JP2005310612A - Solid fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid fuel cell using an electrolyte having high proton conductivity and low methanol permeability, capable of obtaining high current density. <P>SOLUTION: This solid fuel cell has an electrolyte, and negative and positive electrodes provided adjacently to it. The electrolyte contains an organic material with proton conductivity in a hole of a porous film which does not swell with water and methanol, and the porosity of the porous film increases toward the negative electrode side from the positive electrode side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid fuel cell, and more particularly to a direct methanol solid polymer fuel cell.

  A fuel cell is a power generation device that generates electricity by reacting hydrogen and oxygen, and has the excellent property that only water is generated by the power generation reaction, thus addressing global environmental problems such as global warming and ozone layer destruction. It is attracting attention as an energy-saving technology.

  Fuel cells include solid polymer fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells. Among these, the polymer electrolyte fuel cell has an advantage that the operating temperature is low and the electrolyte is a solid (polymer thin film). There are two types of polymer electrolyte fuel cells: a reforming type that converts methanol into hydrogen using a reformer, and a direct type that uses methanol directly without using a reformer (DMFC, Direct Methanol Polymer Fuel Cell). It is roughly divided into two. Since DMFC does not require a reformer, it can be reduced in size and weight, and as a battery or dedicated battery for personal digital assistants (PDAs) for the coming ubiquitous society, Practical use is expected.

  The main components of the polymer electrolyte fuel cell are an electrode catalyst, an electrolyte, and a separator. A polymer proton-conducting electrolyte membrane is used as the electrolyte. Proton conductive electrolyte membranes are used for applications such as ion exchange membranes and humidity sensors, but in recent years, they are also attracting attention for applications as electrolytes in polymer electrolyte fuel cells. For example, a sulfonic acid group-containing fluororesin membrane typified by DuPont's Nafion (R) has been studied for use as an electrolyte in portable fuel cells.

  These conventionally known fluororesin proton conductive membranes have a drawback of high methanol permeability. In order to put a proton conductive membrane into practical use in a new application of a polymer electrolyte fuel cell such as DMFC, development of a membrane having high proton conductivity and low methanol permeability is indispensable.

  Various methods for obtaining a proton conductive membrane by impregnating a porous membrane having pores with a proton conductive polymer have been proposed.

Patent Document 1 aims to provide an electrolyte membrane that suppresses methanol permeation (crossover) as much as possible and can withstand use in a high temperature (about 130 degrees Celsius) environment. An electrolyte membrane is disclosed in which pores of a porous substrate that does not substantially swell are filled with a polymer having proton conductivity. As the porous substrate, an inorganic material such as ceramic, glass or alumina, or a heat resistant polymer such as polytetrafluoroethylene or polyimide is used. In addition, these materials may be used alone, or two or more kinds may be used as a composite material. When used as a composite material, the form may be a laminate of two or more layers. Has been described. In the embodiment, a porous fluororesin is used.
WO00 / 54351 pamphlet

  In order for the proton conductive electrolyte membrane to withstand practical use as an electrolyte of a solid fuel cell, it is an important factor that the proton conductivity is sufficiently high and the methanol permeability is sufficiently low. The technique described in Patent Document 1 focuses on improving methanol permeability and enduring use at high temperatures. However, both technologies have sufficiently high proton conductivity and sufficiently low methanol permeability. Not enough to be satisfied.

  Therefore, an object of the present invention is to provide a solid fuel cell that can obtain a large current density using an electrolyte membrane having sufficiently high proton conductivity and sufficiently low methanol permeability.

The above object of the present invention is to
1) In a solid fuel cell having an electrolyte and a cathode electrode and an anode electrode provided adjacent to the electrolyte, the electrolyte contains a proton conductive organic substance in pores of a porous membrane that does not swell against water and methanol. A porosity of the porous membrane increases from the anode side toward the cathode side,
2) The porous membrane has a porosity of a porous layer adjacent to the anode electrode of 30 to less than 80% and a porosity of the porous layer adjacent to the cathode electrode of 60 to 80%. 1) The solid fuel cell according to 1), which is formed from a porous layer of
3) The solid fuel cell according to 1) or 2), wherein the porous membrane is formed of an inorganic material.
4) In a solid fuel cell having an electrolyte and a cathode electrode and an anode electrode provided adjacent to the electrolyte, the electrolyte contains a proton conductive organic substance in the pores of a porous membrane that does not swell against water and methanol. The average pore diameter of the porous membrane increases from the anode side toward the cathode side,
5) The porous membrane has a plurality of porous layers in which the average pore diameter of the porous layer adjacent to the anode electrode is less than 100 to 300 nm, and the average pore diameter of the porous layer adjacent to the cathode electrode is 300 to 500 nm. 4) The solid fuel cell according to 4), which is formed from a porous layer,
6) The solid fuel cell according to 4) or 5), wherein the porous membrane is formed of an inorganic material.
7) In a solid fuel cell having an electrolyte and a cathode electrode and an anode electrode provided adjacent thereto, the electrolyte contains a proton-conducting organic substance in the pores of a porous membrane that does not swell against water and methanol. A porosity and an average pore diameter of the porous membrane increase from the anode side toward the cathode side,
8) In the porous membrane, the porosity of the porous layer adjacent to the anode electrode is 30 to less than 80%, the average pore diameter is less than 100 to 300 nm, and the porosity of the porous layer adjacent to the cathode electrode is 7) The solid fuel cell according to 7), wherein the solid fuel cell is formed of a plurality of porous layers having an average pore diameter of 300 to 500 nm.
9) The solid fuel cell according to 7) or 8), wherein the porous membrane is formed of an inorganic material.
10) The solid fuel cell according to any one of 1) to 9), wherein the solid fuel cell is a direct methanol solid polymer fuel cell;
Achieved by:

