA step of forming a separator member having a predetermined shape by pressure-molding a raw material made of powder containing at least in a predetermined mold;
  (B) The separator member formed in the step (a) is impregnated with a predetermined impregnating agent, and the gap formed between the powders constituting the raw material in the separator member is closed with the impregnating agent. Process and
  With,
  Assuming that the powder to be subjected to the pressure molding is obtained by pressure-molding a powder made of carbon under the pressure during the pressure molding, a carbon member is obtained between the carbon powders in the carbon member. A powder obtained by further adding a binder in an amount less than the theoretical amount required to close the formed gap, to the carbon powder,From the separator memberWithout firingThe gist is to obtain a fuel cell separator.
[0008]
According to the method for manufacturing a fuel cell separator of the present invention configured as described above, a separator member is formed by pressure molding, and a separator is obtained from the separator member. Therefore, the shape of the separator is cut out from the block by machining. Compared with the manufacturing method, the manufacturing process can be simplified. Further, since the separator member is impregnated with the impregnating agent to close the gap formed in the separator member, a separator having sufficient gas impermeability can be manufactured.
[0009]
Here, as the impregnating agent impregnated in the separator member, for example, a thermosetting resin having sufficient heat resistance at the operating temperature of the fuel cell can be used. When using a thermosetting resin, disperse it in a predetermined solvent, immerse the separator member in this liquid, soak the impregnating agent in the voids in the separator member, and heat the separator member. What is necessary is just to thermoset resin. Moreover, even if it is a thermoplastic resin, if it does not melt | dissolve in the operating temperature range of a fuel cell, it can replace with a thermosetting resin and can be used.
[0011]
  Further, according to the method for manufacturing a fuel cell separator of the present invention,The carbon separator can be produced by a simple method called pressure molding, and there is no need to perform complicated steps such as machining and firing. In addition, since the binder is used in an amount smaller than the theoretical amount described above, the binder oozes out on the surface of the separator member formed by pressure molding during pressure molding, as in the case of using a binder larger than the theoretical amount. And there is no risk of forming a layer. When such a binder layer is formed on the surface of the separator member, the conductivity of the separator obtained from the separator member decreases, and when this separator is used in a fuel cell, the contact resistance in the fuel cell increases. . In addition, if the binder oozes out during pressure molding to form a layer, the releasability of the separator member becomes worse after pressure molding. Furthermore, the “burr” is formed by the oozed binder, and the manufacturing process may be complicated to remove this.
[0012]
In addition, since a smaller amount of the binder than the theoretical amount is used, the carbon powders can sufficiently adhere to each other in the separator member formed by pressure molding. Therefore, a binder layer is not formed between the carbon powders, and the conductivity of the separator is not lowered. Further, when a thermosetting resin is used as the binder, the amount of the binder is small, so that the time required for curing the thermosetting resin is shortened, and the time required for the production can be shortened.
[0013]
Here, the amount of the binder to be added to the carbon powder is not less than the minimum amount at which the member obtained by pressure molding has a strength sufficient to withstand the impregnation process. What is necessary is just to determine suitably as an amount which an undesired amount of binder does not ooze out. The theoretical value of the binder amount is the amount required when it is assumed that a carbon member is obtained by press-molding only carbon powder. In addition, the powder obtained by adding other substances to the carbon powder is molded. Then, it may be an amount required when it is assumed that the carbon member is formed. That is, if a powder obtained by further adding other substances such as a hydrophilic substance to the carbon powder is used as the raw material, it is assumed that a carbon member is obtained by pressure molding the powder containing the other substance. In this case, the binder amount actually used may be set as a smaller amount than the theoretically required binder amount. Of course, when another substance is further added to the carbon powder, if the amount of the other substance is small and the influence is small, the theoretical quantity required when only the carbon powder is used may be used.
[0023]
In addition, the method for producing the fuel cell separator of the present invention includes:
(D) washing the separator member impregnated with the predetermined impregnating agent in the step (b), and washing away the impregnating agent adhering to the surface of the separator member;
Further, it may be provided.
[0024]
According to such a method for manufacturing a separator for a fuel cell, the impregnating agent that deteriorates conductivity is removed because the layer of the impregnating agent formed on the surface of the separator member in the step of impregnating the impregnating agent is removed by a simple method of washing. The manufacturing process is not complicated to remove the layer. Here, the washing operation may be performed using water or warm water if the impregnating agent is water-soluble. When using a non-water-soluble impregnating agent, a solvent capable of dissolving the impregnating agent is appropriately selected. Can be washed.
[0025]
In the manufacturing method of such a fuel cell separator,
The impregnating agent may be a water-soluble thermosetting resin in which an acrylic resin is a main component and an epoxy resin and an ester are copolymerized. Since such a resin is water-soluble, the layer of the impregnating agent formed on the surface of the separator member by the operation of impregnating the separator member can be easily washed away by washing with warm water.
[0026]
In the fuel cell separator of the present invention,
The predetermined impregnating agent used in the step (a) may contain a hydrophilic substance.
