Fuel cell

A fuel cell includes: a membrane electrode assembly; and a separator disposed on one side of the membrane electrode assembly, wherein the separator includes flow path grooves through which reactant gas flows between the separator and the membrane electrode assembly, the flow path grooves include: wavy grooves wavily extending in a first direction and arranged in a second direction orthogonal to the first direction; and a linear groove linearly extending in the first direction, the wavy grooves include: a first wavy groove located closest to the linear groove among the wavy grooves; and a second wavy groove located opposite to the linear groove with respect to the first wavy groove, and amplitude of the first wavy groove is smaller than that of the second wavy groove.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2018-063275, filed on Mar. 28, 2018, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a fuel cell.

BACKGROUND

A separator of a fuel cell is formed with flow path grooves through which reactant gas flows between the separator and a membrane electrode assembly. A part of the reactant gas flowing in the flow path grooves is supplied to the membrane electrode assembly, so that the power generation reaction occurs in the membrane electrode assembly. For example, in Japanese Unexamined Patent Application Publication No. 2014-026960, the separator is formed with wavy grooves and a linear groove as the flow path grooves.

Since the wavy grooves and the linear grooves differ in shape, there is a large interval between the linear groove and the wavy groove closest to the linear groove. If such an interval is too large, the reactant gas might not be sufficiently supplied to the membrane electrode assembly, and the power generation performance of the fuel cell might be deteriorated.

SUMMARY

It is an object of the present disclosure to provide a fuel cell that suppresses deterioration of power generation performance.

The above object is achieved by a fuel cell including: a membrane electrode assembly; and a separator disposed on one side of the membrane electrode assembly, wherein the separator includes flow path grooves through which reactant gas flows between the separator and the membrane electrode assembly, the flow path grooves include: wavy grooves wavily extending in a first direction and arranged in a second direction orthogonal to the first direction; and a linear groove linearly extending in the first direction, the wavy grooves include: a first wavy groove located closest to the linear groove among the wavy grooves; and a second wavy groove located opposite to the linear groove with respect to the first wavy groove, and amplitude of the first wavy groove is smaller than that of the second wavy groove.

Since the amplitude of the first wavy groove closest to the linear groove is smaller than the amplitude of the second wavy groove, it is possible to suppress an increase in the interval between the linear groove and the first wavy groove. It is therefore possible to suppress the reactant gas from not being supplied to a part of the membrane electrode assembly corresponding to a port where the interval is increased, and to suppress the deterioration of the power generation performance of the fuel cell.

Wavelengths of the first and second wavy grooves may be identical to each other.

Phases of the first and second wavy grooves may be identical to each other.

Wavelengths of all of the wavy grooves may be identical to each other, and phases of all of the wavy grooves may be identical to each other.

The linear groove may be located below the wavy grooves in a gravity direction.

The wavy grooves may include a third wavy groove located opposite to the first wavy groove with respect to the second wavy groove, and amplitude of the second wavy groove may be smaller than or equal to amplitude of the third wavy groove.

Amplitude of the wavy groove may be smaller as the wavy groove is located closer to the linear groove.

The separator may be an anode separator disposed on an anode side of the membrane electrode assembly.

DETAILED DESCRIPTION

FIG. 1is an exploded perspective view of a unit cell2of a fuel cell1. The fuel cell1is configured by stacking unit cells2.FIG. 1illustrates only one unit cell2, and omits other unit cells. The unit cell2is stacked with other unit cells in the Z direction illustrated inFIG. 1. The unit cell2has a substantially rectangular shape. The longitudinal direction and the short direction of the unit cell2correspond to the Y direction and the X direction illustrated inFIG. 1, respectively.

The fuel cell1is a polymer electrolyte fuel cell that generates electric power with a fuel gas (for example, hydrogen) and an oxidant gas (for example, oxygen) as reactant gases. The unit cell2includes: a membrane electrode gas diffusion layer assembly (MEGA)10; a support frame18supporting the MEGA10; a cathode separator20and an anode separator40(hereinafter referred to as separators) sandwiching the MEGA10. The MEGA10has a cathode gas diffusion layer16cand an anode gas diffusion layer16a(hereinafter referred to as diffusion layers). The support frame18has a substantially frame shape, and its inner peripheral side is joined to a peripheral region of the MEGA10.

