fuel cells

Abstract

The present invention relates to a fuel cell. A fuel flow channel formed on a fuel electrode current collector of a fuel electrode comprises: a plurality of flow channel portions arranged in parallel; and a plurality of folded-back groove portions connecting the ends of one edge portion or the ends of the other edge portion of two adjacent groups of the plurality of flow channel portions. Each of the plurality of folded-back groove portions comprises an inner sidewall portion of the plurality of folded-back groove portions that opposes the end portion of the flow channel portion, the inner sidewall portion having a curved surface shape, wherein the distance to the opposing end portion of the flow channel portion gradually narrows as it approaches the two ends of the inner sidewall portion in a direction perpendicular to the direction in which the flow channel portion extends.

Description

Technical Field

[0001] The present invention relates to fuel cells. Background Art

[0002] In recent years, various technologies related to fuel cells using liquid fuels such as formic acid and methanol have been proposed. For example, the fuel cell described in Japanese Patent Application Laid-Open No. 2007-95692 includes multiple power generation units arranged at regular intervals along the longitudinal direction, centered around an insulating separator. Each power generation unit consists of an anode portion positioned in close contact with both sides of the separator, a membrane-electrode assembly (MEA) positioned in close contact with the anode portion, and a cathode portion positioned in close contact with the MEA.

[0003] The anode portion is provided with a first flow path, arranged linearly at random intervals along the length of a vertically rectangular first path member, and alternately connected at both ends to form a serpentine shape. The path extends through the thickness of the first flow path. One end (the lower end) of the first flow path communicates with the outflow port of a manifold formed on the separator. Furthermore, the other end (the upper end) of the first flow path communicates with the inflow port of the manifold. Thus, fuel flows from the inflow port of the manifold through the serpentine first flow path and, via the upper outflow port, into the manifold, where it is distributed and supplied to the first electrode layer of the MEA.

[0004] However, in the fuel cell described in Japanese Patent Gazette No. 2007-95692, the two ends of the first flow path are bent at approximately right angles, so there is a problem that carbon dioxide (CO2) produced by the oxidation of the fuel and the fuel are retained in the corner on the upper side of the flow path connecting the two end portions in the vertical direction, making it difficult for the fuel to flow smoothly, resulting in reduced power generation. Summary of the Invention

[0005] The present invention provides a fuel cell capable of preventing stagnation of fuel and carbon dioxide in a fuel flow groove formed in a fuel electrode and suppressing a decrease in power generation.

[0006] According to a first embodiment of the present invention, a direct liquid fuel cell using a liquid containing formic acid or an alcohol as fuel includes: a fuel electrode having a fuel electrode catalyst layer, a fuel electrode diffusion layer, and a fuel electrode current collector; an air electrode having an air electrode catalyst layer, an air electrode diffusion layer, and an air electrode current collector; and an electrolyte membrane disposed between the fuel electrode catalyst layer and the air electrode catalyst layer. The fuel electrode current collector includes a fuel inlet for supplying the fuel; a fuel outlet for discharging the fuel; and a fuel flow groove formed on a fuel flow surface on a side contacting the fuel electrode diffusion layer, for guiding the fuel from the fuel inlet to the fuel outlet. The fuel flow groove includes: a plurality of flow groove portions extending from one side edge portion of the fuel flow surface to another side edge portion opposite to the one side edge portion, and arranged in parallel with each other at predetermined intervals; and a plurality of folded-back groove portions connecting ends of one side edge portion or ends of the other side edge portion of two adjacent groups of the plurality of flow groove portions, such that the fuel flow direction of the plurality of flow groove portions is opposite to each other. Each of the plurality of folded-back groove portions includes a first inner side wall portion of the plurality of folded-back groove portions opposite to the end portion of the flow groove portion, the first inner side wall portion having a curved surface shape in which the distance to the opposing end portion of the flow groove portion gradually narrows as it moves toward the opposite ends of the first inner side wall portion in a direction perpendicular to the direction in which the flow groove portion extends.

[0007] According to a second embodiment of the present invention, in the fuel cell of the first embodiment, the fuel flow groove includes an inlet groove portion connected to the fuel inlet and connected to an end portion of one of the plurality of flow groove portions configured so that the fuel initially flows in, on a side opposite to the folded groove portion, the inlet groove portion including a second inner sidewall portion facing the end portion of the flow groove portion. The second inner sidewall portion has a curved surface shape in which a distance from the end portion of the flow groove portion facing the opposite end portion gradually narrows as it moves toward the outflow-side end portion of the second inner sidewall portion in a direction perpendicular to the direction in which the flow groove portion extends.

[0008] According to a third embodiment of the present invention, in the fuel cell of the first or second embodiment, the fuel flow channel includes an outflow channel portion connected to the fuel outflow port and connected to an end portion of one of the plurality of flow channel portions configured so that the fuel flows in last, the end portion of the outflow channel portion being opposite to the folded-back channel portion, the outflow channel portion including a third inner sidewall portion of the outflow channel portion opposing the end portion of the flow channel portion. The third inner sidewall portion has a curved surface shape in which a distance from the end portion of the flow channel portion opposing the end portion gradually narrows toward the inflow-side end portion of the third inner sidewall portion in a direction perpendicular to the direction in which the flow channel portion extends.

[0009] According to a fourth embodiment of the present invention, in any one of the fuel cells in the first embodiment to the third embodiment, the fuel flow groove has: a plurality of ribs, which are arranged between the plurality of flow groove portions, and the plurality of ribs have a plurality of protrusions at the ends of the flow groove portions respectively opposite to the first inner wall surface portion, the second inner wall surface portion and the third inner wall surface portion, which are directed outward compared to the flow groove portion and protrude in a circular arc shape when viewed from above.

[0010] According to the fifth embodiment of the present invention, in the fuel cell of the fourth embodiment, the multiple protrusions protruding toward the fold-back groove portion are formed so that the protrusion height of the protrusions gradually becomes lower along the boundaries between two groups of the multiple groups of the multiple circulation groove portions that are reversed from the two ends of the fold-back groove portion toward the direction of the fuel flow in a direction perpendicular to the direction in which the circulation groove portion extends.

[0011] According to the first embodiment, a fuel flow groove is formed on the fuel flow surface of the fuel electrode current collector on the side that abuts the fuel electrode diffusion layer. The groove guides a fuel containing formic acid or alcohol from a fuel inlet to a fuel outlet. The groove comprises: a plurality of flow groove portions extending from one edge of the fuel flow surface toward another edge opposite the one edge, and arranged in parallel at predetermined intervals; and a plurality of folded groove portions connecting the ends of one edge or the other edge of two adjacent sets of the plurality of flow groove portions, such that the fuel flows in opposite directions. Furthermore, the inner sidewall surface of each of the folded groove portions, which faces the end of the flow groove portion, is formed into a curved surface, with the distance to the opposing end of the flow groove portion gradually narrowing as the distance toward the opposite end of the flow groove portion is directed perpendicularly to the direction in which the flow groove portion extends.

