JP2008034191A - Manufacturing method for membrane-electrode assembly for fuel cell, and inspection method of catalyst grain for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a membrane electrode assembly for a fuel cell having a hydrophilic distribution with the use of a plurality of catalyst ink consisting of catalyst grains having different water submersion PH as defined by JIS K1474. <P>SOLUTION: In the manufacturing method of a membrane electrode assembly for the fuel cell, when at least one of catalyst layers out of an anode side and a cathode side is formed by preparing at least two kinds of catalyst grains having mutually different submersion PH and by coating on a prescribed coating face, in case the region containing catalyst grains having different submersion PH is distributed in thickness direction and/or plane direction of the catalyst layer and is distributed in thickness direction of the catalyst layer, the relevant catalyst ink is coated on every region so that the region containing catalyst grains having relatively small submersion PH may be distributed at a position near the solid polymer electrolyte membrane. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane / electrode assembly for a fuel cell in which an anode electrode is provided on one side of a polymer electrolyte membrane and a cathode electrode on the other side, and before the membrane / electrode assembly is produced, The present invention relates to a method for inspecting catalyst particles.

  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 configured by laminating a plurality of single cells each having a basic structure of a membrane / electrode assembly (MEA) 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 being easy to downsize and operating at a low temperature. It is attracting attention as a power source for the body.

As an example, in a polymer electrolyte fuel cell using a proton conductive solid electrolyte membrane of a type that requires entrainment of water for proton conduction such as Nafion (trade name, manufactured by DuPont), an anode (fuel electrode) The reaction of formula (1) proceeds.
H ₂ → 2H ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the cathode (oxidant electrode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves in the solid polymer electrolyte membrane from the anode side to the cathode side by electroosmosis while being hydrated with water.
On the other hand, the reaction of the formula (2) proceeds at the cathode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)

In general, each electrode (anode, cathode) is provided with a catalyst layer containing an electrode catalyst to promote the reactions of the above formulas (1) and (2). Examples of the electrode catalyst include platinum and platinum alloys. Is used.
In this type of fuel cell, water management within a single cell is important. Water for entrainment in proton conduction is intentionally supplied by humidifying the anode side as necessary. On the other hand, water is generated by an electrochemical reaction on the cathode electrode side, and water diffuses with protons from the anode side, so that the amount of water tends to be excessive. The water on the cathode side is diffused back to the anode side and used again for proton conduction, or is discharged to the gas flow path (the flow path of an oxidant gas such as air) on the cathode side.

  If the water balance in the single cell is lost, the balance of the electrochemical reaction at both poles is lost, causing the battery performance to deteriorate. That is, when water is insufficient in a region close to the anode side of the anode electrode and the electrolyte membrane, the battery performance is deteriorated because it is in a dry-up state and impedes proton supply. On the other hand, when the amount of water is excessive at the cathode electrode, flooding that closes the pores in the electrode occurs, so that the gas diffusibility is lowered and the supply of the oxidant gas is delayed, so that the battery performance is lowered.

In the solid polymer electrolyte fuel cell, in addition to the moisture distribution in the stacking direction of the membrane-electrode assembly as described above, a moisture distribution in the surface direction of the membrane-electrode assembly is also formed. While the reaction gas (fuel gas, oxidant gas) supplied from the gas flow path inlet into the single cell flows through the single cell from the inlet side to the outlet side of the reactive gas along the surface of the membrane / electrode assembly When the moisture is removed from the membrane / electrode assembly and reaches the gas channel outlet side, the humidity is in a high humidity state. That is, in the membrane / electrode assembly, the upstream side of the reaction gas is easily dried by deprivation of moisture by the reaction gas, and the downstream side of the reaction gas is likely to have a lot of moisture due to humidification by the reaction gas in a high humidity state.
Air that is generally used as an oxidant gas has a low content of reaction components of the electrode reaction as compared with hydrogen gas that is commonly used as a fuel gas, and therefore requires a large flow rate. Therefore, on the upstream side of the oxidant gas at the cathode, the moisture in the single cell is taken away by the flow of the oxidant gas and tends to be easily dried. On the other hand, on the downstream side of the oxidant gas of the cathode, moisture tends to exist excessively due to moisture such as produced water and oxidant gas in a high humidity state.

Fuel cells are required to exhibit high battery performance (high voltage) over a wide range from a low load range (ie, a low current condition) to a high load range (ie, a high current condition).
In addition, a plurality of cells are stacked in the fuel cell. During operation of the fuel cell, it is difficult to keep the amount of reaction gas distributed to each stacked cell completely uniform. Each cell in the same stack is energized at the same current density, even though the amount of reactant gas distribution varies with the position of the cell and / or the operating time. Therefore, the stoichiometric ratio between the cells may vary during the operation of the fuel cell.
Therefore, each cell has high battery performance over a wide range of stoichiometric conditions from low stoichiometric ratio to high stoichiometric ratio, so that even if the stoichiometric ratio of each cell fluctuates during operation of the fuel cell, high battery performance is always obtained. It is desirable to obtain (high voltage).

In Patent Document 1, in a polymer electrolyte fuel cell configured using an electrolyte membrane / electrode assembly in which a catalyst layer and a gas diffusion layer are disposed on both sides of a solid polymer electrolyte membrane, the catalyst layer is a solid polymer. Disclosed is a polymer electrolyte fuel cell comprising a first catalyst layer having a high water content disposed on the electrolyte membrane side and a second catalyst layer having a low water content disposed on the gas diffusion layer side. is doing. In Patent Document 1, when the catalyst layer has such a two-layer structure, the solid polymer electrolyte membrane is held wet by the first catalyst layer having a high water content disposed on the solid polymer electrolyte membrane side, and is high. On the other hand, proton conductivity can be obtained. On the other hand, the second catalyst layer having a low water content disposed on the gas diffusion layer side prevents the gas diffusion passage from being clogged with moisture. Yes.
However, in this technique, the second catalyst layer disposed on the gas diffusion layer side is adjusted to have a low water content by being treated at a temperature equal to or higher than the glass transition temperature of the electrolyte resin. There is a risk that the use efficiency of the system will decrease.

  Patent Document 2 discloses a fuel cell including a fuel electrode provided on one surface of an electrolyte membrane and an oxidant electrode provided on the other surface, wherein the catalyst layer of at least one electrode includes a plurality of divided catalyst portions. A fuel cell is disclosed in which a gap exists between adjacent divided catalyst portions. In this technique, by providing a gap between a plurality of adjacent divided catalyst parts, the gap becomes a flow path of excessively generated water, so that the moisture diffusibility of the catalyst layer is improved and flooding is suppressed. It becomes possible. That is, this technique is intended to prevent flooding of the catalyst layer by utilizing the gap between the divided catalyst portions.

  Further, in this Patent Document 2, when the catalyst layer is composed of at least two or more types of split catalyst portions having different hydrophilicity, and the periphery of the hydrophilic split catalyst portion is dried in a low humidified state, When water is supplied to prevent drying of the electrolyte membrane and water stays in the water-repellent split catalyst part in a highly humidified state, hydrogen and air are supplied by securing the pores of the water-repellent split catalyst part. It is described that it can be supplied smoothly. However, in this technique, a large amount of a solid polymer electrolyte is used as a method for forming a hydrophilic divided catalyst portion, and Teflon (registered trademark) -treated carbon black is calcined as a method for forming a water-repellent divided catalyst portion. Therefore, when using a large amount of the solid polymer electrolyte, the pores of the catalyst layer may be filled and the three-phase interface may be reduced, and the carbon black treated with Teflon (registered trademark) is calcined. When used, the electron conductivity in the catalyst phase is lowered, so that the power generation output may be lowered.

  Further, Patent Document 2 also discloses a fuel cell in which the catalyst layer is composed of two or more types of divided catalyst portions having different metal catalyst compositions. However, this technique is a measure against carbon monoxide contained in the fuel, and specifically, a split catalyst including a platinum-ruthenium alloy catalyst having a high ruthenium content ratio that hardly adsorbs carbon monoxide but has low catalytic activity. Only a combination of a part and a split catalyst part containing a platinum-ruthenium alloy catalyst with a low ruthenium content ratio is described.

