JP2011040362A - Fuel electrode for solid oxide fuel cell, solid oxide fuel cell, and operation method of solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel electrode for a solid oxide fuel cell capable of achieving the solid oxide fuel cell having superior performance even when it is operated in a low temperature atmosphere, to provide the solid oxide fuel cell including the same, and to provide an operating method of that solid oxide fuel cell. <P>SOLUTION: The fuel electrode for the solid oxide fuel cell is used to operate the solid oxide fuel cell in the atmosphere of 900°C or less. The fuel electrode for the solid oxide fuel cell contains iron and a metal oxide, and the solid oxide fuel cell including the same and the operating method of that solid oxide fuel cell are provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel electrode for a solid oxide fuel cell, a solid oxide fuel cell, and a method for operating the solid oxide fuel cell.

  In recent years, clean energy sources have been demanded due to environmental problems and resource problems. For example, a fuel cell is expected as such an energy source. A fuel cell is characterized in that energy that should be generated by combustion is extracted as electric energy instead of heat energy by electrochemically oxidizing fuel.

  Among such fuel cells, the solid oxide fuel cell is operated at an extremely high temperature of about 1000 ° C., and thus has an advantage that, for example, exhaust heat can be effectively used.

FIG. 16 shows a schematic configuration diagram of an example of a conventional solid oxide fuel cell disclosed in Patent Document 1, for example. Here, the solid oxide fuel cell 11 has a structure in which an oxygen electrode 13 and a fuel electrode 14 are respectively disposed on both sides of an electrolyte 12 that is an oxide ion conductor. Then, oxygen or air is introduced into the oxygen electrode 13 side, and hydrogen gas is introduced into the fuel electrode 14 side, and the solid oxide fuel cell 11 is operated in an atmosphere of about 1000 ° C. Then, in the oxygen electrode _{13 (1/2) O 2 + 2e} - → O 2- reaction oxide ions (O ^2-) are produced by the, oxide ions (O ^2-) fuel electrode by conducting electrolyte 12 Move towards 14. When the oxide ions (O ²⁻ ) reach the fuel electrode 14, electrons (e ⁻ ) are released by the reaction of H ₂ + O ²⁻ → H ₂ O + 2e ⁻ , and water (H ₂ O) is generated. (E ⁻ ) flows to the oxygen electrode 13 through an external circuit.

  FIG. 17 is a schematic enlarged conceptual diagram illustrating the behavior of the fuel electrode during operation of the solid oxide fuel cell shown in FIG. In FIG. 17, the fuel electrode 14 is made of cermet of nickel 15 and zirconia 16, and the electrolyte 12 is made of yttria-stabilized zirconia (YSZ) obtained by mixing a small amount of yttrium with zirconia.

Here, at the three-phase interface 17 between the hydrogen gas, nickel 15 and the electrolyte 12, hydrogen (H ₂ ) introduced to the fuel electrode 14 side and oxide ions (O ²⁻ ) conducted through the electrolyte 12 React to release electrons (e ⁻ ) to produce water (H ₂ O).

Further, at the three-phase interface 18 of hydrogen gas, nickel 15 and zirconia 16, hydrogen (H ₂ ) introduced to the fuel electrode 14 side or the hydrogen (H ₂ ) is brought into contact with the surface of the nickel 15 to dissociate. The atomic hydrogen (H _ad ) reacts with the oxide ion (O ²⁻ ) that has been conducted through the electrolyte 12 and the zirconia 16 to release electrons (e ⁻ ) to produce water (H ₂ O). .

  A plurality of such solid oxide fuel cells are connected via an interconnector to form a cell stack. Here, the interconnector separates oxygen gas or air introduced to the oxygen electrode side and hydrogen gas introduced to the fuel electrode side, and electrically connects the individual solid oxide fuel cells in series. It has a function of electrical connection (see, for example, Patent Document 1).

  Recently, as a fuel electrode for a solid oxide fuel cell operated at a lower temperature, research on a fuel electrode containing iron has been advanced (for example, see Non-Patent Documents 1 to 6). .)

Japanese Patent No. 3160993

Zhen Xie et al., “FexCo0.5-xNi0.5-SDC anodes for low-temperature solid oxide fuel cells”, Electrochimica Acta 51 (2006), 3052-3057 Wang Shi-zhong et al., “High Performance Ni-Fe-Lanthanum Gallate Composite Anodes for Dimethyl Ether Fuel Cells”, Electrochemical and Solid-State Letters, 9 (9), A395-A398 (2006) R. Tai et al., “Fe-Ni anode in Direct-Dimethylether Fuel Cell Operated at Intermediate-Temperature Using BaCe0.8Y0.2O3-δas a Solid Electrolyte”, Abstract of 214th ECS Meeting, A1-No.91 Hyeon Cheol Park et al., “Bimetallic (Ni-Fe) anode-supported solid oxide fuel cells with gadolinia-doped ceria electrolyte”, Journal of Power Sources 186 (2009) 133-137 X.C. Lu et al., “Ni-Fe + SDC composite as anode material for intermediate temperature solid oxide fuel cell”, Journal of Power Sources 165 (2007) 678-684 Xinge Zhang et al., “Interactions of a La0.9Sr0.1Ga0.8Mg0.2O3-δelectrolyte with Fe2O3, Co2O3 and NiO anode materials”, Solid State Ionics 139 (2001) 145-152

  Since the conventional solid oxide fuel cell is operated at an extremely high temperature of about 1000 ° C., as a material constituting the interconnector, conventionally, it has high electron conductivity at a high temperature and a high temperature on the fuel electrode side. Ceramic materials that can withstand both the reducing atmosphere and the high-temperature oxidizing atmosphere on the oxygen electrode side have been used.

  However, since the ceramic material used for the interconnector is very expensive, there is a problem that the manufacturing cost of the solid oxide fuel cell becomes high. Therefore, development of a solid oxide fuel cell having high performance at a low temperature is desired, but the performance of the solid oxide fuel cell is greatly reduced when the temperature during operation is lowered.

