JP7341680B2 - membrane electrode assembly - Google Patents

Description

The present invention relates to a membrane electrode assembly, and more particularly to a membrane electrode assembly provided in a fuel cell.

Conventionally, a membrane electrode assembly provided in a fuel cell consists of an electrolyte membrane, a fuel side electrode (anode) connected to one side of the electrolyte membrane, and an air side electrode (cathode) connected to the other side of the electrolyte membrane. ) is known.

It is known that the electrolyte membrane of such a membrane electrode assembly is deteriorated by radicals generated during power generation by the fuel cell.

On the other hand, from the viewpoint of improving the durability of the electrolyte membrane, it has been proposed to incorporate a phenanthroline compound into the electrolyte membrane that transfers protons (see, for example, Patent Document 1).

Since such a phenanthroline compound decomposes radicals, the durability of the electrolyte membrane is improved.

Special table 2017-518602 publication

On the other hand, there is a need to improve the durability of electrolyte membranes that transport anion components (specifically, hydroxide ions).

Furthermore, in a fuel cell equipped with such an electrolyte membrane, the inside of the fuel cell becomes alkaline due to the movement of hydroxide ions, so the electrolyte membrane is also required to have durability against alkali.

When a phenanthroline compound is added to such an electrolyte membrane, radicals can be decomposed, but the durability against alkali is low and the electrolyte membrane deteriorates.

An object of the present invention is to provide a membrane electrode assembly including an electrolyte membrane that has excellent radical resistance and alkali resistance when the electrolyte membrane transfers anion components.

The present invention [1] provides an electrolyte membrane capable of moving an anion component, a fuel-side electrode to which a fuel component is supplied, which are arranged opposite to each other with the electrolyte membrane in between, and an oxygen-side electrode to which oxygen is supplied. A membrane electrode assembly, wherein the electrolyte membrane includes a porphyrin complex.

The membrane electrode assembly of the present invention includes an electrolyte membrane capable of moving an anion component, and the electrolyte membrane includes a porphyrin complex.

This results in excellent radical resistance and alkali resistance.

FIG. 1 is a schematic diagram showing one embodiment of a fuel cell in which the membrane electrode assembly of the present invention is used. FIG. 2 is a graph showing the results of evaluation of radical resistance.

1. Fuel Cell A fuel cell 1 is equipped with a membrane electrode assembly 2 as an embodiment of the present invention.

In FIG. 1, this fuel cell 1 includes a fuel cell S, and the fuel cell S includes a fuel side electrode 2, an oxygen side electrode 3, and an electrolyte layer 4. are placed facing each other with the electrolyte layer 4 sandwiched between them. In other words, the fuel cell S includes an electrolyte layer 4, and a fuel-side electrode 2 and an oxygen-side electrode 3 that are arranged to face each other with the electrolyte layer 4 in between.

The fuel-side electrode 2 is in opposing contact with one surface of the electrolyte layer 4 . The fuel side electrode 2 is formed of an electrode material such as a catalyst carrier supporting a catalyst, for example. Alternatively, catalyst particles may be used as the electrode material without using a catalyst carrier, and the catalyst particles may be directly formed as the fuel side electrode 2.

The catalyst is not particularly limited, and includes, for example, platinum group elements (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt)), iron group elements ( Group 8 to 10 (VIII) elements of the periodic table (according to IUPAC Periodic Table of the Elements (version date 22 June 2007); the same applies hereinafter) such as iron (Fe), cobalt (Co), nickel (Ni), Examples include elements of group 11 (IB) of the periodic table such as copper (Cu), silver (Ag), and gold (Au), metals such as zinc (Zn), and alloys thereof. Moreover, these can be used alone or in combination of two or more.

Examples of the catalyst carrier include porous materials such as carbon.

When the catalyst is supported on a catalyst carrier, the supporting ratio of the catalyst carrier is, for example, 20% by mass or more, preferably 40% by mass or more, and, for example, 80% by mass or more, based on the total amount of the catalyst and the catalyst carrier. % or less, preferably 60% by mass or less.

The thickness of the fuel side electrode 2 is, for example, 10 μm or more, preferably 20 μm or more, and is, for example, 200 μm or less, preferably 100 μm or less.