  That is, the inventor of the present invention provides an electrolyte membrane containing a proton conductive organic substance in pores of a porous membrane that does not swell with respect to water and methanol, and the porosity or average pore size of the porous membrane is an anode electrode. By making the structure increase from the side toward the cathode side, the porous membrane on the anode side is dense and the content of the proton conductive organic material is increased on the cathode side, so that the proton conductivity is sufficiently high. It has been found that an electrolyte membrane having a sufficiently low methanol permeability can be obtained, and that a battery with a large current density can be obtained by using such an electrolyte membrane as an electrolyte of a solid fuel cell, thereby achieving the present invention. It was.

  According to the present invention, an electrolyte membrane having sufficiently high proton conductivity and sufficiently low methanol permeability can be obtained, and by using this as an electrolyte of a solid fuel cell, a solid fuel cell capable of obtaining a large current density Can be provided.

  The present invention is characterized in that an electrolyte having a specific structure is used as the electrolyte of the solid fuel cell. In the first invention, the electrolyte contains a proton conductive organic substance in the pores of the porous membrane that does not swell with water and methanol, and the porosity of the porous membrane is on the anode side. In the second invention, the electrolyte increases in the pores of the porous membrane that does not swell against water and methanol. A proton-conducting organic substance is contained, and the average pore diameter of the porous membrane increases from the anode side toward the cathode side (the invention according to claim 4). In the invention, the electrolyte contains a proton conductive organic substance in the pores of the porous membrane that does not swell with respect to water and methanol, and the porosity and average pore diameter of the porous membrane are anodes. Increase from the pole side toward the cathode side Characterized by (claim 7).

  A preferred embodiment for producing an electrolyte having a specific structure according to the present invention will be described.

  The first step is a step of forming a porous film in which the porosity or average pore diameter has a gradient in the thickness direction. In this step, a plurality of layers of a dispersion liquid containing inorganic fine particles and combustible organic fine particles giving a desired porosity or average pore diameter are laminated or dried simultaneously or sequentially on a combustible support, and then fired. Process. The second step is a step of filling the porous membrane formed in the first step with a proton conductive organic substance.

  The combustible support that can be used in the step of forming the porous membrane according to the present invention includes paper such as filter paper, cloth such as non-woven fabric, polymer film such as polyethylene terephthalate and the like as long as it is combustible. Can be used. The surface of the support is preferably smooth. If it is smooth, the surface of the obtained electrolyte membrane will also be smooth, and when it is set as the electrolyte of a polymer electrolyte fuel cell, the contact in the interface of an electrode and an electrolyte membrane will become close. The surface roughness of the support is not particularly limited, but the surface roughness Rz of the surface on which the dispersion liquid containing inorganic fine particles and combustible organic fine particles is laminated is preferably 3 μm or less. The surface roughness Rz is the ten-point average surface roughness corresponding to JIS Rz (maximum height), and the average surface of the portion extracted from the surface of the roughness by the reference area is used as the reference surface. This is an input conversion of the distance between the average value of the elevation of the fifth mountain and the average value of the depth of the valley from the deepest to the fifth. For the measurement, for example, a stylus type three-dimensional roughness meter (Surfcom 570A-3DF) manufactured by Tokyo Seimitsu Co., Ltd. can be used. In addition, a backing layer is provided on the surface opposite to the surface on which the dispersion liquid is laminated in order to prevent warping (curl), deflection, etc. of the support by laminating the dispersion liquid containing inorganic fine particles and combustible organic fine particles. It may be preferable.

Examples of the inorganic fine particles include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), boron oxide (B ₂ O ₃ ), titania (TiO ₂ ), Ti, Al, B, and Zr. The hydroxide is mentioned. These may be used alone or in combination of several kinds. In the present invention, silica (SiO ₂ ) is preferable. Of the silica (SiO ₂ ), amorphous silica is preferable, and any of a dry method, a wet method, and an airgel method may be used, but wet type colloidal silica is most preferable.

  In the present invention, the inorganic fine particles preferably have an average particle size of 10 nm or more, more preferably 10 to 100 nm, and still more preferably 10 to 50 nm, as a primary average particle size. The average particle diameter of the inorganic fine particles is observed with a scanning electron microscope, the long diameter of 1,000 particles is randomly measured, and the primary average particle diameter is calculated.

