JP2015185321A - Air electrode for solid oxide fuel batteries, and solid oxide fuel battery cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air electrode for solid oxide fuel batteries which is arranged by use of a novel material.SOLUTION: An air electrode for solid oxide fuel batteries comprises an apatite type oxide expressed by the following general formula (1): (LnA)(SiBM)O. (In the formula (1), 0≤X≤2.0; 0≤Y≤3.0; X+Y>0; 0<β≤3.0; Y+β≤4.0; Ln includes at least one of La, Pr and Nd; A includes at least one of Mg, Ca, Sr and Ba; B includes at least one of Mg, Fe, Al, B, Ga, Ge and P; and M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Ta and W.) It is particularly preferable that the apatite type oxide is an oxide expressed by La(SiAlRu)O.

Description

  The present invention relates to an air electrode for a solid oxide fuel cell and a solid oxide fuel cell using a novel material.

As an air electrode material of a solid oxide fuel cell, (1) (Ln + A) (Mn, Fe, Co) O ₃ -based perovskite oxide (Ln = La to Yb; A = Ca, Sr, Ba, Pb) (2) Ln ₂ MO ₄ system K ₂ NiF ₄ type oxide (Ln = La, Pr, Nb: M = Ni, Cu), (3) Pyrochlore type oxide (general formula: A ₂ B ₂ O ₇ ) (4) Brown mirror light type oxide (general formula: A ₂ B ₂ O ₅ ), (5) Spinel type oxide (general formula: AB ₂ O ₄ ) (see Non-Patent Document 1 etc.) .

Among these air electrode materials, various reports have been made on the material (1). For example, (La, Sr) MnO ₃ system, (La, Sr) CoO ₃ system, (La, Sr) (Co, Fe) O ₃ system are mentioned, and among them (La, Sr) (Co, Fe) O ₃ system is the most used material having high electrode activity and a relatively small thermal expansion gap with the electrolyte.

Ekaterina V. Tsipis, Vladislav V. Kharton, J. of Solid State Electrochemistry, 12 (2008) 1367-1391

However, it is difficult to say that (La, Sr) (Co, Fe) O ₃ -based materials also have ideal characteristics as an air electrode. For example, since they react with a ZrO 2 -based electrolyte, the air electrode material and the electrolyte It cannot be used unless a CeO2 reaction preventing layer is introduced between them. Attempts have therefore been made to pursue materials with more ideal properties.

  The present invention has been completed in view of the above circumstances, and is a solid oxide type using a new material expected to exhibit characteristics different from those of conventional materials when used in an air electrode of a solid oxide fuel cell. An object to be solved is to provide an air electrode for a fuel cell and a solid oxide fuel cell using the same.

(A) The air electrode for a solid oxide fuel cell of the present invention that solves the above problems contains an apatite-type oxide represented by the following general formula (1).
Equation _{(1) :( Ln 10-Z} -X A X) (Si 6-Y-β B Y M β) O 27-α

(In the above formula (1), 0 ≦ X ≦ 2.0, 0 ≦ Y ≦ 3.0, X + Y> 0, 0 <β ≦ 3.0, Y + β ≦ 4.0; Ln is La, Pr, And at least one of Nd; A includes at least one of Mg, Ca, Sr, and Ba; B includes at least one of Mg, Fe, Al, B, Ga, Ge, and P M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Ta, and W.)

This material can operate as an air electrode for a solid oxide fuel cell, and an air electrode for a solid oxide fuel cell made of a novel material can be provided. Conventionally, the expression of ionic conductivity has been reported for La ₁₀ (Si _5.8 Al _0.2 ) O _X , which is an apatite type oxide in which the Si site is not replaced by M, and application to an electrolyte is expected. It was. While this apatite type oxide has ionic conductivity, it showed almost no electronic conductivity. The present inventors have completed the present invention based on the discovery that by replacing the Si site with M, electron conductivity can be expressed in addition to ion conductivity.

(B) The following configuration can be adopted in the invention of (A). In the general formula (1), Ln is La, B is Al, M is Ru, X is 0, Y is 0.2, and β is 3.0.

  An air electrode for a solid oxide fuel cell employing this material can sufficiently exhibit the performance required for an air electrode, such as oxygen ion conductivity and electron conductivity. Further, the reactivity with the electrolyte is not so remarkable, and the gap of the thermal expansion coefficient with the electrolyte is sufficiently small.

(C) A solid oxide fuel cell according to the present invention that solves the above-described problems includes an air electrode for a solid oxide fuel cell according to the above (A) or (B), a fuel electrode, and the air electrode. And a solid electrolyte sandwiched between the fuel electrodes.

