KR20200009846A - Polymer electrolyte membrane, membrane electrode assembly and fuel cell comprising the same, and method of manufacturing the polymer electrolyte membrane - Google Patents

Abstract

The present invention relates to a polymer electrolyte membrane including a polymer having 20-30 mol% of a unit represented by chemical formula 1. The present invention also relates to a membrane electrode assembly, a fuel cell comprising the polymer electrolyte membrane, and a method of manufacturing the polymer electrolyte membrane.

Description

Polymer electrolyte membrane, membrane-electrode assembly and fuel cell comprising the same, and method for producing the polymer electrolyte membrane

The present invention relates to a polymer electrolyte membrane, a membrane-electrode assembly and a fuel cell including the same, and a method for producing the polymer electrolyte membrane.

Fuel cell is a clean energy source that can replace fossil energy. The fuel cell directly converts chemical energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas by electrochemical reaction. It is a power generation system to convert.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC), a direct methanol fuel cell (DMFC) using methanol as a fuel, and the like. It is the membrane-electrode assembly (MEA) that determines performance in PEMFC or DMFC.

MEA consists of a solid polymer electrolyte membrane containing a hydrogen ion conductive polymer and two electrodes separated by the two electrodes, which are referred to as an anode (aka "oxidizing electrode" or "fuel electrode") and a cathode (aka "reduction"). Electrode "or" air electrode ").

The ion conductivity of the polymer electrolyte membrane constituting the MEA is an important factor in the performance of the fuel cell.

Korean Patent Publication No. 10-2003-0076057

The present invention provides an improved polymer electrolyte membrane, a membrane-electrode assembly and a fuel cell including the same, and a method of manufacturing the polymer electrolyte membrane.

One embodiment of the present specification

To include a polymer comprising a unit represented by the formula (1),

On the basis of 100 mol% of the polymer, the content of the unit represented by Chemical Formula 1 is 20 mol% to 30 mol%.

[Formula 1]

In Chemical Formula 1,

R1 to R12 are each hydrogen; Or a substituted or unsubstituted alkyl group.

In addition, an exemplary embodiment of the present specification provides a membrane-electrode assembly including the polymer electrolyte membrane.

In addition, an exemplary embodiment of the present disclosure provides a fuel cell including a membrane-electrode assembly.

In addition, an exemplary embodiment of the present specification comprises the steps of preparing a composition for forming a polymer electrolyte membrane by dissolving a polymer comprising a unit represented by the formula (1) in a solvent; And

Coating the polymer electrolyte membrane-forming composition on a substrate;

It provides a method for producing a polymer electrolyte membrane that the content of the unit represented by the formula (1) based on 100 mol% of the polymer is 20mol% to 30mol%.

The polymer electrolyte membrane according to an exemplary embodiment of the present specification has an advantage that the area change due to humidity is small while maintaining excellent hydrogen ion conductivity.

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

Hereinafter, this specification is demonstrated in detail.

In the present specification, when a part "includes" a certain component, this means that, unless specifically stated otherwise, it may further include other components, not to exclude other components.

In this specification, when a member is located "on" another member, this includes not only when one member is in contact with another member but also when another member exists between the two members.

In the present specification, the alkyl group may be linear or branched, and the carbon number is not particularly limited but is preferably 1 to 50. Specific examples include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methylbutyl, 1-ethylbutyl, pentyl, n-pentyl, iso Pentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl , 1-methylhexyl, cyclopentylmethyl, cyclohexylmethyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylhexyl, 4-methylhexyl and 5-methylhexyl, and the like, but are not limited to these.

In the present specification, the aryl group may be monocyclic or polycyclic.

In the present specification, when the aryl group is a monocyclic aryl group, carbon number is not particularly limited, but is preferably 6 to 30 carbon atoms. Specific examples of the monocyclic aryl group include a phenyl group, a biphenyl group and a terphenyl group, but are not limited thereto.

