JP2016225099A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell capable of suppressing an oxygen reduction reaction accompanied with by-production of hydrogen peroxide.SOLUTION: A fuel cell 1 comprises: a membrane electrode assembly 2 including an electrolyte membrane 7, an anode 8 that is formed on one face of the electrolyte membrane 7, and a cathode 9 that is formed on the other face of the electrolyte membrane 7; an anode-side separator 5 that is disposed at one side of the membrane electrode assembly 2; and a cathode-side separator 6 that is disposed at the other side of the membrane electrode assembly 2. Between the cathode 9 and the cathode-side separator 6, a porous body 4 that does not contain carbon is disposed so as to directly contact with the cathode 9.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell mounted on a vehicle or the like.

  Conventionally, fuel cells using gaseous fuel such as hydrogen gas or liquid fuel such as methanol, dimethyl ether or hydrazine are known as fuel cells mounted on vehicles.

  Such a fuel cell is configured as a stack structure in which a plurality of unit cells each including an electrolyte layer and an anode and a cathode stacked on both sides of the electrolyte layer are stacked.

  More specifically, for example, an electrolyte layer made of an anion exchange membrane, and a fuel side electrode and an oxygen side electrode that are arranged to face each other with the electrolyte layer interposed therebetween are provided. A fuel cell is proposed in which oxygen is supplied to the oxygen side electrode via an oxygen side flow path (see, for example, Patent Document 1).

JP 2010-225471 A

  However, in a fuel cell like Patent Document 1, an oxygen reduction reaction in which hydrogen peroxide is by-produced may occur in the oxygen reduction reaction at the oxygen side electrode. When the oxygen reduction reaction accompanied by the by-production of hydrogen peroxide occurs, the output of the fuel cell is reduced correspondingly.

  Therefore, an object of the present invention is to provide a fuel cell capable of suppressing an oxygen reduction reaction accompanied by hydrogen peroxide by-product.

The present invention
[1] A membrane electrode assembly having an electrolyte membrane, an anode formed on one surface of the electrolyte membrane, and a cathode formed on the other surface of the electrolyte membrane, and disposed on one side of the membrane electrode assembly An anode-side separator, a cathode-side separator disposed on the other side of the membrane electrode assembly, and a porous body disposed between the cathode and the cathode-side separator, wherein the porous body comprises carbon. A fuel cell that does not contain and is in direct contact with the cathode,
[2] In the above [1], the cathode contains a fired body of an Fe complex in which a ligand is coordinated to iron, and does not contain carbon other than carbon contained in the ligand. It is a fuel cell of description.

  According to the fuel cell of the present invention, the porous body not containing carbon is disposed between the cathode and the cathode-side separator so as to be in direct contact with the cathode.

  Therefore, it is possible to suppress the oxygen reduction reaction accompanied with the by-product of hydrogen peroxide.

  In addition, if the cathode contains a calcined Fe complex in which the ligand is coordinated to iron without containing carbon other than carbon contained in the ligand, an oxygen reduction reaction accompanied by hydrogen peroxide by-product Can be further suppressed.

FIG. 1 is a schematic configuration diagram showing an embodiment of a fuel cell of the present invention. FIG. 2 is an exploded perspective view of the fuel cell shown in FIG. FIG. 3 is a graph showing the relationship between the blending ratio of the oxygen reduction catalyst, the hydrogen peroxide generation amount, and the open circuit voltage in Examples 2 to 4.

1. Fuel Cell The fuel cell 1 is normally configured as a stack structure in which a plurality of fuel cells S are stacked. In FIG. 1, only one fuel cell S is shown for easy illustration.

  The fuel cell 1 is a direct liquid fuel type fuel cell to which a liquid fuel containing a fuel component and water is directly supplied, and is configured as an anion exchange type fuel cell.

  Examples of the fuel component include hydrogen-containing liquid fuels containing hydrogen atoms in the molecule, and specific examples include alcohols such as methanol, ethers having an alkyl group such as dimethyl ether, and hydrazines. Preferably, alcohols and hydrazines are used, and more preferably, hydrazines are used.

