JP2022043608A - Fuel battery - Google Patents

Abstract

To provide a fuel battery that can efficiently discharge a gaseous reactant generated by electrode reaction to the outside.SOLUTION: A fuel battery includes a permeable membrane 52 that separates carbon dioxide (CO2) or the like which is a gas reactant generated at an anode electrode due to the electrode reaction in a MEA 40 from formic acid which is a liquid fuel by selectively permeating carbon dioxide (CO2) or the like. Alternatively, the fuel cell includes a discharge path 28 formed in a cathode side separator 20. The discharge path 28 is airtightly partitioned with respect to a fuel supply flow path 11 of the anode-side separator 10 by a permeable membrane 52, and discharges carbon dioxide (CO2) or the like that has passed through the permeable membrane 52 to the outside since an air which is a pressurized fluid pressurized in a state where the electrode reaction occurs in the MEA 40 flows.SELECTED DRAWING: Figure 11

Description

The present invention relates to a fuel cell.

A fuel cell, particularly a solid polymer fuel cell, generally includes an electrode structure including an anode electrode formed on one surface side of an electrolyte membrane and a cathode electrode formed on the other surface side. Then, in the polymer electrolyte fuel cell, the fuel is supplied to the anode electrode and the oxidizing agent is supplied to the cathode electrode from the outside, so that an electrode reaction occurs in the electrode structure and power is generated.

In recent years, a direct fuel cell that directly uses a liquid fuel such as methanol or formic acid as a fuel to be supplied to the anode electrode has been developed. When a liquid fuel is used, it is easier to handle and has a higher energy density per volume than when hydrogen gas is used as a fuel, which is extremely useful.

However, when methanol, formic acid, or the like is used as a fuel, gas reactants such as carbon dioxide (CO ₂ ) and carbon monoxide (CO) are generated on the anode electrode side along with the electrode reaction. If the gas reactant remains on the surface of the anode electrode, the contact between the catalyst forming the anode electrode and the liquid fuel may be impaired, and as a result, the power generation efficiency of the fuel cell may decrease.

For this reason, conventionally, for example, Patent Document 1, Patent Document 2, and Patent Document 3 have described a technique of separating the generated gas reactant via a permeable membrane and removing it from the surface of the anode electrode, particularly the catalyst. Is disclosed.

Japanese Unexamined Patent Publication No. 2005-235519 Japanese Unexamined Patent Publication No. 2011-129431 Japanese Unexamined Patent Publication No. 2006-278295

However, the above-mentioned conventional technique does not have a configuration in which the gas reactant that has passed through the permeable membrane is continuously discharged to the outside of the fuel cell. Therefore, in a situation where the gas reactant is not discharged to the outside, there is a possibility that the gas reactant that has already permeated the permeable membrane will be accumulated and a new gas reactant will not be able to permeate the permeable membrane. In this case, for example, a state in which a gas reactant adheres to the anode electrode may occur, and as a result, the power generation efficiency of the fuel cell may decrease. Therefore, there is room for improvement in the above-mentioned conventional technique in that the gas reactant that has permeated the permeable membrane is discharged to the outside.

An object of the present invention is to provide a fuel cell capable of efficiently discharging a gaseous reactant generated by an electrode reaction to the outside.

The fuel cell has an electrode structure having an electrolyte membrane, an anode electrode and a cathode electrode, an anode-side separator having a fuel supply flow path for supplying liquid fuel to the anode electrode, and an oxidant supply flow for supplying an oxidant to the cathode electrode. A fuel cell comprising a cathode side separator having a path, forming a single cell in which an electrode structure is arranged between a pair of anode side separators and a cathode side separator, and generating power by an electrode reaction in the electrode structure. A permeation film that separates the gas reactant from the liquid fuel by selectively permeating the gas reactant generated at the anode electrode during the electrode reaction, and a permeation membrane that is airtight with respect to the fuel supply flow path. It is partitioned and includes a discharge path for discharging the gaseous reactants that have passed through the permeable film to the outside by flowing the fluid in a state where the electrode reaction is occurring in the electrode structure.

According to this, the gas reactant generated by the electrode reaction in the electrode structure is separated from the liquid fuel by penetrating the permeable film. This makes it possible to remove the gas reactant from the vicinity of the electrode structure, for example, the anode electrode. Then, the gas reactant separated from the liquid fuel, that is, permeated through the permeable membrane, is discharged to the outside of the fuel cell together with the fluid through the discharge path through which the fluid flows. As a result, the already generated gas reactant does not accumulate, and the newly generated gas reactant can be efficiently and continuously discharged to the outside. Therefore, even in a situation where the fuel cell continues to generate power, the gas reactant generated by the electrode reaction can be continuously discharged to the outside, and the decrease in the power generation efficiency of the fuel cell due to the generated gas reactant can be suppressed. can do.

It is a figure which shows the structure of a fuel cell. It is a figure which shows the structure of the fuel cell stack formed by the laminated single cell. It is a figure which shows the structure of the anode side separator. It is a figure which shows the structure of one side of a cathode side separator. It is a figure which shows the structure of the other side of a cathode side separator. It is a figure which shows the structure of a seal member. It is a figure which shows the structure of MEA. It is sectional drawing which shows the cross section of MEA in VIII-VIII of FIG. It is a figure which shows the structure of the transmission member. It is a figure for demonstrating the structure of a single cell. It is sectional drawing to explain the separation and discharge of a gas reactant. It is sectional drawing for demonstrating the structure of the 1st example.

