JP5112711B2 - Method for producing electrode for solid oxide fuel cell and solid oxide fuel cell - Google Patents

Description

  The present invention relates to a method for producing an electrode for a solid oxide fuel cell and a solid oxide fuel cell.

A solid oxide fuel cell (SOFC) has a fuel electrode and an air electrode separated by an oxygen ion conductive solid electrolyte, supplies fuel gas to the fuel electrode, and supplies oxidant gas to the air electrode. This is a generic term for a battery that is supplied and causes an electrochemical reaction to proceed at each electrode to extract electric power to the outside, and a solid oxide is used as a constituent material of the battery. Ni-stabilization consisting of nickel (Ni) and zirconia as a fuel electrode material that controls the electrochemical oxidation reaction between oxygen ions supplied from oxygen ion conductive solid electrolyte and fuel gas in solid oxide fuel cells Zirconia cermets, cermets of ceria doped with Ni and rare earth elements, and cermets of Ni and lanthanum gallate (LaGaO ₃ ) -based materials are used. Among these, Ni is responsible for electron conduction in the fuel electrode and acts as a catalyst for the difference in electrochemical reaction. Here, the reason why Ni is frequently used is that Ni satisfies a number of required conditions such as excellent reaction stability between materials with respect to the solid electrolyte, and is also low in cost. .

  On the other hand, in the solid oxide fuel cell, hydrocarbon fuels such as natural gas and coal gasification gas are assumed as the fuel gas, not limited to purified hydrogen. When a hydrocarbon fuel is used, the fuel electrode also serves as a catalyst for reforming or directly reacting the hydrocarbon fuel. In a solid oxide fuel cell using a hydrocarbon-based fuel, carbon is generated by a hydrocarbon decomposition reaction represented by the following formula (1), and the electrode active point is set by depositing this carbon on the fuel electrode. There is a problem in that it deactivates and blocks the porous fuel electrode to prevent gas diffusion.

C _n H _{2n + 2} → nC + (n + 1) H ₂ (1)

  For the purpose of avoiding the above-mentioned problems, a hydrocarbon-based fuel is heated and reacted with a gas containing water vapor or carbon dioxide as a main component, reformed to hydrogen and carbon monoxide, and then used as a fuel for a solid oxide fuel cell. It is common to take a method.

  However, in a fuel cell including this type of reforming process, the reforming reaction does not contribute to power generation and is an endothermic reaction that requires heat for the reaction. There is a loss, and it becomes a problem for high efficiency including thermoelectric supply.

  As a means to solve these problems, in a solid oxide fuel cell using methane, which is the main component of natural gas, as a fuel, a highly ionic conductive substance is used as an electrolyte material, and a reforming reaction can be performed without adding water vapor. A method of performing reforming and power generation without causing carbonaceous precipitation by causing a reaction including a partial oxidation reaction represented by the following formula (2) as an electrode reaction has been found (see Non-Patent Document 1).

CH ₄ + 1 / 2O ₂ = CO + 2H ₂ (2)

  This reaction not only functions as a power generation reaction itself, but also produces carbon monoxide and hydrogen that can be used as fuel for fuel cells. Therefore, the generated fuel is combined with other fuel cells to generate power. By waking up, it is possible to generate electricity with high efficiency. However, this method is only being studied in short-term trials.

As is well known in any of the above-described solid oxide fuel cells, the electrode reaction field is the three-layer interface. For example, the above-described Ni / LaGaO _{3 of} the fuel electrode / electrolyte material system is used. In the material system, the portion where Ni, LaGaO ₃ and fuel gas are in contact corresponds to the three-layer interface. Therefore, an increase in the amount of electrons generated due to an increase in the three-layer interface of the fuel electrode and an efficient supply of the generated electrons to the external circuit are important for improving the output in the solid oxide fuel cell.

  In the case where a hydrocarbon gas is used as the fuel, the reforming of the hydrocarbon fuel or the direct reaction on the electrode and the carbon deposition by the decomposition of the hydrocarbon have a competitive relationship. For this reason, in order to efficiently reform hydrocarbon gas or increase the rate of direct reaction on the electrode to generate electric power efficiently, for example, highly dispersed metal catalyst in the fuel electrode, etc. It is important to improve the catalyst capacity by the above means. In response to this requirement, a ceria-based material is used as the skeleton of the fuel electrode, and Ni and noble metal elements (Ru, Pt, etc.) are supported in a highly dispersed state, thereby providing the fuel electrode with mixed conductivity and a fuel electrode catalyst. A method for improving the activity has been proposed (see Non-Patent Document 2). In addition, by adjusting the particle size and particle size ratio of NiO powder and zirconia powder, which are the raw material powder (powder) of the fuel electrode, studies have been made to increase the three-layer interface by highly dispersing Ni particles and zirconia particles. (See Non-Patent Document 3).

Ishihara et al., 8th SOFC Research Presentation, p93, 1999 Uchida et al., 69th Annual Meeting of Electrochemical Society, p293, 2002 Ito et al., 11th SOFC Research Presentation Summary, p1,2002

However, although the initial power generation characteristics are improved by adjusting the particle size and particle size ratio of the NiO powder and zirconia powder described above, Ni tends to aggregate in a high temperature, reducing atmosphere. This is a solid oxide fuel. This is one factor of performance deterioration with time during battery operation.
In addition, the addition of a noble metal to the fuel electrode is effective for improving the activity of the electrode and improving the carbon deposition resistance, but there are problems in terms of cost and long-term stability.

  In addition, even when Ni is added, since the substance to be added is a single Ni, even if the added Ni is supported in a highly dispersed state, these will aggregate to reduce the three-layer interface, resulting in long-term electrode loss. There was a problem of being alive.

  The technique of Non-Patent Document 3 is intended for the case where hydrogen is used as a fuel. However, when a hydrocarbon-based fuel is used, it may be inactive against the reforming of fuel and carbon deposition. Required.

