JP2009230892A - Catalyst layer, membrane electrode assembly, fuel cell, and method of manufacturing catalyst layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst layer preventing a filler material existing on the surface of the catalyst layer from flowing out and having good water resistance for a long time, a membrane electrode assembly, a fuel cell, and a method of manufacturing the catalyst layer. <P>SOLUTION: The catalyst layer has a catalyst structure layer composed of a catalyst structure containing at least platinum, a proton conductive electrolyte, and a siloxane polymer having a hydrophobic radical, and a hydrophobic coat forming the coat of the catalyst structure layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to the production of a catalyst layer, a membrane electrode assembly, a fuel cell, and a catalyst layer.

In Patent Document 1, a structure composed of porous platinum oxide is contacted with a Si compound having a hydrophobic substituent that generates a polymerizable group by causing a hydrolysis reaction by the catalytic action of platinum oxide, and then platinum. A method for reducing oxides is described. Thereby, the hydrophobic agent which consists of methylsiloxane etc. can be simply added to a catalyst layer.
JP 2006-332041 A

  However, the long-term water resistance of the porous catalyst layer described in Patent Document 1 cannot be said to be sufficient, and further improvement has been desired.

  Accordingly, an object of the present invention is to provide a catalyst layer, a membrane electrode assembly, a fuel cell, and a method for producing the catalyst layer, which prevent the outflow of the hydrophobic agent present on the surface of the catalyst layer and has good water resistance for a long time. To do.

The present invention
A catalyst structure layer comprising a catalyst structure containing at least platinum, a proton conductive electrolyte, and a siloxane polymer having a hydrophobic group;
A hydrophobic coating that is a coating of the catalyst structure layer;
It is a catalyst layer characterized by having.

  The hydrophobic coating is preferably made of a fluoropolymer.

The fluorinated polymer preferably contains any polymer of perfluoropolyether, fluorosilane polymer, and hexafluoropropylene epoxide.
It is preferable that the catalyst structure has a dendritic shape.

Another aspect of the present invention is:
A membrane electrode assembly comprising at least the catalyst layer and a polymer electrolyte membrane.

Another aspect of the present invention is:
A fuel cell comprising the membrane electrode assembly, a gas diffusion layer, and a current collector.

Another aspect of the present invention is:
1) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, -OH bonded to Si, a group bonded to Si and converted to -OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
2) providing a proton conductive electrolyte on the surface of the catalyst precursor layer provided with the Si compound;
3) forming a hydrophobic coating on the surface of the catalyst precursor layer provided with the proton conductive electrolyte;
4) reducing the catalyst precursor layer on which the hydrophobic coating is formed;
It is a manufacturing method of the catalyst layer characterized by having.

  After the step 2) and before the step 3), a step of joining the catalyst precursor layer provided with the proton conductive electrolyte obtained in the step 2) to the surface of the polymer electrolyte membrane is further performed. It is preferable to have.

Another aspect of the present invention is:
i) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, —OH bonded to Si, a group bonded to Si and converted to —OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
ii) providing a proton conductive electrolyte on the surface of the catalyst precursor layer provided with the Si compound;
iii) reducing the catalyst precursor layer provided with the proton conductive electrolyte to obtain a catalyst structure layer (a);
iv) forming a hydrophobic coating on the surface of the catalyst structure layer (a);
It is a manufacturing method of the catalyst layer characterized by having.

  The step of joining the catalyst precursor layer provided with the proton conductive electrolyte obtained by the step ii) to the surface of the polymer electrolyte membrane after the step ii) and before the step iii) It is preferable to have.

  The method further comprises the step of joining the catalyst structure layer (a) obtained by the step iii) to the surface of the polymer electrolyte membrane after the step iii) and before the step iv). Is preferred.

Another aspect of the present invention is:
I) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, —OH bonded to Si, a group bonded to Si and converted to —OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
II) reducing the catalyst precursor layer to a catalyst structure layer (b);
III) providing a proton conductive electrolyte on the surface of the catalyst structure layer (b);
IV) forming a hydrophobic coating on the surface of the catalyst structure layer (b) provided with the proton conductive electrolyte;
It is a manufacturing method of the catalyst layer characterized by having.

  After the step III) and before the step IV), a step of joining the catalyst structure layer (b) provided with the proton conductive electrolyte obtained by the step III) to the polymer electrolyte membrane Furthermore, it is preferable to have.

  The hydrophobic coating is preferably made of a fluoropolymer.

  The fluorine-containing polymer preferably contains any polymer of perfluoropolyether, fluorosilane polymer, and hexafluoropropylene epoxide.

  The group which is bonded to Si and becomes -OH by hydrolysis is any one of -H, -OR (R: an alkyl group having 6 or less carbon atoms), and -Cl. The manufacturing method of the catalyst layer of 7-15.

  The step of forming the catalyst precursor layer containing platinum oxide is preferably performed by a gas phase method.

  According to the present invention, it is possible to provide a catalyst layer, a membrane electrode assembly, a fuel cell, and a method for producing a catalyst layer that have good water resistance for a long time.

  Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the scope of the present invention is determined by the scope of claims, and the following description does not limit the scope of the present invention. For example, the materials, dimensions, shapes, arrangements, manufacturing conditions, and the like described below do not limit the scope of the present invention.

The first of the present invention is
A catalyst structure layer comprising a catalyst structure containing at least platinum, a proton conductive electrolyte, and a siloxane polymer having a hydrophobic group;
A hydrophobic coating that is a coating of the catalyst structure layer;
It is a catalyst layer characterized by having.

