JP2008053095A - Current collector of oxygen supply electrode, electrochemical reaction device, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current collector of an oxygen supply electrode capable of sufficiently supplying oxygen by securing an oxygen passage even when a large load is applied, and to provide an electrochemical device such as a fuel cell capable of obtaining the desired power generation efficiency by using the current collector. <P>SOLUTION: A porous current collector 2 formed in a plate shape as a whole and a skeleton structure 1 are stacked in the plate thickness direction, and the pore parts and the skeletons are used as an oxygen passage of the current collector of the oxygen supply electrode. The skeleton structure has higher mechanical strength than the porous current collector, and is formed by arranging a conductive material in network structure, the porous current collector is formed by filling its part in the skeleton structure in the stacked part, and at least the surface is formed with silver or a silver alloy. Moreover, a wavy pattern is formed in the plate surface direction in the skeleton structure. The electrochemical reaction device such as the fuel cell is formed by stacking so that the surface of the porous current collector is faced to the surface of the oxygen supply electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a current collector for an oxygen supply electrode that supplies oxygen to a solid electrolyte, and an electrochemical reaction device and a fuel cell in which the current collector is formed.

  For example, as shown in Patent Document 1, a fuel cell stack is conventionally housed in a can body. This fuel cell stack is composed of a plurality of single cells that are composed of a power generation cell, a current collector stacked on both outer sides of the power generation cell, and a separator stacked on the outer side of the current collector in the stacking direction. Is configured.

  In addition, this power generation cell has an air electrode formed on one surface of the plate-shaped solid electrolyte and a fuel electrode formed on the other surface. Of the current collectors, the air electrode current collector laminated on the outside of the air electrode is composed of a sponge-like porous sintered metal plate having an oxygen channel such as an Ag-based alloy. .

Furthermore, the fuel cell stack needs to be in close contact with each other in order to maintain electrical connection. In general, a weight is placed on the center of the upper part of the fuel cell stack.
However, in recent years, the output of fuel cells has increased due to technological advances, and the number of single cells stacked in the stacking direction has increased remarkably. As a result, in particular, the air electrode current collector positioned at the lowermost stage is supplied with sufficient oxygen by a load acting on the weight or the upper structural member and the oxygen flow path being crushed. There was a risk of being lost.

  Note that the applicant has previously filed Patent Document 2 as a technique related to the air electrode current collector.

JP 2004-335166 A JP 2002-216807 A

  The present invention has been made in view of such circumstances, and even when a large load is applied due to an increase in the number of stacked single cells, an oxygen supply electrode that can sufficiently supply oxygen by securing an oxygen flow path is provided. It is an object of the present invention to provide an electrochemical reaction device such as a fuel cell that can obtain a desired power generation efficiency using the current collector.

In order to solve the above problems, the invention described in claim 1 is characterized in that a porous current collector formed in a flat plate shape and a skeletal structure are laminated in the plate thickness direction as a whole, Is a current collector for an oxygen supply electrode serving as an oxygen flow path, and the skeleton structure has a higher mechanical strength than the porous current collector, and a conductive material is formed in a network structure. As well as
The porous current collector is a current collector for an oxygen supply electrode, wherein a part of the porous current collector is filled in the skeleton structure in the laminated portion, and at least the surface is formed of silver or a silver alloy. is there.
Here, the mesh structure means a member in which holes such as expanded metal, punching metal, or mesh metal are formed.

  The invention according to claim 2 is the current collector of the oxygen supply electrode according to claim 1, wherein the skeleton structure has a waveform in which unevenness is repeated in the thickness direction toward the plate surface direction. It is characterized by being. For example, corrugating can be used as a method of forming a waveform in the direction of the plate surface.

  According to a third aspect of the present invention, there is provided an electrochemical reaction apparatus in which electrodes are formed on both surfaces of a plate-shaped solid electrolyte, and one of the electrodes is an oxygen supply electrode. In the electrochemical reaction device, the current collector is laminated with the surface of the porous current collector facing the surface of the oxygen supply electrode.

