JPWO2006070635A1 - Membrane electrode assembly for polymer electrolyte fuel cell - Google Patents

Abstract

The present invention eliminates environmental problems by suppressing the generation of partial oxides such as formaldehyde by electrochemical oxidation of liquid fuel in a polymer electrolyte fuel cell. The membrane electrode assembly for a polymer electrolyte fuel cell according to the present invention comprises a by-product decomposition catalyst for decomposing the partial oxide, comprising activated carbon as a constituent component in at least one of the anode and cathode catalyst layers. It has the greatest characteristics in terms of inclusion.

Description

  The present invention relates to a membrane electrode assembly for a polymer electrolyte fuel cell and a polymer electrolyte fuel cell using the membrane electrode assembly.

  In a polymer electrolyte fuel cell, protons generated from fuel at an anode are oxidized by an oxidant at a cathode to generate electricity. Alcohols and the like are used as the fuel, but alcohols that are fuels are partially oxidized during power generation, and aldehydes and carboxylic acids are by-produced. For example, when methanol is used as a fuel, it is known that formaldehyde, formic acid, methyl formate and the like are by-produced in addition to carbon dioxide mainly at the anode. Among these by-products, formaldehyde is a harmful chemical substance that causes sick house syndrome, and it is desirable that the generation of these harmful by-products during power generation be suppressed as much as possible. However, the actual situation is that almost no efforts have been made to control these harmful by-products.

  As a few precedents, Japanese Patent Application Laid-Open No. 2003-123777 discloses a polymer electrolyte fuel cell in which a peroxide decomposition catalyst is added to a catalyst layer. However, the peroxide decomposition catalyst in the art is one in which ruthenium or the like is supported on carbon black, zirconia or the like, and the one used in the examples is only one in which a metal is supported on carbon black.

  However, an electrode catalyst for a polymer electrolyte fuel cell is generally one in which platinum or platinum-ruthenium is supported on carbon black. Therefore, the peroxide decomposition catalyst in the above publication cannot be distinguished at all from conventional electrode catalysts. In addition, according to the knowledge of the present inventors, a catalyst in which a metal is supported on carbon black cannot suppress the generation of harmful by-products in which the fuel is partially oxidized in a solid polymer fuel cell.

  As described above, there are few techniques for suppressing by-products in polymer electrolyte fuel cells, and only a fuel cell having a catalyst for suppressing peroxide is disclosed. However, this technique cannot sufficiently reduce the generation of by-products such as formaldehyde.

  Accordingly, an object of the present invention is to suppress the generation of harmful substances such as formaldehyde which is a partial oxide by-produced during the electrochemical oxidation of liquid fuel in a polymer electrolyte fuel cell using a liquid fuel such as methanol. An object of the present invention is to provide a membrane electrode assembly (MEA) for a polymer electrolyte fuel cell and a fuel cell using the MEA.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies on a catalyst that can efficiently decompose harmful by-products during power generation of a polymer electrolyte fuel cell. As a result, the present invention was completed by finding that a catalyst comprising activated carbon as a component is extremely excellent in such characteristics.

The membrane electrode assembly for a polymer electrolyte fuel cell of the present invention has a polymer electrolyte membrane, and an anode and a cathode on each side thereof,
The anode and the cathode each have a catalyst layer on the side in contact with the polymer electrolyte,
The catalyst layer of at least one of the anode and the cathode contains a by-product decomposition catalyst containing activated carbon as a constituent component in addition to an electrode catalyst in which a metal component is supported on carbon black.

  Moreover, the polymer electrolyte fuel cell of the present invention includes the membrane electrode assembly for a polymer electrolyte fuel cell.

  In the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter sometimes simply referred to as “membrane electrode assembly”), by-product formation of partial oxides during electrochemical oxidation of liquid fuel is suppressed. This eliminates environmental problems caused by harmful substances. Therefore, the membrane electrode assembly of the present invention and the polymer electrolyte fuel cell using the membrane electrode assembly are very useful industrially as those that can be used for power generation systems for home use and business use, and power sources for portable devices and automobiles. It is.

It is a schematic diagram which shows the structure of the membrane electrode assembly of this invention. It is a schematic diagram which shows the other structure of the membrane electrode assembly of this invention.

