JP5202746B1 - Solid oxide fuel cell - Google Patents

Abstract

An SOFC in which an N-type semiconductor film is provided on the surface of an interconnector made of a dense conductive ceramic provided on a fuel-side electrode, and having a bonding strength of an “interface between the interconnector and the N-type semiconductor film” A fuel-side electrode for SOFC that can increase the size of the fuel cell is provided.
An SOFC fuel-side electrode is provided with an interconnector 140 made of lanthanum chromite (LC), and an N-type semiconductor film 150 is formed on the surface of the interconnector. Ratio of “total length of a plurality of portions in contact with each other on the boundary line” to “the length of the line (boundary line) corresponding to the interface between the two in the cross section including the interconnector and the N-type semiconductor film” When the (bonding rate) is 18 to 65%, the bonding strength increases. Furthermore, when the average (joining width) of the lengths of the “plurality portions” is 0.6 to 4.8 μm, the joining strength is particularly increased.
[Selection] Figure 2

Description

  The present invention relates to a solid oxide fuel cell.

  A solid oxide fuel cell (SOFC) (a power generation unit thereof) is formed by sequentially laminating an electrolyte membrane made of a solid electrolyte and an air side electrode on a fuel side electrode. By supplying fuel gas (hydrogen gas etc.) to the fuel side electrode and supplying oxygen-containing gas (air etc.) to the air side electrode to this SOFC (power generation part), oxygen on both sides of the electrolyte membrane A potential difference is generated between the fuel side electrode and the air side electrode based on the potential difference.

  In the SOFC, an interconnector (a conductive connection member for current collection) is usually provided so as to be electrically connected to either one or both of the fuel side electrode and the air side electrode. Electric power based on the potential difference is taken out through the (these) interconnectors.

  With respect to the SOFC provided with the interconnector as described above, in Patent Document 1, an SOFC in which an interconnector made of a dense conductive ceramic is provided on the fuel-side electrode and a P-type semiconductor film is provided on the surface of the interconnector is disclosed. Have been described. It is described that when a P-type semiconductor is provided on the surface of an interconnector made of a dense conductive ceramic in this way, the reason is not clear, but the current can flow efficiently (that is, the conductivity is improved). Yes.

Japanese Patent No. 4146638

  Generally, when a conductive ceramic film such as a P-type semiconductor film is provided on the surface of an interconnector made of dense conductive ceramic, first, the interconnector made of dense conductive ceramic is formed by firing. Thereafter, a green molded body (film) which is a precursor of the conductive ceramic film is formed on the surface of the dense interconnector. The green molded body is fired to form a conductive ceramic film on the surface of the dense interconnector.

  As described above, when the conductive ceramic film is formed on the surface after the dense interconnector is formed, the conductive ceramic film becomes porous. This is because when the volume of the green molded body, which is a precursor of the conductive ceramic film formed on the dense layer (which does not shrink when the conductive ceramic film is fired), decreases due to so-called firing shrinkage, This is considered to be based on the formation of a large number of pores (details will be described later). That is, in this case, the interface between the interconnector and the conductive ceramic film is the boundary between the dense layer and the porous layer.

  In this way, the present inventor, in particular, in the “interface between the interconnector and the conductive ceramic film” that becomes the boundary between the dense layer and the porous layer, in particular, “the dense interconnector and the porous N-type semiconductor film Focused on the “interface”. And this inventor discovered the conditions which joining strength becomes large regarding the joining state (contact state) of this interface.

  That is, the present invention is an SOFC in which a porous N-type semiconductor film is provided on the surface of an interconnector made of a dense conductive ceramic provided on a fuel side electrode. An object of the present invention is to provide a bonding state having a high bonding strength with respect to the bonding state of the interface.

  The SOFC according to the present invention includes a fuel side electrode that reacts with the fuel gas in contact with the fuel gas, an electrolyte membrane made of a solid electrolyte provided on the fuel side electrode, and an air side that reacts with the oxygen-containing gas. A power generation part of a solid oxide fuel cell comprising: an electrode, an air side electrode provided on the electrolyte membrane so as to sandwich the electrolyte membrane between the fuel side electrode and the air side electrode; and the fuel side electrode And an interconnector made of a dense conductive ceramic provided so as to be electrically connected to the substrate, and a porous N-type semiconductor film formed on the surface of the interconnector.

