JP2007035449A - Separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator exerting optimum seal performance. <P>SOLUTION: A seal line L is formed into a shape having circular arcs Ac each having a center at each corner part located inside the seal line L, and formed by connecting the circular arcs Ac adjacent to each other through a circular arc Am having the center located outside the seal line L. By forming such a seal line, contact pressure generated by fastening in assembly can be dispersed, whereby sufficient seal performance can be exerted without breaking a polymer film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a separator provided in a stack type polymer electrolyte fuel cell.

  The fuel cell has two electrodes and an electrolyte sandwiched between the electrodes. At the cathode, the supplied hydrogen is ionized to form hydrogen ions that move through the electrolyte toward the anode. At the anode, the supplied oxygen reacts with hydrogen ions that have moved through the electrolyte to generate water. Electrons generated when hydrogen is ionized move from the cathode through the wiring to the anode, whereby a current flows and electricity is generated.

  The structure of the polymer electrolyte fuel cell consists of an electrolyte membrane with a catalyst electrode on the surface, a separator with an electrolyte membrane sandwiched from both sides and a groove for supplying hydrogen and oxygen, and the electricity generated by the electrode is recovered And a current collecting plate. In addition, since the separator occupies about 80% of the volume and weight of the parts constituting the fuel cell, it is an indispensable part for making the fuel cell compact.

  As the separator material, there are dense carbon, synthetic resin, and the like, but metal is often used from the viewpoint of conductivity, workability, sealing property, and the like. In the assembly process of the fuel cell, in order to prevent leakage of gases such as hydrogen and oxygen, it is necessary to seal the outer periphery of the separator with a sealing material such as an O-ring or to provide a gasket on the outer periphery. On the other hand, the inventors of the present invention have, as a result of previous research, a seal projection that extends in parallel with the catalyst electrode formation surface of the electrolyte on the outer periphery of the metal separator so that the top thereof is pressed against the electrolyte by a spring force. It has been found that gas leakage can be prevented even without a sealing material.

  The seal line of the separator described in Patent Document 1 is provided along the outer periphery thereof, or is provided so as to surround the gas flow path.

Japanese Patent Laid-Open No. 2005-38868

  In the case where the above-described seal protrusion is formed by press working, the seal line has a so-called rounded quadrangular shape in which each corner portion of the separator has an arc shape and each side portion has a straight line connecting the arcs. It becomes a seal line.

When a fuel cell is assembled using such a metal separator that forms a seal line, the tightening pressure may be concentrated on the arcuate portion of the corner, and the electrolyte membrane may be destroyed. Further, when the tightening pressure is such that the electrolyte membrane is not broken, the sealing performance is deteriorated and gas leakage may occur.
An object of the present invention is to provide a separator that exhibits optimum sealing performance.

The present invention is provided between a plurality of electrolyte assemblies each provided with a catalyst electrode on the surface in the thickness direction of an electrolyte layer containing an electrolyte medium, and separating a fuel gas and an oxidant gas flow path; A separator integrated with a seal portion provided to prevent leakage of fuel gas and oxidant gas,
The region corresponding to the seal portion is a seal protrusion that extends in parallel with the catalyst electrode forming surface of the electrolyte assembly, and the top portion of the seal protrusion is pressed against the electrolyte assembly by a spring force. Have
The contact line that virtually shows the location where the top of the seal projection contacts the electrolyte layer is a closed curve,
The shape of the closed curve has a first arc whose center is located inside the closed curve at each corner, the first arc adjacent to each other, and a second arc whose center is located outside the closed curve. It is the separator characterized by having the shape connected through this.

  Further, the present invention is characterized in that a ratio rm / rc of the radius rc of the first arc and the radius rm of the second arc is 2 or more and 8 or less.

  According to the present invention, the separator interposed between the plurality of electrolyte assemblies provided with the catalyst electrodes on the surface in the thickness direction of the electrolyte layer containing the electrolyte medium, and separating the flow path of the fuel gas and the oxidant gas; This is a separator integrated with a seal portion provided in the portion and preventing leakage of fuel gas and oxidant gas.

