JP2010170895A - Method and device for manufacturing membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly excellent in joining property on the interface between a catalyst layer and a diffusion layer and high in durability when an electrolyte membrane in which a contraction percentage when dried from a swelling state to a dry state is 5% or more is used. <P>SOLUTION: A method for manufacturing the membrane electrode assembly includes the steps of: (a) forming a catalyst layer on the surface of the electrolyte membrane; (b) moistening with water the electrolyte membrane on which the catalyst layer is formed; and (c) heat-joining a diffusion layer to the catalyst layer under the environment where the contraction percentage of the electrolyte membrane becomes 3% or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a membrane electrode assembly and a manufacturing apparatus for the membrane electrode assembly included in a fuel cell. Specifically, the present invention relates to an improvement in a method for manufacturing a membrane electrode assembly using an electrolyte membrane having large swelling and shrinkage.

  Conventionally, an energy system using a fuel cell has been proposed as a measure for solving environmental problems such as global warming, air pollution, and resource depletion, and realizing a sustainable recycling society.

As fuel cells, there are not only stationary types installed in factories, houses, etc., but also non-stationary types for automobiles and portable electronic devices.
Particularly, in recent years, an early practical application of a fuel cell is expected as a ubiquitous mobile power source that does not require charging from an AC adapter and can continue to operate the device when fuel is supplied.

  Among such fuel cells, direct oxidation fuel cells that generate electricity by directly supplying organic fuels such as methanol and dimethyl ether to the anode without reforming them to hydrogen have attracted attention, and active research and development has been conducted. ing. The reason is that the organic fuel has a high theoretical energy density, the fuel cell system can be simplified by using the organic fuel, and the organic fuel is easy to store.

  A direct oxidation fuel cell has a unit cell in which a membrane electrode assembly (hereinafter referred to as MEA) is sandwiched between separators. In general, the MEA includes a solid polymer electrolyte membrane and an anode and a cathode disposed on both sides of the membrane. The anode and the cathode each include a catalyst layer and a diffusion layer. This direct oxidation fuel cell generates power by supplying fuel and water to the anode and supplying an oxidant (for example, oxygen) to the cathode.

For example, the electrode reaction of a direct methanol fuel cell (hereinafter referred to as DMFC) using methanol as a fuel is as follows.
Anode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O
That is, at the anode, methanol and water react to generate carbon dioxide, protons, and electrons. Protons generated at the anode reach the cathode through the electrolyte membrane, and electrons reach the cathode via an external circuit. At the cathode, oxygen, protons and electrons combine to produce water.

However, there are some problems in the practical application of DMFC.
One of the problems is related to interfacial bonding between the catalyst layer and the diffusion layer. The MEA is produced, for example, by a method in which a catalyst layer is directly applied and formed on an electrolyte membrane by a spray coating method or the like, and then the catalyst layer and the diffusion layer are thermally bonded by a hot press method. Here, the hot press method is a method in which an electrolyte membrane in which an anode catalyst layer and a cathode catalyst layer are formed is sandwiched between an anode diffusion layer and a cathode diffusion layer, and the catalyst layer and the diffusion layer are heated at a high temperature of 100 to 160 ° C. This is a method of thermal bonding at a pressure of about ˜100 kg / cm ² .

  However, in the MEA obtained by the above method, the diffusion layer is formed by the MEA activation process (a process in which MEA is immersed in water) performed to ensure proton conductivity, the supply of organic fuel at the time of cell power generation, and the like. There arises a problem that a part or all of the catalyst peels from the catalyst layer. Furthermore, in this MEA, the reaction product water and the water transferred from the anode accumulate in a liquid state at the interface separation portion between the catalyst layer and the diffusion layer of the cathode with the power generation time, and this water diffuses the oxidant. As a result, there was a problem that the durability deteriorated (the concentration overvoltage of the cathode increased) and the durability deteriorated.

  Subsequent investigation revealed that the phenomenon that the diffusion layer peeled off from the catalyst layer was mainly caused by a decrease in interfacial bonding between the catalyst layer and the diffusion layer. Specifically, in the conventional hot press method, the catalyst layer and the diffusion layer on the electrolyte membrane are thermally bonded in a state where water is evaporated from the electrolyte membrane and thermally contracted. For this reason, when MEA is immersed in water or when MEA comes into contact with organic fuel, the electrolyte membrane rapidly swells. However, since the diffusion layer cannot follow the swelling of the electrolyte membrane, it is considered that the interface bondability between the catalyst layer and the diffusion layer is lowered.

As a related proposal for dealing with such problems, in order to prevent deformation of the electrolyte membrane when the catalyst layer is thermally transferred to the electrolyte membrane, the electrolyte membrane is pre-wetted and a transfer film on which the catalyst layer is formed is provided. It has been proposed to arrange a protective film having the same thickness as the transfer film on the outer periphery (see Patent Document 1).
Furthermore, in order to suppress the deterioration of the solid polymer electrolyte and improve the durability of the membrane electrode assembly, the catalyst layer and the electrolyte membrane are thermally bonded, and then the membrane electrode assembly in a gas atmosphere containing water vapor. It has been proposed to heat-treat (see Patent Document 2).
JP 2007-141684 A JP 2005-251419 A

However, even if the above-described configuration of the prior art is used, it is difficult to obtain a membrane / electrode assembly having excellent interfacial bondability between the catalyst layer and the diffusion layer and excellent durability.
In the technique disclosed in Patent Document 1, only the electrolyte membrane is infiltrated in advance. For this reason, it is extremely difficult to thermally bond the catalyst layer and the diffusion layer while suppressing moisture evaporation (water vapor dissipation) of the electrolyte membrane under a high temperature condition exceeding 100 ° C.
In the technique disclosed in Patent Document 2, after the membrane / electrode assembly is manufactured, the membrane / electrode assembly is heat-treated in a gas atmosphere containing water vapor. Therefore, the technique disclosed in Patent Document 2 cannot drastically solve the phenomenon of thermal bonding with the catalyst layer in a state where the electrolyte membrane is thermally contracted.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a membrane / electrode assembly having excellent interfacial bondability between a catalyst layer and a diffusion layer and having excellent durability.