[0027]
Thus, by impregnating the impregnating agent containing a hydrophilic substance, predetermined | prescribed hydrophilic property can be provided to a separator. When the separator is imparted with hydrophilicity, the effect of improving drainage can be obtained in the gas flow path formed by the concavo-convex structure provided on the separator surface inside the fuel cell using the separator. That is, in the fuel cell, generated water is generated as the electrochemical reaction proceeds, and this generated water is inconvenient if it stays in the gas flow path and closes the flow path. The drainage from the flow path is improved, and such inconvenience can be prevented. The hydrophilicity of the impregnating agent is imparted to the separator member by impregnating the separator member with the impregnating agent so that the contact angle of the separator obtained from the separator member is 40 degrees or less. It is desirable that it is possible.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
In order to further clarify the configuration and operation of the present invention described above, embodiments of the present invention will be described based on examples. First, for convenience of explanation, the configuration and operation of a fuel cell including a separator manufactured based on the separator manufacturing method according to the first embodiment of the present invention will be described with reference to FIGS. The separator manufacturing method according to the first embodiment of the present invention will be described.
[0035]
A fuel cell including a separator manufactured according to the separator manufacturing method according to the first embodiment of the present invention has a stack structure in which a plurality of single cells as constituent units are stacked. 3 is a schematic cross-sectional view illustrating the configuration of a single cell 28 that is a structural unit of the fuel cell, FIG. 4 is an exploded perspective view illustrating the configuration of the single cell 28, and FIG. 5 is a stack structure in which the single cells 28 are stacked. FIG.
[0036]
  The fuel cell of this example is a polymer electrolyte fuel cell. A polymer electrolyte fuel cell includes a membrane made of a solid polymer exhibiting good conductivity in a wet state as an electrolyte layer. Such fuel cells areanodeThe fuel gas containing hydrogen is supplied on the side,CathodeIn response to the supply of an oxidizing gas containing oxygen on the side, the following electrochemical reaction proceeds.
[0037]
H₂  → 2H⁺+ 2e^-                           ... (1)
(1/2) O₂+ 2H⁺+ 2e^-  → H₂O ... (2)
H₂+ (1/2) O₂  → H₂O ... (3)
[0038]
  Equation (1) isanodeThe reaction in (2) isCathodeThe reaction shown in the equation (3) proceeds in the entire fuel cell. As described above, the fuel cell directly converts chemical energy contained in the fuel supplied to the fuel cell into electric energy, and is known as a device having very high energy efficiency. As shown in FIG. 3, the unit cell 28 that is a constituent unit of the fuel cell is composed of an electrolyte membrane 21, an anode 22, a cathode 23, and separators 30a and 30b.
[0039]
The anode 22 and the cathode 23 are gas diffusion electrodes having a sandwich structure with the electrolyte membrane 21 sandwiched from both sides. Separator 30a, 30b forms the flow path of fuel gas and oxidizing gas between anode 22 and cathode 23, sandwiching this sandwich structure from both sides. A fuel gas channel 24P is formed between the anode 22 and the separator 30a, and an oxidizing gas channel 25P is formed between the cathode 23 and the separator 30b. When the fuel cell is actually assembled, a predetermined number of the single cells 28 are stacked to form the stack structure 14.
[0040]
In FIG. 3, the ribs that form the gas flow paths are formed only on one side of each separator 30a, 30b. However, in an actual fuel cell, as shown in FIG. 30b has a rib 54 and a rib 55 formed on both surfaces thereof, respectively. The ribs 54 formed on one side of each of the separators 30a and 30b form a fuel gas flow path 24P with the adjacent anode 22, and the rib 55 formed on the other side of the separator 30 is provided in the adjacent single cell. An oxidizing gas passage 25P is formed between the cathode 23 and the cathode 23. Accordingly, the separators 30a and 30b form a gas flow path between the gas diffusion electrodes and play a role of separating the flow of the fuel gas and the oxidizing gas between adjacent single cells. Thus, the separators 30a and 30b are not distinguished in terms of form or function in a fuel cell that is actually assembled, and are hereinafter collectively referred to as a separator 30.
[0041]
The ribs 54 and 55 formed on the surface of each separator may have any shape as long as a gas flow path is formed and fuel gas or oxidizing gas can be supplied to the gas diffusion electrode. In the present embodiment, the ribs 54 and 55 formed on the surface of each separator have a plurality of groove-like structures formed in parallel. In FIG. 3, in order to schematically represent the configuration of the single cell 28, the fuel gas flow path 24P and the oxidizing gas flow path 25P are shown in parallel, but in the separator 30 actually used when assembling the fuel cell, The ribs 54 and 55 were formed on both surfaces of the separator 30 so that the ribs 54 and the ribs 55 would be orthogonal to each other.
[0042]
Here, the electrolyte membrane 21 is a proton conductive ion exchange membrane formed of a solid polymer material such as a fluorine resin, and exhibits good electrical conductivity in a wet state. In this example, a Nafion membrane (manufactured by DuPont) was used. On the surface of the electrolyte membrane 21, platinum as a catalyst or an alloy made of platinum and another metal is applied. As a method of applying the catalyst, carbon powder carrying platinum or an alloy made of platinum and other metals is prepared, and the carbon powder carrying the catalyst is dispersed in a suitable organic solvent, and an electrolyte solution (for example, Aldrich Chemical) is used. An appropriate amount of Nafion Solution) was added to form a paste and screen printed on the electrolyte membrane 21. Or the structure which forms the sheet | seat containing the carbon powder which carry | supported the said catalyst into a film, produces a sheet | seat, and presses this sheet | seat on the electrolyte membrane 21 is also suitable.