  The region corresponding to the seal portion is a seal protrusion that extends in parallel with the catalyst electrode forming surface of the electrolyte assembly, and the top portion of the seal protrusion is pressed against the electrolyte assembly by a spring force. Have

  A contact line that virtually shows a position where the top of the seal protrusion abuts the electrolyte layer, a so-called seal line is a closed curve, and the shape of the closed curve is such that the center of each corner is located inside the closed curve. The first arcs having one arc and adjacent to each other are connected via a second arc whose center is located outside the closed curve.

  Thereby, since the contact pressure generated by tightening during assembly can be dispersed, optimum sealing performance can be exhibited without destroying the electrolyte layer.

  According to the present invention, it is preferable that a ratio rm / rc between the radius rc of the first arc and the radius rm of the second arc is 2 or more and 8 or less.

  By setting the ratio rm / rc in such a range, the contact pressure can be more evenly distributed.

  FIG. 1 is a perspective view schematically showing a state in which a polymer electrolyte fuel cell (abbreviated as PEFC) 100 is developed. The PEFC 100 includes a separator 1, a fuel battery cell 2, a current collector plate 3, an insulating sheet 4, an end flange 5, and an electrode wiring 12. The PEFC 100 is configured in a so-called stack state in which a plurality of fuel cells 2 are connected in series in order to obtain a high voltage and a high output. In order to configure this stack state, a separator is disposed between the fuel cells 2, and hydrogen and oxygen are supplied to each fuel cell 2 and the generated electricity is recovered. Therefore, as shown in FIG. 1, the fuel cells 2 and the separators 1 are alternately arranged. The separator 1 is arranged on the outermost layer of this arrangement, and the current collector plate 3 is provided on the outer side of the separator 1. The current collector plate 3 is provided to collect and take out the electricity collected by each separator 1 and is connected to the electrode wiring 12. The insulating sheet 4 is provided between the current collector plate 3 and the end flange 5, and prevents current from leaking from the current collector plate 3 to the end flange 5. The end flange 5 is a case for holding the plurality of fuel cells 2 in a stacked state.

  A hydrogen gas supply port 6, a cooling water supply port 7, an oxygen gas supply port 8, a hydrogen gas discharge port 9, a cooling water discharge port 10 and an oxygen gas discharge port 11 are formed in the end flange 5. The gas and water fluid supplied from each supply port passes through each forward path penetrating in the stacking direction of the fuel cells 2 and is folded back by the outermost separator 1 and is discharged from each discharge port through each return path.

  The forward path and the return path are branched by each separator 1, and each fluid flowing in the forward path flows into the return path through a flow path formed by the separator 1 and parallel to the surface direction of the fuel cell 2. Since hydrogen gas and oxygen gas are consumed in the fuel battery cell 2, unreacted gas is discharged through the return path. The discharged unreacted gas is recovered and supplied again from the supply port. Since water is generated by the reaction between oxygen and hydrogen in the vicinity of the oxygen gas flow path, the discharged oxygen gas contains water. In order to supply the discharged oxygen gas again, it is necessary to remove water.

  The hydrogen gas that is a fuel gas and the oxygen gas that is an oxidant gas do not need to be hydrogen and oxygen alone, but can be any gas other than hydrogen and oxygen that does not deteriorate or denature the flow path in contact. May be included. For example, air containing nitrogen as oxygen gas may be used. The hydrogen source is not limited to hydrogen gas, and may be methane gas, ethylene gas, natural gas, or ethanol.

  FIG. 2 is a horizontal sectional view of the unit battery 101 including the separator 1. The unit battery 101 is composed of one fuel battery cell 2 and two separators 1 arranged on both sides of the unit battery 101. The unit battery 101 has a minimum configuration capable of generating electric power by supplying hydrogen and oxygen.

A fuel cell 2 as an electrolyte assembly includes a polymer film 20 as an electrolyte medium and a catalyst electrode 21 formed on the surface of the polymer film 20 in the thickness direction. The MEA (Membrane Electrode)
Also called Assembly.

  The polymer membrane 20 is a proton conductive electrolyte membrane that transmits hydrogen ions (protons), and a perfluorosulfonic acid resin membrane (for example, a product name “Nafion” manufactured by DuPont) is often used.

