JP5127126B2 - Electrode for fuel cell and solid oxide fuel cell using the same - Google Patents

Description

  The present invention relates to an electrode for a solid oxide fuel cell, and more particularly, a solid electrolyte fuel containing a mixture of an electron conductor and an oxygen ion conductor and / or a mixed electron / oxygen ion conductor, and a proton conductor. The present invention relates to an electrode for a battery, a cell or stack for a solid oxide fuel cell including the electrode and a solid electrolyte, a fuel cell including the cell or stack, and an electrode material for forming the electrode.

  In practical fuel cells, it is necessary to use hydrocarbons as fuel, and it is common to generate hydrogen by steam reforming using a reformer and use it for power generation. This steam reforming is an endothermic reaction and requires a heat source for reforming. Therefore, in the case of using an external reformer, there is an example in which the heat efficiency is increased by utilizing the heat of exhaust gas or recycled gas from the anode (see Patent Document 1). However, it is desirable not to attach a reformer in order to reduce energy loss and improve power generation efficiency, or to simplify the structure of the fuel cell and reduce manufacturing costs.

  In response to this problem, an internal reforming type solid oxide fuel cell having no reformer attached to the outside has been developed (see Patent Document 2 and Patent Document 3). This technology adds a steam reforming catalyst Ru, Rh, Pd or Cu to the fuel electrode of the fuel battery cell to cause a steam reforming reaction on the electrode, and suppresses heat loss due to reforming, It aims to make the system scale compact.

  However, since a large amount of water vapor is entrained in the fuel (S / C = 1 or more), the electromotive force of the fuel cell is reduced (and thus the output is reduced), and additional facilities for evaporation and water vapor circulation are necessary. There is still energy loss associated with it. Furthermore, there is a concern about electrode deterioration such that metal (Ni or the like) constituting the cermet fuel electrode is oxidized by water vapor, or conversely, carbon deposition occurs due to insufficient amount of water vapor accompanied.

In addition, in order to improve the power generation efficiency of the fuel cell, the fuel utilization rate of hydrogen or hydrocarbon fuel must be improved. However, if the fuel utilization rate is increased, the fuel concentration at the fuel electrode decreases, so the electromotive force Tends to decrease (and consequently decrease in output). Therefore, a highly active fuel electrode that realizes an output improvement at a high fuel utilization rate is desired.
JP-A-3-236164 JP 2000-58075 A JP-A-6-140048

  The present invention has been made in view of the above-described problems, and it is not necessary to entrain water vapor when using a fuel containing hydrocarbons. The fuel electrode is formed by carbon deposition and / or oxidation by the accompanying water vapor. It is an object of the present invention to provide a fuel electrode that suppresses deterioration of the fuel, improves durability, and at the same time achieves both improvement in fuel utilization and output when using hydrogen and / or hydrocarbon fuel.

  As a result of intensive studies to achieve the above problems, the present inventors have further added a material having proton conductivity (hereinafter abbreviated as “proton conductor”) to the electron conductor and the oxygen ion conductor. Thus, it has been found that the electrode characteristics can be dramatically improved if a cermet fuel electrode is produced. The present invention has been accomplished based on these findings.