  According to this, since the air electrode for a solid oxide fuel cell composed of a novel material is provided, it can be expected to have different characteristics from the conventional one.

It is the schematic of the apparatus which measures an electromotive force about the solid oxide fuel cell produced in the Example, and it. It is a graph which shows the temperature dependence of the electromotive force of the solid oxide fuel cell measured in the Example. It is a figure which shows XRD of the apatite type oxide manufactured in the Example. It is a graph which shows the Arrhenius plot of the electrical conductivity of the apatite type oxide manufactured in the Example.

  Hereinafter, an air electrode for a solid oxide fuel cell and a solid oxide fuel cell according to the present invention will be described based on embodiments.

(Air electrode for solid oxide fuel cell)
The air electrode of this embodiment is used as an air electrode of a solid oxide fuel cell (SOFC). The form of the SOFC air electrode is not particularly limited, and is characterized by having an apatite type oxide represented by the composition formula shown in the following general formula (1). That is, it has an apatite type oxide structure composed of Ln, Si, and O, and has a structure in which the Ln site may be substituted with the element A and the Si site may be substituted with the element B and / or the element M, respectively. It is made of oxide.

Equation _{(1) :( Ln 10-Z} -X A X) (Si 6-Y-β B Y M β) O 27-α
Here, X indicates the degree of substitution of the Ln site with the element A, and 0 ≦ X ≦ 2.0.

  Z is a numerical value representing the degree of defects at the Ln site, and is not particularly limited as long as the crystal structure exhibits an apatite type. For example, Z = 0.67 is mentioned, and Z <0.67 is mentioned as a more preferable range.

  Y indicates the degree of substitution of the Si site with the element B, and 0 ≦ Y ≦ 3.0. Note that whether the Ln site is substituted with the element A or the Si site is substituted with the element B is indispensable for improving ion conductivity, and therefore X + Y> 0.

  β indicates the degree of substitution of the Si site with the element M, and 0 <β ≦ 3.0. As the lower limit of β, β = 1.0 can be adopted. Y + β ≦ 4.0, and a preferable range is Y + β ≦ 3.2.

  α is a value indicating the degree of oxygen defects and is not particularly limited as long as the crystal structure exhibits an apatite type. For example, α <1.0 is mentioned, and α <0.5 is mentioned as a more preferable range.

  Ln includes at least one of La, Pr, and Nd, preferably La and Pr, and more preferably La. A includes at least one of Mg, Ca, Sr, and Ba, and is preferably selected from Ba and Sr, and more preferably selected from Sr. B includes at least one of Mg, Fe, Al, B, Ga, Ge, and P, and is preferably selected from Mg, Fe, and Al, and further selected from Al and Fe. More preferably. M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Ta, and W, and is selected from V, Ni, Co, Ru, and W It is desirable that V, Ru, and W be selected.

・ Manufacturing method As a method of manufacturing an SOFC air electrode, first, a material composed of an apatite oxide is manufactured by mixing and reacting starting materials containing the target elements (Ln, A, B, and M). To do. After the apatite type oxide is manufactured, it can be formed into a final air electrode shape in a separate process, and at the same time when the apatite type oxide is formed, the air electrode shape is reached. May be.

  Mixing is carried out to as uniform a state as possible, so that the oxide produced by the reaction approaches a homogeneous composition. The mixing is preferably performed as a solution when the starting material can be dissolved in a liquid, and is preferably performed by a so-called pulverization operation when mixing in a solid state. When mixing by a pulverization operation, further homogenization of the mixture can be achieved by carrying out in a liquid medium. Examples of the liquid medium include lower alcohols such as ethanol, methanol, and propanol, water, and acetone.

  The reaction of the starting material is performed by heating in an oxidizing atmosphere such as in the presence of oxygen, a reducing atmosphere, or an inert atmosphere. The selection of the atmosphere is determined by the oxidation state of each element in the starting material, the type of the compounding element, and the like. In order to adjust the composition, it is desirable to heat the calcination state.

  You may repeat mixing operation in the middle of a heating once or more. The heating temperature is not particularly limited, but the final heating is preferably performed at 1500 ° C. or higher, and more preferably at 1600 ° C. or higher in order to finally obtain a dense state. The heating time is not particularly limited and is performed until an oxide having a target composition is obtained.

