JP6625855B2 - Cell for steam electrolysis and method for producing the same - Google Patents

Description

  The present invention relates to a cell for steam electrolysis that has low power consumption and high current efficiency and can efficiently produce hydrogen gas from steam, and a method for producing the same.

  In recent years, a technology for preventing resource depletion and global warming has been demanded. Particularly in the electric power field, the development of renewable energy that suppresses the emission of carbon dioxide, which is one of the greenhouse gases, and does not rely on fossil resources is progressing. Renewable energy is energy obtained from renewable energy sources that are constantly or replenished from nature, such as sunlight, solar heat, hydropower, wind power, geothermal, biomass, etc., for example, producing hydrogen from biomass, Electric power obtained by generating electricity from hydrogen and air using a fuel cell is exemplified.

Recently, research on steam electrolysis has been widely promoted as a promising technology for producing hydrogen. Steam electrolysis uses gaseous water vapor instead of liquid water when electrolyzing H ₂ O to obtain hydrogen and oxygen. Since it can be operated at a high temperature, the voltage required for electrolysis is small. It is characterized by high energy efficiency.

Conventionally, in steam electrolysis, an electrolyte having oxygen ion conductivity has been exclusively used. For example, Patent Document 1 discloses a steam electrolysis technique using yttria-stabilized zirconia having oxygen ion conductivity as a solid electrolyte. When steam electrolysis is performed using an oxygen ion conductive solid electrolyte, the electrode reactions occurring at the anode and the cathode are as follows.
_{^{Anode: 2O 2- → O 2 + 4e}} -
^{_{Cathode: 2H 2 O + 4e - →}} 2H 2 + 2O 2-
As shown in the above formula, in this case, hydrogen is generated on the cathode side, and there is a problem that a separate step of separating from coexisting water vapor is required.

As a technique capable of solving such a problem, for example, a technique of performing steam electrolysis using a proton-conductive electrolyte has been developed as in Patent Document 2. The electrode reactions that occur at the anode and cathode in the art are respectively as follows.
_{Anode: 2H 2 O → O 2 +} 4H + + 4e -
^{Cathode: 4H + + 4e - → 2H} 2
As shown in the above formula, in this case, hydrogen is generated on the cathode side as in the case of using the oxygen ion conductive electrolyte, but since the steam is introduced to the anode side, there is no need to separate hydrogen from the steam. There is an advantage.

The proton conductive solid electrolyte, a composite and oxides _{BaCe 1-x Gd x O 3} -α in the Patent Document 3-4 in barium _{cerium, Ba d Zr 1-xy Ce} x M 3 y O 3-t (M ⁽³ is a trivalent rare earth element) is disclosed as a mixed ionic conductor that conducts both protons and oxide ions, and that high conductivity can be obtained.

JP 2005-150122 A JP 2009-209441 A JP-A-5-28820 JP 2007-197315 A

  As described above, Patent Document 2 discloses a steam electrolysis cell including a proton-conductive solid electrolyte. However, the cell for steam electrolysis described in Patent Document 2 has a problem that the cell terminal voltage is low but the current efficiency is low. Further, the cell for steam electrolysis described in Patent Document 3 has a problem that although the current efficiency is high, the cell terminal voltage is also high. Furthermore, in the proton conductive solid electrolytes described in Patent Documents 3 and 4, a very high firing temperature such as 1600 to 1650 ° C. is required to obtain a dense body. There was a problem of sintering.

Under such circumstances, an object of the present invention is to provide a steam electrolysis cell which can obtain high current efficiency at a low cell terminal voltage and can efficiently produce H ₂ and a method for producing the same. .

The present inventors have made intensive studies in order to solve the above problems, the proton-conducting solid electrolyte layer, wherein (1): Ba (1- a) with _{Sr a Zr b Ce c M d} O x The present inventors have found that by using the perovskite-type proton-conductive metal oxide represented, power consumption is low, high current efficiency can be obtained, and hydrogen can be efficiently produced, as compared with conventional steam electrolysis cells. Was completed.

