WO2024202863A1 - Fuel battery cell - Google Patents

Abstract

A fuel battery cell (1) comprises: a polymer electrolyte membrane (22); an anode electrode (23) and a cathode electrode (24) that are disposed on both sides of the polymer electrolyte membrane (22); and a pair of separators (3) that are disposed opposing the anode electrode (23) and the cathode electrode (24), form an anode flow path (An) that faces the anode electrode (23) and through which a fuel gas flows, and form a cathode flow path (Ca) that faces the cathode electrode (24) and through which an oxidant gas flows. The anode electrode (23) includes a first catalyst that promotes an oxidation reaction of hydrogen and a second catalyst that promotes a decomposition reaction of hydrogen peroxide. The second catalyst is a ceria zirconia sintered material.

Description

Fuel cell

The present invention relates to a fuel cell of a polymer electrolyte fuel cell (PEFC (Polymer Electrolyte Fuel Cell)).

Fuel cells designed to suppress electrolyte membrane degradation have been known for some time (see, for example, Patent Document 1). In PEFCs, a Pt/C catalyst in which platinum particles are supported on a carbon carrier is used as a typical anode catalyst. In this case, oxygen gas that permeates the polymer electrolyte membrane from the cathode side to the anode side reacts with the adsorbed hydrogen on the anode catalyst to generate hydrogen peroxide, which reacts with impurities such as divalent iron ions in the electrolyte membrane to generate hydroxyl radicals, which decompose the electrolyte membrane and accelerate the degradation of the electrolyte membrane. The fuel cell described in Patent Document 1 uses a PtCo/C catalyst in which alloy particles of platinum and a transition metal such as cobalt, which has a low rate of hydrogen peroxide generation, are highly dispersed on a carbon carrier.

International Publication No. 2020/250673

However, the fuel cell described in Patent Document 1 is merely configured to suppress the rate at which hydrogen peroxide is produced, and is unable to sufficiently reduce the amount of hydrogen peroxide produced.

A fuel cell according to one embodiment of the present invention comprises a polymer electrolyte membrane, an anode electrode and a cathode electrode arranged on either side of the polymer electrolyte membrane, and a pair of separators arranged opposite the anode electrode and cathode electrode, forming an anode flow path through which fuel gas flows facing the anode electrode and a cathode flow path through which oxidant gas flows facing the cathode electrode. The anode electrode contains a first catalyst that promotes the oxidation reaction of hydrogen and a second catalyst that promotes the decomposition reaction of hydrogen peroxide. The second catalyst is a ceria-zirconia sintered material.

The present invention makes it possible to sufficiently reduce the amount of hydrogen peroxide generated.

1 is a perspective view showing a schematic overall configuration of a fuel cell stack having fuel cells according to an embodiment of the present invention; 2 is a perspective view showing a schematic configuration of an integrated electrode assembly included in the fuel cell stack of FIG. 1; FIG. 2 is a partial cross-sectional view showing an example of the configuration of the fuel cell of FIG. 1 . FIG. 4 is a diagram for explaining the effect of suppressing deterioration of the electrolyte membrane by adding a second catalyst. FIG. 4 is a diagram for explaining the effect of improving the durability of the electrolyte membrane by adding a second catalyst.

Below, an embodiment of the present invention will be described with reference to Figures 1 to 5. A fuel cell according to an embodiment of the present invention is a cell capable of generating electricity as a unit element constituting a laminate of a fuel cell stack, and is also called a unit cell or a power generating cell. A fuel cell stack is a component of a fuel cell. A fuel cell is mounted, for example, in a vehicle and can generate electricity to drive the vehicle. First, the overall configuration of a fuel cell stack will be described in brief.

FIG. 1 is a perspective view showing a schematic overall configuration of a fuel cell stack 100 having a fuel cell 1 according to an embodiment of the present invention. For convenience, the three mutually orthogonal axial directions shown in the figure are defined below as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part is explained according to these definitions. These directions are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle. For example, the front-rear direction in FIG. 1 may be the front-rear direction, the left-right direction, or the up-down direction of a vehicle.