  As described above, when the catalyst layer and the diffusion layer are thermally bonded, water is evaporated from the electrolyte membrane, and the electrolyte membrane is thermally contracted. That is, the catalyst layer and the diffusion layer on the electrolyte membrane are thermally bonded with the electrolyte membrane contracted. For this reason, when the MEA is immersed in water in the MEA activation process or when the MEA comes into contact with the organic fuel by supplying the organic fuel during power generation, the electrolyte membrane rapidly swells. However, since the diffusion layer cannot follow the swelling of the electrolyte membrane, the interfacial bondability between the catalyst layer and the diffusion layer is reduced. This is considered to be the main cause and the diffusion layer is peeled off from the catalyst layer. Therefore, in the present invention, the catalyst layer and the diffusion layer are thermally bonded while maintaining the state where water is present inside the electrolyte membrane.

That is, the present invention has an electrolyte membrane, a catalyst layer, and a diffusion layer, and when the electrolyte membrane is changed from a swollen state with water to a dry state, the shrinkage rate of the electrolyte membrane is 5% or more. A method for producing a membrane electrode assembly,
(A) forming a catalyst layer on the surface of the electrolyte membrane;
(B) a step of wetting the electrolyte membrane on which the catalyst layer is formed with water;
(C) The present invention relates to a production method comprising a step of thermally bonding a diffusion layer on a catalyst layer in an environment where the shrinkage rate of the electrolyte membrane is 3% or less.

  The thermal bonding in the step (c) is performed at a temperature of 100 to 160 ° C. and a relative humidity of 50% R.D. H. It is preferable to perform in the above atmosphere.

  In the step (c), the thermal bonding is performed by using hot press means provided with a water reservoir communicating with the electrolyte membrane, and the thermal bonding is performed by storing liquid water in the water reservoir. It is preferable to be carried out in a state that has been performed. At this time, it is more preferable that the thermal bonding is performed in a sealed space.

Further, the present invention is an apparatus for manufacturing a membrane electrode assembly having an electrolyte membrane, a catalyst layer, and a diffusion layer,
(I) hot pressing means for thermally bonding the catalyst layer formed on the electrolyte membrane and the diffusion layer; and (ii) the electrolyte membrane when thermally bonding the catalyst layer and the diffusion layer. It is related with a manufacturing apparatus provided with the humidification means for humidifying.

  The hot press means includes two plate-like members that sandwich the electrolyte membrane, the catalyst layer, and the diffusion layer, the humidifying means includes a water reservoir provided in the hot press means, and the water reservoir is Preferably, water is supplied to the electrolyte membrane disposed between the two plate-like members.

  It is preferable that the water reservoir and the two plate-like members on which the electrolyte membrane is disposed communicate with each other.

  When the catalyst layer and the diffusion layer are thermally bonded, it is preferable to seal between the two plate-like members on which the electrolyte membrane is disposed.

  It is preferable that the manufacturing apparatus further includes a sealable chamber that houses the hot press unit and the humidification unit.

  In the present invention, the catalyst layer and the diffusion layer are thermally bonded in an environment in which the shrinkage rate of the electrolyte membrane is 3% or less on the basis of the dimensions of the electrolyte membrane swollen with water. Therefore, according to the present invention, it is possible to provide a membrane / electrode assembly having excellent durability and excellent durability of the interface between the catalyst layer and the diffusion layer even when immersed in water or in contact with an organic fuel. it can.

The production method of the present invention is a production method of a membrane electrode assembly having an electrolyte membrane, a catalyst layer, and a diffusion layer,
(A) forming a catalyst layer on the surface of the electrolyte membrane;
(B) a step of wetting the electrolyte membrane on which the catalyst layer is formed with water;
(C) A step of thermally bonding the diffusion layer on the catalyst layer in an environment where the shrinkage rate of the electrolyte membrane is 3% or less. The present invention is effective when an electrolyte membrane having a shrinkage rate of 5% or more when changed from a swollen state with water to a dry state is used.

In FIG. 1, the longitudinal cross-sectional view of an example of the membrane electrode assembly produced by the manufacturing method of this invention is shown.
The membrane electrode assembly 1 in FIG. 1 includes an electrolyte membrane 10, and an anode 11 and a cathode 12 that sandwich the electrolyte membrane 10. The anode 11 includes an anode catalyst layer 13 in contact with the electrolyte membrane 10 and an anode diffusion layer 14. The cathode 12 includes a cathode catalyst layer 15 in contact with the electrolyte membrane 10 and a cathode diffusion layer 16.

  As described above, in the present invention, the electrolyte membrane 10 is excellent in proton conductivity, heat resistance, chemical stability, etc., and has a shrinkage of 5% when dried from a wet state to a dry state. What is more is used.

The anode catalyst layer 13 can be mainly composed of conductive carbon particles or anode catalyst metal fine particles carrying anode catalyst metal fine particles and a polymer electrolyte. As the anode catalyst metal fine particles, for example, platinum (Pt) -ruthenium (Ru) alloy fine particles can be used. The polymer electrolyte is not particularly limited as long as it has excellent proton conductivity, heat resistance, chemical stability, and the like. As the polymer electrolyte contained in the anode catalyst layer 13, for example, the same material as the electrolyte membrane can be used.
The anode catalyst layer 13 can be directly formed on the electrolyte membrane 10 by using, for example, a wet coating technique such as a spray coating method.

  As the anode diffusion layer 14, a conductive porous substrate having both diffusibility of fuel, discharge of carbon dioxide generated by power generation, and electronic conductivity can be used. Examples of such a conductive porous substrate include carbon paper and carbon cloth. The conductive porous substrate may be subjected to water repellent treatment based on a known technique. Further, a water-repellent carbon layer (not shown) may be provided on the surface of the conductive porous substrate on the anode catalyst layer 13 side.

