JP2002075410A - Current collector of solid oxide fuel cell and solid oxide fuel cell using the same - Google Patents

Abstract

(57) [PROBLEMS] A current collector that eliminates damage to cells due to stress concentration, reduces electrical contact resistance between an electrode surface and a current collector, and increases power generation efficiency, and a solid using the same. An electrolyte fuel cell is provided. SOLUTION: A large number of flat single cells each having a solid electrolyte membrane and a fuel-side electrode film and an oxygen-side electrode film respectively stacked on both surfaces thereof are stacked via a gas separator to form an SO.
When forming the FC, a plate-shaped current collector, which is interposed between the electrode film of the single cell and the gas separator and is incorporated in the space through which the electrode active material flows, is formed into a large number along the electrode active material flow direction. A SOFC is formed by stacking a large number of single cells via a gas separator incorporating the current collector as a current collector having a honeycomb structure provided with a hollow gas flow path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current collector for a solid oxide fuel cell and a solid oxide fuel cell using the same, and more particularly to preventing a cell from being damaged by stress concentration and improving power generation performance. The present invention relates to a flat solid electrolyte fuel cell current collector and a solid electrolyte fuel cell using the same.

[0002]

2. Description of the Related Art Solid oxide fuel cells (hereinafter referred to as SOFCs)
Is generally formed by stacking a large number of three-layer cells each having a fuel-side electrode film and an oxygen-side electrode film on both surfaces of an oxygen ion-conductive solid electrolyte film via an interconnector or a gas separator. Is done. At present, the electrolyte membrane material is, for example, zirconia (YSZ) stabilized with yttria, the fuel-side electrode film material is, for example, a cermet made of nickel and YSZ, and the oxygen-side electrode film material is, for example, lanthanum-strontium-manganite. ((La, Sr) MnO ₃ ) is widely used.

In an SOFC, a gas separator functions to partition a flow path of a fuel gas and an oxygen-containing gas as an electrode active material supplied to a cell, ie, a flow path of a fuel such as hydrogen and oxygen, and electrically connects adjacent cells to each other. It has the role of connecting. In order to distribute the fuel gas and the oxygen-containing gas evenly to the cell electrode surface and to collect the current generated on the electrode surface, a current collector is incorporated in a space between the electrode film of the cell and the gas separator.

FIG. 3 is an explanatory diagram showing a configuration of an SOFC in the prior art, and FIG. 4 is an explanatory diagram showing a cross section of a unit cell portion in FIG. In FIG. 3, a large number of single cells 2 surrounded by a cell frame 1 are stacked via a gas separator 3, and a space between the gas separator 3 and the electrode film of the single cell 2 is, for example, 1 mm wide and deep. A grooved current collector 4 in which grooves of 1 mm are provided in parallel at intervals of 1 mm is arranged. FIG.
In the single cell 2, the oxygen-side electrode film 6 of the single cell 2 has an oxygen-side grooved current collector 4 a,
However, both are arranged such that the groove installation surface is in contact with the electrode film side.

In the fuel cell stack having such a configuration, for example, hydrogen, which is a fuel, flows into the gas separator 3 from the fuel gas inlet 8 and flows through the plurality of grooves of the fuel-side grooved current collector 4b. Is supplied to the fuel-side electrode film 7 of the single cell 2. On the other hand, air as an oxygen-containing gas, for example, air flows into the gas separator 3 from the oxygen-containing gas inlet 9 and flows through a plurality of grooves of the current collector 4 a with oxygen-side grooves, and a part of the current flows into the oxygen-side electrode of the single cell 2. It is supplied to the membrane 6. Thus, an electrode reaction occurs in the single cell 2 to which the fuel and the oxygen are supplied, and electric energy is generated. The electrons generated in the oxygen-side electrode film 6 of the single cell 2 by the electrode reaction are transmitted to the oxygen-side grooved current collector 4a, the gas separator 3, and the fuel-side grooved current collector 4b in this order, and flow to the adjacent unit cell. Each component is pressed with a certain force in order to minimize the electrical contact resistance.

