JP2008257943A - Electrode for solid oxide fuel cell and solid oxide fuel cell having same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a solid oxide fuel cell capable of generating electric power in high power density even in a medium temperature region (600-800°C), and to provide the solid oxide fuel cell having the electrode. <P>SOLUTION: The electrode for the solid oxide fuel cell includes a bismuth-containing oxide attached to the inside of a pore of a porous structure having at least electron conductivity. The bismuth-containing oxide is yttria- or erbia-stabilized bismuth oxide or Bi<SB>4</SB>V<SB>2-x</SB>M<SB>x</SB>O<SB>11</SB>. The solid oxide fuel cell uses this electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an electrode for a solid oxide fuel cell and a solid oxide fuel cell having the electrode, and more specifically, a specific compound is attached to an electrode for a solid oxide fuel cell, and a fuel is produced. The present invention relates to a solid oxide fuel cell electrode with improved battery performance and a solid oxide fuel cell having the electrode.

  Those using ion-conducting ceramics as the electrolyte are called solid oxide fuel cells (SOFC). Solid oxide fuel cells (SOFC) have the highest power generation efficiency and operating temperature among various fuel cells. However, it is expected to be a simple power supply system with high power generation efficiency (50% or more) because it is easy to use exhaust heat because it is as high as about 1000 ° C. and all the constituent materials are solid.

A solid oxide fuel cell (SOFC) is a gas (fuel gas) containing a reducing agent, for example, hydrogen (H ₂ ), carbon monoxide (CO), or a hydrocarbon such as “methane (CH ₄ )” at the fuel electrode. Is supplied to the cathode, and a gas (for example, air) containing an oxidizing agent such as oxygen (O ₂ ) is supplied to the cathode (see Patent Document 1).

The most common oxygen electrode material for solid oxide fuel cells is (La, Sr) MnO ₃ perovskite oxide (LSM), and yttria-stabilized zirconia (YSZ) is mainly used as an electrolyte.

  However, solid oxide fuel cells (SOFCs) are subject to chemical stability in oxidizing and reducing environments, chemical stability of contact materials, electrical conductivity, and thermomechanical compatibility because the constituent materials are exposed to high temperatures. Problems such as material durability and performance degradation, such as being restricted by the properties, occur. On the other hand, generally, when the temperature of the fuel cell is lowered, the conductivity and electrode activity of the electrode material are lowered, so that a sufficient output density cannot be obtained.

  Therefore, research on an intermediate temperature solid oxide fuel cell (IT-SOFC) capable of operating at an intermediate temperature of about 700 ° C. has been actively conducted. For example, thin film yttria-stabilized zirconia (YSZ) can be used by applying thin film technology (see Non-Patent Documents 1 to 3), or any of oxygen molecules, electrons, and oxide ions involved in electrode reactions can react. Thus, the electrode performance is improved by forming a three-phase interface (see Non-Patent Documents 4 to 6).

  Moreover, as a utilization of a bismuth containing oxide, the trial which uses it for an electrolyte is made | formed (refer nonpatent literature 7-8). However, bismuth-containing oxides are unstable under conditions of low oxygen partial pressure, and are limited in use as electrolytes in solid oxide fuel cells (SOFC).

  In addition, studies have been made to mix metal oxide particles having ion conductivity and LSM particles to form an oxygen electrode to lower electrical resistance or increase power density (for LSM-GDC and LSM-YSZ). (See Non-Patent Document 9; see Non-Patent Document 10 for LSM-CBO). However, these are those in which particles are mixed and then fired to form a porous composite. In the intermediate temperature range (600 ° C. to 800 ° C.), sufficient performance as an electrode has been achieved. There wasn't.

  As described above, a sufficient technology has not yet been completed for a solid oxide fuel cell that can be used without any problem in an intermediate temperature range (600 ° C. to 800 ° C.). Moreover, although the examination which impregnates a noble metal and an oxide to a porous electrode (patent document 2, nonpatent literature 11-14) and the bismuth containing oxide were not impregnated to the electrode, the bismuth containing oxide was used. Various studies on electrodes (Non-Patent Documents 15 to 18) have been made. However, as far as the present inventors know, there is no known one that can be crystallized at a low temperature and can be highly dispersed even in a small amount. Therefore, a high-performance electrode with a low impregnation amount is desired. It was the current situation.

