JP2021026994A - Manufacturing method of gas diffusion composite layer for fuel battery - Google Patents

Abstract

To provide a manufacturing method of a gas diffusion composite layer for a fuel battery, capable of achieving high rigidity, high gas diffusion property, and drainage at the same time, and increasing power generation performance of the fuel battery.SOLUTION: A manufacturing method of a gas diffusion composite layer for a fuel battery including a porous gas diffusion layer and a fine porous layer, comprises: a step of manufacturing the porous gas diffusion layer by burning and sintering a molding body obtained by molding a mixture which contains a metal material particle that includes at least one metal element selected from a group consisting of titanium, gold, silver, copper, platinum, tin, iron, and aluminum, and in which a mean particle diameter is 10 μm or more and 150 μm or less, and a foam material; and a step of forming the fine porous layer coating at least one part of a front surface of the porous gas diffusion layer while filling at least one part of fine holes of the porous gas diffusion layer by using a fine porous layer formation material containing a carbon material.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a method for producing a gas diffusion composite layer for a fuel cell.

A fuel cell usually has a basic structure of a membrane electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes, and a plurality of single cells having a structure in which the membrane electrode assembly is sandwiched between a pair of separators having a gas flow path are laminated. It is composed of.
Each electrode generally has a structure in which a catalyst layer and a gas diffusion layer are laminated in this order from the electrolyte membrane side, and the surface of the separator on the side having the gas flow path is brought into contact with the gas diffusion layer. It is arranged.

The gas diffusible electrode base material (GDL) for fuel cells has high gas diffusivity for diffusing the gas supplied from the separator into the catalyst layer, and discharges water generated by the electrochemical reaction to the separator. It is necessary to have high drainage property and high conductivity to take out the generated current. Therefore, a gas diffusion composite layer in which a carbon sheet made of carbon fibers or the like is used as a gas diffusion electrode base material of the gas diffusion composite layer and a microporous layer (MPL) is formed on the surface thereof is widely used (for example, FIG. 9). reference).
In FIG. 9, reference numeral 50 indicates a gas diffusion composite layer, reference numeral 51 indicates a gas diffusing electrode base material made of carbon fiber, reference numeral 52 indicates a microporous layer, and reference numeral 53 indicates a groove-like flow path. There is. A part of the large pores of the gas diffusible electrode base material 51 is filled with a microporous layer 52 having small pores. In the gas diffusion composite layer 50, the gas supplied from the separator is diffused and the water generated by the electrochemical reaction is discharged mainly through the large holes of the gas diffusible electrode base material 51.

Patent Document 1 states that a gas diffusing electrode substrate having at least a porous carbon sheet containing carbon fibers and at least a microporous layer containing a conductive filler has a gas diffusing property of 31.0 to 35.5%. When the gas diffusion electrode base material is divided into a small hole portion and a large hole portion in the thickness direction, the thickness of the large pore portion is made smaller than 3 μm, so that the generated water formed in the large pore portion is formed. An example of a gas diffusion electrode base material in which an increase in the droplet size of the gas is suppressed and a decrease in drainage property and gas diffusibility is suppressed to suppress a decrease in power generation performance is disclosed.

For example, the gas diffusing electrode base material made of carbon fiber as described in Patent Document 1 has an advantage that high drainage property can be obtained because of high in-plane air permeability, but has low rigidity, so that the gas is concerned. When the density of the diffusible electrode base material is reduced, the gas diffusion composite layer tends to bend into the flow path of the separator as the rigidity of the gas diffusible electrode base material decreases (see FIG. 9B). There is a problem that problems such as an increase in pressure loss in the flow path and crushing of the membrane electrode assembly are likely to occur.

On the other hand, Patent Document 2 discloses an example of a membrane electrode assembly including a porous metal gas diffusion layer and a catalyst layer in which pores are formed by chemically etching a metal material.
In Patent Document 2, the above-mentioned porous metal gas diffusion layer is used as the gas diffusion layer to improve the rigidity of the gas diffusion layer, and a fine porous layer is interposed between the porous metal gas diffusion layer and the catalyst layer. By constructing the fine porous layer so as to fill the pores of the porous metal gas diffusion layer and coat the surface of the porous metal gas diffusion layer, the catalyst layer and the porous metal gas diffusion layer are formed. We are trying to prevent water from staying at the interface with the layer and improve the gas diffusivity to the catalyst layer.

JP-A-2017-139219 Special Table 2017-510967

However, even with the membrane electrode assembly described in Patent Document 2, there is a problem that the drainage property and the gas diffusibility cannot be sufficiently enhanced, and the effect of improving the power generation performance cannot be sufficiently obtained.

In view of the above circumstances, the present disclosure manufactures a gas diffusion composite layer for a fuel cell, which can achieve both high rigidity, high gas diffusibility and drainage property, and can improve the power generation performance of the fuel cell. The purpose is to provide a method.

The method for producing a gas diffusion composite layer for a fuel cell according to the present disclosure is a method for producing a gas diffusion composite layer for a fuel cell including a porous gas diffusion layer and a fine porous layer, and is titanium, gold, and silver. Obtained by molding a mixture containing a metal material particle containing at least one metal element selected from the group consisting of copper, platinum, tin, iron and aluminum and having an average particle diameter of 10 μm or more and 150 μm or less, and a foaming agent. At least one of the pores of the porous gas diffusion layer is used in the step of calcining and sintering the molded body to prepare the porous gas diffusion layer and the material for forming a fine porous layer containing a carbon material. It is characterized by having a step of forming the fine porous layer which fills a portion and covers at least a part of the surface of the porous gas diffusion layer.

According to the present disclosure, there is provided a method for manufacturing a gas diffusion composite layer for a fuel cell, which can achieve both high rigidity, high gas diffusibility and drainage property, and can improve the power generation performance of the fuel cell. can do.

