fuel cells

Abstract

To provide a fuel cell capable of efficiently removing reactants generated at electrodes.SOLUTION: A fuel cell 1 includes: a membrane electrode assembly 2 that has an electrolyte film 21, a first electrode 22, and a second electrode 23; a first separator 3 arranged on the first electrode 22; and a second separator 4 arranged on the second electrode 23. The first separator 3 has: a first flow channel 32 provided on an electrode abutting surface 31 abutting on the membrane electrode assembly 2 and configured to be able to supply at least one of fuel and oxidant to the first electrode 22; a reactant flow channel 34 provided on a back face 33 of the electrode abutting surface 31 and configured to be able to lead reactants generated at the first electrode 22 by electrode reaction to the outside of the fuel cell 1; a communication passage 35 provided on a side wall part 321 of the first flow channel 32, having an opening on the electrode abutting surface 31 and communicating between the opening and the reactant flow channel 34; and a drive part 36 configured to be able to expand and contract the communication passage 35.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Fuel cells, such as solid polymer fuel cells, have a membrane electrode assembly (MEA) that includes an electrolyte membrane, an anode electrode provided on one side of the electrolyte membrane, and a cathode electrode provided on the other side of the electrolyte membrane. Fuel cells can generate electrode reactions at each electrode by supplying fuel to the anode electrode of the MEA and an oxidant to the cathode electrode. These electrode reactions generate electromotive forces between the anode electrode and the cathode electrode, enabling electricity generation.

[0003] However, when electrode reactions occur at each electrode, reactants such as water (H2O) and carbon dioxide (CO2) are produced at the electrode. If these reactants remain near the electrode, the contact area between the fuel or oxidant and the electrode tends to decrease, which can lead to a decrease in power generation efficiency.

[0004] To address this problem, for example, Patent Document 1 describes an invention relating to a polymer electrolyte fuel cell in which an air electrode and an anode, which are arranged on either side of a polymer electrolyte membrane, are sandwiched between a pair of separator plates having gas flow channels formed therein for supplying and discharging oxidant gas to and from the air electrode and for supplying and discharging fuel gas to and from the anode, and in which a water removal flow channel is disposed in at least one of the anode, the air electrode, or the separator plates. The water removal flow channel in Patent Document 1 contains, for example, porous silica that has been subjected to a hydrophilic treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-110432 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the invention of Patent Document 1, water as a reactant that has entered the water removal flow path is likely to remain in the pores due to branching of the pores in the porous silica, friction with the wall surface, etc. If the reactant that has entered the water removal flow path remains in the water removal flow path, the efficiency of removing the reactant generated at the electrode decreases, which may lead to a decrease in power generation efficiency.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a fuel cell that can efficiently remove reactants produced at the electrodes. [Means for solving the problem]

[0008] One aspect of the present invention is a fuel cell comprising: a membrane electrode assembly having an electrolyte membrane, a first electrode formed on one surface of the electrolyte membrane, and a second electrode formed on the other surface of the electrolyte membrane; a first separator disposed on the first electrode; a second separator disposed on the second electrode; a fuel cell configured to be capable of generating electricity by an electrode reaction in the membrane electrode assembly, The first separator is a first flow path provided on an electrode contact surface that contacts the membrane electrode assembly, the first flow path being configured to be able to supply either a fuel or an oxidant to the first electrode; a reactant flow path provided on the back surface of the electrode contact surface, the reactant flow path being configured to guide the reactant generated at the first electrode by the electrode reaction to the outside of the fuel cell; and a side wall portion of the first flow path In the space enclosed by , an opening is formed on the electrode contact surface; The relevant a communication passage that communicates the opening with the reactant flow path; a member comprising: a drive unit configured to be able to expand and contract the communication passage; is provided, The communicating passage is configured so that the reactant in the communicating passage can be forcibly moved and guided to the reactant flow path by expanding and contracting the communicating passage. , in fuel cells. [Effects of the Invention]

[0009] The first separator of the fuel cell has a first flow path for supplying either fuel or oxidant to the first electrode, and a reactant flow path for guiding reactants generated at the first electrode to the outside of the fuel cell. The side wall of the first flow path has an opening at the electrode contact surface, a communication path connecting the opening to the reactant flow path, and a drive unit configured to expand and contract the communication path.

[0010] In the fuel cell, reactants generated from the first electrode by an electrode reaction enter the communicating passage through the opening in the electrode contact surface. The fuel cell can forcibly move the reactants in the communicating passage by expanding and contracting the drive unit while the reactants are held in the communicating passage. As a result, the reactants in the communicating passage can be quickly guided to the reactant flow path and efficiently discharged outside the fuel cell.

[0011] As described above, according to the above aspect, it is possible to provide a fuel cell that can efficiently remove reactants generated on the electrodes. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram showing the overall configuration of a fuel cell according to the first embodiment. [Figure 2] FIG. 2 is a partial cross-sectional view showing a main part of the fuel cell according to the first embodiment. [Figure 3] FIG. 3 is an enlarged view of the vicinity of the side wall portion in FIG. [Figure 4] FIG. 4 is a plan view of the membrane electrode assembly in the first embodiment. [Figure 5] FIG. 5 is a plan view of the electrode contact surface of the first separator of the first embodiment. [Figure 6] FIG. 6 is a plan view of the back surface of the electrode contact surface of the first separator of the first embodiment. [Figure 7]FIG. 7 is a plan view of the electrode contact surface of the second separator of the first embodiment. [Figure 8] FIG. 8 is a partially enlarged plan view of a first separator in accordance with the second embodiment, in which a communication path is provided in a partial region of the side wall portion. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. [Figure 10] FIG. 10 is a partially enlarged plan view of a first separator having a piezoelectric element as a driving section in the third embodiment. [Figure 11] FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. [Figure 12] FIG. 12 is an enlarged view of the vicinity of the side wall portion in FIG. [Figure 13] FIG. 13 is an enlarged cross-sectional view of a side wall portion of a first separator according to a fourth embodiment, in which a communication passage is provided extending obliquely downward. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Embodiment 1) An embodiment of the fuel cell will be described with reference to Figures 1 to 7. As shown in Figures 1 and 2, the fuel cell 1 includes a membrane electrode assembly 2 (hereinafter referred to as "MEA") having an electrolyte membrane 21, a first electrode 22 formed on one side of the electrolyte membrane 21, and a second electrode 23 formed on the other side of the electrolyte membrane 21, a first separator 3 arranged on the first electrode 22, and a second separator 4 arranged on the second electrode 23. The fuel cell 1 is configured to be able to generate electricity by an electrode reaction in the MEA 2.

