JP5294649B2 - Cell stack and fuel cell module - Google Patents

Description

The present invention relates to a cell stack and fuel cell module.

  In recent years, various fuel cell modules in which a stack of fuel cells is accommodated in a storage container have been proposed as next-generation energy.

  A solid electrolyte fuel cell module is configured by accommodating a cell stack in which a plurality of fuel cells are electrically connected in series in a storage container, and supplying fuel gas (hydrogen) to the fuel electrode layer side of the fuel cells. Electric power is generated at a high temperature of 600 to 900 ° C. by flowing air (oxygen) to the air electrode layer (also referred to as oxygen electrode layer) side.

  In order to electrically connect the fuel cells in series, a felt-like or plate-like inter-cell connecting member has been conventionally used.

  As such an inter-cell connecting member, an alloy having a high conductivity is adopted, and since it is used at a high temperature, a heat-resistant alloy is preferably adopted. As such a heat-resistant alloy having a high conductivity, Cr is 10 to 10. An alloy containing 30% by mass is generally used.

  The connection between the inter-cell connection member and the oxygen electrode layer of the fuel cell is made by applying Pt or Ag paste to the part where the inter-cell connection member of the oxygen electrode layer made of porous conductive ceramics is joined, This is done by pressing the current collecting member, baking it, and joining it.

Furthermore, in recent years, from the viewpoint of low cost, a conductive perovskite complex oxide such as a lanthanum ferrite type is used instead of Pt and Ag (for example, see Patent Document 1).
JP 2004-265742 A

  However, conductive perovskite complex oxides such as lanthanum ferrites made of porous conductive ceramics are used as conventional conductive bonding materials for bonding fuel cells and inter-cell connecting members. Cracks occurred in the conductive bonding material, the electric resistance of the conductive bonding material increased, and current collection could not be performed sufficiently, leading to a decrease in power generation efficiency.

  An object of this invention is to provide the cell stack and fuel cell module which can suppress generation | occurrence | production of the crack in an electroconductive joining material.

The cell stack of the present invention includes a plurality of solid electrolyte fuel cells, an inter-cell connection member disposed between the solid electrolyte fuel cells, the solid electrolyte fuel cell and the inter-cell connection member. A cell stack comprising a conductive bonding material bonded by heat treatment in an atmosphere having a lower oxygen partial pressure than the atmosphere with a paste interposed therebetween, wherein the conductive bonding material is La the perovskite-type composite oxide containing, characterized in that it contains a ZnO obtained by oxidizing the metal Zn powder by the heat treatment.

  In such a cell stack, since the conductive bonding material contains a perovskite complex oxide containing at least La and a metal oxide, the metal oxide is sintered between the perovskite complex oxide particles during power generation. Can be inhibited, aggregation of the perovskite complex oxide can be suppressed, and generation of cracks in the conductive bonding material can be suppressed.

  In the cell stack of the present invention, the solid oxide fuel cell has a fuel electrode layer formed on one side of the solid electrolyte and an oxygen electrode layer formed on the other side, and the conductive layer is formed on the oxygen electrode layer. The inter-cell connecting member is bonded via a conductive bonding material, and the conductive bonding material is also bonded to a portion of the oxygen electrode layer where the inter-cell connecting member is not bonded. To do.

  In such a cell stack, the conductive bonding material in the portion of the oxygen electrode layer where the inter-cell connecting member is not located can be made more conductive than the oxygen electrode layer. Since the generation of cracks in the bonding material can be suppressed and a decrease in the electrical resistance of the conductive bonding material can be suppressed, current collection from the fuel cell can be sufficiently performed through the conductive bonding material.

  The fuel cell module of the present invention is characterized in that the cell stack is stored in a storage container. In such a fuel cell module, since the electric resistance between the solid oxide fuel cells is small, the power generation efficiency can be improved.

  In the cell stack of the present invention, since the conductive bonding material contains a perovskite complex oxide containing at least La and a metal oxide, the metal oxide is sintered between the perovskite complex oxide particles during power generation. Can be inhibited, aggregation of the perovskite complex oxide can be suppressed, and generation of cracks in the conductive bonding material can be suppressed.