Here, as a material of the interconnector, the chemical formula _{La 1-x A x Cr 1} -y-z B y O 3 ( provided that, A: Ca, Sr, at least one element selected from Ba, B: Co , Ni, Mg, Al, at least one element selected, x range: 0.05 to 0.2, y range: 0.02 to 0.22, z range: 0 to 0.05) Lanthanum chromite (LC) represented by This is based on the fact that one end (inner side) of the interconnector (terminal electrode) of the fuel side electrode is exposed to a reducing atmosphere and the other end (outer side) is exposed to an oxidizing atmosphere. At present, LC is excellent as a conductive ceramic that is stable in both oxidizing and reducing atmospheres.

Incidentally, as the material of the interconnector, the formula _{(A 1-x, B x} ) 1-z (Ti 1-y, D y) O 3 ( provided that, A: at least one selected from alkaline earth element Element, B: at least one element selected from Sc, Y, and lanthanoid elements, D: transition metal of the fourth period, fifth period, and sixth period, and Al, Si, Zn, Ga, Ge, Sn , Sb, Pb, Bi, x range: 0 to 0.5, y range: 0 to 0.5, z range: -0.05 to 0.05) The titanium oxide represented is also suitable. As the titanium oxide, for example, “strontium titanate SrTiO ₃ ” in which strontium Sr is used as A may be employed. SrTiO _{3 is} also stable in both oxidizing and reducing atmospheres.

As a material of the N-type semiconductor film, lanthanum nickel ferrite cobaltite La (Ni, Fe, Cu) O ₃ is suitable.

  The feature of the SOFC according to the present invention is that “the length of a boundary line corresponding to an interface between the interconnector and the N-type semiconductor film in a cross section including the interconnector and the N-type semiconductor film” The “joining rate”, which is a ratio of “the total length of a plurality of portions where the interconnector and the N-type semiconductor film are in contact with each other on the boundary line”, is 18 to 65%.

  In addition, a feature of the SOFC according to the present invention is that the “junction width” that is an average of the lengths of the plurality of portions where the interconnector and the N-type semiconductor film are in contact with each other on the boundary line is 0.6. ˜4.8 μm.

  As will be described later, the present inventor found that when the “joining rate” is 18 to 65%, compared to the case where the “joining rate” is not 18 to 65%, “the interface between the interconnector and the N-type semiconductor film”. And found that the bonding strength is increased. In addition, as will be described later, the present inventors have also found that the bonding strength is particularly increased when the “bonding width” is 0.6 to 4.8 μm.

It is the schematic diagram which showed the structure of SOFC which concerns on embodiment of this invention. It is the figure obtained by enlarging the cross section containing the interconnector and N type semiconductor film which concerns on embodiment of this invention by 1000 time with an electron microscope, and is a figure for demonstrating "joining rate" and "joining width" It is.

(Constitution)
FIG. 1 shows the configuration of a SOFC (cell) 100 according to an embodiment of the present invention. The SOFC 100 includes a fuel side electrode 110, an electrolyte membrane 120 stacked on the upper surface of the fuel side electrode 110, and an air side electrode 130 stacked on the upper surface of the electrolyte membrane 120. A laminate composed of these three layers constitutes a power generation unit of the SOFC 100. Note that a flow path for flowing fuel gas may be provided inside the fuel-side electrode 110.

  In the SOFC 100, the interconnector 140 is provided (bonded) to the lower surface of the fuel-side electrode 100 so as to be electrically connected. A conductive film (N-type semiconductor film) 150 made of an N-type semiconductor is formed on the lower surface of the interconnector 140.

  The shape of the SOFC 100 viewed from above is, for example, a square having a side of 1 to 30 cm, a long side of 5 to 30 cm and a short side of 3 to 15 cm, or a diameter of 1 to 30 cm. The total thickness of the SOFC 100 is 0.1 to 3 mm. The interconnector 140 may be provided on the entire lower surface of the fuel side electrode 110 or may be provided on only a part thereof. Further, the N-type semiconductor film 150 may be provided on the entire lower surface of the interconnector 140 or may be provided only on a part thereof. In addition, an interconnector may be provided on the upper surface of the air-side electrode 130.