However, in the above prior art, a grooved current collector is used as the current collector, and the contact surface between the grooved current collector and the surface of the single cell electrode is the so-called grooved current collector, that is, the so-called current collector. It was limited to the bank. Therefore, if the width of the bank portion is increased to increase the contact area, the electrical contact resistance between the current collector and the single cell is reduced, and the contact pressure applied to the single cell by contact is reduced. Insufficient gas supply to the portion where the bank contacts the electrode surface of the single cell, and effective electrode reaction efficiency cannot be obtained. Conversely, if the area of the current collector bank is reduced by reducing the width of the current collector bank, the supply of gas to the portion where the bank of the current collector and the single cell electrode surface are in contact is sufficient, but the current collector and the The electric contact resistance between the single cells increases, the performance of the fuel cell as a whole deteriorates, and the surface pressure applied to the single cells at the contact surface increases, resulting in stress concentration occurring at the corners of the bank of the current collector. As a result, the unit cell is easily damaged.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to make it possible to uniformly supply fuel or oxygen to the entire surface of a cell electrode film and to apply excessive stress to the cell, which has been difficult to realize in the prior art. A current collector for a solid oxide fuel cell and a solid electrolyte fuel using the same, which can reduce the electrical contact resistance between the electrode surface of the cell and the current collector without causing concentration, thereby increasing power generation efficiency It is to provide a battery.

[0008]

Means for Solving the Problems To solve the above problems, the invention claimed in the present application is as follows. (1) A solid electrolyte fuel cell obtained by laminating a large number of flat unit cells having a solid electrolyte membrane and a fuel-side electrode film and an oxygen-side electrode film respectively laminated on both surfaces of the solid electrolyte membrane via a gas separator. When forming a, between the electrode film of the single cell and the gas separator, a plate-shaped current collector incorporated in the space through which the electrode active material flows,
A current collector for a solid oxide fuel cell, wherein the current collector has a honeycomb structure in which a number of hollow gas flow paths are provided along the electrode active material flow direction. (2) The solid oxide fuel cell according to the above (1), wherein the cross-sectional shape of the hollow gas flow path is a square, and the length of one side of the square is 0.5 to 3 mm. Current collector.

(3) Among the above-mentioned current collectors, the constituent material of the current collector on the oxygen electrode side is porous ceramics mainly composed of lanthanum-strontium-manganite, and the constituent material of the current collector on the fuel electrode side is The current collector for a solid oxide fuel cell according to the above (1) or (2), wherein the current collector is a porous ceramic containing nickel + yttria-stabilized zirconia or nickel + alumina + yttria-stabilized zirconia as a main component. . (4) The current collector for a solid oxide fuel cell according to the above (3), wherein the porosity of the skeleton portion of the current collector is 20 to 60%. (5) A large number of single cells are stacked via a gas separator in which the current collector on the oxygen electrode side described in (4) above is incorporated on the oxygen electrode side and the current collector on the fuel electrode side is incorporated on the fuel electrode side. A solid oxide fuel cell comprising:

[0010]

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an example of the current collector of the solid oxide fuel cell according to the present invention. This current collector 5
Has a honeycomb structure having a large number of hollow gas passages 10 provided along the flow direction of an electrode active material (hereinafter, also simply referred to as gas) (hereinafter, the current collector of the present invention is referred to as a honeycomb structure current collector). The body.).

FIG. 2 is a diagram showing a cross section of a part (unit cell) of a fuel cell stack in which a number of single cells are stacked via a gas separator incorporating the honeycomb structured current collector of FIG. In FIG. 2, the single-cell honeycomb structure current collector 5 a contacts the oxygen-side electrode film 6 of the single cell 2, and the fuel-side honeycomb structure current collector 5 b contacts the fuel-side electrode film 7. Are laminated via a gas separator 3.

In the fuel cell stack having such a structure, the fuel gas, for example, hydrogen, is not shown in FIG.
See) Fuel-side honeycomb structure current collector 5 via fuel gas flow path
b, and flows through the hollow gas flow path 10, and a part thereof is transmitted to the fuel-side electrode film 7 through a current collector plane (hereinafter, also referred to as a current collector outer wall portion). On the other hand, for example, air as an oxygen-containing gas flows into the air-side honeycomb structure current collector 5a through an oxygen-containing gas flow path (not shown), flows through the hollow gas flow path 10, and a part of the current is collected. It is supplied to the oxygen-side electrode film 6 through the outer body wall. An electrode reaction occurs in the single cell 2 to which fuel and oxygen are supplied, and electric energy is generated. The generated electric energy is applied to the honeycomb structure current collectors (5a, 5a,
collected by b) and extracted as electrical energy.