The membrane electrode assembly for a polymer electrolyte fuel cell of the present invention is
A polymer electrolyte membrane, and an anode and a cathode on each side thereof,
The anode and the cathode each have a catalyst layer on the side in contact with the polymer electrolyte,
The catalyst layer of at least one of the anode and the cathode contains a by-product decomposition catalyst containing activated carbon as a constituent component in addition to an electrode catalyst in which a metal component is supported on carbon black.

  As shown in FIG. 1, the membrane electrode assembly of the present invention has at least a polymer electrolyte membrane 1 and an anode 2 and a cathode 3 on each side thereof, and the anode 2 and the cathode 3 are in contact with the polymer electrolyte membrane 1, respectively. On the side, catalyst layers 4 and 5 and a gas diffusion layer are provided.

  Of the above components, conventional ones can be used except for the “catalyst layer”. For example, the polymer electrolyte membrane may be a fluororesin ion exchange membrane such as a perfluorosulfonic acid ion exchange membrane (trade name “Nafion (registered trademark)”). Further, as the gas diffusion layer, carbon paper or carbon cloth having a thickness of about 100 to 300 μm can be used as having excellent gas permeability and conductivity.

  The catalyst layer is conventionally composed of an electrode catalyst, and a polymer electrolyte, a water repellent material, and the like are uniformly mixed as necessary. In the present invention, at least one of the anode and cathode catalyst layers is further mixed with a by-product. Add cracking catalyst. However, since harmful by-products are mainly generated at the anode, a by-product decomposition catalyst is preferably added to at least the catalyst layer of the anode.

  The polymer electrolyte used for the catalyst layer can be the same material as the polymer electrolyte membrane. The anode electrode catalyst is generally a catalyst in which a metal or alloy such as platinum, ruthenium, palladium, molybdenum, tungsten, tin, iridium, or rhodium is supported on carbon black. As a cathode electrode catalyst, a catalyst in which platinum or the like is supported on carbon black is generally used. Further, as an electrode catalyst, carbon nanotubes or carbon nanohorns carrying the above metal component may be added.

  Here, “carbon black” is fine spherical or chain-like carbon produced by gas phase thermal decomposition or incomplete combustion of hydrocarbon gas or the like. The crystallite is an aggregate called a network plane in which about 30 to 40 carbon 6-membered rings are bonded to each other as a minimum unit, and this network plane is stacked at almost equal intervals by 3 to 5 layers by van der Waals force. . 1000 to 2000 crystallites aggregate to form primary particles, and about 2 to 200 primary particles are chemically and physically bonded to each other to form a clustered structure (structure). From such a form, the pores of carbon black are formed as voids between primary particles. The size of the primary particles of carbon black is usually about 10 to 200 nm in diameter.

  In addition, the polymer electrolyte or anode and cathode of the present invention may have general components of solid polymer fuel cells, and such membrane electrode assemblies and fuel cells are also included in the scope of the present invention. It is.

The “by-product decomposition catalyst” of the present invention means a catalyst capable of decomposing a partial oxide by-produced during the electrochemical oxidation of a liquid fuel. Here, “partial oxide by-produced during electrochemical oxidation of liquid fuel” (hereinafter, also simply referred to as “partial oxide”) refers to, for example, the anode side of a polymer electrolyte fuel cell Means a partial oxide by-produced on the anode side during the reaction (anode reaction) that occurs in the reaction (for example, when methanol is used as the liquid fuel, a reaction represented by CH ₃ OH + H ₂ O → 6H ⁺ + 6e ⁻ + CO ₂ ) Specific examples include aldehydes such as formaldehyde and carboxylic acids. In addition, such a partial oxide may be detected on the air electrode side. This is considered that the fuel permeates the polymer electrolyte membrane and is partially oxidized at the air electrode, or the partial oxide generated on the fuel electrode side permeates the polymer electrolyte membrane.

  The “byproduct decomposition catalyst” contains at least activated carbon as a constituent component. According to the knowledge by the present inventors, harmful partial oxides can be remarkably suppressed by adding activated carbon as a by-product decomposition catalyst in addition to the electrode catalyst.

  The byproduct decomposition catalyst is preferably one in which a metal component capable of decomposing a partial oxide is supported on activated carbon.

