JP2023074980A - Fuel battery employing medium temperature membrane - Google Patents

Abstract

To provide a configuration which blocks backflow of liquid water from a manifold or a pipe for an exhaust gas to a membrane electrode assembly of a cell in a fuel battery including the membrane electrode assembly adopting a medium temperature membrane.SOLUTION: In a fuel battery cell, a membrane electrode assembly 13 adopting a medium temperature membrane is held by a pair of separators 10 and 11 and gas passages 10a and 11a in which a reaction gas is circulated are provided between the membrane electrode assembly and the pair of separators. The gas passages are communicated to supply-side manifolds 1a and 2b and exhaust-side manifolds 3a and 3b, and the reaction gas is circulated from the supply-side manifolds through the corresponding gas passages to the corresponding exhaust-side manifolds. A mesh member 16 capable of holding liquid water is disposed between the gas passage and the exhaust-side manifold at a downstream side of the membrane electrode assembly.SELECTED DRAWING: Figure 2

Description

The present invention relates to the structure of a fuel cell, and more particularly, the structure of a gas discharge channel in a fuel cell using a medium temperature membrane (membrane electrode assembly or power generation membrane operating at 100° C. or higher). related to.

In a fuel cell that produces electricity by reacting hydrogen and oxygen, where water is produced and discharged, the cells or stacks of the fuel cell should be designed so that the discharged water does not affect the operation of the fuel cell. Various structures have been proposed. For example, in Patent Document 1, when the fuel cell is stopped, the condensed water that has accumulated in the internal manifold that discharges water is sucked back into the gas flow path, freezes below freezing, and blocks the gas flow path. In order to prevent this, grooves extending in the circumferential direction are formed in the inner wall surface of the internal manifold, and the condensed water is retained in the grooves by capillary action in such grooves and is prevented from being sucked back to the gas flow path. is proposed. In Patent Document 2, liquid water accumulated in the lower portion of the gas manifold flows out into the gas flow path at the connection portion between the gas flow path of the single fuel cell and the gas manifold connected to the gas flow path. A configuration has been proposed in which a projection-shaped water outflow blocking portion is provided to block the flow of water, thereby preventing water from being sucked back into the gas flow path. In Patent Document 3, in order to prevent the gas flow from being obstructed by condensed water in the reaction gas supply path, the reaction gas supply passage and the discharge passage are covered with an insulating sealing member that communicates with each other. A bypass flow path is formed to allow the condensed water in the reactant gas supply path to be discharged. Furthermore, in Patent Document 4, in a fuel cell system used in a low-temperature environment, an air path through which oxygen passes or a hydrogen path through which hydrogen passes so that moisture inside the fuel cell can be removed after operation is stopped. is branched to provide a moisture adsorption section equipped with an adsorbent, and after the normal operation of the fuel cell is stopped, the fluid in the path circulates through the moisture adsorption section to adsorb moisture inside the fuel cell to the moisture adsorption section. A configuration is disclosed that allows the

JP 2007-42538 JP 2006-228625 JP 2006-179455 JP 2002-208429

By the way, in recent years, as a membrane electrode assembly (power generation membrane) in which ion exchange is performed in a fuel cell, a configuration employing a membrane that operates at 100° C. or higher (referred to as a "medium temperature membrane") has been developed. there is As such a medium temperature membrane, a solid substrate membrane impregnated with a liquid acid is proposed as a candidate. In the case of a membrane electrode assembly employing such an intermediate temperature membrane, unlike the one using a normal aqueous ion exchange membrane, the membrane does not require liquid water, so a configuration for humidifying the membrane is not required. Since the water molecules, which are the products of the power generation reaction, are discharged as water vapor, there is no need for a gas-liquid separation process in the treatment of the exhaust gas, and further miniaturization of fuel cells is expected to be facilitated. there is

In the case of a membrane electrode assembly employing a medium temperature membrane as described above, the membrane is a solid substrate membrane impregnated with liquid acid, and contact with liquid water may cause damage to the membrane, such as dissolution of the membrane. There is Regarding this point, the fuel cell adopting the intermediate temperature membrane is maintained at 100° C. or higher during the operation of the fuel cell, and the water molecules become water vapor, so there is no problem. is reduced and water vapor condenses into liquid water in the exhaust gas manifold and piping, and it is necessary to prevent such liquid water from contacting the membrane electrode assembly. Therefore, it is preferable to provide a structure that prevents the liquid water in the exhaust gas manifold or piping from flowing backward to the membrane electrode assembly in the fuel cell.

