WO2012090049A1

WO2012090049A1 - Fuel cell

Info

Publication number: WO2012090049A1
Application number: PCT/IB2011/003119
Authority: WO
Inventors: Shigetaka Hamada
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2010-12-28
Filing date: 2011-12-22
Publication date: 2012-07-05
Also published as: JP2012142135A

Abstract

A fuel cell includes a membrane electrode assembly (10), an anode-side gas diffusion layer (12) and a cathode-side gas diffusion flayer (14) joined to the membrane electrode assembly (10), a separator (20) having formed therein a groove-shaped anode-side gas flow channel for supplying hydrogen gas to the anode-side gas diffusion layer (12), and a porous body layer (34) for supplying air to the cathode-side gas diffusion layer (14). The anode-gas flow channel and the cathode gas flow channel are mutually asymmetrical, and the position of forming the contact region of the groove of the anode-side gas flow channel and the position of forming the contact region of the cathode-side gas flow channel are aligned in the in-plane direction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a fuel cell, and more particularly to reduction of contact resistance between the members thereof.

2. Description of Related Art

[0002] A solid polymer fuel cell has as a smallest unit a cell in which a membrane electrode assembly (MEA) having an electrolyte membrane constituted by a solid polymer membrane and sandwiched between two electrodes, namely, a fuel electrode and an air electrode, is further supported between two separators. A plurality of such unit cells is stacked as a fuel cell stack to obtain a high output.

[0003] The manner of power generation in the solid polymer fuel cell is explained below in a simple manner. For example, a hydrogen-containing gas as a fuel gas is supplied to a fuel electrode (anode-side electrode), and for example, a gas including oxygen as the main component or air is supplied as an oxidizing agent gas to an air electrode (cathode-side electrode). The hydrogen-containing gas is supplied through a fuel gas flow channel to the anode-side electrode and decomposed into electrons and hydrogen ions under the effect of an electrode catalyst. The electrons move via an external circuit to the cathode-side electrode. The hydrogen ions reach the cathode-side electrode by passing through the electrolyte membrane, recombine with oxygen and the electrons that have passed through the external circuit, and form reaction water. The heat generated by the recombination reaction of hydrogen, oxygen, and electrons is recovered by cooling water. Water generated at the cathode-side electrode (referred to hereinbelow as "generated water") is discharged from the cathode side.

[0004] The anode-side electrode and cathode-side electrode of the fuel cell are constituted by respective catalyst layers, and a gas diffusion layer for diffusing the hydrogen-containing gas and oxidizing agent gas is laminated on each catalyst layer. When the discharge of the generated water that has been generated by the above-described reaction is delayed at the cathode side, a closing effect ("flooding effect") can occur at the cathode-side electrode. Accordingly, the gas diffusion layer is constituted by a layer of carbon fibers and a water repelling layer, and the discharge of the generated water is enhanced by the water repelling layer.

[0005] Japanese Application Publication No. 2010-10069 (JP-A-2010-10069) discloses a fuel cell in which a separator, a porous layer, a gas diffusion sheet, a MEA, a gas diffusion sheet, and a separator are laminated in the order of description. This document discloses a structure in which a gas flow channel on the anode side has a groove-type structure, whereas a gas flow channel on the cathode side has a porous structure using a porous body, and the gas flow channel structure on the anode side and the gas flow channel structure on the cathode side are asymmetrical (non-identical), rather than symmetrical (or identical).

[0006] By using a groove-type structure as a gas flow channel structure on the anode side, it is possible to supply the fuel gas and cooling water into the groove on the anode side, and by using a porous body structure as a gas flow channel structure on the cathode side, it is possible to ensure a sufficient reaction cross-section area and also improve the reaction water draining ability even when air is supplied as the oxidizing agent gas.

[0007] However, the following problem can arise when the gas flow channel structure on the anode side and the gas flow channel structure on the cathode side are asymmetrical (non-identical). Thus, since the gas flow channel structure on the anode side is of a groove type, the gas flow channels are formed with the groove formation pitch. Meanwhile, since the gas flow channel structure on the cathode side is of a porous type, the gas flow ^"channels are formed with the pore formation pitch. Therefore, when a fuel cell is configured, the portions where the gas flow channels are present on the anode side are typically different from the portions where the gas flow channels are J

present on the cathode side.