The cathode catalyst layer 15 can be mainly composed of conductive carbon particles carrying cathode catalyst metal fine particles and a polymer electrolyte. For the cathode catalyst metal fine particles, for example, platinum (Pt) fine particles can be used. The polymer electrolyte is not particularly limited as long as it has excellent proton conductivity, heat resistance, chemical stability, and the like. For example, the same material as the electrolyte membrane can be used as the polymer electrolyte contained in the cathode catalyst layer 15.
The cathode catalyst layer 15 can be directly formed on the electrolyte membrane 10 by using, for example, a wet coating technique such as a spray coating method.

  As the cathode diffusion layer 16, it is possible to use a conductive porous substrate having both diffusibility of an oxidant, discharge of water generated by power generation and water discharged from the anode, and electronic conductivity. Examples of such a conductive porous substrate include carbon paper and carbon cloth. The conductive porous substrate may be subjected to water repellent treatment based on a known technique. Furthermore, a water repellent carbon layer (not shown) may be provided on the surface of the conductive porous substrate on the cathode catalyst layer 15 side.

  In the production method of the present invention, first, (a) a catalyst layer is formed on the surface of the electrolyte membrane. Specifically, 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. The anode catalyst layer and the cathode catalyst layer can be formed using a wet coating technique as described above.

  Next, (b) the electrolyte membrane on which the anode catalyst layer and the cathode catalyst layer are formed is wetted with water. This wetting step (b) can be performed by immersing the electrolyte membrane on which the catalyst layer is formed in water.

Next, (c) the diffusion layer is thermally bonded on the catalyst layer in an environment where the shrinkage rate of the electrolyte membrane after wetting is 3% or less.
By performing thermal bonding in an environment where the shrinkage rate of the electrolyte membrane after wetting is 3% or less, the catalyst layer and the diffusion layer are thermally bonded while maintaining the state where water is present inside the electrolyte membrane. be able to. For this reason, even when the electrolyte membrane is immersed in water or comes into contact with the organic fuel, and the electrolyte membrane swells again, it is possible to ensure the interfacial bonding between the catalyst layer and the diffusion layer. As a result, the durability of the membrane electrode assembly, that is, the durability of the fuel cell can be improved.

  When heat bonding is performed in an environment where the shrinkage rate of the electrolyte membrane after wetting is greater than 3%, the diffusion layer may peel off from the catalyst layer when the electrolyte membrane swells again.

  On the other hand, by performing thermal bonding while humidifying the electrolyte membrane, the shrinkage rate of the electrolyte membrane after wetting can be reduced to 3% or less. For example, humidification of the electrolyte membrane can be performed by supplying water to the electrolyte membrane.

The temperature when the catalyst layer and the diffusion layer are thermally bonded is preferably 100 to 160 ° C., the pressure is preferably 50 to 100 kg / cm ² , and the time is 1 to 10 minutes. Is preferred.

  In the step (c), the thermal bonding is performed at a temperature of 100 to 160 ° C. and a relative humidity of 50% R.D. H. It is particularly preferable to carry out in the above atmosphere. Thereby, the catalyst layer and the diffusion layer can be sufficiently thermally bonded while suppressing moisture evaporation (water vapor dissipation) of the electrolyte membrane under a high temperature condition of 100 ° C. or higher.

  If the temperature at which the thermal bonding is performed exceeds 160 ° C., the molecular structure of the electrolyte membrane involved in proton conduction may be destroyed.

In the present invention, the step (c) can be performed using, for example, a manufacturing apparatus (hot press apparatus) as shown in FIG. FIG. 2 shows a schematic diagram of a manufacturing apparatus according to an embodiment of the present invention.
The manufacturing apparatus 20 of FIG. 2 includes (i) hot press means 30 for thermally bonding the catalyst layer formed on the electrolyte membrane and the diffusion layer, and (ii) thermal bonding of the catalyst layer and the diffusion layer. And a humidifying means for humidifying the electrolyte membrane. 2 includes an upper heater block 21 that is also a pressurizer, a lower heater block 22 that is also a base, a temperature controller 23 that controls the temperature of the upper heater block 21 and the lower heater block 22, a chamber 24, and A shutter 25 that can be opened and closed is provided.

In the hot press means 30, the electrolyte membrane on which the catalyst layer is formed and the diffusion layer are arranged so that the catalyst layer and the diffusion layer are in contact with each other.
The catalyst layer and the diffusion layer are thermally bonded by sandwiching the hot press means 30 between the upper heater block 21 and the lower heater block 22 and pressurizing the hot press means 30 at a predetermined temperature and a predetermined pressure. can do.

  An example of the hot press means 30 is shown in FIGS. FIG. 3 is a perspective view of an example of the hot press means used in the present invention, and FIG. 4 is an exploded perspective view of the hot press means of FIG.

As shown in FIG. 4, the hot press means 30 includes two plate-like members that sandwich the electrolyte membrane on which the catalyst layer is formed and the diffusion layer, that is, a rectangular lower plate 34 and an upper plate 36. Between the lower plate 34 and the upper plate 36, a rectangular middle plate 35 and rectangular heat-resistant sheets 37 and 38 are arranged for positioning the electrolyte membrane and the diffusion layer on which the catalyst layer is formed. 4 also shows an electrolyte membrane 10, an anode diffusion layer 14, and a cathode diffusion layer 16 on which an anode catalyst layer (not shown) and a cathode catalyst layer 15 are formed. The anode catalyst layer is provided on the surface of the electrolyte membrane 10 opposite to the surface on which the cathode catalyst layer 15 is formed.
As a constituent material of the lower plate 34, the middle plate 35, and the upper plate 36, for example, aluminum can be used.