  In the fuel cell module of the present invention, the above-described cell stack is housed in a housing container, so that the electrical resistance between the solid oxide fuel cell cells is reduced, and the power generation efficiency can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 shows a state in which the cell stack 25 is provided in the manifold 27, and a fuel gas supply pipe 35 is connected to the manifold 27. As shown in FIG. 1, the cell stack is shown in FIGS. 2 and 3 in which a plurality of the above-described fuel cells 30 are assembled and between one adjacent fuel cell 30 and the other fuel cell 30. A current collecting member (inter-cell connecting member) 33 made of such a metal plate is joined by a conductive joining material 9. The current collecting member may be formed of felt.

  As shown in FIG. 2, the cell stack is configured by joining the fuel battery cell 30 and the current collecting member 33 with a conductive joining material 9 and connecting them together in series.

  As understood from the shape shown in FIG. 4, the fuel cell 30 is formed on the conductive support substrate 4 including the flat portion A and the arc-shaped portions B at both ends of the flat portion A. A fuel electrode layer 3 is provided so as to cover one surface of the flat portion and arc-shaped portions on both sides, and a dense solid electrolyte layer 2 is laminated so as to cover the fuel electrode layer 3. The oxygen electrode layer 5 is laminated on the solid electrolyte layer 2 so as to face the fuel electrode layer 3. An interconnector 6 is formed on the surface of the other flat portion of the support substrate 4 on which the fuel electrode layer 3 and the solid electrolyte layer 2 are not laminated. As is clear from FIG. 4, the fuel electrode layer 3 and the solid electrolyte layer 2 extend to both sides of the interconnector 6 and are configured so that the surface of the conductive support substrate 4 is not exposed to the outside.

  As shown in FIG. 3A, the current collecting member 33 includes an oxygen electrode layer side current collecting piece 33a and an interconnector side current collecting piece 33b, and connecting portions 33c and 33d to which both ends thereof are connected. 3 (a) and 3 (b), the flat oxygen electrode layer-side current collecting piece 33a and the interconnector-side current collecting piece 33b are formed into a flat oxygen electrode layer of the fuel cell 30. 5. It is joined to the interconnector 6 via the conductive joining material 9. An inclined portion 33e is formed between the coupling portions 33c and 33d and the flat plate-like oxygen electrode layer side current collecting piece 33a and interconnector side current collecting piece 33b. The current collecting member 33 is not limited to that shown in FIG.

  In the cell stack of the present invention, the conductive bonding material 9 contains a perovskite complex oxide containing La and a metal oxide. In such a cell stack, since the conductive bonding material 9 contains a perovskite complex oxide containing La and a metal oxide, the metal oxide is sintered between the perovskite complex oxide particles during power generation. Since the binding is inhibited, generation of cracks in the conductive bonding material can be suppressed.

  In the cell stack of the present invention, a paste containing a perovskite-type composite oxide powder containing La and a metal powder is interposed between the solid oxide fuel cell 30 and the current collecting member 33 in the atmosphere. It can be manufactured by heat treatment in an atmosphere having a lower oxygen partial pressure.

  This will be described in detail. As the perovskite type complex oxide powder containing La in the paste, a perovskite type complex oxide conventionally used as an oxygen electrode layer material can be used.

As such a perovskite complex oxide, at least one of transition metal perovskite oxides, particularly LaMnO ₃ oxides, LaFeO ₃ oxides, and LaCoO ₃ oxides having La at the A site is preferable. 600 LaFeO ₃ -based oxides are particularly suitable because they have high electrical conductivity at an operating temperature of about ˜1000 ° C. In the perovskite complex oxide, Sr or the like may be present together with La at the A site, and Co or Mn may be present along with Fe at the B site.

  In particular, it is desirable that the conductive bonding material 9 has the same main component as that of the oxygen electrode layer 5, more preferably the same component, and more preferably the same composition. desirable. Thereby, the joining strength of the conductive joining material 9 to the oxygen electrode layer 5 can be further improved.

  Further, the metal powder in the paste may be any metal as long as it does not adversely affect the fuel cell, but Zn and Fe are particularly desirable.

  The weight ratio of the solid content in the paste is 85 to 98 mass% for the perovskite complex oxide powder and 15 to 2 mass for the metal powder when the total amount of the perovskite complex oxide powder and the metal powder is 100 wt%. % Is desirable.

