JP4900364B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell having a laminated structure, and more particularly to a fuel cell manifold mechanism.

  Solid oxide fuel cells (SOFC) are being developed as third-generation fuel cells for power generation. At present, three types of solid oxide fuel cells have been proposed: a cylindrical type, a monolith type, and a flat plate type, each of which has a solid electrolyte composed of an oxide ion conductor as an air electrode (cathode) from both sides. It has a laminated structure sandwiched between fuel electrodes (anodes). A plurality of power generation cells composed of the stacked body are alternately stacked with separators with a fuel electrode current collector and an air electrode current collector interposed therebetween, thereby forming a fuel cell stack.

As an example, the solid electrolyte layer is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer is composed of a metal such as Ni or Co or a cermet such as Ni-YSZ or Co-YSZ. The air electrode layer is made of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector is made of an Ag-based alloy or the like. And a separator made of stainless steel or the like.

In so-called solid oxide fuel cells, oxidant gas (oxygen) is supplied to the air electrode side and fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode side as reaction gas. The air electrode and the fuel electrode are both porous layers so that the gas can reach the interface with the solid electrolyte.
Oxygen supplied to the air electrode side passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer. At this part, electrons are received from the air electrode and ionized to oxide ions (O ²⁻ ). Is done. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode. Oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and emit electrons to the fuel electrode. This electron can be taken out as an electromotive force in an external circuit of another route.

  By the way, in the fuel cell, a manifold is provided inside the fuel stack as a gas supply mechanism that introduces a reaction gas from the outside and distributes it to each of the stacked power generation cells. This manifold is a tubular body in which a ring member called a manifold ring is interposed between the separators and extends in the stacking direction while joining the separators, and is composed of two fuel gas introduction and oxidant gas introduction.

The reaction gas flowing through these manifolds is distributed at the junction with the separator for each stack, and is supplied to the electrode layer of the power generation cell through a gas passage provided in the separator. For this reason, the connecting portion between the manifold ring and the separator is required to have a high sealing performance (air tightness) that does not cause gas leakage. In order to prevent short circuit, individual manifold rings are required to have reliable electrical insulation.
Such a manifold mechanism is disclosed in, for example, Patent Document 1 and Patent Document 2.

Japanese Patent Application Laid-Open No. 7-201353 JP-A-8-279364

  By the way, as described above, the manifold is required to have high sealing performance and reliable electrical insulation. Conventionally, a mechanism that uses a ceramic manifold ring to ensure insulation between separators and seals the joint with the separator with a glass material to prevent gas leakage has been adopted. Since there is a large difference in the coefficient of thermal expansion between the separator and this ceramic manifold ring, the manifold ring can be damaged by the stress generated by the difference in thermal expansion during repeated heating (heating cycle) during fuel cell operation, In addition, there is a problem that peeling occurs, and in the sealing portion, a liquid seal in which the glass material is melted at the operating temperature of the fuel cell is performed.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a fuel cell including a manifold mechanism having excellent durability and high gas sealability with respect to the thermal cycle of the fuel cell. Yes.

That is, the present invention according to claim 1 is configured by alternately laminating a plurality of power separators configured by arranging electrode layers on both sides of a solid electrolyte layer and metal separators having reaction gas passages therein. And an insulating manifold ring that communicates with the gas passage through a gas introduction hole provided in the thickness direction of the separator, and a reaction gas is supplied to each electrode layer through the gas passage of the separator. In the fuel cell configured to supply, the manifold ring includes a ceramic layer and metal layers disposed on both sides of the ceramic layer via silver brazing . In general, since silver solder has excellent spreadability, the stress caused by the difference in thermal expansion between the metal layer and the ceramic layer under the operating temperature of the fuel cell is relieved, and the manifold ring is damaged by thermal cycling (for example, due to thermal stress). Separation of the joint between the metal layer and the ceramic layer can be prevented.

Further, the present invention according to claim 2 is characterized in that, in the fuel cell according to claim 1, a concave portion for positioning the manifold ring is provided in a surface portion of the separator in contact with the metal layer. Yes.
Since the manifold ring can be positioned and arranged easily and accurately in the power generation cell stacking process, the assembly of the fuel cell stack is simplified, the number of assembly steps can be reduced, and the displacement of the manifold ring can be avoided. Battery performance degradation due to gas leakage can be prevented.