JP-A-9-129256 JP-T-2001-522518 Gaudon, M., Laberty-Robert, Ch., Ansart, F., Stevens, P., 2006, Journal of the European Ceramic Society, 26, pp. 3153-3160. Nomura, H., Parekh, S., Selman J.R., Al-HallaJ, S., 2005, Journalof Applied Electrochemistry, 35, pp. 61-67. Lao, G.J., Herts, J., Tuller H., Horn, Y.S., 2004, Journal of Electroceramics, 13, pp. 691-695. Chen, X.J., Chan, S.H., Khor, K.A., 2004, Electrochimica Acta, 49, pp. 1851-1861. Jiang, S.P., Love, J.G., Ramprakash, Y., 2002, Journalof Power Sources, 110, pp.201-208. Barbucci, A., Viiviani, M., Carpanese, P., Vladikova D., Stoynov, Z., 2006, Electrochimica Acta, 51, pp.1641-1650. Jiang, N.X., Wachsman, E.D., Jung, S.-H., 2002, SolidState Ionics, 150, pp.347-353. Esposito, V., Traversa, E., Wachsman, E.D., 2005, Journalof The Electrochemical Society, 152 (12), pp. A2300-A2305. Murray, E.P., Barnett, S.A., 2001, SolidState Ionics, 143, pp.265-273. Zhao, H., Huo, L., Gao, S., 2004, J. PowerSources, 125, pp. 149-154. Chun, L., Tal, Z.S., Craig, P.J., Steven, J.V., Lutgard, C.D.J., 2006, Journal of The Electrochemical Society, 153 (6), A1115-A1119. Jiang, S.P., Leng, Y.J., Chan, S.H., Khor, A.K., 2003, Electrochemical and Solid-State Letters, 6 (4), A67-A70. Jiang, S.P., Duan, Y.Y., Love, J.G., 2002, Journal of The Electrochemical Society, 149 (9), A1175-A1183. Jiang, S.P., 2006, Materials Science and Engineering A, 418, 199-210. Y. Yamakoshi, T. Kenjo, 1996, Denki Kagaku, 64 (6), 590-595. Changrong, X., Yulan, Z., Meilin, L., 2003, Applied Physics Letters, 82 (6), 901-903. Zhonglin, W., Meilin, L., 1998, Journal of American Ceramic Society, 81 (5), 1215-1220.

  The present invention has been made in view of the above-described background art, and its problem is that an electrode for a solid oxide fuel cell capable of generating power at a high power density even in an intermediate temperature range (600 ° C. to 800 ° C.), and the electrode It is an object of the present invention to provide a solid oxide fuel cell.

  As a result of intensive studies to solve the above problems, the present inventor has found that by attaching a bismuth-containing oxide to an electrode having specific physical properties and structure, the resistance is reduced and the battery performance is improved. The present invention has been reached.

  That is, the present invention provides an electrode for a solid oxide fuel cell, characterized in that a bismuth-containing oxide is deposited in the pores of a porous structure having electronic conductivity.

  The present invention also provides a solid oxide fuel cell having the above electrode.

  According to the present invention, it is possible to provide a solid oxide battery electrode capable of generating power at a high power density even in an intermediate temperature range (600 ° C. to 800 ° C.) and a solid oxide fuel cell having the electrode. Become.

  Hereinafter, although this invention is demonstrated, this invention is not limited to the following embodiment, It can implement by deform | transforming arbitrarily.

In the solid oxide fuel cell electrode of the present invention, it is essential that a bismuth-containing oxide is attached in the pores of the porous structure having electron conductivity. In the present invention, “having electronic conductivity” means having an electron conductivity of 10 ⁻¹ S / cm or more at a battery operating temperature. The electron conductivity is preferably 10 S / cm or more, more preferably 100 S / cm or more. If the electron conductivity at the battery operating temperature is too low, a sufficient output as a battery may not be obtained.

As the “substance having electron conductivity” in the present invention, a metal oxide such as a rare earth perovskite represented by the general formula, A _1-a A ′ _a B _{1 -b} B ′ _b O _{3 -δ} is preferable. Can be mentioned. In the above formula, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, −0.2 ≦ δ ≦ 0.5, and A is at least one rare earth cation such as La, Pr, Nd, Sm or Tb. A ′ is at least one dopant cation, such as alkaline earth cation Sr or Ca, B is at least one transition metal selected from the group consisting of Mn, Co, Fe, Cr and Ni; B ′ is a transition element cation different from B.