In the present invention, the thickness of the honeycomb structure current collector is preferably 1 to 5 mm. If the thickness of the entire current collector is too large, the material cost increases and the amount of unnecessary gas not consumed in the electrode reaction increases, and the performance of the fuel cell decreases. On the other hand, if the thickness of the current collector is too small, the total cross-sectional area of the hollow gas flow passage must be reduced, and supply failure of the electrode active material tends to occur. The cross-sectional shape of the hollow gas flow path is, for example, a square or a rectangle, and the length of one side thereof is
Preferably it is 0.5 to 3 mm. If the cross-sectional area of the hollow gas passage is too large, the pressure loss is reduced, but the mechanical strength of the current collector is reduced. On the other hand, if the cross-sectional area of the hollow gas channel is too small, the pressure loss increases. The thickness of the partition wall between the hollow gas passages is preferably 0.5 to 1.0 mm.
If the thickness of the partition walls is too large, the mechanical strength of the current collector increases and the electrical resistance decreases, but the cross-sectional area of the entire hollow gas passage is reduced, and poor supply of fuel or air to the single cell is likely to occur. On the other hand, if the partition walls are too thin, the mechanical strength of the current collector decreases.

In the present invention, the porosity of the skeleton portion of the current collector having a honeycomb structure is preferably 20 to 60%. If the porosity is too low, the gas permeability decreases, and it becomes impossible to supply a sufficient gas to the electrode surface of the single cell, and the electrode reaction efficiency decreases. On the other hand, if the porosity is too large, the mechanical strength decreases and the electrical resistance increases.

In the present invention, as a constituent material of the honeycomb structure current collector on the oxygen electrode side (hereinafter, also simply referred to as oxygen side), for example, lanthanum-strontium-manganite,
As a constituent material of the honeycomb structure current collector on the fuel electrode side (hereinafter also simply referred to as fuel side), for example, nickel + yttria stabilized zirconia (YSZ) or nickel + alumina + yttria stabilized zirconia (Ni + Al ₂ O ₃ +
YSZ) is preferably used as a porous ceramic. As lanthanum-strontium-manganite, for example, (La _0.85 Sr _0.15 ) MnO ₃ is used, and as nickel + YSZ, for example, the nickel content is 30 to
60 vol% (volume ratio), preferably 40 vol% nickel + YSZ is, as the _{Ni + Al 2 O 3 + YSZ} , Ni is 30~60vol%, Al ₂ O ₃ is from 30 to 4
What consists of 0% and the rest YSZ is preferably used.

In the present invention, the oxygen-side current collector and the fuel-side current collector having a honeycomb structure are manufactured, for example, as follows. That is, lanthanum-strontium-manganite which is a constituent material of the oxygen-side current collector pulverized to a particle size of 0.5 to 100 μm, preferably 10 to 70 μm, and pulverized to a particle size of 0.5 to 100 μm, preferably 10 to 70 μm. For nickel + yttria-stabilized zirconia (YSZ), which is a constituent material of the fuel-side current collector, for example, 1 to 10 wt% of methylcellulose or the like is used as a binder, if necessary, and the mixed powder is used as a plasticizer. For example, 1 to 10% by weight of glycerin or the like is added, and further, for example, 5 to 20% by weight of water is added to the mixed powder, mixed and kneaded to form a clay, and the clay is extruded and formed. A current collector green having a honeycomb structure having a large number of hollow gas passages each having a predetermined cross-sectional area is formed. 600 ° C., preferably at a firing temperature of 1350 to 1450 ° C., for example from 1 to 10 hours, preferably oxygen side current collector of the honeycomb structure and the fuel side current collector is obtained by firing 3-5 hours.
Nickel + alumina + yttria-stabilized zirconia (Ni + Al ₂ O ₃ + YS) as a constituent material of the fuel-side current collector
When Z) is used, similarly, the particle size is 0.5 to 100 μm,
Preferably, after pulverizing to 10 to 70 μm, the same treatment as in the above case is performed to produce a fuel-side current collector.

In the present invention, a porous material may be added at the time of molding the green body in order to increase the porosity of the current collector. In addition, since the extruded current collector green shrinks in the subsequent firing step, it is preferable to select dimensions in consideration of the shrinkage rate in advance as the dimensions of the extrusion die at the time of molding.