  Examples of the starting material include oxides, hydroxides, carbonates, and simple substances that are appropriately selected according to the apatite type oxide to be manufactured and include elements contained in the apatite type oxide to be manufactured. For example, the mixing ratio of the starting materials is calculated so that Ln, A, B, and M each have an element ratio in the composition formula indicating the target apatite type oxide. When conditions where Ln, A, B, and M are not lost during the reaction are adopted, the mixing ratio is determined so that the composition ratio of Ln, A, B, and M contained in the target oxide is obtained. To do.

(Solid oxide fuel cell)
The solid oxide fuel cell of this embodiment has an air electrode, a fuel electrode, and a solid electrolyte sandwiched between them. The form of the solid oxide fuel cell is not particularly limited, and for example, a known form can be adopted. The air electrode employs the air electrode for a solid oxide fuel cell according to the above-described embodiment.

The fuel electrode is not particularly limited except that it has electron and ion conductivity. For example, the fuel electrode is formed of a material obtained by combining metal oxide or metal and stabilized zirconia. An example of the metal oxide is nickel oxide, and an example of the metal is nickel. Examples of stabilized zirconia (including partially stabilized zirconia, the same shall apply hereinafter) include ZrO ₂ in which a rare earth oxide (for example, Y ₂ O ₃ ) is dissolved.

  The solid electrolyte is not particularly limited except that it has ionic conductivity. The above-mentioned stabilized zirconia can be exemplified.

  Hereinafter, an air electrode for a solid oxide fuel cell of the present invention and a solid oxide fuel cell using the same will be described in detail based on examples.

· Apatite type oxides and solid oxide production _{La 10 (Si 2.8 Al 0.2 Ru} 3.0) of the fuel cell _{O 27-alpha} apatite type oxide having a composition formula of using the same (oxidation Article A) was produced. In the general formula (1), Ln is La, B is Al, M is Ru, and X is 0, Y is 0.2, β is 3.0, and Z = 0.

As starting materials, La ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , and RuO ₂ were mixed so as to have a composition ratio of each element excluding oxygen of oxide A. Mixing was performed by grinding with an alumina mortar using ethanol as the liquid medium.

Then, it was left to dry at 100 ° C. for 10 minutes. The obtained mixture was calcined by heating at 1300 ° C. for 5 hours in an alumina crucible. The reaction product obtained again using an alumina mortar was pulverized as it was, and then molded by uniaxial pressing. Then, it baked and the sintered compact of the oxide A was obtained (baking temperature 1600 degreeC, baking time 5 hours). The obtained sintered body was pulverized using an alumina mortar, and a paste of oxide A was prepared by mixing the resin component and the powder.
This paste is applied to a sintered body of stabilized zirconia (diameter 24 mm, thickness 1 mm) to form an air electrode 22 that is a layer made of oxide A. On the other hand, Pt paste was applied as the fuel electrode 21 to the other surface. The laminated body was heat-treated (firing temperature 900 ° C., calcining time 30 minutes) to form a single cell 20 (solid oxide fuel cell) of this example.
Each of the air electrode and the fuel electrode has a thickness of about 10 μm.

Oxide B [La ₁₀ (Si _5.8 Al _0.2 ) O _x ] was produced by the same production method as for oxide A. The starting material was selected according to the composition of oxide B.

-Electricity generation test In the state which hold | maintained this single cell 20 with the holding | maintenance collector 12, the fuel (hydrogen gas containing 3% of water vapor | steam) and air were flowed, and the electric power generation condition was confirmed. The holding current collector 12 has a first holder tube 12a and a second holder tube 12b. The first holder tube 12a is formed in a cylindrical shape to hold the single cell 20 from the fuel electrode 21 side, and the second holder tube 12b was formed in a cylindrical shape and held the single cell 20 from the air electrode 22 side. A first seal tube 12e is interposed between the first holder tube 12a and the fuel electrode 21, and a second seal tube 12g is interposed between the second holder tube 12b and the air electrode 22. Airtight. The first and second seal tubes 12e and 12g were made of a cylindrical glass material. The electromotive force generated by the first electrode body 12 i and the second electrode body 12 j provided on the respective surfaces of the fuel electrode 21 and the air electrode 22 is led to the measuring device 30 through the conducting wires 31 and 32. Each of the first electrode body 12i and the second electrode body 12j is composed of a mesh member made of platinum.