Holes c1to c3are formed along one of two short sides of the separator20, and holes c4to c6are formed along the other side. Likewise, holes s1to s3are formed along one side of two short sides of the support frame18, and holes s4to s6are formed along the other side. Likewise, holes a1to a3are formed along one side of two short sides of the separator40, and holes a4to a6are formed along the other side. The holes c1, s1, and a1communicate with one another to define a cathode inlet manifold. Likewise, the holes c2, s2, and a2define a coolant inlet manifold. The holes c3, s3, and a3define an anode outlet manifold. The holes c4, s4, and a4define an anode inlet manifold. The holes c5, s5, and a5define a coolant outlet manifold. The holes c6, s6, and a6define a cathode outlet manifold. In the fuel cell1according to the present embodiment, liquid cooling water is used as a coolant.

A surface of the separator40facing the MEGA10is formed with an anode flow path portion40A (hereinafter referred to as flow path portion) which communicate the anode inlet manifold with the anode outlet manifold and along which the fuel gas flows. The surface of the separator20facing the MEGA10is formed with a cathode flow path portion20A (hereinafter referred to as flow path portion) which communicate the cathode inlet manifold with the cathode outlet manifold and along which the oxidant gas flows. The surface of the separator40opposite to the flow path portion40A and the surface of the separator20opposite to the flow path portion20A are respectively formed with coolant flow path portions40B and20B (hereinafter referred to as flow path portions) which communicate the coolant inlet manifold with the coolant outlet manifold and along which the coolant flows. The flow path portions20A and20B extend in the longitudinal direction of the separator20(Y direction). Likewise, the flow path portions40A and40B extend in the longitudinal direction of the separator40(Y direction). Each flow path portion is basically provided in a region, facing the MEGA10, of the separator in the XY plane. The separators20and40are made of a material having a gas blocking property and electrical conductivity, and are thin plate shaped members formed by pressing stainless steel, metal such as titanium or titanium alloy.

FIG. 2is a partially cross-sectional view of the fuel cell1where the unit cells2are stacked.FIG. 2illustrates only one unit cell2, and omits the other unit cells.FIG. 2illustrates a cross section orthogonal to the Y direction.

The MEGA10includes the diffusion layers16aand16c, and a membrane electrode assembly (MEA)11. The MEA11includes an electrolyte membrane12, and an anode catalyst layer14aand a cathode catalyst layer14c(hereinafter referred to as catalyst layers) formed on one surface and the other surface of the electrolyte membrane12, respectively. The electrolyte membrane12is a solid polymer thin film, such as a fluorine-based ion exchange membrane, with high proton conductivity in a wet state. The catalyst layers14aand14care made by coating a catalyst ink containing a carbon support carrying platinum (Pt) or the like and an ionomer having proton conductivity on the electrolyte membrane12. The diffusion layers16aand16care made of a material having gas permeability and conductivity, for example, a porous fiber base material such as carbon fiber or graphite fiber. The diffusion layers16aand16care joined to the catalyst layers14aand14c, respectively.

Each of the flow path portions20A,20B,40A, and40B has a wavy shape in cross section when viewed in the Y direction. Specifically, regarding the flow path portion20A, a flow path groove21, recessed away from the diffusion layer16c, and a rib23, protruding to and contacting with the diffusion layer16c, are alternately arranged in the X direction. The cathode gas, flowing along the insides of the flow path grooves21, is supplied to the catalyst layer14cof the MEA11via the diffusion layer16c. Further, regarding the flow path portion20B, a rib22, protruding opposite to the diffusion layer16cand contacting with an anode separator of another unit cell (not illustrated) adjacent to the separator20in the −Z direction, and a flow path groove24, receded away from this anode separator, are alternately arranged in the X direction. The coolant flows along the insides of the flow path grooves24. Herein, the flow path grooves21and the ribs22are formed integrally on the front and rear surfaces, and the ribs23and the flow path grooves24are formed integrally on the front and rear surfaces. The flow path grooves21and24and the ribs22and23extend in the Y direction.

Likewise, regarding the flow path portion40A, a flow path groove41, recessed away from the diffusion layer16a, and a rib43, protruding to and contacting with the diffusion layer16aare alternately arranged in the X direction. The anode gas, flowing along the insides of the flow path grooves41, is supplied to the catalyst layer14aof the MEA11via the diffusion layer16a. Further, regarding the flow path portion40B, a rib42, protruding opposite to the diffusion layer16aand contacting with a cathode separator of another unit cell (not illustrated) adjacent to the separator40in the +Z direction, and a flow path groove44, receded away from this cathode separator, are alternately arranged in the X direction. The coolant flows along the insides of the flow path grooves44. Herein, the flow path grooves41and the ribs42are formed integrally on the front and rear surfaces, and the ribs43and the flow path grooves44are formed integrally on the front and rear surfaces. The flow path grooves41and44and the ribs42and43extend in the Y direction.