In addition, in order to form the fuel side electrode 2, there is no particular restriction, but for example, first, the above catalyst and an ion exchange resin (preferably an anion exchange resin) are mixed, and if necessary, an appropriate solvent such as alcohol or ether is mixed. A dispersion liquid (fuel side electrode ink) of the above catalyst is prepared by adding and adjusting the viscosity. Next, the dispersion liquid is applied to the surface of one side in the thickness direction of the electrolyte layer 4 (hereinafter simply referred to as one side) and dried. Thereby, the fuel side electrode 2 can be formed on one side of the electrolyte layer 4.

Further, in the fuel side electrode 2, the amount of catalyst supported is, for example, 0.05 mg/cm ² or more, preferably 0.1 mg/cm ² or more, and, for example, 10 mg/cm ² or less, preferably 5 mg/cm 2 or more. ^cm2 or less.

The oxygen side electrode 3 is in opposing contact with the other surface of the electrolyte layer 4. This oxygen-side electrode 3 is formed, for example, as a porous electrode on which a metal catalyst (including a fired product of a metal catalyst) is supported, although it is not particularly limited.

The metal catalyst contains a first transition metal, and is formed by, for example, forming a complex between the first transition metal and a complex-forming organic compound, or, for example, the first transition metal is conductive. It is formed by being supported on a carrier made of a polymer.

Examples of the first transition metal include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and 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 can be used alone or in combination of two or more, and alloys of these can also be used.

The complex-forming organic compound is an organic compound that forms a complex with a metal atom by coordinating with the metal atom, and includes, for example, pyrrole, porphyrin, tetramethoxyphenylporphyrin, dibenzotetraazaannulene, phthalocyanine, choline, and chlorin. , phenanthroline, sarcomine, nicarbazin, aminoantipyrine (AAPYr), or polymers thereof. Moreover, these can be used alone or in combination of two or more.

Examples of conductive polymers include compounds that overlap with the above-mentioned complex-forming organic compounds, such as polyaniline, polypyrrole, polythiophene, polyacetylene, polyvinylcarbazole, polytriphenylamine, polypyridine, polypyrimidine, polyquinoxaline, and polyphenylquinoxaline. , polyisothianaphthene, polypyridinediyl, polythienylene, polyparaphenylene, polyflurane, polyacene, polyfuran, polyazulene, polyindole, polydiaminoanthraquinone, and the like. These can be used alone or in combination of two or more.

There are no particular restrictions on forming the metal catalyst, and any known method can be used.

The thickness of the oxygen side electrode 3 is, for example, 10 μm or more, preferably 20 μm or more, and is, for example, 300 μm or less, preferably 150 μm or less.

In order to form the oxygen-side electrode 3 from such a metal catalyst, there is no particular restriction, but in the same manner as the fuel-side electrode 2 described above, for example, first, the metal catalyst and an ion exchange resin (preferably an anion exchange resin) are formed. ) and, if necessary, add an appropriate solvent such as alcohol or ether to adjust the viscosity, thereby preparing a dispersion liquid (oxygen side electrode ink) of the metal catalyst. Next, the dispersion is applied to the other surface of the electrolyte layer 4 in the thickness direction (hereinafter simply referred to as the other surface) and dried. Thereby, the oxygen side electrode 3 can be formed on the other surface of the electrolyte layer 4.

Further, in the oxygen side electrode 3, the amount of metal catalyst supported is, for example, 0.05 mg/cm ² or more, preferably 0.1 mg/cm ² or more, and, for example, 10 mg/cm ² or less, preferably 5 mg. / ^cm2 or less.

Electrolyte layer 4 includes an organic electrolyte and a porphyrin complex.

Examples of the organic electrolyte include ion exchange resins.

A porphyrin complex is a complex in which a porphyrin ring-containing compound is coordinated with a second transition metal.

Examples of the second transition metal include those similar to the first transition metal described above, and preferably manganese (Mn) and platinum (Pt).

These second transition metals can be used alone or in combination of two or more.

A porphyrin ring-containing compound is a compound containing a porphyrin ring (a ring in which four pyrrole rings are bonded at α-positions through four methine groups (-CH=)) in its molecular skeleton.

Such a porphyrin ring-containing compound serves as a ligand in which, for example, the nitrogen atom contained in the porphyrin ring coordinates to the second transition metal in the porphyrin complex.

Porphyrin ring-containing compounds are not particularly limited, but include, for example, porphyrin (unsubstituted product, also known as porphine), tetramethylporphyrin, tetraethylporphyrin, tetraphenylporphyrin, tetraphenoxyporphyrin, tetramethoxyphenylporphyrin (for example, tetrakis (p -methoxyphenyl)porphyrin, etc.), octaethylporphyrin, etc., and preferred are tetraphenylporphyrin and octaethylporphyrin.