It is a flowchart for demonstrating an example of the process of manufacturing a porous gas diffusion layer in the manufacturing method of the gas diffusion composite layer for a fuel cell of this disclosure. FIG. 2A is a schematic cross-sectional view for explaining a state in which the gas diffusion composite layer produced by the method for producing the gas diffusion composite layer of the present disclosure is applied to a fuel cell, and FIG. 2B is a diagram. 2 (a) is an enlarged view showing a part of the gas diffusion composite layer. It is a figure which shows an example of the layer structure of the fuel cell to which the gas diffusion composite layer manufactured by the manufacturing method of this disclosure is applied, and is the figure which shows typically the cross section cut in the stacking direction. It is schematic cross-sectional view for demonstrating the layer structure of the gas diffusion composite layer (2) of Reference Experimental Example 1. It is schematic cross-sectional view for demonstrating the layer structure of the gas diffusion composite layer (5) of Reference Experimental Example 2. It is a figure which shows the measured value of the gas diffusion resistance of the gas diffusion composite layer (1)-(3). It is a figure which shows the measured value of the gas diffusion resistance of the gas diffusion composite layer (4)-(5). It is a figure which shows the measured value of the gas diffusion resistance of the gas diffusion composite layer (6)-(7). FIG. 9A is a schematic cross-sectional view for explaining a state in which a conventional gas diffusion composite layer having a gas diffusing electrode base material made of carbon fiber is applied to a fuel cell, and FIG. 9B is a schematic cross-sectional view. It is a figure which shows the part of the gas diffusion composite layer shown in FIG. 9A enlarged. 10 (a) is a schematic cross-sectional view for explaining a state in which the gas diffusion composite layer manufactured by the conventional manufacturing method is applied to the fuel cell, and FIG. 10 (b) is shown in FIG. 10 (a). It is a figure which shows the part of the gas diffusion composite layer enlarged.

The method for producing a gas diffusion composite layer for a fuel cell according to the present disclosure is a method for producing a gas diffusion composite layer for a fuel cell including a porous gas diffusion layer and a fine porous layer, and is titanium, gold, and silver. Obtained by molding a mixture containing a metal material particle containing at least one metal element selected from the group consisting of copper, platinum, tin, iron and aluminum and having an average particle diameter of 10 μm or more and 150 μm or less, and a foaming agent. At least one of the pores of the porous gas diffusion layer is used in the step of calcining and sintering the molded body to prepare the porous gas diffusion layer and the material for forming a fine porous layer containing a carbon material. It is characterized by having a step of forming the fine porous layer which fills a portion and covers at least a part of the surface of the porous gas diffusion layer.

First, the problem of the gas diffusion composite layer for a fuel cell manufactured by a conventional manufacturing method will be described, and then the manufacturing method of the gas diffusion composite layer for a fuel cell of the present disclosure will be described.

FIG. 10A is a schematic cross-sectional view for explaining a state in which a gas diffusion composite layer manufactured by a conventional manufacturing method is applied to a fuel cell. Specifically, FIG. 10A is a membrane electrode assembly described in Patent Document 2. It is a schematic diagram which shows the state which applied the body to a fuel cell. Further, FIG. 10B is an enlarged view of a part of the gas diffusion composite layer shown in FIG. 10A.

The membrane electrode assembly shown in FIG. 10 is interposed between a porous metal gas diffusion layer 61 having pores 611 formed by chemical etching of a metal material, and the porous metal gas diffusion layer 61 and a catalyst layer 63. It has a fine porous layer 62 provided. As described above, the fine porous layer 62 is formed so as to fill the pores 611 of the porous metal gas diffusion layer 61 and coat the surface of the porous metal gas diffusion layer 61.
In the membrane electrode assembly shown in FIG. 10, the composite layer of the porous metal gas diffusion layer 61 and the fine porous layer 62 corresponds to the gas diffusion composite layer manufactured by the production method of the present disclosure. Therefore, in the following description, the composite layer of the porous metal gas diffusion layer 61 and the fine porous layer 62 shown in FIG. 10 is referred to as a gas diffusion composite layer 60.
In the membrane electrode assembly shown in FIG. 10, through the pores 611 of the porous metal gas diffusion layer 61 formed by chemical etching, to the catalyst layer 63 of the gas supplied from the gas channel 64, which is the gas flow path of the bipolar plate. And drain the water generated in the catalyst layer 63 to the gas channel 64 (see FIGS. 10 (a) and 10 (b)).
The present researcher has found that the porous metal gas diffusion layer 61 shown in FIG. 10, which has pores 611 formed by chemically etching a metal material, is a porous gas diffusion layer 51 made of carbon fibers (see FIG. 9). Although higher rigidity can be obtained in comparison, the following phenomena (1) and (2) occur due to the bridge 612 existing between the pores 611, and the gas diffusibility to the catalyst layer 63 and the gas channel 64 It has been found that the fuel cell to which the gas diffusion composite layer 60 having the porous metal gas diffusion layer 61 has the problem that the drainage property of the fuel cell is not sufficiently improved in power generation performance.
The bridge 612 refers to a region between continuous pores 611 in the porous metal gas diffusion layer 61 formed by chemical etching of a metal material.
(1) The bridge 612 existing between the pores 611 closes a part or all of the opening 641 of each gas channel 64 from the gas channel 64 to the catalyst layer 63 via the gas diffusion composite layer 60. The gas flow path leading up to it is blocked, and the gas diffusibility is reduced (see FIG. 10B).
(2) The bridge 612 existing between the pores 611 closes a part or all of the opening 641 of each gas channel 64, so that the water generated in the catalyst layer 63 passes through the gas diffusion composite layer 60. The flow path leading to the gas channel 64 is blocked, and the drainage property is reduced (see FIG. 10B).

In addition, when the microporous layer 62 shown in FIG. 10 was formed, the present researcher permeated each pore 611 of the porous metal gas diffusion layer 61 with the material for forming the microporous layer, and the porous metal gas. The gas diffusion resistance of the porous metal gas diffusion layer 61 increases when all the pores 611 of the diffusion layer 61 are substantially completely filled with the fine porous layer 62 (see FIG. 10B). It has been found that a fuel cell to which the gas diffusion composite layer 60 having the porous metal gas diffusion layer 61 is applied cannot sufficiently improve the power generation performance.

In contrast to such a conventional manufacturing method, the method for manufacturing a gas diffusion composite layer for a fuel cell of the present disclosure can solve the above problem by having the following features.