  As described above, research has been made on a fuel electrode for a solid oxide fuel cell having excellent performance when operated in a low temperature atmosphere, but further improvement is desired.

  In view of the above circumstances, an object of the present invention is to provide a solid oxide fuel cell fuel electrode capable of realizing a solid oxide fuel cell having excellent performance even when operated in a low temperature atmosphere. A solid oxide fuel cell including the same and a method of operating the solid oxide fuel cell.

The present invention is a fuel electrode for a solid oxide fuel cell for operating a solid oxide fuel cell in an atmosphere of 900 ° C. or lower, comprising iron and a metal oxide, A metal oxide represented by the following composition formula (I):
RE _x Ce _1-x O _{2- (x / 2)} (I)
In the composition formula (I), RE is at least one metal selected from the group consisting of Sm, Gd, Y, La, and Nd, and x is a solid showing a real number that satisfies 0 ≦ x <0.5 This is a fuel electrode for an oxide fuel cell.

  Here, the anode for a solid oxide fuel cell of the present invention is for a solid oxide fuel cell for operating a solid oxide fuel cell by supplying a fuel containing a compound gas of nitrogen and hydrogen. A fuel electrode is preferred.

  The present invention also provides a fuel electrode for a solid oxide fuel cell for supplying a fuel containing a compound gas of nitrogen and hydrogen to operate the solid oxide fuel cell. A fuel electrode for a solid oxide fuel cell.

  The fuel electrode for a solid oxide fuel cell of the present invention further contains nickel, and the ratio of the number of iron atoms to the total number of atoms of iron and nickel in the fuel electrode for the solid oxide fuel cell is 30% or more. It is preferable that

  Moreover, this invention is a solid oxide fuel cell containing said fuel electrode for solid oxide fuel cells, and electrolyte.

  Here, in the solid oxide fuel cell of the present invention, the electrolyte includes zirconia oxide, ceria oxide, lanthanum gallate oxide, barium serate oxide, barium zirconate oxide, strontium. Electrolytes such as serate-based oxides, strontium zirconate-based oxides, and lanthanum silicate-based oxides can be used without particular limitation, but it is preferable to use an electrolyte represented by the following composition formula (II).

_{La 1-s Sr s Ga 1-} (u + v) Co u Mg v O w ... (II)
In the composition formula (II), s represents a real number satisfying 0 ≦ s ≦ 0.25, u represents a real number satisfying 0 ≦ u ≦ 0.1, and v satisfies 0.05 ≦ v ≦ 0.25. It represents a real number, and w preferably represents a real number satisfying 2.7 ≦ w ≦ 3.025.

  Furthermore, the present invention is a method for operating the above solid oxide fuel cell, the step of installing the solid oxide fuel cell in an atmosphere of 900 ° C. or less, and the solid oxidation of the solid oxide fuel cell. Supplying a fuel containing a compound gas of nitrogen and hydrogen to a fuel electrode for a solid fuel cell, and a method for operating a solid oxide fuel cell.

  According to the present invention, a fuel electrode for a solid oxide fuel cell capable of realizing a solid oxide fuel cell having excellent performance even when operated in a low temperature atmosphere, and a solid oxide type including the same A fuel cell and a method for operating the solid oxide fuel cell can be provided.

It is typical sectional drawing of an example of the solid oxide fuel cell of this invention. It is a typical perspective view which shows the structure of the solid oxide fuel cell of Example 1 and Comparative Examples 1-2. It is a flowchart of the manufacturing process of SDC20. (A) And (b) is a figure which shows the voltage-current characteristic of the solid oxide fuel cell of Example 1. FIG. (A) And (b) is a figure which shows the overvoltage-current characteristic of the solid oxide fuel cell of Example 1. FIG. The current density (mA / cm ² ) between the oxygen electrode and the fuel electrode when the overvoltage of the fuel electrode of the solid oxide fuel cell of Example 1 is 0.1 V, and the solid oxide type of Example 1 It is a figure which shows the relationship with the temperature (degreeC) of the atmosphere at the time of the action | operation of a fuel cell. It is a figure which shows the relationship between the overvoltage (V) in the fuel electrode of the solid oxide fuel cell of Example 1, and the ratio of the current density when hydrogen gas is supplied to a fuel electrode, and ammonia gas is supplied. (A) And (b) is a figure which shows the voltage-current characteristic of the solid oxide fuel cell of the comparative example 1. FIG. (A) And (b) is a figure which shows the overvoltage-current characteristic of the solid oxide fuel cell of the comparative example 1. FIG. The current density (mA / cm ² ) between the oxygen electrode and the fuel electrode when the overvoltage of the fuel electrode of the solid oxide fuel cell of Comparative Example 1 is 0.1 V, and the solid oxide type of Comparative Example 1 It is a figure which shows the relationship with the temperature (degreeC) of the atmosphere at the time of the action | operation of a fuel cell. It is a figure which shows the relationship between the overvoltage (V) in the fuel electrode of the solid oxide fuel cell of the comparative example 1, and the ratio of the current density when hydrogen gas is supplied to a fuel electrode, and ammonia gas is supplied. (A) And (b) is a figure which shows the voltage-current characteristic of the solid oxide fuel cell of the comparative example 2. FIG. (A) And (b) is a figure which shows the overvoltage-current characteristic of the solid oxide fuel cell of the comparative example 2. FIG. The current density (mA / cm ² ) between the oxygen electrode and the fuel electrode when the overvoltage of the fuel electrode of the solid oxide fuel cell of Comparative Example 2 is 0.1 V, and the solid oxide type of Comparative Example 2 It is a figure which shows the relationship with the temperature (degreeC) of the atmosphere at the time of the action | operation of a fuel cell. It is a figure which shows the relationship between the overvoltage (V) in the fuel electrode of the solid oxide fuel cell of the comparative example 2, and the ratio of the current density when hydrogen gas is supplied to a fuel electrode, and ammonia gas is supplied. It is a typical block diagram of an example of the conventional solid oxide fuel cell. FIG. 17 is a schematic enlarged conceptual diagram illustrating the behavior of the fuel electrode during the operation of the solid oxide fuel cell shown in FIG. 16. (A) is the electric current which flows into the solid oxide fuel cell of Example 2 when hydrogen gas is supplied to the fuel electrode of the solid oxide fuel cell of Example 2 and the overvoltage of the fuel electrode is 0.15V Is a graph showing the relationship between the current density (mA / cm ² ) and the respective contents (atomic%) of iron and nickel in the fuel electrode of the solid oxide fuel cell of Example 2, (b) Current density of current flowing in the solid oxide fuel cell of Example 2 when ammonia gas is supplied to the fuel electrode of the solid oxide fuel cell of Example 2 and the overvoltage of the fuel electrode is 0.15 V ( and mA / cm ^2), a diagram showing the relationship between the content of each of iron and nickel in the fuel electrode of a solid oxide fuel cell of example 2 (atomic%).

