JP7307977B2 - MEMBRANE-ELECTRODE ASSEMBLY AND FUEL CELL USING THE SAME - Google Patents

Description

The present application relates to a membrane-electrode assembly and a fuel cell using the membrane-electrode assembly.

A polymer electrolyte fuel cell (PEFC) is a clean and highly efficient power generation system, so it is being applied to fuel cell vehicles, household fuel cells, and the like, and is beginning to spread.

Conventionally, when the supply of fuel gas is stopped in polymer electrolyte fuel cells, the fuel gas remaining in the fuel gas flow path leaks from the fuel gas flow path or passes through the polymer electrolyte membrane. As a result, air flows into the fuel gas flow path instead. If the fuel cell is restarted in such a state, an oxygen reduction reaction occurs at the anode, which causes deterioration of the catalyst used for the cathode. In order to avoid such deterioration, when the fuel cell is restarted, the air remaining in the fuel gas flow path is purged with an inert gas before the fuel gas is supplied to the fuel gas flow path.

However, this method requires a tank for storing the inert gas and a device for controlling the supply, which causes an increase in size and cost of the device. Therefore, as a method that does not use an inert gas, Patent Document 1 proposes a technique of increasing the electrical resistance of the anode in an oxygen atmosphere to be higher than that in a hydrogen atmosphere.

In addition, there are Patent Documents 2 and 3 as technologies related to the hydrocarbon-based polymer electrolyte of the present application.

Japanese Patent No. 6150265 JP 2017-179345 A JP 2018-65945 A

However, in the technique proposed in Patent Document 1, it is necessary to use a special catalyst carrier called platinum/tantalum-doped titanium oxide for the anode catalyst layer, and platinum/carbon, which has been widely used as a catalyst carrier, is used. Therefore, it represents a significant change to the catalyst materials used in conventional fuel cells. Therefore, the technique proposed in Patent Document 1 has a problem that it has a low affinity with the conventional method of manufacturing a fuel cell.

The present application provides a membrane-electrode assembly capable of suppressing the oxygen reduction reaction at the anode during startup of the fuel cell, and a fuel cell using the same, without significantly changing the catalyst material of conventional fuel cells. do.

The membrane-electrode assembly disclosed in the present application is a membrane-electrode assembly comprising a polymer electrolyte membrane, an anode, and a cathode, wherein the anode comprises an anode catalyst layer, and the cathode comprises a cathode catalyst layer. wherein the anode catalyst layer is disposed on the first major surface of the polymer electrolyte membrane, the cathode catalyst layer is disposed on the second major surface of the polymer electrolyte membrane, and the anode catalyst layer comprises a catalyst material, a conductive material, and a hydrocarbon-based polymer electrolyte, wherein the hydrocarbon-based polymer electrolyte includes a hydrophilic segment and a hydrophobic segment, and the hydrophilic segment has a sulfonic acid group. and the main chain is mainly composed of aromatic rings, and the hydrophobic segment contains the aromatic rings.

Further, the fuel cell disclosed in the present application is a fuel cell including the membrane-electrode assembly disclosed in the present application.

According to the present application, it is possible to suppress the oxygen reduction reaction at the anode when starting the fuel cell, thereby preventing deterioration of the catalyst used in the cathode, and as a result, improving the durability of the fuel cell.

FIG. 1 is a schematic diagram of a membrane-electrode assembly of an embodiment. FIG. 2 is a schematic diagram showing a state in which a hydrocarbon-based polymer electrolyte (HCPE) is adsorbed on an anode catalyst. FIG. 3 is a diagram showing the electrochemical reaction area (ECA) and Pt oxidation charge (Q _PT ) of the anodes of Examples 1 to 4 and Comparative Example 1 under high humidity conditions. FIG. 4 is a diagram showing the electrochemical reaction area (ECA) and Pt oxidation charge (Q _PT ) of the anodes of Examples 1 to 4 and Comparative Example 1 under low humidity conditions. FIG. 5 is a diagram showing current density-cell voltage characteristics (anode polarization characteristics) of Example 1 and Comparative Example 1. FIG. FIG. 6 is a graph showing the current density-cell voltage characteristics (cell polarization characteristics) and ohmic resistance of Example 1 and Comparative Example 1. FIG. FIG. 7 is a diagram showing the electrochemical reaction area (ECA) of the cathode in the durability test of Example 1 and Comparative Example 1; FIG. 8 is a diagram showing the current density-cell voltage characteristics/IR-included (cell polarization characteristics) before and after the durability test of Example 1 and Comparative Example 1. FIG. FIG. 9 is a diagram showing current density-cell voltage characteristics and ohmic resistance/IR-Free before and after the durability test of Example 1 and Comparative Example 1. FIG.