(1. Overview of fuel cell)
In this example, a polymer electrolyte fuel cell is exemplified as the fuel cell. That is, in the fuel cell of this example, the anode electrode is formed on one surface side of the electrolyte membrane, and the cathode electrode is formed on the other surface side of the electrolyte membrane. Here, the electrolyte membrane, the anode electrode, and the cathode electrode form a MEA (Membrane-Electrode-Assembly: membrane-electrode assembly) which is an electrode structure.

Further, the fuel cell of this example is provided with an anode-side separator (including a collector) for supplying liquid fuel to the anode electrode and a cathode-side separator (including a collector) for supplying an oxidizing agent to the cathode electrode. In the fuel cell of this example, one cell (hereinafter referred to as a single cell) including the MEA, the anode side separator, and the cathode side separator is formed, and a plurality of single cells are stacked to form a fuel cell stack. It is formed.

In this example, as the liquid fuel supplied to the anode electrode of the fuel cell, formic acid (HCOOH), methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH) and the like can be exemplified. Here, in the fuel cell described below, a case where formic acid is directly used as the supplied liquid fuel will be exemplified. That is, the fuel cell of this example is a polymer electrolyte fuel cell, and directly exemplifies a formic acid fuel cell (DFAFC). Further, in this example, as the oxidizing agent (oxidizing agent gas) supplied to the cathode electrode of the fuel cell, oxygen (O ₂ ) gas, air, or the like can be exemplified. Here, in the fuel cell described below, a case where air is used as the oxidant of the supplied gas, that is, the oxidant gas will be exemplified.

The fuel cell of this example includes a permeable membrane that allows only the gas reactant generated at the anode electrode to pass through. Further, the fuel cell of this example includes a discharge path for discharging a gas reactant that has passed through the permeable membrane to the outside.

In the case of a direct formic acid type fuel cell, when formic acid, which is a liquid fuel, is directly supplied to the anode electrode of the MEA, carbon dioxide (CO ₂ ) and carbon monoxide (CO) are generated as gas reactants along with the electrode reaction in the MEA. Occur. Therefore, when formic acid and carbon dioxide (CO ₂ ) (or carbon monoxide (CO)) are mixed in the vicinity of the anode electrode, the permeation film is a gas such as carbon dioxide (CO ₂ ) or carbon monoxide (CO 2). Gas-liquid separation is performed by selectively permeating CO). As a result, only carbon dioxide (CO ₂ ) and carbon monoxide (CO) can pass through the transmission membrane and move to the discharge path, and carbon dioxide (CO ₂ ) and carbon monoxide (CO) can be transmitted from the anode electrode. Will be removed.

Further, the discharge path can be formed, for example, in the cathode side separator constituting the adjacent single cell in the fuel cell stack. That is, the discharge path is adjacent to the anode electrode that generates carbon dioxide (CO ₂ ) and carbon monoxide (CO), and more specifically, the permeation membrane that allows carbon dioxide (CO ₂ ) and carbon monoxide (CO) to permeate. It can be formed on the cathode side separator. In this case, for example, a pressurized oxidant (air) can flow as a pressurized fluid in which the fluid is pressurized in the discharge path. As a result, carbon dioxide (CO ₂ ) and carbon monoxide (CO) that have permeated the permeation membrane are externally present together with, for example, an oxidant (air) through the discharge path formed in the cathode side separator adjacent to the permeation membrane. Is discharged to. As for the fluid, instead of pressurizing it, for example, it is possible to suck it from the outside and let it flow.

(2. Details of the configuration of the direct formic acid fuel cell 1)
Hereinafter, the configuration of the direct formic acid type fuel cell 1 (hereinafter, simply referred to as “fuel cell 1”) of this example will be described with reference to the drawings. As shown in FIG. 1, the fuel cell 1 of this example forms a fuel cell stack S. The fuel cell stack S is in a state in which a plurality of single cells U are stacked, and the plurality of stacked single cells U are held by the holder H and the bolt B. In this example, the plurality of single cells U are arranged along the horizontal direction, and each is stacked vertically upward. A fuel pump P1 that pressurizes and supplies formic acid, which is a liquid fuel stored in the supply tank T1, is connected to the fuel cell stack S via a pipe (not shown). Further, a blower P2 (pressurizing pump) that pressurizes and supplies air as an oxidizing agent (oxidizing agent gas) is connected to the fuel cell stack S via a pipe (not shown).

As shown in FIG. 2, the single cell U of this example has a seal member 30 and a MEA 40 arranged and laminated between the anode side separator 10, the cathode side separator 20, and the anode side separator 10 and the cathode side separator 20. Consists of including. The single cell U of this example has a transmission member 50 that selectively permeates carbon dioxide (CO ₂ ) generated by an electrode reaction in MEA 40 (more specifically, an anode electrode layer AE which is an anode electrode described later). .. Here, the transmission member 50 is a single cell U that is laminated and adjacent to the cathode side separator 20 of the single cell U1 that is vertically arranged and adjacent to the single cell U that is vertically arranged and adjacent to the cathode side separator 20. It is hermetically arranged by being sandwiched between the anode side separator 10 of the cell U2.

