JP2007157547A - Membrane-electrode conjugant, fuel cell, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode conjugant capable of restraining the exhaustion of by-products generated when anode-oxidizing alcohol, and to provide a fuel cell having the membrane-electrode conjugant and an electronic apparatus having the fuel cell. <P>SOLUTION: The membrane-electrode conjugant is formed by interposing an electrolyte membrane 2 between an anode 3 and a cathode 4, and the anode 3 has a catalyst formed by laminating two or more kinds of catalysts different in action. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly, a fuel cell, and an electronic device.

  A direct methanol fuel cell (DMFC) that supplies methanol directly to the anode is known as a technology suitable for miniaturization of the fuel cell. This fuel cell supplies an aqueous methanol solution directly to the anode, eliminating the need for a reformer to extract hydrogen from methanol, reducing the size of the device itself, making it cheaper, as well as the safety and startability of fuel handling. And the entire driving means can be simplified. Although the direct methanol fuel cell has many advantages as described above, there is a problem of low efficiency and low output because the anodic oxidation reaction of methanol has a large overvoltage. Furthermore, the toxicity of methanol can be harmful to human health, and there are certain levels of regulations on storage and handling.

  From this point of view, it has been proposed to use ethanol, dimethyl ether or the like instead of methanol, but the present situation is that output characteristics higher than methanol are not obtained. However, for portable fuel cells represented by small size and ultra-small size, it is considered preferable to use ethanol as a fuel that has extremely low toxicity to the human body and environmental impact.

By the way, in the direct methanol fuel cell, by-products such as formaldehyde, formic acid, methyl formate, and carbon monoxide are detected in the ppm order during the fuel consumption process under actual use conditions. In general formula _{C n H 2n + 1 OH (} n ≧ 2)
If the anodic oxidation reaction of an alcohol having a carbon-carbon bond shown in FIG. 2 is more complicated and the carbon-carbon bond cannot be dissociated, for example, in the case of ethanol, by-products such as acetaldehyde and acetic acid may be generated. . Non-patent documents 1 to 5 disclose the following reaction mechanisms for the anodic oxidation of these alcohols.

  First, the fundamental reaction of anodic oxidation of ethanol is shown in Equation (1).

CH ₃ CH ₂ OH + 3H ₂ O → 2CO ₂ + 12H ⁺ + 12e ⁻ (1)
The anodic oxidation of ethanol begins with chemisorption on the catalyst surface such as platinum, and is ideally released through the oxidation process and finally as carbon dioxide from the electrode surface. Protons pass through the electrolyte membrane and are consumed by the oxygen reduction reaction at the cathode. Further, electrons are consumed from the electron conductor through the current collector and the external circuit in the oxygen reduction reaction at the cathode.

  In Non-Patent Document 1, regarding the anodic oxidation of ethanol represented by formula (1), the reaction proceeds in parallel reaction paths represented by formulas (2) and (3) due to the difference in the chemisorption power of ethanol. It is described.

CH ₃ CH ₂ OH → [CH ₃ CH ₂ OH] _ad → (R) _ad → CO ₂ (2)
CH ₃ CH ₂ OH → [CH ₃ CH ₂ OH] _ad → CH ₃ CHO → CH ₃ COOH (3)
(R) _ad in the formula (2) is an intermediate having a strong chemical adsorption force, and specific examples include (CO) _ad shown in Non-Patent Document 3. Since this intermediate has a strong chemisorption power, it can be a catalyst poisoning species. For this reason, it is necessary to remove this sequentially. It is known that a Pt—Ru alloy in which ruthenium is arranged in the vicinity of platinum has an effect of promoting oxidation of catalyst poisoning species because ruthenium is more likely to adsorb oxygen species than platinum. However, the overvoltage is still large. In particular, when ethanol is used as a fuel, an output less than half that of a fuel cell using methanol as a fuel can be obtained (see Non-Patent Document 6). Therefore, in addition to platinum and ruthenium, an example in which the anodic oxidation of alcohol was evaluated using a catalyst in which elements were further combined (see Non-Patent Document 7 and Patent Document 1), and as a catalyst, instead of Pt—Ru alloy, Pt— An example using an Sn alloy is also known (see Non-Patent Document 8). However, there is a view that these element addition effects only activate the reaction produced by the by-product as shown in Formula (3) (see Non-Patent Document 9).

Formula (3) is a reaction in which an intermediate product such as acetaldehyde or acetic acid is generated from an ethanol intermediate having a weak chemisorption power. As described in Non-Patent Document 1, there is an example in which acetaldehyde is detected as a main intermediate product, and there is an example in which acetic acid is detected as described in Non-Patent Document 5. . From these, it is clear that intermediates that are weakly adsorbed on the surface of the catalyst are easily diffused into the bulk as acetaldehyde and acetic acid, and their quantitative relationship is dependent on the potential. Non-Patent Document 3 describes that, for example, with a platinum catalyst, acetaldehyde is generated at 0.6 V (vs. RHE) or lower, and acetic acid is mainly generated at 0.8 V (vs. RHE) or higher. This is because the polarization potential required for platinum to adsorb oxygen species is 0.6 to 0.8 V (vs. RHE). In the case of methanol, the reaction route represented by the formula (2) is the main, but in the case of ethanol, the contribution of the formula (3) is large, and as a result, the reaction is terminated in steps up to acetaldehyde and acetic acid. The product yield is increased. In Non-Patent Document 10, the product of anodic oxidation of ethanol is quantified, but with a Pt-Ru catalyst, CO ₂ is 40% and acetaldehyde is 60% even under high temperature conditions of 100 ° C. or higher.