(Membrane-electrode assembly)
An embodiment of a membrane electrode assembly (MEA) disclosed in the present application will be described. The membrane-electrode assembly of this embodiment comprises a polymer electrolyte membrane, an anode, and a cathode, the anode comprising an anode catalyst layer, the cathode comprising a cathode catalyst layer, the anode catalyst layer comprising , the cathode catalyst layer is disposed on a first major surface of the polymer electrolyte membrane, the anode catalyst layer is disposed on a second major surface of the polymer electrolyte membrane, the anode catalyst layer comprises a catalyst material, a conductive material, and a hydrocarbon-based polymer electrolyte. Further, the hydrocarbon-based polymer electrolyte includes a hydrophilic segment and a hydrophobic segment, the hydrophilic segment has a sulfonic acid group, the main chain is mainly composed of an aromatic ring, and the hydrophobic segment contains an aromatic ring.

Since the membrane-electrode assembly of the present embodiment contains the hydrocarbon-based polymer electrolyte in its anode catalyst layer, it is possible to suppress the oxygen reduction reaction at the anode during startup of the fuel cell. Deterioration of the catalyst used for the cathode can be prevented, and as a result, durability of the fuel cell can be improved.

Here, "the main chain is mainly composed of aromatic rings" means that the molecular weight of the portion other than the connecting groups (ether group, thioether group, sulfone group, ketone group, sulfide group, etc.) of the main chain in the hydrophilic segment is 100. % means that 70% or more thereof is composed of aromatic rings.

Moreover, the hydrocarbon-based polymer electrolyte preferably has at least one of the following characteristics in order to improve heat resistance and chemical durability.
(1) The hydrophilic segment and the hydrophobic segment are linked by a direct bond of an aromatic ring.
(2) The hydrophobic segment has substantially no sulfonic acid groups.
Here, "substantially no sulfonic acid group" means that the hydrophobic segment has no sulfonic acid group at all, or the number of sulfonic acid groups per repeating unit in the hydrophobic segment is less than the hydrophilic segment It means that the number of sulfonic acid groups per repeating unit in is 1/10 or less.
(3) The plurality of aromatic rings forming the hydrophobic segment are linked by direct bonds of the aromatic rings forming the hydrophobic segment.

Moreover, the hydrocarbon-based polymer electrolyte preferably does not contain a hetero element in the main chain in order to further improve heat resistance and chemical durability. That is, the hydrocarbon-based polymer electrolyte preferably does not contain a linking group containing a hetero element (ether group, thioether group, sulfone group, ketone group, sulfide group, etc.).

Here, the reason why deterioration of the cathode catalyst can be prevented by including the hydrocarbon-based polymer electrolyte in the anode catalyst layer will be described. First, the deterioration mechanism of the cathode catalyst will be described with reference to the drawings.

<Degradation Mechanism of Cathode Catalyst>
FIG. 1 is a schematic diagram of the membrane-electrode assembly of this embodiment. In FIG. 1, the membrane-electrode assembly 10 includes a polymer electrolyte membrane 11, an anode 12 arranged on one main surface of the polymer electrolyte membrane 11, and an anode 12 arranged on the other main surface of the polymer electrolyte membrane 11. a cathode 13;

The anode 12 comprises an anode catalyst layer 14 and an anode gas diffusion layer 15 from the polymer electrolyte membrane 11 side. An anode gas flow path 16 is arranged outside the anode 12 .

The cathode 13 includes a cathode catalyst layer 17 and a cathode gas diffusion layer 18 from the polymer electrolyte membrane 11 side. A cathode gas flow path 19 is arranged outside the cathode 13 .

In FIG. 1, air is usually mixed in the anode gas flow path 16 when the fuel cell is stopped. When fuel gas (hydrogen gas) is supplied to the anode gas channel 16 in this state, the fuel gas is filled from the upstream side of the anode gas channel 16, so that air remains in the downstream part of the anode gas channel 16. become. If the fuel cell is started in such a state, a power generation reaction will occur in the upstream portion where the fuel gas is filled. In this power generation reaction, a hydrogen oxidation reaction of H ₂ →2H ⁺ +2e ⁻ occurs at the anode 12 to generate protons H ⁺ and electrons e ⁻ . The protons H ⁺ move to the cathode 13 through the polymer electrolyte membrane 11, and the electrons e ⁻ move downstream. At the cathode 13, protons H ⁺ from the anode 12 and electrons e ⁻ from the downstream portion of the cathode 13 cause an oxygen reduction reaction of O ₂ +4H ⁺ +4e ⁻ →2H ₂ O.

