JP2010010036A - Film-electrode assembly manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyelectrolyte film-electrode complex manufacturing method for preventing damages to a gas diffusion layer sheet, during thermocompression-bonding of an electrolyte film-catalyst layer complex and the gas diffusion layer sheet. <P>SOLUTION: When a complex 9 of the electrolyte film 1 and catalyst layers 4a, 4b is thermocompression-bonded to gas diffusion layer sheets 10a, 10b that constitute the gas diffusion layers 5a, 5b, or when the electrolyte film 1 is thermocompression-bonded to complexes 11a, 11b of the catalyst layers 4a, 4b and diffusion layers 5a, 5b, the polyelectrolyte film-electrode complex manufacturing method is applied, in advance, of the thermocompression bonding process, an annealing treatment to the electrolyte film 1. The temperature of the annealing treatment is higher than that of the thermocompression bonding during the thermocompression bonding process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane / electrode assembly.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for the body.

  FIG. 1 is a cross-sectional view showing an example of a single cell in a general solid polymer electrolyte fuel cell. The unit cell 100 is a membrane in which a fuel electrode (anode) 2 and an oxidant electrode (cathode) 3 are provided on one surface side of a solid polymer electrolyte membrane for fuel cells (hereinafter sometimes simply referred to as an electrolyte membrane) 1. An electrode assembly 6 is provided. The fuel electrode 2 has a structure in which a fuel electrode side catalyst layer 4a and a fuel electrode side gas diffusion layer 5a are laminated in order from the electrolyte membrane 1 side. Similarly, the oxidant electrode 3 has a configuration in which an oxidant electrode side catalyst layer 4b and an oxidant electrode side gas diffusion layer 5b are laminated in order from the electrolyte membrane 1 side.

Each catalyst layer 4 (4a, 4b) is provided with at least an electrode catalyst having catalytic activity for the electrode reaction in each electrode (2, 3). The electrode catalyst has a catalytic activity for the oxidation reaction of the fuel at the fuel electrode or the reduction reaction of the oxidant at the oxidant electrode, for example, platinum, or a metal such as ruthenium, iron, nickel, manganese, etc. An alloy with platinum (platinum alloy) or the like is used. The electrode catalyst is usually contained in the catalyst layer in a state where it is supported on carbon particles such as carbon black or conductive carbon particles such as carbon fibers. The catalyst layer contains a polymer electrolyte as a binder component of the electrode catalyst and as a component that imparts proton conductivity to the catalyst layer. In addition to the polymer electrolyte, a water repellent resin may be contained for the purpose of improving the water repellency of the catalyst layer.
On the other hand, the gas diffusion layer has the function of improving the supply capability of the reaction gas to the catalyst layer, the drainage property of the catalyst layer, the current collecting property, etc., and is composed of a conductive porous body such as carbon sheet or carbon paper. Is done.

  The membrane / electrode assembly 6 is sandwiched between two separators 7 a and 7 b to constitute a single cell 100. On one side of each of the separators 7a and 7b, grooves for forming a flow path of the reaction gas (fuel gas and oxidant gas) are provided. The fuel is formed by these grooves and the outer surfaces of the fuel electrode 2 and the oxidant electrode 3. A gas flow path 8a and an oxidant gas flow path 8b are defined. In FIG. 1, each electrode (fuel electrode, oxidant electrode) has a structure in which a catalyst layer and a gas diffusion layer are laminated. There is also a structure in which a functional layer is provided in addition to the layer and the gas diffusion layer.

As a method for producing a membrane / electrode assembly, for example, (a) a membrane / catalyst layer composite in which a catalyst layer is formed on both surfaces of an electrolyte membrane is sandwiched between two gas diffusion layer sheets constituting the gas diffusion layer, Examples thereof include a method of thermocompression bonding, and (b) a method of sandwiching an electrolyte membrane between two catalyst layer / gas diffusion layer composites each having a catalyst layer formed on the surface of a gas diffusion layer sheet and thermocompression bonding.
In (a) above, the polymer electrolyte and the water-repellent resin contained in the catalyst layer melt and act as an adhesive during thermocompression bonding, thereby joining the catalyst layer and the gas diffusion layer. In (b) above, during the thermocompression bonding, the polymer electrolyte of the electrolyte membrane, the polymer electrolyte of the catalyst layer, and the water-repellent resin melt and act as an adhesive, thereby joining the electrolyte membrane and the catalyst layer. The At the time of thermocompression bonding, the polymer electrolyte membrane and the catalyst layer, particularly the polymer electrolyte membrane, evaporate due to heating, dry, and shrink in the surface direction. On the other hand, the gas diffusion layer sheet does not shrink, and the flexibility in the surface direction is very small, so it cannot follow the shrinkage of the membrane / catalyst layer composite or the shrinkage of the electrolyte membrane, resulting in cracks, cracks, etc. Cheap.