  FIG. 1 is a schematic view of a part of the first catalyst layer of the present invention taken out. 1 is a projection obtained by irradiating the catalyst layer with light parallel to the substrate.

  In FIG. 1, 11 is a catalyst structure containing at least platinum, 12 is a siloxane polymer having a hydrophobic group, 13 is a proton conductive electrolyte, and 14 is a hydrophobic coating. The catalyst structure layer 19 is a layer made of a structure composed of a catalyst structure 11 containing at least platinum, a siloxane polymer 12 having a hydrophobic group, and a proton conducting electrolyte 13.

  Hereinafter, each part will be described.

  The catalyst structure 11 containing at least platinum may contain transition metal elements such as cobalt, copper and iron, noble metal elements such as ruthenium and iridium, titanium oxide and niobium oxide in addition to platinum containing at least platinum. .

  The catalyst structure 11 preferably has a dendritic shape. Here, the “dendritic shape” refers to a structure in which a large number of rod-like or flake (thin piece) structures are gathered with branch points. When the cross section of the catalyst layer having a dendritic shape is observed with an electron microscope or the like, it looks like a tree that is branched by a plurality of rod-like structures or flake-like structures. One rod-like or flake-like structure preferably has a short-side length of 5 nm to 200 nm. Here, the length in the short direction means the minimum dimension in the virtual projection plane of one rod-like structure or flake-like structure.

  The siloxane polymer 12 having a hydrophobic group is composed of a molecular structure having a main chain composed of continuous —Si—O— bonds (a main chain composed of a siloxane skeleton) and a side chain composed of a hydrophobic group. . When the siloxane polymer 12 has a hydrophobic group, the catalyst structure layer has hydrophobicity and water resistance is improved. Here, “hydrophobic” in the present invention and the present specification indicates a case where the contact angle with water is 90 ° or more. Hereinafter, the siloxane polymer 12 having a hydrophobic group may be simply referred to as a hydrophobic agent 12. Examples of such hydrophobic groups include alkyl groups (such as linear alkyl groups and phenyl groups), fluoroalkyl groups, and the like. Examples of the siloxane polymer having a hydrophobic group include those obtained by polymerizing alkylsilsesquioxane, alkylsiloxane, or a mixture thereof in a network.

  The proton conductive electrolyte 13 is a polymer compound having a proton conductive group. Examples of proton conductive groups include acidic groups such as sulfonic acid groups and phosphoric acid groups. Examples of such proton conducting electrolytes include perfluorocarbon polymers having sulfonic acid groups such as Nafion (registered trademark, manufactured by DuPont), sulfonated or phosphorylated aromatic polyether ketone, polysulfone, and the like. . The proton conductive electrolyte may have a plurality of types of proton conductive groups.

  The hydrophobic coating 14 is a coating of the catalyst structure layer and has hydrophobicity. The presence of the hydrophobic coating 14 improves the hydrophobicity in the pores of the catalyst layer and shortens the contact time between the hydrophobic agent 12 and water. Further, since the hydrophobic agent 12 is covered with the hydrophobic film, the outflow of the hydrophobic agent 12 can be suppressed. The hydrophobic coating 14 substantially covers the entire surface of the catalyst structure layer 19. Here, “substantially covering the entire surface of the catalyst structure layer” means that the siloxane polymer 12 having a hydrophobic group does not flow out even if there are minute holes or cracks in the hydrophobic coating 14. To the extent, it means that the catalyst structure layer 19 is covered. Therefore, even if a part of the siloxane polymer 12 having a hydrophobic group is exposed without being covered with the hydrophobic coating 14, the hydrophobicity of the hydrophobic coating 14 made of the surrounding fluoropolymer causes the hydrophobicity. When the contact time between the siloxane polymer 12 having a group and water is sufficiently short and the outflow is sufficiently suppressed, it is included in the case of “substantially covering the entire surface of the catalyst structure layer”. . The hydrophobic coating 14 preferably covers 90% or more of the surface of the catalyst structure layer 19.

  Examples of the material constituting such a hydrophobic coating include a fluorine-containing polymer (polymer of a compound having fluorine).

  The fluorine-containing polymer preferably contains any polymer of perfluoropolyether, fluorosilane polymer and hexafluoropropylene epoxide. The fluoropolymer may contain two or more polymers of the above materials.

  Next, the second aspect of the present invention will be described.

  FIG. 2 is a view showing a second membrane electrode assembly 8 of the present invention, wherein 1 is a polymer electrolyte membrane, 2 is an anode side catalyst layer, and 3 is a cathode side catalyst layer 3.

  The cathode side catalyst layer 2 or the anode side catalyst layer 3 is the first catalyst layer of the present invention. In the present invention and the present specification, when expressing “A or B is C”, when A is C and B is not C, when A is not C but B is C, The concept includes a case where both A and B are C. Therefore, either the anode side catalyst layer 2 or the cathode side catalyst layer 3 may be the first catalyst layer of the present invention, and either may be the first catalyst layer of the present invention. In addition, it is preferable that at least the cathode side catalyst layer 3 is the first catalyst layer of the present invention because flooding easily occurs in the cathode side catalyst layer where water is generated and the generated water is likely to stay.

The polymer electrolyte membrane 1 is a polymer electrolyte membrane having a proton conductive group and having a function of transmitting protons (H ⁺ ) generated on the anode side to the cathode side (proton conduction function). It consists of a high molecular compound having. Examples of such a polymer electrolyte membrane include perfluorocarbon polymers having a sulfonic acid group such as Nafion (registered trademark, manufactured by DuPont), sulfonated aromatic polyether ketone, polysulfone and the like.