In Patent Document 3, in a fuel cell in which an anode-side catalyst layer and a cathode-side catalyst layer are disposed via a solid polymer electrolyte membrane, the cathode-side catalyst layer includes a portion that reduces oxygen and a portion that reduces oxygen. And a portion exhibiting higher water repellency than the above, and the portion exhibiting high water repellency is unevenly distributed when observed on the surface.
In Patent Document 3, the portion exhibiting high water repellency is uniform in water repellency from the solid electrolyte membrane side to the cathode side catalyst layer surface, and is dispersed in the surface direction of the cathode side catalyst layer. The side catalyst layer is divided into a part that contributes to the electrode reaction and a part that imparts water repellency and dissipates the generated water, and it is described that it is possible to obtain a high output even during operation at a high current density. Yes. However, since no catalyst exists in the portion exhibiting high water repellency and does not contribute to the electrochemical reaction, the power generation output per unit area of the electrode may be reduced.

Patent Document 4 discloses an anode, a cathode, a polymer electrolyte membrane disposed between the anode and the cathode, and an inlet and an outlet disposed on the opposite side of the surface of the cathode in contact with the polymer electrolyte membrane. And a separator formed on a surface in contact with the cathode, wherein the cathode includes a catalyst containing platinum or a platinum alloy and an ion exchange resin. A catalyst layer adjacent to the polymer electrolyte membrane, wherein in the catalyst layer, the amount of platinum contained per unit area in the vicinity of the inlet of the gas flow path is per unit area in the vicinity of the outlet; A solid polymer fuel cell characterized in that it is greater than the amount of platinum contained is disclosed.
In the technique of Patent Document 4, by changing the amount of the catalyst in accordance with each part in the surface of the cathode side catalyst layer, the reaction occurs almost uniformly in the region near the inlet and the region near the outlet of the gas flow path. The object is to improve the output characteristics by making the current density in the catalyst layer substantially uniform.

Japanese Patent Laid-Open No. 2002-42824 JP 2003-77480 A JP 2004-171847 A JP 2003-168443 A JP 2004-47386 A

  In view of the above circumstances, the present inventors have provided a fuel cell membrane / electrode assembly in which an anode electrode having a catalyst layer is provided on one side of a solid polymer electrolyte membrane and a cathode electrode having a catalyst layer is provided on the other side. The catalyst layer of at least one of the anode electrode and the cathode electrode includes two or more regions containing catalyst particles having different hydrophilicity, and each region is in the thickness direction of the catalyst layer. And / or when distributed in the plane direction and in the thickness direction of the catalyst layer, a region containing catalyst particles having relatively large hydrophilicity is distributed near the solid polymer electrolyte membrane. Has been developed and has already filed a patent application (Japanese Patent Application No. 2006-182178, which has not been disclosed at the time of filing this application).

  By using two or more types of catalyst particles having different hydrophilicity and distributing catalyst particles having appropriate hydrophilicity according to the site of the catalyst layer, (1) battery performance in a low load region to a medium load region can be achieved. Fuel cell that can improve and improve drainage and gas diffusibility in high humidification and high load range, and can exhibit high cell performance over a wide range of operating conditions from low load range to high load range Membrane / electrode assembly is provided, or (2) improved battery performance at low stoichiometric ratio to high stoichiometric ratio, and improved drainage and gas diffusivity under low stoichiometric ratio Membrane / electrode bonding for fuel cells that can always demonstrate high battery performance over a wide range of operating conditions from stoichiometric ratio to high stoichiometric ratio, or even under operating conditions in which the amount of reactant gas supplied to each cell varies. The body was provided.

  The hydrophilicity of the catalyst particles can be measured by methods such as XPS (X-ray electron spectroscopy) and contact angle measurement with water. However, the manufacturing cost is increased due to the large size of the apparatus or the time required for measurement. It will contribute.

In Patent Document 5, the catalyst particles composed of carbon black and platinum or a platinum alloy supported on the carbon black are subjected to an acid treatment, whereby carbon black and platinum or carbon supported on the carbon black are treated. An electrode catalyst for a polymer electrolyte fuel cell, which is made of a platinum alloy and has a pH measured by the method described in JIS K1474 within a range of 2 to 7 is disclosed.
However, Patent Document 5 discloses that by treating the carbon black used as a catalyst carrier with an acid, the surface thereof is modified to prepare catalyst particles having high affinity with the electrolyte resin, and the electrolyte resin in the catalyst layer It is an invention for realizing aggregation of the catalyst and adhesion to the catalyst surface in a highly dispersed state. Patent Document 5 only describes that a catalyst layer is formed by using only one type of catalyst particles, and by distributing catalyst particles having different hydrophilicity in accordance with the site of the catalyst layer, the catalyst layer There is no mention of improving the water distribution of the water.

The present invention has been made in view of the above circumstances, and its first object is to use two or more kinds of catalyst particles having different hydrophilicity when producing a membrane / electrode assembly for a fuel cell, By distributing catalyst particles having appropriate hydrophilicity according to the location of the catalyst layer, the water distribution characteristics of the catalyst layer during fuel cell operation can be improved and the hydrophilicity of the catalyst particles used can be easily measured. Another object of the present invention is to provide an efficient production method for a fuel cell membrane / electrode assembly.
The second object of the present invention is a simple inspection method of catalyst particles, which is applied to prepare catalyst particles having appropriate hydrophilicity in advance before producing a membrane / electrode assembly for a fuel cell. Is to provide.

  The fuel cell membrane / electrode assembly production method of the present invention comprises a solid polymer electrolyte membrane, an anode-side catalyst layer provided on one surface of the solid polymer electrolyte membrane, and a cathode provided on the other surface. A method for producing a membrane-electrode assembly for a fuel cell comprising a side catalyst layer, wherein the pH at the time of water immersion of catalyst particles is confirmed by a measurement method defined in JIS K1474, and water immersion within a predetermined range different from each other A catalyst particle preparation step of preparing at least two types of catalyst particles having a pH, a catalyst ink preparation step of preparing a separate catalyst ink using each of the prepared catalyst particles, and each of the prepared catalyst inks When forming at least one catalyst layer of the anode side and the cathode side by coating on the coated surface, the region containing catalyst particles having different pH during water immersion is in the thickness direction and / or the surface direction of the catalyst layer. Distributed, and When there is a distribution in the thickness direction of the catalyst layer, the corresponding catalyst ink for each region so that the region containing catalyst particles having a relatively small pH when immersed in water is distributed near the solid polymer electrolyte membrane. And a catalyst ink coating process for coating the ink.

  As described above, according to the method for producing a membrane / electrode assembly for a fuel cell of the present invention in which the hydrophilicity of the catalyst particles is confirmed by the pH during water immersion, the measurement can be performed by a simple method. Then, by using catalyst particles whose hydrophilicity has been confirmed, by distributing two or more regions containing catalyst particles having different hydrophilicity in the thickness direction and / or the surface direction of the catalyst layer, It is possible to provide a fuel cell membrane / electrode assembly with improved water distribution characteristics and excellent power generation performance.

As one of the specific embodiments of the production method of the present invention, in the catalyst ink application step, when areas containing catalyst particles having different pHs during water immersion are distributed in the surface direction of the catalyst layer, the pH during water immersion is A region containing relatively small catalyst particles is distributed in the upstream region of the reaction gas supplied to the catalyst layer, and a region containing catalyst particles having a relatively large pH during water immersion is present in the catalyst layer. A mode in which the catalyst ink is applied so as to be distributed in the downstream region of the supplied reaction gas can be mentioned.
As described above, by applying the catalyst ink so that each region of the catalyst layer is distributed, drying on the upstream side of the reaction gas and occurrence of flooding on the downstream side of the reaction gas can be suppressed.

In the present invention, the specific pH during water immersion of two or more kinds of catalyst particles having different pHs during water immersion is not particularly limited, but is prepared in the catalyst particle preparation step from the viewpoint of more reliably preventing dry-up and flooding. Among the catalyst particles, the first catalyst particle having the smallest pH during water immersion is in the range of 2 to 5 and the second catalyst particle having the largest pH during water immersion is during water immersion. The pH is preferably in the range of 5-7. At this time, it is particularly preferable that the difference in pH during water immersion between the first catalyst particles and the second catalyst particles is in the range of 0.5 to 5.
The pH at the time of water immersion of the catalyst particles can be adjusted within a predetermined range, for example, by performing a hydrophilic treatment on the catalyst particles in the catalyst particle preparation step.

The method for inspecting catalyst particles for a fuel cell according to the present invention is characterized in that the pH of the catalyst particles when immersed in water is measured by the method defined in JIS K1474, and at least two types of catalysts having different pH values when immersed in a predetermined range. Each grain is determined to be an acceptable product.
According to the method for inspecting catalyst particles for a fuel cell of the present invention, the hydrophilicity of the catalyst particles can be confirmed by a simple method. It is possible to select catalyst particles having hydrophilicity.