[0014] 2 and 3, the first separator 3 has a first flow path 32 provided on an electrode contact surface 31 that contacts the MEA 2 and configured to be able to supply at least one of a fuel and an oxidizer to the first electrode 22, a reactant flow path 34 provided on a back surface 33 of the electrode contact surface 31 and configured to be able to guide reactants generated on the first electrode 22 by an electrode reaction to the outside of the fuel cell 1, a communication path 35 provided on a side wall portion 321 of the first flow path 32 and having an opening (not shown) in the electrode contact surface 31 and communicating the opening with the reactant flow path 34, and a drive unit 36 ​​configured to be able to expand and contract the communication path 35. The configuration of the fuel cell 1 will be described in detail below.

[0015] The fuel cell 1 of this embodiment is configured as a polymer electrolyte fuel cell that uses formic acid as fuel and air as an oxidant. In addition to formic acid, other fuels that can be used to supply to the fuel cell 1 include, for example, hydrogen gas, methanol, and ethanol. In addition to air, other oxidant that can be supplied to the fuel cell 1 include, for example, oxygen gas. The type of fuel cell 1 is not limited to a polymer electrolyte fuel cell.

[0016] As shown in FIGS. 1 and 2, the fuel cell 1 has a unit cell 11 including a first separator 3, an MEA 2, and a second separator 4. The fuel cell 1 may have one unit cell 11, or may have two or more unit cells 11. When the fuel cell 1 has a plurality of unit cells 11, these unit cells 11 may be stacked on top of each other to form a cell stack 12. When the fuel cell 1 has a plurality of unit cells 11, each unit cell 11 may be electrically connected in series or in parallel with the other unit cells 11.

[0017] As shown in Fig. 1, the fuel cell 1 of this embodiment has a cell stack 12 formed by stacking a plurality of unit cells 11 on top of each other. The unit cells 11 constituting the cell stack 12 are arranged so that the first separator 3 of each unit cell 11 and the second separator 4 of the unit cell 11 adjacent to that unit cell 11 abut against each other. As will be described later, the first separator 3 and the second separator 4 of this embodiment are made of an electrical conductor. As a result, the plurality of unit cells 11 in the cell stack 12 are electrically connected in series via the first separator 3 and the second separator 4.

[0018] A pair of holding plates 121 (121a, 121b) for holding the cell stack 12 may be arranged at both ends of the cell stack 12 in the stacking direction. In the fuel cell 1 of this embodiment, a fastening member 122 is inserted into one holding plate 121a of the pair of holding plates 121. The fastening member 122 penetrates the cell stack 12, and one holding plate 121a and the other holding plate 121b are fastened together by the fastening member 122. In this way, the cell stack 12 is held between the pair of holding plates 121. Furthermore, the holding plate 121 in the fuel cell 1 of this embodiment has a terminal 123 for extracting the electric power generated by the fuel cell 1 to an external circuit.

[0019] The fuel cell 1 is configured to generate electricity by supplying fuel and an oxidant to each unit cell 11. For example, the cell stack 12 in the fuel cell 1 of this embodiment is configured so that it can connect a fuel tank 131 that stores fuel to be supplied to each unit cell 11, a fuel pump 132 that is arranged on the fuel path from the fuel tank 131 to the cell stack 12, a fuel recovery tank 141 that recovers fuel discharged from the cell stack 12, and a blower 151 that supplies air as an oxidant to each unit cell 11. The fuel tank 131 and the fuel pump 132 are connected to the cell stack 12 via a fuel supply pipe 133. The fuel recovery tank 141 is connected to the cell stack 12 via a fuel recovery pipe 142. The blower 151 is connected to the cell stack 12 via an oxidant supply pipe 152.

[0020] In the fuel cell 1 of this embodiment, the fuel in the fuel tank 131 is pressurized by the fuel pump 132 and supplied to the cell stack 12. The fuel that enters the cell stack 12 is distributed to each unit cell 11 via a fuel supply path 13 provided in the cell stack 12 and is used for an electrode reaction in the unit cell 11. After being used for the electrode reaction, the fuel discharged from each unit cell 11 joins together in a fuel recovery path 14 provided in the cell stack 12 and is recovered in a fuel recovery tank 141.

[0021] Furthermore, in the fuel cell 1 of this embodiment, the air blown from the blower 151 is distributed to the unit cells 11 via an oxidant supply channel 15 provided in the cell stack 12 and is used for the electrode reaction in the unit cells 11. After being used for the electrode reaction, the air discharged from each unit cell 11 joins together in an oxidant discharge channel 16 (see FIG. 7) provided in the cell stack 12 and is discharged to the outside of the cell stack 12. For convenience, the oxidant discharge channel 16 is not shown in FIG. 1.

