WO2014155929A1 - Method for manufacturing catalyst layer for fuel cell, catalyst layer for fuel cell, and fuel cell - Google Patents

Abstract

A membrane-electrode assembly (50) has a structure in which an anode (22), a solid polymer electrolyte membrane (20), and a cathode (24) are layered. An anode gas-diffusion layer (28) contained in the anode (22) and a cathode gas-diffusion layer (32) contained in the cathode (24) are manufactured by performing a freeze-drying process on a catalyst slurry, the area ratio of holes observed using a cross-section SEM image being 25-50%.

Description

Method for producing catalyst layer for fuel cell, catalyst layer for fuel cell and fuel cell

The present invention relates to a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen.

In recent years, fuel cells that have high energy conversion efficiency and do not generate harmful substances due to power generation reactions have attracted attention. As one of such fuel cells, a polymer electrolyte fuel cell that operates at a low temperature of 100 ° C. or lower is known.

A polymer electrolyte fuel cell has a basic structure in which a polymer electrolyte membrane, which is an electrolyte membrane, is arranged between a fuel electrode and an air electrode. It is a device that supplies the agent gas and generates power by the following electrochemical reaction.
Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (1)
Air electrode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)

The anode and the cathode each have a structure in which a catalyst layer and a gas diffusion layer (GDL) are laminated. The catalyst layers of the electrodes are arranged opposite to each other with the solid polymer film interposed therebetween, thereby constituting a fuel cell. The catalyst layer is a layer formed by binding carbon particles carrying a catalyst with an ion exchange resin. The gas diffusion layer becomes a passage for the oxidant gas and the fuel gas.

In the anode, hydrogen contained in the supplied fuel is decomposed into hydrogen ions and electrons as shown in the above formula (1). Among these, hydrogen ions move inside the solid polymer electrolyte membrane toward the air electrode, and electrons move to the air electrode through an external circuit. On the other hand, in the cathode, oxygen contained in the oxidant gas supplied to the cathode reacts with hydrogen ions and electrons that have moved from the fuel electrode, and water is generated as shown in the above formula (2). In this way, in the external circuit, electrons move from the fuel electrode toward the air electrode, so that electric power is taken out.

JP 2003-109604 A JP 2009-181718 A

Conventionally, when a catalyst layer of a polymer electrolyte fuel cell is produced, a procedure is employed in which a catalyst slurry is applied to a gas diffusion layer and then heated and dried to form a catalyst layer. The catalyst layer produced by the conventional procedure has fine pores serving as reaction gas passages, and the ratio of the pores to the catalyst layer is at most about 15%. For this reason, in order to improve gas diffusivity, it was difficult to raise the ratio of a pore.

The present invention has been made in view of these problems, and an object thereof is to provide a technique capable of improving the gas diffusibility of a catalyst layer for a fuel cell.

An embodiment of the present invention is a method for producing a fuel cell catalyst layer. In this production method, a conductive carrier, a metal catalyst supported on the carrier, and a proton conductor made of a solid polymer material are dispersed in a dispersion containing a lower alcohol and water to obtain a water content of 20 to 60. A step of producing a mass% catalyst slurry, a step of freezing water in the catalyst slurry, and a step of sublimating ice in the catalyst slurry.

In the production method of the above aspect, the lower alcohol may be an aliphatic alcohol or a polyhydric alcohol having 1 to 4 carbon atoms. The area ratio of pores observed by a cross-sectional SEM (Scanning Electron Microscope, Scanning Electron Microscope) image may be 25 to 50%. Moreover, you may provide the process of apply | coating the said catalyst slurry to a gas diffusion layer, before freezing the said water | moisture content. The proton conductor may have an EW of 450 or more and 900 or less.

Another aspect of the present invention is a fuel cell catalyst layer. The fuel cell catalyst layer includes a carrier having conductivity, a metal catalyst supported on the carrier, and a proton conductor made of a solid polymer material, and an area ratio of pores observed by a cross-sectional SEM image Is 25 to 50%.

In the fuel cell catalyst layer of the above aspect, the proton conductor may have an EW of 450 or more and 900 or less.