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

  FIG. 1 shows a schematic cross-sectional view of an example of the solid oxide fuel cell of the present invention. As shown in FIG. 1, the solid oxide fuel cell 1 includes an electrolyte 2, an oxygen electrode 3, and a fuel electrode 4. On one surface of the electrolyte 2, iron and metal oxide are formed. The oxygen electrode 3 is formed on the other surface of the electrolyte 2.

  Here, the content of the metal oxide in the fuel electrode 4 is preferably 10% by mass or more and 70% by mass or less, and more preferably 10% by mass or more and 50% by mass or less of the entire fuel electrode 4. . When the content of the metal oxide in the fuel electrode 4 is 10% by mass or more and 70% by mass or less of the entire fuel electrode 4, particularly when the content is 10% by mass or more and 50% by mass or less, the performance is further improved. There is a tendency that the solid oxide fuel cell 1 can be obtained.

  That is, in order to improve the performance of the solid oxide fuel cell 1 by increasing the electron conductivity of the fuel electrode 4, the content of the metal oxide in the fuel electrode 4 is 70% by mass or less. In particular, it is preferably 50% by mass or less. On the other hand, if the content of the metal oxide in the fuel electrode 4 is too small, the agglomeration of iron proceeds too much in the fuel electrode 4 and the contact between the iron and the metal oxide contributes to the electrode reaction in the fuel electrode 4. In order to improve the performance of the solid oxide fuel cell 1 in consideration of the necessity of the presence of a metal oxide to some extent, the content of the metal oxide in the fuel electrode 4 is It is preferably 10% by mass or more of the entire electrode 4.

  In addition, it is not necessary to use only iron as a material responsible for electron conduction, and a metal that forms an alloy with iron, such as nickel, cobalt, chromium, and manganese, may be added to iron. Also in this case, the preferable range of the content of the metal oxide when the total mass of iron, added metal and metal oxide is 100% by mass is the same as described above.

  In particular, the fuel electrode 4 contains iron and nickel, and the ratio of the number of iron atoms to the total number of iron and nickel atoms in the fuel electrode 4 (100 × (number of iron atoms) / {(number of iron atoms) ) + (Number of nickel atoms)}) (%) is preferably 30% or more. In this case, the performance of the solid oxide fuel cell 1 tends to be improved.

  Moreover, as a metal oxide contained in the fuel electrode 4, it is preferable to use a metal oxide represented by the following composition formula (I). When the metal oxide represented by the following composition formula (I) is used as the metal oxide contained in the fuel electrode 4, the performance of the solid oxide fuel cell 1 may be further improved. It tends to be possible.

RE _x Ce _1-x O _{2- (x / 2)} (I)
In the composition formula (I), RE is at least one metal selected from the group consisting of Sm (samarium), Gd (gadolinium), Y (yttrium), La (lanthanum), and Nd (neodymium). , X represents an atomic ratio of a metal corresponding to RE, 1-x represents an atomic ratio of Ce (cerium), and 2- (x / 2) represents an atomic ratio of O (oxygen). In the composition formula (I), x represents a real number satisfying 0 ≦ x <0.5.

  Here, in the composition formula (I), when x is a real number satisfying 0 ≦ x <0.5, the metal oxide in the fuel electrode 4 can easily maintain the crystal structure of the fluorite structure, There is a tendency that the performance of the solid oxide fuel cell 1 can be further improved.

  Moreover, as the electrolyte 2, it is preferable to use the oxide ion conductor represented by the following compositional formula (II). When an oxide ion conductor represented by the following composition formula (II) is used as the electrolyte 2, the performance of the solid oxide fuel cell 1 tends to be further improved.

_{La 1-s Sr s Ga 1-} (u + v) Co u Mg v O w ... (II)
In the composition formula (II), 1-s indicates an atomic ratio of La (lanthanum), s indicates an atomic ratio of Sr (strontium), and 1- (u + v) indicates an atomic ratio of Ga (gallium). , U represents the atomic ratio of Co (cobalt), v represents the atomic ratio of Mg (magnesium), and w represents the atomic ratio of O (oxygen).

  In the composition formula (II), s represents a real number satisfying 0 ≦ s ≦ 0.25, u represents a real number satisfying 0 ≦ u ≦ 0.1, and v represents 0.05 ≦ v ≦ 0. 25 represents a real number satisfying 25, and w represents a real number satisfying 2.7 ≦ w ≦ 3.025.

  Here, in the composition formula (II), when s is a real number in the range of 0 ≦ s ≦ 0.25, the oxide ion conductivity of the electrolyte 2 tends to be excellent. Further, in the composition formula (II), when s is a real number exceeding 0.25, the content of Sr in the electrolyte 2 is excessively increased and other phases are expressed, and the oxide of the electrolyte 2 Ion conductivity tends to decrease.

  In the composition formula (II), when u is a real number in the range of 0 ≦ u ≦ 0.1, the oxide ion conductivity of the electrolyte 2 tends to be excellent. Further, in the composition formula (II), when u exceeds 0.1, the content of Co in the electrolyte 2 is too large, and an internal short circuit is caused by electronic conduction, and the cell voltage tends to decrease. is there.

