JP5204382B2 - Cathode catalyst layer, membrane catalyst assembly, cathode gas diffusion electrode, membrane electrode assembly and polymer electrolyte fuel cell using the same - Google Patents

Description

  The present invention relates to a cathode catalyst layer for a polymer electrolyte fuel cell, a membrane catalyst layer assembly including the cathode catalyst layer, a gas diffusion electrode and a membrane electrode assembly, and a polymer electrolyte fuel cell including these.

  A polymer electrolyte fuel cell performs an electrochemical reaction (oxidation-reduction reaction) between a fuel gas containing hydrogen obtained by reforming a raw material gas such as city gas and an oxidant gas containing oxygen such as air. Thus, electrons are taken out to an external circuit. A unit cell (cell) mounted on such a polymer electrolyte fuel cell has a membrane electrode assembly (anode and cathode) composed of a polymer electrolyte membrane having hydrogen ion conductivity and a pair of gas diffusion electrodes (anode and cathode). MEA), a gasket, and a pair of conductive separators.

  The gas diffusion electrode of the membrane electrode assembly is composed of a gas diffusion layer responsible for the permeation / diffusion of fuel hydrogen and oxygen gas and the discharge of water generated by power generation, and a catalyst layer responsible for the actual electrochemical reaction. Has been. The catalyst layer includes a carrier made of conductive fine particles, a highly active metal catalyst supported on the carrier, and a polymer electrolyte having hydrogen ion conductivity attached to the carrier or the metal catalyst. Is configured to maintain a space through which gas can permeate.

  A gas flow path for flowing a fuel gas or an oxidant gas (these are called reaction gases) is provided on the surface of the separator that contacts the gas diffusion electrode. A unit cell is configured by sandwiching a membrane electrode assembly in which a gasket is disposed between the two. Since the voltage obtained from a unit cell of a polymer electrolyte fuel cell having such a structure is low, a stack is obtained by stacking a plurality of unit cells, and the adjacent membrane electrode assemblies are electrically connected to each other by fastening the stack. The necessary output voltage is obtained by connecting them in series.

  By the way, the cause of the cell performance degradation of the polymer electrolyte fuel cell is, for example, deterioration of the catalyst constituting the gas diffusion electrode, hindering permeation of the reaction gas to the gas diffusion electrode due to the progress of flooding in the gas flow path, The damage of a unit cell by gas crossover etc. is mentioned, It is important to aim at the improvement of a battery life by suppressing the phenomenon which causes these, and various examination is carried out.

  In particular, deterioration in battery performance due to starting and stopping of the polymer electrolyte fuel cell is serious. In general, a polymer electrolyte fuel cell has a feature that it starts in a relatively low temperature range of 60 ° C. to 100 ° C., and when it is not necessary, the operation is stopped so as not to lower the fuel utilization efficiency. The design is made. However, when the operation is stopped, the gas diffusion electrode of the membrane electrode assembly is subjected to a potential change that does not occur during the operation.

  For example, a stationary polymer electrolyte fuel cell generates electricity at a voltage of about 0.6 V to 0.9 V per cell (approximately the same as the cathode potential) during operation, but inactive gas is supplied to the anode and cathode when stopped. By purging by supplying to the cathode, the potential of the cathode decreases to near 0 V (vs. RHE). When the operation is resumed, the oxidant gas is supplied and purged, and the cathode potential rises to near +1.0 V (vs. RHE) due to OCV (open circuit voltage) without load.

When starting and stopping are repeated in this way, the metal catalyst contained in the catalyst layer aggregates due to a sudden change in potential, and the active reaction surface decreases, resulting in a decrease in battery performance. In order to prevent the aggregation of the active metal catalyst (metal catalyst) with respect to such a problem, for example, in Patent Document 1, the specific surface area of the carrier is reduced and the particle size of the supported active metal catalyst is increased. Thus, it has been proposed to suppress a decrease in the specific surface area of the active metal catalyst. Patent Documents 2 and 3 disclose the use of an alloy that is more stable than a single metal as the supported active metal catalyst.
JP-A-5-94823 Japanese Patent Publication No. 7-63627 JP 2001-68120 A

However, in the catalyst layer disclosed in Patent Document 1, an active metal catalyst having a particle diameter of 50 angstroms or more is used from the beginning, and the specific surface area of the active metal catalyst is, for example, a small particle diameter of 40 angstroms. From the initial stage, the active metal catalyst is smaller than the active metal catalyst, and the initial voltage drops, so there is still room for improvement. In addition, in the catalyst layers disclosed in Patent Documents 2 and 3, an alloy catalyst having a particle size of 3 nm or less or an electrochemical specific surface area of 35 m ² / g or more is used. There was still room for improvement.

Accordingly, the present invention has been made in view of the above problems, and a polymer having a high initial voltage and suppressed degradation due to rapid operation (startup) and stop of the polymer electrolyte fuel cell and voltage drop are suppressed. An object of the present invention is to provide a cathode catalyst layer capable of realizing an electrolyte fuel cell.
In addition, the present invention can realize a polymer electrolyte fuel cell having a high initial voltage and suppressing deterioration due to operation and stop of the polymer electrolyte fuel cell and voltage drop by using the cathode catalyst layer. An object of the present invention is to provide a membrane catalyst layer assembly and a membrane electrode assembly.
Furthermore, the present invention provides a polymer electrolyte fuel cell having a high initial voltage, a deterioration due to operation and stop of the polymer electrolyte fuel cell, and a voltage drop suppressed by using the membrane electrode assembly. With the goal.