  As described above, in the conventional technology, it is not easy to stably maintain the initial performance of the electrodes constituting the solid oxide fuel cell over a long period of time, and when a hydrocarbon fuel is used, There was a problem that high activity of the electrode could not be obtained.

  The present invention has been made in order to solve the above-described problems. The solid oxide fuel cell electrode uses a hydrocarbon-based fuel whose initial performance is stably maintained over a long period of time. The purpose is to obtain high activity even in some cases.

The method for producing an electrode for a solid oxide fuel cell according to the present invention includes a first step in which a porous fuel electrode composed of a sintered body containing a metal oxide is formed, and 2 A second step in which a solution of an organic acid compound containing two or more metals is impregnated in the porous pores of the fuel electrode, and the fuel electrode impregnated with the solution is heated to be contained in the solution. The composite oxide composed of the metal is at least a third step in which the composite oxide is disposed in the porous pores, and the composite oxide is represented by ( 2-x) ((Ce _1-y M ^α ) O ₂ ) −x ( Ni ₂ O) (0.2 ≦ x ≦ 1.2, 0 <y ≦ 0.4, M ^α = Sm, Y) .

  In the method for producing an electrode for a solid oxide fuel cell, the organic acid has an organic acid having 1 to 4 COOH groups, an organic acid having 1 to 3 OH groups, and 1 to 4 N. Any material selected from organic acids may be used. The solution may be prepared by adding ethylene glycol in addition to the organic acid compound and heating to 100 to 150 ° C. The solution may contain an organic binder in addition to the organic acid compound.

  A solid oxide fuel cell according to the present invention includes an electrode manufactured by the above-described method for manufacturing an electrode for a solid oxide fuel cell.

As described above, in the present invention, a solution of an organic acid compound containing two or more metals is impregnated in the porous pores of the fuel electrode, and then heated to be contained in the solution. ( 2-x) ((Ce _1-y M ^α ) O ₂ ) -x ( Ni ₂ O) (0.2 ≦ x ≦ 1.2, 0 <y ≦ 0.4, M ^α = Sm, Y) is arranged in a porous hole. As a result, according to the present invention, the initial performance of the electrode of the solid oxide fuel cell can be stably maintained over a long period of time, and high activity can be obtained even when a hydrocarbon fuel is used. An excellent effect that it can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiment, the description will focus on the results of a power generation test using a solid oxide fuel cell using a fuel electrode having a Ni-stabilized zirconia-based material as a skeleton (base). Is not limited to Ni-stabilized zirconia materials, and the same applies to fuel electrodes using Ni-lanthanum gallate materials as a base material. In the following, cobalt (Co) is used as a representative example of the metal element L ^α constituting the composite oxide introduced into the fuel electrode. However, the present invention is not limited to this, and the same effect can be obtained when Ni is used. .

[Embodiment 1]
First, the manufacturing method of the electrode for solid oxide fuel cells in Embodiment 1 of this invention is demonstrated. FIG. 1 is an explanatory diagram for explaining a method of manufacturing a solid oxide fuel cell electrode according to an embodiment.

First, as a Ni-stabilized zirconia-based material used as a base (skeleton) of a fuel electrode, stabilized zirconia (8YSZ) and NiO in which 8 mol% of Y ₂ O ₃ similar to the electrolyte layer is dissolved as a raw material powder, Are mixed so that the content of NiO is 60 w%, and a slurry in which these mixed powders are dispersed in an organic binder is prepared. For example, a slurry in which the mixed powder is dispersed in an aqueous solution (dispersion medium) in which polyvinyl alcohol (PVA) is dissolved is prepared.

  Next, as shown in FIG. 1A, a YSZ substrate 101 made of 8YSZ is prepared, and the slurry is applied to one surface of the YSZ substrate 101 by, for example, a screen printing method, and is circular in plan view with a diameter of about 1 cm. The fuel electrode coating film 102 is formed. The YSZ substrate 101 is, for example, a disk-shaped structure having a diameter of 3.5 cm and a thickness of 0.35 mm. The YSZ substrate 101 becomes an electrolyte layer of the fuel cell.

  Next, the fuel electrode coating film 102 formed on the YSZ substrate 101 is sintered by heating and sintering at 1400 ° C. for 2 hours in an air atmosphere, and as shown in FIG. It is assumed that the fuel electrode 103 serving as a mother body is formed on the surface. For example, the fuel electrode 103 may be formed with a film thickness of about 0.02 to 0.1 mm. The fuel electrode 103 formed in this way is a sintered body of a mixed powder of 8YSZ powder and NiO powder, and has a porous state having a plurality of pores present between the respective sintered body particles. Formed. In addition, what is necessary is just to perform the temperature of a heating in the range of 1200-1600 degreeC. The thickness may be in the range of the thickness that provides the mechanical strength required when stacking single cells to form a stack structure.

Next, a slurry in which a powder of LaNi _0.6 Fe _0.4 O ₃ is dispersed in a medium containing an aqueous solution of polyvinyl alcohol is prepared, and the prepared slurry is applied to the other surface of the YSZ substrate 101 by a screen printing method. As shown in FIG. 1C, the air electrode coating film 104 having a diameter of about 1 cm and having a circular shape in plan view is formed.

Next, the air electrode coating film 104 formed on the YSZ substrate 101 is sintered by heating and sintering at 1000 ° C. for 2 hours in an air atmosphere, and as shown in FIG. 1D, the other of the YSZ substrate 101 is sintered. It is assumed that the air electrode 105 is formed on the surface. For example, the air electrode 105 should just be formed in the film thickness of about 0.02-0.1 mm. The air electrode 105 is also a sintered body of powder of LaNi _0.6 Fe _0.4 O ₃ , and is formed in a porous state having a plurality of pores present between the respective sintered body particles. As a result, a single cell in which the fuel electrode 103 is formed on one surface of the YSZ substrate 101 and the air electrode 105 is formed on the other surface is obtained.