  Further, when the second membrane electrode assembly of the present invention has a catalyst layer other than the first catalyst layer of the present invention (that is, only one of the cathode side catalyst layer and the anode side catalyst layer is the first layer of the present invention). In the case of a single catalyst layer), the catalyst layers other than the first catalyst layer of the present invention can be composed of a structure containing platinum, a structure made of platinum-supporting carbon, or the like.

Next, the third aspect of the present invention will be described.
FIG. 3 is a cross-sectional view showing an example of a third fuel cell of the present invention, wherein 8 is a second membrane electrode assembly of the present invention, 4 is an anode side gas diffusion layer, 5 is a cathode side gas diffusion layer, Reference numeral 6 denotes an anode-side current collector 6 and 7 denotes a cathode-side current collector.

  The anode side gas diffusion layer 4 and the cathode side gas diffusion layer 5 serve to supply oxygen or fuel to the membrane electrode assembly 8. The anode-side gas diffusion layer 4 and the cathode-side gas diffusion layer 5 are preferably composed of a plurality of sublayers. In the case of being constituted by a plurality of sublayers, the sublayers in contact with the membrane electrode assembly 8 among the sublayers of the anode side gas diffusion layer 4 and the cathode side gas diffusion layer 5 have pores as compared with the other sublayers. It is preferable that the average diameter is small. Specifically, when the gas diffusion layer is composed of two sublayers, as shown in FIG. 4, the gas diffusion layer contacts the membrane electrode assembly 8 of the anode side gas diffusion layer 4 and the cathode side gas diffusion layer 5. The average diameter of the holes in the sublayer 9 is preferably made smaller than the average diameter of the other sublayers 10 constituting the anode side gas diffusion layer 4 and the cathode side gas diffusion layer 5.

  In the following, the sublayers of the anode-side gas diffusion layer 4 and the cathode-side gas diffusion layer 5 that are in contact with the membrane electrode assembly 8 have a smaller average pore diameter than the other sublayers. The sublayer in contact with the membrane electrode assembly 8 may be referred to as a microporous layer (MPL).

  The MPL can be composed of, for example, carbon fine particles using PTFE as a binder. Examples of the carbon fine particles include acetylene black, ketjen black, fibrous carbon formed by vapor phase growth, and carbon nanotube.

  Among the sublayers constituting the anode side gas diffusion layer 4 and the cathode side gas diffusion layer 5, carbon cloth, carbon paper, porous metal, or the like can be used for portions other than the MPL. That is, MPL and these can be stacked and used as a gas diffusion layer having a structure composed of three sublayers. In addition, when using a metal material for a sublayer, it is preferable to use the material excellent in oxidation resistance. Specifically, SUS316L, nickel chromium alloy, titanium, or the like can be used. As an example of the nickel-chromium alloy porous metal, for example, Celmet (registered trademark) manufactured by Toyama Sumitomo Electric Co., Ltd. can be used.

  Next, the fourth to sixth aspects of the present invention will be described.

The fourth aspect of the present invention is
1) The process of providing Si compound which has Si, -OH couple | bonded with this Si, or group which becomes -OH by hydrolysis, and a hydrophobic group on the surface of the catalyst precursor layer containing at least platinum oxide When,
2) providing a proton conductive electrolyte on the surface of the catalyst precursor layer provided with the Si compound;
3) forming a hydrophobic film made of a fluoropolymer on the surface of the catalyst precursor layer provided with the proton conductive electrolyte;
4) reducing the catalyst precursor layer on which the hydrophobic coating is formed;
It is a manufacturing method of the catalyst layer characterized by having.

Each step will be described.
About the process of 1)
The catalyst precursor layer containing at least platinum oxide is preferably a porous body containing at least platinum oxide, and more preferably has a dendritic shape. The definition of the dendritic shape is the same as that of the first dendritic shape of the present invention. For platinum oxide having a dendritic shape, for example, a technique disclosed in JP-A-2006-49278 can be applied to the present invention.

  Platinum oxide can be represented by PtOx. The range of X at that time may be 2 or more, and there is no upper limit as long as the dendritic shape is maintained, but in reality, the upper limit of X is considered to be 2.5.

  When forming a catalyst precursor layer containing at least platinum oxide, it is preferable to use a sputtering method such as reactive sputtering or a reactive gas phase method such as reactive ion plating. When forming the catalyst precursor layer, the film formation conditions (film formation pressure, RF power applied to the target, oxygen partial pressure during film formation, etc.) are appropriately adjusted so as to satisfy the above O / Pt ratio.

  The catalyst precursor layer may be transferred to the surface of the polymer electrolyte membrane after being formed on the substrate, or after being formed on the gas diffusion layer, the gas diffusion layer and the catalyst precursor layer are bonded to the surface of the polymer electrolyte membrane. May be. Further, it may be formed on the surface of the polymer electrolyte membrane.

  When the catalyst precursor layer is formed on the substrate and then transferred to the surface of the polymer electrolyte membrane, the transfer step is performed after step (2) and before step (3) (that is, step (2) and step (3) described later. It is preferable to carry out during (). Even if an attempt is made to transfer or join the catalyst precursor layer to the surface of the polymer electrolyte membrane before the step (2), the proton conductive electrolyte added in the step (2) is not contained in the catalyst precursor layer, This is because the adhesion between the molecular electrolyte membrane and the catalyst precursor layer may not be obtained. In addition, when the catalyst precursor layer is transferred or joined to the electrolyte membrane surface after the step (3), the adhesion between the catalyst precursor layer and the polymer electrolyte membrane is deteriorated by the coating made of the fluoropolymer. There is.