  The fuel side electrode 110 (anode electrode) is a porous thin plate-like fired body composed of nickel oxide NiO and / or nickel Ni and yttria stabilized zirconia YSZ. The thickness of the fuel side electrode 110 is 0.1 to 3 mm. The fuel-side electrode 110 has the largest thickness among the constituent members of the SOFC 100, and the fuel-side electrode 110 functions as a support body (support substrate, member having the highest rigidity) of the SOFC 100.

The fuel side electrode 110 (anode electrode) may be composed of nickel oxide NiO and / or nickel Ni and yttria Y ₂ O ₃ . The fuel side electrode 110 may be composed of two layers, a fuel electrode current collecting layer (interconnector side) and a fuel electrode active layer (electrolyte membrane side). In this case, the anode active portion can be composed of, for example, nickel oxide NiO and yttria stabilized zirconia YSZ (8YSZ). Alternatively, it may be composed of nickel oxide NiO and gadolinium-doped ceria GDC. The fuel electrode current collector may be composed of, for example, nickel oxide NiO and yttria stabilized zirconia YSZ (8YSZ). Alternatively, it may be composed of nickel oxide NiO and yttria Y ₂ O ₃ , or may be composed of nickel oxide NiO and calcia stabilized zirconia CSZ. The thickness of the anode active portion is 5 to 30 μm, and the thickness of the anode current collecting portion is 50 to 500 μm.

  As described above, the fuel electrode current collector includes a substance having electronic conductivity. The fuel electrode active part includes a substance having electron conductivity and a substance having oxygen ion conductivity. “Volume ratio of the substance having oxygen ion conductivity with respect to the total volume excluding the pore part” in the anode active part is “the volume ratio of the substance having oxygen ion conductivity with respect to the whole volume excluding the pore part” It is larger than the “volume ratio”.

  The electrolyte membrane 120 is a dense thin plate-like fired body made of YSZ. The thickness of the electrolyte membrane 120 is 3 to 30 μm.

The air-side electrode 130 (cathode electrode) is a porous thin plate-like fired body made of lanthanum strontium cobalt ferrite LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ). The thickness of the air side electrode 130 is 5-50 micrometers. The air-side electrode 130 includes a first layer (electrolyte membrane side) made of LSCF and lanthanum strontium manganite LSM (La _0.8 Sr _0.2 MnO ₃ ) or lanthanum strontium cobaltite LSC (La _0.8 Sr _0.2 It may be configured by two layers including a second layer (a layer stacked on the upper surface of the first layer) made of CoO ₃ .

  It should be noted that the phenomenon in which the electrical resistance between the electrolyte membrane 120 and the air-side electrode 130 is increased due to the reaction between YSZ in the electrolyte membrane 120 and strontium in the air-side electrode 130 in the SOFC 100 during production or operation of the SOFC. In order to suppress the generation, a reaction preventing layer may be interposed between the electrolyte membrane 120 and the air side electrode 130. The reaction preventing layer is preferably a dense thin plate-like fired body made of ceria. Specific examples of ceria include GDC (gadolinium doped ceria) and SDC (samarium doped ceria).

  The interconnector 140 is a dense thin plate-like conductive connecting member made of a conductive ceramic. The thickness of the interconnector 140 is 1 to 100 μm. The porosity of the interconnector 140 is 5% or less. As the conductive ceramic, for example, lanthanum chromite (LC) whose chemical formula is represented by the following formula (1) is employed. In the following formula (1), A is at least one element selected from Ca, Sr, and Ba. B is at least one element selected from Co, Ni, Mg, and Al. The range of x is 0.05 to 0.2, the range of y is 0.02 to 0.22, and the range of z is 0 to 0.05. δ is a minute value including zero.