[0018]

Next, specific examples of the present invention will be described. Example 1 Lanthanum oxide, strontium acetate, and manganese acetate were weighed at a molar ratio of 17: 6: 40, and ethanol was added to the mixture to form a slurry. The slurry was dried, and then baked at 1500 ° C. for 5 hours. After cooling, the mixture was pulverized to obtain (La _0.85 Sr _0.15 ) MnO ₃ having an average particle size of 50 μm. On the other hand, the respective powders of nickel oxide and yttria-stabilized zirconia are sufficiently kneaded in a slurry form, dried and fired at 1300 ° C., and then pulverized to obtain a 40 vol% nickel-containing nickel oxide + YSZ having an average particle diameter of 40 μm. A powder was obtained.

The obtained (La _0.85 Sr _0.15 ) MnO ₃ and nickel oxide containing 40 vol% nickel (when reduced) + Y
4 g of methylcellulose as a binder, 5 g of glycerin as a plasticizer and 15 g of water were added to 100 g of each of the SZ powder, and the mixture was kneaded to form a clay. Each of the obtained clay-like materials was extruded using an extruder to prepare a current collector green having a honeycomb structure. A green body of (La _0.85 Sr _0.15 ) MnO ₃ was baked at 1450 ° C. for 5 hours and the thickness was 4 mm, the cross section of the hollow gas channel was 3 × 2 mm, and the number of rectangles was 34.
The thickness of the partition wall is 0.5 mm, and the porosity of the skeleton is 40%.
An oxygen-side current collector having a honeycomb structure was obtained. On the other hand, a green body of nickel oxide + YSZ was baked at 1450 ° C. for 5 hours to have a thickness of 2 mm, a hollow gas channel having a cross section of 1 × 1 mm, 80 squares, and a partition wall thickness of 0.5 mm. Thus, a fuel-side current collector having a honeycomb structure in which the porosity of the skeleton portion was 25% was obtained.

A single cell 1 having an effective power generation area of 120 cm ² is formed by using a gas separator incorporating the above-mentioned Ni + YSZ honeycomb current collector on the fuel electrode side and the above-mentioned La-based honeycomb current collector on the oxygen electrode side. A single cell stack is formed by sandwiching the sheets, and humidified hydrogen gas is supplied to the cell stack as fuel at 1000 cm ³ / min, and air is supplied as oxidant at 5 cm ³ / min.
When a power generation test was performed at 1000 ° C. at a supply of 2,000 cm ³ / min, 36 Amp. The stack initial output at (0.3 A / cm ² ) was about 32 W. In addition, the performance deterioration rate after a power generation test for 1,000 hours involving five heat cycles was as low as 5% or less, and high power generation reliability was obtained.

According to this embodiment, since the current collector has a honeycomb structure, unlike the prior art, the current collector contacts the entire surface of the single cell electrode. Cell damage can be prevented. In addition, since the current collector has a honeycomb structure, its mechanical strength is improved by compensating for the weakness of the porous body, so that it can sufficiently withstand the load applied during stack lamination, and as a whole the fuel cell The strength of is improved. According to the present embodiment, the current collector on the oxygen side is a porous body having a porosity of 40%, and the current collector on the fuel side is a porous body having a porosity of 25% (the porosity further increases during reduction). Thereby, the diffusion of the electrode active material flowing through the hollow gas flow path inside the current collector to the single cell electrode surface is promoted, and the electrode reaction efficiency is improved.

In this embodiment, a current collector containing Ni + Al ₂ O ₃ + YSZ as a constituent material can be used as the current collector on the fuel side. The current collector of Ni + Al ₂ O ₃ + YSZ is prepared, for example, as follows. That is, Ni oxide, alumina, and YSZ powders
After sufficiently kneading into a slurry using 30 parts by volume, 30 parts by volume, and drying, baking at 1200 ° C. for 3 hours, and pulverizing the obtained calcined product to obtain a powder having an average particle size of 30 μm.
A binder or the like is added to the obtained powder in the same manner as described above, and the mixture is kneaded to form a clay-like material, and the clay-like material is extruded to prepare a current collector green having a honeycomb structure. By firing the body at 1600 ° C. for 2 hours, for example, the thickness is 2 mm, and the cross-sectional shape of the hollow gas channel is 1 mm ×
1mm square, the number of which is 80, partition wall thickness is 0.5mm,
A fuel-side current collector having a honeycomb structure in which the porosity of the skeleton portion is 20% is obtained.