  In addition, when the film is transferred to the surface of the polymer electrolyte membrane after being formed on the substrate, a material having a heat resistant temperature of 130 ° C. or higher is preferably used for the substrate. When a substrate made of a material having a heat resistant temperature of 130 ° C. or higher is used, it can be performed at a temperature higher than the glass transition temperature of solid polymer electrolyte (130 ° C. in Nafion (registered trademark)) when hot pressing is performed after transfer. Because. In addition, when a material having a high heat-resistant temperature is used, it is possible to easily prevent damage to the substrate during vapor deposition.

  As such a material, for example, a resin sheet having a high heat resistance such as PTFE, polycarbonate, polyimide, or the like is used. When a polycarbonate or polyimide sheet is used, it is desirable that the sheet has a multilayer structure and a release layer made of a fluororesin, fluorosilane, or the like is formed on the catalyst layer forming surface.

  Also when the gas diffusion layer on which the catalyst precursor layer is formed is bonded to the surface of the polymer electrolyte membrane, the transfer step is preferably performed after the step 2) and before the step 3). When the gas diffusion layer on which the catalyst precursor layer has been formed is bonded to the surface of the polymer electrolyte membrane, the gas diffusion layer includes carbon carriers such as carbon particles and carbon fibers, and the carbon carriers are present in layers on the surface of the resin sheet. It may be. Further, it may be present on the surface of the carbon carrier carbon cloth or carbon paper.

  In addition, when forming a catalyst precursor layer on the surface of a polymer electrolyte membrane, the transfer process or joining process to the electrolyte membrane of a catalyst precursor layer as mentioned above is unnecessary.

  In the step 1), the catalyst precursor layer includes Si, —OH bonded to the Si or a group bonded to the Si and converted to —OH by hydrolysis, and a hydrophobic group. Compound is given.

  The Si compound has Si and has —OH bonded to the Si or a group bonded to the Si and converted to —OH upon hydrolysis, and a hydrophobic group.

  When the Si compound has Si—OH (in other words, has —OH bonded to Si), —OH of the formed Si—OH is polymerized by a dehydration condensation reaction that occurs between —OH. Thus, a siloxane polymer having a skeleton of a hydrophobic group and a —Si—O— bond (siloxane bond) is formed on the surface of the catalyst precursor.

  When the Si compound has a group that is bonded to Si and becomes -OH by hydrolysis, the group that is bonded to Si and becomes -OH by hydrolysis is an acid contained in the proton conductive electrolyte or a catalyst precursor. It is hydrolyzed to -OH by using platinum oxide of the body layer and Pt contained in the platinum oxide as a catalyst.

  Here, examples of the group that is bonded to Si and becomes -OH by hydrolysis include -H, -OR (R: an alkyl group having 6 or less carbon atoms), -Cl, and the like.

  Examples of the hydrophobic group include an alkyl group and a fluoroalkyl group. The alkyl group here may have a branched carbon chain or a double bond.

  As such a Si compound, if it has Si, -OH bonded to Si or a group bonded to Si and converted to -OH by hydrolysis, and a hydrophobic group A monomer, an oligomer, or a polymer may be used. Therefore, it may be a siloxane polymer or alkylsilane having the above group. More specific materials for the Si compound include 2,4,6,8-tetraalkylcyclotetrasiloxane, 1,1,1,3,3,3-hexaalkyldisilazane, monoalkylsilane, dialkylsilane, Alkylsilane, polyalkylhydrogensiloxane, 2,4,6,8-tetraalkyltetraalkoxycyclotetrasiloxane, monoalkyltrialkoxysilane, dialkyldialkoxysilane, trialkylmonoalkoxysilane, polyalkylalkoxysiloxane, 2,4 , 6,8-tetraalkyltetrachlorocyclotetrasiloxane, monoalkyltrichlorosilane, dialkyldichlorosilane, trialkylmonochlorosilane, polyalkylchlorosiloxane, and the like. The alkyl group of these compounds may be a fluoroalkyl group in which part or all of the H atoms are substituted with F atoms.

  As a method for applying the Si compound to the surface of the catalyst precursor layer, a method of immersing the catalyst precursor layer in a solution of the Si compound, or applying the solution to the catalyst precursor layer by dropping, brushing, spraying, or the like. A known method such as a method, a method by CVD (described in JP-A-2006-332041, JP-T-1999-510443, and JP-A-2006-164575) can be used.

  An Si compound having Si and -OH bonded to Si or a group bonded to Si and converted to -OH by hydrolysis and a hydrophobic group has a Si / Pt molar ratio of 0. It is preferable to apply in an amount of 1 to 0.25.

  If the amount is too small, the hydrophobicity in the catalyst layer pores may be reduced and the catalyst layer may be easily flooded. If the amount is too large, the catalytic reaction surface area may be reduced, resulting in a decrease in catalyst utilization. Because there is.

  As described in JP-A-2006-332041, Si / Pt molar ratio is set to 0.1 to 0.25, 2,4,6,8-tetramethylcyclotetrasiloxane is used as a source gas, and CVD is performed at room temperature. When performing, for example, the contact time between the catalyst precursor layer made of platinum oxide and the source gas is preferably 3 to 5 minutes.

Step 2) In the step 2), a proton conductive electrolyte is applied to the surface of the catalyst precursor layer to which the Si compound is applied in the step 1).