  In addition, for example, an alkali metal hydroxide such as potassium hydroxide is added to the liquid fuel at an appropriate ratio.

  As shown in FIGS. 1 and 2, the fuel cell S includes a membrane electrode assembly 2, a fuel diffusion sheet 3, a porous body 4, an anode side separator 5, and a cathode side separator 6.

  The membrane electrode assembly 2 includes an electrolyte membrane 7, an anode 8, and a cathode 9.

  The electrolyte membrane 7 is formed of an anion exchange type solid polymer electrolyte membrane.

  The anode 8 is laminated as a thin layer on the surface of one side in the thickness direction of the electrolyte membrane 7. The anode 8 contains, for example, a catalyst carrier that supports a fuel oxidation catalyst. The anode 8 can also be formed directly from the fuel oxidation catalyst without using a catalyst carrier.

  The fuel oxidation catalyst is not particularly limited, and examples thereof include platinum group elements (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt)), and iron group. Periodic table 8-10 (VIII) group elements such as elements (iron (Fe), cobalt (Co), nickel (Ni)), for example, copper (Cu), silver (Ag), gold (Au), etc. Examples include Group 11 (IB) elements of the periodic table. Among these, Preferably, nickel, cobalt, and platinum are mentioned, More preferably, nickel is mentioned. These may be used alone or in combination of two or more.

  Examples of the catalyst carrier used for the anode 8 include carbon particles.

  In order to form the anode 8, for example, an ink obtained by dispersing a fuel oxidation catalyst in a solvent together with a binder is applied to one surface in the thickness direction of the electrolyte membrane 7 and dried. When the anode 8 is directly formed on one surface in the thickness direction of the electrolyte membrane 7 as described above, the binder is selected in consideration of the affinity with the electrolyte membrane 7. For example, when the electrolyte membrane 7 is an anion exchange type solid polymer electrolyte membrane, an anion exchange resin can be used as a binder.

In the anode 8, the loading amount of the fuel oxidation catalyst is, for example, 0.05 mg / cm ² or more, preferably 0.1 mg / cm ² or more, for example, 10 mg / cm ² or less, preferably 5 mg / cm ^2. It is as follows.

  The cathode 9 is laminated as a thin layer on the opposite side of the anode 8 with respect to the electrolyte membrane 7, that is, on the other surface in the thickness direction of the electrolyte membrane 7. The cathode 9 contains an oxygen reduction catalyst.

  Examples of the oxygen reduction catalyst include a material in which a transition metal is supported on a composite composed of a conductive polymer and carbon (hereinafter, this composite is referred to as “carbon composite”).

  Examples of the transition metal include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu ), Yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), lanthanum (La) ), Hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and the like. These transition metals can be used alone or in combination of two or more.

  Examples of the conductive polymer include polyaniline, polypyrrole, polythiophene, polyacetylene, polyvinylcarbazole, polytriphenylamine, polypyridine, polypyrimidine, polyquinoxaline, polyphenylquinoxaline, polyisothianaphthene, polypyridinediyl, polythienylene, polyparaylene. Examples include phenylene, polyflurane, polyacene, polyfuran, polyazulene, polyindole, and polydiaminoanthraquinone. These conductive polymers can be used alone or in combination of two or more.

  Moreover, as an oxygen reduction catalyst, the sintered body of the transition metal complex which the ligand coordinated to the above-mentioned transition metal is mentioned, for example.

  The transition metal is preferably iron. That is, the oxygen reduction catalyst is preferably a fired body of an Fe complex in which a ligand is coordinated to iron. The oxygen reduction catalyst can be contained in the cathode 9 in a state of being supported on a catalyst carrier not containing carbon, for example.

  Examples of the ligand that coordinates to the transition metal include phenanthroline (eg, 1,10-phenanthroline), sarcomin, nicarbazine, pyrrole, porphyrin, tetramethoxyphenylporphyrin, dibenzotetraazaannulene, phthalocyanine, choline, chlorin, or And derivatives thereof.