That is, the cell for steam electrolysis according to the present invention has the following points.
[1] It has an anode layer and a cathode layer, has a proton conductive solid electrolyte layer between the anode layer and the cathode layer, and the proton conductive solid electrolyte layer has the following formula (1):
_{Ba (1-a) Sr a} Zr b Ce c M d O x (1)
(Where Ba is barium, Sr is strontium, Zr is zirconium, Ce is cerium, M is at least one element selected from neodymium, gadolinium, ytterbium and yttrium, O is oxygen,
a, b, c, d and x represent the atomic ratio of Sr, Zr, Ce, M and O, respectively, and 0.1 ≦ a ≦ 0.2, 0.4 ≦ b ≦ 0.7, 0.1 ≦ c ≦ 0.4, 0.1 ≦ d ≦ 0.2, and x is a numerical value determined by the oxidation state of each element.
Including a perovskite-type proton conductive metal oxide represented by
A cell for steam electrolysis, wherein the molar ratio of zirconium to cerium (Zr / Ce ratio) in the proton conductive metal oxide is 1 ≦ (b / c) ≦ 7.
[2] The cathode layer contains one or more metal elements selected from Ni, Co, Fe and oxides thereof and strontium at A site, and belongs to Group 4 to Group 14 of the periodic table at B site. The cell for steam electrolysis according to [1], comprising a perovskite-type metal oxide containing a trivalent or tetravalent element belonging to the cell.
[3] The method for producing a steam electrolysis cell according to [1] or [2], wherein a slurry containing a perovskite-type metal oxide is formed into a sheet and fired at 1,000 ° C or more and 1500 ° C or less in an air atmosphere. A method for producing a steam electrolysis cell, comprising a step of forming a proton-conductive solid electrolyte layer by performing the method.

The cell for steam electrolysis according to the present invention has a higher H ₂ generation rate per electrode area than the conventional cell for steam electrolysis and has a lower power consumption, so that it is industrially extremely useful as a cell capable of efficiently producing H _2. Useful for

1. Proton-Conducting Solid Electrolyte Layer The steam electrolysis cells mainly include an electrolyte-supported cell and an electrode-supported cell. In the case of an electrolyte-supported cell, since the baking temperature of the electrolyte layer is generally the highest among the electrolyte layer, the anode layer, and the cathode layer, the electrolyte layer is first prepared. In the case of an electrode support type cell, an electrolyte layer is formed on an electrode layer serving as a support layer.

As a material of the proton conductive solid electrolyte that can be used in the present invention, a metal oxide having proton conductivity can be used. In the disclosure of the present specification, the following formula (1):
_{Ba (1-a) Sr a} Zr b Ce c M d O x (1)
The perovskite type metal oxide having the ABO ₃ type structure can be used. Here, Ba is barium, Sr is strontium, Zr is zirconium, Ce is cerium, M is at least one element selected from neodymium, gadolinium, ytterbium and yttrium, and O is oxygen. M is particularly preferably yttrium.

In the formula (1), a, b, c, d and x represent an atomic ratio of Sr, Zr, Ce, M and O, respectively, and 0.1 ≦ a ≦ 0.2, 0.4 ≦ b ≦ 0 0.7, 0.1 ≦ c ≦ 0.4, 0.1 ≦ d ≦ 0.2, and x is a numerical value determined by the oxidation state of each element.
a is preferably 0.18 or less, more preferably 0.15 or less, still more preferably 0.12 or less, and even more preferably 0.1, but may be 0.11 or more.
b is preferably 0.45 or more, more preferably 0.50 or more, preferably 0.65 or less, and more preferably 0.60 or less.
c is preferably 0.15 or more, more preferably 0.20 or more, preferably 0.35 or less, and more preferably 0.30 or less.
d is preferably 0.12 or more, more preferably 0.15 or more, further preferably 0.18 or more, and further more preferably 0.2, but may be 0.19 or less.

  In the present invention, the molar ratio of zirconium to cerium (Zr / Ce ratio) is 1 ≦ (b / c) ≦ 7, but is preferably 1.5 or more, more preferably 2.0 or more, and further preferably 2. It is at least 5, more preferably at least 3.0, particularly preferably at least 3.5, preferably at most 6.5, more preferably at most 6.0, even more preferably at most 5.5. By adjusting the Zr / Ce ratio, it is possible to achieve both low power consumption and high current efficiency.

