WO2006070635A1

WO2006070635A1 - Membrane electrode assembly for solid polymer fuel cell

Info

Publication number: WO2006070635A1
Application number: PCT/JP2005/023289
Authority: WO
Inventors: Junji Okamura; Takaaki Hashimoto; Kuninori Miyazaki; Noboru Sugishima
Original assignee: Nippon Shokubai Co., Ltd.
Priority date: 2004-12-27
Filing date: 2005-12-19
Publication date: 2006-07-06
Also published as: TW200635116A; JPWO2006070635A1

Abstract

This invention solves environmental problems of solid polymer fuel cells by suppressing formation of partial oxides such as formaldehyde by electrochemical oxidation of the liquid fuel. Specifically disclosed is a membrane electrode assembly for solid polymer fuel cells whose most significant feature is in that a byproduct decomposition catalyst containing activated carbon as a constituent is contained in the catalyst layer of at least one of the anode and cathode for decomposing the partial oxides.

Description

Specification

Membrane electrode assembly for polymer electrolyte fuel cell

Technical field

[0001] 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.

Background art

In a polymer electrolyte fuel cell, protons generated from fuel in an anode are oxidized with an oxidant in a power sword and power is generated. Alcohols and the like are used as this fuel, but the alcohol as a fuel is 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 and 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 by-products during power generation be suppressed as much as possible. However, the actual situation is that most of these efforts to control harmful by-products have been made.

[0003] 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 peroxidic acid decomposition catalyst in this technology is a catalyst in which ruthenium or the like is supported on carbon black, zircoure or the like, and the catalyst used in the examples is only a catalyst in which metal is supported on carbon black.

[0004] However, a catalyst for an electrode of 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 completely distinguished from the conventional electrode catalyst. In addition, according to the findings by the present inventors, a catalyst in which a metal is supported on carbon black suppresses the generation of harmful by-products in which the fuel is partially oxidized as compared with a solid polymer fuel cell. I can not do such a thing.

Disclosure of the invention [0005] As described above, in the polymer electrolyte fuel cell, the technology for suppressing by-products is only to the extent that a fuel cell having a catalyst for suppressing peroxidic acid is disclosed. However, this technology cannot sufficiently reduce the generation of by-products such as formaldehyde.

[0006] Therefore, an object of the present invention is to formaldehyde, which is a partial oxide by-produced during the electrochemical oxidation of a liquid fuel, in a solid polymer fuel cell using a liquid fuel such as methanol. It is an object to provide a membrane electrode assembly (MEA) for polymer electrolyte fuel cells that can suppress the generation of harmful substances such as, and a fuel cell using the MEA.

[0007] The inventors of the present invention have made extensive studies on a catalyst capable of efficiently decomposing harmful by-products during power generation in a polymer electrolyte fuel cell that solves the above problems. 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.

[0008] The membrane electrode assembly for a polymer electrolyte fuel cell of the present invention has a polymer electrolyte membrane, and an anode and a force sword on each side thereof,

The anode and force sword each have a catalyst layer on the side in contact with the polymer electrolyte, and at least one of the anode and force sword catalyst layers is added to an electrode catalyst in which a metal component is supported on carbon black, and activated carbon is a constituent component. It contains a by-product decomposition catalyst.

[0009] The polymer electrolyte fuel cell of the present invention includes the membrane electrode assembly for a polymer electrolyte fuel cell.

[0010] In the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter sometimes simply referred to as "membrane electrode assembly"), the partial acid concentration during the electrochemical oxidation of the liquid fuel is determined. Since the by-product of soot is suppressed, environmental problems caused by harmful substances are eliminated. Therefore, the membrane electrode assembly of the present invention and the polymer electrolyte fuel cell using the same are very industrially regarded as being usable for power generation systems for home use and business use, as well as power supplies for portable devices and automobiles. Useful.

Brief Description of Drawings

FIG. 1 is a schematic diagram showing a configuration of a membrane electrode assembly of the present invention. FIG. 2 is a schematic view showing another configuration of the membrane / electrode assembly of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] The membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises:

The polymer electrolyte membrane has an anode and a force sword on each side thereof, and the anode and the force sword each have a catalyst layer on the side in contact with the polymer electrolyte, and at least one catalyst layer of the anode and the force sword has In addition to the electrode catalyst having a metal component supported on carbon black, it contains a by-product decomposition catalyst containing activated carbon as a constituent.

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 force sword 3 on each side thereof, and each of the anode 2 and the force sword 3 is a polymer. The catalyst layers 4 and 5 and the gas diffusion layer are provided on the side in contact with the electrolyte membrane 1.