  In Patent Document 1, a conductive porous substrate made of conductive carbon fiber cloth or felt is impregnated with a first dispersion containing a thermoplastic first fluororesin, and the first fluororesin is obtained. And a step (1) of increasing the hardness of the conductive porous substrate by baking at a first baking temperature not lower than the melting point of the first fluororesin and lower than the decomposition temperature of the first fluororesin. A method for producing a gas diffusion layer is described.

  Patent Document 2 discloses a method for producing a membrane / electrode assembly, in which an electrolyte membrane is coated by annealing at 100 to 250 ° C. after coating a coating liquid containing an ion exchange resin on a substrate. By forming a catalyst layer by applying a coating liquid containing an electrode catalyst and an ion exchange resin to the surface of the obtained electrolyte membrane, an intermediate composed of the electrolyte membrane and the catalyst layer is formed. A method of making is described.

Japanese Patent Laid-Open No. 2005-191002 JP 2008-16431 A

  In Patent Document 1, the hardness of the gas diffusion layer is increased by firing at a specific temperature in the manufacturing process of the gas diffusion layer, but when the film-catalyst layer composite and the gas diffusion layer are thermocompression bonded, The shrinkage deformation of the membrane / catalyst layer composite is not considered at all. Further, in Patent Document 2, the electrolyte film is annealed at 100 to 250 ° C. to adjust the water content in the film, and by forming a catalyst layer on the stable film by annealing, The adhesiveness with the catalyst layer is enhanced, and a high output membrane electrode assembly is obtained. However, in Patent Document 2, no consideration is given to shrinkage deformation of the membrane / catalyst layer composite when the membrane / catalyst layer composite and the gas diffusion layer are thermocompression-bonded. The annealing temperature and the hot press temperature are performed under the same temperature condition (140 ° C.).

  The present invention has been accomplished in view of the above circumstances, and when thermocompression bonding a membrane / catalyst layer composite and a gas diffusion layer sheet constituting a gas diffusion layer, or a polymer electrolyte membrane and a catalyst layer / gas An object is to prevent the gas diffusion layer sheet from being damaged when thermocompression bonding with the diffusion layer composite.

The method for producing a membrane / electrode assembly of the present invention has a laminated structure in which a polymer electrolyte membrane and a catalyst layer and a gas diffusion layer are laminated from the polymer electrolyte membrane side, and sandwich the polymer electrolyte membrane. A method for producing a membrane / electrode assembly comprising a pair of electrodes,
An annealing treatment step (A) for annealing the polymer electrolyte membrane or a membrane / catalyst layer composite in which the catalyst layer is provided on the surface of the polymer electrolyte membrane;
The polymer electrolyte membrane annealed in the annealing step (A), and the catalyst layer / gas diffusion layer composite provided with the catalyst layer on the surface of the gas diffusion layer sheet, the polymer electrolyte membrane and the gas diffusion layer The catalyst layer is provided on the surface of the polymer electrolyte membrane annealed in the thermocompression bonding step (B1), in which the catalyst layers are positioned so as to be positioned between the sheets and thermocompression bonded, or in the annealing treatment step (A). A thermocompression bonding step (B2) in which the membrane / catalyst layer composite and the gas diffusion layer sheet are superposed and thermocompression bonded so that the catalyst layer is positioned between the polymer electrolyte membrane and the gas diffusion layer sheet, or The membrane / catalyst layer composite annealed in the annealing step (A) and the gas diffusion layer sheet are overlapped so that the catalyst layer is positioned between the polymer electrolyte membrane and the gas diffusion layer sheet. It includes a thermocompression bonding step (B3) to thermocompression bonding, and
The annealing temperature in the annealing process (A) is higher than the thermocompression bonding temperature in any of the thermocompression bonding processes (B1) to (B3).