  Activated carbon is manufactured by performing an activation treatment after charcoal is sufficiently carbonized. The crystallite has a structure (turbulent structure) in which a network plane in which carbon is bonded at an angle of 120 ° is used as a basic skeleton, and the network plane is irregularly stacked. Activated carbon is obtained by randomly bonding the crystallites, and the pores of the activated carbon are formed as voids between the crystallites. Therefore, the surface area of the activated carbon is very large with respect to the outer surface of the particles. Further, due to the difference in structure, the activated carbon does not have an aggregated form in which primary particles having a diameter of about 10 to 200 nm are bound in a tuft shape like carbon black. The particle diameter of the activated carbon is determined by the degree of pulverization by a pulverizer such as a rod mill, ball mill, jet mill, etc., and the particle diameter is usually larger than that of carbon black. As the activated carbon material used in the present application, one having a diameter of 1 to 50 μm is suitable.

  Thus, carbon black and activated carbon are remarkably different in structure and form.

  Examples of the metal component of the by-product decomposition catalyst include at least one element selected from platinum, ruthenium, palladium, iridium, rhodium, osmium, gold and silver, in particular, a combination of two or more selected from platinum, ruthenium and palladium. Is preferred. Moreover, the form of these metal components is not particularly limited, and any of metal, oxide, hydroxide, alloy, and the like may be used. The said metal component should just carry | support the catalyst amount on activated carbon, and the loading amount is 1-60 mass% normally, Preferably it is 10-30 mass%. There is no restriction | limiting in particular about the support method of a metal component, The preparation method of a general supported catalyst can be used.

  As the activated carbon used as the byproduct decomposition catalyst, those having a volume of pores having a radius of 40 mm or more and less than 100 mm (hereinafter sometimes simply referred to as “pore volume”) of 0.05 ml / g or more are suitable. This is because such activated carbon is particularly excellent in the decomposition effect of partial oxides. More preferably, it is 0.1 ml / g or more, and further 0.2 ml / g or more is suitable. However, if the pore volume is too large, the bulk specific gravity of the byproduct decomposition catalyst is reduced, and as a result, the thickness of the catalyst layer may be increased and the power generation performance may be reduced. Preferably it is 0.4 ml / g or less.

  The pore volume of the activated carbon is measured by a nitrogen adsorption method (77K, 10.5 Torr or less) using, for example, a fully automatic gas adsorption device (such as “Omni Soap 360CX” manufactured by Beckman Coulter, Inc.), and the obtained adsorption isotherm From the above, the pore volume is calculated by the BJH method.

  Activated carbon having a pore volume of 0.05 ml / g or more is easily obtained by controlling the pore structure by appropriately combining heat treatment conditions and activation treatment when carbonizing activated carbon raw materials such as wood powder and coconut shells. be able to. Examples of the activation treatment include a chemical activation method using a zinc chloride solution or a phosphoric acid solution, a gas activation method using water vapor, and the like. Moreover, it can also be set as the activated carbon material which has the pore volume of 0.05 ml / g or more by performing the said activation process to activated carbon with a pore volume less than 0.05 ml / g, and controlling the pore structure. .

  The ratio of the electrode catalyst to the byproduct decomposition catalyst is not particularly limited, but the mass ratio of the electrode catalyst to the byproduct decomposition catalyst is in the range of 1: 0.2 to 2, preferably 1: 0.5 to 1.5. It is better to do so. Moreover, in order to ensure the electroconductivity of a catalyst layer, it is preferable to mix | blend required amount of electroconductive materials, such as carbon black. Specifically, it is preferable to form the catalyst layer together with 10 to 100% by mass of the conductive material with respect to the activated carbon.

  The catalyst layer in the membrane electrode assembly is divided into a first catalyst layer having an electrode catalyst and a second catalyst layer having a by-product decomposition catalyst, and the first catalyst layer is interposed between the polymer electrolyte membrane and the second catalyst layer. It is also a preferable aspect of the present invention to be arranged in the above. This is because the reduction effect of by-products can be further enhanced by configuring the catalyst layer in this way.