  When preparing a catalyst layer in which two or more regions including catalyst particles having different hydrophilicity are distributed, the first catalyst particle having the smallest pH at the time of water immersion is in the range of 2 to 5 at the time of water immersion. By determining a certain catalyst particle and a catalyst particle having a pH of 5 to 7 within the range of 5 to 7 as the second catalyst particle having the largest pH when immersed in water as flooding and dry-up, An effectively prevented catalyst layer can be formed. Further, when the difference in pH during water immersion between the first catalyst particles and the second catalyst particles is in the range of 0.5 to 5, each catalyst particle may be determined as an acceptable product. preferable.

  According to the method for producing a membrane / electrode assembly for a fuel cell of the present invention, two or more types of catalyst particles having different hydrophilicity are used, and catalyst particles having appropriate hydrophilicity are distributed according to the site of the catalyst layer. Thereby, while improving the water distribution characteristic of the catalyst layer at the time of fuel cell operation | movement, the hydrophilic property of the catalyst particle to be used can be measured easily. Further, according to the inspection method of the present invention, catalyst particles having appropriate hydrophilicity can be easily prepared in advance before manufacturing a fuel cell membrane-electrode assembly.

  The fuel cell membrane / electrode assembly production method of the present invention comprises a solid polymer electrolyte membrane, an anode-side catalyst layer provided on one surface of the solid polymer electrolyte membrane, and a cathode provided on the other surface. A method for producing a membrane-electrode assembly for a fuel cell comprising a side catalyst layer, wherein the pH at the time of water immersion of catalyst particles is confirmed by a measurement method defined in JIS K1474, and water immersion within a predetermined range different from each other A catalyst particle preparation step of preparing at least two types of catalyst particles having a pH, a catalyst ink preparation step of preparing a separate catalyst ink using each of the prepared catalyst particles, and each of the prepared catalyst inks When forming at least one catalyst layer of the anode side and the cathode side by coating on the coated surface, the region containing catalyst particles having different pH during water immersion is in the thickness direction and / or the surface direction of the catalyst layer. Distributed, and When there is a distribution in the thickness direction of the catalyst layer, the corresponding catalyst ink for each region so that the region containing catalyst particles having a relatively small pH when immersed in water is distributed near the solid polymer electrolyte membrane. And a catalyst ink coating process for coating the ink.

As described above, some of the present inventors catalyzed two or more types of catalyst particles having different hydrophilicity in order to suppress a decrease in power generation performance due to the distribution of water in the membrane-electrode assembly. We have already proposed a membrane / electrode assembly for a fuel cell that can achieve high battery performance by distributing it appropriately according to the layer site and improving the water distribution characteristics in the membrane / electrode assembly. . The hydrophilicity of the catalyst particles varies depending on the hydrophilicity inherent in the catalyst component itself and the hydrophilicity inherent in the carrier particles supporting the catalyst component, and is adjusted by subjecting the catalyst component and carrier particles to a surface treatment. You can also.
The hydrophilicity of the catalyst particles can be measured by the XPS method, the water contact angle method, or the like. However, the XPS method is troublesome and has a problem that the apparatus is large and expensive.

  Examples of the measurement by the water contact angle method include the following methods. First, a paste is prepared by mixing an electrolyte resin in an appropriate solvent together with catalyst particles to be measured. And after apply | coating and drying this paste on a board | substrate, a hot press is implemented, a contact angle measurement surface is produced, and the water contact angle in this contact angle measurement surface is measured. For two or more types of catalyst particles to be compared, a contact angle measurement surface can be prepared using the same electrolyte resin material, water contact angle measurement can be performed, and the hydrophilicity can be determined from the contact angle comparison. . Thus, since the water contact angle method performs paste preparation, measurement surface preparation, and water contact angle measurement for each catalyst particle, it requires labor.

  On the other hand, in the method for producing a membrane / electrode assembly for a fuel cell according to the present invention, the hydrophilicity of the catalyst particles is confirmed by measuring the pH of the catalyst particles when immersed in water, and catalysts having different pH values when immersed in water. Prepare two or more grains.

Here, the pH of the catalyst particles during water immersion is the pH value of the aqueous solution (suspension) of the catalyst particles, and can be measured according to the measurement method defined in JIS K1474. Specifically, first, 1.0 g of catalyst particles in terms of dry mass is added to 100 ml of water, and heated for 5 minutes so that boiling continues gently. Subsequently, after cooling to room temperature, water is added to make 100 ml, and the mixture is thoroughly stirred. The pH of the resulting solution is measured at a measurement temperature (liquid temperature) of 25 ° C. using a pH meter.
In the case where a partial region of the catalyst layer is formed using a catalyst ink in which two or more types of catalyst particles (the pH during water immersion may be the same or different) is used, The “time pH” is the water-immersion pH of the catalyst particle mixture mixed at the same mixing ratio as that contained in the catalyst ink.

Between two or more types of catalyst particles having different pHs during water immersion within a range of less than pH 8 during water immersion, catalyst particles having a relatively low pH during water immersion have a relatively large amount of acidic groups on the surface of the catalyst particles. Therefore, catalyst particles having a high hydrophilicity and a large pH during water immersion have a low hydrophilicity because a relatively small amount of acidic groups are present on the surface of the catalyst particles.
As described above, the measurement of the pH of the catalyst particles during water immersion is very simple and does not require a special device. Therefore, in the catalyst particle preparation step of the method for producing a membrane / electrode assembly according to the present invention, it is possible to easily select and combine catalyst particles having desired hydrophilicity from among many catalyst particles, In addition, there is an advantage that the hydrophilic treatment can be easily controlled since the degree of the surface treatment can be easily measured when adjusting the hydrophilicity of the catalyst particles by the surface treatment or the like.

In the present invention, “the pH at the time of water immersion is relatively small” and “the pH at the time of water immersion is relatively large” are used in two or more regions having different pH values during water immersion included in the catalyst layer. It refers to the magnitude of the pH during water immersion, which is relatively compared. In the following embodiments, the expressions “high pH during water immersion” and “low pH during water immersion” mean the relative size as described above.
Further, “relatively low hydrophilicity” and “relatively high hydrophilicity” used in the present invention are relatively compared among two or more regions having different hydrophilicities contained in the catalyst layer. It refers to the size of hydrophilicity. In the following embodiments, when simply expressed as “high hydrophilicity” or “low hydrophilicity”, it means the relative size.

  In the method for producing a membrane / electrode assembly for a fuel cell according to the present invention, at least two or more kinds of catalyst particles having different predetermined pH values for water immersion are selected by measuring the pH during water immersion as described above. A catalyst layer is formed in which two or more regions including catalyst particles having different pHs during immersion are distributed.

  In the present invention, the catalyst particles are particles of a catalyst component supported on carrier particles or particles of the catalyst component itself. The catalyst component is not particularly limited as long as it has a catalytic action for an electrode reaction [hydrogen oxidation reaction at the fuel electrode (anode) or oxygen reduction reaction at the oxidizer electrode (cathode)]. Alternatively, an alloy of platinum and a metal such as ruthenium, iron, nickel, manganese, cobalt, chromium, iridium, and molybdenum can be given. As the carrier particles, for example, those made of carbonaceous materials such as carbonaceous particles and carbonaceous fibers, and conductive materials such as metals and inorganic compounds are used. The carrier particles usually have a larger particle size than the supported catalyst component.

  As long as the two or more types of catalyst particles prepared in the catalyst particle preparation step have different water immersion pHs, the pH range of each catalyst particle during water immersion is not particularly limited. However, in order to effectively improve the water distribution characteristics of the membrane / electrode assembly, among the catalyst particles prepared in the catalyst particle preparation step, the first catalyst particle having the smallest pH during water immersion is immersed in water. The pH is preferably 2 or more and 5 or less, particularly 3.5 or more and 4.5 or less, and the pH of the second catalyst particle having the largest pH during water immersion is 5 or more and 7 or less, particularly 6 or more and 7 or less. It is preferable that

  If the pH of the first catalyst particle having the smallest pH during water immersion is less than 2, flooding may occur during high load operation or operation at a low stoichiometric ratio. Further, if the pH of the first catalyst particles when immersed in water is greater than 5, there is a possibility that dry-up during low load operation or operation at a high stoichiometric ratio and dry up on the upstream side of the reaction gas cannot be sufficiently suppressed.

  On the other hand, if the pH of the second catalyst particle having the highest pH during water immersion is less than 5, flooding during high load operation or operation at a low stoichiometric ratio, or flooding downstream of the reaction gas is sufficient. May not be able to be suppressed. On the other hand, if the pH of the second catalyst particles during water immersion is greater than 7, dry-up during low load operation or operation at a high stoichiometric ratio may not be sufficiently suppressed.

