KR102131483B1 - Membrane electrode assembly, fuel cell comprising the same and manufacturing method thereof - Google Patents

Abstract

This specification relates to a membrane electrode assembly, a fuel cell, and a method of manufacturing the membrane electrode assembly.

Description

Manufacturing method of membrane electrode assembly, fuel cell and membrane electrode assembly {MEMBRANE ELECTRODE ASSEMBLY, FUEL CELL COMPRISING THE SAME AND MANUFACTURING METHOD THEREOF}

This specification relates to a membrane electrode assembly, a fuel cell, and a method of manufacturing the membrane electrode assembly.

Recently, as the depletion of existing energy resources such as oil and coal is predicted, interest in energy that can replace them is increasing. As one of these alternative energies, fuel cells are particularly attracting attention due to their advantages such as high efficiency, no emission of pollutants such as NOx and SOx, and rich use of fuel.

A fuel cell is a power generation system that converts the chemical reaction energy of a fuel and an oxidant into electrical energy, and hydrogen, hydrocarbons, such as methanol and butane, and oxygen, are typically used as fuel.

Fuel cells include polymer electrolyte fuel cells (PEMFC), direct methanol fuel cells (DMFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), molten carbonate fuel cells (MCFC), and solid oxide fuel And SOFCs.

Republic of Korea Patent Publication No. 2003-0045324 (released on June 11, 2003)

This specification is intended to provide a method for manufacturing a membrane electrode assembly, a fuel cell and a membrane electrode assembly.

The present specification provides a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer, wherein the cathode catalyst layer includes ceria particles surface-treated with an amine group. do.

In addition, the present specification provides a fuel cell including the membrane electrode assembly.

In addition, the present specification is a method of manufacturing a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer and a polymer electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer, the method comprising: forming ceria particles surface-treated with an amine group; And forming the cathode catalyst layer using a catalyst ink containing the surface-treated ceria particles.

The membrane electrode assembly according to the present specification has an advantage of increasing durability of battery performance in extremely low humidity conditions.

1 is a schematic view showing the principle of electricity generation in a fuel cell.
2 is a view schematically showing the structure of a membrane electrode assembly.
3 is a view schematically showing an embodiment of a fuel cell.

Hereinafter, the present specification will be described in detail.

The present specification relates to a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer.

The anode catalyst layer and the cathode catalyst layer may each include a catalyst and an ionomer.

The catalyst is not limited as long as it can serve as a catalyst in a fuel cell, but may include one of platinum, a transition metal, and a platinum-transition metal alloy.

Here, the transition metal is a group 3 to 11 element in the periodic table, for example, it may be any one of ruthenium, osmium, palladium, molybdenum and rhodium.

Specifically, the catalyst may be selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-molybdenum alloy and platinum-rhodium alloy, but is not limited thereto. Does not.

The catalysts may be used on their own, and may be used supported on a carbon-based carrier.

Examples of the carbon-based carrier include graphite (graphite), carbon black, acetylene black, denka black, cachon black, activated carbon, mesoporous carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon nanoring, carbon nanowire, A preferred example may be any one or a mixture of two or more selected from the group consisting of fullerene (C60) and super P black.

The ionomer serves to provide a passage for ions generated by reaction between a fuel such as hydrogen or methanol and a catalyst to move to the electrolyte membrane.

As the ionomer, a polymer having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups, and derivatives thereof may be used in the side chain.

The ionomer may be a hydrocarbon-based polymer, a partially fluorine-based polymer, or a fluorine-based polymer.

The ionomer is a fluorine-based polymer, benzimidazole-based polymer, polyimide-based polymer, polyetherimide-based polymer, polyphenylene sulfide-based polymer, polysulfone-based polymer, polyethersulfone-based polymer, polyether ketone-based polymer, polyether -It may include one or more hydrogen ion conductive polymers selected from ether ketone-based polymers or polyphenylquinoxaline-based polymers.