[0022] The fuel cell 1 may be configured to be able to recover reactants produced from each unit cell 11 by an electrode reaction. For example, the cell stack 12 in the fuel cell 1 of this embodiment is configured to be able to connect a reactant tank 171 for recovering reactants produced from each unit cell 11. The reactant tank 171 is connected to the cell stack 12 via a reactant recovery pipe 172. The reactant tank 171 communicates with the reactant flow paths 34 provided in the first separator 3 of each unit cell 11, for example, via a reactant recovery path 17 provided in the cell stack 12. The reactants produced by the electrode reaction at the first electrode 22 pass through the reactant flow paths 34 of each unit cell 11, join at the reactant recovery path 17, and are led to the reactant tank 171.

[0023] 2 and 3, a unit cell 11 of the fuel cell 1 has an MEA 2 including an electrolyte membrane 21, a first electrode 22, and a second electrode 23, a first separator 3 arranged on the first electrode 22, and a second separator 4 arranged on the second electrode 23. In the unit cell 11 of this embodiment, as shown in FIG. 2, a sealant 5 is provided between the electrolyte membrane 21 of the MEA 2 and the first separator 3, and between the electrolyte membrane 21 and the second separator 4, and the sealant 5 seals the gap between the MEA 2 and the first separator 3 and the gap between the MEA 2 and the second separator 4.

[0024] 4, the MEA 2 has a rectangular shape in a plan view seen from the thickness direction. As shown in FIGS. 2 and 4, the electrolyte membrane 21 is exposed at the outer periphery of the MEA 2. The electrolyte membrane 21 exposed at the outer periphery of the MEA 2 has a plurality of through-holes 211. These through-holes 211, together with the through-hole 37 provided in the first separator 3, the through-hole 43 provided in the second separator 4, and the through-holes (described later) provided in the sealing material 5, constitute part of the fuel supply channel 13, the fuel recovery channel 14, the oxidant supply channel 15, the oxidant discharge channel 16, the reactant recovery channel 17, and the insertion holes 124 through which the fastening members 122 are inserted, as shown in FIG.

[0025] The electrolyte membrane 21 used in the MEA 2 has electrical insulation properties and is + The cation exchange resin is made of a cation exchange resin that is configured to be selectively permeable to cations such as ammonium nitrate, ammonium nitrate, etc. As the cation exchange resin, for example, a perfluoroalkylsulfonic acid polymer (for example, "Nafion (registered trademark)" manufactured by DuPont) can be used.

[0026] The first electrode 22 and the second electrode 23 are disposed in the center of the electrolyte membrane 21 and are formed in layers on the electrolyte membrane 21 as shown in FIG. 2. The first electrode 22 and the second electrode 23 are configured to be able to catalyze an electrode reaction. For example, the first electrode 22 and the second electrode 23 may include catalyst-supported carbon that supports a precious metal catalyst such as palladium (Pd) or platinum (Pt). The first electrode 22 and the second electrode 23 of this embodiment include catalyst-supported carbon and a binder that holds the catalyst-supported carbon.

[0027] The MEA 2 of this embodiment further includes a first diffusion layer 24 provided on the first electrode 22 and a second diffusion layer 25 provided on the second electrode 23. The first diffusion layer 24 and the second diffusion layer 25 are electrically conductive and have minute voids. By using an electrically conductive material for the first diffusion layer 24 and the second diffusion layer 25, the first electrode 22 and the first separator 3 are electrically connected, and the second electrode 23 and the second separator 4 are electrically connected, allowing the power generated by the MEA 2 to be extracted to the outside.

[0028] Furthermore, by providing minute gaps in the first diffusion layer 24 and the second diffusion layer 25, the fuel and oxidant supplied to the unit cell 11 can be guided to the first electrode 22 and the second electrode 23 while diffusing within the first diffusion layer 24 and the second diffusion layer 25. As a result, the fuel and oxidant can be brought into contact with the first electrode 22 and the second electrode 23 more efficiently, improving power generation efficiency. The first diffusion layer 24 and the second diffusion layer 25 can be made of, for example, carbon cloth or carbon paper made of conductive carbon fiber.

[0029] The first electrode 22 may be configured as an anode, i.e., an electrode in contact with a fuel, or as a cathode, i.e., an electrode in contact with an oxidant, and the second electrode 23 is configured as an electrode of a different polarity from the first electrode 22. More specifically, when the first electrode 22 is configured as an anode, the second electrode 23 becomes a cathode, and when the first electrode 22 is configured as a cathode, the second electrode 23 becomes an anode. In the fuel cell 1 of this embodiment, the first electrode 22 is configured as a cathode, and the second electrode 23 is configured as an anode.

[0030] From the viewpoint of efficiently removing reactants from the first electrode 22, the first electrode 22 is preferably a cathode. At the cathode, hydrogen ions (H + The reaction of carbon dioxide with an oxidizing agent such as oxygen (O) produces water (HO) as a reactant. However, because water has a relatively high surface tension, once water is produced at the cathode, it tends to accumulate in the minute voids present in the cathode and the diffusion layer on the cathode.

[0031] In contrast, in the fuel cell 1 of this embodiment, the reactants in the first electrode 22 and the first diffusion layer 24 can be efficiently discharged to the outside of the fuel cell 1 through the communicating passages 35 and the reactant flow paths 34 provided in the first separator 3. Therefore, by configuring the first electrode 22 as a cathode, water as a reactant can be efficiently removed, and the power generation efficiency of the fuel cell 1 can be further improved.

[0032] 2, the first separator 3 is provided on the surface of the MEA 2 on the side having the first electrode 22. In this embodiment, the first separator 3 is made of an electrical conductor and functions as a current collector that collects electrons generated by the electrode reaction in the MEA 2. The first separator 3 may be made of, for example, a metal material such as gold-plated stainless steel, a conductive non-metal material such as conductive carbon, a conductive composite material, or the like.

