JP4543825B2 - Storage method of fuel cell membrane electrode assembly - Google Patents

Description

The present invention relates to coercive tube method for a solid polymer electrolyte membrane to the oxygen electrode, and a fuel cell catalyst layer is stacked on the fuel electrode membrane electrode assembly.

  A membrane electrode assembly for a fuel cell includes an electrolyte composed of a polymer ion exchange membrane such as a fluororesin ion exchange membrane having a sulfonic acid group, and a catalyst electrode and porous carbon disposed on both sides of the electrolyte. It has a structure consisting of electrodes. For example, an alloy of platinum and ruthenium is used for the anode catalyst layer serving as the fuel electrode, and platinum is used for the cathode catalyst layer serving as the oxygen electrode.

  In the fuel cell membrane electrode assembly having such a structure, the hydrogen gas supplied to the fuel electrode side is hydrogen ionized on the anode catalyst electrode, and the hydrogen ions are present in the presence of water in the electrolyte membrane. And move to the oxygen electrode in a hydrated state. On the cathode catalyst electrode, it reacts with oxygen and electrons to produce water.

  In order for the membrane electrode assembly for a fuel cell to have high durability performance and initial characteristics, it is necessary to maintain the structure in the catalyst layer and the structure of the polymer electrolyte membrane at the time of production. If the metal catalyst in the catalyst layer is lost due to oxidation or elution during long-term storage or the structure of the polymer electrolyte membrane is damaged, the initial characteristics such as voltage-current characteristics and long-term durability characteristics may be degraded. . The adhesion of impurities that accelerate the decomposition of the polymer electrolyte membrane is also a factor that causes the durability characteristics of the membrane electrode assembly to deteriorate.

  As a conventional storage method of a membrane electrode assembly for a fuel cell as a single unit, the membrane electrode assembly was simply packed in a protective polyethylene sheet. In addition, when a porous carbon electrode is stacked on the fuel cell electrode, sandwiched between separators, and assembled as a stack, oxygen remaining in the separator flow path is purged with an inert gas, or oxygen is purged with water. Some have been stored in an atmosphere that excludes (see, for example, Patent Document 1 and Patent Document 2).

In addition, as a technique for storing in an atmosphere excluding oxygen, there has been a technique using an oxygen absorbent (see, for example, Patent Document 3).
JP 2002-93448 A JP-A-6-251788 JP 2000-289380 A

  However, in the method of storing in a state where it is simply packed in a protective vinyl sheet, the protective vinyl sheet does not have a function to prevent permeation of oxygen and humidity, and the membrane electrode assembly is not stored in the storage state. Is exposed to oxygen in the air for a long time. In addition, the membrane / electrode assembly repeatedly absorbs and dries due to ambient humidity fluctuations, so that the polymer electrolyte membrane is damaged. In the long-term oxygen exposure, the anode catalyst layer and the cathode catalyst layer are kept at a high potential state up to about 1 V, so that the carrier carbon, platinum and ruthenium in the catalyst layer were oxidized or eluted. .

  In the conventional configuration, when the membrane electrode assembly for a fuel cell is stored alone, the catalyst layer and the polymer electrolyte membrane are oxidized by oxygen or the like, the moisture in the polymer electrolyte membrane is changed, and impurities such as organic substances are attached. Due to storage for a period, the power generation performance of the membrane electrode assembly is likely to be lowered, and there is a problem that long-term storage is difficult. In addition, the membrane electrode assembly expands and contracts due to moisture absorption and drying when placed in a high humidity condition or in a low humidity condition, resulting in dimensional variations and difficult cell assembly. Or it had the problem of becoming impossible.

  After the fuel cell membrane electrode assembly is assembled as a stack, the configuration of the conventional example enables stable storage, but it is inappropriate for storage as a membrane electrode assembly alone, and the fuel cell There were problems of deteriorating power generation characteristics during storage and distribution of a single unit, and problems of producing defective products due to dimensional variations.

  Also, if the oxygen absorbent is stored in a packaging container with low oxygen permeability and moisture permeability, it can be stored in a low oxygen concentration state, but impurities will be released from the oxygen absorbent. In addition, since moisture may be absorbed when oxygen is absorbed, it is unsuitable for long-term storage of membrane electrode assemblies.

The present invention is the one that solves the conventional problems, long-term retention tube method storable and fuel cell membrane electrode assembly to prevent the degradation or dimensional variation of the power generation characteristics of the membrane electrode assembly for a fuel cell The purpose is to provide.