As a result of intensive studies to achieve the above object, the present inventors have determined that the particle size of the metal catalyst supported on the cathode catalyst layer portion in contact with the polymer electrolyte membrane is the cathode catalyst layer not in contact with the polymer electrolyte membrane. In order to achieve the above-described object of the present invention, it is possible to use an alloy for the metal catalyst supported on the cathode catalyst layer portion which is larger than the particle size of the metal catalyst supported on the portion and is in contact with the polymer electrolyte membrane. The inventors have found that the present invention is extremely effective, and have reached the present invention.
That is, in order to solve the above problems, the present invention provides:
A cathode catalyst layer for a polymer electrolyte fuel cell having a polymer electrolyte membrane having hydrogen ion conductivity and an anode and a cathode sandwiching the polymer electrolyte membrane,
It is composed of at least two catalyst layers including a carrier and catalyst-carrying particles containing a metal catalyst supported on the carrier, and a polymer electrolyte having hydrogen ion conductivity,
The particle diameter R ₁ of the metal catalyst in the first catalyst layer located on the side in contact with the polymer electrolyte membrane side and the particle diameter of the metal catalyst in the second catalyst layer located on the side not in contact with the polymer electrolyte membrane R ₂ satisfies the relational expression: R ₁ > R ₂ ,
At least a metal catalyst contained in the first catalyst layer is Ri Do alloy,
In the first catalyst layer, the ratio Wp / WCAT of the mass Wp of the polymer electrolyte adhering to the mass WCAT and catalyst support particles of the catalyst support carrying particles, that is greater than the ratio Wp / WCAT in the second catalyst layer about,
A cathode catalyst layer for a polymer electrolyte fuel cell is provided.

According to the above configuration of the present invention, since the particle size of the metal catalyst contained in the first catalyst layer in contact with the polymer electrolyte membrane is large, the activated metal catalyst aggregates or dissolves in the first catalyst layer. It is possible to suppress deterioration of the catalytic performance due to the operation. Moreover, since the particle size of the metal catalyst contained in the second catalyst layer not in contact with the polymer electrolyte membrane is small, the catalytic ability of the second catalyst layer can be more reliably exhibited, and the battery voltage can be improved. Can do.
That is, according to the present invention, there is provided a cathode catalyst layer capable of realizing a polymer electrolyte fuel cell having a high initial voltage and suppressed degradation and voltage drop due to operation and stop of the polymer electrolyte fuel cell. Can be provided.

Here, although the above-described configuration of the cathode catalyst layer of the present invention has the above-described configuration, a clear mechanism for obtaining the above-described effects of the present invention has not been elucidated. Guesses as follows.
That is, when the polymer electrolyte fuel cell is started and stopped, a sudden change in potential occurs around 0 to +1.0 V (vs. RHE), the metal catalyst dissolves at a high potential, and the metal catalyst dissolves at a low potential. It is thought that it precipitates and aggregates. In order to dissolve the metal catalyst, a liquid, which is a medium from which the metal ions dissolve, is required. In the membrane electrode assembly of the polymer electrolyte fuel cell, a liquid such as water contained in the polymer electrolyte in contact with the metal catalyst. It corresponds to. This is because a polymer electrolyte membrane sandwiched between a pair of gas diffusion electrodes holds a liquid such as a large amount of moisture and can exhibit hydrogen ion conductivity only after containing such a liquid.

Therefore, it is considered that the amount of the metal catalyst dissolved in the catalyst layer portion in contact with the polymer electrolyte membrane is large. Similarly, it is considered that the amount of dissolution of the metal catalyst is large even in the portion where the mass of the polymer electrolyte contained in the catalyst layer is increased in order to suppress the decomposition of the polymer electrolyte membrane. In this way, when the metal catalyst is repeatedly dissolved and precipitated and a state in which the metal catalyst is aggregated to some extent is formed, the specific surface area of the metal catalyst is reduced, and the contact area between the metal catalyst and the polymer electrolyte is also reduced. It is thought that the amount of dissolution decreases and aggregation is suppressed. Therefore, particularly in the catalyst layer portion in contact with the polymer electrolyte membrane and the catalyst layer portion where the ratio of the mass of the polymer electrolyte to the mass of the metal catalyst carrier is large, the metal catalyst made of an alloy having a large particle size and difficult to dissolve. It is thought that deterioration can be suppressed by using. On the other hand, when the relational expression: R ₁ > R ₂ is not satisfied, it has been confirmed by experiments and the like described later that the above-described deterioration suppressing effect of the present invention cannot be obtained.

  Note that an alloy-supported catalyst (such as a PtCo alloy catalyst) used in a fuel cell generally has a higher cost than a supported catalyst of a single Pt. For example, an alloy (such as a PtCo alloy) has a more complicated manufacturing process than Pt (for example, an alloying firing process and an acid cleaning process with an acid are required). For example, expecting to obtain the above-described deterioration suppressing effect, there is a concern that the cost may be increased if an alloy-supported catalyst (such as a PtCo alloy catalyst) is easily contained in the entire cathode catalyst layer instead of the supported catalyst of Pt alone. The However, as confirmed by experiments and the like to be described later, in the present invention, by adopting the above-described structure of the cathode catalyst layer, the cost of MEA can be sufficiently increased by using an alloy-supported catalyst (such as a PtCo alloy catalyst). While suppressing, an effect of suppressing deterioration equivalent to the case where an alloy-supported catalyst (such as a PtCo alloy catalyst) is contained in the entire cathode catalyst layer can be obtained.

  Here, in the present invention, the “alloy” of a metal catalyst made of an alloy refers to a general alloy (for example, “alloy” described in Iwanami Rikagaku Dictionary (5th edition)), as well as an alloy on a carrier particle. This includes a state in which single metal particles as constituent components are supported in contact with each other. For example, when a PtCo alloy catalyst is used, it includes a state where Pt single particles and Co single particles are supported in contact with each other on carrier particles. And the metal catalyst of the said state may be contained in the cathode catalyst layer of this invention. Furthermore, in the present invention, the cathode catalyst layer may contain a metal catalyst in which the surface of the metal catalyst is combined with oxygen and partially oxidized on the carrier particles.