The manufacturing process of the gas diffusion composite layer for a fuel cell of the present disclosure will be described with reference to FIGS. 1 and 2.
First, it contains metal material particles containing at least one metal element selected from the group consisting of titanium, gold, silver, copper, platinum, tin, iron and aluminum and having an average particle diameter of 10 μm or more and 150 μm or less, and a foaming agent. A porous gas diffusion layer preparation step is performed in which a molded product obtained by molding the mixture is fired and sintered to produce a porous gas diffusion layer (step I).
Next, a fine porous layer forming material containing a carbon material is used to fill at least a part of the pores of the porous gas diffusion layer and cover at least a part of the surface of the porous gas diffusion layer. A microporous layer forming step of forming a microporous layer is performed (step II).

(Step I)
First, a step of producing a porous gas diffusion layer (step I) will be described.
FIG. 1 is a flowchart for explaining an example of a process for producing a porous gas diffusion layer in the method for producing a gas diffusion composite layer for a fuel cell of the present disclosure. The porous gas diffusion layer preparation step (step I) can be performed, for example, by the steps (I-1) to (I-5) shown in FIG.

(Step (I-1))
First, a preparatory step is performed to prepare a mixture containing metal material particles and a foaming agent.

As the metal material particles, particles of a metal material containing at least one metal element selected from the group consisting of titanium, gold, silver, copper, platinum, tin, iron and aluminum are used. As the metal material containing iron, for example, SUS may be used.

The average particle size (D50) of the metal material particles is 10 μm or more and 150 μm or less.
When the average particle size (D50) of the metal material particles is 10 μm or more, it is possible to suppress a decrease in the porosity of the porous gas diffusion layer obtained after the sintering step (step (I-3)) described later. It is possible to suppress an increase in gas diffusion resistance in the porous gas diffusion layer after forming the fine porous layer on the surface of the porous gas diffusion layer.
Further, when the average particle diameter (D50) of the metal material particles is 150 μm or less, the porosity of the porous gas diffusion layer obtained after the sintering step (step (I-3)) described later becomes excessively high. It is possible to suppress a decrease in rigidity of the porous gas diffusion layer.
The average particle size (D50) of the metal material particles is preferably 20 μm or more and 80 μm or less.
The relationship between the porosity of the porous gas diffusion layer before the formation of the fine porous layer and the gas diffusion resistance of the porous gas diffusion layer after the formation of the fine porous layer is evaluated in Reference Experimental Example 3 described later. It will be described in detail in the item.

In the present disclosure, the average particle size of the metal material particles is a value measured by laser diffraction / scattering type particle size distribution measurement. Further, in the present disclosure, the median diameter (D50) is a diameter at which the cumulative volume of the metal material particles becomes half (50%) of the total volume when the particles are arranged in order from the particles having the smallest particle size.

Examples of the foaming agent include an inorganic foaming agent such as sodium hydrogen carbonate.

An aqueous binder such as polyvinyl alcohol may be mixed with the mixture containing the metal material particles and the foaming agent.

The blending ratio of the metal material particles, the foaming agent, and the water-based binder is appropriately adjusted according to the target porosity in the porous gas diffusion layer obtained after the sintering step (step (I-3)) described later. be able to.

(Step (I-2))
Next, the mixture obtained in step (I-1) is filled in a mold, molded into a desired shape and a desired thickness, the thickness of the molded product is made uniform, the surface is smoothed, and then the foaming agent is used. The foaming agent may be foamed by heating at a temperature close to the foaming temperature to obtain a foamed slurry.
In the production method of the present disclosure, a molded product obtained by filling a mold with the mixture obtained in step (I-1) and molding it into a desired shape and a desired thickness is brought into the vicinity of the foaming temperature of the foaming agent. The molded product may be fired and sintered in the sintering step (I-3) described later as it is without heating at the temperature of.

(Step (I-3))
Next, the foamed slurry produced in step (I-2) is dried, then fired and sintered at a temperature corresponding to the material of the metal material particles, and a porous gas diffusion layer which is a sintered metal porous body is obtained. Perform the sintering process to obtain.
Sintering of the foamed slurry can be performed in a vacuum atmosphere from the viewpoint of suppressing an increase in the electrical resistance of the porous gas diffusion layer due to the formation of an oxide layer on the surface of the obtained sintered metal porous body. preferable.

(Step (I-4))
Next, a cutting step of cutting the porous gas diffusion layer produced in the step (I-3) to a desired size is performed.
As a result, a porous gas diffusion layer having a desired size and thickness is obtained.
When a porous gas diffusion layer having a desired size is obtained in the step (I-3), the cutting step (step (I-4)) does not necessarily have to be performed.

(Step (I-5))
Next, an inspection step of inspecting whether or not the cut porous gas diffusion layer produced in the step (I-4) satisfies a desired physical property value is performed.
Items to be inspected include, for example, the porosity and flexural modulus of the porous gas diffusion layer shown below. The inspection step is an arbitrary step and does not necessarily have to be performed.

The thickness of the porous gas diffusion layer is preferably 30 μm or more and 300 μm or less, and more preferably 100 μm or more and 200 μm or less.
By setting the thickness of the porous gas diffusion layer to 30 μm or more, it is possible to suppress a decrease in the in-plane air permeability of the porous gas diffusion layer, and to make the power generation distribution uniform when the gas diffusion composite layer is applied to a fuel cell. The sex can be improved. Further, by setting the thickness of the porous gas diffusion layer to 30 μm or more, it is possible to suppress a decrease in rigidity of the porous gas diffusion layer. If the thickness of the porous gas diffusion layer is less than 30 μm, when the gas diffusion composite layer is applied to the fuel cell, the porous gas diffusion layer bends into the gas flow path, and the gas flow path is accompanied by this. There is a risk that the pressure loss will increase and the gas diffusion composite layer will collapse.
Further, by setting the thickness of the porous gas diffusion layer to 300 μm or less, the material for forming the fine porous layer permeates the entire area of the porous gas diffusion layer in the microporous layer forming step (step II) described later. In this case, it is possible to suppress an increase in the gas diffusion resistance of the porous gas diffusion layer after the formation of the fine porous layer, and to obtain high gas diffusivity in the gas diffusion composite layer having the porous gas diffusion layer. Obtainable.
The relationship between the thickness of the porous gas diffusion layer before the formation of the fine porous layer and the gas diffusion resistance of the porous gas diffusion layer after the formation of the fine porous layer is described in the evaluation item of Reference Experimental Example 2 described later. Will be described in detail in.
In the present disclosure, the in-plane air permeability of the porous gas diffusion layer is an evaluation index indicating the air permeability of the porous gas diffusion layer in the plane direction.