Further, the present invention according to claim 3 is the fuel cell according to claim 1 or 2, wherein a fine groove having a large flow resistance is formed on a surface portion of the metal layer in contact with the separator. It is characterized by the formation of a plurality.
Due to the differential pressure effect due to these fine grooves, high gas sealability (air tightness) can be obtained at the joint surface between the separator and the manifold ring.

According to a fourth aspect of the present invention, in the fuel cell according to any one of the first to third aspects, any one of Ni, Ag, Sn, Zn, and Cr is formed on the surface of the metal layer. It is characterized in that at least one or more coating layers are formed.
By providing the coating layer, the bonding strength by thermal diffusion between the metal layer and the separator is enhanced.

According to the first aspect of the present invention, since the manifold ring is composed of the ceramic layer and the metal layers disposed on both sides of the ceramic layer via the silver brazing , the metal layer and the ceramic layer at the operating temperature of the fuel cell The thermal stress generated by the difference in thermal expansion of the above is relieved by the spreadability of the silver wax , so that damage to the manifold ring due to thermal cycling can be prevented and high sealing performance can be ensured.

  Further, according to the invention described in claim 2, since the concave portion is provided in the surface portion of the separator in contact with the metal layer, the positioning of each manifold ring at the time of stacking can be performed easily and accurately. As a result, the assembly of the fuel cell stack can be simplified and the number of man-hours can be reduced, and the displacement of the manifold ring can be avoided, and the deterioration of the battery performance due to gas leakage can be prevented.

  According to the invention described in claim 3, since a plurality of fine grooves are formed in the surface portion of the metal layer in contact with the separator, a high sealing performance is provided at the joint between the separator and the manifold ring due to the differential pressure effect of the grooves. Can be obtained.

  According to the invention described in claim 4, since at least one coating layer made of any of Ni, Ag, Sn, Zn, and Cr is formed on the surface of the metal layer, the metal layer and the separator It is possible to further strengthen the bonding strength by thermal diffusion.

  Embodiments of a fuel cell according to the present invention will be described below with reference to the drawings.

  FIG. 1 is an exploded perspective view showing a configuration of a flat plate type solid oxide fuel cell to which the present invention is applied, and FIG. 2 is a sectional view taken along line II-II in FIG.

  As shown in FIG. 1, a fuel cell stack 1 includes a power generation cell 5 configured by disposing a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer, and a fuel electrode current collector disposed outside the fuel electrode layer. 6, a single cell composed of an air electrode layer current collector 7 disposed outside the air electrode layer and a separator 8 disposed outside each of the current collectors 6, 7. A large number of rings 15 and an oxidizing agent manifold ring 16 are stacked. In addition, each element which comprises a single cell can use the same physical property as the past.

  Here, the separator 8 is formed of a square stainless steel plate having a thickness of about several millimeters (for example, a laminated structure of two stainless steel plates) having an Ag plating treatment for preventing oxidation. A fuel gas passage 9 through which the fuel gas flows and an oxidant gas passage 10 through which the oxidant gas flows are formed. However, as shown in FIG. 1, only the fuel gas passage 9 is formed for the separator 8 located at the lowermost portion, while only the oxidant gas passage 10 is formed for the uppermost separator 8.

One end of the fuel gas passage 9 communicates with a fuel gas introduction hole 13 provided at the center of the left end of the separator 8, and the other end communicates with a gas discharge hole 11 in the center of the separator facing the fuel electrode current collector 6. is doing. Further, one end of the oxidant gas passage 10 communicates with a fuel gas introduction hole 14 provided at the center of the right end of the separator 8, and the other end of the gas discharge at the center of the separator facing the air electrode current collector 7. It communicates with the hole 12. These gas introduction holes 13 and 14 have an elliptical shape. Note that only the oxidant gas introduction hole 14 is formed in the uppermost separator 8, and the oxidant gas introduction hole 14 is opened only on the lower side. Each of the gas introduction holes 13 and 14 except for the upper and lower ends penetrates in the plate thickness direction.
The lowermost separator 8 has gas introduction passages 24 and 25 for introducing a reaction gas from the outside, and its thickness is thick. Among these, a fuel gas introduction passage through which fuel gas is supplied 25 communicates with the fuel gas introduction hole 13, and an oxidant gas introduction passage 24 to which the oxidant gas is supplied communicates with the oxidant gas introduction hole 14.

