JP2012009426A - Solid oxide type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide type fuel cell (SOFC) which is provided with an interconnector, matched with a standpoint of environmental maintenance and has high electrical conductivity.SOLUTION: A fuel side electrode 110 of SOFC 100 is provided with an interconnector 140 formed of N-type semiconductor (SrTiO), and a P-type semiconductor film 150 is formed on the surface of the interconnector. SOFC 100 is excellent from the viewpoint of environment maintenance because no hexavalent chromium is contained in the interconnector. The P-type semiconductor film functions as a oxygen barrier layer, and thus occurrence of a phenomenon that the electrical resistance of the interconnector (N-type semiconductor) increases can be suppressed even under a condition that the interconnector is exposed to air. A PN junction is implemented at the contact portion between the P-type semiconductor film and the interconnector (N-type semiconductor). Occurrence of a phenomenon that current flows in the reverse direction can be suppressed in SOFC 100 by the property of the PN junction.

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 a fuel gas (hydrogen gas, etc.) to the fuel side electrode and a gas containing oxygen (air, etc.) to the air side electrode, the oxygen conductivity of the solid electrolyte is supplied to the SOFC (power generation unit). Therefore, a potential difference is generated between the fuel side electrode and the air side electrode.

  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.

  Regarding the SOFC provided with the interconnector as described above, in Patent Document 1, as shown in FIG. 2, an interconnector made of conductive ceramics is provided on the fuel side electrode, and a P-type semiconductor film is formed on the surface of the interconnector. The provided SOFC is described. It is described that when a P-type semiconductor is provided on the surface of the interconnector as described above, the reason is not clear, but the current can flow efficiently (that is, the conductivity is improved).

Japanese Patent No. 4146638

By the way, Patent Document 1 discloses lanthanum chromite LaCrO ₃ -based conductive ceramics as conductive ceramics which are materials for interconnectors (see FIG. 2). This lanthanum chromite LaCrO ₃ exhibits the characteristics of a P-type semiconductor. Moreover, the material of this lanthanum chromite LaCrO ₃ usually contains hexavalent chromium. In general, it can be said that it is not preferable to use hexavalent chromium from the viewpoint of maintaining the environment.

  An object of the present invention is to provide an SOFC provided with an interconnector, which matches the viewpoint of environmental maintenance and has high conductivity.

  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 Alternatively, an interconnector made of an N-type semiconductor provided so as to be electrically connected to the air side electrode, and a conductive film formed on the surface of the interconnector. Whether the material is a P-type semiconductor or an N-type semiconductor can be determined 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.

Here, as the N-type semiconductor, for example, 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 B: Sc, Y, and at least one element selected from lanthanoid elements, D: fourth, fifth, and sixth transition metals, 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 ) Can be used. In this case, strontium titanate SrTiO ₃ is preferably used.

In general, a material exhibiting the characteristics of an N-type semiconductor (particularly, titanium oxide described above) does not contain hexavalent chromium. Therefore, the SOFC according to the present invention having the above configuration maintains the environment as compared with the SOFC described in Patent Document 1 (lanthanum chromite LaCrO ₃ containing hexavalent chromium is used as an interconnector material). It can be said that it is excellent in terms of

In addition, when the surface of titanium oxide such as strontium titanate SrTiO ₃ is exposed to a gas having a high oxygen partial pressure such as air, a phenomenon occurs in which the electrical resistance of titanium oxide increases (conductivity decreases). To do. Hereafter, this point is added.

