JP4912576B2 - Fuel cell - Google Patents

Description

The present invention relates to a solid electrolyte fuel cell.

As a next-generation energy, in recent years, a fuel cell containing the fuel cell cell Luz tack storage container have been proposed. For example, Figure 4 shows a cell stack of a conventional solid electrolyte fuel cell, the cell stack, a plurality of fuel cells 1 (1a, 1b) is a well-order, one of the fuel cell 1a and the other A current collecting member 5 made of metal felt is interposed between the fuel cell 1b and the fuel electrode 7 of one fuel cell 1a and the oxygen electrode 11 of the other fuel cell 1b are electrically connected. Was composed. That is, the fuel cell 1 (1a, 1b) is configured by sequentially providing a solid electrolyte 9 and an oxygen electrode 11 made of conductive ceramics on the outer peripheral surface of a fuel electrode 7 made of a cylindrical metal. An interconnector 12 is provided on the fuel electrode 7 exposed from the electrolyte 9 and the oxygen electrode 11 so as not to be connected to the oxygen electrode 11, and is electrically connected to the fuel electrode 7.

  The interconnector 12 in the fuel cell 1 (1a, 1b) is dense and fuel gas for reliably blocking the fuel gas flowing inside the fuel electrode 7 and the oxygen-containing gas flowing outside the oxygen electrode 11. In addition, it is made of a conductive ceramic that is not easily altered by an oxygen-containing gas. The electrical connection between one fuel cell 1a and the other fuel cell 1b is made by connecting the fuel electrode 7 of one fuel cell 1a to the interconnector 12 and the current collecting member 5 provided on the fuel electrode 7. It was performed by connecting to the oxygen electrode 11 of the other fuel battery cell 1b via.

  The fuel cell is configured by housing the cell stack in a storage container, and generates power at about 1000 ° C. by flowing fuel (hydrogen) through the fuel electrode 7 and flowing air (oxygen) through the oxygen electrode 11.

In a fuel cell constituting such a fuel cell, the fuel electrode 7 is generally composed of Ni and stabilized zirconia (YSZ) containing Y ₂ O ₃ , and the solid electrolyte 9 is stabilized zirconia (YSZ). The oxygen electrode 11 is composed of a LaMnO ₃ perovskite oxide.

By the way, as a substance that can obtain higher oxygen ion conductivity than stabilized zirconia in recent years, the following formula:
_{(La 1-x Sr x)} (Ga 1-y Mg y) O 3
The lanthanum gallium perovskite oxide (hereinafter abbreviated as LSGM or lanthanum gallate) represented by the formula has attracted attention, and many studies have been conducted.

  The above-mentioned LSGM sintered body is a substance with little decrease in oxygen ion conductivity even at a low temperature of 600 to 800 ° C., and a part of La and Ga is substituted with a lower valence Sr or Mg due to substitution solid solution. It has been replaced, and this has the property that the oxygen ion conductivity of the sintered body is increased. This material is now considered the best oxide ion conductor.

  However, in the fuel cell in which the solid electrolyte layer is formed by LSGM as described above, although it operates at a low temperature, the contact resistance between the oxygen electrode layer and the solid electrolyte layer is increased, and the performance of the fuel cell in the initial stage is deteriorated. There was a problem.

As a method for solving the above problems, a structure in which an intermediate layer made of a perovskite oxide is formed at the interface between the oxygen electrode layer and the solid electrolyte layer has been proposed (see Patent Documents 1 and 2).
JP 2000-188117 A JP 2002-52722 A

  However, in the fuel cell provided with the intermediate layer as described above, there is a problem that the ionic conductivity of the solid electrolyte layer is lowered and the performance of the fuel cell is lowered. That is, according to the study by the present inventors, in such a fuel cell, since the oxygen electrode layer, the intermediate layer, and the solid electrolyte layer all have the same perovskite crystal structure, the diffusion of elements between the layers Smoothly progresses, and a concentration gradient in which the composition between the layers changes continuously is generated, and the adhesion strength is improved. On the other hand, if power generation is performed over a long period of time, a solid is generated due to element diffusion. It has been found that the ionic conductivity of the electrolyte layer is lowered, and as a result, the performance of the fuel cell is lowered.

Accordingly, the object of the present invention is to increase the adhesion strength between the two layers without increasing the contact resistance between the solid electrolyte layer and the oxygen electrode layer, to obtain high power generation performance in the initial stage, and to be high over a long period of time. to provide a solid oxide fuel cell power generation performance can be maintained.

  As a result of earnestly examining the above problems, the present inventor provided an intermediate layer formed of a non-perovskite complex oxide made of a material having ion conductivity between the solid electrolyte layer and the oxygen electrode layer, In addition, since the oxygen electrode layer has a two-layer structure including a first layer made of a perovskite oxide and a second layer made of the intermediate layer forming material and the perovskite oxide, high power generation is achieved in the initial stage. It has been found that performance can be obtained and high power generation performance can be maintained over a long period of time.

That is, according to the present invention, in the fuel cell in which the perovskite solid electrolyte layer is disposed between the oxygen electrode layer and the fuel electrode layer,
Between the solid electrolyte layer and the oxygen electrode layer, an intermediate layer composed of a complex oxide composed of CeO ₂ and Ln ₂ O ₃ (Ln is a rare earth element) is formed,
The oxygen electrode layer has a two-layer structure of a first oxygen electrode layer and a second oxygen electrode layer, and the first oxygen electrode layer comprises the second oxygen provided on the intermediate layer. The second oxygen electrode layer located on the polar layer and formed from a perovskite oxide and provided on the intermediate layer is composed of a composite oxide constituting the intermediate layer and the perovskite oxide. A fuel cell, characterized in that a porosity ratio B / A between the porosity B of the second oxygen electrode layer and the porosity A of the first oxygen electrode layer is lower than 0.5. A cell is provided .

