JP4143906B2 - Membrane electrode assembly, diffusion layer-containing material, and fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention is preferably applied to a solid polymer electrolyte fuel cell membrane electrode assembly, Diffusion layer-containing materials, and fuel cells using themAbout.
[0002]
[Prior art]
A unit cell, which is the minimum power generation unit of a solid polymer electrolyte fuel cell, generally has a fuel gas (hydrogen etc.) flow path and an oxidant gas (oxygen etc.) flow on both sides of a membrane electrode assembly (hereinafter referred to as “MEA”). It is sandwiched by a separator with a path. A stack of many unit cells is called a stack. The MEA includes a solid polymer electrolyte membrane that does not transmit electrons and transmits ions, and electrodes that sandwich both surfaces of the solid polymer electrolyte membrane. The electrode has a catalyst layer containing a catalyst on the surface in contact with the solid polymer electrolyte membrane. The catalyst layer has a function of catalyzing a reaction between the fuel gas and the oxidant gas. Furthermore, the electrode can have a diffusion layer on the surface of the catalyst layer opposite to the surface in contact with the solid polymer electrolyte membrane. The diffusion layer has a function of diffusing and permeating fuel gas or oxidant gas, water generated by the reaction, and the like, and transmitting electrons generated in the catalyst layer.
[0003]
By the way, in the solid polymer electrolyte fuel cell, treatment of water generated in the process of power generation becomes a problem. The water produced by the reaction mainly comes out to the cathode side, but part of it passes through the solid polymer electrolyte membrane and comes out to the anode side.
[0004]
For the solid polymer electrolyte membrane, a fluorine-based polymer material is most commonly used. A typical electrolyte membrane is a commercially available Nafion^TM(Product name manufactured by DuPont, USA). This solid polymer electrolyte membrane has a higher proton conductivity than other solid polymer electrolytes, but when the solid polymer electrolyte membrane dries, the proton conductivity rapidly decreases (dry up). Conversely, if a large amount of water is present, the performance deteriorates (flooding). For this reason, in a solid polymer electrolyte fuel cell, it is always required to control the solid polymer electrolyte membrane to an appropriate water-containing state. Similarly, it is preferable to maintain a moisture content within a certain range for the catalyst layer. This is because the catalyst layer also contains a solid polymer electrolyte in order to impart ion conductivity. It is reasonable to control this amount of water by using water generated by the battery reaction.
[0005]
Usually, the moisture content of the solid polymer electrolyte membrane or the like is controlled by a diffusion layer. A conventional diffusion layer is a film composed of a mixture of a porous polymer made of a fluororesin for imparting gas permeability and a conductive additive made of carbon powder or the like for imparting conductivity and water permeability. Manufactured by forming on a substrate to improve mechanical properties.
[0006]
Further, Patent Document 1 discloses a method of adjusting the amount of water by including in the catalyst layer a metalloxane polymer that has a high interaction with water and promotes mass transfer.
[0007]
[Patent Document 1]
JP 2001-325963 A
[0008]
[Problems to be solved by the invention]
However, in the conventional fuel cell, although control of gas permeability and water permeability under a certain condition can be achieved to some extent, sufficient characteristics may not be exhibited depending on the operating conditions of the fuel cell. For example, when the fuel cell is operated at a high output, the drainage does not catch up and flooding occurs. As a result, the high efficiency inherent in the fuel cell cannot be fully utilized.
[0009]
  The present invention has been made in view of the above points. An object of the present invention is to provide a fuel cell capable of controlling an appropriate moisture state, and a membrane electrode assembly and an electrode suitable for the fuel cell.Inner diffusion layerCan be used forContains diffusion layerTo provide materials.
[0010]
[Means for Solving the Problems and Effects of the Invention]
As a result of intensive investigations aimed at solving the above-mentioned problems, the present inventors have come up with a method for appropriately varying the water permeability of the electrode according to the generation of water produced by the battery reaction. Specifically, the temperature of the electrode was focused as an index highly correlated with the amount of generated water. The temperature of the electrode changes according to the progress of the cell reaction of the fuel cell. As the cell reaction of the fuel cell proceeds, the amount of generated water increases. Therefore, the amount of generated water and the electrode temperature are considered to have a high correlation.