La _1-x A _x Cr _1-yz B _y O _3-δ (1)

The N-type semiconductor film 150 is a porous thin plate-like conductive film made of an N-type semiconductor. The thickness of the N-type semiconductor film 150 is 1 to 100 μm. The porosity of the N-type semiconductor film is 20 to 50%. As the N-type semiconductor, for example, lanthanum nickel ferrite cobaltite La (Ni, Fe, Cu) O ₃ or the like is employed. As long as the N-type semiconductor material is contained in an amount of 50% by volume or more in the N-type semiconductor film 150, an insulating material (for example, glass) for improving the sinterability is contained in the N-type semiconductor film 150. Or a noble metal material (for example, platinum) for improving conductivity may be added.

By supplying a fuel gas (hydrogen gas or the like) to the fuel side electrode 110 and a gas containing oxygen (air or the like) to the air side electrode 130 to the SOFC 100, the following equations (2) and (3) The chemical reaction shown in FIG. As a result, a potential difference is generated between the fuel side electrode 110 and the air side electrode 130. This potential difference is based on the oxygen potential difference between the two surfaces of the electrolyte membrane 120.
(1/2) · O ₂ + 2e ⁻ → O ²⁻ (where: air side electrode 130) (2)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (where: fuel side electrode 110) (3)

  Due to this potential difference, in SOFC 100, current flows in the direction of N-type semiconductor film 150 → interconnector (LC) 140 → fuel side electrode 110 → electrolyte film 120 → air side electrode 130 (electrons are air side electrode). 130 → electrolyte film 120 → fuel side electrode 110 → interconnector (LC) 140 → flows in the direction of the N-type semiconductor film 150). Then, electric power based on the potential difference is taken out of the SOFC 100 via the interconnector (LC) 140 (and an interconnector (not shown) provided on the air-side electrode 130).

  In this example, the porosity of the membrane was measured as follows. First, a so-called “resin filling” process was performed on the membrane so that the resin entered the pores of the membrane. The surface of the “resin-filled” film was mechanically polished. By performing image processing on the image obtained by observing the microstructure of the mechanically polished surface with a scanning electron microscope, the pore portion (the portion where the resin enters) and the non-pore portion ( The area of the portion where the resin did not enter was calculated. That ratio was taken as the porosity of the membrane.

(Production method)
Next, an example of a method for manufacturing the SOFC 100 shown in FIG. 1 will be described.

  First, the precursor (before firing) of the fuel side electrode 110 was formed as follows. That is, NiO powder and YSZ powder were mixed, and polyvinyl alcohol (PVA) was added as a binder to this mixture to prepare a slurry. This slurry was dried and granulated with a spray dryer to obtain a powder for the fuel side electrode. This powder was molded by a die press molding method to form a precursor of the fuel side electrode 110.

  Next, the precursor of the electrolyte membrane 120 (before firing) was formed on the upper surface of the precursor of the fuel side electrode 110 as follows. That is, water and a binder were added to the YSZ powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. This slurry was applied to the upper surface of the precursor of the fuel side electrode 110 and dried to form a precursor (film) of the electrolyte membrane 120. Note that when the precursor (film) of the electrolyte membrane 120 is formed on the upper surface of the precursor of the fuel-side electrode 110, a tape lamination method, a printing method, or the like may be used.

  Next, a precursor of the interconnector 140 (before firing) is obtained by using a lanthanum chromite powder and using a printing method, a tape lamination method, a slurry dipping method, a plasma spraying method, an aerosol deposition method, or the like, 110 was formed on the lower surface of the precursor.

  From the above, a laminated body (before firing) composed of three layers of the fuel-side electrode 110 precursor, the electrolyte membrane 120 precursor, and the interconnector 140 precursor was formed. This laminate (before firing) is co-sintered at 1300 to 1600 ° C. for 2 hours to form a laminate comprising three layers of a porous fuel-side electrode 110, a dense electrolyte membrane 120, and a dense interconnector 140 ( After firing) was obtained.

  Next, the air side electrode 130 was formed on the upper surface of the electrolyte membrane 120 of the laminate as follows. That is, water and a binder were added to the LSCF powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. This slurry is applied and dried on the upper surface of the electrolyte membrane 120 and baked in air at 1000 ° C. for 1 hour in an electric furnace (in an oxygen-containing atmosphere), so that the porous air-side electrode 130 is formed on the upper surface of the electrolyte membrane 120. Formed.