The porosity of the porous gas diffusion layer before forming the fine porous layer is preferably 60% or more and 90% or less, and more preferably 75% or more and 85% or less.
By setting the porosity of the porous gas diffusion layer before forming the fine porous layer to 60% or more, the material for forming the fine porous layer is the porous gas in the fine porous layer forming step (step II) described later. When it permeates the entire area of the diffusion layer, it is possible to suppress an increase in the gas diffusion resistance of the porous gas diffusion layer after the formation of the fine porous layer, and in the gas diffusion composite layer having the porous gas diffusion layer. , High gas diffusivity can be obtained.
On the other hand, by setting the porosity of the porous gas diffusion layer to 90% or less, it is possible to suppress a decrease in the rigidity of the porous gas diffusion layer.
The relationship between the porosity of the porous gas diffusion layer before the formation of the fine porous layer and the gas diffusion resistance of the porous gas diffusion layer after the formation of the fine porous layer is evaluated in Reference Experimental Example 3 described later. It will be described in detail in the item.

In the present disclosure, the "porosity" is a value obtained from the ratio of the theoretical volume calculated from the density of the material to the actual volume. The porosity can be measured by an immersion method, an exhaust gas volume method, a pressure comparison method, or the like.

The porosity of the porous gas diffusion layer before the formation of the fine porous layer is determined by, for example, the metal material particles, the foaming agent, and the aqueous binder when the mixture is prepared in the above-mentioned mixture preparation step (step (I-1)). It can be prepared in a desired range by adjusting the blending ratio of the above-mentioned compounding ratio or by controlling the foaming temperature and the foaming time in the foaming step (step (I-2)) described above.

The flexural modulus of the porous gas diffusion layer before the formation of the fine porous layer is preferably 15 GPa or more and 60 GPa or less, and more preferably 20 GPa or more and 50 GPa or less.
By setting the flexural modulus of the porous gas diffusion layer before forming the fine porous layer to 15 GPa or more, it is possible to suppress a decrease in rigidity of the porous gas diffusion layer. Therefore, in a fuel cell to which the gas diffusion composite layer is applied, the porous gas diffusion layer is bent into the gas flow path, the pressure loss in the gas flow path is increased due to this, and the gas diffusion composite layer is crushed. The phenomenon can be suppressed.
Further, by setting the flexural modulus of the porous gas diffusion layer before forming the fine porous layer to 60 GPa or less, the porosity of the porous gas diffusion layer can be adjusted to the above-mentioned desired range. ..
In the present disclosure, the flexural modulus is a value measured in accordance with JIS K7171.

(Step II)
In the microporous layer forming step (step II), for example, after applying a fine porous layer forming material containing a carbon material to at least a part of one main surface of the porous gas diffusion layer prepared in step I. , Can be done by drying and / or firing at a predetermined temperature.

The material for forming a fine porous layer includes a carbon material.
As the carbon material, at least one selected from the group consisting of carbon black (carbon powder), acetylene black, expanded graphite, and carbon fiber can be used.
As the material for forming the fine porous layer, in addition to the carbon material described above, a water-repellent resin such as polytetrafluoroethylene (hereinafter, may be referred to as “PTFE”), which is a surfactant for imparting hydrophilicity, is used. It is preferable to include it. Further, the material for forming the fine porous layer may further contain a dispersant or a thickener in order to uniformly disperse and stabilize the carbon material described above in the solvent.

The application of the material for forming a fine porous layer can be performed by using a doctor blade method or a screen printing method.

At least a part of the material for forming a fine porous layer applied to the surface of the porous gas diffusion layer may permeate into the pores of the porous gas diffusion layer. The material for forming the fine porous layer may be allowed to permeate a part of the porous gas diffusion layer, and from the viewpoint of suppressing water droplet formation in the porous gas diffusion layer, the entire porous gas diffusion layer may be used. It may be allowed to penetrate.

After the material for forming the fine porous layer is infiltrated into the porous gas diffusion layer, the surface of the porous gas diffusion layer is coated by further applying the material for forming the fine porous layer to the surface of the porous gas diffusion layer. It is possible to form a layer of a material for forming a fine porous layer.

By drying and / or firing the porous gas diffusion layer after applying the material for forming the fine porous layer as described above, a fine porous layer having a filling region and a surface covering portion described later is formed. be able to.
The ratio of the thickness of the porous gas diffusion layer to the thickness of the surface coating portion of the fine porous layer is not particularly limited, but may be in the range of 1: 4 to 4: 1.

According to the manufacturing method of the present disclosure, the surface of the porous gas diffusion layer which is a sintered metal porous body is filled with at least a part of the pores of the porous gas diffusion layer, and the porous gas diffusion layer is formed. By forming a fine porous layer that covers at least a part of the surface, it has high rigidity when applied to a fuel cell, and it is difficult for water to stay at the interface between the catalyst layer and the porous gas diffusion layer. Further, the gas supplied from the gas flow path is likely to diffuse into the catalyst layer, and a gas diffusion composite layer having excellent drainage and gas diffusivity can be provided.

FIG. 2A is a schematic cross-sectional view for explaining a state in which the gas diffusion composite layer produced by the method for producing the gas diffusion composite layer of the present disclosure is applied to a fuel cell, and FIG. 2B is a diagram. 2 (a) is an enlarged view showing a part of the gas diffusion composite layer.
As shown in FIG. 2, the gas diffusion composite layer 10 has a porous gas diffusion layer 11 and a fine porous layer 12. The fine porous layer 12 has a filling region 121 that fills the pores of the porous gas diffusion layer 11 and a surface covering portion 122 that covers the surface of the porous gas diffusion layer 11. In FIG. 2, reference numeral 13 indicates a catalyst layer, and reference numeral 14 indicates a groove-shaped gas flow path.