These porphyrin ring-containing compounds can be used alone or in combination of two or more.

There are no particular limitations on the production of the porphyrin complex, and known methods can be employed.

For example, salts of second transition metals (e.g., inorganic salts such as sulfates, nitrates, chlorides, phosphates, etc., organic acid salts such as acetates, oxalates, etc.) and porphyrin ring-containing compounds are used. For example, a porphyrin complex can be produced by mixing in a known solvent such as water, alcohol, aliphatic hydrocarbon, aromatic hydrocarbon, halogenated hydrocarbon, or nitrile.

Moreover, in order to form the electrolyte layer 4, the above-mentioned porphyrin complex is blended with an organic electrolyte, although there is no particular restriction.

In order to blend the above-mentioned porphyrin complex into an organic electrolyte, first, the organic electrolyte is blended into a solvent (dimethylacetamide, ethanol, etc.) to prepare an electrolyte solution.

Next, the above porphyrin complex is added to the obtained electrolyte solution to prepare a mixed solution.

The blending ratio of the porphyrin complex is, for example, 0.1 parts by mass or more and, for example, 2 parts by mass or less with respect to 100 parts by mass of the organic electrolyte.

Then, the obtained mixed solution is poured into a predetermined mold and held at, for example, 30° C. or higher and 60° C. or lower for 12 hours or more and 48 hours or less, thereby forming the electrolyte layer 4.

Note that this porphyrin complex was not calcined. In other words, this porphyrin complex is a non-calcined product.

The thickness of the electrolyte layer 4 is, for example, 5 μm or more, preferably 10 μm or more, and, for example, 50 μm or less, preferably 35 μm or less.

The fuel cell S further includes a fuel supply member 5 and an oxygen supply member 6. The fuel supply member 5 is made of a gas-impermeable, electrically conductive member, and one surface thereof is in opposing contact with the fuel-side electrode 2 . In this fuel supply member 5, a fuel-side flow path 7 for bringing the liquid fuel into contact with the entire fuel-side electrode 2 is formed as a meander-shaped groove recessed from one surface. In addition, this fuel side flow path 7 has a supply port 9 and a discharge port 8 that extend through the fuel supply member 5 continuously formed at the upstream end and the downstream end, respectively.

Further, like the fuel supply member 5, the oxygen supply member 6 is also made of a gas-impermeable conductive member, and one surface thereof is in opposing contact with the oxygen side electrode 3. Also in this oxygen supply member 6, an oxygen side flow path 10 for bringing oxygen (air) into contact with the entire oxygen side electrode 3 is formed as a meander-shaped groove recessed from one surface. Note that this oxygen side flow path 10 also has a supply port 11 and a discharge port 12 that penetrate the oxygen supply member 6 and are continuously formed at the upstream end and the downstream end, respectively.

Although not shown, in the fuel cell 1, a known gas diffusion method may be used between the fuel supply member 5 and the fuel side electrode 2, and between the oxygen supply member 6 and the oxygen side electrode 3, as necessary. Layers can be stacked.

The fuel cell 1 is actually formed as a stack structure in which a plurality of the fuel cells S described above are stacked. Therefore, the fuel supply member 5 and the oxygen supply member 6 are actually configured as a separator in which the fuel side flow path 7 and the oxygen side flow path 10 are formed on both sides.

Although not shown, the fuel cell 1 is equipped with a current collector plate made of a conductive material, and the electromotive force generated in the fuel cell 1 is taken out from a terminal provided on the current collector plate. It is configured so that it can be done.

In addition, on a trial basis (model), the fuel supply member 5 and the oxygen supply member 6 of this fuel cell S are connected by an external circuit 13, and a voltmeter 14 is interposed in the external circuit 13. It can also measure voltage.

In the present invention, the fuel component is directly supplied without going through reforming or the like.

Examples of fuel components include gaseous fuels such as hydrogen, liquid fuels such as hydrazine to which potassium hydroxide is added, and the like.

