Polymer electrolyte fuel cell

Abstract

To provide a polymer electrolyte fuel cell having power generation performance that is less likely to decline under a high humidification condition.SOLUTION: A polymer electrolyte fuel cell includes a first cathode gas passage, a second cathode gas passage and a cathode side separator having a rib to partition the first and second cathode gas passages. There are provided, on the surface of the rib, n (n≥2) grooves to connect between the first cathode gas passage and the second cathode gas passage, each of the n grooves being disposed so as to be approximately perpendicular to the rib. At least the two adjacent grooves among the n grooves satisfy SBi / SAi>0.15 and / or SDi / SCi>0.15, where SAi represents an area of a region Ai from an i-th groove to an intermediate line; SBi represents an area of a region Bi where a distance to the i-th groove is shorter than a distance to one of the first or second cathode gas passages; SCi represents an area of a region Ci from the intermediate line to an (i+1)th groove; and SDi represents an area of a region Di where a distance to the (i+1)th groove is shorter than a distance to one of the first or second cathode gas passages.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a polymer electrolyte fuel cell, and more particularly to a polymer electrolyte fuel cell that is resistant to deterioration in power generation performance under highly humidified conditions. [Background technology]

[0002] A polymer electrolyte fuel cell is equipped with a membrane electrode assembly (MEA) in which electrodes (catalyst layers) are bonded to both sides of an electrolyte membrane made of a solid polymer electrolyte. In a polymer electrolyte fuel cell, a gas diffusion layer is generally disposed on the outer side of the catalyst layer. The gas diffusion layer supplies reactant gases and electrons to the catalyst layer, and is made of carbon paper, carbon cloth, or the like. An assembly in which gas diffusion layers are disposed on both sides of an MEA is also called a membrane-electrode-gas diffusion layer assembly (MEGA). Furthermore, a separator with a gas flow path is arranged on the outside of the gas diffusion layer. A polymer electrolyte fuel cell usually has a structure (fuel cell stack) in which a plurality of unit cells each consisting of such an MEA, gas diffusion layer, and separator are stacked.

[0003] In polymer electrolyte fuel cells, the electrolyte membrane must maintain a moderate water content to exhibit good proton conductivity. Therefore, if the temperature of the fuel cell is high during power generation or if the water content of the supply gas is low, the electrolyte membrane will dry out and performance will deteriorate. On the other hand, when generating electricity using a polymer electrolyte fuel cell, water is produced by an electrode reaction on the cathode side. Therefore, when the temperature of the fuel cell is low and the water content in the supply gas is high, water is likely to be produced in the gas diffusion layer on the cathode side. Excess water inhibits oxygen transport and causes a decrease in fuel cell performance.

[0004] Therefore, various proposals have been made in the past to solve this problem. For example, Patent Document 1 states: A plurality of gas flow paths and a plurality of ribs are alternately arranged, The rib is provided with a narrowed portion for partially reducing the cross section of the gas flow path, The surface of the narrowed portion is provided with grooves for communicating adjacent gas flow paths. A separator is disclosed.

[0005] The same document states: (A) If a narrowed portion without a groove is provided in the gas flow channel, the water inside the membrane electrode assembly can be discharged into the gas flow channel, but the pressure loss increases; and (B) By providing a groove in the narrowed portion to allow communication between the gas flow paths, the increase in pressure loss can be suppressed. is stated.

[0006] Patent Document 2 states: A plurality of ribs (convex portions) and a plurality of gas flow paths (concave portions) are alternately arranged, A thin film having electrical conductivity and hydrophilicity is formed on the top surface of the rib, The thin film has grooves for communicating adjacent gas flow paths, A narrowed section (a section that increases flow resistance) is provided on the downstream side of the groove to reduce the cross-sectional area of ​​the gas flow path. A separator is disclosed.

[0007] The same document states: (A) When a groove is provided upstream of the narrowed portion, part of the oxidant gas passes through the groove, so that the water discharged into the groove is easily discharged into the gas flow path. (B) When a material having a higher conductivity than the separator substrate is used as the material for the thin film, an increase in contact resistance between the membrane electrode assembly and the separator substrate can be suppressed, and (C) If a material with higher hydrophilicity than the separator substrate is used as the material for the thin film, water will be more easily discharged into the grooves. is stated.

[0008] As described in Patent Documents 1 and 2, providing grooves on the surface of a rib improves drainage. However, when providing only one groove on the surface of a rib or when providing two intersecting grooves on the surface of a rib, the grooves may not sufficiently improve drainage. Furthermore, as described in Patent Document 2, the method of forming a thin film on the surface of the rib (surface of the convex portion) and then forming grooves in the thin film leads to an increase in costs due to the thin film. Furthermore, there have been no examples of separators that exhibit high water drainage even under high humidity conditions, and no examples of fuel cells equipped with such separators. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2022-169222 [Patent Document 2] Japanese Patent Publication No. 2020-123547 Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is to provide a polymer electrolyte fuel cell that is less likely to experience a decrease in power generation performance under highly humidified conditions. [Means for solving the problem]