The present invention also provides:
A polymer electrolyte fuel cell comprising at least an anode catalyst layer, a cathode catalyst layer, and a polymer electrolyte membrane having hydrogen ion conductivity and disposed between the anode catalyst layer and the cathode catalyst layer A membrane catalyst assembly for
The cathode catalyst layer of the present invention described above is mounted as the cathode catalyst layer, and the first catalyst layer of the cathode catalyst layer is in contact with the polymer electrolyte membrane,
A membrane catalyst assembly for a polymer electrolyte fuel cell is provided.

The membrane catalyst layer assembly of the present invention having such a configuration may include an anode catalyst layer. As the anode catalyst layer, the same cathode catalyst layer as described above can be used, but an anode catalyst layer conventionally known in the art can also be used.
The membrane / catalyst layer assembly of the present invention having such a configuration includes the cathode catalyst layer described above, so that the initial voltage is high, and deterioration and voltage drop due to the operation and stop of the polymer electrolyte fuel cell. It is possible to realize a polymer electrolyte fuel cell in which the above is suppressed.

Furthermore, the present invention provides
The cathode catalyst layer of the present invention described above;
A gas diffusion layer in contact with the second catalyst layer of the cathode catalyst layer;
Having at least
A cathode gas diffusion electrode for a polymer electrolyte fuel cell is provided.
Since the cathode gas diffusion electrode of the present invention having such a configuration includes the cathode catalyst layer described above, the initial voltage is high, deterioration due to operation and shutdown of the polymer electrolyte fuel cell, and voltage drop are reduced. A suppressed polymer electrolyte fuel cell can be realized.

Furthermore, the present invention provides
A membrane electrode assembly for a polymer electrolyte fuel cell, comprising: an anode; a cathode; and a polymer electrolyte membrane having hydrogen ion conductivity and disposed between the anode and the cathode. ,
The cathode includes the above-described cathode catalyst layer of the present invention,
The cathode catalyst layer is disposed so that the first catalyst layer is in contact with the polymer electrolyte membrane;
A membrane electrode assembly for a polymer electrolyte fuel cell is provided.
Since the membrane electrode assembly of the present invention having such a configuration includes the cathode catalyst layer described above, the initial voltage is high, and deterioration due to operation and shutdown of the polymer electrolyte fuel cell and voltage drop are reduced. A suppressed polymer electrolyte fuel cell can be realized.

Furthermore, the present invention provides:
A polymer electrolyte fuel cell comprising the membrane electrode assembly is provided.
Since the polymer electrolyte fuel cell of the present invention having such a configuration includes the membrane electrode assembly of the present invention described above, the initial voltage is high and the operation and stop of the polymer electrolyte fuel cell are performed. Thus, it is possible to realize a polymer electrolyte fuel cell in which deterioration and voltage drop are suppressed.

  According to the present invention, there is provided a cathode catalyst layer capable of realizing a polymer electrolyte fuel cell having a high initial voltage and suppressing deterioration due to operation and stop of the polymer electrolyte fuel cell and voltage drop. Can do. In addition, according to the present invention, by using the cathode catalyst layer, a polymer electrolyte fuel cell having a high initial voltage and suppressed deterioration and voltage drop due to operation and stop of the polymer electrolyte fuel cell is realized. A membrane catalyst layer assembly and a membrane electrode assembly that can be provided can be provided. Furthermore, according to the present invention, there is provided a polymer electrolyte fuel cell having a high initial voltage and suppressed deterioration due to operation and stop of the polymer electrolyte fuel cell and voltage drop by using the membrane electrode assembly. can do.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.
FIG. 1 is a schematic cross-sectional view showing an example of a basic configuration of a unit cell mounted in a preferred embodiment of a polymer electrolyte fuel cell of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a basic configuration of a membrane-electrode assembly (MEA) mounted on the unit cell 1 shown in FIG. First, components of the polymer electrolyte fuel cell of the present invention will be described.

  As shown in FIG. 1, a polymer electrolyte fuel cell (unit cell) 1 according to this embodiment includes a membrane electrode assembly 20 and a pair of plate-like separators 2 that sandwich the membrane electrode assembly 20. Further, as shown in FIG. 2, the membrane electrode assembly 20 includes a polymer electrolyte membrane 11 that selectively transports hydrogen ions (cations), and cathode catalyst layers that are respectively disposed on both surfaces of the polymer electrolyte membrane 11. 12 and the anode catalyst layer 13, and a pair of gas diffusion layers 14 disposed outside the cathode catalyst layer 12 and the anode catalyst layer 13, respectively.

  The cathode catalyst layer 12 and the anode catalyst layer 13 include catalyst-supported particles obtained by supporting a metal catalyst (for example, a platinum-based metal catalyst) on a support such as carbon particles, and the catalyst-supported particles (metal catalyst and / or support). In particular, the cathode catalyst layer 12 has a first catalyst layer 12a located on the side in contact with the polymer electrolyte membrane 11, although details will be described later. The second catalyst layer 12b is located on the side not in contact with the polymer electrolyte membrane 11, and has a feature.

  The polymer electrolyte membrane 11 is not particularly limited, and a polymer electrolyte membrane mounted on a normal solid polymer fuel cell can be used. For example, a polymer electrolyte membrane made of perfluorocarbon sulfonic acid (for example, Nafion (trade name) manufactured by DuPont, USA, Aciplex (trade name) manufactured by Asahi Kasei Co., Ltd., GSII manufactured by Japan Gore-Tex Co., Ltd., etc.) Can be used. Moreover, as a polymer electrolyte which comprises the polymer electrolyte membrane 11, what has a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group as a cation exchange group is mentioned preferably. From the viewpoint of hydrogen ion conductivity, those having a sulfonic acid group are particularly preferred.