That is, the present invention provides a mixture of an electron conductor and an oxygen ion conductor and / or a mixed electron / oxygen ion conductor, and a proton conductor, and has a solid electrolyte layer that conducts oxygen ions and is not humidified. and / or a substance containing a hydrocarbon to a fuel electrode for a fuel cell you use as fuel,
The electronic conductor is a metal and / or its metal oxide;
The oxygen ion conductor is a stabilized zirconia, lanthanum gallate, or ceria-based solid solution, and the ceria-based solid solution is Ce _1-x M _x O _2-δ (where M is Gd, La, Y, Sc, Sm, One or more elements selected from the group consisting of Pr, Nd, Ca, Mg, Sr, Ba, Dy, Yb, Tb, and other divalent or trivalent lanthanoids, and x is 0 <x ≦ 0 And δ represents the amount of oxygen deficiency.)
The electron / oxygen ion mixed conductor is a perovskite solid solution, a pyrochlore solid solution or a fluorite solid solution, and the perovskite solid solution is A _{1 ± a} BO _3-δ (where A is composed of La, Sr, Ca, Y and Pr). At least one selected from the group, B represents at least one selected from the group consisting of Co, Cr, Mn, Ni and Fe, 0 ≦ a ≦ 0.2, and δ represents the amount of oxygen deficiency .), A compound represented by Ba (Ce _1-x Gd _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2). , Ca (Al _1-x Ti _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2), Sr (Zr _1-x Sc _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2) And a pyrochlore solid solution of Ln ₂ ((Zr _1-x Ti _x ) ₂ ) _{1 ± a} O ₇ (wherein Ln is Sc, Y, La and 1 or more elements selected from the group consisting of other lanthanoids, and 0 ≦ x ≦ 0.5 and 0 ≦ a ≦ 0.2.) The fluorite solid solution is Ce _1-x M _x O _{2-δ where} M is Gd, La, Y, Sc, Sm, Pr, Nd, Ca, Mg, Sr, Ba, Dy, Yb, Tb, and other divalent or 3 One or more elements selected from the group consisting of valent lanthanoids, and 0 ≦ x ≦ 0.5.)
The proton conductor is Sr (Zr _1-x Y _x ) _{1 ± a} O _3-δ (where 0 <x ≦ 0.5, 0 ≦ a ≦ 0.2, and δ represents the amount of oxygen deficiency) .) Is a perovskite type compound represented by the above formula, and provides an electrode of a solid oxide fuel cell.

Further, the present invention is to at least one surface of the solid electrolyte layer is intended to provide a fuel cell having the electrode, also provides a fuel cell stack or fuel cell having such a fuel cell.

  According to the present invention, a highly active electrode that can directly oxidize a fuel containing hydrocarbons such as city gas directly at the fuel electrode and is resistant to deterioration, thereby simplifying the structure of the fuel cell. Thus, it is possible to provide a low-cost and highly efficient fuel cell.

Hereinafter, representative examples of the embodiments of the present invention will be shown to describe the present invention in more detail.
1. Electrode The electrode of the solid oxide fuel cell of the present invention includes at least (a) a mixture of an electron conductor and an oxygen ion conductor and / or a mixed electron / oxygen ion conductor, and (b) a proton conductor. It is a feature.

  Component (a) contains (a-1) a mixture of an electron conductor and an oxygen ion conductor and / or (a-2) a mixed electron / oxygen ion conductor, but (a-1) an electron conductor and The mixture of oxygen ion conductors and / or (a-2) the electron / oxygen ion mixed conductor is preferably porous having a three-dimensional network structure. Here, the “three-dimensional network structure” refers to a structure in which a path through which electrons and / or oxygen ions are conducted in an electrode communicates, and the units of “respectively” are “electron conductor” and “oxygen ion”. “Conductor” and “electron / oxygen ion mixed conductor”. That is, when the electrode is formed, it is preferable that both electrons and oxygen ions have conduction as a result. And the electrode of this invention is characterized by further including a component (b) proton conductor there.

  The best modes of the electron conductor, oxygen ion conductor, oxygen / electron mixed conductor, and proton conductor constituting the electrode of the present invention will be described in detail for each item below.

(1) Electron Conductor The electron conductor is not particularly limited as long as it easily conducts electrons at the operating temperature of the fuel cell or is referred to as “electron conductor” in the field of fuel cell electrodes. Is preferably a metal, alloy or oxide thereof at 600 ° C. or higher. Particularly preferred are at least one metal selected from the group consisting of Ni, Co, Cu, Fe, Ag, Pt, Au, Pd, Ru, Mo, W and Ta and / or an oxide thereof.

(2) Oxygen ion conductor The oxygen ion conductor is particularly limited as long as it easily conducts oxygen ions at the operating temperature of the fuel cell or is referred to as an “oxygen ion conductor” in the field of fuel cell electrodes. However, stabilized zirconia, lanthanum gallate or ceria-based solid solution is preferable in terms of high oxygen ion conductivity. Moreover, although it does not specifically limit, the compound whose main component is the same as the solid electrolyte body mentioned later is preferable.

