Separator

Abstract

To provide a separator capable of suppressing a decrease in the power generation performance of fuel cells.SOLUTION: There is provided a separator for fuel cells. The separator includes a plurality of cathode-side gas flow paths. Each of the cathode-side gas flow paths includes a plurality of flow path portions and a plurality of restrictor portions. A flow path cross-sectional area of each of the restrictor portions is smaller than a flow path cross-sectional area of each of the flow path portions. At least one of the restrictor portions is an upstream-side restrictor portion disposed in an upstream of the cathode-side gas flow paths, and at least one of the restrictor portions is a downstream-side restrictor portion disposed in a downstream of the cathode-side gas flow paths. A flow path cross-sectional area of the at least one upstream-side restrictor portion is larger than a flow path cross-sectional area of the at least one downstream-side restrictor portion.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a separator.

Background Art

[0002] Various technologies have been proposed regarding fuel cells as disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses a single cell of a fuel cell having a throttle portion (a portion with a small flow path cross-sectional area) in a flow path. There is a risk that the electrolyte membrane dries on the upstream side of the cathode gas flow path, resulting in a decrease in the power generation performance of the fuel cell.

[0005] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a separator capable of suppressing a decrease in the power generation performance of a fuel cell.

Means for Solving the Problems

[0006] That is, the present disclosure includes the following aspects. <1> A separator for a fuel cell, The separator has a plurality of cathode-side gas flow paths, Each of the cathode-side gas flow paths has a plurality of flow path portions and a plurality of throttle portions, The flow path cross-sectional area of each of the throttle portions is smaller than the flow path cross-sectional area of each of the flow path portions, At least one of the plurality of throttle portions is an upstream-side throttle portion disposed upstream of the cathode-side gas flow path, At least one of the plurality of throttle portions is a downstream throttle portion disposed downstream of the cathode gas flow channel, a flow path cross-sectional area of the at least one upstream throttle portion is larger than a flow path cross-sectional area of the at least one downstream throttle portion; At least one of the downstream tapered portions of the separator satisfies the following formula (1): Rc / Rb>1...Equation (1) Rb is the resistance of the separator ribs to gas getting under them, and Rc is the resistance of each of the constrictions.

[0007] <2> A groove depth of at least one of the upstream constriction portions is greater than a groove depth of at least one of the downstream constriction portions; <1> The separator according to claim 1.

[0008] <3> In two adjacent cathode-side gas flow paths, when the separator is viewed in a plan view, each of the throttle portions in one cathode-side gas flow path is not adjacent to each of the throttle portions in the other cathode-side gas flow path. <1> or <2> The separator according to claim 1.

[0009] <4> Each of the cathode gas flow paths has a plurality of the upstream throttle portions and a plurality of the downstream throttle portions, At least one of the plurality of upstream tapered portions satisfies the following formula (2), At least one of the plurality of downstream tapered portions satisfies the formula (1). <1> ~ <3> 13. The separator according to claim 12, Rc / Rb≦1...Equation (2)

[0010] <5> Each of the cathode gas flow paths has a plurality of the upstream throttle portions and a plurality of the downstream throttle portions, At least one of the plurality of upstream tapered portions satisfies the following formula (2), At least one of the plurality of downstream tapered portions satisfies the following formula (3): <1> ~ <4> 13. The separator according to claim 12, Rc / Rb≦1...Equation (2) Rc / Rb ≥ 3 ··· Equation (3)

[0011] <6> A fuel cell, wherein the fuel cell includes the separator according to any one of <1> to <5> as a cathode separator.

[0012] <7> The fuel cell includes the cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator. The membrane electrode gas diffusion layer assembly has, in order from the anode separator side, an anode side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer, the fuel cell according to <6>.

Advantages of the Invention

[0013] The separator of the present disclosure can suppress a decrease in the power generation performance of the fuel cell.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present disclosure will be described. Note that matters other than those specifically mentioned in this specification and necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of the separator that do not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In the present disclosure, the gas supplied to the anode of the fuel cell is the fuel gas (anode gas), and the gas supplied to the cathode of the fuel cell is the oxidant gas (cathode gas). The fuel gas is a gas that contains mainly hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, etc. In the present disclosure, the fuel gas and the oxidant gas are collectively referred to as reactant gases or gases.