In the fuel battery cell of the present invention, an intermediate layer formed of a Ce-rare earth complex oxide composed of CeO ₂ and Ln ₂ O ₃ (Ln is a rare earth element) is provided between the solid electrolyte layer and the oxygen electrode layer. At the same time, the oxygen electrode layer has a two-layer structure, and the second oxygen electrode layer adjacent to the intermediate layer is a perovskite oxide that is a Ce-rare earth element-based composite oxide and a first oxygen electrode layer forming material. And the ratio B / A between the porosity B of the second oxygen electrode layer and the porosity A of the first oxygen electrode layer is lower than 0.5, so that the solid electrolyte layer It is possible to enhance the adhesion between the oxygen electrode layer and the oxygen electrode layer, to reduce the contact resistance between the two layers, to prevent peeling of these layers during production, and to increase the production yield. Moreover, according to such a layer structure, the oxygen electrode layer, the intermediate layer, and the solid electrolyte layer have different crystal structures, so that element diffusion is unlikely to occur, and as a result, power generation was performed for a long time. In this case, deterioration of the ionic conductivity of the solid electrolyte layer can be prevented, and a decrease in the performance of the fuel cell can be effectively avoided.

In the present invention, the composite oxide (Ce-rare earth element composite oxide) constituting the intermediate layer has the following formula:
(CeO ₂ ) _1-x (LnO _1.5 ) _x
In the formula, Ln is at least one of La, Sm, and Y,
x is a number satisfying 0.1 ≦ x ≦ 0.3,
It is preferable to have the composition represented by these. By using the Ce-rare earth complex oxide having such a composition, the thermal expansion coefficient of the intermediate layer is changed to the thermal expansion coefficient of the solid electrolyte layer, the oxygen electrode layer, the fuel electrode layer, etc. which are other cell constituent layers. It can be approximated, and the occurrence of cracks and delamination due to the difference in thermal expansion can be effectively prevented. In addition, since such Ce-rare earth element-based composite oxide functions as a solid electrolyte and is a mixed conductor having ionic conductivity and electronic conductivity, it does not adversely affect the power generation performance of the fuel cell. Absent.

The intermediate layer preferably has a thickness of 2 to 10 μm . If the thickness of the intermediate layer is increased more than necessary, the intermediate layer itself becomes a resistance component, and the contact resistance at the interface between the oxygen electrode layer and the solid electrolyte layer is slightly increased. Therefore, in order to fully exhibit the power generation performance of the fuel cell, it is preferable that the thickness of the intermediate layer is within the above range.

  Furthermore, the solid electrolyte layer is preferably formed of a lanthanum gallate perovskite oxide. As already described, such a perovskite oxide is currently the most excellent oxide ion conductor, and by forming a solid electrolyte layer with such an oxide, fuel can be produced at a low temperature of, for example, 500 to 700 ° C. A battery cell can be operated and high output can be obtained.

In the present invention, the provided fuel electrode layer is provided on the conductive support substrate, the fuel electrode layer, the solid electrolyte layer, wherein that the intermediate layer and the oxygen electrode layer is provided It is suitable for securing strength characteristics. In particular, the solid electrolyte layer formed of the above lanthanum gallate-based perovskite oxide has low strength, but by using a conductive support substrate and forming a cell constituent layer thereon, strength reduction is effectively avoided. can do.

Furthermore, in the oxygen electrode layer having the two-layer structure described above, the porosity ratio B / A between the porosity B of the second oxygen electrode layer and the porosity A of the first oxygen electrode layer is set to 0. Further , the thickness C of the second oxygen electrode layer is smaller than the thickness D of the first oxygen electrode layer, and the thickness D of the first oxygen electrode layer is 35 to 85 μm. To efficiently supply oxygen-containing gas such as air used for power generation to the electrochemical reaction field, without increasing the cell resistance and increasing the bonding strength between the intermediate layer and the oxygen electrode layer. High power generation performance can be ensured over a long period of time.

Hereinafter, the present invention will be described based on specific examples shown in the accompanying drawings.
1A and 1B are diagrams showing a typical structure of a fuel battery cell according to the present invention. FIG. 1A is a cross-sectional view, and FIG. 1B is a partial perspective view.
2A and 2B are diagrams showing the structure of another example of the fuel battery cell of the present invention. FIG. 2A is a cross-sectional view, and FIG. 2B is a partial perspective view.
FIG. 3 is a schematic cross-sectional view showing the layer structure of the power generation portion in the fuel battery cell of the present invention.

In FIG. 1 showing a typical structure of a fuel battery cell of the present invention (hereinafter sometimes abbreviated as “cell”) , the fuel battery cell indicated by 30 as a whole is a hollow flat plate and has a rod plate shape and a cross section. Is provided with a conductive support substrate 31 which is flat and has an elliptical columnar shape as a whole. Inside the support substrate 31, a plurality of fuel gas passages 31 a are formed penetrating in the length direction at appropriate intervals. The fuel cell 30 is provided with various cell constituent members on the support substrate 31. Has the structure.

  In the example of FIG. 1, the support substrate 31 includes a flat portion and arc-shaped portions at both ends of the flat portion. Both surfaces of the flat portion are formed substantially parallel to each other, and the fuel electrode layer 32 is provided so as to cover one surface of the flat portion and the arc-shaped portions on both sides, and further, this fuel electrode layer 32 is covered. A dense solid electrolyte layer 33 is laminated, and an oxygen electrode is disposed on one surface of the flat portion on the solid electrolyte layer 33 so as to face the fuel electrode layer 32 via an intermediate layer 34. 35 are laminated. An interconnector 37 is formed on the other surface of the flat portion where the fuel electrode layer 32 and the solid electrolyte layer 33 are not stacked. As is clear from FIG. 1, the fuel electrode layer 32 and the solid electrolyte layer 33 extend to both sides of the interconnector 37 and are configured so that the surface of the support substrate 31 is not exposed to the outside.