[0012] As a result, the multiple return grooves formed on the fuel flow surface of the fuel electrode narrow the distance from the inner sidewall surface to the ends of the flow grooves as they approach the ends perpendicular to the direction in which the flow grooves extend. This reduces the amount of fuel and carbon dioxide trapped at the ends perpendicular to the direction in which the flow grooves extend. Furthermore, the fuel flowing from the flow grooves into the return grooves flows along the inner sidewall surface of the return grooves and smoothly flows into the multiple flow grooves on the downstream side. This increases the reaction between the fuel electrode catalyst layer and the fuel, thereby suppressing a decrease in power generation.

[0013] According to the second embodiment, the fuel flow groove has an inflow groove portion connected to the fuel inlet and connected to the end of the plurality of flow groove portions of the group into which the fuel initially flows, on the side opposite to the folded groove portion. Moreover, the inner sidewall surface portion of the inflow groove portion, which is opposite to the end of the flow groove portion, is formed into a curved surface shape in which the distance from the end of the opposite flow groove portion to the outflow side end in a direction perpendicular to the direction in which the flow groove portion extends gradually narrows. Thus, the inflow groove portion can reduce the fuel and carbon dioxide retained at the outflow side end in a direction perpendicular to the direction in which the flow groove portion extends, and can smoothly guide the fuel flowing in from the fuel inlet to the plurality of flow groove portions. As a result, the reaction between the fuel electrode catalyst layer and the fuel increases, which can suppress the reduction in power generation.

[0014] According to a third embodiment, the fuel flow groove has an outflow groove portion connected to the fuel outflow port and connected to the end of the plurality of flow groove portions of the group of the last flow of the fuel on the side opposite to the folded groove portion. Moreover, the inner side wall surface portion of the outflow groove portion opposite to the end of the flow groove portion is formed into a curved surface shape in which the distance from the end of the opposite flow groove portion to the end of the inflow side portion in the direction perpendicular to the direction in which the flow groove portion extends gradually narrows. As a result, the fuel and carbon dioxide retained at the end of the inflow side portion in the direction perpendicular to the direction in which the flow groove portion extends can be reduced, and the fuel flowing in from the plurality of flow groove portions can be smoothly guided to the fuel outflow port. As a result, the reaction between the fuel electrode catalyst layer and the fuel increases, which can suppress the reduction in power generation.

[0015] According to the fourth embodiment, the plurality of ribs disposed between the flow grooves have protrusions at their ends opposite the inner wall surface, extending outward from the adjacent flow grooves in an arcuate shape when viewed from above. This allows fuel flowing out of the flow grooves to be smoothly guided along the outer circumferential surfaces of the protrusions toward the downstream side in a direction perpendicular to the direction in which the flow grooves extend, and then smoothly guided back into the flow grooves disposed downstream. This further reduces the amount of fuel and carbon dioxide trapped in the return grooves, inflow grooves, or outflow grooves at the ends perpendicular to the direction in which the flow grooves extend.

[0016] According to the fifth embodiment, the plurality of protrusions projecting toward the return groove are formed so that the protrusion height gradually decreases as the protrusion height between two sets of the plurality of flow grooves reverses from the ends of the return groove in a direction perpendicular to the direction in which the flow groove extends toward the direction of fuel flow. This allows the fuel flowing from the flow groove into the return groove to be guided so that it flows smoothly toward the substantially central portion in a direction perpendicular to the direction in which the flow groove extends, further reducing the amount of fuel and carbon dioxide accumulated at the ends of the return groove in a direction perpendicular to the direction in which the flow groove extends. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a perspective view illustrating the overall structure of the fuel cell system according to this embodiment.

[0018] Figure 2 It is an exploded perspective view illustrating the structure of the fuel cell according to this embodiment.

[0019] Figure 3 This is a front view of the fuel electrode collector as seen from the fuel flow surface.

[0020] Figure 4 Yes Figure 3 Magnified view of section IV.

[0021] Figure 5 It is from Figure 4 An enlarged stereogram observed as shown by arrow V.

[0022] Figure 6 It means in Figure 3 FIG. 1 is a diagram showing an example of the flow velocity distribution of the fuel flowing through the fuel electrode current collector.

[0023] Figure 7 This is a front view of a fuel electrode current collector of a comparative example as viewed from the fuel flow surface.

[0024] Figure 8 Yes Figure 7 An enlarged stereogram of part VIII.

[0025] Figure 9 It means in Figure 7 FIG. 1 is a diagram showing an example of the flow velocity distribution of the fuel flowing through the fuel electrode current collector.

[0026] Figure 10 This is an enlarged perspective view showing another fuel electrode current collector according to the first embodiment. DETAILED DESCRIPTION

[0027] Hereinafter, an embodiment of the fuel cell of the present invention will be described in detail with reference to the accompanying drawings. Figure 1The schematic structure of a fuel cell system 1 including a fuel cell 7 according to this embodiment will be described. The fuel cell 7 of the fuel cell system 1 described in this embodiment is a direct liquid fuel cell that uses an aqueous solution of formic acid or an alcohol such as methanol as fuel. In the following description, a direct formic acid fuel cell that uses formic acid as fuel will be used as an example.

[0028] Here, a direct liquid fuel cell is a fuel cell in which liquid fuel is directly fed into the fuel electrode without modification. In addition, a direct formic acid fuel cell uses formic acid as fuel and feeds the formic acid directly into the fuel electrode 10 constituting the fuel cell 7 without modification (see Figure 1 ) fuel cell. In addition, the X-axis, Y-axis, and Z-axis in each figure are orthogonal to each other, the Z-axis direction corresponds to the up-down direction (vertical direction), the Y-axis direction corresponds to the thickness direction, and the X-axis direction corresponds to the horizontal width direction.

[0029] [Brief Structure of Fuel Cell System]

[0030] like Figure 1 As shown, the fuel cell system 1 is composed of a fuel tank 50, a pump 52, a fuel cell 7, a drain tank 60, and the like. A solution containing formic acid at a predetermined concentration (formic acid aqueous solution) is stored in the fuel tank 50. The concentration of the formic acid aqueous solution is, for example, approximately 10% to 40%. Furthermore, one end of a fuel supply pipe 51 is connected to the fuel tank 50. The other end of the fuel supply pipe 51 is connected to the fuel inlet 17A opening at the lower end of the fuel cell 7. The pump 52 is an electric pump disposed midway along the fuel supply pipe 51 to supply (pressure-feed) the fuel in the fuel tank 50 to the fuel inlet 17A of the fuel cell 7.

[0031] The drain tank 60 stores fuel that has been used and discharged from the fuel cell 7, as well as water generated and recovered by the air electrode 20 that constitutes the fuel cell 7. The other end of the fuel discharge pipe 61 is connected to the drain tank 60. One end of the fuel discharge pipe 61 is connected to the fuel outflow port 17B that opens at the upper end of the fuel cell 7. Furthermore, the other end of the recovery pipe 62 is connected to the drain tank 60. One end of the recovery pipe 62 is connected to the air outflow port 25B provided below the air electrode 20.

[0032] Furthermore, an exhaust port (not shown) is provided at the top of drain tank 60, connecting the interior to the exterior. If the pressure of the gas within drain tank 60 exceeds a predetermined pressure, the gas is discharged from the exhaust port (not shown) provided at the top of drain tank 60 to the exterior of drain tank 60. Furthermore, fuel cell 7 generates electricity using fuel flowing in through fuel inlet 17A and discharged through fuel outlet 17B. The detailed structure of fuel cell 7 will be described below.