  Preferable examples of the ligand include phenanthroline, salcomine, nicarbazine, and derivatives thereof, and more preferable examples include phenanthroline and nicarbazine.

  The cathode 9 preferably contains an oxygen reduction catalyst made of a fired body of an Fe complex in which a ligand is coordinated to iron, and does not contain carbon other than carbon originating from the ligand.

  Specific examples of carbons other than carbon derived from the ligand that are not contained in the cathode 9 include carbon blacks such as oil furnace black, acetylene black, ketjen black, and channel black, such as graphite and carbon fiber. Can be mentioned.

  The cathode 9 can be formed, for example, in the same manner as the formation of the anode 8 described above.

  The cathode 9 can also be formed on the electrolyte membrane 7 through a resin sheet such as a fluororesin. Specifically, for example, an ink obtained by dispersing an oxygen reduction catalyst in a solvent together with a binder is applied to one side in the thickness direction of a resin sheet, dried and heat-treated to produce a sheet with a catalyst layer, and the obtained catalyst The layered sheet is pressure-bonded to the surface of the electrolyte membrane 7. In this case, the binder is selected in consideration of the affinity with the resin sheet. For example, when the resin sheet is made of a fluororesin, a fluororesin such as polytetrafluoroethylene or a tetrafluoroethylene / hexafluoropropylene copolymer can be used as a binder.

In the cathode 9, the supported amount of the oxygen reduction catalyst is, for example, 0.05 mg / cm ² or more, preferably 0.1 mg / cm ² or more, for example, 10 mg / cm ² or less, preferably 5 mg / cm ^2. It is as follows.

  The fuel diffusion sheet 3 is laminated on one side in the thickness direction of the membrane electrode assembly 2 so as to contact one side in the thickness direction of the anode 8. The fuel diffusion sheet 3 has pores for allowing liquid fuel to pass therethrough.

  Examples of the material for the fuel diffusion sheet 3 include carbon paper, carbon cloth, carbon fiber nonwoven fabric, and preferably carbon cloth. Further, the fuel diffusion sheet 3 may be treated with fluorine as necessary.

  The porous body 4 is laminated on the other side in the thickness direction of the membrane electrode assembly 2 so as to be in contact with the other side in the thickness direction of the cathode 9.

  The porous body 4 is made of a metal (including pure metals and alloys) having rigidity and corrosion resistance, such as nickel (Ni) and stainless steel (SUS310). Examples of the form of the porous body include a net and a punching metal. The porous body 4 does not contain carbon.

  The thickness of the porous body 4 is, for example, 0.5 mm or more, preferably 0.75 mm or more, for example, 1.0 mm or less.

  The hole diameter of the holes of the porous body 4 (when the porous body 4 is a net, it is a mesh, and when it is a punching metal, it is a punch hole) is, for example, 0.1 mm or more, preferably 0. .3 mm or more, for example, 1 mm or less, preferably 0.5 mm or less.

The opening area per unit area of the porous body 4 (1 cm ^2), for example, 0.5 cm ² or more, or preferably, 0.7 cm ² or more, for example, 0.9 cm ² or less, preferably, 0. 8 cm ² or less.

  The anode-side separator 5 is disposed opposite to one side in the thickness direction of the membrane electrode assembly 2 so as to contact one side in the thickness direction of the fuel diffusion sheet 3. The anode-side separator 5 is made of a gas impermeable conductive material. The anode side separator 5 has a fuel flow path 10.

  The fuel flow path 10 is formed on the other surface in the thickness direction of the anode-side separator 5. The fuel flow path 10 is a concave groove that is recessed from the other surface in the thickness direction of the anode-side separator 5 to one side in the thickness direction, and is formed in a folded shape that extends in the vertical direction while being folded back in the width direction. The fuel flow path 10 faces the fuel diffusion sheet 3. That is, the fuel diffusion sheet 3 is interposed between the fuel flow path 10 and the anode 8.

  The cathode-side separator 6 is disposed opposite to the other side in the thickness direction of the membrane electrode assembly 2 so as to contact the other side in the thickness direction of the porous body 4. The cathode side separator 6 is made of a gas impermeable conductive material. The cathode side separator 6 has a recess 11.