  The catalyst electrode 21 is laminated on the surface of the polymer film 20 in the thickness direction as a carbon layer containing a catalyst metal such as platinum or ruthenium. When hydrogen gas or oxygen gas is supplied to the catalyst electrode 21, an electrochemical reaction occurs at the interface between the catalyst electrode 21 and the polymer film 20 to generate DC power.

  The polymer film 20 has a thickness of about 0.1 mm, and the catalyst electrode 21 is formed with a thickness of several μm although it varies depending on the catalyst metal contained therein.

  The separator 1 has a separation part 13 that separates the flow paths of hydrogen gas and oxygen gas, and a seal part 14 that is provided on the outer periphery and prevents leakage of hydrogen gas and oxygen gas. In this embodiment, the catalyst electrode 21 is not formed on the entire surface of the polymer film 20, but the polymer film 20 is exposed on the surface over an outer peripheral width of 1 to 20 mm, preferably 5 to 10 mm. The separator 13 of the separator 1 is formed in a region facing the region where the catalyst electrode 21 is formed, and the seal portion 14 is formed in a region facing the region where the polymer film 20 is exposed.

  As a main material of the separator 1, a flat metal thin plate is used. For example, metal thin plates such as iron, aluminum and titanium, particularly stainless steel (for example, SUS304) steel plates, SPCC (general cold rolled steel plates), and corrosion resistant steel plates are preferred. As for the stainless steel plate, a surface-treated one can be used. For example, a surface pickled, electrolytically etched, containing conductive inclusions, formed with a BA film, or coated with a conductive compound by ion plating can be used. Further, a highly corrosion-resistant stainless steel plate with an ultrafine crystal structure can be used.

  The separating portion 13 and the seal portion 14 can be integrally formed by subjecting the metal thin plate as described above to plastic deformation processing, for example, press processing. In addition, in order to improve heat resistance, what performed the BH (Baked Hardening) process after press work is preferable.

  The separation portion 13 is formed with a plurality of flow channel grooves parallel to each other and parallel to the formation surface of the catalyst electrode 21. This channel groove has a concave shape in a cross section perpendicular to the gas flow direction. The channel groove is composed of the separation wall 15 and the electrode contact wall 16, and the space surrounded by the separation wall 15, the electrode contact wall 16 and the catalyst electrode 21 becomes the hydrogen gas channel 17 and the oxygen gas channel 18. The separation wall 15 separates the hydrogen gas channel 17 and the oxygen gas channel 18 so that hydrogen gas and oxygen gas are not mixed. The electrode contact wall 16 is in contact with the catalyst electrode 21, takes out DC power generated at the interface between the polymer membrane 20 and the catalyst electrode 21 as DC current, and collects it through the separation wall 15, another electrode contact wall 16, and the like. Collected on the electric board.

  The channel grooves adjacent to each other are formed so that the open surfaces are opposite to each other, and accordingly, the hydrogen gas channel 17 and the oxygen gas channel 18 are set to be adjacent to each other. That is, the gas flow path is set so that the same gas contacts the same catalyst electrode 21. Further, as shown in FIG. 2, the two separators 1 constituting one unit battery 101 are arranged so that the open portions of the flow channel grooves face each other with the fuel battery cell 2 interposed therebetween. That is, the two separators 1 are arranged so as to have a plane-symmetrical relationship with the center of the fuel cell 2 as the symmetry plane. However, the setting of the gas flow path is not a plane-symmetrical relationship, and the flow path grooves facing each other with the fuel cell 2 interposed therebetween are set so as to form gas flow paths for different gases. For example, as shown in FIG. 2, one of the gas flow paths facing each other across the fuel cell 2 is a hydrogen gas flow path 17, and the other is an oxygen gas flow path 18.

  Electric power can be generated by arranging the separator 1 and setting the gas flow path as described above.

  The flow path formed by the flow path groove and the catalyst electrode 21 is not limited to hydrogen gas and oxygen gas, and cooling water may flow. When flowing the cooling water, it is preferable to flow in any of the channel grooves facing each other with the fuel battery cell 2 interposed therebetween.