  Here, the electrochemical reaction device means a device having an electrochemical cell that performs a chemical reaction with the exchange of electrons, and is used as an oxygen enricher, a water electrolysis device, etc. in addition to a fuel cell. It is what is done.

  The invention according to claim 4 is the fuel cell characterized in that the other electrode according to claim 3 is a hydrogen supply electrode or a hydrocarbon supply electrode.

  According to the invention described in claim 1 or 2, since a part of the plate-like porous current collector enters the skeletal structure having a high mechanical strength in the thickness direction, the porous material in the part As a result, the mechanical strength of the current collector increases, and as a result, even when a large load is applied in the thickness direction, the oxygen flow path is secured and the oxygen linear velocity is kept constant without being crushed. Can be kept in.

  In addition, by disposing the surface of the porous current collector on the oxygen supply electrode side, it is possible to absorb the thermal strain between the current collector and the electrode, and the current collector and oxygen supply electrode of the oxygen supply electrode By increasing the contact area, the contact resistance can be remarkably reduced.

  In particular, when the skeletal structure is an expanded metal, elasticity is imparted in the thickness direction in the processing process, which is coupled with the porous current collector being filled in the skeleton in the thickness direction. It is possible to provide a current collector for an oxygen supply electrode having excellent elastic deformability.

Furthermore, according to the invention described in claim 2, since the corrugation is formed so as to be uneven in the thickness direction toward the plate surface direction, the thickness of the current collector of the oxygen supply electrode is secured, and the plate A current collector having desired elasticity and mechanical strength in the thickness direction can be easily obtained.
At this time, when the skeleton structure is an expanded metal, unevenness is formed in the thickness direction at the same time as molding, and unevenness is also formed in the thickness direction by corrugating. Excellent elasticity and mechanical strength can be obtained by a synergistic effect with the unevenness caused by processing.

According to invention of Claim 3, while forming an electrode on both surfaces of a plate-shaped solid electrolyte, the collector of the oxygen supply electrode of Claim 1 or 2 is used for the surface of the porous collector. Since the layers are stacked toward the surface of the oxygen supply electrode, the contact resistance between the current collector and the oxygen supply electrode can be reduced, and the reaction efficiency in the solid electrolyte can be significantly increased.
In addition, the porous current collector in the current collector of the oxygen supply electrode absorbs thermal strain, thereby preventing the constituent members of the electrochemical reaction device from cracking.

  In particular, according to the invention described in claim 4, since the fuel cell is configured with the other electrode as a hydrogen supply electrode or a hydrocarbon supply electrode, the contact between the current collector of the oxygen supply electrode and the oxygen supply electrode as described above. The power generation efficiency can be increased by reducing the resistance.

  Even when a large load is applied in the thickness direction, the current collector is not crushed as described above, and the fuel cell stack is prevented from contracting as a whole. It is possible to prevent the deformation and prevent the release of unreacted gas that has not yet contributed to the reaction, and as a result, the efficiency of the power generation reaction can be increased. Moreover, it is possible to prevent the fuel cell from being heated by burning the released unreacted oxygen gas, and causing thermal distortion between the constituent members of the fuel cell. Furthermore, since the porous current collector in the current collector of the oxygen supply electrode absorbs thermal strain, it is possible to prevent the structural members of the fuel cell that are generally made of a fragile material such as ceramics from cracking. .

  Hereinafter, an embodiment of a fuel cell according to the present invention as well as an embodiment of a current collector for an oxygen supply electrode according to the present invention will be described with reference to FIGS.

First, the current collector 3 of the oxygen supply electrode will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the current collector 3 of the oxygen supply electrode in the present embodiment has a porous current collector 2 and a skeleton structure 1 formed in a plate shape as a whole, and are stacked in the plate surface direction. A part of the porous current collector 2 is filled in the skeleton structure 1 in the thickness direction by thermocompression bonding and rolling.

  Since the skeleton structure 1 needs to have conductivity and high mechanical strength, an expanded metal made of pure silver (network structure) or an expanded metal made of SUS316 plated with silver is preferably used. Yes.