In the present specification, when the aryl group is a polycyclic aryl group, carbon number is not particularly limited. It is preferable that it is C10-30. Specific examples of the polycyclic aryl group include naphthyl group, anthracenyl group, phenanthryl group, pyrenyl group, peryllenyl group, chrysenyl group, and fluorenyl group, but are not limited thereto. The fluorenyl group may be substituted, and adjacent substituents may combine with each other to form a ring.

In the present specification, the arylene group refers to a divalent group having two bonding positions in the aryl group. The description of the aforementioned aryl groups can be applied except that they are each divalent.

In one embodiment of the present specification, the polymer electrolyte membrane includes a polymer including a unit represented by Formula 1 below, and the content of the unit represented by Formula 1 based on 100 mol% of the polymer is 20 mol% to 30 mol%. .

[Formula 1]

In Chemical Formula 1,

R1 to R12 are each hydrogen; Or a substituted or unsubstituted alkyl group.

The polymer electrolyte membrane for a fuel cell is exposed to various humidity depending on the driving conditions and the surrounding environment. Humidity is the cause of changing the area of the electrolyte membrane, and if the area change is large, it may cause breakage of the membrane, and thus an improvement is required.

Conventionally, the method of reducing the area change by reducing the amount of sulfonic acid groups per unit mass contained in the polymer is mainly applied. However, when the amount of sulfonic acid groups is reduced, the hydrogen ion conductivity of the polymer electrolyte membrane is reduced.

In order to solve this problem, the inventors of the present invention can obtain a polymer electrolyte membrane having a smaller change in area according to humidity when the polymer is added based on the content of the same sulfonic acid group, by adding a monomer having an icytene structure as shown in Formula 1 above. there was. This means that more sulfonic acid groups can be introduced than in the prior art, resulting in a polymer electrolyte membrane having a high hydrogen ion conductivity.

The monomer of the icistene structure has a structure that can structurally bind with another icistene monomer in the polymer, thereby contributing to reducing the area change in the polymer electrolyte membrane.

In an exemplary embodiment of the present specification, the unit represented by Chemical Formula 1 includes 20 mol% to 30 mol%, preferably 20 mol% to 27 mol%, more preferably 20 mol% to 25 mol% based on 100 mol% of the polymer. .

If the content of the unit represented by the formula (1) is less than 20mol%, the effect of reducing the area change is insignificant, and if more than 30mol%, ion exchange capacity (IEC) indicating the amount of sulfonic acid groups relative to the total weight of the polymer Can lower performance.

In one embodiment of the present specification, the polymer is a linear block copolymer including a hydrophilic block and a hydrophobic block.

As used herein, the term "linear block copolymer" refers to a copolymer in which a hydrophilic block and a hydrophobic block are linearly connected to each other. Linked linearly means that there is no side chain except for a brancher, and the brancher may be included in an amount of 2 mol% or less based on 100 mol% of the polymer.

As used herein, "hydrophilic block" means a block having an ion exchange group as a functional group. Here, the "block having an ion exchange group" means a block which is represented by the number of ion exchange groups per structural unit constituting the block, and contains an average of 0.5 or more, and averages 1.0 or more ion exchangers per structural unit. It is more preferable if it has.

The ion exchange group is ^{_{-SO 3 H, -SO 3 - M}} +, -COOH, -COO - M +, -PO 3 H 2, -PO 3 H - M +, -PO 3 2- 2M +, -O (CF ₂ ) _m SO ₃ H, -O (CF ₂ ) _m SO ₃ ^- M ⁺ , -O (CF ₂ ) _m COOH, -O (CF ₂ ) _m COO ^- M ⁺ , -O (CF _{2 ) m PO 3 H 2, -O} (CF 2) m PO 3 H - M + , and _{-O (CF 2) m PO 3} 2- 2M + may be at least one member selected from. Here, m is an integer of 2-6, M is a group 1 element.

In one embodiment of the present specification, a unit included in the hydrophilic block may be selected from the following structures.