The material of the proton conductive solid electrolyte is not particularly limited as long as it is represented by the above general formula, and preferably has a specific surface area of 3 g / cm ² or more and 20 g / cm ² or less, more preferably 4 g / cm ² or more. , 18 g / cm ² or less, more preferably 5 g / cm ² or more, and 15 g / cm ² or less, particularly preferably a powder form.

  The thickness of the proton conductive solid electrolyte layer is not particularly limited, and may be appropriately set depending on the cell shape and the like. For example, in the case of an electrolyte-supported cell, the thickness is preferably 50 μm or more and 500 μm or less. If the thickness is less than 50 μm, sufficient strength may not be obtained. On the other hand, if the thickness exceeds 500 μm, the proton conductivity may be affected. In the case of an electrode-supporting cell, the thickness is preferably 1 μm or more and 50 μm or less. If the thickness is less than 1 μm, it may be difficult to form the proton conductive solid electrolyte layer by an industrial process such as screen printing. On the other hand, if the thickness exceeds 50 μm, there is a possibility that the proton conductivity may be affected.

  Examples of the method for producing the proton conductive solid electrolyte layer include the following methods. An organic solvent such as ethanol or terpineol, a dispersant, a plasticizer, and a binder such as ethyl cellulose are added to the perovskite-type metal oxide, and the mixture is wet-pulverized and mixed using a ball mill or the like to form a slurry. I do. Then, by firing, a proton conductive solid electrolyte layer can be obtained. In the case of an electrode support type cell, the above-mentioned slurry is applied on an electrode layer to be a support layer and then fired to form a proton conductive solid electrolyte layer on the support electrode layer.

  At this time, preferable baking conditions for forming the proton conductive solid electrolyte layer may be, for example, 1000 ° C. to 1500 ° C. in an air atmosphere for 1 hour to 5 hours. If the firing temperature is lower than 1000 ° C., the strength may not be sufficient, and peeling may occur, and the performance may be degraded. On the other hand, if the firing temperature is higher than 1500 ° C., the components of the firing jig and the components of the cells are partially reduced. There is a risk of reaction, and the cell is liable to be warped or cracked, which lowers the yield, which is not preferable. The firing temperature is preferably 1300 ° C. or higher.

2. Formation of Anode Layer When the steam electrolysis cell of the present invention is an electrolyte-supporting cell, the anode layer paste and the cathode layer paste are applied to the proton conductive solid electrolyte layer and then fired. The anode layer and the cathode layer may be formed by applying each paste to the proton-conducting solid electrolyte layer and then firing them simultaneously, or may be formed by firing them separately. In general, it is not always the same, so it is generally preferable to first form an electrode layer having a higher firing temperature and then form the other electrode layer.

  When the steam electrolysis cell of the present invention is an electrode-supporting cell, an electrolyte layer may be formed on an electrode layer serving as a support layer, and the other electrode layer may be further formed on the electrolyte layer. . In this case, since the firing temperature of the cathode layer is generally higher than that of the anode layer, the cathode layer or a precursor thereof is used as a support layer, an electrolyte layer is formed thereon, and the anode layer is further formed on the electrolyte layer. It is good to form.

The anode layer of the cell for steam electrolysis according to the present invention needs to have a catalytic action to promote the reaction of 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ and have to have electron conductivity. As such a material, a perovskite-type metal oxide containing a transition metal element which is a catalyst component for promoting the above reaction can be used. In the present invention, it is preferable to use a perovskite-type metal oxide as a main component.

  As described above, the main component of the anode layer of the cell for steam electrolysis according to the present invention is preferably a perovskite-type metal oxide. In the present invention, "the perovskite-type metal oxide is a main component of the anode layer" means that, during the formation of the anode layer, perovskite occupies the raw materials of the components constituting the anode layer excluding components that disappear by firing such as binders and solvents. It means that the ratio of the type metal oxide is 60 v / v% or more. The ratio is preferably at least 65 v / v%, more preferably at least 70 v / v%, even more preferably at least 75 v / v%. On the other hand, the upper limit of the ratio is not particularly limited, and substantially 100 v / v% excluding unavoidable impurities and unavoidable residues may be a perovskite-type metal oxide. Since it may be contained, the ratio is preferably 95 v / v% or less, more preferably 90 v / v% or less, and even more preferably 85 v / v% or less.