As shown in FIG. 3, the anode-side separator 10 is formed in a plate shape. The anode-side separator 10 of this example has a current collecting function (so-called collector) for collecting electricity generated by the electrode reaction in MEA40, and is made of a metal material, for example, stainless steel such as SUS316. Conductive treatment such as gold plating is applied to the thin plate or the like. In this example, the anode side separator 10 is formed by using a metal material, but it may also be formed by using a conductive non-metal material (for example, carbon or a composite material with carbon) as a material. It is possible.

At the central portion of the anode side separator 10, that is, at the position facing the anode electrode layer AE of the MEA40, formic acid, which is a liquid fuel, is supplied to the anode electrode layer AE, and carbon dioxide (CO) generated in the anode electrode layer AE is supplied. _A fuel supply flow path 11 for collecting air toward the transmission member 50 is formed. As shown in FIG. 3, the fuel supply flow path 11 of this example is formed so as to meander, and is formed so as to penetrate in the plate thickness direction of the anode side separator 10. In this example, the case where the fuel supply flow path 11 is formed so as to meander is illustrated, but the shape of the fuel supply flow path 11 is not limited to this.

Further, on the peripheral portion of the anode side separator 10, a fuel supply port 12 for supplying formic acid to the fuel supply flow path 11 and a fuel discharge port 13 for discharging formic acid that has passed through the fuel supply flow path 11 are provided. Will be. The fuel supply port 12 is supplied with formic acid pressurized by a fuel pump P1 (see FIG. 1) provided outside the fuel cell stack S. The fuel pump P1 pressurizes and supplies formic acid stored in the supply tank T1 (see FIG. 1). The fuel discharge port 13 is connected to a recovery tank T2 (see FIG. 1) provided outside the fuel cell stack S, and discharges the discharged formic acid to the recovery tank T2.

As a result, in the single cell U of this example, formic acid pressurized by the fuel pump P1 is supplied from the supply tank T1 to the fuel supply flow path 11 from the fuel supply port 12, and the formic acid flowing through the fuel supply flow path 11 is the anode. It reaches the fuel discharge port 13 while in contact with the electrode layer AE. Then, the formic acid that has reached the fuel discharge port 13, that is, unreacted formic acid, is recovered in the recovery tank T2.

Further, a through hole 14 and a through hole 15 for supplying air to the cathode side separator 20 constituting the single cell U and discharging unreacted air are provided on the peripheral portion of the anode side separator 10. The through holes 14 and 15 are provided at positions displaced by, for example, 90 degrees from the fuel supply port 12 and the fuel discharge port 13. Further, a plurality of large-diameter insertion holes 16 (8 locations in FIG. 3) for inserting the bolt B of the holder H are provided on the peripheral portion of the anode side separator 10 and for extracting electricity to the outside. The electrode portion 17 is provided. The electrode portion 17 may be provided only on the anode-side separator 10 constituting the single cell U located at the uppermost portion, for example, when the fuel cell stack S is formed.

The cathode side separator 20 is formed in a plate shape as shown in FIGS. 4 and 5. The cathode side separator 20 of this example also has a current collecting function (so-called collector) for collecting electricity generated by the electrode reaction in the MEA 40, and is made of a metal material such as stainless steel such as SUS316. Conductive treatment such as gold plating is applied to the thin plate or the like. In this example, the cathode side separator 20 is also formed by using a metal material like the anode side separator 10, but a non-metal material having conductivity (for example, carbon or a composite material with carbon) is used. ) Can also be used as a material.

As shown in FIG. 4, an oxidizing agent (oxidizing agent gas) is provided on one side of the cathode side separator 20 facing the MEA 40 (more specifically, the cathode electrode layer CE which is a cathode electrode described later). An oxidizing agent supply flow path 21 for supplying air to the cathode electrode layer CE is formed. The case where the oxidizing agent supply flow path 21 of this example is formed as linear unevenness is exemplified. The oxidant supply channel 21 can be formed in a shape similar to that of the fuel supply channel 11.

Further, at the peripheral portion of the cathode side separator 20, an oxidant supply port 22 for supplying air, that is, oxygen (O ₂ ) to the oxidant supply flow path 21, and air passing through the oxidant supply flow path 21 are discharged. An oxidant discharge port 23 is provided for this purpose. The oxidant supply port 22 is supplied with air pressurized by a blower P2 (see FIG. 1) provided outside the fuel cell stack S. In this example, the fuel cell 1 is provided with a blower P2, and air is pressurized and supplied by the blower P2. However, it is also possible to omit the blower P2 if necessary.

The oxidant discharge port 23 discharges the discharged air to the outside of the fuel cell stack S. As a result, in the single cell U of this example, the air pressurized by the blower P2, that is, oxygen (O ₂ ) is supplied from the oxidant supply port 22 to the oxidant supply flow path 21, and the oxidant supply flow path 21 is provided. The flowing air, that is, oxygen (O ₂ ), reaches the oxidant discharge port 23 while contacting the cathode electrode layer CE. Then, the unreacted air (oxygen (O ₂ )) that has reached the oxidant discharge port 23 is discharged to the outside of the fuel cell stack S.

Further, a through hole 24 and a through hole 25 for supplying formic acid to the anode side separator 10 constituting the single cell U and discharging unreacted formic acid are provided on the peripheral portion of the cathode side separator 20. The through holes 24 and 25 are provided at positions displaced by, for example, 90 degrees from the oxidant supply port 22 and the oxidant discharge port 23.