More preferred examples of these rare earth perovskites include the following. These may be used alone or in combination of two or more.
La _1-a Sr _a MnO _3-δ [wherein 0 ≦ a ≦ 0.5] (hereinafter abbreviated as “LSM”),
Pr _1-a Sr _a MnO _3-δ [where 0 ≦ a ≦ 0.6],
Pr _1-a Sr _a CoO _3-δ [where 0 ≦ a ≦ 0.5],
La _1-a Sr _a Co _1-b Fe _b O _3-δ [where 0 ≦ a ≦ 0.4, 0 ≦ b ≦ 0.8],
La _1-a Sr _a Co _1-b Ni _b O _3-δ [where 0 ≦ a ≦ 0.6, 0 ≦ b ≦ 0.4],
La _1-a Sr _a CrO _3-δ or La _1-a Ca _a CrO _3-δ [where 0 ≦ a ≦ 0.5].

In addition, as other “substances having electron conductivity”
0-90% In ₂ O ₃ , 10-100% PrO _1.83 , 0-50% ZrO _2
In 2 _O 3 _-PrO 1.83 product formed from a mixture of -ZrO ₂ having a composition ratio of,
0-70% Co ₃ O ₄ , 30-100% PrO _1.83 , 0-50% ZrO ₂
A product formed from a mixture of Co ₃ O ₄ —PrO _1.83 —ZrO ₂ having a composition ratio of:
Etc. The above “%” means “mol%”. These may be used alone or in combination of two or more.

In the present invention, it is preferable that the porous structure having electron conductivity further has ion conductivity. “Having ion conductivity” means that the ion conductivity is 10 ⁻³ S / cm or more at the battery operating temperature.

As those having both electron conductivity and ion conductivity, (La, Sr) CoO ₃ , (La, Fe) FeO ₃ , (La, Sr) (Co, Fe) O ₃ , (Sm, Sr) CoO _{3 are used.} Perovskite type oxides such as La ₂ NiO ₄ , (La, Sr) ₂ CoO _{4 and} other oxides of K ₂ NiF ₄ type structure. These may be used alone or in combination of two or more.

  The porous structure in the present invention is required to have a path through which electrons or “electrons and ions” can be conducted. Therefore, it is preferable that the particles are sintered to form a network.

  The pore size of the porous structure is preferably 0.1 μm or more and 100 μm or less, and particularly preferably 1 μm or more and 50 μm or less. If the pore diameter is too large, the electrode surface area decreases, and the active site as a catalyst decreases, so that a sufficient output as a battery may not be obtained. On the other hand, if the pore diameter is too small, the pores are closed when depositing the bismuth-containing oxide, and active sites as a catalyst are reduced, so that a sufficient output as a battery may not be obtained.

  Further, there is no particular limitation on the “porosity” indicating the ratio of the volume of the pores to the total volume of the porous structure, but in terms of maintaining the mechanical strength and increasing the active sites as the catalyst, 10 A range of ˜70% is preferred, and a range of 20˜50% is particularly preferred.

  The method for producing a porous structure in the present invention is not particularly limited, but the particles of the “electron-conducting substance” are applied to an electrolyte together with a “temporary binder” or a dispersion medium, and then sintered. The method of ligating is preferred. As a “temporary binder” or dispersion medium, particles of the above-mentioned “electron-conducting substance” can be coated on the electrolyte, and subsequently disappear from the electrolyte surface by evaporation, firing, etc. of the dispersion medium. There is no particular limitation. In addition, the “temporary binder” and the “dispersion medium” do not need to be separate substances, and may be the same substance having both functions.

  The “temporary binder” is not particularly limited, and specific examples thereof include poly (meth) acrylate, polyvinyl butyral (for example, available from Monsanto as Butvar ™), polyvinylacetone , Organic polymers such as methylcellulose, ethylcellulose, polyethylene glycol, polypropylene glycol, and styrene-butadiene copolymer.

  The “dispersion medium” is not particularly limited as long as it can disperse the particles. Specifically, for example, alcohols such as ethanol, propanol, glycerin, ethylene glycol, and terpineol; hydrocarbons such as toluene Ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and dibutyl phthalate; propylene glycol monoalkyl ether, dipropylene glycol monoalkyl ether, propylene glycol dialkyl ether, dipropylene glycol dialkyl ether, low molecular weight polyethylene Examples thereof include organic substances that are liquid at room temperature, such as glycol derivatives such as glycol, low molecular weight polypropylene glycol, and carbitol.