In the fuel cell having the above structure, the portion of the fuel electrode layer 32 facing the oxygen electrode layer 35 operates as a fuel electrode to generate electric power. That is, an oxygen-containing gas such as air is allowed to flow outside the oxygen electrode layer 35, and a fuel gas (hydrogen) is supplied to the gas passage 31 a in the support substrate 31, and the oxygen electrode layer 35 is heated to a predetermined operating temperature. Then, an electrode reaction of the following formula (1) is generated, and in the portion that becomes the fuel electrode of the fuel electrode layer 32, for example, an electrode reaction of the following formula (2) is generated. Current is collected via 37.
Oxygen electrode layer: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte) (1)
Fuel electrode layer: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻ (2)

  That is, a plurality of fuel cells 30 having the above-described structure are connected in series by a current collecting member 40 to form a cell stack, and the cell stack is accommodated in a predetermined container, and a fuel gas ( Hydrogen) and oxygen-containing gas can be allowed to function as a fuel cell by flowing them through a predetermined portion.

(Support substrate 31)
The support substrate 31 is required to be gas permeable in order to allow fuel gas to permeate to the fuel electrode, and to be conductive in order to collect current via the interconnector 37. For this reason, it is desirable that the support substrate 31 is composed of a metal component such as an iron group and a specific rare earth oxide.

  The iron group metals include iron, nickel, and cobalt. In the present invention, any of them can be used, but Ni and / or NiO is changed to iron group because it is inexpensive and stable in fuel gas. It is preferable to use it as a component.

The rare earth oxide component is used to approximate the thermal expansion coefficient of the support substrate 31 to that of the solid electrolyte layer 33, and maintains high conductivity and prevents diffusion into the solid electrolyte layer 33 and the like. Therefore, an oxide containing at least one rare earth element selected from the group consisting of Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm, and Pr is used in combination with the iron group component. The Specific examples of such rare earth oxides include Y ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , Tm ₂ O ₃ , Er ₂ O ₃ , Ho ₂ O ₃ , Dy ₂ O ₃ , Gd ₂ O. ₃ , Sm ₂ O ₃ and Pr ₂ O ₃ can be exemplified, and Y ₂ O ₃ and Yb ₂ O ₃ are preferable in that they are particularly inexpensive.

  Note that the iron group metal component and the rare earth oxide component constituting the support substrate 31 generally maintain an excellent electrical conductivity and have an appropriate thermal expansion coefficient. It is preferably present in a volume ratio of 35:65 to 65:35.

  The length of the flat portion of the support substrate 31 is usually 15 to 35 mm, and the thickness of the support substrate 31 is preferably about 2.5 to 5 mm. This is because the actual resistance value of the cell component can be lowered.

  In the present invention, the mechanical strength of the cell can be increased by using the support substrate 31 as described above and providing the support substrate 31 with various cell constituent members.

(Fuel electrode layer 32)
The fuel electrode layer 32 causes the electrode reaction of the above-described formula (2), and is formed of a known porous conductive ceramic. For example, it is formed from ceria (CeO ₂ ) in which a rare earth element is dissolved, and Ni and / or NiO.

  The ceria content of the rare earth element in the fuel electrode layer 32 in a solid solution is preferably in the range of 35 to 65% by volume, and the Ni or NiO content is preferably 65 to 35% by volume. Further, the open porosity of the fuel electrode layer 32 is preferably 15% or more, particularly in the range of 20 to 40%, and the thickness is preferably 5 to 30 μm. For example, if the thickness of the fuel electrode 32 is too thin, the performance may be deteriorated, and if it is too thick, there is a possibility that separation due to a difference in thermal expansion occurs between the solid electrolyte layer 33 and the fuel electrode layer 32.

(Solid electrolyte layer 33)
The solid electrolyte layer 33 provided on the support substrate 31 is known per se, and is formed of, for example, various perovskite oxides. In particular, a lanthanum gallate oxide is preferably used. This lanthanum gallate oxide is an ABO ₃ type perovskite oxide, which has La at the A site and Ga at the B site. In particular, the following formula:
(La, Sr) (Ga, Mg) O ₃
The lanthanum gallate in which a part of La (particularly 10 to 20 atomic%) is substituted with Sr and a part of Ga (particularly 10 to 20 atomic%) is further substituted with Mg as shown in FIG. By forming the solid electrolyte layer 33 using such an oxide ion conductor, the fuel cell can be operated at a low temperature of, for example, 500 to 700 ° C., and high output can be obtained. Moreover, said lanthanum gallate can further raise ionic conductivity by substituting 1-20 atomic% of Co, Fe, Ni, Cu etc. in Ga position.

Further, the solid electrolyte layer 33 contains, in addition to the perovskite oxide, fine powder fillers such as Al ₂ O ₃ , MgO, Si ₃ N ₄ , and SiC in an amount of 2% by mass or less, for example. The strength of the solid electrolyte layer 33 can be increased by such a fine powder filler.

  The solid electrolyte layer 33 is desirably dense with a relative density (according to Archimedes method) of 93% or more, particularly 95% or more in terms of preventing gas permeation, and a thickness of 10 to 50 μm. It is desirable that

(Intermediate layer 34)
In the present invention, the intermediate layer 34 provided between the solid electrolyte layer 33 and the oxygen electrode layer 35 is formed of a Ce-rare earth complex oxide composed of CeO ₂ and Ln ₂ O ₃ (Ln is a rare earth element). The That is, the Ce- rare earth element-based composite oxide, as a solid electrolyte to function, because it is mixed conductor having an ion conductivity and electron conductivity, can adversely affect the power generation performance of the fuel cell 30 In addition, there is no perovskite oxide as in the case of the solid electrolyte layer 33 and the oxygen electrode layer 35 to be described later, and the crystal structure of each layer is different, so that element diffusion hardly occurs, and as a result, over a long period of time. Therefore, it is possible to prevent deterioration of the ionic conductivity of the solid electrolyte layer when power generation is performed, and to effectively avoid a decrease in performance of the fuel cell.