  The recess 11 is formed in the central portion of one surface in the thickness direction of the cathode separator 6. The recess 11 is recessed from one surface in the thickness direction of the cathode-side separator 6 to the other in the thickness direction, and is formed in a substantially rectangular shape when viewed from the thickness direction.

  The recess 11 has a size that can accommodate the porous body 4, that is, substantially the same size as the porous body 4, and is formed in a substantially rectangular shape when viewed from the thickness direction. A porous body 4 is accommodated in the recess 11.

When the fuel cell S is configured as a stack structure, a concave portion 11 facing the cathode 9 of the adjacent membrane electrode assembly 2 is formed on one surface in the thickness direction of the anode separator 5. Is done. Further, a fuel flow path 10 facing the anode 8 of the adjacent membrane electrode assembly 2 is formed on the other surface in the thickness direction of the cathode side separator 6.
2. Next, power generation in the fuel cell 1 will be described.

  As shown in FIG. 1, when liquid fuel is supplied to the fuel flow path 10 of the fuel cell 1, the liquid fuel supplied to the fuel flow path 10 passes through the fuel flow path 10 while contacting the fuel diffusion sheet 3. Flow from bottom to top. At this time, the liquid fuel flowing in the fuel flow path 10 passes through the pores of the fuel diffusion sheet 3 and is supplied to the anode 8.

  A part of the liquid fuel supplied to the anode 8 permeates the electrolyte membrane 7 and leaks to the cathode 9 (cross leak). Thereby, water contained in the liquid fuel is supplied to the cathode 9.

  Air from the outside is supplied to the recess 11 of the fuel cell 1.

  The air supplied to the recess 11 flows in the recess 11 from the upper side to the lower side. At this time, the air flowing in the recess 11 passes through the hole of the porous body 4 and is supplied to the cathode 9.

Thereby, in the fuel cell 1, when the fuel component is hydrazine, an electrochemical reaction represented by the following reaction formulas (1) to (3) occurs, and power generation is performed.
(1) N ₂ H ₄ + 4OH ⁻ → N ₂ + 4H ₂ O + 4e ⁻ (reaction at anode 8)
(2) O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (reaction at cathode 9)
(3) N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O (reaction in the entire fuel cell 1)
Further, when the fuel component is methanol, an electrochemical reaction represented by the following reaction formulas (4) to (6) occurs, and power generation is performed.
(4) CH ₃ OH + 6OH ⁻ → CO ₂ + 5H ₂ O + 6e ⁻ (reaction at anode 8)
(5) O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (reaction at cathode 9)
(6) CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O (reaction in the entire fuel cell 1)
By these reactions, fuel components (N ₂ H ₄ or CH ₃ OH) are consumed, and water (H ₂ O) and gas (N ₂ or CO ₂ ) are generated, and electromotive force (e ⁻ ) is generated. To do.
3. In the power generation described above, in the cathode 9, as shown in the following (7), an oxygen reduction reaction accompanied with the generation of hydrogen peroxide is performed as a side reaction in addition to the oxygen reduction reactions shown in (2) and (5) above. May happen.
_{(7) O 2 + H 2} O + 2e - → HO 2 - + OH - ( secondary reaction at the cathode 9)
Here, the side reaction shown in the above (7) tends to be selectively promoted by carbon.

  In addition, when the liquid fuel contains an alkaline electrolyte such as potassium hydroxide, the liquid fuel is caused to cross-leak by the porous layer of the cathode 9 or the air diffusion sheet (air diffusion between the cathode 9 and the cathode-side separator 6). When the sheet is leaked), the side reaction shown in the above (7) tends to be further promoted.

  Therefore, if carbon is present around the cathode 9, the side reaction shown in the above (7) is promoted, and the oxygen reduction reaction shown in the above (2) and (5) is suppressed accordingly. The output of the fuel cell 1 decreases.

  However, according to the fuel cell 1 of the present invention, the porous body 4 containing no carbon is disposed between the cathode 9 and the cathode-side separator 6 so as to be in direct contact with the cathode 9.