  A fuel manifold ring 15 through which fuel gas flows is disposed at the opening of the fuel gas introduction hole 13, and an oxidant manifold ring 16 through which oxidant gas flows through the opening of the oxidant gas introduction hole 14. By stacking single cells and stacking them, a large number of these manifold rings 15 and 16 are connected in the vertical direction (stacking direction) via the gas introduction holes 13 and 14 of the separator 8. A tubular manifold is formed. However, the oxidant gas introduction hole 14 of the separator 8 located at the uppermost part is not a through hole, but has a hole structure that opens only on the lower side as described above. A fuel gas and an oxidant gas supplied from the outside flow through the two manifolds.

Further, as shown in FIG. 2, elliptical recesses 17 for correctly positioning the manifold rings 15 and 16 on the separator surface are formed at the opening edges of the gas introduction holes 13 and 14, respectively. . By providing the concave portion 17, it is possible to arrange the gas introduction holes 13 and 14 and the manifold rings 15 and 16 without misalignment with each other, and stacking can be easily performed. By eliminating the misalignment, the sealing performance of the joint portion between the separator 8 and the manifold rings 15 and 16 is improved, and gas leakage can be completely prevented.
In this embodiment, the upper and lower separators 8 with which the upper and lower end faces of each of the manifold rings 15 and 16 abut are provided with the recesses 17 respectively. However, the positioning is possible even if the recesses 17 are provided only on the lower separator 8. Is possible.

  As shown in FIG. 3A, the fuel manifold ring 15 and the oxidant manifold ring 16 are each formed in an elliptical shape corresponding to the opening shape of the gas introduction holes 13 and 14. The reason why each gas flow path is elliptical is that the length of the separator 8 is not extended and the volume of the gas flow path can be increased as compared to the case of a circular shape, and each gas with respect to the deviation or inclination when single cells are stacked. Of course, the introduction holes 13 and 14 and the manifold rings 15 and 16 can be more consistent with each other.

FIG. 3B shows a reference example of each of the manifold rings 15 and 16 described above, and a ring-shaped glass layer 19 serving as an insulating / seal layer disposed in the middle part, and a ring-shaped glass layer disposed on both surfaces of the glass layer 19. And the metal layer 18.
In this reference example , a ferritic stainless steel is used as the metal layer 18 and a coating layer (plating layer) is formed by applying Ag plating to the underlying Ni plating on the surface. In the case of ferrite-based stainless steel, the adhesion between the plating layer and the stainless steel serving as the base material is particularly excellent, and thus has an advantage that the bonding strength by thermal diffusion with the silver plating on the separator surface becomes extremely strong. As the plating material, Sn, Zn, Cr or the like can be used in addition to the above.

Further, as the glass layer 19, a glass material having a softening point of 800 ° C. or higher which is higher than the operating temperature of the fuel cell (about 750 ° C.) is used. Therefore, the glass layer 19 is not melted during the operation of the fuel cell, and the glass layer 19 is always kept in a solid state, so that the insulation between the metal layers, that is, between the separators is always ensured. Become.
Incidentally, a general gas seal mechanism that has been conventionally employed has a structure in which the flow path joint portion of the manifold is sealed with a glass material softened at the operating temperature of the fuel cell.

Further, by using, for example, SiO ₂ —B ₂ O ₃ —CaO or the like (thermal expansion coefficient: 10.5 × 10 ⁻⁶ / ° C.) having almost the same thermal expansion coefficient as that of the metal layer 18 as a glass material, fuel can be obtained. It is possible to eliminate the generation of thermal stress accompanying the process of raising and lowering the battery temperature and to form an insulating layer that can withstand thermal cycling.
Incidentally, the thermal expansion coefficient of the metal layer 18 (for example, SUS430) is about 10.6 × 10 ⁻⁶ / ° C.

Next, FIG. 4 shows an implementation form of these manifolds 15 and 16, together with arranging the ring-shaped ceramic layer 20 to the middle portion, through a brazing material 21 a metal layer 18 on both surfaces of the ceramic layer 20 It has a joined structure.
In the case of this configuration, it uses a brazing material 21 having a higher softening point than the operating temperature of the fuel cell, for example, a softening point is suitable Ginro c such JIS standard BAg-8 in 870 ° C.. In particular, since silver solder not only has a high softening point but also has excellent spreadability, this spreadability can relieve stress caused by the difference in thermal expansion between the metal layer 18 and the ceramic layer 20 at the operating temperature of the fuel cell. Further, peeling of the metal layer 18 and the ceramic layer 20 that are likely to occur during the thermal cycle of the fuel cell can be prevented.
In this case as well, it is preferable to form at least one coating layer made of any of Ni, Ag, Sn, Zn, and Cr on the surface of the metal layer 18 as in the above reference example .