Thus, one object of the present invention is to prevent backflow of liquid water from the exhaust gas manifold or piping to the cell's membrane electrode assembly in a fuel cell having a membrane electrode assembly employing a medium temperature membrane. It is to provide a configuration that

According to the present invention, the above problem is solved by sandwiching a membrane electrode assembly employing a medium-temperature membrane between a pair of separators, and reacting gas between the membrane electrode assembly and the pair of separators. Flow paths are provided, each of said gas flow paths communicating with a supply manifold and an exhaust manifold, and from each of said supply manifolds through corresponding respective ones of said gas flow paths to corresponding ones of said exhaust manifolds. A fuel cell configured to allow the reaction gas to flow through each of the fuel cells, wherein liquid water can be retained between the gas flow path on the downstream side of the membrane electrode assembly and the discharge side manifold. is achieved by a fuel cell in which a mesh member is arranged.

In the above configuration, the "membrane electrode assembly employing a medium temperature membrane" is, as described above, an assembly of a membrane that performs ion exchange at 100°C or higher and an electrode layer. It may be an impregnated solid membrane. Such a membrane electrode assembly is sandwiched between a pair of separators in a normal manner, and a gas flow path through which reaction gas flows is formed between the separator and the membrane electrode assembly in a normal manner. As for the reactant gas, the gas flowing through the gas passage on the anode side is the fuel gas (hydrogen gas), and the gas flowing through the gas passage on the cathode side is the oxidant gas (air). The gas passages through which these gases flow communicate with the supply-side manifold and the discharge-side manifold, respectively, and the fuel gas and the oxidant gas are supplied from the supply-side manifold to the gas passages, It contributes to the power generation reaction in the membrane electrode assembly and is discharged to the discharge side manifold. In one embodiment of the power generation reaction, hydrogen molecules release electrons to the electrode on the anode side, hydrogen ions move toward the cathode side in the film, and oxygen molecules release electrons from the electrode on the cathode side. is received, ionized, and combined with hydrogen ions that have migrated from the anode side to produce water. In this case, water vapor is contained in the oxidizing gas discharge side manifold. In another aspect of the power generation reaction, hydrogen molecules release electrons to the electrode on the anode side and become ionized, and on the cathode side, oxygen molecules receive electrons from the electrode and become oxygen ions, which travel toward the anode side. It may also be a reaction in which hydrogen ions migrate through the membrane and combine with hydrogen ions on the anode side to produce water. In this case, water vapor is contained in the manifold on the fuel gas discharge side. Note that, typically, a plurality of fuel cells form a stack, and the gas flow path of each cell communicates with a common supply-side manifold and discharge-side manifold.

In the fuel cell as described above, since the membrane electrode assembly is heated to 100° C. or more during the operation of the fuel cell, the water generated by the power generation reaction is discharged from the gas flow path in the form of water vapor. When the operation of the fuel cell stops at the point where it flows out to the manifold, the temperature drops and the water vapor condenses in the discharge side manifold to become liquid water. If it reaches the zygote, it may damage the mesophilic membrane. Therefore, in the case of the present invention, as described above, liquid water is introduced between the gas flow path on the downstream side of the membrane electrode assembly, that is, the gas flow path through which the gas after the power generation reaction flows and the discharge side manifold. A retainable mesh member is positioned. With such a configuration, even if the water vapor contained in the gas after the power generation reaction condenses in the discharge side manifold after the fuel cell is stopped and turns into a liquid and flows back through the gas flow path, the liquid water is retained in the mesh member. Therefore, it is blocked from reaching the membrane electrode assembly. It should be noted that the gas flow path in which the mesh member is arranged may be only on the side where water vapor is contained in the gas flowing therethrough. In the power generation reaction, when hydrogen ions move through the membrane from the anode side to the cathode side and water is produced on the cathode side, the mesh member is placed between the gas flow path on the cathode side and the discharge side manifold. In a power generation reaction, when oxygen ions move through the membrane from the cathode side to the anode side and water is produced on the anode side, the mesh member is formed between the gas flow path on the anode side and the discharge side manifold. may be placed between The mesh member is a porous or net-like member made of any material that can withstand the operating temperature of the fuel cell, and is permeable to gas but retains liquid water by capillary action and adsorption action. can be The mesh member may preferably be made of a material having a hydrophilic surface.