  As described above, when the first catalyst particles have a water immersion pH of 2 to 5, and the second catalyst particles have a water immersion pH of 5 to 7, the first catalyst particles and the The difference in pH during water immersion between the second catalyst particles is preferably in the range of 0.5 to 5, particularly 1 from the viewpoint of more effectively improving the water distribution characteristics of the membrane-electrode assembly. It is preferable to be within the range of ~ 3.

  In the catalyst particle preparation step, in order to prepare catalyst particles having a desired pH during water immersion, the pH during catalyst water immersion may be adjusted as necessary. The pH at the time of water immersion of the catalyst particles can be adjusted by, for example, subjecting the catalyst particles before supporting the catalyst particles or catalyst components or the catalyst components before supporting the catalyst particles to a hydrophilic treatment or a water repellent treatment. . As described above, of the catalyst particles prepared in the catalyst particle preparation step, the preferred water pH of the first catalyst particle having the smallest pH during water immersion is 2 to 5, and the pH during water immersion is the highest. Since the preferred pH at the time of water immersion of the second catalyst particles is 5 to 7, adjustment of the pH at the time of water immersion of the catalyst particles is usually performed by hydrophilic treatment.

Examples of the hydrophilic treatment of the catalyst particles include a method in which carrier particles before supporting the catalyst particles or catalyst components are immersed in an acid solution and heated as necessary. It does not specifically limit as an acid solution used for such an acid treatment, Inorganic acids, such as nitric acid, hydrochloric acid, a sulfuric acid, can be used. As the solvent of the acid solution, for example, water or the like can be used. What is necessary is just to set the density | concentration of an acid solution, immersion time, heating temperature, etc. suitably. Moreover, the pH at the time of water immersion of a catalyst particle can also be made small by immersing the carrier particle before carrying | supporting a catalyst particle or a catalyst component in hydrogen peroxide water.
Normally, catalyst components and carrier particles constituting the catalyst particles have a pH greater than 7 when immersed in water and have no hydrophilic groups. However, by controlling the acid concentration, temperature, treatment time, etc. in the acid treatment, It is possible to easily control the pH during immersion.

  The water repellent treatment of the catalyst particles is not particularly limited. For example, a method of removing the hydrophilic group by heat-treating the carrier particles before supporting the catalyst particles or the catalyst component, or before supporting the catalyst particles or the catalyst component And the like, and the like. By such a water repellent treatment, the pH of the catalyst particles during water immersion can be increased.

  As a combination of catalyst particles having different pH at the time of water immersion without performing hydrophilic treatment or water repellent treatment, for example, a combination of a platinum alloy (low pH at the time of water immersion) and pure platinum (high pH at the time of water immersion) may be used. Can be mentioned. Specifically, Pt—Co alloy (low pH during water immersion) and pure Pt (high pH during water immersion), Pt—Fe alloy (low pH during water immersion) and pure platinum (high pH during water immersion), Pt -A combination of a Cr alloy (low pH during water immersion) and pure Pt (high pH during water immersion).

  In the catalyst ink preparation step, separate catalyst inks (that is, two or more types of catalyst inks) are prepared using two or more types of catalyst particles having different pH during water immersion prepared in the catalyst particle preparation step. Each catalyst ink containing catalyst particles having different pHs when immersed in water is used to form different regions of the catalyst layer, and regions including catalyst particles having different pHs when immersed in the catalyst layer in the thickness direction and / or Alternatively, it is applied to a predetermined application surface so as to be distributed in the surface direction.

The catalyst ink usually contains a proton conductive resin in addition to the catalyst particles, and is obtained by dissolving or dispersing the catalyst particles and the proton conductive resin in an appropriate solvent.
The proton conductive material can be appropriately selected from materials used as electrolyte membranes. Specifically, fluorine-based electrolyte resins and polyethers represented by Nafion (trade name) perfluorocarbon sulfonic acid resin can be used. Hydrocarbons in which proton conductive groups such as sulfonic acid groups, boronic acid groups, phosphonic acid groups, hydroxyl groups, and carboxylic acid groups are introduced into hydrocarbon resins such as sulfones, polyimides, polyether ketones, polyether ether ketones, and polyphenylenes. System electrolyte resin. Examples of the solvent for the catalyst ink include a mixture of alcohols such as ethanol, methanol, propanol, and propylene glycol and water, other organic solvents, and a mixture of other organic solvents and water.

  Other materials such as a water repellent polymer and a binder may be added to the catalyst ink as necessary. Further, the concentration of each component in the catalyst ink, the mixing procedure and method when preparing the catalyst ink are not particularly limited.

  Using the catalyst ink prepared in the catalyst ink preparation step, a catalyst layer is formed in which regions containing catalyst particles having different pHs during water immersion are distributed. That is, the catalyst ink corresponding to each region is applied to a predetermined application surface (polymer electrolyte membrane) so that regions containing catalyst particles having different pHs during water immersion are distributed in the thickness direction and / or the surface direction of the catalyst layer. (Catalyst ink coating step). The distribution form of the region containing catalyst particles having different pH during water immersion is not particularly limited, and can be appropriately designed so as to obtain a membrane / electrode assembly exhibiting desired power generation characteristics. Specific distribution forms will be described in detail later by giving some embodiment examples (first to fourth embodiments).

In the catalyst ink application step, the application surface on which the catalyst ink is applied differs depending on the method of forming the catalyst layer, and may be, for example, the electrolyte membrane surface, the gas diffusion layer sheet surface that becomes the gas diffusion layer, or the transfer group. It may be the material surface. The method for applying the catalyst ink to a predetermined application surface (electrolyte film, gas diffusion layer sheet, substrate surface, etc.) is not particularly limited. For example, spray method, screen printing method, doctor blade method, gravure printing method, die coating Law. As a method for applying the catalyst ink in a predetermined pattern, screen printing or gravure printing is preferable.
The amount of catalyst ink applied varies depending on the composition of the catalyst ink and the catalyst performance of the catalyst metal used for the electrode catalyst, but the amount of catalyst component per unit area is about 0.1 to 1.0 mg / cm ^2. What should I do? The thickness of the catalyst layer is not particularly limited, but may be about 1 to 50 μm.

  Here, examples of the electrolyte membrane for applying the catalyst ink or joining the catalyst layer include those used in general fuel cells. For example, Nafion (trade name, manufactured by DuPont), Flemion (product) Name, manufactured by Asahi Glass Co., Ltd.), Aciplex (trade name, manufactured by Asahi Kasei Co., Ltd.), Dow membrane (manufactured by Dow Chemical Co., Ltd.), and other fluorine-based electrolyte resin membranes represented by perfluorocarbon sulfonic acid resins, as well as polyethersulfone and polyimide Hydrocarbon electrolyte resin in which proton conductive groups such as sulfonic acid group, boronic acid group, phosphonic acid group, hydroxyl group and carboxylic acid group are introduced into hydrocarbon resin such as polyetherketone, polyetheretherketone and polyphenylene Polymer electrolyte membranes such as membranes, basic polymers such as polybenzimidazole, polypyrimidine, polybenzoxazole Composite electrolyte membrane with basic polymer and the strong acid doped with a strong acid and the like. Among them, a preferable electrolyte membrane is a perfluorocarbon sulfonic acid resin membrane. Although the thickness of the electrolyte membrane is not particularly limited, it is usually about 15 to 150 μm.

  The gas diffusion layer sheet has gas diffusibility, conductivity, and a strength required as a material constituting the gas diffusion layer, for example, carbon paper, carbon cloth, which can efficiently supply gas to the catalyst layer. Carbonaceous porous bodies such as carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium, tantalum, iron, stainless steel , Metal mesh composed of a metal such as gold or platinum, or a conductive porous material such as a metal porous material. The thickness of the conductive porous body is preferably about 50 to 300 μm.

  The gas diffusion layer sheet forming the gas diffusion layer may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The water-repellent layer is not necessarily required, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.

  The method for forming the water repellent layer on the conductive porous body is not particularly limited. For example, water repellent obtained by mixing conductive particles such as carbon particles, water repellent resin, and other components as necessary with an organic solvent such as ethanol, propanol, propylene glycol, water or a mixture thereof. The layer ink may be applied to at least the side facing the catalyst layer of the conductive porous body, and then dried and / or fired.

  At this time, the water repellent layer ink may be impregnated inside the conductive porous body. Further, the shape of the water repellent layer is not particularly limited, and may be, for example, a shape that covers the entire surface of the conductive porous layer on the catalyst layer side or a shape having a predetermined pattern such as a lattice shape. The thickness of the water repellent layer may usually be about 1 to 50 μm. Examples of the method for applying the water repellent layer ink to the conductive porous body include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.