Further, as shown in FIG. 5, it is preferable that the manifold rings 15 and 16 shown in FIG. 3B have a structure in which many fine grooves 18 a are formed in the surface portion of the metal layer 18 in contact with the separator 8.
Since the fine groove 18a provided on the contact surface between the metals has a large flow resistance, even if the reaction gas is introduced into each manifold, the gas flows into the groove due to the differential pressure effect by the groove 18a. In other words, gas leakage at the joint surface between the separator 8 and each manifold ring 15 and 16 is prevented, and the gas sealability of the joint portion can be made higher than when smooth metal surfaces are joined together. Such a structure is naturally applicable to the manifold rings 15 and 16 having the structure shown in FIG.
Although the groove 18a is very delicate, it is drawn greatly in an easy-to-understand manner in FIG.

Next, the assembly of the fuel cell according to the embodiment of the present invention will be described with reference to FIG.
In the case of the manifold rings 15 and 16 having a structure in which the ceramic layer 20 is arranged in the middle portion as shown in FIG. 4, the silver braze is melted in a high-temperature atmosphere having a softening point of 870 ° C. or higher of the silver braze 21, The ceramic layer 20 and the metal layer 18 are joined and produced by the adhesive action.

  After the fabrication of the manifold rings 15, 16, the fuel manifold ring 15 is disposed at the opening of the fuel gas introduction hole 13 of the separator 8, and the oxidant manifold ring 16 is disposed at the opening of the oxidant gas introduction hole 14. Then, the single cells are sequentially stacked to assemble the fuel cell stack 1. The assembled fuel cell stack 1 is supported at four corners by four fastening rods 22 inserted through attachment holes 23 provided at the corners of the separators 8 and is tightened in the stacking direction from above by bolts or the like (not shown). As a result, the plurality of single cells are brought into close contact with each other and fixed together. This completes the assembly of the fuel cell.

  In the assembly of the fuel cell described above, the positioning recesses 17 are provided at the opening edge portions of the gas introduction holes 13 and 14, respectively. Therefore, the arrangement of the manifold rings 15 and 16 when stacking single cells is easy. And it can arrange | position in the exact site | part on a separator surface, without both hole positions shifting | deviating.

Further, as described above, since the fuel electrode current collector 6 and the air electrode current collector 7 interposed between the separators are each made of a sponge-like porous sintered metal, these are tightened by tightening the stack. The sponge-like member is elastically deformed, and the manifold rings 15 and 16 are pressed and sandwiched between the upper and lower separators 8 with a certain degree of elasticity, and this elasticity causes vibration and external impact. The movement of the manifold rings 15 and 16 is restricted, and it is possible to prevent the manifold rings 15 and 16 from being displaced after stack assembly.
Thus, in the present invention, there is no need for a special member for fixing the manifold rings 15 and 16 at the time of assembly, and the elastic fixing structure using the elastic deformation of the current collectors 6 and 7 by tightening is used. The stack assembly is further simplified.

When the fuel cell is operated in this state, the upper and lower metal layers 18 of the manifold rings 15 and 16 and the upper and lower separators 8 in contact with the upper and lower metal layers 18 are heated by the high temperature atmosphere (about 700 to 750 ° C.) when the temperature is raised. Joined by diffusion. However, as described above, since the softening point of the Carlo c agent 21 used in each manifold ring 15, 16 is 800 ° C. or higher, the heat during the operation of the insulating seal the fuel cell of each manifold ring 15, 16 It does not soften and maintains a solid state at all times.
As described above, in the present invention, it is possible to assemble a fuel cell stack having excellent gas sealing performance by utilizing thermal diffusion bonding between metals. As a result, the manifold rings 15 and 16 are connected in the vertical direction (stacking direction) via the gas introduction holes 13 and 14 of the separator 8, respectively, so that two tubular manifolds for fuel gas and oxidant gas ( The connected state is not shown).