  Therefore, the oxygen reduction reaction (shown in the above (7)) accompanied by hydrogen peroxide by-product can be suppressed.

  Further, when the cathode 9 does not contain carbon other than carbon contained in the ligand and contains a fired body of an Fe complex in which the ligand is coordinated to iron, an oxygen reduction reaction accompanied by by-production of hydrogen peroxide. (Shown in (7) above) can be further suppressed.

  As a result, a decrease in the output of the fuel cell 1 can be suppressed.

  In the above-described embodiment, hydrogen gas can be used instead of the liquid fuel.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example. “Part” and “%” are based on mass unless otherwise specified. In addition, specific numerical values such as a blending ratio (content ratio), physical property values, and parameters used in the following description are described in the above-mentioned “Mode for Carrying Out the Invention”, and a blending ratio corresponding to them ( Substituting the upper limit value (numerical value defined as “less than” or “less than”) or the lower limit value (number defined as “greater than” or “exceeded”) such as content ratio), physical property values, parameters, etc. be able to.
1. Examples and Comparative Examples Example 1
(1) Production of membrane electrode assembly (1-1) Formation of anode 0.15 g of Ni-supported carbon catalyst (manufactured by Cataler) and solvent (mixture of tetrahydrofuran and 1-propyl alcohol in a mass ratio of 1: 1) 1.5 g was dispersed by sonication at 25 ° C. for 10 minutes.

  Next, 1.0 g of a 2 mass% anion exchange resin solution (solvent: a mixture of tetrahydrofuran and 1-propyl alcohol at a mass ratio of 1: 1) was added to the obtained mixture.

  Subsequently, the ink for anodes was prepared by disperse | distributing with an ultrasonic wave at 25 degreeC for 3 minute (s).

  The obtained anode ink was applied by a spray method so as to cover one surface of the anion exchange membrane (electrolyte membrane).

  Then, the anode was formed by drying at 25 degreeC.

The amount of catalyst supported on the anode was 2.6 mg / cm ² .
(1-2) Formation of cathode Platinum catalyst (AY1020, manufactured by Tanaka Kikinzoku Co., Ltd.), water 1.2 g, 1-propyl alcohol 1.1 g, 40 mass% PTFE (polytetrafluoroethylene) solution 0.12 g, and 40 0.12 g of a mass% FEP (tetrafluoroethylene / hexafluoropropylene copolymer) solution was dispersed at 25 ° C. for 5 minutes by ultrasonic treatment.

  Thereafter, the mixture was further stirred with a stirrer for 60 minutes to prepare a cathode ink.

  The obtained cathode ink was applied on a fluororesin sheet, dried at 35 ° C. for 30 minutes, and then heat treated at 260 ° C. for 30 minutes to form a sheet with a catalyst layer.

The amount of catalyst supported on the sheet with the catalyst layer was 2.0 mg / cm ² .

Thereafter, the obtained sheet with the catalyst layer was cut out and pressure-bonded to the other surface of the anion exchange membrane (the surface opposite to the surface on which the anode was formed) at 100 ° C. and 25 MPa to form a cathode.
(2) Assembly of fuel cell A carbon sheet (fuel diffusion sheet) is joined to the anode of the membrane electrode assembly in which the anode and cathode are formed by the method of (1) above, and the cathode is made of nickel (Ni). A porous separator (porous body) was joined.

  A fuel cell was assembled by attaching a sealing material to the obtained joined body and sandwiching it between an anode side separator and a cathode side separator.

Example 2
(1) Production of membrane electrode assembly (1-1) Formation of anode An anode was formed on one surface of the anion exchange membrane in the same manner as in Example 1.
(1-2) Formation of Cathode Fe Nicarbazin-based catalyst (NPC-2000, manufactured by Pajarito) 0.05 g and 1.5 g of a solvent (a mixture of tetrahydrofuran and 1-propyl alcohol at a mass ratio of 1: 1). Dispersion was carried out at 25 ° C. for 10 minutes by ultrasonic treatment.