  As the flammable organic fine particles, organic fine particles of any material can be used as long as they are finally burned away, but those that do not swell in the solvent as a dispersion medium used in the dispersion are preferable. In the present invention, water is preferable as the dispersion medium from the viewpoint of safety, and as the flammable organic fine particles, acrylic resin, styrene resin, styrene / acrylic resin, styrene / divinylbenzene type that does not dissolve or swell in water. Polymer beads such as resin, styrene / butadiene resin, polyester resin, and urethane resin can be used.

  The porous film according to the first aspect of the present invention has a porosity that increases from the anode side toward the cathode side, and the porous film can be produced by laminating a plurality of porous layers. it can. In this case, the porosity of the porous layer adjacent to the anode electrode is preferably approximately 20% or more, and particularly preferably 30% to less than 80% from the viewpoint of proton conductivity and methanol permeability. In addition, the porosity of the porous layer adjacent to the cathode electrode is preferably 80% or less, and particularly preferably 60 to 80% from the viewpoint of proton conductivity and methanol permeability.

The porosity can be calculated from the mass W (g) per unit area S (cm ² ), the average thickness t (μm), and the density d (g / cm ³ ) by the following equation.

Porosity (%) = (1- (10 ⁴ · W / (S · t · d))) × 100
The porosity of the porous film is almost dependent on the volume ratio of the inorganic fine particles and the combustible organic fine particles when the porous film is produced. For example, in order to set the porosity of the porous film to less than 30 to 80%, the ratio of inorganic fine particles to about 20 to 70% by volume and combustible organic fine particles to 30 to 80% by volume (inorganic fine particles and combustible organic fine particles The total sum of the volumes may be adjusted to 1). In order to adjust the porosity to 60 to 80%, the ratio of inorganic fine particles to 20 to 40% by volume and combustible organic fine particles to 60 to 80% by volume (the sum of the volume of inorganic fine particles and combustible organic fine particles 1).

  The porous membrane according to the second aspect of the present invention has an average pore diameter that increases from the anode side toward the cathode side. The porous membrane can be produced by laminating a plurality of porous layers. it can. In this case, the average pore diameter of the porous layer adjacent to the anode electrode is preferably approximately 50 nm or more, and particularly preferably from 100 to less than 300 nm from the viewpoint of proton conductivity and methanol permeability. Further, the average pore diameter of the porous layer adjacent to the cathode electrode is preferably about 800 nm or less, and particularly preferably 300 nm to 500 nm or less from the viewpoint of proton conductivity and methanol permeability.

  The average particle diameter of the combustible organic fine particles is related to the average pore diameter of the porous film according to the present invention. Therefore, combustible organic fine particles having an average particle diameter that gives a desired average pore diameter are selected. The porous film according to the present invention is formed by laminating a dispersion containing inorganic fine particles and flammable organic fine particles on a flammable support and firing it, so that the inorganic fine particles adhere to form a thin film. To do. In the thin film, the portion occupied by the combustible organic fine particles forms innumerable pores in the thin film. The average pore size of these innumerable pores generally corresponds to the average particle size of combustible fine particles. For example, when polystyrene particles having an average particle diameter of 83 nm are used as combustible organic fine particles, polystyrene particles having an average pore diameter of 110 nm and 304 nm are used when polystyrene particles having an average pore diameter of 80 nm and 112 nm are used. In the case where polystyrene fine particles having an average pore diameter of 300 nm and 464 nm were used, the average pore diameter was 460 nm. The average pore diameter was measured by a mercury intrusion porosimeter method using a pore sizer 9310 manufactured by Shimadzu Corporation. The measured values are rounded off to the first decimal place.

  The porous membrane according to the third aspect of the present invention has a porosity and an average pore diameter that increase from the anode side toward the cathode side. The porous membrane is formed by laminating a plurality of porous layers. Can be produced. In this case, the porosity of the porous layer adjacent to the anode electrode is preferably about 20% or more, and the average pore diameter is preferably about 50 nm or more. From the viewpoint of proton conductivity and methanol permeability, it is particularly preferable that the porosity is The rate is 30 to less than 80%, and the average pore diameter is 100 to less than 300 nm. Further, the porosity of the porous layer adjacent to the cathode electrode is preferably 80% or less, and the average pore diameter is preferably about 800 nm or less. From the viewpoint of proton conductivity and methanol permeability, the porosity is particularly preferable. Is 60 to 80% and the average pore diameter is 300 nm to 500 nm or less.

  Next, a method for preparing a dispersion containing inorganic fine particles and combustible organic fine particles according to the present invention will be described. The use ratio of the inorganic fine particles and the combustible organic fine particles is as described above, but the solid content concentration may be 5 to 80% by mass, preferably 10 to 40% by mass.

  As the dispersion medium, an aqueous solvent is preferable. Various known solvents such as water and alcohols can be used as the aqueous solvent, but water or a mixed solvent containing water as a main component is preferably used.

  Examples of the dispersion aid for dispersing inorganic fine particles and combustible organic fine particles include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, Various surfactants such as polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, and amine oxide can be used. .