[0008] Since, as described hereinabove, a fuel cell has a separator/porous body layer/gas diffusion layer/membrane electrode assembly/gas diffusion layer/separator configuration in which separators are disposed at both sides, where the positions of gas flow channels on the anode side do not coincide with the positions of the gas flow channels on the cathode side, the contact resistance at the interface of the gas flow channels and the gas diffusion layer, or the contact resistance at the interface of the gas diffusion layer and the membrane electrode assembly differs depending on a position and the cell output is decreased. For example, where the gas flow channels are present on the anode side, but no gas flow channels are present at the corresponding positions on the cathode side, a constant surface pressure for ensuring electron conduction at such positions cannot be obtained and the cell output is decreased.

SUMMARY OF THE INVENTION

[0009] The invention provides a fuel cell that makes it possible to increase the cell output even when the gas flow channel structure on the anode side is different from the gas flow channel structure on the cathode side.

[0010] One aspect of the invention relates to a fuel cell including: a membrane electrode assembly, an anode-side gas diffusion layer joined to one side of the membrane electrode assembly, a cathode-side gas diffusion layer joined to the other side of the membrane electrode assembly, an anode-side gas flow channel for supplying a fuel gas to the anode-side gas diffusion layer, and a cathode-side gas flow channel for supplying an oxidizing agent gas to the cathode-side gas diffusion layer. The anode-side gas flow channel and the cathode-side gas flow channel are mutually asymmetrical. In the anode-side gas flow channel, first contact regions that are in contact with the anode-side gas diffusion layer and first non-contact regions that are not in contact with the anode-side^" gas diffusion layer are present alternately in an in-plane direction of the anode-side gas diffusion layer. In the cathode-side gas flow channel, second contact regions that are in contact with the cathode-side gas diffusion layer and second non-contact regions that are not in contact with the cathode-side gas diffusion layer are present alternately in the in-plane direction of the cathode-side gas diffusion layer. A position of forming the first contact region of the anode-side gas flow channel and a position of forming the second contact region of the cathode-side gas flow channel are aligned in the in-plane direction. The "in-plane direction" as referred to in the invention is a direction parallel to the surface of the membrane electrode assembly. Examples of the anode-side gas flow channel include a porous body and a groove-type separator, but in the invention, the entire porous body and the entire groove-type separator including this gas flow channel can be regarded as the anode-side gas flow channel in accordance with the invention.

[0011] The anode-side gas flow channel may include a gas flow channel constituted by a recess and a protrusion of the separator; the cathode-side gas flow channel may include a gas flow channel constituted by a porous body layer; and one of the recess and protrusion of the separator may be a gas flow channel and the other one of the recess and protrusion may be a coolant flow channel.

[0012] When a width of the first contact region of the anode-side gas flow channel in a direction perpendicular to an anode gas flow direction in the first non-contact region is denoted by B, the width of the second contact region of the cathode-side gas flow channel in the perpendicular direction to the anode gas flow direction is denoted by E, and a width of the second non-contact region in the perpendicular direction to the anode gas flow direction is denoted by F, the relationship B = mE + nF is satisfied, where m and n are natural numbers.

[0013] When a width of the first non-contact region of the anode-side gas flow channel in the perpendicular direction is denoted by C, a ratio of the width B to the width C is constant in the anode-side gas flow channel and the m and n are constant in the anode-side gas flow channel.

[0014] When a width of the first non-contact region of the anode-side gas flow channel in the perpendicular direction is denoted by C, a ratio of the width B to the width C changes in the anode-side gas flow channel and the m and n change in the anode-side gas flow channel.

[0015] The ratio B/C of the width B to the width C is larger downstream than upstream of the anode-side gas flow channel.

