JP2008034197A - Solid polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte fuel cell improved in reactivity in a catalyst electrode layer. <P>SOLUTION: The solid polymer electrolyte fuel cell comprises at least a solid electrolyte membrane, catalyst electrode layers arranged on both sides of the solid electrolyte membrane, and gas diffusion layers arranged further outside of them. The ratio of the electrolyte which at least one of the catalyst electrode layers contains is higher on the gas diffusion layer side than on the solid electrolyte membrane side of the catalyst electrode layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid polymer electrolyte fuel cell with improved reactivity in a catalyst electrode layer.

  A unit cell, which is the minimum power generation unit of a solid polymer electrolyte fuel cell (hereinafter sometimes referred to simply as a fuel cell), generally comprises a membrane electrode assembly in which a catalyst electrode layer is bonded to both sides of a solid electrolyte membrane. A gas diffusion layer is disposed on both sides of the membrane electrode assembly. Furthermore, a separator having a gas flow path is arranged outside thereof, and the fuel gas and the oxidant gas supplied to the catalyst electrode layer of the membrane electrode composite are passed through the gas diffusion layer, It works to transmit the current obtained by power generation to the outside.

  In the catalyst electrode layer used in the fuel cell, an electrolyte similar to that used in the solid electrolyte membrane and a conductive material carrying the catalyst are permeated to allow hydrogen gas and oxygen gas necessary for the reaction to permeate. It is common to form a three-phase interface where the electrolyte, the catalyst, and the reaction gas-supplied pores are in contact with each other by kneading into a state having pores. The power generation characteristics of such a fuel cell are determined by how many three-phase interfaces can be formed per unit volume. However, even if the three-phase interface as described above is formed, the power generation reaction does not occur if the opening to which the reaction gas is to be supplied cannot be reached. Therefore, the three-phase interface does not contribute to the power generation reaction. Become.

  In order to prevent the above problem, in Patent Document 1 or the like, the ratio of the electrolyte contained in the gas diffusion layer side region of the catalyst electrode layer is reduced, and the ratio of the electrolyte contained in the solid electrolyte membrane side region of the catalyst electrode layer A catalyst electrode layer having a high height is disclosed. With the above configuration, gas diffusion and permeability in the region of the catalyst electrode layer on the gas diffusion layer side can be improved, and proton conductivity in the region on the solid electrolyte membrane side can be improved. Patent Document 2 discloses a method for producing a catalyst electrode layer in which the concentration of the catalyst-supporting carrier is inclined in the catalyst electrode layer.

  However, since the region on the solid electrolyte membrane side of the catalyst electrode layer is a region where a large amount of water generated by the power generation reaction is generated, flooding is likely to occur. Increasing the electrolyte content in this region is likely to deteriorate the flooding. . In addition, the proton conductivity of the gas diffusion layer side region where the electrolyte content is low decreases, and protons do not reach the catalyst placed in this region, so even if an expensive catalyst is placed, it does not contribute to the power generation reaction It becomes.

Japanese Patent Laid-Open No. 8-88008 JP 2004-87267 A

  The present invention has been made in view of the above problems, and has as its main object to provide a solid polymer electrolyte fuel cell with improved reactivity in the catalyst electrode layer.

  In order to achieve the above object, the present invention provides a solid polymer electrolyte comprising at least a solid electrolyte membrane, a catalyst electrode layer disposed on both sides of the solid electrolyte membrane, and a gas diffusion layer disposed on the outside thereof. In the solid fuel cell, the solid polymer, wherein the ratio of the electrolyte contained in at least one of the catalyst electrode layers is higher on the gas diffusion layer side than on the solid electrolyte membrane side of the catalyst electrode layer An electrolyte fuel cell is provided.

  By increasing the ratio of the electrolyte contained in the catalyst electrode layer on the gas diffusion layer side, protons can be supplied preferentially to the gas diffusion layer side, and the portion of the portion where the reaction gas is supplied abundantly. The reactivity can be improved. Since the gas diffusion layer side of the catalyst electrode layer is in contact with the reaction gas flow path, flooding is unlikely to occur even if the proportion of the electrolyte contained in the region is large, and the reactivity of the catalyst electrode layer is improved without problems such as flooding. Can be made.