Stabilized zirconia is not particularly limited, but general formula (ZrO ₂ ) _1-x (M ₂ O ₃ ) _x (wherein M is selected from the group consisting of Y, Sc, Sm, Nd, Gd and Yb) _X represents one or more elements) and / or (ZrO ₂ ) _1-x (MO) _x (wherein M represents one or more elements selected from the group consisting of Ca and Mg). Solid solutions with 0 <x ≦ 0.3 are preferred. Particularly preferable examples include (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 . Hereinafter, (ZrO ₂ ) _1-x (Y ₂ O ₃ ) _x (where 0 <x ≦ 0.3) is abbreviated as “yttria-stabilized zirconia” or “YSZ”. In addition, generally, for example, the expression “wherein A represents one or more elements selected from the group consisting of Q, R, and T” is expressed by, for example, a solid body in which A is Q and A In addition to indicating that a solid solution in which R is R may be mixed, the solid solution having A and Q at the same time as the crystal site is also indicated.

Although lanthanum gallate is not particularly limited, general _{formula, La 1-x Sr x Ga} 1-y-z Mg y A z O 3 ( wherein, A is Co, Fe, any one or more of Ni or Cu Element is represented by x = 0.05 to 0.3, y = 0 to 0.29, z = 0.01 to 0.3, y + z = 0.025 to 0.3). A solid solution is preferred. Specific examples include La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Co _0.05 O _3-δ (where δ represents the amount of oxygen deficiency).

The ceria-based solid solution is not particularly limited, but Ce _1-x M _x O ₂ (wherein M is Gd, La, Y, Sc, Sm, Pr, Nd, Ca, Mg, Sr, Ba, Dy, Yb, A solid solution in which x is 0 <x ≦ 0.5 in Tb and one or more elements selected from the group consisting of other divalent or trivalent lanthanoids) is preferable. Particularly preferred ceria-based solid solutions include Ce _0.8 Gd _0.2 O _2-δ (where δ represents the amount of oxygen deficiency).

(3) Electron / oxygen ion mixed conductor As the electron / oxygen ion mixed conductor, it is easy to conduct both electrons and oxygen ions, or in the field of fuel cell electrodes, it is called “electron / oxygen ion mixed conductor”. Any known perovskite solid solution, pyrochlore solid solution or fluorite solid solution is preferable.

The perovskite solid solution refers to a solid solution having a perovskite-type crystal structure, and is represented by a general formula, A _{1 ± a} BO _3-δ (where A is at least one selected from the group consisting of La, Sr, Ca, Y and Pr). And B represents at least one selected from the group consisting of Co, Cr, Mn, Ni and Fe, and 0 ≦ a ≦ 0.2. Of these, substances based on LaCoO ₃ , LaMnO ₃ , LaCrO _{3 and the} like are preferred. _{Specifically, La 0.6 Sr 0.4 Fe 0.8 Co} 0.2 O 3, La 0.75 Sr 0.2 Cr 0.5 Mn 0.5 O 3 , and the like.

In other perovskite solid solutions, Ba (Ce _1-x Gd _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2), Ca (Al _1-x Ti _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2), Sr (Zr _1-x Sc _x ) _{1 ± a} O ₃ (where 0 ≦ _x x ≦ 0.5 and 0 ≦ a ≦ 0.2) are also preferable. _{Specifically, BaCe 0.9 Gd 0.1 O 3,} CaAl 0.7 Ti 0.3 O 3, SrZr 0.9 Sc 0.1 O 3 and the like.

The pyrochlore solid solution refers to a solid solution having a pyrochlore type crystal structure. For example, Ln ₂ ((Zr _1-x Ti _x ) ₂ ) _{1 ± a} O ₇ (wherein Ln is Sc, Y, La and One or more elements selected from the group consisting of other lanthanoids are shown, and 0 ≦ x ≦ 0.5 and 0 ≦ a ≦ 0.2) are preferred. Specifically, for example, Gd ₂ ((Zr _1-x Ti _x ) ₂ ) _{1 ± a} O ₇ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2), Y ₂ ( (Zr _1-x Ti _x ) ₂ ) _{1 ± a} O ₇ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2).