According to the production method of the present disclosure, a mixture containing a foaming agent and metal material particles containing at least one metal element selected from the group consisting of titanium, gold, silver, copper, platinum, tin, iron and aluminum is fired. By connecting to form a porous gas diffusion layer which is a sintered metal porous body, a porous gas having higher rigidity as compared with the porous gas diffusion layer 51 made of carbon fibers (see FIG. 9). A gas diffusion composite layer provided with a diffusion layer can be obtained.
Therefore, when applied to a fuel cell, the deflection of the porous gas diffusion layer into the gas flow path and the accompanying increase in pressure loss in the gas flow path and the collapse of the gas diffusion composite layer are suppressed. A gas diffusion composite layer can be obtained.

Further, according to the manufacturing method of the present disclosure, since the porous gas diffusion layer which is a sintered metal porous body is produced by sintering the mixture containing the metal material particles and the foaming agent described above, carbon fibers Compared with the case where the porous gas diffusion layer 51 (see FIG. 9) made of the above is used, it is easy to obtain high rigidity in the porous gas diffusion layer after forming the fine porous layer.
Therefore, as compared with the case where the porous gas diffusion layer 51 made of carbon fibers is used, it is possible to increase the porosity in the porous gas diffusion layer before the formation of the fine porous layer, and the fine porous layer is formed. In the porous gas diffusion layer after this, it is possible to suppress an increase in gas diffusion resistance.
The relationship between the porosity of the porous gas diffusion layer before the formation of the fine porous layer and the gas diffusion resistance of the porous gas diffusion layer after the formation of the fine porous layer will be described in detail in the evaluation items described later. ..

Further, according to the production method of the present disclosure, a porous gas diffusion layer which is a sintered metal porous body is produced by sintering a mixture containing the above-mentioned metal material particles and a foaming agent. It is possible to obtain a gas diffusion composite layer provided with a porous gas diffusion layer having fine pores formed by a foaming agent as a whole.
Therefore, in the fuel cell to which the gas diffusion composite layer produced by the production method of the present disclosure is applied, the catalyst layer of the gas supplied from the gas flow path through the pores of the porous gas diffusion layer formed by the foaming agent. Diffusion into the gas flow path and drainage of the water generated in the catalyst layer to the gas flow path are performed.
That is, according to the manufacturing method of the present disclosure, a gas diffusion composite layer having no bridge 612 (see FIG. 10B) can be obtained. Therefore, when the gas diffusion composite layer is applied to a fuel cell, each gas flow It is possible to provide a gas diffusion composite layer capable of suppressing the phenomenon that a part or all of the opening of the road is blocked.
Therefore, according to the manufacturing method of the present disclosure, when applied to a fuel cell, a phenomenon that the gas flow path from the gas flow path to the catalyst layer via the gas diffusion composite layer is blocked, and the catalyst layer It is possible to suppress the phenomenon that the flow path from the water generated in the above to the gas flow path via the gas diffusion composite layer is blocked, and it is a simple structure consisting of pores formed in the entire porous gas diffusion layer. It is possible to diffuse the gas supplied from the gas flow path to the catalyst layer and drain the water generated in the catalyst layer to the gas flow path.

Further, according to the production method of the present disclosure, by sintering a mixture containing metal material particles and a foaming agent, a porous gas diffusion layer having pores formed by the foaming agent in the entire layer is produced. A fine porous layer is formed on the surface of the porous gas diffusion layer. Therefore, as compared with the case where the fine porous layer 62 is formed on the surface of the porous metal gas diffusion layer 61 having pores 611 formed by chemical etching of a metal material, for example, as shown in FIG. 10, it is porous. The phenomenon that the material for forming a fine porous layer permeates into all the pores of the gas diffusion layer is unlikely to occur, and all the pores of the porous gas diffusion layer are almost completely filled with the fine porous layer. (For example, see FIG. 10 (b).) Can be suppressed.
Therefore, it is possible to suppress an increase in the gas diffusion resistance of the porous gas diffusion layer, and it is possible to obtain a gas diffusion composite layer capable of obtaining high power generation performance when applied to a fuel cell.

In the present disclosure, the porous gas diffusion layer means, for example, a layer having an average pore diameter in the range of 10 to 100 μm, and the fine porous layer means, for example, an average pore diameter of 0.1 to 2.0 μm. It can be anything that is in range.
In the present disclosure, the average pore diameter means the number average pore diameter (P50) at 50% of the cumulative pore distribution measured by the mercury intrusion method.

The gas diffusion resistance of the gas diffusion composite layer is preferably 80 s / m or less, and more preferably 60 s / m or less.
By setting the gas diffusion resistance of the gas diffusion composite layer to 80 s / m or less, when the gas diffusion composite layer is applied to a fuel cell, the gas supplied from the gas flow path is uniformly diffused into the gas diffusion composite layer. It is possible to obtain a fuel cell having good power generation performance.
The gas diffusion resistance is an index value indicating the difficulty of gas diffusion. In the present disclosure, the gas diffusion resistance can be measured by a known method.

FIG. 3 is a diagram showing an example of a layer structure of a fuel cell to which a gas diffusion composite layer produced by the production method of the present disclosure is applied, and is a diagram schematically showing a cross section cut in the stacking direction. The fuel cell 100 is a film composed of a solid polymer electrolyte membrane having hydrogen ion conductivity (hereinafter, may be simply referred to as an electrolyte membrane) 101, and a pair of anode electrodes 106 and cathode electrodes 107 sandwiching the electrolyte membrane 101. A pair of anode-side separators 109 and cathode-side separators 110 that include the electrode-bonded body 108 and further sandwich the film-electrode-bonded body 108 from the outside of the electrode. Gas flow paths 111 and 112 are secured at the boundary between the separator and the electrode, and fuel typified by hydrogen gas is continuously supplied on the anode side, and oxygen-containing gas (usually air) is continuously supplied on the cathode side. Usually, as an electrode, one configured by laminating a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side is used. That is, the anode electrode 106 is composed of the anode catalyst layer 102 and the anode side gas diffusion layer 104 laminated, and the cathode electrode 107 is composed of the cathode catalyst layer 103 and the cathode side gas diffusion layer 105 laminated.
As the anode-side gas diffusion layer 104 and the cathode-side gas diffusion layer 105, the gas diffusion composite layer produced by the production method of the present disclosure is applied.

As the anode catalyst contained in the anode catalyst layer, a catalyst component supported on conductive particles is used. The catalyst component is not particularly limited as long as it is a component that catalyzes the oxidation reaction of the fuel supplied to the anode catalyst layer, and for example, platinum or the like is used. As the conductive particles as the catalyst carrier, carbon particles such as carbon black are used.