[0033] [Brief structure of a fuel cell]

[0034] Next, based on Figure 1 as well as Figure 2 The brief structure of the fuel cell 7 is described. Figure 1 as well as Figure 2 As shown, the fuel cell 7 is integrally formed by an air electrode 20 and a fuel electrode 10 sandwiching an electrolyte membrane 30 in the thickness direction. The air electrode 20 is composed of an air electrode catalyst layer 21, an air electrode diffusion layer 22, and an air electrode current collector 23 stacked in this order, which are in close contact with one side of the electrolyte membrane 30. The fuel electrode 10 is composed of a fuel electrode catalyst layer 11, a fuel electrode diffusion layer 12, and a fuel electrode current collector 13 stacked in this order, which are in close contact with the other side of the electrolyte membrane 30.

[0035] The air electrode current collector 23 is formed of a conductive flat plate of metal or the like with a thickness of about 1 to 10 mm. Figure 1 As shown, one end of the electric load (such as an electric motor) is electrically connected to the air electrode current collector 23. Figure 2 As shown, the air electrode current collector 23 has an air circulation surface 23A that contacts the air electrode diffusion layer 22 , and air circulation grooves 23B that open toward the air electrode diffusion layer 22 are formed on the air circulation surface 23A.

[0036] The air circulation grooves 23B allow air supplied (pressurized) from the air inlet 25A formed diagonally above the air outlet 25B of the air electrode current collector 23 to contact the air electrode diffusion layer 22 and be guided toward the air outlet 25B formed below the air electrode current collector 23. Therefore, the air flowing through the air circulation grooves 23B diffuses in the air electrode diffusion layer 22. Alternatively, dry oxygen may be supplied (pressurized) to the air inlet 25A from the outside.

[0037] The air circulation groove 23B is provided with a plurality of circulation groove portions 23C, which extend from one side edge side of the air circulation surface 23A (for example, at Figure 2 , the left edge side) to the other side edge side opposite to one side edge (for example, Figure 2 The air electrode current collector 23 and the air electrode diffusion layer 22 are connected to each other by a plurality of ribs 23E. The ribs 23E extend from the air electrode current collector 23 to the air electrode diffusion layer 22, extending from the air electrode current collector 23 to the air electrode diffusion layer 22 at predetermined intervals. Furthermore, a boss portion (rib) 23E is formed between the air electrode current collector 23 and the air electrode diffusion layer 22 in the vertical direction, for example, with a vertical width substantially equal to the vertical width of the air electrode current collector 23C. The boss portion (rib) 23E provides electrical communication between the air electrode current collector 23 and the air electrode diffusion layer 22.

[0038] In addition, Figure 2 In FIG, the air inlet 25A is connected to the inlet groove 23F extending in the vertical direction at the upper left corner. Figure 2 In the figure, the air outlet 25B is connected to the outflow groove 23G extending in the vertical direction at the lower right corner. Moreover, each of the plurality of flow grooves 23C is connected by the respective folded grooves 23D1 to 23D4 formed near one side edge or the other side edge of the air electrode current collector 23 and extending in the substantially vertical direction. Figure 2 In the embodiment, a plurality of flow grooves 23C are connected to the inflow groove 23F at the upper left corner. Figure 2 In the middle, it is connected to the outflow groove portion 23G at the lower right corner.

[0039] Therefore, the air flowing into the inlet 25A into the inlet groove 23F is guided from one side edge to the other side edge in each flow groove 23C, and repeatedly changes direction in each return groove 23D1 to 23D4, flows in the air flow groove 23B, and diffuses in the air electrode diffusion layer 22. Then, the air flowing into the outlet groove 23G is discharged from the air outlet 25B to the recovery pipe 62 (see FIG. Figure 1 )flow.

[0040] The air electrode diffusion layer 22 is formed into a layer with a thickness of approximately 0.05 to 0.5 mm. The air electrode diffusion layer 22 is a porous material that is permeable to water and air and has electron conductivity. For example, carbon paper or carbon cloth can be used. The air electrode diffusion layer 22 diffuses air (oxygen) flowing in from the air inlet 25A of the air electrode current collector 23 and guides it toward the air electrode catalyst layer 21. Oxygen contained in the external air permeates the air electrode diffusion layer 22 and reaches the electrode catalyst particles in the air electrode catalyst layer 21.

[0041] The air electrode catalyst layer 21 is formed into a layer having a thickness of about 0.05 to about 0.5 [mm]. The air electrode catalyst layer 21 includes electrode catalyst particles (not shown) of the air electrode, and an electrode catalyst carrier (not shown) that carries the electrode catalyst particles. The electrode catalyst particles of the air electrode 20 are particles of a catalyst that promotes the reaction rate of the reaction of reducing oxygen in the air, for example, platinum (Pt) particles can be used. The electrode catalyst carrier only needs to be able to carry the electrode catalyst particles and have conductivity, for example, carbon powder can be used. When formic acid is used as a fuel, the redox reaction shown in the following formula (1) is carried out by the electrode catalyst particles of the air electrode catalyst layer 21. In addition, the generated water (H2O) flows in the air circulation groove 23B, and is guided from the air outlet 25B of the air electrode collector 23 to the drain tank 60 via the recovery pipe 62 (see Figure 1 、 Figure 2 ).

[0042] 2H + +1 / 2O2+2e -→H2O···(1)

[0043] The fuel electrode current collector 13 is formed from a conductive, flat metal plate with a thickness of approximately 1.0 to 10 mm. The fuel electrode current collector 13 has a fuel flow surface 13A that contacts the fuel electrode diffusion layer 12. Fuel flow grooves 13B are formed on the fuel flow surface 13A, opening toward the fuel electrode diffusion layer 12. Fuel flow grooves 13B allow fuel supplied from a fuel inlet 17A formed on the lower side of the fuel electrode current collector 13 to contact the fuel electrode diffusion layer 12 and guide it toward a fuel outlet 17B formed on the upper side of the fuel electrode current collector 13. Consequently, fuel flowing through the fuel flow grooves 13B diffuses within the fuel electrode diffusion layer 12.

[0044] The fuel flow groove 13B is provided with a plurality of flow groove portions 13C, which extend from one edge side of the fuel flow surface 13A (for example, at Figure 2 In the example, the right edge side) to the other edge side opposite to one edge (for example, Figure 2 In the middle, the left edge side is extended and arranged in parallel with each other at a predetermined interval, and fuel is flowed. In addition, in order to recover electrons e - Between the flow groove portion 13C in the vertical direction, a rib-shaped boss portion (rib portion) 13E is formed, for example, with a vertical width substantially the same as the vertical width of the flow groove portion 13C, which contacts the fuel electrode diffusion layer 12. Figure 1 As shown, the other end of the electric load (eg, an electric motor) is connected to the fuel electrode current collector 13 .

[0045] The fuel electrode diffusion layer 12 is formed into a layer with a thickness of approximately 0.05 to 0.5 mm. It is made of a porous material that allows for the penetration of the formic acid aqueous solution and exhibits electron conductivity. Examples of such materials include carbon paper and carbon cloth. The fuel electrode diffusion layer 12 diffuses the fuel flowing into the fuel flow grooves 13B formed in the fuel flow surface 13A of the fuel electrode current collector 13 and guides the fuel toward the fuel electrode catalyst layer 11.