On the other hand, Non-Patent Document 11 reports that the products produced by the anodic oxidation of ethanol are only acetaldehyde and CO ₂ , and the catalyst having high activity against acetaldehyde is Pt ₂ Sn. In Non-Patent Document 11, power is generated using acetaldehyde as a fuel, and if acetic acid is not generated, even in formula (3), oxidation is performed from acetaldehyde to carbon dioxide through dissociation of carbon-carbon bonds. It is suggested that there is a reaction pathway that is

However, in the anodic oxidation of ethanol, the selectivity and reaction activity in the complete oxidation reaction from ethanol to carbon dioxide are poor for any catalyst.
JP 2004-152748 A K. A. Friedrich et al, Journal of Electrical Analytical Chemistry, 472 (1999), 120-125. C. Lamy et al, Journal of Applied Electrochemistry, 31 (2001), 799-809. C. Lamy et al, Journal of Power Sources, 105 (2002), 283-296. M.M. Watanabe et al, Langmuir, 17 (2001), 146-154. T.A. Iwashita, J .; Braz. Chem. Soc. , Vol. 13 No. 4 (2002), 401-409 Fujita et al., Abstracts of Battery Conference, 42nd, 590-591 (2001) J. et al. -M. Leger et al, Journal of Applied Electrochemistry, 31 (2001), 379-386. W. Zhou et al, Applied Catalysis, 46 (2003), 273-285. Kamiya et al., Proceedings of the Electrochemical Society, 72nd, 211 (2005) J. et al. Wang et al, J.A. Electrochem. Soc. 142 (1995), 4218-4224. Yamazaki et al., 2005 Electrochemical Society Autumn Meeting Abstracts, 46 (2005)

  The present invention has been made in view of the above-described problems of the prior art, and includes a membrane electrode assembly capable of suppressing discharge of byproducts generated when anodizing alcohol, a fuel cell having the membrane electrode assembly, and An object is to provide an electronic device having the fuel cell.

  According to the first aspect of the present invention, in the membrane electrode assembly in which the electrolyte membrane is sandwiched between the anode and the cathode, the anode has a catalyst layer in which two or more kinds of catalysts having different functions are laminated. Features. Thereby, the membrane electrode assembly which can suppress discharge | emission of the by-product produced | generated when alcohol anodizes can be provided.

  According to a second aspect of the present invention, in the membrane electrode assembly according to the first aspect, the two or more types of catalysts are active in an oxidation reaction not involving dissociation of a carbon-carbon bond of an alcohol having 2 or more carbon atoms. A first catalyst and a second catalyst active in a carbon-carbon bond dissociation reaction of the product of the oxidation reaction, and a layer containing the first catalyst is formed with the electrolyte membrane of the catalyst layer. A layer having an interface and containing the second catalyst is provided on the surface of the catalyst layer. Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  According to a third aspect of the present invention, in the membrane electrode assembly in which the electrolyte membrane is sandwiched between the anode and the cathode, the anode has a catalyst layer in which two or more types of catalysts having different functions are mixed. Features. Thereby, the membrane electrode assembly which can suppress discharge | emission of the by-product produced | generated when alcohol anodizes can be provided.

  According to a fourth aspect of the present invention, in the membrane electrode assembly according to the third aspect, the composition ratio of the two or more types of catalyst continuously changes in the thickness direction of the catalyst layer. And Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  According to a fifth aspect of the present invention, in the membrane electrode assembly according to the third aspect, the composition ratio of the two or more kinds of catalysts changes stepwise with respect to the thickness direction of the catalyst layer. And Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  The invention according to claim 6 is the membrane electrode assembly according to claim 4 or 5, wherein the two or more types of catalysts are oxidation reactions not involving dissociation of carbon-carbon bonds of alcohols having 2 or more carbon atoms. Active first catalyst and second catalyst active in dissociation reaction of carbon-carbon bond of the product of the oxidation reaction, and the ratio of the first catalyst to the two or more catalysts is The catalyst layer is higher on the electrolyte membrane side than the catalyst layer surface side, and the ratio of the second catalyst to the two or more catalysts is higher than that on the electrolyte membrane side of the catalyst layer. It is characterized by being high on the surface side. Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  The invention according to claim 7 is the membrane electrode assembly according to claim 3, wherein the composition ratio of the two or more types of catalysts continuously changes with respect to the surface direction of the catalyst layer. To do. Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  The invention according to claim 8 is the membrane electrode assembly according to claim 3, wherein the composition ratio of the two or more kinds of catalysts changes stepwise with respect to the surface direction of the catalyst layer. To do. Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  The invention according to claim 9 is the membrane electrode assembly according to claim 7 or 8, wherein the two or more types of catalysts are oxidation reactions not involving dissociation of carbon-carbon bonds of alcohols having 2 or more carbon atoms. Active first catalyst and second catalyst active in dissociation reaction of carbon-carbon bond of the product of the oxidation reaction, and the ratio of the first catalyst to the two or more catalysts is The ratio of the second catalyst to the two or more catalysts is higher than the side of the catalyst layer from which the alcohol is discharged, and the ratio of the second catalyst to the two or more catalysts is It is characterized in that it is higher on the side of the catalyst layer where the alcohol is discharged than on the side where the catalyst is discharged. Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  The invention according to claim 10 is the membrane electrode assembly according to any one of claims 2, 6 and 9, wherein the first catalyst is Ib, IVb, Vb, VIb, VIIb of the periodic table. And at least one selected from the group consisting of simple substances and compounds of elements belonging to the fourth, fifth and sixth periods of the VIIIb group, and the second catalyst comprises IIIa, IVa, IVb, Vb of the periodic table , VIb and VIIIb group, which is composed of one or more selected from the group consisting of simple substances and compounds belonging to the third, fourth, fifth and sixth periods. Thereby, discharge | emission of the by-product produced | generated when an alcohol is anodized can be suppressed further.

  According to an eleventh aspect of the present invention, in a fuel cell, the membrane electrode assembly according to any one of the first to tenth aspects is provided. Thereby, the fuel cell which can further suppress discharge | emission of the by-product produced | generated when anodic oxidation of alcohol can be provided.

  The invention according to claim 12 is the fuel cell according to claim 11, comprising a plurality of the membrane electrode assemblies, wherein the plurality of membrane electrode assemblies are arranged on at least one plane, It is electrically connected in series. Thereby, a fuel cell can be reduced in size.

  A thirteenth aspect of the present invention is the fuel cell according to the eleventh aspect, wherein a plurality of the membrane electrode assemblies are provided, and the plurality of membrane electrode assemblies are sequentially stacked via a bipolar plate. Features. Thereby, the output of the fuel cell can be improved.