As the cathode catalyst contained in the cathode catalyst layer, one in which a catalyst component is supported on conductive particles is used. As the catalyst component, for example, platinum or the like is used. As the conductive particles as the catalyst carrier, carbon particles such as carbon black are used.

The electrolyte membrane is usually a layer existing between the anode catalyst layer and the cathode catalyst layer. Ions are conducted between the anode catalyst layer and the cathode catalyst layer via the electrolyte membrane.
The material of the electrolyte membrane is not particularly limited as long as it is usually used for a fuel cell, and examples thereof include a perfluorocarbon sulfonic acid membrane such as a Nafion (registered trademark, manufactured by DuPont) membrane.

A separator may be further provided on the outside of the membrane / electrode assembly including the anode catalyst layer, the cathode catalyst layer, the cathode side gas diffusion layer, the anode side gas diffusion layer, and the electrolyte membrane.

The anode-side separator and the cathode-side separator are formed of a member having gas-blocking property and electron conductivity. For example, a carbon member such as dense carbon obtained by compressing carbon to make it gas-impermeable, or press-molded stainless steel. It is formed of metal members such as.

An example of a method for manufacturing a fuel cell will be described below. First, an anode catalyst layer is formed on one surface of the electrolyte membrane, and a cathode catalyst layer is formed on the other surface of the electrolyte membrane. Next, with respect to the obtained conjugate, the anode side gas diffusion layer and the anode side separator are arranged on the side facing the anode catalyst layer, and the cathode side gas diffusion layer and the cathode side separator are arranged on the side facing the cathode catalyst layer. By doing so, the fuel cell is completed.

[Reference Experiment Example 1]
1. 1. Preparation of gas diffusion composite layer (1) 1) Preparation of porous gas diffusion layer (sintered metal porous body) Metal material particles (titanium particles, average particle size (D50) 100 μm) and sodium hydrogen carbonate as a foaming agent , A mixture 1 for forming a porous gas diffusion layer was prepared by mixing with polyvinyl alcohol as an aqueous binder (step I-1).

Next, the mixture 1 was filled in a mold and molded to make the thickness of the molded product uniform and the surface smoothed, and then the foaming agent was foamed by heating to obtain a foamed slurry 1 (step (I-). 2)).

Next, the foamed slurry 1 obtained in step (I-2) was dried, and then fired and sintered under vacuum conditions to obtain a porous gas diffusion layer which is a sintered metal porous body (I-2). Step (I-3)).

Next, the porous gas diffusion layer produced in the step (I-3) was cut to a desired size to obtain a porous gas diffusion layer (1) having a thickness A (step (I-4)).

Next, an inspection step of inspecting whether or not the porous gas diffusion layer (1) obtained in the step (I-4) satisfies the desired physical property values was performed (step (I-5)).
The porosity of the porous gas diffusion layer (1) was 50%, and the flexural modulus was 50 GPa.

2) Formation of Microporous Layer The material for forming the microporous layer was prepared by preparing carbon powder, a surfactant (TRITON X-114 manufactured by Sigma-Aldrich), and PTFE and mixing them.
The obtained material for forming a fine porous layer is placed on one side of the porous gas diffusion layer (1) and dried, and the surface coating portion of thickness B is placed on the porous gas diffusion layer (1) of thickness A. A gas diffusion composite layer (1) including the fine porous layer (1) having the above was obtained. The porosity of the fine porous layer (1) was 50%.
The thickness of each layer of the gas diffusion composite layer (1) is shown in Table 1.
In Table 1 and Tables 2 to 3 described later, the region of the porous gas diffusion layer that does not have a filling region by the fine porous layer is referred to as "GDL" for convenience, and is fine in the porous gas diffusion layer. The region having the filling region by the porous layer is conveniently referred to as "GDL + MPL", and the region of the fine porous layer which is the surface coating portion is conveniently referred to as "MPL". Further, "B" in Tables 1 to 3 is a thickness corresponding to "A / 2". In addition, "-" in Tables 1 to 3 indicates that the target area does not exist.

2. 2. Preparation of Gas Diffusion Composite Layer (2) A material for forming a fine porous layer is applied to the surface of the porous gas diffusion layer (2) having a thickness A obtained by the same method as that of the porous gas diffusion layer (1). After coating by the method, the material for forming the fine porous layer is infiltrated to the depth A / 2 of the porous gas diffusion layer (2), and further, the fine porous layer is formed in the porous gas diffusion layer (2). A material for forming a fine porous layer is applied to a surface impregnated with the material for use and dried to obtain a fine porous layer (2) having a filling region having a thickness of A / 2 and a surface coating portion having a thickness of B / 2. A gas diffusion composite formed and comprising a porous gas diffusion layer (2) having a thickness A and a fine porous layer (2) having a filling region having a thickness A / 2 and a surface coating portion having a thickness B / 2. Layer (2) was obtained. The porosity of the surface coating portion of the fine porous layer (2) was 50%.
The thickness of each layer of the gas diffusion composite layer (2) is shown in Table 1.
FIG. 4 is a schematic cross-sectional view for explaining the layer structure of the gas diffusion composite layer (2) produced in Reference Experimental Example 1.
Reference numeral C in FIG. 4 indicates the thickness of a region (GDL + MPL) of the porous gas diffusion layer having a filling region by the fine porous layer.

3. 3. Preparation of Gas Diffusion Composite Layer (3) The material for forming a fine porous layer is infiltrated to the depth A of the porous gas diffusion layer (3) having a thickness A obtained by the same method as the porous gas diffusion layer (1). Then, a material for forming a fine porous layer is applied on one surface of the porous gas diffusion layer (3) and dried to obtain the porous gas diffusion layer (3) having a thickness A and the thickness A. A gas diffusion composite layer (3) including a packed region and a fine porous layer (3) having a surface coating portion having a thickness of B / 2 was obtained. The porosity of the surface coating portion of the fine porous layer (3) was 50%.
The thickness of each layer of the gas diffusion composite layer (3) is shown in Table 1.