  As a specific method for applying the proton conductive electrolyte to the surface of the catalyst precursor layer, a solution is prepared by dissolving the proton conductive electrolyte in a solvent, and the catalyst precursor provided with the Si compound in the step 1). Apply to the surface of the layer. At this time, the concentration of the solution is preferably 1% or less. When the concentration is higher than 1%, the viscosity of the solution becomes high, and it may be difficult to uniformly apply the solution to the surface of the catalyst precursor layer to which the Si compound is applied.

  The proton conductive electrolyte is made of a polymer compound having a proton conductive group such as a sulfonic acid group or a phosphoric acid group. Examples of such proton conductive electrolytes include perfluorocarbon polymers having sulfonic acid groups such as Nafion (registered trademark, manufactured by DuPont), sulfonated aromatic polyether ketones, polysulfones, and the like.

3) Step In the step 3), a hydrophobic film made of a fluoropolymer is formed on the surface of the catalyst precursor layer provided with the proton conductive electrolyte.

  As the fluorine-containing polymer, a polymer composed of perfluoropolyether, fluorosilane polymer, and hexafluoropropylene epoxide can be used.

  Examples of the method for forming a hydrophobic film made of a fluorine-containing polymer on the surface of the catalyst precursor layer provided with the proton conductive electrolyte include an immersion method, a spray method, a spin coating method, and a dip coating method.

Step 4) In step 4), the catalyst precursor layer on which the hydrophobic coating obtained in steps 1) to 3) is formed is reduced to form a catalyst layer. The method of reducing the catalyst precursor layer obtained in the steps 1) to 3) to the catalyst layer may be reduction with hydrogen gas, reduction with a solution, or electrochemical reduction. In the step 4) of the fourth aspect of the present invention, the shape of the catalyst precursor layer is reduced even after reduction by performing reduction after applying the proton conductive electrolyte to the surface of the catalyst precursor layer in step 3). Easy to maintain.

The fifth aspect of the present invention is
i) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, —OH bonded to Si, a group bonded to Si and converted to —OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
ii) providing a proton conductive electrolyte on the surface of the catalyst precursor layer provided with the Si compound;
iii) reducing the catalyst precursor layer provided with the proton conductive electrolyte to a catalyst structure layer (a);
iv) forming a hydrophobic coating on the surface of the catalyst structure layer (a);
It is a manufacturing method of the catalyst layer characterized by having.

  The fifth aspect of the present invention is the same as the fourth aspect of the present invention except that the order of the steps 3) and 4) in the fourth aspect of the present invention is changed.

  When the catalyst precursor layer or the catalyst structure layer is transferred or bonded to the surface of the polymer electrolyte membrane, after the step ii) and before the step iii), or after the step iii) It is preferable to carry out before the step iv).

The sixth aspect of the present invention is
I) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, —OH bonded to Si, a group bonded to Si and converted to —OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
II) reducing the catalyst precursor layer to which the Si compound has been added to form a catalyst structure layer (b);
III) providing a proton conductive electrolyte on the surface of the catalyst structure layer (b);
IV) forming a hydrophobic film made of a fluoropolymer on the surface of the catalyst structure layer provided with the proton conductive electrolyte;
It is a manufacturing method of the catalyst layer characterized by having.

  The sixth aspect of the present invention is the same as the fourth aspect of the present invention except that the step 4) in the fourth aspect of the present invention is performed after the step 1) and before the step 2). In addition, when the catalyst structure is transferred or bonded to the surface of the polymer electrolyte membrane, it is preferably performed after the step III) and before the step IV).

  Moreover, a membrane electrode assembly can be formed by performing hot pressing with a polymer electrolyte membrane sandwiched between two catalyst layers including the catalyst layers obtained by the production methods described in the fourth to sixth aspects of the present invention. . In this case, as described above, the step of transferring or joining the catalyst structure to the surface of the polymer electrolyte membrane can be incorporated in the course of the production process of the catalyst layer.

  Further, when a fuel cell is obtained using the obtained catalyst layer, the anode side gas diffusion layer is brought into contact with the anode side catalyst layer of the obtained membrane electrode assembly, and the cathode side gas diffusion layer is contacted with the cathode side gas catalyst layer. Place the layers in contact. Then, the current collector is formed by contacting the cathode side gas diffusion layer and the anode side gas diffusion layer, respectively.

  Next, specific examples will be shown to describe the present invention in detail.

Example 1
FIG. 5 is a schematic cross-sectional view of the polymer electrolyte fuel cell used in this example.

  Hereinafter, the manufacturing process of the polymer electrolyte fuel cell of this example will be described in detail.

(Process 1)
First, as a catalyst precursor layer forming step, a catalyst precursor is formed by an RF reactive sputtering method using a Pt (4N) target on the surface of a PTFE sheet (manufactured by Nitto Denko, Nitoflon: hereinafter sometimes referred to as “substrate”). A PtOx layer as a layer was formed to a thickness of 2 μm. As a reactive sputtering apparatus, CS-200 manufactured by ULVAC was used. Here, the reactive sputtering was performed at a total pressure of 5 Pa, an oxygen gas of 100%, and a substrate heater temperature of 40 ° C. Specifically, the power of RF (13.56 MHz high frequency) applied to the Pt target was 5.4 W / cm ² .

(Process 2)
According to a known technique described in JP-A-2006-332041, a Si compound was applied to the PtOx surface. Specifically, the catalyst precursor layer obtained in (Step 1) is placed in a closed container for 4 minutes at room temperature (vapor pressure of about 1.2 kPa) with 2,4,6,8-tetramethyltetracyclosiloxane vapor. Made contact. The Si / Pt molar ratio in the catalyst precursor was 0.10.