[0011] In order to solve the above problems, the polymer electrolyte fuel cell according to the present invention has the following configuration. (1) The polymer electrolyte fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode-side catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode-side catalyst layer; an anode-side separator disposed on the outer side of the anode-side gas diffusion layer; a cathode-side separator disposed on the outside of the cathode-side gas diffusion layer; It is equipped with: (2) The cathode separator is a first cathode gas flow path; a second cathode gas flow channel disposed adjacent to the first cathode gas flow channel; a rib that separates the first cathode gas flow channel and the second cathode gas flow channel; It is equipped with: (3) The rib has n (n≧2) grooves formed on the contact surface with the cathode-side gas diffusion layer for connecting the first cathode gas flow channel and the second cathode gas flow channel, The n grooves are arranged so as not to intersect with each other, Among the n grooves, at least two adjacent grooves satisfy the following formula (1) and / or formula (2).

[0012] S Bi / S Ai >0.15 …(1) S Di / S Ci >0.15 …(2) however, S Ai is the area A from the i-th (1≦i≦n−1) groove to the midline between the i-th groove and the (i+1)-th groove in the contact surface between the rib and the cathode-side gas diffusion layer. i Area of, S Bi is a region B in the contact surface where the shortest distance to the i-th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of, S Ci is the area C of the contact surface from the midline to the (i+1)th groove i Area of, S Di is a region D in the contact surface where the shortest distance to the (i+1)th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of. [Effects of the Invention]

[0013] When grooves are provided on the surface of the separator ribs, the water staying at a certain point X in the gas diffusion layer directly below the ribs may be discharged either to the gas flow path or the grooves. Here, let the shortest distance from point X to the grooves be Lg, and the shortest distance from point X to the gas flow path be Lf. In this case, when Lg < Lf, the probability that the water staying at point X is discharged to the grooves increases. Conversely, when Lg > Lf, the water staying at point X is likely to stay at point X as it is, or is discharged to the gas flow path. Therefore, when the interval between the grooves is relatively shortened so as to satisfy formula (1) and / or formula (2), the discharge of water through the grooves is promoted.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram of the contact surface between the rib including the grooves and the cathode side gas diffusion layer. [Figure 2] It is a schematic diagram of a separator having a structure in which the cross-sectional area ratio (S2in / S1in) at the inlet of the gas flow path is different from the cross-sectional area ratio (S2out / S1out) at the outlet. [Figure 3] It is a schematic diagram of the pattern of the grooves formed on the rib. [Figure 4] Figure 4(A) is a schematic diagram of the drainage process of the water generated directly below the rib when the interval between the grooves is 2.4 mm. Figure 4(B) is a schematic diagram of the drainage process of the water generated directly below the rib when the interval between the grooves is 0.96 mm. Figure 4(C) is a cross-sectional view taken along the line A - A' of Figure 4(A). [Figure 5] It is a diagram showing the relationship between the ratio (w / 2p) of the region where the grooves are closer than the flow path and the liquid water thickness.

Embodiments for Carrying Out the Invention

[0015] [Configuration 1] A solid polymer fuel cell having the following configuration. (1) The solid polymer fuel cell a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode-side catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode-side catalyst layer; an anode-side separator disposed on the outer side of the anode-side gas diffusion layer; a cathode-side separator disposed on the outside of the cathode-side gas diffusion layer; It is equipped with: (2) The cathode separator is a first cathode gas flow path; a second cathode gas flow channel disposed adjacent to the first cathode gas flow channel; a rib that separates the first cathode gas flow channel and the second cathode gas flow channel; It is equipped with: (3) The rib has n (n≧2) grooves formed on the contact surface with the cathode-side gas diffusion layer for connecting the first cathode gas flow channel and the second cathode gas flow channel, The n grooves are arranged so as not to intersect with each other, Among the n grooves, at least two adjacent grooves satisfy the following formula (1) and / or formula (2).

[0016] S Bi / S Ai >0.15 …(1) S Di / S Ci >0.15 …(2) however, S Ai is the area A from the i-th (1≦i≦n−1) groove to the midline between the i-th groove and the (i+1)-th groove in the contact surface between the rib and the cathode-side gas diffusion layer. i Area of, S Bi is a region B in the contact surface where the shortest distance to the i-th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of, S Ciis the area C of the contact surface from the midline to the (i+1)th groove i Area of, S Di is a region D in the contact surface where the shortest distance to the (i+1)th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of.

[0017] [Configuration 2] The n grooves are arranged at substantially equal intervals, and / or The n grooves are arranged so as to be substantially perpendicular to the ribs. 10. The polymer electrolyte fuel cell according to claim 1.

[0018] [Configuration 3] the cathode-side separator and / or the cathode-side gas diffusion layer has a cross-flow region; 3. The polymer electrolyte fuel cell according to claim 1, wherein at least two of the grooves are formed on the surface of the rib located within the cross-flow region. The "crossflow region" refers to a region including the contact surface between the rib and the cathode-side gas diffusion layer, where gas flow (crossflow) occurs between the cathode gas flow channels through the cathode-side gas diffusion layer.