  This mixing ratio varies depending on the firing shrinkage ratio of the material used as the perovskite complex oxide powder and the firing shrinkage ratio of the metal used as the metal powder.

A paste containing such a perovskite-type composite oxide powder, a metal powder, and a resin is applied, for example, on the oxygen electrode layer of the fuel cell, on the interconnector, and thus the paste is applied. A current collecting member is disposed between the plurality of fuel cells, pressed from both sides, and heat-treated in this state. The heat treatment temperature is baked at 1000 to 1100 ° C., which is lower than that at the time of forming the oxygen electrode layer. The heat treatment is performed in an atmosphere having a lower oxygen partial pressure than the atmosphere (hereinafter, sometimes referred to as a low oxygen partial pressure). In particular, there are an atmosphere in which nitrogen and air are mixed, an atmosphere in which nitrogen and water vapor are mixed, and the like.

  By performing the heat treatment under a low oxygen partial pressure, as shown in FIG. 5, the sintering of the perovskite-type composite oxide powder proceeds and the firing shrinkage starts. However, the expansion of the metal powder suppresses the oxidation of the metal powder. It progresses slowly, and the large shrinkage of the perovskite type complex oxide powder and the expansion of the metal powder overlap, so that the expansion and shrinkage of the conductive bonding material 9 is offset, and the fuel battery cell does not expand and shrink so much. The bonding strength with respect to can be improved.

  Therefore, not only the bonding strength by the conductive bonding material 9 between the current collecting member and the fuel battery cell is improved, but also the current collecting member is not present and is formed to be exposed to the oxygen electrode layer of the fuel battery cell. Even the conductive bonding material 9 can suppress the generation of cracks and sufficiently exhibit the function as a conductive layer.

  In addition, after baking under a low oxygen partial pressure, the conductive bonding material 9 can also function as an oxygen electrode layer by heat treatment in the atmosphere. In this case, it is desirable that the conductive bonding material 9 is composed of the same material as that of the oxygen electrode layer 5 described later, and in particular, it is desirable that the conductive bonding material 9 is composed of the same component. By forming the conductive bonding material 9 with such a material, the metal oxide inhibits the sintering of the perovskite complex oxide, suppresses aggregation, makes it difficult to lower the electrode activity, and also serves as an oxygen electrode layer. Can function.

  Moreover, it is desirable that a large number of recesses are formed on the surface of the oxygen electrode layer 5, and that the conductive ceramic particles of the conductive bonding material 9 exist in the recesses. Thereby, the joining strength of the conductive joining material 9 to the oxygen electrode layer 5 can be further improved. The recess can be formed by a pore forming agent when the oxygen electrode layer 5 is formed.

  The conductive bonding material 9 preferably has a porosity of 20 to 35%. Thereby, oxygen can be sufficiently supplied to the oxygen electrode layer 5.

  In such a cell stack, the heat treatment of the metal powder is performed in an atmosphere having a lower oxygen partial pressure than the air, so that rapid oxidative expansion is suppressed, oxidative expansion is small, and perovskite type complex oxidation containing La that shrinks by firing. The shrinkage difference with the product is reduced, the strength of the solid electrolyte fuel cell, the current collecting member and the conductive bonding material can be improved, and the generation of cracks during the production of the conductive bonding material can be suppressed. A decrease in electrical resistance of the bonding material can be suppressed.

  In the cell stack of the present invention, as shown in FIG. 3B, the conductive bonding material 9 is also bonded to the portion of the oxygen electrode layer 5 where the current collecting member 3 is not located. As a result, the conductive bonding material 9 in the portion of the oxygen electrode layer 5 where the current collecting member is not located can be made more conductive than the oxygen electrode layer 5, and the generation of cracks in the conductive bonding material 9 is suppressed. In addition, since it is possible to suppress a decrease in the electrical resistance of the conductive bonding material 9, it is possible to sufficiently collect current from the fuel cell via the conductive bonding material.