  A first gas introduction pipe 12k having a small diameter is coaxially disposed in the first holder pipe 12a. Similarly, the second gas inlet pipe 121 having a small diameter is coaxially disposed in the second holder pipe 12b. The tip of the first gas introduction tube 12k is in contact with the first electrode body 12i, and the tip of the second gas introduction tube 12l is in contact with the second electrode body 12j. The first gas introduction pipe 12k supplies the fuel gas and supplies the fuel gas to the fuel electrode 21 through the first electrode body 12i. The fuel off-gas provided for the reaction returns through the gap between the first holder pipe 12a and the first gas introduction pipe 12k. The second gas introduction pipe 121 supplies air and supplies air to the air electrode 22 through the second electrode body 12j. The air off-gas provided for the reaction returns through the gap between the second holder pipe 12b and the second gas introduction pipe 12l.

  The power generation status was confirmed by measuring the electromotive force while lowering the temperature of the single cell 20 from 800 ° C. to 600 ° C. As a reference example, a single cell in which Pt was baked on both sides of stabilized zirconia was prepared, and the electromotive force was measured in the same manner. The results are shown in FIG. FIG. 2 shows three potentials: a single cell of the example (apatite cathode: Δ), a single cell of the reference example (Pt cathode: ◆), and a theoretical value (dashed line).

  As is clear from FIG. 2, the theoretical value and the reference example using Pt almost coincide with each other, and the unit cell of the example is almost the same as or slightly lower than the theoretical value. It was found to show an equivalent electromotive force.

・ Analysis of oxide A (X-ray diffraction)
XRD of oxide A was measured using an X-ray diffractometer. The results are shown in FIG. As is clear from the analysis of FIG. 3, the observed peak was derived from an apatite-type crystal structure although it was also confirmed that it was derived from impure surgery (derived from La ₂ O ₃ system: ▼, unknown origin: ◇). It became clear that the peak (La-Si apatite: ●) was the main structure.

・ Analysis of oxide A (Measurement of conductivity: Arrhenius plot)
The electrical conductivity in the air was measured for oxide A and oxide B. The conductivity was measured by the DC four-terminal method while changing the temperature from about 770K to about 1100K. The results are shown in FIG. As is clear from FIG. 4, it was suggested that the oxide A (◇) has a conductivity higher than that of the oxide B (◯) by three orders of magnitude and also has a lower activation energy.

-Reactivity analysis of oxide A and stabilized zirconia The single cell 20 of the above-mentioned Example was heat-treated at 1100 ° C for 1 hour. Thereafter, the interface between the air electrode 22 and the electrolyte 23 was analyzed to confirm the presence or absence of element diffusion.
As a result, no element diffusion was observed, and the reactivity with the electrolyte is considered to be low.

・ Summary From the above results, the oxide A can cause a reaction to turn O ₂ into 2O, and has ion conduction characteristics and electron conduction characteristics. Further, the temperature is from room temperature to 600 ° C., further to 800 ° C. Even if it was raised, power generation could be continued without separation from the electrolyte. Moreover, it is thought that the reactivity with an electrolyte is lower than the air electrode generally used.

  Therefore, it turned out that the oxide A employ | adopted as the single cell of an Example has the characteristic which can be utilized for an air electrode. This characteristic is considered to be caused by the partial replacement of the Si site with Ru. Here, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ta, and W, which are elements having an electronic structure similar to Ru, are similarly replaced with part of the Si site. As a result, it was speculated that the oxide could be employed in the air electrode of a solid oxide fuel cell.

DESCRIPTION OF SYMBOLS 12 ... Holding current collector 12a, 12b ... 1st and 2nd holder pipe | tube 12i, 12j ... 1st and 2nd electrode body 12k and 12l ... 1st and 2nd gas introduction pipe | tube 20 ... Single cell (solid oxide fuel) Battery cell) 21 ... Fuel electrode 22 ... Air electrode 23 ... Electrolyte 30 ... Measuring instrument

Claims (3)

An air electrode for a solid oxide fuel cell containing an apatite oxide represented by the following general formula (1).
Equation _{(1) :( Ln 10-Z} -X A X) (Si 6-Y-β B Y M β) O 27-α
(In the above formula (1), 0 ≦ X ≦ 2.0, 0 ≦ Y ≦ 3.0, X + Y> 0, 0 <β ≦ 3.0, Y + β ≦ 4.0; Ln is La, Pr, And at least one of Nd; A includes at least one of Mg, Ca, Sr, and Ba; B includes at least one of Mg, Fe, Al, B, Ga, Ge, and P M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Ta, and W.)   2. The solid oxide fuel cell according to claim 1, wherein, in the general formula (1), Ln is La, B is Al, M is Ru, X is 0, Y is 0.2, and β is 3.0. Air pole. An air electrode for a solid oxide fuel cell according to claim 1 or 2,
An anode,
A solid oxide fuel cell having a solid electrolyte sandwiched between the air electrode and the fuel electrode.

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