  In order to achieve the above object, a storage device and storage method for a membrane electrode assembly for a fuel cell according to the present invention is a catalyst by oxygen that affects the degradation of power generation characteristics in the storage device and storage method for a single membrane electrode assembly. It is stored in a sealed state in a container that prevents permeation of oxygen, moisture, and impurities from the outside in order to prevent oxidation of the layers, moisture content fluctuations in the polymer electrolyte membrane, and contact of impurities. To do.

  In order to achieve the above object, the storage device and storage method of the present invention are stored in an atmosphere excluding oxygen, in an atmosphere in which moisture fluctuation is prevented, and in a sealed container in which contact with impurities is prevented. By purging the active gas into the container and simultaneously enclosing hydrogen gas in the container, a small amount of oxygen remaining inside the container or flowing from the outside is removed by a combustion reaction in the catalyst layer of the membrane electrode assembly. It is characterized by that.

  In order to achieve the above object, the inert gas and the fuel gas purged in the sealed container have the same humidity as the gas in the sealed container before purging, thereby preventing humidity fluctuations during the gas purge. It is characterized by.

  As a result, the inside of the sealed container has an atmosphere excluding oxygen, and due to the effect of hydrogen gas remaining in the container, the potential of the catalyst layer in the container can be lowered to around 0 V that is the hydrogen reference potential. Prevents the catalyst layer from being damaged or deteriorated due to being held at a high potential, and prevents fluctuations in the amount of moisture in the sealed container to prevent dimensional fluctuations due to humidity fluctuations in the membrane electrode assembly. Therefore, it is possible to prevent performance deterioration such as initial characteristics and durability characteristics due to long-term storage of the membrane electrode assembly.

As described above, according to the holding tube method for a fuel cell membrane electrode assembly of the present invention, oxygen which is a factor of lowering the dimensional variation of the power generation characteristics of the membrane electrode assembly for a fuel cell, the water content varies and impurities Thus, it is possible to provide a storage device and a storage method having a function of preventing contact with each other over a long period of time.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic view of a storage device for storing a membrane electrode assembly for a fuel cell according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 11 denotes a fuel cell membrane electrode assembly, in which an anode catalyst layer 13 and a cathode catalyst layer 14 are laminated on both sides of a solid polymer electrolyte membrane 12, and a porous carbon electrode 15 is bonded to each catalyst layer. Has a structured. A protective film 16 is attached to each of the porous carbon electrodes on both sides. By attaching the protective film, the catalyst surface has a role of preventing contact with impurities from the outside and a role of preventing the catalyst surface from being damaged. A polymer film resin is used as a material. The fuel cell electrode having such a configuration is stored in a state of being sealed in a sealed container 21 having a high sealing property that prevents permeation of oxygen, moisture, and impurities. The sealed container is preferably a film seal with low oxygen permeability and moisture permeability. Packaging material laminated to K coat (polyvinylidene chloride coat) film, packaging material laminated to a film with low oxygen permeability such as EVOH, aluminum vapor deposited film For example, a packaging material laminated on aluminum foil or a packaging material laminated on aluminum foil can be used. A packaging material laminated to an aluminum foil is particularly desirable, but if the oxygen permeation amount is 0.01 ml / (m ² · day · atm) or less and the moisture permeability is 0.01 g / (m ² · day) or less, the aluminum foil It is not limited to the packaging material laminated. By making hermetic packaging, it is possible to prevent water vapor leaking from the inside of the container, and to prevent fluctuations in the amount of water inside the container. Thereby, the fluctuation | variation of the moisture content in a polymer electrolyte can be prevented, and deterioration of a polymer electrolyte membrane can be prevented. In addition, it is possible to prevent impurities from entering from the outside, and it is possible to prevent deterioration of the fuel cell electrode due to the impurities.

  Further, the membrane electrode assembly for a fuel cell can be stored in the middle of the assembly of the membrane electrode assembly having a structure in which the porous carbon electrode is not bonded. At this time, since the catalyst layer is prevented from coming into contact with impurities from the outside by adhering the protective film, it is possible to further prevent the power generation performance of the membrane electrode assembly from being deteriorated by long-term storage. The fuel cell membrane electrode assembly having such a configuration is also stored in a sealed state in a hermetically sealed container that prevents permeation of oxygen, moisture, and impurities.

  FIG. 2 is a schematic view of a storage method for storing a plurality of membrane electrode assemblies for fuel cells. Inside the sealed container, a plurality of membrane electrode assemblies are stacked and sealed, and the individual membrane electrode assemblies are in contact with each other by protective films attached to the anode catalyst layer and the cathode catalyst layer, A plurality of membrane electrode assemblies can be stored without being damaged. Each membrane electrode assembly for a fuel cell may be in a state in which the porous carbon electrode is not bonded or in a bonded state.