[0016] In accordance with the invention, contact resistance at the interface can be reduced and cell output can be increased even when the anode-side gas flow channel structure is different from the cathode-side gas flow channel structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a cross-sectional configuration diagram of the fuel cell according to the first embodiment;

FIG. 2 is a planar view of the separator;

FIG. 3 is an explanatory drawing illustrating the size of the anode-side gas flow channel region and the cathode-side gas flow channel region;

FIG. 4 is an explanatory drawing illustrating the positional relation among the gas flow channels in the first embodiment;

FIG. 5 is an explanatory drawing illustrating the positional relation among the gas flow channels in the conventional example;

FIG. 6 is a schematic diagram illustrating the positional relation among the protrusion of the groove-type separator and micropores of the porous body layer, when they are viewed from the anode gas flow direction;

FIG. 7 is a schematic diagram illustrating the positional relation among the protrusion of the groove-type separator and micropores of the porous body layer, when they are viewed from the direction perpendicular to the MEGA surface;

FIG. 8 is a graph showing the relationship between the gas flow direction and the ratio B/C in the second embodiment;

FIG. 9 is an explanatory drawing illustrating the positional relation among the gas flow channels in the second embodiment;

FIG. 10 is an explanatory drawing illustrating the positional relation among the gas flow channels in the case where both the anode side and the cathode side are groove-type flow channels in the third embodiment;

FIG. 11 is an explanatory drawing illustrating the positional relation among the gas flow channels in the case where both the anode side and the cathode side are groove-type flow channels in the related art;

FIG. 12 is an explanatory drawing illustrating the positional relation among the gas flow channels in a variation example of the first embodiment; and

FIG. 13 is an explanatory drawing illustrating the positional relation among the gas flow channels in another variation example of the first embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0018] 1. Basic Principle.

The basic principle of the invention is described below.

[0019] The basic configuration of the embodiment is that of an asymmetrical fuel cell in which the anode-side gas flow channel structure and the cathode-side gas flow channel structure (shape) differ from each other. Because the structures of the anode-side and cathode-side gas flow channels are different, the pitches or positions of the anode-side and cathode-side gas flow channels are different and the positions of the gas flow channel on the anode side and the gas flow channel on the cathode side are also different, when viewed from the membrane electrode - gas diffusion layer assembly (MEGA) in which the membrane electrodes are joined with the gas diffusion layer. Therefore, there are regions in which the MEGA cannot be supported by the gas flow channels from both the anode side and the cathode side and a constant surface pressure cannot be ensured.

[0020] Accordingly, in the embodiment, the positions of the anode-side gas flow channel and the cathode-side gas flow channel are adjusted so that the region in which the MEGA is supported by both the anode-side gas flow channel and the cathode-side gas flow channel is maximized, even if the anode-side gas flow channel pitch and the cathode-side gas flow channel pitch differ from each other (here, the "gas flow channel" indicates only a space in which the gas flows). Thus, the position of the region of the anode-side gas flow channel that is in contact with the MEGA and the position of the region of the cathode-side gas flow channel that is in contact with the MEGA in the in-plane direction of the MEGA are aligned with each other. Where the position of a gas flow channel is represented as a phase of the gas flow channel, in the embodiment, the phase of the contact region of the anode-side gas flow channel and the phase of the contact region of the cathode-side gas flow channel can be said to be matched.

[0021] For example, where the anode-side gas flow channel structure is of a groove type and the cathode-side gas flow channel is of a porous type, the pitch of the anode-side gas flow channel is denoted by A, the contact width of the gas flow channel with the MEGA is denoted by B, the non-contact width is denoted by C, the pitch of the cathode-side gas flow channel is denoted by D (A > D), the contact width of the gas flow channel with the MEGA is denoted by E (B > E), and the non-contact width is denoted by F (C > F), the positions are aligned so that the following conditions are satisfied: B = E + F + E = 2E + F and C = F + E + F = E + 2F.

[0022] By adjusting the respective positions so that the aforementioned relationships are satisfied, it is possible to maximize the surface area of contact with the MEGA for both the anode-side gas flow channel and the cathode-side gas flow channel (here, the "gas flow channel" indicates only a space in which the gas flows). As a result, a constant pressure is applied to the MEGA from both the anode side and the cathode side and the contact resistance at the interface of the gas flow channels and the gas diffusion layer and the contact resistance at the interface of the gas diffusion layer and the MEA can be reduced.

[0023] Among the abovementioned relationship formulas, the formula, which relates to both the region of the anode-side gas flow channel that is in contact with the MEGA and the region of the cathode-side gas flow channel that is in contact with the MEGA, is B = 2 E + F. The contact surface area can be maximized by satisfying at least this condition.