  In the said invention, it is preferable to have the ion conduction part which penetrates the said catalyst electrode layer in the lamination direction in the said catalyst electrode layer. Providing the ion conductive portion in the catalyst electrode layer as described above enables efficient supply of protons to the gas diffusion layer side of the catalyst electrode layer, thereby further improving the reactivity on the gas diffusion layer side. it can.

  The present invention has an effect that the reactivity of the catalyst electrode layer can be improved.

  The present invention intends to improve the reaction characteristics of a fuel cell by using a catalyst electrode layer containing a large amount of electrolyte on the gas diffusion layer side as at least one catalyst electrode layer.

Hereinafter, the fuel cell of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view showing an example of the configuration of the fuel cell of the present invention. As shown in FIG. 1, in the fuel cell 1 of the present invention, a solid electrolyte membrane 2 is sandwiched between catalyst electrode layers 3, and a gas diffusion layer 4 and a separator 5 are disposed on the outside thereof. The catalyst electrode layer 3 is formed by laminating a plurality of catalyst electrode formation layers 3a to 3c having different proportions of electrolytes contained therein, and penetrates the catalyst electrode layer 3 in the lamination direction in the catalyst electrode layer 3. An ion conducting portion 6 is formed.

  In this example, the catalyst electrode layer 3 is formed by laminating a plurality of catalyst electrode forming layers 3a to 3c having different ratios of electrolytes contained therein. In the catalyst electrode layer 3, the ratio of the electrolyte contained in the catalyst electrode formation layer 3 a adjacent to the gas diffusion layer 4 is the highest among all the catalyst electrode formation layers, and the catalyst electrode adjacent to the solid electrolyte membrane 2. The formation layer 3c is formed so that the ratio of the electrolyte contained is the lowest. The catalyst electrode formation layer 3b located between the two catalyst electrode formation layers is formed so as to contain an electrolyte in a proportion between the catalyst electrode formation layer 3a and the catalyst electrode formation layer 3c. . In the catalyst electrode layer 3, an ion conducting portion 6 that penetrates the catalyst electrode layer 3 in the stacking direction is formed.

By increasing the ratio of the electrolyte contained in the gas diffusion layer 4 side region of the catalyst electrode layer 3 in this way, proton conductivity in the catalyst electrode forming layer 3a adjacent to the gas diffusion layer 4 side is improved. The catalyst disposed in this region where the reaction gas is abundantly supplied can be used effectively, and the reactivity can be improved. Since this region is adjacent to the gas flow path, flooding is unlikely to occur even if the proportion of the electrolyte contained is high. Moreover, the flooding of this area | region can be suppressed by making low the ratio of the electrolyte which the catalyst electrode formation layer 3c by the side of the solid electrolyte membrane 2 in which flooding easily occurs is contained. In addition, since the ion conductive portion is formed in the catalyst electrode layer, even if the ion conductivity in the region on the solid electrolyte membrane side of the catalyst electrode layer is not so high, the ion diffusion portion in the region of the catalyst electrode layer on the gas diffusion layer side. Ions can be supplied efficiently, and the reactivity of the catalyst electrode layer can be further increased.
Hereafter, each structural member which comprises such a fuel cell of this invention is each demonstrated separately.

1. Catalytic electrode layer
(1) Catalyst electrode layer First, the catalyst electrode layer used in the present invention will be described.
At least one of the catalyst electrode layers used in the present invention is characterized in that the ratio of the electrolyte contained is higher on the gas diffusion layer side than on the solid electrolyte membrane side of the catalyst electrode layer. . As described above, by increasing the proportion of the electrolyte contained in the gas diffusion layer side region of the catalyst electrode layer, the proton conductivity of the region is improved, so that the reactivity of the region can be improved. The above-mentioned region is a region located away from the solid electrolyte membrane, and has low reactivity due to a small amount of reaching protons, and the catalyst disposed in this region has not been effectively used in the conventional catalyst electrode layer. Therefore, in the present invention, the ratio of the electrolyte contained in the gas diffusion layer side region of the catalyst electrode layer is increased to increase the reactivity of this region, thereby being arranged in this region where the reactant gas is supplied abundantly. It became possible to use the catalyst effectively.