On the other hand, a corrosion reaction of the catalyst of the cathode catalyst layer 17 occurs in the downstream portion of the anode gas channel 16 where air remains. That is, at the cathode 13, a corrosion reaction of C+2H ₂ O→CO ₂ +4H ⁺ +4e ⁻ occurs to generate protons H ⁺ and electrons e ⁻ . The protons H ⁺ move to the anode 12 through the polymer electrolyte membrane 11, and the electrons e ⁻ move upstream. At the anode 12, protons H ⁺ from the cathode 13 and electrons e ⁻ from the upstream cause an oxygen reduction reaction of O ₂ +4H ⁺ +4e ⁻ →2H ₂ O to produce water. As this reaction progresses, the Pt/carbon catalyst of the cathode 13 deteriorates due to corrosion.

<Reasons for preventing deterioration of the cathode catalyst>
On the other hand, if the anode catalyst layer 14 contains the hydrocarbon-based polymer electrolyte disclosed in the present application, the corrosion reaction of the catalyst of the cathode catalyst layer 17 can be suppressed in the downstream portion of the anode gas channel 16 where air remains. Conceivable. That is, the downstream portion of the anode gas channel 16 where air remains becomes a high potential region, while the upstream portion filled with the fuel gas becomes a low potential region. As shown, the hydrocarbon-based polymer electrolyte (HCPE) is adsorbed on the anode catalyst, and it is believed that the oxygen reduction reaction of O ₂ +4H ⁺ +4e ⁻ →2H ₂ O at the anode 12 is suppressed. As a result, the migration of protons H ⁺ in the downstream portion and the corrosion reaction of C+2H ₂ O→CO ₂ +4H ⁺ +4e ⁻ in the cathode 13 are suppressed, and the corrosion of the catalyst (Pt/carbon) of the cathode 13 in the downstream portion is suppressed. It is thought that deterioration of the catalyst can be prevented.

After that, when the entire flow area of the anode gas channel 16 is filled with the fuel gas, the entire anode 12 becomes a low potential region, and the hydrocarbon-based polymer electrolyte adsorbed on the anode catalyst is desorbed from the anode catalyst. , the anode catalyst becomes able to exhibit its original catalytic function, only the above-mentioned power generation reaction occurs, and it is thought that the fuel cell can be stably operated.

Each constituent member of the membrane-electrode assembly of this embodiment will be described below.

<Hydrocarbon polymer electrolyte>
The hydrocarbon-based polymer electrolyte contained in the anode catalyst layer of the membrane-electrode assembly of the present embodiment has a hydrophilic segment (hereinafter also referred to as a hydrophilic portion) and a hydrophobic segment (hereinafter also referred to as a hydrophobic portion). wherein the hydrophilic segment has a sulfonic acid group, the main chain is mainly composed of an aromatic ring, and the hydrophobic segment contains an aromatic ring.

Since the hydrocarbon-based polymer electrolyte has the structure described above, by including it in the anode catalyst layer as described above, the hydrocarbon-based polymer electrolyte adsorbs to the anode catalyst at the time of starting the fuel cell, Since the oxygen reduction reaction at the anode is suppressed, the corrosion reaction at the cathode is suppressed and deterioration of the cathode catalyst can be prevented.

The hydrocarbon-based polymer electrolyte should have the structure described above, and is disclosed in detail in, for example, Patent Document 2 (Japanese Patent Application Laid-Open No. 2017-179345). A method for producing the hydrocarbon-based polymer electrolyte is also disclosed in detail in Patent Document 3 (JP-A-2018-65945).

Among the above hydrocarbon-based polymer electrolytes, those having structures represented by the following general formulas (1) and (2) are particularly preferred.

In the above formula, x is an integer of 1-2000, and y is an integer of 1-1500.

In the above formula, x is an integer of 1-2000, y is an integer of 1-2000, and z is an integer of 1-1500.

The hydrocarbon-based polymer electrolyte represented by the general formulas (1) and (2) includes a hydrophilic segment and a hydrophobic segment, and the hydrophilic segment has an aromatic ring having a sulfonic acid group in the main chain. The hydrophobic segment consists of an aromatic ring whose main chain does not have a sulfonic acid group. In addition, the hydrophilic segment and the hydrophobic segment are linked by direct bonds of aromatic rings, and the plurality of aromatic rings constituting the hydrophobic segment are linked by direct bonds of the aromatic rings that constitute the hydrophobic segment. It is

The hydrocarbon-based polymer electrolyte represented by the above general formula (1) is a random copolymer of sulfonated polyphenylene (hydrophilic portion) and kinkephenyl (hydrophobic portion), and is also abbreviated as SPP-QP hereinafter. Further, the hydrocarbon-based polymer electrolyte represented by the above general formula (2) is a random copolymer of sulfonated polyphenylene (hydrophilic portion) and biphenyl (hydrophobic portion), and hereinafter abbreviated as SPP-BP. .

