Fuel Cells

Abstract

To provide a fuel cell that can efficiently discharge produced water generated by electrode reaction to the outside.SOLUTION: A fuel cell includes a discharge mechanism F that discharges produced water (H2O) generated at a cathode electrode as a result of electrode reaction in an MEA 40 to an outside. The discharge mechanism F includes a discharge channel 28 through which air, the oxidant, flows, a passageway 29 that connects an oxidant supply channel 21 and the discharge channel 28 so as to be communicated, and allows the produced water generated at the cathode electrode to move into the discharge channel 28, and a discharge unit 20c that discharges the produced water that has moved to the discharge channel 28 to the outside.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a fuel cell. [Background technology]

[0002] Fuel cells, particularly solid polymer electrolyte fuel cells, generally include an electrode structure consisting of an anode electrode formed on one side of an electrolyte membrane and a cathode electrode formed on the other side. In solid polymer electrolyte fuel cells, fuel is supplied to the anode electrode and an oxidant is supplied to the cathode electrode from the outside, causing an electrode reaction in the electrode structure to generate electricity.

[0003] In recent years, direct fuel cells have been developed that directly use liquid fuels such as methanol and formic acid as the fuel supplied to the anode electrode. Liquid fuels are easier to handle and have a higher energy density per volume than hydrogen gas fuels, making them extremely useful.

[0004] In fuel cells, even when hydrogen gas or liquid fuel is used, water is generated on the cathode electrode side due to the electrode reaction. In particular, when the water in a liquid state covers the surface of the cathode electrode, that is, when flooding occurs, the contact between the catalyst forming the cathode electrode and oxygen (O2) is impaired, and as a result, the power generation efficiency of the fuel cell may decrease.

[0005] For this reason, for example, Patent Documents 1 and 2 disclose techniques for removing the generated water from the surface of the cathode electrode. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-108573 A [Patent Document 2] JP 2012-38569 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the above-mentioned conventional technology, the generated water present near the surface of the cathode electrode is removed along the surface of the cathode electrode by applying the pressure of the oxidizer to the generated water without actively moving it away from the cathode electrode. In this case, even if the generated water in a liquid state is present on the surface of the cathode electrode and flooding phenomenon may occur, depending on the surface shape of the cathode electrode, the generated water may not be continuously and efficiently discharged to the outside of the fuel cell. In this case, as the power generation of the fuel cell continues, a large amount of generated water in a liquid state may be present on the surface of the cathode electrode, which may result in flooding phenomenon and decrease the power generation efficiency of the fuel cell. Therefore, the above-mentioned conventional technology has room for improvement in terms of efficiently discharging the generated generated water in a gaseous state and a liquid state to the outside.

[0008] An object of the present invention is to provide a fuel cell that can efficiently discharge water generated in the electrode reaction to the outside. [Means for solving the problem]

[0009] One aspect of the present invention is an electrode structure having an electrolyte membrane, an anode electrode, and a cathode electrode; The above an anode-side separator having a fuel supply flow path for supplying a liquid fuel to the anode electrode; The above a cathode-side separator having an oxidant supply flow path for supplying an oxidant to the cathode electrode; A pair The above Between the anode side separator and the cathode side separator The above forming a single cell in which the electrode structure is disposed; The above A fuel cell that generates electricity by an electrode reaction in an electrode structure, The cathode side separator is an oxidant supply flow path that is a flow path formed on a surface facing the cathode electrode, the oxidant flowing through the oxidant and that supplies the oxidant to the cathode electrode; The oxidant supply channel from The above In the thickness direction of the cathode separator The above Towards the back of the opposing surface Penetrate Having a passageway, The water generated at the cathode in association with the electrode reaction is supplied from the oxidant supply passage to the Through the passage The above Move to back After that, Discharge mechanism to the outside and, Equipped with , in fuel cells.

[0010] According to this, the discharge mechanism can move the water generated at the cathode electrode by the electrode reaction in the electrode structure from the opposing surface facing the cathode electrode toward the rear surface of the cathode separator through the passage provided in the cathode-side separator, and discharge it to the outside. That is, the discharge mechanism can move the water generated at the cathode electrode in a direction away from the cathode electrode through the passage and continuously discharge it to the outside. This prevents a large amount of water from accumulating on the surface of the cathode electrode even when the fuel cell continues to generate power, and as a result, it is possible to suppress the occurrence of the flooding phenomenon. Therefore, it is possible to suppress a decrease in the power generation efficiency of the fuel cell due to the water generated at the cathode electrode. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the configuration of a fuel cell. [Diagram 2] FIG. 1 is a diagram showing the configuration of a fuel cell stack formed by stacking unit cells. [Diagram 3] FIG. 2 is a diagram showing the structure of an anode-side separator. [Figure 4] FIG. 4 is a diagram showing the configuration of the opposing surface of a cathode-side separator. [Diagram 5] FIG. 4 is a diagram showing the configuration of the rear surface side of the cathode-side separator. [Figure 6] 5A and 5B are diagrams illustrating a configuration of a seal member. [Figure 7] FIG. 2 is a diagram showing the configuration of an MEA. [Figure 8]FIG. 8 is a cross-sectional view showing a cross section of the MEA taken along line VIII-VIII in FIG. [Figure 9] FIG. 11 is a cross-sectional view for explaining the discharge of generated water. [Figure 10] FIG. 11 is a cross-sectional view for explaining a configuration of a first modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (1. Overview of fuel cells) In this embodiment, a solid polymer fuel cell is used as an example of the fuel cell. That is, in the fuel cell of this embodiment, an anode electrode is formed on one side of an electrolyte membrane, and a cathode electrode is formed on the other side of the electrolyte membrane. Here, the electrolyte membrane, the anode electrode, and the cathode electrode form an MEA (Membrane-Electrode-Assembly), which is an electrode structure.