  In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater, etc. It may be processed so as to be discharged well.

  In the catalyst ink application step, for example, when the catalyst ink is applied to the surface of the electrolyte membrane, the catalyst layer is formed on the surface of the electrolyte membrane by drying the catalyst ink. The electrolyte membrane having the catalyst layer formed on the surface in this manner is obtained by joining the catalyst layer and the gas diffusion layer sheet so as to sandwich the catalyst layer between the gas diffusion layer sheet and the electrolyte membrane. A membrane / electrode assembly including an electrode composed of a gas diffusion layer can be produced.

  Further, when the catalyst ink is applied to the surface of the gas diffusion layer sheet on the catalyst layer side, the catalyst layer is formed on the surface of the gas diffusion layer sheet by drying the catalyst ink. In this way, the gas diffusion layer sheet having the catalyst layer formed on the surface is obtained by joining the catalyst layer and the electrolyte membrane so that the catalyst layer is sandwiched between the electrolyte membrane and the gas diffusion layer sheet. Can be produced.

Further, when the catalyst ink is applied onto a transfer substrate such as polytetrafluoroethylene, the catalyst layer sheet obtained by drying the catalyst ink on the surface of the transfer substrate is joined to the electrolyte membrane or the gas diffusion layer sheet, After the substrate is peeled off, the membrane / electrode assembly can be produced by joining the gas diffusion layer sheet or the electrolyte membrane so that the catalyst layer is sandwiched between the electrolyte membrane and the gas diffusion layer.
Bonding between the electrolyte membrane and each layer in the membrane / electrode assembly can be performed, for example, by hot pressing.

In the method for producing a membrane / electrode assembly for a fuel cell according to the present invention, the catalyst layer in which the regions containing catalyst particles having different pHs from each other as described above are distributed is formed only on the anode side. Alternatively, it may be formed only on the cathode side, or may be formed on both the anode side and the cathode side. In general, since the cathode side catalyst layer is easily affected by moisture under operating conditions in a high humidification / high load range, application of the present invention to the cathode side catalyst layer can effectively improve battery performance. it can. Even in the anode side catalyst layer, there is a risk of excessive moisture in a high humidification / high load range depending on the design and operating conditions of the battery. By applying the present invention, the battery performance can be improved.
The catalyst layer in which two or more kinds of regions as described above are not distributed can be formed using a kind of catalyst ink according to a general method.

Hereinafter, a configuration example of a single cell including a fuel cell membrane-electrode assembly provided by the manufacturing method of the present invention will be described with reference to the drawings.
<First embodiment>
FIG. 1 is a cross-sectional view schematically showing an embodiment of a single cell (first embodiment, single cell 101). In this embodiment, the catalyst layer on the cathode side is composed of two layers containing catalyst particles having different pHs when immersed in water, and the pH close to the solid polymer electrolyte membrane is low when immersed in water, that is, hydrophilic. Has a laminated structure in which layers containing large catalyst particles are arranged.

  The unit cell 101 includes a membrane / electrode assembly 11 in which an anode 5 is provided on one surface side of a solid polymer electrolyte membrane (hereinafter, simply referred to as an electrolyte membrane) 1 and a cathode 10 is provided on the other surface side. Yes. The anode 5 is configured by laminating an anode side catalyst layer 2 and an anode side gas diffusion layer 4 in this order from the side close to the electrolyte membrane 1. On the other hand, the cathode 10 is configured by laminating a first cathode side catalyst layer 6a, a second cathode side catalyst layer 6b, and a cathode side gas diffusion layer 9 in this order from the side close to the electrolyte membrane 1. In this embodiment, each electrode (fuel electrode, oxidant electrode) has a structure in which a catalyst layer and a gas diffusion layer are laminated, but has a single-layer structure composed of only the catalyst layer. Alternatively, a structure in which a functional layer is provided in addition to the catalyst layer and the gas diffusion layer may be used.

  The membrane / electrode assembly 11 is sandwiched between two separators 12 and 14 to form a single cell 101. On one side of each separator 12, 14, a groove for forming a flow path for a reaction gas (fuel gas, oxidant gas) is provided, and a fuel gas flow path is formed between these grooves and the outer surfaces of the anode 5 and the cathode 10. 13. An oxidant gas flow path 15 is defined. The fuel gas channel 13 is a channel for supplying fuel gas (a gas containing hydrogen or generating hydrogen) to the anode 5, and the oxidant gas channel 15 is an oxidant gas (oxygen gas) to the cathode 10. A flow path for supplying a gas that contains or generates oxygen.

  Each separator may be provided with a groove (not shown) for forming a cooling water channel on the surface opposite to the surface on which the groove for the reaction gas channel is formed. As the separator, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with a resin, a metal separator using a metal material, or the like can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

  In the first embodiment, the cathode side catalyst layer 6 has a two-layer structure in which the first catalyst layer 6a and the second catalyst layer 6b are laminated in order from the electrolyte membrane side, and the first catalyst layer 6a is immersed in water. The catalyst particles contain relatively small pH (that is, relatively high hydrophilicity), and the second catalyst layer 6b has relatively high pH when immersed in water (that is, relatively low hydrophilicity). Contains catalyst particles.

Since the first cathode catalyst layer 6a is adjacent to the electrolyte membrane 1, the proton supply amount is abundant. In the catalyst layer, proton conductivity becomes a rate-determining factor for the electrochemical reaction, but the catalyst layer on the first cathode side is made to contain catalyst particles having high hydrophilicity in the catalyst layer at a position where the amount of proton supply is abundant. In 6a, a large amount of protons accompanying water reach the surface of the catalyst particles, and an electrochemical reaction is actively performed. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited under operating conditions from the low load range to the medium load range.
In addition, the water generated in the first cathode catalyst layer 6a diffuses through the gaps in the second cathode catalyst layer 6b located on the side far from the electrolyte membrane 1 and is discharged to the oxidant gas flow path. Since the catalyst particles contained in the second cathode side catalyst layer 6b are less hydrophilic than the catalyst particles contained in the first cathode side catalyst layer, the water diffused from the first cathode side catalyst layer is catalyst particles. In the second cathode side catalyst layer 6b, the surroundings of the catalyst particles are not clogged with water even in an excessive amount of water, and the electrochemical reaction is active. Done. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited without being adversely affected by moisture even under high humidification / high load operating conditions.

  In the first embodiment, the ratio between the amount of the catalyst component supported on the catalyst particles having high hydrophilicity and the amount of the catalyst component supported on the catalyst particles having low hydrophilicity prevents flooding and increases from a low load range to a high level. From the viewpoint of improving battery performance over a wide load range, it is preferable that the amount of the catalyst component supported on the highly hydrophilic catalyst particles is larger. Specifically, the ratio of supported amount per unit area of catalyst component supported on catalyst particles having high hydrophilicity and catalyst component supported on catalyst particles having low hydrophilicity [high hydrophilicity: low hydrophilicity (weight ratio) ] Is preferably 1: 1 or more, and more preferably 3: 1 or more.

In this embodiment, the cathode-side catalyst layer has a two-layer structure, but even when the catalyst layer has a laminated structure of three or more layers, the layer closer to the electrolyte membrane contains catalyst particles that are more hydrophilic. By adopting such a stacking order, the same effect can be obtained.
In the present invention, it is not necessary that two or more regions containing catalyst particles having different pHs (different in hydrophilicity) when immersed in water form a clear multilayer structure. For example, as the cathode side catalyst layer is closer to the electrolyte membrane in the thickness direction, the amount of catalyst particles having higher hydrophilicity gradually increases, and as the distance from the electrolyte membrane increases, the amount of catalyst particles having lower hydrophilicity gradually increases. The gradient distribution may be increased.
In the first embodiment, the hydrophilicity of the first cathode side catalyst layer 6a and the second cathode side catalyst layer 6b is the catalyst layer from the viewpoint of exhibiting high battery performance from a low load range to a high load range. Even when compared as a whole, the first cathode-side catalyst layer 6a is preferably larger.

  When the catalyst layer has a two-layer structure like the cathode side catalyst layer in the present embodiment, after applying the catalyst ink for the first catalyst layer on the substrate, the second catalyst is formed thereon. The catalyst inks for the layers are applied in layers, or the first catalyst layer and the second catalyst layer are formed on separate substrates and bonded together by a method such as stacking and thermocompression bonding. May be. In addition, as one method for providing the above-described gradient distribution in the thickness direction of the catalyst layer, the other catalyst is applied while the ink layer formed by applying one catalyst ink to a predetermined position is not yet dried. There is a method in which the ink is applied adjacent to the previously formed ink layer.