[0016] The present disclosure provides a separator for a fuel cell, comprising: The separator has a plurality of cathode gas flow channels, Each of the cathode gas flow paths has a plurality of flow path portions and a plurality of throttle portions, A flow path cross-sectional area of each of the throttle portions is smaller than a flow path cross-sectional area of each of the flow path portions, At least one of the plurality of throttle portions is an upstream throttle portion disposed upstream of the cathode gas flow passage, At least one of the plurality of throttle portions is a downstream throttle portion disposed downstream of the cathode gas flow channel, a flow path cross-sectional area of the at least one upstream throttle portion is larger than a flow path cross-sectional area of the at least one downstream throttle portion; The at least one downstream tapered portion of the separator satisfies the following formula (1). Rc / Rb>1...Equation (1) Rb is the resistance of the separator ribs to gas getting under them, and Rc is the resistance of each of the constrictions.

[0017] In a gas flow path in which a throttle portion of a separator is provided, the flow resistance of the gas increases due to the reduction in the flow cross-sectional area caused by the throttle portion. When a throttle portion is provided in a cathode gas flow path through which an oxidant gas flows, and a throttle portion is not provided in a cathode gas flow path adjacent to the cathode gas flow path, a difference in flow resistance between the two gas paths occurs, and a pressure loss difference occurs when the same gas flow rate flows through each gas flow path. Therefore, in order to eliminate this pressure loss difference, a part of the gas flowing through the cathode gas flow path flows into an adjacent cathode gas flow path that does not have a throttle portion and has a low flow resistance. The gas flowing into this adjacent cathode gas flow path sneaks under the ribs of the separator and flows through a gas diffusion layer (GDL) adjacent to the separator. Therefore, the gas flow through this GDL promotes material transport between the membrane electrode assembly and the cathode gas flow path, leading to a reduction in concentration overvoltage in a fuel cell, and therefore a throttle portion is provided in the cathode gas flow path of the separator through which an oxidant gas flows. However, in the upstream part of the cathode gas flow path, where the relative humidity of the gas is low, the gas flowing through this gas diffusion layer acts to lower the relative humidity of the electrolyte membrane, resulting in an increase in the proton resistance of the electrolyte membrane and a decrease in the power generation performance of the fuel cell. In the present disclosure, the flow resistance between the cathode gas flow channel and the adjacent cathode gas flow channel is reduced by making the flow channel cross-sectional area of the upstream narrowed portion of the cathode gas flow channel larger than that of the downstream narrowed portion. This suppresses the gas flow through the GDL, and the material transport between the membrane electrode assembly and the cathode gas flow channel can be suppressed compared to the conventional technology. As a result, the decrease in the relative humidity of the electrolyte membrane is suppressed, the humidity balance between the upstream and downstream sides of the cathode gas flow channel can be made closer to equal, the increase in the proton resistance of the electrolyte membrane can be suppressed, and the decrease in the power generation performance of the fuel cell can be suppressed. Since the oxygen partial pressure in the cathode gas flow channel is higher on the upstream side than on the downstream side, the increase in the concentration overvoltage caused by increasing the flow channel cross-sectional area of the upstream narrowed portion is smaller, and the effect of reducing the resistance overvoltage is greater, resulting in an increase in the voltage of the fuel cell.

[0018] The separator collects the current generated by power generation and functions as a partition. In a fuel cell cell, the separator is usually arranged on both sides in the stacking direction of the power generation body so that a pair of separators sandwich the power generation body. One of the pair of separators is an anode separator, and the other is a cathode separator. As the separator, for example, a dense carbon obtained by compressing carbon to make it gas-impermeable, a press-molded metal (for example, iron, aluminum, stainless steel, etc.), or the like may be used. The separator may have holes that constitute a manifold such as supply holes and discharge holes for allowing fluids such as reaction gas and refrigerant to flow in the stacking direction of the cell. Examples of the refrigerant include water, a mixed solvent of water and ethylene glycol, and the like.