  According to the present invention, a membrane / electrode assembly comprising the step of thermocompression bonding the membrane / catalyst layer composite and the gas diffusion layer sheet, or the step of thermocompression bonding the polymer electrolyte membrane and the catalyst layer / gas diffusion layer composite. In the production method of the present invention, prior to the thermocompression bonding step, the polymer electrolyte membrane or the membrane / catalyst layer composite is annealed at a temperature higher than the thermocompression bonding temperature in the thermocompression bonding step. The shrink deformation of the polymer electrolyte membrane at the time can be suppressed. Therefore, according to the method for producing a membrane / electrode assembly of the present invention, it is possible to suppress damage such as cracking of the gas diffusion layer due to shrinkage deformation of the polymer electrolyte membrane in the thermocompression bonding step.

Since the hydrocarbon-based polymer electrolyte membrane has particularly large shrinkage deformation during heating, the effect of the present invention is particularly great when a hydrocarbon-based polymer electrolyte membrane is used as the polymer electrolyte membrane.
A preferable range of the annealing temperature in the annealing step (A) is a temperature range of 130 to 200 ° C.

  According to the method for producing a membrane / electrode assembly of the present invention, when the membrane / catalyst layer composite and the gas diffusion layer sheet constituting the gas diffusion layer are thermocompression bonded, or the polymer electrolyte membrane and the catalyst layer / gas It is possible to prevent the gas diffusion layer sheet from being damaged during thermocompression bonding with the diffusion layer composite. Therefore, according to the present invention, the productivity of the membrane / electrode assembly can be improved.

The method for producing a membrane / electrode assembly of the present invention has a laminated structure in which a polymer electrolyte membrane and a catalyst layer and a gas diffusion layer are laminated from the polymer electrolyte membrane side, and sandwich the polymer electrolyte membrane. A method for producing a membrane / electrode assembly comprising a pair of electrodes,
An annealing treatment step (A) for annealing the polymer electrolyte membrane or a membrane / catalyst layer composite having the catalyst layer provided on the surface of the polymer electrolyte membrane, and annealing in the annealing treatment step (A) The treated polymer electrolyte membrane and the catalyst layer / gas diffusion layer composite having the catalyst layer provided on the surface of the gas diffusion layer sheet are disposed between the polymer electrolyte membrane and the gas diffusion layer sheet. A thermocompression bonding step (B1) for superposing and thermocompression bonding, or a membrane / catalyst layer composite in which the catalyst layer is provided on the surface of the polymer electrolyte membrane annealed in the annealing treatment step (A), In the thermocompression bonding step (B2) in which the gas diffusion layer sheet is overlaid and thermocompression bonded so that the catalyst layer is positioned between the polymer electrolyte membrane and the gas diffusion layer sheet, or in the annealing treatment step (A) Thermocompression bonding step (B3) in which the annealed membrane / catalyst layer composite and the gas diffusion layer sheet are superposed and thermocompression bonded so that the catalyst layer is positioned between the polymer electrolyte membrane and the gas diffusion layer sheet. The annealing temperature in the annealing step (A) is higher than the thermocompression bonding temperature in any of the thermocompression bonding steps (B1) to (B3).

  Hereinafter, the membrane / electrode assembly according to the present invention and the membrane / electrode assembly provided by the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing an embodiment of a unit cell provided with a membrane / electrode assembly provided by the present invention, and FIG. It is a schematic diagram.

  In FIG. 1, a single cell 100 is a membrane in which a fuel electrode (anode) 2 and an oxidant electrode (cathode) 3 are provided on one side of a solid polymer electrolyte membrane (hereinafter sometimes simply referred to as an electrolyte membrane) 1. -It has the electrode assembly 6. The fuel electrode 2 has a structure in which a fuel electrode side catalyst layer 4a and a fuel electrode side gas diffusion layer 5a are laminated in order from the electrolyte membrane 1 side. Similarly, the oxidant electrode 3 has a configuration in which an oxidant electrode side catalyst layer 4b and an oxidant electrode side gas diffusion layer 5b are laminated in order from the electrolyte membrane 1 side.