Further, a plurality of large-diameter insertion holes 26 (8 locations in FIGS. 4 and 5) for inserting the bolt B of the holder H are provided on the peripheral portion of the cathode side separator 20, and electricity is supplied to the outside. An electrode portion 27 for taking out is provided. The electrode portion 27 can be provided only on the cathode side separator 20 constituting the single cell U located at the lowermost portion, for example, when the fuel cell stack S is formed.

Here, the fuel supply port 12 of the anode side separator 10 can communicate with the through hole 24 of the cathode side separator 20, and the fuel discharge port 13 of the anode side separator 10 can communicate with the through hole 25 of the cathode side separator 20. Ru. Further, the oxidant supply port 22 of the cathode side separator 20 can communicate with the through hole 14 of the anode side separator 10, and the oxidant discharge port 23 of the cathode side separator 20 can communicate with the through hole 15 of the anode side separator 10. Will be done. That is, the through holes 14 and 15 of the anode side separator 10 are formed corresponding to the oxidant supply port 22 and the oxidant discharge port 23 of the cathode side separator 20, and the through holes 24 and 25 of the cathode side separator 20 are the anode side separators. It is formed corresponding to the fuel supply port 12 and the fuel discharge port 13 of 10.

Further, as shown in FIG. 5, on the other side of the central portion of the cathode side separator 20, that is, on the back side of the formation surface of the oxidizing agent supply flow path 21, is a gas reactant separated by the transmission member 50. A discharge path 28 for discharging carbon dioxide (CO ₂ ) to the outside is formed. The discharge passage 28 of this example is formed in a concave shape. Then, one end side, that is, the upstream side of the discharge path 28 is connected to the oxidant supply port 22, and the other end side, that is, the downstream side of the discharge path 28 is connected to the oxidant discharge port 23.

As a result, in a state where the single cells U are laminated to form the fuel cell stack S, a part of the air pressurized by the blower P2 and supplied to the oxidant supply port 22 is an oxidant (oxidizer gas). The other part flows through the discharge passage 28 as a pressurized fluid while flowing through the oxidant supply flow path 21. That is, the air supplied to the oxidant supply port 22 flows through the oxidant supply flow path 21 and the discharge path 28 by being branched.

As a result, as will be described later, the carbon dioxide (CO ₂ ) that has permeated through the permeation member 50 is discharged to the outside of the fuel cell stack S from the oxidant discharge port 23 together with the air that is the pressurized fluid flowing through the discharge path 28. .. Here, in order to facilitate the permeation of carbon dioxide (CO ₂ ) toward the discharge path 28 through the transmission film 52, the cross-sectional area of the oxidant supply flow path 21 that supplies air to the cathode electrode layer CE is compared with the flow path cross-sectional area. The cross-sectional area of the flow path of the discharge path 28 is reduced. As a result, the flow velocity of the air flowing through the discharge passage 28 can be made larger than the flow velocity of the formic acid flowing through the fuel supply passage 11, and the pressure inside the discharge passage 28 is larger than the pressure inside the fuel supply passage 11. Can be lowered. As a result, carbon dioxide (CO ₂ ) generated in the anode electrode layer AE permeates the permeable membrane 52 due to the pressure difference (differential pressure) generated inside the fuel supply flow path 11 and the inside of the discharge path 28. As a result, it becomes easy to enter toward the discharge path 18.

As shown in FIG. 6, the seal member 30 is formed in a plate shape. Here, the sealing member 30 is formed of an elastic material, for example, a rubber material such as EPDM, an elastomer material, or the like. The seal members 30 are used in pairs, and each seal member 30 sandwiches the MEA 40 and is sandwiched by the anode side separator 10 and the cathode side separator 20.

The seal member 30 has an accommodating portion 31 penetrating so as to accommodate the anode electrode layer AE and the cathode electrode layer CE of the MEA 40 in the central portion. As a result, formic acid supplied through the fuel supply flow path 11 of the anode side separator 10 is supplied to the anode electrode layer AE by flowing inside the accommodating portion 31 in a state where the seal member 30 sandwiches the MEA 40. To. Further, in a state where the seal member 30 sandwiches the MEA 40, the air supplied through the oxidizing agent supply flow path 21 of the cathode side separator 20 flows inside the accommodating portion 31 and is supplied to the cathode electrode layer CE. To.

Further, a fuel supply port 12 (corresponding to a through hole 24 of the cathode side separator 20) and a fuel discharge port provided in the anode side separator 10 with a single cell U formed on the peripheral portion of the seal member 30. Through holes 32 and 33 are formed at positions corresponding to 13 (corresponding to the through hole 25 of the cathode side separator 20). As a result, in the state where the single cell U is formed, the fuel supply port 12 (through hole 24) communicates with the through hole 32, and the fuel discharge port 13 (through hole 25) communicates with the through hole 33.

Further, an oxidant supply port 22 (corresponding to the through hole 14 of the anode side separator 10) and an oxidant discharge port provided on the cathode side separator 20 with a single cell U formed on the peripheral portion of the seal member 30. Through holes 34 and 35 are formed at positions corresponding to 23 (corresponding to the through hole 15 of the anode side separator 10). As a result, in the state where the single cell U is formed, the oxidant supply port 22 (through hole 14) communicates with the through hole 34, and the oxidant discharge port 23 (through hole 15) communicates with the through hole 35. Further, an insertion hole 36 formed so as to insert the bolt B of the holder H is formed in the peripheral portion of the seal member 30.