  Examples of the dispersion method for dispersion include a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker. These may be used alone or in appropriate combination. Can be used.

  The step of laminating a dispersion containing inorganic fine particles and flammable organic fine particles on a flammable support is carried out by filtering the dispersion with a membrane filter using a vacuum suction filter, and forming inorganic fine particles and flammable organic on the filter paper. There are a method in which a layer containing fine particles is deposited and dried, or a method in which a dispersion is applied to a combustible support and dried.

  Any known technique can be adopted as a method for producing the porous film according to the present invention by laminating a plurality of porous layers. For example, a method in which a dispersion containing inorganic fine particles and combustible organic fine particles adjusted to have a desired porosity or average pore size on a combustible support is applied sequentially or simultaneously in a multilayer, and dried. And a method of sequentially depositing a dispersion liquid containing inorganic fine particles and combustible organic fine particles adjusted to have a porosity or an average pore size.

  In the present invention, a method of applying a dispersion containing inorganic fine particles and combustible organic fine particles to a combustible support is preferred. As a coating method, for example, a well-known coating method such as a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method, or an extrusion method can be employed.

  In order to form a porous film formed of inorganic fine particles, a flammable support on which a dispersion containing inorganic fine particles and flammable organic fine particles is laminated is heated in an electric furnace in a nitrogen atmosphere and fired. The heat treatment can be performed using, for example, an electric furnace provided with a heating element such as molybdenum silicide, and is performed at 1000 ° C. or lower, more preferably at 400 to 900 ° C. The time for heating can be set as appropriate depending on the size of the target porous film. Specifically, for example, a heating time of about 2 hours can be used. If the heating time is too long, the sintering proceeds too much and the average pore diameter may be reduced. Although cooling is performed after the firing step, the temperature of this cooling is not particularly limited, but it is preferable to cool the porous film to room temperature in terms of ease of handling. The temperature increase rate and the temperature decrease rate in the heat treatment for obtaining the porous film can be appropriately set. It is preferable to set it as 200-300 degrees C / h about both a temperature increase rate and a temperature decrease rate.

  The thickness of the porous membrane according to the present invention is not particularly limited, but is generally about 500 μm or less, preferably 300 μm or less, and more preferably 50 to 200 μm.

  The above has described a method for producing a porous film by burning a flammable support on which a dispersion containing inorganic fine particles and flammable organic fine particles is laminated, in a nitrogen atmosphere by heat treatment in an electric furnace. As the porous membrane according to the present invention, those made of various resins can be used in addition to those obtained by the above production method. Examples of such resins include fluorine resins such as polytetrafluoroethylene, 6,6-nylon, various polyamide resins, polyester resins such as polyethylene terephthalate, polyether resins such as dimethylphenylene oxide and polyether ether ketone, Α-olefins such as ethylene and propylene, alicyclic unsaturated hydrocarbons such as norbornene, (co) polymers such as conjugated dienes such as butadiene and isoprene, such as polyethylene resins, polypropylene resins, and ethylene-propylene rubbers And aliphatic hydrocarbon resins such as elastomers such as butadiene rubber, isoprene rubber, butyl rubber and norbornene rubber, and hydrogenated products thereof.

  The method for filling the pores of the porous membrane according to the present invention with the proton conductive organic material is not particularly limited. For example, the pores of the porous membrane can be filled with a proton conductive organic substance by a method of applying a proton conductive polymer solution to the porous membrane or a method of immersing the porous membrane in the proton conductive polymer solution. . At that time, it is possible to easily fill the pores with the proton conductive organic material by using ultrasonic waves or reducing the pressure.

  Alternatively, in-situ polymerization can be performed by filling the pores of the porous membrane with a polymerizable proton conductive organic substance. Specifically, after the pore surface of the porous film is activated by energy such as plasma, ultraviolet ray, electron beam, gamma ray, etc., a monomer having an ion exchange group is contacted or coated on the surface, and the porous surface A graft polymerization reaction is caused on the membrane surface and inside the pores, and the pores are substantially filled with a proton conducting polymer. Alternatively, a method of vaporizing a polymerizable proton conductive organic material and performing plasma polymerization may be performed. Moreover, it can also superpose | polymerize by adding a polymerization initiator to a polymerizable proton conductive organic substance and heating.

As the proton conductive organic substance, a monomer or polymer having proton conductivity is used. Examples of proton conductive monomers excellent in oxygen solubility and diffusibility include fluorinated sulfonic acid derivatives such as trifluoromethanesulfonic acid and tetrafluoroethanedisulfonic acid, (HO) ₂ OP (CF ₂ ) PO (OH) ₂ , (HO) ₂ OP (CF ₂ ) ₂ PO (OH) _{2 and} other fluorinated diphosphate derivatives, (CF ₃ SO ₂ CH ₂ SO ₂ CF ₂ CF ₂ ) ₂ , CF ₃ SO ₂ NHSO ₂ C _And derivatives of fluorinated sulfonyl acids such as ₄ F ₉ . Examples of the proton conductive polymer having similar properties include ion exchange resins having an organic fluorine-containing polymer as a skeleton, such as perfluorocarbon sulfonic acid resins. It can be obtained as Nafion 112 (trade name, manufactured by DuPont), Nafion 117 (trade name, manufactured by DuPont) or DOW membrane (trade name, manufactured by Dow Chemical).