  The membrane / electrode assembly 6 is sandwiched between two separators 7 a and 7 b to constitute a single cell 100. Each separator 7a, 7b is formed with a groove that forms a flow path for each reaction gas (fuel gas, oxidant gas), and a flow for supplying and discharging the reaction gas and the outermost surface of each electrode 2, 3. Paths 8a and 8b are defined. The flow path 8a on the fuel electrode side is a flow path for supplying fuel gas (a gas containing hydrogen or generating hydrogen) to the fuel electrode 2 and discharging unreacted fuel gas, and on the oxidant electrode side. The flow path 8b is a flow path for supplying an oxidant gas (a gas containing oxygen or generating oxygen) to the oxidant electrode 3 and discharging an unreacted portion of the oxidant gas.

  The membrane / electrode assembly 6 includes a membrane / catalyst layer composite 9 in which the catalyst layer 4 is provided on the surface of the electrolyte membrane 1 and a gas diffusion layer sheet 10 (10a, 10b) constituting the gas diffusion layer 5 (5a, 5b). 10b) is thermocompression-bonded (see 2A in FIG. 2), or the catalyst layer / gas diffusion layer composite 11 in which the electrolyte membrane 1 and the catalyst layer 4 (4a, 4b) are provided on the surface of the gas diffusion layer 5 ( 11a and 11b) can be formed by thermocompression bonding (see 2B in FIG. 2) (hereinafter sometimes simply referred to as thermocompression bonding).

  The method for producing a membrane / electrode assembly according to the present invention is characterized in that, prior to the thermocompression bonding step, the electrolyte membrane is preliminarily annealed at a temperature higher than the thermocompression bonding temperature in the thermocompression bonding step. is there. By subjecting the electrolyte membrane to an annealing treatment, distortion generated during the formation of the electrolyte membrane is reduced, or when a crystalline polymer resin is included, the crystallinity of the polymer resin is increased, thereby Hardness and dimensional stability are improved. The present invention is capable of suppressing shrinkage deformation of the electrolyte membrane in the thermocompression bonding step by annealing the electrolyte membrane at a temperature higher than the thermocompression bonding step before the thermocompression bonding step. It has been found that the gas diffusion layer can be prevented from being damaged due to shrinkage deformation of the electrolyte membrane.

In general, the electrolyte membrane undergoes shrinkage deformation when heated. As a result of investigation based on this knowledge, the present inventor has determined that the amount of shrinkage in thermocompression bonding [(film in the initial state] when the annealing treatment is performed at a temperature higher than the thermocompression bonding temperature in the thermocompression bonding process in advance. Surface direction dimension-surface direction dimension of film after thermocompression bonding) / (surface direction dimension of film in initial state) x 100%] is the contraction amount [(surface direction dimension of film in initial state-annealing process) It was found to be smaller than (the surface direction dimension of the subsequent film) / (the surface direction dimension of the film in the initial state) × 100%] (see Reference Experiments 1 and 2, FIG. 3). Generally, the higher the heating temperature, the greater the amount of shrinkage in the surface direction of the electrolyte membrane due to heating.
In addition, when exposed to a low temperature and high humidity environment (typically normal temperature and normal humidity) after heating, the dimensions of the electrolyte membrane are restored to some extent, but the larger the dimensional change during heating, The dimensional stability after heating increases and the contracted state is maintained.
As described above, according to the present invention, since the polymer electrolyte membrane is put into the thermocompression bonding step with its dimensional stability improved, the dimensional change of the electrolyte membrane during thermocompression bonding can be suppressed. As a result, the load applied in the surface direction of the gas diffusion layer is reduced by thermocompression bonding with the electrolyte membrane, and the occurrence of cracks and the like of the gas diffusion layer can be suppressed.

Hereinafter, the procedure of the manufacturing method of the present invention will be described.
First, the annealing process will be described.
In the present invention, the annealing treatment may be performed on the electrolyte membrane itself, or may be performed on a membrane / catalyst layer composite in which a catalyst layer is formed on the surface of the electrolyte membrane. The membrane / catalyst layer composite may be one in which catalyst layers (a fuel electrode side catalyst layer and an oxidant electrode side catalyst layer) are provided on both surfaces of the electrolyte membrane, or a catalyst is formed only on one surface of the electrolyte membrane. A layer (either one of the fuel electrode side catalyst layer and the oxidant electrode side catalyst layer) may be provided.