The average thickness of the anode catalyst layer and the cathode catalyst layer may be 5 μm or more and 15 μm or less, respectively. If it exceeds 15 μm, gas permeation becomes a problem, and performance may be deteriorated. If it is less than 5 μm, a short-circuit may occur because the gas directly contacts the electrolyte membrane.

At least one of the cathode catalyst layer and the anode catalyst layer may further include ceria particles, and may further include ceria particles surface-treated with a hydrophilic group, and more specifically, ceria particles surface-treated with an amine group. have.

The cathode catalyst layer preferably further comprises ceria particles surface-treated with an amine group. In this case, the amine group on the surface of the ceria particle catches moisture generated from water at the cathode, and thus water discharge is suppressed, thereby improving the performance at extremely low humidity.

The reactant gas in the fuel cell passes through a humidifier (bubbler) heated with a metal container containing water so that the temperature of the gas line is about 10°C to 30°C rather than the setting temperature of the humidifier (bubbler) so that it does not condense in the gas line to the battery cell. Adjust it high. At this time, the relative humidity of the battery cell is calculated according to the relative humidity conversion relation formula based on the temperature of the battery cell after measuring the temperature of the water in the humidifier through which the reactant gas passes, that is, the dew point temperature.

Since the proton ion conductivity of the electrolyte membrane is an important factor in the performance of the membrane electrode assembly, and it is greatly influenced by the relative humidity, the relative humidity is the variation of the electrolyte membrane proton ion conductivity when measuring the electrolyte membrane proton ion conductivity according to the relative humidity. It was classified based on a large section.

Specifically, in the low-humidity condition, the humidity condition means a relative humidity measured at a cell temperature of 70°C. In this specification, the low-humidity condition is a case where the relative humidity is more than 40% and 65% or less, and the extremely low-humidity condition is the relative humidity. It means the case of 0% or more and 40% or less.

Based on the weight of the catalyst in the cathode catalyst layer, the content of the ceria particles may be 0.01% by weight or more and 5% by weight or less. In this case, the amine group having the property of absorbing moisture has the advantage of effectively trapping moisture in the membrane electrode assembly to help improve battery performance.

When the OH radical generated due to an incomplete reaction during the oxygen reaction at the cathode of the fuel cell enters the electrolyte membrane, chemical degradation occurs.

The ceria particles surface-treated with an amine group included in the cathode catalyst layer may give a hydrogen atom to the OH radical generated in the cathode to eliminate radicals.

The ceria particles may have an average diameter of 1 nm or more and 5000 nm or less. In this case, there is an advantage in that OH radical scavenging can be effectively performed as a radical scavenger without deteriorating the performance of the membrane electrode assembly.

The membrane electrode assembly further includes a cathode gas diffusion layer provided on an opposite side of the cathode catalyst layer provided with an electrolyte membrane, and an anode gas diffusion layer provided on an opposite side of the anode catalyst layer provided with an electrolyte membrane. can do.

The anode gas diffusion layer and the cathode gas diffusion layer are respectively provided on one surface of the catalyst layer, and have a porous structure as a passage for reaction gas and water together with a role as a current conductor. Therefore, the gas diffusion layer may be formed of a conductive substrate.

As the conductive substrate, a conventional material known in the art may be used, but, for example, carbon paper, carbon cloth, or carbon felt may be preferably used and limited thereto. Does not work.

The average thickness of the gas diffusion layer may be 100 μm or more and 500 μm or less. In this case, there is an advantage of minimizing the resistance of transfer of reactant gas through the gas diffusion layer and being in an optimal state from the viewpoint of containing adequate moisture in the gas diffusion layer.

The polymer electrolyte membrane is provided between the cathode catalyst layer and the anode catalyst layer, and the polymer contained in the polymer electrolyte membrane may be an ion conductive polymer.