Further, as such a Ce-rare earth element-based composite oxide, the following formula (3):
(CeO ₂ ) _1-x (LnO _1.5 ) _x (3)
In the formula, Ln is at least one of La, Sm, and Y,
x is a number satisfying 0.1 ≦ x ≦ 0.3,
It is preferable to have the composition represented by these. That is, the rare earth element Ln is La, a Sm or Y, when forming the intermediate layer 34 by and those having the above composition, bringing the thermal expansion coefficient of the intermediate layer 34 in the thermal expansion coefficient of the other cell components Therefore, generation of cracks and peeling due to a difference in thermal expansion can be suppressed.

In the present invention, the thickness of the intermediate layer 34 is preferably in the range of 2 to 10 μm , particularly 2 to 7 μm. If the thickness of the intermediate layer 34 is increased more than necessary, the intermediate layer 34 itself becomes a resistance component, and the contact resistance at the interface between the oxygen electrode layer 35 and the solid electrolyte layer 34 may be slightly increased. If it is thin, the element diffusion preventing function of the intermediate layer 34 is not sufficiently exhibited, and the ionic conductivity of the solid electrolyte layer 33 may be deteriorated when power is generated for a long time.

(Oxygen electrode layer 35)
The oxygen electrode layer 35 is usually formed of an ABO ₃ type perovskite oxide. In particular, in the present invention, the oxygen electrode layer 35 is divided into the first oxygen electrode layer 35a and the second oxygen electrode layer 35b. It is important to have a two-layer structure. That is, the first oxygen electrode layer 35 a is formed on the second oxygen electrode layer 35 b provided on the intermediate layer 34, and the first oxygen electrode layer 35 a is converted into an ABO ₃ type perovskite oxide. The second oxygen electrode layer 35b provided in the intermediate layer 34 is formed from the perovskite oxide and the Ce-rare earth element composite oxide forming the intermediate layer 34. is important. That is, by adopting such a two-layer structure, the second oxygen electrode layer 35b serves as an adhesive layer between the first oxygen electrode layer 35a and the intermediate layer 34, and the adhesion strength between both layers is increased. Further, peeling of these layers can be effectively prevented, and stable power generation performance can be ensured over a long period of time. Moreover, since the Ce-rare earth element-based composite oxide in the second oxygen electrode layer 35b is a mixed conductor having ionic conductivity and electron conductivity, it is mixed with a perovskite oxide so-called three-phase. An interface is formed, and the three-layer interface, which is an electron reaction field, is increased in the oxygen electrode layer 35, so that the output of the fuel cell 10 can be increased. Therefore, as the Ce-rare earth element-based composite oxide in the second oxygen electrode layer 35b, the one having the composition represented by the above formula (3) is preferable as in the intermediate layer 34.

The perovskite oxide in the first oxygen electrode layer 35a or the second oxygen electrode layer 35b is a transition metal perovskite oxide, particularly a La-based perovskite oxide having La at the A site (for example, LaMnO ₃ system). Oxides, LaFeO ₃ -based oxides, LaCoO ₃ -based oxides) are preferable, and LaFeO ₃ -based oxides are particularly preferable because of their high electrical conductivity at an operating temperature of about 600 to 1000 ° C. In the perovskite oxide, Sr and the like may exist together with La at the A site, and Co and Mn may exist together with Fe at the B site. Further, the quantity ratio of the Ce-rare earth element-based composite oxide to the perovskite oxide in the second oxygen electrode layer 35b is Ce-rare earth element-based oxide: perovskite oxide = 1 on a weight basis. A range of 9 to 3: 7 is preferred.

  Further, the oxygen electrode layer 35 having such a two-layer structure must have gas permeability, and therefore, its open porosity is desirably 20% or more, particularly 30 to 50%. .

  Furthermore, in the present invention, the ratio B / A between the porosity B of the second oxygen electrode layer 35b and the porosity A of the first oxygen electrode layer 35a is preferably smaller than 0.5, in particular , 0.01 <B / A <0.3. That is, by forming the second oxygen electrode layer 35b denser than the first oxygen electrode layer 35a, oxygen supplied to the outside of the oxygen electrode layer 35 can be easily supplied to the electrochemical reaction field. The resistance component of the cell can be reduced.

  The thickness C of the second oxygen electrode layer 35b is preferably thinner than the thickness D of the first oxygen electrode layer 35a, and in particular, the thickness C of the second oxygen electrode layer 35b is 3 to 30 μm. Most preferred. If the thickness C of the second oxygen electrode layer 35b is thicker than the thickness D of the first oxygen electrode layer 35a, the mechanical bonding strength becomes weak, and peeling between the intermediate layer 34 and the oxygen electrode layer 35 is likely to occur. In addition, the resistance of the cell is increased, and the power generation characteristics may be deteriorated. Furthermore, in order to ensure a sufficient power generation function and maintain high power generation performance over a long period of time, the thickness D of the first oxygen electrode layer is particularly preferably in the range of 35 to 85 μm, particularly 40 to 60 μm.

(Junction layer 36)
In the present invention, a bonding layer 36 can be provided to bond the interconnector 37 to the support substrate 31. The bonding layer 36 is made of Ni metal and / or an oxide of Ni metal and zirconia stabilized with rare earth, and the stabilized zirconia content in the bonding layer 36 is preferably in the range of 35 to 45% by volume, The Ni or NiO content is preferably 65 to 55% by volume. That is, by making the Ni content in the bonding layer 36 larger than the Ni content in the fuel electrode layer 32, the potential drop due to the bonding layer 36 can be reduced, so that a decrease in power generation performance can be avoided. it can.

  The thickness of the bonding layer 36 is preferably 10 μm or less, particularly preferably 7 μm or less, in order to suppress the occurrence of cracks in the interconnector 37 or the peeling of the interconnector 37 from the support substrate 31. It is.