[0013] The fuel cell of this example is provided with an anode-side separator (including a collector) that supplies fuel to the anode electrode, and a cathode-side separator (including a collector) that supplies an oxidant (oxidant gas) to the cathode electrode. The fuel cell of this example is formed into one cell (hereinafter referred to as a single cell) including an MEA, an anode-side separator, and a cathode-side separator, and a fuel cell stack is formed by stacking a plurality of single cells.

[0014] In this example, the fuel supplied to the anode electrode of the fuel cell can be exemplified by liquid fuels such as formic acid (HCOOH), methanol (CH3OH), and ethanol (C2H5OH). Here, in the fuel cell described below, a case where formic acid is directly used as the liquid fuel supplied is exemplified. That is, the fuel cell in this example is a polymer electrolyte fuel cell, and a direct formic acid fuel cell (DFAFC) is exemplified. In addition, in this example, the oxidant (oxidant gas) supplied to the cathode electrode of the fuel cell can be exemplified by oxygen (O2) gas, air, and the like. Here, in the fuel cell described below, a case where air is used as the oxidant gas, i.e., the oxidant gas, supplied is exemplified.

[0015] In the case of a direct formic acid fuel cell, when formic acid, which is a liquid fuel, is directly supplied to the anode electrode of the MEA and air (O2), which is an oxidant (oxidant gas), is supplied to the cathode electrode of the MEA, water (H2O) is generated on the cathode electrode side due to the electrode reaction in the MEA. When the generated water condenses and becomes liquid as it is cooled, it covers the surface of the cathode electrode (more specifically, the catalyst layer constituting the cathode electrode) and inhibits contact between the cathode electrode and the air. In order to discharge the generated water to the outside, the fuel cell of this example is provided with a discharge mechanism that moves the generated water generated at the cathode electrode away from the surface of the cathode electrode and discharges the moved generated water to the outside.

[0016] For this reason, the cathode-side separator of the fuel cell of this example has a supply channel formed on the surface facing the cathode electrode to supply an oxidant (oxidant gas), and a discharge channel formed on the back surface of the cathode-side separator that is the back side of the facing surface in the plate thickness direction, and the supply channel and the discharge channel are connected by a passage formed along the plate thickness direction. As a result, water generated on the cathode electrode side can move through the passage from the facing surface side of the cathode-side separator to the discharge channel formed on the back surface side, and is discharged to the outside through the discharge channel. Therefore, water generated due to the electrode reaction is continuously and efficiently removed from the cathode electrode.

[0017] In addition, since the discharge path is formed in the cathode-side separator, a pressurized fluid, for example, an oxidant (oxidant gas) that is pressurized and supplied to the cathode electrode, i.e., air, can be branched and flowed to the discharge path. As a result, the generated water that has passed through the passage and reached the discharge path is discharged to the outside together with the oxidant (air). Note that instead of pressurizing the fluid, for example, it is also possible to suck the fluid from the outside and flow it.

[0018] (2. Details of the configuration of direct formic acid fuel cell 1) Hereinafter, the configuration of a direct formic acid fuel cell 1 (hereinafter simply referred to as "fuel cell 1") of this embodiment will be described with reference to the drawings. As shown in FIG. 1, the fuel cell 1 of this embodiment forms a fuel cell stack S. The fuel cell stack S is in a state where a plurality of unit cells U are stacked, and the stacked plurality of unit cells U are held by a holder H and a bolt B. The fuel cell stack S of this embodiment is horizontally placed with a plurality of unit cells U arranged vertically stacked along a horizontal direction. A fuel pump P1 that pressurizes and supplies formic acid, which is a liquid fuel stored in a supply tank T1, is connected to a connection part K1 via a pipe (not shown) to the fuel cell stack S. In addition, a blower P2 (pressurizing pump) that pressurizes and supplies air as an oxidant (oxidant gas) is connected to a connection part K2 via a pipe (not shown) to the fuel cell stack S.

[0019] 2, the unit cell U includes an anode side separator 10 and a cathode side separator 20. The unit cell U of this example includes a seal member 30 and an MEA 40 that are disposed between the anode side separator 10 and the cathode side separator 20 and laminated therebetween.

