JP2010021025A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which suppresses effectively a gap that is caused between a catalyst layer and a gas diffusion layer at the time a pressing force is applied to the fuel battery cell at stacking, and thereby, suppresses effectively deterioration of the power generation performance and support of flooding brought about by formation of the gap. <P>SOLUTION: The fuel cell (fuel battery cell 10) is composed of a membrane electrode assembly 5 consisting of an electrolyte membrane 1, catalyst layers 2a, 2B arranged on its both sides, and gas diffusion layers 4A, 4B arranged on both sides of the catalyst layer, and separators 8, 8 that are arranged on both sides of the membrane electrode assembly 5 and are made of a surface material. The separator 8 includes a groove strip 6 which demarcates a gas passage opposed to the gas diffusion layer and a contact surface 7 which is connected to the groove strip 6 and in contact with the gas diffusion layer, all having a continued shape. The contact surface 7 includes a displacement means (projection 7a) which makes small the width of the contact surface 7 when a compression force is applied on it from the groove strips 6, 6 on both sides of the contact surface 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell, and in particular, effectively suppresses a gap that can be formed between a gas diffusion layer and an electrode catalyst layer when a pressing force is applied to the gas diffusion layer constituting the membrane electrode assembly during stacking. It is related with the fuel cell which can be used.

  A single cell of a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) comprising an ion permeable electrolyte membrane and catalyst layers on the anode side and the cathode side sandwiching the electrolyte membrane, or A membrane electrode assembly (MEGA: Membrane Electrode & Gas Diffusion Layer Assembly) in which the catalyst layer is sandwiched between gas diffusion layers (GDL), and a fuel gas or an oxidant gas to the membrane electrode assembly and electric At least a gas flow path layer and a separator for collecting electricity generated by a chemical reaction are provided. A cell structure in which the separator also functions as a gas flow path layer is generally known. The fuel cell stack is formed by stacking a predetermined number of single cells according to required power.

  In the fuel cell described above, hydrogen gas or the like is provided as fuel gas to the anode electrode, oxygen or air is provided as the oxidant gas to the cathode electrode, and each electrode has its own gas flow path layer (gas formed in the separator). The gas flows in the in-plane direction (including the channel groove), and then the gas diffused in the gas diffusion layer is guided to the electrode catalyst to cause an electrochemical reaction.

  In a fuel cell having a separator in which a groove serving as a gas flow path and an abutting surface that abuts the gas diffusion layer are alternately arranged, the groove of the separator is caused by the pressing force applied to each cell during stack formation. It has been specified by the present inventors that a gap is easily formed between the gas diffusion layer and the catalyst layer in the gas diffusion layer region facing the strip (gas flow path). For example, Patent Documents 1 and 2 are cited as conventional technologies related to a fuel cell including a separator having a groove (concave portion) serving as a gas flow path layer and a contact surface (convex portion) continuous therewith. it can.

  The structure of the fuel battery cell having the separator described above will be described with reference to the schematic diagram of FIG. In the fuel cell shown in FIG. 5, MEAc is formed from an electrolyte membrane a and cathode and anode catalyst layers b and b on both sides thereof, and this is formed into a gas diffusion layer d on the cathode side and anode side, d is sandwiched to form a membrane electrode assembly (MEGA), and the MEGA is formed by sandwiching cathode and anode separators e and e. In addition, the separator e is comprised from the continuous body of the groove | channel e1 which comprises a gas flow path, and the contact surface e2 connected to this and contact | abutted with the gas diffusion layer d.

  Here, in the gas diffusion layer region below the contact surface e2, the applied pressing force P directly presses the gas diffusion layer d and MEAc via the corresponding contact surface e2, whereas the groove e1. The pressing force does not act directly on the lower gas diffusion layer d. Therefore, the gas diffusion layer d is fixed by the catalyst layer below the contact surface e2, and easily deforms to the groove e1 side under the groove e1. The line L in the figure simulates a meandering line at the lower end of the gas diffusion layer d formed by the pressing force, and a peak Y rising to the groove e1 side is formed under the groove e1.

  If a gap is formed between the crest Y in the lower end line of the gas diffusion layer d and the catalyst layer, this gap increases the electric resistance between the catalyst layer and the gas diffusion layer, and the power generation performance is reduced. It becomes a cause. Furthermore, this gap becomes a water pool, and particularly on the cathode side, water generated by an electrochemical reaction can be accommodated in this water pool and cause flooding. A gap is formed between the catalyst layer and the gas diffusion layer by the pressing force at the time of stacking, and the problem that the gap in power generation performance and flooding is aided by the gap is caused by the fuel cell disclosed in Patent Documents 1 and 2 above. Is not solved.