Next, as shown in FIG. 1E, the exposed surfaces of the YSZ substrate 101 and the air electrode 105 other than the fuel electrode 103 are covered with a mask layer 111. These are evacuated to a predetermined pressure (first pressure) inside a container having a composition of (2-x) (CeO ₂ ) -x (CoO) (0.2 ≦ x ≦ 1.2). Immerse in a solution of an organic acid metal salt (organic acid compound) that can be a complex oxide. For example, it is immersed in a solution of a gluconic acid compound. Note that (2-x) (CeO ₂ ) -x (CoO) is (2-x) (CeO ₂ ) -x (L ^α O) (0.2 ≦ x ≦ 1.2, L ^α = Co, This is a case where L ^α of Ni) is Co.

Next, by raising the internal pressure of the container to atmospheric pressure, for example, as shown in FIG. 1 (f), the fuel electrode 103a impregnated with the above solution was formed in a plurality of porous pores. State. Thereafter, after this single cell (fuel electrode 103a) is dried, the dried single cell is subjected to heat treatment at 850 ° C. for 4 hours in the atmosphere. Accordingly, as shown in FIG. 1 (g), (2-x) (CeO ₂ ) -x (CoO) (0.2 ≦ x ≦ 1.2) is contained in the plurality of porous pores. Thus, a state is obtained in which the composite oxide-introduced fuel electrode 113 having the interface resistance value and the like in a desired state (value) is formed. In addition, the temperature of heat processing should just be the range of 800-900 degreeC.

  According to the solid oxide fuel cell using the composite oxide-introduced fuel electrode 113 thus obtained, the initial performance is stably maintained over a long period of time, and high activity is achieved even when using a hydrocarbon fuel. Can be obtained.

  As described above, when the fuel electrode into which the composite oxide was introduced was observed with an electron microscope, a film with a thickness of 50 nm to 150 nm was formed on the surface of the sintered particles in each porous pore. It was confirmed. Further, this film was confirmed to be the above complex oxide by X-ray diffraction measurement.

  In the above description, the fuel electrode 103 is immersed in a solution of the gluconic acid compound that can be the composite oxide. However, the present invention is not limited to this. For example, after adding ethylene glycols to the above solution and heating it to 100 to 150 ° C., the fuel electrode 103 is immersed and the fuel electrode 103 is impregnated with the solution, and then the heat treatment is performed as described above. May be performed. Moreover, you may make it use organic binders, such as polyvinyl alcohol, instead of ethylene glycol. For example, 1 to 5 wt% of polyvinyl alcohol may be added to the above solution. By impregnating the resin-added solution as described above, the adhesion between the sintered particles (skeleton) constituting the fuel electrode and the impregnated solution can be improved.

  Examples of the ethylene glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and isopropyl glycol. These ethylene glycols may be used in an amount of 0.1 to 10 mol added to the composite oxide produced by heating and baking.

  As the organic binder, vinyl polymer compounds, cellulose polymer compounds, acrylic polymer compounds, and the like are applicable. Examples thereof include vinyl polymer compounds such as polyvinyl alcohol and polyvinyl butyral, cellulose polymer compounds such as methyl cellulose and hydroxypropyl cellulose, and acrylic polymer compounds such as poly (meth) acrylate.

By the way, in general, when a reduction treatment of a fuel electrode is performed in a hydrogen atmosphere at a normal solid oxide fuel cell operating temperature of 650 to 1000 ° C., NiO is reduced to a metallic Ni, and the electrode reaction is caused. At the same time, it becomes a catalyst for controlling the electrons and a medium for transferring electrons in the fuel electrode. In the fuel electrode into which the composite oxide in Embodiment 1 as described above is introduced, (2-x) (CeO ₂ ) which is the introduced composite oxide together with Ni constituting the base (skeleton). Even in -x (CoO), Co in a metallic state is generated from the composite oxide by the same reduction as described above. Ni and Co particles are generated (precipitated) on the surface of the sintered particles in each porous pore. This state has been confirmed by observation with an electron microscope and X-ray diffraction measurement. By observation with an electron microscope, a particle having a particle diameter of 5 to 50 nm is confirmed in the fuel electrode into which (2-x) (CeO ₂ ) -x (CoO) is introduced. It has been confirmed that.

On the other hand, when a solution of a gluconic acid compound that can be an oxide of only Co, for example, cobalt gluconate only is impregnated in a fuel electrode and heated and fired, a reduction treatment similar to the above results in a particle size of 200 nm or more It has been confirmed that Co is generated.
From the above, it can be seen that when introduced into the fuel electrode in the form of a complex oxide, the size of the metal fine particles produced by the reduction becomes smaller.

  Next, the characteristics of the composite oxide-introduced fuel electrode 113 produced by the manufacturing method described above will be described. Below, the solid oxide fuel cell is assembled using the single cell described above, and the measurement results of the assembled solid oxide fuel cell are shown. First, the configuration of the solid oxide fuel cell will be described. In the assembled solid oxide fuel cell, as shown in FIG. 2A, the fuel electrode 201 is disposed on one side of the electrolyte layer 202 serving as a support substrate, and the air electrode 203 is disposed on the other side of the electrolyte layer 202. A single cell provided with a reference electrode 204 on the air electrode side of the electrolyte 202 is used. The reference electrode 204 is formed in the same manner as the air electrode 203. Further, a solid oxide fuel cell as shown in the cross-sectional view of FIG. The solid oxide fuel cell shown in FIG. 2B will be described. The fuel electrode 201 of the single cell is provided with a current collector layer 211 made of Au mesh, and the air electrode 203 has a current collector made of platinum mesh. An electric conductor layer 212 is provided.