  Fixing pins 40 and 41 are provided on the periphery of the upper surface of the lower plate 34. Through holes 48 and 49 are provided at positions facing the fixing pins 40 and 41 of the intermediate plate 35, and through holes 65 and 66 are provided at positions facing the fixing pins 40 and 41 of the upper plate 36. Yes. The fixing pin 40 is inserted into the through hole 48 of the intermediate plate 35 and the through hole 65 of the upper plate 36, and the fixing pin 41 is inserted into the through hole 49 of the intermediate plate 35 and the through hole 66 of the upper plate 36. Misalignment between the lower plate 34, the middle plate 35 and the upper plate 36 is prevented.

  Further, a rectangular base portion 42 is provided at the center of the surface of the lower plate 34 where the fixing pins are provided. A heat-resistant sheet 37 and the anode diffusion layer 14 are disposed on the base portion 42. The anode diffusion layer 14 is disposed in the opening 50 provided in the heat resistant sheet 37.

  Fixing pins 43 and 44 are provided on the periphery of the base portion 42. Further, through holes 51 and 52 are provided at positions facing the fixing pins 43 and 44 of the heat-resistant sheet 37. Since the fixing pin 43 is inserted into the through hole 51 and the fixing pin 44 is inserted into the through hole 52, the heat-resistant sheet 37 is prevented from being displaced.

  A portion of the intermediate plate 35 that faces the pedestal 42 is an opening 45, and the pedestal 42 is fitted into the opening 45. Therefore, by making the thickness of the base portion 42 and the thickness of the intermediate plate 35 the same, when the intermediate plate 35 is stacked on the lower plate 34, the height of the upper surface of the base portion 42 and the upper surface of the intermediate plate 35 are The height can be the same. For this reason, when the intermediate plate 35 is overlaid on the lower plate 34, the anode catalyst layer and the anode diffusion layer 14 formed on the electrolyte membrane 10 can be laminated without a gap.

  A plurality of fixing pins 46 are provided on a surface facing the upper plate 36 of the middle plate 35 along a first side parallel to the longitudinal direction of the opening 45, and a first parallel to the longitudinal direction of the opening 45 is provided. A plurality of fixing pins 47 are provided along the two sides. The plurality of fixing pins 46 and 47 are provided adjacent to the opening 45.

  A through hole 56 is provided at a position facing the fixing pin 46 of the electrolyte membrane 10, and a through hole 57 is provided at a position facing the fixing pin 47 of the electrolyte membrane 10. Further, through holes 58 and 59 are provided at positions facing the fixing pins 43 and 44 of the electrolyte membrane 10, respectively. Since the fixing pins 43 and 44 and the fixing pins 46 and 47 are inserted into the through holes 58 and 59 and the through holes 56 and 57 of the electrolyte membrane 10, displacement of the electrolyte membrane 10 can be prevented.

  A heat resistant sheet 38 is disposed on the electrolyte membrane 10. An opening 53 is provided in a portion of the heat-resistant seed 38 that faces the cathode catalyst layer 15. Through holes 54 and 55 are provided at positions facing the fixing pins 43 and 44 of the heat-resistant sheet 38. Since the fixing pins 43 and 44 are inserted into the through holes 54 and 55, the heat-resistant sheet 38 is prevented from being displaced.

  The cathode diffusion layer 16 is disposed in the opening 53 of the heat-resistant sheet 38 so as to be in direct contact with the cathode catalyst layer 15.

  The heat-resistant sheet 37 is preferably thinner than the anode diffusion layer. The material of the heat-resistant sheet 37 is not particularly limited as long as it has excellent heat resistance and mechanical strength. The same applies to the heat resistant sheet 38.

  An upper plate 36 is laminated on the cathode diffusion layer 16 and the heat-resistant sheet 38. Similar to the lower plate 34, a base 60 is provided on the surface facing the middle plate 35 of the upper plate 36. By providing the pedestal portion 60, the cathode catalyst layer 15 and the cathode diffusion layer 16 can be stacked without a gap when the upper plate 36 is overlaid on the intermediate plate 35 as described above.

  Through holes 61 and 62 are provided at positions of the upper plate 36 facing the fixing pins 46 and 47. Through holes 63 and 64 are provided at positions of the upper plate 36 facing the fixing pins 43 and 44. The fixing pins 46 and 47 are inserted into the through holes 61 and 62, and the fixing pins 43 and 44 are inserted into the through holes 63 and 64.

  As described above, the manufacturing apparatus of the present invention includes humidifying means for humidifying the electrolyte membrane when the catalyst layer and the diffusion layer are thermally bonded. For example, in the case of the hot press means 30 shown in FIGS. 3 and 4, the humidifying means can include a water reservoir communicating with the electrolyte membrane 10.

  When the lower plate 34 and the upper plate 36 are laminated with the electrolyte membrane and the diffusion layer formed with the catalyst layer interposed therebetween, the through holes 61, 62, 63, and 64 provided in the upper plate 36 are connected to the electrolyte membrane 10 with each other. You will communicate. That is, in the case of the hot press means 30 shown in FIGS. 3 and 4, the through holes 61, 62, 63 and 64 function as a water reservoir. At this time, the diameter of the through hole is preferably larger than the diameter of the fixing pin inserted therein. The diameter of the through hole refers to the maximum diameter of the through hole in a direction perpendicular to the stacking direction of the lower plate 34 and the upper plate 36. The diameter of the fixing pin refers to the maximum diameter of the fixing pin in a direction perpendicular to the stacking direction of the lower plate 34 and the upper plate 36.

  When the hot press means 30 shown in FIGS. 3 and 4 is used, thermal bonding between the catalyst layer and the diffusion layer may be performed in a state where water in a liquid state is accommodated in a water reservoir communicating with the electrolyte membrane 10. preferable. The air inside the hot press means in which the electrolyte membrane on which the catalyst layer is formed and the diffusion layer are arranged is replaced with water vapor, and hot pressing can be performed in a water vapor atmosphere. For this reason, the catalyst layer and the diffusion layer can be thermally bonded before the electrolyte membrane is dried and thermally contracted. That is, with the above configuration, thermal bonding can be performed in an environment where the shrinkage rate of the electrolyte membrane after wetting is 3% or less.