  The perovskite-type metal oxide constituting the anode layer includes, for example, an A site containing one or more elements selected from Ba, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, and Yb, and a B site It is preferable that one or more elements selected from Co, Ni and Fe are included, and that the A site contains one or more elements selected from Ba, Sr, La, Pr, Nd, and Sm. More preferred. Specifically, Ba-La-Co system, Sm-Sr-Co system, La-Sr-Co system, La-Ba-Co-Fe system, Pr-Sr-Co system, Nd-Sr-Co system, Ba And perovskite-type metal oxides such as -Sr-Co-Fe system. These can be used alone, or an electrode to which the above-mentioned proton conductive oxide or the like is added can also be used.

  The anode layer of the cell for steam electrolysis according to the present invention may contain an electron conductive component in addition to the perovskite-type metal oxide. Examples of the electron conductive component include metals such as silver, nickel, cobalt, iron, platinum, palladium, and ruthenium; and silver oxide, nickel oxide, cobalt oxide, iron oxide, etc. in a reducing atmosphere or an air atmosphere. A variable metal oxide; or a composite metal oxide such as nickel ferrite or cobalt ferrite containing two or more of these metal oxides. These can be used alone or, if necessary, in combination of two or more. Among these, silver, metallic nickel, metallic cobalt, metallic iron or their oxides are preferred.

  The use amount of the electron conductive component is not particularly limited, but is preferably, for example, not less than 2.0% by mass and not more than 25% by mass based on the whole electrode. When the ratio is 2.0% by mass or more, the electron conductivity is more reliably exhibited. On the other hand, if the ratio is too large, the porosity of the electrode may be excessively reduced. Therefore, the ratio is preferably 25% by mass or less.

  The thickness of the anode layer is not particularly limited, and may be appropriately determined depending on the cell shape and the like. The thickness of the anode layer is, for example, preferably 5 μm or more, more preferably 10 μm or more, preferably 100 μm or less, more preferably 80 μm or less in any of the electrolyte-supported cell and the electrode-supported cell. preferable.

  The anode layer can be formed by an ordinary method. For example, after preparing the paste of the above-described constituent components in the same manner as in the case of the proton conductive solid electrolyte layer, the paste may be applied on the proton conductive solid electrolyte layer so as to obtain a desired film thickness, and then fired. In the case of an electrode-supporting cell having an electrode layer as a support layer, after forming the electrode layer also serving as a support, a proton-conductive solid electrolyte layer is formed thereon, and Then, the other electrode layer may be formed. Alternatively, a porous support layer may be formed below the electrode layer (on the side opposite to the electrolyte layer).

As a main raw material for forming the anode layer, a perovskite-type metal oxide powder having a BET specific surface area of 2.0 m ² / g or more when fired under the same firing conditions as for forming the anode layer is used. Is preferred. Preferably at least 2.1 m ² / g as the BET specific surface area, more preferably at least 2.2 m ² / g, more preferably not less than 2.4 m ² / g. The larger the BET specific surface area is, the more the production efficiency of H ₂ is improved. However, if the BET specific surface area is excessively large, the strength of the anode layer may not be sufficiently secured, so that the BET specific surface area is preferably 15 m ² / g or less, preferably 10 m ² / g. ² / g or less is more preferable, and 8 m < ² > / g or less is still more preferable. The firing of the perovskite-type metal oxide powder, which is a raw material powder for the anode layer, is performed only to measure the BET specific surface area that is an index of the present invention, and is used to actually form the anode layer. As the raw material perovskite-type metal oxide powder, the powder before the above-mentioned firing is used. That is, the above-mentioned baking and the measurement of the BET specific surface area are performed independently of the formation of the anode layer.