<Second embodiment>
FIG. 2 is a cross-sectional view schematically showing a second embodiment (unit cell 102) of a unit cell including a fuel cell membrane-electrode assembly provided by the manufacturing method according to the present invention. FIG. 3 is a plan view of the cathode side catalyst layer of the second embodiment (unit cell 102).
In the second embodiment, the cathode-side catalyst layer has a single-layer structure, but two types of regions 7a and 7b containing catalyst particles having different pHs (different hydrophilicity) when immersed in water are alternately arranged in the plane direction. The structure is distributed (in this example, distributed in a checkered pattern). Other points are the same as those of the single cell 101 of the first embodiment.

  In the second embodiment, the first region 7a of the cathode-side catalyst layer contains catalyst particles having a relatively low pH during water immersion (that is, high hydrophilicity), and the second region 7b is immersed in water. It contains catalyst particles having a relatively high pH (ie, low hydrophilicity).

In the first region 7a of the cathode side catalyst layer containing catalyst particles having high hydrophilicity, a large amount of protons accompanying water reaches the surface of the catalyst particles, and an electrochemical reaction is actively performed. According to this membrane / electrode assembly, high battery performance is exhibited under operating conditions from a low load region to a medium load region.
Moreover, since the catalyst particles contained in the second region 7b of the cathode side catalyst layer are less hydrophilic than the catalyst particles contained in the first region, it functions as a drainage channel for water generated in the first region, In the second region, even if the amount of water is excessive, the periphery of the catalyst particles is not blocked by water, and the electrochemical reaction is actively performed. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited without being adversely affected by moisture even under high humidification / high load operating conditions.

  In the second embodiment, the area ratio between the first region 7a containing catalyst particles having high hydrophilicity and the second region 7b containing catalyst particles having low hydrophilicity prevents flooding and increases from a low load region to a high region. From the viewpoint of improving battery performance over a wide load range, the first region 7a is preferably larger. Specifically, the area ratio (first region: second region) of the first region 7a and the second region 7b is preferably 1: 1 or more, and more preferably 3: 1 or more. preferable. FIG. 3 shows a checkered pattern with an area ratio (first region: second region) of 1: 1, and FIG. 4 shows a checkered pattern with an area ratio (first region: second region) of 3: 1. It is a pattern.

  In this embodiment, two types of regions are distributed in a checkered pattern in the plane direction, but the first and second regions are alternately two types of regions such as vertical stripes and horizontal stripes as shown in FIG. As long as they are arranged in a distributed manner so as to be adjacent to each other, they can be combined in various patterns. In addition, the cathode-side catalyst layer can obtain the same effect even when three or more types of regions containing catalyst particles having different hydrophilicity are distributed in the plane direction. In any case, there are a plurality of regions containing catalyst particles having different hydrophilicity, and good drainage can be obtained by arranging them so as to be alternately adjacent in the surface direction.

Similarly to the first embodiment having the region distributed in the thickness direction of the catalyst layer, this embodiment having the region distributed in the surface direction of the catalyst layer also contains two catalyst particles having different hydrophilicity from each other. These areas do not have to be separated by clear boundaries. For example, in an adjacent portion of the first region 7a and the second region 7b distributed in the plane direction, the inclination is such that the catalyst particles having a large hydrophilicity gradually decrease and the catalyst particles having a small hydrophilicity gradually increase. It may be distributed.
Further, in the second embodiment, the hydrophilicity of the first region 7a and the second region 7b is also the case where the entire region is compared from the viewpoint of exhibiting high battery performance from the low load region to the high load region. The first region 7a is preferably larger.

  As in the second embodiment, the catalyst layer in which two types of regions are distributed in the plane direction includes a catalyst layer ink for the first region and a catalyst layer ink for the second region on a substrate. It can be formed by applying in a pattern. In addition, as one method for providing the above-described inclination distribution also in the surface direction of the catalyst layer, the other catalyst ink is applied while the ink layer formed by applying one catalyst ink to a predetermined position is not yet dried. May be applied adjacent to the side of the previously formed ink layer.

  The first embodiment shows an example in which two or more regions are distributed in the thickness direction of the catalyst layer, and the second embodiment shows an example in which two or more regions are distributed in the surface direction of the catalyst layer. However, in the present invention, two or more types of regions may be distributed in both the thickness direction and the surface direction in the catalyst layer.

  Hereinafter, the third embodiment and the fourth embodiment will be exemplified as other configuration examples of the unit cell including the membrane-electrode assembly provided by the manufacturing method according to the present invention. In the membrane / electrode assembly of the third embodiment and the fourth embodiment, when each region of the catalyst layer is distributed in the surface direction of the catalyst layer, catalyst particles having a low pH (high hydrophilicity) at the time of water immersion are used. The containing region is a region with relatively little moisture retention, and the region containing catalyst particles having a large pH during water immersion (low hydrophilicity) is a region with relatively much moisture retention. To do.

<Third embodiment>
FIG. 6 is a cross-sectional view schematically showing the third embodiment (unit cell 103). FIG. 7 is a plan view of the cathode side catalyst layer of the third embodiment (single cell 103). On the cathode side, the oxidant gas enters the oxidant gas flow path 15 in the single cell from the oxidant gas inlet 3 and is discharged out of the single cell from the oxidant gas outlet 8. On the other hand, on the anode side, the fuel gas enters the fuel gas flow path 13 in the single cell from the fuel gas inlet 17 and is discharged out of the single cell from the fuel gas outlet 16.
In the third embodiment, the cathode-side catalyst layer has a first region 7a existing in the region on the upstream side of the reaction gas (particularly the upstream side of the cathode-side gas flow channel) where the moisture retention in the cathode-side catalyst layer is relatively small, and the cathode-side catalyst layer The second region present in the region on the downstream side of the reactive gas (especially the downstream side of the cathode-side gas flow channel) where the moisture stays relatively is distributed in the surface direction. The other points are the same as the single cell 101 of the first embodiment and the single cell 102 of the second embodiment 2.

  In the third embodiment, the first region 7a of the cathode-side catalyst layer contains catalyst particles having a relatively low pH during water immersion (that is, high hydrophilicity), and the second region 7b is immersed in water. It contains catalyst particles having a relatively high pH (ie, low hydrophilicity).

  Since the first region 7a of the cathode side catalyst layer is located on the upstream side of the reaction gas and is an environment that is easy to dry, by adding catalyst particles having relatively large hydrophilicity to the first region 7a, Drying of the electrolyte membrane is suppressed, and protons that have moved from the anode side accompanying water easily reach the surface of the catalyst particles. For this reason, an electrochemical reaction is actively performed in the first region 7a. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited under operating conditions with a high stoichiometric ratio.

  Further, since the second region 7b of the cathode side catalyst layer is located on the downstream side of the reaction gas, it tends to be excessively wet. By adding catalyst particles having relatively small hydrophilicity to the second region 7b, Water staying in the reaction gas downstream area of the cathode side catalyst layer is easily discharged from the catalyst layer to the reaction gas flow path, and the catalyst particles are not blocked by water even in an excessive amount of water in the second area. Electrochemical reaction is actively performed. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited without being adversely affected by moisture even under low stoichiometric operating conditions.

In the third embodiment, the area ratio of the region containing catalyst particles having relatively high hydrophilicity to the region containing catalyst particles having relatively low hydrophilicity may be 1 or less to prevent flooding. From the viewpoint of improving battery performance over a wide range from low stoichiometric ratio to high stoichiometric operating conditions, it is particularly preferable from the viewpoint that wet performance is excellent, that is, the cathode stoichiometric ratio can be reduced.
In the third embodiment, the region containing catalyst particles having relatively high hydrophilicity may be a region that is not less than ¼ and not more than ½ of the upstream side of the reaction gas channel length. preferable.

Here, “relatively” in a section of “region where water retention is relatively small” or “region where water retention is relatively high” means “a certain region exists in a plane or three-dimensionally surroundings” It means "relatively in relation to the area to do".
In addition, the “region with relatively little moisture retention” means that it is difficult for moisture to stay in the surrounding area due to local variations in the operating environment within the fuel cell, or moisture is discharged to the surrounding region. Since it is easy to be done, it means a region where the drying rate is faster than the surroundings, and therefore the water content decreases when the fuel cell is operated. On the other hand, the “region where water stays relatively much” means that water tends to stay in the surrounding area due to local variations in the operating environment within the fuel cell, or moisture is discharged to the surrounding region. This means that the drying rate is slower than that of the surroundings, and thus the moisture content increases when the fuel cell is operated.