The fluorite solid solution refers to a solid solution having a fluorite-type crystal structure. Among them, a ceria-based solid solution is preferable, and Ce _1-x M _x O ₂ (wherein M is Gd, La, Y, Sc). , Sm, Pr, Nd, Ca, Mg, Sr, Ba, Dy, Yb, Tb, and one or more elements selected from the group consisting of other divalent or trivalent lanthanoids, 0 ≦ x ≦ 0.5). As a particularly preferred ceria-based solid solution, Ce _0.8 Gd _0.2 O _2-δ (where δ represents the amount of oxygen deficiency) and the like can be mentioned.

When the electrode of the present invention is a fuel electrode, a perovskite solid solution (for example, La _0.6 Sr _0.4 Fe _0.8 Co _0.2 O ₃ ) or a fluorite solid solution (for example, Ce _0.8 Gd _{0 .2} O _2−δ (where δ represents the amount of oxygen deficiency) is preferable from the standpoint of having high mixed conductivity.

(4) Proton Conductor The present invention is characterized in that a proton conductor is contained in an electrode of a solid oxide fuel cell. The proton conductor is not particularly limited as long as it easily conducts protons at the operating temperature of the fuel cell. In the present invention, the proton conductor is 10 ⁻⁴ Scm ⁻¹ or more at the operating temperature of the fuel cell. It is preferable to use a substance having proton conductivity of Particularly preferred are substances having a proton conductivity of 10 ⁻³ Scm ⁻¹ or more, and more preferred are substances having a proton conductivity of 10 ⁻² Scm ⁻¹ or more.

The proton conductor contained in the electrode according to the present invention is not particularly limited, but a substance mainly composed of the same metal as the main component metal of the oxygen ion conductor or the solid electrolyte can provide good bonding between particles. It is preferable in that it is easy to generate reaction products with poor conductivity. A perovskite proton conductor is preferable in that it has high proton conductivity. Particularly preferred as the proton conductor is an oxygen ion conductor or a perovskite compound in which the main component metal of the solid electrolyte occupies 50% or more of the B site of the perovskite crystal structure.

The perovskite type compound as the proton conductor of the present invention is A (B _1-x B ′ _x ) _{1 ± a} O _3-δ (wherein A is one selected from the group consisting of Ba, Ca and Sr) B represents one or more elements selected from the group consisting of Ce and Zr, and B ′ represents Y, Nd, La, Ca, Yb, Sc, In, Gd, and other divalent elements. Alternatively, one represented by one or more elements selected from the group consisting of trivalent lanthanoids, and 0 <x ≦ 0.5 and 0 ≦ a ≦ 0.2) is preferable. More specifically, SrZr _0.95 Y _0.05 O _3-δ , SrCe _0.95 Yb _0.05 O _3-δ , BaCe _0.9 Y _0.1 O _3-δ (where δ is Indicating the amount of oxygen deficiency).

When typical YSZ is employed in a solid electrolyte body to be described later, a particularly preferable example of the proton conductor of the present invention includes Y-doped SrZrO _{3 and the} like, and a specific composition is SrZr _0.95. Y _0.05 O _3-δ (where δ represents the amount of oxygen deficiency) and the like.

When YSZ is employed, a particularly preferred example of the electrode of the solid oxide fuel cell of the present invention is Ni / (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 -SrZr _0.95 Y _0.05 O _3.

  Regarding the contents of (A) electron conductor, (B) oxygen ion conductor, (C) electron / oxygen ion mixed conductor, and (D) proton conductor with respect to the entire electrode of the solid oxide fuel cell of the present invention. Although it is not limited, preferable content is described below for every composite composition of an electrode.

  When the composite composition of the electrode is (A) an electron conductor, (B) an oxygen ion conductor, and (D) a proton conductor, both (A) and (B) are 10% by mass or more based on the entire electrode. In order to form a three-dimensional network structure of conduction paths of electrons and oxygen ions, it is particularly preferably 20% by mass or more. Moreover, it is preferable that it is 80 mass% or less, and it is especially preferable that it is 70 mass% or less.