  Further, a wave height (for example, about 0.9 mm) that is 2 to 3 times the thickness (for example, about 0.3 mm) toward the plate surface direction, and a wavelength that is substantially the same as the wave height, or A waveform having the following wavelength (for example, about 1 mm or less) is formed, and a convex portion having a wave height is exposed from the porous current collector 2.

  On the other hand, the porous current collector 2 is a foam metal in which an oxide is dispersed in a silver base, has a porosity of 60% to 97%, and is slightly thicker than the wave height of the skeleton structure 1. (For example, 0.9 mm). A surface portion (for example, about 0.1 mm) is exposed from the skeleton structure 1. Examples of the oxide include tin oxide, indium oxide, lanthanum oxide, copper oxide, chromium oxide, titanium oxide, aluminum oxide, iron oxide, nickel oxide, vanadium oxide, magnesium oxide, calcium oxide, strontium oxide, and barium oxide. Although tin oxide is most preferred.

The dispersion of the oxide as described above has an effect of promoting dissociation of oxygen (O ₂ → 2O) and generation of oxygen ions (O + 2e → O ²⁻ ) in the current collector 3 of the oxygen supply electrode. The exchange current density between the current collector 3 and the electrode of the oxygen supply electrode increases, and oxygen ions move from the current collector 3 to the electrode quickly.
Moreover, it is preferable that the oxide is disperse | distributed in 3-50 mass%. When the oxide content is less than 3% by mass, the mechanical strength as the current collector 3 of the fuel cell becomes insufficient. When the oxide content exceeds 50% by mass, the electrical conduction as the current collector 3 occurs. The nature will decline.

  Furthermore, in order to raise the melting point, one or more of copper, zinc, cadmium, nickel, tin, gold, platinum, palladium, iridium and rhodium are contained in a total amount of 40% by mass or less. Is preferred. The reason why the content is set to 40% by mass or less is that when the content exceeds this range, the catalytic action (dissociation of oxygen, generation of oxygen ions) by silver decreases.

As described above, the surface portion (for example, about 0.1 mm) of the porous current collector 2 is exposed from the skeleton structure 1, and the convex portions of the skeleton structure 1 are exposed to the porous current collector. A current collector (for example, about 1 mm) 3 of an oxygen supply electrode exposed from the electric body 2 is configured.
The current collector 3 is required to have a thickness of 0.5 mm or more, more preferably 0.8 mm or more, in order to set the linear velocity of oxygen within an optimum range.

  The porous current collector 2 may be made of a metal or alloy having excellent mechanical strength at the operating temperature (400 ° C. to 800 ° C.) of the fuel cell. In this case, a nickel plating base layer is formed on the surface, and silver plating is formed thereon to ensure the generation of oxygen ions.

Next, an embodiment of a fuel cell using the above-described current collector 3 of the oxygen supply electrode according to the present invention will be described.
As shown in FIGS. 3 and 4, the fuel cell according to the present embodiment has the fuel cell stack 10 integrally fixed to an electrically insulative gantry 18 inside the can 21, and is vertically and horizontally 2 in the plane. A total of 16 fuel cell stacks 10 are installed in a row and stacked in four stages in the height direction.

  Here, the outer periphery of the can body 21 is surrounded by a heat insulating member 23, a cavity is formed inside, the 16 fuel cell stacks 10 are disposed, and each fuel cell stack is disposed on the lower side surface. A preheating burner 24 is installed so as to face 10.

  As shown in FIG. 5, the fuel cell stack 10 includes a power generation cell 7 in which the air electrode 5 is formed on one surface of the solid electrolyte layer 4 and the fuel electrode 6 is formed on the other surface. The current collector 3 of the oxygen supply electrode is laminated with the surface of the porous current collector 2 facing the surface of the air electrode 5. Furthermore, a current collector 8 is laminated on the surface of the fuel electrode 6 and a separator 9 is laminated outside the current collectors 3 and 8 to constitute a single cell. It is schematically configured by stacking several tens or more in the direction.