As shown in FIG. 1, the fuel cell stack 100 has a cell stack 101 formed by stacking a number of fuel cells 1 in the front-rear direction, and end units 102 arranged at both the front and rear ends of the cell stack 101, and has an approximately rectangular parallelepiped shape overall. The length of the cell stack 101 in the left-right direction is longer than its length in the up-down direction. For convenience, FIG. 1 shows a single fuel cell 1. The fuel cell 1 has a unitized electrode assembly (UEA) 2, which is a membrane electrode structure including an electrolyte membrane and electrodes, and separators 3, 3 arranged on both the front and rear sides of the unitized electrode assembly 2 and sandwiching the unitized electrode assembly 2. The unitized electrode assemblies 2 and the separators 3 are arranged alternately in the front-rear direction.

Separator 3 has a pair of front and rear thin metal plates with a corrugated cross section, which are joined together at their outer peripheries. Separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel. Inside separator 3, a cooling flow path through which a cooling medium flows is formed by press molding or the like, and the power generation surface of fuel cell 1 is cooled by the flow of the cooling medium. Water, for example, can be used as the cooling medium. The surface (front and rear) of separator 3 facing integrated electrode assembly 2 is unevenly configured to form a gas flow path between integrated electrode assembly 2.

The separator 3 on the front side of the integrated electrode assembly 2 is, for example, an anode side separator (anode separator), and an anode flow path through which fuel gas flows is formed between the anode separator 3 and the integrated electrode assembly 2. The separator 3 on the rear side of the integrated electrode assembly 2 is, for example, a cathode side separator (cathode separator), and a cathode flow path through which oxidizer gas flows is formed between the cathode separator 3 and the integrated electrode assembly 2. For example, hydrogen gas can be used as the fuel gas, and for example, air can be used as the oxidizer gas. Sometimes, the fuel gas and the oxidizer gas are referred to as reactant gases without distinguishing between them.

Figure 2 is a perspective view showing the schematic configuration of the integrated electrode assembly 2. As shown in Figure 2, the integrated electrode assembly 2 has a membrane electrode assembly (MEA) 20 having a substantially rectangular shape, and a frame 21 that supports the membrane electrode assembly 20. The membrane electrode assembly 20 has an electrolyte membrane, an anode electrode provided on the front surface of the electrolyte membrane, and a cathode electrode provided on the rear surface of the electrolyte membrane.

The electrolyte membrane is, for example, a solid polymer electrolyte membrane, and a thin film of perfluorosulfonic acid containing water can be used. It is not limited to fluorine-based electrolytes, and hydrocarbon-based electrolytes can also be used.

The anode electrode has a catalyst layer formed on the front surface of the electrolyte membrane and a gas diffusion layer formed on the front surface of the catalyst layer. The cathode electrode has a catalyst layer formed on the rear surface of the electrolyte membrane and a gas diffusion layer formed on the rear surface of the catalyst layer. The catalyst layer of each electrode contains a catalytic metal that promotes the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, an electrolyte with proton conductivity, and carbon particles with electron conductivity. The gas diffusion layer of each electrode is composed of a conductive material with gas permeability, such as a carbon porous body.

At the anode electrode, the fuel gas (hydrogen) supplied through the anode flow path and gas diffusion layer is ionized by the action of a catalyst and passes through the electrolyte membrane to move to the cathode electrode side. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode, the oxidant gas (oxygen) supplied through the cathode flow path and gas diffusion layer reacts with the hydrogen ions guided from the anode electrode and the electrons that have moved from the anode electrode to generate water. The generated water provides an appropriate humidity to the electrolyte membrane, and excess water is discharged outside the integrated electrode assembly 2.

The frame 21 is a thin plate with a generally rectangular shape, and is made of insulating resin, rubber, or the like. A generally rectangular opening 21a is provided in the center of the frame 21, and the membrane electrode assembly 20 is provided to cover the entire opening 21a. On the left side of the opening 21a of the frame 21, three through holes 211-213 that penetrate the frame 21 in the front-to-rear direction are opened in a line up in the vertical direction, and on the right side of the opening 21a, three through holes 214-216 that penetrate the frame 21 in the front-to-rear direction are opened in a line up in the vertical direction.