  Examples of the electrolyte membrane include those known as so-called solid polymer electrolyte membranes, for example, those containing fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes. Here, the fluorinated polymer electrolyte includes perfluorocarbon sulfonic acid resin represented by Nafion (trade name, manufactured by DuPont), Aciplex (trade name, manufactured by Asahi Kasei), and Flemion (trade name, manufactured by Asahi Glass). Refers to fluoropolymer electrolyte.

  The hydrocarbon-based polymer electrolyte typically does not contain any fluorine, but may be partially fluorine-substituted because the effects of the present invention are sufficiently obtained. Specific examples of hydrocarbon polymer electrolytes include polyether ether ketone, polyether ketone, polyether sulfone, polyphenylene sulfide, polyphenylene ether, polyparaphenylene, and other engineering plastics, polyethylene terephthalate, polyethylene, polypropylene, polystyrene, etc. Examples of these general-purpose plastics include those obtained by introducing proton conductive groups such as sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, and boronic acid groups, or copolymers thereof.

The electrolyte membrane may contain a plurality of hydrocarbon polymer electrolytes and fluorine polymer electrolytes as described above, or may contain components other than the polymer electrolyte.
Hydrocarbon polymer electrolyte membranes composed mainly of hydrocarbon polymer electrolytes as described above are heated compared to fluorine polymer electrolyte membranes composed mainly of fluorine polymer electrolytes. The shrinkage deformation at the time is large. According to the method for producing a membrane / electrode assembly according to the present invention, even when a hydrocarbon polymer electrolyte membrane is used as an electrolyte membrane, it is possible to suppress shrinkage deformation of the electrolyte membrane during thermocompression bonding. is there. That is, when using a hydrocarbon-based polymer electrolyte membrane, it can be said that the effect obtained by the present invention is particularly great. Here, the phrase “consisting mainly of a hydrocarbon-based polymer electrolyte” refers to an electrolyte membrane containing 90 wt% or more of a hydrocarbon-based polymer electrolyte.
The thickness of the electrolyte membrane is not particularly limited, and is usually about 10 to 100 μm.

A membrane / catalyst layer composite in which a catalyst layer is provided on the surface of an electrolyte membrane can be produced according to a general method. For example, it can be formed using a catalyst ink containing an electrode catalyst having catalytic activity for an electrode reaction in each electrode and an electrolyte material.
As the electrode catalyst, one in which a catalyst component is supported on conductive particles is usually used. The catalyst component is not particularly limited as long as it has catalytic activity for the oxidation reaction of the fuel at the fuel electrode or the reduction reaction of the oxidant at the oxidant electrode, and is generally used for polymer fuel cells. What is used for can be used. For example, platinum or an alloy of platinum and a metal such as ruthenium, iron, nickel, manganese, cobalt, copper, and the like can be given. As the conductive particles as the catalyst carrier, carbon particles such as carbon black, conductive carbon materials such as carbon fibers, and metal materials such as metal particles and metal fibers can also be used.
As the electrolyte material, the polymer electrolyte exemplified above as the polymer electrolyte constituting the electrolyte membrane can be used.

  The catalyst ink is obtained by dissolving or dispersing the electrode catalyst and the electrolyte material as described above in a solvent. The solvent of the catalyst ink may be appropriately selected. For example, alcohols such as methanol, ethanol and propanol, organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO), or organic solvents such as these Mixtures and mixtures of these organic solvents and water can be used. In addition to the electrode catalyst and the electrolyte material, the catalyst ink may contain other components such as a binder and a water repellent resin as necessary.