  In addition, before performing hot press, it is preferable to seal between the two plate-like members of the hot press means 30 so that liquid water does not leak to the outside. That is, it is preferable that the manufacturing apparatus of the present invention includes means for sealing between two plate-like members. For example, the two plate-like members 34 and 36 can be sealed by covering the side surface portion 32 of the hot press means 30 with a heat-resistant member 33 such as a heat-resistant tape or heat-resistant rubber.

  The amount of water stored in the water reservoir is preferably, for example, 30 cc or more, although it depends on the temperature at which thermal bonding is performed.

In the present invention, it is preferable that the thermal bonding in the step (c) is performed using the hot pressing means in a sealed space. That is, it is preferable that the manufacturing apparatus of the present invention includes a sealable chamber that accommodates the hot press means and the humidifying means.
By making the chamber containing the hot pressing means and the humidifying means sealable, the inside of the hot pressing means can be made into a high water vapor pressure atmosphere (relative humidity 100% RH). For this reason, it is possible to thermally bond the catalyst layer and the diffusion layer while sufficiently suppressing the electrolyte membrane from drying and thermally shrinking.
Furthermore, by using a sealable chamber, the temperature is 100 to 160 ° C. and the relative humidity is 50% R.D. H. The above atmosphere can be easily realized.

  In the manufacturing apparatus 20 of FIG. 2, the upper heater block 21 and the lower heater block 22 are disposed in a space 26 in a chamber 24 made of a material having heat resistance and pressure resistance. The chamber 24 can be sealed by closing the shutter 25.

  In addition, the following values can be used for the relative humidity of the atmosphere in which hot pressing is performed. During the hot pressing, the relative humidity of the atmosphere in the vicinity of the side surface portion 32 of the hot press means 30 is measured using the humidity measuring means 27 installed on the side surface portion 32 of the hot press means 30. The obtained value can be the relative humidity of the atmosphere in which hot pressing is performed. As the humidity measuring means 27, for example, a high temperature digital thermohygrometer can be used.

The present invention will be described in detail based on examples, but these examples do not limit the present invention in any way.
Example 1
A membrane electrode assembly as shown in FIG. 1 was produced.
The anode catalyst layer was produced as follows. Pt—Ru alloy fine particles (Pt: Ru weight ratio = 2: 1) having an average particle diameter of 3 nm were used as the anode catalyst.

  The anode catalyst was ultrasonically dispersed in an aqueous solution of isopropanol. An aqueous solution containing 5% by weight of a polymer electrolyte was added to the obtained dispersion, and the resulting mixture was stirred with a disper to prepare an anode catalyst ink. At this time, the weight ratio of the Pt—Ru alloy fine particles and the polymer electrolyte in the anode catalyst ink was set to 2: 1. As the polymer electrolyte, perfluorocarbon sulfonic acid ionomer (Flemion manufactured by Asahi Glass Co., Ltd.) was used.

Next, an anode catalyst layer having a size of 6 cm × 6 cm was formed on the electrolyte membrane 10 using a spray coating apparatus. The amount of the Pt—Ru catalyst contained in the anode catalyst layer was 6.2 mg / cm ² . The amount of the Pt—Ru catalyst is the weight of the Pt—Ru catalyst contained per projected unit area of the anode catalyst layer (unit area of the anode catalyst layer when the main surface of the anode catalyst layer is viewed from the normal direction). It is.

  As the electrolyte membrane 10, a hydrocarbon-based electrolyte membrane (polyfuel, 62 μm thickness) cut to a size of 15 cm × 10 cm was used.

  The cathode catalyst layer was produced as follows. As the cathode catalyst, Pt having an average particle diameter of 3 nm was used. The cathode catalyst was supported on conductive carbon particles having an average primary particle diameter of 30 nm. Carbon black (Ketjen Black EC manufactured by Mitsubishi Chemical Corporation) was used as the conductive carbon particles. The proportion of Pt in the total weight of the conductive carbon particles and Pt was 46% by weight.

  The cathode catalyst was ultrasonically dispersed in an aqueous solution of isopropanol. An aqueous solution containing 5% by weight of a polymer electrolyte was added to the obtained dispersion and stirred with a disper to prepare a cathode catalyst ink. At this time, the ratio of the weight of the polymer electrolyte to the weight of the conductive carbon particles in the cathode catalyst ink was set to 0.45. As the polymer electrolyte, perfluorocarbon sulfonic acid ionomer (Flemion manufactured by Asahi Glass Co., Ltd.) was used.

Next, using a spray coating apparatus, a cathode catalyst layer having a size of 6 cm × 6 cm is provided on the surface of the electrolyte membrane opposite to the surface where the anode catalyst layer is formed so as to face the anode catalyst layer. Formed. The amount of Pt catalyst contained in the cathode catalyst layer was 1.25 mg / cm ² . The amount of Pt catalyst is the weight of the Pt catalyst contained per projected unit area of the cathode catalyst layer (unit area of the catalyst layer when the main surface of the cathode catalyst layer is viewed from the normal direction), as described above. It is.

  The electrolyte membrane on which the anode catalyst layer and the cathode catalyst layer were formed was immersed in ion exchange water at 70 ° C. for 6 hours. Thereafter, the water adhering to the surface of the electrolyte membrane was wiped off with Kimwipe (Tech Jam Kay Dry).

