JP5272314B2 - Membrane / electrode assembly for direct methanol fuel cell and direct methanol fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly for a direct methanol fuel cell having, between an electrode and a cation exchange membrane, a structure for preventing a liquid fuel from moving to a cathode through the cation exchange membrane. <P>SOLUTION: In this membrane-electrode assembly for a direct methanol fuel cell formed by sandwiching the cation exchange membrane between an anode catalyst layer and a cathode catalyst layer, and structured to supply methanol to the anode catalyst layer, each of the anode catalyst layer and the cathode catalyst layer contains a carbon material, a cation exchange resin and a catalyst. The membrane-electrode assembly is characterized by satisfying at least one of conditions such as (a) including a methanol adsorbent in the cation exchange membrane, (b) providing a layer containing a cation exchange resin and a methanol adsorbent between the anode catalyst layer and the cation exchange membrane, and (c) providing a layer containing a cation exchange resin and a methanol adsorbent between the cathode catalyst layer and the cation exchange membrane. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a membrane / electrode assembly for a direct methanol fuel cell and a direct methanol fuel cell using the same.

  In recent years, countermeasures to environmental problems and resource problems have become important, and direct fuel cells are being actively developed as one of the countermeasures. In particular, direct methanol fuel cells (hereinafter abbreviated as “DMFC”) are used for direct power generation without reforming or gasifying the fuel, compared with solid polymer fuel cells (hereinafter abbreviated as “PEFC”). Therefore, since the system structure is simple, it is easy to reduce the size and weight.

  The DMFC includes a cation exchange membrane, an anode electrode and a cathode electrode provided between the cation exchange membranes, and a separator having a flow path for supplying and discharging liquid fuel to the anode electrode and air to the cathode electrode. Composed.

  In DMFC, power is obtained by supplying a methanol aqueous solution as a fuel to an anode and oxygen as an oxidant to a cathode. The following electrochemical reactions proceed at the anode and cathode, respectively.

Anode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O
Overall: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O
In such DMFC, a cation exchange membrane mainly composed of perfluorosulfonic acid represented by Nafion (registered trademark of Dupont) has been used as an electrolyte. The anode catalyst layer includes an electrode catalyst in which nano-sized platinum and ruthenium are supported on a carbon powder having a high specific surface area such as acetylene black, PTFE (polytetrafluoroethylene) for imparting water repellency, and A mixture of a perfluorosulfonic acid-based cation exchange resin that imparts proton conductivity and acts as a binder is used.

  The cathode catalyst layer has basically the same structure as the anode catalyst layer, but the cathode catalyst layer is less susceptible to CO poisoning. Therefore, an electrode catalyst having platinum supported on carbon powder having a high specific surface area is used. Yes.

  On the outside of the anode catalyst layer and the cathode catalyst layer, carbon paper or carbon cloth imparted with water repellency by PTFE is disposed as a gas diffusion layer also serving as a current collector. Further, a separator having a methanol aqueous solution as a fuel and an air flow path is disposed outside the gas diffusion layer.

  In the present invention, the anode catalyst layer and the anode gas diffusion layer are collectively referred to as “anode electrode”, and similarly, the cathode catalyst layer and the cathode gas diffusion layer are collectively referred to as “cathode electrode”.

  When liquid fuel such as methanol is used as the fuel, a crossover, which is a phenomenon in which methanol or the like permeates clusters of water molecules formed in the cation exchange membrane, occurs. At this time, not only unreacted methanol permeates to the cathode but also methanol is directly oxidized (burned) by oxygen in the air. For this reason, the catalytic site of the electrochemical reaction at the cathode is reduced, oxygen is consumed, the overvoltage is increased, and a sufficient output cannot be obtained.

  The cluster of water molecules formed in the cation exchange membrane is described in detail in Non-Patent Document 1 and Non-Patent Document 2.

  In the prior art, in order to suppress this crossover, for example, as disclosed in Patent Documents 1 to 3, development of a cation exchange membrane replacing a cation exchange membrane mainly composed of perfluorosulfonic acid is actively performed. Has been done. Moreover, in patent document 4, crossover is suppressed by impregnating a liquid fuel impermeability substance in a catalyst layer.

Furthermore, Patent Document 5 discloses that a crossover limited transmission layer containing carbon nanohorns is provided between an anode or a cathode and a cation exchange membrane.
JP 2005-005134 A JP 2005-032454 A JP 2006-031970 A JP 2005-251405 A Japanese Patent No. 3780971 T. T. et al. D. Gierke and W. Y. Hsu Perfluorinated Ionomer Membranes ed. by A. Eise enberg H. L. Yeager ACS Symposium series 180, American Chemical Society, WashintonD. C. , (1982)

  In order to obtain a sufficient output using a liquid fuel such as methanol as the fuel of the fuel cell, it is necessary to suppress crossover. However, when the cation exchange membranes disclosed in Patent Documents 1 to 3 are used, these cation exchange membranes have poor adhesion to the catalyst layer, so that the internal resistance increases, resulting in a large overvoltage. Therefore, there is a problem that sufficient output characteristics cannot be obtained. Furthermore, the cation exchange membrane disclosed in Patent Documents 1 to 3 has a problem that its durability is low.

  Further, in the technique disclosed in Patent Document 4, since the liquid fuel impervious substance is impregnated in the holes where the liquid fuel diffuses, the diffusibility of the fuel decreases, so that the overvoltage becomes large and sufficient. Output may not be obtained.

  Further, the technique disclosed in Patent Document 5 has a problem that carbon nanohorns are extremely expensive and cannot be used industrially.

  In order to improve the characteristics of the DMFC, in addition to the high diffusivity of the liquid fuel in the anode electrode and the high conductivity of the protons generated by the electrode reaction, the fuel material passes through the cation exchange membrane in the cathode. It is indispensable to suppress the movement.

  Therefore, an object of the present invention is to provide a structure for suppressing liquid fuel from moving to the cathode through the cation exchange membrane without impairing the diffusibility and proton conductivity of the fuel in the anode. An object of the present invention is to provide a DMFC membrane / electrode assembly (hereinafter, “membrane / electrode assembly” is abbreviated as “MEA”) and a DMFC using the MEA.

The invention according to claim 1 is a membrane / electrode assembly for a direct methanol fuel cell in which a cation exchange membrane is sandwiched between an anode catalyst layer and a cathode catalyst layer, and methanol is supplied to the anode catalyst layer. And the cathode catalyst layer includes a carbon material, a cation exchange resin, and a catalyst, and (b) a layer that includes a cation exchange resin and a methanol adsorbent between the anode catalyst layer and the cation exchange membrane, Or (c) a layer containing a cation exchange resin and a methanol adsorbent between the cathode catalyst layer and the cation exchange membrane;
The thickness of the layer containing the cation exchange resin and the methanol adsorbent provided between the anode catalyst layer and the cation exchange membrane or between the cathode catalyst layer and the cation exchange membrane is in the range of 30 to 100 μm. And (b) or (c) includes a carbon material.

In the invention of claim 2, the ratio of the methanol adsorbent contained in the layer containing the cation exchange resin and the methanol adsorbent to the cation exchange resin is from 10% by mass to 200% by mass.

  The invention of claim 3 is characterized in that the membrane / electrode assembly for a direct methanol fuel cell according to claim 1 or 2 is used for a direct methanol fuel cell.

  In the DMFC using the DMFC MEA of the present invention, fuel crossover can be suppressed while maintaining the diffusibility of the fuel in the anode catalyst layer. That is, (a) a methanol adsorbent is contained in the cation exchange membrane, (b) a layer containing a cation exchange resin and a methanol adsorbent is provided between the anode catalyst layer and the cation exchange membrane. ) By providing at least one condition of comprising a layer containing a cation exchange resin and a methanol adsorbent between the cathode catalyst layer and the cation exchange membrane, unreacted methanol that has permeated the anode catalyst layer Permeation to the cathode side can be suppressed. Hereinafter, the layers (a), (b), and (c) containing the methanol adsorbent are referred to as “methanol permeation suppression layers”.

  In addition, since the methanol adsorbent contained in the methanol permeation suppression layer absorbs the unreacted methanol, crossover can be further suppressed.

  In addition, the methanol permeation suppression layer provided between the anode catalyst layer and the cation exchange membrane or between the cathode catalyst layer and the cation exchange membrane contains a cation exchange resin, so that proton conductivity does not decrease. Therefore, it hardly affects the output of DMFC. Furthermore, since the anode catalyst layer remains the same, the diffusibility of the fuel in the catalyst layer is maintained.

  Thus, by providing the methanol permeation suppression layer containing the cation exchange resin and the methanol adsorbent, crossover can be suppressed without reducing the diffusibility of the fuel in the anode catalyst layer and the proton conductivity. As a result, it is possible to provide a DMFC in which the crossover is significantly suppressed as compared with the conventional DMFC.

  And (b) a layer containing a cation exchange resin and a methanol adsorbent between the anode catalyst layer and the cation exchange membrane, and (c) a cation exchange between the cathode catalyst layer and the cation exchange membrane. By satisfying at least one of the conditions including a layer containing a resin and a methanol adsorbent, and the thickness of the layer containing the cation exchange resin and the methanol adsorbent within a range of 30 to 100 μm, It is possible to suppress the unreacted methanol that has permeated the anode catalyst layer from permeating to the cathode side without degrading the characteristics, and also reduce the diffusibility and proton conductivity of the fuel in the anode catalyst layer. Crossover can be suppressed without causing As a result, it is possible to provide a DMFC in which the crossover is significantly suppressed as compared with the conventional DMFC without degrading the characteristics of the DMFC.

  Hereinafter, the present invention will be described in detail according to embodiments of the present invention.

  The present invention provides a membrane / electrode assembly for a direct methanol fuel cell in which a cation exchange membrane is sandwiched between an anode catalyst layer and a cathode catalyst layer, and methanol is supplied to the anode catalyst layer. (C) The cathode catalyst layer, comprising a layer containing a cation exchange resin and a methanol adsorbent between the anode catalyst layer and the cation exchange membrane. And a layer containing a cation exchange resin and a methanol adsorbent between the cation exchange membrane and the cation exchange membrane.

  That is, in the present invention, (a) includes a methanol adsorbent in a cation exchange membrane, and the cation exchange membrane itself is used as a “methanol permeation suppression layer”, and (b) is an anode catalyst layer. And (c) is provided with a “methanol permeation suppression layer” between the cathode catalyst layer and the cation exchange membrane. . In the present invention, any one of (a), (b), and (c) may be satisfied, but two or more conditions are satisfied, for example, (a) and (b) are satisfied simultaneously. Also good.

  However, in that case, it is preferable that the total thickness of both the methanol permeation suppression layers (b) and (c) be in the range of 30 to 100 μm. When the thickness of the methanol permeation suppression layer of the present invention is less than 30 μm, the permeation suppression effect of methanol is small and the characteristics are degraded. Moreover, when the thickness of the methanol permeation suppression layer is thicker than 100 μm, the permeation suppression effect of methanol is increased, but the proton conduction path is lengthened, and the characteristics are deteriorated.

  The membrane / electrode assembly for a direct methanol fuel cell of the present invention will be described with reference to the drawings. 1 to 7 are schematic views of a cross section of a membrane / electrode assembly for a direct methanol fuel cell of the present invention, and FIG. 8 is a schematic view of a cross section of a conventional membrane / electrode assembly for a direct methanol fuel cell. It is. 1 to 8, 1 is a cation exchange membrane, 2 is an anode catalyst layer, 3 is a cathode catalyst layer, 4 is an anode side gas diffusion layer, 5 is a cathode side gas diffusion layer, 6 is a methanol adsorbent, 7 is a methanol permeation suppression layer provided between the anode catalyst layer and the cation exchange membrane, and 8 is a methanol permeation suppression layer provided between the cathode catalyst layer and the cation exchange membrane.

  FIG. 8 shows a conventional membrane / electrode assembly for a direct methanol fuel cell, in which an anode catalyst layer 2 and a cathode catalyst layer 3 are joined to both surfaces of a cation exchange membrane 1, and an anode side gas diffusion layer is joined to the anode catalyst layer. 4 is provided, and the cathode catalyst layer 3 is provided with a cathode side gas diffusion layer 5. And the methanol permeation suppression layer containing a cation exchange resin and a methanol adsorbent is not provided.

  FIG. 1 shows a membrane / electrode assembly for a direct methanol fuel cell according to the present invention in which a methanol adsorbent is contained in a cation exchange membrane and the cation exchange membrane itself is a “methanol permeation suppression layer”. The cation exchange membrane 1 contains a methanol adsorbent 6 and suppresses methanol permeation between the anode catalyst layer and the cation exchange membrane and between the cathode catalyst layer and the cation exchange membrane. There is no layer. This example satisfies the condition (a) of the present invention.

  FIG. 2 shows a membrane / electrode assembly for a direct methanol fuel cell according to the present invention having a “methanol permeation suppression layer” between an anode catalyst layer and a cation exchange membrane. 1 and the anode catalyst layer 2 are provided with a methanol permeation suppression layer 7 containing a cation exchange resin and a methanol adsorbent 6, and the cation exchange membrane 1 does not contain a methanol adsorbent, Further, no methanol permeation suppression layer is provided between the cation exchange membrane 1 and the cathode catalyst layer 3. This example satisfies the condition (b) of the present invention.

  FIG. 3 shows a membrane / electrode assembly for a direct methanol fuel cell according to the present invention having a “methanol permeation suppression layer” between a cathode catalyst layer and a cation exchange membrane. 1 and a cathode catalyst layer 3 are provided with a methanol permeation suppression layer 8 containing a cation exchange resin and a methanol adsorbent 6, and the cation exchange membrane 1 does not contain a methanol adsorbent, Further, no methanol permeation suppression layer is provided between the cation exchange membrane 1 and the anode catalyst layer 2. This example satisfies the condition (c) of the present invention.

  FIG. 4 shows a membrane / electrode for a direct methanol fuel cell according to the present invention having a “methanol permeation suppression layer” between the anode catalyst layer and the cation exchange membrane and between the cathode catalyst layer and the cation exchange membrane. A joined body is shown, and a methanol permeation suppression layer 7 including a cation exchange resin and a methanol adsorbent 6 is provided between the cation exchange membrane 1 and the anode catalyst layer 2, and the cation exchange membrane 1 A methanol permeation suppression layer 8 including a cation exchange resin and a methanol adsorbent 6 is provided between the cathode catalyst layer 3 and the cation exchange membrane 1 does not contain a methanol adsorbent. This example satisfies the conditions (b) and (c) of the present invention.

  FIG. 5 shows a direct methanol fuel cell according to the present invention in which a methanol adsorbent is contained in a cation exchange membrane and a “methanol permeation suppression layer” is provided between the anode catalyst layer and the cation exchange membrane. 1 shows a membrane / electrode assembly, a cation exchange membrane 1 containing a methanol adsorbent 6, and a cation exchange resin and a methanol adsorbent between the cation exchange membrane 1 and the anode catalyst layer 2. 6 is provided with a methanol permeation suppression layer 7, and no methanol permeation suppression layer is provided between the cation exchange membrane 1 and the cathode catalyst layer 3. This example satisfies the conditions (a) and (b) of the present invention.

  FIG. 6 shows a direct methanol fuel cell according to the present invention in which a methanol adsorbent is contained in a cation exchange membrane and a “methanol permeation suppression layer” is provided between the cathode catalyst layer and the cation exchange membrane. 1 shows a membrane / electrode assembly, a cation exchange membrane 1 containing a methanol adsorbent 6 and a cation exchange resin and a methanol adsorbent between the cation exchange membrane 1 and the cathode catalyst layer 3. 6 and a methanol permeation suppression layer 8 is provided, and no methanol permeation suppression layer is provided between the cation exchange membrane 1 and the anode catalyst layer 2. This example satisfies the conditions (a) and (c) of the present invention.

  FIG. 7 shows that a methanol adsorbent was included in the cation exchange membrane, and a “methanol permeation suppression layer” was provided between the anode catalyst layer and the cation exchange membrane and between the cathode catalyst layer and the cation exchange membrane. 1 shows a membrane / electrode assembly for a direct methanol fuel cell according to the present invention, in which a methanol adsorbent 6 is contained in the cation exchange membrane 1 and the cation exchange membrane 1 and the anode catalyst layer 2 are Is provided with a methanol permeation suppression layer 7 containing a cation exchange resin and a methanol adsorbent 6, and methanol permeation suppression containing a cation exchange resin and a methanol adsorbent 6 between the cation exchange membrane 1 and the cathode catalyst layer 3. Layer 8 is provided. This example satisfies the conditions (a), (b), and (c) of the present invention.

  In the present invention, the thickness of the methanol permeation suppression layer is preferably 30 to 100 μm. Specifically, the thickness of the methanol permeation suppression layer 7 provided between the anode catalyst layer and the cation exchange membrane in FIGS. 2 and 5 is in this range, and the cathode catalyst layer and the positive catalyst layer in FIGS. The thickness of the methanol permeation suppression layer 8 provided between the ion exchange membrane is in this range, and the thickness of the methanol permeation suppression layer 7 provided between the anode catalyst layer and the cation exchange membrane of FIGS. In this range, the thickness of the methanol permeation suppression layer 7 provided between the anode catalyst layer and the cation exchange membrane of FIGS. 4 and 7 and the methanol provided between the cathode catalyst layer and the cation exchange membrane. The total thickness of the permeation suppression layer 8 is preferably within this range.

  Here, the methanol adsorbent binds methanol by a relatively weak interaction other than a covalent bond typified by hydrogen bond or van der Waals force. Moreover, this adsorbent can be easily combined by a catalytic reaction with methanol and can be adsorbed stably.

  The methanol adsorbent that can be used in the present invention is 1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1,2,2-tetrakis (4-hydroxyphenyl) ethane, 1,1,2,2-tetrakis. Phenolic host compounds such as (4-hydroxyphenyl) ethylene, amide based host compounds such as diphenic acid bis (dicyclohexylamide) and fumaric acid bisdicyclohexylamide, 2- (m-cyanophenyl) phenanthro [9,10- d] An imidazole host compound such as imidazole is excellent in terms of inclusion ability, and in particular, a phenol host compound such as 1,1-bis (4-hydroxyphenyl) cyclohexane is industrially easy to use. Is preferable.

  The above-mentioned methanol adsorbents may be used alone or in combination of two or more. Further, the amount of methanol that can be contained in the above methanol adsorbent is not particularly limited, but is usually about 10 to 80% by mass with respect to the adsorbent.

  In the methanol permeation suppression layer of the present invention containing a cation exchange resin and a methanol adsorbent, the ratio of the weight of the methanol adsorbent to the weight of the cation exchange resin (hereinafter referred to as “methanol adsorbent / cation exchange resin ratio”) Is preferably 10% by mass or more and 200% by mass or less. When the ratio of the methanol adsorbent / cation exchange resin is smaller than 10% by mass, the amount of methanol adsorbent contained in the methanol permeation suppression layer is reduced, so that the methanol permeation suppression effect is reduced. Also, if the methanol adsorbent / cation exchange resin ratio is greater than 200% by mass, the amount of methanol adsorbent that is an insulator will increase so much that the proton conductivity of the methanol permeation suppression layer will decrease. Decreases.

  The carbon material that can be used for the anode catalyst layer and the cathode catalyst layer of the DMFC MEA of the present invention is preferably one having high electron conductivity. In addition to carbon black such as furnace black, channel black, and acetylene black, vapor grown carbon, Activated carbon or graphite can be used.

  In addition, a carbon material or the like can be added to the methanol permeation suppression layer of the present invention in order to control the thickness of the layer. As the carbon material, the same carbon material as that used for the anode catalyst layer and the cathode catalyst layer can be used.

  In addition, a water repellent material such as PTFE (polytetrafluoroethylene) or FEP (fluoroethylenepropylene) or a binder may be used in the methanol permeation suppression layer of the present invention as necessary. By using the water repellent material, the water permeation from the anode to the cathode is reduced, so that flooding at the cathode can be suppressed.

  Examples of the cation exchange resin and cation exchange membrane that can be used in the anode catalyst layer and the cathode catalyst layer of the MEA for DMFC of the present invention include perfluorocarbon sulfonic acid type and styrene-divinylbenzene sulfonic acid type cation exchange. A resin or a cation exchange resin having a carboxylic acid group, a phosphonic acid group and a phosphoric acid group as ion exchange groups is preferred.

  The anode and cathode catalyst metals that can be used in the anode catalyst layer and cathode catalyst layer of the MEA for DMFC of the present invention are preferably those having a catalytic action in the oxidation reaction of methanol and the reduction reaction of oxygen, such as platinum, ruthenium, iridium, It can be selected from platinum group metals such as rhodium, palladium, osmium, or alloys thereof.

Methanol is supplied to the anode electrode of the DMFC as fuel, but when methanol decomposes to produce H ₂ and CO ₂ , a small amount of CO is produced at the same time, and this CO poisons the surface of the Pt catalyst. The catalytic activity is greatly reduced. Therefore, it is preferable to use a Pt—Ru alloy that can suppress a decrease in activity against the oxidation reaction of hydrogen due to CO poisoning, instead of the Pt catalyst, for the catalyst layer of the anode electrode.

  The catalyst layer of the MEA for DMFC of the present invention is composed of a catalytic metal material, a cation exchange resin, a carbon material, and the like, and if necessary, PTFE (polytetrafluoroethylene), FEP (fluoroethylenepropylene), etc. It is also possible to use a water repellent material or a binder. As a method of dispersing the cation exchange resin in the catalyst layer, a method of mixing and forming the constituent materials of the catalyst layer or a method of mixing and forming the constituent materials other than the cation exchange resin in advance, The method of impregnation etc. is mentioned.

  When the DMFC MEA obtained in the present invention is used in a DMFC, a gas diffusion layer made of a conductive porous substrate such as carbon paper or carbon cloth may be disposed outside the anode and cathode of the MEA. preferable. A gas containing an aqueous methanol solution and oxygen is supplied to the cathode and anode of the MEA, respectively. Specifically, a gas or aqueous solution serving as a fuel is supplied to the MEA by disposing a separator formed with a groove to be a flow path for the aqueous solution or gas outside the both electrodes of the MEA and flowing the aqueous solution or gas through the flow channel. Supply.

  Hereinafter, the present invention will be described using preferred embodiments.

[Examples 1 to 12 and Comparative Examples 1 and 2]
[Example 1]
The anode catalyst layer was prepared by the following procedure. Cation exchange resin (manufactured by Aldrich) consisting of 1.0 g of platinum-ruthenium catalyst-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 30.5 mass% platinum, 23.5 mass% ruthenium) and a perfluorocarbon polymer having a sulfonic acid group. 6.7 g of a 5% by mass solution), 0.5 g of a water repellent (Mitsui / DuPont Fluorochemicals, PTFE, 60% by mass dispersion) and 8.0 g of purified water were weighed and mixed with a stir bar. Furthermore, an anode catalyst layer slurry was prepared by kneading using a planetary ball mill.

  Next, after impregnating carbon paper (made by Toray Industries, Inc., 300 μm thick) cut into a square with a side of 5 cm in a water repellent (Mitsui / DuPont Fluoro Chemical Co., PTFE, 5 mass% dispersion) and drying it. By baking at 360 ° C., carbon paper with water repellency was obtained. This carbon paper was used as a gas diffusion layer.

The anode catalyst layer slurry was applied to one side of the carbon paper by a spray coater and dried to form an anode catalyst layer. The amount of catalyst supported on the anode catalyst layer was 3.0 mg (Pt—Ru) / cm ² . A carbon paper having an anode catalyst layer formed on one side was obtained as an anode electrode.

  The methanol permeation suppression layer was manufactured by the following procedure. Stir after weighing 20.0 g of cation exchange resin (manufactured by Aldrich, 5 mass% solution) and 0.5 g of methanol adsorbent (manufactured by Kurita Kogyo Co., Ltd., 1,1-bis (4-hydroxyphenyl) cyclohexane). The slurry for methanol permeation suppression layer was adjusted by mixing with a stick and further kneading using a planetary ball mill. This slurry contains 1.0 g of cation exchange resin.

  Next, the methanol permeation suppression layer was formed on the anode catalyst layer formed on one side of the carbon paper by applying and drying the slurry for methanol permeation suppression layer with a spray coating machine. The methanol adsorbent / cation exchange resin ratio in the obtained methanol permeation suppression layer was 50% by mass, and the thickness was 50 μm.

  The cathode catalyst layer was prepared by the following procedure. Platinum catalyst-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd., platinum 50 mass%) 1.0 g, cation exchange resin (Aldrich 5 mass% solution) 7.2 g and water repellent (Mitsui / DuPont Fluoro Chemical Co., Ltd.) PTFE, 60 mass% dispersion) 0.5 g and purified water 12.0 g were weighed, mixed with a stir bar, and further kneaded using a planetary ball mill to prepare a cathode catalyst layer slurry.

Next, the cathode catalyst layer was formed on one side of the carbon paper subjected to the same water repellency as that used for the anode by applying and drying the slurry for the cathode catalyst layer with a spray coating machine. The amount of catalyst supported on this cathode catalyst layer was 2.0 mg (Pt) / cm ² . A cathode electrode obtained by forming a cathode catalyst layer on one surface of carbon paper was used as a cathode electrode.

  The DMFC MEA was manufactured by the following procedure. Cation exchange is performed by placing an anode electrode on one side of a cation exchange membrane (made by Dupont, thickness 125 μm) made of a perfluorocarbon polymer having a sulfonic acid group so that the anode catalyst layer and the cation exchange membrane are in contact with each other. An MEA was obtained by hot pressing under conditions of 10 MPa and 150 ° C. after arranging the cathode electrode so that the cathode catalyst layer and the cation exchange membrane were in contact with the other surface of the membrane. This MEA satisfies the condition (b) of the present invention.

  Finally, this MEA was sandwiched between a pair of conductive flow plates, and further sandwiched between a pair of current collector plates to produce a DMFC. This was designated as DMFC of Example 1.

[Example 2]
An MEA was produced in the same procedure as in Example 1 except that the weight of the methanol adsorbent was 0.05 g. A DMFC of Example 2 was produced using this MEA.

[Example 3]
An MEA was produced in the same procedure as in Example 1 except that the weight of the methanol adsorbent was 0.1 g. A DMFC of Example 3 was produced using this MEA.

[Example 4]
An MEA was produced in the same procedure as in Example 1 except that the weight of the methanol adsorbent was 1.0 g. A DMFC of Example 4 was produced using this MEA.

[Example 5]
An MEA was produced in the same procedure as in Example 1 except that the weight of the methanol adsorbent was 2.0 g. A DMFC of Example 5 was produced using this MEA.

[Example 6]
An MEA was produced in the same procedure as in Example 1 except that the weight of the methanol adsorbent was 2.5 g. A DMFC of Example 6 was produced using this MEA.

[Example 7]
Example 1 except that the methanol permeation suppression layer was not formed on the anode catalyst layer, and the slurry for methanol permeation suppression layer was applied and dried with a spray coating machine on the cathode catalyst layer formed on one side of the carbon paper. The MEA was manufactured in the same procedure as above. This MEA satisfies the condition (c) of the present invention. The DMFC of Example 7 was produced using this MEA.

[Example 8]
In the same manner as in Example 1, a methanol permeation suppression layer was formed on the anode catalyst layer, and in the same manner as in Example 7, a methanol permeation suppression layer was formed on the cathode catalyst layer. Produced. This MEA satisfies the conditions (b) and (c) of the present invention. The DMFC of Example 8 was produced using this MEA.

[ Reference Example 9]
Cation exchange membrane (thickness) in which 20% by mass of a methanol adsorbent (manufactured by Kurita Kogyo Co., Ltd., 1,1-bis (4-hydroxyphenyl) cyclohexane) is dispersed in 80% by mass of a perfluorocarbon polymer having a sulfonic acid group. The MEA was manufactured in the same procedure as in Example 1 except that the methanol permeation suppression layer was not provided between the anode catalyst layer and the cation exchange membrane. This MEA satisfies the condition (a) of the present invention. A DMFC of Reference Example 9 was produced using this MEA.

[Example 10]
An MEA was produced in the same procedure as in Example 1 except that the same cation exchange membrane as that used in Reference Example 9 was used. This MEA satisfies the conditions (a) and (b) of the present invention. The DMFC of Example 10 was produced using this MEA.

[Example 11]
An MEA was produced in the same procedure as in Example 7 except that the same cation exchange membrane as that used in Reference Example 9 was used. This MEA satisfies the conditions (a) and (c) of the present invention. A DMFC of Example 11 was produced using this MEA.

[Example 12]
An MEA was produced in the same procedure as in Example 8 except that the same cation exchange membrane as that used in Reference Example 9 was used. This MEA satisfies the conditions (a), (b), and (c) of the present invention. A DMFC of Example 12 was produced using this MEA.

[Comparative Example 1]
The MEA was carried out in the same procedure as in Example 1 except that the cation exchange resin solution was applied directly on the anode catalyst layer formed on one side of the carbon paper and dried with a spray coater without using a methanol adsorbent. Was made. A DMFC of Comparative Example 1 was produced using this MEA.

[Comparative Example 2]
An MEA was produced in the same procedure as in Example 1 except that the methanol permeation suppression layer was not formed. A DMFC of Comparative Example 2 was produced using this MEA.

Table 1 summarizes the contents of the DMFC MEAs of Examples 1 to 8, Examples 10 to 12 , Reference Example 9, and Comparative Examples 1 and 2.

[Measurement of DMFC characteristics]
The DMFCs of Examples 1 to 8, Examples 10 to 12 , Reference Example 9 and Comparative Examples 1 and 2 were prepared using a cell temperature of 70 ° C., an anode fuel 1 mol / l methanol aqueous solution, an anode fuel flow rate of 4 ml / min, and a cathode gas Under the condition that the flow rate of air and cathode gas was 500 ml / min, the oxygen concentration at the inlet and outlet of the cathode was measured after 5 minutes in a no-load condition after flowing fuel and air to the anode.

  Since the methanol crossed over from the anode to the cathode reacts with oxygen in the air supplied to the cathode, there is a difference in the oxygen concentration between the inlet and the outlet of the cathode. This difference is oxygen used for consuming methanol, and Table 1 shows values obtained by converting this amount of oxygen into an amount of electricity (current density flowing when electrochemically oxidized at the anode).

Further, the DMFCs of Examples 1 to 8, Examples 10 to 12 , Reference Example 9 and Comparative Examples 1 and 2 were prepared using a cell temperature of 70 ° C., an anode fuel 1 mol / l aqueous methanol solution, an anode fuel flow rate of 4 ml / min, and a cathode. When operating at a current density of 30 mA / cm 2 under conditions where the gas was air and the cathode gas flow rate was 500 ml / min, the cell voltage one minute after applying the current was measured. In addition, the open circuit voltage was measured 5 minutes after flowing fuel to the anode and air to the cathode. The results are shown in Table 2.

As is clear from Table 2, the DMFCs of the present inventions of Examples 1 to 8, Examples 10 to 12 , and Reference Example 9 have a smaller amount of methanol crossover than the DMFCs of Comparative Examples 1 and 2. I understood it. When the methanol crossover amounts of Examples 1 to 6 were compared, it was found that the crossover amount decreased with an increase in the proportion of the methanol adsorbent contained in the methanol permeation suppression layer. In particular, it was found that when the ratio of the methanol adsorbent in the methanol permeation suppression layer was 10% by mass or more, the crossover amount was further suppressed. From this result, the effect of the methanol permeation suppression layer became clear. Furthermore, it turned out that the case where the ratio of the methanol adsorbent contained in the layer is 10% by mass or more is more suitable.

  The reason for this is that by providing a methanol permeation suppression layer comprising a cation exchange resin and a methanol adsorbent, unreacted methanol that has permeated the anode catalyst layer is prevented from permeating to the cathode side, and further methanol permeation is suppressed. Since the methanol adsorbent contained in the suppression layer absorbs the unreacted methanol, it is considered that the crossover is further suppressed. When the ratio of the methanol adsorbent is less than 10% by mass, the amount of adsorbent contained in the methanol permeation suppression layer is too small, and thus the crossover suppression effect is considered to be small.

Furthermore, in all of the DMFCs of the present invention of Example 1, Examples 7 to 8, Examples 10 to 12 , and Reference Example 9 , since the amount of crossover was small, the MEA satisfies the conditions (a), ( It was found that the effect of suppressing crossover can be obtained by satisfying at least one of b) and (c).

Further, as is clear from Table 1, the DMFCs of the present inventions of Examples 1 to 8, Examples 10 to 12 , and Reference Example 9 have higher open circuit voltages than those of Comparative Examples 1 and 2. all right. It was also found that the open circuit voltage was similar to the crossover amount relationship. As the crossover amount increases, the open circuit voltage also decreases because the cathode potential decreases. Also from this result, the effect of the methanol permeation suppression layer was clarified, and further, it was found that the case where the ratio of the methanol adsorbent contained in the layer was 10% by mass or more was more preferable.

Furthermore, as is clear from Table 1, the DMFCs of the present invention of Examples 1 to 5, 7 to 8, Examples 10 to 12 , and Reference Example 9 are 30 mA / cm 2 as compared with those of Comparative Examples 1 and 2. It can be seen that the cell voltage at the current density is high. The amount of methanol crossover decreases due to an increase in methanol consumption at the anode with increasing current density. For this reason, at a low current density, the cell voltage is affected by the amount of methanol crossover. Therefore, it can be said that the higher the cell voltage, the smaller the crossover amount.

  Note that the decrease in the cell voltage in the DMFC of Example 6 is considered to be due to the fact that proton conduction was inhibited because the amount of methanol adsorbent without proton conductivity was too large. This result also revealed the effect of the methanol permeation suppression layer. Furthermore, it turned out that the case where the ratio of the methanol adsorbent contained in the methanol permeation suppression layer is 200% by mass or less is more suitable.

[Examples 13 to 15]
[Example 13]
A procedure similar to that in Example 1 except that 1,1,2,2-tetrakis (4-hydroxyphenyl) ethane was used in place of 1,1-bis (4-hydroxyphenyl) cyclohexane as the methanol adsorbent. I made an MEA. The DMFC of Example 13 was produced using this MEA.

[Example 14]
The same procedure as in Example 1 except that 1,1,2,2-tetrakis (4-hydroxyphenyl) ethylene was used as the methanol adsorbent instead of 1,1-bis (4-hydroxyphenyl) cyclohexane. I made an MEA. The DMFC of Example 14 was produced using this MEA.

[Example 15]
An MEA was produced in the same procedure as in Example 1 except that diphenic acid bis (dicyclohexylamide) was used in place of 1,1-bis (4-hydroxyphenyl) cyclohexane as the methanol adsorbent. The DMFC of Example 15 was produced using this MEA.

For the DMFCs of Examples 13 to 15, the cell voltage was measured under the same conditions as in Example 1 when operated with a methanol crossover amount, an open circuit voltage, and a current density of 30 mA / cm ² . The measurement results are shown in Table 3.

  From the results in Table 3, it was found that the methanol crossover amount of DMFC can be suppressed even when the type of methanol adsorbent is different.

[Examples 16 to 23 and Comparative Examples 3 to 8]
[Example 16]
An MEA was produced in the same procedure as in Example 1 except that the thickness of the methanol permeation suppression layer was 30 μm. A DMFC of Example 2 was produced using this MEA.

[Example 17]
An MEA was produced in the same procedure as in Example 1 except that the thickness of the methanol permeation suppression layer was 100 μm. The DMFC of Example 17 was produced using this MEA.

[Example 18]
An MEA was produced in the same procedure as in Example 7 except that the thickness of the methanol permeation suppression layer was 30 μm. The DMFC of Example 18 was produced using this MEA.

[Example 19]
An MEA was produced in the same procedure as in Example 7 except that the thickness of the methanol permeation suppression layer was 100 μm. The DMFC of Example 19 was produced using this MEA.

[Example 20]
In both the anode catalyst layer and the cathode catalyst layer, the slurry for methanol permeation suppression layer was applied and dried with a spray coating machine on the catalyst layer formed on one side of the carbon paper, and the thickness of each methanol permeation suppression layer was adjusted. An MEA was produced in the same procedure as in Example 8 except that the thickness was 15 μm (total 30 μm). This MEA satisfies the conditions (b) and (c) of the present invention. A DMFC of Example 20 was produced using this MEA.

[Example 21]
In both the anode catalyst layer and the cathode catalyst layer, the slurry for methanol permeation suppression layer was applied and dried with a spray coating machine on the catalyst layer formed on one side of the carbon paper, and the thickness of each methanol permeation suppression layer was adjusted. An MEA was produced in the same procedure as in Example 20 except that the thickness was 25 μm (50 μm in total). A DMFC of Example 21 was produced using this MEA.

[Example 22]
In both the anode catalyst layer and the cathode catalyst layer, the slurry for methanol permeation suppression layer was applied and dried with a spray coating machine on the catalyst layer formed on one side of the carbon paper, and the thickness of each methanol permeation suppression layer was adjusted. An MEA was produced in the same procedure as in Example 20 except that the thickness was 50 μm (100 μm in total). The DMFC of Example 22 was produced using this MEA.

[Example 23]
An MEA was produced in the same procedure as in Example 17 except that 0.3 g of carbon black (Ketjen Black International, Ketjen Black EC) was added to the methanol permeation suppression layer slurry. The DMFC of Example 23 was produced using this MEA.

[Comparative Example 3]
An MEA was produced in the same procedure as in Example 1 except that the thickness of the methanol permeation suppression layer was 25 μm. A DMFC of Comparative Example 3 was produced using this MEA.

[Comparative Example 4]
An MEA was produced in the same procedure as in Example 1 except that the thickness of the methanol permeation suppression layer was 105 μm. A DMFC of Comparative Example 4 was produced using this MEA.

[Comparative Example 5]
An MEA was produced in the same procedure as in Example 7 except that the thickness of the methanol permeation suppression layer was 25 μm. A DMFC of Comparative Example 5 was produced using this MEA.

[Comparative Example 6]
An MEA was produced in the same procedure as in Example 7 except that the thickness of the methanol permeation suppression layer was 105 μm. A DMFC of Comparative Example 6 was produced using this MEA.

[Comparative Example 7]
In both the anode catalyst layer and the cathode catalyst layer, the methanol permeation suppression layer slurry was applied and dried on the catalyst layer formed on one side of the carbon paper with a spray coater, and the thickness of the anode side methanol permeation suppression layer The MEA was manufactured in the same procedure as in Example 20 except that the thickness of the methanol permeation suppression layer on the cathode side was 10 μm (total 25 μm). A DMFC of Comparative Example 7 was produced using this MEA.

[Comparative Example 8]
In both the anode catalyst layer and the cathode catalyst layer, the methanol permeation suppression layer slurry was applied and dried on the catalyst layer formed on one side of the carbon paper with a spray coater, and the thickness of the anode side methanol permeation suppression layer The MEA was manufactured in the same procedure as in Example 20 except that the thickness of the methanol permeation suppression layer on the cathode side was 50 μm (total of 105 μm). A DMFC of Comparative Example 8 was produced using this MEA.

  The contents of the DMFC MEAs in Examples 16 to 23 and Comparative Examples 3 to 8 are summarized in Table 4. In Table 54, the contents of the MEAs of Example 1 and Example 7 are also shown for comparison.

[Measurement of DMFC characteristics]
For the DMFCs of Examples 16 to 23 and Comparative Examples 3 to 8, the oxygen concentrations at the cathode inlet and outlet after 5 minutes were measured under the same conditions as in Example 1 under no load. In the same manner as in Example 1, the value obtained by converting the amount of oxygen used to consume methanol into the amount of electricity (current density flowing when electrochemically oxidized at the anode) was obtained.

Further, under the same conditions as in Example 1, when the plant is operated at a current density of 30 mA / cm ² and 300 mA / cm ^2, the cell voltage was measured for 1 minute after the application of a current. Furthermore, the open circuit voltage was measured 5 minutes after flowing fuel to the anode and air to the cathode. These measurement results are summarized in Table 5. In Table 5, the measurement results of Example 1 and Example 7 are also shown for comparison.