Here, the solid electrolyte layer 4 is composed of stabilized zirconia (YSZ) or the like to which yttria is added, the fuel electrode 6 is composed of a metal such as Ni or a cermet such as Ni—YSZ, and the air electrode 5 is composed of LaMnO ₃ , LaCoO. _The anode current collector 8 is made of a sponge-like porous sintered metal plate such as Ni.

  The separator 9 is made of stainless steel or the like, and has a function of electrically connecting the power generation cells 7 and supplying a reaction gas such as fuel gas or air to the power generation cells 7. Thus, during operation, the air discharged from the central portion of the separator 9 toward the power generation cell 7 is diffused in the outer peripheral direction of the power generation cell 7, and is distributed over the entire surface of the air electrode 5 through the current collector 3 of the oxygen supply electrode 7. In addition, the fuel gas is distributed to the fuel electrode 6 through the current collector 8 in the same manner, thereby generating a power generation reaction.

  Further, the fuel cell stack 10 employs a sealless structure in which no gas leakage prevention seal is provided on the outer periphery of the power generation cell 7, and the remaining gas that has not been consumed in the power generation reaction is removed from the outer periphery of the power generation cell 7. It is designed to release outward from the outside.

  Furthermore, between the fuel cell stacks 10 arranged in two rows in the vertical and horizontal directions, the radiant heat from the upper fuel cell stack 10 to the lower fuel cell stack 10 can be received efficiently and positioned at the highest temperature. Thus, a fuel reformer 30 having a cross-shaped cross section is disposed along the height direction of the fuel cell stack 10.

  Furthermore, a side fuel heat exchanger 40 and a side air heat exchanger 50 that efficiently receive the radiant heat from the fuel cell stack 10 are disposed outside the side portion of the fuel cell stack 10. A fuel buffer tank 45 that supplies fuel gas to the fuel cell stack 10 and an air buffer tank 55 that supplies air are arranged along the height direction of the fuel cell stack 10. It is installed.

An upper heat exchanger 41 connected to the downstream side of the side fuel heat exchanger 40 is disposed above the uppermost fuel cell stack 10 in the horizontal direction, and the side air An upper air heat exchanger 51 connected to the downstream side of the heat exchanger 50 is disposed in the horizontal direction.
The upper heat exchanger 41 has a downstream side connected to the upper portion of the fuel reformer 30, and the fuel reformer 30 has a discharge pipe 32 for discharging a reformed gas provided at the lower end thereof. The fuel buffer tank 45 is connected to the downstream side. On the other hand, the upper air heat exchanger 51 is connected to the air buffer tank 55 on the downstream side.

  The fuel buffer tank 45 is connected to the fuel cell stack 10 via a plurality of fuel distribution pipes 28 provided in parallel, and the air buffer tank 55 includes a plurality of air buffer tanks 55 provided in parallel. The fuel cell stack 10 is connected via an air distribution pipe 29.

In addition, a steam generator 60 for obtaining high-temperature steam for fuel reforming is disposed below the can body 21.
The steam generator 60 is disposed in the lower exhaust pipe 19 b that penetrates the heat insulating member 23 at the lower portion of the can body 21 in order to use the heat amount of the exhaust gas heated by the burner 24. A water supply pipe 17 having a supply port is connected to the outside of the can body 21 on the upstream side, and a fuel mixing section 27 provided on the upstream side of the side fuel heat exchanger 40 on the downstream side. Is connected.

On the other hand, on the upstream side of the fuel mixing section 27, a fuel supply pipe 15 provided in parallel with the water supply pipe 17 and having a supply port outside the can body 21 is connected.
On the other hand, on the upstream side of the side air heat exchanger 50, it is supplied to the outside of the can body 21 through a cooling air pipe 25 that is provided on the outer periphery of the burner 24 and also acts as a cooling jacket for the burner 24. It is connected to an air supply pipe 16 having a mouth.
As shown in FIG. 3, an exhaust pipe 19 a is provided at the center of the upper portion of the can body 21 to discharge the high-temperature exhaust gas discharged from each fuel cell stack 10 into the can body 21 to the outside. .

  Next, the operation of the above fuel cell using the current collector 3 of the oxygen supply electrode according to the present invention will be described.