[0011]
  That is, the membrane electrode assembly of the present invention includes a solid polymer electrolyte membrane and a catalyst layer bonded on the solid polymer electrolyte membrane.And a diffusion layer joined to the catalyst layerAn electrode disposed on the solid polymer electrolyte membrane, and a membrane electrode assembly comprising:The diffusion layer is composed of a conductive assistant that is porous carbon powder, acrylamide, N-isopropylacrylamide, pentafluoropropyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid (polyethylene oxide) monomethyl ether, and acrylic acid. A homopolymer or copolymer comprising one or more monomers selected from the group consisting of the thermosensitive material covalently bonded to the surface of the conductive additiveIt is characterized byTheIn other words, the water permeability of the electrode is varied depending on the temperature of the electrode by including in the electrode a temperature-sensitive material whose physical properties change with temperature change.
[0012]
BurningIn the battery, the amount of generated water increases as the battery reaction proceeds, and it is necessary to promote drainage from the electrode. As the battery reaction proceeds, the temperature of the electrode rises. Therefore, the permeability of the electrode decreases below a predetermined temperature.The
[0013]
For example, since the cell reaction is more active than expected and the amount of generated water is increased above the steady temperature assumed as the operating temperature of the stabilized fuel cell, the water permeability of the electrode is improved. In order to prevent flooding by promoting drainage from the electrode. On the other hand, as the battery starts up, the battery reaction is reduced below the steady temperature, so the amount of generated water is also reduced, and water is retained in the electrode by reducing the water permeability of the electrode. To prevent dry-up. Therefore, the humidity of the catalyst layer can be properly controlled by adopting a steady temperature or the like when operating the fuel cell as the predetermined temperature for changing the water permeability of the electrode.
[0014]
ElectricThe humidity of the catalyst layer at the pole is affected by the flow path structure of the produced water. The diffusion layer is closely related to the flow path structure of the generated water. Therefore, the water permeability is changed by the diffusion layer to control the humidity of the electrode.Is a thing. Here, the diffusion layer has a function of collecting electrons generated by the battery reaction of the catalyst layer. In order for the diffusion layer to efficiently exhibit the current collecting action from the catalyst layer, a conductive assistant having a particle size comparable to that of the particles contained in the catalyst layer (for example, particles having catalyst fine particles such as Pt supported on carbon powder). Contains agents. In order for the diffusion layer to efficiently perform the current collecting action and the moisture content adjusting function, a temperature sensitive material is bonded to the surface of the conductive additive.The
[0015]
  The conductive additive is porous carbon powder.ThePorous carbon powder is excellent in availability, current collecting performance, and the like, and can effectively exhibit the effect of the temperature-sensitive material bonded to the surface due to the large specific surface area. The bond between the carbon powder and the temperature sensitive material is a covalent bond so that it can withstand the harsh environment in the electrode of the fuel cell.The
[0016]
A membrane electrode assembly of the present invention that solves the above problems comprises a solid polymer electrolyte membrane, a catalyst layer bonded on the solid polymer electrolyte membrane, and a diffusion layer bonded to the catalyst layer. An electrode disposed on the solid polymer electrolyte membrane, and a membrane electrode assembly comprising:
The diffusion layer includes a conductive assistant that is porous carbon powder, and a polymer material having a chemical structure represented by any of the following general formulas (1) to (7) (m, n, l, and a in each are And the temperature sensitive material covalently bonded to the surface of the conductive additive.
[0020]
  Furthermore, the present invention that solves the above problemsContains diffusion layerthe material is,PorousCarbon powder and one or more monomers selected from the group consisting of acrylamide, N-isopropylacrylamide, pentafluoropropyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid (polyethylene oxide) monomethyl ether and acrylic acid A temperature-sensitive material which is a homopolymer or a copolymer and is covalently bonded to the surface of the carbon powder. In addition,Contains diffusion layerA material is an electrode similar to a conductive additive contained in a diffusion layer.Inner diffusion layerIt is a material that exhibits the effect of forming a conductive path in the electrode by containing it in the electrode and has the function of controlling the water permeability of the electrode according to the temperature of the electrode.