[0014] Of the above-described components, a conventional general element can be used except for the "catalyst layer". For example, the polymer electrolyte membrane can be a fluorocoagulant ion exchange membrane such as a perfluorosulfonic acid ion exchange membrane (trade name “Nafion (registered trademark)”). In addition, 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.

[0015] The catalyst layer is conventionally composed of an electrode catalyst, and a force obtained by uniformly mixing a polymer electrolyte, a water repellent material, or the like as required. In the present invention, at least one catalyst layer of an anode and a force sword Further, a by-product decomposition catalyst is added. However, since harmful by-products are mainly generated at the anode, it is preferable to add a by-product decomposition catalyst to at least the catalyst layer of the anode.

[0016] As the polymer electrolyte used for the catalyst layer, the same material as the polymer electrolyte membrane can be used. 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 force sword electrode catalyst, a catalyst in which platinum or the like is supported on carbon black is generally used. Further, as an electrode catalyst, carbon nano tube or carbon nano horn or the like carrying the above metal component may be added.

Here, “carbon black” refers to gas phase pyrolysis or incomplete combustion of hydrocarbon gas or the like. The fine powder is spherical or chain-like carbon. The crystallite consists of an assembly called a network plane consisting of about 30 to 40 carbon 6-membered rings, and this network plane is stacked almost evenly by 3-5 layers by van der Waals force. is there. 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 primary particles of carbon black is usually about 10 to 200 nm in diameter.

[0018] In addition, the polymer electrolyte, anode and force sword of the present invention include such membrane electrode assemblies and fuel cells that may have general components of solid polymer fuel cells. It is included in the scope of the present invention.

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”) means, for example, that of a polymer electrolyte fuel cell Reaction that takes place on the anode side (anode reaction) (for example, when methanol is used as the liquid fuel, it is expressed as CH OH + HO → 6H + + 6e— + CO

3 2 2 reaction) means a partial acid product formed as a by-product on the anode side, and specific examples include aldehydes such as formaldehyde and carboxylic acids. In addition, such partial oxides may be detected on the air electrode side. This is thought to be because 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.

[0020] "By-product decomposition catalyst" includes at least activated carbon as a constituent component. According to the knowledge of the present inventors, harmful partial acid oxides can be remarkably suppressed by adding activated carbon as a by-product decomposition catalyst in addition to the electrode catalyst.

[0021] The by-product decomposition catalyst is preferably one in which a metal component capable of decomposing a partial oxide is supported on activated carbon.

[0022] Activated carbon is produced by performing an activation treatment after charcoal or the like is sufficiently carbonized. The crystallite has a network plane in which carbons are bonded at an angle of 120 ° as a basic skeleton, and the network plane is irregularly laminated (L layer structure). This crystallite is randomly bonded This is activated carbon, and the pores of the activated carbon are formed as voids between crystallites. Therefore, the surface area of the activated carbon is very large relative to the outer surface of the particles. In addition, due to structural differences, activated carbon does not have an agglomerated form in which primary particles with a diameter of about 10 to 200 nm are bound in a tuft shape like carbon black. The particle size of the activated carbon is determined by the degree of pulverization with a pulverizer such as a rod mill, ball mill, jet mill or the like, and the particle size 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 m is suitable.

[0023] Thus, carbon black and activated carbon are significantly different in structure and form.

[0024] The metal component of the byproduct decomposition catalyst is selected from, for example, platinum, ruthenium, palladium, iridium, rhodium, osmium, gold and silver power, in particular, white gold, ruthenium and palladium carbonate. A combination of two or more of these is preferred. In addition, the form of these metal components is not particularly limited, and any of metal, oxide, hydroxide, alloy and the like may be used. The metal component may be supported on the activated carbon by a catalytic amount. The supported amount is usually 1 to 60% by mass, preferably 10 to 30% by mass. There is no particular limitation on the method for supporting the metal component, and a general method for preparing a supported catalyst can be used.

[0025] Activated carbon used as a by-product decomposition catalyst is preferably one having a pore volume with a radius of 40 A or more and less than 100 A (hereinafter sometimes simply referred to as “pore volume”) of 0.05 mlZg or more. Is. This is because the activated carbon is particularly excellent in the partial oxide decomposition effect. More preferred is 0.1 mlZg or more, and more preferred is 0.2 mlZg or more. However, if the pore volume is excessively large, the bulk specific gravity of the by-product 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. Therefore, it is preferably 0.5 mlZg or less, more preferably 0.4ml or less.

[0026] 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 Isothermal force Calculate pore volume by BJH method.