[0019] The separator of the present disclosure is a cathode separator. The cathode separator has a plurality of cathode-side gas flow paths on the surface on the power generation body side. The cathode separator may have a plurality of ribs, and may have a cathode-side gas flow path between adjacent ribs. The cathode separator may have a plurality of cooling channels and a plurality of ribs on the surface opposite to the surface on the power generation body side. The anode separator may have a plurality of anode-side gas flow paths and a plurality of ribs on the surface on the power generation body side, and may have a plurality of cooling channels and a plurality of ribs on the surface opposite to the surface on the power generation body side. The anode-side gas flow path only needs to have a flow path portion, and may or may not have a throttle portion.

[0020] Each of the cathode-side gas flow paths has a plurality of flow path portions and a plurality of throttle portions. The flow path cross-sectional area of each of the throttle portions is smaller than the flow path cross-sectional area of each of the flow path portions. At least one of the plurality of throttle portions is an upstream-side throttle portion arranged upstream of the cathode-side gas flow path. At least one of the plurality of throttle portions is a downstream-side throttle portion arranged downstream of the cathode-side gas flow path. In the present disclosure, the flow path portion of the cathode-side gas flow path means an area other than the throttle portion of the cathode-side gas flow path. The area from the inlet of the cathode-side gas flow path to the throttle portion, the area between the throttle portions of the cathode-side gas flow path, and the area from the throttle portion to the outlet of the cathode-side gas flow path all correspond to the flow path portion. In the present disclosure, the upstream of the cathode-side gas flow path means the area of 50% (half of the area from the inlet side) of the cathode-side gas flow path from the inlet side when the entire area of the cathode-side gas flow path is regarded as 100%. In the present disclosure, the downstream of the cathode-side gas flow path means the area of 50% (half of the area from the outlet side) of the cathode-side gas flow path from the outlet side when the entire area of the cathode-side gas flow path is regarded as 100%. The cathode-side gas flow path may be provided with a plurality of throttle portions at predetermined intervals. The flow path cross-sectional area of at least one of the upstream throttle portions is larger than the flow path cross-sectional area of at least one of the downstream throttle portions. The flow path cross-sectional area of at least one of the plurality of upstream throttle portions may be larger than the flow path cross-sectional area of at least one of the plurality of downstream throttle portions. The groove depth of at least one of the upstream throttle portions may be larger than the groove depth of at least one of the downstream throttle portions. The groove depth of at least one of the plurality of upstream throttle portions may be larger than the groove depth of at least one of the plurality of downstream throttle portions. The groove width of at least one of the upstream throttle portions may be larger than the groove width of at least one of the downstream throttle portions. The groove width of at least one of the plurality of upstream throttle portions may be larger than the groove width of at least one of the plurality of downstream throttle portions. In two adjacent cathode-side gas flow paths, when the separator is viewed in a plan view, each throttle portion of one cathode-side gas flow path may not be adjacent to each throttle portion of the other cathode-side gas flow path. The air permeability in the plane in the gas flow direction of the gas diffusion layer (cathode-side gas diffusion layer) in contact with the cathode-side gas flow path may be equal to or greater than the in-plane air permeability in the direction perpendicular to the gas flow and the in-plane air permeability in the direction parallel to the gas flow of the flow path portion of the cathode-side gas flow path. The gas diffusion layer has an air permeability of, for example, 5 m 3 / Pa·s or more 17m 3 / Pa·s or less. The relative humidity of the oxidant gas supplied to the fuel cell may be less than 100%.

[0021] FIG. 1 is a schematic diagram showing an example of a surface of a separator according to the present disclosure facing a power generating body as viewed from above. The separator has a plurality of ribs 11, and a cathode-side gas flow passage 10 is provided between adjacent ribs 11. The cathode-side gas flow passage 10 has a plurality of flow passage sections 12, a plurality of upstream throttle sections 20 arranged upstream 40 of the cathode-side gas flow passage 10, and a plurality of downstream throttle sections 30 arranged downstream 50 of the cathode-side gas flow passage 10. The cross-sectional area of the upstream throttle section 20 disposed on the upstream side 40 of the cathode gas flow passage 10 is larger than the cross-sectional area of the downstream throttle section 30 disposed on the downstream side 50 thereof. In a plan view of the separator, a throttle portion may be provided in every other cathode-side gas flow channel 10 in the direction perpendicular to the gas flow direction. This allows gas that cannot pass through the throttle portion to penetrate into the gas diffusion layer below the rib 11, and to easily flow to the flow channel portion 12 of the adjacent cathode-side gas flow channel 10.