  When the composite composition of the electrode is (C) an electron / oxygen ion mixed conductor and (D) a proton conductor, (C) is 10% by mass or more with respect to the entire electrode. It is preferable for forming a three-dimensional network structure of ion conduction paths, and is particularly preferably 20% by mass or more. Moreover, it is preferable that it is 80 mass% or less, and it is especially preferable that it is 70 mass% or less.

  When the composite composition of the electrode is (A) an electron conductor, (B) an oxygen ion conductor, (C) an electron / oxygen ion mixed conductor and (D) a proton conductor, (A) and (B) In order to form a three-dimensional network structure of electron and oxygen conduction paths, it is preferable that each of both of (C) and (C) is 10% by mass or more with respect to the entire electrode. It is particularly preferred. Moreover, it is preferable that it is 80 mass% or less, and it is especially preferable that it is 70 mass% or less.

  (D) The content of the proton conductor is preferably 70% by mass or less, and particularly preferably 50% by mass or less, with respect to the entire electrode regardless of the composite composition. Moreover, it is preferable that it is 1 mass% or more, and it is especially preferable that it is 5 mass% or more. When there are too few proton conductors, the above effects of the present invention may not be obtained.

When the most common YSZ is adopted as the solid electrolyte body, a particularly preferable example of the electrode of the solid electrolyte fuel cell of the present invention is Ni / (ZrO ₂ ) _0.92 (Y ₂ O, as described above. ₃ ) _0.08- SrZr _0.95 Y _0.05 O ₃ , and the mass composition ratio of Ni is 20 to 70 mass% with respect to the entire electrode, (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 is preferably 20 to 70% by mass, and SrZr _0.95 Y _0.05 O ₃ is preferably 5 to 50% by mass, particularly preferably Ni / (ZrO ₂ ) _0.92 (Y ₂ O ₃ ). _0.08 / SrZr _0.95 Y _0.05 O ₃ = 6 / 2.8 / 1.2.

2. Solid electrolyte body The solid electrolyte body is not particularly limited, and examples thereof include YSZ and calcia-stabilized zirconia. A ceria solid solution or a lanthanum gallate solid solution may be used. A typical one is (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 or the like.

3. Air electrode The air electrode is a general one and is not particularly limited. Examples thereof include perovskite-type lanthanum-based composite oxides such as La _1-x Sr _x MnO ₃ and LaCoO ₃ . More specific examples thereof include _La 0.85 _Sr 0.15 MnO ₃ and the like.

4). A cell or a stack cell is one in which a fuel electrode and an air electrode are respectively disposed on both surfaces of a solid electrolyte body as shown in FIG. 1, and the shape of the cell may be a flat plate type or a cylindrical type. These single cells are overlapped to form a stack that is an aggregate of cells.

  The method for producing the electrode material for forming the electrode of the present invention is not particularly limited, but the ceramic powder as the electrode material may be prepared by using, for example, an oxide, carbonate, nitrate, metal alkoxide, etc. It can be prepared by the method, complex method, combustion method, spray pyrolysis method, sol-gel method and the like. This ceramic powder is subjected to calcination and ball milling as necessary.

  The average particle of the electrode material is preferably 10 μm or less, and particularly preferably 6 μm or less. Moreover, it is preferable to set it as 0.01 micrometer or more, and it is especially preferable to set it as 0.1 micrometer or more.

  This electrode material (ceramic powder) is dispersed in a solvent, and an organic binder or the like is added to prepare a slurry. The slurry is applied to a doctor blade device or the like to produce a green sheet, or an extrusion molding machine or the like to produce a tube. These ceramic powder, slurry or green molded body is used for forming the electrode of the present invention.

  Next, a method for manufacturing electrodes and cells will be described. In order to form a multilayer structure of cells composed of electrodes and electrolytes, tape calendering that bonds the electrode and electrolyte green sheets, green sheets and molded tubes, or the surfaces after calcination or firing of these, In order to form the layer, a slurry coating method, a spray coating method, a dipping method, a sol-gel method, or the like can be used. The multilayer structure is further sintered to produce a single cell.