[0024] It goes without saying that the aforementioned conditional formulas are satisfied when B, E, and F are specific values. Depending on the values of B, E, and F, the relationship B = 3E + 2F or B = 4E + 3F can be satisfied. Generalizing, the alignment may be performed such that the condition B = mE + nF is satisfied, where m and n are natural numbers.

[0025] When the anode-side gas flow channels and cathode-side gas flow channels are disposed randomly, the aforementioned conditional formulas are not satisfied and generally B is equal to iE + jF where i and j are rational numbers other than natural numbers. Comparing with respect to identical B, E, and F, the condition m > i is satisfied and the surface area of the region of contact with the MEGA is less than that in the embodiment.

[0026] The configuration of the embodiment is explained below in greater detail.

[0027] 2. First Embodiment.

FIG. 1 shows a cross-sectional configuration of the fuel cell of the embodiment. The entire configuration is an asymmetrical fuel cell in which the anode-side gas flow channel structure and the cathode-side gas flow channel structure differ from each other.

[0028] The fuel cell is constituted by laminating a separator 20, a separator 30, a porous body layer 34, a gas diffusion sheet 14, a MEA 10, a gas diffusion sheet 12, a separator 20, and a separator 30 in the order of description. The gas diffusion sheet 12, separator 20, and separator 30 are on the anode side, and the separator 20, separator 30, porous body layer 34, and gas diffusion sheet 14 are on the cathode side. The gas diffusion sheet 14, MEA 10, and gas diffusion sheet 12 are bonded together and constitute a MEGA.

[0029] The separator 20 and separator 30 have a rectangular outer shape. A plurality of through holes is provided and manifolds are formed on the outer circumferential side. The separator 20 is formed by pressing a single metal sheet, and recesses and protrusions alternate between the front surface and back surface. The separator 20 has recesses 22a and recesses 22b. In a planar view of the separator 20, the recesses 22a and recesses 22b each have a comb-shaped pattern, and the two comb-shaped patterns are disposed so as to be engaged with each other. A high-pressure hydrogen gas is supplied into the recesses 22a via a manifold formed by a through hole provided on the outer circumferential side of the separator 20 on the anode side. The recesses 22b are connected to an anode gas discharge system via a manifold formed by another through hole provided on the outer circumferential side of the separator 20. Therefore, the hydrogen gas supplied into the recesses 22a flows into the adjacent recesses 22b through the gas diffusion sheet 12 that is in contact with the separator 20, as shown by the arrows in FIG. 1. In this flow process, hydrogen is supplied from the gas diffusion sheet 12 to the anode-side electrode catalyst layer of the MEA 10. A protrusion 24 of the separator 20 is formed in a zigzag manner inside the separator surface and, together with the separator 30, functions as a coolant flow channel for a coolant such as cooling water.

[0030] FIG. 2 is a planar view of the separator 20. In FIG. 2, arrows are used to show how the hydrogen gas supplied to the recess 22a flows into the recess 22b and how the coolant flows along the protrusion 24 formed in a zigzag shape. In FIG.2, the region P shows a power generation region used for power generating reaction within the surface ofthe MEA lO.

[0031] Meanwhile, the air is supplied to the gas diffusion layer 14 via the porous body layer 34 that has a density lower than that of the gas diffusion layer 14 and causes the gas to pass therethrough by diffusion through micropores. As a result, oxygen is supplied from the gas diffusion sheet 14 to the cathode-side electrode catalyst layer of the MEA 10.

[0032] FIG. 3 shows schematically the relationship between the MEGA and the groove-type gas flow channel formed by recesses and protrusion in the separator 20 and the relationship between the MEGA and the porous body gas flow channel formed in the porous body layer 34. As described hereinabove, the MEGA 40 is constituted by the MEA 10 and the gas diffusion layers 12, 14. A region of the anode-side groove-type gas flow channel that is in contact with the MEGA 40 and can become an electron path is taken as a region 50, and a region of the cathode-side porous body gas flow channel that is in contact with the MEGA 40 and can become an electron path is taken as a region 60. In the embodiment, the dimensions of the regions 50 and 60 are set to be substantially identical. Thus, where the transverse width in the in-plane diction of the region 50 is denoted by Wa, the longitudinal width in the in-plane direction is denoted by Ha, the transverse width in the in-plane diction of the region 60 is denoted by Wb, and the longitudinal width in the in-plane direction is denoted by Hb, the separator 20 and the porous body layer 34 are formed in the embodiment such that Wa = Wb, Ha = Hb.