As shown in FIGS. 7 and 8, the MEA40 as an electrode structure is formed by laminating an electrolyte membrane EF and a predetermined catalyst on the electrolyte membrane EF in a layered manner, and an anode electrode to which formic acid is supplied. The anode electrode layer AE as a main component and the cathode electrode layer CE as a cathode electrode to which air is supplied are the main components. Since the electrode reactions of the electrolyte membrane EF, the anode electrode layer AE, and the cathode electrode layer CE are widely known, detailed description thereof will be omitted in the following description.

The electrolyte membrane EF of this example is formed from an ion exchange membrane (for example, Nafion (registered trademark) manufactured by DuPont) that selectively permeates cations (more specifically, hydrogen ions (H ⁺ )). Then, as shown in FIG. 7, a single cell U is formed on the peripheral portion of the electrolyte membrane EF, and the fuel supply port 12 (corresponding to the through hole 24 of the cathode side separator 20) provided in the anode side separator 10 is formed. ), The through holes 41 and 42 are formed at the positions corresponding to the through holes 32 and 33 of the fuel discharge port 13 (corresponding to the through hole 25 of the cathode side separator 20) and the seal member 30. As a result, in the state where the single cell U is formed, the fuel supply port 12 (through holes 24 and 32) communicates with the through hole 41, and the fuel discharge port 13 (through holes 25 and 33) communicates with the through hole 42.

Further, in a state where a single cell U is formed on the peripheral portion of the electrolyte membrane EF, an oxidant supply port 22 (corresponding to a through hole 14 of the anode side separator 10) and an oxidant discharge port provided on the cathode side separator 20 are provided. Through holes 43 and 44 are formed at positions corresponding to the through holes 15 of the anode side separator 10 and the through holes 34 and 35 of the sealing member 30. As a result, in the state where the single cell U is formed, the oxidant supply port 22 (through holes 14, 34) communicates with the through hole 43, and the oxidant discharge port 23 (through holes 15, 35) communicates with the through hole 44. do. Further, an insertion hole 45 formed so as to insert the bolt B of the holder H is formed in the peripheral portion of the electrolyte membrane EF.

The anode electrode layer AE and the cathode electrode layer CE as the electrode layer are mainly composed of carbon (supporting carbon) carrying a noble metal catalyst (for example, palladium (PD), platinum (Pt), etc.), and FIG. As shown in, the electrolyte membrane EF is formed in a layered manner with respect to the surface in the central portion. Here, the anode electrode layer AE and the cathode electrode layer CE formed in layers are formed so that the thickness is slightly larger than the thickness of the seal member 30. Further, the anode electrode layer AE and the cathode electrode layer CE formed in a layered shape have external dimensions slightly smaller than the size of the accommodating portion 31 of the seal member 30.

Further, as shown in FIG. 8, the anode electrode layer AE and the cathode electrode layer CE are covered with carbon cloth (or carbon paper) CC as a diffusion layer formed of fibers having conductivity on each surface side. The carbon cloth CC diffuses formic acid supplied to the anode electrode layer AE and air supplied to the cathode electrode layer CE, and efficiently supplies electricity generated by the electrode reaction to the anode side separator 10 and the cathode side separator 20. It is something to do.

That is, since the carbon cloth CC is fibrous, the supplied formic acid and air are uniformly diffused by conducting between the fibers. Further, since the carbon cloth CC has conductivity, the generated electricity can be efficiently flowed to the anode side separator 10 and the cathode side separator 20.

As shown in FIG. 9, the transmission member 50 is formed in a plate shape. The permeation member 50 prevents formic acid flowing through the fuel supply flow path 11 of the anode side separator 10 from leaking to the outside, and also produces carbon dioxide (CO ₂ ), which is a gas reaction product generated by the electrode reaction in the anode electrode layer AE. It is discharged to the outside by making it permeate. In this example, the transmission member 50 is arranged between adjacent single cells U, for example, between single cell U1 and single cell U2, with the fuel cell stack S formed (see FIG. 2).

The transmission member 50 has a frame 51 and a transmission film 52. The frame 51 has an opening portion in the central portion and supports the permeable membrane 52. The frame 51 exhibits a sealing function of preventing formic acid flowing through the fuel supply flow path 11 of the anode-side separator 10 from leaking to the outside. Therefore, the frame 51 is formed by using, for example, a resin material (including an elastic material), a metal plate coated with the elastic material, or the like.

Further, the frame 51 has a fuel supply port 12 (corresponding to a through hole 24 of the cathode side separator 20) and a fuel discharge port 13 (cathode) provided in the anode side separator 10 in a state where a single cell U is formed on the peripheral portion. (Corresponding to the through hole 25 of the side separator 20), through holes 53, 54 are formed at positions corresponding to the through holes 32, 33 of the seal member 30 and the through holes 41, 42 of the MEA 40. As a result, in the state where the single cell U is formed, the fuel supply port 12 (through holes 24, 32, 41) communicates with the through hole 53, and the fuel discharge port 13 (through holes 25, 33, 42) communicates with the through hole 54. Communicate with.