(Interconnector 37)
The interconnector 37 provided on the support substrate 31 so as to face the oxygen electrode layer 32 is made of conductive ceramics, but is in contact with the fuel gas (hydrogen) and the oxygen-containing gas. It is necessary to have oxidation resistance. For this reason, lanthanum chromite perovskite oxides (LaCrO ₃ oxides) are generally used as the conductive ceramics. Further, in order to prevent leakage of the fuel gas passing through the inside of the support substrate 31 and the oxygen-containing gas passing through the outside of the support substrate 31, such conductive ceramics must be dense, for example, 93% or more, particularly 95%. It is preferable to have the above relative density.

  The interconnector 37 preferably has a thickness of 100 to 500 μm from the viewpoint of preventing gas leakage and electrical resistance. That is, if the thickness is smaller than this range, gas leakage is likely to occur, and if the thickness is larger than this range, the electric resistance is large, and the current collecting function may be reduced due to a potential drop. .

(P-type semiconductor layer 38)
Further, as shown in FIG. 1, a P-type semiconductor layer 38 is preferably provided on the outer surface (upper surface) of the interconnector 37. That is, in a cell stack (not shown) assembled from the fuel cells, a conductive current collecting member is connected to the interconnector 37. By connecting this current collecting member to the interconnector 37 via the P-type semiconductor layer 38, it is possible to reduce a potential drop due to contact resistance and effectively avoid a decrease in current collecting performance. The current from the oxygen electrode layer 35 of the fuel cell 30 can be efficiently transmitted to the support substrate 31 of the other fuel cell 30. As such a P-type semiconductor, a transition metal perovskite oxide can be exemplified. Specifically, those having higher electron conductivity than LaCrO ₃ oxides constituting the interconnector 37, for example, LaMnO ₃ oxides and LaFeO ₃ oxides in which Mn, Fe, Co, etc. are present at the B site P-type semiconductor ceramics made of at least one of LaCoO ₃ -based oxides can be used, and it is particularly preferable that the P-type semiconductor ceramic be made of a material used for forming the oxygen electrode layer 35.

  In general, the thickness of the P-type semiconductor layer 38 is preferably in the range of 30 to 100 μm. The P-type semiconductor layer 38 preferably has an open porosity of 20% or more, particularly 30 to 50%.

(Reaction prevention layer 39)
In the present invention, in order to avoid formation of an interface resistance layer due to mutual element diffusion between the fuel electrode layer 32 and the solid electrolyte layer 33, it is preferable to provide a reaction preventing layer 39 on the fuel electrode layer 32. The reaction preventing layer 39 is made of CeO ₂ in which La is dissolved, La ₂ O ₃ in which Ce is dissolved, or a mixture thereof. Such a complex oxide is generally represented by the following formula (4):
(CeO ₂ ) _1-y (LaO _1.5 ) _y (4)
In the formula, y is a number satisfying 0.3 <y ≦ 0.6.
It is preferable that it has a composition represented by the following formula in that the effect of blocking or suppressing the diffusion of Ni from the fuel electrode layer 32 to the solid electrolyte layer 33 can be enhanced. In particular, when the value of y in the formula (4) is in the range of 0.35 ≦ y ≦ 0.45, the thermal expansion coefficient of the reaction preventing layer 39 can be brought close to the values of other cell constituent members, and the thermal expansion It is most preferable in that the generation of cracks and peeling due to the difference can be suppressed.

  In addition, in the reaction preventing layer 39, in order to increase the effect of blocking or suppressing element diffusion, other rare earth elements other than La, such as Sc, Y, Pr, Nd, Pm, Sm, Eu, Gd, It may contain oxides such as Tb, Dy, Ho, Er, Tm, Yb, and Lu.

  In addition, the composite oxide constituting the reaction preventing layer 39 is a mixed conductor having ionic conductivity and electronic conductivity, but has a lower conductivity than the solid electrolyte layer 33. However, by setting the thickness of the reaction preventing layer 39 to about 1 to 20 μm, it is possible to maintain the desired element diffusion preventing effect and hardly affect the power generation performance of the fuel cell.

(Current collection auxiliary layer 40)
In the present invention, it is preferable to provide the current collection auxiliary layer 40 on the upper surface of the P-type semiconductor layer 38 and the upper surface of the oxygen electrode layer 35. That is, in a cell stack (not shown) assembled from the fuel battery cell 30 , a conductive current collecting member is connected to the interconnector 37, but when the current collecting member is connected to the P-type semiconductor layer 38, Since the contact resistance is large, the potential drop becomes large, and the current collecting performance is deteriorated. However, by connecting the current collecting member to the interconnector 37 via the current collecting auxiliary layer 40 and the P-type semiconductor layer 38, the contact resistance is reduced, the potential drop is reduced, and the current collecting performance is effectively reduced. For example, the current from the oxygen electrode layer 35 of one fuel battery cell 30 can be efficiently transmitted to the support substrate 31 of the other fuel battery cell 30. As such a current collection auxiliary layer 40, a noble metal can be exemplified, and in particular, the current collection auxiliary layer 40 is formed of Pt, Ag, Pd, etc., which are not easily oxidized in an oxygen-containing gas atmosphere and have a high melting point. Is preferred. In general, the thickness of the current collection auxiliary layer 40 is preferably in the range of 10 to 80 μm.

Fuel cell 30 of the present invention having the structure shown in FIG. 1 described above, but has a shape having a Tokoro I楕 circular cross-section, the present invention is not limited to such a shape, for example, in FIG. 2 The present invention can also be applied to a cylindrical fuel cell as shown.

  In the cylindrical fuel cell shown in FIG. 2, the fuel electrode layer 32, the reaction preventing layer 39, the solid electrolyte layer 33, the middle, leaving a part of the space on the outer surface of the substantially cylindrical conductive support 31. The layer 34 and the oxygen electrode layer 35 (the first oxygen electrode layer 35a and the second oxygen electrode layer 35b) are stacked in this order, and the bonding layer 36 is formed in the space where these layers are not stacked. In this way, an interconnector 37 having a current collecting function is provided. Further, the outer intermediate layer 34 and the oxygen electrode layer 35 are formed in a non-contact manner with the interconnector 37 in order to prevent electrical leakage.