In the above configurations, the mesh members may be arranged in various forms. In one aspect, the mesh member may be arranged so as to cover substantially the entire cross section of the region between the gas flow path and the discharge side manifold. Further, when a gas flow path is formed between the membrane electrode assembly and the separator, typically, a plurality of skewed ribs are formed in the separator along the direction of gas flow, and each of the ribs is spaced between the ribs. A gas flow path is defined in the , which joins and communicates with the discharge side manifold. In that case, the mesh members may be arranged in a spit-like arrangement along each rib, or arranged in a spit-like arrangement along the gas flow path. Alternatively, a mesh member may be arranged at each of the outlets where the gas flow paths between the ribs join together. Furthermore, in another aspect, a narrow portion is formed at the portion where the gas flow paths defined by the ribs merge and communicate with the discharge side manifold, and the mesh member is arranged at the narrow portion. may be In this case, liquid water is collected in the narrow portion by capillary action, where the liquid water is retained by the mesh member. Alternatively, if the cell is arranged with its surface direction along the vertical direction, the liquid water will accumulate at the bottom of the region between the gas flow path and the discharge side manifold. A mesh member may be arranged at a site where water is accumulated. In the fuel cell, more specifically, the gas diffusion layer is sandwiched between the membrane electrode assembly and the separator, and the gas diffusion layer is formed in a mesh structure. Therefore, the gas diffusion layer having such a mesh structure is formed to extend to the region between the gas flow path and the discharge side manifold, and the liquid water flowing back from the discharge side manifold to the gas flow path is diverted to the vicinity of the discharge side manifold. It may be possible to hold the

According to the above configuration of the present invention, in a fuel cell using a medium temperature membrane, liquid water generated in the discharge side manifold flows back through the gas flow path and reaches the membrane electrode assembly while the operation is stopped. is prevented and damage to the mesophilic membrane can be avoided. In the construction of the present invention, it is only necessary to dispose a mesh member between the gas flow path and the discharge side manifold, so it is possible to inexpensively protect the intermediate temperature membrane from liquid water, which is advantageous. When the fuel cell is restarted, the liquid water held in the mesh member is pushed to the discharge side manifold by the gas flowing through the gas flow path and discharged.

Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention.

FIG. 1A is a schematic perspective view of a fuel cell to which this embodiment is applied. FIG. 1(B) is a schematic perspective view separately showing a pair of separators and a membrane electrode assembly in a single cell of a fuel cell to which the present embodiment is applied. FIG. 2A is a schematic cross-sectional view of part of the separator to which the present embodiment is applied, and FIG. 1B is a schematic plan view for explaining the configuration of a region viewed from the direction of the arrow in FIG. 2B in FIG. FIGS. 3A, 3B, and 3C are schematic plan views of the discharge side manifold vicinity of a single cell to which a preferred aspect of the present embodiment is applied. FIGS. 4A, 4B, and 4C are schematic plan views in the vicinity of the discharge side manifold of a single cell to which a preferred aspect of the present embodiment is applied. In FIG. 4(C), the right figure is a sectional view of the structure of the left figure. FIGS. 5A and 5B are schematic plan views of the vicinity of the discharge side manifold of the single cell to which the preferred mode of the present embodiment is applied.

Reference Signs List 1 Fuel cell stack 2a Fuel gas (hydrogen gas) supply side manifold 2b Oxidant gas (air) supply side manifold 3a Fuel gas (hydrogen gas) discharge side manifold 3b Oxidant gas (air) discharge side manifold 5 Single cell 10 Anode side separator 10a Fuel gas channel 11 Cathode side separator 11a Oxidant gas channel 11g Grooved channel 11r Rib 12 Membrane electrode assembly support layer 13 Membrane electrode assembly ( power generation membrane)
16... Mesh member 17... Gas diffusion layer (mesh structure)
20...Refrigerant channel W _L ...Water droplet

The present invention will now be described in detail with respect to preferred embodiments with reference to the accompanying drawings. In the drawings, the same reference numerals denote the same parts.