Further, an oxidant supply port 22 (corresponding to the through hole 14 of the anode side separator 10) and an oxidant discharge port 23 provided in the cathode side separator 20 with a single cell U formed on the peripheral portion of the frame 51. (Corresponding to the through hole 15 of the anode side separator 10), the through holes 55 and 56 are formed at the positions corresponding to the through holes 34 and 35 of the sealing member 30 and the through holes 43 and 44 of the MEA 40. As a result, in the state where the single cell U is formed, the oxidant supply port 22 (through hole 14) communicates with the through hole 55, and the oxidant discharge port 23 (through holes 15, 34, 43) communicates with the through hole 56. do. Further, an insertion hole 57 formed so as to insert the bolt B of the holder H is formed in the peripheral portion of the frame 51.

The permeable membrane 52 covers the opening portion of the frame 51 and is adhered to the frame 51. The permeable membrane 52 is a porous membrane, and is a membrane that allows only carbon dioxide (CO ₂ ), which is a gas reactant generated by an electrode reaction in the anode electrode layer AE, to permeate. That is, the permeable membrane 52 permeates carbon dioxide (CO ₂ ), which is a gas, while blocking the permeation of formic acid, which is a liquid. The permeable membrane 52 is formed by using a porous membrane based on Poly Tetra Fluoro Ethylene (PTEF) (for example, Gore-Tex (registered trademark) manufactured by Nippon Gore Co., Ltd.). The permeable membrane 52 is not limited to the porous membrane using PTFE as a base material, and can be formed by using, for example, a water-repellent treated carbon sheet or the like.

Then, as shown in FIGS. 2 and 10, the single cell U is formed by sequentially laminating the cathode side separator 20, the seal member 30, the MEA 40, the seal member 30, the anode side separator 10, and the transmission member 50. In FIG. 10, the seal member 30 is omitted for convenience of explanation. Here, when forming a single cell U, it is possible to airtightly bond the members to each other by using, for example, a conductive adhesive, if necessary. At the time of forming the fuel cell stack S, it is possible to omit the discharge path 28 for the cathode side separator 20 constituting the single cell U located at the lowermost part.

Then, a plurality of the formed single cells U are stacked according to the required output, and more specifically, a plurality of the formed single cells U are stacked along the vertical direction to form the fuel cell stack S. In the fuel cell stack S configured as described above, the fuel supply port 12 and the fuel discharge port 13 of each anode side separator 10 have through holes 24, 25 and the like of the cathode side separator 20 between the stacked single cells U. It becomes a state of communication through. Further, in the fuel cell stack S, the oxidant supply port 22 and the oxidant discharge port 23 of each cathode side separator 20 are interposed between the laminated single cells U through the through holes 14, 15 and the like of the anode side separator 10. It will be in a state of communication.

In the following description, the communication passage formed by the fuel supply port 12 of the anode side separator 10 and the through hole 24 of the cathode side separator 20 through which formic acid flows is referred to as a “fuel side manifold”. Further, a communication passage formed by the oxidant supply port 22 of the cathode side separator 20 and the through hole 14 of the anode side separator 10 through which air flows is referred to as an "oxidizer side manifold".

(3. Operation of fuel cell 1)
Next, the operation of the fuel cell 1 in which the fuel cell stack S is configured as described above will be described. In the fuel cell 1, the formic acid pressurized by the fuel pump P1 is supplied to the anode electrode layer AE of each single cell U via the fuel side manifold. Further, in the fuel cell 1, the air from the blower P2 is supplied to the cathode electrode layer CE of each single cell U via the oxidant side manifold.

That is, in each single cell U, as shown in FIG. 11, formic acid supplied through the fuel supply port 12 of the anode-side separator 10 flows through the fuel supply flow path 11 toward the fuel discharge port 13. As a result, formic acid, which is a liquid fuel, is supplied to the anode electrode layer AE of the MEA40. Further, in each single cell U, the air supplied through the oxidant supply port 22 of the cathode side separator 20 is branched, so that a part of the air is branched to the oxidant supply flow path 21 and the oxidant discharge port 23. And the other part flows toward the oxidant discharge port 23 through the discharge path 28. As a result, air, which is an oxidizing agent (oxidizing agent gas) flowing through the oxidizing agent supply flow path 21, is supplied to the cathode electrode layer CE of the MEA 40.

Here, in the MEA40 of each single cell U, as is well known, carbon dioxide, which is a gas reactant in the anode electrode layer AE, is subjected to an electrode reaction using formic acid (HCOOH) and air (oxygen (O ₂ )). Carbon (CO ₂ ) is generated. Specifically, in this example, the electrolyte membrane EF of MEA40 is formed of an ion exchange membrane that selectively permeates cations. Therefore, in MEA40, carbon dioxide (CO ₂ ) is generated in the anode electrode layer AE according to the following chemical reaction formulas 1 and 2.
Anode electrode layer AE: HCOOH → 2H ⁺ + 2e ⁻ + CO ₂ ↑… Chemical reaction formula 1
Cathode electrode layer CE: 2H ⁺ + ^2e- + (1/2) O ₂ → H ₂ O… Chemical reaction formula 2

Here, in the fuel cell 1 of this example, each single cell U is stacked upward in the vertical direction. Further, in the fuel cell 1 of this example, in the single cell U1 and the single cell U2 adjacent to each other in the vertical direction, as shown in FIG. 11, the fuel cell 1 is vertically aligned with the anode side separator 10 of the lower single cell U1. A transmission member 50 is provided between the upper single cell U2 and the cathode side separator 20. Further, the cathode side separator 20 of the single cell U2 is provided with a discharge path 28 so as to face the transmission member 50.