JP 2003-10031 A JP 2004-192932 A

  The present invention has been made in view of the above-described problems, and the groove that forms the gas flow path facing the membrane electrode assembly and the contact surface that contacts the membrane electrode assembly are alternately continuous. With regard to a fuel cell having a separator in a form, the gap that may be generated between the catalyst layer and the gas diffusion layer when a pressing force is applied to the fuel cell at the time of stacking can be effectively suppressed, and thus the formation of the gap can be discouraged. An object of the present invention is to provide a fuel cell capable of effectively suppressing the decrease in power generation performance and the subsidy for flooding.

  In order to achieve the above object, a fuel cell according to the present invention comprises a membrane electrode joint comprising an electrolyte membrane, a catalyst layer disposed on both sides of the electrolyte membrane, and a gas diffusion layer disposed on both sides of the catalyst layer. And separators made of face materials disposed on both sides of the membrane electrode assembly, the separator comprising a groove that defines a gas flow path facing the gas diffusion layer, and a gas diffusion layer In the fuel cell, in which the contact surface is in contact with the contact surface, the contact surface has a contact surface when a compressive force is applied to the contact surface from the grooves on both sides of the contact surface. Displacement means for reducing the width is provided.

  The fuel cell of the present invention has a sheet-like separator in which a groove forming a gas flow path and a contact surface in contact with the gas diffusion layer are alternately continuous, and grooves on both sides of the contact surface are provided on the contact surface. Displacement means for reducing the width of the contact surface when a compressive force is applied from a flat top surface and a side surface continuous with the top surface is provided.

  This compressive force is such that the pressing force acting on the top surface of the groove during stacking is transmitted to the contact surface via the side surface of the groove, and acts as a compressive force on the corresponding contact surface. When a compressive force is applied to the contact surface from the side surfaces of the grooves on both sides, the width of the contact surface is reduced by the displacement means provided on the contact surface. In the process of reducing the width of the contact surface, for example, a compressive force toward the center side also acts on the gas diffusion layer in the region immediately below the contact surface due to the frictional force between the contact surface and the gas diffusion layer. Become. As a result, a tensile force acts on the gas diffusion layer in the region immediately below the groove from the gas diffusion layer in the region immediately below the contact surfaces on both sides.

  Due to this tensile force, the gas diffusion layer in which the peak Y of the meandering line L is easily formed in the region immediately below the groove as shown in FIG. 5 is pulled from both sides, and the formation of the meandering line as shown in FIG. Therefore, the formation of a gap between the gas diffusion layer and the catalyst layer formed by the meandering line is also suppressed, an increase in electrical resistance due to this gap, and generation of flooding due to retention of generated water in this gap, etc. Is effectively deterred.

  Here, as an embodiment of the displacement means, a protrusion formed by bending a part of the abutting surface to the opposite side to the gas diffusion layer can be mentioned.

  For example, at the center position or substantially the center position of the contact surface, there is provided a projection that rises from the contact surface with a certain gradient, is bent at the top, and similarly falls down with a certain gradient to reach the contact surface. Such a protrusion has a space inside thereof, and it is easy to understand that the protrusion is deformed to the central space side when a compressive force (force to crush the protrusion) is applied from both sides of the protrusion. When the protrusion receives a compressive force and deforms toward the central space, the side surface forming the protrusion comes closer to 90 degrees than the initial standing slope, and this deformation causes the contact surface to face the protrusion. The overall width is reduced while being displaced. In the process in which the contact surface is displaced toward the protrusion, the gas diffusion layer immediately below the contact surface is subjected to frictional force to the position below the protrusion (the position corresponding to the protrusion of the gas diffusion layer) from the left and right. A compression force acts. Due to this compressive force, a tensile force acts on the gas diffusion layer in the region immediately below the groove, and the formation of the meandering line is suppressed as described above.

  Further, as another embodiment of the displacement means, a cross-sectional defect portion provided on the contact surface can be cited.