[0020] The anode side separator 10 is formed in a plate shape as shown in Fig. 3. The anode side separator 10 in this example 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, for example, a thin plate of stainless steel such as SUS316, which is subjected to a conductive treatment such as gold plating. Note that, although the anode side separator 10 is made of a metal material in this example, it is also possible to form it from a conductive nonmetallic material (for example, carbon or a composite material with carbon).

[0021] A fuel supply flow channel 11 for supplying formic acid, which is a liquid fuel, to the anode electrode layer AE is formed in the central portion of the anode-side separator 10, i.e., in a position facing the MEA 40 (more specifically, the anode electrode layer AE, which is the anode electrode described later). In this example, the fuel supply flow channel 11 is formed in a serpentine shape, as shown in Fig. 3. In addition, a fuel supply port 12 for supplying formic acid to the fuel supply flow channel 11 and a fuel discharge port 13 for discharging formic acid that has passed through the fuel supply flow channel 11 are provided in the peripheral portion of the anode-side separator 10.

[0022] The fuel supply port 12 is supplied with pressurized formic acid 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 a 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 discharged formic acid to the recovery tank T2. Note that the anode-side separator in this example is illustrated as having the fuel supply port 12 provided on the lower side in the vertical direction and the fuel discharge port 13 provided on the upper side in the vertical direction when the fuel cell stack S is installed. However, if necessary, the fuel supply port 12 may be provided on the upper side in the vertical direction and the fuel discharge port 13 may be provided on the lower side in the vertical direction.

[0023] As a result, in the unit cell U of this example, formic acid pressurized by the fuel pump P1 from the supply tank T1 is supplied from the fuel supply port 12 to the fuel supply flow path 11, and the formic acid flowing through the fuel supply flow path 11 reaches the fuel outlet 13 while contacting the anode electrode layer AE. That is, in this example, the formic acid supplied from the fuel supply port 12 flows vertically from the lower side to the upper side in the fuel supply flow path 11 and reaches the fuel outlet 13. Then, the formic acid that has reached the fuel outlet 13, i.e., the unreacted formic acid, is recovered in the recovery tank T2.

[0024] The peripheral portion of the anode-side separator 10 is provided with through-holes 14 and 15 for supplying air to the cathode-side separator 20 constituting the unit cell U and discharging unreacted air. The through-holes 14 and 15 are provided, for example, at positions shifted by 90 degrees from the fuel supply port 12 and the fuel discharge port 13. The peripheral portion of the anode-side separator 10 is further provided with a plurality of large-diameter insertion holes 16 (eight in FIG. 3) for inserting the bolts B of the holder H, and an electrode portion 17 for extracting electricity to the outside. The electrode portion 17 may be provided, for example, only in the anode-side separator 10 constituting the unit cell U located at the end when the fuel cell stack S is formed.

[0025] The cathode-side separator 20 is formed in a plate shape, as shown in Figures 4 and 5. The cathode-side separator 20 in 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, for example, a thin plate of stainless steel such as SUS316, which is subjected to a conductive treatment such as gold plating. Note that in this example, the cathode-side separator 20 is also made of a metal material like the anode-side separator 10, but it is also possible to form it using a conductive nonmetallic material (for example, carbon or a composite material with carbon).

[0026] In the central portion of the cathode-side separator 20, on the side of the opposing surface 20a facing the MEA 40 (more specifically, the cathode electrode layer CE, which is the cathode electrode described later), an oxidant supply flow path 21 for supplying air, which is an oxidant (oxidant gas), to the cathode electrode layer CE is formed as shown in Fig. 4. In this example, the oxidant supply flow path 21 is formed as a meandering unevenness (groove), as shown in Fig. 4.

[0027] Also, an oxidant supply port 22 for supplying air, i.e., oxygen (O2), to the oxidant supply passage 21, and an oxidant discharge port 23 for discharging the air that has passed through the oxidant supply passage 21 are provided at the peripheral portion of the cathode side separator 20. 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 the blower P2, and the air is pressurized by the blower P2 and supplied. However, the blower P2 may be omitted if necessary.

[0028] 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, air pressurized by the blower P2, i.e., oxygen (O2), is supplied from the oxidant supply port 22 to the oxidant supply flow path 21, and the air, i.e., oxygen (O2), flowing through the oxidant supply flow path 21 reaches the oxidant discharge port 23 while contacting the cathode electrode layer CE. Then, the air (oxygen (O2)) that has reached the oxidant discharge port 23, i.e., the unreacted air, is discharged to the outside of the fuel cell stack S.

[0029] Further, a through hole 24 and a through hole 25 are provided in the peripheral portion of the cathode side separator 20 for supplying formic acid to the anode side separator 10 constituting the single cell U and discharging unreacted formic acid. The through holes 24, 25 are provided at positions shifted by, for example, 90 degrees from the oxidant supply port 22 and the oxidant discharge port 23.