As a result, as shown in FIG. 11, carbon dioxide (CO ₂ ) generated by the electrode reaction in the anode electrode layer AE has a smaller specific gravity than that of formic acid, so that it is directed upward in the vertical direction, that is, toward the transmission member 50. And move. The permeation member 50 selectively permeates only the gas and separates the gas and liquid. Therefore, in the anode electrode layer AE, carbon dioxide (CO ₂ ) collected in contact with the permeation member 50 in formic acid permeates the permeation member 50.

Carbon dioxide (CO ₂ ) that has passed through the permeation member 50 enters the discharge path 28 of the adjacent cathode side separator 20. The discharge path 28, in a state of being partitioned by the permeable membrane 52, allows air branched at the oxidant supply port 22 to flow toward the oxidant discharge port 23. Here, when the flow velocity (flow rate) of the air flowing through the discharge passage 28 is larger than the flow velocity (flow rate) of the formic acid flowing through the fuel supply flow path 11, the pressure in the discharge passage 28 is higher than the pressure in the fuel supply flow path 11. It becomes relatively small (negative pressure). That is, it is possible to generate a pressure difference (differential pressure) in which the pressure on the discharge path 28 side is relatively small between the discharge path 28 side and the fuel supply flow path 11 side with respect to the permeation member 50.

As a result, the carbon dioxide (CO ₂ ) collected so as to come into contact with the permeation member 50 easily permeates to the discharge path 28 side of the adjacent cathode side separator 20. Then, the carbon dioxide (CO ₂ ) that has permeated to the discharge path 28 side is discharged to the outside of the fuel cell stack S together with the air through the oxidant discharge port 23, as shown by the broken line with an arrow in FIG.

By the way, as described above, the fuel cell 1 (more specifically, the fuel cell stack S) has a transmission member 50 and a discharge path 28, and an electrode is formed by flowing air as a pressurized fluid through the discharge path 28. Carbon dioxide (CO ₂ ) generated by the reaction is continuously discharged from the anode electrode layer AE. This makes it difficult for carbon dioxide (CO ₂ ) to exist in the vicinity of the anode electrode layer AE, and as a result, the contact area where formic acid supplied through the fuel supply flow path 11 contacts the anode electrode layer AE is reduced. Is prevented. Therefore, for example, even when the power generation of the fuel cell 1 is continued, the electrode reaction efficiency in the anode electrode layer AE does not decrease, and as a result, the power generation efficiency of the fuel cell 1 is prevented from decreasing. Can be done.

As can be understood from the above explanation, according to the fuel cell 1 of this example, carbon dioxide (CO ₂ ), which is a gas reaction product generated in the anode electrode layer AE by the electrode reaction in the MEA 40, which is an electrode structure, and the like. Carbon dioxide (CO) is separated from the liquid fuel formic acid by permeating through the permeation film 52. As a result, carbon dioxide (CO ₂ ) and the like can be removed from the vicinity of the anode electrode layer AE. Then, carbon dioxide (CO ₂ ) or the like separated from formic acid, that is, permeated through the permeable film 52, is air through the discharge path 18 through which the air branched at the oxidant supply port 22 flows as a pressurized fluid. At the same time, it is discharged to the outside of the fuel cell 1. As a result, carbon dioxide (CO2) or the like that has already been generated does not accumulate in the discharge path 28, and carbon dioxide ( _CO2 ) or the like can be efficiently and continuously discharged to the outside. Therefore, even if the fuel cell 1 continues to generate power, carbon dioxide (CO ₂ ) or the like generated by the electrode reaction can be continuously discharged to the outside, and the generated carbon dioxide (CO ₂ ) or the like can be used. It is possible to suppress a decrease in the power generation efficiency of the fuel cell 1.

(4. First alternative example)
In the above-mentioned example, the air supplied to the cathode electrode layer CE is branched and used as a pressurized fluid, and carbon dioxide (CO ₂ ) generated in the anode electrode layer AE is discharged to the outside. However, it is also possible to branch the formic acid supplied to the anode electrode layer AE and use it as a pressurized fluid to discharge carbon dioxide (CO ₂ ) generated in the anode electrode layer AE to the outside. In this case, as shown in FIG. 12, for example, the discharge path 18 is formed in the anode-side separator 10 by partitioning with the permeable membrane 52.

Here, as shown in FIG. 12, the flow of the fuel supply flow path 11 that supplies formic acid to the anode electrode layer AE in order to facilitate the permeation of carbon dioxide (CO ₂ ) toward the discharge path 18 through the transmission membrane 52. The channel cross-sectional area of the discharge path 18 is made smaller than the path cross-sectional area. As a result, the flow velocity of formic acid flowing through the discharge passage 18 becomes larger than the flow velocity of formic acid flowing through the fuel supply passage 11, and the pressure inside the discharge passage 18 can be made lower than the pressure inside the fuel supply passage 11. can. As a result, carbon dioxide (CO ₂ ) that has permeated through the permeation membrane 52 can be discharged to the outside together with formic acid flowing in the discharge path 18. Therefore, the same effect as that of this example described above can be obtained in the first alternative example.

(5. Second example)
In this example and the first alternative example described above, carbon dioxide (CO ₂ ) generated by the electrode reaction in the anode electrode layer AE is discharged to the outside. However, it is also possible to recover and utilize carbon dioxide (CO ₂ ) generated in the anode electrode layer AE. In this case, the recovered carbon dioxide (CO ₂ ) can be used to generate formic acid, which is a liquid fuel, by producing a recycled raw material such as sodium formic acid. In this way, carbon dioxide (CO ₂ ) generated by the power generation of the fuel cell 1 is used to generate liquid fuel, thereby suppressing the emission (release) of carbon dioxide (CO ₂ ) into the atmosphere. can do.