In the structure Q1 to Q11 are each ^{_{-SO 3 H, -SO 3 - M}} +, -COOH, -COO - M +, -PO 3 H 2, -PO 3 H - M +, -PO 3 2- 2M + , -O (CF ₂ ) _m SO ₃ H, -O (CF ₂ ) _m SO ₃ ^- M ⁺ , -O (CF ₂ ) _m COOH, -O (CF ₂ ) _m COO ^- M ⁺ , -O (CF _{2 ) m PO 3 H 2, -O} (CF 2) m PO 3 H - m + , or _{-O (CF 2) m PO 3} 2- 2M + , and

m is an integer from 2 to 6,

M is a group 1 element,

는 상기 고분자의 주쇄에 연결되는 부위이다.

Is a site connected to the main chain of the polymer.

By “hydrophobic block” herein is meant the polymer block which is substantially free of ion exchange groups.

The " block having substantially no ion exchange group " means a block having an average of less than 0.1 represented by the number of ion exchange groups per structural unit constituting the block, and more preferably 0.05 or less on average, and more preferably an ion exchange group. It is more preferable if it has no block at all.

In one embodiment of the present specification, the hydrophobic block includes a repeating unit represented by Formula 2 below.

[Formula 2]

In Chemical Formula 2,

Ar is a direct bond; Or a substituted or unsubstituted arylene group,

R1 to R12 are each hydrogen; Or a substituted or unsubstituted alkyl group,

n is an integer from 1 to 10,000.

In one embodiment of the present specification, R1 to R12 are each hydrogen.

In one embodiment of the present specification, Ar is a direct bond.

In one embodiment of the present specification, Ar is a divalent benzophenone group.

In one embodiment of the present specification, Ar is a divalent diphenylsulfane group.

In one embodiment of the present specification, Ar is a divalent sulfonyldibenzene group.

In one embodiment of the present specification, Ar is a divalent naphthalene group.

In one embodiment of the present specification, Ar is a divalent biphenyl group.

In one embodiment of the present specification, Ar may be selected from the following structures.

는 상기 화학식 1의 주쇄에 연결되는 부위이다.In the above structure

Is a site connected to the main chain of the formula (1).

In one embodiment of the present specification, the polymer may further include a brancher, and the brancher serves to connect or crosslink the polymer chain.

In one embodiment of the present specification, the brancher may be selected from the following structures.

는 상기 고분자의 주쇄에 연결되는 부위이다.In the above structure

Is a site connected to the main chain of the polymer.

According to the exemplary embodiment of the present specification, in the case of the block polymer, since the partitions and division of the hydrophilic block and the hydrophobic block are clear, phase separation is easy, and thus there is an advantage of easy ion transfer.

In one embodiment of the present specification, the weight average molecular weight of the polymer is 100,000 g / mol to 1,000,000 g / mol.

In one embodiment of the present specification, the unit represented by Chemical Formula 1 is included in the hydrophobic block.

In one embodiment of the present specification, the hydrophilic block and the hydrophobic block in the block copolymer may be included in a ratio of 10: 1 to 1:10, preferably 10: 1 to 1: 2, more preferably 5 It may be included in a ratio of 4: 4 to 5: 6.

In one embodiment of the present specification, the membrane-electrode assembly includes an anode; Cathode; And the polymer electrolyte membrane described above provided between the anode and the cathode.

The membrane-electrode assembly may be prepared according to conventional methods known in the art, except for including the polymer electrolyte membrane according to one embodiment of the present specification. For example, cathode; Anode; And it may be prepared by thermal compression at 100 ℃ to 400 ℃ in a state in which the polymer electrolyte membrane positioned between the cathode and the anode in close contact.

1 is a view schematically showing a structure of a fuel cell membrane-electrode assembly, wherein the membrane-electrode assembly includes an electrolyte membrane 10 and a cathode 50 positioned to face each other with the electrolyte membrane 10 interposed therebetween. An anode 51 may be included. Specifically, the cathode may include a cathode catalyst layer 20 and a cathode gas diffusion layer 40 sequentially provided from the electrolyte membrane 10, and the anode includes an anode catalyst layer 21 sequentially provided from the electrolyte membrane 10 and An anode gas diffusion layer 41 may be included.