Next, an N-type semiconductor film 150 was formed on the lower surface of the interconnector 140 as follows. That is, water and a binder were added to La (Ni, Fe, Cu) O ₃ powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. Using the slurry, a film was formed on the lower surface of the interconnector 140 by a spray method or the like. By baking this film at 1000 to 1400 ° C. for 2 hours, a porous N-type semiconductor film 150 was formed on the lower surface of the interconnector 140.

  As a method for forming the N-type semiconductor film, a printing method, a tape laminating method, and a slurry dip method are also applicable. Note that when the firing of the N-type semiconductor film is performed at the same temperature as the firing of the air-side electrode, the N-type semiconductor film and the air-side electrode may be fired simultaneously. Further, when the firing of the N-type semiconductor film is performed at a higher temperature than the firing of the air-side electrode, the firing of the N-type semiconductor film may be performed before the firing of the air-side electrode, or the firing of the interconnector It may be executed at the same time.

  In addition, when an N-type semiconductor film is formed on the surface after the interconnector made of a dense conductive ceramic is formed (completed) in this way, the N-type semiconductor film becomes porous. This is considered based on the following reasons. That is, when the slurry (green molded body), which is a precursor of the N-type semiconductor film, is fired, the green molded body (before firing) tends to shrink by so-called firing shrinkage, while the already fired dense layer (interlayer) Connector) does not shrink. That is, while the volume of the entire green molded body tends to be reduced, the so-called anchor effect prevents the reduction of the dimension in the plane direction (direction along the interface) in the portion near the interface with the dense layer in the green molded body. . As a result, a large number of pores are formed inside the green molded body. That is, the N-type semiconductor film that is a fired body is porous. As described above, the interface between the interconnector 140 and the N-type semiconductor film 150 is a boundary between the dense layer and the porous layer.

  Thus, the lamination of the members constituting the SOFC 100 is completed. Here, the fuel side electrode 110 needs to have conductivity. Therefore, heat treatment (reduction treatment) for supplying a reducing gas at a high temperature of 800 ° C. is performed on the fired fuel-side electrode 110 (fired body). By this reduction treatment, NiO is reduced to Ni, and the fuel side electrode 110 acquires electrical conductivity. In the above, an example of the manufacturing method of SOFC100 shown in FIG. 1 was demonstrated.

  Hereinafter, a method for determining whether a material is a P-type semiconductor or an N-type semiconductor will be additionally described. This determination can be made based on the Seebeck coefficient. In general, it can be determined that the one with a positive Seebeck coefficient is a P-type semiconductor and the one with a negative Seebeck coefficient is an N-type semiconductor.

  Specifically, for example, the determination is made as follows. First, the material powder is molded using a uniaxial press, and the molded body is fired at 1400 ° C. for 2 hours to obtain a sintered body. A test piece of φ3.0 mm and L = 10 mm is prepared from the obtained sintered body, and the Seebeck coefficient is measured using a ZVAC-3 series evaluation device manufactured by ULVAC Riko. This measurement is performed at, for example, 750 ° C. in an inert gas atmosphere. As a result of this measurement, it can be determined that a Seebeck coefficient becomes positive as a P-type semiconductor, and a negative Seebeck coefficient as an N-type semiconductor. In the above-described N-type semiconductor film 150, the Seebeck coefficient is negative.

(Interface between interconnector and N-type semiconductor film)
Hereinafter, attention is focused on the interface between the interconnector 140 and the N-type semiconductor film 150, that is, the boundary between the dense layer and the porous layer. FIG. 2 is a cross-section including a cross-connector 140 and an N-type semiconductor film 150 according to an embodiment of the present invention (a cross-section along the stacking direction (film thickness direction), and perpendicular to the planar direction of each element (each film). The cross section) is observed with an electron microscope magnified 1000 times.