  According to a fourteenth aspect of the present invention, in the electronic device, the fuel cell according to any one of the eleventh to thirteenth aspects is provided. Thereby, it is possible to provide an electronic device equipped with a fuel cell capable of suppressing discharge of by-products generated when the alcohol is anodized.

  According to the present invention, there is provided a membrane electrode assembly capable of suppressing discharge of by-products generated when an alcohol is anodized, a fuel cell having the membrane electrode assembly, and an electronic device having the fuel cell. Can be provided.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  In the membrane electrode assembly of the present invention, the electrolyte membrane is sandwiched between the anode and the cathode, and the anode has a catalyst layer in which two or more kinds of catalysts having different functions are laminated or mixed. At this time, the catalyst may be used alone or may be supported on a conductive substrate. Such a membrane electrode assembly can be directly used for an alcohol fuel cell.

  A direct alcohol fuel cell is a power generation device that supplies alcohol to the anode as a fuel, supplies oxygen to the cathode as an oxidant, and converts chemical energy directly into electrical energy by its oxidation-reduction reaction. The energy density (kWh / kg) of ethanol and other long carbon chain alcohols is greater than that of liquid hydrogen and methanol, and the theoretical efficiency is greater than that of fuel cells using hydrogen. However, at present, the reaction resistance of anodic oxidation is large and a sufficient output cannot be obtained.

  The electrolyte membrane is a membrane having ion conductivity, and in particular, a membrane having the ability to propagate protons is preferable. For example, Nafion (manufactured by DuPont), Aciplex (manufactured by Asahi Kasei), Flemion (manufactured by Asahi Glass) Etc.

  The anode (or cathode) is used to propagate a catalyst having a particle size of several nanometers, a conductive base material for supporting the catalyst or propagating electrons generated by the reaction, and a proton generated by the oxidation-reduction reaction. It is preferable to have a catalyst layer made of a mixture of the electrolyte component and a diffusion layer on the side surface to which the fuel (or oxidant) is supplied. As the conductive substrate, for example, carbon fine particles having a particle diameter of several tens of nanometers such as Vulcan (manufactured by Cabot), Ketjen Black (manufactured by Lion) and the like can be used. At this time, the carbon fine particles supporting the catalyst are aggregated and become secondary particles having a particle diameter of several hundred nanometers and are present in the electrode.

  As the diffusion layer, a porous substrate such as carbon paper or carbon cloth can be used. If necessary, a water repellent represented by polytetrafluoroethylene (PTFE) can be added to or laminated on the diffusion layer.

  The membrane electrode assembly can be produced by joining the three members by a method of sandwiching an electrolyte membrane between an anode and a cathode, hot pressing, cast film formation, or the like.

  A Pt—Ru alloy is suitable for an anode catalyst of a direct methanol fuel cell. Here, the alloy means that platinum and ruthenium are close to each other at the atomic level. This is because ruthenium that easily adsorbs oxygen species needs to be present in the vicinity of platinum in order to oxidize poisonous species to carbon dioxide in the process where methanol adsorbed on the surface of platinum is oxidized. (Bi-functional mechanism). Here, the poisoned species is a substance that covers the surface of platinum and inactivates it because of its strong adsorption power, and is mainly carbon monoxide.

  However, for fuels that require carbon-carbon bond dissociation, such as ethanol, ethanol is adsorbed and active in oxidation reactions that do not involve carbon-carbon bond dissociation, and the product is desorbed. When an alloy of a first catalyst (eg, Pt—Ru catalyst) and a catalyst (eg, Pt—Sn catalyst) active in the dissociation reaction of the product carbon-carbon bond is used, the product is converted into a carbon-carbon bond. It is thought that it is desorbed from the surface of the catalyst before dissociating. As a result, the function of the second catalyst is not exhibited. When ethanol is used, the adsorption of ethanol on the surface of platinum, the oxidation reaction without the carbon-carbon bond dissociation of ethanol, the carbon-carbon bond dissociation reaction of the product, the oxidation of carbon monoxide and the carbon dioxide It is considered difficult to perform all of the desorption. Therefore, by arranging the first catalyst and the second catalyst at a predetermined distance that does not affect the catalytic action of each other, ethanol can be efficiently oxidized to carbon dioxide, and a by-product It is considered that the generation of can be suppressed.

  In the membrane electrode assembly of the present invention, when two or more types of catalysts having different actions are laminated, the two or more types of catalysts are oxidized without dissociation of carbon-carbon bonds of alcohols having 2 or more carbon atoms. A first catalyst active in the reaction and a second catalyst active in the carbon-carbon bond dissociation reaction of the product of the oxidation reaction, and the layer containing the first catalyst is an interface with the electrolyte membrane of the catalyst layer And a layer containing the second catalyst is preferably provided on the surface of the catalyst layer. In addition, when two or more kinds of catalysts are composed of the first catalyst and the second catalyst, the layer containing the first catalyst and the layer containing the second catalyst are sequentially laminated on the electrolyte membrane. Is preferred.

  In the membrane / electrode assembly of the present invention, when two or more kinds of catalysts having different functions are mixed, the composition ratio of the two or more kinds of catalysts is preferably changed with respect to the thickness direction of the catalyst layer. The change in the composition ratio of the catalyst with respect to the thickness direction of the catalyst layer includes both cases where the total molar concentration of the catalyst is constant and changes with respect to the thickness direction of the catalyst layer. At this time, the change may be continuous or stepwise. At this time, the surface of the catalyst layer on the side in contact with the electrolyte membrane or the diffusion layer may be composed of a single catalyst or a plurality of catalysts. In the thickness direction of the catalyst layer, there are a surface in contact with the electrolyte membrane and a surface in contact with the diffusion layer, and the concentration of alcohol and the concentration of the product are different from the electrolyte membrane toward the diffusion layer.