(Process 3)
Subsequently, the obtained PtOx layer was subjected to a reduction treatment by exposing it to a 2% H ₂ / He atmosphere for 30 minutes to obtain a catalyst structure layer (a) having a dendritic shape on the surface of the PTFE sheet and made of Pt. . The amount of Pt supported was 0.6 mg / cm ² .

(Process 4)
Thereafter, 8 μl of 1% Nafion solution (Sigma Nadrich Nafion 5% solution diluted to 1% with IPA) was dropped into the catalyst structure layer (b) obtained in (Step 3) per 1 cm ² of catalyst area, and vacuum was applied. The solvent was volatilized in. This formed an interface with the electrolyte on the catalyst surface. By the above (Step 1) to (Step 4), a catalyst structure layer (b) containing a proton conductive electrolyte was obtained.

(Process 5)
In order to form the anode catalyst layer, a platinum-supporting carbon layer was formed on the surface of the PTFE sheet by a doctor blade method so that the amount of Pt supported was 0.3 mg / cm ² . The catalyst slurry used here is a kneaded product of 1 part by mass of platinum-supporting carbon (manufactured by Johnson Matthey, HiSPEC 4000), 0.07 part by mass of Nafion, 1 part by mass of IPA, and 0.4 part by mass of water.

(Step 6)
A catalyst structure layer (b) containing the proton conductive electrolyte prepared in (Step 4) and a PTFE sheet with a catalyst layer prepared in (Step 5) so that the catalyst layer is on the inside, and a solid polymer electrolyte membrane (Dupont Nafion112, thickness 50 μm) was sandwiched, and hot pressing was performed under pressing conditions of 4 MPa, 150 ° C., 10 min. Thereafter, the PTFE sheet was removed from both the anode and cathode catalyst layers to remove the PTFE sheet.

(Step 7)
The structure obtained in (Step 6) is immersed in a fluorosilane polymer solution (Novec (R) EGC1720, manufactured by Sumitomo 3M), which is a fluoropolymer solution, pulled up and air-dried to form a hydrophobic film, MEA (membrane electrode assembly) was obtained.

(Comparative Example 1)
In Example 1, except that (Step 7) was not performed, an MEA composed of a catalyst layer having no hydrophobic coating composed of a fluoropolymer and a polymer electrolyte membrane was prepared in the same manner. The Si / Pt molar ratio in the catalyst was 0.11. The amount of Pt supported was 0.6 mg / cm ² .

(Example 2)
MEAs were produced in the same manner as in Example 1 (Step 7) except that the fluoropolymer solution was a perfluoropolyether solution (Fluorolink® S10, manufactured by Solvay Solexis). The Si / Pt molar ratio in the catalyst was 0.11. The amount of Pt supported was 0.6 mg / cm ² .

(Example 3)
In Example 1 (Step 2), the Si compound to be provided was changed from 2,4,6,8-tetramethyltetracyclosiloxane to methylhydrogen-modified silicone oil (KF-9901, manufactured by Shin-Etsu Chemical Co., Ltd.). KF9901 was diluted with IPA in a solvent to a concentration of 2% by weight, and then 18 μL was added per 1 cm 2 of catalyst precursor layer area. (Step 3) After that, MEA was produced in the same manner as in Example 1. The Si / Pt molar ratio in the catalyst was 0.11. The amount of Pt supported was 0.6 mg / cm ² .

(Comparative Example 2)
In Example 3, except that (Step 7) was not performed, an MEA comprising a catalyst layer having no hydrophobic film made of a fluoropolymer and a polymer electrolyte membrane was obtained in the same manner as in Example 3. Produced. The Si / Pt molar ratio in the catalyst was 0.11. The amount of Pt supported was 0.6 mg / cm ² .

(Evaluation of Examples 1-3 and Comparative Examples 1-2)
The MEA of Examples 1 to 3 and Comparative Examples 1 and 2 was analyzed by X-ray fluorescence analysis (X-ray Fluorescence Analysis, hereinafter abbreviated as XRF), and the amount of Si as a constituent element of the siloxane polymer having a hydrophobic group Was measured. ZSX1009e (manufactured by Rigaku Corporation) was used as the analyzer.

  Thereafter, a test was conducted in which each MEA was immersed and stored in warm water at 50 ° C. for 4 days. Next, the MEA was air-dried, and the Si amount was measured again by XRF. Since the catalyst layer in this MEA has a history of contact with water for a long time, the outflow amount of the siloxane polymer functioning as a hydrophobic agent can be measured by comparing the Si amount before and after the hot water immersion test. .

  Table 1 shows the residual amounts of Si before and after the tests of the MEAs of Examples 1 and 2 and Comparative Example 1. The remaining amount of Si was calculated by dividing the amount of Si after each MEA test by the amount of Si before the test.

  As can be seen from Table 1, in Comparative Examples 1 and 2, only about 1/3 and about 1/2 Si remained in the catalyst layer after the test, respectively, and the outflow of the hydrophobic agent occurred. On the other hand, in Examples 1-3, the outflow of the siloxane polymer which is a hydrophobic agent was significantly suppressed. Thus, it can be seen that the outflow of the hydrophobic agent is greatly suppressed by adding the hydrophobic film made of the fluoropolymer to the catalyst structure.