As shown in FIG. 1, the separators 3 at the front and rear of the integrated electrode assembly 2 are provided with through holes 311-316 that penetrate the separators 3 in the front-rear direction at positions corresponding to the through holes 211-216 in the frame 21. The through holes 311-316 are connected to the through holes 211-216 in the frame 21, respectively. The collection of the through holes 211-216 and 311-316 that communicate with each other forms flow paths PA1-PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-rear direction. The flow paths PA1-PA6 are sometimes called manifolds (exhaust manifolds). The flow paths PA1-PA6 are connected to a manifold external to the fuel cell stack 100.

Flow path PA1 (solid arrow) extending forward through through holes 211, 311 is a fuel gas supply flow path. Flow path PA6 (solid arrow) extending rearward through through holes 216, 316 is a fuel gas exhaust flow path. Fuel gas supply flow path PA1 and fuel gas exhaust flow path PA6 are connected to the anode flow path facing the front surface of the membrane electrode assembly 20, and as shown by the solid arrow, fuel gas flows left and right through the anode flow path via fuel gas supply flow path PA1 and fuel gas exhaust flow path PA6. The fuel gas flowing through fuel gas exhaust flow path PA6 is the fuel gas after a portion of it has been used at the anode electrode, and is sometimes called fuel exhaust gas.

The flow path PA4 (dotted arrow) extending forward through the through holes 214, 314 is an oxidant gas supply flow path. The flow path PA3 (dotted arrow) extending rearward through the through holes 213, 313 is an oxidant gas discharge flow path. The oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3 are connected to the cathode flow path facing the rear surface of the membrane electrode assembly 20, and as shown by the dotted arrow, the oxidant gas flows left and right through the cathode flow path via the oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3. The oxidant gas flowing through the oxidant gas discharge flow path PA3 is the oxidant gas after a portion of it has been used at the cathode electrode, and this is sometimes called oxidant exhaust gas. The fuel exhaust gas and the oxidant exhaust gas are sometimes called reaction exhaust gas without distinguishing between them.

Flow path PA5 (dash-dotted arrow) extending forward through through holes 215, 315 is a cooling medium supply flow path. Flow path PA2 (dash-dotted arrow) extending rearward through through holes 212, 312 is a cooling medium discharge flow path. Cooling medium supply flow path PA5 and cooling medium discharge flow path PA2 are connected to the cooling flow path inside separator 3, and the cooling medium flows through the cooling flow path via cooling medium supply flow path PA5 and cooling medium discharge flow path PA2.

The end units 102 arranged on both the front and rear sides of the cell stack 101 each have a terminal plate 4, an insulating plate 5, and an end plate 6. The front end unit 102 is sometimes called the dry side end unit, and the rear end unit 102 is sometimes called the wet side end unit. The pair of front and rear terminal plates 4, 4 are arranged on both the front and rear sides of the cell stack 101, sandwiching them. The pair of front and rear insulating plates 5, 5 are arranged on both the front and rear sides of the terminal plate 4, 4. The pair of front and rear end plates 6, 6 are arranged on both the front and rear sides of the insulating plate 5, 5, sandwiching them.

The terminal plate 4 is a roughly rectangular metal plate member, and has a terminal portion for extracting the power generated by the electrochemical reaction in the cell stack 101. The insulating plate 5 is a roughly rectangular non-conductive resin or rubber plate member, and electrically insulates the terminal plate 4 from the end plate 6. The end plate 6 is a metal or high-strength resin plate member, and a connecting member elongated in the front-rear direction that connects the front and rear end plates 6, 6 to each other is fixed to the end plate 6 by a bolt, for example. The fuel cell stack 100 is held in a state where it is pressed in the front-rear direction by the end plates 6, 6 via the connecting member.