Next, the electrolyte membrane and the diffusion layer on which the catalyst layer was formed were sandwiched between the hot press means 30 as described above.
Specifically, the electrolyte membrane 10 on which the catalyst layer was formed was attached to the fixing pins 46 and 47 of the intermediate plate 35. On the other hand, a heat resistant sheet 37 was attached to the fixing pins 43 and 44 on the base portion 42 of the lower plate 34. Thereafter, the anode diffusion layer 14 was disposed in the opening 50 of the heat resistant sheet 37. As the anode diffusion layer 14, carbon paper (TGP-H090 manufactured by Toray Industries, Inc.) was used. On one side of the carbon paper, a water repellent carbon layer (containing PTFE 40%) was provided with a thickness of about 30 μm. The anode catalyst layer and the anode diffusion layer were laminated so that the water-repellent carbon layer of the anode diffusion layer was in contact with the anode catalyst layer.

  Next, the middle plate 35 was placed on the lower plate 34 to bring the anode diffusion layer and the anode catalyst layer into contact with each other. Thereafter, the heat resistant sheet 38 was attached to the fixing pins 43 and 44 protruding from the through holes 58 and 59 of the electrolyte membrane 10. The cathode diffusion layer 16 was disposed in the opening 53 of the heat-resistant sheet 38, and the cathode catalyst layer and the cathode diffusion layer were brought into contact with each other. As the cathode diffusion layer 16, a carbon cloth (LT2500W manufactured by E-TEK Co.) provided with a water-repellent carbon layer on one side was used. The cathode catalyst layer and the cathode diffusion layer were laminated so that the water-repellent carbon layer of the cathode diffusion layer was in contact with the cathode catalyst layer.

  Next, the fixing pins 46 and 47 of the intermediate plate 35 are inserted into the through holes 61 and 62 of the upper plate 36, and the fixing pins 43 and 44 are inserted into the through holes 63 and 64 of the upper plate 36, so that An upper plate 36 was superimposed on the plate 35.

  Next, the side surface portion 32 of the hot press means 30 was covered with a heat-resistant member 33 (Nitoflon adhesive tape manufactured by Nitto Denko Corporation) so that the space between the lower plate 34 and the upper plate 36 was sealed. Thereafter, ion exchange water was injected into the plurality of through holes 61 and 62 and the through holes 63 and 64 of the upper plate 36 to provide a water reservoir. The total amount of ion-exchanged water injected was about 40 cc.

The hot press means 30 assembled in this manner is inserted between the upper heater block 21 and the lower heater block 22 of the hot press apparatus 20, and the temperature is 120 ° C., the pressure is 41 kg / cm ² , and the condition is 3 minutes. The catalyst layer and the diffusion layer on the electrolyte membrane were thermally bonded. At this time, the shutter 25 was opened. The relative humidity of the atmosphere in the vicinity of the side surface portion 32 of the hot press means 30 at the end of the hot press is 51% RP. H. Met.

  The membrane / electrode assembly obtained by the above method was designated as membrane / electrode assembly A.

Next, using the membrane electrode assembly A, a direct oxidation fuel cell was produced.
First, a gasket was installed around the anode 11 and the cathode 12 of the membrane electrode assembly A so as to sandwich the electrolyte membrane 10. As the gasket, a three-layer structure having a polyetherimide layer as an intermediate layer and silicone rubber layers on both sides thereof was used.

Next, the membrane electrode assembly A was sandwiched from both sides by a separator, a current collector plate, a sheet-like heater, an insulating plate, and an end plate each having an outer dimension of 12 cm × 12 cm, and fixed with a fastening rod. The fastening pressure was 12 kgf / cm ² per unit area of the separator.
As the separator, a resin-impregnated graphite material (G347B manufactured by Tokai Carbon Co., Ltd.) having a thickness of 4 mm was used. A serpentine channel having a width of 1.5 mm and a depth of 1 mm was formed on the surface of the resin-impregnated graphite material in contact with the electrode. As the current collector plate, a stainless steel plate subjected to gold plating was used. As the sheet heater, a samicon heater (manufactured by Sakaguchi Electric Heat Co., Ltd.) was used.

  The direct oxidation fuel cell obtained as described above was designated as fuel cell A.

Example 2
A membrane / electrode assembly B was produced in the same manner as in Example 1 except that the temperature at the time of hot pressing was 130 ° C. The relative humidity of the atmosphere near the side surface 32 of the hot press means 30 at the end of the hot press is 35% R.D. H. Met.

  Using the membrane electrode assembly B, a fuel cell B was produced in the same manner as in Example 1.

Example 3
A membrane / electrode assembly C was produced in the same manner as in Example 1 except that the space 26 containing the hot press means and the humidifying means was sealed by closing the shutter 25 of the hot press apparatus 20. The relative humidity of the atmosphere near the side surface portion 32 of the hot press means 30 at the end of the hot press is 97% R.D. H. Met.

  Using the membrane electrode assembly C, a fuel cell C was produced in the same manner as in Example 1.

<< Comparative Example 1 >>
A comparative membrane electrode assembly 1 was produced in the same manner as in Example 1 except that hot pressing was performed without injecting ion exchange water into the water reservoir of the hot pressing means 30. The relative humidity of the atmosphere in the vicinity of the side surface portion 32 of the hot press means 30 at the end of the hot press is 2% RP. H. Met.

  A comparative fuel cell 1 was produced in the same manner as in Example 1 using the comparative membrane electrode body 1.

<< Comparative Example 2 >>
A comparative membrane electrode assembly 2 was produced in the same manner as in Example 1 except that the temperature was set to 130 ° C. and hot pressing was performed without injecting ion exchange water into the water reservoir of the hot pressing means 30. . The relative humidity of the atmosphere in the vicinity of the side surface portion 32 of the hot press means 30 at the end of the hot press is 1% RP. H. Met.

  A comparative fuel cell 2 was produced in the same manner as in Example 1 using the comparative membrane electrode assembly 2.

<< Comparative Example 3 >>
Comparative membrane electrode in the same manner as in Example 1 except that the temperature was set to 130 ° C., the time was set to 8 minutes, and hot pressing was performed without injecting ion exchange water into the water reservoir of the hot pressing means 30. A joined body 3 was produced. The relative humidity of the atmosphere in the vicinity of the side surface portion 32 of the hot press means 30 at the end of the hot press is 1% RP. H. Met.