[0021]
  A fuel cell according to the present invention for solving the above-mentioned problems is characterized by having the above-described membrane electrode assembly.The
[0022]
DETAILED DESCRIPTION OF THE INVENTION
[Membrane electrode assembly]
The membrane electrode assembly of this embodiment has a solid polymer electrolyte membrane and an electrode disposed on the solid polymer electrolyte membrane. The solid polymer electrolyte membrane is made of a material that is excellent in ion (proton) permeability and does not flow current. Currently used materials include perfluorosulfonic acid polymers (for example, trade name: Nafion).^TM). This solid polymer electrolyte membrane can be used in a general thickness that is not particularly limited.
[0023]
The electrode contains a temperature sensitive material and has a catalyst layer. The catalyst layer is a member that catalyzes the reaction between a fuel gas such as hydrogen and an oxidant gas such as oxygen. The catalyst layer is bonded on the solid polymer electrolyte membrane. The structure of a catalyst layer is not specifically limited, The thing of a normal structure is employable. For example, a catalyst in which catalyst fine particles containing noble metal such as platinum or platinum alloy are dispersed on a catalyst carrier such as carbon powder can be formed into a film and used. For example, the catalyst layer can be formed by mixing the catalyst with a binder made of a solid polymer electrolyte to produce an ink, and coating and drying on the surface of the solid polymer electrolyte membrane to form a film.
[0024]
  The electrode also has a diffusion layerOne.The diffusion layer is bonded to the catalyst layer (the surface on the side opposite to the surface on which the solid polymer electrolyte membrane is bonded). The diffusion layer is a member that collects electrons generated in the catalyst layer while controlling the flow of fuel gas, oxidant gas, and generated water into and out of the catalyst layer. Diffusion layerIt has a conductive additive made of carbon powder for imparting electrical conductivity and water permeability. More, Porous polymer made of fluororesin or the like for imparting gas permeabilityCan have. theseForming a mixture film on a substrate such as carbon fiber to improve mechanical propertiesSuchManufactured by.
[0025]
  A temperature-sensitive material is a material whose physical properties change with changes in temperature, and changes in physical properties (changes in physical properties include the case where hydrophilicity changes and water easily permeates, and the pore diameter of the material changes and water ), The water permeability of the electrode is changed. As a temperature-sensitive material, a material whose water permeability decreases at a predetermined temperature or lower (or whose water permeability improves at a predetermined temperature or higher)Is.
[0026]
As the predetermined temperature, a steady electrode temperature (for example, 80 ° C.) when the fuel cell to which the membrane electrode assembly is applied is in steady operation can be used. The steady temperature of the electrode is controlled by the temperature of a heat medium such as water that is circulated in order to stabilize the electrode temperature. When the temperature of the electrode is lower than the steady temperature, the generated water generated at the electrode tends to evaporate with a relatively high-temperature heat medium and becomes dry, so reducing the water permeability of the electrode reduces the generated water to the electrode. Prevents dry-up by holding. On the other hand, when the electrode temperature is higher than the steady temperature, the water generated at the electrode tends to condense due to the relatively low-temperature heat medium and becomes moist, so it is generated by increasing the water permeability of the electrode. Prevent flooding by promoting drainage of water from the electrode.
[0027]
FeelingInclude warm material in the diffusion layerThe ExpansionThe scattering layer has a conductive aid such as carbon powder, and a temperature sensitive material is bonded to the surface of the conductive aid.The
[0028]
  As a conductive aid, porous carbon powder is used to increase the specific surface area.TheThe size of the conductive auxiliary agent is preferably about the same as the particle size of the catalyst carrier used in the catalyst layer, and can be about 1 to 3 μm. The temperature-sensitive material is bonded to the surface of the conductive additive and has a length of about several tens to several hundreds of nanometers. When the conductive additive is a carbon material, the amount of the temperature-sensitive material to be bonded can be about 1: 1000 to 2: 1 in a mass ratio of the temperature-sensitive material: carbon material.
[0029]
  Conductive aid and temperature sensitive material are covalently bonded. as a result,Stability in fuel cellsWill improve.
[0030]
  The temperature-sensitive material can be exemplified by a homopolymer or copolymer comprising one or more monomers selected from the group consisting of acrylamide, N-substituted acrylamide, acrylic acid and acrylate ester.In particular, Acrylamide, N-isopropylacrylamide, pentafluoropropyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid (polyethylene oxide) monomethyl ether and a homopolymer or copolymer comprising a monomer consisting of at least one of acrylic acidIs. The molecular weight of these polymer compounds is not particularly limited, but can be several hundred to tens of thousands. When these temperature-sensitive materials are copolymers, the molecular structure of the block copolymer, random copolymer, etc. is not particularly limited.