The rear end unit 102 has a number of through holes 102a-102f that penetrate the end unit 102 in the front-rear direction. The through holes 102a-102f include a through hole that penetrates the terminal plate 4, a through hole that penetrates the insulating plate 5, and a through hole that penetrates the end plate 6, but in FIG. 1, for convenience, these are collectively shown as through holes 102a-102f. The through hole 102a is opened on an extension of the fuel gas supply flow path PA1 and communicates with the fuel gas supply flow path PA1. The through hole 102b is opened on an extension of the cooling medium discharge flow path PA2 and communicates with the cooling medium discharge flow path PA2. The through hole 102c is opened on an extension of the oxidizing gas discharge flow path PA3 and communicates with the oxidizing gas discharge flow path PA3. The through hole 102d is opened on an extension of the oxidizing gas supply flow path PA4 and communicates with the oxidizing gas supply flow path PA4. The through hole 102e is opened on an extension of the cooling medium supply passage PA5 and is connected to the cooling medium supply passage PA5. The through hole 102f is opened on an extension of the fuel gas discharge passage PA6 and is connected to the fuel gas discharge passage PA6.

More specifically, a fuel gas tank that stores high-pressure fuel gas is connected to through-hole 102a via an ejector, injector, etc., and the fuel gas in the fuel gas tank is supplied to fuel cell stack 100 via through-hole 102a. A gas-liquid separator is connected to through-hole 102f, and the fuel gas (fuel exhaust gas) discharged through through-hole 102f is separated into fuel gas and water by the gas-liquid separator. The separated fuel gas is sucked in through the ejector and supplied again to fuel cell stack 100. The separated water is discharged to the outside via a drain passage.

A compressor for supplying oxidant gas is connected to through-hole 102d, and the oxidant gas compressed by the compressor is supplied to the fuel cell stack 100 through through-hole 102d. The oxidant gas (oxidant exhaust gas) flows out from through-hole 102c. A pump for supplying a cooling medium is connected to through-hole 102b, and the cooling medium is supplied to the fuel cell stack 100 through through-hole 102b. The cooling medium is discharged from through-hole 102e. The discharged cooling medium is cooled by heat exchange in the radiator and is supplied again to the fuel cell stack 100 through through-hole 102b.

The above is the general configuration of the fuel cell stack 100. The fuel cell stack 100 is housed in a roughly box-shaped case and mounted on the vehicle.

Figure 3 is a partial cross-sectional view showing an example of the configuration of a fuel cell 1. As shown in Figure 3, the membrane electrode assembly 20 of the integrated electrode assembly 2 has an electrolyte membrane 22, an anode electrode 23 provided on the front surface of the electrolyte membrane 22, and a cathode electrode 24 provided on the rear surface of the electrolyte membrane 22. The front surface of the membrane electrode assembly 20, i.e., the surface of the anode electrode 23, constitutes the anode surface 20a of the membrane electrode assembly 20. The rear surface of the membrane electrode assembly 20, i.e., the surface of the cathode electrode 24, constitutes the cathode surface 20b of the membrane electrode assembly 20. The separator 3 has a pair of front and rear thin plates 3a, 3b.

The anode flow path An, through which the fuel gas flows, is formed between the rear thin plate 3a of the anode separator 3 on the front side of the integrated electrode assembly 2 and the anode surface 20a of the membrane electrode assembly 20. The cathode flow path Ca, through which the oxidizer gas flows, is formed between the front thin plate 3b of the cathode separator 3 on the rear side of the integrated electrode assembly 2 and the cathode surface 20b of the membrane electrode assembly 20. The cooling flow path Co, through which the cooling medium flows, is formed between the pair of front and rear thin plates 3a, 3b of the separator 3.