For example, in the specification of Japanese Patent No. 3723189, the conductivity of Sr _0.9 La _0.1 TiO _{3 in} an oxidizing atmosphere (high oxygen partial pressure) and the conductivity in a reducing atmosphere (low oxygen partial pressure) were measured. Results are shown. (See FIGS. 35 and 36). According to this, the conductivity in the oxidizing atmosphere (high oxygen partial pressure) is about 1/10 of the conductivity in the reducing atmosphere (low oxygen partial pressure). This is considered based on the following reasons. That is, in a reducing atmosphere, tetravalent Ti is reduced to trivalent and electrons become excessive, so that SrTiO ₃ exhibits N-type conductivity. As a result, the conductivity in a reducing atmosphere (low oxygen partial pressure) increases. On the other hand, in an oxidizing atmosphere, tetravalent Ti cannot be reduced to trivalent. As a result, SrTiO ₃ cannot exhibit N-type conductivity. As a result, the conductivity in an oxidizing atmosphere (high oxygen partial pressure) is reduced.

  Therefore, in a situation where the SOFC interconnector is exposed to air or the like, the electrical resistance of the interconnector increases if any oxygen barrier film is not provided on the surface of the interconnector made of titanium oxide or the like. As a result, the conductivity of the SOFC as a whole is lowered.

  On the other hand, in the SOFC having the above configuration, a (dense) conductive film that can function as an oxygen barrier layer is formed on the surface of the interconnector. Therefore, even when the SOFC interconnector is exposed to air or the like, the occurrence of a phenomenon in which the electrical resistance of the interconnector increases can be suppressed. As a result, a decrease in conductivity as a whole SOFC can be suppressed. Thus, according to the above configuration, an SOFC that matches the viewpoint of environmental maintenance and has high conductivity can be provided.

  In the SOFC having the above configuration, it is preferable that the above-mentioned “interconnector made of an N-type semiconductor” is provided on the fuel side electrode, and the conductive film is made of a P-type semiconductor.

  In the SOFC, the fuel side electrode functions as a negative electrode (anode electrode), and the air side electrode functions as a positive electrode (cathode electrode). Therefore, when an “interconnector made of an N-type semiconductor” is provided on the fuel-side electrode and a “conductive film made of a P-type semiconductor” is formed on the surface of the interconnector, in SOFC, the current is Conductive film (P-type semiconductor) → interconnector (N-type semiconductor) → fuel-side electrode → electrolyte membrane → air-side electrode (electrons are air-side electrode → electrolyte membrane → fuel-side electrode → interconnector (N-type) Semiconductor) → flows in the direction of conductive film (P-type semiconductor).

  Here, a so-called “PN junction” is realized at the junction between the conductive film (P-type semiconductor) and the interconnector (N-type semiconductor). In the PN junction, the current flows in the direction of P-type semiconductor → N-type semiconductor, but does not flow in the direction of N-type semiconductor → P-type semiconductor. Therefore, in the SOFC having the above configuration, the current flows in the direction of the conductive film (P-type semiconductor) → interconnector (N-type semiconductor), but the interconnector (N-type semiconductor) → conductive film (P-type semiconductor). It is difficult to flow in the direction.

  As a result, a reverse current (current in the direction of air side electrode → electrolyte film → fuel side electrode → interconnector (N-type semiconductor) → conductive film (P-type semiconductor)) flows in the SOFC due to some factor outside the SOFC. Even if such a tendency occurs, the occurrence of a phenomenon in which a current flows in the reverse direction can be suppressed due to the properties of the PN junction described above. Therefore, according to the SOFC having the above-described configuration, it is possible to suppress the occurrence of damage to the SOFC caused by the reverse current flowing in the SOFC.

  Hereinafter, the reason why the reverse current flows will be described. In general, SOFC power generation systems are often used in conjunction with grid power. In this case, a protection device for protecting each other is provided between the SOFC power generation system and the grid power. For example, Japanese Unexamined Patent Application Publication No. 2008-104334 describes a fuel cell system linked to system power (see FIG. 1 and paragraph 0003). This document states that “locations where distributed generators are used due to grid interconnection abnormalities (occurrence of overvoltage or undervoltage, increase or decrease in frequency, isolated operation, generation of reverse power flow, etc.) Describes a grid connection protection device 22 ”for preventing the electrical quality of the distribution line from being deteriorated, the electrical product from being adversely affected, and the human body from being adversely affected. However, if this protection device does not operate for some reason, a current based on the grid power may flow into the SOFC power generation system. In such a case, the above-described reverse current may flow.