[0022] At least one of the downstream tapered portions satisfies the following formula (1). Rc / Rb>1...Equation (1) Rb is the resistance of the separator ribs to gas getting under them, and Rc is the resistance of each of the constrictions.

[0023] The cathode gas flow channel may have a plurality of upstream throttle sections and a plurality of downstream throttle sections. At least one of the plurality of upstream tapered portions may satisfy the following formula (2). Rc / Rb≦1...Equation (2) At least one of the plurality of downstream tapered portions may satisfy the above formula (1) and may also satisfy the following formula (3). Rc / Rb≧3...Equation (3)

[0024] In the prior art, how to effectively improve the power generation performance of a fuel cell by adjusting the throttle ratio of the throttle section has not been studied. The improvement of the power generation performance of a fuel cell by the throttle section is not determined only by the throttle ratio, and it is necessary to consider the gas distribution within the separator plane including the GDL. In the present disclosure, the rib-under convection ratio Rc / Rb has been found as an index for improving the power generation performance of a fuel cell including the influence of the GDL in addition to the throttle ratio. The effect of improving the power generation performance in the high-voltage region of a fuel cell is manifested by making the rib-under convection ratio (Rc / Rb) of the throttle section formed in the cathode-side gas flow path of the cathode separator greater than 1. Furthermore, in an environment where the operating temperature of the fuel cell is high (dry condition), excessive drainage under the ribs of the separator causes significant drying of the electrolyte membrane and the power generation performance of the fuel cell does not improve. Therefore, in the above environment, the rib-under convection ratio (Rc / Rb) is set to 1 or less. In the present disclosure, it is not limited to the case where the rib-under convection ratio (Rc / Rb) of all upstream throttle sections in the cathode-side gas flow path is 1 or less, and the rib-under convection ratio (Rc / Rb) of all downstream throttle sections in the cathode-side gas flow path is greater than 1. For example, if the rib-under convection ratio (Rc / Rb) of at least one upstream throttle section among a plurality of upstream throttle sections in the cathode-side gas flow path is 1 or less, the rib-under convection ratio (Rc / Rb) of the remaining upstream throttle sections is not particularly limited. For example, if the rib-under convection ratio (Rc / Rb) of at least one downstream throttle section among a plurality of downstream throttle sections in the cathode-side gas flow path is greater than 1, the rib-under convection ratio (Rc / Rb) of the remaining downstream throttle sections is not particularly limited. For example, the rib-under convection ratio (Rc / Rb) of the throttle section between the first upstream throttle section from the upstream and the first downstream throttle section from the downstream in the cathode-side gas flow path may be in the range of 1 to 3.

[0025] [Definition of rib-under convection ratio (Rc / Rb)] In the high current range of a fuel cell, the power generation performance of the fuel cell is significantly reduced due to an increase in concentration overvoltage. In order to reduce this concentration overvoltage, it is important to increase the gas permeation rate under the ribs due to the constriction. Here, the under-rib convection ratio (Rc / Rb) is introduced as an index indicating the gas permeation rate under the ribs. The pressure loss that determines the gas flow is determined by the flow path resistance and the gas flow rate. This flow path resistance is regarded as electrical resistance. Here, Ra shown in Figure 1 is the resistance determined by the cross-sectional shape of the flow path, Rb is the resistance of the rib against the gas that sneaks under the rib of the separator, and Rc is the resistance of each of the constrictions. For example, if Rc is increased while keeping Rb constant, the gas convection rate increases. Therefore, the gas convection rate is determined by Rc and Rb, and the under-rib convection rate Rc / Rb is used as an index of the gas convection rate.