  As described above, the catalyst electrode layers having different electrolyte contents depending on the region can be formed by, for example, laminating a plurality of catalyst electrode forming layers having different electrolyte contents. In this case, the number of the catalyst electrode forming layers forming one catalyst electrode layer is not particularly limited as long as it is 2 or more. For example, when a catalyst electrode layer is formed using three or more catalyst electrode formation layers, the ratio of the electrolyte contained in the catalyst electrode formation layer adjacent to the gas diffusion layer is the highest and adjacent to the solid electrolyte membrane. The ratio of the electrolyte contained in the catalyst electrode formation layer is the lowest, and the catalyst electrode formation layer located between them is formed so as to contain an electrolyte in an intermediate ratio between the two catalyst electrode formation layers.

  The catalyst electrode layer may be one in which the proportion of the electrolyte contained continuously changes in the stacking direction. In this case, the ratio of the electrolyte contained in the catalyst electrode layer is the highest in the region on the gas diffusion layer side, and is formed such that the content ratio of the electrolyte continuously decreases as it approaches the solid electrolyte membrane side.

  In the present invention, the ratio of the electrolyte in the catalyst electrode layer is the ratio of the weight of the conductive material (excluding the catalyst), which is the carrier on which the catalyst is supported, to the dry weight of the electrolyte ((dry weight of the electrolyte) / ( It shall mean the value of the weight of the conductive substance)). For example, when a carbon material is used as the conductive material and a polymer electrolyte is used as the electrolyte, the ratio of the weight of the conductive material to the dry weight of the polymer electrolyte is the ratio of the electrolyte in the catalyst electrode layer.

  In the present invention, the ratio of the electrolyte contained in each region of the catalyst electrode layer is not particularly limited as long as the gas diffusion layer side is higher than the solid electrolyte membrane side, but the most electrolyte in the catalyst electrode layer. The content ratio of the region adjacent to the gas diffusion layer having a high content ratio is preferably in the range of 0.8 to 1.5, and more preferably in the range of 1.0 to 1.3. Further, the content ratio of the region adjacent to the solid electrolyte membrane having the lowest electrolyte content ratio in the catalyst electrode layer is within the range of 0.3 to 1.0, and particularly within the range of 0.5 to 0.8. Preferably there is. Furthermore, the difference between the proportion of the electrolyte contained in the region adjacent to the gas diffusion layer and the proportion of the electrolyte contained in the region adjacent to the solid electrolyte membrane is within the range of 0.1 to 0.4, particularly 0.2 to It is preferable to be within the range of 0.3. By setting the difference in the electrolyte content within the above range, flooding of the region on the solid electrolyte membrane side of the catalyst electrode layer can be suppressed, and the reactivity of the region on the gas diffusion layer side can be improved.

  In addition, the material which forms the catalyst electrode layer used for this invention is not specifically limited, The normal thing conventionally used can be used. For example, a catalyst-supporting conductive material in which a catalyst such as platinum or a platinum alloy is supported on a conductive material such as carbon powder or carbon nanotube, and Nafion (trade name: Nafion, manufactured by DuPont) used for a solid electrolyte membrane A catalyst electrode layer can be formed from an electrolyte such as

  As described above, a catalyst electrode layer formed by laminating a plurality of catalyst electrode formation layers having different compositions is obtained by applying a single coating solution for forming a catalyst electrode formation layer by an application method such as an inkjet method, a spray method, or a screen printing method. It can be formed by coating and solidifying a solid electrolyte membrane or other substrate, and then applying and solidifying a coating solution for forming a catalyst electrode layer having a composition different from the above. It can also be formed using an applicator. Furthermore, the catalyst electrode layer in which the ratio of the electrolyte contained in the catalyst electrode layer continuously changes can be formed using a voltage and a magnetic field as disclosed in JP-A-2004-87267.