  The fuel cell will be described in detail. As shown in FIG. 4, the fuel battery cell includes a conductive support substrate 4 having a flat cross section and a rod-like plate shape as a whole. A plurality of fuel gas passages 41 provided at appropriate intervals in the width direction of the conductive support substrate 4 are formed inside the conductive support substrate 4 so as to penetrate in the axial direction. Various members are provided on the conductive support substrate 4.

  As described above, the conductive support substrate 4 includes a flat portion and arc-shaped portions at both ends of the flat portion as understood from the shape shown in FIG. A fuel electrode layer 3 is provided so as to cover one surface of the flat portion and the arc-shaped portions on both sides, and a dense solid electrolyte layer 2 is laminated so as to cover the fuel electrode layer 3. An oxygen electrode layer 5 is laminated on the solid electrolyte layer 2 so as to face the fuel electrode layer 3. An interconnector 6 is formed on the surface of the other flat portion of the support substrate 4 on which the fuel electrode layer 3 and the solid electrolyte layer 2 are not laminated. As is clear from FIG. 4, the fuel electrode layer 3 and the solid electrolyte layer 2 extend to both sides of the interconnector 6 and are configured so that the surface of the conductive support substrate 4 is not exposed to the outside.

  Then, power is generated at a portion where the solid electrolyte layer 2 is sandwiched between the oxygen electrode layer 5 and the fuel electrode layer 3. That is, an oxygen-containing gas such as air is allowed to flow outside the oxygen electrode layer 5 and a fuel gas (hydrogen) is allowed to flow through the gas passage 41 in the conductive support substrate 4 and heated to a predetermined operating temperature. Electricity is generated by causing an electrode reaction in the layer 5 and the fuel electrode layer 3. The current generated by such power generation is collected through an interconnector 6 attached to the conductive support substrate 4.

  In the fuel cell having the structure as described above, the conductive support substrate 4 is gas permeable to allow the fuel gas to permeate to the fuel electrode layer 3 and collects current through the interconnector 6. Therefore, in order to satisfy such a requirement and at the same time avoid inconvenience caused by simultaneous firing, the conductive support substrate 4 is composed of an iron group metal component and a specific rare earth oxide. Configure.

The fuel electrode layer 3 causes an electrode reaction, and is formed of a well-known porous conductive cermet. For example, it is formed from ZrO _{2 in which a} rare earth element is dissolved or CeO ₂ in which a rare earth element is dissolved, and Ni and / or NiO.

  In the example of FIG. 4, the fuel electrode layer 3 extends to both sides of the interconnector 6. However, if the fuel electrode layer 3 is formed at a position facing the oxygen electrode layer 5. Therefore, for example, the fuel electrode layer 3 may be formed only in the flat portion on the side where the oxygen electrode layer 5 is provided. Further, the fuel electrode layer 3 can be formed over the entire circumference of the conductive support substrate 4.

The solid electrolyte layer 2 provided on the outer surface of the conductive support substrate 4 is a dense material composed of partially stabilized or stabilized ZrO ₂ containing 3 to 15 mol% of Y / and / or rare earth elements such as Sc and Yb. Ceramics are used.

The oxygen electrode layer 5 is mainly composed of conductive ceramics made of a so-called ABO ₃ type perovskite complex oxide. The oxygen electrode layer 5 is composed of a porous conductive ceramic layer made of conductive ceramic.

The oxygen electrode layer 5 is made of a perovskite type complex oxide that has been used as an oxygen electrode layer material. The perovskite type complex oxide includes a transition metal perovskite type oxide, particularly La at the A site. LaMnO ₃ -based composite oxide, LaFeO ₃ -based composite oxide, and LaCoO ₃ -based composite oxide are preferable, and LaFeO ₃ has high electrical conductivity at an operating temperature of about 600 to 1000 ° C. The composite oxide is particularly suitable. In the perovskite complex oxide, Sr or the like may be present together with La at the A site, and Co or Mn may be present along with Fe at the B site.

The interconnector 6 provided on the conductive support substrate 4 at a position facing the oxygen electrode layer 5 is made of conductive ceramics, but is in contact with the fuel gas (hydrogen) and the oxygen-containing gas. It is necessary to have resistance and oxidation resistance. Therefore, lanthanum chromite perovskite complex oxides (LaCrO ₃ oxides) are generally used as the conductive ceramics.