  FIG. 2 is a diagram schematically showing the two-layer structure. In the figure, 1, 2, 3 and 5 have the same meaning as in FIG. 1, but the catalyst layer in the anode 2 is divided into a first catalyst layer 41 in contact with the polymer electrolyte membrane 1 and this second catalyst. The second catalyst layer 42 is provided in contact with the layer 41. Here, the first catalyst layer 41 includes an anode electrode catalyst, and the second catalyst layer 42 includes the byproduct decomposition catalyst of the present invention.

  The ratio of the thickness of the first catalyst layer 41 and the second catalyst layer 42 is not particularly limited, but the ratio of the electrode catalyst to the byproduct decomposition catalyst (electrode catalyst: byproduct decomposition catalyst (mass ratio)). Is preferably 1: 0.2 to 2, preferably 1: 0.5 to 1.5. The two-layer structure of the catalyst layer is not limited to the above-mentioned anode catalyst layer, but can also be applied to the cathode catalyst layer. In particular, the anode catalyst layer has a two-layer structure. Is preferable.

  The membrane electrode assembly of the present invention can be produced according to a conventional method. For example, a paste is prepared by uniformly mixing an anode and cathode electrode catalyst and a by-product decomposition catalyst, and an organic solvent such as water or isopropyl alcohol, and this is applied to a gas diffusion layer such as carbon paper and then dried. Electrodes (anode and cathode) can be formed. In addition to the electrode catalyst, etc., appropriately select and use general components used for the formation of solid polymer fuel cell electrodes, such as polymer electrolytes, conductive materials, water repellent materials, binders, etc. Can do. That is, the electrode of the membrane electrode assembly of the present invention can be formed according to a conventional method using a mixture containing an arbitrary electrode catalyst and the by-product decomposition catalyst of the present invention. The mixing ratio of each component can be general and is not particularly limited. For example, the ratio of electrode catalyst: byproduct decomposition catalyst is 1: 0.2 to 2, preferably 1: 0 in terms of mass ratio. .5 to 1.5.

  When the electrode layer of the present invention has a two-layer structure as shown in FIG. 2, the paste containing the electrode catalyst is first applied to the gas diffusion layer and dried, and then the paste containing the by-product decomposition catalyst is applied thereon. What is necessary is just to apply | coat and dry.

  The obtained anode and cathode can be made into a membrane electrode assembly by hot pressing with a polymer electrolyte membrane interposed therebetween. At this time, in each electrode, it is necessary to dispose the catalyst layer in contact with the polymer electrolyte membrane. Moreover, the pressure and temperature in a hot press should just follow the conditions of a conventional method.

  The obtained membrane electrode can be made into a polymer electrolyte fuel cell according to a conventional method together with a separator and the like.

  The polymer electrolyte fuel cell uses a fuel that can be handled as a liquid at a general operating temperature (usually from room temperature to 100 ° C.), such as oxygen-containing hydrocarbons such as methanol, ethanol, and dimethyl ether. However, in conventional polymer electrolyte fuel cells, these fuels are partially oxidized on the anode side, or aldehydes and carboxylic acids that are partially oxidized on the cathode side of the fuel that has permeated the polymer electrolyte membrane are by-produced. was there.

  On the other hand, in the polymer electrolyte fuel cell of the present invention, a by-product decomposition catalyst is added to at least one of the catalyst layers of the anode and the cathode, and the generation of partial oxides can be remarkably suppressed. Don't give. Therefore, the polymer electrolyte fuel cell of the present invention is also suitable for a power source in an environment close to humans, such as a power source for portable devices and automobiles, or a power generation system for home use.

  The invention is further illustrated by the following examples, which illustrate advantageous embodiments of the invention. The byproduct decomposition catalyst of the present invention was prepared according to the following catalyst preparation example.

Catalyst preparation example 1
Activated carbon having a mesh of 45 μm or less (volume of pores having a radius of 40 to 100 μm: 0.27 ml / g) was impregnated with a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate. Next, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours using hydrogen gas to obtain Catalyst A. The supported amounts of platinum and ruthenium in the catalyst A were 20% by mass and 10% by mass, respectively.

Catalyst preparation example 2
Activated carbon having a mesh of 45 μm or less (volume of pores having a radius of 40 to 100 μm: 0.12 ml / g) was impregnated with a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate. Next, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours using hydrogen gas to obtain Catalyst B. The supported amounts of platinum and ruthenium in the catalyst B were 20% by mass and 10% by mass, respectively.