[0043]
Both the anode 22 and the cathode 23 are formed of carbon cloth woven with yarns made of carbon fibers. In the present embodiment, the anode 22 and the cathode 23 are formed of carbon cloth, but a configuration in which the anode 22 and the cathode 23 are formed of carbon paper or carbon felt made of carbon fiber is also suitable.
[0044]
The separator 30 is formed of molded carbon obtained by compressing a carbon material. Four hole structures are provided in the periphery of the separator 30. The fuel gas holes 50 and 51 communicate with the rib 54 forming the fuel gas flow path 34P, and the oxidation gas holes 52 and 53 communicate with the rib 55 forming the oxidation gas flow path 35P. When the fuel cell is assembled, the fuel gas holes 50 and 51 provided in each separator 30 form a fuel gas supply manifold 56 and a fuel gas discharge manifold 57 that penetrate the inside of the fuel cell in the stacking direction. Further, the oxidizing gas holes 52 and 53 provided in each separator 30 form an oxidizing gas supply manifold 58 and an oxidizing gas discharge manifold 59 that penetrate the inside of the fuel cell in the stacking direction.
[0045]
When assembling a fuel cell including the above-described members, the separator 30, anode 22, electrolyte membrane 21, cathode 23, and separator 30 are sequentially stacked in order, and current collecting plates 36 and 37, insulating plates 38, 39, end plates 40 and 41 are arranged to complete the stack structure 14 shown in FIG. The current collector plates 36 and 37 are provided with output terminals 36A and 37A, respectively, so that the electromotive force generated in the fuel cell can be output.
[0046]
The stacking order of the respective members when configuring the stack structure 14 is as described above, but a predetermined seal member is provided in the peripheral portion of the electrolyte membrane 21 in a region in contact with the separator 30. The seal member plays a role of preventing the fuel gas and the oxidizing gas from leaking from the inside of each single cell and preventing the fuel gas and the oxidizing gas from being mixed in the stack structure 14.
[0047]
The end plate 40 has two hole structures as shown in FIG. One is a fuel gas hole 42 and the other is an oxidizing gas hole 44. The insulating plate 38 and the current collecting plate 36 adjacent to the end plate 40 form two similar hole structures at positions corresponding to the two hole structures provided in the end plate 40. The fuel gas hole 42 opens at the center of the fuel gas hole 50 provided in the separator 30. When the fuel cell is operated, the fuel gas hole 42 and a fuel supply device (not shown) are connected, and hydrogen-rich fuel gas is supplied into the fuel cell. Similarly, the oxidizing gas hole 44 is formed at a position corresponding to the central portion of the oxidizing gas hole 52 provided in the separator 30. When the fuel cell is operated, the oxidant gas hole 44 is connected to an oxidant gas supply device (not shown), and an oxidant gas containing oxygen is supplied into the fuel cell. Here, the fuel gas supply device and the oxidizing gas supply device are devices that supply a fuel cell by humidifying and pressurizing a predetermined amount of each gas.
[0048]
Further, the end plate 41 has two hole structures at positions different from the end plate 40. The insulating plate 39 and the current collecting plate 37 also form two hole structures at the same positions as the end plate 41. One fuel gas hole 43 of the hole structure provided in the end plate 41 opens at a position corresponding to the central portion of the fuel gas hole 51 provided in the separator 30. The oxidizing gas hole 45, which is another hole structure, opens at a position corresponding to the central portion of the oxidizing gas hole 53 provided in the separator 30. When the fuel cell is operated, a fuel gas discharge device (not shown) is connected to the fuel gas hole 43, and an oxidizing gas discharge device (not shown) is connected to the oxidation gas hole 45.
[0049]
The stack structure 14 composed of each member described above is held in a state where a predetermined pressing force is applied in the stacking direction, and the fuel cell is completed. The configuration for pressing the stack structure 14 is not shown because it does not directly correspond to the main part of the present invention. In order to hold the stack structure 14 while pressing, the stack structure 14 may be tightened using bolts and nuts, or a stack storage member having a predetermined shape is prepared, and the stack structure 14 is stacked inside the stack storage member. The structure 14 may be stored and the both ends of the stack storage member may be bent to apply a pressing force to the stack structure 14.
[0050]
  Next, the flow of the fuel gas and the oxidizing gas in the fuel cell having the above configuration will be described. The fuel gas is introduced into the fuel cell from the predetermined fuel gas supply device described above through the fuel gas hole 42 formed in the end plate 40. Inside the fuel cell, the fuel gas is supplied to the fuel gas flow path 24P included in each single cell 28 via the fuel gas supply manifold 56, andanodeIt is subjected to an electrochemical reaction that proceeds on the side. The fuel gas discharged from the fuel gas flow path 24P gathers in the fuel gas discharge manifold 57 and reaches the fuel gas hole 43 of the end plate 41, and is discharged from the fuel gas hole 43 to the outside of the fuel cell. Guided to the fuel gas discharge device.
[0051]
  Similarly, the oxidizing gas is introduced from the predetermined oxidizing gas supply device described above into the fuel cell through the oxidizing gas hole 44 formed in the end plate 40. Inside the fuel cell, the oxidizing gas is supplied to the oxidizing gas flow path 25P included in each single cell 28 via the oxidizing gas supply manifold 58, andCathodeIt is subjected to an electrochemical reaction that proceeds on the side. The oxidizing gas discharged from the oxidizing gas flow path 25P gathers in the oxidizing gas discharge manifold 59, reaches the oxidizing gas hole 45 of the end plate 41, and is discharged from the oxidizing gas hole 45 to the predetermined oxidizing gas discharge device. .