  To adjust the BET specific surface area of the raw material perovskite-type metal oxide powder fired under the same conditions as the firing conditions for forming the anode layer to a predetermined range, for example, the raw material perovskite-type metal oxide powder before firing The constituent elements, the composition ratio, the grinding conditions, the grinding method and the like may be adjusted. As a specific pulverization method, any of dry pulverization, wet pulverization or freeze pulverization may be used, and a ball mill, a bead mill, an attritor, a rod mill, a hammer mill, a freezer mill, a jet mill, or the like can be used. The conditions should be appropriately selected depending on the above-mentioned pulverizing method or the characteristics of the pulverizer, and cannot be specified unconditionally. For example, when a rotary pulverizer such as a ball mill, a bead mill, and an attritor is used, the rotation speed is 10 rpm. As mentioned above, the pulverization may be performed at 150 rpm or less for 1 hour or more and 200 hours or less, and it is preferable to perform wet pulverization at a rotation speed of 50 rpm or more and 100 rpm or less for 1 hour or more and 100 hours or less.

  In this specification, the BET specific surface area refers to a surface area obtained by adsorbing nitrogen molecules to a substance to be measured at a liquid nitrogen temperature of -196 ° C. and obtaining the amount of the adsorbed nitrogen molecules using the BET equation.

  As a method for forming the anode layer, for example, after preparing a paste of the above-described components in the same manner as in the case of the proton-conductive solid electrolyte layer, coating is performed so that a desired film thickness is obtained on the proton-conductive solid electrolyte layer. After that, firing may be performed. Preferred firing conditions for forming the anode layer may be, for example, 700 ° C. or more and 900 ° C. or less in an air atmosphere for 30 minutes or more and 2 hours or less. If the firing temperature is lower than 700 ° C., peeling may occur due to low adhesion of the electrode, and the performance may decrease. On the other hand, if the firing temperature is higher than 900 ° C., the hydrogen generation rate may decrease, which is not preferable. . The firing temperature is preferably from 750 ° C to 900 ° C, more preferably from 800 ° C to 900 ° C. The firing time is preferably 45 minutes or more and 1 hour 30 minutes or less.

3. Formation of Cathode Layer The cathode layer of the cell according to the present invention needs to have a catalytic action to promote the reaction of 4H ⁺ + 4e ⁻ → 2H ₂ and have to have electron conductivity. Examples of such a material include metal elements such as Pt, Pd, Ni, Co, Fe, and Ru, and a mixture of the metal element and a perovskite-type metal oxide that is a material of the proton-conductive solid electrolyte layer. The cathode layer preferably contains a mixture of a metal element and a perovskite-type metal oxide from the viewpoint of affinity and adhesion to the proton-conductive solid electrolyte layer.

  Examples of the metal element include metals such as Pt, Pd, Ni, Co, Fe, and Ru; metal oxides such as nickel oxide, cobalt oxide, and iron oxide that change into electron-conductive metals in a reducing atmosphere; Composite metal oxides such as nickel ferrite and cobalt ferrite containing two or more kinds of substances. These can be used alone, and if necessary, two or more kinds may be used in appropriate combination. Among them, one or more selected from Ni, Co, Fe and oxides thereof, and more preferably nickel oxide are preferable.

The perovskite-type metal oxide contains a strontium at the A site and a trivalent or tetravalent element belonging to the 4th to 14th groups of the periodic table at the B site, and the perovskite-type metal oxide. Part of the A site and / or B site of the product is selected from La, Pr, Nd, Sm, Gd, Yb, Sc, Y, Ce, In, Ga, Fe, Co, Ni, Zn, Ta and Nb. A perovskite-type metal oxide substituted with one or more elements can be used. The cathode layer of the present invention has the following general formula (2):
Sr ₁ Zr _b1 Ce _c1 Y _d1 O _x (2)
(Here, b1, c1, d1 and x represent the atomic ratio of Zr, Ce, Y and O, respectively, and 0.4 ≦ b1 ≦ 0.7, 0.1 ≦ c1 ≦ 0.6, 0.1 ≦ d1 ≦ 0.2, and x is a numerical value determined by the oxidation state of each element.)
A perovskite-type metal oxide represented by the following formula is preferably used.

In equation (2),
b1 is preferably 0.45 or more, more preferably 0.47 or more, preferably 0.65 or less, and more preferably 0.60 or less.
c1 is preferably 0.15 or more, more preferably 0.20 or more, preferably 0.55 or less, and more preferably 0.50 or less.
d1 is preferably 0.18 or less, more preferably 0.15 or less, still more preferably 0.12 or less, and even more preferably 0.1.