Yet another embodiment of the present invention is a fuel cell. The fuel cell includes an electrolyte, a cathode provided on one side of the electrolyte, an anode provided on the other side of the electrolyte,
The fuel cell catalyst layer according to claim 7 is used only for the cathode.

According to the present invention, the gas diffusibility of the catalyst layer for the fuel cell can be improved.

1 is a perspective view schematically showing the structure of a fuel cell according to an embodiment. It is sectional drawing on the AA line of FIG. It is a cross-sectional SEM image of the cathode catalyst layer of an Example. It is a cross-sectional SEM image of the cathode catalyst layer of a comparative example. It is a graph which shows the relationship between the output voltage and P / C of each membrane electrode assembly of an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

FIG. 1 is a perspective view schematically showing the structure of the fuel cell 10 according to the first embodiment. FIG. 2 is a cross-sectional view taken along the line AA in FIG. The fuel cell 10 includes a flat membrane electrode assembly 50, and a separator 34 and a separator 36 are provided on both sides of the membrane electrode assembly 50. In this example, only one membrane electrode assembly 50 is shown, but a plurality of membrane electrode assemblies 50 may be stacked via the separator 34 or the separator 36 to constitute a fuel cell stack. The membrane electrode assembly 50 includes a solid polymer electrolyte membrane 20, an anode 22, and a cathode 24.

The anode 22 has a laminate composed of a catalyst layer 26 and a gas diffusion layer 28. On the other hand, the cathode 24 has a laminate composed of a catalyst layer 30 and a gas diffusion layer 32. The catalyst layer 26 of the anode 22 and the catalyst layer 30 of the cathode 24 are provided to face each other with the solid polymer electrolyte membrane 20 interposed therebetween.

A gas flow path 38 is provided in the separator 34 provided on the anode 22 side. Fuel gas is distributed to a gas flow path 38 from a fuel supply manifold (not shown), and the fuel gas is supplied to the membrane electrode assembly 50 through the gas flow path 38. Similarly, a gas flow path 40 is provided in the separator 36 provided on the cathode 24 side.

Oxidant gas is distributed to the gas flow path 40 from an oxidant supply manifold (not shown), and the oxidant gas is supplied to the membrane electrode assembly 50 through the gas flow path 40. Specifically, when the fuel cell 10 is operated, a reformed gas containing a fuel gas, for example, hydrogen gas, flows through the gas flow path 38 along the surface of the gas diffusion layer 28 from the upper side to the lower side. The fuel gas is supplied to 22.

On the other hand, during operation of the fuel cell 10, an oxidant gas, for example, air flows through the gas flow path 40 from the upper side to the lower side along the surface of the gas diffusion layer 32, whereby the oxidant gas is supplied to the cathode 24. The Thereby, an electrochemical reaction occurs in the membrane electrode assembly 50. When hydrogen gas is supplied to the catalyst layer 26 via the gas diffusion layer 28, hydrogen in the gas becomes protons, and these protons move through the solid polymer electrolyte membrane 20 to the cathode 24 side. At this time, the emitted electrons move to the external circuit and flow into the cathode 24 from the external circuit. On the other hand, when air is supplied to the catalyst layer 30 through the gas diffusion layer 32, oxygen is combined with protons to become water. As a result, electrons flow from the anode 22 toward the cathode 24 in the external circuit, and power can be taken out.

The solid polymer electrolyte membrane 20 exhibits good ionic conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the anode 22 and the cathode 24. The solid polymer electrolyte membrane 20 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer. A fluorocarbon polymer or the like can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112. Examples of non-fluorine polymers include sulfonated aromatic polyetheretherketone and polysulfone. A typical film thickness of the solid polymer electrolyte membrane 20 is 20 to 50 μm.