  The seal portion 14 is formed with a seal protrusion that extends parallel to the surface on which the catalyst electrode 21 is formed. This seal projection has a U-shaped or V-shaped cross section perpendicular to the gas flow direction. The top 19 of the seal projection is pressed against the exposed polymer film 20 by a spring force. Sealing at this pressure contact position can prevent leakage of hydrogen gas and oxygen gas. In addition, the U-shaped or V-shaped seal protrusion is used to reduce the membrane contact area of the top 19 and realize a high-pressure seal similar to an O-ring.

  In order to press-contact the top 19 of the seal protrusion against the polymer film 20 by a spring force, the position of the top 19 of the seal protrusion in the separator 1 in a state where it does not come into contact with the polymer film 20, that is, before the PEFC 1 is assembled. However, the seal part 14 is formed in advance so that the PEFC 1 is assembled and the polymer film 20 side is further from the position where it is in contact with the polymer film 20. Specifically, as shown in FIG. 3A, when the PEFC 1 is assembled, the position of the top 19 of the seal protrusion is determined based on the virtual contact surface A with the catalyst electrode 21. The distance between the contact surface and the top portion 19 is a position where the thickness t1 of the catalyst electrode 21 is obtained. Therefore, in a state before the PEFC 1 is assembled, as shown in FIG. 3B, the position of the top portion 19 of the seal projection is such that the distance from the contact surface with the catalyst electrode 21 is t2 larger than t1. What is necessary is just to form. Since the connecting portion between the separation portion 13 and the seal protrusion acts as a spring, the pressure when the top portion 19 is pressed against the polymer film during assembly is determined by this spring force and the contact area. The spring force is obtained by multiplying the spring constant (elastic constant) by the amount of displacement according to Hooke's law. In the separator 1, the spring constant is determined by the material of the separator 1 and the shape of the seal portion 14. The amount of displacement is Δt = t2−t1. Therefore, the seal pressure can be easily adjusted by changing t2 at the time of press work in a state where the material and shape are determined in advance and the spring constant is determined. Needless to say, the material and shape may be changed in order to achieve the optimum sealing pressure.

  FIG. 4 is a plan view of the separator 1 according to the embodiment of the present invention. FIG. 5 is a cross-sectional view of the separator 1 taken along the line SS.

  When the separator 1 is used, the top portion 19 of the seal protrusion is in contact with the polymer film 20, and a contact line that virtually indicates the contact portion is referred to as a seal line L.

  The shape of the seal line L has an arc Ac whose center is located on the inner side of the seal line L at each corner, and the adjacent arcs Ac are connected via an arc Am whose center is located on the outer side of the seal line L. It has a shape. By using such a seal line, the contact pressure generated by tightening during assembly can be dispersed, so that sufficient sealing performance can be exhibited without destroying the polymer film 20. The ratio rm / rc between the radius rc of the arc Ac and the radius rm of the arc Am is preferably 2 or more and 8 or less, and most preferably 2.

  The change of the contact pressure when the ratio of the shape of the seal line L, in particular, the radius rc of the arc Ac and the radius rm of the arc Am is changed is verified by simulation based on the finite element method as follows.

  FIG. 6 is a diagram showing a finite element model of the separator when performing the simulation. 6A is a plan view, and FIG. 6B is a cross-sectional view taken along the line TT.

In this finite element model, the material of the metal separator is SUS (longitudinal elastic modulus = 200000 N / mm ² , Poisson's ratio = 0.3), and a virtual rigid plane (corresponding to a polymer film) 22 holding an external force of 5.9 N 22 The simulation is performed under the condition of pressing against the separator. Considering the shape of the separator and the plane of mechanical symmetry, a 1/8 portion of the entire separator is modeled.

  A model in which the ratio rm / rc between the radius rc of the arc Ac and the radius rm of the arc Am is changed, and the Mises stress distribution is calculated, whereby the apex portion 19 of the seal protrusion and the polymer film 20 are brought into contact with each other. Evaluate the pressure distribution.

7 to 13 are diagrams illustrating simulation models of the examination examples 1 to 7, respectively.
Examination Example 1 is a model in which the radius rc of the arc Ac = 5 mm and the radius rm of the arc Am = 0 mm.