  In addition, sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, sulfonated polyphenylene and other sulfonated plastic electrolytes, sulfoalkylated polyetheretherketone, sulfoalkyl There are sulfoalkylated plastic electrolytes such as sulfonated polyethersulfone, sulfoalkylated polyetherethersulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene. The sulfonic acid equivalent of these electrolyte materials is about 0.5 to 2.0 meq / g dry resin, preferably 0.7 to 1.6 meq / g dry resin. When the sulfonic acid equivalent is less than 0.5 meq / g dry resin, the ionic conduction resistance increases, and when it is greater than 2.0 meq / g dry resin, it becomes easier to dissolve in water.

Moreover, as a fluorine-type electrolyte material, for example,
Formula _{CF 2 = CF- (OCF 2 CFX} ) m-Oq- (CF 2) n-A
(Wherein, m = 0 to 3, n = 0 to 12, q = 0 or 1, X = F or CF ₃ , A = sulfonic acid type functional group), tetrafluoroethylene, hexafluoro And copolymers with perfluoroolefins such as propylene, chlorotrifluoroethylene or perfluoroalkyl vinyl ether. Preferable examples of the fluorovinyl compound include, for example, CF ₂ ═CFO (CF ₂ ) aSO ₂ F, CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) aSO ₂ F, CF ₂ ═CF (CF ₂ ) bSO ₂ F, CF ₂ = CF (OCF ₂ CF (CF ₃ )) cO (CF ₂ ) ₂ SO ₂ F (where a = 1 to 8, b = 0 to 8, c = 1 to 5) It can also be used.

  The average film thickness of the electrolyte membrane according to the present invention is not particularly limited, but is usually 500 μm or less, preferably 300 μm or less, more preferably 50 to 200 μm. The film thickness can be measured with a 1/10000 thickness gauge. The average film thickness can be obtained by measuring five points at arbitrary locations and calculating the average.

  The electrolyte membrane according to the present invention can be used in a methanol fuel cell. In particular, it can be preferably used for a direct methanol solid polymer fuel cell.

  Next, a direct methanol solid polymer fuel cell will be described with reference to FIG. FIG. 1 is a schematic view showing an embodiment of a direct methanol solid polymer fuel cell using an electrolyte membrane according to the present invention as an electrolyte membrane.

  In FIG. 1, reference numeral 1 denotes an electrolyte (consisting of three layers: a porous layer on the anode electrode side indicated by reference numeral 12, a porous layer on the cathode electrode side indicated by reference numeral 13, and an intermediate porous layer indicated by reference numeral 11). 2 represents an anode electrode (fuel electrode), 3 represents a cathode electrode (air electrode), and 4 represents an external circuit. As the fuel, an aqueous methanol solution is used.

At the anode 2, methanol reacts with water to generate carbon dioxide and hydrogen ions (H ⁺ ) and release electrons (e ⁻ ). Hydrogen ions (H ⁺ ) pass through the electrolyte 1 toward the cathode electrode 3, and electrons (e ⁻ ) flow to the external circuit 4. On the other hand, the aqueous solution A ′ in which the methanol component containing carbon dioxide is reduced is discharged out of the system. The reaction at the anode 2 is represented by the following formula.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
At the cathode 3, oxygen in the air B, hydrogen ions (H ⁺ ) that have passed through the electrolyte 1, and electrons (e ⁻ ) from the external circuit 4 react to generate water. On the other hand, the air B ′ in which oxygen containing water is reduced is discharged out of the system. The reaction at the cathode electrode 3 is represented by the following formula.

3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O
The overall reaction of the fuel cell is as follows:

CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O
The structure of the anode 2 can be a conventionally known structure. For example, it is comprised from the support body which supports a catalyst layer and a catalyst layer from the electrolyte 1 side. The structure of the cathode electrode 3 can also be a conventionally known structure. For example, it is comprised from the support body which supports a catalyst layer and a catalyst layer from the electrolyte 1 side.

  As the catalyst for the anode electrode 2 and the cathode electrode 3, known catalysts can be used. For example, a noble metal catalyst such as platinum, palladium, ruthenium, iridium, or gold, or an alloy such as platinum-ruthenium, iron-nickel-cobalt-molybdenum-platinum, or the like is used.

  The catalyst layer preferably contains an electron conductor (conductive material) material for the purpose of improving conductivity. The electron conductor (conductive material) is not particularly limited, but an inorganic conductive material is preferably used from the viewpoints of electron conductivity and touch resistance. Among these, carbon black, graphite or carbonaceous carbon material, metal or metalloid can be mentioned. Here, as the carbon material, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used from the viewpoint of electron conductivity and specific surface area. In particular, it is used as an electron conductor (conductive material) carrying a catalyst, such as platinum-carrying carbon.