  For this reason, two or more types of catalysts are a first catalyst active in an oxidation reaction not involving dissociation of carbon-carbon bonds of alcohols having 2 or more carbon atoms, and a carbon-carbon bond dissociation reaction of the product of the oxidation reaction. The ratio of the first catalyst to the two or more catalysts is higher on the electrolyte membrane side of the catalyst layer than on the surface side of the catalyst layer, and the ratio for the two or more catalysts. The ratio of the two catalysts is preferably higher on the surface side of the catalyst layer than on the electrolyte membrane side of the catalyst layer. As a result, a large amount of the second catalyst is disposed in a region where the concentration of the product of the oxidation reaction without carbon-carbon bond dissociation is high, so that the outside of the fuel cell system (liquid feeding line, fuel storage tank, air Middle product) can be prevented from being discharged.

  In the membrane / electrode assembly of the present invention, when two or more kinds of catalysts having different functions are mixed, the composition ratio of the two or more kinds of catalysts is preferably changed with respect to the surface direction of the catalyst layer. Note that the change in the composition ratio of the catalyst with respect to the surface direction of the catalyst layer includes both cases where the total molar concentration of the catalyst is constant and changes with respect to the surface direction of the catalyst layer. At this time, the change may be continuous or stepwise. In a fuel cell in which alcohol is circulated forcibly, a fuel supply path called a separator having a groove for feeding fuel is used separately from the diffusion layer. As a result, the alcohol concentration and the product concentration differ between the vicinity of the alcohol supply port and the vicinity of the discharge port.

  For this reason, two or more types of catalysts are a first catalyst active in an oxidation reaction not involving dissociation of carbon-carbon bonds of alcohols having 2 or more carbon atoms, and a carbon-carbon bond dissociation reaction of the product of the oxidation reaction. The ratio of the first catalyst to the two or more catalysts is higher on the side of the catalyst layer where alcohol is supplied than on the side where the alcohol of the catalyst layer is discharged. The ratio of the second catalyst to the above catalyst is preferably higher on the side of the catalyst layer where the alcohol is discharged than on the side where the alcohol of the catalyst layer is supplied. As a result, a large amount of the second catalyst is disposed in a region where the concentration of the product of the oxidation reaction without carbon-carbon bond dissociation is high, so that the outside of the fuel cell system (liquid feeding line, fuel storage tank, air Middle product) can be prevented from being discharged.

  Said 1st catalyst consists of 1 or more types selected from the group which consists of the element of the periodic table Ib, IVb, Vb, VIb, VIIb, and the element which belongs to the 4th-6th period of the VIIIb group, and a compound, The second catalyst is a kind selected from the group consisting of simple substances and compounds belonging to the third, fourth, fifth and sixth periods of groups IIIa, IVa, IVb, Vb, VIb and VIIIb of the periodic table It is preferable to consist of the above. At this time, the first catalyst and the second catalyst may be an alloy composed of one or more selected from the group consisting of the simple elements and compounds of the above elements. As the first catalyst, platinum, a mixture of platinum and ruthenium or platinum and ruthenium, and a simple substance or compound (oxide, etc.) such as molybdenum, tungsten, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper ) And a mixture thereof. Examples of the second catalyst include platinum, tin, cobalt, nickel, rhodium, palladium, or a mixture of these and oxides of aluminum, zinc, and titanium.

  The method for producing the membrane electrode assembly of the present invention is not particularly limited, but a specific example in the case of forming an anode catalyst layer in which the first catalyst and the second catalyst are laminated is shown below. .

  The first method is a method of forming an anode catalyst layer using a first catalyst ink containing a first catalyst and a second catalyst ink containing a second catalyst.

  Specifically, the catalyst layer can be formed by applying and drying the first catalyst ink on the electrolyte membrane and then applying and drying the second catalyst ink.

  In addition, after the PTFE sheet, in which the second catalyst ink and the first catalyst ink are sequentially applied and dried on the electrolyte membrane, is pressure-bonded by hot pressing or the like, the PTFE sheet is peeled off to form a catalyst layer on the electrolyte membrane. Can be transferred.

  On the other hand, a diffusion layer may be used as the coated substrate instead of the electrolyte membrane. Specifically, carbon paper in which a carbon layer made of carbon paper or carbon black and a binder (electrolyte component or PTFE component) is formed on the surface can be used. In this case, the catalyst layer can be formed by applying and drying the second catalyst ink on the carbon paper and then applying and drying the first catalyst ink.

  The catalyst ink can be prepared by mixing carbon carrying the catalyst and a solution or dispersion of the electrolyte component with a solvent such as water or alcohol. As a method for applying the catalyst ink, a spray, a spin coater, an applicator, a wire bar, a doctor blade, a roller, or the like can be used depending on the viscosity of the catalyst ink.

  The catalyst layer of the cathode may be formed using any one of an application method to an electrolyte membrane or carbon paper and a transfer method.

  When the catalyst layer is formed on the electrolyte membrane, the membrane electrode assembly can be produced by pressing the diffusion layer on the surface of the catalyst layer by hot pressing. When a catalyst layer is formed on the diffusion layer, a membrane electrode assembly can be produced by pressure bonding an electrolyte membrane to the surface of the catalyst layer by hot pressing.

  FIG. 4 shows the junction between the anode and the electrolyte membrane of the membrane / electrode assembly thus prepared.

  The second method is a method of forming an anode catalyst layer by using a catalyst ink and a dry synthesis method or a dry synthesis method and a wet synthesis method in combination. Here, examples of the dry synthesis method include a PVD (Physical Vapor Deposition) method such as a sputtering method, a vacuum deposition method, and a gas evaporation method, and a CVD (Chemical Vapor Deposition) method such as a cat-CVD method and a thermal CVD method. . At this time, any method may be used as long as the diffusion of the fuel and the product is not inhibited. Examples of the wet synthesis method include electrolytic plating, electroless plating, colloidal impregnation method, and the like. The layer formed by the dry and wet synthesis methods is composed only of the catalyst.

  Specifically, on the carbon paper having the carbon paper or carbon layer formed on the surface, the second catalyst ink is applied and dried in the same manner as described above, and then a layer made of the first catalyst is formed by a sputtering method. Thus, a catalyst layer can be formed. At this time, when the first catalyst has two or more components, sputtering may be performed simultaneously, or these alloys may be sputtered. In addition, you may apply | coat the solution or dispersion liquid of an electrolyte component on the layer formed by sputtering as needed. Thereby, the adhesiveness with the electrolyte membrane is improved.