[0052]
Next, the manufacturing method of the separator 30 corresponding to the principal part of this invention is demonstrated. FIG. 1 is an explanatory view showing a manufacturing process of the separator 30 of this embodiment, and FIG. 2 is an explanatory view showing a state of press molding in the process shown in FIG. The manufacturing process of the separator 30 shown in FIG. 1 is to form by heating press using raw material powder obtained by adding a binder to carbon powder. However, the amount of binder added to the raw material powder is small, It is characterized by further comprising a step of impregnating the press-molded member with an impregnating agent after the step.
[0053]
First, before explaining the manufacturing method of the separator 30, the necessary theoretical binder amount serving as a reference for the amount of binder added to the raw fuel powder will be explained. FIG. 6 is an explanatory diagram showing the relationship between the molding pressure and the green compact bulk density. In FIG. 6, the horizontal axis represents the pressure applied to the raw material powder during pressing for molding. The vertical axis represents the bulk density of the green compact. This is the result of pressing the carbon powder only with the pressure shown on the horizontal axis without adding a binder, the theoretical density of the resulting member, and the density of the carbon crystal. 100 is a relative value. Such a value of the theoretical density can be obtained by comparing the density obtained from the volume and weight of the member formed by press-molding only the powder with the density of the carbon crystal. The graph of FIG. 6 was prepared by measuring the green compact density at five different points with respect to the pressure during press molding.
[0054]
When carbon powder is press-molded in this way, the carbon particles in the carbon powder are pressure-bonded to each other. With this, in the member obtained by press molding, a void having a size corresponding to the pressure at the time of pressing is each carbon particle. Formed between. The size of the gap decreases as the pressure during pressing increases. Therefore, the higher the pressure during pressing, the higher the density of the member obtained by press molding, and the air tightness (gas impermeability) of this member is improved.
[0055]
  The theoretically required binder amount is given in parentheses at the five points measured in FIG. This theoretically required binder amount is the amount of voids (parts obtained by pressure molding) in each member made by press-molding only carbon powder from the theoretical density obtained as described above.MaterialThe total amount of voids formed between each particle of the carbon powder is calculated, and the weight of the binder necessary to fill the voids with a binder described later is expressed as a percentage of the weight of the carbon powder. It is. When a molded carbon member is produced by hot press molding with a binder added to the carbon powder, ideally, a molded carbon member having no voids can be produced by adding a binder corresponding to the theoretically required binder amount. It will be. Conventionally, when heat press molding is actually performed, pressure unevenness occurs in the press surface depending on the shape of the mold used for press molding, etc., so that molded carbon with sufficiently closed gaps is obtained. For this reason, an amount of the binder exceeding the theoretically required amount of binder is added to the carbon powder to perform press molding.
[0056]
Next, the manufacturing method of the separator 30 is demonstrated based on FIG. In order to manufacture the separator 30, first, raw material powder is prepared (step S100). The raw material powder was prepared by uniformly mixing a flaky natural graphite powder as a carbon powder and a binder diluted with methyl ethyl ketone (MEK) as an organic solvent to form a slurry, which was dried and then pulverized. . Here, a thermosetting resin and a curing accelerator are used as the binder, and the amount of the binder to be added is determined corresponding to the molding pressure based on FIG. 6 at the molding pressure selected in the hot press molding process described later. The amount was less than the theoretical binder amount.
[0057]
The amount of binder added to the carbon powder at the time of preparing the raw material powder in step S100 is smaller than the theoretical binder amount as described above, and when the thermosetting resin constituting the binder is once softened by heating performed together with press molding. In addition, the amount is determined such that the binder is sufficiently spread between the carbon powders and the strength of the member obtained by press molding is ensured to a minimum. The strength of the member obtained by press molding needs to be able to sufficiently withstand the subsequent steps (treatment of impregnating the impregnating agent).
[0058]
Furthermore, the amount of the binder added to such carbon powder also affects the time required for thermosetting the thermosetting resin during hot press molding. As the amount of the binder added to the carbon powder increases, the time required for thermosetting the thermosetting resin constituting the binder becomes longer, so the time required for hot press molding becomes longer. The time required will also be longer. In addition, when the amount of the binder added to the carbon powder increases, the binder softened by heating oozes out on the surface of the member formed by press molding during the hot press molding, and as a result, partially on the separator surface produced as a result. A binder layer is formed. Further, when the amount of binder added to the carbon powder is large, in the hot press molding process, in the mold for press molding, the softened binder enters between the members constituting the mold, and the press molded member A “burr” is formed. When such “burrs” occur, a process of removing these “burrs” after press molding is required. In addition, since the binder has a predetermined adhesiveness, the amount of the binder is large, and when the binder oozes out on the surface of the member formed by press molding, the binder is removed from the press molding die. Release properties will deteriorate.
[0059]
Considering the above-mentioned disadvantages that may occur when the binder amount is increased, the binder amount added to the carbon powder is preferably 50 to 80% of the theoretical binder amount obtained from FIG. In this embodiment, the amount of the binder is such that the surface pressure during molding is 0.5 ton / cm.²The amount of binder required (10% of carbon powder) was 60% (6% of carbon powder).