The ion conductive polymer may be a hydrocarbon-based polymer, a partially fluorine-based polymer, or a fluorine-based polymer. Specifically, the polymer electrolyte membrane may be a hydrocarbon-based polymer electrolyte membrane or a fluorine-based polymer electrolyte membrane, and preferably, the electrolyte membrane may be a hydrocarbon-based polymer electrolyte membrane.

The hydrocarbon-based polymer may be a hydrocarbon-based sulfonated polymer without a fluorine group, and on the contrary, the fluorine-based polymer may be a sulfonated polymer saturated with a fluorine group, and the partially fluorine-based polymer may not be saturated with a fluorine group. It may be a non-sulfonated polymer.

The ion conductive polymer is a perfluorsulfonic acid polymer, a hydrocarbon polymer, an aromatic sulfone polymer, an aromatic ketone polymer, a polybenzimidazole polymer, a polystyrene polymer, a polyester polymer, a polyimide polymer, polyvinylidene fluorine Ride-based polymer, polyether sulfone-based polymer, polyphenylene sulfide-based polymer, polyphenylene oxide-based polymer, polyphosphazene-based polymer, polyethylene naphthalate-based polymer, polyester-based polymer, doped polybenzimidazole-based polymer, It may be one or more polymers selected from the group consisting of polyether ketone polymers, polyether ether ketone polymers, polyphenylquinoxaline polymers, polysulfone polymers, polypyrrole polymers, and polyaniline polymers. The polymer may be sulfonated, and may be a single copolymer, an alternating copolymer, a random copolymer, a block copolymer, a multi-block copolymer, or a graft copolymer, but is not limited thereto.

The polymer electrolyte membrane is preferably a hydrocarbon-based polymer, and may be a hydrocarbon-based polymer that is a block-type copolymer including the hydrophilic block and hydrophobic block.

The average thickness of the polymer electrolyte membrane may be 1 μm or more and 100 μm or less.

The present specification provides a fuel cell including the membrane electrode assembly.

FIG. 1 schematically shows the principle of electricity generation in a fuel cell, and in a fuel cell, the most basic unit for generating electricity is a membrane electrode assembly (MEA), which is an electrolyte membrane M and this electrolyte membrane M It consists of an anode (A) and a cathode (C) formed on both sides of. Referring to Fig. Showing the electricity generating principle of a fuel cell 1, an anode (A) in the hydrogen or methanol, butane and the oxidation of the fuel (F) of the hydrocarbon and so on up the hydrogen ions (H ⁺⁾ and electron (e ^-), such as Is generated, and hydrogen ions move to the cathode C through the electrolyte membrane M. In the cathode C, hydrogen ions transferred through the electrolyte membrane M react with oxidizing agent O such as oxygen and electrons to generate water W. The reaction causes electron movement to occur in the external circuit.

As shown in FIG. 2, the membrane electrode assembly may include an electrolyte membrane 10 and a cathode 50 and an anode 51 positioned to face each other with the electrolyte membrane 10 interposed therebetween. Specifically, the cathode includes the cathode catalyst layer 20 sequentially provided from the electrolyte membrane 10 and the cathode gas diffusion layer 30, and the anode includes the anode catalyst layer 21 and the anode sequentially provided from the electrolyte membrane 10. It may include a gas diffusion layer (31).

3 schematically illustrates the structure of a fuel cell, and the fuel cell includes a stack 60, an oxidizing agent supply unit 70, and a fuel supply unit 80.

The stack 60 includes one or more of the above-described membrane electrode assemblies, and when two or more membrane electrode assemblies are included, includes a separator interposed therebetween. The separator serves to prevent the electrical connection of the membrane electrode assemblies and transfer fuel and oxidant supplied from the outside to the membrane electrode assembly.

The oxidizing agent supply unit 70 serves to supply the oxidizing agent to the stack 60. As an oxidizing agent, oxygen is typically used, and oxygen or air may be injected into the pump 70 to be used.