  In order to keep the inside of the sealed container in an atmosphere excluding oxygen, it is previously purged with an inert gas containing a fuel gas. Nitrogen gas is preferably used as the inert gas, but other inert gases can also be used. Hydrogen gas is used as the fuel gas. FIG. 3 shows an example of a method of purging an airtight container with an inert gas containing a fuel gas. Insert a tube that exhausts and supplies the gas inside the container while holding down the sealing port of the sealed container. The gas exhaust pipe is connected to a gas exhaust device and is opened and closed by an exhaust valve. The gas supply pipe is connected to a gas supply device and is opened and closed by a supply valve. After the air inside the container is sucked and evacuated, the valve is switched, an inert gas containing fuel gas is sealed in the container, the pipe is pulled out, and at the same time, the sealing port is heat-sealed to heat the container. It can be purged with an inert gas containing fuel gas and sealed. The gas exhaust pipe and the gas supply pipe may be the same pipe, or may be independent pipes. When the same pipe is used, a valve for switching a gas exhaust line and a gas supply line is used for the pipe.

  For sealing, a thermocompression bonding method, a chucking method, and a pressurizing method can be used. However, the thermocompression bonding method is preferable because it has high sealing performance and is simple.

  Further, the inert gas containing the fuel gas can be formed inside the container by using a method of sealing the fuel gas after purging the inert gas or a method of purging the inert gas after sealing the fuel gas. Can also be purged. At this time, it is possible to individually enclose the gas by separately using a tube that encloses the inert gas and a tube that encloses the fuel gas, and switching the valve at the time of enclosing in the sealed container.

  The supplied inert gas and fuel gas, or the mixed gas of inert gas and fuel gas, has a humidity equivalent to the humidity at the time of manufacturing the membrane electrode assembly, thereby preventing humidity fluctuations during gas purge. it can.

  The fuel gas contained in the purge gas and the oxygen gas remaining in a minute amount in the sealed container or flowing in from a small amount from the outside of the container are consumed by the combustion reaction in the catalyst layer of the membrane electrode assembly. Therefore, oxygen gas does not remain inside the container, and the catalyst layer is not held at a high potential due to oxidation of the membrane electrode assembly or oxygen, and the function deterioration of the membrane electrode assembly can be prevented.

Next, based on FIG. 4, it is verified that it is possible to realize a reduction in power generation performance and a decrease in durability performance of the membrane electrode assembly stored by the storage device and storage method for a fuel cell membrane electrode assembly according to the present invention. The results will be described. FIG. 6 shows the change in cell voltage over time. In each figure, solid line A shows the result of generating electricity after leaving the fuel cell electrode having a storage function according to the present invention for about one year, and solid line B is The result of generating electricity after leaving a conventional fuel cell electrode packaged in a simple polyethylene sheet for about one year is shown. For comparison, the result of power generation of the fuel cell electrode immediately after manufacture is shown by a broken line. In the verification test, hydrogen gas was supplied as fuel to the anode electrode, and air was supplied as a gas containing an oxidant to the cathode electrode. The operating conditions are a cell temperature of about 70 ° C., a fuel utilization of about 70%, an air utilization of about 40%, and a current density of about 0.2 A / cm ² .

  FIG. 5 shows the change over time of the cell voltage until the operation time reaches 3000 hours. The cell voltage of the fuel cell electrode according to the storage method of the present invention and that of the fuel cell electrode according to the conventional storage method are initially higher in the cell voltage of the method according to the present invention, and the fuel cell electrode immediately after production is generated. It was equivalent to the cell voltage. Moreover, even when looking at the voltage drop rate up to 3000 hours, the voltage drop rate of the cell voltage is lower with the method of the present invention, which is equivalent to the voltage drop rate of the cell voltage generated by the fuel cell electrode immediately after production. there were. Furthermore, when power generation was continued for a long time, the cell using the fuel cell electrode by the normal storage method progressed faster than usual, and the cell using the fuel cell electrode immediately after production was generated. It was confirmed that a sudden voltage drop occurred in a much earlier time than in the case, and power generation became impossible. Therefore, the use of the solid polymer electrolyte fuel cell having the storage function according to the method of the present invention prevents the deterioration of the power generation performance and durability performance of the fuel cell electrode due to long-term storage, as compared with the storage by the conventional method. I found out that I could do it.