  Further, on the fuel electrode 201 side of the single cell, a fuel gas exhaust pipe 213 made of aluminum oxide is fixed to the periphery of the electrolyte layer 202 via a ring 214, and inside the fuel gas exhaust pipe 213. A fuel gas supply pipe 215 is arranged. On the other hand, on the air electrode 203 side of the single cell, an oxidant gas exhaust pipe 216 made of aluminum oxide is fixed to the periphery of the electrolyte layer 202 via a ring 217, and the oxidant gas exhaust pipe 216 An oxidant gas supply pipe 218 is disposed inside. The ring 214 and the ring 217 are made of glass having a softening point near the test temperature. Note that the reference electrode 204 is disposed in a region outside the exhaust pipe 216. A terminal wire 219 made of Au is connected to the current collector layer 211, and a terminal wire 220 made of platinum is connected to the current collector layer 212. A terminal wire 221 made of platinum is connected to the reference electrode 204. Note that the solid oxide fuel cell having the above-described configuration is disposed inside the electric furnace 230.

In the solid oxide fuel cell configured as described above, the fuel gas is supplied from the fuel gas supply pipe 215 to the fuel electrode 201, and the oxidant gas is supplied from the oxidant gas supply pipe 218 to the air electrode 203. Then, test the power generation operation. This power generation operation is performed in the electric furnace 230 while being heated to 800 ° C. Here, as the fuel gas, hydrogen (humidified H ₂ ) added with 3 vol% of water vapor, methane (64% CH ₄ ) added with 64 vol% of water vapor, and dry methane (CH ₄ ) are used. 64% CH ₄ is water vapor volume: methane volume = 2: 1. On the other hand, air (oxygen: nitrogen = 1: 4, volume ratio) is used as the oxidant gas.

  Further, before each test, Co is precipitated in a metallic state from the composite oxide introduced into the fuel electrode by a reduction treatment in which the fuel electrode is in an atmosphere of dry hydrogen. Even in this state, the same measurement as described above is performed (test atmosphere: dry hydrogen). For comparison, the same measurement is performed for a solid oxide fuel cell similar to the prior art in which no complex oxide is introduced.

In the test, overvoltage measurement at the fuel electrode using the current interruption method and cell interface resistance at the fuel electrode obtained from the AC impedance method near the open circuit voltage (OCV) were measured, To do. In the evaluation of the overvoltage characteristic by the current interruption method, the voltage of the test cell is around 0.6 to 0.8V. Further, the interfacial resistance value obtained by the AC impedance method has a representative value of the overvoltage at the fuel electrode at a current value of 0.5 A / cm ² flowing per unit area of the electrode.

  In addition, after the test in the power generation state described above, the surface of the test cell is visually observed. In addition, the concentration of carbon atoms contained in each of the supplied gas and the exhausted gas was measured with a gas chromatograph, the measured carbon atom supply amount and carbon atom emission amount were measured, and the difference between these was supplied. The state of carbonaceous precipitation from hydrocarbons in the fuel gas is evaluated.

In the evaluation, a sample unit cell composed of a complex oxide-introduced fuel electrode 113 in which a complex oxide was introduced into a plurality of porous pores was produced by the manufacturing method shown in FIG. 1, and this sample unit cell was used. Then, the solid oxide fuel cell shown in FIG. In addition, three types of sample single cells in which x of (2-x) (CeO ₂ ) -x (CoO), which is a composite oxide to be introduced, are set to 0.4, 1.0, and 1.2 are manufactured. Measurement is performed on a single sample cell. As shown in Table 1 below, in any fuel gas condition, a sample in which a composite oxide is added compared to a conventional solid oxide fuel cell in which a composite oxide is not introduced (added) The single cell has a greatly reduced interface resistance of about 1/10 to 1/26. Further, the overvoltage at the fuel electrode is reduced to about 1/3 to 1/5. As can be seen from Table 1, under the condition of x = 1.0, the interface resistance and overvoltage are the lowest.

  From these facts, it was confirmed that excellent power generation characteristics were exhibited by introducing a complex oxide into the fuel electrode. In particular, when the fuel gas to be supplied is in a dry state such as dry hydrogen or dry methane, the effect of the above reduction is greater than the condition in which water vapor is added. In any of the above-described tests, the supply amount of carbon atoms and the discharge amount of carbon atoms were balanced in the gas chromatographic comparison between the supply gas and the exhaust gas performed at the initial stage of the power generation state. From this, it is considered that in the power generation of the solid oxide fuel cell using the fuel electrode manufactured by the manufacturing method according to the first embodiment, carbonaceous precipitation does not occur even when a hydrocarbon fuel is used. .

Further, in the above power generation test conditions in which the test gas in which the composite oxide is introduced by the manufacturing method of the first embodiment and the test cell in which the conventional composite oxide is not introduced are dry methane as the fuel gas, After holding the current value flowing per unit area of each electrode at 0.5 A / cm ² for 500 hours, after switching the gas supplied to the fuel electrode to inert nitrogen gas and returning to normal temperature (25 ° C.), The state of the fuel electrode in each test cell was observed. As a result, a black deposit was visually confirmed on the fuel electrode of the test cell into which the complex oxide was not introduced. The precipitate was confirmed to be carbonaceous by elemental analysis. On the other hand, carbonaceous deposition was not confirmed on the fuel electrode of the test cell into which the composite oxide was introduced.

  In the above-described test, an inert nitrogen gas is introduced instead of the fuel gas into the fuel electrode of the test cell into which the composite oxide has been introduced, and the normal temperature (about 25 ° C.) is maintained while maintaining the reduction treatment state in the fuel electrode. After returning, the fuel electrode of the test cell was observed with an electron microscope. In any of the sample cells under any conditions, the surface of the sintered particle was 5 to 20 nm in the plurality of pores in the porous state of the fuel electrode. It was confirmed that fine particles were generated.