The catalyst layer of the anode electrode is where the oxidation reaction of the fuel occurs, the catalyst is selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-transition metal alloy. Can be used.

The catalyst layer of the cathode electrode is where the reduction reaction of the oxidant occurs, platinum or platinum-transition metal alloy may be preferably used as a catalyst. The catalysts can be used on their own as well as supported on a carbon-based carrier.

The process of introducing the catalyst layer may be performed by conventional methods known in the art, for example, the catalyst ink may be directly coated on the electrolyte membrane or coated on the gas diffusion layer to form the catalyst layer. At this time, the coating method of the catalyst ink is not particularly limited, but spray coating, tape casting, screen printing, blade coating, die coating or spin coating may be used. The catalyst ink may typically be composed of a catalyst, a polymer ionomer and a solvent.

The gas diffusion layer acts as a current conductor and serves as a passage for the reaction gas and water, and has a porous structure. Therefore, the gas diffusion layer may include a conductive substrate. As the conductive substrate, carbon paper, carbon cloth, or carbon felt may be preferably used.

The gas diffusion layer may further include a microporous layer between the catalyst layer and the conductive substrate. The microporous layer may be used to improve the performance of the fuel cell in low-humidity conditions, and serves to make the polymer electrolyte membrane in a sufficient wet state by reducing the amount of water flowing out of the gas diffusion layer.

In one embodiment of the present specification, the fuel cell includes two or more of the aforementioned membrane-electrode assemblies; A stack including a bipolar plate provided between the membrane-electrode assemblies; A fuel supply unit supplying fuel to the stack; And an oxidant supply for supplying an oxidant to the stack.

A fuel cell is an energy conversion device that converts chemical energy of a fuel directly into electrical energy. That is, a fuel cell is a power generation method that uses fuel gas and an oxidant and generates electric power by using electrons generated during the redox reaction.

Referring to FIG. 1, which illustrates the electricity generation principle of a fuel cell, in the anode A, an oxidation reaction of a fuel (F) such as hydrogen or a hydrocarbon such as methanol and butane occurs to generate hydrogen ions (H +) and electrons (e−). Generated, and the hydrogen ions move to the cathode C through the electrolyte membrane M. In the cathode C, the hydrogen ions transferred through the electrolyte membrane M, the oxidant O such as oxygen, and the electrons react to generate water (W). This reaction causes the movement of electrons in the external circuit.

In one embodiment of the present specification, the fuel cell may be manufactured according to conventional methods known in the art, except for including the aforementioned membrane-electrode assembly.

Referring to FIG. 3, the fuel cell includes a stack 60, a fuel supply unit 80, and an oxidant supply unit 70.

The stack 60 includes one or more membrane-electrode assemblies (MEAs), and when two or more membrane-electrode assemblies are included, a separator interposed therebetween. It serves to transfer the externally supplied fuel and oxidant to the membrane-electrode assembly.

The fuel supply unit 80 serves to supply fuel to the stack, and includes 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. The fuel may be a gas or liquid hydrogen or hydrocarbon fuel, examples of the hydrocarbon fuel may be methanol, ethanol, propanol, butanol or natural gas.

The oxidant supply unit 70 serves to supply an oxidant to the stack. Oxygen is typically used as the oxidant, and may be used by injecting oxygen or air into the pump 82.

In one embodiment of the present specification, a method of preparing a polymer electrolyte membrane may include preparing a composition for forming a polymer electrolyte membrane by dissolving a polymer including a unit represented by Formula 1 in a solvent; And coating the polymer electrolyte membrane forming composition on a substrate, wherein the content of the unit represented by Chemical Formula 1 is based on 100 mol% of 20 mol% to 30 mol%.

In one embodiment of the present specification, the method of manufacturing the polymer electrolyte membrane may refer to the description of the polymer electrolyte membrane described above.

In one embodiment of the present specification, the end group of the polymer may be -OH, -SO ₃ H or -H.

In an exemplary embodiment of the present specification, the substrate may be a polymer film, a glass substrate, stainless steel, or the like, and the polymer film may include polyethylene terephthalate (PET) or polyimide, but is not limited thereto. no.