(6. Other examples)
In this example, the first example, and the second example described above, the case where the electrolyte membrane EF is a proton conductor which is an ion conductive film that allows protons to permeate has been described. However, the electrolyte membrane EF can also be an anion conductor, which is an ion conductive film that allows anions such as hydroxide ions to permeate.

Further, in this example, the first example, and the second example described above, the fuel cell stack S is formed by vertically stacking a plurality of single cells U arranged in the horizontal direction. However, by collecting carbon dioxide (CO ₂ ) and carbon monoxide (CO), which are gas reactants, and allowing the permeated membrane to permeate the collected gas reactants, the discharge path permeated the permeation membrane. The present invention is not limited to this as long as the gaseous reactant can be discharged to the outside. That is, in this case, the fuel cell stack can be placed horizontally instead of the fuel cell stack S placed vertically as in the above-mentioned example.

Further, in this example, the first example and the second example described above, the oxidizing agent is air which is an oxidizing agent supplied to the cathode electrode layer CE or formic acid which is a liquid fuel supplied to the anode electrode layer AE. It was branched at the supply port 22 or the fuel supply port 12, so that the branched air or formic acid, that is, the pressurized fluid flows through the discharge path 28 or the discharge path 18. However, it is also possible to flow air or formic acid, which is a separately supplied fluid, as a pressurized fluid without branching air or formic acid to the discharge passage 28 or the discharge passage 18. In this case as well, the same effects as those of the present example, the first example and the second example described above can be obtained. When the fluid is separately supplied, it is also possible to suck the fluid air or formic acid from the outside and let the sucked air or formic acid flow through the discharge passage 28 or the discharge passage 18.

1 ... Direct formic acid type fuel cell (fuel cell), 10 ... Anode side separator, 11 ... Fuel supply flow path, 12 ... Fuel supply port, 13 ... Fuel discharge port, 14, 15 ... Through hole, 16 ... Insertion hole, 17 ... Electrode portion, 18 ... Discharge path, 20 ... Cathode side separator, 21 ... Oxidizing agent supply flow path, 22 ... Oxidizing agent supply port, 23 ... Oxidizing agent discharging port, 24, 25 ... Through hole, 26 ... Insertion hole, 27 ... Electrode part, 28 ... Discharge path, 30 ... Seal member, 31 ... Accommodation part, 32 to 35 ... Through hole, 36 ... Insertion hole, 40 ... MEA (electrode structure), 41 ... Through hole, 41 to 44 ... Through hole Hole, 45 ... Insertion hole, 50 ... Transmission member, 51 ... Frame, 52 ... Transmission film, 53-56 ... Through hole, 57 ... Insertion hole, AE ... Anode electrode layer, CE ... Cathode electrode layer, EF ... Electrolyte film, CC ... carbon cloth, S ... fuel cell stack, U ... single cell, U1 ... single cell, U2 ... single cell, H ... holder, B ... bolt, P1 ... fuel pump, P2 ... blower, T1 ... supply tank, T2 ... Collection tank

Claims (7)

An electrode structure having an electrolyte membrane, an anode electrode and a cathode electrode,
An anode-side separator having a fuel supply flow path for supplying liquid fuel to the anode electrode,
A cathode side separator having an oxidant supply flow path for supplying the oxidant to the cathode electrode is provided.
A fuel cell in which a single cell in which the electrode structure is arranged is formed between a pair of the anode-side separator and the cathode-side separator, and power is generated by an electrode reaction in the electrode structure.
A permeable film that separates the gas reactant from the liquid fuel by selectively permeating the gas reactant generated at the anode electrode with the electrode reaction.
The gas reaction that has permeated the permeation membrane by flowing a fluid in a state where the permeation membrane is airtightly partitioned with respect to the fuel supply flow path and the electrode reaction is occurring in the electrode structure. A discharge channel that discharges things to the outside,
Equipped with a fuel cell. The pressure inside the discharge passage is smaller than the pressure inside the fuel supply flow path partitioned by the permeable membrane because the fluid flows as a pressurized fluid, according to claim 1. Fuel cell. The oxidant supplied to the oxidant supply flow path or the oxidant or the liquid fuel branched from the liquid fuel supplied to the fuel supply flow path flows through the discharge path, claim 1 or 2. The fuel cell according to 2. The fuel cell according to any one of claims 1-3, wherein the permeable membrane is a porous membrane that blocks the permeation of the liquid fuel while allowing only the gas reactant to permeate. The fuel cell according to any one of claims 1-4, wherein the transmission membrane and the discharge path are arranged vertically above the fuel supply flow path formed in the anode-side separator. .. A plurality of the single cells are stacked to form a fuel cell stack.
When the fuel cell stack is formed in a state where the permeable membrane is arranged between the single cells adjacent to each other in the vertical direction.
Among the adjacent single cells, the cathode side separator of the single cell above in the vertical direction is adjacent to the anode side separator of the single cell below in the vertical direction via the transmission membrane. ,
The discharge channel is
1 The fuel cell according to any one of -5. The fuel cell according to any one of claims 1-6, wherein the liquid fuel supplied to the anode electrode is formic acid (HCOOH).

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