  In the paste-like or slurry-like coating liquid in which the particles of the “substance having electron conductivity” are dispersed in the temporary binder and / or dispersion medium, a temporary pore forming agent, for example, It is also preferable to include carbon particles, carbon fibers, and the like, and their use is preferable in terms of being able to increase the porosity and the pore diameter of the porous structure by burning below the sintering temperature.

  Moreover, it is preferable that the coating solution further contains a dispersant. Examples of such a dispersant include ammonium polyacrylate and ammonium polycarboxylate.

  If necessary, the coating solution may be further used together with a plasticizer, an antifoaming agent, a surfactant, etc., for example, using a dispersing machine such as a ball mill, a three-roll mill, a planetary mill, an automatic mortar, a jet mill, a homogenizer, After the particles of “substance having electron conductivity” are dispersed to form a coating solution having an appropriate viscosity, it is coated on the solid electrolyte by, for example, screen printing, tape formation, doctor blade or the like.

  After coating, the porous structure is formed by sintering. Although there is no limitation in particular as sintering temperature, 1000 to 1300 degreeC is preferable.

  The film thickness of the porous structure after sintering is not particularly limited, but is preferably 1 μm or more and 500 μm or less. If the film thickness is too thick, an excess of bismuth-containing oxide is required to deposit uniformly in the pores, which may be disadvantageous in terms of cost. If it is too thin, the electrode surface area decreases and the activity as a catalyst is reduced. In some cases, sufficient output cannot be obtained as a battery because the number of sites decreases.

The present invention is characterized in that a bismuth-containing oxide is deposited in the pores of the porous structure. In the present invention, the “bismuth-containing oxide” is not particularly limited as long as it is an oxide containing at least a bismuth element. However, bismuth oxide stabilized with yttria or erbia, or Bi ₄ V _2−x M _x O ₁₁ [wherein M represents Cu, Ni, Co, Al, Ti, Nb or Ta, and x represents a real number satisfying 0 ≦ x <0.5] represents a high oxide ion conductivity. As a result, it is preferable because power can be generated at a high power density even in the intermediate temperature range (600 ° C. to 800 ° C.).

As the “bismuth-containing oxide”, a rare-earth element-containing oxide such as yttria or erbia, and an oxide having a fluorite structure in which the δ phase is stabilized is preferable because the above effect is exhibited. Particularly preferably, (Bi ₂ O ₃ ) _1-x (Er ₂ O ₃ ) _x [wherein bismuth oxide stabilized with erbia represented by 0 <x <0.5] (hereinafter “ESB”) Abbreviated). In the above formula, x is particularly preferably 0.2 ≦ x ≦ 0.3 in the above formula because x has high oxide ion conductivity.

In addition, as the “bismuth-containing oxide”, those represented by Bi ₄ V _2−x M _x O ₁₁ , which is an oxide having a layered structure generically named BIMEVOX, are also preferable. In the above formula, M represents Cu, Ni, Co, Al, Ti, Nb or Ta. X represents a real number of 0 ≦ x <0.5.

  In the present invention, if the bismuth-containing oxide is adhered in the pores of the porous structure, the adhesion state is not particularly limited, but the surface of the pores of the porous structure is not coated but dispersed. It is preferable that it is attached by. An example is shown in FIG. In FIG. 3, (a) is LSM only, and (b) is a scanning electron microscope (SEM) photograph of ESB deposited in the LSM pores, but ESB particles are present in the porous structure (LSM). It is attached in a dispersed state to the surface of the hole to be formed.

  Although the bismuth-containing oxide may be attached to some of the pores of the porous structure, it is preferable that the bismuth-containing oxide is attached to substantially all the pores. Further, when the bismuth-containing oxide is a particle, the particles may be in an overlapping state, but it is preferable that they are uniformly attached. “Uniform” refers to a state in which particles or particles in an overlapping state exist at approximately equal intervals. From the viewpoint of increasing the number of three-phase interfaces, it is more preferable that the particles or particles having a small overlapping state are used.

  In the present invention, when the “bismuth-containing oxide” is attached in a dispersed state in the pores of the porous structure, the dispersed particle diameter of the “bismuth-containing oxide” is not particularly limited, but is 500 nm. The following is preferable, and particularly preferably 0.1 nm or more and 250 nm or less. If the dispersed particle size is too large, the three-phase interface will be reduced, and if it is severe, the pores may be blocked and the battery output may be greatly reduced. On the other hand, if it is too small, the crystallinity of the bismuth-containing oxide will be reduced. However, the oxide ion conductivity may be deteriorated, and the output of the battery may be reduced. The dispersed particle size is determined by selecting 20 particles at random using a scanning electron microscope (SEM) and measuring the diameter of the particles.