At the anode electrode 23, hydrogen, which is the fuel gas flowing through the anode flow path An, is ionized by an oxidation reaction of the following formula (i). The hydrogen ions generated at the anode electrode 23 pass through the electrolyte membrane 22 and move to the cathode electrode 24. At the cathode electrode 24, oxygen in the oxidant gas flowing through the cathode flow path Ca reacts with the hydrogen ions from the anode electrode 23 by a reduction reaction of the following formula (ii), generating water. A portion of the water generated at the cathode electrode 24 is supplied to the electrolyte membrane 22 to moisten the electrolyte membrane 22.
H ₂ →2H ⁺ +2e ^- (i)
O ₂ +4H ⁺ +4e ^- →2H ₂ O (ii)

A portion of the oxygen in the oxidant gas flowing through the cathode flow channel Ca permeates the electrolyte membrane 22 made of a gas-permeable material such as a solid polymer electrolyte membrane, and moves to the anode electrode 23. At the anode electrode 23, the oxygen that has permeated the electrolyte membrane 22 and reached the anode electrode 23 reacts with the hydrogen ions produced by the oxidation reaction of formula (i) and the adsorbed hydrogen before being ionized, through the reduction reactions of the following formulas (iii) to (v), to generate hydrogen peroxide.
O ₂ +2H ⁺ +2e ^- →H ₂ O ₂ (iii)
O ₂ +H ₂ (ads)→H ₂ O ₂ (iv)
O ₂ +2H (ads) → H ₂ O ₂ (v)

The membrane electrode assembly 20 of the integrated electrode assembly 2, which includes the electrolyte membrane 22, is maintained in a wet state and is disposed adjacent to the separator 3, which is made of a material such as stainless steel that contains iron as a main component. For this reason, impurities such as divalent iron ions are inevitably present in the membrane electrode assembly 20. In the anode electrode 23, these divalent iron ions react with hydrogen peroxide generated by the reduction reactions of formulas (iii) to (v) to generate hydroxyl radicals (.OH). The hydroxyl radicals decompose and deteriorate the electrolyte membrane 22.

In order to improve the durability of the electrolyte membrane 22, it is necessary to sufficiently reduce the amount of hydrogen peroxide that generates such hydroxyl radicals. Therefore, in this embodiment, a catalyst that decomposes hydrogen peroxide is added to the anode electrode 23, and the fuel cell 1 is configured as follows so that the final amount of hydrogen peroxide generated can be sufficiently reduced.

<Composition of the catalytic layer of the anode electrode>
The catalyst layer of the anode electrode 23 is formed by mixing a powdered catalyst and an ionomer that bonds the catalyst powders together in a solvent such as water or alcohol to prepare a paste-like catalyst ink, applying this catalyst ink to the electrolyte membrane 22, and then drying to remove the solvent. As the ionomer, for example, a polymer electrolyte similar to that of the electrolyte membrane 22 can be used.

The catalyst to be mixed into the catalytic ink includes a first catalyst that promotes the oxidation reaction of hydrogen as shown in formula (i) and a second catalyst that promotes the decomposition reaction of hydrogen peroxide. As the first catalyst, for example, a platinum catalyst (Pt/C) supported on a carbon carrier such as carbon black can be used. An alloy catalyst (PtCo/C) in which alloy particles of platinum and a transition metal such as cobalt are supported on a carbon carrier may also be used as the first catalyst. As the second catalyst, for example, a ceria ( _CeO2 ) zirconia ( _ZrO2 ) sintered material (CZ) can be used.

From the viewpoint of ensuring sufficient decomposition performance of hydrogen peroxide, the weight ratio of cerium (Ce) contained in the second catalyst to platinum (Pt) contained in the first catalyst is preferably 0.2 or more. Furthermore, from the viewpoint of ensuring the amount of the first catalyst that promotes the hydrogen oxidation reaction (proton production reaction) shown in formula (i) and ensuring a sufficient amount of power generation, the weight ratio of cerium contained in the second catalyst to platinum contained in the first catalyst is preferably 0.4 or less. In other words, the weight ratio of cerium contained in the second catalyst to platinum contained in the first catalyst is preferably 0.2 or more and 0.4 or less.