[0031]
  Further, a polymer compound represented by the structural formula shown below (m, n, l,a is a natural number) can also be adopted as a temperature sensitive material. Copolymer by copolymerizing a monomer having fluorine element in the side chain and a low hydrophilic monomer (fluorine-containing monomer) with a monomer having a certain degree of hydrophilicity such as N-isopropylacrylamide and having a change in affinity for water due to temperature change. Thus, the water permeability of the temperature sensitive material can be made preferable.
[0032]
That is, by copolymerizing the fluorine-containing monomer, the water permeability change of the temperature-sensitive material (the difference in the absolute value of the water permeability before and after the water permeability change or the ratio of the water permeability before and after the water permeability change) can be increased. When the water-permeable material of the temperature-sensitive material is low, water can be reliably held on the electrode, and on the contrary, when the water-permeable material of the temperature-sensitive material becomes high, the water release from the electrode can be promoted.
[0033]
Specifically, when the water permeability is low due to the action of N-isopropylacrylamide or the like as at low temperatures, the hydrophilicity of the temperature-sensitive material as a whole decreases due to the action of the copolymerized fluorine-containing monomer. Thus, the water permeability can be lowered. At high temperatures, the hydrophilicity of the temperature-sensitive material is improved by the action of N-isopropylacrylamide and the like, so it is considered that the influence of the decrease in hydrophilicity due to the fluorine-containing monomer is reduced.
[0034]
[Chemical 1]
[0035]
[Chemical 2]
[0036]
[Chemical 3]
[0037]
[Formula 4]
[0038]
[Chemical formula 5]
[0039]
[Chemical 6]
[0040]
[Chemical 7]
[0041]
As a method of bonding a temperature sensitive material made of a polymer compound to the surface of a conductive auxiliary agent such as carbon powder, for example, it can be performed by polymerizing a monomer constituting the temperature sensitive material in the presence of the conductive auxiliary agent. . In particular, when a temperature-sensitive material is polymerized by radical polymerization, radicals are also generated on the surface of the conductive assistant by a radical transfer reaction, so that the temperature-sensitive material can be covalently bonded to the surface of the conductive assistant.
[0042]
It does not specifically limit as a method of manufacturing a membrane electrode assembly. For example, a paste made by adding a catalyst comprising a catalyst carrier such as carbon powder having catalyst fine particles supported on the surface of a solid polymer electrolyte membrane comprising a solid polymer electrolyte into the solid polymer electrolyte solution and mixing it The catalyst layer can be formed by coating and drying. By adding a temperature-sensitive material to the ink constituting the catalyst layer, the temperature-sensitive material can be added to the catalyst layer, and the water permeability of the catalyst layer changes depending on the temperature. Adds a temperature-sensitive material to the diffusion layer by adding a temperature-sensitive material to the ink in which the materials that make up the diffusion layer (conductive aid, substrate, solid polymer electrolyte, etc.) are dispersed on the surface of the catalyst layer The water permeability of the diffusion layer varies depending on the temperature. When adding a temperature-sensitive material, the stability of the temperature-sensitive material in the electrode is improved by adding the temperature-sensitive material in a state of being bonded to the constituent material.
[0043]
  [Catalyst material]
The catalyst material of the present embodiment is a material that is added in the electrode of the fuel cell, particularly in the diffusion layer of the electrode, and exhibits the function of controlling the water permeability of the electrode. Specifically, carbon powder,Acrylamide, N-isopropylacrylamide, pentafluoropropyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid (polyethylene oxide) monomethyl ether and acrylic acidAnd a temperature-sensitive material bonded to the surface of the carbon powder. The homopolymer or copolymer is composed of one or more monomers selected from the group consisting of: Since the manufacturing method and other details are the same as described in the section of “Membrane electrode assembly”, further description is omitted.