As the hydrocarbon-based polymer electrolyte, one having a structure represented by the following general formula (3) can also be used depending on the usage conditions of the fuel cell. Conditions for using the fuel cell will be described later.

In the above formula, x is an integer of 1-2000, and y is an integer of 1-1500.

The hydrocarbon-based polymer electrolyte represented by the general formula (3) includes a hydrophilic segment and a hydrophobic segment, the hydrophilic segment is composed of an aromatic ring having a sulfonic acid group in the main chain, and the above The hydrophobic segment contains an aromatic ring that does not have a sulfonic acid group, and the aromatic rings are linked by a fluorine-containing linking group. Moreover, the hydrophilic segment and the hydrophobic segment are linked by a direct bond of the aromatic ring.

The hydrocarbon-based polymer electrolyte represented by the general formula (3) is a random copolymer of sulfonated polyphenylene (hydrophilic portion) and 2,2-bis(phenyl)hexafluoropropane (hydrophobic portion), It is also abbreviated as SBAF below.

As the hydrocarbon-based polymer electrolyte, those having a structure represented by the following general formula (4) or (5) can also be used.

In the above formula, m is an integer of 1-2000, n is an integer of 1-1500, and o is an integer of 1-1500.

The hydrocarbon-based polymer electrolyte represented by the general formula (4) or (5) includes a hydrophilic segment and a hydrophobic segment, and the hydrophilic segment has an aromatic ring having a sulfonic acid group in the main chain. wherein the hydrophobic segment contains an aromatic ring, and the aromatic ring is linked by a fluorine-containing linking group. Moreover, the hydrophilic segment and the hydrophobic segment are linked by a direct bond of the aromatic ring.

The hydrocarbon-based polymer electrolyte represented by the above general formula (4) is a random copolymer of sulfonated polyphenylene (hydrophilic portion) and 1,8-bis(sulfonated phenyl) perfluorooctane (hydrophobic portion). and the hydrocarbon-based polymer electrolyte represented by the general formula (5) is a random copolymer of sulfonated polyphenylene (hydrophilic portion) and 1,8-bis(phenyl)perfluorooctane (hydrophobic portion). Both are abbreviated as SPAF.

<Polymer electrolyte membrane>
The polymer electrolyte membrane that constitutes the membrane-electrode assembly of the present embodiment is made of a material that exhibits good ion (proton) conductivity in a wet state. ) A conductive ion exchange membrane is used. Examples of the fluororesin include "Nafion" (registered trademark) manufactured by DuPont and represented by the following formula (6).

In addition, since the hydrocarbon-based polymer electrolyte used in the anode catalyst layer described above has ion conductivity, the polymer electrolyte membrane can also be formed using the above-described hydrocarbon-based polymer electrolyte.

<Anode catalyst layer>
The anode catalyst layer constituting the membrane-electrode assembly of the present embodiment is arranged on the first main surface of the polymer electrolyte membrane, and the anode catalyst layer comprises a catalyst material, a conductive material, and the above-described hydrocarbon system polyelectrolyte.

As described above, when the fuel cell is started, the hydrocarbon-based polymer electrolyte is adsorbed on the anode catalyst, and the oxygen reduction reaction at the anode is suppressed. Deterioration can be prevented. The hydrocarbon-based polymer electrolyte also functions as a binder in the anode catalyst layer. Furthermore, since the hydrocarbon-based polymer electrolyte has ionic conductivity, ions (protons) in the anode catalyst layer are well conducted, and the catalyst can be effectively used.

The catalyst material is not particularly limited as long as it is a material that has activity against the hydrogen oxidation reaction in the power generation reaction. can. Among them, platinum or a platinum alloy is preferable in consideration of the oxidizing ability of the fuel and the durability of the catalyst.

The conductive material is not particularly limited, but in consideration of catalyst carrying capacity, electronic conductivity, electrochemical stability, etc., high surface area carbon such as carbon black, ketjen black, activated carbon, carbon nanohorn, and carbon nanotube is used. preferable.