  Next, the MEA (state before the test) of Example 1 and the MEA (state before the test) obtained in Comparative Example 1 were combined into the anode side gas diffusion layer 4 (carbon cloth, LT2500-W manufactured by E-TEK). A single fuel cell was formed by sandwiching the cathode side gas diffusion layer 5, the anode side current collector 6, and the cathode side current collector 7 in this order as shown in FIG. For the cathode side gas diffusion layer 5, a gas diffusion layer made of carbon cloth (LT 1200-W manufactured by E-TEK) composed of MPL 9 and sublayer 10 and foam metal 16 was used. Furthermore, using the MEA after immersion in warm water of Example 1 and Comparative Example 1, fuel cell single cells were produced in the same manner as described above.

Although not shown in FIG. 5, the periphery of the anode side gas diffusion layer 4 and the cathode side gas diffusion layer 5 is sealed with an O-ring 15. Then, an electronic load device and a hydrogen gas pipe were connected to each fuel cell single cell as shown in FIG. 6, and a current sweep test of the fuel cell was performed to evaluate the power generation characteristics. In FIG. 6, the anode-side current collector 6 is provided with a slit so that hydrogen gas can freely pass therethrough. The anode current collector was filled with hydrogen gas at a dead end at 0.15 MPa, and the cathode electrode side was opened to the air. The evaluation of power generation characteristics was performed at a battery temperature of 25 ° C. and a relative humidity of the external environment of 100%. The current sweep rate (sweep plate) was 1 mA / cm ² / sec.

  Under this condition, since the anode side is dead-end, moisture evaporation from the anode side is suppressed. Furthermore, since the air humidity on the cathode side is 100% RH, moisture evaporation from the cathode side is also small. That is, under this condition, moisture movement outside the cell is suppressed, so that flooding in the cathode catalyst layer is likely to occur. Furthermore, the current value sweep plate at the time of measurement is small, and the power generation time at the time of measurement is increased to generate a lot of water. Therefore, flooding in the catalyst layer easily occurs at a high current density. When the cell power generation characteristics of the MEAs of Example 1 and Comparative Example 1 are compared under conditions where flooding is likely to occur, the difference in material diffusivity in the cathode catalyst layer of each MEA appears as a large difference in the power generation characteristics. It is easy to judge the effect on the power generation characteristics by the outflow of the hydrophobic agent.

The results of the voltage-current density characteristics of the MEAs of Example 1 and Comparative Example 1 are shown in FIG. The current density before the test of Example 1 at 0.4 V was 465 mA / cm ² , which was smaller than Comparative Example 1 (475 mA / cm ² ). However, after the test, the current density of Example 1 was 452 mA / cm ^2. And larger than Comparative Example 1 (157 mA / cm ² ).

This is presumed to be because, in Example 1, 95% of the hydrophobic agent remains after the test, so that the hydrophobicity of the catalyst layer is sufficiently maintained. In Comparative Example 1, since 2/3 of the hydrophobic agent flowed out by the immersion test, it is presumed that the hydrophobicity of the catalyst layer was lowered and flooding was likely to occur. The current density at 0.4V, when comparing the difference before and after the test, whereas Comparative Example 1 was 318mA / cm ^2, Example 1 was 13 mA / cm ^2, deterioration of the power generation characteristics is much It was suppressed.

The power generation characteristics of the fuel cell using the MEA after the immersion test of Example 2 are shown in FIG. 8 together with the data of Comparative Example 1. The current density of Example 2 at 0.4 V was 422 mA / cm ^2, which was larger than Comparative Example 1 (157 mA / cm ² ), and the deterioration of battery characteristics was significantly suppressed. This is presumed to be because in Example 2, the hydrophobicity of the catalyst layer was sufficiently maintained because 95% of the hydrophobic agent remained after the test.

The power generation characteristics of the fuel cell using the MEA before and after the immersion test of Example 3 are shown in FIG. As can be seen from FIG. 9, the MEA of Example 3 shows almost the same power generation characteristics before and after the immersion test, and it can be seen that there is almost no deterioration. The current density of Example 3 MEA (after the test) at 0.4 V was 431 mA / cm ^2, which was significantly suppressed from deterioration of the battery characteristics as compared with the value after the test of Comparative Example 1 (157 mA / cm ² ). This is presumed to be because the hydrophobicity of the catalyst layer was sufficiently maintained in Example 3 because there was almost no outflow of the hydrophobic agent during the immersion test.

  The MEA of Example 3 (state before the test) and the MEA of Comparative Example 1 (state before the test) were combined with the anode side gas diffusion layer 4 (carbon cloth, LT1400-W manufactured by E-TEK), the cathode side gas diffusion layer. 5 (carbon cloth, LT1400-W made by E-TEK), anode side separator 17, cathode side separator 18, anode side current collector 6 and cathode side current collector 7 are sandwiched in this order as shown in FIG. A single cell was formed.

  The power generation characteristics after the constant voltage power generation test of the fuel cells using the MEAs of Example 3 and Comparative Example 1 are shown in FIGS. 11 and 12, respectively. The power generation test was performed at a cell temperature of 40 ° C., a cell voltage of 0.75 V, an anode gas and a cathode gas of H 2 (flow rate 50 ccm) / air (flow rate 200 ccm), and both gas dew points 40 ° C. Further, in the power generation test, a program operation was performed so that power generation and stop were repeated for 10 minutes each.