  When a mixture of a metal element and a perovskite-type metal oxide is used as the cathode material, the proportions thereof are not particularly limited, and may be appropriately adjusted in consideration of the electronic conductivity, catalytic ability, and the like of the specifically used material. However, for example, the ratio of the perovskite-type metal oxide to the total of the metal element and the perovskite-type metal oxide can be set to 20 v / v% or more and 80 v / v% or less. The ratio is more preferably 25 v / v% or more, and further preferably 70 v / v% or less.

  The thickness of the cathode layer is not particularly limited and may be appropriately determined depending on the cell shape and the like. For example, in the case of an electrolyte-supported cell, the thickness is preferably 5 μm or more and 100 μm or less. In the case of an electrode-supporting cell having the electrode layer as a support layer, the thickness is preferably 100 μm or more and 2000 μm or less, more preferably 150 μm or more and 1000 μm or less. The reasons for defining the lower and upper limits are the same as in the case of the electrolyte-supported cell.

As a method of forming the cathode layer, for example, after preparing a paste of the above-described components in the same manner as in the case of the proton conductive solid electrolyte layer, the paste was applied on the proton conductive solid electrolyte layer so as to obtain a desired film thickness. After that, firing may be performed. In the case of an electrode-supported cell having the cathode layer as a support layer, after forming the cathode layer also serving as a support, a proton-conductive solid electrolyte layer is formed thereon, and further the electrolyte layer is formed. An anode layer may be formed thereover. Alternatively, a porous support layer may be formed below the cathode layer (on the side opposite to the electrolyte layer). When a metal oxide is used as the metal element material, the metal oxide is reduced to the metal element by actively performing the reduction treatment, and the volume is reduced to make the cathode layer porous. Can be. The cell for steam electrolysis having such a porous cathode layer has a higher H ₂ production capacity.

  Preferred firing conditions for forming the cathode layer may be, for example, 1000 ° C. or more and 1500 ° C. or less, and 1 hour or more and 5 hours or less. If the firing temperature is lower than 1000 ° C., the strength is not sufficient, and peeling may occur, and the performance may be degraded. On the other hand, if the firing temperature is higher than 1500 ° C., the components of the firing jig and the components of the cathode or the electrolyte may be inconsistent. There is a possibility that a partial reaction may occur, and furthermore, the cell may be easily warped or cracked, and the yield is undesirably reduced. The firing temperature is preferably 1100 ° C. or higher, more preferably 1300 ° C. or higher. The firing time is preferably 1 hour 30 minutes or more and 4 hours or less.

By using the cell for steam electrolysis according to the present invention and supplying steam to the anode while applying a voltage between the electrodes and supplying a current, H ₂ can be efficiently produced.

The cell for steam electrolysis according to the present invention has higher current efficiency, which is the production efficiency of H ₂ with respect to the supplied current, than the conventional cell, and consumes less power. Such a difference is more remarkable as the current density is higher.

  Hereinafter, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to the following Examples, and may be appropriately modified within a range that can be adapted to the purpose of the preceding and the following. It is of course possible to carry out them, and all of them are included in the technical scope of the present invention.

Example 1
(1) Preparation of cathode support precursor A commercially available nickel oxide powder (manufactured by Seido Chemical Co., Ltd., product name “Green”) and SrZr _0.5 Ce _0.4 Y _0.1 O _x particles as electrolyte particles were mixed with the nickel oxide powder 72 vol. %, And 28 vol% of electrolyte particles. A binder and a solvent were added to these particles, and further, a plasticizer, a dispersant, a lubricant and an antifoaming agent were added. The mixture was wet-pulverized and mixed with a ball mill for 30 hours to prepare a slurry. The obtained slurry was formed into a sheet by a tape casting method, and then dried at 80 ° C. for 1 hour to prepare a cathode support precursor.