[0030] Furthermore, a plurality of large-diameter insertion holes 26 (eight in Figs. 4 and 5) for inserting the bolts B of the holder H are provided in the peripheral portion of the cathode-side separator 20, and an electrode portion 27 for extracting electricity to the outside is also provided. Note that when the fuel cell stack S is formed, the electrode portion 27 can be provided, for example, only in the cathode-side separator 20 constituting the unit cell U located at the end.

[0031] Here, the fuel supply port 12 of the anode side separator 10 can be communicated with the through hole 24 of the cathode side separator 20, and the fuel discharge port 13 of the anode side separator 10 can be communicated with the through hole 25 of the cathode side separator 20. Also, the oxidant supply port 22 of the cathode side separator 20 can be communicated with the through hole 14 of the anode side separator 10, and the oxidant discharge port 23 of the cathode side separator 20 can be communicated with the through hole 15 of the anode side separator 10. That is, the through holes 14, 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, 25 of the cathode side separator 20 are formed corresponding to the fuel supply port 12 and the fuel discharge port 13 of the anode side separator 10.

[0032] Furthermore, in the central portion of the back surface 20b behind the opposing surface 20a in the plate thickness direction of the cathode-side separator 20, as shown in Fig. 5, a discharge mechanism F is formed to discharge water (H2O) generated by the electrode reaction in the MEA 40 (cathode electrode layer CE) to the outside of the fuel cell stack S (single cell U). As shown in Fig. 5, the discharge mechanism F includes a discharge portion 20c, a discharge path 28, and a passage 29.

[0033] In this example, the discharge path 28 is formed by a plurality of linear projections and recesses, specifically, six linear grooves 28a in Fig. 5. The discharge path 28 in this example is formed, for example, rotated by 90 degrees with respect to the linear portion of the oxidant supply flow path 21 formed in the opposing surface 20a. One end side, i.e., the upstream side, of the groove 28a of the discharge path 28 is connected to the oxidant supply port 22, and the other end side, i.e., the downstream side, of the groove 28a of the discharge path 28 is connected to the discharge part 20c formed in the cathode separator 20 so as to communicate with the outside when the fuel cell stack S is constructed.

[0034] In this example, the discharge mechanism F includes the discharge portion 20c and the discharge path 28, and the discharge path 28 is configured to be connected to the discharge portion 20c. However, instead of the discharge portion 20c (by omitting the discharge portion 20c), the discharge path 28 (groove 28a) can be extended to the end of the cathode-side separator 20 to discharge the generated water (H2O) to the outside of the fuel cell stack S (single cell U).

[0035] Here, in the cathode separator 20 of this example, the oxidant supply port 22 is disposed on the upper side in the vertical direction and the discharge portion 20c is disposed on the lower side in the vertical direction when the fuel cell stack S is installed. That is, in the discharge path 28 of this example, the upstream side connected to the oxidant supply port 22 is the upper side in the vertical direction, and the downstream side connected to the discharge portion 20c is the lower side in the vertical direction.

[0036] As a result, in a state in which the unit cells U are stacked 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 flows through the oxidant supply flow path 21 as an oxidant (oxidant gas), and the other part flows through the discharge path 28 (groove 28a) as a pressurized fluid. That is, the air supplied to the oxidant supply port 22 is branched to flow through the oxidant supply flow path 21 and the discharge path 28 (groove 28a).

[0037] The passages 29 connect the oxidant supply flow path 21 (more specifically, the groove forming the oxidant supply flow path 21) formed in the opposing surface 20a of the cathode-side separator 20 to the discharge path 28 (more specifically, the groove 28a) formed in the back surface 20b of the cathode-side separator 20 so as to be communicable in the plate thickness direction of the cathode-side separator 20. As shown by the dashed circle in Figures 4 and 5, the passages 29 in this example are provided in a plurality (e.g., 90) such that the openings in the opposing surface 20a and the back surface 20b are slit-shaped and the cross section perpendicular to the axial direction is a rectangular through-hole.

[0038] Here, in this example, for example, the groove of the oxidant supply flow channel 21 is formed on the opposing surface 20a so as to have a depth half the plate thickness of the cathode-side separator 20, and the groove 28a of the discharge channel 28 is formed on the back surface 20b so as to have a depth half the plate thickness of the cathode-side separator 20 along a direction rotated 90 degrees with respect to the oxidant supply flow channel 21. That is, in this example, as shown in Figures 4 and 5, the formation direction of the groove of the oxidant supply flow channel 21 at the formation position of the passage 29 intersects with the formation direction of the groove 28a of the discharge channel 28 at the formation position of the passage 29. As a result, in this example, by forming the oxidant supply flow channel 21 and the discharge channel 28, the passage 29 having a rectangular cross section is formed.

[0039] As a result, as described below, the produced water (H2O) generated in the cathode electrode layer CE by the electrode reaction in the MEA 40 moves through the passage 29 from the opposing surface 20a to the back surface 20b of the cathode-side separator 20, that is, from the oxidant supply flow path 21 to the discharge path 28. The produced water (H2O) that reaches the discharge path 28 through the passage 29 is discharged to the outside from the discharge portion 20c of the cathode-side separator 20 together with the air flowing through the discharge path 28. That is, the discharge mechanism F having the discharge portion 20c, the discharge path 28, and the passage 29 can move the produced water (H2O) generated in the cathode electrode layer CE by the electrode reaction in the MEA 40 in a direction away from the cathode electrode layer CE and discharge it to the outside.