[0046] The fuel electrode catalyst layer 11 is formed into a layer having a thickness of about 0.05 to about 0.5 [mm]. The fuel electrode catalyst layer 11 includes electrode catalyst particles (not shown) and an electrode catalyst support (not shown) that supports the electrode catalyst particles. The electrode catalyst particles of the fuel electrode 10 are particles of a catalyst that accelerates the oxidation reaction of formic acid as a fuel, and for example, palladium (Pd) particles can be used. The electrode catalyst support only needs to be able to support the electrode catalyst particles and have conductivity, and for example, carbon powder can be used. When formic acid is used as a fuel, the oxidation reaction shown in the following formula (2) is carried out by the electrode catalyst particles of the fuel electrode catalyst layer 11.

[0047] HCOOH→CO2+2H + +2e - ···(2)

[0048] The electrolyte membrane 30 is formed into a thin film with a thickness of about 0.01 to 0.3 mm. The electrolyte membrane 30 is sandwiched between the fuel electrode catalyst layer 11 of the fuel electrode 10 and the air electrode catalyst layer 21 of the air electrode 20. It does not have electron conductivity, but can pass water and hydrogen ions (protons) H + The electrolyte membrane 30 can be a perfluorosulfonic acid membrane such as Nafion (registered trademark) manufactured by DuPont. Alternatively, the fuel electrode catalyst layer 11, fuel electrode diffusion layer 12, electrolyte membrane 30, air electrode catalyst layer 21, and air electrode diffusion layer 22 may be joined and integrated.

[0049] [Structure of the fuel flow channel]

[0050] Next, based on Figures 2 to 5 The structure of the fuel flow groove 13B of the fuel electrode current collector 13 will be described. Figure 2 as well as Figure 3 As shown, the fuel flow groove 13B is provided with a plurality of flow groove portions 13C, which are arranged along the horizontal width direction from one side edge side of the fuel flow surface 13A (for example, at Figure 2 , the right edge side) to the other edge side (for example, Figure 2 In the middle, it extends to the left edge side), is arranged in parallel with each other at a predetermined interval, and allows fuel to flow.

[0051] Furthermore, one side edge side of the four flow groove portions 13C on the lower end side (at Figure 3 Each end portion (on the right side) of the fuel inlet 17A formed at the lower end is connected to an inflow groove portion 13F in the shape of the upper half of a lower semi-ellipse in front view, which extends upward from the fuel inlet 17A formed at the lower end and protrudes outward in the width direction. In addition, the other side edge side of the four flow groove portions 13C on the lower end side (at Figure 3 The ends of the left side and the other side edge of the three flow grooves 13C on the upper side (in Figure 3 Each end portion (on the left side) is connected to a folded groove portion 13D1 having a semi-elliptical shape in the front view, for example, extending in the vertical direction and protruding outward in the width direction.

[0052] Thus, the fuel flowing from the fuel inlet 17A into the inflow groove 13F flows into the four flow grooves 13C on the lower end side and flows toward the other side edge (at the Figure 3The fuel flowing into the return groove 13D1 flows into the three flow grooves 13C arranged on the upper side of the return groove 13D1 and flows toward one side edge (at the bottom of the return groove 13D1). Figure 3 Therefore, the four flow grooves 13C on the lower end side and the three flow grooves 13C on the upper side thereof constitute two mutually adjacent flow groove groups 131 and 132 in which the fuel flows in opposite directions.

[0053] In addition, one side edge side (at Figure 3 The ends of the three flow grooves 13C on the upper side (on the right side) and the edges of the three flow grooves 13C on the upper side (on the Figure 3 Each end portion (on the right side) is connected to a folded groove portion 13D2 having a semi-elliptical shape in the front view, for example, extending in the up-down direction and protruding outward in the width direction.

[0054] Thus, the fuel flowing from the three flow grooves 13C constituting the flow groove group 132 to the lower side of the return groove 13D2 flows into the three flow grooves 13C arranged on the upper side of the return groove 13D2 and flows to the other side edge side (at the Figure 3 Therefore, the three flow grooves 13C arranged above the three flow grooves 13C constituting the flow groove group 132 are arranged adjacent to the upper side of the flow groove group 132, and constitute a flow groove group 133 in which the fuel flows in the opposite direction.

[0055] In addition, the other side edge side (at the Figure 3 The ends of the left side and the other side edge of the three flow grooves 13C on the upper side (in Figure 3 Each end portion (on the left side) is connected to a folded groove portion 13D3 having a semi-elliptical shape in the front view, for example, extending in the up-down direction and protruding outward in the width direction.

[0056] Thus, the fuel flowing from the three flow grooves 13C constituting the flow groove group 133 to the lower side of the return groove 13D3 flows into the three flow grooves 13C arranged on the upper side of the return groove 13D3 and flows toward one side edge side (at Figure 3 Therefore, the three flow grooves 13C arranged above the three flow grooves 13C constituting the flow groove group 133 are arranged adjacent to the upper side of the flow groove group 133, and constitute a flow groove group 134 in which the fuel flows in the opposite direction.

[0057] In addition, one side edge side (at Figure 3The ends of the four flow grooves 13C on the upper side (on the right side) and the edges of the four flow grooves 13C on the upper side (on the Figure 3 Each end portion (in the middle, right side) is connected to a folded groove portion 13D4, for example, which extends in the up-down direction and protrudes outward in the width direction in the front view and has a semi-elliptical shape.

[0058] Thus, the fuel flowing from the three flow grooves 13C constituting the flow groove group 134 to the lower side of the return groove 13D4 flows into the four flow grooves 13C arranged on the upper side of the return groove 13D4 and flows to the other side edge side (at the Figure 3 Therefore, the four flow grooves 13C arranged above the three flow grooves 13C constituting the flow groove group 134 are arranged adjacent to the upper side of the flow groove group 134 and constitute a flow groove group 135 in which the fuel flows in the opposite direction.

[0059] Furthermore, the other side edge side (at the Figure 3 Each end portion (left side) of the fuel electrode collector 13 is connected to an outflow groove portion 13G in the shape of the lower half of a lower semi-ellipse in the front view, which extends downward from the fuel outflow outlet 17B formed at the upper end portion and protrudes outward in the width direction. As a result, the fuel flowing from the four flow groove portions 13C constituting the flow groove portion group 135 to the outflow groove portion 13G is discharged from the fuel outflow outlet 17B to the fuel discharge pipe 61 (see Figure 1 )flow.

[0060] Here, based on Figure 4 as well as Figure 5 The structure of the folded groove 13D4 will be described. The folded groove 13D2 has a structure that is substantially identical to the folded groove 13D4. The inflow groove 13F has a structure that is substantially identical to the upper half of the folded groove 13D4 in the vertical direction. Furthermore, each of the folded grooves 13D1 and 13D3 has a structure that is substantially identical to a structure that is line-symmetrical with respect to a vertical line of the folded groove 13D4. The outflow groove 13G has a structure that is substantially identical to the lower half of a structure that is line-symmetrical with respect to a vertical line of the folded groove 13D4.