[0019] [Configuration 4] The cathode-side separator comprises: (a) Channel structure with a constriction, (b) an alternating occlusion type flow channel structure; and (c) End-narrowed flow channel structure 4. A polymer electrolyte fuel cell according to any one of configurations 1 to 3, comprising one or more structures selected from the group consisting of:

[0020] An embodiment of the present invention will be described in detail below. [1. Polymer electrolyte fuel cell] The polymer electrolyte fuel cell according to the present invention comprises: a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode-side catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode-side catalyst layer; an anode-side separator disposed on the outer side of the anode-side gas diffusion layer; a cathode-side separator disposed on the outside of the cathode-side gas diffusion layer; It is equipped with:

[0021] [1.1. Membrane electrode assembly] The membrane electrode assembly (MEA) consists of a cathode catalyst layer and an anode catalyst layer bonded to both sides of an electrolyte membrane made of a solid polymer electrolyte. The cathode catalyst layer and the anode catalyst layer each consist of a composite of an electrode catalyst and a catalyst layer ionomer. In the present invention, the type of solid polymer electrolyte constituting the electrolyte membrane is not particularly limited, and an optimum material can be selected depending on the purpose. Similarly, the types of electrode catalyst and catalyst layer ionomer contained in the catalyst layer are not particularly limited, and the most suitable materials can be selected depending on the purpose.

[0022] [1.2. Anode-side gas diffusion layer] The anode-side gas diffusion layer is disposed on the outer side of the anode-side catalyst layer. In the present invention, the structure and material of the anode-side gas diffusion layer are not particularly limited, and an optimum material can be selected depending on the purpose. The anode-side gas diffusion layer is particularly A water-repellent treated substrate; a water-repellent layer formed on the catalyst layer side surface of the substrate; It is preferable that the device has the following.

[0023] [1.3. Cathode-side gas diffusion layer] The cathode-side gas diffusion layer is disposed on the outer side of the cathode-side catalyst layer. In the present invention, the structure and material of the cathode-side gas diffusion layer are not particularly limited, and an optimum material can be selected depending on the purpose. The cathode-side gas diffusion layer is particularly A water-repellent treated substrate; a water-repellent layer formed on the catalyst layer side surface of the substrate; It is preferable that the device has the following.

[0024] Optimizing the structure of the cathode-side gas diffusion layer and / or cathode-side separator may sometimes result in a crossflow, where "crossflow" refers to the gas flow between cathode gas channels through the cathode-side gas diffusion layer. The cathode-side gas diffusion layer may have a region where such crossflow can occur (hereinafter simply referred to as a "crossflow region"), or may not have such a region. If the cathode-side gas diffusion layer has a crossflow region, the discharge of water remaining in the cathode-side gas diffusion layer may be promoted. Details of the crossflow region will be described later.

[0025] [1.4. Anode side separator] The anode-side separator extracts electrons from the anode-side catalyst layer and supplies anode gas (fuel gas) to the anode-side catalyst layer. The anode-side separator is disposed on the outside of the anode-side gas diffusion layer. The anode-side separator is provided with an anode gas flow path for the anode gas to flow. In the present invention, the structure and material of the anode-side separator are not particularly limited, and an optimum structure and material can be selected depending on the purpose. The anode-side separator may have the same structure as the cathode-side separator described below, or may have a different structure.

[0026] [1.6. Cathode-side separator] The cathode-side separator is for supplying electrons and cathode gas (oxidant gas) to the cathode-side catalyst layer. The cathode-side separator is disposed on the outer side of the cathode-side gas diffusion layer. In the present invention, the cathode-side separator is a first cathode gas flow path; a second cathode gas flow channel disposed adjacent to the first cathode gas flow channel; a rib that separates the first cathode gas flow channel and the second cathode gas flow channel; It is equipped with:

[0027] [1.6.1. Materials] In the present invention, the material of the cathode separator is not particularly limited, and an optimum material can be selected depending on the purpose. Examples of the material of the cathode separator include stainless steel and carbon.

[0028] 1.6.2. Gas flow path and rib structure In the present invention, the structures of the first cathode gas flow channel, the second cathode gas flow channel, and the ribs are not particularly limited, and an optimum structure can be selected depending on the purpose. For example, the first cathode gas flow path, the second cathode gas flow path, and the ribs may have a structure that extends linearly from one end to the other end of the cathode-side separator, or may have a bent or curved structure. Furthermore, the numbers of the first cathode gas flow channels, the second cathode gas flow channels, and the ribs are not particularly limited, and the optimum numbers can be selected depending on the purpose.

[0029] The cathode-side separator may or may not have a cross-flow region. If the cathode-side separator has a cross-flow region, the discharge of water remaining in the cathode-side gas diffusion layer may be promoted. Furthermore, if the cathode-side separator has a cross-flow region and grooves are formed on the surface of the ribs within the cross-flow region, the discharge of water remaining in the cathode-side gas diffusion layer may be further promoted.