  Moreover, after forming the layer which consists of a 1st catalyst by sputtering method in an electrolyte membrane, a catalyst layer can be formed by apply | coating a 2nd catalyst ink.

  The catalyst layer of the cathode may be formed using any one of an application method to an electrolyte membrane or carbon paper and a transfer method.

  When the catalyst layer is formed on the electrolyte membrane, the membrane electrode assembly can be produced by pressing the diffusion layer on the surface of the catalyst layer by hot pressing. When a catalyst layer is formed on the diffusion layer, a membrane electrode assembly can be produced by pressure bonding an electrolyte membrane to the surface of the catalyst layer by hot pressing.

  FIG. 5 shows the junction between the anode and the electrolyte membrane of the membrane / electrode assembly produced in this manner.

  Next, a method for forming an anode catalyst layer in which the composition ratio of the first catalyst and the second catalyst varies with respect to the thickness direction of the catalyst layer will be described below. Specifically, the anode catalyst layer is formed using a mixed ink in which the volume ratio of the first catalyst ink and the second catalyst ink is mixed.

  First, the third catalyst ink, the fourth catalyst ink, and the fifth catalyst are mixed by mixing so that the first catalyst ink: second catalyst ink (volume ratio) is 75:25, 50:50, and 25:75, respectively. Prepare ink. Next, the catalyst layer can be formed by applying and drying the catalyst ink on the electrolyte membrane in the order of the first, third, fourth, fifth and second. In addition, a catalyst layer may be formed by applying and drying catalyst ink in the order of second, fifth, fourth, third and first on carbon paper or carbon paper having a carbon layer formed on the surface. it can.

  The catalyst layer of the cathode may be formed using any one of an application method to an electrolyte membrane or carbon paper and a transfer method.

  When the catalyst layer is formed on the electrolyte membrane, the membrane electrode assembly can be produced by pressing the diffusion layer on the surface of the catalyst layer by hot pressing. When a catalyst layer is formed on the diffusion layer, a membrane electrode assembly can be produced by pressure bonding an electrolyte membrane to the surface of the catalyst layer by hot pressing.

  Next, a specific example in the case of forming an anode catalyst layer in which the composition ratio of the first catalyst and the second catalyst varies with respect to the surface direction of the catalyst layer is shown below.

  The first method is to apply the first catalyst ink (or the second catalyst ink) on the electrolyte membrane or the carbon paper or the carbon paper having the carbon layer formed on the surface by using a blade whose gap width is changed. In this method, after drying, the second catalyst ink (or the first catalyst ink) is applied using a blade having a constant gap width.

  The second method is a method of controlling the mechanical spray coating device when applying the first catalyst ink and the second catalyst ink on the electrolyte membrane or the carbon paper or the carbon paper on which the carbon layer is formed. is there. Examples of the method for controlling the mechanical spray coating apparatus include a method for controlling the movement (distance and speed) of the spray gun and a method for controlling the coating pressure.

  In the third method, the first catalyst ink and the second catalyst ink are simultaneously spray-coated on the electrolyte membrane or the carbon paper or the carbon paper on which the carbon layer is formed, and the coating amount of each catalyst ink is controlled. Is the method. The amount of catalyst ink applied can be controlled by the application pressure.

  The catalyst layer of the cathode may be formed using any one of an application method to an electrolyte membrane or carbon paper and a transfer method.

  When the catalyst layer is formed on the electrolyte membrane, the membrane electrode assembly can be produced by pressing the diffusion layer on the surface of the catalyst layer by hot pressing. When a catalyst layer is formed on the diffusion layer, a membrane electrode assembly can be produced by pressure bonding an electrolyte membrane to the surface of the catalyst layer by hot pressing.

  The fuel cell of the present invention has a plurality of the membrane electrode assemblies of the present invention, and the plurality of membrane electrode assemblies may be arranged on at least one plane and electrically connected in series. preferable. Thereby, when the supply power of a single cell is weak, electric power can be supplemented by connecting in series. Generally, when arranged on a flat surface, a pump and a blower for circulating the fuel are not necessary, and the thickness of the entire apparatus can be reduced, which is suitable for a small fuel cell.

  The fuel cell of the present invention has a plurality of the membrane electrode assemblies of the present invention, but the plurality of membrane electrode assemblies are preferably laminated sequentially via a bipolar plate. Thereby, compared with the case where it connects on a plane, since the electrical resistance by connection can be reduced, supply of large electric power is attained.

  FIG. 1 shows a first embodiment of the fuel cell of the present invention. The fuel cell of FIG. 1 has an electrolyte membrane 2 having ion conductivity in housings 1a and 1b and a pair of electrodes (anode 3 and cathode 4) sandwiching the electrolyte membrane 2, and a fuel supply path 5 outside them. And an oxidant supply path 6. In addition, although alcohol aqueous solution is illustrated as a fuel, gaseous fuels, such as hydrogen gas and a reformed gas fuel, may be sufficient.

  A fuel supply path 5 is provided on the anode 3 side. The fuel supply path 5 may be a part for storing fuel, but may be a flow path with an external fuel storage part (not shown). At this time, the fuel is preferably stirred by natural convection and / or forced convection. If forced convection is required, forced convection means (not shown) may be provided.

  An oxidant supply path 6 is provided on the cathode 4 side. An oxidant introduction hole for introducing an oxidant (in many cases, air) is provided above, while an oxidant discharge for discharging unreacted air and product (in many cases, water) is provided below. A hole is provided. In this case, forced intake and / or forced exhaust means may be provided (not shown). Moreover, you may provide the natural convection hole of air in the housing | casing 1a.

  When the fuel cell of the present invention is used as a direct ethanol fuel cell, the fuel supplied to the anode 3 may be commercially available ethanol, but bioethanol obtained by fermentation of plants such as corn and sugarcane is used. It is preferable to do.