[Reference Experiment Example 2]
4. Preparation of gas diffusion composite layer (4) 1) Preparation of porous gas diffusion layer (porous metal sintered body) Porous by the same method as the porous gas diffusion layer (1) except that the thickness is A / 2. A quality gas diffusion layer (4) was obtained.
The porosity of the porous gas diffusion layer (4) was 50%, and the flexural modulus was 35 GPa.

2) Formation of a fine porous layer A material for forming a fine porous layer obtained by the same method as in Reference Experimental Example 1 is placed on one surface of the porous gas diffusion layer (4) and dried to obtain a thickness A. A gas diffusion composite layer (4) including a / 2 porous gas diffusion layer (4) and a fine porous layer (4) having a surface coating portion having a thickness B was obtained. The porosity of the fine porous layer (4) was 50%.
The thickness of each layer of the gas diffusion composite layer (4) is shown in Table 2.

5. Preparation of Gas Diffusion Composite Layer (5) Reference Experimental Example 1 up to the depth A / 2 of the porous gas diffusion layer (5) having a thickness of A / 2 obtained by the same method as the porous gas diffusion layer (4). The material for forming a fine porous layer was impregnated with the material for forming a fine porous layer obtained by the same method as in A fine porous layer having a porous gas diffusion layer (5) having a thickness of A / 2, a filling region having a thickness of A / 2, and a surface covering portion having a thickness of B / 2 by applying and drying. A gas diffusion composite layer (5) comprising (5) was obtained. The porosity of the surface coating portion of the fine porous layer (5) was 50%.
The thickness of each layer of the gas diffusion composite layer (5) is shown in Table 2.
FIG. 5 is a schematic cross-sectional view for explaining the layer structure of the gas diffusion composite layer (5) produced in Reference Experimental Example 2.
Reference numeral C in FIG. 5 indicates the thickness of a region (GDL + MPL) of the porous gas diffusion layer having a filling region by the fine porous layer.

[Reference Experiment Example 3]
6. Preparation of gas diffusion composite layer (6) 1) Preparation of porous gas diffusion layer (sintered metal porous body) The thickness of the porous gas diffusion layer obtained after the sintering treatment is A / 2, and the porosity is 75%. A porous gas diffusion layer (6) was obtained in the same manner as in Reference Experimental Example 1 except that the above was achieved.
The porosity of the porous gas diffusion layer (6) was 75%, and the flexural modulus was 20 GPa.

2) Formation of a fine porous layer By arranging a material for forming a fine porous layer on one surface of a porous gas diffusion layer (6) having a thickness of A / 2 and drying it, a porous layer having a thickness of A / 2 is formed. A gas diffusion composite layer (6) including a gas diffusion layer (6) and a fine porous layer (6) having a surface coating portion having a thickness B was obtained. The porosity of the fine porous layer (6) was 50%.
The thickness of each layer of the gas diffusion composite layer (6) is shown in Table 3.

7. Preparation of Gas Diffusion Composite Layer (7) Reference Experimental Example 1 and up to depth A / 2 of a porous gas diffusion layer (7) with a thickness of A / 2 obtained by the same method as the porous gas diffusion layer (6) The fine porous layer forming material obtained by the same method was impregnated, and the fine porous layer forming material was further impregnated on the surface of the porous gas diffusion layer (7) in which the fine porous layer forming material was impregnated. By applying and drying, a fine porous layer (7) having a porous gas diffusion layer (7) having a thickness of A / 2 and a filling region having a thickness of A / 2 and a surface coating portion having a thickness of B / 2 ), A gas diffusion composite layer (7) was obtained. The porosity of the surface coating portion of the fine porous layer (7) was 50%.
The thickness of each layer of the gas diffusion composite layer (7) is shown in Table 3.

[Evaluation methods]
(Measurement of gas diffusion resistance)
The gas diffusion resistance was measured for the gas diffusion composite layers (1) to (7).
The gas diffusion resistance is measured in the regions (GDL) of the porous gas diffusion layers (1) to (7) of the gas diffusion composite layers (1) to (7) that do not have a filling region due to the fine porous layer, and gas diffusion. Of the porous gas diffusion layers (1) to (7) of the composite layers (1) to (7), a region (GDL + MPL) having a filling region by the fine porous layer, and the gas diffusion composite layers (1) to (7). The surface coating portion (MPL) of the fine porous layers (1) to (7) of the above was performed.

Specifically, the gas diffusion resistance was measured as follows.
Under the conditions of 45 ° C., 165% RH, low oxygen concentration (oxygen concentration: 1%), and measuring device (equipment manufactured by Toyo Technica Co., Ltd.), IV measurement of each layer and each part of the gas diffusion composite layer was performed. The value calculated from the following equation from the critical current density was defined as the gas diffusion resistance.
R _total = _PO2 / ( _Ilim / 4F) × RT
In the formula, R _total : gas diffusion resistance, _Ilim : limit current density, F: Faraday constant, R: gas constant, T: absolute temperature, _PO2 : oxygen partial pressure.

(Evaluation)
6 to 8 are diagrams showing the measurement results of the gas diffusion resistance of the gas diffusion composite layers (1) to (7).
6 (a) to 8 (a) show the measured values of the gas diffusion resistance of the gas diffusion composite layers (1) to (7), and each of them is a porous gas diffusion layer (1). Measured values for a region (GDL) having no filling region with a fine porous layer among (7), and a region having a filling region with a fine porous layer among the porous gas diffusion layers (1) to (7) (7) The measured values for GDL + MPL) and the measured values for the surface coating portion (MPL) of the fine porous layers (1) to (7) are shown separately.
Further, FIGS. 6 (b) to 8 (b) show a region (GDL) of the porous gas diffusion layers (1) to (7) that does not have a filling region due to the fine porous layer, and a porous gas diffusion layer (GDL). The same configuration is used for each of the region (GDL + MPL) having a filling region by the microporous layer among 1) to (7) and the surface covering portion (MPL) of the microporous layers (1) to (7). It is a figure which shows the relationship between the thickness of the layer made from a material, and the gas diffusion resistance.