[0033] The first separator 3 of this embodiment has a flat plate shape and, as shown in Figures 5 and 6, has approximately the same outer dimensions as the MEA 2 when viewed from above in the thickness direction. A plurality of through holes 37 (37a to 37f) are provided in the outer periphery of the first separator 3. The positions of these through holes 37 are the same as the positions of the through holes 211 provided in the electrolyte membrane 21 of the MEA 2 when the cell stack 12 is constructed. The through holes 37 of the first separator 3 form part of the fuel supply channel 13, fuel recovery channel 14, oxidant supply channel 15, oxidant discharge channel 16, reactant recovery channel 17, and insertion holes 124 through which the fastening members 122 are inserted, as shown in Figure 1.

[0034] 5, the first separator 3 has an electrode contact surface 31 that contacts the MEA 2 at the center of the surface facing the first electrode 22. More specifically, the electrode contact surface 31 of the first separator 3 in this embodiment contacts the first diffusion layer 24 of the MEA 2 as shown in FIG.

[0035] The electrode contact surface 31 of the first separator 3 is provided with a first flow path 32 configured to be able to supply either a fuel or an oxidant to the first electrode 22. As shown in Fig. 5 , the first flow path 32 in the fuel cell 1 of this embodiment is a groove that extends from a through-hole 37a, which constitutes a part of the oxidant supply path 15, to a through-hole 37b, which constitutes a part of the oxidant discharge path 16, in the first separator 3, and is open to the MEA 2 side. This allows the first flow path 32 to supply the oxidant distributed by the oxidant supply path 15 to the first diffusion layer 24 and the first electrode 22.

[0036] The shape and arrangement of the first flow path 32 may take various forms. For example, the cross-sectional shape of the first flow path 32 may be rectangular, triangular, or semicircular, but is not limited to these shapes. As shown in FIG. 5 , the first flow path 32 has a plurality of straight portions 322 arranged in parallel to one another and folded portions 323 connecting the end of each straight portion 322 to the end of the adjacent straight portion 322. In a plan view from the electrode contact surface 31 side, the first flow path 32 may be arranged to meander between a through hole 37a constituting a part of the oxidant supply path 15 and a through hole 37b constituting a part of the oxidant discharge path 16, but other arrangements are also possible.

[0037] 6, a reactant flow path 34 is provided on the back surface 33 of the electrode contact surface 31 of the first separator 3. The reactant flow path 34 is configured to be able to guide the reactants produced from the first electrode 22 to the outside of the fuel cell 1. Specifically, the reactant flow path 34 in the fuel cell 1 of this embodiment is a groove provided on the back surface 33 of the electrode contact surface 31 of the first separator 3 and connected to a through-hole 37c that forms part of the reactant recovery channel 17. The reactant flow path 34 only needs to be arranged so as to overlap at least a part of the side wall portion 321 of the first flow path 32 in a plan view from the thickness direction of the first separator 3.

[0038] 3 and 6, in this embodiment, a porous body 351 and a cylindrical elastic body 361 (described later) provided on the side wall portion 321 of the first flow channel 32 are exposed at the bottom surface of the reactant flow channel 34, and a communication channel 35 formed by the pores of the porous body 351 opens to the reactant flow channel 34. This allows the reactant generated from the first electrode 22 to be introduced into the reactant flow channel 34 via the communication channel 35.

[0039] When the first electrode 22 is configured as a cathode, the inner surfaces of the reactant flow channels 34 are preferably subjected to a hydrophilic treatment. In this case, when water present in the communicating channels 35 reaches the reactant flow channels 34, it is more likely to wet and spread over the surfaces of the reactant flow channels 34, making it easier to draw the water in the communicating channels 35 into the reactant flow channels 34. Furthermore, water as a reactant present in the first electrode 22, the first diffusion layer 24, and the communicating channels 35 may evaporate and become water vapor during operation of the fuel cell 1. By subjecting the inner surfaces of the reactant flow channels 34 to a hydrophilic treatment, the evaporated water vapor is more likely to collect in the reactant flow channels 34. As a result, the movement of water from the first electrode 22 and the like to the reactant flow channels 34 is promoted, and water as a reactant can be more efficiently removed from the first electrode 22.

[0040] The shape and arrangement of the reactant flow channel 34 may be variously modified as long as the above-described effects are not impaired. For example, the cross-sectional shape of the reactant flow channel 34 may be rectangular, triangular, semicircular, or the like, but is not limited to these shapes. Furthermore, as shown in FIG. 6 , the reactant flow channel 34 may have a main flow channel portion 341 directly connected to a through-hole 37c that constitutes a part of the reactant recovery channel 17, and a plurality of branch flow channel portions 342 branching from the main flow channel portion 341. The main flow channel portion 341 in the fuel cell 1 of this embodiment extends so as to intersect with the longitudinal center portions of each straight portion 322 of the first flow channel 32. Furthermore, when viewed in a plan view from the back surface 33 side of the electrode abutment surface 31, the branch flow path section 342 branches off to both the left and right sides from the main flow path section 341, and when the fuel cell 1 is installed so that the outlet (i.e., the through hole 37c) of the reactant from the single cell 11 faces downward, the branch flow path section 342 is arranged in a direction that is inclined downward relative to the horizontal direction as it approaches the main flow path section 341.

[0041] As shown in FIG. 6 , the reactant flow channel 34 of this embodiment is configured such that, when the fuel cell 1 is installed with the reactant outlet facing downward, the downstream side of the reactant flow is positioned lower in the vertical direction than the upstream side. That is, the reactant flow channel 34 of this embodiment is configured to allow the reactant to move downward as it moves downstream. By configuring the reactant flow channel 34 in this manner and installing the fuel cell 1 with the reactant outlet facing downward, water as a reactant that has entered the reactant flow channel 34 can be guided to the reactant outlet by gravity. As a result, the movement of water within the reactant flow channel 34 is promoted, and water as a reactant can be more efficiently removed from the first electrode 22.