[0040] Here, by flowing air through the straight-line discharge path 28 (groove 28a), the pressure in the discharge path 28 is relatively lower than the pressure in the serpentine oxidant supply flow path 21 due to the difference in air flow speed (or the difference in pressure loss), and the produced water (H2O) in a gaseous state (water vapor) is more likely to move through the passage 29 toward the discharge path 28. In addition, when the produced water (H2O) is condensed and liquefied, a capillary phenomenon occurs due to the surface tension of the produced water (H2O) in a liquid state, and the produced water (H2O) is more likely to move through the passage 29 toward the discharge path 28. Therefore, the discharge mechanism F can efficiently discharge the produced water (H2O) to the outside of the fuel cell stack S (single cell U).

[0041] The seal member 30 is formed in a plate shape, as shown in Fig. 6. Here, the seal member 30 is formed from an elastic material, for example, a rubber material such as EPDM, an elastomer material, etc. Two seal members 30 are used as a pair, and each seal member 30 holds an MEA 40 and is also held between the anode-side separator 10 and the cathode-side separator 20.

[0042] The sealing member 30 has a receiving portion 31 that penetrates in the center so as to receive the anode electrode layer AE and cathode electrode layer CE of the MEA 40. With this, when the sealing member 30 holds the MEA 40, formic acid supplied via the fuel supply flow passage 11 of the anode-side separator 10 flows inside the receiving portion 31, and is supplied to the anode electrode layer AE. Furthermore, with the sealing member 30 holding the MEA 40, air supplied via the oxidant supply flow passage 21 of the cathode-side separator 20 flows inside the receiving portion 31, and is supplied to the cathode electrode layer CE.

[0043] Furthermore, in the peripheral portion of the seal member 30, through holes 32, 33 are formed at positions corresponding to the fuel supply port 12 (corresponding to the through hole 24 of the cathode side separator 20) and the fuel discharge port 13 (corresponding to the through hole 25 of the cathode side separator 20) provided in the anode side separator 10 when the unit cell U is formed. As a result, when the unit 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.

[0044] Furthermore, in the peripheral portion of the seal member 30, through holes 34, 35 are formed at positions corresponding to the oxidant supply port 22 (corresponding to the through hole 14 of the anode side separator 10) and the oxidant discharge port 23 (corresponding to the through hole 15 of the anode side separator 10) provided in the cathode side separator 20 when the unit cell U is formed. As a result, in the state where the unit 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. Furthermore, in the peripheral portion of the seal member 30, an insertion hole 36 is formed so that the bolt B of the holder H can be inserted therethrough.

[0045] 7 and 8, the MEA 40 as an electrode structure has as its main components an electrolyte membrane EF, an anode electrode layer AE as an anode electrode to which formic acid is supplied, and a cathode electrode layer CE as a cathode electrode to which air is supplied, which are formed by stacking layers of a predetermined catalyst on the electrolyte membrane EF. Note that the electrode reactions of the electrolyte membrane EF, anode electrode layer AE, and cathode electrode layer CE are widely known, and therefore detailed description thereof will be omitted in the following description.

[0046] The electrolyte membrane EF of this embodiment is a cation (more specifically, a hydrogen ion (H + 7, the electrolyte membrane EF is formed of an ion exchange membrane (e.g., Nafion (registered trademark) manufactured by DuPont) that selectively transmits fuel (e.g., ethylenediaminetetraacetate) and propylene glycol (e.g., propylene glycol stearate) to the anode-side separator 10. Then, in the peripheral portion of the electrolyte membrane EF, as shown in FIG. 7, in a state in which the unit cell U is formed, through holes 41 and 42 are formed at positions corresponding to the fuel supply port 12 (corresponding to the through hole 24 of the cathode-side separator 20), the fuel discharge port 13 (corresponding to the through hole 25 of the cathode-side separator 20), and the through holes 32 and 33 of the seal member 30. As a result, in a state in which the unit 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.

[0047] Furthermore, in a state where the unit cell U is formed, the peripheral portion of the electrolyte membrane EF is provided with through holes 43, 44 at positions corresponding to the oxidant supply port 22 (corresponding to the through hole 14 of the anode side separator 10), the oxidant discharge port 23 (corresponding to the through hole 15 of the anode side separator 10) provided in the cathode side separator 20, and the through holes 34, 35 of the seal member 30. As a result, in a state where the unit 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. Furthermore, in a state where the unit cell U is formed, the electrolyte membrane EF is provided with an insertion hole 45 formed to insert the bolt B of the holder H.