(2) Preparation of Electrolyte Powder The solid phase method was used to synthesize the proton conductive metal oxide used in this example. A commercially available powder of BaCO ₃ , SrCO ₃ , ZrO ₂ , CeO ₂ , and Y ₂ O _{3 having} a purity of 99.9% by mass was mixed so as to have a composition of Ba _0.9 Sr _0.1 Zr _0.5 Ce _0.4 Y _0.1 O _x . Ethanol was added to the obtained mixture, and the mixture was wet-pulverized with a planetary ball mill for 2 hours and then dried at 120 ° C. for 10 hours. Next, the powder was fired at 1200 ° C. for 10 hours in an air atmosphere to obtain an electrolyte powder. Further, ethanol was added to the obtained electrolyte powder, wet-pulverized by a planetary ball mill for 3 hours, and dried at 120 ° C. for 10 hours to obtain an electrolyte powder usable as an electrolyte layer material for steam electrolysis. The composition of the resulting electrolyte powder, a _{Ba 0.9 Sr 0.1 Zr 0.5 Ce 0.4} Y 0.1 O x, the X-ray diffraction, was confirmed to be a single phase containing the perovskite.

(3) Preparation of Half Cell Ba _0.9 Sr _0.1 Zr _0.5 Ce _0.4 Y _0.1 O _x obtained in the above (2), ethyl cellulose and α-terpineol were mixed in a mortar. Thereafter, the mixture was kneaded using a three-roll mill (manufactured by EXAKT technologies, model “M-80S”) to obtain an electrolyte layer paste.
The paste is applied on the cathode support precursor prepared in the above (1) by a screen printing method, dried at 80 ° C. for 30 minutes, and then baked at 1400 ° C. in an air atmosphere for 2 hours to obtain proton conduction. A half cell was prepared in which the thickness of the conductive solid electrolyte layer was 15 μm and the thickness of the cathode support was 250 μm.

(4) Preparation of Anode Layer A commercially available powder of La ₂ O ₃ , BaCO ₃ and Co ₃ O _{4 having} a purity of 99.9% by mass was mixed so as to have a composition of La _0.5 Ba _0.5 CoO _x . Ethanol was added to the obtained mixture, and the mixture was wet-pulverized with a ball mill for 60 hours, and then dried at 120 ° C. for 10 hours. Next, a powder was obtained by performing a heat treatment at 1100 ° C. for 10 hours. Further, ethanol was added to the obtained powder, wet-pulverized with a ball mill for 100 hours, and then dried at 120 ° C. for 10 hours to obtain a raw material powder that could be used as an anode layer material for steam electrolysis. The composition of the obtained anode layer raw material powder was La _0.5 Ba _0.5 CoO _x , and it was confirmed by X-ray diffraction that it was a single phase composed of perovskite.
Ethyl cellulose as a binder and α-terpineol as a solvent were added to the anode layer raw material powder, and mixed in a mortar. Subsequently, the mixture was kneaded using a three-roll mill (manufactured by EXAKT technologies, model “M-80S”) to obtain an anode paste.
The above-mentioned anode paste is applied to the opposite side of the cathode support in the proton-conductive metal oxide of the half cell obtained in the above (3) by a screen printing method, and then baked at 850 ° C. for 1 hour in an air atmosphere. An anode layer having a thickness of 30 μm was formed.

Examples 2 to 6
A cell was produced in the same manner as in Example 1, except that the proton-conductive metal oxide in (2) was changed to a perovskite-type metal oxide shown in Table 1.

Comparative Example 1
The electrolyte particles in (1) of Example 1 were changed to BaZr _0.44 Ce _0.36 Y _0.2 O _x particles, and the proton conductive metal oxide in (2) was changed to BaZr _0.44 Ce _0.36 Y _0.2 O _x , and the firing temperature was changed. A cell was fabricated in the same manner except that the temperature was changed to 1550 ° C.

Comparative Example 2
The proton conductive metal oxide in (1) of Example 1 was changed to SrZr _0.5 Ce _0.4 Y _0.1 O _x particles, and the proton conductive metal oxide in (2) was changed to BaZr _0.44 Ce _0.36 Y _0.2 O _x . A cell was fabricated in the same manner as in Example 1 except for the above.

Comparative Example 3
Example 1 was repeated except that the electrolyte particles in (1) were changed to SrZr _0.5 Ce _0.4 Y _0.1 O _x particles and the proton conductive metal oxide in (2) was changed to SrZr _0.5 Ce _0.4 Y _0.1 O _x. To produce a cell.