  To the obtained mixture, 1.0 g of a 2% by mass anion exchange resin solution (solvent: a mixture of tetrahydrofuran and 1-propyl alcohol at a mass ratio of 1: 1) was added.

  Then, an ink for a cathode was prepared by dispersing with ultrasonic waves at 25 ° C. for 3 minutes.

  The obtained cathode ink was applied by spraying so as to cover the other side of the anion exchange membrane (the surface opposite to the surface on which the anode is formed).

  Then, the cathode was formed by drying at 25 degreeC.

The amount of catalyst supported on the cathode was 1.0 mg / cm ² .
(2) Assembly of fuel cell A fuel cell was assembled in the same manner as in Example 1.

Example 3
In the same manner as in Example 2, except that the cathode ink in which 0.03 g of Fe nicarbazine catalyst and 0.02 g of Ketjen Black were used was used instead of 0.05 g of Fe nicarbazine catalyst, a fuel cell unit Got.

Example 4
A fuel cell was obtained in the same manner as in Example 2 except that the cathode ink in which 0.05 g of ketjen black was dispersed was used instead of 0.05 g of the Fe nicarbazine-based catalyst.

Comparative Example 1
Instead of the porous separator, a fuel cell was obtained in the same manner as in Example 1 except that a carbon sheet was joined as in the anode and a cathode separator having the same flow path shape as that of the anode separator was used. It was.
2. Performance Test (1) Measurement of Open Circuit Voltage For the fuel cells obtained in each Example and each Comparative Example, the open circuit voltage was measured with an electronic load (manufactured by Scribner).

At the time of measurement, a hydrated hydrazine 1 mol / dm ³ · 1N potassium hydroxide aqueous solution was supplied to the anode at a rate of 1.2 mL / min, and saturated humidified air at 25 ° C. was supplied to the cathode at a rate of 0.1 L / min. Feeded at speed. The cell operating temperature of the fuel cell was 60 ° C.

  The open circuit voltage of Example 1 was 0.9V. Moreover, the open circuit voltage of the comparative example 1 was 0.8V.

  When Example 1 and Comparative Example 1 are compared, the open circuit voltage can be improved from 0.8 V to 0.9 V by using a porous separator made of nickel (Ni) instead of the carbon sheet on the cathode side. Recognize.

Moreover, the open circuit voltage of Examples 2-4 is shown in FIG.
(2) Measurement of hydrogen peroxide generation The waste liquid on the cathode side when measuring the open circuit voltage was collected, and the amount of hydrogen peroxide generation in the waste liquid was measured with a hydrogen peroxide test paper (manufactured by Hishoe Chemical Co., Ltd.). . The amount of hydrogen peroxide generated in Examples 2 to 4 is shown in FIG.

  As shown in FIG. 3, when Example 2 is compared with Examples 3 and 4, the blending ratio of the Fe nicarbazine-based catalyst with respect to the total amount of the Fe nicarbazine-based catalyst and Ketjen black increases (the blending of Ketjen black). It can be seen that as the ratio decreases, the amount of hydrogen peroxide generated decreases and the open circuit voltage increases.

  From this tendency, it can be considered that when the blending ratio of ketjen black is reduced, the oxygen reduction reaction accompanied by the generation of hydrogen peroxide is suppressed, and the battery performance is improved.

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Membrane electrode assembly 4 Porous body 5 Anode side separator 6 Cathode side separator 7 Electrolyte membrane 8 Anode 9 Cathode

Claims (2)

A membrane electrode assembly having an electrolyte membrane, an anode formed on one surface of the electrolyte membrane, and a cathode formed on the other surface of the electrolyte membrane;
An anode separator disposed on one side of the membrane electrode assembly;
A cathode separator disposed on the other side of the membrane electrode assembly;
A porous body disposed between the cathode and the cathode separator,
The fuel cell according to claim 1, wherein the porous body does not contain carbon and directly contacts the cathode.   2. The fuel cell according to claim 1, wherein the cathode contains a fired body of an Fe complex in which a ligand is coordinated with iron, and does not contain carbon other than carbon contained in the ligand. .

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