First, the burner 24 is activated, and city gas is supplied to the fuel supply pipe 15, oxygen is supplied to the air supply pipe 16, and water is supplied to the water supply pipe 17.
Then, water is supplied to the steam generator 60 and indirectly heated by the gas below the can body 21 heated by the burner 24, so that steam is gradually generated. To be supplied.

  On the other hand, the city gas is supplied from the fuel supply pipe 15 to the fuel mixing section 27 and is supplied to the side fuel heat exchanger 40 while being mixed with the water vapor. Then, while being indirectly heated by the gas inside the can body 21 heated by the burner 24, the gas rises and is supplied to the upper heat exchanger 41. Furthermore, in the upper heat exchanger 41, the temperature is increased to near the reforming reaction temperature by being indirectly heated by the high-temperature gas above the can body 21, and then supplied to the fuel reformer 30.

  Next, in the fuel reformer 30, while flowing downward, the fuel reformer 30 is further heated by radiant heat from the fuel cell stack 10, so that it is gradually reformed to become fuel gas. The fuel gas is supplied to the fuel buffer tank 45 via the discharge pipe 32 and then supplied to each fuel cell stack 10 via the fuel distribution pipe 28.

  On the other hand, oxygen is supplied to the cooling air pipe 25, heated while cooling the peripheral portion of the burner 24, and supplied to the side air heat exchanger 50. Then, while being heated by the gas inside the can 21, it rises and is supplied to the upper air heat exchanger 51. Further, after being heated in the upper air heat exchanger 51, it is supplied to the air buffer tank 55 and supplied to each fuel cell stack 10 via the air distribution pipe 29.

  Then, in the fuel cell stack 10 heated by the radiant heat from the burner 24, oxygen is supplied from the separator 12 to the current collector 3 of the oxygen supply electrode and diffuses around the current collector 3, while the air electrode 5 is supplied in the vicinity. Then, it is decomposed into oxygen atoms in the vicinity of the air electrode 5 and becomes oxygen ions by receiving electrons. The oxygen ions move to the air electrode 5 and are supplied to the solid electrolyte 4.

  On the other hand, the fuel gas is supplied from the separator 12 to the current collector 8 of the fuel electrode, is decomposed into hydrogen atoms in the vicinity of the fuel electrode 6, and emits electrons to become hydrogen ions. The hydrogen ions move to the fuel electrode 6 and are supplied to the solid electrolyte 4.

  Then, the oxygen ions and hydrogen ions react with each other in the solid electrolyte 4 to generate water vapor. At this time, electricity is taken out by the potential difference between the air electrode 5 and the fuel electrode 6.

  According to the fuel cell described above, the current collector 3 of the oxygen supply electrode described above is excellent in elastic deformability in the thickness direction because a part of the porous current collector 2 is filled in the expanded metal 1. As a result, even when several tens of single cells are stacked and a larger load is applied, the oxygen flow path can be secured. Moreover, since the plate | board thickness of the electrical power collector 3 is 0.8 mm or more, and the linear velocity of oxygen can be set to the optimal range, desired power generation efficiency can be obtained.

  Further, the surface portion of the porous current collector 2 comes into contact with the air electrode 5 to absorb the thermal strain between the current collector 3 and the air electrode 5, so that the current collector 3, the air electrode 5, etc. While preventing a structural member from cracking and increasing the contact area between the current collector 3 and the oxygen electrode 5, the contact resistance is reduced, and the power generation efficiency can be increased.

On the other hand, since the convex part of the surface portion of the expanded metal 1 is in contact with the separator 9, the mechanical strength is high, a desired oxygen linear velocity can be obtained, and shrinkage in the thickness direction is suppressed. The constituent members can be prevented from changing in the plate thickness direction.
Therefore, mechanical stress can be prevented from acting on the fuel distribution pipe 28 connecting the separator 9 and the fuel buffer tank 45, and mechanical stress can be applied to the air distribution pipe 29 connecting the separator and the air buffer tank 55. I can prevent it. As a result, the fuel distribution pipe 28 and the air distribution pipe 29 are prevented from being damaged, and unreacted fuel gas and oxygen are prevented from being released to the outside of the fuel stack 10, thereby improving the power generation efficiency. Can be maintained.