In the first embodiment described above, the fuel electrode is made of a mixed powder of 8YSZ and NiO and the electrolyte layer is made of 8YSZ. However, the present invention is not limited to this. For example, an electrolyte layer (substrate) is formed from ZrO ₂ (10SZSZ) in which 10 mol% of Sc ₂ O ₃ and 1 mol% of Al ₂ O _3, which are Ni—ZrO ₂ fuel electrode materials, are dissolved, and 10 SZSZ. A fuel electrode may be composed of a mixture of NiO and NiO, and a complex oxide may be introduced into the fuel electrode. In this case, when the test was performed in the same manner as described above, the same effect was confirmed as shown in Table 2 below.

  In the above description, the test temperature was set to 800 ° C., but the same result (effect) as described above was confirmed in the test temperature range of 650 to 1000 ° C.

  As described above, a metal active in the power generation reaction of fuel gas (Co, Ni, etc.) is introduced into the fuel electrode in the form of a composite oxide, and the metal fine particles are precipitated from the composite oxide in a reduced state such as in a hydrogen atmosphere. As a result, it was confirmed that the reaction capacity of the fuel electrode was increased and, at the same time, the effect of suppressing the precipitation of carbonaceous matter due to the decomposition of the hydrocarbon fuel was exhibited over a long-term test. In addition, these effects are remarkable in improving the characteristics of the electrode reaction of the fuel gas when using a dry fuel gas to which water vapor is not added. When using the dry fuel gas, the fuel electrode according to the present invention is used. Was confirmed to be effective.

[Embodiment 2]
Next, a second embodiment of the present invention will be described. In the manufacturing method of the electrode for the solid oxide fuel cell according to the second embodiment, a part of the Ce site when x = 1 in (2-x) (CeO ₂ ) -x (CoO) is converted to samarium (Sm Or a composite oxide having a composition of ((Ce _1-y M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4) substituted with yttrium (Y). In the same manner as in the first embodiment, a fuel electrode is produced. In the second embodiment, gluconic acid that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4). A compound electrode-introduced fuel electrode is produced by immersing and impregnating a fuel electrode in a compound solution, followed by heating and firing. For example, an aqueous solution in which cerium gluconate, cobalt gluconate, and M ^α glucone oxide are dissolved may be used. Note that ((Ce _1-y M ^α _y ) O ₂ )-(CoO) is (2-x) ((Ce _1-y M ^α _y ) O ₂ ) -x (L ^α O) (0.2 ≦ x ≦ 1.2, 0 <y ≦ 0.4, L ^α = Co, Ni) where x is 1 and L ^α is Co.

Also in the second embodiment, when the fuel electrode into which the composite oxide is introduced is observed with an electron microscope, a film of 50 nm to 150 nm is formed on the surface of the sintered body particle in each porous pore. It was confirmed that Further, this film was confirmed to be the above complex oxide by X-ray diffraction measurement. Further, when the reduction treatment is performed in the same manner as in the first embodiment, Co in a metallic state is generated from the composite oxide in the fuel electrode into which the composite oxide has been introduced. This state has been confirmed by observation with an electron microscope and X-ray diffraction measurement. By observation with an electron microscope, particles having a particle diameter of 5 to 50 nm were confirmed in the fuel electrode into which ((Ce _1-y M ^α _y ) O ₂ )-(CoO) was introduced. It has been confirmed that the particles are Co.

  Also in the second embodiment, after adding ethylene glycol to the solution and heating it to 100 to 150 ° C., the fuel electrode is immersed and the solution is impregnated in the fuel electrode. Heat treatment may be performed in the same manner as described above. Moreover, you may make it use organic binders, such as polyvinyl alcohol, instead of ethylene glycol. For example, 1 to 5 wt% of polyvinyl alcohol may be added to the above solution. By impregnating the resin-added solution as described above, the adhesion between the sintered particles (skeleton) constituting the fuel electrode and the impregnated solution can be improved.

Next, as described above, glucone that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4). The characteristics of the composite oxide-introduced fuel electrode produced using the acid compound solution will be described using the results of producing and testing a sample cell in the same manner as in the first embodiment. In this test, _{y of} ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4), which is a compound to be introduced, is 0.05. , 0.2, and 0.4, three types of sample cells are prepared, and measurement is performed on each sample cell.

As a result of this test, as shown in Table 3 below, in any fuel gas condition, the composite oxide was compared with the conventional solid oxide fuel cell in which the composite oxide was not introduced (added). The added sample single cell has a reduced interface resistance. Moreover, the overvoltage at the fuel electrode is also reduced. Moreover, the condition of y = 0.2 has the lowest interface resistance and overvoltage. In the second embodiment, the fuel electrode overvoltage is larger than that in the first embodiment. This is because the addition of the metal component M ^alpha, decreases the concentration of Co (composition ratio) of the composite oxide to be introduced, because the amount of Co in a metal state to be generated in the fuel electrode is reduced.

As shown above, gluconic acid that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4) By using the compound solution, it was confirmed that even if the complex oxide was introduced into the fuel electrode, the reaction capacity in the fuel electrode was further enhanced. _{Incidentally, ((Ce 1-y Sm} y) O 2) - (CoO) and _{((Ce 1-y Y y} ) O 2) - is not limited to (CoO), (2-x ) (CeO 2) -x (CoO) When x = 1, even in the case of a complex oxide in which some Ce sites are substituted for Sm and some Ce sites are substituted for Y, It has been confirmed that the same effect as described above is exhibited when the total dissolution rate is in the range of 0 <y ≦ 0.4. Further, in the second embodiment, x = 1 in (2-x) (CeO ₂ ) −x (CoO). However, the present invention is not limited to this, and in the range of 0.2 ≦ x ≦ 1.2, Similar effects have been confirmed. In the second embodiment, the same results (effects) as described above were confirmed in the test temperature range of 650 to 1000 ° C.