As a method of forming a catalyst layer on the electrolyte membrane surface using the catalyst ink, for example, a method of applying and drying the catalyst ink on the electrolyte membrane surface, a method of applying and drying the catalyst ink on the surface of the transfer substrate Examples include a method in which a transfer sheet is joined to an electrolyte membrane by thermocompression bonding or the like, and a catalyst layer is transferred to the surface of the electrolyte membrane.
A method for applying the catalyst ink to the electrolyte membrane surface or the transfer substrate surface, a method for drying the catalyst ink, and the like can be appropriately selected. For example, examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. Examples of the drying method include vacuum drying, heat drying, and vacuum heat drying. There is no restriction | limiting in the specific conditions in reduced pressure drying and heat drying, What is necessary is just to set suitably.
The amount of catalyst ink applied varies depending on the composition of the catalyst ink and the catalyst performance of the catalyst metal used in the electrode catalyst, but the catalyst component amount per unit area of the catalyst layer is 0.1 to 2.0 mg / cm ^2. What is necessary is just to become a grade. The thickness of the catalyst layer is not particularly limited, but may be about 1 to 50 μm.

The annealing temperature of the electrolyte membrane or the membrane / catalyst layer composite in the annealing process is not particularly limited as long as it is higher than the thermocompression bonding temperature in the thermocompression bonding process, but it is 10 to 50 ° C. higher than the thermocompression bonding temperature, particularly 10 It is preferable that it is higher by ˜40 ° C. The annealing temperature is preferably set according to the thermal decomposition point or glass transition point of the polymer electrolyte constituting the electrolyte membrane. Specifically, many polymer electrolyte membranes, particularly hydrocarbon-based polymer electrolyte membranes, have a thermal decomposition (desulfonation) point at 100 to 300 ° C., so that the temperature is lower than the thermal decomposition point of the electrolyte membrane. It is preferable to be in the range.
In general, it is preferable that the annealing temperature is in the range of 130 to 200 ° C, particularly 130 to 180 ° C.

  The annealing treatment time is not particularly limited and may be appropriately set according to the annealing treatment temperature or the like, but is usually preferably 2 to 10 minutes, and particularly preferably 3 to 7 minutes. If the annealing time is shorter than 2 minutes, the effect of annealing may not be sufficiently obtained. Further, if the annealing time is longer than 10 minutes, the productivity is lowered.

  In the annealing treatment step, the electrolyte membrane or the membrane / catalyst layer composite heated at the annealing treatment temperature is allowed to cool and once cooled.

Next, the thermocompression bonding process will be described.
In the annealing treatment step, when the electrolyte membrane itself is annealed, the annealed electrolyte membrane and the catalyst layer / gas diffusion layer composite provided with the catalyst layer on the surface of the gas diffusion layer sheet are combined with the electrolyte membrane. A membrane / catalyst layer composite is prepared by using an electrolyte membrane that is superposed and thermocompression-bonded (B1) or annealed so that the catalyst layer is disposed between the gas diffusion layers. The gas diffusion layer, the catalyst layer, and the electrolyte membrane are bonded together by stacking the composite and the gas diffusion layer sheet so that the catalyst layer is disposed between the electrolyte membrane and the gas diffusion layer and thermocompression bonding (B2). Membrane / electrode assembly can be obtained.
On the other hand, when the membrane / catalyst layer composite is annealed in the annealing step, the annealed membrane / catalyst layer composite and the gas diffusion layer sheet are placed between the electrolyte membrane and the gas diffusion layer. By laminating and thermocompression bonding so that the layers are arranged (B3), a membrane / electrode assembly in which the gas diffusion layer, the catalyst layer, and the electrolyte membrane are joined can be obtained.

As the gas diffusion layer sheet constituting the gas diffusion layer, one having gas diffusibility, conductivity, and strength required as a material constituting the gas diffusion layer, which can efficiently supply gas to the catalyst layer, for example, Carbonaceous porous bodies such as carbon paper, carbon cloth, carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium A conductive porous body such as a metal mesh or a metal porous body made of a metal such as tantalum, iron, stainless steel, gold, or platinum can be used.
The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, or may be provided with a water repellent layer on the side facing the catalyst layer. The water repellent layer usually has a porous structure including conductive particles such as carbon particles and carbon fibers, water repellent resin such as polytetrafluoroethylene (PTFE), and the like. It can be formed using a water repellent layer ink containing a water repellent resin. The gas diffusion layer sheet is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side of the conductive porous body facing the catalyst layer with a bar coater. It may be processed so as to be efficiently discharged out of the layer.