  In the present invention, the catalyst electrode layers having different electrolyte content ratios as described above may be used for both the fuel electrode side and the air electrode side catalyst electrode layer, or the fuel electrode side or the air electrode. It may be used only on either side. In the present invention, among the above, at least the air electrode side is preferably the catalyst electrode layer as described above. Since the air electrode is a place where generated water is generated, the effect of the catalyst electrode layer of the present invention, such as suppression of flooding, can be effectively utilized by using the catalyst electrode layer as described above on the air electrode side. it can.

(2) Ion Conducting Part In the present invention, it is preferable that an ion conducting part for conducting ions is formed in the catalyst electrode layer as described above. Ion conductivity can be improved by providing an ion conduction part in the catalyst electrode layer that serves as a passage for protons, and protons can be efficiently supplied to a region away from the solid electrolyte membrane in the catalyst electrode layer. . In the present invention, the region on the gas diffusion layer side of the catalyst electrode layer has a high proton conductivity because it contains a high proportion of the electrolyte contained therein, and is also a region where abundant reactant gases are supplied. By preferentially supplying protons, the reactivity of this region can be further improved. Even if the power generation reaction is actively performed and a large amount of generated water is generated, flooding is unlikely to occur because this region is adjacent to the gas flow path. Therefore, by forming the ion conductive portion, the region on the gas diffusion layer side of the catalyst electrode layer can be made to be a region having higher reactivity and less likely to generate flooding.

  The shape or the like of the ion conducting part is not particularly limited as long as it can conduct ions from the solid electrolyte membrane to the inside of the catalyst electrode layer, particularly to the gas diffusion layer side. It is preferable that one end of the ion conducting portion is in contact with the solid electrolyte membrane from the function of the ion conducting portion that conducts ions from the solid electrolyte membrane into the catalyst electrode layer. For example, one end may be in contact with the solid electrolyte membrane, and the catalyst electrode layer may have a shape such as a protrusion protruding from the solid electrolyte membrane side to the gas diffusion layer side.

  In the present invention, as illustrated in FIG. 1, the ion conductive portion preferably penetrates the catalyst electrode layer in the stacking direction. By forming the ion conductive portion in this manner, it becomes possible to efficiently and reliably supply protons from the solid electrolyte membrane to the gas diffusion layer side region of the catalyst electrode layer.

  In the present invention, the size of the ion conducting portion is not particularly limited as long as protons can move inside the ion conducting portion. Usually, the diameter of the ion conducting portion is in the range of 0.1 to 100 μm. It is preferable to arrange a large number of ion conducting portions having a small diameter. In addition, in an arbitrary cross section of the catalyst electrode layer perpendicular to the stacking direction, the ratio of the cross-sectional area occupied by the ion conductive portion is preferably in the range of 5 to 50%, more preferably in the range of 20 to 35%.

  Since the ion conducting part having ion conductivity is usually formed from a hydrophilic material, if the diameter of the ion conducting part is too large or the cross-sectional area occupied by the ion conducting part is too wide, the water content of the catalyst electrode layer is large. There is a possibility that flooding occurs due to too much. Also, it is possible to supply protons to a wider area in the catalyst electrode layer and improve the utilization rate of the catalyst when a large number of small-diameter ion conductive portions are disposed rather than a small number of large-diameter ion conductive portions. be able to.

  As illustrated in FIG. 2, the ion conductive portions may be evenly arranged in a plane perpendicular to the stacking direction of the catalyst electrode layers. Moreover, drying can also be suppressed by arrange | positioning the ion conduction part which is more hydrophilic than another area | region in the area | region which is easy to dry of a fuel cell. Alternatively, on the downstream side of the gas flow path of the fuel cell system, most of the flowing gas is already used for the reaction, and the concentration of the flowing reactive gas is often low. By maintaining the ratio of the electrolyte contained in the downstream region of the catalyst and using a catalyst-carrying conductive material carrying the catalyst at a high density, the power generation characteristics are maintained well even in a low-concentration reaction gas atmosphere. be able to.