Basic Configuration of Fuel Cell Referring to FIG. A plurality of unit cells 5 are stacked to form a stack 1, similar to a type fuel cell. A fuel gas supply side manifold 2a and an oxidant gas supply side manifold 2b are connected to the stack 1, and hydrogen gas (H ₂ ), which is a fuel gas, and oxygen gas, which is an oxidant gas, are supplied from the respective manifolds. Air containing gas (O ₂ ) is supplied to the anode and the cathode, respectively, to cause a power generation reaction. It flows out from the manifold 3a and the oxidizing gas discharge side manifold 3b.

Each of the unit cells 5 stacked in the stack 1 is provided with an insulating resin between an anode separator 10 and a cathode separator 11, as schematically shown in FIG. 1(B). The membrane electrode assembly 13 supported by the support layer 12 formed of the like is sandwiched (in practice, between the separators 10 and 11 and the membrane electrode assembly 3, A gas diffusion layer is interposed, and in the membrane electrode assembly 12, a structure is provided in which the electrode layers are electrically connected to the outside on both sides, but is omitted in FIG. 1(B) for the purpose of explanation. .). In such a configuration, more specifically, on the sides of the anode-side separator 10 and the cathode-side separator 11 facing the membrane electrode assembly 12, as schematically depicted in FIG. gas channels 10a and 11a are formed by ribs 11r and groove-shaped channels 11g. As shown in 1(B), the four corner openings 2a, 2b, 3a, and 3b are aligned, and a plurality of cells 5 are stacked to form a fuel gas supply side manifold 2a and an oxidant gas supply side manifold. 2b, a fuel gas discharge side manifold 3a and an oxidant gas discharge side manifold 3b are formed. The gas channel 10a on the anode side separator 10 communicates with the fuel gas supply side manifold 2a and the fuel gas discharge side manifold 3a. , passes over the membrane electrode assembly 13, and is discharged to the fuel gas discharge side manifold 3a. On the other hand, the gas channel 11a on the cathode side separator 11 communicates with the oxidant gas supply side manifold 2b and the oxidant gas discharge side manifold 3b, and the oxidant gas flows from the oxidant gas supply side manifold 2a to the gas channel 11a. 11a, passes over the membrane electrode assembly 13, and is discharged to the oxidizing gas discharge side manifold 3a. Between the fuel gas supply side manifold 2a and the oxidant gas discharge side manifold 3b, and between the oxidant gas supply side manifold 2b and the fuel gas discharge side manifold 3a, for adjusting the temperature of the fuel cell. A flow path 20 for circulating the refrigerant may be provided.

In the operation of the above fuel cell, to put it simply, the fuel gas is supplied from the fuel gas supply side manifold 2a to the gas passage 10a, and the oxidant gas is supplied from the oxidant gas supply side manifold 2b to the gas passage 11a. When supplied to the membrane electrode assembly 13, a power generation reaction is induced. In such a power generation reaction, typically, hydrogen molecules release electrons at the anode, become hydrogen ions, move to the cathode through the ion exchange membrane, and at the cathode, oxygen molecules (from the anode to the load It accepts the electrons that have passed through it to the cathode) and combines with the hydrogen ions to form water molecules. As shown in FIG. 2B, the remaining oxidant gas and water molecules pass through the gas channel 11a, which is formed by the groove-like channel 11g between the skewed ribs 11r on the cathode side. , and flows out to the oxidizing gas discharge side manifold 3b. At the anode, the remaining fuel gas (such as unreacted hydrogen gas) passes through the anode-side gas passage 10a and flows out to the fuel gas discharge side manifold 3a. Depending on the type of ion exchange membrane, oxygen ions may move through the ion exchange membrane and water molecules may be formed at the anode. In that case, the water molecules generated by the power generation reaction pass through the anode-side gas passage 10a and flow out to the fuel gas discharge side manifold 3a.