  In the present embodiment, the cathode side catalyst layer has two types of regions, but the region closer to the upstream side of the reaction gas channel contains catalyst particles having relatively higher hydrophilicity, and the reaction gas channel If the order is such that the closer to the downstream side of the catalyst, the catalyst particles having relatively small hydrophilicity are contained, three or more types of regions containing catalyst particles having different hydrophilicity follow the flow of the reaction gas. Even if distributed in the plane direction, the same effect can be obtained. In the present embodiment, the first region 7a and the second region 7b are distributed on the same straight line. For example, as shown in FIG. 8, a serpentine type that matches the form of the reaction gas channel is used. There may be.

<Fourth embodiment>
FIG. 9 is a cross-sectional view schematically showing the fourth embodiment (unit cell 104). In the fourth embodiment, the cathode-side catalyst layer has a relatively small moisture retention, a first region 7a that exists in a region not subjected to a relatively pressing force, and a relatively large moisture retention. The second region 7b existing in the region receiving the light has a structure distributed in the plane direction. Other points are the same as the single cell 101 of the first embodiment, the single cell 102 of the second embodiment 2, and the single cell 103 of the third embodiment.

  Specific examples of the region that is not subjected to the relatively pressing force include a region in contact with the reaction gas flow path. Moreover, the area | region which contact | connects a separator is mentioned as an area | region which receives comparatively pressing force (refer FIG. 9).

  In the fourth embodiment, the first region 7a of the cathode-side catalyst layer contains catalyst particles having a relatively low pH during water immersion (that is, high hydrophilicity), and the second region 7b is immersed in water. It contains catalyst particles having a relatively high pH (ie, low hydrophilicity).

The first region 7a of the cathode side catalyst layer does not receive the pressing force of the separator and faces the gas flow path, so that it is easy to dry. However, the first region 7a is relatively hydrophilic. By including large catalyst particles, drying of the electrolyte membrane is suppressed, and protons that have moved from the anode side accompanying water easily reach the surface of the catalyst particles. For this reason, an electrochemical reaction is actively performed in the first region 7a. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited under operating conditions with a high stoichiometric ratio.
In addition, the second region 7b of the cathode side catalyst layer is subjected to the pressing force of the separator and does not face the gas flow path. In addition, the inclusion of catalyst particles with low hydrophilicity makes it easier for the accumulated water to be discharged to the surrounding area, and the catalyst particles are not clogged with water even in an excessive amount of water in the second region. Electrochemical reaction is actively performed. Therefore, according to the membrane / electrode assembly of the present embodiment, high battery performance is exhibited without being adversely affected by moisture even under low stoichiometric operating conditions.

  In the third embodiment, the region containing catalyst particles having relatively high hydrophilicity is a region on the upstream side of the reaction gas flow path, and the region containing catalyst particles having relatively low hydrophilicity is An example of a membrane / electrode assembly, which is a downstream region of the reaction gas flow path, is shown. In the fourth embodiment, a region containing catalyst particles having relatively high hydrophilicity is relatively not subjected to a pressing force. An example of a membrane / electrode assembly in which the region containing catalyst particles having relatively small hydrophilicity is a region that receives a relatively pressing force is shown in the present invention. You may combine embodiment. That is, the region on the upstream side of the reaction gas flow path that is relatively free of pressing force is a region containing catalyst particles having the greatest hydrophilicity, and the region on the downstream side of the reaction gas that is relatively free of pressing force is hydrophilic. In other regions, catalyst particles having different hydrophilicities may be distributed in accordance with the relative strength and weakness of the water retention tendency.

  The method for inspecting catalyst particles for a fuel cell according to the present invention is characterized in that the pH of the catalyst particles when immersed in water is measured by the method defined in JIS K1474, and at least two types of catalysts having different pH values when immersed in a predetermined range. Each grain is determined to be an acceptable product.

  According to the method for inspecting catalyst particles for a fuel cell of the present invention, since the hydrophilicity of the catalyst particles can be confirmed by a simple method, it is easy to determine and select whether the catalyst particles have a desired hydrophilicity. Is possible. Further, when the hydrophilicity is adjusted by subjecting the catalyst particles to a hydrophilic treatment or a water repellent treatment, the hydrophilicity can be easily controlled by changing the conditions of the hydrophilic treatment or the water repellent treatment.

  The method for inspecting catalyst particles of the present invention can be employed to prepare catalyst particles having appropriate hydrophilicity in the catalyst particle preparation step of the method for producing a membrane / electrode assembly for a fuel cell according to the present invention described above. Alternatively, it may be carried out as a pre-manufacturing procedure independent of the series of steps in the manufacturing process as described above. For example, it can be used as one of the criteria for selecting the catalyst particles when selecting new catalyst particles accompanying a change in the design of the fuel cell, or it can be used as one of the criteria for developing new catalyst particles. . Furthermore, it may be used as a screening method for selecting an optimum sample from a large number of catalyst particle samples. In addition, when storing the catalyst particles in preparation for production, it can be adopted as an inspection method for confirming in advance that the catalyst particles meet the specifications of the fuel cell that have already been determined.

(Example 1)
<Preparation of catalyst ink>
(1) Preparation of catalyst ink A containing catalyst particles having pH 4.0 at the time of water immersion 5 g of commercially available Pt / C catalyst (Pt loading: 50 wt%) was immersed in 1000 ml of 1N nitric acid, and at 80 ° C. for 30 minutes. Acid treatment was performed. The acid-treated Pt / C catalyst (1.0 g) was added to 100 ml of water, heated for 5 minutes so that boiling continued gently, cooled to room temperature, water was added to make 100 ml, and the mixture was stirred well. The pH of the resulting solution was measured using a pH meter, and the pH during immersion of the Pt / C catalyst after acid treatment was confirmed to be 4.0.
5 g of water and 7 g of ethanol were mixed with 2 g of a water / alcohol mixed solution of perfluorocarbon sulfonic acid resin (concentration: 20 wt%, trade name: DE2020, manufactured by DuPont) to prepare an electrolyte resin solution. To this electrolyte resin solution, 1 g of Pt / C catalyst having a pH of 4.0 when immersed in water was added and dispersed with a stirrer to obtain catalyst ink A.

(2) Preparation of catalyst ink B containing catalyst particles having pH 6.5 at the time of water immersion 1.0 g of commercially available Pt / C catalyst (Pt loading: 50 wt%) was added to 100 ml of water so that boiling continued gently. After heating for 5 minutes and cooling to room temperature, water was added to make 100 ml and stirred well. The pH of the obtained solution was measured using a pH meter, and the pH of the Pt / C catalyst (untreated) at the time of water immersion was confirmed to be 6.5.
Similarly to catalyst ink A, 5 g of water and 7 g of ethanol were mixed with 2 g of a water / alcohol mixed solution of perfluorocarbon sulfonic acid resin (concentration: 20 wt%, trade name: DE2020, manufactured by DuPont) to prepare an electrolyte resin solution. To this electrolyte resin solution, 1 g of Pt / C catalyst having a pH of 6.5 at the time of water immersion was added and dispersed with a stirrer to obtain catalyst ink B.

<Fabrication of single cell for fuel cell>
First, a dispersion containing PTFE and carbon black at a mass ratio of 1: 1 is prepared, applied to a carbon paper for gas diffusion layer (thickness: 200 μm), dried, and baked at about 350 ° C. The carbon paper for the diffusion layer was subjected to water repellent treatment.
One side of a fluorine-based solid polymer electrolyte membrane (trade name Nafion, film thickness 50 μm, manufactured by DuPont) is spray-coated with catalyst ink B, and the ink is volatilized and dried to form an anode catalyst layer (catalyst particles immersed in water). No pH distribution). The amount of platinum per unit area of the anode catalyst layer was 0.2 mg / cm ² .

On the other hand, the catalyst ink A and the catalyst ink B were spray-coated and dried on the other side of the fluorine-based solid polymer electrolyte membrane to form a cathode-side catalyst layer. At this time, in the cathode side catalyst layer, a region containing catalyst particles having a relatively low pH during water immersion (4.0) is distributed upstream of the reaction gas, and the pH during water immersion is relatively high (6 .5) The catalyst ink A is applied to the region upstream of the reaction gas (see 7a in FIG. 7; the region on the reaction gas inlet side half) so that the region including the catalyst particles is distributed downstream of the reaction gas. B was applied to the region on the downstream side of the reaction gas (see 7b in FIG. 7; the region on the reaction gas outlet side half). The area ratio of the region containing catalyst particles having pH 4.0 during water immersion to the region containing catalyst particles having pH 6.5 during water immersion was 1: 1. Moreover, the platinum amount per unit area of each area | region in a cathode side catalyst layer was 0.2 mg / cm < ² >.