The catalyst layer 26 constituting the anode 22 is composed of a proton conductor (ion exchange resin), a metal catalyst, and a conductive carrier carrying the metal catalyst. A typical film thickness of the catalyst layer 26 is 10 μm. The proton conductor in the catalyst layer 26 connects the conductive carrier carrying the metal catalyst and the solid polymer electrolyte membrane 20, and has a role of transmitting protons between the two. The proton conductor may be formed of the same polymer material as that of the solid polymer electrolyte membrane 20, but the dry weight (EW) per equivalent of ion exchange groups is preferably 450 or more and 900 or less, and 500 or more and 800. The following is more preferable. If the EW of the proton conductor is less than 450, the ion exchange group concentration becomes too high, and the solid polymer constituting the proton conductor becomes unstable. To do. If the EW is greater than 900, the solid polymer swells less, and a sufficient gas diffusion path is ensured even when the porosity is low. Therefore, the effect of producing the pores of the catalyst layer 26 by the method described later becomes poor. .

As the metal catalyst used for the catalyst layer 26, for example, an alloy catalyst made of noble metal and ruthenium can be cited. Examples of the noble metal used in the alloy catalyst include platinum and palladium. Examples of the conductive carrier that supports the metal catalyst include acetylene black, ketjen black, carbon nanotube, and carbon nano-onion.

The gas diffusion layer 28 constituting the anode 22 has a gas diffusion base material 27 and a microporous layer 29 (microporous layer: MPL) applied to the gas diffusion base material. The gas diffusion base material 27 is preferably composed of a porous body having electronic conductivity, and for example, carbon paper, carbon woven fabric or nonwoven fabric can be used.

The microporous layer 29 applied to the gas diffusion base material 27 is a kneaded product (paste) obtained by kneading a conductive powder and a water repellent. For example, carbon black can be used as the conductive powder. In addition, as the water repellent, a fluorine resin such as tetrafluoroethylene resin (PTFE) or tetrafluoroethylene / hexafluoropropylene copolymer (FEP) can be used. The water repellent agent preferably has binding properties. Here, the binding property refers to a property that can be made sticky (state) by joining things that are less sticky or those that tend to break apart. Since the water repellent has binding properties, a paste can be obtained by kneading the conductive powder and the water repellent.

The catalyst layer 30 constituting the cathode 24 is composed of a proton conductor (ion exchange resin), a metal catalyst, and a conductive carrier carrying the metal catalyst. The proton conductor connects the conductive carrier carrying the metal catalyst and the solid polymer electrolyte membrane 20, and has a role of transmitting protons between the two. The proton conductor may be formed from the same polymer material as the solid polymer electrolyte membrane 20. The proton conductor preferably has a dry weight (EW) of from 450 to 900, more preferably from 500 to 800, per equivalent of ion exchange group. If the EW of the proton conductor is less than 450, the ion exchange group concentration becomes too high, and the solid polymer constituting the proton conductivity becomes unstable. To do. If EW is greater than 900, the swelling of the solid polymer is reduced, and a gas diffusion path is sufficiently ensured even in a state where the porosity is low. Therefore, the effect of producing the pores of the catalyst layer 30 by the method described later becomes poor. .

In the cathode 24, generated water is generated during operation of the fuel cell 10, and the proton conductor easily swells due to the generated water. For this reason, by setting the EW of the proton conductor in the above range, the effect of producing the pores of the catalyst layer 30 by a method described later is further increased.

Examples of the metal catalyst used for the catalyst layer 30 include platinum or a platinum alloy. Examples of the metal used for the platinum alloy include cobalt, nickel, iron, manganese, iridium and the like. Examples of the conductive carrier supporting the metal catalyst include acetylene black, ketjen black, carbon nanotube, and carbon nano-onion.

The gas diffusion layer 32 constituting the cathode 24 has a gas diffusion base material 31 and a microporous layer 33 applied to the gas diffusion base material 31. The gas diffusion base material 31 is preferably composed of a porous body having electronic conductivity, and for example, carbon paper, carbon woven fabric or nonwoven fabric can be used. In consideration of productivity, it is preferable to use a common carbon paper as a base material for the gas diffusion layer 32 and the gas diffusion layer 28.

The microporous layer 33 applied to the gas diffusion base material 31 is a paste-like kneaded material obtained by kneading the conductive powder and the water repellent, and the micropores applied to the gas diffusion base material 27 described above. Similar to layer 29.