  The mass ratio of the porous structure and the bismuth-containing oxide in the electrode is not particularly limited, but is preferably 10 to 100 parts by mass of the bismuth-containing oxide with respect to 100 parts by mass of the porous structure. 80 parts by mass is more preferable. If the amount of bismuth-containing oxide is relatively small, the effect of increasing the three-phase interface due to the addition of the bismuth-containing oxide may be small, and sufficient power density may not be obtained. In severe cases, the pores of the porous structure are blocked, the three-phase interface is reduced, and a sufficient power density may not be obtained.

  The method for attaching the bismuth-containing oxide to the pores of the porous structure is not particularly limited. For example, the porous structure may be impregnated with a liquid containing the bismuth-containing oxide, and then dried and fired. The porous structure may be impregnated with a solution of a bismuth-containing oxide precursor, and then dried and fired. Here, the “precursor of bismuth-containing oxide” is not particularly limited as long as it becomes a bismuth-containing oxide by firing, but the solution can be dissolved in an organic solvent or water. This is preferable in that it uniformly enters the pores of the porous structure and uniformly deposits the bismuth-containing oxide in the pores. Moreover, it is preferable at the point which is easy to make the bismuth containing oxide particle | grains with a small particle size adhere uniformly in a dispersed state. Specifically, the “bismuth-containing oxide precursor” is preferably, for example, nitrate, acetate, citrate and the like.

  The firing temperature is not particularly limited, but is preferably 550 ° C to 800 ° C, and particularly preferably 600 ° C to 750 ° C. If the temperature is too high, the bismuth-containing oxide may melt, and if it is too low, it may not crystallize. Moreover, although baking time is not specifically limited, 1 minute-2 hours are preferable at the point of crystallinity and cost, and 5 minutes-1 hour are especially preferable.

  The solid oxide fuel cell has at least an oxygen electrode, a fuel electrode, and an electrolyte. The electrode for a solid oxide fuel cell of the present invention can be used as an oxygen electrode or a fuel electrode. It is also possible to use both an oxygen electrode and a fuel electrode. However, oxides containing bismuth may be reduced and decomposed under conditions with a low oxygen partial pressure, or electron conductivity may occur and the transport number of oxide ions may decrease, so use as an oxygen electrode. It is preferable. Moreover, in order to use as a fuel electrode, in order to have electronic conductivity, it is preferable to contain Ni, Cu, etc.

  When the electrode for the solid oxide fuel cell of the present invention is used as an oxygen electrode, the other fuel electrode is a known fuel used for a solid oxide fuel cell in addition to the electrode material of the present invention. Polar materials can be used. As the oxygen electrode when the electrode for the solid oxide fuel cell of the present invention is used as a fuel electrode, a known oxygen electrode material used for a solid oxide fuel cell is used in addition to the electrode material of the present invention. be able to.

  There is no limitation in particular as electrolyte, The electrolyte material used for a solid oxide fuel cell can be used. The electrolyte is preferably made of a material that has high ion conductivity and is chemically stable and resistant to thermal shock under conditions from an oxidizing atmosphere on the oxygen electrode side to a reducing atmosphere on the fuel electrode side.

Examples of materials that satisfy such requirements include, in addition to zirconia, alkaline earth metal oxides such as MgO, CaO, SrO, and BaO, Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₂ O ₃ , and Nd. Rare earth metal oxides such as ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O ₃ , A zirconia-based ceramic containing one or more of Sc ₂ O ₃ , Bi ₂ O ₃ , In ₂ O _{3 and the} like can be used. In addition to CeO ₂ or Bi ₂ O ₃ , the alkaline earth metal oxide, the rare earth metal oxide, Sc ₂ O ₃ , In ₂ O ₃ , PbO, WO ₃ , MoO ₃ , V ₂ Os, Nb A ceria-based or bismuth-based ceramic containing one or more of ₂ O _{5 and the} like can be used. In addition, AZrO ₃ having a perovskite structure (A: alkaline earth metal such as Sr) is doped with In or Ga; LaGaO ₃ is doped with the alkaline earth metal oxide, rare earth metal oxide, Sc Transition metal oxidation such as ₂ O ₃ , TiO ₂ , V ₂ O ₅ , Cr ₂ O ₃ , Mn ₂ O ₃ , Fe ₂ O ₃ , Co ₃ O ₄ , NiO, CuO, ZnO, Nb ₂ O ₅ , WO ₃ , Lanthanum gallate ceramics doped or dispersion strengthened with typical metal oxides such as Al ₂ O ₃ , SiO ₂ , In ₂ O ₃ , Sb ₂ O ₃ , Bi ₂ O _3, etc .; Ba having a brown mirror light type structure Examples thereof include indium-based ceramics such as ₂ In ₂ O ₅ . These ceramics may further contain other oxides such as SiO ₂ , Al ₂ O ₃ , GeO ₂ , SnO ₂ , Sb ₂ O ₃ , PbO, Ta ₂ O ₅ , Nb ₂ O _{5 and the} like. Good.