In the fuel cell stack 1 having the above-described configuration, the fuel gas and the oxidant gas supplied from the outside are oxidized with the fuel gas introduction path 25 and the oxidation gas through the openings 25a and 24a provided in the side portions of the separator 8 located at the lowermost layer. They are individually introduced into the fuel gas manifold and the oxidant gas manifold via the agent gas introduction passage 24.
Although not shown, a fuel gas supply pipe for supplying fuel gas from the outside is connected to the opening 25a, and an oxidant gas supply pipe for supplying oxidant gas from the outside is connected to the opening 24a. It is assumed that The reaction gases introduced from the gas supply pipes are distributed from the gas introduction holes 13 and 14 of the respective layers (single cells) in the course of flowing through the pipes of the manifolds extending in the longitudinal direction. The gas is supplied to the electrode portion of each power generation cell 5 through each gas passage.

That is, the fuel gas in the fuel gas manifold is introduced into the fuel gas passage 9 from the fuel gas introduction hole 13 of each separator 8 and discharged from the fuel gas discharge hole 11 at the end of the passage to face the fuel electrode current collector 6. And pass through here while diffusing to reach the fuel electrode layer of the power generation cell 5.
On the other hand, the oxidant gas in the oxidant gas manifold is introduced into the oxidant gas passage 10 from the oxidant gas introduction hole 14 of each separator 8 and is discharged from the oxidant gas discharge hole 12 at the end of the passage to face the air. It is supplied to the polar current collector 7 and passes through here while diffusing and reaches the air electrode layer of the power generation cell 5.
Hereinafter, the electrochemical reaction in each single cell is as described in the section of the prior art, and the high temperature exhaust gas generated by this electrochemical reaction is discharged from the single cell to the outside of the stack through a predetermined exhaust route. Will be.

Here, the gas introducing holes 13, 14 of each manifold ring 15, 16 and the separator 8 constituting each manifold hole positions I by the positioning recesses 17 provided on the separator side is reliably aligned, and In the contact portion between them, a high sealing performance is obtained by a synergistic effect of the seal by thermal diffusion bonding and the differential pressure by the fine groove 18a on the contact surface, and no gas leakage occurs.
In each manifold ring 15 and 16, both sides of the metal layer 18 is more insulated ceramic layer 2 0 through the brazing material 21 is joined, moreover, within the operating temperature range of the fuel cell, b c with timber 21 maintains the solidified state without softening, to mitigate the thermal expansion difference between the metal layer 1 8 and the ceramic layer 20 by a is its malleability to b c material 21, the heat due to thermal cycling Damage to the manifold rings 15 and 16 due to stress is avoided, and high sealing performance is maintained.

  As described above, in the fuel cell stack 1 of the present embodiment, one fuel manifold and one oxidizer manifold are provided. However, the present invention is not limited to this, and there are a plurality of manifolds depending on the supply amount of the reaction gas. Of course, it is also possible to provide them.

The disassembled perspective view which shows the structure of the fuel cell which concerns on this invention. II-II sectional drawing of FIG. The manifold ring used for the fuel cell of this invention is shown, (a) is a perspective view, (b) is a side view. The side view of the manifold ring different from FIG. The side view of the manifold ring different from FIG. The perspective view which shows the assembly of the fuel cell which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 5 Power generation cell 8 Separator 9 Fuel gas passage 10 Oxidant gas passage 13 Fuel gas introduction hole 14 Oxidant gas introduction hole 15 Manifold ring for fuel 16 Manifold ring for oxidant 17 Recess 18 Metal layer 18a Groove 19 Glass layer 20 Ceramics layer 21 Brazing material (silver brazing)

Claims (4)

A fuel cell stack constructed by alternately stacking a plurality of metal separators having a reaction gas passage inside and a power generation cell constructed by arranging electrode layers on both surfaces of the solid electrolyte layer, and the thickness direction of the separator In a fuel cell comprising an insulating manifold ring that communicates with the gas passage through a gas introduction hole provided in the fuel cell, and configured to supply a reaction gas to each electrode layer through the gas passage of the separator.
The said manifold ring is comprised by the ceramic layer and the metal layer distribute | arranged on both surfaces of the said ceramic layer through the silver brazing , The fuel cell characterized by the above-mentioned.   2. The fuel cell according to claim 1, wherein a concave portion for positioning the manifold ring is provided in a surface portion of the separator in contact with the metal layer.   3. The fuel cell according to claim 1, wherein a plurality of fine grooves having a large flow resistance are formed in a surface portion of the metal layer in contact with the separator.   4. The coating layer according to claim 1, wherein at least one coating layer made of any one of Ni, Ag, Sn, Zn, and Cr is formed on the surface of the metal layer. Fuel cell.

Images