The catalyst layer 26 that constitutes the anode 22 and the catalyst layer 30 that constitutes the cathode 24 described above are formed by a manufacturing method including freeze-drying processing, which will be described later, and a cross-sectional SEM cut by an Ar ion beam, a Ga ion beam, or the like. The area ratio of the pores observed by the image is 25 to 50%, preferably 35 to 40%. The area ratio of the pores observed by the cross-sectional SEM image is obtained by binarizing the cross-sectional SEM image (7000 times or 15 μm square) to separate the pore portion and the portion other than the pore, and then with respect to the entire evaluation area. It is obtained by calculating the ratio of the pore portion.

(Catalyst layer production method)
Here, a method for producing the catalyst layers (catalyst layer 26 and catalyst layer 30) will be described.

First, a conductive carrier, a proton conductor made of a metal catalyst supported on the conductive carrier and a solid polymer material are dispersed in a dispersion containing a lower alcohol and water to have a water content of 20 to 60% by mass. A catalyst slurry is prepared. Examples of the lower alcohol include aliphatic alcohols and polyhydric alcohols having 1 to 4 carbon atoms. More specifically, examples of the aliphatic alcohol include ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol, and examples of the polyhydric alcohol include ethylene glycol and glycerol.

Lower alcohol has the effect of uniformly dispersing a metal catalyst and a proton conductor formed of a solid polymer material, and evaporates at a lower temperature and lower pressure than water. Do not disturb. When lower alcohols are not used, the proton conductors formed of the metal catalyst and the solid polymer material are not uniformly dispersed but form aggregates individually, so the proton conduction path in the catalyst layer and the reaction field of the fuel cell The three-phase interface (catalyst, proton conductor, and gas interface) cannot be sufficiently formed, and the power generation characteristics deteriorate.

Next, the obtained catalyst slurry is applied to the gas diffusion layer using a coating method such as a screen printing method.

Subsequently, a freezing treatment is performed in which the gas diffusion layer coated with the catalyst slurry is immersed in liquid nitrogen for about 10 minutes to freeze moisture in the catalyst slurry. At this time, it is preferable to install the gas diffusion layer on a metal flat plate made of stainless steel, aluminum, aluminum alloy material, titanium, titanium alloy material or the like and having good thermal conductivity. According to this, the temperature of the catalyst slurry can be reduced more instantaneously, and the moisture in the catalyst slurry can be instantaneously frozen. Further, since stainless steel, aluminum, aluminum alloy material, titanium, or titanium alloy material is formed with a passive film, it exhibits excellent corrosion resistance against moisture in the catalyst slurry. Moreover, since these metal materials have a large heat capacity, they can easily maintain a low temperature state for a long time, and are also suitable for an ice sublimation process described later.

Subsequently, the gas diffusion layer and the frozen catalyst slurry are vacuum-dried at room temperature for about 2 hours using a vacuum chamber. Thereby, the ice in the catalyst slurry is sublimated, and the space where the ice was present becomes pores or voids to form a catalyst layer. The conditions for sublimating the ice in the catalyst slurry are determined by the temperature and pressure of the catalyst slurry in a frozen state, so that the gas diffusion layer and the frozen catalyst slurry are separated from the water in the water phase diagram. For example, the temperature may be increased so that the pressure is lower than the point of importance. As mentioned above, the gas diffusion layer can be kept on a metal flat plate made of frozen stainless steel, aluminum, aluminum alloy material, titanium, titanium alloy material, etc. It is possible to facilitate the freeze-drying process.

Subsequently, the gas diffusion layer and the catalyst layer are dried at 80 to 100 ° C. for 10 minutes to 3 hours, and then heat treated at 100 to 190 ° C. for 30 minutes to 2 hours. The heat treatment temperature is preferably higher than the glass transition temperature of the solid polymer material used for the catalyst slurry and lower than the decomposition temperature.

Through the above steps, a catalyst layer having a pore area ratio of 25 to 50% can be formed.