When the fuel component is hydrogen, the above fuel component is supplied to the fuel side flow path 7 of the fuel supply member 5 while supplying oxygen (air) to the oxygen side flow path 10 of the oxygen supply member 6. For example, at the oxygen side electrode 3, as described below, electrons (e ^- ) generated at the fuel side electrode 2 and transferred via the external circuit 13, water (H ₂ O), and oxygen (O ₂ ) to generate hydroxide ions (OH ⁻ ). The generated hydroxide ions (OH ^- ) move through the electrolyte layer 4 from the oxygen side electrode 3 to the fuel side electrode 2 . At the fuel-side electrode 2, the hydroxide ions (OH ^- ) that have passed through the electrolyte layer 4 react with the liquid component to generate electrons (e ^- ). The generated electrons (e ⁻ ) are transferred from the fuel supply member 5 to the oxygen supply member 6 via the external circuit 13 and supplied to the oxygen side electrode 3. Due to such an electrochemical reaction at the fuel side electrode 2 and the oxygen side electrode 3, an electromotive force is generated and power generation is performed.

Such an electrochemical reaction can be expressed by the following reaction formulas (1) to (3) for the fuel side electrode 2, the oxygen side electrode 3, and the whole.
(1) H ₂ +2OH ⁻ →2H ₂ O+2e ⁻ (fuel side electrode)
(2) 1/2O ₂ +H ₂ O+2e ^- →2OH ^- (oxygen side electrode)
(3) H ₂ + 1/2O ₂ →H ₂ O (total)
On the other hand, when the fuel cell 1 is used for a long period of time, hydrogen peroxide (H ₂ O ₂ ) may be generated as a byproduct, as shown in reaction formula (4).
(4) O ₂ +2H ⁺ →H ₂ O ₂
Then, this hydrogen peroxide is decomposed and OH radicals are generated inside the fuel cell 1. Then, this OH radical reacts with the ion exchange group of the organic electrolyte in the electrolyte layer 4, causing the electrolyte layer 4 to deteriorate.

On the other hand, in the above-mentioned fuel cell 1, the electrolyte layer 4 contains a porphyrin complex, so that OH radicals can be decomposed, and the electrolyte layer 4 has excellent radical resistance. As a result, deterioration of the electrolyte layer 4 can be suppressed.

Further, in this fuel cell 1, the inside of the fuel cell 1 becomes alkaline due to the movement of hydroxide ions.

In contrast, in the fuel cell 1 described above, the electrolyte layer 4 contains a porphyrin complex, and therefore has high durability against alkali. As a result, deterioration of the electrolyte layer 4 can be suppressed.

In other words, since the electrolyte layer 4 contains the porphyrin complex, it has excellent radical resistance, and the electrolyte layer 4 has high durability against alkalis. As a result, when the electrolyte membrane 4 moves anion components, it has excellent durability.

Note that the operating conditions of this fuel cell 1 are not particularly limited, but for example, the pressurization on the fuel side electrode 2 side is 200 kPa or less, preferably 100 kPa or less, the pressurization on the oxygen side electrode 3 side is 200 kPa or less, Preferably, the pressure is 100 kPa or less, and the temperature of the fuel cell S is set at 0 to 120°C, preferably 20 to 80°C.

Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited thereto, and the design can be modified as appropriate without changing the gist of the present invention.

Applications of the fuel cell of the present invention include, for example, power sources for drive motors in automobiles, ships, aircraft, etc., and power sources for communication terminals such as mobile phones.

Examples and Comparative Examples are shown below to further specifically explain the present invention. Note that the present invention is not limited to the Examples and Comparative Examples. In addition, the specific numerical values of the blending ratio (content ratio), physical property values, parameters, etc. used in the following description are the corresponding blending ratios ( Substitute with the upper limit value (value defined as "less than" or "less than") or lower limit value (value defined as "more than" or "exceeding") of the relevant description, such as content percentage), physical property value, parameter, etc. be able to.

Note that "parts" and "%" are based on mass unless otherwise specified.
1. Manufacturing of electrolyte membrane Example 1
100 mg of the organic electrolyte was dissolved in 7 mL of N,N'-dimethylacetamide solution and 3 mL of ethanol at room temperature to obtain an electrolyte solution. Next, 1 mg of manganese (II) tetraphenylporphyrin complex (Mn-TPP) was added to the obtained electrolyte solution to obtain a mixed solution. Next, this liquid mixture was poured into a PFA Petri dish (circular diameter: 4 cm) heated to 50° C. on a hot plate and kept overnight to evaporate and remove the solvent. Thereby, an electrolyte membrane was obtained. Next, the obtained electrolyte membrane was taken out from the petri dish and cut into 2 cm x 3 cm pieces, which were used as test samples of the electrolyte membrane.

Example 2
A test sample of an electrolyte membrane was obtained in the same manner as in Example 1, except that the manganese (II) tetraphenylporphyrin complex (Mn-TPP) was changed to a platinum (II) octaethylporphyrin complex (Pt-OEP). .

Comparative example 1
A test sample of an electrolyte membrane was obtained in the same manner as in Example 1, except that the manganese (II) tetraphenylporphyrin complex (Mn-TPP) was not blended.

Comparative example 2
A test sample of an electrolyte membrane was obtained in the same manner as in Example 1, except that the manganese (II) tetraphenylporphyrin complex (Mn-TPP) was changed to cesium (III) nitrate (Ce(NO ₃ ) ₃ ). .

Comparative example 3
A test sample of an electrolyte membrane was prepared in the same manner as in Example 1, except that the manganese (II) tetraphenylporphyrin complex (Mn-TPP) was changed to a cesium (III) 1,10-phenanthroline complex (Ce-Phen). Obtained.

Comparative example 4
A test sample of an electrolyte membrane was prepared in the same manner as in Example 1, except that the manganese (II) tetraphenylporphyrin complex (Mn-TPP) was changed to a platinum (II) 1,10-phenanthroline complex (Pt-Phen). Obtained.
2. Evaluation (radical resistance)
The weight of the test sample of each Example and each Comparative Example was measured, and this was taken as the pre-test weight.

Next, 100 mL of a 3% by mass hydrogen peroxide solution adjusted to pH 11 with potassium hydroxide was poured into a pressure-resistant container made of PFA (tetrafluoroethylene/perfluoroalkoxyethylene copolymer resin). Next, the test samples of each Example and each Comparative Example were placed in this container, and a PTFE (tetrafluoroethylene resin) mesh was placed on top as a weight. Then, the container was sealed and kept in a constant temperature bath at 80° C. for 8 hours. Thereafter, the test sample was removed from the container and washed three times with ultrapure water. The washed test samples were then dried in air overnight. After drying, the weight of the test sample was measured, and this was taken as the post-test weight.

Then, the weight before the test was divided by the weight after the test, and the weight retention rate was expressed as a percentage. The results are shown in Table 1 and FIG. 2.

(alkali resistance)
The test samples of Example 1, Example 2, and Comparative Example 4 were immersed in aqueous solutions adjusted to pH 7, 11, and 14 with potassium hydroxide, respectively.

The appearance after immersion was evaluated for superiority or inferiority based on the following criteria. The results are shown in Table 1. ○: The aqueous solution was not colored.
Δ: The aqueous solution was slightly colored.
×: The aqueous solution was colored.
3. Evaluation Regarding the evaluation of radical resistance, in Examples 1 and 2 using porphyrin complexes, the weight retention rates were 94.1% and 98.6%, indicating that they were excellent in radical resistance.

On the other hand, Comparative Example 4 using a phenanthroline complex (platinum (II) 1,10-phenanthroline complex) also had a weight retention rate of 97.7%, which indicates that it has excellent radical resistance.

However, when comparing Examples 1 and 2 with Comparative Example 4 regarding the evaluation of alkali resistance, it was found that in Examples 1 and 2, even when the pH was changed from 7 to 14, the aqueous solution was not colored. There wasn't. This shows that the porphyrin complex does not elute from the organic electrolyte. On the other hand, in Comparative Example 4, when the pH was changed from 7 to 14, the aqueous solution became colored. This shows that the phenanthroline complex is eluted from the organic electrolyte. This shows that the porphyrin complex has better alkali resistance than the phenanthroline complex.

From the above, it can be seen that when a porphyrin complex is used, both radical resistance and alkali resistance are excellent.

2 Membrane electrode assembly 5 Electrolyte membrane 6 Fuel side electrode 7 Air side electrode

Claims (1)

an electrolyte membrane that can move anion components;
comprising a fuel-side electrode to which a fuel component is supplied and an oxygen-side electrode to which oxygen is supplied, which are arranged opposite to each other with the electrolyte membrane in between,
the electrolyte membrane includes a porphyrin complex,
A membrane electrode assembly, wherein the porphyrin complex includes a manganese (II) tetraphenylporphyrin complex or a platinum (II) octaethylporphyrin complex.

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