  In the composition formula (II), when v is a real number in the range of 0.05 ≦ v ≦ 0.25, the oxide ion conductivity of the electrolyte 2 tends to be excellent. Further, in the composition formula (II), when v is a real number exceeding 0.25, the content of Mg in the electrolyte 2 is excessively increased and other phases are expressed, and the oxide of the electrolyte 2 Ion conductivity tends to decrease.

  Further, in the composition formula (II), the value of w is a value within the range of 2.7 ≦ w ≦ 3.025 when calculated from the values of s, u, and v.

  As the oxygen electrode 3, for example, conventionally known Pt (platinum) can be used without any particular limitation. Further, the oxygen electrode 3 may be formed using the same material as the material described as the material used for the fuel electrode 4.

  The solid oxide fuel cell 1 shown in FIG. 1 described above can be operated as follows, for example.

  First, the solid oxide fuel cell 1 shown in FIG. 1 is installed in an atmosphere of 900 ° C. or lower. Next, in a state where the solid oxide fuel cell 1 is installed in an atmosphere of 900 ° C. or lower, a fuel containing a gas of a compound of hydrogen and nitrogen is supplied to the fuel electrode 4 of the solid oxide fuel cell 1, An oxidant containing oxygen gas is supplied to the oxygen electrode 3.

As a result, in the oxygen electrode 3, oxide ions (O ²⁻ ) are generated from the reaction of (1/2) O ₂ + 2e ⁻ → O ²⁻ due to the oxygen gas contained in the oxidizing agent. The oxide ions (O ²⁻ ) conduct through the electrolyte 2 toward the fuel electrode 4.

In the fuel electrode 4, H ₂ + O ²⁻ → H ₂ O + 2e ⁻ is generated by oxide ions (O ²⁻ ) that have been conducted through the electrolyte 2 and a gas of a compound of hydrogen and nitrogen contained in the fuel. Water (H ₂ O) and electrons (e ⁻ ) are generated from the reaction. Water (H ₂ O) is released to the outside, and electrons (e ⁻ ) flow into the oxygen electrode 3 through the external circuit.

  By operating the solid oxide fuel cell 1 as described above, power generation by the solid oxide fuel cell 1 becomes possible.

Here, as a gas of a compound of hydrogen and nitrogen contained in the fuel supplied to the fuel electrode 4, for example, hydrogen such as NH ₃ (ammonia) gas and / or N ₂ H ₄ (hydrazine) gas, nitrogen and At least one gas consisting of the above compounds can be used.

Further, the compound gas of hydrogen and nitrogen in the fuel supplied to the fuel electrode 4 may be supplied to the fuel electrode 4 in the state of a compound of hydrogen and nitrogen, and hydrogen (H ₂ ) gas and nitrogen ( N ₂ ) may be supplied to the fuel electrode 4 in a state of being decomposed into gas.

Moreover, as an oxidizing agent supplied to the oxygen electrode 3, for example, an oxidizing agent containing at least one kind of gas containing oxygen such as air and / or oxygen (O ₂ ) gas can be used.

  The solid oxide fuel cell 1 having the configuration shown in FIG. 1 is excellent when it is operated in a low temperature atmosphere of 900 ° C. or lower by supplying a fuel containing a gas of a compound of hydrogen and nitrogen to the fuel electrode 4. Has performance.

  In particular, when a fuel containing ammonia gas is supplied to the fuel electrode 4 in a low temperature atmosphere of 900 ° C. or lower, the solid oxide fuel cell 1 having further excellent performance can be obtained. This is considered because iron contained in the fuel electrode 4 has high activity of decomposing ammonia gas into hydrogen gas and nitrogen gas.

The fuel supplied to the fuel electrode 4 of the solid oxide fuel cell 1 is not limited to a fuel containing a gas of a compound of hydrogen and nitrogen, and for example, a fuel containing hydrogen (H ₂ ) gas, etc. It is also possible to operate the solid oxide fuel cell 1 by supplying a conventionally known fuel. The solid oxide fuel cell 1 can also be operated in a high-temperature atmosphere at a temperature higher than 900 ° C.

  However, as described above, the solid oxide fuel cell 1 having the configuration shown in FIG. 1 supplies a fuel containing a compound gas of hydrogen and nitrogen to the fuel electrode 4 in a low temperature atmosphere such as 900 ° C. or less. The solid oxide fuel cell 1 is particularly useful in that it has excellent performance when operated.

  Moreover, in order to liquefy hydrogen, it is necessary to cool to extremely low temperature. Moreover, it is necessary to fill an ultra-high pressure container in order to transport the same amount of hydrogen as the liquid at room temperature. Therefore, transporting hydrogen is very laborious and expensive. On the other hand, for example, ammonia is easily liquefied and is liquefied at 20 ° C. at a pressure of about 0.857 MPa (8.46 atm). For example, hydrazine is a liquid at room temperature. Therefore, a compound of hydrogen and nitrogen such as ammonia and hydrazine is superior in transporting fuel as compared with hydrogen. In addition, when a compound of hydrogen and nitrogen is used as a hydrogen energy source, it is usually necessary to convert it into hydrogen and then introduce it into the apparatus. In this case, the compound of hydrogen and nitrogen can be reformed into a hydrogen molecule and a nitrogen molecule inside the apparatus, or can be directly reacted. Therefore, the compound of hydrogen and nitrogen is a fuel for a solid oxide fuel cell. Suitable as

<Example 1>
A solid oxide fuel cell 1 of Example 1 having the configuration shown in the schematic perspective view of FIG. 2 was produced and various experiments were performed. A porous circular oxygen electrode 3 and a columnar reference electrode 5 are formed on one surface of a dense disc-shaped electrolyte 2 of the solid oxide fuel cell 1, and the other surface of the electrolyte 2 is formed on the other surface. A porous circular fuel electrode 4 was formed.

  Here, the diameter D1 of the circular surface of the oxygen electrode 3 and the diameter D2 of the circular surface of the fuel electrode 4 were each 6 mm. Moreover, the circular surface D3 of the electrolyte 2 was 15 mm, and the thickness H of the electrolyte 2 was 0.5 mm.