  As described above, when the ion conductive portion is provided in the catalyst electrode layer in which the electrolyte content varies depending on the region, the ratio of the electrolyte contained in the region on the solid electrolyte membrane side is set to be lower than the case where the ion conductive portion is not provided. It can be further lowered. When the ion conducting portion is not provided, protons are conducted to the region on the gas diffusion layer side by the electrolyte in the region on the solid electrolyte membrane side of the catalyst electrode layer. However, when an ion conduction part is provided, the ion conduction part plays its role, and proton conduction from the solid electrolyte membrane to the gas diffusion layer side region of the catalyst electrode layer is caused by the ion conduction part. It can be done efficiently. Therefore, the region on the solid electrolyte membrane side of the catalyst electrode layer only needs to contain the electrolyte necessary for the power generation reaction, and the content ratio of the electrolyte can be reduced. Therefore, flooding of this region can be more effectively performed. Can be suppressed. In this case, the content ratio of the region adjacent to the solid electrolyte membrane of the catalyst electrode layer is within the range of 0.3 to 1.0% by weight among the range described in the above “(1) Catalyst electrode layer”. In particular, it is preferably within the range of 0.3 to 0.6% by weight.

  In the present invention, the material for forming the ion conducting portion is not particularly limited as long as it conducts ions, and an electrolyte used for a catalyst electrode layer or a solid electrolyte membrane can be used. For example, organic resin such as fluorine resin represented by Nafion (trade name: Nafion, manufactured by DuPont), hydrocarbon resin represented by amide resin, or silicon oxide Examples thereof include inorganic materials such as those having a main component.

  The method for producing the catalyst electrode layer as described above and having the ion conducting portion formed thereon is not particularly limited as long as the catalyst electrode layer having the above-described configuration can be produced. For example, in the above-described method for forming a catalyst electrode layer in which the content ratio of the electrolyte changes stepwise, when applying each coating solution for forming a catalyst electrode layer, do not apply to the portion where the ion conductive portion is formed. The catalyst electrode layer having the above-described structure is manufactured by coating and solidifying the coating solution for forming the catalyst electrode forming layer in a pattern and then filling the through hole of the laminate with an electrolyte to form an ion conducting portion. can do.

  Further, the catalyst electrode layer having the above-described configuration can also be formed by forming a laminated body having a hole for forming an ion conductive portion using a mold having a desired shape and filling the hole with an electrolyte to form the ion conductive portion. Can be manufactured. Further, conversely to the above, it is also possible to form the ion conductive portion first using a mold or the like and form the catalyst electrode layer around the ion conductive portion using the coating solution for forming the catalyst electrode forming layer. The ion conduction part may be formed in the catalyst electrode layer as described above, or the solid electrolyte membrane and the ion conduction part may be integrally formed, and then the catalyst electrode layer may be formed. .

  In the present invention, the catalyst electrode layer having the above-described electrolyte content ratio depending on the region and provided with the ion conducting portion may be used for both the fuel electrode side and the air electrode side catalyst electrode layers. However, it may be used only on either the fuel electrode side or the air electrode side. In the present invention, among the above, it is preferable that at least the catalyst electrode layer on the air electrode side has a different electrolyte content depending on the region and is provided with the ion conductive portion. Since the air electrode is a place where generated water is generated, the ion conductive part is provided in the catalyst electrode layer on the air electrode side, and the solid electrolyte membrane side region contains a lower proportion of the electrolyte. Flooding of the region can be prevented without reducing the reactivity of the region on the electrolyte membrane side.

2. Solid Electrolyte Membrane The solid electrolyte membrane used in the present invention is not particularly limited as long as it is made of a material that is excellent in proton conductivity and does not pass current. Examples of the electrolyte material for forming such a solid electrolyte membrane include fluorine resins such as Nafion (trade name: Nafion, manufactured by DuPont) and hydrocarbon resins such as amide resins. Examples thereof include organic materials such as organic materials, and inorganic materials such as those containing silicon oxide as a main component.

3. Gas Diffusion Layer The gas diffusion layer used in the present invention is not particularly limited as long as it has gas permeability and can collect generated electricity, and is used for conventional fuel cells. Can be used. In general, a porous body such as carbon cloth or carbon paper made of carbon fiber is preferably used. The thickness of the gas diffusion layer is not particularly limited as long as it can function as a gas diffusion layer in a fuel cell.