[0027] Activated carbon with a pore volume of 0.05mlZg or more carbonizes activated carbon raw materials such as wood powder and coconut shells. It can be easily obtained by controlling the pore structure by appropriately combining the heat treatment conditions and the activation treatment. Examples of the powerful activation treatment include a chemical activation method using a zinc chloride solution and a phosphoric acid solution, and a gas activation method using water vapor. Further, the activated carbon material having a pore volume of 0.05 mlZg or more can be obtained by subjecting the activated carbon having a pore volume of less than 0.05 mlZg to the above activation treatment to control its pore structure.

[0028] 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. It is better to be 5. In order to ensure the conductivity of the catalyst layer, a necessary amount of a conductive material such as carbon black is preferably blended. Specifically, it is preferable to form a catalyst layer together with a conductive material of 10 to LOO mass% with respect to activated carbon.

[0029] 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 byproduct decomposition catalyst, and the first catalyst layer is divided into a polymer electrolyte membrane and a second catalyst. It is also a preferred aspect of the present invention to be arranged between the layers. This is because the reduction effect of by-products can be further enhanced by making the catalyst layer in such a configuration.

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 the first catalyst layer 41 in contact with the polymer electrolyte membrane 1 and the second catalyst. The second catalyst layer 42 is provided in contact with the layer 41. Here, the first catalyst layer 41 includes an anode electrocatalyst, and the second catalyst layer 42 includes the byproduct decomposition catalyst of the present invention.

[0031] The thickness ratio between the first catalyst layer 41 and the second catalyst layer 42 is not particularly limited, but the ratio between the electrode catalyst and the byproduct decomposition catalyst (electrode catalyst: byproduct decomposition catalyst (mass) The ratio)) is preferably 1: 0.2 to 2, preferably 1: 0.5 to 1.5. Note that the two-layer structure of the catalyst layer is not limited to the anode catalyst layer described above, and can be applied to a force sword catalyst layer. It is preferable to do.

[0032] The membrane electrode assembly of the present invention can be produced according to a conventional method. For example, anode and power sword electrocatalysts and byproduct decomposition catalysts, and water and isopropyl alcohol. An electrode (anode and force sword) can be formed by uniformly mixing any organic solvent to prepare a paste, applying the paste to a gas diffusion layer such as carbon paper, and drying. In addition to electrode catalysts, etc., general components used for forming electrodes of polymer electrolyte fuel cells, such as polymer electrolytes, conductive materials, water repellent materials, and binders, are selected and used as necessary. be able to. 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 any electrode catalyst and the byproduct 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 the electrocatalyst to the by-product decomposition catalyst is 1: 0.2 to 2, preferably 1: 0.0 by mass ratio. 5 to 1.5.

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

[0034] The obtained anode and force sword can be formed 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 the hot press may be in accordance with ordinary conditions.

[0035] 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.

[0036] A polymer electrolyte fuel cell is a fuel that can be handled as a liquid at a general operating temperature (usually about room temperature to 100 ° C), such as oxygen-containing hydrocarbons such as methanol, ethanol, and dimethyl ether. And However, in conventional polymer electrolyte fuel cells, these fuels are partially oxidized on the anode side, or aldehydes and carboxylic acids partially oxidized on the fuel force S sword side that have permeated the polymer electrolyte membrane are by-produced. There was a problem.

[0037] 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 power sword, and generation of partial oxides can be remarkably suppressed. Does not adversely affect the environment or humans. 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 household power generation system. Example

[0038] The present invention will be described more specifically with reference to the following examples illustrating advantageous embodiments of the present invention. The by-product decomposition catalyst of the present invention was prepared according to the following catalyst preparation example.

[0039] Catalyst Preparation Example 1

A mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was impregnated in activated carbon (radius force 0 A or more and less than 100 A pore volume: 0.27 mlZg) with a mesh of 45 μm or less. 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 A. The supported amounts of platinum and ruthenium on catalyst A were 20% by mass and 10% by mass, respectively.

[0040] Catalyst Preparation Example 2

A mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was impregnated in activated carbon (radius force 0 A or more and less than 100 A pore volume: 0.12 mlZg) with a mesh of 45 μm or less. 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 B. The supported amounts of platinum and ruthenium on catalyst B were 20% by mass and 10% by mass, respectively.

[0041] Catalyst Preparation Example 3

A mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was impregnated in activated carbon (radius force 0 A or more and less than 100 A pore volume: 0.06 mlZg) with a mesh of 45 μm or less. 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 C. The supported amounts of platinum and ruthenium on catalyst C were 20% by mass and 10% by mass, respectively.