[0048] The anode electrode layer AE and cathode electrode layer CE serving as electrode layers are mainly composed of carbon (supported carbon) carrying a precious metal catalyst (e.g., palladium (Pd) or platinum (Pt)), and are formed in layers on the surface of the central portion of the electrolyte membrane EF, as shown in FIG. 8. The anode electrode layer AE and cathode electrode layer CE formed in layers are formed so that their thicknesses are slightly larger than the thickness of the seal member 30. Furthermore, the anode electrode layer AE and cathode electrode layer CE formed in layers have outer dimensions that are slightly smaller than the size of the accommodation portion 31 of the seal member 30.

[0049] In addition, the anode electrode layer AE and the cathode electrode layer CE are each covered on their surface sides with carbon cloth (or carbon paper) CC as a diffusion layer formed from conductive fibers, as shown in Fig. 8. The carbon cloth CC diffuses the formic acid supplied to the anode electrode layer AE and the 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.

[0050] That is, since the carbon cloth CC is fibrous, the fibers are electrically conductive, so that the supplied formic acid and air are uniformly diffused. Also, since the carbon cloth CC is electrically conductive, the generated electricity can be efficiently passed through the anode-side separator 10 and the cathode-side separator 20.

[0051] 2, the unit cell U is formed by sequentially stacking an anode-side separator 10, a sealing member 30, an MEA 40, a sealing member 30, and a cathode-side separator 20 in the horizontal direction. When forming the unit cell U, the respective members can be airtightly bonded together, as necessary, using, for example, a conductive adhesive.

[0052] A plurality of the formed unit cells U are stacked according to the required output to constitute a fuel cell stack S. In the fuel cell stack S configured in this manner, the fuel supply port 12 and the fuel discharge port 13 of each anode side separator 10 are in communication with each other between the stacked unit cells U via the through holes 24, 25, etc. of the cathode side separator 20. In the fuel cell stack S, the oxidant supply port 22 and the oxidant discharge port 23 of each cathode side separator 20 are in communication with each other between the stacked unit cells U via the through holes 14, 15, etc. of the anode side separator 10.

[0053] 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 the "fuel side manifold." Also, the 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 the "oxidant side manifold."

[0054] (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, formic acid pressurized by the fuel pump P1 is supplied to the anode electrode layer AE of each unit cell U via the fuel-side manifold. Also, in the fuel cell 1, air from the blower P2 is supplied to the cathode electrode layer CE of each unit cell U via the oxidant-side manifold.

[0055] That is, in each unit cell U, as shown in Fig. 9, 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 exhaust port 13. As a result, formic acid, which is a liquid fuel, is supplied to the anode electrode layer AE of the MEA 40. Also, in each unit cell U, air supplied through the oxidant supply port 22 of the cathode side separator 20 is branched so that one part flows through the oxidant supply flow path 21 toward the oxidant exhaust port 23 and the other part flows through the exhaust path 28 toward the exhaust section 20c. As a result, the air, which is an oxidant (oxidant gas) flowing through the oxidant supply flow path 21, is supplied to the cathode electrode layer CE of the MEA 40.

[0056] As is well known, in the MEA 40 of each unit cell U, an electrode reaction using formic acid (HCOOH) and air (oxygen (O2)) generates water (H2O) in the cathode electrode layer CE. Specifically, in this example, the electrolyte membrane EF of the MEA 40 is formed of an ion exchange membrane that selectively allows cations to pass through. Therefore, in the MEA 40, water (H2O) is generated in the cathode electrode layer CE in accordance with the following chemical reaction formulas 1 and 2. Anode electrode layer AE: HCOOH → 2H + +2e - +CO2…Chemical reaction formula 1 Cathode electrode layer CE: 2H + +2e - +(1 / 2)O2→H2O … Chemical reaction equation 2

[0057] Here, in the fuel cell 1 of this example, each unit cell U is stacked in a horizontal direction to form a fuel cell stack S. Also, in the fuel cell 1 of this example, a discharge mechanism F is provided along the vertical direction. As a result, as shown by the dashed line in Fig. 9, product water (H2O) in a gaseous state (water vapor) or liquid state generated by the electrode reaction in the cathode electrode layer CE passes through a passage 29 of the discharge mechanism F and moves from the opposing surface 20a of the cathode-side separator 20 (i.e., the cathode electrode layer CE side) to the back surface 20b (i.e., the discharge path 28 side).

[0058] In the discharge path 28 (groove 28a), air branched at the oxidant supply port 22 flows toward the discharge portion 20c. Therefore, the produced water (H2O) that has moved through the passage 29 is discharged from the discharge portion 20c to the outside of the fuel cell stack S together with the air flowing through the discharge path 28. The discharge mechanism F is formed along the vertical direction, that is, the discharge portion 20c is disposed on the lower side in the vertical direction. Therefore, when the produced water (H2O) that has been generated in a gaseous state (water vapor) by the heat accompanying the electrode reaction of the MEA 40 is cooled and liquefied by passing through the passage 29, the produced water (H2O) moves toward the discharge portion 20c due to the pressure of the air flowing through the discharge path 28 and the weight of the produced water (H2O) in a liquid state, and is discharged to the outside of the fuel cell stack S.