  According to this configuration, the fuel cell membrane electrode assembly alone is stored in a sealed container that prevents permeation of oxygen, moisture, and impurities, in an oxygen-removed atmosphere state, and in a state that prevents fluctuations in the moisture content in the container. It is possible to prevent a decrease in power generation performance during storage of the membrane electrode assembly for fuel cells by using a storage method that performs the process, and the performance of the membrane electrode assembly alone is not deteriorated over a long period of time. A storage device and a storage method can be provided.

(Embodiment 2)
FIG. 4 is a schematic diagram of a storage device for storing a fuel cell membrane electrode assembly according to Embodiment 2 of the present invention.

  Similar to Embodiment 1, the fuel cell membrane electrode assembly is stored in a storage container with a protective film attached thereto. The membrane / electrode assembly may be in a state in which a porous carbon electrode is adhered, or a state in which a catalyst layer is only laminated on a polymer electrolyte membrane.

  As the storage container, a metal or resin sealed container that prevents permeation of oxygen, moisture, and impurities from the outside can be used. If it is a metal container with low oxygen permeability and moisture permeability compared with Embodiment 1, a more stable storage state is realizable. Further, the volume of the container can be increased, and a large amount of the membrane electrode assembly can be stored inside.

  In a sealed state, the storage container includes a gas exhaust port for degassing the gas inside the container, and a gas supply port for purging inert gas and fuel gas. A gas exhaust pipe and a gas supply pipe are connected to the gas exhaust port and the gas supply port, and gas exhaust and gas supply inside the container can be performed using the respective on-off valves. The gas exhaust port and the gas supply port may be the same. In this case, the connection between the exhaust pipe and the supply pipe is changed using a valve. The gas exhaust pipe is connected to a gas exhaust device. The gas supply pipe is connected to a device that supplies a mixed gas of an inert gas and a fuel gas. Further, the inert gas containing the fuel gas can be formed inside the container by using a method of sealing the fuel gas after purging the inert gas or a method of purging the inert gas after sealing the fuel gas. Can also be purged. At this time, it is possible to individually enclose the gas by separately using a tube that encloses the inert gas and a tube that encloses the fuel gas, and switching the valves when supplying the gas to the gas supply tube.

Holding tube method for a fuel cell membrane electrode assembly of the present invention has a storage function to prevent the deterioration of power generation performance due to long-term storage of the fuel cell electrodes, electrical reacting a gas containing a fuel gas an oxidant It can be applied in applications preventing coercive tube method in performance degradation due to storage in the long term chemical devices.

Schematic which shows the storage apparatus of the membrane electrode assembly in Embodiment 1 of this invention. Schematic which shows the storage apparatus of the several membrane electrode assembly in Embodiment 1 of this invention Schematic which shows the gas purge method of the storage apparatus in Embodiment 1 of this invention Schematic which shows the gas purge method of the storage apparatus in Embodiment 2 of this invention. Diagram showing changes in cell voltage over time

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Membrane electrode assembly for fuel cells 12 Solid polymer electrolyte membrane 13 Anode catalyst layer 14 Cathode catalyst layer 15 Porous carbon electrode 16 Protective membrane 21 Sealed vessel 31 Gas exhaust pipe 32 Gas supply pipe 33 Gas exhaust device 34 Gas exhaust on-off valve 35 Gas supply device 36 Gas supply on / off valve 51 Sealed container device

Claims (7)

In a membrane electrode assembly for a fuel cell in which a catalyst layer is formed in each of one surface and the other surface of a solid polymer electrolyte membrane,
The conjugate moisture permeability 0.01g / (m ² · day) or less, and wherein the benzalkonium stored in oxygen permeability of ^{0.01ml / (m 2 · day ·} atm) or less in the closed container Storage method of membrane electrode assembly for fuel cell. Purging the inside of the sealed container with an inert gas and enclosing hydrogen gas in the container to remove oxygen in the sealed container,
The storage method of the membrane electrode assembly for fuel cells of Claim 1. Storage method of a fuel cell membrane electrode assembly according to claim 1 or 2 porous carbon electrode is bonded to the respective surfaces of the front Kisawa medium layer. The method for storing a membrane electrode assembly for a fuel cell according to claim 3, wherein a polymer film resin is further attached to each surface of the porous carbon electrode. The membrane electrode for a fuel cell according to any one of claims 1 to 4 , wherein a surface of the outermost layer of the electrolyte membrane that is opposite to the electrolyte membrane side is in close contact with the sealed container. Storage method of the joined body. The method for storing a membrane electrode assembly for a fuel cell according to any one of claims 2 to 5 , wherein the inert gas is nitrogen gas. The method for storing a membrane electrode assembly for a fuel cell according to any one of claims 2 to 6 , wherein the inert gas has the same humidity as the gas in the container before purging.

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