Catalyst preparation example 3
Activated carbon having a mesh of 45 μm or less (volume of pores having a radius of 40 to 100 μm: 0.06 ml / g) was impregnated with a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate. Next, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed at 300 ° C. for 2 hours using hydrogen gas to obtain Catalyst C. The supported amounts of platinum and ruthenium in the catalyst C were 20% by mass and 10% by mass, respectively.

Catalyst preparation example 4
Activated carbon having a mesh of 45 μm or less (volume of pores having a radius of 40 to 100 μm: 0.03 ml / g) was impregnated with a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate. Next, after drying at 90 ° C. in a nitrogen atmosphere, a reduction treatment was performed using hydrogen gas at 300 ° C. for 2 hours to obtain Catalyst D. The supported amounts of platinum and ruthenium in the catalyst D were 20% by mass and 10% by mass, respectively.

Catalyst preparation example 5
Activated carbon having a mesh of 45 μm or less (volume of pores having a radius of 40 to 100 μm: 0.12 ml / g) was impregnated with a mixed aqueous solution of palladium nitrate and dinitrodiammine platinum. Next, after drying at 90 ° C. in a nitrogen atmosphere, reduction treatment was performed using hydrogen gas at 300 ° C. for 2 hours to obtain Catalyst E. The supported amounts of palladium and platinum in the catalyst E were 15% by mass and 15% by mass, respectively.

Example 1
Catalyst A, platinum-ruthenium-supported carbon black made by E-TEK (platinum-supported amount: 20% by mass, ruthenium-supported amount: 10% by mass, carrier carbon black is Vulcan XC-72 manufactured by Cabot), 5% Nafion solution (Aldrich), water and isopropyl alcohol were mixed at a mass ratio of 1: 1: 40: 20: 14 and uniformly dispersed to prepare a catalyst-containing paste. This was uniformly coated on carbon paper (Toray Industries, Inc.) so that the total supported amount of platinum-ruthenium was 1 mg / cm ^2, and then dried for 15 hours to obtain an anode. In addition, platinum-supported carbon black manufactured by E-TEK (platinum supported amount: 60% by mass, carbon black of the carrier is Vulcan XC-72 manufactured by Cabot), 5% Nafion solution (manufactured by Aldrich), water, and 10% poly A tetrafluoroethylene solution was mixed at a mass ratio of 1: 20: 10: 5 and dispersed uniformly to prepare a catalyst-containing paste. This was applied onto carbon paper (manufactured by Toray Industries, Inc.) uniformly so that the amount of platinum supported was 1 mg / cm ^2, and then dried for 15 hours to form a cathode.

A Nafion 117 membrane (manufactured by DuPont) was sandwiched between the cathode and anode thus obtained so that the effective electrode area was 25 cm ^2, and the surfaces coated with the catalyst were overlapped so as to be in contact with the Nafion membrane. Thereafter, hot pressing was performed for 5 minutes under the conditions of 130 ° C. and 100 kg / cm ² to manufacture a membrane electrode assembly. This membrane / electrode assembly was incorporated into an experimental fuel cell, a 1 mol / L aqueous methanol solution was supplied to the anode at 6 ml / min, and air was supplied to the cathode at 1 L / min. It was. The amount of partial oxides (formaldehyde, methyl formate, formic acid) by-produced at the anode and cathode during the power generation test was measured as follows. That is, under the above conditions, a constant current of 300 mA / cm ² is maintained for 2 hours, and partial oxides by-produced at the anode and the cathode are collected by a dry ice / methanol trap, and the collected mass is weighed and quantitatively determined. It was used for analysis. Formaldehyde and methyl formate were quantitatively analyzed by gas chromatograph, and formic acid was quantitatively analyzed by high performance liquid chromatograph. The results are shown in Table 1.