[0059] Incidentally, as described above, the fuel cell 1 (more specifically, the fuel cell stack S) has the discharge mechanism F, so that excess water (H2O) generated in association with the electrode reaction is continuously and efficiently discharged from the cathode electrode layer CE. This makes it difficult for the water (H2O) to accumulate in the vicinity of the cathode electrode layer CE, and as a result, it is possible to suppress the occurrence of a flooding phenomenon in which the water (H2O) condenses (liquefies) and covers the surface of the cathode electrode layer CE. This prevents a decrease in the contact area of ​​the air (O2) supplied via the oxidant supply flow path 21 with the cathode electrode layer CE. This prevents, for example, a decrease in the electrode reaction efficiency in the cathode electrode layer CE even when the fuel cell 1 continues to generate electricity, and as a result, it is possible to prevent a decrease in the power generation efficiency of the fuel cell 1.

[0060] As can be understood from the above description, according to the fuel cell 1 of this example, the produced water (H2O) generated in the cathode electrode layer CE (cathode electrode) by the electrode reaction in the MEA 40, which is the electrode structure, is moved away from the vicinity of the cathode electrode layer CE by the discharge mechanism F having the discharge section 20c, the discharge path 28, and the passage 29, and is discharged together with air to the outside of the fuel cell 1. As a result, even when the fuel cell 1 continues to generate power, the excess (large amount) produced water (H2O) generated by the electrode reaction can be continuously discharged to the outside, and a decrease in the power generation efficiency of the fuel cell 1 due to the flooding phenomenon caused by the excess (large amount) produced water (H2O) can be suppressed.

[0061] (4. First alternative example) In the above-described embodiment, the water generated in the cathode electrode layer CE is discharged to the outside of the fuel cell stack S (single cell U) together with the air flowing through the discharge passage 28 of the discharge mechanism F. However, in the fuel cell 1, when power generation continues, for example, contamination of the precious metal catalyst in the anode electrode layer AE or the carbon cloth CC serving as the diffusion layer may occur, resulting in a decrease in power generation efficiency. For this reason, the fuel cell 1 performs a refresh operation to clean the anode electrode layer AE side at regular intervals. This refresh operation is, for example, an operation to circulate cleaning water on the anode electrode layer AE side instead of formic acid, which is a liquid fuel. By circulating the cleaning water, the anode electrode layer AE side is cleaned, and the power generation efficiency can be improved again.

[0062] Therefore, in the first modified example, the generated water generated in the cathode electrode layer CE is made usable as cleaning water. Specifically, in the first modified example, as shown in Fig. 10, the generated water (in a gaseous or liquid state) discharged from a discharge mechanism F is collected and stored in a reservoir tank R, for example, via a tube (not shown). The generated water discharged in a gaseous state is cooled before being collected in the reservoir tank R, and is collected and stored in the reservoir tank R as generated water in a liquid state.

[0063] The generated water stored in the reservoir tank R is added to cleaning water prepared separately for the refresh operation, for example, and circulated on the anode electrode layer AE side to clean the anode electrode layer AE. This allows the generated water to be effectively used for the refresh operation, and also allows the power generation efficiency of the fuel cell 1, which has decreased due to the refresh operation, to be restored to normal power generation efficiency.

[0064] (5. Other Examples) In the present embodiment and the first modified embodiment described above, the discharge channel 28 having a plurality of linear grooves 28a is formed on the rear surface 20b of the cathode-side separator 20. Alternatively, the discharge channel 28 may be a wide recess formed in the center of the rear surface 20b, with one end (upstream side) connected to the oxidant supply port 22 and the other end (downstream side) connected to the discharge portion 20c, without forming the plurality of grooves 28a. In this case, the passage 29 is formed, for example, by drilling or the like, and connects the oxidant supply flow path 21 and the discharge channel 28 formed as described above so that they can communicate with each other in the plate thickness direction of the cathode-side separator 20. In this case, the same effects as those of the present embodiment and the first modified embodiment described above can be obtained.

[0065] In the present embodiment and the first modified embodiment described above, the cross-sectional shape of the passage 29 perpendicular to the axis is rectangular. However, the cross-sectional shape of the passage 29 is not limited to a rectangular shape, and it goes without saying that the cross-sectional shape may be, for example, a circular shape or a polygonal shape other than a rectangular shape. Even if the cross-sectional shape of the passage 29 is a shape other than a rectangular shape, the passage 29 can connect the oxidizer supply channel 21 and the discharge channel 28 so that they can communicate with each other, thereby obtaining the same effects as those of the present embodiment and the first modified embodiment described above.

[0066] In the above-described present example and first modified example, the discharge channel 28 and the passage 29 are formed in the central portion of the cathode-side separator 20 in accordance with the position of the oxidant supply flow path 21. However, the positions of the discharge channel 28 and the passage 29 and the size of the discharge channel 28 are not limited to being formed in the central portion of the cathode-side separator 20 in accordance with the position and size of the oxidant supply flow path 21. For example, the discharge channel 28 and the passage 29 can be provided in the peripheral portion of the cathode-side separator 20 as long as the formation of the oxidant supply port 22, the oxidant discharge port 23, and the through-holes 24, 25 is not affected.