[0033] Further, in the embodiment, the position of the anode-side groove-type gas flow channel and the position of the cathode-side porous body gas flow channel are adjusted. More specifically, the unit fuel cell is constituted by laminating the separators 20, 30, porous body layer 34, and MEGA shown in FIG. 1, inserting into a metal mold, and molding a gasket around the through holes of the separators. In this case, the recesses and protrusions (grooves) of the separator 20 are molded by pressing, and the micropores of the porous body layer 34 are formed according to the width of the groove in the separator 20. The porous body layer 34 is constituted, for example, by a metal such as titanium and formed by machining such as expand metal or molded by sintering. The separator 30 and porous body layer 34 having flat surfaces are brought into intimate contact with each other over the entire surface and spot welded. The separator 20 and the porous body layer 34 are spot welded over the entire surface. The separator 30 integrated with the porous body layer 34 is laminated with the MEGA and the laminate is inserted into the metal mold, while adjusting the positions of the groove of the separator 20 and the micropores of the porous body layer 34.

[0034] The positional relation among the groove-type gas flow channel formed by the anode-side separator 20 and the gas flow channel of micropores formed by the cathode-side porous body layer 34 will be explained below.

[0035] FIG. 4 shows schematically the positional relation among the groove flow channel of the separator 20 passing through the MEGA and the flow channel of the porous body layer 34. For comparison, FIG. 5 shows schematically the positional relation among the conventional groove flow channel of the separator 20 and the flow channel of the porous body layer 34. In FIG. 4, the groove flow channel is formed by the recesses and protrusion of the separator 20, the recess 22a is a hydrogen gas flow channel, and the protrusion 24 is a coolant flow channel. The protrusion 24 is a region that is in contact with the MEGA, and the recesses 22a are non-contact regions that are not in contact with the MEGA because the recesses are open on the MEGA side. The recesses 22b are hydrogen gas flow channels, and since they are similar to the recesses 22a, the recesses 22a and 22b will be explained hereinbelow as the recesses 22a.

[0036] The flow channel of the porous body layer 34 is constituted by micropores of the porous body layer 34. Non-microporous zones 34b are contact regions that are in contact with the MEGA, and the micropores 34a are non-contact regions that are not in contact with the MEGA because these regions are open on the MEGA side. In the region where the protrusion 24 of the separator 20 and the non-microporous zone 34b of the porous body layer 34 face each other, both the protrusion 24 and the non-microporous zone 34b are in contact with the MEGA. In such a region, the MEGA is held from both sides and a predetermined surface pressure is applied thereto. As a result, the contact resistance at the interface becomes relatively small. By contrast, in the region where the protrusion 24 of the separator and the micropore 34a of the porous body layer 34 face each other, only the protrusion 24 is in contact with the MEGA and therefore the contact resistance at the interface becomes relatively large. In the region where the recess 22a of the separator 20 and the non-microporous zone 34b of the porous body layer 34 face each other, only the non-microporous zone 34b is in contact with the MEGA and therefore the contact resistance at the interface becomes relatively large.

[0037] Accordingly, in the embodiment, the positions of the recesses 24, which are the regions of the separator 20 that are in contact with the MEGA, and the non-microporous zones 34b, which are the regions of the porous body layer 34 that are in contact with the MEGA, are matched and adjusted so that the following conditional formulas are satisfied.

[0038] Thus, where the pitch of the separator 20 in the in-plane direction is denoted by A, the width of the protrusion 24 in the in-plane direction (direction perpendicular to the anode gas flow direction in the non-contact region) is denoted by B, the width of the recess 22a in the in-plane direction is denoted by C, the pitch of the porous body layer 34 in the in-plane direction is denoted by D, the width of the non-microporous zone 34b in-plane direction is denoted by E, and the width of the micropore 34a in-plane direction is denoted by F, the adjustment is performed such that the following conditions are satisfied:

A = B + C

D = E + F

B > E, F

C > E, F

B = E + F + E = 2E + F

C = F + E + F = E + 2F.