  A P-type semiconductor 7 is preferably provided on the outer surface (upper surface) of the interconnector 6 as shown in FIG. By connecting the current collecting member to the interconnector 6 via the P-type semiconductor 7, the contact between them becomes an ohmic contact, the potential drop is reduced, and it is possible to effectively avoid a decrease in current collecting performance.

An example of such a P-type semiconductor 7 is a transition metal perovskite complex oxide. Specifically, those having higher electron conductivity than the LaCrO ₃ composite oxide constituting the interconnector 6, for example, LaMnO ₃ composite oxide, LaFeO ₃ system in which Mn, Fe, Co, etc. exist at the B site P-type semiconductor ceramics made of at least one of complex oxides, LaCoO ₃ -based complex oxides, and the like can be used. In general, the thickness of the P-type semiconductor 7 is preferably in the range of 30 to 100 μm. In FIG. 4, the description of the P-type semiconductor 7 is omitted.

  The interconnector 6 can also be provided directly on the flat portion of the conductive support substrate 4 on the side where the solid electrolyte layer 2 is not provided. The fuel electrode layer 3 is also provided on this portion, and this fuel electrode layer is provided. An interconnector 6 can also be provided on 3. That is, the fuel electrode layer 3 can be provided over the entire circumference of the conductive support substrate 4, and the interconnector 6 can be provided on the fuel electrode layer 3. That is, when the interconnector 6 is provided on the conductive support substrate 4 via the fuel electrode layer 3, a potential drop at the interface between the conductive support substrate 4 and the interconnector 6 can be suppressed. This is advantageous.

  The fuel cell module of the present invention is configured by accommodating the cell stack of FIG. 1 in a storage container. The storage container is provided with an introduction pipe for introducing a fuel gas such as hydrogen into the fuel battery cell 30 from the outside, and an introduction pipe for introducing an oxygen-containing gas such as air into the external space of the fuel battery cell 30. The fuel cell is heated to a predetermined temperature (for example, 600 to 900 ° C.) to generate electric power, and the used fuel gas and oxygen-containing gas are discharged out of the storage container.

  In addition, this invention is not limited to the said form, A various change is possible in the range which does not change the summary of invention. For example, the shape of the support substrate 4 can be cylindrical, and an intermediate layer having appropriate conductivity can be formed between the oxygen electrode layer 5 and the solid electrolyte layer 2. Further, in the above embodiment, the case where the fuel electrode layer 3 is formed on the support substrate 4 has been described. However, the support substrate itself is provided with a function as a fuel electrode layer, and a solid electrolyte and an oxygen electrode layer are formed on the support substrate. May be.

  The invention is illustrated by the following examples.

First, NiO powder having an average particle size of 0.5 μm and Y ₂ O ₃ powder having an average particle size of 0.9 μm are mixed so that the volume ratio is 48% by volume of Ni and 52% by volume of Y ₂ O ₃ , A clay prepared with an organic binder and a solvent was molded by extrusion molding, dried and degreased to prepare a support substrate molded body.

Next, a slurry in which Ni powder having an average particle size of 0.5 μm, ZrO ₂ powder in which a rare earth element is dissolved, an organic binder, and a solvent is mixed is prepared, and applied to the support substrate molded body by a screen printing method and dried. Thus, a coating layer for the fuel electrode layer was formed. Next, a slurry obtained by mixing ZrO ₂ powder in which 8 mol% of scandium is dissolved, an organic binder, and a solvent is used to prepare a solid electrolyte layer sheet having a thickness of 30 μm by a doctor blade method, and a support substrate molded body It was affixed on the coating layer for the upper fuel electrode layer and dried.

  Next, the laminated molded body in which the support substrate molded body, the coating layer of the fuel electrode layer, and the solid electrolyte sheet were laminated was calcined at 1000 ° C.

Next, CeO ₂ 85 mol%, the addition of acrylic binder and toluene into a composite oxide powder containing Sm ₂ O ₃ 15 mol%, a slurry of elemental diffusion barrier layer prepared by mixing, resulting tentative It apply | coated to the surface of the solid electrolyte molded object of a sintered body by the screen-printing method.