[0060]
The thermosetting resin is a resin that undergoes a thermosetting reaction when heated to a predetermined temperature, gives a predetermined hardness to the separator 30 mainly composed of carbon powder, and binds the carbon powder to each other. Play the role of wearing. As the thermosetting resin that can be used as the binder, a thermosetting reaction may be caused at the time of heating as long as it is stable with respect to the operating temperature of the fuel cell and each component of the gas supplied to the fuel cell. For example, a phenol resin, an epoxy resin, a urea resin, a melamine resin, an unsaturated polyester resin, an alkyd resin, or the like can be used. In order to achieve sufficient binding and strength in the separator 30, a plurality of the thermosetting resins may be selected and used in combination. In this example, a cresol novolac type epoxy resin having an epoxy equivalent of 214 gram equivalent and a novolac type epoxy resin having an OH equivalent of 103 gram equivalent are used as the thermosetting resin, and further, an epoxy resin curing accelerator is used. The imidazole compound was added at a ratio of 0.5% with respect to the epoxy resin. The binder having such a configuration was diluted with an organic solvent (MEK) and added in the above-described ratio with respect to the carbon powder.
[0061]
In step S100, the slurry prepared by mixing the carbon powder and the binder was dried and then pulverized to prepare the raw material powder. However, drying and granulation may be performed simultaneously using a spray dryer or the like. Good. In addition, if the raw material powder can be mixed uniformly, instead of the above-described wet kneading, dry kneading in which the raw material powder is mixed without using a solvent at a temperature that does not cure the resin (room temperature to about 100 ° C.). You may do it.
[0062]
Here, at the time of adjusting the raw materials described above, the materials used were powders, but these materials only have to be in a shape that can be mixed uniformly to an acceptable level by the above-described wet kneading or dry kneading. . In order to mix with sufficient uniformity, the raw material is preferably composed of particles of about 1 to 300 μm.
[0063]
The raw material powder thus prepared is put into a mold having a predetermined shape (step S110). FIG. 2A schematically shows a state in which the raw fuel powder is put into the mold 60. The mold 60 has an uneven shape on the inner surface that enables the separator 30 having the shape shown in FIG. 4 to be formed by press-molding the raw fuel powder using the mold 60. Here, the surface pressure is 0.5 ton / cm.²By pressing at 180 ° C., a separator member having the same shape as the separator 30 shown in FIG. 4 is obtained (step S120). The surface pressure at the time of pressing may be a different value as long as the manufactured separator 30 has sufficient strength, and the binder amount described above may be appropriately adjusted according to the selected surface pressure. As described above, the amount of the binder that the separator member obtained in step S120 has is less than the theoretically required amount of binder (6% of the carbon powder in this embodiment). The density is about 92%, and the gas impermeability is insufficient.
[0064]
During the press molding in step S120, the mold is heated at 180 ° C., so that the thermosetting resin constituting the binder is dissolved and a thermosetting reaction occurs, and at the same time as the press molding, a predetermined strength is given to the separator member. be able to. Here, the heating temperature at the time of press molding should just be the conditions which the above-mentioned resin melt | dissolution and thermosetting reaction occur, for example, determines suitably in the range of 1 to 30 minutes in the temperature range of 140-220 degreeC. be able to. Alternatively, after the press molding is performed in a temperature range (80 to 100 ° C.) in which the thermosetting resin dissolves but does not cause a thermosetting reaction, the molded separator member is placed in a predetermined heating furnace at 140 to 220 ° C. for 30. Thermosetting of the thermosetting resin may be performed by heating for ~ 600 minutes. In this case, by dissolving the thermosetting resin at the time of press molding, the thermosetting resin can be spread between the carbon powders to obtain sufficient binding properties. In addition, it is not necessary to complete the thermosetting reaction at the time of pressing, so the time of the pressing process can be shortened, and the thermosetting reaction can be performed collectively later, which is advantageous when manufacturing a large amount of separators. It becomes. The heating for the thermosetting reaction may be performed within a temperature range and a heating time in which the selected thermosetting resin can be thermoset and the constituent materials such as the thermosetting resin are not deteriorated.
[0065]
When performing the above-described press molding, if the air in the mold is taken into the raw material powder and the press is performed, the air remains in the molded separator member and bubbles are formed in the separator member. Sometimes. The separator member is provided with sufficient gas impermeability by the impregnating step described later, but in order to prevent the formation of undesired bubbles locally, A configuration may be adopted in which the air is exhausted to 10 torr or less to prevent air from remaining in the separator member.
[0066]
Since the separator member obtained in the hot press molding step of step S130 is insufficient in gas impermeability as described above, the separator member is then impregnated with an impregnating agent to constitute the separator member. The gap between the carbon powders is closed with this impregnating agent, and sufficient gas impermeability is imparted to the separator member (step S130). In this step S130, as the impregnating agent, it can be easily washed off from the surface of the separator member in a cleaning process described later, and can be thermally cured in a drying process described later, thereby imparting a predetermined hydrophilicity to the separator. (The separator impregnated with the impregnating agent uses a thermosetting resin that exhibits hydrophilicity with a contact angle of 40 ° C. or lower). For example, an organic resin obtained by copolymerizing an acrylic resin as a main component and further an epoxy resin and an ester resin, a silicate-based composite inorganic polymer (silicon resin), or the like can be used. The separator member is immersed in an impregnation tank filled with these impregnation agents under vacuum (under a reduced pressure of 20 torr or less), followed by pressure impregnation (pressure of 5 atm or more).