[0026] The flow path resistance Ra and the resistance of the throttle portion Rc were expressed as the following formulas (a) and (c) using the Darcy-Weisbach formulas (A) and (C), respectively. Formula (A) ΔPa = (32 μl ÷ d 4 )×Qa Formula (C)ΔPc=(32μl res ÷d 4 res )×Qc Formula (a) Ra = (32 μl ÷ d 4 ) Formula (c) Rc=(32μl res ÷d 4 res ) Here, ΔP is the pressure loss, Q is the flow rate, μ is the air viscosity, l is the unit length, d is the hydraulic diameter, and the subscript res indicates that the object is a throttle portion.

[0027] In addition, the resistance Rb of the separator rib against the gas that penetrates under the rib was expressed as formula (b) from formula (B) of Darcy's law, which shows the relationship between the gas pressure and flow rate in the GDL. Formula (B)ΔPb=(l rib ÷k GDL )×Qb Formula (b) Rb=l rib ÷kGDL Here, k GDL is the permeability of the GDL, and l rib represents the rib width.

[0028] [Means for controlling Rb] Rb is a function of the rib width l rib and the air permeability k of the GDL GDL , and the means for controlling Rb is to control these two parameters. To control the rib-bottom convection ratio Rc / Rb within the separator plane, the following means can be used to control Rb. 1. Change the rib width along the gas flow direction. 2. Use a GDL with an air permeability that increases along the gas flow direction. 3. The air permeability of the GDL depends on the surface pressure of the separator. When the surface pressure increases, the air permeability decreases. Therefore, the flow channel structure of the separator is designed to have a decreasing surface pressure along the gas flow direction.

[0029] [Relationship between rib-bottom convection ratio Rc / Rb and concentration overvoltage] When the rib-bottom convection ratio Rc / Rb at the throttle part of the cathode-side gas flow channel of the separator is changed to the values in Reference Experimental Examples 1 to 5, the concentration overvoltage at a current density of 3.8 A / cm 2 of a predetermined fuel cell including each separator was measured. Figure 2 is a graph showing an example of the relationship between the rib-bottom convection ratio Rc / Rb at the throttle part of the cathode-side gas flow channel of the separator and the concentration overvoltage of a predetermined fuel cell at a current density of 3.8 A / cm 2 . The values of Rc / Rb and the concentration overvoltage of the fuel cell in Reference Experimental Examples 1 to 5 are shown in Table 1.

[0030]

Table 1

[0031] As shown in FIG. 2, by making the rib-under convection ratio (Rc / Rb) of the throttle portion formed in the gas flow path of the cathode separator greater than 1, the concentration overvoltage is reduced, and the performance improvement effect in the high-current region (current density 3.8 A / cm 2 ) of the fuel cell appears. On the other hand, under low humidity conditions, due to excessive drainage under the ribs of the separator, drying of the electrolyte membrane becomes prominent, and the effect of reducing the concentration overvoltage when the rib-under convection ratio (Rc / Rb) is greater than 1 as shown in FIG. 2 cannot be expected. Therefore, under low humidity conditions, the rib-under convection ratio (Rc / Rb) of the throttle portion may be, for example, 1 or less, or may be 0.3 or more. In an actual fuel cell, at the downstream of the cathode-side gas flow path, since the oxygen concentration is low and the humidity is high due to the generated water, the rib-under convection ratio (Rc / Rb) of at least one of the plurality of downstream throttle portions in the cathode-side gas flow path may be made larger than the rib-under convection ratio (Rc / Rb) of the upstream throttle portion. The rib-under convection ratio (Rc / Rb) of at least one of the plurality of downstream throttle portions in the cathode-side gas flow path may be greater than 1, may be 3 or more, or may be 3 or more and 60 or less. Upstream of the cathode-side gas flow path, since the amount of generated water is relatively small, the humidity is relatively low, and the oxygen concentration is relatively high, the rib-under convection ratio (Rc / Rb) of at least one of the plurality of upstream throttle portions in the cathode-side gas flow path may be made smaller than the rib-under convection ratio (Rc / Rb) of the downstream throttle portion. The rib-under convection ratio (Rc / Rb) of at least one of the plurality of upstream throttle portions in the cathode-side gas flow path may be, for example, 1 or less, or may be 0.3 or more and 1 or less.