In the fuel cell 10 described above, the catalyst layer is formed by a manufacturing method including freeze-drying, and the pore area ratio observed by a cross-sectional SEM image of a sample cut by an Ar ion beam, a Ga ion beam, or the like is 25 to 25%. By setting it to 50%, the catalyst layer can be made to have a porous and uniform pore structure as compared with a normal production method. As a result, the gas diffusibility in the catalyst layer can be increased, and a higher concentration solid polymer can be used for the catalyst layer as a proton conductor, and as a result, the output voltage of the fuel cell 10 can be increased. In addition, since the pore size in the catalyst layer is uniform, when carbon is used as the catalyst carrier, the pores are not easily destroyed when the carbon corrodes, and the catalyst layer structure is destroyed when it deteriorates. It is possible to greatly suppress the gas diffusivity decrease (voltage decrease) due to the above.

(Example)
<Preparation of cathode gas diffusion layer>
Carbon paper (Toray Industries, Inc .: TGPH060H) serving as a base material for the cathode gas diffusion layer was prepared, and the weight ratio of carbon paper: FEP (tetrafluoroethylene-hexafluoropropylene copolymer) = 95: 5. The carbon paper is immersed in the FEP dispersion, dried at 60 ° C. for 1 hour, and then subjected to heat treatment (FEP water repellent treatment) at 380 ° C. for 15 minutes. Thereby, the carbon paper is subjected to water repellent treatment almost uniformly.

Vulcan XC-72 (manufactured by CABOT: Vulcan XC72R) and terpineol (manufactured by Kishida Chemical Co.) as a solvent and triton (manufactured by Kishida Chemical Co., Ltd.) as a solvent, the weight ratio of Vulcan XC-72: terpineol: Carbon paste A is prepared by mixing uniformly at room temperature for 60 minutes using a universal mixer (manufactured by DALTON) so that Triton = 20: 150: 3. Ketjen Black EC300J (manufactured by Ketjen Black International) and terpineol (manufactured by Kishida Chemical Co.) as a solvent and Triton (manufactured by Kishida Chemical Co.) as a solvent have a weight ratio of Ketjen Black EC300. : Terpineol: Triton = 20: 150: 3 In a universal mixer (manufactured by DALTON), the mixture is mixed uniformly at room temperature for 60 minutes to prepare carbon paste B.

The weight ratio of the low molecular fluorine resin (made by Daikin: Lubron LDW40E) and the high molecular fluorine resin (made by DuPont: PTFE30J) to the fluorine resin contained in the dispersion is low molecular fluorine resin: high molecular fluorine resin = 20. : Mix to make 3 to produce a mixed fluororesin for cathode. The carbon paste A is put into a hybrid mixer container and cooled until the carbon paste A reaches 10 to 12 ° C. The above-mentioned mixed fluororesin for cathode is added to the cooled carbon paste A so that the weight ratio is carbon paste: mixed fluororesin for cathode (fluorine resin component contained in the dispersion) = 31: 1. Mix for 12 to 18 minutes in a mixing mode of EC500 manufactured by Keyence Corporation. The timing of stopping the mixing is until the paste temperature reaches 50 to 55 ° C., and the mixing time is appropriately adjusted. After the paste temperature reaches 50 to 55 ° C., the hybrid mixer is switched from the mixing mode to the defoaming mode and defoamed for 1 to 3 minutes. The paste after defoaming is naturally cooled to produce cathode gas diffusion layer paste A. Similarly to this procedure, the cathode gas diffusion layer paste B is prepared using the carbon paste B described above.

After the cathode gas diffusion layer paste B cooled to room temperature is applied to the surface of the carbon paper subjected to FEP water repellent treatment so that the application state in the carbon paper surface is uniform, the cathode gas diffusion layer paste A is applied. It applies | coats so that an application | coating state may become uniform on the gas diffusion layer paste B for cathodes, and it dries at 60 degreeC for 60 minute (s) with a hot air dryer (made by a thermal company). Finally, heat treatment is performed at 360 ° C. for 2 hours to complete the cathode gas diffusion layer.