  The fuel cell shown in FIG. 1 represents a single cell, but in the present invention, a single cell may be used as it is, or a plurality of cells are connected in series and / or in parallel to form a mounted fuel cell. You can also.

  FIG. 2 shows a second embodiment of the fuel cell of the present invention. The fuel cell shown in FIG. 2 has a flat rectangular parallelepiped shape with a small thickness. A fuel supply path 5 is formed in the fuel cell to partition it vertically. In addition, this fuel cell has a fuel storage portion constituted by, for example, a cylindrical container 7. The container 7 is detachable from the fuel cell. The container 7 has a small hole 7a formed on its side surface. The fuel stored in the container 7 is supplied through the small hole 7a. The small hole 7 a is sealed by a predetermined sealing means (not shown) before the container 7 is attached to the housing 1, and the fuel can be hermetically accommodated in the container 7. Yes. The small hole 7 a is formed at a position where the small hole 7 a communicates with the fuel supply path 5 when the container 7 is mounted in the fuel cell.

  In the fuel cell according to the present embodiment, a first cell group including four cells is disposed on the upper side of the fuel supply path 5. On the other hand, a second cell group consisting of four cells is also arranged below the fuel supply path 5. Each cell is composed of an anode 3, a cathode 4, and an electrolyte membrane 2 interposed between them, and is independent of each other. The cells in each cell group are arranged in a plane and are connected in series. The cells of the first cell group and the cells of the second cell group are arranged so that their anodes 3 face each other across the fuel supply path 5. At the same time, the cells of the first cell group and the cells of the second cell group are arranged so that their cathodes 4 face outward. By arranging the cells in this way, the fuel cell can be easily downsized, and is suitable as a small power source, particularly as a power source for portable devices. Further, since the container 7 containing the fuel is detachable, the fuel can be easily replenished, and this also makes the fuel cell of the present invention suitable as a power source for portable equipment.

When supplying the fuel from the container 7 to the fuel supply path 5, it is preferable to use a liquid fuel mainly composed of alcohol. However, in order to supply the fuel smoothly, the fuel supply path 5 is, for example, , SiO ₂ , Al ₂ O _3, etc. are preferably composed of a porous body, a polymer fiber, a polymer porous film, and the like obtained by sintering. When polymer fibers or polymer porous membranes are used, they need not be deformed even if they come into contact with fuel.

  In FIG. 2, it is desirable to arrange a member having a fuel cutoff function between the cells adjacent in the lateral direction in order to suppress the unreacted fuel from reaching the cathode 4 (a kind of crossover) (FIG. 2). Not shown). For example, the fuel can be blocked from reaching the cathode 4 by filling between adjacent cells with a polymer material typified by polyethylene and polypropylene, or an inorganic oxide thin film such as glass and aluminum oxide. it can.

  The cathode 4 in each cell group cell faces outward and faces the housing 1. A space is provided between the cathode 4 and the housing 1. In addition, the housing 1 is provided with a vent hole (not shown) that allows communication between the space and the outside. Therefore, air circulates in the space between the cathode 4 and the housing 1 by natural convection. As a result, oxygen (oxidant) is supplied to the cathode 4. When it is desired to control the supply of air to the cathode 4, forced convection means such as a fan may be attached to a predetermined part of the housing.

  Each material used in the fuel cell in FIG. 2 can be the same as in FIG.

  The fuel cell of the present invention is not limited to the above embodiment. For example, the embodiment shown in FIG. 1 and FIG. 2 is an example for explaining the present invention, and it is quite possible to use known methods other than those shown in the drawings for the arrangement, arrangement, connection, etc. of each cell. There is no.

  FIG. 3 shows a third embodiment of the fuel cell of the present invention. In this fuel cell, a membrane electrode assembly composed of an anode 3, a cathode 4 and an electrolyte membrane 2 similar to FIG. 1 is sandwiched between porous membranes constituting a fuel supply unit 5 and an oxidant supply unit 6. The cell is configured. Such a cell has a structure in which the upper and lower sides of the cell are sandwiched between bipolar plates 8 and 9 made of dense carbon and the like, and such a structure is stacked. In the configuration of FIG. 3, fuel supply holes penetrating the stack-structured cells are formed, and alcohol fuel is supplied to the fuel supply path 5 in each cell. On the other hand, an oxidant supply hole penetrating the stack-structured cell group is formed, and the oxidant is supplied to the oxidant supply path 6 in each cell. In order to uniformly diffuse the supplied fuel and oxidant along the fuel supply path 5 and the oxidant supply path 6 respectively, grooves are formed on the anode 3 and cathode 4 sides of the bipolar plates 8 and 9. (Not shown). In such a stack type fuel cell, a large number of cells can be connected in series, and as a result, a desired output voltage corresponding to the number of stacks of cells can be obtained.

  Embodiments of the electronic apparatus of the present invention will be described below. The electronic device of this embodiment has the fuel cell of the present invention. In the present embodiment, an information processing apparatus such as a portable personal computer will be described.

  FIG. 6 shows an image of mounting the power supply unit 51 on a personal computer. FIG. 7 is a block diagram schematically showing the configuration of the information processing apparatus of the present embodiment. 8 and 9 are a schematic diagram and a block schematic diagram of the power supply unit 51, respectively.

  As shown in FIG. 7, the information processing apparatus includes a CPU (Central Processing Unit) 52 that performs various operations and centrally controls each unit, a ROM (Read Only Memory) 53 that stores BIOS and the like, and operations of the CPU 52. A RAM (Random Access Memory) 54 serving as an area is connected by a bus 55. The bus 55 includes data from a storage device 59 such as a hard disk drive (HDD) 56, a display device 57 such as an LCD (Liquid Crystal Display), an input device 58 such as a keyboard and a mouse, and a CD and DVD. A data reading device 60 such as an optical disk device and a power supply unit 51 for supplying power are connected via various controllers (not shown).

  Various programs are stored in the storage medium 59. These programs are read by the data reading device 60 and installed in the HDD 56. As the storage medium 59, various types of media such as optical disks such as CD and DVD, magneto-optical disks, and flexible disks can be used. As the data reading device 60, an optical disk device, a magneto-optical disk device, an FDD, or the like is used according to the method of the storage medium 59. Various programs may be downloaded from a network (not shown) and installed in the HDD 56 instead of being read from the storage medium 59.