  A comparative fuel cell 3 was produced in the same manner as in Example 1 using the comparative membrane electrode assembly 3.

The shrinkage rate when the electrolyte membrane used in Examples 1 to 3 and Comparative Examples 1 to 3 was changed from the swollen state to the dry state was calculated by the following method.
First, a straight line serving as a dimensional measurement reference was drawn on the surface of the electrolyte membrane. Next, the length A of the reference straight line after the electrolyte membrane was immersed in ion exchange water at 70 ° C. for 6 hours was measured. Thereafter, the length B immediately after the electrolyte membrane was dried under reduced pressure on a heater at 70 ° C. for 2 hours was measured. The shrinkage was calculated by dividing the value of length B by the value of length A. As a result, the shrinkage rate when the electrolyte membranes used in Examples 1 to 3 and Comparative Examples 1 to 3 were dried from a wet state to a dry state was 7.0%.

[Evaluation]
For the membrane electrode assemblies A to C produced in Examples 1 to 3 and the comparative membrane electrode assemblies 1 to 3 produced in Comparative Examples 1 to 3, measurement of the shrinkage rate of the electrolyte membrane during thermal bonding, and the catalyst layer and The state of interface bonding with the diffusion layer was observed. Furthermore, the durability characteristics of the fuel cells A to C and the comparative fuel cells 1 to 3 were also evaluated.

(Shrinkage rate of electrolyte membrane during thermal bonding)
First, a straight line serving as a reference for dimensional measurement was drawn in a region where the catalyst layer on the surface of the electrolyte membrane was formed. Next, the length A of the reference straight line after the electrolyte membrane was immersed in ion exchange water at 70 ° C. for 6 hours was measured. The water adhering to the surface of the electrolyte membrane was wiped off with a Kimwipe (Keidry made by Tech Jam), and then attached to the intermediate plate 35 of the hot press means 30. Next, instead of the anode diffusion layer and the cathode diffusion layer, a polytetrafluoroethylene sheet (Naflon PTFE sheet manufactured by Nichias) was installed. Except for the above, the hot press means 30 was assembled in the same procedure as in Example 1.

Thereafter, the obtained hot press means was inserted between the upper heater block and the lower heater block of the hot press apparatus, and hot pressing was performed under the same conditions as in Example 1. Immediately after hot pressing, the hot pressing means 30 was disassembled, and the length B of the reference straight line on the electrolyte membrane surface was measured. The shrinkage was calculated by dividing the value of length B by the value of length A.
The obtained results are shown in Table 1. In Table 1, the shrinkage rate is expressed as a percentage value.

(Interface bonding state between catalyst layer and diffusion layer)
After the membrane electrode assemblies produced in Examples 1 to 3 and Comparative Examples 1 to 3 were immersed in ion exchange water at 70 ° C. for 3 hours, the interface bonding state between the catalyst layer and the diffusion layer was visually observed. The results are shown in Table 1. In Table 1, the symbol “◯” indicates that the diffusion layer is not peeled off from the catalyst layer, the symbol “Δ” indicates that a part of the diffusion layer is peeled off from the catalyst layer, and the diffusion layer is completely peeled from the catalyst layer This case is indicated by a symbol “x”.

(Durability)
The fuel cells produced in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to the following evaluation.
A 4M methanol aqueous solution was supplied to the anode at a flow rate of 0.27 cc / min, air was supplied to the cathode at a flow rate of 0.26 L / min, and each fuel cell was continuously generated at a constant voltage of 0.4V. The battery temperature during power generation was 60 ° C. The power density value was calculated from the current density value when 4 hours passed from the start of power generation. The obtained value was defined as the initial power density. Furthermore, the power density value was calculated from the current density value at the time when 1000 hours passed from the start of power generation. The ratio of the power density when 1000 hours passed with respect to the initial power density was defined as the power density maintenance rate. The obtained results are shown in Table 1. In Table 1, the power density maintenance rate is expressed as a percentage value.

As shown in Table 1, in Examples 1 to 3, the shrinkage rate of the electrolyte membrane during thermal bonding showed a small value. Furthermore, the interfacial bondability between the catalyst layer and the diffusion layer in the membrane electrode assemblies A to C showed good results.
In the present invention, the air inside the hot press means for disposing the electrolyte membrane on which the catalyst layer is formed and the diffusion layer is replaced with water vapor, and the inside of the hot press means is filled with water vapor. In order that hot pressing of the catalyst layer and the diffusion layer can be performed while the inside of the hot press means is filled with water vapor, the catalyst layer and the diffusion layer are bonded before the electrolyte membrane is dried and thermally contracted. Thermal bonding can be performed. For this reason, it is considered that the interfacial bondability between the catalyst layer and the diffusion layer could be maintained well.

  In particular, as in Example 3, when hot pressing was performed in a sealed space, the shrinkage rate of the electrolyte membrane during thermal bonding showed the smallest value. In this method, the air inside the hot press means can be replaced with water vapor, and the pressure of the water vapor in the atmosphere inside the hot press means can be increased. Therefore, it is considered that the shrinkage rate of the electrolyte membrane during thermal bonding in Example 3 showed the smallest value because the electrolyte membrane was sufficiently suppressed from being dried and thermally contracted during hot pressing.

  As described above, in Examples 1 to 3, the catalyst layer and the diffusion layer are thermally bonded while maintaining the state where water is present inside the electrolyte membrane, that is, in a state in which the shrinkage of the electrolyte membrane is suppressed. can do. For this reason, the dimensional change of the electrolyte membrane at the time of MEA activation processing and cell power generation can be reduced, and thus it is possible to ensure interfacial bonding between the catalyst layer and the diffusion layer. As a result, it is considered that the fuel cells A to C produced in Examples 1 to 3 exhibited excellent durability characteristics.