Comparative Example 1
Platinum-ruthenium-supported carbon black made by E-TEK (platinum supported amount: 20% by mass, ruthenium supported amount: 10% by mass, carbon black of the carrier is Vulcan XC-72 manufactured by Cabot), 5% Nafion solution (Aldrich) Product), water and isopropyl alcohol were mixed at a mass ratio of 1: 20: 10: 7 and dispersed uniformly to prepare a catalyst-containing paste. This was applied onto carbon paper (manufactured by Toray Industries, Inc.) uniformly so that the total supported amount of platinum-ruthenium was 1 mg / cm ^2, and then dried for 15 hours to obtain an anode. A membrane electrode assembly was produced. Using this membrane / electrode assembly, a power generation test was conducted in the same manner as in Example 1 to quantitatively analyze the partial oxide produced as a by-product. The results are shown in Table 1.

Example 2
A membrane electrode assembly was produced in the same manner as in Example 1 except that the catalyst B was used instead of the catalyst A, a power generation test was performed using this membrane electrode assembly, and quantitative analysis of the partial oxide produced as a by-product Went. The results are shown in Table 1.

Example 3
A membrane electrode assembly was produced in the same manner as in Example 1 except that the catalyst C was used in place of the catalyst A, and a power generation test was performed using this membrane electrode assembly to quantitatively analyze the partial oxide produced as a by-product. Went. The results are shown in Table 1.

Example 4
A membrane electrode assembly was produced in the same manner as in Example 1 except that the catalyst D was used in place of the catalyst A, and a power generation test was performed using this membrane electrode assembly to quantitatively analyze the partial oxide produced as a by-product. Went. The results are shown in Table 1.

Example 5
Platinum-ruthenium-supported carbon black made by E-TEK (platinum supported amount: 20% by mass, ruthenium supported amount: 10% by mass, carbon black of the carrier is Vulcan XC-72 manufactured by Cabot), 5% Nafion solution (Aldrich) Product), water and isopropyl alcohol were mixed at a mass ratio of 1: 20: 10: 7 and dispersed uniformly to prepare a catalyst-containing paste. This was uniformly coated on carbon paper (manufactured by Toray Industries Inc.) so that the amount of platinum supported was 1 mg / cm ^2, and then dried for 15 hours to obtain an anode. Catalyst E, platinum-supported carbon black manufactured by E-TEK (platinum supported amount: 60 mass%, carbon black of the carrier is Vulcan XC-72 manufactured by Cabot), 5% Nafion solution (manufactured by Aldrich), water and A 10% polytetrafluoroethylene solution was mixed at a mass ratio of 1: 1: 40: 20: 10 and uniformly dispersed to prepare a catalyst-containing paste. This was uniformly coated on carbon paper (manufactured by Toray Industries Inc.) so that the amount of platinum supported was 1 mg / cm ^2, and then dried for 15 hours to form a cathode.

  Using the thus obtained cathode and anode, a membrane / electrode assembly was produced in the same manner as in Example 1, and a power generation test was performed using this membrane / electrode assembly to determine the by-product partial oxide. Analysis was carried out. The results are shown in Table 1.

Example 6
In this embodiment, the catalyst layer has a two-layer structure as shown in FIG. 2, and the second catalyst layer 42 is formed using the byproduct decomposition catalyst of the present invention. That is, platinum-ruthenium-supported carbon black manufactured by E-TEK (platinum supported amount: 20% by mass, ruthenium supported amount: 10% by mass, carbon black of the carrier is Vulcan XC-72 manufactured by Cabot), 5% Nafion solution ( Aldrich), water and isopropyl alcohol were mixed at a mass ratio of 1: 20: 10: 7 and uniformly dispersed to prepare a catalyst-containing paste. This was uniformly coated on carbon paper (manufactured by Toray Industries Inc.) so that the total supported amount of platinum-ruthenium was 0.5 mg / cm ^2, and then dried for 15 hours to produce the first catalyst layer 41. Next, catalyst D, carbon black (manufactured by Cabot, Vulcan XC-72), water and isopropyl alcohol were mixed at a mass ratio of 1: 20: 10: 7 and dispersed uniformly to prepare a catalyst-containing paste. This was uniformly coated on the first catalyst layer so that the total supported amount of platinum-ruthenium was 1 mg / cm ^2, and then dried for 15 hours to form the second catalyst layer 42, whereby an anode having a two-layer structure Was made. Thereafter, a membrane / electrode assembly was produced in the same manner as in Example 1 except that the anode had the above two-layer structure, and the power generation test was performed. The results are shown in Table 1.