The fuel supply unit 80 serves to supply fuel to the stack 60, and a fuel tank 81 for storing fuel and a pump 82 for supplying fuel stored in the fuel tank 81 to the stack 60. Can be configured. The fuel may be gaseous or liquid hydrogen or hydrocarbon fuel. Examples of hydrocarbon fuels include methanol, ethanol, propanol, butanol or natural gas.

The present specification is a method of manufacturing a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer, the method comprising: forming ceria particles surface-treated with an amine group; And forming the cathode catalyst layer using a catalyst ink containing the surface-treated ceria particles.

The method of manufacturing the membrane electrode assembly includes forming a polymer electrolyte membrane; Forming a cathode catalyst layer on one surface of the polymer electrolyte membrane; And forming an anode catalyst layer on the other surface of the polymer electrolyte membrane.

The forming of the polymer electrolyte membrane may include forming a pure membrane with a composition for a polymer electrolyte membrane, or forming a reinforcement membrane by impregnating a composition for a polymer electrolyte membrane on a porous substrate, or forming a composite membrane including one or more pure membranes and one or more reinforcement membranes. .

The method of introducing the catalyst layer into the polymer electrolyte membrane is by directly coating the catalyst ink on the polymer electrolyte membrane, or by forming a catalyst layer on the release substrate, followed by thermocompression bonding to the polymer electrolyte membrane and removal of the release substrate, or by coating the gas diffusion layer. The catalyst layer may be formed and the catalyst layer may be introduced due to assembly of the gas diffusion layer provided with the catalyst layer and the polymer electrolyte membrane. In this case, the coating method of the catalyst ink is not particularly limited, but spray coating, tape casting, screen printing, blade coating, inkjet coating, die coating or spin coating may be used.

The step of forming the ceria particles surface-treated with the amine group may include ceria having a hydroxyl group; And reacting a compound having a functional group and an amine group capable of reacting with the hydroxyl group of ceria to surface-treat the surface of the ceria with a compound having an amine group.

The step of forming the ceria particles surface-treated with the amine group may include dispersing ceria having a hydroxyl group in an alcohol-based solvent; Reacting a compound having a functional group and an amine group capable of reacting with the hydroxyl group of ceria to surface-treat the surface of the ceria with a compound having an amine group; Washing the surface-treated ceria; And drying.

The functional group capable of reacting with the hydroxyl group of ceria may be at least one of hydrogen, an alkyl group including a methane group (-CH ₃ ), a hydroxyl group (-0H), and a halogen group.

The amine group includes a primary amine group, a secondary amine group, a tertiary amine group and a quaternary amine group, and the amine group is preferably a primary amine group (-NH ₂ ).

The compound having a functional group and an amine group capable of reacting with the hydroxyl group of ceria may be a compound represented by the following Chemical Formula 1.

[Formula 1]

In Formula 1, L is a direct bond, -O-, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group, R1 to R3 are the same or different from each other, and each independently a carbon number It is an alkyl group of 1 to 5 or a substituent represented by the following formula (2).

[Formula 2]

In Chemical Formula 2, R4 is an alkyl group having 1 to 5 carbon atoms,

는 결합위치이다.

Is the binding position.

The alkyl group may be straight chain or branched chain, and the number of carbon atoms is not particularly limited, but is preferably 1 to 12. Specific examples include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, t-butyl, pentyl, hexyl, heptyl, and the like.

The halogen group may be fluorine, chlorine, bromine or iodine.

The aryl group may be monocyclic or polycyclic, and the number of carbon atoms is not particularly limited, but is preferably 6 to 60. Specific examples of the aryl group include monocyclic aromatic and naphthyl groups such as phenyl group, biphenyl group, triphenyl group, terphenyl group, and stilbene group, binaphthyl group, anthracenyl group, phenanthrenyl group, pyrenyl group, perenylenyl group, tetrasenyl group Polycyclic aromatics such as a group, a chrysenyl group, a fluorenyl group, an acenaphthacenyl group, a triphenylene group, and a fluoranthene group, but are not limited thereto.

The term "substituted or unsubstituted" herein means substituted with one or more amine groups, or having no substituents.