[0039] When the aforementioned conditions are satisfied, as shown in FIG. 4 two non-microporous zones 34b, which are the regions of the porous body layer 34 that are in contact with the MEGA, are present at positions facing the protrusion 24, which is the region of the separator 20 that is in contact with the MEGA, the surface area of the regions that are in contact with the MEGA from both side is maximized and the contact resistance at the interface is reduced. More specifically, the following settings can be made: Wa = Wb = 200 mm, Ha = Hb = 100 mm, A = 2.25 mm, B = 1.0 mm, C = 1.25 mm, D = 0.75 mm, E = 0.25 mm, and F = 0.5 mm.

[0040] FIG. 6 is a schematic diagram illustrating the positional relation among the protrusion 24 of the groove-type separator 20 and micropores 34a of the porous body layer 34, when the positional relation is viewed from the anode gas flow direction. FIG. 7 is a schematic diagram illustrating the positional relation among the protrusion 24 of the groove-type separator 20 and micropores 34a of the porous body layer 34, when the positional relation is viewed from the direction perpendicular to the MEGA surface. As shown in FIG. 6, the non-microporous zones 34b have a trapezoidal shape. The upper base of some non-microporous zones 34b matches one end (end in the direction perpendicular to the direction of the anode gas flow) of the protrusion 24 of the groove-type separator 20. The lower base of the other non-microporous zones 34b matches the other end of the protrusion 24 of the groove-type separator 20. Generally speaking, when the configuration is viewed from the direction perpendicular to the MEA surface, the porous body layer 34 and the anode-side separator are disposed so that the position of the edge of the non-microporous zone 34b matches the position of the edge of the protrusion 24 of the separator, so that the number of non-microporous zone 34b entering the protrusion 24 of the anode-side separator becomes larger than the number of non-microporous zone 34b entering the gas flow channel in the anode-side separator. In the present embodiment, the non-microporous zone has a trapezoidal shape, but it may also have other shapes, e.g., a polygonal shape such as a square shape, a rectangle shape and a triangle shape. It would be obvious to a person skilled in the art that in the porous body layer 34, the micropores are connected to each other to supply gas to the MEA, instead of being separated into individual micropores. Therefore, despite the shape such as shown in FIG. 6, this layer can be referred to as a porous body.

[0041] In the conventional structure shown in FIG. 5, the positions of the protrusion 24 of the separator 20 and the non-microporous zones 34b of the porous body layer 34 are not adjusted. Therefore, the number of the non-microporous zones 34b that are present at the positions facing the protrusion 24 is less than 2, for example, only 1.5. The non-microporous zones 34b are the regions of the porous body layer 34, which are in contact with the MEGA. The protrusion 24 is the region of the separator 20, which is in contact with the MEGA. As a result, the desired surface pressure is not obtained and the contact resistance at the interface increases. The effect of the embodiment can be clearly understood by comparing FIG. 4 with FIG. 5.

[0042] 3. Second Embodiment.

In the above-described first embodiment, the recess-protrusion ratio of the anode-side groove-type gas flow channel is constant, but the recess-protrusion ratio may be also varied. Thus, in FIG. 4, although the pitch A is constant, the ratio of the width B of the protrusion 24 to the width C of the recess 22a may be changed.

[0043] FIG. 8 shows an example in which the ratio B/C of the width B of the protrusion 24 and the width C of the recess 22a is caused to change along the gas flow channel. In FIG. 8, the flow of hydrogen gas is plotted against the abscissa, the downstream side being on the right side in FIG. 8. The ratio B/C is plotted against the ordinate. In FIG. 8, the width B of the protrusion 24 gradually increases or the width C of the recess 22a gradually decreases and the ratio B/C increases in the downstream direction as shown by a solid line 100. By decreasing the width C of the recess 22a in the gas downstream direction, it is possible to reduce the cross-sectional area of the flow channel of hydrogen gas and increase the hydrogen gas flow rate on the gas downstream side. Further, by increasing the width B of the protrusion 24 in the gas downstream direction, it is possible to increase the coolant flow rate and improve cooling performance on the gas downstream side. It goes without saying that the ratio B/C may be increased not only continuously. Thus, the ratio B/C may be increased in a stepwise or discontinuous manner as shown by a dot-dash line 200 in the figure. In the figure the gas flow is divided into an upstream region, a medium-stream region, and a downstream region, and the ratio B/C is increased in a stepwise manner between the regions, while remaining constant in each of the regions.