Test example 1
The cells prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were gas-sealed by sandwiching a glass ring so as not to contact the anode layer and softening at 800 ° C. Then, after the temperature was lowered to 600 ° C. is operating temperature, and reduced the NiO in the cathode support by introducing N ₂ gas containing 10v / v% H ₂ gas. An argon gas containing 20 v / v% of steam and 1 v / v% of oxygen is introduced at a flow rate of 100 NmL / min to the anode layer side, and an argon gas containing 2 v / v% of steam and 1 v / v% of hydrogen is introduced to the cathode layer side. The flow was introduced at a flow rate of 100 NmL / min. A current-voltage curve was obtained by measuring the voltage while changing the current using a potentiogalvanostat.
In addition, the concentration of hydrogen generated in the cathode layer was determined by gas chromatography, and the flow rate of the cathode outlet gas was measured by a high-precision precision membrane flow meter (manufactured by HORIBA STEC). From the obtained measurement values, the H ₂ generation rate was calculated by the following equation.
H ₂ production rate ^{(μmol / h · cm 2)} = [{(Qv 0 × Hc 0/100) - (Qv 1 × Hc 1/100)} × 60 × 10 6] / (22400 × S)
Qv ₀ : Cathode outlet gas flow rate when no current is applied (NmL / min)
Hc ₀ : H ₂ concentration (v / v%) in the cathode outlet gas when no current is applied
Qv ₁ : Cathode outlet gas flow rate during energization (NmL / min)
Hc ₁ : H ₂ concentration (v / v%) in the cathode outlet gas during energization
S: Anode electrode area (cm ² )
The theoretical H ₂ generation rate was calculated by the following equation.
Theoretical H ₂ generation rate (μmol / h · cm ² ) = {current passed (A) × 3600 (s) × 10 ⁶ } / {2 × F × current area (cm ² )}
F: Faraday constant addition, H ₂ from the production rate and the theoretical H ₂ production rate based on the measured values was calculated current efficiency by the following equation.
Current efficiency (%) = (H ₂ generation rate / theoretical H ₂ generation rate) × 100
Table 1 shows the composition of the anode layer, cathode layer and electrolyte layer, cell terminal voltage and current efficiency at a current density of 0.5 A / cm ² in each cell.

  As shown in Table 1, the proton conductive solid electrolyte of the present invention and the method for producing the same enable low power consumption and high current efficiency, and can be sintered at a lower temperature than conventional proton conductive solid electrolytes. .

Claims (3)

It has an anode layer and a cathode layer, has a proton conductive solid electrolyte layer between the anode layer and the cathode layer, and the proton conductive solid electrolyte layer has the following formula (1):
_{Ba (1-a) Sr a} Zr b Ce c M d O x (1)
(Where Ba is barium, Sr is strontium, Zr is zirconium, Ce is cerium, M is at least one element selected from neodymium, gadolinium, ytterbium and yttrium, O is oxygen,
a, b, c, d and x represent the atomic ratio of Sr, Zr, Ce, M and O, respectively, and 0.1 ≦ a ≦ 0.2, 0.4 ≦ b ≦ 0.7, 0.1 ≦ c ≦ 0.4, 0.1 ≦ d ≦ 0.2, and x is a numerical value determined by the oxidation state of each element.)
Including a perovskite-type proton conductive metal oxide represented by
A cell for steam electrolysis, wherein a molar ratio of zirconium to cerium (Zr / Ce ratio) in the proton conductive metal oxide is 1 ≦ (b / c) ≦ 7.   The cathode layer contains one or more metal elements selected from Ni, Co, Fe and oxides thereof, strontium at A site, and trivalent material belonging to Group 4 to Group 14 of the periodic table at B site. Alternatively, the cell for steam electrolysis according to claim 1, which contains a perovskite-type metal oxide containing a tetravalent element.   The method for producing a steam electrolysis cell according to claim 1, wherein the slurry containing the perovskite-type metal oxide is formed into a sheet and fired at 1,000 ° C. or more and 1500 ° C. or less in an air atmosphere. A method for producing a cell for steam electrolysis, comprising a step of forming a conductive solid electrolyte layer.