The catalyst layer / gas diffusion layer composite in which a catalyst layer is provided on the surface of the gas diffusion layer sheet is prepared by using a gas diffusion layer sheet instead of the electrolyte membrane in the above-described method for preparing a membrane / catalyst layer composite. be able to.
A membrane / catalyst layer composite in which a catalyst layer is provided on an annealed electrolyte membrane can be produced in the same manner as the above-described membrane / catalyst layer composite.

  The thermocompression bonding temperature in the thermocompression bonding process is not particularly limited, and is usually about 100 to 180 ° C. The specific thermocompression bonding temperature is the glass transition of the polymer electrolyte composing the electrolyte membrane and the polymer electrolyte composing the catalyst layer when the electrolyte membrane and the catalyst layer are joined in the thermocompression bonding process (in the case of B1 above). It is preferable to determine in consideration of the points. Moreover, when joining a catalyst layer and a gas diffusion layer in the thermocompression bonding process (in the case of B2 and B3 above), it is preferable to determine the glass transition point of the polymer electrolyte constituting the catalyst layer.

The thermocompression bonding pressure in the thermocompression bonding step is not particularly limited, and is usually about 0.5 to 8 MPa.
Examples of the thermocompression bonding method include a hot roll press, a flat pressure press, a mold press and the like, and among these, a mold press is preferable.

Example 1
Carbon black carrying platinum (Pt / C catalyst, Pt carrying ratio: 45 wt%) 1.0 g, perfluorocarbon sulfonic acid resin (Aldrich, Nafion solution, concentration 10 wt%) 5.5 g, ethanol and water The mixture was stirred and mixed to prepare a catalyst ink.

  The catalyst ink was spray-coated on both sides of a hydrocarbon polymer electrolyte membrane (sulfonated polyethersulfone) and dried to form a catalyst layer to obtain a membrane / catalyst layer composite.

  The obtained membrane / catalyst layer composite was annealed at 150 ° C. for 10 minutes. Thereafter, the membrane (electrode non-power generation region) was sandwiched between two pieces of carbon paper immersed in a perfluorocarbon sulfonic acid resin solution, and thermocompression bonded at 130 ° C. and 3 MPa for 5 minutes to obtain a membrane / electrode assembly. No cracks occurred in the carbon paper of the obtained membrane / electrode assembly.

(Comparative Example 1)
A membrane / electrode assembly was obtained in the same manner as in Example 1, except that the membrane / catalyst layer composite was annealed at 130 ° C. for 5 minutes. Cracks occurred in the carbon paper of the obtained membrane / electrode assembly.

(Reference Experiment 1)
A membrane / catalyst layer composite was prepared in the same manner as in Example 1, and allowed to stand at room temperature and normal humidity (23 ° C., 50% RH) for 24 hours. The length L1 in the surface direction of the electrolyte membrane of the membrane / catalyst layer composite Was measured.
Subsequently, the membrane / catalyst layer composite was annealed at 150 ° C. for 10 minutes as in Example 1, and the length L2 in the surface direction of the electrolyte membrane of the membrane / catalyst layer composite immediately after that was measured.
The membrane / catalyst layer composite subjected to the annealing treatment was allowed to stand at room temperature and normal humidity (23 ° C., 50% RH) for 24 hours, and the length L3 in the surface direction of the electrolyte membrane of the membrane / catalyst layer composite was measured. .
Further, after the annealing treatment, the membrane / catalyst layer composite exposed to normal temperature and humidity is subjected to thermocompression bonding at 130 ° C. and 3 MPa for 5 minutes, and the length of the membrane / catalyst layer composite in the surface direction immediately after that is L4 was measured.
Based on the above L1, the contraction amount ΔLn of L2 to L4 with respect to L1 [(L1−Ln) / L1 × 100%: Ln is L1, L2, L3 or L4]. The results are shown in FIG.

(Reference Experiment 2)
In Reference Experiment 1, the amount of contraction in the surface direction of the membrane / catalyst layer composite was calculated in the same manner except that the annealing temperature was 130 ° C. and the annealing time was 5 minutes. The results are also shown in FIG.