The solid oxide fuel cell 1 shown in FIG. 2 was produced as follows. First, LSGM prepared by wet-mixing lanthanum oxide, strontium carbonate, gallium oxide and magnesium oxide in ethanol at a predetermined ratio in ethanol, and then repeating calcination at 1150 ° C. for 18 hours and the above wet mixing twice alternately. The powder was CIP-molded at a pressure of 294 MPa, and then fired at 1500 ° C. for 10 hours to prepare a cylindrical electrolyte 2 made of La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O _{3 -δ} (LSGM).

  Next, a paste containing Pt is applied to the center of one circular surface of the electrolyte 2 in a cylindrical shape, and then a paste containing Pt is applied to the vicinity of the paste in a cylindrical shape smaller than the paste. Was baked at 1000 ° C. for 3 hours to form the oxygen electrode 3 and the reference electrode 5, respectively.

Next, as shown in FIG. 3, Sm (NO ₃ ) ₃ .6H ₂ O (samarium nitrate hexahydrate) powder and Ce (NO ₃ ) ₃ · 6H ₂ O (cerium nitrate hexahydrate) powder These powders were mixed in an aqueous HNO ₃ (nitric acid) solution having a nitric acid concentration of 0.2 (mol / dm ³ ) so that the molar ratio of Sm to Ce was Sm: Ce = 2: 8. .

Next, a mixed solution in which an aqueous solution of (COOH) ₂ .2H ₂ O (oxalic acid dihydrate) and an aqueous ammonia solution were mixed (oxalic acid concentration: 0.2 (mol / dm ³ ), pH: 6.7. The mixture was added to the HNO ₃ aqueous solution mixed with the above powder and stirred for 12 hours.

Then, after the above-mentioned liquid after stirring was subjected to adsorption filtration, the powder obtained by the adsorption filtration was calcined in air at a temperature of 700 ° C. to obtain SDC20 (Sm _0.2 Ce _0.8 O _1.9 ) powder. .

Then, a SDC20 prepared as described above, and Fe ₂ O ₃ (iron oxide) powder to obtain a mixed powder were mixed at a ratio in which the content is 70 mass% of the total Fe. The mixed powder was placed in a cylindrical shape on a circular surface opposite to the side where the oxygen electrode 3 and reference electrode 5 of the electrolyte 2 were formed, and then fired at 1250 ° C. for 3 hours to form the fuel electrode 4. Thus, the solid oxide fuel cell 1 of Example 1 having the configuration shown in FIG. 2 was produced.

4 (a) and 4 (b) respectively show the voltage (V) between the oxygen electrode 3 and the fuel electrode 4 of the solid oxide fuel cell 1 of Example 1 manufactured as described above, and the implementation. The relationship (voltage-current characteristic) with the current density (mA / cm < ² >) of the electric current which flows into the solid oxide fuel cell 1 of Example 1 is shown. In FIG. 4A and FIG. 4B, the horizontal axis indicates the current density (mA / cm ² ), and the vertical axis indicates the voltage (V).

  4A shows that the solid oxide fuel cell 1 of Example 1 is installed in each atmosphere of 700 ° C., 800 ° C., and 900 ° C., air is supplied to the oxygen electrode 3, and the fuel electrode 4 It is a voltage-current characteristic when hydrogen gas is supplied to. 4B shows that the solid oxide fuel cell 1 of Example 1 is installed in each atmosphere at 700 ° C., 800 ° C., and 900 ° C., air is supplied to the oxygen electrode 3, and the fuel electrode 4 It is a current-voltage characteristic when ammonia gas is supplied to.

  As shown in FIGS. 4 (a) and 4 (b), the voltage-current characteristics of the solid oxide fuel cell 1 of Example 1 are shown in the fuel at any temperature of 700 ° C., 800 ° C., and 900 ° C. It is shown that the curve spread in the current density direction is about the same when the hydrogen gas is supplied to the electrode 4 and when the ammonia gas is supplied. Therefore, it was confirmed that the solid oxide fuel cell 1 of Example 1 has excellent voltage-current characteristics equivalent to those when hydrogen gas is supplied even when ammonia gas is supplied to the fuel electrode 4. .

5 (a) and 5 (b), respectively, the overvoltage (V) at the anode 4 of the solid oxide fuel cell 1 of Example 1 produced as described above, and the solid oxide form of Example 1 are shown. The relationship (overvoltage-current characteristic) with the current density (mA / cm < ² >) of the electric current which flows into the fuel cell 1 is shown. 5A and 5B, the horizontal axis indicates the current density (mA / cm ² ), and the vertical axis indicates the overvoltage (V) at the fuel electrode 4.

  As shown in FIGS. 5 (a) and 5 (b), the overvoltage-current characteristic of the solid oxide fuel cell 1 of Example 1 is the fuel in any atmosphere of 700 ° C., 800 ° C., and 900 ° C. When the hydrogen gas was supplied to the electrode 4 and when the ammonia gas was supplied, the increase in overvoltage was suppressed almost unchanged, which was excellent. Therefore, it was confirmed that the solid oxide fuel cell 1 of Example 1 has excellent overvoltage-current characteristics equivalent to those when hydrogen gas is supplied even when ammonia gas is supplied to the fuel electrode 4. .

FIG. 6 shows the current density (mA / cm ² ) of the current flowing through the solid oxide fuel cell 1 when the overvoltage of the fuel electrode 4 of the solid oxide fuel cell 1 of Example 1 is 0.1V. The relationship with the temperature (degreeC) of the atmosphere in which the solid oxide fuel cell 1 of Example 1 was installed is shown. FIG. 6 is created from the experimental results shown in FIGS. 5 (a) and 5 (b). In FIG. 6, the horizontal axis indicates the ambient temperature (° C.), and the vertical axis indicates the current density (mA / cm ² ).

  As shown in FIG. 6, as the temperature of the atmosphere decreased, the current density of the current flowing through the solid oxide fuel cell 1 tended to decrease, but in any atmosphere of 700 ° C., 800 ° C., and 900 ° C. Also in temperature, the current density when ammonia gas is supplied to the fuel electrode 4 of the solid oxide fuel cell 1 shows a large value equivalent to that when hydrogen gas is supplied.