  Among these, zirconia stabilized with one or more of Y, Ce, Sm, Pr, Sc, and Yb is more preferable. Examples thereof include stabilized zirconia such as yttria stabilized zirconia (hereinafter abbreviated as “YSZ”) and scandia stabilized zirconia (ScSZ).

As the stabilized zirconia, general formula (ZrO ₂ ) _1-x (M ₂ O ₃ ) _x [wherein M is selected from the group consisting of Y, Sc, Sm, Al, Nd, Gd, Yb and Ce. One or more elements are shown. However, here, when M is Ce, it is CeO ₂ instead of M ₂ O ₃ . ] Or
_{X in the} general formula (ZrO ₂ ) _1-x (MO) _x [wherein M represents one or more elements selected from the group consisting of Ca and Mg] is 0 <x ≦ 0.3. A solid solution is preferred. Particularly preferable examples include (ZrO ₂ ) _1-x (Y ₂ O ₃ ) _x (where 0 <x ≦ 0.3), and more preferably 0.08 ≦ x ≦ 0.1. More preferable examples include (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 .

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

The ceria-based solid solution is not particularly limited, but Ce _1-x M _x O ₂ (wherein M is Gd, La, Y, Sc, Sm, Al, Pr, Nd, Ca, Mg, Sr, Ba, Dy, A solid solution in which x is 0 <x ≦ 0.5 in Yb, Tb, and one or more elements selected from the group consisting of other divalent or trivalent lanthanoids) is preferable. Among them, Ce _1-x Gd _x O ₂ where M is Gd (where 0 <x ≦ 0.5), or Ce _1-x Sm _x O ₂ where M is Sm (where 0 <x ≦ 0.5) is more preferable, and in any formula, 0.03 ≦ x ≦ 0.4 is particularly preferable. Particularly preferable ceria-based solid solutions include Ce _0.8 Gd _0.2 O _2-δ (where δ represents the amount of oxygen deficiency), Ce _0.67 Gd _0.33 O _2-δ (wherein , Δ represents an oxygen deficiency amount), Ce _0.9 Gd _0.1 O _2-δ (where δ represents an oxygen deficiency amount), and the like.

  When the mechanical strength is handled by another member as in the anode-supported cell, the thickness of the electrolyte is preferably as small as possible so that the reducing agent (fuel) and the oxidizing agent do not permeate, and is not particularly limited. Usually 1 to 500 μm.

When using an electrode in which a bismuth-containing oxide is attached in the pores of a porous structure having at least electronic conductivity according to the present invention, the electrode is not attached at a temperature of 700 ° C. and a cell voltage of 0.7 V during power generation. In comparison with the above, at least the power density can be increased by 1.5 times, and further by 2 times or more. Specifically, the power density can be 100 mW / cm ² or more.

  Although the action and effect of the solid oxide fuel cell using the electrode of the present invention exhibiting excellent cell performance is not clear, the following can be considered. However, this invention is not limited to the range of the following effects. That is, it is considered that the electrode of the present invention increases the three-phase interface by attaching bismuth-containing oxides to the pores of the porous structure having at least electronic conductivity.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to these Examples and a comparative example, unless the summary is exceeded.

Example 1
<Production of LSM-EBS electrode>
[Production of porous structure having electron conductivity]
50% by mass of powdered La _0.8 Sr _0.2 MnO ₃ (LSM, manufactured by Anan Kasei Co., Ltd.) and 50% by mass of polyethylene glycol (PEG, average molecular weight 200) were treated at 500 rpm for 30 minutes using a ball mill. . At this time, the particle size of La _0.8 Sr _0.2 MnO ₃ (LSM) was 1 μm.