Moreover, it is preferable that the catalyst material is supported on the surface of the conductive material. This is because the electron conductivity of the catalyst material is improved.

The anode catalyst layer is formed by preparing a catalyst ink containing a support in which the catalyst material is supported on the conductive material, the hydrocarbon-based polymer electrolyte, and a solvent, and applying the catalyst ink to the polymer electrolyte membrane. It can be formed by removing the solvent after coating on the surface.

<Cathode catalyst layer>
The cathode catalyst layer constituting the membrane-electrode assembly of the present embodiment is arranged on the second main surface of the polymer electrolyte membrane, and the cathode catalyst layer is formed from a catalyst material, a conductive material, and a binder. can. As the catalyst material and the conductive material, the same materials as the catalyst material and the conductive material used for the anode catalyst layer can be used. As the binder, an ion-conductive binder is preferable, and a binder composed of an ion-conductive fluorine-based resin is preferable. Examples of the ion-conducting fluororesin include the aforementioned "Nafion" (registered trademark) manufactured by DuPont.

Also in the cathode catalyst layer, the catalyst material is preferably supported on the surface of the conductive material. Also, the cathode catalyst layer can be formed in the same manner as the anode catalyst layer described above.

(Fuel cell)
Embodiments of the fuel cell disclosed in the present application will be described. The fuel cell of this embodiment includes the membrane-electrode assembly of the above embodiment. Therefore, as described above, it is possible to suppress the oxygen reduction reaction at the anode when the fuel cell is started, thereby preventing deterioration of the catalyst used in the cathode, and as a result, improving the durability of the fuel cell. can.

The gas diffusion layer, gas channel and other components used in the fuel cell of this embodiment are not particularly limited, and for example, those disclosed in Patent Document 1 (Japanese Patent No. 6150265) are used. be able to.

Examples of the fuel cell using the membrane-electrode assembly disclosed in the present application will be described below, but the fuel cell disclosed in the present application is not limited to the following examples.

(Example 1)
<Preparation of anode catalyst ink>
A hydrocarbon-based polymer electrolyte SPP-BP represented by the general formula (2) was synthesized. The weight average molecular weight of the synthesized SPP-BP was measured by the GCP method and found to be 136,400. Next, SPP-BP was dissolved in N,N-dimethylacetamide (DMAc) to prepare a binder solution.

Next, a Pt/CB catalyst (“TEC10E50E” manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., Pt loading: 0.50 mg/cm ² ), deionized water, and DMAc are added to the binder solution and mixed for 30 minutes using a ball mill. to obtain an anode catalyst ink. In this anode catalyst ink, the mass ratio between the SPP-BP binder and the carbon carrier was adjusted to 0.7.

<Preparation of Cathode Catalyst Ink>
Pt/CB catalyst (“TEC10E50E” manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., Pt loading: 0.50 mg/cm ² ), fluororesin binder (“Nafion”/registered trademark manufactured by DuPont), deionized water, ethanol, Mixed for 30 minutes using a ball mill to obtain a cathode catalyst ink. In this cathode catalyst ink, the mass ratio between the Nafion binder and the carbon carrier was adjusted to 0.7.

<Production of fuel cell>
As the polymer electrolyte membrane, a DuPont Nafion (registered trademark) membrane (thickness: 25 μm) was used, one main surface of the Nafion membrane was spray-coated with an anode catalyst ink, and the other main surface of the Nafion membrane was coated with an anode catalyst ink by spraying. was sprayed with a cathode catalyst ink. After that, it was dried at 60° C. for 12 hours, and hot-pressed for 3 minutes at 140° C. and 10 kgf to obtain a catalyst-coated electrolyte membrane (CCM).

Next, this CCM was sandwiched between gas diffusion layers (“29BC” manufactured by SGL Carbon Co., Ltd.), and incorporated into a cell equipped with a carbon separator having a serpentine gas flow path for both the anode and cathode electrodes of the fuel cell of Example 1. was made.

(Example 2)
A hydrocarbon-based polymer electrolyte SPP-QP represented by the general formula (1) was synthesized. The weight average molecular weight of the synthesized SPP-QP was measured by GCP method and found to be 120,400.

An anode catalyst ink was prepared in the same manner as in Example 1 except that the hydrocarbon-based polymer electrolyte SPP-QP was used instead of the hydrocarbon-based polymer electrolyte SPP-BP, and this anode catalyst ink was used. A fuel cell of Example 2 was produced in the same manner as in Example 1 except for the above.

(Example 3)
A hydrocarbon-based polymer electrolyte SPAF represented by the general formula (4) was synthesized. The weight average molecular weight of the synthesized SPAF was measured by GCP method and found to be 856,000.