[Embodiment 3]
Next, a third embodiment of the present invention will be described. In the manufacturing method of the electrode for the solid oxide fuel cell according to the third embodiment, a part of Ce sites when S = 1 or Sm or Y in (2-x) (CeO ₂ ) -x (CoO). Embodiment 1 Using a composite oxide having a composition of ((Ce _1-y M ^α _y ) O ₂ ) — (CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4) substituted with In the same manner as described above, a fuel electrode is manufactured. In the third embodiment, malic acid that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4). A fuel electrode is immersed and impregnated in a compound (organic acid metal salt) solution, and this is heated and fired to produce a composite oxide-introduced fuel electrode. For example, an aqueous solution in which cerium malate, cobalt malate, and ^Mα malate are dissolved may be used.

Also in the third embodiment, when the fuel electrode into which the composite oxide is introduced is observed with an electron microscope, a film of 50 nm to 150 nm is formed on the surface of the sintered particles in each porous pore. It was confirmed that Further, this film was confirmed to be the above complex oxide by X-ray diffraction measurement. Further, when the reduction treatment is performed in the same manner as in the first embodiment, Co in a metallic state is generated from the composite oxide in the fuel electrode into which the composite oxide has been introduced. This state has been confirmed by observation with an electron microscope and X-ray diffraction measurement. By observation with an electron microscope, particles having a particle diameter of 5 to 50 nm were confirmed in the fuel electrode into which ((Ce _1-y M ^α _y ) O ₂ )-(CoO) was introduced. It has been confirmed that the particles are Co.

  Also in the third embodiment, after adding ethylene glycol to the above solution and heating it to 100 to 150 ° C., the fuel electrode is immersed, and this solution is impregnated in the fuel electrode. Heat treatment may be performed in the same manner as described above. Moreover, you may make it use organic binders, such as polyvinyl alcohol, instead of ethylene glycol. For example, 1 to 5 wt% of polyvinyl alcohol may be added to the above solution. By impregnating the resin-added solution as described above, the adhesion between the sintered particles (skeleton) constituting the fuel electrode and the impregnated solution can be improved.

Next, as described above, an apple that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4). The characteristics of the composite oxide-introduced fuel electrode produced using the acid compound solution will be described using the results of producing and testing a sample cell in the same manner as in the first embodiment. Also in this test, _{y of} ((Ce _1-y M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4), which is a compound to be introduced, is 0.05. , 0.2, and 0.4, three types of sample cells are prepared, and measurement is performed on each sample cell.

As a result of this test, as shown in Table 4 below, in any fuel gas condition, the composite oxide was compared with the conventional solid oxide fuel cell in which the composite oxide was not introduced (added). The added sample single cell has a reduced interface resistance. Moreover, the overvoltage at the fuel electrode is also reduced. Moreover, the condition of y = 0.2 has the lowest interface resistance and overvoltage. In the third embodiment, the fuel electrode overvoltage is larger than that in the first embodiment. This is because the addition of the metal component M ^alpha, decreases the concentration of Co (composition ratio) of the composite oxide to be introduced, because the amount of Co in a metal state to be generated in the fuel electrode is reduced.

As shown above, malic acid that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4) By using the compound solution, it was confirmed that even if the complex oxide was introduced into the fuel electrode, the reaction capacity in the fuel electrode was further enhanced. _{Incidentally, ((Ce 1-y Sm} y) O 2) - (CoO) and _{((Ce 1-y Y y} ) O 2) - is not limited to (CoO), (2-x ) (CeO 2) -x (CoO) When x = 1, even in the case of a complex oxide in which some Ce sites are substituted for Sm and some Ce sites are substituted for Y, It has been confirmed that the same effect as described above is exhibited when the total dissolution rate is in the range of 0 <y ≦ 0.4. In the third embodiment, x = 1 is set in (2-x) (CeO ₂ ) −x (CoO). However, the present invention is not limited to this, and in the range of 0.2 ≦ x ≦ 1.2, Similar effects have been confirmed. In the third embodiment, the same results (effects) as described above were confirmed in the test temperature range of 650 to 1000 ° C.

[Embodiment 4]
Next, a fourth embodiment of the present invention will be described. In the manufacturing method of the electrode for the solid oxide fuel cell according to the fourth embodiment, a part of the Ce site when x = 1 in (2-x) (CeO ₂ ) -x (CoO) is converted into Sm or Y Embodiment 1 Using a composite oxide having a composition of ((Ce _1-y M ^α _y ) O ₂ ) — (CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4) substituted with In the same manner as described above, a fuel electrode is manufactured. In the fourth embodiment, a lactic acid compound that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4). A fuel electrode is immersed and impregnated in a solution of (organic acid metal salt), and this is heated and fired to produce a composite oxide-introduced fuel electrode. For example, lactate, cerium, lactic cobalt, and may be used an aqueous solution of lactic acid product is dissolved in M ^alpha.

Also in the fourth embodiment, when the fuel electrode into which the composite oxide is introduced is observed with an electron microscope, a film of 50 nm to 150 nm is formed on the surface of the sintered particles in each porous pore. It was confirmed that Further, this film was confirmed to be the above complex oxide by X-ray diffraction measurement. Further, when the reduction treatment is performed in the same manner as in the first embodiment, Co in a metallic state is generated from the composite oxide in the fuel electrode into which the composite oxide has been introduced. This state has been confirmed by observation with an electron microscope and X-ray diffraction measurement. By observation with an electron microscope, particles having a particle diameter of 5 to 50 nm were confirmed in the fuel electrode into which ((Ce _1-y M ^α _y ) O ₂ )-(CoO) was introduced. It has been confirmed that the particles are Co.