[0030] [1.6.3. Groove] In the present invention, the rib has n (n≧2) grooves formed on the surface that comes into contact with the cathode-side gas diffusion layer, for connecting the first cathode gas flow channel and the second cathode gas flow channel. The n grooves are arranged so as not to intersect with each other. Furthermore, among the n grooves, at least two adjacent grooves satisfy the formula (1) and / or formula (2) described below.

[0031] [A. Number of grooves] The number of grooves formed on the surface of the rib may be two or more. Generally, the more grooves there are, the more easily water is expelled through the grooves. On the other hand, even if the number of grooves is increased more than necessary, there is no difference in the effect and no practical benefit. Therefore, it is preferable to select the optimal number of grooves within a range that satisfies the conditions described below.

[0032] If the cathode separator has a crossflow region, it is preferable that at least two of the grooves are formed on the surface of the rib within the crossflow region. In general, the more grooves formed in the crossflow region, the easier it is for water retained in the cathode gas diffusion layer to be discharged. The number of grooves formed in the crossflow region is more preferably 3 or more, 4 or more, 5 or more, 6 or more, or 7 or more.

[0033] Even if the grooves are formed outside the crossflow region, a pressure difference may accidentally occur between the first and second cathode gas channels. When a pressure difference occurs between the gas channels, the cathode gas flows from the opening of the groove on the high-pressure side to the opening of the groove on the low-pressure side. As a result, water discharged into the groove is pushed into the gas channel on the low-pressure side. When grooves are formed in the crossflow region, crossflow is promoted in the region where the grooves are formed, and therefore, when grooves are formed in the crossflow region, the discharge of water remaining in the cathode-side gas diffusion layer is promoted compared to when grooves are formed outside the crossflow region.

[0034] [B. Groove Spacing] The groove spacing is (a) The intersection of the center line of the rib and the outer edge of the i-th groove (the outer edge of the (i+1)-th groove side), (b) The intersection of the center line of the rib and the outer edge of the (i+1)th groove (the outer edge of the i-th groove side) The distance between In the present invention, the grooves may be arranged at approximately equal intervals or at different intervals, as long as the conditions described below are met. It is particularly preferable that the grooves are arranged at approximately equal intervals, which can prevent water from accumulating locally in the cathode-side gas diffusion layer immediately below the ribs.

[0035] Here, "grooves are arranged at approximately equal intervals" means that the coefficient of variation of the groove spacing (=standard deviation of groove spacing / average groove spacing) is equal to or less than a predetermined critical value. In order to prevent localized water accumulation, the smaller the coefficient of variation (CV) of the groove spacing, the better. Specifically, the CV is preferably 0.20 or less. The CV is more preferably 0.15 or less, 0.10 or less, or 0.05 or less.

[0036] [C. Groove Angle] The "groove angle" refers to the angle between the longitudinal direction of the groove and the center line direction of the rib. The "longitudinal direction of the groove" refers to the direction from the opening of the groove on the first cathode gas flow channel side to the opening of the groove on the second cathode gas flow channel side, or the opposite direction. The "direction of the center line of the rib" refers to the direction of the tangent to the center line of the rib that passes through the intersection of the center line of the rib and the center line of the groove.

[0037] In the present invention, the grooves may be arranged so as to be approximately perpendicular to the ribs, or may not be arranged so as to be approximately perpendicular to the ribs. In particular, the grooves are preferably arranged so as to be approximately perpendicular to the ribs. When the grooves are arranged so as to be approximately perpendicular to the ribs, the grooves are easily processed and the groove spacing (i.e., drainage performance) is easily adjusted.

[0038] Here, "the grooves are substantially perpendicular to the ribs" means that the deviation of the groove angle from 90° is less than a predetermined critical value. To facilitate groove processing and adjustment of drainage, the groove angle is preferably 90°±10°. The groove angle is more preferably 90°±5°.

[0039] [D. Equation (1) and Equation (2)] In the present invention, of the n grooves, at least two adjacent grooves satisfy the following formula (1) and / or formula (2). The higher the percentage of grooves that satisfy formulas (1) and (2), the better. To improve drainage, the percentage is preferably 50% or more. The percentage is preferably 70% or more, or 90% or more. When all of the n grooves satisfy formulas (1) and (2), the highest drainage is achieved.

[0040] S Bi / S Ai >0.15 …(1) S Di / S Ci >0.15 …(2) however, S Ai is the area A from the i-th (1≦i≦n−1) groove to the midline between the i-th groove and the (i+1)-th groove in the contact surface between the rib and the cathode-side gas diffusion layer. i Area of, S Bi is a region B in the contact surface where the shortest distance to the i-th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of, S Ci is the area C of the contact surface from the midline to the (i+1)th groove i Area of, S Di is a region D in the contact surface where the shortest distance to the (i+1)th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of.

[0041] "Median line" refers to the line connecting the first midpoint and the second midpoint. The "first midpoint" refers to the midpoint of the line connecting the opening end of the i-th groove on the first cathode gas flow channel side and the opening end of the (i+1)-th groove on the first cathode gas flow channel side. The "second midpoint" refers to the midpoint of the line connecting the open end of the ith groove on the second cathode gas flow channel side and the open end of the (i+1)th groove on the second cathode gas flow channel side.