[0061] like Figure 4 as well as Figure 5 As shown, the folded groove portion 13D4 is formed into a semi-elliptical shape in the front view extending in the vertical direction and protruding outward in the width direction, and is recessed in the thickness direction by a depth of about twice the depth of each flow groove portion 13C. In addition, the folded groove portion 13D4 is formed into a semi-elliptical shape in the front view extending in the vertical direction and protruding outward in the width direction, and is recessed in the thickness direction by a depth of about twice the depth of each flow groove portion 13C. Figure 4The inner wall surface 15 opposite the end portion (on the right side) of the folded groove portion 13D4 is formed into a curved surface shape in which the distance from the vertical center portion of the folded groove portion 13D4 toward the two vertical ends of the folded groove portion 13D4 to the ends of the opposite flow groove portion 13C gradually narrows. Here, the inner wall surface 15 of the folded groove portions 13D1 to 13D4 can also be referred to as, for example, the first inner wall surface. The inner wall surface 15 of the inflow groove portion 13F can also be referred to as, for example, the second inner wall surface. The inner wall surface 15 of the outflow groove portion 13G can also be referred to as, for example, the third inner wall surface.

[0062] Specifically, for example, the inner wall surface portion 15 of the folded-back groove portion 13D4 is formed into a semi-elliptical shape as follows, that is, the length of approximately 1 / 2 of the distance from the upper side wall portion 71 of the circulation groove portion 13C located at the upper end to the lower side wall portion 72 of the circulation groove portion 13C located at the lower end is set as the long radius R1, and the length of approximately 2 times the depth of the folded-back groove portion 13D4, that is, approximately 4 times the depth of each circulation groove portion 13C, is set as the short radius R2 in the front view.

[0063] Furthermore, a protrusion 73 is formed at each end of each boss portion (rib) 13E that faces the inner wall surface portion 15. This protrusion 73 extends from the bottom surface of the folded-back groove portion 13D4 over the entire height of each boss portion 13E and projects outward in the width direction relative to the adjacent flow groove portion 13C in a circular arc shape when viewed from above. Furthermore, the major diameter of the semi-elliptical inner wall surface portion 15 when viewed from above is arranged, for example, so as to pass through the tip of each protrusion 73.

[0064] Thus, the fuel flowing through each of the flow grooves 13C of the flow groove group 134 is guided by the protrusions 73 and the lower portion of the inner wall surface 15, and flows smoothly into the lower side of the return groove 13D4. Furthermore, the fuel flowing into the return groove 13D4 is guided upward within the return groove 13D4 by the protrusions 73 and the upper portion of the inner wall surface 15, and flows into each of the flow grooves 13C of the flow groove group 135.

[0065] Next, based on Figure 6 The following describes an example of the flow velocity distribution of the fuel obtained by CAE (Computer Aided Engineering) analysis when a fuel of a formic acid aqueous solution with a concentration of about 10% to 40% is supplied (pressurized) to the fuel electrode current collector 13 of the fuel cell 7 constructed as described above. Figure 6 As shown, the fuel flowing from the fuel inlet 17A formed at the lower end of the fuel electrode current collector 13 into the inflow groove 13F flows into each of the four flow grooves 13C constituting the flow groove group 131 without stagnating.

[0066] Furthermore, the fuel flowing from the four circulation grooves 13C constituting the circulation groove group 131 into the return groove 13D1 flows into the three circulation grooves 13C constituting the circulation groove group 132 without stagnating in the return groove 13D1. Therefore, the flow rate of the fuel flowing through the three circulation grooves 13C constituting the circulation groove group 132 is slightly faster than the flow rate of the fuel flowing through the four circulation grooves 13C constituting the circulation groove group 131.

[0067] Then, the fuel flowing from the three circulation grooves 13C constituting the circulation groove group 132 into the return groove 13D2 flows into the three circulation grooves 13C constituting the circulation groove group 133 without stagnating in the return groove 13D2. Therefore, the flow rate of the fuel flowing through the three circulation grooves 13C constituting the circulation groove group 133 is substantially the same as the flow rate of the fuel flowing through the three circulation grooves 13C constituting the circulation groove group 132.

[0068] Then, the fuel flowing from the three circulation grooves 13C constituting the circulation groove group 133 into the return groove 13D3 flows into the three circulation grooves 13C constituting the circulation groove group 134 without stagnating in the return groove 13D3. Therefore, the flow rate of the fuel flowing through the three circulation grooves 13C constituting the circulation groove group 134 is substantially the same as the flow rate of the fuel flowing through the three circulation grooves 13C constituting the circulation groove group 133.

[0069] Then, the fuel flowing from the three circulation grooves 13C constituting the circulation groove group 134 into the return groove 13D4 flows into the four circulation grooves 13C constituting the circulation groove group 135 without stagnating in the return groove 13D4. Therefore, the flow rate of the fuel flowing through the four circulation grooves 13C constituting the circulation groove group 135 is slightly slower than the flow rate of the fuel flowing through the three circulation grooves 13C constituting the circulation groove group 134.

[0070] Then, the fuel flowing from each of the four flow grooves 13C constituting the flow groove group 135 into the outflow groove 13G hardly stagnates within the outflow groove 13G and flows into and is discharged from the fuel outflow port 17B. Therefore, the flow rate of the fuel flowing through the fuel outflow port 17B is substantially the same as the flow rate of the fuel flowing through the fuel inlet 17A.

[0071] As described above, the distance from the inner wall surface portion 15 to the end of the flow groove portion 13C decreases as the inflow groove portion 13F, the return groove portions 13D1 to 13D4, and the outflow groove portion 13G move toward their respective vertical ends. Therefore, it is presumed that the flow velocity of the fuel at the vertical ends of the inflow groove portion 13F, the return groove portions 13D1 to 13D4, and the outflow groove portion 13G is zero [m / sec], and the stagnation area is almost eliminated.

[0072] As a result, the carbon dioxide (CO 2 ) generated by the oxidation reaction of formic acid represented by the above formula (2) flows smoothly through each flow groove portion 13C along with the fuel (formic acid aqueous solution). Therefore, it is possible to suppress the accumulation of carbon dioxide into bubbles in the inflow groove portion 13F, the return groove portions 13D 1 to 13D 4 , and the outflow groove portion 13G, thereby preventing the fuel (formic acid aqueous solution) and carbon dioxide from accumulating. In other words, the oxidation reaction of the fuel (formic acid aqueous solution) caused by the electrode catalyst particles in the fuel electrode catalyst layer 11 is increased, thereby suppressing a decrease in the power generation of the fuel cell 7 .

[0073] [Comparative Example]

[0074] Here, based on Figures 7 to 9 A fuel electrode collector 81 is described as a comparative example of the fuel electrode collector 13 of the fuel cell 7. In the following description, the same reference numerals as those in the structure of the fuel electrode collector 13 of the above embodiment indicate the same or corresponding parts.

[0075] First, based on Figure 7 as well as Figure 8 The structure of the fuel electrode collector 81 will be described. Figure 7 as well as Figure 8 As shown, the structure of the fuel electrode collector 81 is substantially the same as that of the fuel electrode collector 13. Figure 7 As shown, the fuel electrode current collector 81 is different in that a fuel flow groove 81B is provided instead of the fuel flow groove 13B. Also, the protrusion 73 is not formed at both ends of each boss portion (rib portion) 13E in the horizontal width direction.