<Preparation of cathode catalyst slurry>
As a cathode catalyst, platinum cobalt-supported carbon (Pt: Co = 3: 1 (element ratio), TEC36F52, Tanaka Kikinzoku Kogyo Co., Ltd.) was used, and as a proton conductor, a 10 wt% ionomer solution SS500 (manufactured by Asahi Kasei E-materials, (Hereinafter referred to as “SS500 solution”). To 5 g of platinum-supporting carbon, 10 mL of ultrapure water was added and stirred, and then 15 mL of ethanol was added. The catalyst dispersion solution was subjected to ultrasonic stirring and dispersion for 1 hour using an ultrasonic stirrer. A predetermined SS500 solution was diluted with an equal amount of ultrapure water and stirred with a glass rod for 3 minutes. Thereafter, ultrasonic dispersion was performed for 1 hour using an ultrasonic cleaner to obtain an SS500 aqueous solution. Thereafter, the SS500 aqueous solution was slowly dropped into the catalyst dispersion. During the dropping, stirring was continuously performed using an ultrasonic stirrer. After completion of the dropwise addition of the SS500 aqueous solution, 10 g (1: 1 by weight) of a mixed solution of 1-propanol and 1-butanol was dropped, and the resulting solution was used as a catalyst slurry for the cathode. During mixing, the water temperature was adjusted to about 60 ° C., and ethanol was evaporated and removed.

<Production of cathode>
The cathode catalyst slurry prepared by the above method was applied to the cathode gas diffusion layer by screen printing (150 mesh). The cathode gas diffusion layer coated with the catalyst slurry for cathode was placed on a stainless steel plate, and the stainless steel plate was immersed in liquid nitrogen for 10 minutes for freezing treatment. Subsequently, the cathode gas diffusion layer coated with the catalyst slurry for cathode is vacuum-dried for about 2 hours at room temperature using a vacuum chamber (vacuum constant temperature dryer DRR420DA, manufactured by Advantech Toyo Co., Ltd.) together with the stainless steel plate, and the cathode catalyst slurry The ice inside was sublimated. Subsequently, the cathode gas diffusion layer coated with the cathode catalyst slurry was dried at 80 ° C. for 1 hour, and then heat treated at 180 ° C. for 30 minutes.

<Preparation of anode gas diffusion layer>
Carbon paper (Toray Industries, Inc .: TGPH060H) serving as a base material for the anode gas diffusion layer was prepared, except that the carbon paper: FEP (tetrafluoroethylene-hexafluoropropylene copolymer) = 60: 40 in mass ratio. In the same manner as the cathode gas diffusion layer, the water repellent treatment is performed.

Vulcan XC-72 (manufactured by CABOT: Vulcan XC72R) and terpineol (manufactured by Kishida Chemical Co.) as a solvent and triton (manufactured by Kishida Chemical Co., Ltd.) as a solvent, the weight ratio of Vulcan XC-72: terpineol: A carbon paste is prepared by mixing uniformly at room temperature for 60 minutes using a universal mixer (manufactured by DALTON) so that Triton = 20: 150: 3.

The carbon paste and the low molecular fluororesin are mixed in a hybrid mixer container with a weight ratio of carbon paste: low molecular fluororesin (hereinafter referred to as anode fluororesin) (fluororesin component contained in the dispersion) = 26. : Add to 3 and mix for 15 minutes in the mixing mode of the hybrid mixer. After mixing, the hybrid mixer is switched from the mixing mode to the defoaming mode and defoamed for 4 minutes. When the supernatant liquid accumulates on the upper part of the paste after defoaming, the supernatant liquid is discarded, and the paste is naturally cooled to complete the anode gas diffusion layer paste.

The anode gas diffusion layer paste cooled to room temperature was applied to the surface of the carbon paper subjected to FEP water repellency treatment so that the coating state in the carbon paper surface was uniform, and using a hot air dryer (manufactured by Thermal) Dry at 60 ° C. for 60 minutes. Finally, heat treatment is performed at 360 ° C. for 2 hours to complete the anode gas diffusion layer.

<Preparation of catalyst slurry for anode>
The catalyst slurry for anode is prepared by using platinum ruthenium-supported carbon (Pt: Ru = 2: 3 (element ratio), TEC61E54, Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst. It is the same.