[0042] Figure 1 shows a schematic diagram of the contact surface between a rib containing grooves and a cathode-side gas diffusion layer. Only the region between the i-th groove and the (i+1)-th groove of the contact surface is shown in Figure 1. In Figure 1, the vertical direction of the paper represents the longitudinal direction of the rib. w i is the length of the ith groove in the contact area between the rib and the cathode diffusion layer. i+1 represents the length of the (i+1)th groove in the contact surface between the rib and the cathode-side catalyst layer. i represents the distance between the i-th groove and the (i+1)-th groove. Furthermore, the i-th groove and the (i+1)-th groove are arranged so as to be perpendicular to the cathode gas flow path.

[0043] In addition, if the cross section of the rib perpendicular to the longitudinal direction of the rib is rectangular, w i and w i+1 are the same as the width of the actual groove formed on the rib. On the other hand, if the cross section of the rib is not rectangular (for example, if the cross section of the rib is rounded), w i and w i+1 may be shorter than the width of the actual groove formed on the rib.

[0044] Water tends to accumulate in the cathode gas diffusion layer directly below the rib. The water in the area from the i-th groove to the midline between the grooves (area A i ) has a high probability of being discharged to either the cathode gas flow passages on the left and right sides of the rib or the i-th groove.

[0045] The triangular area drawn under the i-th groove (area Bi ) represents the region where the shortest distance Lg from point X on the contact surface to the i-th groove is shorter than the shortest distance Lf from point X to the cathode gas flow channel. i The probability that the water remaining in the area B will be discharged to the i-th groove is high. i Area A excluding i is a region where Lg>Lf, the water that has accumulated there will either remain at point X or will be highly likely to be discharged into the cathode gas flow channel.

[0046] Similarly, the area from the midline between the grooves to the (i+1)th groove (area C i ) has a high probability of being discharged to either the cathode gas flow passages on the left and right sides of the rib or the (i+1)th groove. The triangular area drawn on the (i+1)th groove (area D i ) represents the region where the shortest distance Lg from point X to the (i+1)th groove is shorter than the shortest distance Lf to the cathode gas flow path. i The water remaining in the (i+1)th groove has a high probability of being discharged to the (i+1)th groove. i Area C excluding i is a region where Lg>Lf, the water that has accumulated there will either remain at point X or will be highly likely to be discharged into the cathode gas flow channel.

[0047] In general, S Bi / S Ai and / or S Di / S Ci The larger the area, the more water is expelled through the grooves. i To promote the discharge of water that has accumulated in the Bi / S Ai must be greater than 0.15. Bi / S Ai is preferably 0.175 or more, 0.20 or more, 0.225 or more, 0.25 or more, 0.275 or more, or 0.30 or more. Similarly, area C iTo promote the discharge of water that has accumulated in the Di / S Ci must be greater than 0.15. Di / S Ci is preferably 0.175 or more, 0.20 or more, 0.225 or more, 0.25 or more, 0.275 or more, or 0.30 or more.

[0048] w i =w i+1 If area A i The area of ​​is w i ×p i / 2, and area B i The area of ​​is w i 2 Similarly, the area C i The area of ​​is w i+1 ×p i / 2, and the area D i The area of ​​is w i+1 2 / 4. Therefore, w i =w i+1 In this case, formulas (1) and (2) can also be expressed as the following formulas (1′) and (2′). p i ×0.3 <w i …(1') p i ×0.3 <w i+1 …(2')

[0049] In addition, w i ≠w i+1 If the i-th groove and the (i+1)-th groove are arranged non-parallel, or if the areas above and below the midline are not identical (A i ≠C i ), if the groove width and groove length are optimized to satisfy formula (1) and / or formula (2), a corresponding effect can be obtained.

[0050] [E. Groove Depth] The depth of the grooves may be different for each groove or may be the same for each groove, but in order to facilitate the processing of the grooves, it is preferable that the depth of each groove is the same. The depth of the grooves is not particularly limited, and an optimum value can be selected depending on the purpose. Generally, the deeper the grooves, the more easily the water is discharged through the grooves. On the other hand, even if the grooves are made deeper than necessary, there is no difference in the effect and no practical benefit. It is preferable to select an optimum value for the depth of the grooves taking these points into consideration.

[0051] [F. Groove Width] The width of each groove may be different from one another or may be the same, but in order to facilitate the processing of the grooves, it is preferable that the width of each groove is the same. The width of the groove is not particularly limited, and an optimum value can be selected depending on the purpose. Generally, the wider the groove width, the more easily water is discharged through the groove. It is preferable to select an optimum value for the groove width taking these points into consideration.

[0052] [1.7. Crossflow Region] Overview The cathode-side separator and / or the cathode-side gas diffusion layer may have a cross-flow region. When the cathode-side separator and / or the cathode-side gas diffusion layer has a cross-flow region, a large pressure difference occurs between the gas flow channels. Therefore, forming two or more grooves on the surface of the rib in the cross-flow region makes it easier for the cathode gas to flow through the grooves, and water remaining in the grooves is more easily discharged into the gas flow channels.