[0042] As shown in FIGS. 3 and 5 , the sidewall 321 of the first flow channel 32, i.e., the portion of the first separator 3 that constitutes the side surface of the first flow channel 32, has an opening (not shown) at the electrode contact surface 31, and is provided with a communication channel 35 that connects the opening to the reactant flow channel 34. The communication channel 35 may be provided over the entire sidewall 321 of the first flow channel 32, or may be provided in a partial region of the sidewall 321. In the latter case, the number of regions provided with the communication channel 35 in the sidewall 321 may be one or two or more. Note that the communication channel 35 does not open on the surface of the sidewall 321 of the first flow channel 32 that faces the first flow channel 32. Therefore, in the fuel cell 1 of this embodiment, the fuel and oxidant flowing through the first flow channel 32 do not directly enter the communication channel 35 without passing through the first electrode 22 and the first diffusion layer 24.

[0043] The communicating paths 35 are preferably composed of minute gaps or pores having a size equal to or smaller than the size of the gaps present in the first electrode 22 and the first diffusion layer 24. In this case, reactants generated in the first electrode 22 or the first diffusion layer 24 can easily enter the communicating paths 35. As a result, the reactants can be more efficiently removed from the first electrode 22. When the communicating paths 35 are pores, the size of the communicating paths 35 can be expressed by an average pore diameter. When the communicating paths 35 are gaps, the size of the communicating paths 35 can be expressed by an equivalent pore diameter. The average pore diameter or the average value of the equivalent pore diameter can be on the order of, for example, 10 μm.

[0044] The method for providing the communicating passages 35 in the side wall 321 is not particularly limited. For example, a method can be used in which a member having pores or gaps to serve as the communicating passages 35 is prepared and this member is embedded in the side wall 321 of the first separator 3. In this case, the member to be embedded in the first separator 3 can be, for example, a porous body with pores or a laminate made of multiple plates stacked on top of each other with gaps between the plates. That is, the side wall 321 may have a porous body with pores to serve as the communicating passages 35. Alternatively, the side wall 321 may have a laminate made of multiple plates stacked on top of each other, with the communicating passages 35 being the gaps between the plates in the laminate. At least one surface of the plates used in the laminate may be roughened.

[0045] The fuel cell 1 of this embodiment has a porous body 351 having pores serving as the communication passages 35 in the portion of the sidewall portion 321 between the straight portions 322 of the first flow passage 32. The porous body 351 extends along the straight portions 322 of the first flow passage 32. The porous body 351 may be made of, for example, ceramics, or an organic material such as rubber or elastomer. The porous body 351 may be an electrical conductor or an insulator. From the viewpoint of reducing the electrical internal resistance of the unit cell 11, it is preferable that the porous body 351 has electrical conductivity.

[0046] Additionally, a drive unit 36 ​​configured to be able to expand and contract the communicating passage 35 is provided on the side wall 321. The drive unit 36 ​​may be, for example, a component configured to be deformable by pressure fluctuations, application of voltage, or the like, such as a tubular member made of an elastic body or a piezoelectric body. By providing such a drive unit 36 ​​adjacent to the communicating passage 35, the communicating passage 35 can be expanded and contracted in accordance with the deformation of the drive unit 36.

[0047] 3, the driving unit 36 ​​in the fuel cell 1 of this embodiment is a cylindrical elastic body 361 made of an elastic material, having an opening 362 in the reactant flow path 34 and a closed end 363 on the electrode contact surface 31 side. The cylindrical elastic body 361 is disposed adjacent to the porous body 351 provided in the side wall portion 321. As shown in FIG. 5, the cylindrical elastic body 361 extends over the entire space between the linear portions 322 of the first flow path 32 in the side wall portion 321. The elastic body constituting the cylindrical elastic body 361 can be, for example, rubber or elastomer.

[0048] The fuel cell 1 of this embodiment has a pressure adjusting unit 173 connected to the reactant flow path 34 and configured to adjust the pressure inside the reactant flow path 34. The cylindrical elastic body 361 serving as the drive unit 36 ​​has an opening in the reactant flow path 34, and therefore expands when the pressure inside the reactant flow path 34 increases and contracts when the pressure inside the reactant flow path 34 decreases. Therefore, by connecting the pressure adjusting unit 173 to the reactant flow path 34 and varying the pressure inside the reactant flow path 34 with the pressure adjusting unit 173, the cylindrical elastic body 361 can be expanded or contracted. Expanding or contracting the cylindrical elastic body 361 deforms the porous body 351 adjacent to the cylindrical elastic body 361, and thereby expands or contracts the pores serving as the communication paths 35 inside the porous body 351.

[0049] 1, the pressure adjustment unit 173 in the fuel cell 1 of this embodiment is provided on the reactant recovery pipe 172 between the cell stack 12 and the reactant tank 171. For example, a pump or an oscillator configured to generate sonic vibrations can be used as the pressure adjustment unit 173. Specifically, the pressure adjustment unit 173 in the fuel cell 1 of this embodiment is a pump configured to adjust the pressure in the reactant flow path 34.

[0050] 2, a second separator 4 is provided on the surface of the MEA 2 on the side having the second electrode 23. The second separator 4 in this embodiment is made of an electrical conductor, similar to the first separator 3, and functions as a current collector that collects electrons generated by the electrode reaction in the MEA 2. The second separator 4 may be made of, for example, a metal material such as gold-plated stainless steel, a conductive non-metallic material such as conductive carbon, a conductive composite material, or the like.