  For example, a cutout is provided in the side surface on the gas diffusion layer side at the center position or substantially center position of the contact surface to form a cross-sectional defect portion. As the shape of the cross-sectional defect portion, an arbitrary shape such as a triangle, a semicircular shape, and a semi-elliptical shape opened on the gas diffusion layer side can be applied.

  When compressive force is applied from both sides of the contact surface, the contact surface regions located on both sides of the cross-sectional defect portion are displaced toward the defect space of the cross-sectional defect portion, and a part of the region is accommodated in the defect space. . In the gas diffusion layer in the region immediately below the abutting surface, a compressive force directed to a position corresponding to the cross-sectional defect portion acts via a frictional force due to the displacement of the abutting surface. By this compressive force, a tensile force acts on the gas diffusion layer in the region immediately below the groove, and the formation of the meandering line is suppressed.

  Further, the groove and the contact surface are formed of a material having different rigidity with conductivity. As still another embodiment of the displacement means, the groove and the contact surface are formed of a material having a lower rigidity than the groove. Can be mentioned.

  By forming the contact surface from a material having a lower rigidity than the groove, it becomes easier to elastically contract (elastically deform) the contact surface by the compressive force acting from the groove, and the frictional force during this elastic contraction Thus, for example, a compressive force toward the center position can be applied to the gas diffusion layer in the region immediately below the contact surface. By this compressive force, a tensile force acts on the gas diffusion layer in the region immediately below the groove, and the formation of the meandering line is suppressed.

  Here, as a combination of materials having different rigidity having conductivity, a separator in which grooves are formed from stainless steel (SUS) and a contact surface is formed from titanium, aluminum, or an alloy thereof can be exemplified. . Here, the Young's modulus of stainless steel is about 200 GPa, that of titanium is about 110 GPa, and aluminum and its alloys are about 70 GPa. For example, the abutment surface made of aluminum has a deformability that is much higher than that of a stainless steel groove. It will be expensive.

  Further, in terms of the side surface of the groove, it is preferable that the groove has a tapered surface that widens the gas flow path toward the gas diffusion layer.

  The side surface forming the groove forms a tapered surface that widens the gas flow path width toward the gas diffusion layer side, so that the pressing force acting on the top surface of the groove is passed through the tapered side surface. Can be easily transmitted to the contact surface (the flow of the force applied to the contact surface on the top surface becomes smooth), and the compression force can be applied to the contact surface more effectively. it can.

  As can be understood from the above description, according to the fuel cell of the present invention, in the fuel cell having the separator in which the groove and the contact surface are alternately continuous, by providing an appropriate displacement means on the contact surface, Effectively suppresses gaps that may occur between the catalyst layer and gas diffusion layer when a pressing force is applied to the fuel cell during stacking, thus reducing the power generation performance and subsidizing flooding, which is caused by the formation of gaps. Can be deterred.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a longitudinal sectional view of an embodiment of a fuel cell constituting the fuel cell of the present invention. A fuel cell 10 shown in FIG. 1 includes an MEA 3 formed of an electrolyte membrane 1 that is an ion exchange membrane and catalyst layers 2A and 2B on the cathode side and anode side, and a cathode side and an anode side sandwiching the MEA 3 and the MEA 3 therebetween. The membrane electrode assembly 5 (MEGA) formed from the gas diffusion layers 4A and 4B and the cathode side and anode side separators 8 and 8 sandwiching the membrane electrode assembly 5 are not shown at the periphery. The resin gasket is integrally formed.

  The electrolyte membrane 1 constituting the MEA 3 is a fluorine-based ion exchange membrane having a sulfonic acid group or a carbonyl group, a non-fluorine such as a substituted phenylene oxide, a sulfonated polyaryletherketone, a sulfonated polyarylethersulfone, or a sulfonated phenylene sulfide. The catalyst layers 2A and 2B are made of a porous material in which a catalyst made of platinum or an alloy thereof is supported on carbon or the like. Further, the gas diffusion layers 4A and 4B are formed of a gas permeable material such as carbon paper or carbon cloth, and are subjected to appropriate water repellent treatment.

  The separator 8 is formed from a face material made of a gas-impermeable dense carbon material, dense graphite material, or the like, and as shown in the figure, a linear or meandering groove 6 that defines a gas flow path. And the contact surface 7 which contacts the gas diffusion layers 4A and 4B continuously with the groove 6 has an alternately continuous shape. In addition, the groove | channel defined on the opposite side to gas flow path layer 4A, 4B of the contact surface 7 formed in the separator 8 is provided for the flow path for cooling water.