The cathode catalyst layer 12 is composed of at least two layers, and the particle size R _{1 of the} metal catalyst contained in the first catalyst layer 12 a in contact with the polymer electrolyte membrane 11 is not in contact with the polymer electrolyte membrane 11. larger than the particle size R ₂ metal catalyst contained in 12b, and the metal catalyst contained in the first catalyst layer 12a is composed of an alloy. With such a configuration, it is possible to realize a cathode catalyst layer having a high initial voltage and little deterioration during operation / stop.

  Furthermore, when the particle size of the metal catalyst made of the alloy contained in the first catalyst layer 12a is, for example, 5 nm or more, the aggregation of the metal catalyst becomes very slow, and a catalyst layer with little deterioration especially during operation / stop is realized. The performance of the polymer electrolyte fuel cell can be maintained. For the metal catalyst contained in the first catalyst layer 12a, it is preferable to use an alloy catalyst such as an alloy containing a noble metal catalyst such as Pt and an element component for improving the activity of the noble metal catalyst. Examples thereof include transition metal elements such as Co. Pt—Co alloy catalysts are preferred because they are readily available and have high activity.

  On the other hand, in order to improve the initial voltage of the polymer electrolyte fuel cell, the second catalyst layer 12b has a particle size smaller than that of the metal catalyst contained in the first catalyst layer 12a (for example, about 2 to 4 nm). It is preferred to use a metal catalyst having As such a metal catalyst, a noble metal catalyst such as Pt or an alloy catalyst can be used to further improve the activity.

  Here, in the present embodiment, the ratio Wp / Wcat between the mass Wcat of the carrier of the catalyst-carrying particles and the mass Wp of the polymer electrolyte attached to the catalyst-carrying particles is from the second catalyst layer 12b to the first catalyst layer. The ratio Wp / Wcat in the first catalyst layer 12a is 0.8 to 3.0, and the ratio Wp / Wcat in the second catalyst layer 12b is 0.2 to 0.8. It is preferable. By adopting such a configuration, a polymer electrolyte fuel cell capable of maintaining battery performance with a high initial voltage, little deterioration during operation / stop, and further suppression of decomposition of the polymer electrolyte membrane. A realizable cathode catalyst layer can be realized more reliably.

  Here, in the cathode catalyst layer 12, the ratio Wp / Wcat between the mass Wcat of the catalyst-carrying particle carrier and the mass Wp of the polymer electrolyte attached to the catalyst-carrying particle is changed from the second catalyst layer 12b to the first catalyst layer 12a. The state of “increasing toward” is in contact with the polymer electrolyte membrane 11 at one end of the cathode catalyst layer 12 on the assumption that the cathode catalyst layer 12 is composed of two or more layers (a plurality of layers). The ratio Wp / Wcat in the innermost layer (first catalyst layer 12a) is more final than the ratio Wp / Wcat in the outermost layer (second catalyst layer 12b) not in contact with the polymer electrolyte membrane 11 at the other end of the cathode catalyst layer 12. When the plurality of layers are viewed as a whole, the ratio Wp / Wcat in each layer is roughly increased from the outermost layer to the innermost layer. It is.

  For example, the ratio Wp / Wcat may monotonously increase from the outermost layer to the innermost layer. When the cathode catalyst layer 12 is composed of three or more layers, for example, among the layers arranged between the innermost layer and the outermost layer, the ratio Wp / Wcat between some adjacent layers is the same value. It may be in a state of taking Furthermore, when the ratio Wp / Wcat of some adjacent layers among the layers arranged between the innermost layer and the outermost layer is compared, the ratio Wp / Wcat of the layer located on the outermost layer side is the highest. It may be larger than the ratio Wp / Wcat of the layers located on the inner layer side. However, from the viewpoint of gas diffusivity, the ratio Wp / Wcat monotonously increases from the outermost layer to the innermost layer, or some of the layers arranged between the innermost layer and the outermost layer. A state where the ratio Wp / Wcat between adjacent layers takes the same value is preferable.

  As the metal catalyst contained in the anode catalyst layer 13, those known in the art can be used. For example, a noble metal catalyst such as Pt or a gas obtained by reforming city gas with a fuel reformer or the like. An alloy catalyst (for example, a Pt—Ru alloy) having resistance to CO contained therein can be used.

  The amount of the polymer electrolyte contained in the cathode catalyst layer 12 and the anode catalyst layer 13 may be an amount that does not hinder the permeation of hydrogen gas and the movement of protons. In the cathode catalyst layer 12 and the anode catalyst layer 13, the polymer electrolyte is partially attached to the surface of catalyst-carrying particles including a metal catalyst and carbon particles that carry the metal catalyst. Good. That is, the polymer electrolyte only needs to cover at least a part of the catalyst-carrying particles, and does not necessarily have to cover the entire catalyst-carrying particles. Of course, the polymer electrolyte may cover the entire surface of the catalyst-carrying particles.

  As the carrier in the cathode catalyst layer 12 and the anode catalyst layer 13, carbon particles (conductive carbon particles) are mainly used. The carbon particles are preferably a carbon material having conductive pores, and for example, carbon black, activated carbon, carbon fiber, and carbon tube can be used. Examples of carbon black include channel black, furnace black, thermal black, and acetylene black. Activated carbon can be obtained by carbonizing and activating materials containing various carbon atoms.

Moreover, it is preferable that the specific surface area of a carbon particle is 50-1500 m < ² > / g. A specific surface area of 50 m ² / g or more is preferable because the supporting rate of the metal catalyst is easily improved and the catalyst performance of the cathode catalyst layer 12 and the anode catalyst layer 13 does not deteriorate, and the specific surface area is 1500 m ² / g. The following is preferable because the pores are not too fine and the coating with the polymer electrolyte is easier, and the output characteristics of the cathode catalyst layer 12 and the anode catalyst layer 13 are not likely to deteriorate. The specific surface area is particularly preferably 200 to 900 m ² / g.