[0051] The second separator 4 may be configured to supply the second electrode 23 with one of the fuel and the oxidant, which is different from the substance supplied to the first electrode 22. The second separator 4 of this embodiment is flat and, as shown in FIG. 7 , has approximately the same outer dimensions as the MEA 2 when viewed from above in the thickness direction. A plurality of through-holes 43 (43a to 43f) are provided in the outer periphery of the second separator 4, and the positions of these through-holes 43 are the same as the positions of the through-holes 211 provided in the electrolyte membrane 21 of the MEA 2 when the cell stack 12 is constructed. That is, the through-holes 43 of the second separator 4 form part of the fuel supply channel 13, the fuel recovery channel 14, the oxidant supply channel 15, the oxidant discharge channel 16, the reactant recovery channel 17, and the insertion holes 124 through which the fastening members 122 are inserted, as shown in FIG. 1 .

[0052] The second separator 4 has an electrode contact surface 41 that contacts the MEA 2 at the center of the surface facing the second electrode 23. More specifically, the electrode contact surface 41 of the second separator 4 in this embodiment contacts the second diffusion layer 25 of the MEA 2 as shown in FIG. 2 . The periphery of the electrode contact surface 41 contacts the sealing material 5.

[0053] A second flow path 42 is provided on the electrode contact surface 41 of the second separator 4. The second flow path 42 is configured to be able to supply the fuel and the oxidant that have not been supplied to the first electrode 22 to the second electrode 23. As shown in FIG. 7 , the second flow path 42 in the fuel cell 1 of this embodiment is a groove that extends from a through-hole 43d that constitutes part of the fuel supply path 13 to a through-hole 43e that constitutes part of the fuel recovery path 14 in the second separator 4 and is open to the MEA 2 side. This allows the second flow path 42 to supply the fuel distributed via the fuel supply path 13 to the second diffusion layer 25 and the second electrode 23.

[0054] The shape and arrangement of the second flow path 42 can take various forms, similar to the first flow path 32. The second flow path 42 of the present embodiment has a plurality of straight portions 422 arranged parallel to one another and folded portions 423 connecting the end of each straight portion 422 to the end of the straight portion 422 adjacent to the straight portion 422, and is arranged to meander between a through hole 43d that constitutes a part of the fuel supply path 13 and a through hole 43e that constitutes a part of the fuel recovery path 14 in a plan view seen from the electrode abutment surface 41 side. In addition, the straight portion 422 of the second flow path 42 extends in a direction parallel to the straight portion 322 of the first flow path 32.

[0055] 2, a sealant 5 is provided between the electrolyte membrane 21 and the first separator 3 in the MEA 2, and between the electrolyte membrane 21 and the second separator 4. By providing the sealant 5 between the electrolyte membrane 21 and the first separator 3 and between the electrolyte membrane 21 and the second separator 4, the gaps therebetween can be sealed, preventing leakage of fuel and the like from the inside to the outside of the unit cell 11. The sealant 5 may be made of an elastic material such as EPDM (ethylene propylene diene rubber) or an elastomer.

[0056] Although not shown in the figure, the sealing material 5 of this embodiment is plate-shaped and has approximately the same outer dimensions as the first separator 3 and the second separator 4. An opening is provided in the center of the sealing material 5 in the thickness direction, and as shown in FIG. 2, when the MEA 2 and the sealing material 5 are superimposed, the first electrode 22 and the second electrode 23 are disposed within the opening. In addition, a plurality of through-holes are provided in the outer periphery of the sealing material 5. The positions of these through-holes are the same as the positions of the through-holes 211 provided in the electrolyte membrane 21 of the MEA 2 when the cell stack 12 is constructed. The through-holes in the sealing material 5 form part of the fuel supply channel 13, fuel recovery channel 14, oxidant supply channel 15, oxidant discharge channel 16, reactant recovery channel 17, and insertion holes 124 through which the fastening members 122 are inserted, as shown in FIG.

[0057] Next, the operation of the fuel cell 1 of this embodiment will be described. When fuel is supplied to the cell stack 12 from the fuel tank 131 shown in Fig. 1 and oxygen is supplied to the cell stack 12 from the blower 151, the fuel and oxidant are distributed to each unit cell 11. Then, in each unit cell 11, the oxidant flowing in the first flow path 32 comes into contact with the first electrode 22 serving as a cathode, and the fuel flowing in the second flow path 42 comes into contact with the second electrode 23 serving as an anode, thereby generating electricity.

[0058] When an electrode reaction occurs at the first electrode 22, water is generated as a reactant at the first electrode 22. The water generated at the first electrode 22 enters the communicating passage 35 due to the pressure difference and concentration gradient between the first flow passage 32 and the reactant flow passage 34. At this time, the pressure in the reactant flow passage 34 can be periodically changed by operating a pressure adjustment pump connected to the cell stack 12 while periodically varying its output. When the pressure in the reactant flow passage 34 periodically changes, the cylindrical elastic body 361 periodically expands and contracts accordingly. This causes the communicating passage 35 of the porous body 351 adjacent to the cylindrical elastic body 361 to expand and contract, forcing the water in the communicating passage 35 to move. The effect of forcing the water in the communicating passage 35 and the effects of the pressure difference and concentration gradient between the first flow passage 32 and the reactant flow passage 34 synergistically work to quickly guide the water in the communicating passage 35 to the reactant flow passage 34 and efficiently discharge it to the outside of the fuel cell 1.

[0059] (Embodiment 2) In this embodiment, another aspect of the arrangement of the region having the communication passages 35 in the side wall portion 321 will be described. Note that, among the symbols used in the second and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

[0060] Although not shown in the figure, the first separator 302 of this embodiment has a flat plate shape, and in plan view in the thickness direction, has approximately the same outer dimensions as the MEA 2. The outer periphery of the first separator 302 is provided with a plurality of through-holes 37 that constitute part of the fuel supply channel 13, fuel recovery channel 14, oxidant supply channel 15, oxidant discharge channel 16, reactant recovery channel 17 in the cell stack 12, and insertion holes 124 through which the fastening members 122 are inserted.