FIG. 3Ais an enlarged view illustrating a part of the flow path portion40A of the separator40in a present embodiment.FIG. 3Aillustrates grooves411to416which are a part of flow path grooves41, and ribs431to435which are a part of the ribs43. The grooves411to416and the ribs431to435are arranged in the X direction. Among the grooves411to416, the groove411is located furthest from the center in the −X direction, and the groove416is located furthest from the center in the +X direction. The ribs431,432,433,434, and435are located between the grooves411and412, between the grooves412and413, between the grooves413and414, between the grooves414and415, and between the grooves415and416, respectively.

Although the groove411has a linear shape, each of the grooves412to416has a wavy shape. Additionally, inFIG. 1, the flow path portion40A is simply illustrated by straight lines. The grooves412to416are examples of wavy grooves wavily extending in the Y direction and arranged in the X direction orthogonal to the Y direction. The groove411is an example of a linear groove linearly extending in the Y direction. Each of the ribs432to435also has a wavy shape, and the boundary between the rib431and the groove412also has a wavy shape. Among the grooves412to416, the groove412is located closest to the groove411. The groove412is an example of a first wavy groove located closest to the groove411among the grooves412to416. Each of the grooves413to416is an example of a second wavy groove located opposite to the groove411with respect to the groove412.

In a case where the groove413is an example of the second wavy groove, any grooves414to416are an example of a third wavy groove located opposite to the groove412with respect to the groove413. In a case where the groove414is an example of the second wavy groove, any grooves415and416are an example of the third wavy groove located opposite to the groove412with respect to the groove414. In a case where the groove415is an example of the second wavy groove, the groove416is an example of the third wavy groove located opposite to the groove412with respect to the groove415.

The pitch intervals between the grooves411to416in the X direction are substantially the same. The grooves412to416each having a wavy shape have substantially the same wavelength and the same phase, but have different amplitude. Specifically, the grooves412to416are arranged in ascending order of the amplitude. In other words, the amplitude of the groove is smaller as being closer to the linear groove411. For example, as illustrated inFIG. 3A, amplitude A2of the groove412is smaller than amplitude A6of the groove416. In addition, the shape of the groove, located away from the groove416in the +X direction and not illustrated inFIG. 3A, is not limited.

Referring toFIG. 2, a description will be given of one of the main reasons why at least the grooves412to416and the ribs431to435are partially wavy shaped. For example, in a case where all of the flow path grooves41and the ribs43of the separator40and all of the flow path grooves21and the ribs23of the separator20are linear, if the relative position between the separators20and40is displaced from the desired position in the planar direction, the rib23of the separator20is positionally displaced from the rib43of the separator40in the X direction in the state where the MEGA10is sandwiched therebetween. Since the MEGA10has low rigidity, if the ribs23of the separator20are positionally displaced from the ribs43of the separator40in the X direction in a long range (for example, 4 mm or more) in the Y direction, the MEGA10might be bent to be locally subjected to strong stress, so that the strength of the MEA11might decrease. In contrast, in a case where the flow path grooves21and the ribs23of the separator20, facing the grooves412to416and the ribs431to435each having a wavy shape via the MEGA10, each has a linear shape, or a wavy shape different from the wavy shape of the grooves412to416in phase, amplitude, wavelength or the like, even if the relative position between the separators20and40is displaced from the desired position as described above, the MEGA10is suppressed from being bent by positionally displacing the ribs23of the separator20from the ribs43of the separator40in the X direction in a long range in the Y direction. This suppresses the decrease in strength of the MEA11. In the present embodiment, the flow path grooves21and the ribs23of the separator20, facing the grooves412to416and the ribs431to435via the MEGA10, each has a linear shape, but they not limited thereto.