[0053] Here, the "crossflow region" refers to a region where crossflow occurs within the region including the contact surface between the rib and the cathode-side gas diffusion layer. "Crossflow" refers to the gas flow between cathode gas flow channels through the cathode-side gas diffusion layer. In other words, when the first cathode gas flow channel and the second cathode gas flow channel are arranged adjacent to each other with a rib in between, all or part of the cathode gas flowing through either the first cathode gas flow channel or the second cathode gas flow channel passes through the cathode-side gas diffusion layer located immediately below the rib and flows to the other channel.

[0054] The crossflow volume in the crossflow region is (a) the structure of the cathode-side separator (e.g., the cross-sectional area of ​​the cathode gas flow channel, the arrangement of the cathode gas flow channel, etc.), and / or (b) The structure of the cathode-side gas diffusion layer (e.g., the in-plane permeability coefficient of the cathode-side gas diffusion layer (especially the in-plane permeability coefficient of the cathode-side gas diffusion layer directly under the rib) and the thickness of the cathode-side gas diffusion layer (especially the thickness of the cathode gas diffusion layer directly under the rib)). It can be controlled by:

[0055] There are various cathode separator structures that can generate crossflow. (a) Channel structure with a constriction, (b) Alternating blockage type flow channel structure; (c) End-narrowed flow channel structure The cathode separator may contain one of these structures, or may contain two or more of them.

[0056] 1.7.2. Cathode-side separator with narrowed flow channel structure "Flow path structure with a narrowed section" means (a) A plurality of cathode gas flow paths, each open at both ends, are arranged in one direction; (b) At least one cathode gas flow channel has a non-uniform cross-sectional area and has a narrowed portion (a region where the cross-sectional area of ​​the flow channel is locally reduced) in the middle of the flow channel. This refers to the structure.

[0057] Note that "multiple cathode gas flow channels are arranged in one direction" does not necessarily mean that the multiple cathode gas flow channels are arranged perfectly parallel (i.e., the angle between the center lines of two cathode gas flow channels is zero), but rather means that the arrangement of the multiple cathode gas flow channels may be slightly deviated from perfect parallelism as long as the cathode gas can flow in approximately the same direction. The angle between the center lines of two cathode gas flow channels is preferably 10° or less, or 5° or less.

[0058] In a cathode-side separator with a flow channel structure with constrictions, cathode gas is introduced into one end of each cathode gas channel and flows in the same direction through each channel. When the cathode gas introduced into a cathode gas channel reaches a constriction, the pressure of the cathode gas increases. As a result, some of the cathode gas passes through the cathode-side gas diffusion layer located directly below the rib and flows into the adjacent cathode gas channel (i.e., crossflow occurs). In this case, the amount of crossflow can be controlled by optimizing the number, position, and cross-sectional area of ​​the constrictions. Furthermore, if two or more grooves are formed at a predetermined interval on the surface of the narrowed portion or the rib on the upstream side thereof, the discharge of water through the grooves can be promoted.

[0059] 1.7.3. Cathode-side separator with alternating blocked flow channel structure "Alternate blocked flow channel structure" means: (a) Multiple cathode gas flow paths are arranged in one direction, (b) A first cathode gas flow channel with a blocked outlet side and a second cathode gas flow channel with a blocked inlet side are arranged adjacent to each other. This refers to the structure.

[0060] In a cathode-side separator with an alternating blocked flow channel structure, cathode gas is introduced into the inlet of the first cathode gas channel. Because the outlet of the first cathode gas channel is blocked, when cathode gas is introduced into the first cathode gas channel, the pressure inside the first cathode gas channel increases. As a result, the cathode gas in the first cathode gas channel cross-flows into the adjacent second cathode gas channel. The cathode gas that has flowed into the second cathode gas channel is discharged from the outlet of the second cathode gas channel.

[0061] In this case, the cross flow amount can be controlled by optimizing the in-plane permeability coefficient of the cathode side gas diffusion layer and the thickness of the cathode side gas diffusion layer. The in-plane permeability coefficient of the cathode-side gas diffusion layer can be controlled, for example, by the penetration depth of the water-repellent layer (microporous layer) into the substrate. The amount of crossflow can also be controlled by, for example, the height and width of the ribs and the thickness of the cathode-side gas diffusion layer immediately below the ribs. Furthermore, if two or more grooves are provided at a predetermined interval on the surface of the rib near the closed end of the first cathode gas flow channel or on the upstream side thereof, it is possible to promote the discharge of water through the grooves.

[0062] 1.7.4. Cathode-Side Separator with End-Narrowed Flow Channel Structure "End narrowed flow channel structure" means (a) Multiple cathode gas flow paths are arranged in one direction, (b) A first cathode gas flow channel having a narrowed outlet side and a second cathode gas flow channel having a narrowed inlet side are arranged adjacent to each other. This refers to the structure.