Configuration for protection of the intermediate temperature membrane Regarding the single cell of the above fuel cell, as described in the "Summary of the Invention" column, the ion exchange membrane of the membrane electrode assembly 13 has a temperature of 100 ° C. or higher. When a medium-temperature membrane that operates in an environment is used, liquid water is not used in the membrane, so there is no need for a structure for humidifying the supplied gas or the membrane, and liquid water does not exist in the discharged gas. Therefore, the gas-liquid separation process or the like becomes unnecessary in the treatment of the exhaust gas, and the fuel cell system can be made compact or miniaturized. In a fuel cell employing such an intermediate temperature membrane, among various types of materials, the use of a membrane-like member impregnated with an acid is typically considered as the intermediate temperature membrane. In this case, if liquid water comes into contact with the intermediate temperature membrane, the intermediate temperature membrane may be damaged by dissolution or the like. Regarding this point, since the single cell is placed in a temperature environment of 100° C. or higher during the operation of the fuel cell, water droplets do not come into contact with the membrane electrode assembly 13, but the operation of the fuel cell does not occur. After stopping, water molecules discharged from the discharge-side manifold 3b (or 3a) condense into a liquid, and the liquid water flows back through the gas flow path 11a (or 10a), resulting in a membrane electrode assembly. 13 may come into contact with water droplets. Therefore, in the present embodiment, in a fuel cell employing a medium temperature membrane, liquid water or water droplets are prevented from flowing back from the discharge side manifold 3b (or 3a) to the gas flow path 11a (or 10a). Arrangements are provided to protect the membrane from water droplets.

Specifically, in this embodiment, referring to FIG. 2(B), backflow of liquid water from the discharge side manifold 3b (or 3a) to the membrane electrode assembly 13 having the intermediate temperature membrane is prevented. As a configuration for doing so, a mesh member 16 is arranged in a connection region 15 between the gas flow path 11a (or 10a) and the discharge side manifold 3b (or 3a). The mesh member 16 is made of a material having a porous or mesh structure (mesh structure) that is stable under the operating temperature environment of the fuel cell and allows gas to pass therethrough. It is formed of a material that can be held within the structure. According to this configuration, while the gas discharged from the gas flow path passes through the mesh member 16 during the operation of the fuel cell, the discharge side manifold 3b (or 3a) and the cell 5 after the operation of the fuel cell stops. When the temperature of the gas flow path 11a (or 10a) drops from the discharge side manifold 3b (or 3a), the liquid water flows back through the gas flow path 11a (or 10a). Even so, it is possible to prevent such liquid water from being collected by the mesh member 16 and water droplets reaching the membrane electrode assembly 13 . Note that the mesh member 16 is arranged in the flow path of the exhaust gas containing water vapor. Therefore, in the power generation reaction, when hydrogen ions generated at the anode migrate through the medium-temperature membrane and water molecules are generated at the cathode, the mesh member 16 serves as a membrane electrode in the gas flow path 11a for the oxidant gas. It is arranged in the region between the downstream of the junction body 13 and the discharge side manifold 3b, and in the power generation reaction, when oxygen ions generated at the cathode move through the intermediate temperature membrane and water molecules are generated at the anode , the mesh member 16 is arranged in the region between the downstream side of the membrane electrode assembly 13 in the gas flow path 10a of the fuel gas and the discharge side manifold 3a.

Various Aspects of Mesh Member Arrangement The mesh member 16 arranged in the connection region 15 between the gas flow path 11a (or 10a) and the discharge side manifold 3b (or 3a) is arranged from the discharge side manifold 3b (or 3a). As long as the liquid water flowing toward the membrane electrode assembly 13 can be captured, it may be arranged in any manner as exemplified below. In the following example, the structure of the oxidant gas discharge side manifold 3b is explained. may be provided and still be within the scope of this embodiment.

Specifically, first, as shown in FIG. 3A, a mesh member 16 may be arranged so as to cover the entire area 15 between the gas flow path 11a and the discharge side manifold 3b. With such a configuration, liquid water can be collected more reliably.