5. Fuel cell The fuel cell is a fuel gas and oxidant gas supply system to the stack as a balance of plant, a heat exchanger for preheating and exhaust heat recovery of these supply gases, and steam if necessary. And a fuel gas reformer, and a control system for controlling the operation of the fuel cell. According to the present invention, the supply of water vapor is unnecessary or can be greatly reduced, and the heat exchanger associated therewith can also be unnecessary or reduced, so that the structure of the fuel cell can be simplified and made compact. The fuel cell manufacturing cost can be reduced and the power generation efficiency can be improved.

6). Fuel The electrode of the present invention is used in a fuel cell using hydrogen and / or hydrocarbon as fuel, but is preferably used in a fuel cell using hydrocarbon fuel. The hydrocarbon used in the present invention is not particularly limited, and examples thereof include city gas, methane, ethane, propane, butane, methanol, ethanol, propanol, butanol, dimethyl ether, natural gas, LPG, naphtha, and kerosene. Although the fuel may be used after being humidified, the present invention is characterized in that dry fuel that is not humidified can be used. Therefore, in order to achieve the effects of the present invention, it is preferable to use dry fuel that is not humidified. .

  EXAMPLES Next, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited by a following example, unless the summary is exceeded.

Example 1
<Preparation of fuel electrode oxide powder>
NiO was 3N manufactured by Kanto Chemical Co., and the average particle size was 4.7 μm. YSZ was TZ-8Y manufactured by Tosoh Corporation, fired at 1250 ° C. for 4 hours, and ball milled in ethanol. As the proton conductor, SrZr _0.95 Y _0.05 O _3-δ (hereinafter abbreviated as “SrZY”) was synthesized by the glycine nitrate method, and fired at 1250 ° C. for 4 hours after wet ball milling. After pulverizing with a mortar, baking was further performed at 1250 ° C. for 4 hours. In addition, the composition of TZ-8Y made by Tosoh is (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 .

<Preparation of fuel electrode paste>
Each powder was weighed so that the weight ratio of NiO to oxide powder was 6: 4 and the weight ratio of oxide powder was YSZ: SrZY = 7: 3. Α-Terpineol was added in an amount of 1.2 times by weight with respect to the oxide powder, and it was put on a planetary ball mill at 600 rpm for 1 hour. To the collected paste, 10% of the weight of powder of ethyl cellulose was added and mixed well while heating to 60 to 70 ° C. to obtain an electrode paste.

<Cell fabrication>
Masking was performed on one side of a Tosoh YSZ disk having a diameter of 20 mmφ and a thickness of 0.3 mm, and the fuel electrode paste was applied by a doctor blade method. After drying at 90 ° C. for 5 hours or longer, firing was performed at 1250 ° C. for 4 hours in an electric furnace. Subsequently, the same masking was performed on the other surface, and an air electrode was similarly applied by the doctor blade method. As the air electrode paste, a powder of La _0.85 Sr _0.15 MnO _3-δ was prepared in the same manner as the fuel electrode paste. The electrode size was 0.53 to 0.55 cm ² , the thickness of the fuel electrode after firing was about 40 μm, and that of the air electrode was 15 to 20 μm. The obtained fuel electrode is referred to as “Ni / YSZ-SrZY”.

Comparative Example 1
A fuel electrode oxide powder, a fuel electrode paste, and a cell were prepared in the same manner as in Example 1 except that SrZY, which is a proton conductor, was not used. Two fuel electrodes were prepared, and the obtained fuel electrodes were named “Ni / YSZ A” and “Ni / YSZ B”, respectively. Hereinafter, A and B are collectively referred to as “Ni / YSZ”.

<Proton conductivity>
The proton conductivity of SrZY at 900 ° C. is 2 × 10 ⁻³ Scm ⁻¹ (Hiroshige Matsumoto, Stellar Integration, Vol. 18, No. 7, p. 5 (2005)).

<Evaluation method>
Hydrogen that was not humidified was passed through the fuel electrode at 200 ccm, and O ₂ was passed through the air electrode at 60 ccm, and the relationship between current and potential at 900 ° C. was measured using a potentiogalvanostat (ADVANTEST R6240A). Using the current interrupt method, the overvoltage of the fuel electrode was separated, the oxygen activity a ₀ at the three-phase interface was determined using the following equation, and the relationship between the main activity and the current was investigated.

a ₀ = exp (2FE / RT)
(In the formula, F represents the Faraday constant, E represents the fuel electrode potential, R represents the gas constant, and T represents the temperature.)