[0067]
Next, the separator member impregnated with the impregnating agent is washed with warm water to wash away the impregnating agent adhering to the surface of the separator member (step S140). Further, the separator member whose surface has been cleaned is dried at 100 to 150 ° C., and the thermosetting resin as the impregnating agent is thermoset (step S150), thereby completing the separator 30 having sufficient gas impermeability. .
[0068]
FIG. 7 shows the result of assembling the fuel cell using the separator 30 manufactured as described above and examining the current-voltage characteristics thereof. In FIG. 7, as a comparative example, current-voltage characteristics in a fuel cell each using a graphitized carbon produced according to a conventionally known technique and a separator made of molded carbon produced according to a conventionally known technique are also shown. Here, a separator made of graphitized carbon produced according to a conventionally known technique is a product obtained by kneading and molding carbon powder and a phenolic resin, followed by graphitization and machining to obtain a predetermined shape. The resin is impregnated to ensure gas impermeability. In addition, a separator made of molded carbon produced according to a conventionally known technique is produced by adding a sufficient amount of a binder made of a thermosetting resin to carbon powder and kneading, followed by hot press molding. That is, when hot press molding is performed under the same conditions as in the above embodiment, the amount exceeds the theoretical binder amount (10% of the carbon powder amount) necessary to fill the voids of the formed carbon (specifically, the carbon powder amount). 14%) of the separator.
[0069]
As shown in FIG. 7, the fuel cell assembled using the separator 30 of the present example exhibits substantially the same current-voltage characteristics as a fuel cell assembled using a conventionally known separator made of graphitized carbon. The battery characteristics are superior to those of a fuel cell assembled using a conventionally known separator made of molded carbon. That is, even when the output current value is increased, a sufficiently high output voltage can be maintained. Here, the battery characteristics of a fuel cell assembled using a separator made of conventionally known molded carbon are inferior because the binder melted by heating on the surface of the molded separator is stained when molded by a hot press. This is because a binder layer is formed on the separator surface. Since a binder made of thermosetting resin is not conductive, when a fuel cell is assembled using such a separator, the internal resistance of the fuel cell increases and a sufficient output voltage is secured when the output current value is large. Difficult to do.
[0070]
According to the separator manufacturing method of the present embodiment described above, since the separator member is produced by hot press molding without performing the firing step, the machining step for cutting out a predetermined shape from the fired body Becomes unnecessary, the manufacturing process can be simplified and the manufacturing cost can be reduced. In addition, since the separator member is impregnated with the impregnating agent after the hot press molding step, a separator with sufficient gas impermeability and sufficient strength can be manufactured.
[0071]
Further, in the separator manufacturing method of this example, the amount of binder added to the raw material used for hot press molding is the binder that is theoretically required to completely close the voids formed between the carbon particles by press molding. Since it is less than the amount, the following effects are obtained. First, the time required for thermosetting the thermosetting resin constituting the binder can be shortened, and the time for hot press molding can be shortened. Second, since no excessive binder is interposed between the carbon powders constituting the separator, the conductivity of the separator can be sufficiently ensured. If the amount of binder that exceeds the theoretical binder amount described above is added to the carbon powder and subjected to hot press molding, an excessive amount of binder will form a binder layer between the carbon powders, and the carbon powders will not contact each other and become conductive. May be impaired. As described above, when the amount of the binder is small, press molding is performed in a state where the carbon powders are sufficiently in contact with each other, so that good conductivity can be ensured.
[0072]
Third, since excessive binder does not ooze out on the surface of the separator member during hot press molding, the internal resistance of the fuel cell increases when a fuel cell is assembled using such a separator. Thus, a fuel cell exhibiting sufficient current-voltage characteristics can be obtained. When carbon powder mixed with a binder exceeding the theoretical binder amount is hot-press molded as in the past, a binder layer may be formed on the separator surface, and a fuel cell incorporating such a separator Then, the internal resistance of the fuel cell increases and the cell performance decreases. In order to avoid such a situation, it was necessary to further add a step of scraping off the binder layer that oozes out on the surface of the separator in the manufacturing process of the separator.
[0073]
Further, in the separator manufacturing method of the present embodiment, as the impregnating agent impregnated into the separator member manufactured by hot press molding, a resin that can be easily washed away by hot water cleaning is used. It is possible to easily suppress an increase in contact resistance that occurs when the separators are stacked. Since the layer of the impregnating agent formed on the separator surface can be easily washed away by warm water washing, it is not necessary to perform a complicated mechanical treatment such as scraping the surface of the separator.
[0074]
  Moreover, in the manufacturing method of the separator of a present Example, since hydrophilic resin was used as the impregnating agent which impregnates the separator member manufactured by hot press molding, predetermined hydrophilicity can be provided to the manufactured separator. When a fuel cell is assembled using such a separator, drainage in the gas flow path in the fuel cell can be improved, and the gas flow path in the fuel cell is blocked by generated water generated by the cell reaction. It is possible to prevent the inconvenience of being generated. In the fuel cell, the electrochemical reaction shown in the above-described formulas (1) to (3) proceeds. At this time, as shown in the formula (2),CathodeProduct water is produced on the side. When the separator that forms the irregularities forming the gas flow path has a hydrophilic property, the generated water is guided and discharged to the wall surface of the gas flow channel having the hydrophilicity. Thus, it is possible to prevent the gas flow path from being blocked and blocked.