  In the fuel cell shown in FIG. 2, all of the constituent parts of the cell are formed of the same material as in FIG. 1, but the internal space of the cylindrical conductive support substrate 31 is a gas flow path through which fuel gas flows. The oxygen-containing gas is allowed to flow outside the cell (outside the oxygen electrode layer 35). In the case of forming a cell stack, the cells are stacked. For example, the interconnector 37 of one cell is connected to the oxygen electrode layer of the upper cell via the P-type semiconductor layer 38 and the current collecting auxiliary layer 40 on the interconnector 37. What is necessary is just to make it the structure joined to 35. In such a fuel cell, the same effect as the fuel cell 10 of FIG. 1 is exhibited.

  In the fuel cell of FIG. 2, the layer structure can be reversed. For example, a layer in which the fuel electrode layer 32, the solid electrolyte layer 33, and the oxygen electrode layer 35 are formed inside the cylindrical support substrate 31. A structure is also possible. In this case, the oxygen-containing gas is caused to flow in the internal space of the support substrate 31 and the fuel gas is caused to flow outside.

  That is, in the present invention, as shown in the schematic cross-sectional structure of the power generation unit in FIG. 3, the fuel electrode layer 32 and the solid electrolyte layer 33 are formed on one surface of the conductive support substrate 31. As long as the two oxygen electrode layers 35 are formed thereon via the intermediate layer 33, various structures can be adopted. Furthermore, as long as a predetermined strength is maintained, the conductive support substrate 31 is formed. It is also possible to form such a support substrate with the fuel electrode layer 32 itself without providing it.

(Manufacture of fuel cells)
The fuel battery cell having the above structure is manufactured as follows.

First, a powder of a predetermined iron group metal component (for example, Ni or NiO), a powder of a rare earth element oxide (for example, Y ₂ O ₃ ), an organic binder, a solvent, and, if necessary, a commercially available pore former are mixed. Then, a molding slurry is prepared, and a support body molded body having a predetermined shape is produced using this slurry according to a conventional method.

Moreover, an organic binder, a solvent, and a commercially available dispersant are mixed into a mixed powder obtained by mixing CeO ₂ powder in which a rare earth element having a predetermined fine particle size is dissolved and Ni and / or NiO powder in a predetermined amount ratio. And a slurry is prepared, and the slurry is applied to a predetermined position of the support substrate molded body by a method such as screen printing and dried to form a fuel electrode coating layer.

Next, for a reaction prevention layer in which a mixed oxide powder such as CeO ₂ powder in which La is dissolved or La ₂ O ₃ powder in which Ce is dissolved, an organic binder (acrylic resin), and a solvent (toluene) are mixed. The paste is applied on the above fuel electrode coating layer by screen printing or the like, and dried to form a coating layer for the reaction preventing layer. A laminated molded body in which the coating layer and the coating layer for the reaction preventing layer are laminated is obtained.

  Furthermore, a slurry for molding is prepared by adding a solvent such as toluene, a binder, and a commercially available dispersant to a solid electrolyte raw material powder such as lanthanum gallate powder, and molding is performed by a method such as a doctor blade to form a sheet-like solid electrolyte molding Create a body. In this case, it is preferable that the solid electrolyte raw material powder is produced by a liquid phase method such as a Petini method because the amount of impurities is small and the synthesis rate is very high. In addition, the average particle diameter of the solid electrolyte raw material powder is preferably in the range of 0.5 to 1.5 μm, particularly 0.6 to 1.2 μm, in that sintering can be performed at a lower temperature. That is, the LSGM solid electrolyte molded body formed using such a fine raw material powder has a dense (for example, a relative density of 98% or more) solid electrolyte layer 33 formed by firing at a low temperature described below, for example. Since it can be formed, it is extremely advantageous in that diffusion of elements from the support substrate 31 and the oxygen electrode layer 35 to the solid electrolyte layer 33 during firing is suppressed.

  Next, the solid electrolyte molded body is laminated on the coating layer for the reaction prevention layer of the previously obtained laminated molded body, dried, and calcined at a temperature of about 600 to 1000 ° C. if necessary.

  On the other hand, the intermediate layer forming raw material powder such as Ce-rare earth element composite oxide powder having the composition represented by the formula (3) is mixed with a solvent or an organic binder such as an acrylic binder to form an intermediate layer forming slurry. The slurry is applied onto the solid electrolyte molded body of the above-mentioned laminated molded body by screen printing or the like and dried to form a coating layer for an intermediate layer. The intermediate layer forming raw material powder may be used after adjusting the particle shape and particle size by crushing, calcining, re-crushing, or the like, if necessary.

  In addition, a raw material for an interconnector such as lanthanum chromite oxide is mixed with a solvent or an organic binder to prepare a slurry, and a sheet-like interconnector molded body is prepared by using the slurry by a doctor blade method or the like. On one surface of the interconnector, a slurry prepared using a mixed powder containing Ni powder, stabilized zirconia powder, and the like is applied to form a bonding layer coating layer. Also, a slurry or paste containing the raw material powder for the P-type semiconductor layer is applied to the other surface of the interconnector and dried to form a P-type semiconductor layer coating layer.

  Next, the interconnector molded body is laminated on a predetermined portion of the laminated molded body so that the coating layer for the bonding layer faces and degreased, and then, for example, 1200 to 1450 ° C. in an oxygen-containing atmosphere. Are fired at the same temperature to produce a laminated sintered body comprising P-type semiconductor layer / interconnector / bonding layer / support substrate / fuel electrode layer / reaction prevention layer / solid electrolyte layer / intermediate layer. (The P-type semiconductor layer can also be formed by forming a coating layer on the interconnector of this laminated sintered body and baking this coating layer simultaneously with the oxygen electrode layer described below.