  In this specification, a line corresponding to the interface between the interconnector 140 (dense layer) and the N-type semiconductor film 150 (porous layer) in this cross section (the line segment L in the example shown in FIG. 2) is referred to as “boundary line”. " This boundary line can be defined as follows, for example. That is, a plurality of pores that are present facing the dense layer among a large number of pores included in the porous layer on the cross section are extracted. For each of the plurality of extracted pores, the point on the dense layer side in the region corresponding to the inside of the pore (in the example shown in FIG. 2, the lowermost point in the region corresponding to the inside of the pore) is plotted ( (See the plurality of black dots in the example shown in FIG. 2). Using the plotted points and one of the well-known statistical techniques (eg, least squares method), a line (straight line or curve) passing through each of the plotted points is determined. . This line (in the example shown in FIG. 2, the line segment L) is a “boundary line”. In the example shown in FIG. 2, since the interconnector has a flat plate shape, the “boundary line” is a straight line. For example, when the interconnector is warped or curved, the “boundary line” Becomes a curve. Further, the “boundary line” may be composed of a combination of a straight line and a curved line.

  With respect to the “boundary line” defined in this way, “joining rate” and “joining width” are defined as follows. “Joint rate” refers to the interconnector 140 and the N-type semiconductor film 150 on the “boundary line” with respect to the length of the “boundary line” (the length of the line segment L in the figure in the example shown in FIG. 2). Is defined as a ratio of the total length of “a plurality of portions” (a plurality of portions that do not correspond to pores) in contact with each other. “Junction width” is defined as the average length of the “plurality of portions”.

  Hereinafter, “junction width” will be additionally described. In calculating the “junction width”, the interconnector and N which were magnified by a magnification of 10000 times by a field emission scanning electron microscope (FE-SEM) using an in-lens secondary electron detector were used. An SEM image of a cross section including a type semiconductor film (cross section along the thickness direction of the film) can be used. More specifically, an SEM image obtained using an FE-SEM (model: ULTRA55) manufactured by Zeiss (Germany) set at an acceleration voltage of 1 kV and a working distance of 2 mm can be used. This cross section is subjected to ion milling processing by IM4000 of Hitachi High-Technologies Corporation after being polished by a precision machine. The SEM image is subjected to image analysis using image analysis software HALCON manufactured by MVTec (Germany), for example.

  When calculating the “joining width”, that is, calculating the “average” of the lengths of the “plurality of parts”, the length of “less than 0.2 μm” recognized by the above image analysis software among the “plurality of parts”. "Sano part" is not used. According to the observation result at a higher magnification, the existence itself of “a portion having a length of 0.2 μm or less” recognized by the above-described image analysis software is uncertain, and these are regarded as “interconnector and N-type semiconductor”. It is based on the fact that it is not appropriate to take it into account as a factor governing the “bond strength at the interface with the film”.

  The present inventor found that when the “joining rate” is 18 to 65%, the joining strength is higher at the “interface between the interconnector and the N-type semiconductor film” than when the “joining rate” is not 18 to 65%. I found it to be bigger. Hereinafter, test A in which this has been confirmed will be described.

(Test A)
In test A, the interconnector and N-type semiconductor film joined body (hereinafter referred to as “joined body”), which is a part of the SOFC according to the present embodiment, is made of the interconnector material and the N-type semiconductor film. A plurality of samples having different combinations of materials and “joining rates” were produced. Specifically, as shown in Table 1, eight levels (combinations) were prepared. Twenty samples (N = 20) were made for each level. In the column of “Material of N-type semiconductor film” in Table 1, “LNFC” represents La (Ni, Fe, Cu) O ₃ (the same applies to Table 2 described later).

Each sample (joint) has an interconnector with a circular shape (diameter: about 2 cm) and a thickness of about 1 mm as viewed from above, and a circular shape (diameter: about 1 cm) and a thickness of about 100 μm as viewed from above. A stacked body in which the N-type semiconductor film was stacked was used. Each sample (joined body) was produced by forming an N-type semiconductor film on the surface of the interconnector that was already completed by firing. Adjustment of the “bonding rate” is performed by adjusting the particle size and specific surface area of powder (La (Ni, Fe, Cu) O ₃ powder, etc.) used for firing the N-type semiconductor film, and the organic components (binder, pore former). This was achieved by adjusting the amount, the firing temperature of the N-type semiconductor film, and the like.