As shown in FIG. 6, since the porous gas diffusion layer (1) of the gas diffusion composite layer (1) does not have a filling region (GDL + MPL) due to the fine porous layer (1), the entire gas diffusion composite layer (1) The gas diffusion resistance of the gas was about 80 s / m.
On the other hand, in the porous gas diffusion layer (2) of the gas diffusion composite layer (2), a region having a thickness of 1/2 of the total thickness A is filled with the fine porous layer (2) (GDL + MPL). ), The gas diffusion resistance in the region was increased as compared with the gas diffusion resistance of the porous gas diffusion layer (1) of the gas diffusion composite layer (1). Therefore, the gas diffusion resistance of the gas diffusion composite layer (1) as a whole exceeds 80 s / m, but can be kept at a desired value, and both rigidity, gas diffusivity and drainage property can be achieved at the same time.
Further, the entire area of the porous gas diffusion layer (3) of the gas diffusion composite layer (3) is filled with the fine porous layer (3) (GDL + MPL), and the gas diffusion resistance in the region is the gas diffusion composite. Compared with the gas diffusion resistance of the porous gas diffusion layer (1) of the layer (1), it was increased but can be kept at a desired value, and both rigidity, gas diffusion property and drainage property are compatible. Was done.
From the above results, when the porosity of the porous gas diffusion layer is 50%, if the entire area of the porous gas diffusion layer is filled with the fine porous layer, the gas diffusion resistance increases, but it should be kept at a desired value. It was clarified that both rigidity and gas diffusivity and drainage property can be achieved.
On the other hand, for example, as shown in FIG. 10, the porous metal gas diffusion layer 61 having pores formed by chemical etching of a metal material generally has voids similar to those of the porous gas diffusion layer used in Reference Experimental Example 1. Since it has only a ratio (about 50%), the gas of the gas diffusion composite layer having the porous gas diffusion layer 61 is caused by the permeation of the material for forming the fine porous layer into the entire area of the porous gas diffusion layer 61. It is estimated that the diffusion resistance is significantly increased as compared with the gas diffusion composite layer (3).

As shown in FIG. 7, the porous gas diffusion layer (4) of the gas diffusion composite layer (4) has a thickness A of the porous gas diffusion layer (1) of the gas diffusion composite layer (1) of Reference Experimental Example 1. Since the porous gas diffusion layer (4) does not have a filling region due to the fine porous layer (4), the gas diffusion resistance of the gas diffusion composite layer (4) as a whole is halved. , 80 s / m or less.
On the other hand, the entire area of the porous gas diffusion layer (5) of the gas diffusion composite layer (5) is filled with the fine porous layer (5) (GDL + MPL), and the gas diffusion resistance in the region is the gas diffusion composite. Although it is increased as compared with the gas diffusion resistance of the porous gas diffusion layer (4) of the layer (4), the increase width is the fine porous layer of the porous gas diffusion layer (3) in Reference Experimental Example 1. Compared with the increase width of the gas diffusion resistance of the filling region (GDL + MPL) according to (3), it was significantly reduced.
From the above results, when the thickness of the porous gas diffusion layer is reduced, the gas diffusion resistance in the porous gas diffusion layer is increased even when the entire area of the porous gas diffusion layer is filled with the fine porous layer. It can be seen that it can be significantly suppressed.

As shown in FIG. 8, the porous gas diffusion layer (6) of the gas diffusion composite layer (6) has a thickness A of the porous gas diffusion layer (1) of the gas diffusion composite layer (1) of Reference Experimental Example 1. The porosity of the porous gas diffusion layer (6) is 75%, which is higher than the porosity of the porous gas diffusion layer (1) of Reference Experimental Example 1. ing. Since the porous gas diffusion layer (6) of the gas diffusion composite layer (6) does not have a filling region formed by the fine porous layer (6), the gas diffusion resistance of the gas diffusion composite layer (6) as a whole is 80 s. It was below / m.
On the other hand, the entire area of the porous gas diffusion layer (7) of the gas diffusion composite layer (7) is filled with the fine porous layer (7), and the gas diffusion resistance of the porous gas diffusion layer (7) is high. Although it is increased as compared with the gas diffusion resistance of the porous gas diffusion layer (6) of the gas diffusion composite layer (6), the increase width is that of the porous gas diffusion layer (5) in Reference Experimental Example 2. Compared with the increase width of the gas diffusion resistance of the filling region (GDL + MPL) by the fine porous layer (5), it is further reduced, and the gas diffusion resistance of the gas diffusion composite layer (7) as a whole is 80 s / m. It was below.
From the above results, when the porosity of the porous gas diffusion layer is 75% or more, the gas diffusion resistance in the porous gas diffusion layer even when the entire area of the porous gas diffusion layer is filled with the fine porous layer. It can be seen that the amount of increase in can be suppressed.

10 Gas Diffusion Composite Layer, 11 Porous Gas Diffusion Layer, 12 Fine Porous Layer, 121 Filled Region, 122 Surface Coating, 13 Catalyst Layer, 14 Gas Flow Channel, 50 Gas Diffusion Composite Layer, 51 Gas Diffusion Consisting of Carbon Fiber Sex electrode substrate, 52 microporous layer, 53 channels, 60 gas diffusion composite layer, 61 porous metal gas diffusion layer, 611 pores, 612 bridges, 62 microporous layer, 63 catalyst layer, 64 gas channels, 641 Gas channel 64 opening, 100 fuel cell, 101 solid polymer electrolyte membrane, 102 anode catalyst layer, 103 cathode catalyst layer, 104 anode side gas diffusion layer, 105 cathode side gas diffusion layer, 106 anode electrode, 107 cathode electrode, 108 film / electrode junction, 109 anode side separator, 110 cathode side separator, 111,112 gas flow path

Claims (1)

A method for producing a gas diffusion composite layer for a fuel cell, which includes a porous gas diffusion layer and a fine porous layer.
A mixture containing at least one metal element selected from the group consisting of titanium, gold, silver, copper, platinum, tin, iron and aluminum, and a metal material particle having an average particle diameter of 10 μm or more and 150 μm or less, and a foaming agent. The step of producing the porous gas diffusion layer by firing and sintering the molded body obtained by molding the above-mentioned
The fine particles that fill at least a part of the pores of the porous gas diffusion layer and cover at least a part of the surface of the porous gas diffusion layer by using a material for forming a fine porous layer containing a carbon material. A method for producing a gas diffusion composite layer for a fuel cell, which comprises a step of forming a porous layer and a step of forming the porous layer.