  The catalyst loading rate of the supported metal catalyst (ratio of the mass of the supported metal catalyst to the total mass of the support) may be 20 to 80% by mass, and particularly preferably 40 to 60% by mass. . Within this range, high battery output can be obtained. As described above, when the catalyst loading is 20% by mass or more, sufficient battery output can be obtained more reliably, and when it is 80% by mass or less, the metal catalyst particles are supported on the carbon powder with good dispersibility. And the effective catalyst area can be further increased.

  As the polymer electrolyte having hydrogen ion conductivity contained in the cathode catalyst layer 12 and the anode catalyst layer 13 and adhering to the catalyst, a polymer electrolyte constituting the polymer electrolyte membrane 11 may be used. The polymer electrolyte constituting the cathode catalyst layer 12, the anode catalyst layer 13, and the polymer electrolyte membrane 11 may be the same type or different types. For example, commercially available products such as Nafion (trade name) manufactured by DuPont, USA, Flemion (trade name) manufactured by Asahi Glass Co., Ltd., and Aciplex (trade name) manufactured by Asahi Kasei Co., Ltd. may be used.

Next, as shown in FIG. 2, a gas diffusion layer 14 having both air permeability and electronic conductivity is formed on the outside of the cathode catalyst layer 12 and the anode catalyst layer 13 by using, for example, carbon paper subjected to water repellent treatment. It is formed. A cathode 15 is configured by a combination of the cathode catalyst layer 12 and the gas diffusion layer 13, and an anode 16 is configured by a combination of the anode catalyst layer 13 and the gas diffusion layer 14.
The gas diffusion layer 14 is made of carbon fine powder having a developed structure structure, a pore former, carbon paper, carbon cloth, or the like to have gas permeability, and has a porous structure. A substrate can be used. In addition, a water repellent polymer typified by a fluororesin may be dispersed in the gas diffusion layer 14 in order to provide drainage. In order to give electron conductivity, the gas diffusion layer 14 may be made of an electron conductive material such as carbon fiber, metal fiber, or carbon fine powder.

  Further, a water repellent carbon layer composed of a water repellent polymer and carbon powder may be provided on the surface of the gas diffusion layer 14 that is in contact with the cathode catalyst layer 12 or the anode catalyst layer 13. The same gas diffusion layer or different gas diffusion layers may be used on the cathode side and the anode side.

As shown in FIG. 1, a unit cell 10 that is a basic unit of a polymer electrolyte fuel cell according to the present embodiment includes a membrane electrode assembly 20, a pair of gaskets 1, and a pair of separators 2.
The gasket 1 is disposed around the cathode 15 and the anode 16 (see FIG. 2) with the polymer electrolyte membrane 11 interposed therebetween in order to prevent leakage and mixing of the supplied fuel gas and oxidant gas to the outside. . The gasket 1 is integrated with the cathode 15 or the anode 16 and the polymer electrolyte membrane 11 in advance, and a combination of them is sometimes called a membrane electrode assembly 20.

  A pair of separators 2 for mechanically fixing the membrane electrode assembly 20 is disposed outside the membrane electrode assembly 20. An oxidant gas is supplied to the cathode 15, a fuel gas is supplied to the anode 16, and a gas containing an electrode reaction product and an unreacted reaction gas is supplied to a reaction field at a portion of the separator 2 that contacts the membrane electrode assembly 20. The gas flow path 3 for carrying away from the cathode 15 and the anode 16 outside is formed. The gas flow path 3 can be provided separately from the separator 2, but in FIG. 1, the gas flow path 3 is formed by providing a groove on the surface of the separator 2. Further, a cooling water flow path 4 formed of a groove is also provided on the side of the separator 2 opposite to the membrane electrode assembly 20.

  Thus, the membrane electrode assembly 20 is fixed by the pair of separators 2, the fuel gas is supplied to the gas passage 3 of the separator 2 on the anode side, and the oxidant gas is supplied to the gas passage 3 of the separator 2 on the cathode side. By supplying, an electromotive force of about 0.6 to 0.9 V can be generated by one single cell 1 when a practical current density of several tens to several hundred mA / cm 2 is applied. However, in general, when a polymer electrolyte fuel cell is used as a power source, a voltage of several volts to several hundred volts is required. Therefore, in actuality, the required number of unit cells 1 are connected in series. Used as a stack (not shown).

  In order to supply the reaction gas to the gas flow path 3, the piping for supplying the reaction gas is branched into a number corresponding to the number of separators 2 to be used, and the branch destinations are directly connected to the gas flow path 3 on the separator 2. Although a manifold that is a member to be connected to the first and second manifolds is necessary, although not specifically shown in the present embodiment, either an external manifold or an internal manifold can be employed.

Next, a method for producing the polymer electrolyte fuel cell of this embodiment will be described.
First, the cathode catalyst layer 12 and the anode catalyst layer 13 are disposed on both surfaces of the polymer electrolyte membrane 11 as described above. The cathode catalyst layer 12 (the first catalyst layer 12a and the second catalyst layer 12b) and the anode catalyst layer 13 use a plurality of inks for forming a catalyst layer prepared to have a component composition capable of realizing the configuration of the catalyst layer in the present invention. Can be formed.

  The dispersion medium used to prepare the ink for forming the catalyst layer may be a polymer electrolyte that can be dissolved or dispersible (part of the polymer electrolyte is dissolved and the other part is dispersed without being dissolved) It is preferable to use a liquid containing an alcohol. The dispersion medium preferably contains at least one of water, methanol, ethanol, propanol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol. These water and alcohol may be used alone or in combination of two or more. The alcohol is particularly preferably a straight chain having one OH group in the molecule, and ethanol is particularly preferable. This alcohol includes those having an ether bond such as ethylene glycol monomethyl ether.