[0063] In a cathode-side separator with an end-narrowed flow channel structure, cathode gas is introduced into one end of the first and second cathode gas channels and flows in the same direction through the first and second cathode gas channels. Because the outlet of the first cathode gas channel is narrowed, when cathode gas is introduced into the first cathode gas channel, the pressure within the first cathode gas channel increases. As a result, part of the cathode gas in the first cathode gas channel cross-flows into the adjacent second cathode gas channel.

[0064] In this case, the cross flow amount can be controlled by optimizing the in-plane permeability coefficient of the cathode gas diffusion layer and the thickness of the cathode gas diffusion layer. Furthermore, if two or more grooves are provided at a predetermined interval on the surface of the rib near the outlet of the first cathode gas flow channel or on the upstream side thereof, it is possible to promote the discharge of water through the grooves.

[0065] [2. Effect] In ribbed separators, a flow path for cooling water is usually provided on the back side of the ribs (the side opposite the contact surface with the gas diffusion layer). When both sides of a membrane-electrode-gas diffusion layer assembly (MEGA) are sandwiched between such ribbed separators, the temperature of the gas diffusion layer directly below the ribs on the cathode separator drops. As a result, water tends to accumulate in the gas diffusion layer directly below the ribs.

[0066] In this case, if grooves connecting the gas flow paths are provided on the surface of the rib, water remaining in the gas diffusion layer is easily discharged into the grooves. Furthermore, the water discharged into the grooves is easily discharged into the gas flow paths by the cathode gas flowing into the grooves. However, if the number and arrangement of the grooves provided on the rib are inappropriate, water may not be sufficiently discharged through the grooves.

[0067] On the other hand, when grooves are provided on the surface of the ribs of the separator, water staying at a certain point X in the gas diffusion layer directly below the rib may be discharged either to the gas flow path or the grooves. Here, let the shortest distance from point X to the grooves be Lg, and the shortest distance from point X to the gas flow path be Lf. In this case, when Lg < Lf, the probability that the water staying at point X is discharged to the grooves increases. Conversely, when Lg > Lf, the water staying at point X is likely to remain at point X or be discharged to the gas flow path. Therefore, when the interval between the grooves is relatively shortened so as to satisfy Equation (1) and / or Equation (2), the discharge of water through the grooves is promoted.

Example

[0068] [1. Fabrication of fuel cell] FIG. 2 shows a schematic diagram of a separator having a structure in which the cross-sectional area ratio (S 2in / S 1in ) of the inlet of the gas flow path is different from the cross-sectional area ratio (S 2out / S 1out ) of the outlet. In FIG. 2, the separator 10 includes ribs 12, and first and second cathode gas flow paths 14 and 16 that are arranged in parallel with the ribs 12 interposed therebetween.

[0069] A first gas introduction pipe 14a is connected to the inlet of the first cathode gas flow path 14, and a first gas discharge pipe 14b is connected to the outlet of the first cathode gas flow path 14. The cross-sectional area (S 1in ) of the first gas introduction pipe 14a is larger than the cross-sectional area (S 1out ) of the first gas discharge pipe 14b. On the other hand, a second gas introduction pipe 16a is connected to the inlet of the second cathode gas flow path 16, and a second gas discharge pipe 16b is connected to the outlet of the second cathode gas flow path 16. The cross-sectional area (S 2in ) of the second gas introduction pipe 16a is smaller than the cross-sectional area (S 2out ) of the second gas discharge pipe 16b. Therefore, the separator 10 has S 2in / S 1in < S 2out / S 1outThe relationship is fulfilled.

[0070] When gas is supplied to each of the first cathode gas flow channel 14 and the second cathode gas flow channel 16 of the separator 10 having such a structure, the pressure in the first cathode gas flow channel 14 becomes higher than the pressure in the second cathode gas flow channel 16. As a result, part of the gas supplied to the first cathode gas flow channel 14 is forced out into the second cathode gas flow channel 16 through the cathode-side gas diffusion layer 18.

[0071] As shown in Figure 2, a separator 10 was used for the cathode separator, with the diameter of the piping connected to the gas flow channel tapered in an alternating manner. A separator with the same diameter of the piping connected to the gas flow channel was used for the anode separator. A cathode gas diffusion layer, a Nafion (registered trademark) membrane coated with catalyst layers on both sides, and an anode gas diffusion layer were sandwiched between these separators to fabricate a fuel cell. The length of the gas flow channel was 6.0 mm. The width of the cathode separator was 2.7 mm.

[0072] Grooves were formed on the ribs of the cathode-side separator. Figure 3 shows a schematic diagram of the groove pattern formed on the rib. Note that Figure 3 corresponds to a schematic diagram of the cathode-side separator viewed from the GDL side. Nine, six, or three grooves were formed at approximately equal intervals so as to be approximately perpendicular to the rib. The groove intervals were 0.6 mm, 0.96 mm, or 2.4 mm, respectively. The groove depth was 0.03 mm, and the groove width was 0.15 mm. Furthermore, for comparison, a fuel cell was fabricated that had a cathode separator with no grooves formed on the ribs.