Next, the two carbon papers and the fluorine-based solid polymer electrolyte membrane on which the anode-side catalyst layer and the cathode-side catalyst layer are formed as described above are overlapped and thermocompression bonded (press pressure: 5 MPa, press temperature: 130 ° C.) to prepare a membrane / electrode assembly.
Furthermore, the membrane / electrode assembly was sandwiched between two separators made of a composite material of carbon fiber and a thermosetting resin and having a groove serving as a gas flow path, thereby producing a single cell.

(Comparative Example 1)
A single cell was produced in the same manner as in Example 1, except that the cathode side catalyst layer was formed using only the catalyst ink B (no pH distribution when the catalyst particles were immersed in water).

(Comparative Example 2)
A single cell was produced in the same manner as in Example 1 except that the cathode side catalyst layer was formed using only the catalyst ink A (no pH distribution when the catalyst particles were immersed in water).

<Evaluation of single-cell power generation performance>
For the single cells of Example 1 and Comparative Examples 1 and 2, the stoichiometric ratio characteristics were evaluated under the following conditions. The results are shown in FIG.
Operating conditions / cell temperature: 80 ° C
・ Humidity dew point to hydrogen / air: 45 ℃ / 55 ℃
Current density: 1.0 A / cm ²

As shown in FIG. 10, the single cell of Comparative Example 1 in which the entire surface of the cathode-side catalyst layer contains only catalyst particles having a pH of 6.5 at the time of water immersion is under low stoichiometric ratio conditions where flooding is particularly likely to occur on the downstream side of the reaction gas. Shows good power generation characteristics, but it was inferior to the power generation characteristics under the high stoichiometric conditions where the upstream side of the reaction gas is particularly easy to dry.
On the other hand, the single cell of Comparative Example 2 in which the entire surface of the cathode side catalyst layer contains only catalyst particles having a pH of 4.0 at the time of water immersion showed excellent power generation characteristics under a high stoichiometric condition where the reaction gas upstream side is particularly easy to dry. However, the power generation characteristics greatly deteriorated under low stoichiometric conditions where flooding is particularly likely to occur on the downstream side of the reaction gas.

  With respect to the single cells of these comparative examples, a region containing catalyst particles having pH 4.0 at the time of water immersion is distributed on the upstream side of the reaction gas that is easily dried, and pH 6. It was confirmed that the single cell of Example 1 in which the region containing 5 catalyst particles is distributed has a high voltage under a wide range of operating conditions from a low stoichiometric ratio to a high stoichiometric ratio and has excellent power generation characteristics. The single cell of Example 1 was found to be capable of generating power even under conditions with a small air flow rate, particularly with little performance degradation at a low stoichiometric ratio.

It is sectional drawing which shows typically one Embodiment of the single cell provided with the membrane electrode assembly provided by the manufacturing method which concerns on this invention. It is sectional drawing which shows typically another embodiment of the single cell provided with the membrane electrode assembly provided by the manufacturing method which concerns on this invention. It is sectional drawing which shows typically an example of the surface direction distribution of the catalyst layer contained in the membrane electrode assembly provided by the manufacturing method which concerns on this invention. It is sectional drawing which shows typically another example of the surface direction distribution of the catalyst layer contained in the membrane electrode assembly provided by the manufacturing method which concerns on this invention. It is sectional drawing which shows typically another example (vertical stripe, horizontal stripe) of the surface direction distribution of the catalyst layer contained in the membrane electrode assembly provided by the manufacturing method which concerns on this invention. Another embodiment of the membrane / electrode assembly provided by the production method according to the present invention (two types of catalyst layers having different hydrophilicity in the upstream region of the reaction gas channel and the downstream region of the reaction gas channel) Is a cross-sectional view schematically illustrating Example of the surface direction of the catalyst layer included in the membrane / electrode assembly provided by the production method according to the present invention (the hydrophilicity is different between the upstream region of the reaction gas channel and the downstream region of the reaction gas channel) It is sectional drawing which shows typically 2 types of catalyst layers are distributed. Another example of the surface direction of the catalyst layer included in the membrane / electrode assembly provided by the production method according to the present invention (the region upstream of the reaction gas channel and the region downstream of the reaction gas channel are hydrophilic) 2 is a cross-sectional view schematically showing the distribution of two different catalyst layers. Another embodiment of the membrane / electrode assembly provided by the production method according to the present invention (two types of catalyst layers having different aqueous properties are distributed in a region that receives relatively pressing force and a region that does not receive relatively pressing force) It is sectional drawing which shows this typically. It is a graph which shows the power generation performance evaluation result of the single cell obtained by the Example and the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Anode side catalyst layer 3 ... Oxidant gas flow path inlet 4 ... Anode side gas diffusion layer 5 ... Anode 6a ... First cathode side catalyst layer 6b ... Second cathode side catalyst layer 7a ... Cathode side 1st area | region of catalyst layer 7b ... 2nd area | region of cathode side catalyst layer 8 ... Oxidant gas flow path exit 9 ... Cathode side gas diffusion layer 10 ... Cathode 11 ... Membrane / electrode assembly 12, 14 ... Separator 13 ... Fuel gas flow path 15 ... Oxidant gas flow path 16 ... Fuel gas flow path outlet 17 ... Fuel gas flow path inlet 101, 102, 103, 104 ... Single cell

Claims (8)

Production of fuel cell membrane / electrode assembly comprising a solid polymer electrolyte membrane, an anode side catalyst layer provided on one surface of the solid polymer electrolyte membrane, and a cathode side catalyst layer provided on the other surface A method,
The catalyst particle preparation step of confirming the pH of the catalyst particles when immersed in water by a measurement method stipulated in JIS K1474, and preparing at least two types of catalyst particles having different pH values when immersed in water.
A catalyst ink preparation step of preparing a separate catalyst ink using each prepared catalyst particle, and
When each prepared catalyst ink is applied to a predetermined application surface to form at least one of the catalyst layer on the anode side and the cathode side, a region containing catalyst particles having different pH during water immersion is the thickness of the catalyst layer. When distributed in the vertical direction and / or the plane direction and distributed in the thickness direction of the catalyst layer, a region containing catalyst particles having a relatively small pH at the time of water immersion is located near the solid polymer electrolyte membrane. A method for producing a membrane / electrode assembly for a fuel cell, comprising a catalyst ink application step of applying a catalyst ink corresponding to each region so as to be distributed.   In the catalyst ink application step, when each of the regions is distributed in the surface direction of the catalyst layer, a region containing catalyst particles having a relatively small pH during water immersion is an upstream region of the reaction gas supplied to the catalyst layer. The catalyst ink is applied so that a region containing catalyst particles having a relatively high pH during water immersion is distributed in a downstream region of the reaction gas supplied to the catalyst layer. The manufacturing method of the membrane-electrode assembly for fuel cells as described in this article.   Of the catalyst particles prepared in the catalyst particle preparation step, the first catalyst particle having the smallest pH during water immersion is in the range of 2 to 5 and the second pH having the largest pH during water immersion. The method for producing a membrane / electrode assembly for a fuel cell according to claim 1 or 2, wherein the pH of the catalyst particles when immersed in water is in the range of 5-7.   The membrane-electrode assembly for a fuel cell according to claim 3, wherein the difference in pH during water immersion between the first catalyst particles and the second catalyst particles is in the range of 0.5 to 5. Manufacturing method.   The fuel according to any one of claims 1 to 4, wherein in the catalyst particle preparation step, the catalyst particle is subjected to a hydrophilic treatment to adjust the pH of the catalyst particle when immersed in a predetermined range. Manufacturing method of battery membrane / electrode assembly.   The pH at the time of water immersion of the catalyst particles is measured by a method defined in JIS K1474, and at least two types of catalyst particles having pH at the time of water immersion within a predetermined range different from each other are determined as acceptable products, respectively. A method for inspecting fuel cell catalyst particles.   As the first catalyst particle having the smallest pH during water immersion, the catalyst particle having a pH within the range of 2 to 5 when immersed in water, and as the second catalyst particle having the largest pH during water immersion, the pH during water immersion is 5 The method for inspecting catalyst particles for a fuel cell according to claim 6, wherein the catalyst particles within a range of ˜7 are determined as acceptable products, respectively.   The catalyst particles are determined to be acceptable products when the difference in pH during water immersion between the first catalyst particles and the second catalyst particles is in the range of 0.5 to 5. The inspection method of the catalyst particle | grain for fuel cells as described in any one of.

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