4). Separator In the present invention, it is preferable that a separator is disposed further outside the gas diffusion layer. By forming the gas flow path in the separator, it is possible to efficiently supply the reaction gas to the fuel cell and discharge the generated water. Further, by forming from a conductive material, it is possible to efficiently collect current using the separator as a current collector.

  In the present invention, the separator is not particularly limited, and those used in general fuel cells can be used. As an example of the separator that can be used, a gas flow path is formed on the surface on the gas diffusion layer side, and a gas supply device for supplying fuel gas and oxidant gas is connected to the opposite surface. Can be mentioned. The thing in which the flow path of the cooling water is formed is also included. As a material for forming such a separator, carbon or metal is generally used, and they can be used by forming them in the same thickness as a conventional one. In addition, when the gas flow path is formed in the gas diffusion layer used together, it is not necessary to form the gas flow path in the separator, and a separator having a smooth surface can be used.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example]
(Preparation of catalyst electrode layer)
As illustrated in FIG. 3A, three catalyst electrode forming layer forming coating liquids having different compositions are spray-applied on the polytetrafluoroethylene (PTFE) sheet 11 on the ion conductive portion forming mold 10. As a result, the catalyst electrode layer 3 having different compositions on the solid electrolyte membrane side and the gas diffusion layer side was formed. In the catalyst electrode layer 3, each catalyst electrode formation layer is formed so that the ratio of the electrolyte contained in the catalyst electrode formation layer 3a on the PTFE sheet 11 is the highest and the ratio of the electrolyte contained in the catalyst electrode formation layer 3c is the lowest. The composition ratio of the forming coating solution was prepared. In forming each of the above layers, the catalyst electrode forming layer forming coating solution of the previous layer applied was completely dried by a vacuum dryer, and then the next layer was formed. The coating solution for forming the catalyst electrode forming layer is composed of porous carbon (supported amount: 0.4 mg / cm ² ) supporting platinum, Nafion (trade name: Nafion, manufactured by DuPont), and solvent (alcohol, water). I used. The Nafion / carbon weight ratio at that time was adjusted so that the catalyst electrode forming layer 3a was 0.9, the catalyst electrode forming layer 3b was 0.8, and the catalyst electrode forming layer 3c was 0.7. Next, as illustrated in FIG. 3B, the ion conduction part forming mold 10 is removed from the laminate, and the electrolyte 12 is applied to the surface of the laminate as illustrated in FIG. Then, the electrolyte 12 was impregnated in the through-holes, and excess electrolyte 12 on the surface layer of the laminate was removed using a squeegee 13 (vacuum coater SVM-250 (manufactured by Tokai Shoji Co., Ltd.)). Thereafter, the solvent was removed by a vacuum dryer to form the ion conducting part 6 (see FIG. 3D), and a catalyst electrode layer was produced.

(Production of fuel cell)
The catalyst electrode forming layer 3c side of the catalyst electrode layer 3 was hot-pressed on both sides of the solid electrolyte membrane (at 130 ° C. for 2 minutes), and the PTFE sheet 11 was removed. Further, a fuel cell was manufactured by bonding a gas diffusion layer and a separator on the catalyst electrode forming layer 3a.

(Fuel cell operation)
The fuel cell produced by the above method was operated. As a result, good power generation characteristics were exhibited without occurrence of flooding or the like.

It is a schematic sectional drawing which shows an example of the fuel cell of this invention. It is a schematic plan view which shows an example of the catalyst electrode layer used for this invention. It is a schematic process drawing which shows an example of the manufacturing method of a catalyst electrode layer in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Solid electrolyte membrane 3 ... Catalyst electrode layer 4 ... Gas diffusion layer 6 ... Ion conduction part

Claims (2)

In a solid polymer electrolyte fuel cell having at least a solid electrolyte membrane, a catalyst electrode layer disposed on both sides of the solid electrolyte membrane, and a gas diffusion layer disposed further outside thereof,
A solid polymer electrolyte fuel cell, wherein a ratio of the electrolyte contained in at least one of the catalyst electrode layers is higher on the gas diffusion layer side than on the solid electrolyte membrane side of the catalyst electrode layer. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the catalyst electrode layer has an ion conducting portion penetrating the catalyst electrode layer in a stacking direction.

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