  Examination Example 2 is a model in which the radius rc of the arc Ac is 5 mm and the radius rm of the arc Am is 50 mm, and the ratio of the radius rc of the arc Ac to the radius rm of the arc Am is rm / rc = 10.

  Examination Example 3 is a model in which the radius rc of the arc Ac is 5 mm and the radius rm of the arc Am is 40 mm, and the ratio rm / rc = 8 between the radius rc of the arc Ac and the radius rm of the arc Am.

  Examination Example 4 is a model in which the radius rc of the arc Ac is 5 mm and the radius rm of the arc Am is 30 mm, and the ratio rm / rc = 6 between the radius rc of the arc Ac and the radius rm of the arc Am.

  Examination Example 5 is a model in which the radius rc of the arc Ac is 5 mm and the radius rm of the arc Am is 20 mm, and the ratio rm / rc = 4 between the radius rc of the arc Ac and the radius rm of the arc Am.

  Examination Example 6 is a model in which the radius rc of the arc Ac is 5 mm and the radius rm of the arc Am is 10 mm, and the ratio rm / rc = 2 between the radius rc of the arc Ac and the radius rm of the arc Am.

  The examination example 7 is a model in which the radius rc of the arc Ac is 5 mm and the radius rm of the arc Am is 5 mm, and the ratio rm / rc = 1 between the radius rc of the arc Ac and the radius rm of the arc Am.

  The results of simulations using these models under the above conditions are shown in the stress distribution diagrams of FIGS.

In Study Example 1, the Mises stress is 229 N / mm ² in the arc Ac, and in such a seal line shape, the contact pressure is concentrated on the arc Ac, that is, the polymer film may be destroyed. I understand that it is expensive. In addition, since the stress at the straight line connecting the arcs Ac is small, there is a high possibility that the sealing performance will be lowered if tightening is performed to such an extent that the polymer film is not broken. If the tightening force is increased to increase the sealing performance, the polymer The possibility of breaking the film is further increased.

In Study Example 2, Mises stresses in the arc Ac is 135N / mm ^2, a 38.2N / mm ² in the arc Am. In the case of such a seal line shape, the contact pressure is distributed between the arc Ac and the arc Am, so that the contact pressure in the arc Ac is reduced, that is, the possibility that the polymer film is broken is reduced. I understand. However, since the pressure at the portion connecting the arc Ac and the arc Am is 0, the sealing performance is not exhibited. If the tightening force is increased in order to exhibit the sealing performance, the possibility of breaking the polymer film increases.

In Study Example 3, Mises stresses in the arc Ac is 128N / mm ^2, a 35.3N / mm ² in the arc Am. In the case of such a seal line shape, the contact pressure is distributed between the arc Ac and the arc Am, so that the contact pressure in the arc Ac is reduced, that is, the possibility that the polymer film is broken is reduced. I understand. In addition, it can be seen that an appropriate pressure is also generated at the portion connecting the arc Ac and the arc Am, and the sealing performance is maintained.

In Study Example 4, Mises stresses in the arc Ac is 117N / mm ^2, a 42.1N / mm ² in the arc Am. In the case of such a seal line shape, the contact pressure is distributed between the arc Ac and the arc Am, so the contact pressure in the arc Ac is reduced. In addition, it can be seen that an appropriate pressure is also generated at the portion connecting the arc Ac and the arc Am, and the sealing performance is maintained.

In Study Example 5, Mises stresses in the arc Ac is 105N / mm ^2, a 55.9N / mm ² in the arc Am. In the case of such a seal line shape, the contact pressure is distributed between the arc Ac and the arc Am, so that the contact pressure in the arc Ac is further reduced. In addition, it can be seen that an appropriate pressure is also generated at the portion connecting the arc Ac and the arc Am, and the sealing performance is maintained.

In study example 6, Mises stresses in the arc Ac is 83.3N / mm ^2, a 89.2N / mm ² in the arc Am. In the case of such a seal line shape, since the contact pressure is distributed between the arc Ac and the arc Am, the contact pressure in the arc Ac is further reduced, and the contact pressure in the arc Ac and the contact pressure in the arc Am are reduced. Are almost equal. Further, it can be seen that an appropriate pressure is also generated at the portion connecting the arc Ac and the arc Am, the sealing performance is maintained, and the seal line shape is particularly suitable.