<Evaluation results>
As shown in FIG. 2, the slope when using the Ni / YSZ-SrZY electrode was about 2/3, which was smaller than the slope when using the Ni / YSZ electrode. Moreover, the current density at the low oxygen activity was improved as compared with the Ni / YSZ electrode. A decrease in the slope in the logarithmic scale diagram, that is, a decrease in the order of a ₀ with respect to the current i corresponds to an increase in the oxygen coverage rate involved in the reaction at the three-phase interface as the reaction site (M Ihara et al., J. Electrochem. Soc., 148 (3) A209-A219 (2001)).

In general, it is said that the order of a ₀ with respect to the current i is reduced and the oxygen coverage is increased, which indicates that the resistance to dry fuel is improved. Therefore, from this, the Ni / YSZ-SrZY electrode is The use of hydrogen and hydrocarbon fuel improves the output, improves the resistance to electrode degradation caused by carbon deposition in dry hydrocarbon fuel, and improves the electrode characteristics in a direction that enables stable power generation. all right.

  In the first embodiment, a single cell is used, but the same effect can be expected in a stack.

Example 2
<Preparation of fuel electrode oxide powder>
NiO and YSZ were the same as those in Example 1, and the same pretreatment as YSZ was performed. As a proton conductor, SrCe _0.95 Yb _0.05 O _3-δ (hereinafter abbreviated as “SrCY”) was used. As SrCY, a powder made by Seimi Chemical was used.

<Preparation of fuel electrode paste>
Each powder was weighed so that the weight ratio of NiO to oxide powder was 6: 4 and the weight ratio of oxide powder was YSZ: SrCY = 9: 1 and 1: 1. These powders were treated in the same manner as in Example 1 to prepare electrode pastes.

<Cell fabrication>
As in Example 1, the fuel electrode paste Ni / YSZ-SrCY (three kinds of oxide weight ratios 9: 1, 1: 1, and 1: 0) was applied to one side of a YSZ disk. After drying at 90 ° C. for 5 hours or more, baking was performed at 1300 ° C. for 4 hours in an electric furnace. The air electrode was produced in the same manner as in Example 1.

<Proton conductivity>
The proton conductivity of SrCY at 900 ° C. is 1 × 10 ⁻² Scm ⁻¹ (Hiroshige Matsumoto, Stellar Integration, Vol. 18, No. 7, p. 5 (2005)).

<Evaluation method>
In the same manner as in Example 1, the oxygen activity a ₀ at the three-phase interface was determined, and the relationship with the current was examined.

<Evaluation results>
As shown in FIG. 3, the slope of the Ni / YSZ-SrCY electrode is smaller than the slope of Ni / YSZ about 1, and about 2/3 for Ni / YSZ-SrCY (9: 1), Ni / YSZ-SrCY ( The slope decreased with the SrCY amount at 1/2) or less at 1: 1).

  Moreover, Ni / YSZ-SrCY (9: 1) improved the current density at the same oxygen activity as compared with Ni / YSZ. In Ni / YSZ-SrCY (1: 1), the current density was lower than in Ni / YSZ. The amount of YSZ in this system is 20% by mass, and there is a possibility that the network of YSZ, which is a path for oxygen ion conduction, is interrupted. For this reason, it is presumed that the three-phase interface as a reaction site has been reduced.

The smaller slope of the logarithmic scale in FIG. 3 indicates that, as described in Example 1, the oxygen coverage involved in the reaction increased at the three-phase interface. In fact, in Ni / YSZ-SrCY (9: 1) which secured a network path for oxygen ion conduction, a current density exceeding Ni / YSZ was obtained. In other words, by using the Ni / YSZ-SrCY electrode, the output is improved when hydrogen and hydrocarbon fuel are used, and the resistance to electrode deterioration due to carbon deposition in dry hydrocarbon fuel is improved, and stable power generation is possible. The electrode characteristics were improved.