  As can be seen from FIG. 11, the MEA of Example 3 shows slightly better power generation characteristics after the 160-hour power generation test than before the test, and it can be seen that the MEA has not deteriorated. On the other hand, as can be seen from FIG. 12, in the MEA of Comparative Example 1, it can be seen that the power generation characteristics decrease with the test time. This is because even when the cathode side catalyst layer of Example 3 is exposed to the generated water generated during power generation for a long time, the outflow of the hydrophobic agent is less than that of Comparative Example 1, and the hydrophobicity of the catalyst layer is sufficiently maintained. It is thought that this is because

It is a schematic diagram which shows a part of example of the catalyst layer of this invention. It is a schematic cross section which shows an example of the membrane electrode assembly of this invention. It is a schematic cross section which shows an example of the fuel battery cell of this invention. It is a schematic cross section which shows an example of the fuel battery cell of this invention. It is a schematic cross section which shows an example of the fuel battery cell of this invention. It is a schematic cross section which shows an example of the fuel battery cell of a present Example. It is a figure which shows the voltage-current density characteristic of the fuel cell of Example 1 and Comparative Example 1. It is a figure which shows the voltage-current density characteristic of the fuel cell of Example 2 and Comparative Example 1. FIG. 6 is a graph showing voltage-current density characteristics of the fuel battery cell of Example 3. 3 is a schematic cross-sectional view showing the configuration of fuel cells of Example 3 and Comparative Example 1. FIG. It is a figure which shows the change of the electric current value in the constant voltage electric power generation test of the fuel cell of Example 3. It is a figure which shows the change of the electric current value in the constant voltage power generation test of the fuel cell of the comparative example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Anode side catalyst layer 3 Cathode side catalyst layer 4 Anode side gas diffusion layer 5 Cathode side gas diffusion layer 6 Anode side current collector 7 Cathode side current collector 8 MEA (membrane electrode assembly)
9 MPL
10 Sublayer 11 Catalyst layer 12 Siloxane polymer having hydrophobic group (hydrophobic agent)
13 Proton Conducting Electrolyte 14 Fluoropolymer 15 O Ring Seal 16 Foamed Metal Layer 17 Anode Side Separator 18 Cathode Side Separator 19 Catalyst Structure Layer

Claims (17)

A catalyst structure layer comprising a catalyst structure containing at least platinum, a proton conductive electrolyte, and a siloxane polymer having a hydrophobic group;
A hydrophobic coating that is a coating of the catalyst structure layer;
A catalyst layer characterized by comprising:   The catalyst layer according to claim 1, wherein the hydrophobic coating is made of a fluoropolymer.   The catalyst layer according to claim 2, wherein the fluorine-containing polymer contains a polymer of perfluoropolyether, fluorosilane polymer, or hexafluoropropylene epoxide.   The catalyst layer according to claim 1, wherein the catalyst structure has a dendritic shape.   5. A membrane / electrode assembly comprising at least the catalyst layer according to claim 1 and a polymer electrolyte membrane.   A fuel cell comprising the membrane electrode assembly according to claim 5, a gas diffusion layer, and a current collector. 1) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, -OH bonded to Si, a group bonded to Si and converted to -OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
2) providing a proton conductive electrolyte on the surface of the catalyst precursor layer provided with the Si compound;
3) forming a hydrophobic coating on the surface of the catalyst precursor layer provided with the proton conductive electrolyte;
4) reducing the catalyst precursor layer on which the hydrophobic coating is formed;
A method for producing a catalyst layer, comprising:   After the step 2) and before the step 3), a step of joining the catalyst precursor layer provided with the proton conductive electrolyte obtained in the step 2) to the surface of the polymer electrolyte membrane is further performed. The method for producing a catalyst layer according to claim 7, comprising: i) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, —OH bonded to Si, a group bonded to Si and converted to —OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
ii) providing a proton conductive electrolyte on the surface of the catalyst precursor layer provided with the Si compound;
iii) reducing the catalyst precursor layer provided with the proton conductive electrolyte to obtain a catalyst structure layer (a);
iv) forming a hydrophobic coating on the surface of the catalyst structure layer (a);
A method for producing a catalyst layer, comprising:   The step of joining the catalyst precursor layer provided with the proton conductive electrolyte obtained by the step ii) to the surface of the polymer electrolyte membrane after the step ii) and before the step iii) The method for producing a catalyst layer according to claim 9, wherein:   The method further comprises the step of joining the catalyst structure layer (a) obtained by the step iii) to the surface of the polymer electrolyte membrane after the step iii) and before the step iv). The method for producing a catalyst layer according to claim 9. I) On the surface of the catalyst precursor layer containing at least platinum oxide, Si, —OH bonded to Si, a group bonded to Si and converted to —OH by hydrolysis, and a hydrophobic group Providing a Si compound having:
II) reducing the catalyst precursor layer to a catalyst structure layer (b);
III) providing a proton conductive electrolyte on the surface of the catalyst structure layer (b);
IV) forming a hydrophobic coating on the surface of the catalyst structure layer (b) provided with the proton conductive electrolyte;
A method for producing a catalyst layer, comprising:   After the step III) and before the step IV), a step of joining the catalyst structure layer (b) provided with the proton conductive electrolyte obtained by the step III) to the polymer electrolyte membrane The method for producing a catalyst layer according to claim 12, further comprising:   The method for producing a catalyst layer according to any one of claims 7 to 13, wherein the hydrophobic film is made of a fluoropolymer.   The method for producing a catalyst layer according to claim 14, wherein the fluorine-containing polymer includes any one of a perfluoropolyether, a fluorosilane polymer, and a hexafluoropropylene epoxide.   The group which is bonded to Si and becomes -OH by hydrolysis is any one of -H, -OR (R: an alkyl group having 6 or less carbon atoms), and -Cl. The manufacturing method of the catalyst layer of 7-15.   The method for producing a catalyst layer according to any one of claims 7 to 16, wherein the step of forming the catalyst precursor layer containing platinum oxide is performed by a gas phase method.

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