Also, as shown in FIG. 3B, the mesh member 16 may be arranged along the rib portion 11r of the gas flow path 11a. In this case, since no mesh member is arranged in the groove-shaped flow path 11g through which the gas flows, the pressure loss of the gas during operation of the fuel cell can be suppressed to a lower level.

Alternatively, as shown in FIG. 3(C), the mesh member 16 may be arranged along the groove-like channel 11g of the gas channel 11a. In this case, water droplets trying to enter the groove-shaped flow passage 11g can be more reliably collected, and since the mesh member is not placed on the extension line of the rib portion 11r, fuel consumption is reduced more than in the case of FIG. 3(A). Gas pressure loss during battery operation can be suppressed to a lower level.

Furthermore, as shown in FIG. 4(A), the mesh member 16 may be arranged so as to be inclined with respect to the extending direction of the groove-like channel 11g of the gas channel 11a. In this case, since there is no path to enter the groove-shaped flow path 11g straight from the discharge side manifold 3b, water droplets can be collected more effectively. The pressure loss of gas is suppressed to a lower level.

Furthermore, as shown in FIG. 4(B), the mesh member 16 may be arranged so as to enter the outlet of the grooved channel 11g of the gas channel 11a. In this case, water droplets entering the groove-shaped flow path 11g can be more reliably collected, and the space for arranging the mesh member between the gas flow path 11a and the discharge-side manifold 3b can be saved, thereby reducing the number of cells. This means that the size can be further reduced.

Alternatively, referring to FIG. 4(C), in part of the region 15 between the gas flow path 11a and the discharge side manifold 3b, as shown on the right side of the figure, the separator 11 and the support layer 12 are separated from each other. The parts may form a shape in which the parts are close to each other to form a part narrower than the surroundings, and the mesh member 16 may be arranged in this part as shown on the left side of the figure. In this case, the liquid water _WL is collected by capillary action as shown in the figure at a portion narrower than the surrounding area, where it is collected by the mesh member, thus more reliably removing water droplets _WL . It can be collected. In addition, since the portion where the mesh member 16 is arranged becomes a part of the region 15, the flow path of the gas is ensured, and the pressure loss of the gas during the operation of the fuel cell is suppressed to a lower level.

Furthermore, in the case of a structure in which the surface direction of the cell is arranged in the vertical direction, as shown in FIG. Since the water _WL stays and flows at the bottom of the region 15 due to gravity, the mesh member 16 may be arranged at the bottom of the region 15 . In this case, the liquid water is collected by the mesh member 16, and the portion where the mesh member 16 is arranged becomes a part of the region 15, so that the flow path of the gas is secured and the fuel cell is operated. , the pressure loss of the gas is suppressed to a lower level.

By the way, in the single cell, as already mentioned, the gas diffusion layer is sandwiched between the membrane electrode assembly and the separator, and the gas diffusion layer is formed of a mesh material. Therefore, as schematically depicted in FIG. 5B, the gas diffusion layer 17 is extended to the discharge side manifold 3b so as to cover the region 15 between the gas flow path 11a and the discharge side manifold 3b. may be formed. With such a configuration, the gas diffusion layer 17 functions in the same manner as the mesh member 16, captures liquid water from the discharge side manifold 3b, and protects the intermediate temperature membrane from liquid water. Moreover, in this case, there is no need to separately provide the mesh member 16, and an increase in the number of parts can be suppressed.

Although the above description has been given with reference to the embodiments of the present invention, many modifications and changes will readily occur to those skilled in the art, and the present invention is limited only to the above-exemplified embodiments. It will be clear that the invention is non-limiting and can be applied to a variety of devices without departing from the concept of the invention.

Claims (1)

A membrane electrode assembly employing a medium-temperature membrane is sandwiched between a pair of separators, and a gas flow path through which a reactant gas flows is provided between the membrane electrode assembly and the pair of separators, and the gas flow path includes: Each of them communicates with a supply side manifold and a discharge side manifold, and is configured such that the reaction gas flows from each of the supply side manifolds through corresponding ones of the gas flow paths to corresponding respective discharge side manifolds. a fuel cell comprising:
A fuel cell in which a mesh member capable of retaining liquid water is arranged between the gas flow path on the downstream side of the membrane electrode assembly and the discharge side manifold.

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