  The support that supports the catalyst layer, that is, the electrode base material, can be used without particular limitation as long as it has a low electrical resistance and can collect current. Examples of the constituent material of the electrode base material include those mainly composed of a conductive substance. Examples of the conductive substance include a fired body from polyacrylonitrile, a fired body from pitch, and carbon such as graphite and expanded graphite. Examples include raw materials, the aforementioned nanocarbon materials, stainless steel, molybdenum, and titanium.

  The form of the conductive inorganic substance of the electrode base material is not particularly limited, and for example, it is used in the form of fibers or particles. From the viewpoint of gas permeability, fibrous conductive inorganic substances (inorganic conductive fibers), particularly carbon fibers are used. preferable. As an electrode base material using inorganic conductive fibers, either a woven fabric or a non-woven fabric structure can be used. For example, carbon paper TGP series, SO series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, etc. are used. As the woven fabric, a plain weave, a twill weave, a satin weave, a crest weave, a binding weave and the like are used without particular limitation. The nonwoven fabric is not particularly limited, and may be a papermaking method, a needle punch method, a spun bond method, a water jet punch method, a melt blow method, or the like. It may be a knitted fabric. In particular, when carbon fibers are used in these fabrics, carbonized plain fabric using flame-resistant spun yarn is carbonized or graphitized, and flame-resistant yarn is carbonized after being processed into a nonwoven fabric by the needle punch method or water jet punch method. Alternatively, a graphitized nonwoven fabric, a flame-resistant yarn, a carbonized yarn, or a mat nonwoven fabric by a paper making method using a graphitized yarn is preferably used. In particular, it is preferable to use a non-woven fabric because a thin and strong fabric can be obtained. It is also effective to use carbon nanofibers or the like (see Japanese Patent Application Laid-Open No. 2003-109618).

  When inorganic conductive fibers made of carbon fibers are used as the electrode substrate, examples of the carbon fibers include polyacrylonitrile (PAN) -based carbon fibers, phenol-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers. Of these, PAN-based carbon fibers are preferable.

Examples of the conductive inorganic particles include SiO ₂ , ZrO ₂ , B ₂ O ₃ , TiO ₂ , Al ₂ O _3, and optionally hydroxides of Ti, Al, B and Zr, and any combination thereof. SiO ₂ is preferred.

  As a method for producing a membrane-electrode assembly (MEA) by joining a solid polymer electrolyte membrane and an electrode, for example, a polytetrafluoroethylene suspension of platinum catalyst powder supported on carbon particles is used. There is a method in which a catalyst layer is formed by mixing with a carbon paper, heat-treating to form a catalyst layer, and then applying the same electrolyte solution as the electrolyte membrane to the catalyst layer, and hot pressing with the electrolyte membrane for integration. In addition, a method in which the same electrolyte solution as the electrolyte membrane is coated on platinum catalyst powder in advance, a method in which a catalyst paste is applied to the electrolyte membrane, a method in which an electrode is electrolessly plated on the electrolyte membrane, and a metal complex of white metal on the electrolyte membrane. There is a method of reducing ions after adsorbing them.

  A fuel distribution plate (separator) as a current collector in which grooves for forming a fuel flow path and an oxidant flow path are formed outside the joined body of the electrolyte membrane and the electrode produced as described above, and an oxidant A fuel cell is formed by stacking a plurality of single cells via a cooling plate or the like, with a single cell provided with a flow distribution plate (separator). The separator may have a current collecting function.

  Examples of the fuel that can be used in the fuel cell of the present invention include hydrogen gas, methanol, ethanol, 1-propanol, dimethyl ether, ammonia, and the like, and methanol is preferable.

  Hereinafter, the fuel cell of the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

(Example 1)
<Manufacture of proton conductive electrolyte membrane>
<Preparation of porous membrane>
(Preparation of porous membrane No. 1)
Dilute a mixture of polystyrene fine particles (made by Seradyn, average particle size 474 nm) and colloidal silica (trade name: Snowtex 10, Nissan Chemical Co., average particle size 20 nm) (polystyrene fine particles 25% by volume, colloidal silica 75% by volume). The mixture was stirred and dispersed in an aqueous surfactant solution using a high-speed homogenizer. The concentration of the dispersion was adjusted to 30% by mass (referred to as the first layer coating solution). The first layer coating solution was applied on a polyethylene terephthalate support having a surface roughness Rz of 1 μm using a doctor blade so that the dry film thickness was 60 μm (referred to as the first layer).

  Next, a mixture of polystyrene fine particles (manufactured by Seradyn, average particle size 474 nm) and colloidal silica (trade name: Snowtex 10, Nissan Chemical Co., average particle size 20 nm) (polystyrene fine particles 35% by volume, colloidal silica 65% by volume) Was stirred and dispersed in a dilute surfactant aqueous solution using a high-speed homogenizer. The concentration of the dispersion was adjusted to be 30% by mass (referred to as the second layer coating solution). The second layer coating solution was applied on the first layer using a doctor blade so that the dry film thickness was 60 μm (referred to as the second layer).