According to this embodiment, the following advantageous effects can be obtained.
(1) The fuel cell 1 includes an electrolyte membrane 22, an anode electrode 23 and a cathode electrode 24 disposed on both sides of the electrolyte membrane 22, and a pair of separators 3 disposed opposite the anode electrode 23 and the cathode electrode 24, forming an anode flow path An through which a fuel gas flows facing the anode electrode 23 and a cathode flow path Ca through which an oxidant gas flows facing the cathode electrode 24 (FIG. 3). The anode electrode 23 includes a first catalyst that promotes an oxidation reaction of hydrogen and a second catalyst that promotes a decomposition reaction of hydrogen peroxide. The second catalyst is a ceria-zirconia sintered material (CZ). By adding CZ as the second catalyst to the anode electrode 23 and promoting the decomposition reaction of hydrogen peroxide in the anode electrode 23, the final amount of hydrogen peroxide generated can be sufficiently reduced. This sufficiently suppresses the decomposition deterioration of the electrolyte membrane 22 and sufficiently improves durability.

(2) The first catalyst is a platinum catalyst (Pt) or an alloy catalyst (PtCo) of platinum and a transition metal such as cobalt. This sufficiently promotes the hydrogen oxidation reaction (proton production reaction) shown in formula (i), ensuring sufficient power generation.

(3) The weight ratio of cerium (Ce) contained in the second catalyst to platinum (Pt) contained in the first catalyst is 0.2 or more. This ensures sufficient decomposition performance of hydrogen peroxide and can sufficiently reduce the final amount of hydrogen peroxide generated.

(4) The weight ratio of cerium (Ce) contained in the second catalyst to platinum (Pt) contained in the first catalyst is 0.2 or more and 0.4 or less. This ensures the amount of Pt that promotes the hydrogen oxidation reaction (proton production reaction) shown in formula (i), and ensures sufficient power generation.

(5) The separator 3 is a metal separator containing iron. When a metal separator is used, impurities such as divalent iron ions are inevitably present in the membrane electrode assembly 20 of the integrated electrode assembly 2 including the electrolyte membrane 22, and these impurities react with the hydrogen peroxide generated in the anode electrode 23 to generate hydroxyl radicals (.OH) that decompose and deteriorate the electrolyte membrane 22. Even in a fuel cell 1 that uses such a metal separator, by adding CZ as a second catalyst to the anode electrode 23 to promote the decomposition reaction of hydrogen peroxide, the final amount of hydrogen peroxide generated can be sufficiently reduced and the decomposition and deterioration of the electrolyte membrane 22 can be sufficiently suppressed.

In the above embodiment, FIG. 3 and other figures show an example of separators 3, 3 having a pair of thin plates 3a, 3b and forming an anode flow path An, a cathode flow path Ca, and a cooling flow path Co, but the pair of separators arranged opposite the anode electrode and the cathode electrode, facing the anode electrode to form an anode flow path through which fuel gas flows, and facing the cathode electrode to form a cathode flow path through which oxidizer gas flows, are not limited to this. Each separator 3 may not form a cooling flow path Co, and is not limited to having a pair of thin plates 3a, 3b.

In the above embodiment, a metal catalyst supported on a carbon carrier is used as the first catalyst, but the first catalyst that promotes the oxidation reaction of hydrogen is not limited to this. For example, it may be a highly dispersed metal catalyst without using a carrier, a metal catalyst supported on a carrier other than carbon, or a combination of a carbon carrier and a carrier other than carbon.

The above description is merely an example, and the present invention is not limited to the above-mentioned embodiment and modifications as long as the characteristics of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above-mentioned embodiment and modifications, and it is also possible to combine modifications together.

<Effect of adding second catalyst>
Fig. 4 is a diagram for explaining the effect of suppressing deterioration of the electrolyte membrane 22 by adding the second catalyst. Fig. 5 is a diagram for explaining the effect of improving the durability of the electrolyte membrane 22 by adding the second catalyst. Figs. 4 and 5 show test results when durability tests were conducted on the fuel cell 1 with different compositions of the catalyst layer of the anode electrode 23.