[0032] The separator of the present disclosure is for a fuel cell. The fuel cell includes the separator of the present disclosure as a cathode separator. The fuel cell may have only one single cell of the fuel cell, or may be a fuel cell stack in which a plurality of cells are stacked. In the present disclosure, both the cell and the fuel cell stack may be referred to as a fuel cell in some cases. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, 2 to several hundreds.

[0033] The cell may have a power generation body. The shape of the power generation body may be rectangular in plan view. The power generation body may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes sandwiching the electrolyte membrane. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as thin films of perfluorosulfonic acid containing moisture, and hydrocarbon-based electrolyte membranes. As the electrolyte membrane, for example, a Nafion membrane (manufactured by DuPont) may be used. One of the two electrodes is an anode (fuel electrode), and the other is a cathode (oxidant electrode). The electrode includes a catalyst layer and may optionally include a gas diffusion layer. The power generation body may be a membrane electrode gas diffusion layer assembly (MEGA). In this case, the fuel cell may include a cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator. The membrane electrode gas diffusion layer assembly has an anode-side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode-side gas diffusion layer in this order. The anode catalyst layer and the cathode catalyst layer are collectively referred to as the catalyst layer. The anode-side gas diffusion layer and the cathode-side gas diffusion layer are collectively referred to as the gas diffusion layer. The catalyst layer includes a catalyst, and the catalyst may include a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, a carrier having electron conductivity, and the like. As the catalyst metal, for example, platinum (Pt) and alloys composed of Pt and other metals (for example, Pt alloys mixed with cobalt, nickel, etc.) can be used. The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst may be the same or different. As the electrolyte, a fluororesin or the like may be used. As the fluororesin, for example, Nafion solution or the like may be used. The catalyst metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalyst metal (catalyst-supporting carrier) and the electrolyte may be mixed. Examples of the carrier for supporting the catalyst metal include carbon materials such as commercially available carbon. The gas diffusion layer (GDL) may be composed of a base material and a mesoporous layer (MPL). The GDL may have a base material on the side in contact with the separator and an MPL on the side in contact with the catalyst layer. The base material may be a conductive member having gas permeability or the like. Examples of the base material include carbon porous bodies such as carbon cloth and carbon paper, and metal porous bodies such as metal mesh and foamed metal. The MPL may contain a mixture of a water-repellent resin such as PTFE and a conductive material such as carbon black. The MPL may contain an antioxidant such as Ce. The antioxidant can prevent the generation of radicals. The cell may include an insulating resin frame disposed on the outer side (outer periphery) in the plane direction of the membrane electrode assembly between the anode separator and the cathode separator. The resin frame is formed into a plate-like and frame-like shape using a thermoplastic resin, and seals between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. As the resin frame, for example, resins such as PE, PP, PET, and PEN can be used. The resin frame may be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0034] The fuel cell stack may have a gasket, a resin sheet, etc. between the cells to seal each gas.

Example

[0035] A fuel cell was prepared, which had a membrane electrode gas diffusion layer assembly having an anode-side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode-side gas diffusion layer in this order, and two separators (a cathode separator and an anode separator) sandwiching the membrane electrode gas diffusion layer assembly. Each gas diffusion layer included an MPL layer, and the air permeability of each gas diffusion layer was 9 m 3 / Pa·s. A plurality of cathode separators with different shapes of throttle portions in the cathode-side gas flow path were prepared, and the power generation performance of each fuel cell using each cathode separator was compared. [Configuration of the cathode-side gas flow path of the cathode separator] Seven throttle portions (throttle portions 1 to 7) were provided at seven locations in each cathode-side gas flow path along the gas flow direction of the oxidant gas. Among the seven throttle portions, there were four upstream throttle portions and three downstream throttle portions. The upstream throttle portions were throttle portions 1 to 4, and the downstream throttle portions were throttle portions 5 to 7. The length of each throttle portion in the gas flow direction was 33 mm.