[0044]
〔Fuel cell〕
The fuel cell of this embodiment is a solid polymer electrolyte fuel cell. As the fuel cell of this embodiment, a stack in which fuel cells are singly or plurally stacked is formed. The fuel cell has the membrane electrode assembly described above, and the membrane electrode assembly is sandwiched between separators. As the temperature at which the temperature sensitive material contained in the membrane electrode assembly changes the water permeability, it is preferable to adopt a steady temperature when operating the fuel cell. The steady temperature can be approximated by the coolant temperature of the fuel cell. It is preferable that the temperature sensitive material contained in the membrane electrode assembly of the present fuel cell is particularly controlled within the cathode to generate water.
[0045]
Gas supply devices for supplying fuel gas and oxidant gas to the electrodes on both sides of the membrane electrode assembly sandwiching the solid polymer electrolyte membrane are connected from the corresponding separators. As the fuel gas, air is defined for convenience, using hydrogen gas as an oxidant gas.
[0046]
The separator can also use the material and form generally used. The separator is provided with a flow path through which fuel gas or oxidant gas flows, and a gas supply device for supplying the fuel gas is connected to the flow path. A means for removing is connected.
[0047]
【Example】
  In the following, a temperature-sensitive material that can be used for the membrane electrode assembly of the present invention was bonded onto acetylene black as a conductive auxiliary agent.Contains diffusion layerA test sample as a material will be described in detail. In order to apply this test sample to a fuel cell, a membrane formed by binding these test samples with a solid polymer electrolyte such as Nafion can be used as a diffusion membrane. Depending on the steady operating temperature of the applied fuel cell, a selected test sample can be used.
[0048]
[Preparation of test sample]
Example 1
To 60 g of an aqueous solution prepared with a mixing ratio of 20 parts by mass of acrylamide, 2 parts by mass of 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamide] and 78 parts by mass of water, 10 g of acetylene black was added and the reaction was performed by heating at 100 ° C. for 3 hours. Acrylamide homopolymers act as temperature sensitive materials. After completion of the reaction, a water-insoluble part (insoluble part) was collected by filtration. The insoluble part was put into 200 mL of water, and the operation of heating and stirring at 100 ° C. for 5 minutes and then filtering was repeated 5 times for washing. From the analysis of the amount of the polymer compound that flowed into the washing water, the introduction ratio of the temperature-sensitive material to the conductive auxiliary agent was 100: 9.6 (= conductive auxiliary agent: temperature-sensitive material) in mass ratio.
[0049]
When 1 g of the obtained insoluble part was put in 100 mL of water and the state was observed, it was observed that the dispersibility in water was improved and it was well adapted to water. On the other hand, acetylene black before reaction showed remarkable water repellency. Furthermore, although the hydrophilic state was observed also about the insoluble part immediately after reaction, the hydrophilic property similar to the insoluble part after 5 times washing | cleaning was observed. Therefore, it was confirmed that the polymer compound capable of exhibiting hydrophilicity was bonded with good durability to the surface of acetylene black.
[0050]
The obtained insoluble part was dried at 120 ° C. for 12 hours in an air-heat dryer, and the obtained powder was used as a test sample of Example 1.
[0051]
(reference)
Carbon of 1 cm × 1 cm square was added to 10 g of an aqueous solution prepared with a mixing ratio of 20 parts by mass of acrylamide, 2 parts by mass of 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamide], and 78 parts by mass of water. The sheet was dipped and reacted by heating at 100 ° C. for 3 hours. Thereafter, a water-soluble substance was extracted from the carbon sheet after the reaction. The extraction was performed for 16 hours using a Soxhlet extractor and water. The extracted carbon sheet was dried at 120 ° C. for 12 hours in a wind-heat dryer. When the contact angle with respect to the water of the carbon sheet before and after the reaction was measured, it was found that the hydrophilicity of the carbon sheet surface was improved by 95 ° before the reaction and 55 ° after the reaction. This contact angle can be considered to decrease with increasing temperature. Since the hydrophilicity of the carbon sheet after the reaction was recognized even after the extraction of the aqueous solution, it can be inferred that acrylamide was firmly bonded to the surface of the carbon sheet.