  Further, a mixture of polystyrene fine particles (made by Seradyn, average particle size 474 nm) and colloidal silica (trade name: Snowtex 10, manufactured by Nissan Chemical Industries, average particle size 20 nm) (polystyrene fine particles 50 vol%, colloidal silica 50 vol%) Was stirred and dispersed in a dilute surfactant aqueous solution using a high-speed homogenizer. The concentration of the dispersion was adjusted to be 30% by mass (referred to as the third layer coating solution). The third layer coating solution was applied on the second layer using a doctor blade so that the dry film thickness was 60 μm (referred to as the third layer).

  A sample in which the first to third layers are laminated on a support is baked at 800 ° C. for about 1 hour in an electric furnace set at a heating rate of 200 ° C./h, and is porous with a film thickness of 180 μm. A membrane was obtained (porous membrane No. 1).

(Preparation of porous membrane No. 2-6)
Porous membrane no. 1 except that the polystyrene fine particles and the colloidal silica in the first layer coating solution to the third layer coating solution were replaced as shown in Table 1. 1 in the same manner as in the preparation of No. 1 2-6 were produced.

(Preparation of porous membrane No. 7)
Dilute a mixture of polystyrene fine particles (made by Seradyn, average particle size 474 nm) and colloidal silica (trade name: Snowtex 10, manufactured by Nissan Chemical Industries, average particle size 20 nm) (polystyrene fine particles 30% by volume, colloidal silica 70% by volume). The mixture was stirred and dispersed in an aqueous surfactant solution using a high-speed homogenizer. The concentration of the dispersion was adjusted to 30% by mass, and applied to a polyethylene terephthalate support having a surface roughness Rz of 1 μm using a doctor blade so that the dry film thickness was 180 μm. Then, it baked for about 1 hour at 800 degreeC with the electric furnace which set the temperature increase rate to 200 degrees C / h, and obtained the porous film with a film thickness of 180 micrometers (porous film No. 7).

  Porous membrane no. Table 2 shows the average pore diameter and porosity of 1-7.

The porosity was calculated from the mass W (g) per unit area S (cm ² ), the average thickness t (μm), and the density d (g / cm ³ ) by the following formula. The 1's place is rounded off.

Porosity (%) = (1- (10 ⁴ · W / (S · t · d))) × 100
The average pore diameter was measured by a mercury intrusion porosimeter method using a pore sizer 9310 manufactured by Shimadzu Corporation. The measured value is rounded off to the first decimal place.

<Preparation of proton conductive electrolyte membrane>
Porous membrane No. produced above. Each of 1 to 7 was filled with a proton conductive organic material by the following method to produce proton conductive electrolyte membranes (proton conductive electrolyte membranes Nos. 1 to 7).

  In isopropyl alcohol: water == 4: 1, 2-acrylamido-2-methylpropanesulfonic acid as a monomer, N, N′methylene-bisacrylamide as a crosslinking agent, and AIBN (N, N′-azobis as a polymerization initiator) Isovaleronitrile) was mixed at a mass ratio of 100: 20: 1, and the porous membrane was immersed in the mixed solution. In this state, the mixture was slowly heated and kept at 60 ° C. for 2 hours, further slowly heated and kept at 80 ° C. for 2 hours. This operation was repeated three times to produce a proton conductive electrolyte membrane. The average film thickness of the proton conductive electrolyte membrane was 180 μm. The average film thickness was obtained by measuring five arbitrary points with a 1/10000 thickness gauge and calculating the average. As a control, Nafion 117 (manufactured by DuPont) having a film thickness of 180 μm was also prepared.

<Evaluation>
<Methanol permeability>
A proton conductive electrolyte membrane is sandwiched between the H-type cell shown in FIG. 2, and the permeability coefficient of methanol permeating into the pure water of the B cell from the 2M methanol aqueous solution containing 0.1 M sulfuric acid in the A cell is 70 ° C. Measured with

  As a sample, proton conductive electrolyte membrane No. Samples in which the first layers 1 to 6 are arranged on the A cell side and the third layer on the B cell side are designated as sample Nos. 1-6. In addition, proton conductive electrolyte membrane No. Samples having the third layers 1 to 6 on the A cell side and the first layer on the B cell side were respectively referred to as comparative sample Nos. 1-6. Proton conductive electrolyte membrane No. 7 is a comparative sample No. 7 and Nafion 117 was used as a control sample.

  The results are shown in Table 3.

  From the results in Table 3, it can be seen that the sample according to the present invention has improved methanol permeability. In particular, Samples 5 and 6, which are proton-conducting electrolyte membranes made from a porous membrane constructed such that the porosity and average pore diameter of the porous membrane increase from the anode side toward the cathode side, are permeated with methanol. It can be seen that the sex is dramatically improved.

(Example 2)
Using the proton conductive electrolyte membrane (electrolyte membrane Nos. 1 to 7) and Nafion 117 produced in Example 1, a membrane-electrode assembly (MEA) was produced by the following method.