On the other hand, in Comparative Examples 1 to 3, the shrinkage rate of the electrolyte membrane during heat bonding showed a large value. Furthermore, the interfacial bondability between the catalyst layer and the diffusion layer in the comparative membrane electrode assemblies 1 to 3 was deteriorated.
In the case of Comparative Examples 1 to 3, since the electrolyte membrane is not humidified during hot pressing, water is evaporated from the electrolyte membrane and thermally contracted, and the catalyst layer and the diffusion layer on the electrolyte membrane are in a contracted state. And are thermally bonded. When the obtained membrane / electrode assembly is immersed in water, the electrolyte membrane swells over the interfacial bonding force between the catalyst layer and the diffusion layer, so that the interfacial bondability between the catalyst layer and the diffusion layer has deteriorated. It is done.

  Further, the durability of the comparative fuel cells 1 to 3 produced in Comparative Examples 1 to 3 was deteriorated. As described above, in the membrane electrode assembly used in these comparative fuel cells, the bondability between the catalyst layer and the diffusion layer is lowered. For this reason, in the comparative fuel cells 1 to 3, the reaction product water and the water that has moved from the anode accumulate in a liquid state at the interface peeling portion between the cathode catalyst layer and the cathode diffusion layer with the power generation time. This water reduces the diffusibility of oxygen, which is an oxidant, and increases the cathode overvoltage. As a result, it is thought that durability deteriorated.

  Since the membrane / electrode assembly produced by the production method of the present invention has good interfacial bonding between the catalyst layer and the diffusion layer and has excellent durability, the direct oxidation fuel cell including the membrane / electrode assembly is , Has excellent durability. Accordingly, the direct oxidation fuel cell can be suitably used as a power source for portable small electronic devices such as a mobile phone, a notebook computer, and a digital still camera. Furthermore, the direct oxidation fuel cell can be suitably used as a power source for, for example, an electric scooter or an automobile.

It is a longitudinal cross-sectional view which shows an example of the membrane electrode assembly produced by the manufacturing method of this invention. It is the schematic which shows the manufacturing apparatus of the membrane electrode assembly which concerns on one Embodiment of this invention. It is a perspective view of an example of the hot press means contained in the manufacturing apparatus of this invention. It is a disassembled perspective view of the hot press means of FIG.

DESCRIPTION OF SYMBOLS 1 Membrane electrode assembly 10 Electrolyte membrane 11 Anode 12 Cathode 13 Anode catalyst layer 14 Anode diffusion layer 15 Cathode catalyst layer 16 Cathode diffusion layer 20 Hot press apparatus 21 Heater block upper part 22 Heater block lower part 23 Temperature controller 24 Chamber 25 Shutter 26 In chamber Space 27 Humidity measuring means 30 Hot press means 32 Side surface portion 33 Heat-resistant member 34 Lower plate 35 Middle plate 36 Upper plate 37, 38 Heat-resistant sheet 40, 41, 43, 44 Fixed pins 42, 60 provided on the lower plate 45, 50, 53 Opening 46, 47 Fixing pins 48, 49 provided in the middle plate Through holes 51, 52 provided in the middle plate Through holes 54, 55 provided in the heat resistant sheet 37 Provided in the heat resistant sheet 38 Through-hole 56, 57, 58, 59 Electrolyte membrane Through hole provided in 61, 62, 63, 64, 65, 66 Through hole provided in upper plate

Claims (9)

A method for producing a membrane electrode assembly, comprising an electrolyte membrane, a catalyst layer, and a diffusion layer, wherein the electrolyte membrane has a shrinkage rate of 5% or more when the electrolyte membrane is dried from a swollen state to a dry state. And
(A) forming a catalyst layer on the surface of the electrolyte membrane;
(B) a step of wetting the electrolyte membrane on which the catalyst layer is formed with water, and (c) a diffusion layer on the catalyst layer in an environment where the shrinkage rate of the electrolyte membrane is 3% or less, The manufacturing method of a membrane electrode assembly which has the process of heat-joining.   The method for producing a membrane / electrode assembly according to claim 1, wherein in the step (c), the thermal bonding is performed at a temperature of 100 to 160 ° C in an atmosphere having a relative humidity of 50% RH or higher.   In the step (c), the thermal bonding is performed by using a hot press means provided with a water reservoir communicating with the electrolyte membrane, and the thermal bonding contains liquid water in the water reservoir. The method for producing a membrane / electrode assembly according to claim 1, wherein the method is performed in a state of being performed.   The manufacturing method of the membrane electrode assembly according to claim 3, wherein in the step (c), the thermal bonding is performed in a sealed space. An apparatus for producing a membrane electrode assembly having an electrolyte membrane, a catalyst layer, and a diffusion layer,
(I) hot pressing means for thermally bonding the catalyst layer formed on the electrolyte membrane and the diffusion layer; and (ii) the electrolyte membrane when thermally bonding the catalyst layer and the diffusion layer. An apparatus for producing a membrane electrode assembly, comprising a humidifying means for humidifying the water. The hot press means includes two plate-like members that sandwich the electrolyte membrane, the catalyst layer, and the diffusion layer,
The said humidification means contains the water reservoir provided in the said hot press means, The said water reservoir supplies water to the said electrolyte membrane arrange | positioned between the said 2 plate-shaped members. Manufacturing apparatus for membrane electrode assembly.   The apparatus for manufacturing a membrane electrode assembly according to claim 6, wherein the water reservoir and the two plate-like members on which the electrolyte membrane is disposed communicate with each other.   The apparatus for manufacturing a membrane electrode assembly according to claim 6 or 7, further comprising means for sealing between two plate-like members sandwiching the catalyst layer and the diffusion layer.   The manufacturing apparatus of the membrane electrode assembly in any one of Claims 5-8 further equipped with the chamber which can seal the said hot press means and the said humidification means.

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