[0044] In the configuration in which the ratio B/C increases in such a manner, the ratio of the micropores 34a and non-microporous zones 34b in the porous body layer 34 also changes according to the variations in the ratio B/C in the separator 20.

[0045] FIG. 9 shows schematically the positional relation among the groove flow channel of the separator 20 and the flow channel of the porous body layer 34 in the embodiment.

[0046] In the gas upstream region, the positional relation is similar to that of the first embodiment, and the following relationships are satisfied:

A = B + C

D = E + F B > E, F

C > E, F

B = E + F + E = 2E + F

C = F + E + F = E + 2F.

[0047] Meanwhile, in the gas downstream region, although the pitch A is equal to the pitch A of the upstream region, the width B' of the protrusion 24 is different from the width B in the upstream region, and the width C of the recess 22a is different from the width C in the upstream region. Thus, the following conditions are satisfied:

B' > B

C^* < C

B7C > B/C.

[0048] In this case, the width E of the non-microporous zone 34b and the width F of the micropore 34a change to E' and F', respectively, according to the width B' of the protrusion 24 and the width C of the recess 22a, the position of the protrusion 24 and the position of the non-microporous zone 34b are aligned, and the adjustment is performed such that the following condition is satisfied: B' = E' + F^* + E' + F + E' = 3E' + 2F.

[0049] With such a configuration, even when the ratio B/C of the width of the protrusion 24 and the width of the recess 22a changes along the gas flow, the surface area of the regions that are in contact from both sides with the MEGA is maximized and the contact resistance at the interface is reduced.

[0050] The abovementioned relationship B' = E' + F + E' + F + E' = 3E^* + 2F' is merely an example, and generally the representation B = mE + nF is possible, without distinction of the upstream region, medium-stream region and downstream region. Here, m and n are natural numbers. When the ratio B/C does not change, m and n are also constant values, and when the B/C ratio changes along the gas flow, m and n can change correspondingly.

[0051] 4. Variation Example.

The embodiments of the invention are explained above, but a variety of variation examples can be considered in addition thereto. [0052] For example, in the first embodiment, the width B of the protrusion 24 and the width C of the recess 22a satisfy the condition B < C, but the two widths may be identical (B = C), or the following condition may be satisfied: B > C. The separator 20 is constituted by a metal and also functions as a collector plate in the fuel cell. Therefore, the contact resistance can be decreased by increasing the width B of the protrusion 24 and increasing the contact surface area with MEGA.

[0053] Further, in the embodiment, the gas flow channel of the anode side is the groove-type gas flow channel and the cathode side is the porous gas flow channel, but other combinations of different gas flow channels can be also used for the anode side and cathode side. In one example of such a combination, a porous body layer is also provided on the anode side and the anode-side porous body layer and the cathode-side porous body layer have mutually different, rather than identical, structures. In such a case, the alignment may be also performed such that the pitch A of the anode-side porous body layer, the width B of the non-microporous zone, and the width C of the micropore, satisfy the conditional formulas shown in the embodiments.

[0054] An example of another combination relates to the case where both the anode side and the cathode side are groove-type gas flow channels, as shown in FIG. 10.

[0055] In the example shown in FIG. 10, when the pitch of the separator 20 in the in-plane direction is denoted by A, the width of the protrusion 24 in the in-plane direction (direction perpendicular to the anode gas flow direction) is denoted by B, the width of the recess 22a in the in-plane direction is denoted by C, the width of the protrusion 74 of the cathode-side separator 70 in the in-plane direction is denoted by E, and the width of the recess 74a in the in-plane direction is denoted by F, the adjustments are made such that the following conditions are satisfied:

A = B + C

B > E, F

C > E, F

B = E + F + E = 2E + F

C = F + E + F = E + 2F. [0056] FIG. 11 illustrates the conventional example (related art) relating to the case where both the gas flow channels of the anode side and the cathode side are groove-type gas flow channels. In the example shown in FIG. 11, when the pitch of the separator 20 in the in-plane direction is denoted by A, the width of the protrusion 24 in the in-plane direction (direction perpendicular to the anode gas flow direction) is denoted by B, the width of the recesses 22a in the in-plane direction is denoted by C, the width of the protrusion 74 of the cathode-side separator 70 in the in-plane direction is denoted by E, and the width of the recess 74a in the in-plane direction is denoted by F, the adjustments are made such that the following conditions are satisfied:

A = B + C

B > E, F

C > E, F

B = F + E + F = E + 2F

C = E + F + E = 2E + F.