<Production of electrode>
After carbon fiber cloth substrate is treated with 20% polytetrafluoroethylene (PTFE) for water repellency, a carbon black dispersion containing 20% by mass of PTFE is applied and heated at 350 ° C. to produce an electrode substrate. did. On this electrode substrate, an anode electrode catalyst coating solution composed of a Pt—Ru-supported carbon and Nafion (DuPont) solution is applied and dried to form an anode electrode, and Pt-supported carbon and Nafion (DuPont). The cathode electrode catalyst coating solution comprising a solution was applied and dried to prepare a cathode electrode.

<Production of membrane-electrode assembly (MEA)>
A membrane-electrode assembly (MEA) is produced by holding the proton conductive electrolyte membrane (electrolyte membrane Nos. 1 to 7) and Nafion 117 produced in Example 1 between the anode electrode and the cathode electrode and heating and pressing. did.

  Proton conductive electrolyte membrane No. Samples in which the first layers 1 to 6 are arranged on the anode electrode side and the third layer on the cathode electrode side are respectively MEANo. 1-6. In addition, proton conductive electrolyte membrane No. Samples in which the third layers 1 to 6 are arranged on the anode electrode side and the first layer on the cathode electrode side are respectively referred to as comparative MEA Nos. It was set as Comparative 1 to Comparative 6. Proton conductive electrolyte membrane No. 7 is MEANo. Comparative 7 was used, and Nafion 117 was used as a control sample.

  Table 4 shows the values of the porosity and average pore diameter of the porous membrane used in each sample of MEA.

<Evaluation>
<Current-voltage characteristics and series resistance components>
Each MEA sample is sandwiched between separators, 2M methanol aqueous solution on the anode side, air is flowed on the cathode side, and the fuel cell is operated at 70 ° C. The current-voltage characteristics and membrane resistance (series resistance component) are impedance meter KFM2030 (Kikusui Electronics). Evaluation was carried out using (Industry). Table 5 shows the results of current density and series resistance component at a voltage of 0.4V.

  From the results of Table 5, it can be seen that the sample according to the present invention has a small series resistance component representing the evaluation of proton conductivity, good proton conductivity, a large current density compared to the comparative sample, and is excellent as a fuel cell. . Comparative sample 7, which is a sample having a uniform porosity and average pore diameter of the porous membrane, has a small series resistance component and good proton conductivity. However, as can be seen from the results shown in Table 3, methanol is compared with the sample of the present invention. Since the permeability coefficient is large, the current density is small and it can be seen that the performance as a fuel cell is not sufficient.

It is the schematic which shows one Embodiment of the direct methanol type solid polymer fuel cell of this invention. It is the schematic of the H-type cell for evaluating methanol permeability.

Explanation of symbols

1 Electrolyte membrane 2 Anode electrode (fuel electrode)
3 Cathode electrode (air electrode)
4 External circuit

Claims (10)

In a solid fuel cell having an electrolyte and a cathode electrode and an anode electrode provided adjacent to the electrolyte, the electrolyte contains a proton conductive organic substance in pores of a porous membrane that does not swell against water and methanol. The porosity of the porous membrane increases from the anode side toward the cathode side. The porous membrane has a plurality of porous layers in which the porosity of the porous layer adjacent to the anode electrode is less than 30 to 80%, and the porosity of the porous layer adjacent to the cathode electrode is 60 to 80%. 2. The solid fuel cell according to claim 1, wherein the solid fuel cell is formed of a porous layer. The solid fuel cell according to claim 1, wherein the porous membrane is formed of an inorganic material. In a solid fuel cell having an electrolyte and a cathode and an anode provided adjacent thereto, the electrolyte contains a proton conductive organic substance in the pores of a porous membrane that does not swell against water and methanol. And the average pore diameter of the porous membrane increases from the anode side toward the cathode side. The porous membrane has a plurality of porous layers in which an average pore diameter of the porous layer adjacent to the anode electrode is less than 100 to 300 nm, and an average pore diameter of the porous layer adjacent to the cathode electrode is 300 to 500 nm The solid fuel cell according to claim 4, wherein the solid fuel cell is formed from the following. 6. The solid fuel cell according to claim 4, wherein the porous membrane is formed of an inorganic material. In a solid fuel cell having an electrolyte and a cathode and an anode provided adjacent thereto, the electrolyte contains a proton conductive organic substance in the pores of a porous membrane that does not swell against water and methanol. A solid fuel cell, wherein the porosity and average pore diameter of the porous membrane increase from the anode side toward the cathode side. The porous membrane has a porosity of the porous layer adjacent to the anode electrode of 30 to less than 80%, an average pore diameter of less than 100 to 300 nm, and a porosity of the porous layer adjacent to the cathode electrode of 60. The solid fuel cell according to claim 7, wherein the solid fuel cell is formed of a plurality of porous layers having an average pore diameter of 300 to 500 nm of ˜80%. The solid fuel cell according to claim 7 or 8, wherein the porous membrane is formed of an inorganic material. The solid fuel cell according to any one of claims 1 to 9, wherein the solid fuel cell is a direct methanol solid polymer fuel cell.

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