  Thereafter, a raw material powder for the second oxygen electrode layer containing a perovskite oxide powder and a Ce-rare earth element-based composite oxide powder is mixed with a solvent such as toluene, an organic binder, a commercially available dispersant and the like to prepare a slurry. Then, the slurry is applied on the intermediate layer of the laminated sintered body by a method such as screen printing and dried to form a second oxygen electrode layer coating layer.

  Also, a first oxygen electrode layer raw material powder such as perovskite oxide powder is mixed with a solvent and a commercially available dispersant to prepare a slurry, and this slurry is applied onto the second oxygen electrode layer coating layer. Then, by performing drying and baking, an oxygen electrode layer having a two-layer structure in which the first oxygen electrode layer is provided on the second oxygen electrode layer can be formed. In this case, in order to adjust the porosity ratio B / A between the porosity B of the second oxygen electrode layer and the porosity A of the first oxygen electrode layer to the above-described range, The slurry is applied by a printing method such as a screen printing method, and the first oxygen electrode layer is preferably formed by spraying. That is, the first oxygen electrode layer formed by baking the coating layer by spraying has a higher porosity than the second oxygen electrode layer by the printing method, and the porosity ratio B / A is the predetermined value described above. Can be adjusted to the range. In order to apply the slurry by spraying, it is preferable that the slurry (first oxygen electrode forming slurry) is prepared without using a binder, and the baking of the slurry layer is performed at a high temperature ( For example, it can be performed at about 900 to 1200 ° C.

  After forming the first and second oxygen electrode layers as described above, a noble metal paste such as Pt paste is applied as a current collecting auxiliary layer on the first oxygen electrode layer and the P-type semiconductor layer, By drying at about 200 ° C., a fuel battery cell as shown in FIG. 1 or FIG. 2 can be produced. A plurality of such fuel battery cells are connected in series to form a cell stack, It can be made to function as a fuel cell by disposing the fuel gas and the oxygen-containing gas through a predetermined portion and heating them to a predetermined operating temperature.

  In addition, since the Ni component in the fuel electrode layer 32 is NiO due to the firing in the oxygen-containing atmosphere, the fuel battery cell 30 then flows a reducing fuel gas from the gas flow path 31a to allow NiO to flow. Reduction treatment is performed at 800 to 1000 ° C. Further, this reduction process may be performed during power generation.

  The invention is illustrated by the following experimental example.

(Experimental example 1)
First, a NiO powder having an average particle size of 0.5 μm and a Y ₂ O ₃ powder having an average particle size of 0.9 μm are baked and reduced, and the volume ratio of Ni is 48% by volume and Y ₂ O ₃ is 52% by volume. The slurry prepared with the organic binder and the solvent was molded by an extrusion molding method, dried and degreased to prepare a support substrate molded body.

Then a Ni powder having an average particle diameter of 0.5 [mu] _m, the Y 2 _{O 3} (hereinafter abbreviated as YDC20) CeO ₂ was dissolved 20 mol% CeO ₂ (hereinafter the powder or _Sm 2 _{O 3} were dissolved 20 mole% SDC20 The powder was mixed with an organic binder and a solvent to prepare a slurry, which was applied to the support substrate molded body by a screen printing method and dried to form a coating layer for the fuel electrode layer.

A slurry is prepared by mixing CeO ₂ (hereinafter abbreviated as YDC40) powder in which Y ₂ O ₃ is dissolved in 40 mol%, an organic binder and a solvent, and a coating layer for the fuel electrode layer on the support substrate molded body is prepared. The coating layer for the reaction preventing layer was formed thereon by applying and drying by screen printing.

Next, a perovskite type (La _0.9 Sr _0.1 ) (Ga _0.8 Mg _0.2 ) O ₃ powder, an organic binder, and a solvent are mixed to prepare a slurry. A sheet for a solid electrolyte layer having a thickness of 30 μm was prepared by a blade method, attached onto the coating layer for the reaction prevention layer, and dried to prepare a laminated molded body.

  The laminated molded body produced above was degreased at 600 ° C. for 4 hours, and then calcined at 1000 ° C. for 1 hour.

Next, CeO ₂ (hereinafter abbreviated as LDC20) powder in which 20 mol% of La ₂ O ₃ is solid-dissolved is pulverized for 24 hours with a vibration mill, and then calcined at 900 ° C. for 4 hours. The powder was crushed to adjust the degree of powder aggregation (particle diameter by laser diffraction / pseudo-spherical particle diameter calculated from specific surface area) to 10-20. To this powder, an acrylic binder and toluene are added and mixed to prepare a slurry for the intermediate layer, and this slurry is applied to the surface of the solid electrolyte molded body of the above-mentioned laminated calcined body by a screen printing method and dried. did.

A slurry was prepared by mixing LaCrO ₃ powder having an average particle size of 0.3 μm, an organic binder and a solvent, and this slurry was molded by a doctor blade method to produce a sheet-like interconnector molded body.

  Further, YDC20 powder or SDC20 powder and NiO powder are mixed at a volume ratio of 45:55, an organic binder and a solvent are added to prepare a slurry for a bonding layer, and this slurry is interleaved by screen printing. It apply | coated to the connector molded object and the coating layer for joining layers was formed.

  Next, the interconnector molded body was laminated on the exposed surface of the calcined support substrate molded body, and co-fired at 1400 ° C. for 2 hours in an oxygen-containing atmosphere to obtain a laminated sintered body.

Further, as the perovskite oxide powder for the oxygen electrode layer, the following LSCF powder having an average particle diameter of 0.8 μm was prepared.
(La _0.6 Sr _0.4 ) (Co _0.6 Fe _0.4 ) O ₃ powder: Abbreviated as 6464.
(La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ powder: Abbreviated as 6428.

  The LDC20 powder used previously and the above LSCF powder are mixed in the proportions shown in Table 1, an organic binder and a solvent are added to prepare a slurry, and this slurry is formed into a laminated sintered body by a screen printing method. It apply | coated with various thickness on the formed intermediate | middle layer, and it dried at 130 degreeC, and formed the 2nd oxygen electrode layer.