An anode catalyst ink was prepared in the same manner as in Example 1, except that the hydrocarbon-based polymer electrolyte SPAF was used instead of the hydrocarbon-based polymer electrolyte SPP-BP, and this anode catalyst ink was used. A fuel cell of Example 3 was produced in the same manner as in Example 1.

(Example 4)
A hydrocarbon-based polymer electrolyte SBAF represented by the general formula (3) was synthesized. When the weight average molecular weight of the synthesized SBAF was measured by GCP method, it was 180,000.

An anode catalyst ink was prepared in the same manner as in Example 1 except that the hydrocarbon-based polymer electrolyte SBAF was used instead of the hydrocarbon-based polymer electrolyte SPP-BP, and this anode catalyst ink was used. A fuel cell of Example 4 was produced in the same manner as in Example 1.

(Comparative example 1)
<Production of catalyst ink>
Pt/CB catalyst (“TEC10E50E” manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., Pt loading: 0.50 mg/cm ² ), fluororesin binder (“Nafion”/registered trademark manufactured by DuPont), deionized water, ethanol, A ball mill was used to mix for 30 minutes to obtain a catalyst ink. In this catalyst ink, the mass ratio of the Nafion binder to the carbon carrier was adjusted to 0.7.

<Production of fuel cell>
As the polymer electrolyte membrane, a DuPont Nafion (registered trademark) membrane (thickness: 25 μm) was used, and both surfaces of the Nafion membrane were spray-coated with the catalyst ink. After that, it was dried at 60° C. for 12 hours, and hot-pressed for 3 minutes at 140° C. and 10 kgf to obtain a catalyst-coated electrolyte membrane (CCM).

A fuel cell of Comparative Example 1 was produced in the same manner as in Example 1, except that the above CCM was used.

<Anode reactivity evaluation>
Using the fuel cells of Examples 1 to 4 and Comparative Example 1, the cyclic voltammogram (CV) of the anode catalyst layer was obtained by cyclic voltammetry under high temperature and high humidity conditions of 80° C. and 100% relative humidity. . As for the measurement conditions, hydrogen gas with a flow rate of 100 mL/min was used as the gas on the cathode catalyst layer side, and nitrogen gas with a flow rate of 0 mL/min was used as the gas on the anode catalyst layer side.

Next, from the CV of this anode catalyst layer, the electrochemical reaction area (ECA) calculated from the hydrogen adsorption-desorption reaction at low potential (0.2 V) and Pt oxidation at high potential (0.8 V) The quantity of electricity (Q _PT ) was determined. The results are shown in FIG.

From FIG. 3, the ECA, which indicates the reactivity of the hydrogen oxidation reaction (normal power generation reaction at the anode) in the low potential region (hydrogen gas atmosphere), shows almost the same value in Examples 1 to 4 and Comparative Example 1. I understand. From these results, under high-temperature and high-humidity conditions, the hydrocarbon-based polymer electrolyte binders used in Examples 1 to 4 exhibit functions equivalent to those of the fluororesin-based binder used in Comparative Example 1 in normal power generation reactions. I know you can.

On the other hand, from FIG. 3, Q _PT indicating the reactivity of the Pt oxidation reaction (corresponding to the oxygen reduction reaction at the anode during start-up) in the high potential region (oxygen or air atmosphere) , it can be seen that compared with Comparative Example 1, it is significantly lower. From these results, under high-temperature and high-humidity conditions, the hydrocarbon-based polymer electrolyte binders used in Examples 1 to 3 showed better Pt oxidation reaction at the anode during startup than the fluororesin-based binder used in Comparative Example 1. It can be seen that it is possible to remarkably suppress This is probably because the hydrocarbon-based polymer electrolyte binder used in Examples 1 to 3 adsorbs to the anode catalyst in the high potential region and suppresses the Pt oxidation reaction (oxygen reduction reaction). As a result, the catalyst corrosion reaction of the cathode is suppressed, and deterioration of the cathode catalyst can be prevented.

Subsequently, using the fuel cells of Examples 1 to 4 and Comparative Example 1, the cyclic voltammogram (CV) of the anode catalyst layer was obtained by cyclic voltammetry under high temperature and low humidity conditions of 80° C. and a relative humidity of 53%. asked for As for the measurement conditions, hydrogen gas with a flow rate of 100 mL/min was used as the gas on the cathode catalyst layer side, and nitrogen gas with a flow rate of 0 mL/min was used as the gas on the anode catalyst layer side.