The compound having a functional group and an amine group capable of reacting with the hydroxyl group of ceria may be a compound represented by the following Chemical Formula 3.

[Formula 3]

When the surface of the ceria is surface-treated as a compound having an amine group by reacting a compound having a functional group and an amine group capable of reacting with the hydroxyl group of the ceria, ceria is surface-treated through the reaction as shown in the following reaction formula 1 Can be.

[Scheme 1]

Hereinafter, the present specification will be described in more detail through examples. However, the following examples are only intended to illustrate the present specification and are not intended to limit the present specification.

[Example]

[Example 1]

0.3 g ceria (average diameter: 25 nm) was added to 15 ml of ethanol and sonication was performed for 1 hour. To this, 0.3 ml of APTMS ((3-Aminopropyl)trimethoxysilane) was added and stirred at room temperature for 6 hours. Thereafter, the surface-treated ceria was separated, washed, and dried in an oven.

3M 825 fluorine-based ionomer was mixed with 1-propanol and glycerol. After this, after the surface-treated ceria was added to the mixed solution (0.5 wt% compared to the catalyst), ultrasonic dispersion was performed for 1 hour. After maintaining at a low temperature of 2° C. for 30 minutes, a TEC 10V50E catalyst sold by Tanaka was added to the solution in accordance with the mass ratio (I/C) of ionomers (I, Ionomer) and carbon (C, Carbon) to 0.6. After ultrasonic dispersion for 1 hour, the electrode slurry was completed. Using the prepared electrode slurry, cast an electrode catalyst layer on a PTFE (Polytetrafluoroethylene) film using a doctor blade on a horizontal plate of an applicator in a clean bench, and then 30 minutes at 140°C for 30 minutes at 35°C. During drying, the electrode catalyst layer was finally prepared.

The membrane electrode assembly to which the electrode catalyst layer was applied was evaluated. At this time, as the electrolyte membrane, a sPEEK (sulfonated polyetheretherketone)-based hydrocarbon membrane was used, and the gas diffusion layer (GDL) used SGL's 10BB, and a thickness of 380 μm to 420 μm was used. The compression ratio of GDL was set to 25% and a glass fiber sheet was used to maintain it. The active area of the membrane electrode assembly was 25 cm ² .

[Example 2]

An electrode catalyst layer and a membrane electrode assembly were prepared in the same manner as in Example 1, except that the content of the surface-treated ceria was added at 1 wt% compared to the catalyst.

[Comparative Example 1]

An electrode catalyst layer and a membrane electrode assembly were prepared in the same manner as in Example 1, except that the surface-treated ceria was not added.

[Comparative Example 2]

An electrode catalyst layer and a membrane electrode assembly were prepared in the same manner as in Example 1, except that the surface-treated ceria was added in an amount of 0.5 wt% compared to the catalyst instead of the surface-treated ceria.

[Experimental Example 1]

Durability evaluation

The unit cells of Examples 1 to 2 and Comparative Examples 1 to 2 were evaluated for durability. Durability evaluation was conducted according to the U.S. Department of Energy's (Department of Energy, DOE) OCV (Open Circuit Voltage) pressurized long-term durability evaluation protocol, and at 90°C, 30%RH, and 1.5 bar pressurized conditions Durability evaluation as shown in Table 1 was conducted for 88 hours.

The performance of OCV and battery performance before and after durability evaluation for the unit cells of Examples 1 to 2 and Comparative Examples 1 to 2 was measured using constant current mode IV performance using PEMFC station equipment of Nara Cell. Specifically, 0 ~ 1,500mA / cm ² was measured by scanning the range, the value of V in 0mA / cm ² OCV value, the performance value shows the mA / cm ² in value of 0.6V. The temperature of the cell was measured by operating under conditions of 70°C, relative humidity of 50%, and 32% RH. Table 2 shows the results.