FIG. 3Bis an enlarged view illustrating a part of a flow path portion40X of a separator40xin a comparative example.FIG. 3Bcorresponds toFIG. 3A. Grooves412xto416xand the ribs432xto435xof the separator40xhave substantially the same amplitude as well as wavelength and phase. Specifically, as illustrated inFIG. 3B, each amplitude of the grooves412xto415xand the ribs432xto435xis substantially the same as amplitude A6xof the groove416x. Herein, the interval, in the X direction, between the groove411having a linear shape and the groove412xhaving a wavy shape closest to the groove411, in other words, the width of the rib431xin the X direction differs depending on a position in the Y direction. The rib431xhas a part W1xwhere the width is the maximum. Therefore, the contact area between the rib431xand the diffusion layer16ais increased at this part W1x. Thus, the anode gas flowing in the groove411and the groove412xmight not be sufficiently supplied to a part of the MEA11that is positioned away from the part W1xin the +Z direction. As described above, in the case of using the separator40xin the comparative example, the anode gas might not be sufficiently supplied to a part of the MEA11, so that the power generation performance might be deteriorated.

However, in the present embodiment as illustrated inFIG. 3A, the amplitude A2of the groove412closest to the groove411is smaller than each amplitude of the grooves413to416. Therefore, a part W1where the width of the rib431between the grooves411and412in the X direction is the largest is smaller than the part W1xdescribed above. It is therefore possible to suppress the anode gas from not being partially supplied to a part of the MEA11, and to suppress the deterioration of the power generation performance. This also suppresses the deterioration of the power generation performance due to the deterioration of the catalyst layer14acaused by hydrogen deficiency.

The grooves412to416are arranged in ascending order of the amplitude, and in ascending order of the distance from the groove411. This suppresses an increase in the width of the rib432, in the X direction, between the grooves412and413slightly different in amplitude. The same applies to each of the ribs433to435. As described above, the increase in the width of each of the ribs432to435in the X direction is suppressed, thereby uniformly suppling the anode gas to the MEA11.

Further, if the amplitude difference between the grooves411and412xis large as in the comparative example, the difference in pressure loss of the anode gas between the grooves411and412xmight increase, so that the anode gas might not be supplied to a part of the MEA11. In the present embodiment, since the amplitude A2of the groove412is smaller than amplitude A2xof the groove412x, the increase in the difference in pressure loss of the anode gas between the grooves411and412is suppressed. This suppresses the anode gas from not being supplied to a part of the MEA11, which suppresses the deterioration of the power generation performance. Additionally, the increase in difference in pressure loss of the anode gas between the grooves412and413is suppressed. The same applies to the grooves413to416. It is thus possible to uniformly supply the anode gas to the MEA11.

Further, as described above, the flow path groove44through which the coolant flows is formed on the rear side of the rib43. Thus, the two flow path grooves44are formed on the rear side of the ribs431and432, and are formed into substantially the same shape as the ribs431and432. It is therefore possible to suppress an increase in the difference in pressure loss of the coolant between the flow path grooves44formed on the rear side of the ribs431and432. It is thus possible to suppress the MEA11from not being partially cooled due to a part where the coolant hardly flows, and to suppress the deterioration of the power generation performance. The same applies to the pressure loss of the coolant between the flow path grooves44on the rear side of the ribs433to435. Accordingly, the MEA11is uniformly cooled.

Further, as for the separator40xin the comparative example, in the region from the groove412xto the groove416x, the elongation percentage of the base material in the press working might increase, and the yield rate might decrease. In the present embodiment, since the amplitude gradually changes between the grooves412to416, it is possible to suppress the increase in the elongation percentage of the base material in the region from the groove412to the groove416, and to suppress the decrease in the yield rate.

Further, the separator40xin the comparative example might be subjected to the large residual stress in the press working due to the difference in shape between the groove411and the groove412xclosest thereto. This residual stress might cause warpage in the separator40x. In the present embodiment, the grooves416to412are arranged in descending order of the amplitude, in other words, in order of similarity to a linear shape. It is thus possible to reduce the residual stress in the press working, and to reduce the possibility that the warpage occurs in the separator40.

Conceivably, the fuel cell1in the present embodiment is used in a posture in which the groove411is located below the grooves412to416in the gravity direction such that the −X direction is the downward gravity direction. In this case, for example, even if water generated on the anode side flows into the groove411, since the groove411has a linear shape, the staying of water in the groove411is suppressed, and the anode gas flowing in the groove411allows water to flow to the downstream side. In this way, the drainability is improved. Even in the case where the fuel cell1is used in a posture in which the X direction is inclined with respect to the gravity direction, the staying of water in the groove411is suppressed and the drainability is ensured as long as the groove411is positioned below the grooves412to416in the gravity direction.