  FIG. 9 is a block diagram schematically showing the configuration of the power supply unit 51. The arrow indicates the flow of fuel or the like.

  As shown in FIG. 9, the power supply unit 51 includes a fuel cell 61, a liquid fuel cartridge 71 containing liquid fuel, a mixer 72 connected to the liquid fuel cartridge 71, and between the liquid fuel cartridge 71 and the mixer 72. A provided valve 73, a liquid fuel pump 74 for supplying liquid fuel to the fuel cell 61, a concentration sensor 75 for detecting the concentration of the liquid fuel, and a gas-liquid separator 76 for separating the fuel after power generation into gas and liquid. A heat exchanger 79 having a temperature sensor 77 and a cooling element 78, an air pump 80 for supplying air to the fuel cell 61, a moisture condenser 83 having a temperature sensor 81 and a cooling element 82, and a moisture condenser 83. Water tank 84 for storing water, a valve 85 provided between the water tank 84 and the mixer 72, a control circuit 86 for controlling each of these parts, and fuel Positive and negative electrodes of the pond 61 is formed from the connected DCDC converter 87 and the like. In addition, each part through which liquid fuel etc. pass is connected by flow paths, such as a tube.

  In such a power supply unit 51, the fuel that has passed through the mixer 72 is guided to the concentration sensor 75 via the liquid fuel pump 74. When the concentration of the liquid fuel detected by the concentration sensor 75 is lower than a predetermined concentration, the control circuit 86 opens the valve 73 of the liquid fuel cartridge 71. The liquid fuel is guided to the fuel cell 61. The liquid fuel after power generation is divided into a gas component (carbon dioxide gas) and a liquid component by the gas-liquid separator 76, and the liquid component is guided to the heat exchanger 79. When the liquid temperature detected by the temperature sensor 77 is lower than the predetermined temperature, the control circuit 86 does not cool the liquid by the cooling element 78, and when the liquid temperature is higher than the predetermined temperature, the control circuit 86 The liquid is cooled by the cooling element 78. The liquid fuel that has passed through the heat exchanger 79 is returned to the mixer 72 again. Such a flow functions as a fuel line.

Air from the air pump 80 is guided to the fuel cell 61. The gas-liquid mixed gas that has passed through the fuel cell 61 is guided to the moisture condenser 83. When the gas temperature detected by the temperature sensor 81 is lower than the predetermined temperature, the control circuit 86 does not cool the gas-liquid mixed gas by the cooling element 82, and when the gas temperature is higher than the predetermined temperature, the control circuit 86 performs control. The circuit 86 cools the gas-liquid mixed gas by the cooling element 82. The exhaust gas is discharged outside the power supply unit 51. Here, an exhaust port (not shown) for exhausting the exhaust gas is preferably provided at a position facing the outside of the information processing apparatus, although it varies depending on the mounting position of the power supply unit 51 with respect to the information processing apparatus. The water condensed by the water condenser 83 is returned to the mixer 72 via the water tank 84. Such a flow functions as an oxidant line (air line).

  In this way, the liquid fuel and air are supplied to the fuel cell 61, so that the fuel cell 61 generates power and applies predetermined power (electromotive force) to the DCDC converter 87. In this embodiment, the power storage element is not used. However, the present invention is not limited to this. For example, the power storage element may be provided inside or outside the power supply unit 61.

[Example 1]
The preparation procedure of the anode is shown below.

  Distilled water, 5 wt% Nafion solution (manufactured by DuPont) was added to Vulcan XC72R (manufactured by Cabot) of carbon black, and the mixture was stirred with an ultrasonic dispersion and a stirrer to prepare Nafion carbon ink.

  Distilled water and a 5 wt% Nafion solution were added to platinum-ruthenium-supported carbon (33 wt% platinum, 22 wt% ruthenium), and after ultrasonic dispersion, the first catalyst ink was prepared by stirring with a stirrer.

  Distilled water and a 5 wt% Nafion solution were added to platinum tin-supported carbon (33 wt% platinum, 7 wt% tin), and after ultrasonic dispersion, the second catalyst ink was prepared by stirring with a stirrer.

A conductive carbon layer was formed by applying Nafion carbon ink on a water-repellent treated carbon paper (manufactured by Toray Industries, Inc.) using an applicator. At this time, the dry coating amount of the conductive carbon layer was 0.5 mg / cm ² , and the weight ratio was 58% by weight of carbon and 42% by weight of Nafion. Next, the second catalyst layer is formed by spray-coating the second catalyst ink on the carbon paper on which the conductive carbon layer is formed so that the dry coating amount of platinum is 0.8 mg / cm ^2. did. Furthermore, the first catalyst layer was formed by spray coating the first catalyst ink so that the dry coating amount of platinum was 0.2 mg / cm ² . This is referred to as anode 1.

  The procedure for producing the cathode electrode is shown below.

  Teflon (registered trademark) carbon ink was prepared by adding ethanol and 58-62 wt% Teflon (registered trademark) emulsion (manufactured by DuPont) to carbon black and mixing with a homogenizer.

  Distilled water and a 5 wt% Nafion solution were added to platinum-supported carbon (platinum 50 wt%), and after ultrasonic dispersion, the catalyst ink was prepared by stirring with a stirrer.

On the carbon paper, Teflon (registered trademark) carbon ink was applied using an applicator and held at 360 ° C. for 15 minutes using an electric furnace to form a conductive carbon layer. Next, the catalyst layer was formed by spray-coating the catalyst ink on the carbon paper on which the conductive carbon layer was formed so that the dry coating amount of platinum was 1.0 mg / cm ² . This is referred to as a cathode 1.

  As the electrolyte membrane, Nafion (manufactured by DuPont) having a thickness of 180 μm was used.