[0042] Catalyst Preparation Example 4

A mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was impregnated in activated carbon (radius force 0 A or more and less than 100 A pore volume: 0.03 mlZg) with a mesh of 45 μm or less. 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 on catalyst D were 20% by mass and 10% by mass, respectively. [0043] Catalyst Preparation Example 5

Activated carbon with a mesh aligned to 45 μm or less (pore volume with a radial force of 0 A or more and less than 100 A: 0.12 mlZg) 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 at 300 ° C. for 2 hours using hydrogen gas to obtain Catalyst E. The supported amounts of palladium and platinum on the catalyst E were 15% by mass and 15% by mass, respectively.

[0044] Example 1

Catalyst A, E-TEK made of platinum-one ruthenium carrying carbon black (platinum content: 20 mass ^_0/0, ruthenium amount: 10 mass ^_0/0, the carrier of the carbon black is manufactured by Cabot Corporation Barka down XC 72 ), 5% naphthion solution (manufactured by 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 (made by Torayen earth) so that the total supported amount of platinum-ruthenium was 1 mg / cm ^2, and then dried for 15 hours to form an anode. In addition, E-TEK platinum-supported carbon black (platinum support amount: 60% by mass, carbon black of the carrier is Cabot Vulcan XC-72), 5% Nafion solution (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 uniformly applied onto carbon paper (manufactured by Toray Industries Inc.) so that the amount of platinum supported was lmgZcm ^2, and then dried for 15 hours to form a force sword.

[0045] effective electrode area during the thus obtained force Sword and anode sandwich the Nafuion 117 membrane (DuPont Co.) so that the 25 cm ^2, the surface of the catalyst is applied to contact the Nafuion film Then, the membrane electrode assembly was manufactured by hot pressing for 5 minutes under the conditions of 130 ° C. and lOOkgZcm ² . This membrane / electrode assembly was assembled in an experimental fuel cell, and a power generation test was conducted at a cell temperature of 90 ° C with an ImolZL methanol aqueous solution supplied at 6 mlZmin to the anode and air at 1 L Zmin. During the power generation test, the amount of partial oxides (formaldehyde, methyl formate, formic acid) by-produced at the anode and the power sword was measured as follows. In other words, under the above conditions, a constant current of 300 mAZcm ² was maintained for 2 hours, and the partial acid oxides produced as a by-product at the anode and the power sword were each dried ice The sample was collected by a wrap, and the collected mass was weighed and then subjected to quantitative 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.

[0046] Comparative Example 1

Manufactured by E-TEK platinum - ruthenium carbon black (amount of platinum supported: 20 wt%, Le Te - © arm supporting amount: 10 mass ^_0/0, the carrier of the carbon black is manufactured by Cabot Corporation Vulcan XC 72), 5 % Catalyst solution (Aldrich), 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 (made of Torayen earth) uniformly so that the total supported amount of platinum-ruthenium was lmgZcm ² and then dried for 15 hours to obtain an anode, which was the same as in Example 1. A membrane electrode assembly was produced. Using this membrane / electrode assembly, in the same manner as in Example 1, a power generation test was performed, and a quantitative analysis of by-product partial oxides was performed. The results are shown in Table 1.

[0047] Example 2

A membrane / electrode assembly was produced in the same manner as in Example 1 except that catalyst B was used instead of catalyst A, 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.

[0048] Example 3

A membrane / electrode assembly was produced in the same manner as in Example 1 except that catalyst C was used instead of catalyst A, 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.

[0049] Example 4

A membrane / electrode assembly was produced in the same manner as in Example 1 except that Catalyst D was used instead of Catalyst A, 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.

[0050] Example 5

Manufactured by E-TEK platinum - ruthenium carbon black (amount of platinum supported: 20 wt%, Le Te - © arm supporting amount: 10 mass ^_0/0, the carrier of the carbon black manufactured by Cabot Corporation of Vulcan XC- 72), 5% naphthion solution (manufactured by 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 (made by Torayen earth) so that the amount of platinum supported was lmgZcm ^2, and then dried for 15 hours to form an anode. Moreover, the catalyst E, E- TEK made of platinum responsible lifting carbon black (amount of platinum supported: 60 wt ^_0/0, Vulcan XC 72 carbon black from Cabot Corporation of carrier) (manufactured by Aldrich) 5% Nafuion solution Then, water and a 10% polytetrafluoroethylene solution were mixed at a mass ratio of 1: 1: 40: 20: 10 and dispersed uniformly to prepare a catalyst-containing paste. This was uniformly applied onto carbon paper (manufactured by Toray Industries, Inc.) so that the amount of platinum supported was lmgZcm ^2, and then dried for 15 hours to form a force sword.