  The composition of the ink for forming the catalyst layer may be appropriately adjusted according to the configurations of the cathode catalyst layer 12 (first catalyst layer 12a and second catalyst layer 12b) and the anode catalyst layer 13, but the solid content concentration is 0. It is preferable that it is 1-20 mass%. When the solid content concentration is 0.1% by mass or more, a catalyst layer having a predetermined thickness can be formed without spraying or coating many times in preparing the catalyst layer by spraying or coating the ink for forming the catalyst layer. Good production efficiency. Moreover, the viscosity of a liquid mixture can be hold | maintained moderately as solid content concentration is 20 mass% or less, and it is easy to make the obtained catalyst layer uniform. The solid content concentration is particularly preferably 1 to 10% by mass.

  The ink for forming the catalyst layer (the ink for forming the cathode catalyst layer 12 and the ink for forming the anode catalyst layer 12, and the ink for forming the first catalyst layer 12a and the ink for forming the second catalyst layer 12b) is obtained by a conventionally known method. Can be prepared on the basis. Specifically, a method using a stirrer such as a homogenizer or a homomixer, a method using high-speed rotation such as using a high-speed rotating jet flow method, or a high-pressure emulsifying apparatus or the like is used to push the dispersion from a narrow part. The method of giving a shearing force to a dispersion liquid by taking out is mentioned.

  When the cathode catalyst layer 12 (first catalyst layer 12a and second catalyst layer 12b) and anode catalyst layer 13 are formed using the catalyst layer forming ink, the cathode catalyst layer 12 is directly formed on the polymer electrolyte membrane 11. It is possible to employ any of the indirect coating methods that are indirectly formed even if it is a direct coating method. Examples of the coating method include a screen printing method, a die coating method, a spray method, and an ink jet method. A membrane catalyst assembly can be formed by direct application in this way.

As an indirect coating method, for example, after forming the catalyst layer 12 on the support made of polypropylene or polyethylene terephthalate by the above method, it is formed on the polymer electrolyte membrane 11 or the previously formed catalyst layer 12 by thermal transfer. The method of doing is mentioned. A catalyst layer alone can be formed by applying a catalyst layer to such a support. After the cathode catalyst layer 12 and the anode catalyst layer 13 are formed on the gas diffusion layer 14, the polymer electrolyte membrane 11 and They can be joined. Thus, the gas diffusion electrode can be formed by applying to the gas diffusion layer 14.

In particular, the polymer electrolytes of the first catalyst layer 12a and the second catalyst layer 12b include the mass Wcat of the catalyst-carrying particle carrier and the mass Wp of the polymer electrolyte having hydrogen ion conductivity attached to the catalyst-carrying particle. When the ratio Wp / Wcat is different, the ink for forming the first catalyst layer 12a and the ink for forming the second catalyst layer 12b are prepared and applied by spraying or the like.
As described above, the membrane catalyst layer assembly or the gas diffusion electrode of the present embodiment can be obtained.

Next, as shown in FIG. 2, the membrane electrode assembly 20 can be obtained by sandwiching the membrane catalyst layer assembly obtained as described above with a pair of gas diffusion layers 14. At this time, the membrane catalyst layer assembly and the pair of gas diffusion layers 14 may be joined by hot pressing or the like.
Further, a pair of gaskets 1 are arranged on the periphery of the polymer electrolyte membrane 11 in the membrane electrode assembly 20 so as to sandwich the periphery, and the whole is sandwiched between the pair of separators 2. The polymer electrolyte fuel cell (single cell) 10 of the form can be obtained.

When a stack including a plurality of unit cells 10 is configured, a plurality of unit cells 10 are laminated by a conventional method to obtain a laminate, and a current collector, an insulating plate, and an end plate are attached to both ends of the laminate. A polymer electrolyte fuel cell comprising a stack can be manufactured by arranging and fastening the whole.
As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the said embodiment. For example, the cathode catalyst layer 12 may be composed of three or more layers, and the anode catalyst layer 13 may be the same as the cathode catalyst layer 12.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

Example 1
In this example, a membrane catalyst assembly having the structure shown in FIG. 2 was first prepared.
First, a first catalyst layer forming ink was prepared. Catalyst-carrying particles (PtCo catalyst-carrying carbon) (made by Tanaka Kikinzoku Co., Ltd., 50% by mass platinum-cobalt alloy) in which platinum-cobalt alloy particles having an average particle diameter of about 5 nm are supported on carbon particles, and hydrogen ion conduction The polymer electrolyte solution having the property (trade name “Flemion” manufactured by Asahi Glass Co., Ltd.) was dispersed in a mixed dispersion medium (mass ratio 1: 1) of ethanol and water. Furthermore, the first catalyst layer forming ink was prepared so that the ratio Wp / Wcat of the mass Wp of the polymer electrolyte to the mass Wcat of the carrier of the catalyst-carrying particles was 2.0. Using this first catalyst layer forming ink, a first catalyst layer 12a having a total platinum carrying amount of 0.12 mg / cm ² and a size of 60 mm × 60 mm was formed into a polymer electrolyte membrane 11 (manufactured by Japan Gore-Tex Co., Ltd.). The product name “GSII”, 150 mm × 150 mm) was applied by spraying to form one surface.

Next, a second catalyst layer forming ink was prepared. Catalyst-supported particles (Pt catalyst-supported carbon) in which platinum cobalt particles having an average particle diameter of about 2 nm are supported on carbon particles (Tanaka Kikinzoku Kogyo Co., Ltd., 50% by mass platinum-cobalt alloy), and hydrogen ion conductivity A polymer electrolyte solution (trade name “Flemion” manufactured by Asahi Glass Co., Ltd.) having a water content was dispersed in a mixed dispersion medium (mass ratio 1: 1) of ethanol and water. Further, the second catalyst layer forming ink was prepared so that the ratio Wp / Wcat of the mass Wp of the polymer electrolyte to the mass Wcat of the carrier of the catalyst-carrying particles was 0.8. Using this second catalyst layer forming ink, a second catalyst layer 12b having a total platinum carrying amount of 0.48 mg / cm ² and dimensions of 60 mm × 60 mm was applied onto the first catalyst layer 12a by a spray method. Formed.