  Also in the fourth embodiment, after adding ethylene glycol to the above solution and heating it to 100 to 150 ° C., the fuel electrode is immersed, and this solution is impregnated in the fuel electrode. Heat treatment may be performed in the same manner as described above. Moreover, you may make it use organic binders, such as polyvinyl alcohol, instead of ethylene glycol. For example, 1 to 5 wt% of polyvinyl alcohol may be added to the above solution. By impregnating the resin-added solution as described above, the adhesion between the sintered particles (skeleton) constituting the fuel electrode and the impregnated solution can be improved.

Next, as described above, lactic acid that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4). The characteristics of the composite oxide-introduced fuel electrode produced using a compound (organic acid metal salt) solution will be described using the results of producing and testing a sample cell in the same manner as in the first embodiment. Also in this test, _{y of} ((Ce _1-y M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4), which is a compound to be introduced, is 0.05. , 0.2, and 0.4, three types of sample cells are prepared, and measurement is performed on each sample cell.

As a result of this test, as shown in Table 5 below, in any fuel gas condition, the composite oxide was compared with the conventional solid oxide fuel cell in which the composite oxide was not introduced (added). The added sample single cell has a reduced interface resistance. Moreover, the overvoltage at the fuel electrode is also reduced. Moreover, the condition of y = 0.2 has the lowest interface resistance and overvoltage. In the fourth embodiment, the fuel electrode overvoltage is larger than that in the first embodiment. This is because the addition of the metal component M ^alpha, decreases the concentration of Co (composition ratio) of the composite oxide to be introduced, because the amount of Co in a metal state to be generated in the fuel electrode is reduced.

As described above, a lactic acid compound that can be a composite oxide having a composition of ((Ce _{1 -y} M ^α _y ) O ₂ )-(CoO) (M ^α = Sm, Y; 0 <y ≦ 0.4) By using this solution, it was confirmed that even if the complex oxide was introduced into the fuel electrode, the reaction capacity of the fuel electrode was further enhanced. _{Incidentally, ((Ce 1-y Sm} y) O 2) - (CoO) and _{((Ce 1-y Y y} ) O 2) - is not limited to (CoO), (2-x ) (CeO 2) -x (CoO) When x = 1, even in the case of a complex oxide in which some Ce sites are substituted for Sm and some Ce sites are substituted for Y, It has been confirmed that the same effect as described above is exhibited when the total dissolution rate is in the range of 0 <y ≦ 0.4. In the fourth embodiment, x = 1 is set in (2-x) (CeO ₂ ) −x (CoO). However, the present invention is not limited to this, and in the range of 0.2 ≦ x ≦ 1.2, Similar effects have been confirmed. In the fourth embodiment, the same results (effects) as described above were confirmed in the test temperature range of 650 to 1000 ° C.

Next, the time change of the overvoltage of the fuel electrode in the sample cell when the value of the current flowing per unit area of the electrode is held for 0.5 hours at 0.5 A / cm ² will be described. This test consists of a sample cell with a conventional fuel electrode that does not introduce a complex oxide, a sample cell with a fuel electrode into which a complex oxide having a composition of (CeO ₂ )-(CoO) is introduced using a gluconic acid compound, And a gluconic acid compound in a sample cell by a fuel electrode into which a composite oxide having a composition of ((Ce _0.8 Sm _0.2 ) O ₂ )-(CoO) is introduced. The battery operating temperature is 800 ° C.

The results of this test are shown in Table 6. As shown in Table 6, both the interfacial resistance and the fuel electrode overvoltage are low over a period of ˜500 hours, as compared with the test cell in which the composite oxide was not introduced. Maintained. In particular, in a sample cell using a fuel electrode into which a composite oxide having a composition of ((Ce _0.8 Sm _0.2 ) O ₂ )-(CoO) is introduced, an increase in the fuel electrode overvoltage is further suppressed, and the solid oxide fuel cell It was confirmed that it is useful for long-term power generation operation.

  After the above test, after switching the gas supplied to the fuel electrode to an inert nitrogen gas and returning to room temperature (25 ° C.), the state of the fuel electrode in each test cell was observed, and then the composite oxide was introduced. A black deposit was visually confirmed on the fuel electrode of the test cell that was not used. The precipitate was confirmed to be carbonaceous by elemental analysis. On the other hand, no carbonaceous deposition was observed in the fuel electrode of any test cell in which the composite oxide was introduced.

In the above description, x = 1 in (2-x) (CeO ₂ ) −x (CoO). However, the present invention is not limited to this, and the same results are obtained in the range of 0.2 ≦ x ≦ 1.2. It has been confirmed that The same applies not only to ((Ce _0.8 Sm _0.2 ) O ₂ ) — (CoO) but also to Sm as Y. Further, not only y = 0.2, but if the total ratio of the elements substituting the Ce site is in the range of 0 <y ≦ 0.4, the increase rate of the fuel electrode overvoltage is reduced as described above. The effect to do is confirmed.

  In the results shown in Table 6, the fuel gas is dry methane. However, the present invention is not limited to this, and the same applies to the case where hydrocarbons added with water vapor are supplied as fuel gas.

  In the above-described embodiment, gluconate, malate, and lactate are used as the organic acid metal salt. However, the present invention is not limited to this. Organic acids used for the synthesis of organic acid metal salts include organic acids having 1 to 4 carboxyl groups (COOH groups), organic acids having 1 to 3 hydroxyl groups (OH groups), 1 to 4 Any organic acid having nitrogen (N) may be used. Examples include gluconic acid, malic acid, maleic acid, lactic acid, succinic acid, fumaric acid, propionic acid, methacrylic acid, acrylic acid, citric acid, tartaric acid, itaconic acid, formic acid, acetic acid, malonic acid and the like.