<Production of anode>
The cathode catalyst slurry prepared by the above method was applied to the anode gas diffusion layer by screen printing (150 mesh), subjected to freezing treatment and vacuum treatment under the same conditions as the cathode preparation method, impression treatment and Heat treatment was performed.

<Preparation of membrane electrode assembly>
Hot pressing is performed in a state where a solid polymer electrolyte membrane having a thickness of 30 μm is sandwiched between the anode and the cathode produced by the above method. Aciplex (registered trademark) (SF7202, manufactured by Asahi Kasei E-Materials) was used as the solid polymer electrolyte membrane. The membrane electrode assembly of the example was manufactured by hot pressing the anode, the solid polymer electrolyte membrane, and the cathode under the bonding conditions of 170 ° C. and 200 seconds.

The cathode catalyst layer of the example was subjected to cross-section cutting using ion milling (Ar ion beam, E-3500, manufactured by Hitachi High-Tech), and a cross-sectional SEM image (7000 times, see FIG. 3) was taken. The obtained cross-sectional SEM image was binarized by image processing / image measurement / data processing software WinROOF (manufactured by Mitani Shoji Co., Ltd.), and the area ratio occupied by the pores was calculated. (31-39%). In addition, the average porosity can be changed by changing the moisture in the catalyst layer slurry to 20 wt% to 60 wt%. As the moisture content increases, the average porosity increases, and the porosity can be arbitrarily changed between 25% and 50% at 20 wt% to 60 wt%. When the water content is less than 20 wt%, there is little ice formation and sufficient pores cannot be formed. Moreover, when it becomes more than 60 wt%, since the amount of lower alcohol is relatively reduced, the catalyst slurry is agglomerated and the performance is lowered.

Cross section polisher (registered trademark) (Ar ion beam IB-09010CP, manufactured by JEOL Ltd.), focused ion beam processing observation device (Ga ion beam, FB2200, manufactured by Hitachi High-Tech), (Ga An ion beam, JIB-4000, manufactured by JEOL Ltd.) can be used.

(Comparative example)
The membrane electrode assembly of the comparative example except that the catalyst slurry was applied to the gas diffusion layer, followed by drying at 80 ° C. for 3 hours and heat treatment at 180 ° C. for 45 minutes in the production of the cathode and anode. Then, it was produced in the same manner as the membrane electrode assembly of the example.

For the cathode catalyst layer of the comparative example, cross-section cutting was performed using ion milling (Ar ion beam, E-3500, manufactured by Hitachi High-Tech), and a cross-sectional SEM image (7000 times, see FIG. 4) was taken. The obtained cross-sectional SEM image was binarized by image processing / image measurement / data processing software WinROOF (registered trademark), and the area ratio occupied by the pore portion was calculated. As a result, the average pore ratio of 15 μm square was 5% (1 to 1). 9%).

About the membrane electrode assembly of an Example and a comparative example, what changed P / C (ratio of the mass (P) of proton conductor and the mass (C) of carbon used as a support | carrier) was prepared, and P of output voltage was prepared. The / C dependency was examined. FIG. 5 shows the relationship between the output voltage and P / C of each membrane electrode assembly of the example and the comparative example. As shown in FIG. 5, in the membrane electrode assembly of the comparative example, the output voltage peaks when P / C is around 0.65, and the optimum value of ion conductivity is around P / C = 0.65. . On the other hand, in the membrane electrode assembly of the example, the output voltage peaks when P / C is around 1, and the optimum value of ion conductivity is around P / C = 1. That is, in the membrane electrode assembly of the example, a higher concentration solid polymer can be used for the catalyst layer as the proton conductor. In addition, it was confirmed that the peak voltage when the membrane electrode assembly of the example was used was significantly increased as compared with the peak voltage of the membrane electrode assembly of the comparative example.

The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The form can also be included in the scope of the present invention.