[0052]
(Examples 2 to 4)
20 parts by mass of a mixture of acrylamide and N-isopropylacrylamide mixed at a mass ratio of 20:80 (Example 2), 30:70 (Example 3), and 50:50 (Example 4), 2, 2 ′ -10 g of acetylene black was added to 60 g of a solution prepared at a mixing ratio of 2 parts by mass of azobis [N- (2-carboxyethyl) -2-methylpropionamide] and 78 parts by mass of methanol, and heated in an oil bath at 80 ° C. Then, methanol was refluxed for 3 hours to carry out the reaction. A copolymer of acrylamide and N-isopropylacrylamide acts as a temperature sensitive material. After completion of the reaction, a portion insoluble in methanol (insoluble portion) was collected by filtration. The insoluble part was placed in 200 mL of methanol, and the operation of stirring for 5 minutes and then filtering was repeated 5 times for washing. From the analysis of the amount of the polymer compound that has flowed into the washing water, the introduction ratio of the temperature-sensitive material to the conductive assistant is 100: 10.2 (Example 2), 100: 8.3 (Example 3) by mass ratio, 100: 9.4 (Example 4) (= conductive aid: temperature-sensitive material). The obtained insoluble part was dried at 120 ° C. for 12 hours in an air-heat dryer. The obtained powders were used as test samples of Examples 2 to 4, respectively.
[0053]
(Example 5)
To 60 g of a solution prepared with a mixing ratio of 20 parts by mass of N-isopropylacrylamide, 2 parts by mass of 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamide] and 78 parts by mass of methanol, acetylene black was added. 10 g was added, and the reaction was performed by heating at 80 ° C. for 3 hours. A homopolymer of N-isopropylacrylamide acts as a temperature sensitive material. After completion of the reaction, a portion insoluble in methanol (insoluble portion) was collected by filtration. The insoluble part was placed in 200 mL of methanol, and the operation of stirring for 5 minutes and then filtering was repeated 5 times for washing. From the analysis of the amount of the polymer compound that flowed into the washing water, the introduction ratio of the temperature-sensitive material to the conductive auxiliary agent was 100: 9.0 (= conductive auxiliary agent: temperature-sensitive material) in mass ratio. The obtained insoluble part was dried at 120 ° C. for 12 hours in an air-heat dryer. The obtained powder was used as a test sample of Example 5.
[0054]
(Example 6)
To 60 g of a solution prepared with a blending ratio of 20 parts by mass of pentafluoropropyl acrylate, 2 parts by mass of 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamide] and 78 parts by mass of toluene, acetylene was added. Black 10g was added and it reacted by heating at 100 degreeC for 3 hours. A homopolymer of pentafluoropropyl acrylate acts as a temperature sensitive material. After completion of the reaction, a portion insoluble in toluene (insoluble portion) was collected by filtration. This insoluble part was put in 200 mL of toluene, and the operation of stirring for 5 minutes and then filtering was repeated 5 times for washing. From the analysis of the amount of the polymer compound that flowed into the washing water, the introduction ratio of the temperature-sensitive material to the conductive auxiliary agent was 100: 44 (= conductive auxiliary agent: temperature-sensitive material) in mass ratio. The obtained insoluble part was dried at 120 ° C. for 12 hours in an air-heat dryer. The obtained powder was used as a test sample of Example 6.
[0055]
(Comparative example)
The acetylene black used in Examples 1 to 6 was used as a test sample for comparison.
[0056]
(Water permeability test)
As shown in FIG. 1, a sample 10 in which 200 mg of each of the test samples of Examples 1 to 6 and the comparative example are uniformly sandwiched between two filter papers (diameter 6 cm) is further added to two glass tubes having an inner diameter of 2.8 cm. The water-permeable test tube 1 was produced by being sandwiched between 11 and 12 tube ports.
[0057]
Water W at various temperatures was passed through the produced water-permeable test tube 1 at a pressure of 101 kPa, and the mass of the water that passed in 1 minute was measured.
[0058]
The results are shown in Fig. 2 (Example 1), Fig. 3 (Example 2), Fig. 4 (Example 3), Fig. 5 (Example 4), Fig. 6 (Example 5), Fig. 7 (Example 6), This is shown in FIG. 8 (comparative example). It turned out that the amount of water permeability increases when all the test samples of each example become above a specific temperature. In the test sample of Example 1 (FIG. 2), it was found that the water permeability changed around 70 to 80 ° C. In the test sample of Example 2 (FIG. 3), it was found that the water permeability changed at about 60 to 70 ° C. In the test sample of Example 3 (FIG. 4), it was found that the water permeability changed at about 60 to 70 ° C. In the test sample of Example 4 (FIG. 5), it was found that the water permeability changed around 60 ° C. In the test sample of Example 5 (FIG. 6), it was found that the water permeability changed at about 50 to 60 ° C. In the test sample of Example 6 (FIG. 7), it was found that the water permeability changed at about 60 to 70 ° C. On the other hand, it was found that the water permeability of the test sample of the comparative example (FIG. 8) was almost constant regardless of the temperature.