[0076] Specifically, the fuel flow groove 81B is provided with a plurality of flow groove portions 13C, which extend from one edge side of the fuel flow surface 13A (for example, at Figure 7 the right edge side) to the other edge side (e.g. Figure 7 The four flow grooves 13C on the lower side are arranged in parallel with each other at a predetermined interval and are used to flow fuel. Figure 7 Each end portion (on the right side) is connected to a substantially rectangular inflow groove portion 81F extending upward from the fuel inlet 17A formed at the lower end and closing the upper end in a front view. In addition, the other side edge side of the four flow groove portions 13C on the lower end side (at Figure 7 The ends of the left side and the other side edge of the three flow grooves 13C on the upper side (in Figure 7Each end portion (on the left side) is connected to a folded groove portion 81D1 that is vertically elongated and substantially rectangular in a front view and extends in the up-down direction and protrudes outward in the width direction, for example.

[0077] Thus, the fuel flowing from the fuel inlet 17A into the inflow groove 81F flows into the four flow grooves 13C on the lower end side and flows toward the other side edge (at the Figure 7 Then, the fuel flowing into the return groove 81D1 flows into the three flow grooves 13C arranged on the upper side of the return groove 81D1 and flows to the side edge (at the bottom of the return groove 81D1). Figure 7 Therefore, the four flow grooves 13C on the lower end side and the three flow grooves 13C on the upper side thereof constitute two mutually adjacent flow groove groups 131 and 132 in which the fuel flows in opposite directions.

[0078] In addition, one side edge side (at Figure 7 The ends of the three flow grooves 13C on the upper side (on the right side) and the edges of the three flow grooves 13C on the upper side (on the Figure 7 Each end portion (in the middle, right side) is connected to a folded-back groove portion 81D2 that is, for example, a vertically long, substantially rectangular shape in a front view and extends in the up-down direction and protrudes outward in the width direction.

[0079] Thus, the fuel flowing from the three flow grooves 13C constituting the flow groove group 132 to the lower side of the folded groove 81D2 flows into the three flow grooves 13C arranged on the upper side of the folded groove 81D2 and flows to the other side edge side (at the Figure 7 Therefore, the three flow grooves 13C arranged above the three flow grooves 13C constituting the flow groove group 132 are arranged adjacent to the upper side of the flow groove group 132, and constitute a flow groove group 133 in which the fuel flows in the opposite direction.

[0080] In addition, the other side edge side (at the Figure 7 The ends of the left side and the other side edge of the three flow grooves 13C on the upper side (in Figure 7 Each end portion (on the left side) is connected to a folded groove portion 81D3 that is vertically elongated and generally rectangular in a front view and extends in the up-down direction and protrudes outward in the width direction, for example.

[0081] Thus, the fuel flowing from the three flow grooves 13C constituting the flow groove group 133 toward the lower side of the return groove 81D3 flows toward the three flow grooves 13C arranged above the return groove 13D3 and flows toward one side edge side (at Figure 3Therefore, the three flow grooves 13C arranged above the three flow grooves 13C constituting the flow groove group 133 are arranged adjacent to the upper side of the flow groove group 133, and constitute a flow groove group 134 in which the fuel flows in the opposite direction.

[0082] In addition, one side edge side (at Figure 7 The ends of the four flow grooves 13C on the upper side (on the right side) and the edges of the four flow grooves 13C on the upper side (on the Figure 7 Each end portion (in the middle, right side) is connected to a folded-back groove portion 81D4 that is, for example, extended in the up-down direction and protrudes outward in the width direction in a front view and is vertically elongated and roughly rectangular.

[0083] Thus, the fuel flowing from the three flow grooves 13C constituting the flow groove group 134 to the lower side of the return groove 81D4 flows into the four flow grooves 13C arranged on the upper side of the return groove 81D4 and flows to the other side edge side (at the Figure 7 Therefore, the four flow grooves 13C arranged above the three flow grooves 13C constituting the flow groove group 134 are arranged adjacent to the upper side of the flow groove group 134 and constitute a flow groove group 135 in which the fuel flows in the opposite direction.

[0084] Furthermore, the other side edge side (at the Figure 7 Each end portion (left side) of the fuel electrode collector 81 is connected to a substantially rectangular outflow groove portion 81G extending downward from the fuel outflow outlet 17B formed at the upper end portion of the fuel electrode collector 81 and protruding outward in the width direction in the front view. As a result, the fuel flowing from the four flow groove portions 13C constituting the flow groove portion group 135 into the outflow groove portion 81G is discharged from the fuel outflow outlet 17B to the fuel discharge pipe 61 (see FIG. Figure 1 )flow.

[0085] Here, based on Figure 7 as well as Figure 8 The structure of the folded groove 81D4 will be described. The folded groove 81D2 has a substantially identical structure to the folded groove 81D4. The inflow groove 81F has a substantially identical structure to the upper half of the folded groove 81D4 in the vertical direction. Furthermore, each of the folded grooves 81D1 and 81D3 has a substantially identical structure to a structure that is line-symmetrical with respect to a vertical line of the folded groove 81D4. The outflow groove 81G has a substantially identical structure to the lower half of a structure that is line-symmetrical with respect to a vertical line of the folded groove 81D4.

[0086] like Figure 7 as well as Figure 8As shown, the folded groove portion 81D4 is formed into a generally rectangular shape in the front view extending in the up-down direction and protruding outward in the width direction, and is recessed in the thickness direction by a depth of about 2 times the depth of each flow groove portion 13C. Figure 8 The inner wall surface portion 83 opposite the end portion (in the middle, right side) is formed so that the distance to the end portion of the opposite flow groove portion 13C is substantially constant throughout the entire length in the up-down direction.

[0087] Specifically, for example, the folded-back groove portion 81D4 is formed into a roughly rectangular shape with the length of the distance from the upper side wall portion 71 of the circulation groove portion 13C located at the upper end to the lower side wall portion 72 of the circulation groove portion 13C located at the lower end being set as one side in the up-down direction, and a length of approximately 2 times the depth of the folded-back groove portion 81D4, that is, approximately 4 times the depth of each circulation groove portion 13C being set as one side in the left-right width direction in the front view.

[0088] Therefore, the ends of each boss (rib) 13E facing the inner wall surface 83, together with the ends of each flow groove 13C facing the inner wall surface 83, form a wall surface parallel to the inner wall surface 83. Specifically, the ends of each boss (rib) 13E facing the inner wall surface 83 lack arc-shaped protrusions 73 when viewed from above, which also differs from the structure of the fuel flow groove 13B. Therefore, the fuel flowing through each flow groove 13C of the flow groove group 134 flows downward into the return groove 81D4. The fuel flowing into the return groove 81D4 then passes through the upper portion of the inner wall surface 83, is guided upward within the return groove 81D4, and flows into each flow groove 13C of the flow groove group 135.