In addition, when each organic acid described above constitutes an organic acid metal salt, the ratio of the organic acid to the metal is 1 to 4 times equivalent, and the concentration of the composite oxide to be introduced is adjusted to 0.1 to 2 M / liter. In the case where metals such as Ce, Sm, Y, Co, and Ni are difficult to dissolve in the above-described organic acid, a chelating agent or the like is added to the mixed solution so that these metals are dissolved as ions. good. For example, ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetraacetic acid ammonium (EDTA · 2NH _4), hydroxyethylene diamine triacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetramine 6 acetate (TTHA), ethylenediamine tetra propylene and ethylene A chelating agent such as glycol may be used.

  The above-described present invention is a fuel electrode in which the metal catalyst in the fuel electrode material of the solid oxide fuel cell is highly dispersed, the electrode reaction field is increased, the aggregation of the metal catalyst is suppressed, and the long-term stability is excellent. It is what I tried to provide. In addition, the present invention described above is intended to improve the performance of a solid oxide fuel cell that uses a hydrocarbon-based fuel as a fuel gas, which is assumed in practical use, and has high activity and long-term stability under the use of hydrocarbon-based fuel. It is an object of the present invention to provide a fuel electrode having excellent properties.

For this purpose, it is necessary to search for a metal catalyst having a high oxidation ability for fuel gas equivalent to or higher than that of Ni, and to stably arrange such a catalyst in the fuel electrode with high dispersion. In the present invention, attention is focused on Co and Ni as the above-described metals having high catalytic ability, and attention is focused on cerium oxide (CeO ₂ ) -based oxides in consideration of carbon deposition as a support. To make a complex oxide. Furthermore, it was studied to stably deposit fine metal particles by reducing the composite oxide. In addition, by adding (introducing) the above complex oxide into the skeleton of a conventional fuel electrode, the electrode reaction field is increased without impairing the dynamic structure and electronic conductivity of the original fuel electrode, and the electrode performance. Was further improved.

  For this reason, in the present invention, a mixed oxide containing Ce and at least one of Sm and Y, or a mixed oxide containing Ce, at least one of Sm and Y, and at least one of Co and Ni. Regarding the ratio and composition ratio, by converting each element into an organic acid solution, a solid solution that is uniformly crystallized regularly at the atomic level is formed in the fuel electrode. Highly dispersed in the fuel electrode stably and effectively.

As described above, in the present invention, a skeleton (a mixture of a metal oxide having oxygen ion conductivity and a metal having electron conductivity or a mixture of these oxide particles as a porous material of a fuel electrode of a solid oxide fuel cell ( In the matrix), the general formula: (2-x) (CeO ₂ ) -x (L ^α O) (L ^α = Co, Ni; 0.2 ≦ x ≦ 1.2) or (2-x) (( ^{_{ce 1-y M α y)}} O 2) -x (L α O) (M α = Sm, Y, L α = Co, Ni; 0.2 ≦ x ≦ 1.2,0 <y ≦ 0.4 The composite oxide represented by (2) was impregnated into the skeleton in the form of an organic acid solution capable of forming the oxide, and then heat-treated to form the composite oxide particles in the fuel electrode. In addition, reduction treatment was performed under fuel cell operating conditions so that Co and Ni metal particles that would become fine electrode catalysts were deposited in the fuel electrode.

  As a result, the electrode reaction field can be increased in the fuel electrode, the electrode overvoltage caused by the fuel electrode can be reduced, and the interface resistance of the fuel electrode in the vicinity of the open circuit voltage can be reduced. In addition, since a fine metal catalyst is generated (deposited) from the composite oxide in the fuel electrode, it is easy to maintain a highly dispersed state by suppressing aggregation of the electrode catalyst. For this reason, deterioration of electrode characteristics can be suppressed even during long-time power generation. Furthermore, when a hydrocarbon fuel is used as the fuel for the fuel cell, it is possible to suppress the deposition of carbonaceous matter on the fuel electrode due to the decomposition of the hydrocarbon fuel, and this effect can be maintained for a long time. it can.

It is explanatory drawing explaining the manufacturing method of the electrode for solid oxide fuel cells in embodiment. It is a block diagram which shows the structural example of the solid oxide fuel cell using the electrode for solid oxide fuel cells in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... YSZ board | substrate, 102 ... Fuel electrode coating film, 103 ... Fuel electrode, 103a ... Fuel electrode, 104 ... Air electrode coating film, 105 ... Air electrode, 111 ... Mask layer, 113 ... Compound oxide introduction fuel electrode.

Claims (5)

In the method for producing a solid oxide fuel cell electrode,
A first step of forming a porous fuel electrode composed of a sintered body containing a metal oxide; and
A second step in which a solution of an organic acid compound containing two or more metals is impregnated in the porous pores of the fuel electrode;
A third step of heating the fuel electrode impregnated with the solution so that the composite oxide composed of the metal contained in the solution is disposed in the porous hole; Comprising at least
The composite oxide, (2-x) (( Ce 1-y M α) O 2) -x (Ni O) (0.2 ≦ x ≦ 1.2,0 <y ≦ 0.4, M α = Sm, Y) A method for producing an electrode for a solid oxide fuel cell, wherein: In the manufacturing method of the electrode for solid oxide fuel cells of Claim 1,
The organic acid is selected from an organic acid having 1 to 4 COOH groups, an organic acid having 1 to 3 OH groups, and an organic acid having 1 to 4 N. A method for producing an electrode for a solid oxide fuel cell. In the manufacturing method of the electrode for solid oxide fuel cells of Claim 1 or 2,
The solution is
A method for producing an electrode for a solid oxide fuel cell, comprising adding an ethylene glycol in addition to the organic acid compound and heating to 100 to 150 ° C. In the manufacturing method of the electrode for solid oxide fuel cells of Claim 1 or 2,
The solution is
An organic binder is added in addition to the organic acid compound. A method for producing an electrode for a solid oxide fuel cell, wherein:   The solid oxide fuel cell provided with the electrode manufactured by the manufacturing method of the electrode for solid oxide fuel cells of any one of Claims 1-4.

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