[0059]
From the results of Examples 1 to 5, when the mixing ratio of N-isopropylacrylamide is 50% or more (the mixing ratio of acrylamide is 50% or less), it is prominent from around a specific temperature of about 50 ° C to 60 ° C. A significant improvement in water permeability was observed.
[0060]
On the other hand, when the mixing ratio of N-isopropylacrylamide was less than 50% (acrylamide mixing ratio was more than 50%), it became clear that the water permeability gradually improved as the temperature of the water passing through increased. It can be inferred that the test sample of Example 6 to which poly (acrylic acid) pentafluoropropyl was bonded improved the fluidity of the molecular chain bonded to the surface of the conductive assistant due to temperature change, and the water flow started to flow.
[0061]
Moreover, when the water permeation amount per minute when the temperature of water to be permeated was alternately changed between 20 ° C. and 60 ° C. for the test sample of Example 2 was measured, as shown in Table 1, the water temperature It was confirmed that the water permeability is small when the water temperature is low, the water permeability is large when the water temperature is high, and the water permeability can be reversibly controlled by the water temperature.
[0062]
[Table 1]
[0063]
By containing the conductive assistant having the temperature-sensitive material as described in Examples 1 to 6 bound to the surface thereof in the electrode of the solid polymer electrolyte fuel cell, the water permeability of the electrode can be appropriately controlled. It is considered possible.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a test method of a water permeability test.
2 is a graph showing the temperature dependence of the water permeability in the test sample of Example 1. FIG.
3 is a graph showing the temperature dependence of the water permeability in the test sample of Example 2. FIG.
4 is a graph showing the temperature dependence of the water permeability in the test sample of Example 3. FIG.
5 is a graph showing the temperature dependence of the water permeability in the test sample of Example 4. FIG.
6 is a graph showing the temperature dependence of the water permeability in the test sample of Example 5. FIG.
7 is a graph showing the temperature dependence of the water permeability in the test sample of Example 6. FIG.
FIG. 8 is a graph showing the temperature dependence of the water permeability in a test sample of a comparative example.
[Explanation of symbols]
1 ... Permeability test tube
10 ... Sample 11, 12 ... Glass tube
2 ... Beak
3 ... Scale

Claims (4)

A solid polymer electrolyte membrane, a catalyst layer bonded on the solid polymer electrolyte membrane, and a diffusion layer bonded to the catalyst layer, and an electrode disposed on the solid polymer electrolyte membrane. A membrane electrode assembly,
The diffusion layer is composed of a conductive assistant that is porous carbon powder, acrylamide, N-isopropylacrylamide, pentafluoropropyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid (polyethylene oxide) monomethyl ether, and acrylic acid. A membrane electrode assembly comprising the temperature-sensitive material that is a homopolymer or copolymer composed of one or more monomers selected from the group consisting of, and is covalently bonded to the surface of the conductive additive. A solid polymer electrolyte membrane, a catalyst layer bonded on the solid polymer electrolyte membrane, and a diffusion layer bonded to the catalyst layer, and an electrode disposed on the solid polymer electrolyte membrane. A membrane electrode assembly,
The diffusion layer includes a conductive assistant that is porous carbon powder, and a polymer material having a chemical structure represented by any of the following general formulas (1) to (7) (m, n, l, and a in each are A temperature-sensitive material that is a natural number) and is covalently bonded to the surface of the conductive additive.
Porous carbon powder,
Homopolymers or copolymers comprising one or more monomers selected from the group consisting of acrylamide, N-isopropylacrylamide, pentafluoropropyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid (polyethylene oxide) monomethyl ether and acrylic acid , and the characterized in that it has a temperature sensitive material that is covalently bonded to the surface of the carbon powder, a diffusion layer containing material contained in the diffusion layer in the electrode of the solid polymer electrolyte fuel cell.   A fuel cell comprising the membrane electrode assembly according to claim 1.