In one embodiment of the present specification, a method of coating the composition on a substrate may use a known method such as spin coating, roll coating, curtain coating, and casting.

In one embodiment of the present specification, as the solvent of the composition for forming the polymer electrolyte membrane, dimethyl sulfoxide (DMSO), N-methyl-pyrrolidone (NMP), dimethylacetamide (DMAc), and dimethylformamide (DMF) ) Can be used one or more selected.

In one embodiment of the present specification, the polymer may be included 1wt% to 15wt%, preferably 2wt% to 8wt%, more preferably 3wt% to 7wt% based on 100wt% of the composition for forming the polymer electrolyte membrane. have.

When the content of the polymer is 1wt% or more, it is possible to form a film, and when it is 15wt% or less, it can be formed with an appropriate viscosity.

In one embodiment of the present specification, the composition for forming a polymer electrolyte membrane may further include cerium oxide particles, manganese particles, platinum particles, or a compound thereof as an additive. The content of the additive may be 0.01wt% to 1wt% based on 100wt% of the composition for forming the polymer electrolyte membrane.

In one embodiment of the present specification, the remainder other than the polymer and the additive in the polymer electrolyte membrane-forming composition is a solvent.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present disclosure may be modified in various other forms, and the scope of the present specification is not interpreted to be limited to the embodiments described below. The embodiments of the present specification are provided to more fully describe the present specification to those skilled in the art.

Example: Preparation of Block Copolymers

Example 1.

3 g of biphenol, disodium 3,3'-disulfonate-4,4'-difluorobenzophenone (Disodium 3,3'-disulfonate) in 500 mL three-neck round bottom flask reactor 5.939 g of -4,4'-difluorobenzophenone) and 0.129 g of 1,3,5-benzenetricarbonyl chloride (dimethyl sulfoxide) and toluene solvent are added. Was prepared in a nitrogen atmosphere using K ₂ CO ₃ as a catalyst.

The reaction mixture was then stirred at a temperature of 140 ° C. for 4 hours to remove the azeotropic mixture by adsorbing to the molecular sieves of Dean-Stark while toluene was refluxed, followed by reaction temperature. The temperature was raised to 160 ℃ and polycondensation reaction for 20 hours.

After the reaction was completed, the temperature of the reactant was reduced to 60 ° C., and 3.164 g of 4,4′-diflourobenzophenone (4,4′-diflourobenzophenone) in the same reactor, trypticene-1,4-hydroquinone ( 3.827 g of triptycene-1,4-hydroquinone) and 0.142 g of 1,3,5-benzenetricar-bonyl chloride were added to the nitrogen atmosphere using DMSO and toluene. The reaction was restarted using K ₂ CO ₃ as catalyst.

The reaction mixture was then stirred again at a temperature of 150 ° C. for 4 hours to remove the azeotropic mixture by adsorbing to the molecular sieves of Dean-Stark while toluene was refluxed, followed by reaction. The temperature was raised to 160 ° C. and polycondensation reaction was carried out for 20 hours. The temperature of the reaction was then cooled to room temperature and the product diluted by further DMSO, after which the diluted product was poured into excess methanol to separate the copolymer from the solvent. After removing excess K ₂ CO ₃ with water, the obtained copolymer was dried in a vacuum oven at 80 ° C. for at least 12 hours to form a sulfonated block copolymer in which hydrophobic blocks and hydrophilic blocks were alternately formed by chemical bonding. Was prepared.

The content of the unit represented by the following Chemical Formula A in the prepared copolymer was 22.8 mol%.

[Formula A]

The weight average molecular weight of the prepared copolymer was 779,000 g / mol.

Comparative Example 1.

Unit represented by the following formula (B) using 4.684 g of 9,9-bis (hydroxyphenyl) fluorene (9,9-bis (hydroxyphenyl) fluorene) instead of trypticene-1,4-hydroquinone in Example 1 A polymer was prepared in the same manner as in Example 1, except that 22.8 mol% was prepared.

[Formula B]

Comparative Example 2.