  FIG. 7 shows the overvoltage (V) at the fuel electrode 4 and the fuel electrode 4 when the temperature of the atmosphere during operation of the solid oxide fuel cell 1 of Example 1 is 700 ° C., 800 ° C., and 900 ° C., respectively. Ratio of current density when hydrogen gas is supplied to the current density when ammonia gas is supplied ((current density when ammonia gas is supplied) / (current density when hydrogen gas is supplied)) ). FIG. 7 is created from the experimental results shown in FIGS. 5 (a) and 5 (b). In FIG. 7, the horizontal axis indicates the overvoltage (V), and the vertical axis indicates the ratio.

  As shown in FIG. 7, the above ratio tended to decrease with a decrease in the temperature of the atmosphere, but the above ratio was relative at any temperature of 700 ° C., 800 ° C., and 900 ° C. Shows a large value.

<Comparative Example 1>
A solid oxide fuel cell 1 of Comparative Example 1 having the configuration shown in FIG. 2 was produced in the same manner as in Example 1 except that NiO powder was used instead of Fe ₂ O ₃ powder.

FIG. 8A and FIG. 8B respectively compare the voltage (V) between the oxygen electrode 3 and the fuel electrode 4 of the solid oxide fuel cell 1 of Comparative Example 1 manufactured as described above. The relationship (voltage-current characteristic) with the current density (mA / cm < ² >) of the electric current which flows into the solid oxide fuel cell 1 of Example 1 is shown. 8A and 8B, the horizontal axis indicates the current density (mA / cm ² ), and the vertical axis indicates the voltage (V).

  8A shows that the solid oxide fuel cell 1 of Comparative Example 1 is installed in each atmosphere at 700 ° C., 800 ° C., and 900 ° C., air is supplied to the oxygen electrode 3, and the fuel electrode 4 It is a voltage-current characteristic when hydrogen gas is supplied to. FIG. 8B shows that the solid oxide fuel cell 1 of Comparative Example 1 is installed in each atmosphere at 700 ° C., 800 ° C., and 900 ° C., air is supplied to the oxygen electrode 3, and the fuel electrode 4 It is a voltage-current characteristic when ammonia gas is supplied to.

  As shown in FIGS. 8 (a) and 8 (b), the voltage-current characteristics of the solid oxide fuel cell 1 of Comparative Example 1 are the same in any atmosphere at 700 ° C., 800 ° C., and 900 ° C. Compared to when hydrogen gas was supplied to the pole 4, the spread of the curve in the direction of current density when ammonia gas was supplied was greatly narrowed. Therefore, the voltage-current characteristics when ammonia gas is supplied to the fuel electrode 4 of the solid oxide fuel cell 1 of Comparative Example 1 can be greatly deteriorated as compared with the solid oxide fuel cell of Example 1. confirmed. This is clear when FIGS. 4A to 4B are compared with FIGS. 8A to 8B.

9 (a) and 9 (b), the overvoltage (V) at the anode 4 of the solid oxide fuel cell 1 of Comparative Example 1 manufactured as described above, and the solid oxide form of Comparative Example 1, respectively. The relationship (overvoltage-current characteristic) with the current density (mA / cm < ² >) of the electric current which flows into the fuel cell 1 is shown. 9A and 9B, the horizontal axis indicates the current density (mA / cm ² ), and the vertical axis indicates the overvoltage (V) at the fuel electrode 4.

  As shown in FIGS. 9 (a) and 9 (b), the overvoltage-current characteristics of the solid oxide fuel cell 1 of Comparative Example 1 are the fuel electrode in each atmosphere at 700 ° C., 800 ° C., and 900 ° C. When hydrogen gas was supplied to No. 4, the overvoltage was greatly increased at any time when ammonia gas was supplied. Therefore, the solid oxide fuel cell 1 of Comparative Example 1 is the same as the solid oxide fuel cell of Example 1 in both cases of supplying hydrogen gas to the fuel electrode 4 and supplying ammonia gas. In comparison, the overvoltage-current characteristics were not good. This is clear when FIGS. 5 (a) to 5 (b) are compared with FIGS. 9 (a) to 9 (b).

FIG. 10 shows the current density (mA / cm ² ) of the current flowing through the solid oxide fuel cell 1 when the overvoltage of the fuel electrode 4 of the solid oxide fuel cell 1 of Comparative Example 1 is 0.1V. The relationship with the temperature (degreeC) of the atmosphere in which the solid oxide fuel cell 1 of the comparative example 1 was installed is shown. FIG. 10 is created from the experimental results shown in FIGS. 9 (a) and 9 (b). In FIG. 10, the horizontal axis indicates the ambient temperature (° C.), and the vertical axis indicates the current density (mA / cm ² ).

  As shown in FIG. 10, the solid oxide fuel cell 1 of Comparative Example 1 has a tendency that the current density of the current flowing through the solid oxide fuel cell 1 decreases as the temperature of the atmosphere decreases, and is 700 ° C. In each atmosphere of 800 ° C. and 900 ° C., when hydrogen gas is supplied to the fuel electrode 4 and when ammonia gas is supplied, the current density is higher than that of the solid oxide fuel cell of Example 1. Was not big. This is clear when FIG. 6 and FIG. 10 are compared.

  FIG. 11 shows the overvoltage (V) at the fuel electrode 4 and the fuel electrode 4 when the ambient temperature during operation of the solid oxide fuel cell 1 of Comparative Example 1 is 700 ° C., 800 ° C., and 900 ° C. Ratio of current density when hydrogen gas is supplied to the current density when ammonia gas is supplied ((current density when ammonia gas is supplied) / (current density when hydrogen gas is supplied)) ). FIG. 11 is created from the experimental results shown in FIGS. 9 (a) and 9 (b). In FIG. 11, the horizontal axis represents the overvoltage (V), and the vertical axis represents the above ratio.