Specifically, the average particle diameter of the powder was adjusted within a range of 0.5 to 5 μm. The specific surface area of the powder was adjusted within a range of 3 to 30 m ² / g. The amount (weight) of the organic component was adjusted within a range of 10 to 50% with respect to the total weight of the powder. Cellulose, carbon, PMMA, etc. were used as the pore former. The firing temperature was adjusted within the range of 850 to 1300 ° C. The firing time was adjusted within a range of 1 to 20 hours.

  And tensile strength was measured about each sample (joined body). This measurement was made as follows. That is, jigs for tensile tests were attached to the upper and lower surfaces (the upper surface of the N-type semiconductor film and the lower surface of the interconnector), respectively. A force (tensile force) for pulling up and down was applied to the upper and lower jigs, and this tensile force was gradually increased. The magnitude of the tensile force (hereinafter referred to as “tensile strength”) at the time when the joining portion of the sample (joined body) (site near the interface between the interconnector and the N-type semiconductor film) peeled was measured. The measurement results of the tensile strength are as shown in Table 1. As a measurement result, an average value of N = 20 was adopted for each level.

  As can be understood from Table 1, when the “joining rate” is less than 18%, the tensile strength is small.

  Further, when the “joining rate” is larger than 65%, the tensile strength is small. The reason for this is not clear, but is considered as follows. That is, an increase in the “joining rate” means that the sintering of the interconnector and the N-type semiconductor film at the joining interface has progressed. As the sintering proceeds, the respective elements diffuse to each other, and phases having different compositions are generated at the bonding interface. When such a heterogeneous phase is generated, it can be a starting point for debonding of the bonding interface.

  From the above, it is considered that when the “joining rate” is large, the tensile strength becomes small as in the case where the “joining rate” is small. The generation of a heterogeneous phase at the above-described bonding interface is described in detail, for example, on page 2338 of J. Electrochem. Soc., Vol. 143, No. 7, July 1996.

  On the other hand, when the “joining rate” is 18 to 65%, the tensile strength is larger than when the “joining rate” is not 18 to 65%. That is, when the “joining rate” is 18 to 65%, the joining strength is higher at the “interface between the interconnector and the N-type semiconductor film” than when the “joining rate” is not 18 to 65%. be able to.

  In addition, when the “joining rate” is 18 to 65% and the “joining width” is 0.6 to 4.8 μm, the present inventor determines that “the interface between the interconnector and the N-type semiconductor film”. In particular, it has also been found that the bonding strength is increased. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In Test B as well as Test A, the “connector” of the interconnector and the N-type semiconductor film, which is a part of the SOFC according to this embodiment, is made of the interconnector material, the N-type semiconductor film material, A plurality of samples having different combinations of “rate” and “joining width” were produced. Specifically, as shown in Table 2, eight levels (combinations) were prepared. Twenty samples (N = 20) were made for each level. The shape of each sample (joint) was the same as that of Test A. The “joining rate” of each sample (joined body) is in the range of 18 to 65%. The adjustment of “bonding width” is the same as the adjustment of “bonding rate”, the particle size and specific surface area of powder (La (Ni, Fe, Cu) O ₃ powder etc.) used for firing the N-type semiconductor film, organic This was achieved by adjusting the amount of components (binder, pore former), the firing temperature of the N-type semiconductor film, and the like. Each adjustment range of the average particle diameter of the powder, the specific surface area of the powder, the amount (weight) of the organic component, the firing temperature, and the firing time is the same as in the case of Test A described above.

  And about each sample (joined body), the tensile strength was measured by the method similar to the test A. FIG. The measurement results are as shown in Table 2. As can be understood from Table 2, when the “joining rate” is 18 to 65%, when the “joining width” is 0.6 to 4.8 μm, the “joining width” is not 0.6 to 4.8 μm. Compared to the case, the tensile strength is large. That is, when the “joining rate” is 18 to 65%, when the “joining width” is 0.6 to 4.8 μm, the joining strength is particularly high at the “interface between the interconnector and the N-type semiconductor film”. It can be said.