2.215 g of 4,4'-diflourobenzophenone (4,4'-diflourobenzophenone), 2.541 g of triptycene-1,4-hydroquinone in Example 1 and 1,3 The same method as in Example 1, except that 0.099 g of 1,3,5-benzenetricar-bonyl chloride was prepared to contain 17.8 mol% of the unit represented by Formula A. To prepare a polymer.

Experimental Example 1 Measurement of Area Change of Polymer Electrolyte Membrane

The polymers prepared in Example 1, Comparative Examples 1 and 2, respectively, were dissolved in DMSO at a concentration of 5wt%, coated on a PET film with a thickness of 300 μm by a bar coating method, and then dried at 60 ° C. for 24 hours.

Then, it was immersed in an aqueous 1 M sulfuric acid solution at 80 ℃ for 8 hours, washed with water and dried at 50 ℃.

The dried membrane was cut to a size of 5 cm x 5 cm, soaked in water at room temperature for 2 minutes, and the area in water was measured. Thereafter, the membrane was left in an 80 ° C. oven for 2 minutes and the area was measured again.

Substituting the area measured in Equation 1 below to calculate the area change rate, the results are shown in Table 1 below.

[Equation 1]

Area change rate (%) = (measured area-initial area) / initial area × 100

Added monomer Monomer content after polymerization % Wet area change Area change rate after drying (%) Example 1 Trypsin-1,4-hydroquinone 22.8mol% +11.4 -16.4 Comparative Example 1 9,9-bis (hydroxyphenyl) fluorene 22.8mol% +19.0 -24.5 Comparative Example 2 Trypsin-1,4-hydroquinone 17.8 mol% +16.6 -26.0

Comparative Example 1 and the unit represented by Formula 1 using a polymer that does not include the unit represented by Formula 1 Example 1 using a polymer containing 22.8 mol% of the unit represented by the formula 1 through the results of Table 1 Compared to Comparative Example 2 containing less than 20mol% it can be seen that the area change rate is significantly lower in both wet and dry conditions.

That is, when the polymer electrolyte membrane is manufactured according to one embodiment of the present specification, a membrane having a small area change according to humidity may be obtained, which may lead to an improvement in durability of the fuel cell.

10: electrolyte membrane
20: cathode catalyst layer
21: anode catalyst layer
40: cathode gas diffusion layer
41: anode gas diffusion layer
50: cathode
51: anode
60: stack
70: oxidant supply
80: fuel supply
81: fuel tank
82: pump

Claims (7)

To include a polymer comprising a unit represented by the formula (1),
Based on 100 mol% of the polymer, the content of the unit represented by Chemical Formula 1 is 20 mol% to 30 mol%.
[Formula 1]

In Chemical Formula 1,
R1 to R12 are each hydrogen; Or a substituted or unsubstituted alkyl group. The method according to claim 1,
The polymer is a polymer electrolyte membrane that is a linear block copolymer comprising a hydrophilic block and a hydrophobic block. The method according to claim 2,
The unit represented by Formula 1 is included in the hydrophobic block. Anode; Cathode; And a polymer electrolyte membrane of any one of claims 1 to 3 provided between the anode and the cathode. Two or more membrane-electrode assemblies;
A stack including a bipolar plate provided between the membrane-electrode assemblies;
A fuel supply unit supplying fuel to the stack; And
A fuel cell comprising an oxidant supply unit for supplying an oxidant to the stack. Preparing a composition for forming a polymer electrolyte membrane by dissolving a polymer including a unit represented by Formula 1 in a solvent; And
Coating the polymer electrolyte membrane-forming composition on a substrate;
Method for producing a polymer electrolyte membrane is that the content of the unit represented by the formula (1) based on 100 mol% of the polymer is 20 mol% to 30 mol%:
[Formula 1]

In Chemical Formula 1,
R1 to R12 are each hydrogen; Or a substituted or unsubstituted alkyl group. The method according to claim 6,
The polymer is a method of producing a polymer electrolyte membrane will be contained 1wt% to 15wt% based on 100wt% of the composition for forming the polymer electrolyte membrane.

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