  As shown in FIG. 11, as the temperature of the atmosphere decreases, the above ratio tends to increase. At any temperature of 700 ° C., 800 ° C., and 900 ° C., the above ratio is the same as in Example 1. Compared to the solid oxide fuel cell, the value was small. This is clear when FIG. 7 and FIG. 11 are compared.

<Comparative Example 2>
A solid oxide fuel cell 1 of Comparative Example 2 having the configuration shown in FIG. 2 was produced in the same manner as in Example 1 except that Co ₂ O ₃ powder was used instead of Fe ₂ O ₃ powder.

FIGS. 12 (a) and 12 (b) respectively compare the voltage (V) between the oxygen electrode 3 and the fuel electrode 4 of the solid oxide fuel cell 1 of Comparative Example 2 manufactured as described above. The relationship (voltage-current characteristic) with the current density (mA / cm < ² >) of the electric current which flows into the solid oxide fuel cell 1 of Example 2 is shown. 12A and 12B, the horizontal axis indicates the current density (mA / cm ² ), and the vertical axis indicates the voltage (V).

  12A shows that the solid oxide fuel cell 1 of Comparative Example 2 is installed in each atmosphere at 700 ° C., 800 ° C., and 900 ° C., air is supplied to the oxygen electrode 3, and the fuel electrode 4 It is a voltage-current characteristic when hydrogen gas is supplied to. 12B shows that the solid oxide fuel cell 1 of Comparative Example 2 is installed in each atmosphere at 700 ° C., 800 ° C., and 900 ° C., air is supplied to the oxygen electrode 3, and the fuel electrode 4 It is a voltage-current characteristic when ammonia gas is supplied to.

  As shown in FIGS. 12 (a) and 12 (b), the voltage-current characteristics of the solid oxide fuel cell 1 of Comparative Example 2 are as follows: the fuel electrode in each atmosphere at 700 ° C., 800 ° C., and 900 ° C. Compared to when hydrogen gas is supplied to 4, the spread of the curve in the current density direction when ammonia gas is supplied is greatly narrowed. Therefore, in the solid oxide fuel cell 1 of Comparative Example 2, the voltage-current characteristics when ammonia gas is supplied to the fuel electrode 4 are greatly deteriorated as compared with the solid oxide fuel cell of Example 1. It was confirmed. This is clear when FIGS. 4A to 4B are compared with FIGS. 12A to 12B.

13 (a) and 13 (b), the overvoltage (V) at the anode 4 of the solid oxide fuel cell 1 of Comparative Example 2 produced as described above and the solid oxide form of Comparative Example 2, respectively. The relationship (overvoltage-current characteristic) with the current density (mA / cm < ² >) of the electric current which flows into the fuel cell 1 is shown. 13A and 13B, the horizontal axis indicates the current density (mA / cm ² ), and the vertical axis indicates the overvoltage (V) at the fuel electrode 4.

  As shown in FIGS. 13 (a) and 13 (b), the overvoltage-current characteristics of the solid oxide fuel cell 1 of Comparative Example 2 are the fuel electrode in the respective atmospheres of 700 ° C., 800 ° C., and 900 ° C. When hydrogen gas was supplied to No. 4 and when ammonia gas was supplied, the overvoltage was greatly increased. Therefore, the solid oxide fuel cell 1 of Comparative Example 2 is the same as the solid oxide fuel cell of Example 1 in both cases where hydrogen gas is supplied to the fuel electrode 4 and when ammonia gas is supplied. In comparison, the overvoltage-current characteristics were not good. This is clear when FIGS. 5 (a) to 5 (b) are compared with FIGS. 13 (a) to 13 (b).

FIG. 14 shows the current density (mA / cm ² ) of the current flowing through the solid oxide fuel cell 1 when the overvoltage of the fuel electrode 4 of the solid oxide fuel cell 1 of Comparative Example 2 is 0.1V. The relationship with the temperature (degreeC) of the atmosphere in which the solid oxide fuel cell 1 of the comparative example 2 was installed is shown. FIG. 14 is created from the experimental results shown in FIGS. 13 (a) and 13 (b). In FIG. 14, the horizontal axis indicates the ambient temperature (° C.), and the vertical axis indicates the current density (mA / cm ² ).

  As shown in FIG. 14, as the temperature of the atmosphere decreases, the current density of the current flowing through the solid oxide fuel cell 1 also tends to decrease. At each ambient temperature of 700 ° C., 800 ° C., and 900 ° C. The solid oxide fuel cell 1 of Comparative Example 2 is compared with the solid oxide fuel cell of Example 1 in both cases of supplying hydrogen gas to the fuel electrode 4 and supplying ammonia gas. The current density was not large. This is clear when FIG. 6 and FIG. 14 are compared.

  FIG. 15 shows the overvoltage (V) at the fuel electrode 4 and the fuel electrode 4 when the temperature of the atmosphere during operation of the solid oxide fuel cell 1 of Comparative Example 2 is 700 ° C., 800 ° C., and 900 ° C. Ratio of current density when hydrogen gas is supplied to the current density when ammonia gas is supplied ((current density when ammonia gas is supplied) / (current density when hydrogen gas is supplied)) ). FIG. 15 is created from the experimental results shown in FIGS. 13 (a) and 13 (b). In FIG. 15, the horizontal axis indicates the overvoltage (V), and the vertical axis indicates the ratio.

  As shown in FIG. 15, the above ratio tends to increase as the temperature of the atmosphere decreases, and the above ratio is the same as that of Example 1 even at temperatures of 700 ° C., 800 ° C., and 900 ° C. Compared to the solid oxide fuel cell, the value was small. This is clear when FIG. 7 and FIG. 15 are compared.

<Evaluation>
From the above experimental results, the solid oxide fuel cell 1 of Example 1 provided with the fuel electrode 4 made of a mixture of Fe and SDC 20 can be used regardless of whether hydrogen gas or ammonia gas is supplied to the fuel electrode 4. When operated in an atmosphere at a temperature of 700 ° C. to 900 ° C., it was confirmed that the battery had superior performance as compared with the solid oxide fuel cells 1 of Comparative Examples 1 and 2.