[0036] (Comparative Example 1) At all seven throttle portions in each cathode-side gas flow path of the cathode separator, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 3, and the flow path cross-sectional area was narrowed to 6% with respect to 100% of the flow path cross-sectional area of the flow path portion. Hereinafter, a throttle portion with a flow path cross-sectional area narrowed to 6% with respect to 100% of the flow path cross-sectional area of the flow path portion may be referred to as a "normal throttle portion". Hereinafter, a throttle portion with a flow path cross-sectional area narrowed to 30% with respect to 100% of the flow path cross-sectional area of the flow path portion may be referred to as a "throttle portion with a larger flow path cross-sectional area than the normal throttle portion". The ratio of the throttle portion with a larger flow path cross-sectional area than the normal throttle portion in the cathode-side gas flow path was 0%.

[0037] (Example 1) Among the seven throttle portions in each cathode-side gas flow path of the cathode separator, at the upstream throttle portions from the second one from the upstream of the flow path, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 1, and the flow path cross-sectional area was narrowed to 30% with respect to 100% of the flow path cross-sectional area of the flow path portion. In the remaining five throttle portions, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 3, and the flow path cross-sectional area was narrowed to 6% with respect to 100% of the flow path cross-sectional area of the flow path portion. The ratio of the throttle portions in the cathode-side gas flow path having a larger flow path cross-sectional area than the normal throttle portions was 29%.

[0038] (Example 2) Among the seven throttle portions of each cathode-side gas flow path of the cathode separator, in the upstream throttle portions from the upstream side to the third one, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 1, and the flow path cross-sectional area was narrowed to 30% with respect to 100% of the flow path cross-sectional area of the flow path portion. In the remaining four throttle portions, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 3, and the flow path cross-sectional area was narrowed to 6% with respect to 100% of the flow path cross-sectional area of the flow path portion. The ratio of the throttle portions in the cathode-side gas flow path having a larger flow path cross-sectional area than the normal throttle portions was 43%.

[0039] (Example 3) Among the seven throttle portions of each cathode-side gas flow path of the cathode separator, in the upstream throttle portions from the upstream side to the fourth one, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 1, and the flow path cross-sectional area was narrowed to 30% with respect to 100% of the flow path cross-sectional area of the flow path portion. In the remaining three throttle portions, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 3, and the flow path cross-sectional area was narrowed to 6% with respect to 100% of the flow path cross-sectional area of the flow path portion. The ratio of the throttle portions in the cathode-side gas flow path having a larger flow path cross-sectional area than the normal throttle portions was 57%.

[0040] (Comparative Example 2) In all seven throttle portions of each cathode-side gas flow path of the cathode separator, the rib-under convection ratio (Rc / Rb) of the throttle portion was set to 1, and the flow path cross-sectional area was narrowed to 30% with respect to 100% of the flow path cross-sectional area of the flow path portion. The ratio of the throttle portions in the cathode-side gas flow path having a larger flow path cross-sectional area than the normal throttle portions was 100%. Table 2 shows the configurations of the cathode-side gas flow paths of the cathode separators in Examples 1 to 3 and Comparative Examples 1 and 2. Note that the throttle ratio shown in Table 2 means the opening ratio of the throttle portion, and is the ratio (%) of the flow path cross-sectional area of the throttle portion to the flow path cross-sectional area of the flow path portion when the flow path cross-sectional area of the flow path portion is 100%.

[0041]

Table 2

[0042] [Power Generation Performance Evaluation of Fuel Cell] The power generation performances of the fuel cells in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated under the following conditions. Power generation conditions: cell temperature 105°C, oxidant gas (air) dew point 81°C, fuel gas (hydrogen) dew point 74°C, oxidant gas flow rate stoichiometry 1.4, fuel gas flow rate stoichiometry 1.25, gas inlet pressure 280 kPa abs, current density 3.5 A / cm 2 。 For Comparative Example 2 in which the rib-to-convection ratio (Rc / Rb) of all the throttle portions in the cathode-side gas flow path was set to 1, the ratio of the throttle portions provided with a rib-to-convection ratio (Rc / Rb) of 3 was changed as in Comparative Example 1 and Examples 1 to 3, and the power generation performance of the fuel cell was evaluated. The results are shown in FIG. 3 and Table 3.