It is the schematic diagram which showed the structure of SOFC which concerns on embodiment of this invention. It is the schematic diagram which showed the structure of the conventional SOFC.

(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 flat laminate composed of these three layers constitutes a power generation unit of the SOFC 100.

  In the SOFC 100, the interconnector 140 is provided (bonded) to the lower surface of the fuel side electrode 110 so as to be electrically connected. A conductive film (P-type semiconductor film) 150 made of a P-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 P-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 composed of nickel oxide NiO and / or nickel Ni (material having electronic conductivity) and yttria-stabilized zirconia YSZ (material having oxidative ion (oxygen ion) conductivity). It is a porous thin plate-like fired body. 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 current collecting layer is configured to include a material having electron conductivity (Ni or the like). The fuel electrode active layer includes a substance having electron conductivity (Ni or the like) and a substance having oxidizing ion (oxygen ion) conductivity (YSZ or the like). In the anode active layer, the “volume ratio of the substance having oxidative ion conductivity relative to the total volume excluding the pore portion” has the “oxidative ion conductivity relative to the total volume excluding the pore portion” in the anode current collecting layer. It is larger than the “volume ratio of the substance”.

  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 an N-type semiconductor. The thickness of the interconnector 140 is 1 to 100 μm. As the N-type semiconductor, for example, a titanium oxide 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 alkaline earth elements. B is at least one element selected from Sc, Y, and lanthanoid elements. D is at least one element selected from transition metals of the fourth period, the fifth period, and the sixth period, and Al, Si, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The range of x is 0-0.5, the range of y is 0-0.5, and the range of z is -0.05-0.05. δ is a minute value including zero. As the titanium oxide, for example, “strontium titanate SrTiO ₃ ” in which strontium Sr is used as A may be employed.

(A _1-x , B _x ) _1-z (Ti _1-y , D _y ) O _3-δ (1)

  The P-type semiconductor film 150 is a thin plate-like conductive film made of a P-type semiconductor. The thickness of the P-type semiconductor film 150 is 1 to 100 μm. As will be described later, the porosity of the P-type semiconductor film 150 is preferably 25% or less. As the P-type semiconductor, for example, LSCF, LSC, LSM, or the like, which is the same material as the air-side electrode 130, is employed.

  As shown in FIG. 1, for example, a current collector film 160 may be formed on the lower surface of the P-type semiconductor film 150. For example, the air-side electrode 130 of another SOFC 100 is connected to the lower surface of the current collecting film 160. Thereby, two adjacent SOFCs 100 are electrically connected in series. As the material of the current collecting film 160, for example, LSCF, LSC, LSM, or the like, which is the same material as the air-side electrode 130, is employed. In consideration of the diffusibility of gas (air) to the air-side electrode, the porosity of the current collecting film 160 is usually larger than 25% and not larger than 50%.

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 conductivity of the electrolyte membrane 120.
(1/2) · O ₂ +2 ^e− → O ²⁻ (where: air side electrode 130) (2)
H ₂ + O ²⁻ → H ₂ O + 2 ^e− (in the fuel side electrode 110) (3)

  Due to this potential difference, in the SOFC 100, as indicated by arrows in FIG. 1, the current is P-type semiconductor film 150 → interconnector (N-type semiconductor) 140 → fuel side electrode 110 → electrolyte film 120 → air side electrode 130. (Electrons flow in the direction of air-side electrode 130 → electrolyte film 120 → fuel-side electrode 110 → interconnector (N-type semiconductor) 140 → P-type semiconductor film 150). Then, the electric power based on the potential difference is taken out of the SOFC 100 via the interconnector (N-type semiconductor) 140 (and an interconnector (not shown) provided on the air-side electrode 130).

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

  The fuel side electrode 110 was manufactured 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, and then fired in air at 1400 ° C. for 3 hours in an electric furnace (in an oxygen-containing atmosphere) to produce a fuel-side electrode 110.

  The electrolyte membrane 120 was formed on the upper surface 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 is applied and dried on the upper surface of the fuel side electrode 110, and is co-sintered in air at 1400 ° C. for 2 hours in an electric furnace (in an oxygen-containing atmosphere), and the electrolyte membrane 120 is formed on the upper surface of the fuel side electrode 110. Formed. In forming a film that will later become the electrolyte membrane 120 on the upper surface of the fuel-side electrode 110, a tape lamination method, a printing method, or the like may be used.

  The air side electrode 130 was formed on the upper surface of the electrolyte membrane 120 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 at 1000 ° C. for 1 hour in the air in an electric furnace (in an oxygen-containing atmosphere) to form the air-side electrode 130 on the upper surface of the electrolyte membrane 120. It was.

  The interconnector 140 was formed on the lower surface of the fuel side electrode 110 as follows. That is, a film for an interconnector was formed on the lower surface of the fuel side electrode 110 by plasma spraying using strontium titanate powder. The interconnector 140 was formed on the lower surface of the fuel side electrode 110 by annealing the interconnector film at 1000 ° C. for 2 hours. An example of a method for forming a film for an interconnector is an aerosol deposition method.

  In addition, after forming the laminate (before firing) of the precursor of the fuel side electrode 110 (before firing) and the precursor of the electrolyte membrane 120 (before firing), printing is performed on the fuel side electrode side of this laminate. It is also possible to form the interconnector 140 by further forming and laminating a film for an interconnector using a method, a tape laminating method, a slurry dip method, and the like, and co-firing the laminate composed of these three layers. .

  The P-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 the LSCF 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. The P-type semiconductor film 150 is formed on the lower surface of the interconnector 140 by baking the P-type semiconductor film at 1000 ° C. for 2 hours. As a method for forming a P-type semiconductor film, a printing method, a tape lamination method, and a slurry dip method are also applicable.

  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 interconnector 140 described above, the Seebeck coefficient is negative, and in the P-type semiconductor film 150 described above, the Seebeck coefficient is positive.

(Characteristics and functions / effects of SOFC100)
In the SOFC 100, a so-called “PN junction” is realized at the junction between the P-type semiconductor film 150 and the interconnector (N-type semiconductor) 140. In the PN junction, the current flows in the direction of P-type semiconductor → N-type semiconductor, but hardly flows in the direction of N-type semiconductor → P-type semiconductor. That is, in the SOFC 100, the current flows in the direction of the P-type semiconductor film 150 → interconnector (N-type semiconductor) 140, but hardly flows in the direction of the interconnector (N-type semiconductor) 140 → P-type semiconductor film 150.

  From the above, during the operation of the SOFC 100, due to the nature of the PN junction, the current flows in the direction of P-type semiconductor film 150 → interconnector (N-type semiconductor) 140 → fuel side electrode 110 → electrolyte film 120 → air side electrode 130. Can flow (see FIG. 1).

  On the other hand, the current in the reverse direction in SOFC 100 (current in the direction of air-side electrode 130 → electrolyte film 120 → fuel-side electrode 110 → interconnector (N-type semiconductor) 140 → P-type semiconductor film 150) due to some factor outside SOFC 100) (See the summary of the invention for the reason why the reverse current flows), due to the nature of the PN junction, the phenomenon of the reverse current flowing may occur. Can be suppressed. Therefore, in the SOFC 100, it is possible to suppress the occurrence of damage or the like inside the SOFC 100 due to the reverse current flowing in the SOFC 100.

Further, the N-type semiconductor (particularly the titanium oxide described above) constituting the interconnector 140 does not include hexavalent chromium. Therefore, the SOFC 100 is superior to the SOFC described in Patent Document 1 (the lanthanum chromite LaCrO ₃ containing hexavalent chromium is used as an interconnector material) in terms of maintaining the environment. .

In addition, when the surface of a titanium oxide such as strontium titanate SrTiO ₃ is exposed to a gas having a high oxygen partial pressure such as air, the electrical resistance of the titanium oxide increases (conductivity decreases). See the Summary of Invention section). Therefore, in the situation where the interconnector 140 of the SOFC 100 is exposed to air or the like, if no oxygen barrier film is provided on the surface of the interconnector 140 (particularly, the lower surface in FIG. 1), Due to the increase in resistance, the conductivity of the SOFC 100 as a whole is lowered.

  On the other hand, in the SOFC 100, a P-type semiconductor film 150 that can function as an oxygen barrier layer is formed on the surface of the lower surface of the interconnector 140. Therefore, even when the interconnector 140 of the SOFC 100 is exposed to air or the like, the occurrence of a phenomenon in which the electrical resistance of the interconnector 140 increases can be suppressed. As a result, a decrease in conductivity as the entire SOFC 100 can be suppressed.

  In the following, a test that investigates the relationship between the porosity of a P-type semiconductor film functioning as an oxygen barrier layer and the effect of suppressing the increase in electrical resistance of the interconnector by the P-type semiconductor film will be added. In this experiment, a plurality of test films each having a P-type semiconductor film formed on one surface of a dense strontium titanate film and having different porosities of the respective P-type semiconductor films were prepared. Humidification of one side of the test membrane (ie, the surface where the P-type semiconductor is exposed) is exposed to air and the other side of the test membrane (ie, the surface where the strontium titanate is exposed) is 30 ° C. The electrical resistance of each test membrane maintained at 800 ° C. in the state exposed to hydrogen was measured.

  The porosity of the P-type semiconductor film was measured as follows. First, a so-called “resin filling” process was performed on the P-type semiconductor film so that the resin entered the pores of the P-type semiconductor film. The surface of the P-type semiconductor film treated with “resin filling” 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. The ratio was taken as the porosity of the P-type semiconductor film.

  The results of this experiment are shown in Table 1. In Table 1, the ratio (non-dimensional) of the electrical resistance of each test film to the electrical resistance of the test film in which the porosity of the P-type semiconductor film is 2% is shown as “electric resistance”.

  As can be understood from Table 1, the smaller the porosity of the P-type semiconductor film, the smaller the electrical resistance of the test product. This is because the smaller the porosity of the P-type semiconductor film, the stronger the function of the P-type semiconductor film as an oxygen barrier layer, and the greater the effect of suppressing the increase in the electrical resistance of the interconnector by the P-type semiconductor film. means.

  According to Table 1, it can be said that the electrical resistance of the test product is sufficiently small when the porosity of the P-type semiconductor film is 25% or less compared to the case where the porosity of the P-type semiconductor film is larger than 25%. Furthermore, when the porosity of the P-type semiconductor film is 15% or less, it can be said that the electrical resistance of the test product is even smaller. From the above, from the viewpoint of the effect of suppressing the increase in electrical resistance of the interconnector by the P-type semiconductor film, the porosity of the P-type semiconductor film is preferably 25% or less, and more preferably 15% or less. .

  Conventionally, as a conductive film formed on the surface of an interconnector film, a porous film having a porosity of more than 25% in consideration of gas diffusibility, such as a current collecting film 160 shown in FIG. Have been used. On the other hand, in SOFC 100, priority is given to suppressing the increase in electrical resistance of the interconnector film, and a relatively dense film having a porosity of 25% or less can be used as the conductive film formed on the surface of the interconnector film. In this respect, the SOFC 100 is completely different from the conventional one.

  Hereinafter, the ratio (T2 / T1) of the film thickness T2 of the P-type semiconductor to the film thickness T1 of the interconnector, and the presence or absence of cracks at the interface between the interconnector film and the P-type semiconductor film during firing of the P-type semiconductor film I will add to the study that investigated the relationship with. In this experiment, a P-type semiconductor film was formed by firing on the surface of the interconnector film in the laminate (fired body) obtained by co-firing the fuel side electrode, the electrolyte film, and the interconnector film (strontium titanate film). A plurality of test products having different combinations of T1 and T2 were produced. Five samples were made for each combination of T1 and T2.

As shown in Table 2, in each sample, the thickness of the interconnector film (strontium titanate film) was 20 to 100 μm, and the porosity of the interconnector film was 5% or less. The film thickness of the P-type semiconductor film was 5 to 100 μm, and the porosity of the P-type semiconductor film was adjusted to 25% or 15%. LSCF was used as the P-type semiconductor. The porosity and thickness of the P-type semiconductor film are as follows: raw material synthesis method (solid phase method, liquid phase method (citric acid method, coprecipitation method)), average raw material particle size (0.2 to 1.0 μm), It adjusted by adjusting the specific surface area (1-25 m < ² > / g) of a raw material, and the baking temperature (900-1200 degreeC) of a P-type semiconductor film.

  About each sample, the presence or absence of the crack generation | occurrence | production in the interface of an interconnector film | membrane and a P-type semiconductor film was determined. The determination of the presence or absence of cracks was made visually or by viewing an image obtained with a scanning electron microscope. The results of this experiment are shown in Table 2.

  As understood from Table 2, when T2 / T1 is larger than 2.5, a crack is generated. On the other hand, when T2 / T1 is 0.05 to 2.5, no crack occurs. As described above, from the viewpoint of suppressing the occurrence of cracks at the interface between the interconnector film and the P-type semiconductor film, T2 / T1 is preferably 0.05 to 2.5.

  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 P-type semiconductor film 150 as the conductive film is formed on the surface of the interconnector (N-type semiconductor) 140, but the N-type as the conductive film is formed on the surface of the interconnector (N-type semiconductor) 140. A type semiconductor film may be formed. In this case, the “suppression effect of reverse current generation due to the nature of the PN junction” does not work. Further, a film made of a noble metal (Au, Ag, etc.) may be used as the conductive film.

  In the above embodiment, the interconnector (N-type semiconductor) 140 is provided on the fuel-side electrode 110, but the interconnector (N-type semiconductor) 140 may be provided on the air-side electrode 130.

  Further, 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.

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

Claims (6)

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 an N-type semiconductor provided to be electrically connected to the fuel side electrode or the air side electrode;
A conductive film formed on the surface of the interconnector;
A solid oxide fuel cell. The solid oxide fuel cell according to claim 1, wherein
The interconnector, as the N-type semiconductor, the formula _{(A 1-x, B x} ) 1-z (Ti 1-y, D y) O 3 ( provided that, A: at least selected from alkaline earth element One element, B: at least one element selected from Sc, Y, and lanthanoid elements, D: transition metals of the fourth, fifth, and sixth periods, and Al, Si, Zn, Ga, At least one element selected from Ge, Sn, Sb, Pb, Bi, x range: 0 to 0.5, y range: 0 to 0.5, z range: -0.05 to 0. A solid oxide fuel cell comprising the titanium oxide represented by (05). The solid oxide fuel cell according to claim 2, wherein
The interconnector is a solid oxide fuel cell made of strontium titanate SrTiO ₃ as the N-type semiconductor. The solid oxide fuel cell according to any one of claims 1 to 3,
The interconnector is provided on the fuel side electrode,
The conductive film is a solid oxide fuel cell made of a P-type semiconductor. The solid oxide fuel cell according to any one of claims 1 to 4, wherein
A solid oxide fuel cell, wherein the conductive film has a porosity of 25% or less. The solid oxide fuel cell according to claim 5, wherein
The solid oxide fuel cell, wherein the ratio of the thickness of the conductive film to the thickness of the film of the interconnector is 0.05 to 2.5.

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