In this test A (Table 1) and test B (Table 2), only lanthanum chromite LC is adopted as the material of the interconnector, but “titanium oxide” described in the “Summary of Invention” section. "Is adopted, it is confirmed that the same result as that obtained when LC is adopted is obtained. In addition, only La (Ni, Fe, Cu) O ₃ is adopted as the material of the N-type semiconductor film, but the same result can be obtained when N-type semiconductor films made of other materials are adopted. Has been confirmed.

From the above contents and the results shown in Tables 1 and 2, more specifically, LC or titanium oxide is adopted as the material of the interconnector, and La (Ni, Fe, Cu as the material of the N-type semiconductor film). ) When O ₃ is employed, the tensile strength is large when the “joining ratio” is 18 to 65%, and the tensile strength is particularly large when the “joining width” is 0.6 to 4.8 μm. it can.

  In addition, this invention is not limited to the said embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the above embodiment, the fuel gas flow path is not formed in the fuel side electrode 110, but the fuel gas flow path may be formed in the fuel side electrode. In addition, although the laminated body which comprises SOFC100 exists independently (refer FIG. 1), this laminated body may exist as a part of the whole certain apparatus.

  Further, the “joining rate is 18 to 65%” (and the joining width is 0.6 to 4.8 μm) may be established for any one cross section including the interconnector and the N-type semiconductor film. Alternatively, the “junction rate is 18 to 65%” (and the junction width is 0.6 to 4.8 μm) is an arbitrary plurality of cross sections including the interconnector and the N-type semiconductor film (for example, 2 parallel to a certain direction). And two cross sections parallel to a direction orthogonal to the direction).

  DESCRIPTION OF SYMBOLS 100 ... SOFC, 110 ... Fuel side electrode, 120 ... Electrolyte membrane, 130 ... Air side electrode, 140 ... Interconnector, 150 ... N-type semiconductor membrane

Claims (4)

A fuel-side electrode that reacts with the fuel gas in contact with the fuel gas; an electrolyte membrane made of a solid electrolyte provided on the fuel-side electrode; and an air-side electrode that reacts with the gas containing oxygen, the electrolyte membrane An air-side electrode provided on the electrolyte membrane so as to sandwich the fuel-side electrode and the air-side electrode, and a power generation unit of a solid oxide fuel cell,
An interconnector made of a dense conductive ceramic provided to be electrically connected to the fuel side electrode;
A porous N-type semiconductor film formed on the surface of the interconnector;
In a solid oxide fuel cell comprising:
The interconnector and the N type on the boundary line with respect to the length of the boundary line corresponding to the interface between the interconnector and the N type semiconductor film in a cross section including the interconnector and the N type semiconductor film The joining ratio, which is the total ratio of the lengths of the plurality of portions in contact with the semiconductor film, is 18 to 65%, and the interconnector and the N-type semiconductor film are in contact with each other on the boundary line. A solid oxide fuel cell, wherein a junction width, which is an average length of the plurality of portions, is 0.6 to 4.8 μm. The solid oxide fuel cell according to claim 1, wherein
The interconnector is
Formula _{La 1-x A x Cr 1} -y-z B y O 3 ( provided that, A: Ca, at least one element Sr, is selected from Ba, B: is selected Co, Ni, Mg, from Al Solid oxidation comprising at least one element, lanthanum chromite represented by x range: 0.05 to 0.2, y range: 0.02 to 0.22, z range: 0 to 0.05) Physical fuel cell. The solid oxide fuel cell according to claim 1, wherein
The interconnector is
Formula _{(A 1-x, B x} ) 1-z (Ti 1-y, D y) O 3 ( provided that, A: at least one element selected from alkaline-earth element, B: Sc, Y, and At least one element selected from lanthanoid elements, D: selected from transition metals in the fourth, fifth, and sixth periods, and Al, Si, Zn, Ga, Ge, Sn, Sb, Pb, and Bi At least one element, x range: 0 to 0.5, y range: 0 to 0.5, z range: −0.05 to 0.05) Oxide fuel cell. The solid oxide fuel cell according to any one of claims 1 to 3,
The N-type semiconductor film is
A solid oxide fuel cell comprising lanthanum nickel ferrite cobaltite La (Ni, Fe, Cu) O ₃ .