  In particular, the solid oxide fuel cell 1 of Example 1 supplied ammonia gas to the fuel electrode 4, and the performance when operated in an atmosphere at a temperature of 700 ° C. to 900 ° C. was that of Comparative Examples 1-2. It was superior to the solid oxide fuel cell 1.

<Example 2>
Instead of Fe ₂ O ₃ powder, except for using a mixed powder prepared by changing the mixing ratio of the Fe ₂ O ₃ powder, NiO powder, respectively in the same manner as in Example 1, the configuration shown in FIG. 2 A solid oxide fuel cell 1 of Example 2 was produced.

Here, as the mixed powder of Fe ₂ O ₃ powder and NiO powder, Fe (iron) with respect to the total number of atoms of Fe (iron) and Ni (nickel) in the fuel electrode 4 of the solid oxide fuel cell 1 of Example 2 is used. Fe ₂ O ₃ powder and NiO powder so that the ratio (%) of the number of atoms of iron is 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 (%), respectively. Was used.

FIG. 18A and FIG. 18B show Example 2 when the overvoltage (V) at the fuel electrode 4 of the solid oxide fuel cell 1 of Example 2 manufactured as described above is 0.15 V, respectively. Current density (mA / cm ² ) of the current flowing through the solid oxide fuel cell 1 and the contents (atomic%) of iron and nickel in the fuel electrode 4 of the solid oxide fuel cell 1 of Example 2. Shows the relationship.

The current density (mA / cm ² ) in FIG. 18 (a) is obtained by installing the solid oxide fuel cell 1 of Example 2 in each atmosphere at 700 ° C., 800 ° C., and 900 ° C. Current density (mA / cm ² ) when air is supplied to the fuel electrode 4 and hydrogen gas is supplied to the fuel electrode 4. Further, the current density (mA / cm ² ) in FIG. 18B is obtained by installing the solid oxide fuel cell 1 of Example 2 in each atmosphere at 700 ° C., 800 ° C., and 900 ° C. Is the current density (mA / cm ² ) when air is supplied to the fuel electrode 4 and ammonia gas is supplied to the fuel electrode 4.

As shown in FIG. 18 (a) and FIG. 18 (b), in any atmosphere of 700 ° C., 800 ° C., and 900 ° C., when the iron content is 30 (atomic%) or more (that is, with iron The ratio of the number of iron atoms to the total number of nickel atoms (100 × (number of iron atoms) / {(number of iron atoms) + (number of nickel atoms)}) (%) is 30% or more) It was confirmed that the current density (mA / cm ² ) of the solid oxide fuel cell 1 of Example 2 increased and the performance tends to be excellent.

In particular, as shown in FIGS. 18 (a) and 18 (b), the solid oxidation of Example 2 was performed when the iron content was 30 (atomic%) or more in a low-temperature atmosphere at 700 ° C. and 800 ° C. It has been confirmed that the current density (mA / cm ² ) of the physical fuel cell 1 is particularly high and the performance tends to be particularly excellent.

  The solid oxide fuel cell 1 of Example 2 has excellent performance when air is supplied to the oxygen electrode 3 of the solid oxide fuel cell 1 of Example 2 and ammonia gas is supplied to the fuel electrode 4. The reason is that an alloy containing iron is generally used as the ammonia gas synthesis catalyst, and such an alloy containing iron is also excellent as an ammonia gas dissociation catalyst. It is considered that excellent performance is obtained when an alloy containing iron (iron-nickel alloy) is used for the fuel electrode 4 of the physical fuel cell 1.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be suitably used in a fuel electrode for a solid oxide fuel cell, a solid oxide fuel cell, and a method for operating a solid oxide fuel cell.

  1 Solid oxide fuel cell, 2 electrolyte, 3 oxygen electrode, 4 fuel electrode, 5 reference electrode.

Claims (7)

A solid oxide fuel cell fuel electrode for operating a solid oxide fuel cell in an atmosphere of 900 ° C or lower,
Including iron and metal oxides,
The metal oxide is a metal oxide represented by the following composition formula (I):
RE _x Ce _1-x O _{2- (x / 2)} (I)
In the composition formula (I), RE is at least one metal selected from the group consisting of Sm, Gd, Y, La and Nd, and x represents a real number satisfying 0 ≦ x <0.5. Fuel electrode for solid oxide fuel cells.   2. The solid electrode according to claim 1, which is a solid oxide fuel cell fuel electrode for supplying a fuel containing a compound gas of nitrogen and hydrogen to operate the solid oxide fuel cell. 3. Fuel electrode for oxide fuel cells. A fuel electrode for a solid oxide fuel cell for supplying a fuel containing a compound gas of nitrogen and hydrogen to operate the solid oxide fuel cell,
A fuel electrode for a solid oxide fuel cell, comprising iron and a metal oxide. Further comprising nickel,
The ratio of the number of atoms of the iron to the total number of atoms of the iron and the nickel in the solid oxide fuel cell anode is 30% or more. A fuel electrode for a solid oxide fuel cell as described.   A solid oxide fuel cell comprising the solid oxide fuel cell fuel electrode according to claim 1 and an electrolyte. The electrolyte is represented by the following composition formula (II):
_{La 1-s Sr s Ga 1-} (u + v) Co u Mg v O w ... (II)
In the composition formula (II), s represents a real number satisfying 0 ≦ s ≦ 0.25, u represents a real number satisfying 0 ≦ u ≦ 0.1, and v represents 0.05 ≦ v ≦ 0.25. 6. The solid oxide fuel cell according to claim 5, wherein a real number satisfying the condition is shown, and w is a real number satisfying 2.7 ≦ w ≦ 3.025. A method of operating a solid oxide fuel cell according to claim 5, comprising:
Installing the solid oxide fuel cell in an atmosphere of 900 ° C. or lower;
Supplying a fuel containing a compound gas of nitrogen and hydrogen to the fuel electrode for the solid oxide fuel cell of the solid oxide fuel cell, and a method for operating the solid oxide fuel cell.

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