[0089] Next, based on Figure 9 The following describes an example of the flow velocity distribution of the fuel obtained by CAE (Computer Aided Engineering) analysis when a fuel of a formic acid aqueous solution with a concentration of about 10% to 40% is supplied (pressurized) to the fuel electrode current collector 81 of the fuel cell 7 constructed as described above. Figure 9 As shown, the fuel flowing from the fuel inlet 17A formed at the lower end of the fuel electrode collector 81 into the inflow groove 81F flows outward in the width direction of the inflow groove 81F (at the Figure 9 In the middle, the upper corner portion on the right side forms a retention area 85A where the flow rate is substantially zero [m / sec] and flows into each of the four flow groove portions 13C constituting the flow groove portion group 131.

[0090] Furthermore, the fuel flowing from the four flow grooves 13C constituting the flow groove group 131 into the return groove 81D1 is located outside the width direction of the return groove 81D1 (at the Figure 9 In the figure, the lower and upper corners (on the left side) form stagnation areas 85B and 85C with a flow velocity of approximately zero [m / sec], and the fuel flows into the three flow groove sections 13C constituting the flow groove section group 132. Furthermore, the flow velocity of the fuel flowing through the three flow groove sections 13C constituting the flow groove section group 132 is slightly faster than the flow velocity of the fuel flowing through the four flow groove sections 13C constituting the flow groove section group 131.

[0091] Then, the fuel flowing from the three flow grooves 13C constituting the flow groove group 132 into the return groove 81D2 is discharged outside the width direction of the return groove 81D2 (at the outer side of the width direction of the return groove 81D2). Figure 9 The fuel flows into the three flow groove sections 13C constituting the flow groove section group 133. Furthermore, the flow velocity of the fuel flowing through the three flow groove sections 13C constituting the flow groove section group 133 is substantially the same as the flow velocity of the fuel flowing through the three flow groove sections 13C constituting the flow groove section group 132.

[0092] Furthermore, the fuel flowing from the three flow grooves 13C constituting the flow groove group 133 into the return groove 81D3 is located outside the width direction of the return groove 81D3 (at the outer side of the width direction of the return groove 81D3). Figure 9 The fuel flows into the three flow groove sections 13C constituting the flow groove section group 134. The flow velocity of the fuel flowing through the three flow groove sections 13C constituting the flow groove section group 134 is substantially the same as the flow velocity of the fuel flowing through the three flow groove sections 13C constituting the flow groove section group 133.

[0093] Then, the fuel flowing from the three flow grooves 13C constituting the flow groove group 134 into the return groove 81D4 is discharged outside the width direction of the return groove 81D4 (at the outer side of the width direction of the return groove 81D4). Figure 9 The lower and upper corners (on the right side) of the flow channel 135 form stagnation areas 85H and 85I with a flow velocity of approximately zero [m / sec], and the fuel flows into the four flow groove sections 13C constituting the flow groove section group 135. The flow velocity of the fuel flowing through the four flow groove sections 13C constituting the flow groove section group 135 is slightly slower than the flow velocity of the fuel flowing through the three flow groove sections 13C constituting the flow groove section group 134.

[0094] Then, the fuel flowing from each of the four flow grooves 13C constituting the flow groove group 135 into the outflow groove 81G is discharged outside the width direction of the outflow groove 81G (at the outer side of the width direction of the outflow groove 81G). Figure 9The lower corner portion (left side) of the fuel outlet 17A forms a stagnation region 85J with a flow velocity of substantially zero [m / sec], and the fuel flows into and is discharged from the fuel outlet 17B. Therefore, the flow velocity of the fuel flowing through the fuel outlet 17B is substantially the same as the flow velocity of the fuel flowing through the fuel inlet 17A.

[0095] As described above, the inflow groove 81F, the return grooves 81D1 to 81D4, and the outflow groove 81G are formed into a generally vertically long rectangular shape in a front view, extending in the vertical direction and protruding outward in the width direction. Therefore, it is presumed that the inflow groove 81F, the return grooves 81D1 to 81D4, and the outflow groove 81G form stagnation areas 85A to 85J at the upper and lower corners on the width direction outer sides, where the fuel flow rate is substantially zero (m / sec).

[0096] Therefore, carbon dioxide (CO 2 ) generated by the oxidation reaction of formic acid represented by formula (2) above accumulates in each accumulation region 85A to 85J along with the fuel of the formic acid aqueous solution, forming bubbles and potentially accumulating on the surface of the electrode catalyst particles (e.g., Pd) in the fuel electrode catalyst layer 11. Consequently, if carbon dioxide accumulates on the surface of the electrode catalyst particles (e.g., Pd) in the fuel electrode catalyst layer 11, it becomes difficult for formic acid to adsorb on the surface of the electrode catalyst particles. This may hinder the progress of the formic acid oxidation reaction represented by formula (2) above, leading to a concern that the power generation of the fuel cell 7 may decrease.

[0097] As described in detail above, in the fuel cell 7 of this embodiment, the distance from the inner wall surface 15 to the end of the flow channel portion 13C of the inflow groove portion 13F, each of the folded groove portions 13D1 to 13D4, and the outflow groove portion 13G constituting the fuel flow channel 13B of the fuel electrode current collector 13 gradually narrows toward their respective ends in the vertical direction. In other words, the inner wall surface 15 of the inflow groove portion 13F, each of the folded groove portions 13D1 to 13D4, and the outflow groove portion 13G is formed into a curved surface shape in which the distance to the opposing end of the flow channel portion 13C gradually narrows toward both ends in the vertical direction.

[0098] As a result, there are virtually no locations at the upper and lower ends of the inflow groove 13F, the return grooves 13D1 to 13D4, and the outflow groove 13G where the fuel's flow rate reaches zero [m / sec] and stagnates. As a result, carbon dioxide (CO2) generated by the oxidation reaction of formic acid expressed in equation (2) flows smoothly through each flow groove 13C along with the formic acid aqueous solution fuel. This prevents carbon dioxide from accumulating into bubbles and stagnating the fuel (formic acid aqueous solution) and carbon dioxide in the inflow groove 13F, the return grooves 13D1 to 13D4, and the outflow groove 13G. This increases the oxidation reaction of the fuel (formic acid aqueous solution) caused by the electrode catalyst particles in the fuel electrode catalyst layer 11, thereby preventing a decrease in the power generation of the fuel cell 7.

[0099] Furthermore, the plurality of bosses 13E disposed between the flow grooves 13C have protrusions 73 at their ends facing the inner wall surface 15, projecting outward from the adjacent flow grooves 13C in an arcuate shape when viewed from above. This allows the fuel flowing out of the flow grooves 13C to be smoothly guided upward along the outer circumference of the protrusions 73 and then smoothly directed back into the flow grooves 13C disposed above, further reducing the amount of fuel and carbon dioxide accumulated at the vertical ends of the return grooves 13D1 to 13D4, the inflow groove 13F, or the outflow groove 13G.

[0100] In addition, the present invention is not limited to the above-mentioned embodiment, and various improvements, deformations, additions, and deletions can be made without departing from the scope of the present invention. Figures 1 to 6 The same reference numerals as those in the configuration and the like of the fuel cell system 1 of the above-described embodiment indicate the same or corresponding parts as those in the configuration and the like of the fuel cell system 1 of the above-described embodiment.