(result)
As shown in FIG. 3, in Reference Experiment 1 where the annealing temperature is higher than the thermocompression bonding temperature (the same conditions as in Example 1), the shrinkage amount ΔL4 of the electrolyte film after thermocompression bonding is the shrinkage of the electrolyte film after annealing. It was smaller than the amount ΔL2. On the other hand, in Reference Experiment 2 where the annealing treatment temperature is the same as the thermocompression bonding temperature (same conditions as in Comparative Example 1), the shrinkage amount ΔL4 of the electrolyte membrane after thermocompression bonding is smaller than the shrinkage amount ΔL2 of the electrolyte membrane after annealing treatment. Was also big.
Further, the dimensional change (ΔL4−ΔL3) of the electrolyte membrane before and after thermocompression bonding was 1% in Reference Experiment 1 and increased to 2% in Reference Experiment 2.
That is, in Comparative Example 1, since the shrinkage deformation in the surface direction of the electrolyte membrane is large before and after the thermocompression bonding step, a large force is applied in the surface direction to the gas diffusion layer that is thermocompression bonded to the electrolyte membrane. It is thought that the crack of has occurred. On the other hand, in Example 1, since the shrinkage deformation in the surface direction of the electrolyte membrane is small in the thermocompression bonding step, the gas diffusion layer can follow the shrinkage deformation of the electrolyte membrane, and the force applied in the surface direction of the gas diffusion layer is small. It is thought that no cracking occurred.

It is sectional drawing which shows one example of a single cell provided with the membrane electrode assembly provided by this invention. It is a schematic diagram explaining 1 process of the manufacturing method of the membrane electrode assembly of this invention. 6 is a graph showing the results of Reference Experiment 1 and Reference Experiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Fuel electrode (anode)
3 ... Oxidant electrode (cathode)
4a ... Anode side catalyst layer 4b ... Cathode side catalyst layer 5a ... Anode side gas diffusion layer 5b ... Cathode side gas diffusion layer 6 ... Membrane / electrode assembly 7a ... Anode side separator 7b ... Cathode side separator 8a ... Anode side gas flow path 8b ... Cathode side gas flow path 9 ... Membrane / catalyst layer composite 10 (10a, 10b) ... Gas diffusion layer sheet 11 (11a, 11b) ... Catalyst layer / gas diffusion layer composite 100 ... Single cell

Claims (3)

A membrane-electrode assembly comprising a polymer electrolyte membrane and a pair of electrodes having a laminated structure in which a catalyst layer and a gas diffusion layer are laminated from the polymer electrolyte membrane side and sandwiching the polymer electrolyte membrane A manufacturing method comprising:
An annealing treatment step (A) for annealing the polymer electrolyte membrane or a membrane / catalyst layer composite in which the catalyst layer is provided on the surface of the polymer electrolyte membrane;
The polymer electrolyte membrane annealed in the annealing step (A), and the catalyst layer / gas diffusion layer composite in which the catalyst layer is provided on the surface of the gas diffusion layer sheet, the polymer electrolyte membrane and the gas diffusion layer The catalyst layer is provided on the surface of the polymer electrolyte membrane annealed in the thermocompression bonding step (B1), in which the catalyst layers are positioned so as to be positioned between the sheets and thermocompression bonded, or in the annealing treatment step (A). A thermocompression bonding step (B2) in which the membrane / catalyst layer composite and the gas diffusion layer sheet are superposed and thermocompression bonded so that the catalyst layer is positioned between the polymer electrolyte membrane and the gas diffusion layer sheet, or The membrane / catalyst layer composite annealed in the annealing step (A) and the gas diffusion layer sheet are overlapped so that the catalyst layer is positioned between the polymer electrolyte membrane and the gas diffusion layer sheet. So, a thermocompression bonding step of thermocompression bonding (B3), provided with,
A method for producing a membrane / electrode assembly, characterized in that the annealing temperature in the annealing step (A) is higher than the thermocompression bonding temperature in any of the thermocompression bonding steps (B1) to (B3). .   The method for producing a membrane-electrode assembly according to claim 1, wherein the polymer electrolyte membrane is a hydrocarbon-based polymer electrolyte membrane.   The method for producing a membrane / electrode assembly according to claim 1 or 2, wherein the annealing temperature in the annealing step (A) is 130 to 200 ° C.

Images