[0061] The first separator 302 has an electrode contact surface 31 at the center of the surface facing the first electrode 22, which contacts the first diffusion layer 24 of the MEA 2 as shown in Fig. 8, and a first flow path 32 is provided on the electrode contact surface 31. In addition, a reactant flow path 34 is provided on the back surface 33 of the electrode contact surface 31 of the first separator 302 as shown in Fig. 9.

[0062] 8 and 9, in the first separator 302 of this embodiment, a plurality of communicating passage assemblies 38 including a cylindrical sleeve 381, a porous body 352 disposed in the sleeve 381, and a cylindrical elastic body 364 disposed adjacent to the porous body 352 are embedded in the portions of the side wall portion 321 between the straight portions 322 of the first flow path 32. As shown in Fig. 8, the communicating passage assemblies 38 are disposed at intervals from one another in the extension direction of the straight portions 322 of the first flow path 32.

[0063] 9, the porous body 352 in the communication passage assembly 38 is exposed to the electrode abutment surface 31 and the bottom surface of the reactant flow passage 34, and the pores of the porous body 352 serving as communication passages 35 open to the electrode abutment surface 31 and the reactant flow passage 34. The cylindrical elastic body 364 is disposed adjacent to the porous body 352 within the sleeve 381, and its end on the electrode abutment surface 31 side is closed and its end on the reactant flow passage 34 side is open.

[0064] 9, the side wall 321 of this embodiment has a protruding portion 324 that protrudes toward the MEA2 side from the surrounding area, and the opening of the communicating path 35 is provided in the protruding portion 324. More specifically, in this embodiment, the porous body 352 in the communicating path assembly 38 provided in the side wall 321 protrudes toward the MEA2 side from the surrounding area, and the part of the porous body 352 that protrudes toward the MEA2 side constitutes the protruding portion 324. The rest is the same as the first separator 302 of the first embodiment.

[0065] The first separator 302 of this embodiment has pores of the porous body 352 as the communication passages 35 and a cylindrical elastic body 364 as the drive section 36 in the side wall section 321 of the first flow passage 32, and also has a reactant flow passage 34 on the back surface 33 of the electrode abutting surface 31. Therefore, even when the first separator 302 of this embodiment is incorporated into a fuel cell in place of the first separator 3 of embodiment 1, the same effects as those of the fuel cell of embodiment 1 can be achieved.

[0066] Furthermore, as in the first separator 302 of this embodiment, by making the region of the side wall 321 having the opening of the communicating channel 35 protrude toward the MEA 2, the contact area between the MEA 2 and the region having the opening of the communicating channel 35 can be increased. This allows reactants generated in the MEA 2 to be taken into the communicating channel 35 more efficiently. Furthermore, by pressing the MEA 2 with the protruding portion 324, the MEA 2 is deflected toward the second separator 4, reducing contact between the corners of the side wall 321 and the MEA 2. As a result, stress concentration on the MEA 2 due to contact with the corners of the side wall 321 can be reduced.

[0067] (Embodiment 3) In this embodiment, an example of a first separator 303 having a piezoelectric element 365 as a driving unit 36 ​​will be described. Although not shown in the figure, the first separator 303 of this embodiment is flat and has approximately the same outer dimensions as the MEA 2 when viewed from above in the thickness direction. The outer periphery of the first separator 303 is provided with a plurality of through-holes 37 that constitute part of the fuel supply channel 13, fuel recovery channel 14, oxidant supply channel 15, oxidant discharge channel 16, reactant recovery channel 17 in the cell stack 12, and insertion holes 124 through which the fastening members 122 are inserted.

[0068] The first separator 303 has an electrode contact surface 31 that contacts the MEA 2 at the center of the surface facing the first electrode 22, as shown in Fig. 10. As shown in Figs. 10 to 12, a first flow path 32 is provided on the electrode contact surface 31. Furthermore, as shown in Figs. 11 and 12, a reactant flow path 34 is provided on a back surface 33 of the electrode contact surface 31 of the first separator 303.

[0069] 10 , the communicating passages 35 in the first separator 303 of this embodiment are provided in the sidewall portion 321 of the first flow passage 32, in a portion between the straight portions 322 of the first flow passage 32. More specifically, the sidewall portion 321 has two porous bodies 353 with pores that serve as the communicating passages 35, and a piezoelectric body 365 serving as the driving unit 36 ​​sandwiched between the porous bodies 353. The two porous bodies 353 are made of electrically insulating ceramics, and each extends along the straight portions 322 of the first flow passage 32.

[0070] The piezoelectric element 365 serving as the driving unit 36 ​​is electrically connected to the first separator 303 and the second separator 4 electrically insulated from the first separator 303. Specifically, as shown in FIG. 10 , the piezoelectric element 365 of this embodiment is in contact with the side wall portion 321 of the first flow path 32 at both ends in the extension direction of the straight portion 322 of the first flow path 32. This electrically connects the piezoelectric element 365 to the first separator 303 on which the piezoelectric element 365 is provided. Furthermore, as shown in FIGS. 11 and 12 , the piezoelectric element 365 is also in contact with the electrically conductive first diffusion layer 24, and is therefore electrically connected to the first separator 303 via the first diffusion layer 24.

[0071] 12, one end of an insulated wire 367 is connected to a portion of an end surface 366 of the piezoelectric body 365 exposed to the reactant flow path 34, the portion being disposed in the main flow path section 341 of the reactant flow path 34. As shown in FIG. 11, the insulated wire 367 passes through the main flow path section 341 of the reactant flow path 34 and the reactant recovery path 17, and is connected to the second separator 4 of the unit cell 11 having the piezoelectric body 365. This electrically connects the piezoelectric body 365 to the first separator 303 and the second separator 4 of the unit cell 11 having the piezoelectric body 365. The remaining configuration is the same as that of the first separator 302 of the second embodiment.