Next, variations will be described. In variations, the same reference numerals are given to the same components as those of the above-described embodiment, and duplicated explanation is omitted.FIG. 4Ais an enlarged view illustrating a part of a flow path portion40Aa of a separator40ain a first variation. The flow path portion40Aa includes the groove411having a linear shape and grooves412ato416aeach having a wavy shape. The grooves412ato416ahave substantially the same wavelength and the same phase. The grooves413ato416ahave substantially the same amplitude, for example, each amplitude of the grooves413ato415ais the same as amplitude A6aof the groove416aas illustrated inFIG. 4A. In a case where the groove413ais an example of the second wavy groove, any grooves414ato416aare an example of the third wavy groove. In this variation, the amplitude of the second wavy groove and the amplitude of the third wavy groove are the same. In contrast, amplitude A2aof the groove412a, which is an example of the first wavy groove, is smaller than each amplitude of the grooves413ato416a. Even in such a configuration, it is possible to suppress the increase in the width of the rib431ain the X direction between the grooves411and412a, and to suppress the anode gas from not being supplied to a part of the MEA11. This suppresses the deterioration of the power generation performance. Due to the above-described shapes of the grooves412ato416a, the width of the rib432ain the X direction changes depending on a position in the Y direction, but each width of the ribs433ato435ain the X direction is constant in the Y direction.

Additionally, the grooves413ato416ahave substantially the same wavelength, the same phase, the same amplitude, and the common shape. Here, in general, as for pressing, the shape of a metal plate formed by dies is not always the same as the reversed shape of the die. After the metal plate is deformed by the die, the shape of the metal plate slightly becomes to its original shape before the molding, due to the elasticity of the metal plate. This is called spring back. For this reason, this spring back is taken into consideration in designing the dies. In a case where groove shapes differ from each other, it might be needed to design the dies for the respective groove shapes, and it might take a long time for designing the dies. In the present embodiment, the grooves have the common shape. It is thus possible to suppress the long time required to design the dies. In the case of forming a precise shape like a separator for a fuel cell, the metal plate is pressed with different dies several times, so that the metal plate is gradually expanded to achieve the final product shape. In a case where the wavy shapes in the final product shape differ from each other, the design of the dies used in pressing is different, so that the time required to design the dies might be further prolonged. On the other hand, the grooves413ato416ahave the common shape in the present embodiment. It is thus possible to form the common shape in the dies for pressing, and to suppress the prolongation of the time required to design the dies for producing the separator40a.

FIG. 4Bis an enlarged view illustrating a part of a flow path portion40Ab of a separator40bin a second variation. The amplitude of a groove413blocated between the grooves412aand414ais substantially the same as the amplitude of the groove412a. Therefore, the width, in the X direction, of a rib432blocated between the grooves412aand413bis substantially constant in the Y direction. In contrast, since there is an amplitude difference between the grooves413band414a, the width of a part W3bwhich has the maximum width of the rib433blocated between the grooves413band414ais greater than the width of the rib432bin the X direction. The width of the part W3bis substantially the same as the width of the part W1awhich has the maximum width of the rib431a. In this way, the parts W1aand W3bwhere widths are increased are distant away from each other in the X direction via the groove412a, the rib432b, and the groove413b. Therefore, as compared with a case where such two parts are adjacent to each other via one groove, it is possible to suppress parts, to which the anode gas is relatively difficult to be supplied, from being adjacent to each other, and to supply uniformly the anode gas to the MEA11.

The flow path grooves in the present embodiment and variations described above may be applied to the cathode separator.

Although the separators40,40a, and40eare adopted in the water-cooled fuel cell1using liquid as the coolant, they are not limited thereto, and may be adopted in an air-cooled fuel cell using air as the coolant.

The wavy groove described above may have a sine wave shape, or a wavy shape with a straight line and an arc.

In the above-described embodiment and variation, the wavy grooves have substantially the same wavelength and the same phase, but they are not limited thereto. In any case, it is possible to suppress the increase in the interval between the linear groove and the wavy groove closest to the linear groove, as long as the amplitude of the wavy groove closest to the linear groove is smaller than the amplitude of the other wavy groove located opposite to the linear groove with respect to the wavy groove. Further, in the above-described embodiment and variations, the wavy grooves and the linear groove are formed at substantially the same pitch interval, but they are not limited thereto.

Although some embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the specific embodiments but may be varied or changed within the scope of the present disclosure as claimed.