  As is clear from Table 5, the DMFCs of the present invention of Examples 1, 7, and 16 to 23 were found to have less methanol crossover than the DMFCs of Comparative Examples 3, 5, and 7. . When the methanol crossover amounts of Examples 1, 7, and 16 to 23 were compared, it was found that the crossover amount decreased with an increase in the thickness of the methanol permeation suppression layer. Further, the DMFCs of Comparative Examples 4, 6, and 8 had a smaller amount of methanol crossover than the DMFCs of Examples 1, 7, and 16 to 23 of the present invention. From these results, it was found that the thickness of the methanol permeation suppression layer is preferably 30 μm or more.

  The reason for this is that by setting the methanol permeation suppression layer composed of the cation exchange resin and the methanol adsorbent to 30 μm, the unreacted methanol that has permeated the anode catalyst layer is suppressed from permeating to the cathode side, Since the methanol adsorbent contained in the methanol permeation suppression layer absorbs the unreacted methanol, it is considered that crossover is further suppressed. When the thickness of the methanol permeation suppression layer is less than 30 μm, the thickness of the methanol permeation suppression layer is too thin, and it is considered that the crossover suppression effect is reduced.

  Further, as is clear from Table 5, the DMFCs of Examples 1, 7, and 16 to 23 of the present invention have higher open circuit voltages than those of Comparative Examples 3, 5, and 7, Comparative Example 4, It was found that the DMFCs 6 and 8 had a higher open circuit voltage than the DMFCs of the present invention of Examples 1, 7, and 16-23. It was also found that the open circuit voltage was similar to the crossover amount relationship. As the crossover amount increases, the cathode potential decreases and the open circuit voltage also decreases. From these results, it was found that the thickness of the methanol permeation suppression layer is preferably 30 μm or more.

Furthermore, as is clear from Table 5, DMFC of the present invention of Example 1,7,16～23, compared to DMFC of Comparative Example 3-8, at a current density of 30 mA / cm ² and 300 mA / cm ² It was found that the cell voltage was high. The amount of methanol crossover decreases because the amount of methanol consumed at the anode increases with increasing current density. For this reason, since the cell voltage is affected by the amount of methanol crossover at a low current density, it can be said that the higher the cell voltage, the smaller the crossover amount.

Further, DMFC of Comparative Examples 4, 6 and 8, but exhibited a 30 mA / in cm ² higher cell voltage, it was found that the cell voltage is significantly reduced at a current density of 300 mA / cm ^2. This is considered to be due to the fact that although the methanol crossover amount decreased as the thickness of the methanol permeation suppression layer increased, the characteristics deteriorated due to the longer proton conduction path. From these results, it was found that the thickness of the methanol permeation suppression layer was preferably 100 μm or less.

  Further, since the DMFCs of Examples 1, 7, and 16 to 23 of the present invention all have high characteristics and a small amount of crossover, the MEA is at least one of the conditions (b) and (c) of the present invention. By satisfying the above, it has been found that the effect of suppressing the crossover can be obtained without degrading the characteristics of the DMFC.

  From the above, by providing a methanol permeation suppression layer between at least one of the anode catalyst layer and the cation exchange membrane and between the cathode catalyst layer and the cation exchange membrane, the diffusibility of fuel in the anode catalyst layer It was revealed that the methanol crossover amount of DMFC can be remarkably suppressed without lowering proton conductivity.

The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol type fuel cells which satisfy | fills condition (a) of a reference example . The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol fuel cells which satisfy | fills the conditions (b) of this invention. The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol fuel cells which satisfy | fills conditions (c) of this invention. The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol fuel cells which satisfy | fills conditions (b) and (c) of this invention. The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol fuel cells which satisfy | fills conditions (a) and (b) of this invention. The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol fuel cells which satisfy | fills conditions (a) and (c) of this invention. The schematic diagram of the cross section of the membrane / electrode assembly for direct methanol fuel cells which satisfy | fills conditions (a), (b), (c) of this invention. The schematic diagram of the cross section of the conventional membrane / electrode assembly for direct methanol fuel cells.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cation exchange membrane 2 Anode catalyst layer 3 Cathode catalyst layer 4 Anode side gas diffusion layer 5 Cathode side gas diffusion layer 6 Methanol adsorbent 7 Methanol permeation suppression layer provided between anode catalyst layer and cation exchange membrane 8 Cathode Methanol permeation suppression layer provided between catalyst layer and cation exchange membrane

Claims (3)

In a direct methanol fuel cell membrane / electrode assembly in which a cation exchange membrane is sandwiched between an anode catalyst layer and a cathode catalyst layer, and methanol is supplied to the anode catalyst layer, the anode catalyst layer and the cathode catalyst layer include: A carbon material, a cation exchange resin, and a catalyst, and (b) a layer containing a cation exchange resin and a methanol adsorbent between the anode catalyst layer and the cation exchange membrane, or (c) the cathode catalyst. A layer comprising a cation exchange resin and a methanol adsorbent between the layer and the cation exchange membrane;
The thickness of the layer containing the cation exchange resin and the methanol adsorbent provided between the anode catalyst layer and the cation exchange membrane or between the cathode catalyst layer and the cation exchange membrane is in the range of 30 to 100 μm. And (b) or (c) is a membrane / electrode assembly for a direct methanol fuel cell containing a carbon material .   2. The direct methanol fuel cell according to claim 1, wherein the ratio of the methanol adsorbent contained in the layer containing the cation exchange resin and the methanol adsorbent to the cation exchange resin is 10% by mass or more and 200% by mass or less. Membrane / electrode assembly. A direct methanol fuel cell comprising the membrane / electrode assembly for a direct methanol fuel cell according to claim 1 or 2.