[0072] The first separator 303 of this embodiment has pores of a porous body 353 serving as communication paths 35 in the side wall portion 321 of the first flow path 32, and has a reactant flow path 34 on the back surface 33 of the electrode contact surface 31. In addition, a piezoelectric body 365 serving as a drive unit 36 ​​is provided on the side wall portion 321.

[0073] Direct current fuel cells using formic acid or the like as fuel are sometimes configured to generate electricity intermittently to prevent a decrease in the cell's electromotive force due to continuous operation. When operating intermittently, the potential difference between the first separator 303 and the second separator 4 during power generation differs from the potential difference between the first separator 303 and the second separator 4 when power generation is interrupted. Therefore, when the first separator 303 of this embodiment is incorporated into the fuel cell 1, the voltage applied to the piezoelectric element 365 during power generation differs from the voltage applied to the piezoelectric element 365 when power generation is interrupted, and the difference between these voltages changes the degree of deformation of the piezoelectric element 365. As a result, the piezoelectric element 365 expands and contracts the communicating passage 35, facilitating the movement of reactants within the communicating passage 35.

[0074] (Embodiment 4) In this embodiment, a specific example of the communicating path 35 will be described. The communicating path 35 may have any configuration as long as it can communicate between the electrode abutment surface 31 and the reactant flow path 34. For example, the communicating path 35 may extend in a direction oblique to the arranging direction of the first separator 3 and the second separator 4. In the first separator 304 of this embodiment, as shown in FIG. 13 , the porous body 354 provided in the side wall portion 321 of the first flow path 32 has pores 355 extending in a direction oblique to the arranging direction of the first separator 304 and the second separator 4. The first separator 304 of this embodiment is otherwise similar to the first separator 3 of the first embodiment.

[0075] In the fuel cell 1 incorporating the first separator 304 of this embodiment, for example, the first separator 304 and the second separator 4 are arranged horizontally, and the pores serving as the communicating channels 35 extend obliquely downward from the electrode abutment surface 31 toward the reactant channels 34. This facilitates the movement of water in the communicating channels 35 toward the reactant channels 34 by gravity. As a result, the movement of water in the communicating channels 35 is promoted, and water as a reactant can be removed from the first electrode 22 more efficiently.

[0076] The present invention is not limited to the above-described embodiments and can be applied to various embodiments without departing from the spirit of the present invention. For example, the second separator 4 in Embodiment 1 can be configured, like the first separator 3, to have a communication path and a drive unit in the side wall portion 421 (see FIGS. 2 and 7) of the second flow path 42 and a reactant flow path on the back surface of the electrode contact surface 41. In this case, the reactants generated at the first electrode 22 can be efficiently removed from the first electrode 22, and the reactants generated at the second electrode 23 can be efficiently removed from the second electrode 23.

[0077] Furthermore, in the third embodiment, an example has been shown in which the piezoelectric element 365 as the driving unit 36 ​​is connected to the first separator 304 and the second separator 4 of the single cell 11 having the piezoelectric element 365. However, for example, it is also possible to provide a separate power source in the fuel cell for driving the piezoelectric element, and to connect the piezoelectric element and the power source via an insulated wire or the like. [Explanation of symbols]

[0078] 1 fuel cell 2 Membrane electrode assembly 21 Electrolyte membrane 22 First electrode 23 Second electrode 3, 302, 303, 304 First separator 31 Electrode contact surface 32 First Channel 321 Side wall 33 Back 34 Reactant flow path 35 Communication path 36 Drive unit 4 Second separator

Claims

1. a membrane electrode assembly having an electrolyte membrane, a first electrode formed on one surface of the electrolyte membrane, and a second electrode formed on the other surface of the electrolyte membrane; a first separator disposed on the first electrode; a second separator disposed on the second electrode; a fuel cell configured to be capable of generating electricity by an electrode reaction in the membrane electrode assembly, The first separator is a first flow path provided on an electrode contact surface that contacts the membrane electrode assembly, the first flow path being configured to be able to supply either a fuel or an oxidant to the first electrode; a reactant flow path provided on the back surface of the electrode contact surface and configured to guide the reactants generated at the first electrode by the electrode reaction to the outside of the fuel cell, a member provided in a space surrounded by a side wall portion of the first flow path with an opening on the electrode contact surface and a communication passage that communicates the opening with the reactant flow path; a drive unit configured to be able to expand and contract the communication passage, The fuel cell is configured such that the reactants in the communication passage can be forcibly moved and guided to the reactant flow path by expanding and contracting the communication passage.

2. 2. The fuel cell according to claim 1, wherein the driving unit is made of an elastic material and has a cylindrical elastic body having an opening in the reactant flow path, and the fuel cell has a pressure adjustment unit connected to the reactant flow path and configured to adjust the pressure inside the reactant flow path.

3. 3. The fuel cell according to claim 2, wherein the pressure adjusting unit is a pump or an oscillator configured to generate sonic vibrations.

4. 2. The fuel cell according to claim 1, wherein the driving unit has a piezoelectric element, and the piezoelectric element is electrically connected to each of the first separator and the second separator electrically insulated from the first separator.

5. 5. The fuel cell according to claim 1, wherein the communication passage extends in a direction oblique to the direction in which the first separator and the second separator are arranged.

6. 6. The fuel cell according to claim 1, wherein the first electrode is configured as a cathode, and the inner surface of the reactant channel is subjected to a hydrophilic treatment.

7. 7. The fuel cell according to claim 1, wherein the member is a porous body having pores as the communication paths.

8. 7. The fuel cell according to claim 1, wherein the member is a stack of a plurality of plates stacked on top of each other, and the communication passage is a gap between the plates in the stack.

9. The fuel cell according to any one of claims 1 to 8, wherein the member has a protruding portion that protrudes toward the membrane electrode assembly side more than the side wall portion, and the opening of the communication passage is provided in the protruding portion.

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