  Also, a LSCF powder shown in Table 1 and isopropyl alcohol are mixed to prepare a slurry, and this slurry is sprayed onto the second oxygen electrode layer coating layer to form a first oxygen electrode layer coating layer. Baking was carried out at the temperatures shown in Table 1 to form a two-layered oxygen electrode layer to obtain a fuel cell.

  The obtained fuel cell was measured for the thicknesses of the first and second oxygen electrode layers using a scanning electron microscope and shown in Table 1. The porosity of the first and second oxygen electrode layers was also measured and shown in Table 1. The porosity is determined by partially cutting the produced fuel cell in the cross-sectional direction and embedding it in a resin, then polishing the observation surface and observing the polishing surface with a scanning electron microscope (SEM). It was calculated by an analyzer.

  The size of the produced fuel cell is 25 mm × 200 mm, the thickness of the support substrate is 3 mm, the open porosity is 35%, the thickness of the fuel electrode layer is 10 μm, the open porosity is 24%, and the total thickness of the oxygen electrode layer. Was 50 μm (open porosity 40%), the thickness of the solid electrolyte layer was 25 μm, the relative density was 97%, the thickness of the reaction preventing layer was 10 μm, and the thickness of the intermediate layer was 5 μm.

  Next, hydrogen gas was allowed to flow inside the fuel cell, and the support substrate and the fuel electrode layer were subjected to reduction treatment at 850 ° C. Thereafter, the fuel gas is circulated through the fuel gas flow path of the obtained fuel cell, the oxygen-containing gas is circulated outside the cell, the fuel cell is heated to 850 ° C. using an electric furnace, and a power generation test is performed. Went. The power generation characteristics at this time were confirmed and shown in Table 1.

  From the results in Table 1, sample No. 2 having no second oxygen electrode layer was obtained. 1 has a low reaction density with respect to surface diffusion and a low power density because it relies on volume diffusion of the second oxygen electrode layer. Sample Nos. 2 and 4, which do not contain LDC20 in the second oxygen electrode layer, have a low output density because the surface diffusion in the second oxygen electrode layer has a small number of reaction fields inside the air electrode and is not fully utilized. Is low.

  On the other hand, when the thickness of the second oxygen electrode layer exceeds 25 μm (sample No. 3), the thickness is thick even when oxygen gas reaches the second oxygen electrode layer, and the movement to the reaction field at the electrolyte interface is only volume diffusion. Therefore, power generation characteristics are low.

  In addition, oxygen ions supplied by volume diffusion in the first oxygen electrode layer and air supplied to the second oxygen electrode layer through the voids of the first oxygen electrode layer are sent to the reaction field by surface diffusion. Balanced sample no. Since 5 to 18 show high output characteristics, the weight ratio of LDC20 and LSCF of the second oxygen electrode layer is preferably between 1: 9 and 3: 7, and the thickness of the second oxygen electrode layer is 5 μm to 20 μm. Is good. The composition of the LSCF is not particularly affected as long as it is in a temperature range considering the decomposition of Co during baking.

It is a figure which shows the typical structure of the fuel cell of this invention, (a) is a cross-sectional view in FIG. 1, (b) is a fragmentary perspective view. It is a figure which shows the structure of the other example of the fuel cell of this invention, (a) is a cross-sectional view in FIG. 2, (b) is a fragmentary perspective view. It is a schematic cross-sectional view showing the layer structure of the power generation part in the fuel battery cell of the present invention. It is a cross-sectional view which shows the cell stack which consists of the conventional fuel cell.

Explanation of symbols

30 ... fuel cell 31 ... supporting substrate 31a ... fuel gas passages 32 fuel electrode layer 33 ... solid electrolyte layer 34 ... intermediate layer 35a ... first oxygen electrode layer 35b ... Second oxygen electrode layer

Claims (7)

In the fuel cell in which the perovskite solid electrolyte layer is disposed between the oxygen electrode layer and the fuel electrode layer,
Between the solid electrolyte layer and the oxygen electrode layer, an intermediate layer composed of a complex oxide composed of CeO ₂ and Ln ₂ O ₃ (Ln is a rare earth element) is formed,
The oxygen electrode layer has a two-layer structure of a first oxygen electrode layer and a second oxygen electrode layer, and the first oxygen electrode layer comprises the second oxygen provided on the intermediate layer. The second oxygen electrode layer located on the polar layer and formed from a perovskite oxide and provided on the intermediate layer is composed of a composite oxide constituting the intermediate layer and the perovskite oxide. A fuel cell, characterized in that a porosity ratio B / A between the porosity B of the second oxygen electrode layer and the porosity A of the first oxygen electrode layer is lower than 0.5. cell. The composite oxide constituting the intermediate layer has the following formula:
(CeO ₂ ) _1-x (LnO _1.5 ) _x
In the formula, Ln is at least one of La, Sm, and Y,
x is a number satisfying 0.1 ≦ x ≦ 0.3,
The fuel cell according to claim 1, which has a composition represented by:   The fuel cell according to claim 1, wherein the intermediate layer has a thickness of 2 to 10 μm. The fuel cell according to any one of claims 1 to 3, wherein the solid electrolyte layer is formed of a lanthanum gallate perovskite oxide. 5. The fuel electrode layer according to claim 1, wherein the fuel electrode layer is provided on a conductive support substrate, and the solid electrolyte layer, the intermediate layer, and the oxygen electrode layer are provided on the fuel electrode layer. The fuel cell described. Before SL thinner than the thickness D of the thickness C of the second oxygen electrode layer is the first oxygen electrode layer, one and the thickness D of the first oxygen electrode layer of claim 1 to 5 is 35~85μm A fuel battery cell according to claim 1. 7. A fuel cell comprising at least one cell stack formed by electrically connecting a plurality of the fuel cells according to claim 1 in series in a container.

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