[0101] [Other first embodiments]

[0102] (A) For example, instead of the fuel electrode current collector 13, Figure 10 The fuel electrode current collector 91 shown. Figure 10 The structure of the fuel electrode collector 91 will be described. Figure 10 As shown, the fuel electrode current collector 91 has a substantially identical structure to the fuel electrode current collector 13, but differs in that the projections 73 are not formed at both ends of each boss portion 13E in the horizontal width direction. Therefore, the ends of each boss portion (rib portion) 13E facing the inner sidewall surface portion 15 and the ends of each flow groove portion 13C facing the inner sidewall surface portion 15 together form a flat surface portion 92 extending in the vertical direction.

[0103] In addition, if Figure 10As shown, the inner sidewall surface 15 opposing the flat surface 92 is formed into a curved surface such that the distance to the opposing ends of the flow groove 13C gradually narrows as it moves from the vertical center of the folded groove 13D4 toward the vertical ends of the folded groove 13D4. As a result, fuel flowing from each flow groove 13C of the flow groove group 134 into the folded groove 13D4 is guided upward by the flat surface 92 and the inner sidewall surface 15 and flows into each flow groove 13C of the flow groove group 135.

[0104] Therefore, the fuel flowing from the three flow grooves 13C constituting the flow groove group 134 to the return groove 13D4 flows into the four flow grooves 13C constituting the flow groove group 135 without stagnating in the return groove 13D4. Figure 3 ) The distance from the inner wall surface portion 15 to the end of the flow groove portion 13C narrows toward the respective ends in the vertical direction. Therefore, it is estimated that there are almost no locations in the inlet groove portion 13F, the return groove portions 13D1 to 13D4, and the outlet groove portion 13G where the flow velocity of the fuel reaches zero [m / sec] and stagnates at the respective ends in the vertical direction.

[0105] As a result, the carbon dioxide (CO 2 ) generated by the oxidation reaction of formic acid represented by the above formula (2) flows smoothly through each flow groove portion 13C along with the fuel (formic acid aqueous solution). This prevents carbon dioxide from agglomerating into bubbles and accumulating in the inflow groove portion 13F, the return groove portions 13D 1 to 13D 4 , and the outflow groove portion 13G, thereby preventing the fuel (formic acid aqueous solution) and carbon dioxide from accumulating. In other words, the oxidation reaction of the fuel (formic acid aqueous solution) caused by the electrode catalyst particles in the fuel electrode catalyst layer 11 is increased, thereby preventing a decrease in the power generation of the fuel cell 7 .

[0106] [Other Second Embodiment]

[0107] (B) Alternatively, for example, the protrusions 73 projecting outward in the horizontal width direction from the ends of the bosses 13E into the folded grooves 13D1 to 13D4 may be formed so that their protrusion height gradually decreases between adjacent flow groove groups 131 to 135 that reverse the direction of fuel flow from the vertical ends of the folded grooves 13D1 to 13D4. This allows the fuel flowing from the flow grooves 13C into the folded grooves 13D1 to 13D4 to flow smoothly toward the approximately vertical center, further reducing the amount of fuel and carbon dioxide accumulated at the vertical ends of the folded grooves 13D1 to 13D4.

[0108] This application is based on Japanese patent application No. 2019-189185 filed on October 16, 2019, the contents of which are incorporated herein by reference.

Claims

1. A fuel cell, which is a direct liquid fuel cell using a liquid containing formic acid or alcohol as fuel, comprising: A fuel electrode having a fuel electrode catalyst layer, a fuel electrode diffusion layer, and a fuel electrode current collector; an air electrode having an air electrode catalyst layer, an air electrode diffusion layer, and an air electrode current collector; and an electrolyte membrane disposed between the fuel electrode catalyst layer and the air electrode catalyst layer; The fuel electrode current collector has: a fuel inlet for supplying the fuel; a fuel outflow port for discharging the fuel; and A fuel flow groove is formed on the fuel flow surface on the side contacting the fuel electrode diffusion layer, and guides the fuel from the fuel inlet to the fuel outlet. The fuel flow channel has: a plurality of flow grooves extending from one edge portion of the fuel flow surface to another edge portion opposite to the one edge portion, and arranged in parallel at predetermined intervals; and A plurality of return grooves are provided, wherein the ends of the one side edge portions or the other side edge portions of two adjacent groups of the plurality of flow grooves are connected in a manner that includes a plurality of adjacent groups of the plurality of flow grooves in which the direction of the fuel flow is opposite to that of the fuel flow, Each of the plurality of folded-back grooves has a first inner wall surface portion of the plurality of folded-back grooves that is opposite to the end portion of the flow groove. The first inner wall surface portion has a curved surface shape in which a distance to opposing ends of the flow groove portion gradually narrows toward both ends of the first inner wall surface portion in a direction perpendicular to the direction in which the flow groove portion extends.

2. The fuel cell according to claim 1, wherein The fuel flow channel has: an inflow groove portion connected to the fuel inlet and connected to an end portion of one of the plurality of flow groove portions configured so that the fuel initially flows in, on the side opposite to the folded groove portion; The inflow groove portion includes a second inner wall surface portion of the inflow groove portion that is opposite to the end portion of the flow groove portion. The second inner wall surface portion has a curved surface shape in which a distance to an end portion of the opposite flow groove portion gradually narrows toward an outflow-side end portion of the second inner wall surface portion in a direction perpendicular to the direction in which the flow groove portion extends.

3. The fuel cell according to claim 1, wherein The fuel flow channel has: an outflow groove portion connected to the fuel outflow port and connected to an end portion of one of the plurality of flow groove portions configured so that the fuel finally flows in, on the side opposite to the folded groove portion; The outflow groove portion includes a third inner wall portion of the outflow groove portion that is opposite to the end portion of the flow groove portion. The third inner wall surface portion has a curved surface shape in which a distance to an end portion of the flow groove portion facing the third inner wall surface portion gradually narrows toward an inflow-side end portion thereof in a direction perpendicular to the direction in which the flow groove portion extends.

4. The fuel cell according to claim 2, wherein The fuel flow channel has: an outflow groove portion connected to the fuel outflow port and connected to an end portion of one of the plurality of flow groove portions configured so that the fuel finally flows in, on the side opposite to the folded groove portion; The outflow groove portion includes a third inner wall portion of the outflow groove portion that is opposite to the end portion of the flow groove portion. The third inner wall surface portion has a curved surface shape in which a distance to an end portion of the flow groove portion facing the third inner wall surface portion gradually narrows toward an inflow-side end portion thereof in a direction perpendicular to the direction in which the flow groove portion extends.

5. The fuel cell according to any one of claims 1 to 4, wherein The fuel flow channel has: A plurality of ribs are arranged between the plurality of flow grooves. The plurality of ribs have a plurality of protrusions at the ends of the flow grooves respectively facing the first inner wall surface, the second inner wall surface, and the third inner wall surface, which protrude outward from the flow grooves in an arc shape in a plan view.

6. The fuel cell according to claim 5, wherein The above-mentioned multiple protrusions protruding toward the above-mentioned fold-back groove portion are formed so that the protrusion height of the above-mentioned protrusions gradually becomes lower along the boundaries between two groups of the above-mentioned multiple circulation groove portions in the above-mentioned multiple groups that are reversed from the two ends of the above-mentioned fold-back groove portion toward the direction of the above-mentioned fuel flow in a direction orthogonal to the direction in which the above-mentioned circulation groove portion extends.

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