Comparative Example 1 A one-cell stack was formed in the same manner as in Example 1 except that the current collector having a groove shown in FIG. 4 was used instead of the current collector having a honeycomb structure. When a similar power generation test was performed, 36 Amp. At (0.3 A / cm ² ), the stack initial output was about 27 W, and the performance degradation rate after a 1000-hour power generation test involving five thermal cycles was about 20%. From Example 1 and Comparative Example 1,
It has been found that the output of the fuel cell stack using the current collector having the honeycomb structure according to the present invention is increased by about 20% as compared with the prior art, and the power generation reliability is more than four times higher.

[0024]

According to the invention described in claim 1 of the present application,
Since the current collector has a honeycomb structure, the entire surface of the current collector becomes a contact surface with the electrode surface of the single cell, so that excessive concentrated load on the single cell electrode surface is avoided to prevent the damage. Can be prevented. Further, the electrical contact resistance between the single cell and the current collector can be reduced. According to the invention described in claim 2 of the present application, in addition to the effect of the above invention, increase in pressure loss is suppressed and mechanical strength is improved by forming the cross section of the hollow gas flow path into a square having a predetermined dimension. Can be. Further, the gas diffusion amount to the cell electrode surface can be sufficiently ensured.

According to the third aspect of the present invention, by using a specific porous ceramic as a constituent material, the mechanical strength is further improved in addition to the effect of the above-mentioned invention. According to the invention as set forth in claim 4 of the present application, by setting the porosity of the skeletal portion to 20 to 60%, in addition to the effect of the above invention, the electrode active material penetrates the outer wall surface of the current collector and is simply Diffusion and supply to the cell electrode surface are facilitated. Claim 5 of the present application
According to the invention described in (1), by forming a solid oxide fuel cell using a gas separator incorporating a honeycomb structure current collector, the power generation efficiency is high, the mechanical strength is excellent, and the performance is less deteriorated and reliable. It is possible to provide a solid oxide fuel cell having high performance.

[Brief description of the drawings]

FIG. 1 is a perspective view of a current collector having a honeycomb structure according to an embodiment of the present invention.

FIG. 2 is a diagram showing a cross section of a unit cell of the solid oxide fuel cell of the present invention.

FIG. 3 is a diagram showing a configuration of a fuel cell stack according to the prior art.

FIG. 4 is a diagram showing a cross section of a unit cell in the prior art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cell frame, 2 ... Single cell, 3 ... Gas separator, 4 ... Groove current collector, 4a ... Oxygen side current collector, 4b ... Fuel side groove current collector, 5 ... Honeycomb structure current collector, 5a ... Oxygen-side honeycomb structure current collector, 5b ... Fuel-side honeycomb structure current collector, 6 ... Oxygen-side electrode film, 7 ... Fuel-side electrode film, 8 ... Fuel gas inlet, 9 ... Oxygen-containing gas inlet, 10 ... Hollow gas flow path.

Claims (5)

[Claims] 1. A solid electrolyte membrane formed by laminating a large number of flat single cells having a solid electrolyte membrane and fuel-side electrode films and oxygen-side electrode films respectively laminated on both surfaces of the solid electrolyte membrane via a gas separator. When forming a fuel cell, a plate-shaped current collector sandwiched between the electrode film of the single cell and a gas separator and incorporated in a space through which an electrode active material flows, wherein the electrode active material flow direction A current collector for a solid oxide fuel cell, having a honeycomb structure provided with a number of hollow gas flow paths along the same. 2. The solid oxide fuel cell according to claim 1, wherein the cross-sectional shape of the hollow gas flow path is a square, and the length of one side of the square is 0.5 to 3 mm. Current collector. 3. The current collector comprises a porous ceramic mainly composed of lanthanum-strontium-manganite as a constituent material of the current collector on the oxygen electrode side, and nickel as a constituent material of the current collector on the fuel electrode side. 3. The current collector for a solid oxide fuel cell according to claim 1, wherein the current collector is a porous ceramic containing + yttria-stabilized zirconia or nickel + alumina + yttria-stabilized zirconia as a main component. 4. The porosity of the skeleton portion of the current collector is 20 to
The current collector of the solid oxide fuel cell according to claim 3, wherein the current collector is 60%. 5. A plurality of single cells are stacked via a gas separator in which the current collector on the oxygen electrode side according to claim 4 is mounted on the oxygen electrode side and the current collector on the fuel electrode side is mounted on the fuel electrode side. A solid oxide fuel cell, comprising: