JP2012038586A - Structure of fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a fuel cell of "lateral stripe type" in which cracks hardly occur in a dense membrane or around the dense membrane.SOLUTION: A solid electrolyte membrane 40 (a dense membrane) between adjacent power generating elements A and a solid electrolyte membrane 40 in the power generating element A are continuously formed by dipping. The "dense membrane" made of a solid electrolyte is filled into the region between adjacent fuel electrodes 20. A part of the region between the fuel electrode 20 of one of the adjacent power generating elements A and the air electrode 50 of the other is connected via the "dense membrane" made of the solid electrolyte. The thickness t of the solid electrolyte membrane 40 in the power generating element is in the range of 10 to 100 μm. If the distance L between facing ends of the adjacent fuel electrodes 20 is 0.1 mm or larger, cracks hardly occur in the "dense membrane" or around the "dense membrane".

Description

  The present invention relates to a fuel cell structure.

  Conventionally, "a porous support substrate having a gas flow path formed therein" and "provided at a plurality of locations separated from each other on the outer surface of the support substrate, at least an inner electrode, a solid electrolyte membrane, and an outer A plurality of power generation element portions formed by stacking electrodes ”and“ one or more sets of adjacent power generation element portions, each of which is formed between one inner electrode and the other outer electrode ” There is known a structure of a solid oxide fuel cell provided with “one or a plurality of electrical connection portions that electrically connect each other” (see, for example, Patent Document 1). Such a configuration is also called a “horizontal stripe type”.

  In the “horizontal stripe type” fuel cell structure described in Patent Document 1, each inner electrode is provided so as to protrude outward from the outer surface of the support substrate. In addition, in this structure, a dense film made of a solid electrolyte that prevents mixing (gas leakage) of the gas supplied to the inner electrode and the gas supplied to the outer electrode is formed between adjacent power generation element portions. ing. The dense film continuously covers both opposite end portions of the adjacent inner electrode protruding from the outer surface of the support substrate, and the outer surface of the support substrate between the adjacent inner electrodes, and within the power generation element portion. The solid electrolyte membrane is formed continuously. In this document, the dense membrane is made of the same material as the solid electrolyte membrane in the power generation element portion, and the solid electrolyte membrane and the dense membrane are filled and filled simultaneously using a dipping method using a slurry made of the same material. Is formed.

JP 2010-16000 A

  By the way, in the “horizontal stripe type” fuel cell structure described in Patent Document 1 having the above-described configuration, the thickness of the solid electrolyte membrane in the power generation element portion is generally set to 10 to 100 μm. If the film thickness is less than 10 μm, it is difficult to form a film using a dipping method or the like, and if the film thickness is greater than 100 μm, the electric resistance of the film increases (ion conductivity decreases).

  In the fuel cell structure having the above-described configuration, the inventor determines that the dense membrane or the periphery of the dense membrane is cracked during the operation of the fuel cell depending on the “distance between opposite ends of the adjacent inner electrodes”. We have learned that gas leaks occur due to the occurrence of gas. The generation mechanism of this crack will be described later. As a result of various studies, the present inventor has found a condition necessary for suppressing the occurrence of such cracks with respect to “a distance between opposite ends of adjacent inner electrodes”. As described above, an object of the present invention is to provide a “horizontal stripe type” fuel cell structure that is less susceptible to cracking around the dense film or the dense film.

  The structure of the fuel cell according to the present invention includes a porous support substrate having a gas flow path formed therein, and “at least an inner electrode, provided at a plurality of locations apart from each other on the outer surface of the support substrate. A plurality of power generation element portions formed by laminating a solid electrolyte membrane and an outer electrode, wherein each of the inner electrodes is provided so as to protrude outward from the outer surface of the support substrate; One or a plurality of electrical connections that are formed between one or a plurality of adjacent power generation element portions and electrically connect one inner electrode and the other outer electrode of the adjacent power generation element portions. A part. That is, this structure is a “horizontal stripe type” fuel cell structure.

  Here, the inner electrode and the outer electrode may be an air electrode and a fuel electrode, respectively, or may be a fuel electrode and an air electrode. When the inner electrode is a fuel electrode, the gas flow path is a flow path for fuel gas, and when the inner electrode is an air electrode, the gas flow path is a flow path for gas containing oxygen. The fuel electrode may be composed of a fuel electrode active part in contact with the solid electrolyte and a fuel electrode current collector that is the remaining part other than the fuel electrode active part.

  Further, the fuel cell structure according to the present invention is formed between one or a plurality of adjacent power generation element portions, and a gas supplied to the inner electrode and a gas supplied to the outer electrode, In the adjacent inner electrode that protrudes from the outer surface of the support substrate, and is formed of a solid electrolyte made of the same or different material as the solid electrolyte membrane in the power generation element portion. Both end portions facing each other and the outer surface of the support substrate between the adjacent inner electrodes are continuously (directly) covered and continuously formed with the solid electrolyte membrane in the power generation element portion. A dense membrane is provided.

  Here, when the dense membrane is made of the same material as the solid electrolyte membrane, the solid electrolyte membrane and the dense membrane can be formed using a dipping method using a slurry made of the same material.

  The fuel cell structure according to the present invention is characterized in that the thickness (t) of the solid electrolyte membrane is 10 to 100 μm, and the distance (L) between opposite ends of the adjacent inner electrodes is 0.1 mm. That is the above (see FIG. 13).

  When the value L is less than 0.1 mm, the inventor easily generates cracks around the dense film or the dense film, while the value L is 0.1 mm or more as in the above configuration. It has been found that the crack is difficult to occur (details will be described later). Therefore, according to the said structure, the structure of the fuel cell which can suppress generation | occurrence | production of the gas leak resulting from the dense film or the crack which generate | occur | produces around a dense film can be provided.

  In the fuel cell structure according to the present invention, the electrical connection portion includes an interconnector formed on an outer surface of one inner electrode of the adjacent power generation element portion, and the interconnector and the adjacent power generation element. A connecting member made of a porous material that electrically connects the other outer electrode of the portion, the connecting member formed to cover a portion between the adjacent inner electrodes in the dense film, Can be configured.

It is a perspective view which shows the structure of the fuel cell of this invention. (A) shows a type in which the direction of current on the upper surface of the structure and the direction of current on the lower surface of the structure are reversed, and (b) shows the direction of current on the upper surface of the structure and the current on the lower surface of the structure. Indicates the type with the same direction. It is a top view of the structure of the fuel cell shown in FIG. It is a longitudinal cross-sectional view which expands and shows the principal part of the structure of the fuel cell shown in FIG. FIG. 4 is a diagram corresponding to FIG. 3 showing a flow of current when the fuel cell shown in FIG. 1 is operated. FIG. 2 is a first view showing a manufacturing process of the fuel cell structure shown in FIG. 1. FIG. 5 is a second view showing a manufacturing process of the structure of the fuel cell shown in FIG. 1. FIG. 4 is a third view showing a manufacturing process of the structure of the fuel cell shown in FIG. 1. FIG. 6 is a fourth view showing a manufacturing process of the structure of the fuel cell shown in FIG. 1. FIG. 10 is a fifth diagram showing a manufacturing process of the structure of the fuel cell shown in FIG. 1. FIG. 6 is a sixth view illustrating a manufacturing process of the fuel cell structure shown in FIG. 1. FIG. 8 is a seventh view showing a manufacturing process of the structure of the fuel cell shown in FIG. 1. FIG. 10 is an eighth diagram showing a manufacturing process of the structure of the fuel cell shown in FIG. 1. It is a figure for demonstrating the short circuit current which flows through the inside of a solid electrolyte membrane between adjacent electric power generation element parts.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing a structure of a fuel cell according to the present invention, and FIG. 2 is a plan view thereof. 1 and 2 show a state before the power generating element connecting member 60 (see FIG. 3) is attached.

  In the structure of the fuel cell according to the present invention, a plurality of power generating element portions A are arranged along the longitudinal direction of the support substrate 10 on the hollow and flat support substrate 10, and these are connected to the interconnector 30 (and The power generation element connection member 60) is electrically connected in series. This structure is also called “horizontal stripe type”. The power generation element portion A is formed on each of the upper surface and the lower surface of the support substrate 10.

  FIG. 1A shows a power generation element portion A (not shown) at one end in the longitudinal direction of the upper surface of the structure of the fuel cell and a power generation element portion at one end in the longitudinal direction of the lower surface of the structure. A (not shown) is electrically connected in series by a metal band that circulates the structure along the longitudinal direction, and the direction of the current on the upper surface of the structure is opposite to the direction of the current on the lower surface of the structure. Indicates the type to be.

  FIG. 1B shows an interconnector 30 in which each power generating element portion A on the upper surface of the structure of the fuel cell and the corresponding power generating element portion A on the lower surface of the structure circulate around the structure along the width direction. The power generation element part A on the upper surface of the structure and the power generation element part A on the lower surface of the structure are electrically connected in parallel to each other so that the direction of current on the upper surface of the structure and the structure The type in which the direction of the current on the lower surface of the same is the same is shown. FIG. 3 is a cross-sectional view of the structure showing a portion where the power generation element portion A is formed, corresponding to line 3-3 in FIG.

  In this fuel cell structure, a plurality of power generating element portions A are arranged on the surface of the support substrate 10 at a predetermined interval in the longitudinal direction. Each power generating element section A includes a current collecting fuel electrode 21, an active fuel electrode 22 (the current collecting fuel electrode 21 and the active fuel electrode 22 are collectively referred to as “fuel electrode 20”), a solid electrolyte membrane 40, and an air electrode 50. It has a layer structure obtained by sequentially laminating.

  Adjacent power generation element portions A and A are electrically connected in series by the interconnector 30 and the power generation element connection member 60. That is, the interconnector 30 is formed on the fuel electrode 20 of one power generation element part A, and the interconnector 30 and the air electrode 50 of the other power generation element part A are electrically connected by the power generation element connection member 60. It is connected. The interconnector 30 and the power generation element connection member 60 correspond to the “electrical connection portion”.

  Inside the support substrate 10, a plurality of fuel gas passages 11 having a small inner diameter are formed penetrating in the longitudinal direction (see FIG. 1). In this way, by forming a plurality of fuel gas passages 11 inside the support substrate 10, the support substrate 10 has a flat plate shape as compared with the case where one large fuel gas passage is formed inside the support substrate 10. It can be. As a result, when a stack is produced by arranging a plurality of support substrates, the plurality of support substrates can be arranged more densely than in a cylindrical shape. As a result, a more compact stack can be created.

A fuel gas (hydrogen gas) is allowed to flow through the fuel gas flow path 11 and the air electrode 50 is exposed to an oxygen-containing gas such as air, so that an oxygen partial pressure difference between the air electrode 50 and the fuel electrode 20 is generated. Electric power is generated. In this state, by connecting a load to the outside, electrode reactions shown in the following formulas (1) and (2) occur. As a result, current flows as shown by arrow C in FIG.
Air electrode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte) (1)
Fuel electrode: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻ (2)

  Hereinafter, the material of each member constituting the structure of the fuel cell will be described in detail.

First, the support substrate 10 is made of Ni or Ni oxide (NiO) and ZrO _{2 in} which, for example, a rare earth element oxide is dissolved. Examples of the rare earth element constituting the rare earth element oxide include Y, La, Yb, Tm, Er, Ho, Dy, Gd, Sm, and Pr. Preferred is an oxide of Y. . Y ₂ O ₃ and Yb ₂ O ₃ , particularly Y ₂ O ₃ are preferred. Further, as the support substrate 10, for example, spinel, forsterite, calcium zirconate, or the like can be used instead of ZrO _{2 in} which a rare earth element oxide is dissolved.

Ni or NiO (NiO is usually reduced by hydrogen gas and present as Ni during power generation) is contained in the support substrate 10 in a range of 5 to 25% by volume, particularly 5 to 10% by volume, in terms of Ni. It is good to have. The thermal expansion coefficient of the support substrate 10 is usually about 10.5 to 11.5 × 10 ⁻⁶ (1 / K).

The support substrate 10 needs to be electrically insulating in order to prevent an electrical short circuit between the power generating element portions. When the content of Ni or the like is in the above range, it preferably has a resistivity of 10 Ω · cm or more. Further, the remaining amount other than Ni or the like is usually ZrO _{2 in} which a rare earth element oxide is dissolved. However, other oxides such as MgO and SiO ₂ or composite oxides such as calcium zirconate may be contained in a small amount of, for example, 5% by weight or less.

  Note that the support substrate 10 must be able to introduce the fuel gas in the fuel gas flow path 11 up to the surface of the fuel electrode 20, and therefore needs to be porous. In general, the open porosity should be 25% or more, especially in the range of 30-40%.

The fuel electrode 20 causes the electrode reaction of the above formula (2). In this embodiment, the fuel electrode 20 has two layers of an active fuel electrode 22 on the solid electrolyte side and a collecting fuel electrode 21 on the support substrate 10 side. Formed in the structure. The active fuel electrode 22 on the solid electrolyte side is formed of porous conductive ceramics. For example, it is composed of ZrO ₂ (stabilized zirconia) in which a rare earth element is dissolved, and Ni and / or Ni oxide NiO (hereinafter referred to as Ni or the like). As the stabilized zirconia in which the rare earth element is dissolved, those similar to those used in the solid electrolyte membrane 40 described later can be used. Further, for example, spinel, forsterite, calcium zirconate, or the like can be used in place of ZrO _{2 in} which the rare earth element oxide is dissolved.

  The stabilized zirconia content in the active fuel electrode 22 is preferably in the range of 35 to 65% by volume, and the content of Ni or the like is 65 to 35% by volume in terms of Ni in order to exhibit good current collecting performance. It is good to be in the range. Furthermore, the open porosity of the active fuel electrode 22 is preferably 20% or more, particularly 25 to 40%.

The thermal expansion coefficient of the active fuel electrode 22 is usually about 12.3 × 10 ⁻⁶ (1 / K). The thickness of the active fuel electrode 22 is desirably in the range of 3 μm or more and less than 10 μm. If the thickness is 10 μm or more, the thermal stress generated due to the difference in thermal expansion from the solid electrolyte membrane 40 cannot be absorbed, and the active fuel electrode may be cracked or peeled off. The active fuel electrode 22 is preferably conductive, and the content of Ni or the like is in the above range, and can have a conductivity of 400 S / cm or more.

On the other hand, the current collecting fuel electrode 21 on the support substrate 10 side of the fuel electrode 20 is a mixture of Ni or Ni oxide and rare earth element oxide. Examples of the rare earth element constituting the rare earth element oxide include Y, La, Yb, Tm, Er, Ho, Dy, Gd, Sm, and Pr. Preferred is an oxide of Y. . Y ₂ O ₃ and Yb ₂ O ₃ , particularly Y ₂ O ₃ are preferred.

Ni or Ni oxide (NiO is usually reduced by hydrogen gas and exists as Ni during power generation) is contained in the rare earth element oxide in a range of 35 vol% to 60 vol% in terms of Ni. It is good. By preparing in this range, the thermal expansion coefficient of the current collecting fuel electrode 21 is usually about 11.5 × 10 ⁻⁶ (1 / K). Therefore, the difference in thermal expansion between the support substrate 10 and the current collecting fuel electrode 21 can be set to 1.0 × 10 ⁻⁶ / ° C. or less.

  As with the active fuel electrode 22, the current collecting fuel electrode 21 is preferably conductive so as not to impair the flow of current, and the content of Ni or the like is within the above range and has a conductivity of 400 S / cm or more. Can do. In addition, the thickness of the current collecting fuel electrode 21 is desirably 100 μm or more. If the thickness is less than 100 μm, resistance when a current flows in the longitudinal direction increases, and a voltage drop that cannot be ignored is generated inside the fuel cell structure.

As described above, if the fuel electrode 20 is formed in two layers, that is, the active fuel electrode 22 on the solid electrolyte side and the current collecting fuel electrode 21 on the support substrate side, the current collecting fuel electrode 21 on the support substrate side is formed. By adjusting the Ni amount or NiO amount in terms of Ni within the range of 35 to 60% by volume, the thermal expansion coefficient of the support substrate 10 can be determined without impairing the bondability with the active fuel electrode 22. Can be approached. For example, the difference in thermal expansion between them can be made less than 1.0 × 10 ⁻⁶ / ° C.

  Accordingly, since the thermal stress generated due to the difference in thermal expansion between the fuel electrode 20 and the support substrate 10 can be reduced when the fuel cell structure is manufactured, heated, cooled, etc. Cracks and peeling can be suppressed. Even in the case where power generation is performed by flowing fuel gas (hydrogen gas), the consistency of the thermal expansion coefficient with the support substrate 10 is stably maintained.

The solid electrolyte membrane 40 has a function as an electrolyte that bridges electrons between the electrodes, and needs to have a gas barrier property in order to prevent leakage of fuel gas and oxygen-containing gas such as air. It is. Therefore, as the solid electrolyte membrane 40, it is preferable to use dense ceramics having such characteristics, for example, stabilized ZrO _{2 in} which ₃ to 15 mol% of a rare earth element is dissolved. Examples of rare earth elements in the stabilized ZrO ₂ include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. However, Y and Yb are preferable because they are inexpensive. A lanthanum gallate solid electrolyte having a thermal expansion coefficient substantially equal to that of 8YSZ (stabilized ZrO ₂ in which 8 mol% of Y is dissolved) can also be suitably used.

  The solid electrolyte membrane 40 has a thickness of 10 to 100 μm from the viewpoint of preventing gas permeation, and it is desirable that the relative density (according to Archimedes method) is 93% or more, particularly 95% or more. The solid electrolyte membrane 40 corresponds to the “dense membrane”.

The air electrode 50 formed on the solid electrolyte membrane 40 causes the above-described electrode reaction of the formula (1), and is formed of a conductive ceramic made of a so-called ABO ₃ type perovskite oxide. As such a perovskite oxide, at least one of a transition metal type perovskite oxide, particularly a LaMnO ₃ oxide, a LaFeO ₃ oxide, or a LaCoO ₃ oxide having La at the A site is suitable. A LaFeO ₃ oxide is particularly suitable because it has high electrical conductivity at a relatively low temperature of about 600 to 1000 ° C.

  In the perovskite oxide, Sr may exist together with La at the A site, and Fe, Co, and Mn may coexist at the B site. Further, the air electrode 50 must have gas permeability, and the open porosity thereof is preferably 20% or more, and particularly preferably in the range of 30 to 50%. Furthermore, the thickness is preferably 30 to 100 μm from the viewpoint of current collection.

  The interconnector 30 used for electrically connecting adjacent power generation element portions in series connects the fuel electrode 20 of one power generation element portion and the air electrode 50 of the other power generation element portion. , Formed from conductive ceramics. The interconnector 30 needs to have reduction resistance and oxidation resistance in order to come into contact with an oxygen-containing gas such as fuel gas (hydrogen gas) and air.

The interconnector 30 is a conductor having a thickness of about 10 μm to 100 μm. The interconnector 30 connects the active fuel electrode 22 of one power generation element part and the air electrode 50 of the other power generation element part via a power generation element connection member 60, and is formed of conductive ceramics. In order to come into contact with fuel gas (hydrogen gas) and oxygen-containing gas such as air, it is necessary to have reduction resistance and 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 between the fuel gas passing through the fuel gas passage 11 and oxygen-containing gas such as air passing outside the air electrode 50, the conductive ceramics must be dense, for example, 93% or more In particular, it is preferable to have a relative density (Archimedes method) of 95% or more. In addition, a sealing property can also be improved by interposing an appropriate bonding layer (for example, Y ₂ O ₃ ) between the end face of the interconnector 30 and the end face of the solid electrolyte membrane 40.

  The power generation element connection member 60 is for electrically connecting the interconnector 30 of one adjacent power generation element part A and the air electrode 50 of the other power generation element part A. It is formed of a material having oxidation resistance. However, since the gas barrier property is not required, it may not be as dense as the interconnector 30.

The fuel cell structure described above can be manufactured, for example, as follows. First, as a material for the support substrate 10, a ZrO ₂ powder in which a rare earth element oxide such as Y ₂ O ₃ having an average particle diameter of 0.1 to 10 μm is dissolved and a Ni powder (NiO powder may be used) are prepared. The These powders are mixed in a predetermined ratio. The mixed powder is mixed with a pore agent, a cellulose-based organic binder, and a solvent made of water, extruded, and formed into a hollow and flat support substrate molded body 10 having a fuel gas channel 11 inside. Is produced.

Next, a material for the current collecting fuel electrode is prepared. For example, NiO powder, Ni powder, and rare earth element oxide powder such as Y ₂ O ₃ are mixed, a pore agent is added thereto, and an acrylic binder and toluene are added to obtain a slurry. Using this slurry, a collector fuel electrode tape having a thickness of 100 to 150 μm is produced by a doctor blade method. Hereinafter, the fuel cell structure will be described with reference to FIGS.

  Next, in the cut current collecting fuel electrode tape 21, a portion corresponding to a region between adjacent fuel electrodes is punched (FIG. 5). Next, the active fuel electrode 22 is printed on the entire surface of the current collecting fuel electrode tape 21 (FIG. 6). Subsequently, the interconnector 30 is printed on the active fuel electrode 22 (FIG. 7).

  Next, in this state, the fuel electrode tape 21 is attached to the support substrate molded body 10 in a horizontal stripe pattern. At that time, the adjacent fuel electrode tapes 21, 21 are arranged with an interval of about 3 mm. And this laminated body is dried and calcined in the temperature range of 900-1100 degreeC. (FIG. 8).

Next, an organic material sheet (masking tape) 70 is affixed to the central portion of the interconnector 30 in the longitudinal direction (FIG. 9). Next, this laminate is immersed in a solid electrolyte solution that is a slurry obtained by adding an acrylic binder and toluene to 8YSZ (ZrO ₂ powder in which 8 mol% of Y is dissolved). Then, this laminated body is taken out from the solid electrolyte solution. By this dip, the layer of the solid electrolyte membrane 40 is applied to one surface of the laminate, and the space punched in FIG. 5 (that is, the region between adjacent fuel electrodes) is filled with the solid electrolyte membrane 40 as an insulator. The

  In this state, calcination is performed at 800 ° C. for 1 hour. During this calcining, the organic material sheet 70 and the layer of the solid electrolyte membrane 40 applied thereon are removed (FIG. 10). Next, the air electrode 50 is printed on the portion where the air electrode is formed in the solid electrolyte membrane 40 and baked at 1050 ° C. for 2 hours (FIG. 11). Finally, a power generation element connection member 60 for connecting the interconnector 30 of one power generation element section and the air electrode 50 of the power generation element section adjacent thereto is attached (FIG. 12), and the structure of the fuel cell The body is completed.

(Conditions for suppressing the occurrence of cracks)
As described above, the solid electrolyte membrane 40 is formed by dipping the support substrate molded body 10 in a state where each fuel electrode 20 protrudes from the outer surface of the support substrate molded body 10 (see FIG. 10). ). As a result, as shown in FIG. 13, between the adjacent power generation element portions A and A, the dense solid electrolyte membrane 40 is opposed to each other in the adjacent fuel electrodes 20 and 20 protruding from the outer surface of the support substrate 10. In addition, it is filled and formed so as to continuously and directly cover the outer surface of the support substrate 10 between the adjacent fuel electrodes 20 and 20 and to be continuous with the solid electrolyte membrane 40 in the power generation element portion. . Hereinafter, the solid electrolyte membrane 40 between the adjacent power generation element portions A and A is particularly referred to as a “dense membrane”. The “dense film” exhibits a function of preventing a leak (gas leak) between the fuel gas and an oxygen-containing gas such as air.

  The thickness t (see FIG. 13) of the solid electrolyte membrane 40 in the power generation element portion is set within a range of 10 to 100 μm. This is because if the film thickness is less than 10 μm, it is difficult to form a film using a dipping method or the like, and if the film thickness is greater than 100 μm, the electric resistance of the film increases (the ionic conductivity decreases). Note that t may be an average value of the thickness of the solid electrolyte membrane 40 in the power generation element portion.

  The present inventor found that the fuel cell in the range of 10 to 100 μm was not in operation depending on the “distance L between opposite ends of the adjacent fuel electrodes 20 and 20 (see FIG. 13)”. In other words, the inventors have found that cracks are generated around the dense film or around the dense film, resulting in gas leaks. And this inventor discovered the conditions required in order to suppress the generation | occurrence | production of the crack regarding the distance L. FIG. The condition is that L is 0.1 mm or more. Note that L may be an average value or a minimum value of the distance between the opposite ends of the adjacent fuel electrodes 20 and 20.

  Hereinafter, a test performed to confirm this will be described. In this test, as shown in Table 1, a plurality of samples having different combinations of t and L values for the fuel cell structure corresponding to the above-described embodiments shown in FIGS. Was made. t is in the range of 10-100 μm. The shape, size, material, etc. of each member other than the values of t and L were the same for all samples.

For each sample, the fuel cell was operated according to a predetermined pattern. Specifically, in a state where Ar is supplied to the fuel electrode 20 side and air is supplied to the air electrode 50 side, the fuel cell is heated to 800 ° C., and hydrogen is humidified at 30 ° C. to the fuel electrode 20 side at 800 ° C. Was supplied and the fuel electrode 20 was reduced. Thereafter, a power generation test was performed under the conditions of a current density of 0.20 A / cm ² and a fuel utilization rate of 80%. After completion of the power generation test, the fuel cell was cooled to room temperature with Ar supplied to the fuel electrode 20 side and air supplied to the air electrode 50 side. Thereafter, for each sample, the presence or absence of cracks in the vicinity of the dense film or the dense film was confirmed. This confirmation was made using visual observation and an optical microscope. The results are shown in Table 1. The values t and L were measured using an actual cross section obtained by cutting the fuel cell after operating according to the predetermined pattern along a cross section corresponding to FIG. Table 1 also shows the effective power generation area ratio (%) for each sample. The effective power generation area ratio refers to the ratio of the total area occupied by the power generation element portion A (that is, the total area that can contribute to power generation) to the total area of the structure when the structure of the fuel cell is viewed from above. .

  As can be understood from Table 1, when L is less than 0.1 mm, cracks have occurred. On the other hand, when L is 0.1 mm or more, no crack is generated. That is, it can be said that L is required to be 0.1 mm or more in order to suppress the occurrence of cracks. In the following, this point will be analyzed.

The occurrence of such cracks is presumed to be caused by a current that short-circuits between the adjacent power generation element portions A and A (hereinafter referred to as “short-circuit current”). Hereinafter, this point will be described with reference to FIG. As shown in FIG. 4 described above, in the operating fuel cell, a current flows as shown by an arrow C. More specifically, the “current flow” includes, as shown in FIG. 13, “electron e ⁻ flow indicated by arrow E” and “oxide ion (oxygen ion O ²⁻ ) flow indicated by arrow I”. Is comprised.

Here, the “flow of oxide ions indicated by arrow I” is based on the characteristics of the solid electrolyte membrane. That is, in the solid electrolyte membrane, when the following conditions X, Y, and Z are satisfied, a flow of oxide ions from one surface to the other surface is generated. The flow of oxide ions (ion conductivity) becomes more active as the distance between the one side surface and the other side surface (corresponding to the thickness of the solid electrolyte membrane) is smaller.
Condition X: the presence of a catalyst (air electrode) that promotes the reaction represented by the above-described formula (1) on one surface;
Condition Y: The presence of a catalyst (fuel electrode) that promotes the reaction shown in the above formula (2) on the other surface;
Condition Z: The oxygen partial pressure of the gas exposed to the one side surface is larger than the oxygen partial pressure of the gas exposed to the other side surface.

  On the other hand, as can be understood from FIG. 13, in the above-described embodiment, a part of the region between one fuel electrode 20 and the other air electrode 50 of the adjacent power generation element portions A and A is a solid electrolyte. They are connected via a “dense membrane” (see reference numeral 41). In other words, the above-described conditions X, Y, and Z are also established for the “dense film” interposed between one fuel electrode 20 and the other air electrode 50 of the adjacent power generation element portions A and A. . As a result, as shown in FIG. 13, “a flow of oxide ions indicated by an arrow I ′” may occur. This flow becomes a current that short-circuits between the adjacent power generation element portions A and A (the short-circuit current).

  This short circuit current passes through the shortest path between one fuel electrode 20 and the other air electrode 50 of the adjacent power generation element portions A and A. Therefore, the place where oxide ions corresponding to the short-circuit current flows in the fuel electrode 20 is in the vicinity of the portion in contact with the “dense film” at the end of the fuel electrode 20. Since this place is in the vicinity of the “dense film”, it can be said that the fuel gas easily stays there. In such a place where the fuel gas tends to stay, the power generation reaction shown in the above-described formula (2) occurs with the inflow of oxide ions. That is, fuel gas is consumed.

  Therefore, the fuel gas concentration at this location decreases, and accordingly, the oxygen partial pressure at this location increases. When the oxygen partial pressure increases, Ni in the fuel electrode 20 can be reoxidized to NiO. As a result, the fuel electrode 20 expands locally. In addition, the power generation reaction shown in the above formula (2) is an exothermic reaction. Therefore, heat concentrates on the above-mentioned place in the fuel electrode 20, and as a result, a thermal stress is locally generated in the fuel electrode 20.

  When L is small (that is, when L is less than 0.1 mm), the distance between one fuel electrode 20 and the other air electrode 50 of the adjacent power generation element portions A and A is also sufficiently small. As a result, the “flow of oxide ions indicated by arrow I ′” can be actively generated to a degree that cannot be ignored with respect to the “flow of oxide ions indicated by arrow I”. In other words, a short circuit current that cannot be ignored can flow. As a result, the above-mentioned “local expansion of the fuel electrode 20” and “local thermal stress of the fuel electrode 20” become prominent, and it is considered that cracks are likely to occur in the “dense film”.

  On the other hand, when L is sufficiently large (that is, when L is 0.1 mm or more), the distance between one fuel electrode 20 and the other air electrode 50 of adjacent power generation element portions A and A is also sufficiently large. Thus, in practice, the “flow of oxide ions indicated by arrow I ′” occurs only in a negligible amount relative to the “flow of oxide ions indicated by arrow I”. As a result, it is considered that the above-mentioned “local expansion of the fuel electrode 20” and “local thermal stress of the fuel electrode 20” hardly occur, and the “dense film” is hardly cracked.

  From the above, for fuel cells in the range of t to 10 to 100 μm, if L is 0.1 mm or more, cracks hardly occur around the dense film or the dense film. However, as can be understood from Table 1, as L increases, the effective power generation area ratio decreases. When the effective power generation area ratio decreases, the power generation output of the fuel cell decreases. Therefore, in order to ensure sufficient power generation output of the fuel cell, it is desirable that L is 5 mm or less.

  The embodiment of the present invention has been described above. The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above embodiment, the “dense membrane” and the solid electrolyte membrane 40 in the power generation element portion A are made of the same material, and the “dense membrane” and the solid electrolyte membrane 40 in the power generation element portion A are dipped. Although formed simultaneously, the “dense membrane” and the solid electrolyte membrane 40 in the power generation element portion A may be made of different materials, or the “dense membrane” and the solid electrolyte membrane 40 in the power generation element portion A May be formed individually. Further, the “dense membrane” and the solid electrolyte membrane 40 in the power generation element portion A may be formed using a technique different from dipping.

  In addition, in the above-described embodiment, the support substrate 10 has a flat plate shape, and the plurality of fuel gas flow paths 11 are provided inside the support substrate 10, but the support substrate 10 may have a cylindrical shape. Of course, the number of the fuel gas passages 11 may be one. In addition, various modifications can be made within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 10 ... Support substrate, 11 ... Fuel gas flow path, 20 ... Fuel electrode, 21 ... Current collecting fuel electrode, 22 ... Active fuel electrode, 30 ... Interconnector, 40 ... Solid electrolyte membrane, 50 ... Air electrode, 60 ... Power generation element Connecting member, A ... power generation element part

Claims (4)

A porous support substrate having a gas flow path formed therein;
A plurality of power generating element portions, each provided at a plurality of locations separated from each other on the outer surface of the support substrate, wherein at least an inner electrode, a solid electrolyte membrane, and an outer electrode are stacked, each inner electrode being the support A plurality of power generation element portions provided to protrude outward from the outer surface of the substrate;
One or a plurality of electrical connections that are formed between one or a plurality of adjacent power generation element portions and electrically connect one inner electrode and the other outer electrode of the adjacent power generation element portions. And
A dense film formed between one or a plurality of adjacent power generation element portions, which prevents mixing of gas supplied to the inner electrode and gas supplied to the outer electrode, It is composed of a solid electrolyte made of the same or different material as the solid electrolyte membrane in the element portion, and both end portions facing each other in the adjacent inner electrodes protruding from the outer surface of the support substrate, and the adjacent inner electrodes A dense membrane formed so as to continuously cover the outer surface of the support substrate in between and continuously with the solid electrolyte membrane in the power generation element portion;
In a fuel cell structure comprising:
The thickness (t) of the solid electrolyte membrane in the power generation element portion is 10 to 100 μm,
A structure of a fuel cell, wherein a distance (L) between opposite ends of the adjacent inner electrodes is 0.1 mm or more. The fuel cell structure according to claim 1,
The dense membrane is made of the same material as the solid electrolyte membrane,
A structure of a fuel cell, wherein the solid electrolyte membrane and the dense membrane are formed using a dipping method using a slurry made of the same material. In the structure of the fuel cell according to claim 1 or 2,
The electrical connection is
An interconnector formed on the outer surface of one inner electrode of the adjacent power generation element part;
A connecting member made of a porous material for electrically connecting the interconnector and the other outer electrode of the adjacent power generation element portion so as to cover a portion between the adjacent inner electrodes in the dense film A formed connection member;
A structure of a fuel cell comprising: In the structure of the fuel cell according to any one of claims 1 to 3,
The inner electrode and the outer electrode are a fuel electrode and an air electrode, respectively.
The gas flow path formed inside the support substrate is a flow path for fuel gas,
The fuel electrode is a fuel cell structure comprising a fuel electrode active part in contact with the solid electrolyte membrane and a fuel electrode current collector part which is the remaining part other than the fuel electrode active part.

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