[0043]

Table 3

[0044] FIG. 3 is a graph showing the relationship between the ratio of the throttle portions having a larger flow path cross-sectional area than the normal throttle portions and the voltage of the fuel cell. As shown in FIG. 3, by setting the cross-sectional area of the downstream throttle portion arranged downstream of the cathode-side gas flow path to 6% with respect to the flow path cross-sectional area of the flow path portion of 100%, and setting the cross-sectional areas of at least two of the upstream throttle portions arranged upstream of the cathode-side gas flow path to 30% with respect to the flow path cross-sectional area of the flow path portion of 100%, an improvement in the voltage of the fuel cell was confirmed.

[0045] In Comparative Example 2 where the rib-under convection ratio (Rc / Rb) of all the throttle portions in the cathode-side gas flow path is 1, in Comparative Example 1 where the rib-under convection ratio (Rc / Rb) of all the throttle portions in the cathode-side gas flow path is 3, the voltage of the fuel cell was improved due to the reduction of the concentration overvoltage. Further, in Example 2 where the rib-under convection ratio (Rc / Rb) of the upstream throttle portions up to the third one from the upstream was set to 1 in consideration of the depletion of moisture in the upstream of the cathode-side gas flow path, it was confirmed that the voltage of the fuel cell was further improved due to the reduction of the resistance overvoltage in addition to the reduction of the concentration overvoltage.

Explanation of Signs

[0046] 10 Cathode-side gas flow path 11 Rib 12 Flow path portion 20 Upstream throttle portion 30 Downstream throttle portion 40 Upstream 50 Downstream

Claims

1. A separator for a fuel cell, comprising: The separator has a plurality of cathode gas flow channels, Each of the cathode gas flow paths has a plurality of flow path portions and a plurality of throttle portions, A flow path cross-sectional area of each of the throttle portions is smaller than a flow path cross-sectional area of each of the flow path portions, At least one of the plurality of throttle portions is an upstream throttle portion disposed upstream of the cathode gas flow passage, At least one of the plurality of throttle portions is a downstream throttle portion disposed downstream of the cathode gas flow passage, a flow path cross-sectional area of the at least one upstream throttle portion is larger than a flow path cross-sectional area of the at least one downstream throttle portion; At least one of the downstream tapered portions satisfies the following formula (1): Rc / Rb>1...Formula (1) Rb is the resistance of the separator ribs to gases penetrating under the ribs, and Rc is the resistance of each of the constrictions.

2. The separator according to claim 1 , wherein a groove depth of the at least one upstream constriction portion is greater than a groove depth of the at least one downstream constriction portion.

3. 2. The separator according to claim 1, wherein in two adjacent cathode side gas flow paths, when the separator is viewed in a plane, each of the throttle portions in one cathode side gas flow path is not adjacent to each of the throttle portions in the other cathode side gas flow path.

4. Each of the cathode gas flow paths has a plurality of the upstream throttle portions and a plurality of the downstream throttle portions, At least one of the plurality of upstream tapered portions satisfies the following formula (2), The separator according to claim 1 , wherein at least one of the plurality of downstream tapered portions satisfies the formula (1). Rc / Rb≦1...Formula (2)

5. Each of the cathode gas flow paths has a plurality of the upstream throttle portions and a plurality of the downstream throttle portions, At least one of the plurality of upstream tapered portions satisfies the following formula (2), The separator according to claim 1 , wherein at least one of the plurality of downstream tapered portions satisfies the following formula (3): Rc / Rb≦1...Formula (2) Rc / Rb≧3...Formula (3)

6. 1. A fuel cell comprising: The fuel cell comprises the separator according to claim 1 as a cathode separator.

7. the fuel cell includes the cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator, The membrane electrode gas diffusion layer assembly of the fuel cell according to claim 6 has, in order from the anode separator side, an anode-side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode-side gas diffusion layer.

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