The durability test was performed on a fuel cell cell 1 (unit cell (power generation area: 12.5 cm2)) with a specified amount of iron added to the catalyst layer of the anode electrode 23 (iron-containing compounds such as ferrous sulfate (II) heptahydrate were added when preparing the catalyst ink) under OCV conditions, where an open circuit voltage (OCV) was maintained at which no current flows in the external circuit. In addition, the temperature of the unit cell and the humidity of the supply gas were adjusted to perform the test under specified high temperature and low humidity conditions (110°C, RH 25%, 150 kPa (absolute pressure)) that accelerate the chemical deterioration of the electrolyte membrane 22.

Figure 4 shows the comparative results of the decomposition rate (fluorine release) of the electrolyte membrane 22 estimated based on the quantitative results of fluorine ions, which are decomposition products of the electrolyte membrane 22, contained in wastewater collected during a durability test for a specified period of time (e.g., 150 hours). The quantitative determination of fluorine ions was performed by ion chromatography. When perfluorosulfonic acid constituting the electrolyte membrane 22 decomposes, decomposition products containing fluorine are generated, and fluorine ions are eluted into the wastewater. The more fluorine ions in the wastewater, the faster the decomposition rate of the electrolyte membrane 22, and vice versa.

Figure 5 shows a comparison of the time it takes for the crossover current of the electrolyte membrane 22 to rise to a predetermined value and reach a gas cross leak state, as measured by the Linear Sweep Voltammetry (LSV) method. When the gas cross leak state is reached, in which the reactant gas passes through the electrolyte membrane 22, the OCV drops to a predetermined voltage corresponding to the leakage current. The longer the time it takes to reach gas cross leak, the longer the life and durability of the electrolyte membrane 22. The shorter the time it takes to reach gas cross leak, the shorter the life and durability of the electrolyte membrane 22.

[Comparative Example 1]
A durability test was carried out on the fuel cell 1 in which the catalyst layer of the anode electrode 23 was composed only of the first catalyst, and the first catalyst was a platinum catalyst (Pt/C) supported on a carbon carrier. In Fig. 4 and Fig. 5, the test result of Comparative Example 1 is used as the reference value.

[Comparative Example 2]
A durability test was performed on a fuel cell 1 in which the catalyst layer of the anode electrode 23 was composed only of the first catalyst, and the first catalyst was a platinum-cobalt alloy catalyst (PtCo/C) supported on a carbon carrier. The Pt content in the catalyst layer of the anode electrode 23 was the same as that in Comparative Example 1. As shown in FIG. 4, in Comparative Example 2, the fluorine release in the wastewater was reduced by 65% compared to Comparative Example 1, and it was confirmed that the decomposition and deterioration of the electrolyte membrane 22 was suppressed more than in Comparative Example 1. In addition, as shown in FIG. 5, it was confirmed that the gas cross leak arrival time was longer than in Comparative Example 1, and the durability of the electrolyte membrane 22 was improved. It is believed that the application of Co to the first catalyst reduced the rate of hydrogen peroxide production, suppressed the decomposition and deterioration of the electrolyte membrane 22, and improved durability.

[Comparative Example 3]
A durability test was performed on a fuel cell 1 in which the catalyst layer of the anode electrode 23 was composed of a first catalyst and a second catalyst, the first catalyst being Pt/C, and the second catalyst being ceria (CeO ₂ ). The Pt content in the catalyst layer of the anode electrode 23 was the same as in Comparative Examples 1 and 2. The weight ratio of Ce (cerium) in the ceria (CeO ₂ ) to Pt in the catalyst layer of the anode electrode 23 was 0.2. As shown in FIG. 4 , in Comparative Example 3, the fluorine release in the wastewater was reduced by 57% compared to Comparative Example 1, and it was confirmed that the decomposition and deterioration of the electrolyte membrane 22 was suppressed more than in Comparative Example 1. Also, as shown in FIG. 5 , it was confirmed that the gas cross leak arrival time was longer than in Comparative Example 1, and the durability of the electrolyte membrane 22 was improved. It is believed that the addition of the second catalyst promoted the decomposition reaction of hydrogen peroxide, suppressed the decomposition and deterioration of the electrolyte membrane 22, and improved durability.