MEA Humidity condition Before durability evaluation After durability evaluation OCV Performance (@0.6V)
(mA/cm ² ) OCV Performance (@0.6V)
(mA/cm ² ) Comparative Example 1 50% 0.938 1,257 0.840 840 32% 0.955 1,034 0.838 735 Comparative Example 2 50% 0.954 1,226 0.942 1,115 32% 0.975 1,035 0.935 0.975 Example 1 50% 0.968 1,297 0.955 1,236 32% 0.972 1,158 0.952 1,098 Example 2 50% 0.955 1,263 0.942 1,169 32% 0.971 1,133 0.953 1,122

Through Table 2, it can be seen that compared to Comparative Example 1, Comparative Example 2, Example 1, and Example 2 containing ceria had almost no OCV value after durability evaluation. This confirms that ceria effectively prevents the OH radical from the electrode, thereby enhancing the durability of the membrane electrode assembly. At the same time, it can be confirmed that ceria surface-treated with an amine group also has the same effect.

In addition, when comparing Comparative Example 2 and Examples 1 and 2, it can be confirmed that the performance of the example is high in the extremely low-humidity performance before the durability evaluation. In particular, when viewed as a result of a large improvement in performance under 32% RH condition than 50% RH condition, the amine group-treated ceria effectively improves performance by effectively holding water to the membrane electrode assembly even under extremely low-humidity conditions due to the amine group on the surface. You can confirm that you can.

In addition, when comparing Comparative Examples 2 and Examples 1 and 2, it can be seen that Examples 1 and 2 had a lower performance drop than Comparative Example 2 in extremely low-humidity performance after durability evaluation. It can be seen that even if the durability of the electrolyte membrane decreases, the particles having hygroscopicity in the electrode can prevent the performance from dropping. In particular, when comparing Examples 1 and 2, it can be seen that when the content of the particles increases, the effect of improving performance in extremely low humidity increases.

10: electrolyte membrane
20: cathode catalyst layer
21: anode catalyst layer
30: cathode gas diffusion layer
31: anode gas diffusion layer
50: cathode
51: anode
60: stack
70: oxidizing agent supply unit
80: fuel supply
81: fuel tank
82: Pump

Claims (6)

A membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and a polymer electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer,
The cathode catalyst layer is a membrane electrode assembly comprising a ceria particle surface-treated with a compound represented by the following formula (1):
[Formula 1]

In Chemical Formula 1, L is a direct bond, -O-, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group, and R1 to R3 are the same or different from each other, and each independently has a carbon number. It is an alkyl group of 1 to 5 or a substituent represented by the following formula (2),
[Formula 2]

In Chemical Formula 2, R4 is an alkyl group having 1 to 5 carbon atoms,

Is the binding position. The membrane electrode assembly according to claim 1, wherein the content of the ceria particles is 0.01% by weight or more and 5% by weight or less based on the weight of the catalyst in the cathode catalyst layer. The membrane electrode assembly according to claim 1, wherein the ceria particles have an average diameter of 1 nm to 5000 nm. A fuel cell comprising the membrane electrode assembly according to claim 1. A method of manufacturing a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer and a polymer electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer,
Forming ceria particles surface-treated with a compound represented by Formula 1 below; And
Method of manufacturing a membrane electrode assembly comprising the step of forming the cathode catalyst layer using a catalyst ink containing the surface-treated ceria particles:
[Formula 1]

In Chemical Formula 1, L is a direct bond, -O-, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group, and R1 to R3 are the same or different from each other, and each independently has a carbon number. It is an alkyl group of 1 to 5 or a substituent represented by the following formula (2),
[Formula 2]

In Chemical Formula 2, R4 is an alkyl group having 1 to 5 carbon atoms,

Is the binding position. The method according to claim 5, Forming a ceria particles surface-treated with the compound represented by the formula (1),
Ceria having hydroxyl groups; And reacting the ceriaic hydroxyl group with the compound represented by Formula 1 to surface-treat the surface of the ceria with a compound represented by Formula 1.

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