[0051] Using the force sword and the anode thus obtained, 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 produce a by-product. Quantitative analysis of oxides was performed. The results are shown in Table 1.

[0052] Example 6

In this example, the catalyst layer had a two-layer structure as shown in FIG. 2, and the second catalyst layer 42 was formed using the byproduct decomposition catalyst of the present invention. That is, 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% naphthion solution (Aldrich), 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 coated on carbon paper (manufactured by Toray Industries, Inc.) uniformly so that the total supported amount of platinum and ruthenium was 0.5 mgZcm ^2, and then dried for 15 hours to produce the first catalyst layer 41. Next, catalyst D, carbon black (Valkan XC-72, manufactured by Cabot), 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 lmgZcm ^2, and then dried for 15 hours to form the second catalyst layer 42, whereby an anode having a two-layer structure was formed. Produced. Thereafter, a membrane / electrode assembly was prepared 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.

[0053] Example 7 A membrane / electrode assembly was produced in the same manner as in Example 6 except that catalyst Β was used in place of catalyst D, 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.

[table 1]

[0055] When Example 1 and Comparative Example 1 are compared, in Comparative Example 1, which is a conventional membrane electrode assembly, formaldehyde or the like, which is a partial acid oxide of methanol, is generated on the anode side in a power generation experiment. ing. In addition, formaldehyde is also generated on the power sword side. This is probably because methanol partial acid oxide by-produced at the fuel electrode permeates the polymer electrolyte membrane. It is thought that methanol permeated the polymer electrolyte membrane and was partially oxidized on the force sword 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 power sword side was suppressed below the detection limit. Therefore, when a membrane electrode assembly including the by-product decomposition catalyst of the present invention in the catalyst layer is used, it is possible to effectively suppress the by-production of partial acid oxides.

[0056] According to the results of Examples 1 to 3, in the byproduct decomposition catalyst of the present invention, if the pore volume of activated carbon having a radius of 40A or more and less than 100A is 0.05mlZg or more, a better byproduct It was clarified that the effect of suppressing the generation was obtained, and that the larger the pore volume, the higher the effect.

[0057] As a result of Example 5, when the by-product decomposition catalyst of the present invention was added to the catalyst layer of the power sword, generation of formaldehyde and the like on the anode side could not be suppressed, but methanol produced as a by-product at the fuel electrode. The generation of formaldehyde and the like on the force sword side, which was thought to have been caused by the partial oxidation of the permeation of the polymer electrolyte membrane, or the partial permeation of the methanol permeated through the polymer electrolyte membrane, was suppressed.

[0058] According to the results of Example 4, when activated carbon is used as the material for the byproduct decomposition catalyst at the anode, the pore volume having a radius of 40A or more and less than 100A is lower than 0.05mlZg (0.03ml / g). However, the generation of formaldehyde and the like could be suppressed. However, the effect was low as compared with Examples 1 to 3 with the pore volume being 0.05 mlZg.

Therefore, as Example 6, 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 membrane electrode assembly was used, the generation of formaldehyde and the like could be remarkably suppressed even when the activated carbon having a pore volume of less than 0.05 mlZg was used. This result demonstrates that such a two-layer structure has an excellent effect. Further, as the result of Example 7, when activated carbon having a pore volume of 0.05 mlZg or more is used, a more excellent effect can be obtained if the catalyst layer has a two-layer structure.

Claims

The scope of the claims

[1] A membrane electrode assembly for a solid polymer fuel cell having a polymer electrolyte membrane and an anode and a force sword on each side thereof,

The anode and force sword each have a catalyst layer on the side in contact with the polymer electrolyte, and at least one of the anode and force sword catalyst layers is added to an electrode catalyst in which a metal component is supported on carbon black, and activated carbon is a constituent component. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising a by-product decomposition catalyst as described above.

[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 40A or more and less than 100A is 0.05mlZg or more.

[3] 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 A or more and less than 100 A is 0.2 mlZg or more.

[4] The catalyst layer containing the byproduct decomposition catalyst is divided into a first catalyst layer having an electrode catalyst and a second catalyst layer having a byproduct decomposition catalyst, and the first catalyst layer is a polymer electrolyte membrane. 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 first catalyst layer and the second catalyst layer.

[5] By-product decomposition catalyst is platinum, ruthenium, palladium, iridium, rhodium, osmium

The membrane electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein at least one element selected from gold, silver and the like is supported on activated carbon.

[6] 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.