[0075]
In the first embodiment, the carbon powder used as the raw material of the separator 30 is a scaly natural graphite powder, but other types of carbon powder may be used. In addition to the scale-like natural graphite powder, for example, carbon black, thermally expanded graphite, or the like can be used, and may be appropriately selected in consideration of conditions such as cost.
[0076]
In the first embodiment, carbon powder was used as a raw material for the separator, and a separator was manufactured by impregnating a separator member obtained by adding a binder to the carbon powder and hot press molding. The same manufacturing method can be applied to the case where a metal material is used. Usually, when a separator is manufactured from a metal material, a method of cutting a member having a predetermined shape from a metal block is used. However, the metal powder is used as a raw material and the metal powder is press-molded to form the first embodiment. Similarly, a separator member can be produced, and the separator member can be further impregnated with an impregnating agent to produce a separator. Such a method will be described below as a second embodiment.
[0077]
FIG. 8 is an explanatory view showing a manufacturing process of the separator 130 of the second embodiment. The separator 130 has the same shape as the separator 30 of the first embodiment and is used by being incorporated in the fuel cell described above, but is characterized by using metal powder as a raw material. In order to manufacture the separator 130, first, raw material powder is prepared (step S200). In the second example, a metal powder obtained by tin-plating each titanium particle of a titanium powder was prepared as a raw material powder. In the metal powder used as the raw material powder, the powder base material may be any metal that is stable under the operating conditions (supplied gas and temperature) of the fuel cell. For example, titanium, nickel, chromium, stainless steel, etc. You can choose. When the separator is made of a metal instead of carbon, generally, the surface of the metal is further coated with a particularly stable metal for the purpose of imparting sufficient corrosion resistance to the separator. In this example, plating was applied to each particle of the metal powder used as the raw material powder. As the metal used for plating, for example, titanium, nickel, titanium nitride, chromium nitride, gold, carbon, tin, and the like can be used, and can be appropriately selected in consideration of durability and cost required for the fuel cell. Good. The particle size of the metal powder prepared in Step S200 was set to several tens of μm.
[0078]
The raw material powder thus prepared is put into a mold having a predetermined shape (step S210). The step of putting the raw material powder into the mold is the same as the step S210 shown in FIG. 1 in the first embodiment, and the used mold is the same as the mold 60 shown in FIG. It is a mold. When raw fuel powder is put into a mold having a predetermined shape and then pressed at a predetermined surface pressure, a metal separator member having the same shape as the separator 30 shown in FIG. 4 is obtained (step S220). . The surface pressure at the time of pressing is set as a pressure at which the separator 130 finally manufactured from the separator member obtained by press molding has sufficient strength. The temperature at the time of press molding may be room temperature, but it may be heated to about 100 ° C. to improve the fluidity of the raw material powder. In this example, 0.5 ton / cm²Then, press molding was performed at 80 ° C.
[0079]
Next, the separator member obtained by the press molding in step S220 is sintered (step S225). By performing the sintering process, the conductivity and strength of the separator member are improved. If the separator member not subjected to the sintering process has sufficient conductivity and strength as a separator to be incorporated into the fuel cell, the step S225 may be omitted. The separator member sintered in step S225 has a porosity (ratio of the total amount of voids formed therein to the separator member volume) of about 20%, and the gas impermeability is insufficient as a separator. It is in a state.
[0080]
Since the separator member obtained in the press molding step of step S225 has insufficient gas impermeability as described above, the separator member is then impregnated with an impregnating agent as in the first embodiment. Thus, the gap between the carbon powders constituting the separator member is closed with this impregnating agent, and sufficient gas impermeability is imparted to the separator member. Steps S230 to S250 in which the separator member is impregnated with the impregnating agent, the surface of the separator is cleaned, and the impregnating agent is dried and cured are the steps from step S130 described in the first embodiment based on FIG. Since the process is the same as that up to S150, detailed description is omitted. The same process as step S130 to step S150 is performed to close the voids in the separator member with the impregnating agent, thereby completing the separator 130 having sufficient gas impermeability.
[0081]
FIG. 7 shows the result of assembling the fuel cell using the separator 130 of the second embodiment manufactured as described above and examining the current-voltage characteristics together with the result of the first embodiment. As shown in FIG. 7, the fuel cell assembled using the separator 130 of the second example showed sufficient battery characteristics superior to the fuel cell assembled using the conventionally known separator made of molded carbon. . That is, even when the output current value is increased, a sufficiently high output voltage can be maintained.
[0082]
According to the separator manufacturing method of the second embodiment described above, the following effects can be obtained in the same manner as the separator manufacturing method of the first embodiment. That is, since the separator member is produced by press molding, a machining process for cutting out a predetermined shape is not necessary, and the manufacturing process can be simplified and the manufacturing cost can be suppressed. Moreover, since the separator member is impregnated with the impregnating agent after the press molding step, a separator having sufficient gas impermeability can be manufactured. Furthermore, as the impregnating agent to be impregnated into the separator member, a resin that can be easily washed away by hot water washing is used, so that a contact resistance generated when the separators are stacked increases by a simple operation of hot water washing. Can be easily suppressed. Since the layer of the impregnating agent formed on the separator surface can be easily washed away by warm water washing, it is not necessary to perform a complicated mechanical treatment such as scraping the surface of the separator. Moreover, since the impregnating agent impregnated in the separator member is a hydrophilic resin, a predetermined hydrophilicity can be imparted to the manufactured separator. Therefore, when a fuel cell is assembled using such a separator, drainage performance in the gas flow path in the fuel cell can be improved, and the gas flow path in the fuel cell is blocked by generated water generated by the cell reaction. It is possible to prevent the inconvenience of peeling off.