[Example 1]
A durability test was performed on a fuel cell 1 in which the catalyst layer of the anode electrode 23 was composed of a first catalyst and a second catalyst, the first catalyst being Pt/C, and the second catalyst being a ceria-zirconia sintered material (CZ). The Pt content in the catalyst layer of the anode electrode 23 was the same as in Comparative Examples 1 to 3. The weight ratio of Ce (cerium) in CZ (CeO ₂ -ZrO ₂ ) to Pt in the catalyst layer of the anode electrode 23 was 0.2. As shown in FIG. 4, in Example 1, the fluorine release in the wastewater was reduced by 82% compared to Comparative Example 1, and it was confirmed that the decomposition and deterioration of the electrolyte membrane 22 was significantly suppressed compared to Comparative Example 1. Also, as shown in FIG. 5, it was confirmed that the gas cross leak arrival time was extended by more than twice as long as that of Comparative Example 1, and the durability of the electrolyte membrane 22 was significantly improved. It is believed that the addition of CZ as the second catalyst sufficiently promoted the decomposition reaction of hydrogen peroxide, significantly suppressed the decomposition and deterioration of the electrolyte membrane 22, and significantly improved the durability.

[Example 2]
A durability test was performed on a fuel cell 1 in which the catalyst layer of the anode electrode 23 was composed of a first catalyst and a second catalyst, the first catalyst being PtCo/C, and the second catalyst being CZ. The Pt content in the catalyst layer of the anode electrode 23 was the same as in Comparative Examples 1 to 3 and Example 1. The weight ratio of Ce in CZ to Pt in the catalyst layer of the anode electrode 23 was 0.2. As shown in FIG. 4, in Example 2, the fluorine release in the wastewater was reduced by 95% compared to Comparative Example 1, and it was confirmed that the decomposition and deterioration of the electrolyte membrane 22 was further suppressed than in Example 1. Also, as shown in FIG. 5, it was confirmed that the gas cross leak arrival time was extended by more than four times compared to Comparative Example 1, and the durability of the electrolyte membrane 22 was further improved than in Example 1. It is considered that the application of Co to the first catalyst reduced the generation rate of hydrogen peroxide, and the addition of CZ as the second catalyst sufficiently promoted the decomposition reaction of hydrogen peroxide, and the decomposition and deterioration of the electrolyte membrane 22 was further suppressed than in Example 1, and the durability was improved.

1 Fuel cell, 2 Integrated electrode assembly, 3 Separator, 20 Membrane electrode assembly, 20a Anode surface, 20b Cathode surface, 22 Electrolyte membrane, 23 Anode electrode, 24 Cathode electrode, An Anode flow path, Ca Cathode flow path, Co Cooling flow path

Claims (7)

A polymer electrolyte membrane;
an anode electrode and a cathode electrode disposed on either side of the polymer electrolyte membrane;
a pair of separators disposed opposite the anode and the cathode, the separators facing the anode to form an anode flow path through which a fuel gas flows, and the separators facing the cathode to form a cathode flow path through which an oxidant gas flows,
The anode electrode is
A first catalyst that promotes an oxidation reaction of hydrogen;
and a second catalyst that promotes the decomposition reaction of hydrogen peroxide,
The second catalyst is a ceria-zirconia sintered material. The fuel cell according to claim 1 ,
The fuel cell, wherein the first catalyst is a platinum catalyst. The fuel cell according to claim 1 ,
The first catalyst is an alloy catalyst of platinum and a transition metal. The fuel cell according to claim 3 ,
The fuel cell is characterized in that the transition metal is cobalt. The fuel cell according to any one of claims 2 to 4,
A fuel cell, wherein a weight ratio of cerium contained in the second catalyst to platinum contained in the first catalyst is 0.2 or more. The fuel cell according to any one of claims 2 to 4,
A fuel cell, wherein a weight ratio of cerium contained in the second catalyst to platinum contained in the first catalyst is 0.2 or more and 0.4 or less. The fuel cell according to any one of claims 1 to 4,
The fuel cell, wherein the separator is a metal separator containing iron.

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