In Study Example 7, Mises stresses in the arc Ac is 74.5N / mm ^2, is 149N / mm ² in the arc Am. In the case of such a seal line shape, the contact pressure is distributed between the arc Ac and the arc Am, so that the contact pressure in the arc Ac is further reduced, but the contact pressure is concentrated on the arc Am. It can be seen that the polymer film is highly likely to be destroyed. Further, since the pressure at the portion connecting the arc Ac and the arc Am is 0, the sealing performance is not exhibited. If the tightening force is increased to exert the sealing performance, the possibility of breaking the polymer film increases.

  As described above, since the arcs adjacent to each other are seal lines having a shape in which the centers are connected via the arc Am located outside the seal line L, the contact pressure can be dispersed. Sufficient sealing performance can be exhibited without destroying 20.

  Further, if the ratio rm / rc between the radius rc of the arc Ac and the radius rm of the arc Am is set to 10 and 1 as in Examination Example 2 and Examination Example 7, the sealing performance is not exhibited, so the ratio rm / rc is 2 or more and 8 or less are preferable, and 2 is most preferable because the contact pressure in the arc Ac and the contact pressure in the arc Am are substantially equal.

1 is a perspective view schematically showing a polymer electrolyte fuel cell (abbreviated as PEFC) 100 in a developed state. FIG. 2 is a horizontal sectional view of a unit battery 101 including a separator 1. FIG. It is a figure explaining the shape of the seal part 14 for a spring force to generate | occur | produce. It is a top view of separator 1 which is one embodiment of the present invention. FIG. 3 is a cross-sectional view of the separator 1 taken along the line SS. It is a figure which shows the finite element model of the separator at the time of performing simulation. It is a figure which shows the simulation model of the examination example 1. FIG. It is a figure which shows the simulation model of the examination example 2. FIG. It is a figure which shows the simulation model of the examination example 3. FIG. It is a figure which shows the simulation model of the examination example 4. FIG. It is a figure which shows the simulation model of the examination example 5. FIG. It is a figure which shows the simulation model of the examination example 6. FIG. It is a figure which shows the simulation model of the examination example 7. FIG. 6 is a stress distribution diagram showing a simulation result of Study Example 1. FIG. It is a stress distribution figure which shows the simulation result of the examination example 2. It is a stress distribution figure which shows the simulation result of the examination example 3. It is a stress distribution figure which shows the simulation result of the examination example 4. It is a stress distribution figure which shows the simulation result of the examination example 5. FIG. It is a stress distribution figure which shows the simulation result of the examination example 6. It is a stress distribution figure which shows the simulation result of the examination example 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separator 2 Fuel cell 3 Current collector plate 4 Insulation sheet 5 End flange 6 Hydrogen gas supply port 7 Cooling water supply port 8 Oxygen gas supply port 9 Hydrogen gas discharge port 10 Cooling water discharge port 11 Oxygen gas discharge port 12 Electrode wiring 13 Separation part 14 Seal part 15 Separation wall 16 Electrode contact wall 17 Hydrogen gas flow path 18 Oxygen gas flow path 19 Top part 20 Polymer membrane 21 Catalyst electrode

Claims (2)

A separator disposed between a plurality of electrolyte assemblies each provided with a catalyst electrode on a surface in a thickness direction of an electrolyte layer containing an electrolyte medium, separating a flow path of a fuel gas and an oxidant gas; A separator integrated with a seal portion that prevents leakage of gas and oxidant gas,
The region corresponding to the seal portion is a seal protrusion that extends in parallel with the catalyst electrode forming surface of the electrolyte assembly, and the top portion of the seal protrusion is pressed against the electrolyte assembly by a spring force. Have
The contact line that virtually shows the location where the top of the seal projection contacts the electrolyte layer is a closed curve,
The shape of the closed curve has a first arc whose center is located inside the closed curve at each corner, the first arc adjacent to each other, and a second arc whose center is located outside the closed curve. A separator characterized by having a shape connected via a wire.   The separator according to claim 1, wherein a ratio rm / rc of a radius rc of the first arc to a radius rm of the second arc is 2 or more and 8 or less.