  In actual fuel cells, fuel cells 10 are stacked in predetermined stages according to a desired power generation amount to form a fuel cell stack. Further, the fuel cell stack includes an end plate, a tension plate, and the like on the outermost side, and a pressing force (compression force) is applied between the tension plates at both ends to form a fuel cell stack having a fixed size structure.

  A fuel cell system mounted on an electric vehicle or the like includes this fuel cell, various tanks for storing hydrogen gas and air, a blower for supplying these gases to the fuel cell, a radiator for cooling the fuel cell, a fuel The battery is generally composed of a battery that stores electric power generated by the battery, a drive motor that is driven by the electric power, and the like.

  The separator 8 shown in FIG. 1 has a top surface 61 in which the groove 6 defining the gas flow path is flat, and a gas flow path width that continuously extends toward the gas diffusion layers 4A and 4B. The side surfaces 62 and 62 are tapered, and the side surfaces 62 and the contact surface 7 are continuous.

  The abutment surface 7 is provided with a projection 7a protruding at the center position on the side opposite to the gas diffusion layers 4A and 4B. This is a displacement means for deforming the contact surface 7 toward the protrusion 7 a when the pressing force at the time of stacking is applied to the fuel cell 10, thereby reducing the width of the contact surface 7.

  Next, with reference to FIG. 2, the force generated when the pressing force during stacking acts on the fuel cell 10 and the mechanism by which the separator is displaced by this force will be described. The cathode side separator 8 and the gas diffusion layer 4A are taken up for explanation, but this is also applicable to the anode side as well.

  FIG. 2a is an enlarged view of a part of the separator 8, the gas diffusion layer 4A, and the catalyst layer 2A when a pressing force is applied to the fuel cell 10 during stacking, and FIG. It is the figure which simulated the force and deformation which arise in the case.

  The pressing force P at the time of stacking acts on the top surface 61 and the contact surface 7 of the groove 6 of the separator.

  The pressing force P acting on the top surface 61 of the groove 6 becomes an axial force through the side surface 62 that is tapered toward the gas diffusion layer 4 </ b> A and acts on the contact surface 7.

  Axial force is transmitted to the arbitrary abutting surface 7 from the side surfaces 62, 62 of the grooves 6, 6 on both sides thereof, and this axial force is applied to the compression force Q, which is directed toward the protrusion 7a located at the center of the abutting surface 7. Q acts on the corresponding contact surface 7.

  For convenience, in the gas diffusion layer 4A, the area immediately below the contact surface is divided into areas A1 and the area directly below the grooves is divided into areas A2.

  When compressive forces Q, Q directed toward the protrusion 7a act on the abutment surface 7, the protrusion 7a is deformed so that its rising slope is closer to 90 degrees, and is opposite to the gas diffusion layer 4A (upward in FIG. 2b). Is displaced by δ.

  Due to this displacement, the entire width of the abutting surface 7 is narrowed, and the region A1 immediately below the abutting surface of the gas diffusion layer 4A has a compressive force applied to its center side via a frictional force according to the displacement of the abutting surface 7. Will receive.

  When the region A1 immediately below the contact surface receives a compressive force, the region A2 immediately below the groove of the gas diffusion layer 4A receives the tensile forces T and T from the regions A1 directly below the contact surfaces on both sides.

  The region A2 directly below the groove of the gas diffusion layer 4A receives tensile forces T and T from both sides thereof, thereby forming a meandering line (see FIG. 5) that can be generated between the lower surface of the region A2 and the catalyst layer 2A. It becomes difficult to form a gap that may occur between the crest of the meandering line and the catalyst layer 2A.

  That is, by the extremely simple structural change by simply providing the protrusion 7a on the contact surface 7, the generation of the gap can be effectively suppressed, and the increase in electrical resistance and the aid of flooding due to the gap are effectively suppressed. .

  FIG. 3 is a longitudinal sectional view of another embodiment of the fuel cell constituting the fuel cell of the present invention.

  This fuel cell 10A is provided with a cross-sectional defect portion 7Aa at the center position of the contact surface 7A of the separator 8A constituting the fuel cell 10A.

  Although detailed illustration of the mechanism of force and displacement is omitted, even when this cross-sectional defect portion 7Aa is provided, the corresponding contact surface 7A is directed toward the cross-sectional defect portion 7Aa by the compressive force acting from both sides of the contact surface 7A. The deformation can be applied, and a compressive force can be applied to the region immediately below the contact surface of the gas diffusion layer 4A through the frictional force due to this deformation. A tensile force can be applied to the region.