[0057] Thus, the surface area over which the anode-side protrusion 24 and the cathode-side gas flow channel are together in contact with the MEGA is less and the surface area over which the anode-side gas flow channel and the cathode-side gas flow channel are together in contact with the MEGA is greater in the variation example of the first embodiment shown in FIG. 10 than in the fuel cell of related art that is shown in FIG. 11.

[0058] Further, in the embodiments, the protrusion 24, which is the anode-side contact region, and the non-microporous zone 34b, which is the cathode-side contact region, are aligned, in the in-plane direction, but the "alignment", as used in the embodiments, means that the two positions match within the design tolerance limits, rather than necessarily meaning that the two positions match perfectly. (For example, the difference between the end portion of the protrusion 24 and the end portion of the non-microporous zone 34b which is equal to or less than 10% of the width of the end portion of the protrusion 24 can be taken as the tolerance limit). Thus, even if the two positions shift with respect to each other within the predetermined tolerance limits, the two positions can be assumed to match substantially and be "aligned". Variation examples in which the protrusion 24 which is the anode-side contact region and the non-microporous zone 34b which is the cathode-side contact region are aligned in the in-plane direction are shown in FIG. 12 that relates to the case in which only one end portion of the anode-side contact region is aligned with the end portion of the cathode-side contact region and FIG. 13 that relates to the case in which the anode-side contact region and the cathode-side contact region are matched over the entire surface.

Claims

CLAIMS:

1. A fuel cell comprising:

a membrane electrode assembly;

an anode-side gas diffusion layer joined to one side of the membrane electrode assembly;

a cathode-side gas diffusion layer joined to the other side of the membrane electrode assembly;

an anode-side gas flow channel for supplying a fuel gas to the anode-side gas diffusion layer; and

a cathode-side gas flow channel for supplying an oxidizing agent gas to the cathode-side gas diffusion layer, wherein

the anode-side gas flow channel and the cathode-side gas flow channel are mutually asymmetrical;

in the anode-side gas flow channel, first contact regions that are in contact with the anode-side gas diffusion layer and first non-contact regions that are not in contact with the anode-side gas diffusion layer are present alternately in an in-plane direction of the anode-side gas diffusion layer;

in the cathode-side gas flow channel, second contact regions that are in contact with the cathode-side gas diffusion layer and second non-contact regions that are not in contact with the cathode-side gas diffusion layer are present alternately in the in-plane direction of the cathode-side gas diffusion layer; and

a position of forming the first contact region of the anode-side gas flow channel and a position of forming the second contact region of the cathode-side gas flow channel are aligned in the in-plane direction.

2. The fuel cell according to claim 1 , wherein

^' the anode-side gas flow channel includes a gas flow channel constituted by a recess and a protrusion of the separator;

the cathode-side gas flow channel includes a gas flow channel constituted by a porous body layer; and

one of the recess and protrusion of the separator is a gas flow channel and the other one of the recess and protrusion of the separator is a coolant flow channel.

3. The fuel cell according to claim 1 or 2, wherein when a width of the first contact region of the anode-side gas flow channel in a direction perpendicular to an anode gas flow direction in the first non-contact region is denoted by B, a width of the second contact region of the cathode-side gas flow channel in the perpendicular direction is denoted by E, and a width of the second non-contact region in the perpendicular direction is denoted by F, the relationship B = mE + nF is satisfied, where m and n are natural numbers.

4. The fuel cell according to claim 3, wherein when a width of the first non-contact region of the anode-side gas flow channel in the perpendicular direction is denoted by C, a ratio of the width B to the width C is constant in the anode-side gas flow channel and the m and n are constant in the anode-side gas flow channel.

5. The fuel cell according to claim 3, wherein when a width of the first non-contact region of the anode-side gas flow channel in the perpendicular direction is denoted by C, a ratio of the width B to the width C changes in the anode-side gas flow channel and the m and n change in the anode-side gas flow channel.

6. The fuel cell according to claim 5, wherein the ratio B/C of the width B to the width C is larger downstream than upstream of the anode-side gas flow channel.