  In the second embodiment, a single cell is used, but the same effect can be expected in a stack.

  The present invention eliminates the need for entraining water vapor into a fuel containing hydrocarbons, suppresses deterioration of the fuel electrode due to carbon deposition and oxidation with water vapor, improves durability, and achieves both improvement in fuel utilization and output Can provide the pole. That is, since it is possible to provide a highly active electrode that can directly oxidize fuel containing hydrocarbons such as city gas at the fuel electrode, it can be widely used in fuel cell application fields.

It is sectional drawing of the solid oxide fuel cell of this invention. 6 is a graph showing a relationship between an oxygen activity a ₀ and a current i in Example 1 and Comparative Example 1. 6 is a graph showing a relationship between an oxygen activity a ₀ and a current i in Example 2.

Explanation of symbols

1 ... Solid electrolyte fuel cell 2 ... Anode (fuel electrode)
3 ... Cathode (Air electrode)
4 ... Electrolyte layer 5a..Anode (fuel electrode) side current collector 5b..Cathode (air electrode) side current collector

Claims (5)

Non-humidified hydrogen and / or hydrocarbons comprising a mixture of an electron conductor and an oxygen ion conductor and / or a mixed conductor of electrons and oxygen ions, and a proton conductor and having a solid electrolyte layer for conducting oxygen ions a fuel electrode for a fuel cell you use a substance as a fuel containing, electron conductor is a metal and / or metal oxides,
The oxygen ion conductor is a stabilized zirconia, lanthanum gallate, or ceria-based solid solution, and the ceria-based solid solution is Ce _1-x M _x O _2-δ (where M is Gd, La, Y, Sc, Sm, One or more elements selected from the group consisting of Pr, Nd, Ca, Mg, Sr, Ba, Dy, Yb, Tb, and other divalent or trivalent lanthanoids, and x is 0 <x ≦ 0 And δ represents the amount of oxygen deficiency.)
The electron / oxygen ion mixed conductor is a perovskite solid solution, a pyrochlore solid solution or a fluorite solid solution, and the perovskite solid solution is A _{1 ± a} BO _3-δ (where A is composed of La, Sr, Ca, Y and Pr). At least one selected from the group, B represents at least one selected from the group consisting of Co, Cr, Mn, Ni and Fe, 0 ≦ a ≦ 0.2, and δ represents the amount of oxygen deficiency .), A compound represented by Ba (Ce _1-x Gd _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2). , Ca (Al _1-x Ti _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2), Sr (Zr _1-x Sc _x ) _{1 ± a} O ₃ (where 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 0.2) And a pyrochlore solid solution of Ln ₂ ((Zr _1-x Ti _x ) ₂ ) _{1 ± a} O ₇ (wherein Ln is Sc, Y, La and 1 or more elements selected from the group consisting of other lanthanoids, and 0 ≦ x ≦ 0.5 and 0 ≦ a ≦ 0.2.) The fluorite solid solution is Ce _1-x M _x O _{2-δ where} M is Gd, La, Y, Sc, Sm, Pr, Nd, Ca, Mg, Sr, Ba, Dy, Yb, Tb, and other divalent or 3 One or more elements selected from the group consisting of valent lanthanoids, 0 ≦ x ≦ 0.5, and δ represents the amount of oxygen deficiency),
The proton conductor is Sr (Zr _1-x Y _x ) _{1 ± a} O _3-δ (where 0 <x ≦ 0.5, 0 ≦ a ≦ 0.2, and δ represents the amount of oxygen deficiency) An electrode of a solid oxide fuel cell, characterized by being a perovskite type compound represented by.   2. The electrode according to claim 1, wherein the mixture of the electron conductor and the oxygen ion conductor and / or the electron / oxygen ion mixed conductor is a porous material having a three-dimensional network structure. The electrode according to claim 1, wherein the proton conductor is a substance having a proton conductivity of 10 ⁻⁴ Scm ⁻¹ or more at an operating temperature of the fuel cell.   A fuel cell having the electrode according to any one of claims 1 to 3 on at least one surface of the solid electrolyte layer. A fuel cell stack or fuel cell comprising the fuel cell according to claim 4.

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