Next, catalyst-supported particles (PtRu catalyst-supported carbon) in which platinum ruthenium alloy (material amount ratio; platinum: ruthenium = 1: 1.5 molar ratio) particles are supported on carbon particles (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 50% by mass of Pt—Ru alloy) and a polymer electrolyte solution having hydrogen ion conductivity (trade name “Flemion” manufactured by Asahi Glass Co., Ltd.) and a mixed dispersion medium of ethanol and water (mass ratio 1: 1). Furthermore, an anode catalyst layer forming ink was prepared such that the ratio Wp / Wcat of the mass Wp of the polymer electrolyte to the mass Wcat of the catalyst-supported particles was 0.8. This ink for forming an anode catalyst layer is applied to the surface of the polymer electrolyte membrane 11 opposite to the surface on which the cathode catalyst layer 12 is formed by a spray method, has a single layer (one layer) structure, and is made of platinum. An anode catalyst layer having a loading amount of 0.35 mg / cm ² and dimensions of 60 mm × 60 mm was formed.
By forming the anode catalyst layer 13 in this manner, a membrane catalyst layer assembly of the present invention having the structure shown in FIG. 2 was produced.

A gas diffusion layer (a product made by Japan Gore-Tex Co., Ltd.) comprising a carbon cloth that has been subjected to water repellent treatment, and a water-repellent carbon layer that contains a fluororesin and carbon provided on one surface of the carbon cloth. Name “CARBEL-CL”), and sandwiching the membrane-catalyst layer assembly between two gas diffusion layers so that the central portion of the water-repellent carbon layer is in contact with the cathode catalyst layer 12 and the anode catalyst layer 13; The whole was hot-pressed with a hot press (120 ° C., 30 minutes, 10 kgf / cm ² ) to obtain a membrane electrode assembly 20 of the present invention having the structure shown in FIG.

Finally, using the membrane / electrode assembly obtained as described above, a polymer electrolyte fuel cell (unit cell) 10 having the structure shown in FIG. 1 was produced. The membrane electrode assembly 20 is sandwiched between a separator 2 having a gas flow path 3 for supplying a fuel gas and a cooling water flow path 4 and a separator 2 having a gas flow path for supplying an oxidant gas and a cooling water flow path. A gasket made of fluoro rubber was disposed between the separators around the cathode and the anode to obtain a unit cell (polymer electrolyte fuel cell of the present invention) having an effective electrode (anode or cathode) area of 36 cm ² .

<< Comparative Example 1 >>
A membrane catalyst layer assembly, a membrane electrode assembly, and a unit cell were produced in the same manner as in Example 1 except that a Pt catalyst having an average particle diameter of 2 nm was used as the metal catalyst contained in the first catalyst layer 12a.

<< Comparative Example 2 >>
A membrane catalyst layer assembly, a membrane electrode assembly, and a single cell were produced in the same manner as in Example 1 except that a PtCo catalyst having an average particle size of 5 nm was used as the metal catalyst contained in the second catalyst layer 13.

[Evaluation test]
The cell temperature of the unit cell 10 obtained in Example 1 and Comparative Examples 1 and 2 is controlled to 70 ° C., hydrogen gas is supplied as a fuel gas to the gas flow path on the anode side, and the gas flow on the cathode side is Air was supplied to each road. At this time, the utilization rate of hydrogen gas was set to 70%, the utilization rate of air was set to 40%, and humidification was performed so that the dew points of hydrogen gas and air were about 70 ° C., respectively. Then, aging was performed by operating the cell at a current density of 0.3 mA · cm ⁻² for 12 hours.

(1) Evaluation by Electrochemical Surface Area (ECSA) Measurement of Cathode Catalyst Layer In order to evaluate ECSA of the cathode catalyst layer 12, the load current density is stopped and the gas supplied to the cathode is nitrogen gas. To completely replace the cathode with an inert atmosphere. Furthermore, the flow rate of the gas flowing through the cathode and the anode was set to 300 ccm, respectively. The other conditions were the same as the above aging conditions. In this state, using an electrochemical measurement apparatus (HZ-3000 manufactured by Hokuto Denko Co., Ltd.), the cathode is the working electrode, the anode is the counter electrode and the reference electrode, the cathode potential is REST to +1.0 V (vs. RHE), and the triangular wave The cyclic voltammetry (CV) of the cathode was measured at a sweep rate of 10 mV / sec.
The charge amount of the oxidation wave of H ₂ was calculated from the obtained CV result, and the ECSA of the cathode catalyst was derived from the amount of H ₂ adsorbed on Pt.

(2) Battery output characteristic evaluation test In order to evaluate the battery output characteristic under a certain condition, after the CV measurement of the cathode, the load current density is 0.2 mA · cm ^−2, and other conditions are the same as the above aging. Each cell was operated under the conditions, and the output voltage after 10 hours was recorded.

(3) Cathode potential cycle test In order to evaluate the resistance against aggregation of the metal catalyst supported on the cathode, the cathode potential is set to +0.1 V to +0.1 V based on the anode potential under the same conditions as the ECSA evaluation of the cathode catalyst layer. It was cycled thousands of times to + 1.0V. In such a cycle test, since the potential changes rapidly from around 0V to around + 1V, the operation / stop of the fuel cell is almost simulated by a single cell. In addition, since such deterioration of the catalyst material is not affected by the adjacent cell even if it is stacked, it deteriorates independently, so that there is no particular problem in the evaluation with a single cell. The cycle test was stopped at any number of such cycle tests, and (1) the ECSA of the cathode catalyst layer and (2) the battery output were measured to grasp the deterioration state of the cathode catalyst layer. The results are summarized in Table 1. Table 1 also shows the configuration of the cathode.