[0073] 2. Test Method Using this fuel cell, power was generated at a cell temperature of 40°C and a voltage of 0.1 V, and the amount of liquid water in the gas diffusion layer during power generation was quantified. The cathode gas supplied during power generation was air, and the anode gas was H2. The flow rate of the cathode gas was 380 cm 3 / min, and the relative humidity of the cathode gas was 80% RH. The liquid water distribution during power generation was quantified by X-ray radiography measurements as shown in Reference 1. [Reference 1] D. Hayashi et al., Synchrotron X-Ray Visualization and Simulation for Operating Fuel Cell Diffusion Layers, SAE, 2017-01-1181

[0074] [3. Results] The results are shown in Table 1. In Table 1, the liquid water thickness represents the thickness of the liquid water in the X-ray transmission direction (6 mm). The amount of liquid water was smallest when the groove spacing was 0.6 mm. When the groove spacing was 0.96 mm, the amount of liquid water increased slightly, but was still less than when there were no grooves. On the other hand, when the groove spacing was 2.4 mm, the amount of liquid water was the same as when there were no grooves. Table 1 shows that in order to improve drainage, it is necessary to make the spacing of the grooves formed on the rib smaller to a certain extent.

[0075] [Table 1]

[0076] The relationship between the spacing of the grooves on the ribs and drainage performance can be considered from the drainage process of water generated in the gas diffusion layer directly below the ribs. Figure 4(A) shows a schematic diagram of the drainage process of water generated directly below the ribs when the groove spacing is 2.4 mm. Figure 4(B) shows a schematic diagram of the drainage process of water generated directly below the ribs when the groove spacing is 0.96 mm. Figure 4(C) shows a cross-sectional view taken along line A-A' in Figure 4(A).

[0077] It is believed that water generated directly below the ribs is discharged from either the gas flow path or the groove, whichever is closer. However, when the groove spacing is 2.4 mm, a large proportion of the water trapped directly below the ribs is located near the gas flow path, so it is thought that drainage is the same as when there are no grooves. See Figure 4(A). On the other hand, when the groove spacing is 0.96 mm, the proportion of water near the grooves increases, which is thought to improve drainage (see Figure 4(B)).

[0078] When the grooves are arranged at approximately equal intervals and approximately perpendicular to the rib, the groove spacing is p, and the groove width w is constant, the ratio of the area closer to the flow path to the grooves can be expressed as w / 2p. Figure 5 shows the relationship between the ratio (w / 2p) of the area closer to the flow path to the grooves and the liquid water thickness. From Figure 5, it can be seen that in order to keep the liquid water thickness at 0.45 mm or less, w / 2p > 0.15.

[0079] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0080] The polymer electrolyte fuel cell according to the present invention can be used as an in-vehicle power source, a small stationary power generator, and the like.

Claims

1. A polymer electrolyte fuel cell having the following configuration: (1) The polymer electrolyte fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode-side catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode-side catalyst layer; an anode-side separator disposed on the outer side of the anode-side gas diffusion layer; a cathode-side separator disposed on the outside of the cathode-side gas diffusion layer; It is equipped with: (2) The cathode-side separator is a first cathode gas flow path; a second cathode gas flow channel disposed adjacent to the first cathode gas flow channel; a rib that separates the first cathode gas flow channel and the second cathode gas flow channel; It is equipped with: (3) The rib has n (n≧2) grooves formed on a contact surface with the cathode-side gas diffusion layer for connecting the first cathode gas flow channel and the second cathode gas flow channel, The n grooves are arranged so as not to intersect with each other, Among the n grooves, at least two adjacent grooves satisfy the following formula (1) and / or formula (2). S Bi / S Ai >0.15 …(1) S Di / S Ci >0.15 …(2) however, S Ai is the area A from the i-th (1≦i≦n−1) groove to the midline between the i-th groove and the (i+1)-th groove in the contact surface between the rib and the cathode-side gas diffusion layer. i Area of, S Bi is a region B in the contact surface where the shortest distance to the i-th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of, S Ci is the area C of the contact surface from the intermediate line to the (i+1)th groove i Area of, S Di is a region D in the contact surface where the shortest distance to the (i+1)th groove is shorter than the shortest distance to the first cathode gas flow channel or the second cathode gas flow channel. i Area of.

2. The n grooves are arranged at substantially equal intervals, and / or The n grooves are arranged so as to be substantially perpendicular to the ribs. The polymer electrolyte fuel cell according to claim 1 .

3. the cathode-side separator and / or the cathode-side gas diffusion layer has a cross-flow region; 2. The polymer electrolyte fuel cell according to claim 1, wherein at least two of the grooves are formed on the surface of the rib within the cross-flow region. The "crossflow region" refers to a region including the contact surface between the rib and the cathode-side gas diffusion layer, where gas flow (crossflow) occurs between the cathode gas flow channels through the cathode-side gas diffusion layer.

4. The cathode-side separator comprises: (a) A flow channel structure with a constriction; (b) an alternating occlusion type flow channel structure; and (c) End narrowed flow channel structure 2. The polymer electrolyte fuel cell according to claim 1, comprising at least one structure selected from the group consisting of:

Images