The obtained LSM-PEG slurry was screen printed on both sides of a Zr ₂ O ₂ (YSZ) electrolyte stabilized with 8 mol% of Y ₂ O ₃ to produce a symmetrical cell. At this time, the YSZ pellet had a diameter of 23 mm and a thickness of 300 μm, and the effective size of the electrode was 1 cm × 1 cm. The structure of the symmetric cell is shown in FIG.

  These electrodes and YSZ electrolyte were fired at 1200 ° C. for 4 hours to obtain an electrode-conductive porous structure electrode having a thickness of 10 μm and a mass of 10 mg (hereinafter abbreviated as “LSM electrode”). At this time, paste-like platinum and platinum mesh were used as the current collector.

[Adhesion of bismuth-containing oxide into pores of porous structure]
99.5% pure _{Bi (NO 3) 3 · 5H} 2 O ( manufactured by Nacalai Tesque, Inc.), _Er the _{(NO 3) 3 · 5H 2} O ( manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed, Bi A mixed aqueous solution (Bi: Er = 80 mol%: 20 mol%) of (NO ₃ ) ₃ and Er (NO ₃ ) ₃ was prepared. The metal ion concentration of this mixed aqueous solution was 2 mol / L. Next, 4 μL of the mixed solution containing this bismuth-containing oxide (bismuth-containing oxide corresponds to 18% by mass with respect to LSM) was dropped on both ends of the LSM electrode prepared above, and impregnation was performed. LSM (hereinafter referred to as “LSM-EBS”) which was dried and fired for 1 hour and (Bi ₂ O ₃ ) _0.8 (Er ₂ O ₃ ) _0.2 (ESB) adhered as a bismuth-containing oxide. An abbreviated electrode was obtained.

Comparative Example 1
<Creation of LSM electrode>
In Example 1, the one before the deposition of the bismuth-containing oxide into the pores of the porous structure was designated as “LSM electrode” and used for the following evaluation.

<Preparation of cell>
The LSM oxygen electrode was printed on a commercially available NiO-YSZ / YSZ green pellet with an area of 0.5 cm ² (circle with a diameter of 8 mm). FIG. 1 (b) shows a schematic diagram thereof. At this time, the thickness of the YSZ electrolyte was about 15 μm. The impregnation with the ESB precursor solution was performed after firing the LSM oxygen electrode, and heated at 600 ° C. for 1 hour to obtain ESB.

FIG. 2 shows (a) an LSM electrode, (b) an LSM electrode dispersed with ESB sintered at 600 ° C. for 1 hour, and (c) an LSM electrode dispersed with ESB sintered at 800 ° C. for 4 hours. The X-ray diffraction pattern of each electrode is shown. The LSM electrode in which ESB was dispersed was (b) sintered at 600 ° C. for 1 hour, and (c) sintered at 800 ° C. for 4 hours, and a cubic Bi ₂ O ₃ peak was observed. (Indicated by “↓” in FIG. 2). This indicates that ESB is formed in the pores of the LSM porous structure without forming a new phase.

  FIG. 3 shows scanning electron microscope (SEM) images of (a) LSM electrode and (b) LSM electrode in which ESB is dispersed. (A) The LSM electrode was porous as a result of firing at 1200 ° C. for 4 hours. It was also found that (b) the ESB-dispersed LSM electrode had ESB nano-sized particles uniformly dispersed and attached to the surface of the LSM, that is, within the LSM pores.

  Next, the polarization resistance of the LSM-ESB was compared with the polarization resistance of the “electrode based on LSM” already reported. Table 1 shows the results.

  “Mixing of LSM and GDC” and “Mixing of LSM and YSZ” are those described in Murray, EP, Barnett, SA, 2001, Solid State Ionics, 143, pp. 265-273 (Non-patent Document 9). , “Mixing of LSM and CBO” is described in Zhao, H., Huo, L., Gao, S., 2004, J. Power Sources, 125, pp. 149-154 (Non-Patent Document 10). is there.

  GDC, YSZ, and CBO are LSM particles mixed with these particles and coated on the electrolyte (YSZ). That is, a porous composite composed of LSM and GDC, LSM and YSZ, and LSM and CBO is used as an electrode. In that respect, Example 1 is one in which an oxide (ESB) containing bismuth is adhered (dispersed and adhered in the case of Example 1) on the surface in the pores of the LSM. Is fundamentally different in electrode configuration.