For example, in the above-described embodiment, a catalyst layer that has been freeze-dried on both the anode and the cathode is used, but a catalyst layer that has been freeze-dried on either the anode or the cathode may be used. . In particular, the effect of increasing the gas diffusibility by applying freeze-drying treatment to the catalyst layer after setting the EW of the proton conductor to 450 to 900 is significant in the cathode. A proton conductor of 450 to 900 may be used, and the catalyst layer may be freeze-dried.

10 fuel cell, 20 solid polymer electrolyte membrane, 22 anode, 24 cathode, 26 catalyst layer, 28 gas diffusion layer, 29 microporous layer, 30 catalyst layer, 32 gas diffusion layer, 33 microporous layer, 34 separator, 36 separator 38 gas flow path, 40 gas flow path

The present invention can be used for a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen.

Claims (16)

1. A catalyst slurry having a water content of 20 to 60 mass% by dispersing a proton carrier made of a carrier having conductivity, a metal catalyst supported on the carrier and a solid polymer material in a dispersion containing a lower alcohol and water. A step of producing
   Freezing the water in the catalyst slurry;
   Sublimating ice in the catalyst slurry;
   The manufacturing method of the catalyst layer for fuel cells provided with.
2. The method for producing a fuel cell catalyst layer according to claim 1, wherein the lower alcohol is an aliphatic alcohol or a polyhydric alcohol having 1 to 4 carbon atoms.
3. The fuel according to claim 2, wherein the lower alcohol is at least one selected from the group consisting of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, ethylene glycol, and glycerol. A method for producing a battery catalyst layer.
4. The method for producing a fuel cell catalyst layer according to any one of claims 1 to 3, wherein the area ratio of the pores observed by the cross-sectional SEM image is 25 to 50%.
5. The method for producing a fuel cell catalyst layer according to any one of claims 1 to 4, wherein the proton conductor has an EW of 450 or more and 900 or less.
6. The method for producing a fuel cell catalyst layer according to any one of claims 1 to 5, further comprising a step of applying the catalyst slurry to a gas diffusion layer before freezing the moisture.
7. 7. The fuel cell catalyst according to claim 6, wherein the step of freezing water in the catalyst slurry is performed by installing the gas diffusion layer on a member made of a material having high thermal conductivity and high corrosion resistance. Layer manufacturing method.
8. The catalyst layer for a fuel cell according to claim 7, wherein the material having high thermal conductivity and high corrosion resistance is at least one material selected from the group consisting of stainless steel plate, aluminum, aluminum alloy material, titanium, and titanium alloy material. Manufacturing method.
9. The method for producing a catalyst layer for a fuel cell according to claim 6, wherein the step of sublimating ice in the catalyst slurry is performed by installing the gas diffusion layer on a member made of a material having a high heat capacity. .
10. 10. The method for producing a fuel cell catalyst layer according to claim 9, wherein the high heat capacity material is stainless steel plate, aluminum and aluminum alloy material, titanium and titanium alloy material.
11. 11. The production of a fuel cell catalyst layer according to claim 1, wherein the step of sublimating ice in the catalyst slurry raises the temperature at a lower pressure side than the triple point of water. Method.
12. The method for producing a fuel cell catalyst layer according to any one of claims 1 to 11, wherein the step of sublimating ice in the catalyst slurry is performed using a vacuum chamber.
13. The method further includes a step of heat-treating the catalyst layer formed by sublimating ice in the catalyst slurry at a temperature higher than the glass transition temperature of the solid polymer material and lower than the decomposition temperature of the solid polymer material. The method for producing a fuel cell catalyst layer according to any one of claims 1 to 12, wherein:
14. A conductive carrier;
    A metal catalyst supported on the carrier;
    A proton conductor made of a solid polymer material,
    A fuel cell catalyst layer having an area ratio of pores of 25 to 50% as observed by a cross-sectional SEM image.
15. 15. The fuel cell catalyst layer according to claim 14, wherein the proton conductor has an EW of 450 or more and 900 or less.
16. Electrolyte,
    A cathode provided on one side of the electrolyte;
    An anode provided on the other side of the electrolyte;
    With
    A fuel cell in which the fuel cell catalyst layer according to claim 15 is used only for the cathode.

Images