Example 7
A membrane / electrode assembly was produced in the same manner as in Example 6 except that catalyst B was used in place of catalyst D. A power generation test was performed using this membrane / electrode assembly, and quantitative analysis of by-product partial oxides was performed. Went. The results are shown in Table 1.

  Comparing Example 1 and Comparative Example 1, in Comparative Example 1, which is a conventional membrane electrode assembly, formaldehyde, which is a partial oxide of methanol, is generated on the anode side in a power generation experiment. Formaldehyde and the like are also generated on the cathode side. This is probably due to methanol partial oxide by-produced at the fuel electrode permeating the polymer electrolyte membrane or methanol permeating the polymer electrolyte membrane. However, it is thought that it was partially oxidized on the cathode side. On the other hand, in Example 1 in which a by-product decomposition catalyst was added to the anode, formaldehyde generated on the anode side was remarkably reduced, and the by-product on the cathode side was suppressed below the detection limit. Therefore, it has been found that by using a membrane electrode assembly containing the by-product decomposition catalyst of the present invention in the catalyst layer, the by-product of partial oxide can be effectively suppressed.

  According to the results of Examples 1 to 3, in the by-product decomposition catalyst of the present invention, when the pore volume of the activated carbon having a radius of 40 mm or more and less than 100 mm is 0.05 ml / g or more, better generation of by-products is suppressed. It was clarified that the effect was higher as the pore volume was larger.

  As a result of Example 5, when the by-product decomposition catalyst of the present invention was added to the catalyst layer of the cathode, the generation of formaldehyde and the like on the anode side could not be suppressed, but the partial oxide of methanol by-produced at the fuel electrode Was able to suppress the generation of formaldehyde and the like on the cathode side, which was thought to have been permeated through the polymer electrolyte membrane, or methanol partially permeated through the polymer electrolyte membrane.

  According to the results of Example 4, even when activated carbon having a pore volume with a radius of 40 mm or more and less than 100 mm is lower than 0.05 ml / g (0.03 ml / g) as a by-product decomposition catalyst material at the anode, Generation of formaldehyde and the like could be suppressed. However, the effect was low as compared with Examples 1 to 3 where the pore volume was 0.05 ml / g.

  Therefore, as Example 6, a membrane electrode joint in which the catalyst layer has a two-layer structure including a first catalyst layer and a second catalyst layer as shown in FIG. 2, and the second catalyst layer is formed by the byproduct decomposition catalyst of the present invention. When the body was used, even when activated carbon having a pore volume of less than 0.05 ml / g was used, generation of formaldehyde and the like could be remarkably suppressed. This result demonstrates that such a two-layer structure exhibits an excellent effect.

  Moreover, as the result of Example 7, when the activated carbon having a pore volume of 0.05 ml / g or more is used, a more excellent effect can be obtained if the catalyst layer has a two-layer structure.

Claims (6)

A membrane electrode assembly for a polymer electrolyte fuel cell having a polymer electrolyte membrane and an anode and a cathode on each side thereof,
The anode and the cathode each have a catalyst layer on the side in contact with the polymer electrolyte,
For a polymer electrolyte fuel cell, wherein the catalyst layer of at least one of an anode and a cathode contains a by-product decomposition catalyst having activated carbon as a constituent component in addition to an electrode catalyst in which a metal component is supported on carbon black Membrane electrode assembly.   2. The membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1, wherein the pore volume of the activated carbon having a radius of 40 mm or more and less than 100 mm is 0.05 ml / g or more.   2. The membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1, wherein the pore volume of the activated carbon having a radius of 40 mm or more and less than 100 mm is 0.2 ml / g or more.   The catalyst layer containing a by-product decomposition catalyst is divided into a first catalyst layer having an electrode catalyst and a second catalyst layer having a by-product decomposition catalyst, and the first catalyst layer is a polymer electrolyte membrane and a second catalyst. The membrane electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the membrane electrode assembly is disposed between the layers.   The solid polymer according to any one of claims 1 to 4, wherein the by-product decomposition catalyst is obtained by supporting at least one element selected from platinum, ruthenium, palladium, iridium, rhodium, osmium, gold and silver on activated carbon. Type membrane electrode assembly for fuel cell.   A polymer electrolyte fuel cell comprising the membrane electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 5.

Images