  FIG. 4 is a longitudinal sectional view of still another embodiment of the fuel cell constituting the fuel cell of the present invention.

  In this fuel cell 10B, the groove 6 and the contact surface 7B are integrally formed from different materials having different rigidity to form a separator 8B.

  Here, the contact surface 7B is formed of a material having a low rigidity (a material having a low Young's modulus) as compared with the groove 6 in order to promote deformation when a compressive force generated by a pressing force during stacking is applied. . For example, the groove 6 can be formed from stainless steel (SUS), and the contact surface 7B can be formed from titanium, aluminum, or an alloy thereof. Here, the Young's modulus of stainless steel is about 200 GPa, that of titanium is about 110 GPa, and aluminum and its alloys are about 70 GPa.

  Even when the contact surface 7B is made of a relatively low-rigidity material, the corresponding contact surface 7B can be deformed (elastically deformed) toward the center position by a compressive force acting from both sides of the contact surface 7B. This elastic deformation allows a compressive force to act on the region immediately below the contact surface of the gas diffusion layer 4A via a frictional force, and a tensile force to act on the region directly below the groove of the gas diffusion layer 4A.

  According to the fuel battery cells 10, 10A, 10B of the present invention described above, when the pressing force at the time of stacking is applied by using the separators 8, 8A, 8B provided with appropriate displacement means as their constituent members. In addition, it is possible to effectively prevent the gas diffusion layer from meandering at the interface with the catalyst layer, effectively preventing problems such as increased electrical resistance caused by gaps created by this meandering and subsidizing flooding due to water pools. Can be resolved.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

It is a longitudinal cross-sectional view of one embodiment of the fuel cell constituting the fuel cell of the present invention. (A) is the figure which expanded the separator, the gas diffusion layer, and a part of catalyst layer when pressing force acted on the fuel cell of FIG. 1 at the time of stacking, (b) is pressing force acting It is the figure which simulated the force and deformation which arise when doing. It is a longitudinal cross-sectional view of other embodiment of the fuel cell which comprises the fuel cell of this invention. It is a longitudinal cross-sectional view of further another embodiment of the fuel cell which comprises the fuel cell of this invention. It is a longitudinal cross-sectional view of the fuel cell which comprises the conventional fuel cell, and is the figure which simulated that the side surface by the side of the catalyst layer of a gas diffusion layer forms a meandering line when pressing force acts at the time of stacking.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane, 2A, 2B ... Catalyst layer, 3 ... MEA, 4A, 4B ... Gas diffusion layer (GDL), 5 ... Membrane electrode assembly (MEGA), 6 ... Groove, 61 ... Top surface, 62 ... Side surface 7, 7A, 7B ... contact surface, 7a ... projection, 7Aa ... cross-sectional defect, 8, 8A, 8B ... separator, 10, 10A, 10B ... fuel cell, A1 ... area just below the contact surface, A2 ... Area just below the groove, P ... Pressing force, Q ... Compressive force, T ... Tensile force

Claims (5)

A membrane electrode assembly comprising an electrolyte membrane, a catalyst layer disposed on both sides of the electrolyte membrane, and a gas diffusion layer disposed on both sides of the catalyst layer; and disposed on both sides of the membrane electrode assembly. The separator has a shape in which the groove that defines the gas flow path facing the gas diffusion layer and the contact surface that contacts the gas diffusion layer are alternately and continuously formed. Presenting a fuel cell,
The fuel cell, wherein the contact surface is provided with a displacement means for reducing the width of the contact surface when a compressive force is applied from the groove on both sides of the contact surface.   2. The fuel cell according to claim 1, wherein the displacement means is a protrusion formed by bending a part of the abutting surface to the opposite side to the gas diffusion layer.   The fuel cell according to claim 1, wherein the displacement means is a cross-sectional defect portion provided on the contact surface. The groove and the contact surface are formed of materials having different rigidity with conductivity,
The fuel cell according to claim 1, wherein the displacing means is a contact surface formed of a low-rigidity material as compared with the groove.   The fuel cell according to any one of claims 1 to 4, wherein a side surface of the groove connected to the contact surface is a tapered surface in which a gas flow path width is widened toward the gas diffusion layer side.

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