[0083]
  Furthermore, according to the separator manufacturing method of the second embodiment, the raw material made of metal powderTheSince it is formed by pressing, it has the advantage that the degree of freedom in shape when manufacturing a metal separator is higher than when a member having a predetermined shape is cut out from a metal block. Therefore, in addition to simplifying the manufacturing process compared to the case of cutting out by machining, the uneven shape provided on the separator surface to form the gas flow path in the fuel cell should be designed to have a more free shape. Is possible. In addition, by press-molding the metal powder, voids are generated between the metal powders in the separator, so that the weight of the separator is reduced compared to a metal separator manufactured by cutting a predetermined shape from a metal block. Therefore, the weight of the whole fuel cell assembled using the separator can be reduced, and this is particularly advantageous when manufacturing a fuel cell used as a power source for movement.
[0084]
Moreover, since the raw material of the separator 130 is plated with individual metal powders, there is an effect that the corrosion resistance of the entire separator can be improved. That is, even if a part of the surface layer of the separator is damaged due to deterioration over time or external force applied to the separator during operation of the fuel cell, the individual particles in the metal powder constituting the separator are plated. Therefore, the corrosion resistance does not deteriorate. In contrast, in a separator manufactured by cutting out a member of a predetermined shape from a metal block, the surface is usually plated to improve corrosion resistance. In such a case, plating is applied only to the surface of the separator. Since the layer is formed, it is difficult to realize sufficient corrosion resistance. That is, if a part of the surface plating layer is damaged due to the above-described deterioration or external force, the effect of protecting the inside of the separator is lost, and the corrosion resistance of the separator is lowered.
[0085]
In the embodiment described above, the fuel cell including the separator 30 and the separator 130 is a solid polymer fuel cell. However, if the manufactured separator can withstand the use environment of the fuel cell, the separator according to the present invention is used. It may be applied to other types of fuel cells.
[0086]
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a manufacturing process of a separator 30 according to a first embodiment.
FIG. 2 is an explanatory view showing a state in which a separator 30 is manufactured by pressure molding.
3 is a schematic cross-sectional view showing the configuration of a single cell 28. FIG.
FIG. 4 is an exploded perspective view showing a configuration of a fuel cell.
FIG. 5 is a perspective view showing an appearance of a stack structure 14 in which single cells 28 are stacked.
FIG. 6 is an explanatory diagram showing the relationship between molding pressure and green compact bulk density.
7 is an explanatory diagram showing current-voltage characteristics of a fuel cell assembled using a separator 30. FIG.
FIG. 8 is an explanatory view showing a manufacturing process of the separator 130 of the second embodiment.
[Explanation of symbols]
14 ... Stack structure
21 ... electrolyte membrane
22 ... Anode
23 ... Cathode
30a, 30b ... separator
24P ... Fuel gas flow path
25P ... Oxidizing gas flow path
28 ... Single cell
30 ... Separator
34P ... Fuel gas flow path
35P ... oxidizing gas flow path
36, 37 ... current collector
36A, 37A ... Output terminal
38, 39 ... Insulating plate
40, 41 ... End plate
42 ... Fuel gas hole
43 ... Fuel gas hole
44 ... Oxidizing gas hole
45 ... Oxidizing gas hole
50, 51 ... Fuel gas hole
52, 53 ... oxidizing gas hole
54, 55 ... ribs
56 ... Fuel gas supply manifold
57 ... Fuel gas discharge manifold
58 ... Oxidizing gas supply manifold
59 ... Oxidizing gas discharge manifold
60 ... Mold
130 ... Separator

Claims (4)

A method for producing a separator for a fuel cell, comprising:
(A) A step of forming a separator member having a predetermined shape by pressure-molding a raw material made of powder containing at least carbon in a predetermined mold;
(B) The separator member formed in the step (a) is impregnated with a predetermined impregnating agent, and the gap formed between the powders constituting the raw material in the separator member is closed with the impregnating agent. and a step,
Assuming that the powder to be subjected to the pressure molding is obtained by pressure-molding a powder made of carbon under the pressure during the pressure molding, a carbon member is obtained between the carbon powders in the carbon member. Manufacture of a separator, which is a powder obtained by further adding to the carbon powder a binder less than the theoretical amount required to close the formed gap, and obtaining a fuel cell separator without firing from the separator member Method. A method of manufacturing a separator for fuel cell according to claim 1 Symbol placement,
( C ) A method for producing a fuel cell separator, further comprising the step of washing the separator member impregnated with a predetermined impregnating agent in the step (b) and washing away the impregnating agent adhering to the surface of the separator member. The method for producing a fuel cell separator according to claim 2 , wherein the impregnating agent is a water-soluble thermosetting resin containing an acrylic resin as a main component and further copolymerizing an epoxy resin and an ester. A method for producing a fuel cell separator according to any one of claims 1 to 3 ,
The predetermined impregnating agent used in the step (a) contains a hydrophilic substance. A method for producing a separator for a fuel cell.

Images