Next, a manufacturing method for the current collector 3 of the oxygen supply electrode will be described.
First, corrugation processing was performed on the expanded metal 1 made of pure silver having a thickness of 0.3 mm to form a waveform having a wave height of 0.9 mm and a wavelength of 1 mm.

  In parallel with this, 50.0% by mass of pure silver atomized powder, 1.5% by mass of n-hexane, 5.0% by mass of HPMC, 2.0% by mass of DBS, 3.0% by mass of glycerin, 38.5% by mass of distilled water After preparing a mixed slurry having the composition consisting of the following, this mixed slurry was formed into a molded body having a thickness of 2 mm by the doctor blade method. Next, the molded body was foamed at a humidity of 90%, a temperature of 35 ° C., and a holding time of 10 minutes, and then degreased at an air temperature of 450 ° C. and a holding time of 60 minutes. Thereafter, the air temperature was 910 ° C. and the holding time. The porous current collector 2 having a thickness of 1.5 mm was produced by sintering under the condition of 120 minutes.

Next, an expanded metal 1 having a wave height of 0.9 mm and a porous current collector 2 having a thickness of 1 mm were stacked in the plate thickness direction, and thermocompression bonded under conditions of a load of 2.5 kg, 800 ° C. for 3 hours.
Then, a part of the porous current collector 2 enters the expanded metal 1 so that the expanded metal 1 is filled, and the thickness of the laminate of the expanded metal 1 and the porous current collector 2 is about 1.3 mm. became.

  Next, this laminate was rolled, and a part of the porous current collector 2 was filled in the expanded metal 1. Then, the expanded metal 1 was stretched to the limit in the plane direction together with the porous current collector 2 while the wave height was reduced, and the diameter became about 1.04 times. As a result, the corrugated convex portion of the expanded metal 1 is exposed from the porous current collector 2, and the surface portion (thickness 0.1 mm) of the porous current collector 2 is exposed from the expanded metal 1. A current collector 3 of 10 mm was obtained.

It is explanatory drawing which shows one Embodiment of the electrical power collector 3 of the oxygen supply electrode which concerns on this invention, Comprising: It is a whole perspective view. It is sectional drawing of the electrical power collector 3 shown in FIG. It is explanatory drawing which shows 1st embodiment of the fuel cell which concerns on this invention, Comprising: It is a longitudinal cross-sectional view. FIG. 4 is a cross-sectional view of the fuel cell shown in FIG. 3. FIG. 4 is a partially enlarged explanatory view of the fuel cell stack 10 shown in FIG. 3.

Explanation of symbols

1 Expanded metal (skeleton structure)
2 Porous current collector 3 Oxygen supply electrode current collector

Claims (4)

A current collector for an oxygen supply electrode in which a porous current collector and a skeleton structure formed in a flat plate shape as a whole are laminated in the thickness direction, and the pores and the skeleton serve as an oxygen flow path. ,
The skeleton structure has a mechanical strength higher than that of the porous current collector, and a conductive material is formed in a network structure.
A current collector for an oxygen supply electrode, wherein the porous current collector is partially filled in the skeleton structure in the laminated portion and at least the surface is formed of silver or a silver alloy.   The current collector for an oxygen supply electrode according to claim 1, wherein the skeleton structure has a waveform in which unevenness is repeated in the thickness direction toward the plate surface direction.   3. An electrochemical reaction device in which electrodes are formed on both surfaces of a plate-shaped solid electrolyte, and one of the electrodes is an oxygen supply electrode. 3. The oxygen supply electrode current collector according to claim 1 or 2, wherein the current collector of the oxygen supply electrode is the porous current collector. An electrochemical reaction device characterized in that the body surface is laminated with the surface of the oxygen supply electrode facing the surface.   4. The fuel cell according to claim 3, wherein the other electrode is a hydrogen supply electrode or a hydrocarbon supply electrode.

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