As is apparent from the results in Table 1, the initial voltage in Example 1 is equivalent to the initial voltage in Comparative Example 1 using Pt with a particle size of 2 nm, and Comparative Example 2 using PtCo with a particle size of 5 nm. Compared to the initial voltage of. Further, the decrease rate of ECSA after 3000 cycles in the cathode potential cycle test is suppressed in Example 1 and Comparative Example 2 as compared with Comparative Example 1, and the decrease in voltage is small. From the above results, it was confirmed that Example 1 can improve the initial voltage as compared with Comparative Example 1 and Comparative Example 2, and can further suppress deterioration during operation / stop.
Moreover, compared with the comparative example 2, Example 1 compared with the case where only a Pt catalyst is used, and it was confirmed that the cost increase of MEA by using a PtCo alloy catalyst can fully be suppressed.

  According to the present invention, a cathode catalyst capable of realizing a polymer electrolyte fuel cell that has a high initial voltage and that is suppressed from deterioration due to rapid operation (startup) and stop of the polymer electrolyte fuel cell and voltage drop. A layer can be provided. In addition, according to the present invention, by using the cathode catalyst layer, a polymer electrolyte fuel cell having a high initial voltage and suppressed deterioration and voltage drop due to operation and stop of the polymer electrolyte fuel cell is realized. A membrane catalyst layer assembly and a membrane electrode assembly that can be provided can be provided. Furthermore, according to the present invention, there is provided a polymer electrolyte fuel cell having a high initial voltage and suppressed deterioration due to operation and stop of the polymer electrolyte fuel cell and voltage drop by using the membrane electrode assembly. can do. Such a polymer electrolyte fuel cell of the present invention is useful as a highly durable stationary type and mobile type fuel cell.

It is a schematic sectional drawing which shows an example of the basic composition of the single cell mounted in suitable one Embodiment of the polymer electrolyte fuel cell of this invention. It is a schematic sectional drawing which shows an example of the basic composition of the membrane electrode assembly mounted in the single battery 1 shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gasket, 2 ... Separator, 3 ... Gas flow path, 4 ... Cooling water flow path, 10 ... Single cell, 11 ... Polymer electrolyte membrane, 12 ... Cathode catalyst Layer, 12a ... first catalyst layer, 12b ... second catalyst layer, 13 ... anode catalyst layer, 14 ... gas diffusion layer, 15 ... cathode, 16 ... anode, 20. ..Membrane electrode assemblies

Claims (8)

A cathode catalyst layer for a polymer electrolyte fuel cell, comprising: an anode; a cathode; and a polymer electrolyte membrane having hydrogen ion conductivity and disposed between the anode and the cathode. There,
It is composed of at least two catalyst layers including a carrier and catalyst-carrying particles containing a metal catalyst supported on the carrier, and a polymer electrolyte having hydrogen ion conductivity,
The particle size R _{1 of the} metal catalyst in the first catalyst layer located on the side in contact with the polymer electrolyte membrane side and the metal in the second catalyst layer located on the side not in contact with the polymer electrolyte membrane The particle size R _{2 of the} catalyst satisfies the relational expression: R ₁ > R ₂ ,
Ri said metallic catalyst is included in at least the first catalyst layer Do alloy,
The ratio Wp / Wcat between the mass Wcat of the catalyst-carrying particle carrier in the first catalyst layer and the mass Wp of the polymer electrolyte adhering to the catalyst-carrying particle is greater than the ratio Wp / Wcat in the second catalyst layer. Rukoto also have increased,
A cathode catalyst layer for a polymer electrolyte fuel cell. 2. The cathode catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein a particle diameter R _{1 of the} metal catalyst in the first catalyst layer is 5 nm or more.   The cathode catalyst layer for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the alloy catalyst is a Pt-Co alloy. In the first catalyst layer, a ratio Wp / Wcat between a mass Wcat of the catalyst-carrying particle carrier and a mass Wp of the polymer electrolyte adhering to the catalyst-carrying particle is from the second catalyst layer to the first catalyst layer. Has increased over time,
The ratio Wp / Wcat in the first catalyst layer is 0.8 to 3.0, and the ratio Wp / Wcat in the second catalyst layer is 0.2 to 0.8;
The cathode catalyst layer for a polymer electrolyte fuel cell according to any one of claims 1 to 3. A polymer electrolyte fuel cell comprising at least an anode catalyst layer, a cathode catalyst layer, and a polymer electrolyte membrane having hydrogen ion conductivity and disposed between the anode catalyst layer and the cathode catalyst layer A membrane catalyst assembly for
The cathode catalyst layer according to any one of claims 1 to 4 is mounted as the cathode catalyst layer, and the first catalyst layer of the cathode catalyst layer is in contact with the polymer electrolyte membrane. about,
A membrane catalyst assembly for a polymer electrolyte fuel cell characterized by The cathode catalyst layer according to any one of claims 1 to 4,
A gas diffusion layer in contact with the second catalyst layer of the cathode catalyst layer;
Having at least
A cathode gas diffusion electrode for a polymer electrolyte fuel cell. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising: an anode; a cathode; and a polymer electrolyte membrane having hydrogen ion conductivity and disposed between the anode and the cathode. ,
The cathode includes the cathode catalyst layer according to any one of claims 1 to 4,
The cathode catalyst layer is disposed so that the first catalyst layer is in contact with the polymer electrolyte membrane;
A membrane electrode assembly for a polymer electrolyte fuel cell characterized by   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 7.

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