A membrane electrode assembly was produced by performing hot pressing for 15 minutes at a pressure of 4.5 MPa and a temperature of 140 ° C. with the catalyst layer sides of the anode 1 and the cathode 1 being aligned with both surfaces of the electrolyte membrane. At this time, the first catalyst layer is present near the electrolyte membrane of the anode 1 and the second catalyst layer is present near the carbon paper.
[Example 2]
Similar to the anode preparation procedure of Example 1, a conductive carbon layer and a second catalyst layer were formed on water-repellent treated carbon paper. Next, the pressure during sputtering was 5.0 Pa, high frequency power of 200 W was applied to the platinum target, high frequency power of 460 W was applied to the ruthenium target, and sputtering was performed for 12 minutes, thereby forming the first catalyst layer. . At this time, the first catalyst layer was composed of 67% by weight of platinum and 33% by weight of ruthenium, and the supported weight of platinum was 0.2 mg / cm ² . Further, a 5 wt% Nafion solution was spray applied so that the dry application amount of Nafion was 1.0 mg / cm ² . This is referred to as anode 2.

  A membrane / electrode assembly was produced in the same manner as in Example 1 except that the anode 2 was used.

It is a figure which shows 1st Embodiment of the fuel cell of this invention. It is a figure which shows 2nd Embodiment of the fuel cell of this invention. It is a figure which shows 3rd Embodiment of the fuel cell of this invention. It is a figure which shows an example of the junction part of an anode and an electrolyte membrane. It is a figure which shows the other example of the junction part of an anode and an electrolyte membrane. It is a figure which shows embodiment of the electronic device of this invention. It is a block diagram which shows embodiment of the electronic device of this invention. It is a figure which shows the power supply part of FIG.6 and FIG.7. It is a block diagram which shows the power supply part of FIG.6 and FIG.7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a, 1b Case 2 Electrolyte membrane 3 Anode 3a Diffusion layer 4 Cathode 5 Fuel supply path 6 Oxidant supply path 7 Container 7a Small hole 8, 9 Bipolar plate 10 Carbon support body 11 First catalyst 12 Second catalyst 51 Power supply 52 CPU
53 ROM
54 RAM
55 bus 56 HDD
57 Display device 58 Input device 59 Recording medium 60 Data reader 61 Fuel cell 71 Liquid fuel cartridge 72 Mixer 73, 85 Valve 74 Liquid fuel pump 75 Concentration sensor 76 Gas-liquid separator 77, 81 Temperature sensor 78, 82 Cooling element 79 Heat exchanger 80 Air pump 83 Moisture condenser 84 Water tank 86 Control circuit 87 DCDC converter 88 Terminal

Claims (14)

In a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode and a cathode,
The anode has a catalyst layer in which two or more kinds of catalysts having different functions are laminated. The two or more types of catalysts are used for a first catalyst active in an oxidation reaction not involving dissociation of a carbon-carbon bond of an alcohol having 2 or more carbon atoms, and in a dissociation reaction of a carbon-carbon bond of a product of the oxidation reaction. Contains an active second catalyst,
Having a layer containing the first catalyst at the interface of the catalyst layer with the electrolyte membrane;
The membrane electrode assembly according to claim 1, further comprising a layer containing the second catalyst on a surface of the catalyst layer. In a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode and a cathode,
The anode has a catalyst layer in which two or more kinds of catalysts having different functions are mixed.   4. The membrane electrode assembly according to claim 3, wherein the composition ratio of the two or more types of catalysts continuously changes in the thickness direction of the catalyst layer. 5.   4. The membrane electrode assembly according to claim 3, wherein the composition ratio of the two or more types of catalysts changes stepwise in the thickness direction of the catalyst layer. 5. The two or more types of catalysts are used for a first catalyst active in an oxidation reaction not involving dissociation of a carbon-carbon bond of an alcohol having 2 or more carbon atoms, and in a dissociation reaction of a carbon-carbon bond of a product of the oxidation reaction. Contains an active second catalyst,
The ratio of the first catalyst to the two or more catalysts is higher on the electrolyte membrane side of the catalyst layer than on the surface side of the catalyst layer;
6. The membrane according to claim 4 or 5, wherein the ratio of the second catalyst to the two or more types of catalysts is higher on the surface side of the catalyst layer than on the electrolyte membrane side of the catalyst layer. Electrode assembly.   4. The membrane electrode assembly according to claim 3, wherein a composition ratio of the two or more kinds of catalysts continuously changes with respect to a surface direction of the catalyst layer. 5.   4. The membrane electrode assembly according to claim 3, wherein the composition ratio of the two or more types of catalysts changes stepwise with respect to the surface direction of the catalyst layer. 5. The two or more types of catalysts are used for a first catalyst active in an oxidation reaction not involving dissociation of a carbon-carbon bond of an alcohol having 2 or more carbon atoms, and in a dissociation reaction of a carbon-carbon bond of a product of the oxidation reaction. Contains an active second catalyst,
The ratio of the first catalyst to the two or more catalysts is higher on the side of the catalyst layer to which the alcohol is supplied than on the side of the catalyst layer to which the alcohol is discharged,
8. The ratio of the second catalyst to the two or more catalysts is higher on the side of the catalyst layer where the alcohol is discharged than on the side of the catalyst layer where the alcohol is supplied. Or the membrane electrode assembly of 8. The first catalyst may be one or more selected from the group consisting of simple substances and compounds belonging to the fourth, fifth and sixth periods of groups Ib, IVb, Vb, VIb, VIIb and VIIIb of the periodic table. Become
The second catalyst is selected from the group consisting of simple elements and compounds belonging to the third, fourth, fifth and sixth periods of groups IIIa, IVa, IVb, Vb, VIb and VIIIb of the periodic table. It consists of 1 or more types, The membrane electrode assembly as described in any one of Claim 2, 6, and 9 characterized by the above-mentioned.   A fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 10. A plurality of the membrane electrode assemblies,
12. The fuel cell according to claim 11, wherein the plurality of membrane electrode assemblies are arranged on at least one plane and are electrically connected in series. A plurality of the membrane electrode assemblies,
The fuel cell according to claim 11, wherein the plurality of membrane electrode assemblies are sequentially stacked via a bipolar plate.   An electronic apparatus comprising the fuel cell according to any one of claims 11 to 13.

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