Also, a slurry in which a LaCrO ₃ composite oxide, an organic binder and a solvent were mixed was prepared, and this was laminated on the exposed support substrate molded body, and co-fired at a firing temperature of 1485 ° C. in an oxygen-containing atmosphere. .

Next, the obtained sintered body is paste made of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder having an average particle diameter of 2 μm, a solvent (normal paraffin) and a pore-forming agent. Dipping in, providing a coating layer of the oxygen electrode layer on the surface of the solid electrolyte layer formed in the sintered body, and simultaneously applying the paste to the outer surface of the interconnector, providing a coating layer for P-type semiconductor, Furthermore, it baked at 1150 degreeC in air | atmosphere, and formed the oxygen electrode layer and the P-type semiconductor. The oxygen electrode layer had a pore diameter of 15 μm and an open porosity of 40%.

Thereafter, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder having an average particle diameter of 2 μm and metal powder having an average particle diameter of 0.5 μm shown in Table 1 are formed on the entire upper surface of the oxygen electrode layer. The paste which mixes the quantity shown in Table 1 and a solvent (normal paraffin) was apply | coated. Sample No. 8, the amount of La _0.6 Sr _0.4 CoO ₃ powder having an average particle size of 2 μm and metal powder having an average particle size of 0.5 μm shown in Table 1 are shown in Table 1 over the entire upper surface of the oxygen electrode layer, A paste formed by mixing a solvent (normal paraffin) was applied.

  Thereafter, the current collecting member as shown in FIG. 3 (c) made of a heat-resistant alloy plate containing Cr is laminated so as to alternate with the fuel cells, and in the pressed state, the atmosphere shown in Table 1, Baking was performed at 1000 ° C., and the fuel cell and the current collecting member were joined with a conductive joining material. Table 1 shows the thickness of the conductive bonding material.

  Thereafter, the occurrence of cracks was observed with an SEM photograph at a magnification of 5000 times. Furthermore, the peeling strength measured the intensity | strength when a current collection member peels from a fuel cell using a tensile testing machine, and described the value.

  From Table 1, Sample No. in which no metal powder is added to the paste of the conductive bonding material. In No. 1, it is found that cracks are generated during the formation of the conductive bonding material, the baking is poor, and the peel strength of the current collecting member is small. On the other hand, in the sample of this invention, it turns out that the crack generation at the time of formation of a conductive joining material does not occur, and the peeling strength of a current collection member is as high as 0.15 MPa or more.

It is sectional drawing which shows the state which provided the cell stack in the manifold. It is sectional drawing which shows the state which has joined the fuel cell with the electroconductive joining material. (A) is a plan view of the cell stack of the present invention, (b) is a side view showing a state in which the oxygen electrode layer-side current collecting piece is bonded to the oxygen electrode layer by a conductive bonding material, and (c) is a current collector. It is a perspective view of a member. (A) is a cross-sectional view of a fuel cell, (b) is a longitudinal cross-sectional view of (a). It is a figure which shows a firing shrinkage curve.

Explanation of symbols

2 ... Solid electrolyte layer 3 ... Fuel electrode layer 4 ... Support substrate 5 ... Oxygen electrode layer 9 ... Conductive bonding layer 30 ... Fuel cell 33 ... Current collecting member

Claims (3)

A plurality of solid electrolyte fuel cells, inter-cell connection members respectively disposed between the solid electrolyte fuel cells, and a paste interposed between the solid electrolyte fuel cells and the inter-cell connection members A cell stack comprising a conductive bonding material bonded by heat treatment in an atmosphere having a lower oxygen partial pressure than the atmosphere , wherein the conductive bonding material contains a perovskite-type composite oxide containing La the cell stack, characterized in that it contains the object, and a ZnO obtained by oxidizing the metal Zn powder by the heat treatment.   The solid electrolyte fuel cell has a fuel electrode layer on one side of the solid electrolyte and an oxygen electrode layer on the other side, and the oxygen electrode layer is connected between the cells via the conductive bonding material. The cell stack according to claim 1, wherein the conductive bonding material is bonded to a portion of the oxygen electrode layer where the connecting member is bonded and the inter-cell connecting member is not bonded.   A fuel cell module comprising the cell stack according to claim 1 or 2 accommodated in a storage container.

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