Next, the electrochemical reaction area (ECA) calculated from the hydrogen adsorption/desorption reaction at a low potential (0.2 V) from the CV of this anode catalyst layer and the Pt oxidation electricity at a high potential (0.8 V) A quantity (Q _PT ) was determined. The results are shown in FIG.

From FIG. 4, the ECA, which indicates the reactivity of the hydrogen oxidation reaction (normal power generation reaction at the anode) in the low potential region (hydrogen gas atmosphere), shows almost the same value in Examples 1 to 4 and Comparative Example 1. I understand. From these results, under high-temperature and low-humidity conditions, the hydrocarbon-based polymer electrolyte binders used in Examples 1 to 4 exhibit functions equivalent to those of the fluororesin-based binder used in Comparative Example 1 in normal power generation reactions. I know you can.

On the other hand, from FIG. 4, Q _PT indicating the reactivity of the Pt oxidation reaction (corresponding to the oxygen reduction reaction at the anode during start-up) in the high potential region (oxygen or air atmosphere) is It can be seen that the . From these results, under high-temperature and low-humidity conditions, the hydrocarbon-based polymer electrolyte binders used in Examples 1 to 4 showed better Pt oxidation reaction at the anode during startup than the fluororesin-based binder used in Comparative Example 1. It can be seen that it is possible to remarkably suppress This is probably because the hydrocarbon-based polymer electrolyte binder used in Examples 1 to 4 adsorbs to the anode catalyst in the high potential region and suppresses the Pt oxidation reaction. As a result, the catalyst corrosion reaction of the cathode is suppressed, and deterioration of the cathode catalyst can be prevented.

As described above, the SPP-BP used in Example 1, the SPP-QP used in Example 2, and the SPAF used in Example 3 were all affected by deterioration of the cathode catalyst under both high and low humidity conditions. can be prevented.

In contrast, Nafion used in Comparative Example 1 cannot prevent deterioration of the cathode catalyst under both high and low humidity conditions.

On the other hand, under high humidity conditions, SBAF used in Example 4 cannot prevent the deterioration of the cathode catalyst as with Nafion used in Comparative Example 1, but under low humidity conditions, the cathode catalyst It can be seen that deterioration can be prevented, and a certain effect is recognized under low humidity conditions compared to Nafion used in Comparative Example 1. SBAF is also soluble in an alcoholic solvent such as ethanol as a solvent for forming an ink, and has the advantage of being easily applicable to the process of forming an ink using an alcoholic solvent similar to the conventional Nafion.

<Evaluation of hydrogen oxidation activity of anode catalyst layer>
Using the fuel cells of Example 1 and Comparative Example 1, anode polarization characteristics were measured under conditions of 80° C. and 100% relative humidity. Hydrogen gas with a flow rate of 1 L/min was used as the anode gas and the cathode gas. The results are shown in FIG. FIG. 5 shows current density-cell voltage characteristics (anode polarization characteristics). From FIG. 5, it can be seen that Example 1 using SPP-BP exhibits anode polarization characteristics equivalent to Comparative Example 1 using Nafion.

<Power generation performance evaluation>
Using the fuel cells of Example 1 and Comparative Example 1, power generation performance was measured under conditions of 80° C. and 100% relative humidity. Hydrogen gas was supplied to the fuel cell as the anode gas, and oxygen gas or air was supplied as the cathode gas. The results are shown in FIG. FIG. 6 shows current density-cell voltage characteristics (cell polarization characteristics) and ohmic resistance. From FIG. 6, it can be seen that Example 1 using SPP-BP exhibits the same cell polarization characteristics and ohmic resistance as Comparative Example 1 using Nafion.

From the results of the evaluation of the hydrogen oxidation activity of the anode catalyst layer and the evaluation of the power generation performance, Example 1 using SPP-BP has the same polarization characteristics as Comparative Example 1 using Nafion in the steady state of the fuel cell. It can be seen that

<Durability evaluation>
Using the fuel cells of Example 1 and Comparative Example 1, a durability test using a gas replacement cycle was conducted. Table 1 shows the test conditions for the gas replacement cycle durability test.

First, the temperature of the fuel cells of Example 1 and Comparative Example 1 was kept at 45° C., dry air was supplied to the anode gas flow channel of each cell, and humidified air was supplied to the cathode gas flow channel of each cell for 90 seconds, Executed mode 1 processing. Next, mode 2 processing was performed at a temperature of 45° C. for 90 seconds by supplying humidified hydrogen to the anode gas flow path and supplying humidified air to the cathode gas flow path of each cell. Subsequently, dry nitrogen was supplied to the anode gas flow path of each cell and dry nitrogen was supplied to the cathode gas flow path of each cell at a temperature of 45° C. for 60 seconds to perform the mode 3 process.

The series of treatments in Modes 1 to 3 was repeated 1,000 times as one cycle. Then, the cyclic voltammogram (CV) of the cathode was obtained by cyclic voltammetry every 200 cycles. From the CV of this cathode, the electrochemical reaction area (ECA) at the cathode was obtained. The results are shown in FIG.

From FIG. 7, in Example 1 using SPP-BP, the ECA retention rate at 1000 cycles was maintained at a high level of 66%, whereas in Comparative Example 1 using Nafion, at 1000 cycles It can be seen that the ECA retention rate of 1 is lowered to 36%. From this result, it can be seen that deterioration of the catalyst in the cathode catalyst layer of Comparative Example 1 using Nafion is greater than that of Example 1 using SPP-BP.

<Evaluation of power generation performance before and after durability test>
Using the fuel cells of Example 1 and Comparative Example 1, power generation performance was measured before and after the durability test under conditions of 80° C. and 100% relative humidity. Hydrogen gas was supplied as the anode gas and oxygen gas was supplied as the cathode gas to the fuel cell. The results are shown in FIGS. 8 and 9. FIG.

FIG. 8 shows current density-cell voltage characteristics/IR-included (cell polarization characteristics). From FIG. 8, the polarization characteristics after the durability test are compared to before the test, and the current density at 0.5 V after 1000 cycles is about 0.8 A/cm ² in Example 1 using SPP-BP. Comparative Example 1 using Nafion had a value of about 0.4 A/cm ² , and Example 1 exhibited about twice the performance of Comparative Example 1.

FIG. 9 shows current density-cell voltage characteristics and ohmic resistance/IR-Free. From FIG. 9, the cell resistance value after the durability test shows a certain increase in the cell resistance value of Example 1 using SPP-BP compared to before the test, but Comparative Example 1 using Nafion. It can be seen that the increase in cell resistance value is small compared to . On the other hand, in Comparative Example 1, an increase in cell resistance value of about 1.5 times that in Example 1 was observed.

From the results of FIGS. 8 and 9, it can be seen that the use of SPP-BP as the anode binder improves the durability of the fuel cell.

The membrane-electrode assembly disclosed in the present application and the fuel cell using the same can suppress the oxygen reduction reaction at the anode during start-up, thereby preventing deterioration of the catalyst used in the cathode, and as a result, The durability of the fuel cell can be improved, and it can be effectively used for fuel cell vehicles, domestic fuel cells, and the like.

REFERENCE SIGNS LIST 10 membrane-electrode assembly 11 polymer electrolyte membrane 12 anode 13 cathode 14 anode catalyst layer 15 anode gas diffusion layer 16 anode gas channel 17 cathode catalyst layer 18 cathode gas diffusion layer 19 cathode gas channel

Claims (5)

A membrane-electrode assembly comprising a polymer electrolyte membrane, an anode and a cathode,
the anode comprises an anode catalyst layer;
the cathode comprises a cathode catalyst layer;
The anode catalyst layer is arranged on the first main surface of the polymer electrolyte membrane,
The cathode catalyst layer is arranged on the second main surface of the polymer electrolyte membrane,
The anode catalyst layer includes a catalyst material, a conductive material, and a hydrocarbon-based polymer electrolyte,
The hydrocarbon-based polymer electrolyte is a polymer electrolyte represented by any one selected from the group consisting of the following general formulas (1), (2), (3), (4), and (5) A membrane-electrode assembly comprising:

(Wherein, x is an integer of 1 to 2000, and y is an integer of 1 to 1500.)

(Wherein, x is an integer of 1 to 2000, y is an integer of 1 to 2000, and z is an integer of 1 to 1500.)

(Wherein, x is an integer of 1 to 2000, and y is an integer of 1 to 1500.)

(Wherein, m is an integer of 1 to 2000, n is an integer of 1 to 1500, and o is an integer of 1 to 1500.)

(Wherein, m is an integer of 1 to 2000, n is an integer of 1 to 1500, and o is an integer of 1 to 1500.) 2. The membrane-electrode assembly according to claim 1, wherein said catalyst material is platinum or a platinum alloy. 3. The membrane-electrode assembly according to claim 1, wherein said conductive material is carbon. The membrane-electrode assembly according to any one of claims 1 to 3, wherein the catalyst material is supported on the surface of the conductive material. A fuel cell comprising the membrane-electrode assembly according to any one of claims 1 to 4.

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