[0067] In the above-described present example and first modified example, the fuel cell stack S is formed by stacking a plurality of unit cells U arranged vertically in the horizontal direction. However, this is not limited to the above, as long as the generated water (H2O) generated in the cathode electrode layer CE can be discharged to the outside by passing through the passage 29, the discharge path 28, and the discharge portion 20c. That is, in this case, instead of placing the fuel cell stack S horizontally as in the above-described present example, it is possible to form a fuel cell stack by stacking a plurality of unit cells U arranged horizontally in the vertical direction, that is, to place the fuel cell stack S vertically.

[0068] Furthermore, in the present embodiment and the first modified embodiment described above, the air, which is the oxidant supplied to the cathode electrode layer CE, is branched at the oxidant supply port 22, and the branched air, i.e., the pressurized fluid, flows through the discharge path 28. However, it is also possible to not branch the air to the discharge path 28, that is, to flow air, which is a fluid supplied separately, as the pressurized fluid. Even in this case, the same effects as those of the present embodiment and the first modified embodiment described above can be obtained. Note that, when a fluid is supplied separately, it is also possible to suck the air, which is the fluid, from the discharge portion 20c side, for example, and to cause the sucked air to flow through the discharge path 28. [Explanation of symbols]

[0069] 1...direct formic acid fuel cell (fuel cell), 10...anode side separator, 11...fuel supply flow path, 12...fuel supply port, 13...fuel exhaust port, 14, 15...through hole, 16...insertion hole, 17...electrode portion, 20...cathode side separator, 20a...opposing surface, 20b...back surface, 20c...exhaust portion, 21...oxidant supply flow path, 22...oxidant supply port, 23...oxidant exhaust port, 24, 25...through hole, 26...insertion hole, 27...electrode portion, 28...exhaust path, 28a...groove, 29...passage, 30...sealing member, 31...accommodating section, 32-35...through holes, 36...insertion hole, 40...MEA (electrode structure), 41...through holes, 41-44...through holes, 45...insertion hole, AE...anode electrode layer, CE...cathode electrode layer, EF...electrolyte membrane, CC...carbon cloth, S...fuel cell stack, U...single cell, H...holder, B...bolt, P1...fuel pump, P2...blower, T1...supply tank, T2...recovery tank, R...reservoir tank

Claims

1. 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 a liquid fuel to the anode; a cathode-side separator having an oxidant supply flow path for supplying an oxidant to the cathode electrode; a fuel cell comprising a single cell in which the electrode structure is disposed between a pair of the anode-side separator and the cathode-side separator, and which generates power by an electrode reaction in the electrode structure, The cathode side separator is an oxidant supply flow path that is a flow path formed on a surface facing the cathode electrode, the oxidant flowing through the oxidant and that supplies the oxidant to the cathode electrode; a discharge mechanism having a passage penetrating from the oxidant supply flow path toward the rear surface of the opposing surface in a plate thickness direction of the cathode-side separator, and configured to move water generated at the cathode electrode in association with the electrode reaction from the oxidant supply flow path through the passage to the rear surface and then discharge the water to the outside.

2. the discharge mechanism has a discharge passage provided on the rear surface and communicating with the passage, The fuel cell according to claim 1 , wherein the passage connects the oxidant supply channel and the discharge channel so as to be able to communicate with each other.

3. The discharge path is 3. The fuel cell according to claim 2, wherein the produced water that has migrated to the rear surface through the passage is discharged to the outside by a fluid flowing while the electrode reaction is occurring in the electrode structure.

4. 4. The fuel cell according to claim 3, wherein the oxidant branched from the oxidant supplied to the oxidant supply channel flows as the fluid through the discharge channel.

5. the oxidant supply passage is formed in a serpentine shape, and the discharge passage is formed in a straight line shape, 5. The fuel cell according to claim 3, wherein the pressure inside the discharge passage is smaller than the pressure inside the fuel supply passage by the flow of the fluid.

6. 6. The fuel cell according to claim 2, wherein a direction in which the oxidant supply flow channel is formed at a position where the passage is formed intersects with a direction in which the discharge channel is formed at a position where the passage is formed.

7. The fuel cell according to any one of claims 2 to 6, wherein the exhaust passage is disposed along a vertical direction.

8. 7. The fuel cell according to claim 1, wherein the passage has openings in the opposing surface and the rear surface, the openings being slit-shaped.

9. 9. The fuel cell according to claim 1, wherein a cross-sectional shape of the passage perpendicular to the axial direction is either a circular shape or a polygonal shape.

10. 10. The fuel cell according to claim 1, further comprising a reservoir tank for collecting and storing the generated water discharged by the discharge mechanism.

11. 11. The fuel cell according to claim 10, wherein the produced water stored in the reservoir tank is used as washing water for washing the anode electrode.

12. The fuel cell according to any one of claims 1 to 11, wherein the liquid fuel supplied to the anode electrode is formic acid (HCOOH).

Images