Table 1 shows the LSM-ESB of the present invention (82% by mass to 18% by mass) (Example 1), “Mixing of LSM and GDC” (50% by mass / 50% by mass), “Mixing of LSM and YSZ” ( 50 mass% / 50 mass%), and the value of polarization resistance (unit: Ωcm) of “mixing of LSM and CBO” (50 mass% / 50 mass%). “CBO” is Ce _0.7 Bi _0.3 O ₂ .

  As can be seen from Table 1, the electrode of Example 1 had a lower polarization resistance than the other three types of electrodes including 50% by mass even though it contained only 18% by mass of ESB. It was found that the adhesion of ESB can suppress the electrode polarization and realize a low electrode resistance. This excellent result is considered to be because the three-phase interface increased due to the high oxide ion conductivity of the bismuth-containing oxide and the dispersion and adhesion of the bismuth-containing oxide in the pores of the porous structure.

  Next, the power density (Cell Power Density) was measured for the LSM-ESB electrode in which the bismuth-containing oxide was dispersed (Example 1) and the LSM electrode in which the bismuth-containing oxide was not dispersed (Comparative Example 1). . The performance as a solid oxide battery was measured in a fuel electrode support cell using the LSM-EBS electrode (Example 1) and the LSM electrode (Comparative Example 1) as an oxygen electrode. The measurement apparatus and measurement conditions are as follows.

[Measurement method of cell power density]
Measuring device: solartron 1260-1287
Measurement conditions: 97% H ₂ + 3% H ₂ O on the fuel electrode side, air electrode side open to atmosphere
Holds each potential for 30 seconds at -0.05V step from OCV, measures the current value
(Each potential was measured 5 times)
Measurement temperature: 700 ° C

The result of evaluating the performance of the battery at 700 ° C. is shown in FIG. Compared to the LSM oxygen electrode of Comparative Example 1, the LSM-ESB oxygen electrode of Example 1 had a higher power density and improved electrode performance. From FIG. 4, the power density by dispersing bismuth-containing oxide (ESB), in 0.7 V, was found to improve from 0.08 W / cm ² to 0.20 W / cm ^2. That is, the power density could be increased by about 2.5 times by dispersing and attaching ESB in the holes of the LSM.

  As a result of measuring the performance of an electrode in which ESB, which is a bismuth-containing oxide, was deposited in the pores of a porous structure (LSM) having electronic conductivity in a temperature range of 600 to 800 ° C., the results were as follows. It has been found that the non-ohmic resistance is drastically reduced by the adhesion. And as mentioned above, it turned out that the power density of a battery is increased dramatically.

  The solid oxide fuel cell of the present invention can be widely used in fields where fuel cells are generally used because sufficient power density can be obtained even when the operating temperature is as low as 600 ° C. to 800 ° C. .

It is a figure which shows the structure of the cell used for the measurement. (A) Symmetric cell (b) Fuel electrode supported cell (A) LSM electrode, (b) LSM electrode in which ESM is dispersed is sintered at 600 ° C. for 1 hour, (c) LSM electrode in which ESM is dispersed is sintered at 800 ° C. for 4 hours. It is an X-ray diffraction pattern. It is a scanning electron microscope (SEM) photograph of (a) LSM electrode and (b) LSM electrode in which ESB is dispersed. It is a graph which shows the result of having measured the power density of the battery of a LSM oxygen electrode (-■-) and the battery of a LSM-ESB oxygen electrode (-●-) in 700 degreeC.

Claims (6)

  A solid oxide fuel cell electrode, characterized in that a bismuth-containing oxide is adhered in the pores of a porous structure having electron conductivity.   2. The solid oxide fuel cell electrode according to claim 1, wherein the porous structure having electron conductivity further has ion conductivity. _{3. The} electrode for a solid oxide fuel cell according to claim 1, wherein the porous structure is LaMnO ₃ doped with strontium. 4.   The solid oxide fuel cell electrode according to any one of claims 1 to 3, wherein the bismuth-containing oxide is bismuth oxide stabilized with yttria or erbia. The bismuth-containing oxide is Bi ₄ V _2-x M _x O ₁₁ [wherein M represents Cu, Ni, Co, Al, Ti, Nb or Ta, and x is 0 ≦ x <0.5. The solid oxide fuel cell electrode according to any one of claims 1 to 3, wherein a real number is shown].   A solid oxide fuel cell comprising the electrode according to any one of claims 1 to 5.