JP2023056800A - Electrochemical cell and hydrocarbon manufacturing apparatus - Google Patents

Abstract

To provide an electrochemical cell used for the production of a hydrocarbon by co-electrolysis with carbon dioxide and water vapor.SOLUTION: An electrochemical cell 1 comprises a cathode 2 and an anode 3 arranged on two opposite surfaces 12 and 13 of an oxide ion conductor 11. The cathode 2 has a laminated structure, in which a conductive metallic layer 2A that is configured with a first particle 21 having silver as a principal component and is arranged so as to contact a raw material gas G including carbon dioxide and water vapor, a complex oxide layer 2B that is configured with a second particle 22 having a complex oxide including a transition metal element as a principal component and is arranged so as to contact the oxide ion conductor 11, and an interlayer 2C that is arranged between the conductive metallic layer 2A and the complex oxide layer 2B and is configured with the first particle 21 and the second particle 22 are stacked.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrochemical cell used to produce hydrocarbons and a hydrocarbon production apparatus using the electrochemical cell.

In recent years, from the viewpoint of reducing carbon dioxide emissions and carbon recycling, it is expected to establish a technique for co-electrolyzing carbon dioxide and water vapor by an electrochemical process and converting them into hydrocarbons such as methane. As an electrochemical cell used in such a process, a solid oxide electrolysis cell (Solid Oxide Electrolysis Cell; SOEC) using a solid oxide as a material is generally known, and a desired reaction proceeds to improve reaction efficiency. In order to increase the resistance, investigations are being conducted on composite oxides, additive components, electrode structures, etc., which are used as electrode materials.

For example, in Patent Document 1, in an electrochemical cell used in a fuel cell, in order to improve the reaction activity of the air electrode active layer functioning as a cathode, an electrode provided with two regions having different average particle diameters of electrode materials A structure is disclosed. Specifically, the average particle size of the first region on the side of the solid electrolyte layer, which tends to affect reaction activity, is smaller than that of the second region located outside the air electrode active layer. It increases the total surface area and increases the adsorption/reaction field.

Patent Document 1 proposes to use a perovskite-type composite oxide as an electrode material, and to increase the reaction activity of the electrode as a whole by adjusting the types and proportions of the elements partially substituted for each region. It is Further, for example, a method of adding a metal component such as a platinum group metal to the electrode material to improve the catalytic activity of the electrode has been proposed.

JP 2018-26339 A

Thus, the selection of electrode materials and the improvement of electrode structures are important for the performance of electrochemical cells. On the other hand, in order to produce hydrocarbons using an electrochemical cell, it is necessary to electrolyze carbon dioxide and water vapor, which are the raw materials, and further proceed with the reaction between carbon monoxide and hydrogen produced by the electrolysis. . However, even if a conventional electrochemical cell is simply applied, it is difficult to proceed these reactions, and a single electrochemical cell suitable for generating hydrocarbons has not yet been known.

The present invention has been made in view of such problems, and provides an electrochemical cell capable of converting carbon dioxide and water vapor into hydrocarbons by an electrochemical process, and a hydrocarbon production apparatus using the electrochemical cell. It is in.

One aspect of the present invention is
In an electrochemical cell (1) comprising an oxide ion conductor (11) and a cathode (2) and an anode (3) provided on two opposite sides (12, 13) of said oxide ion conductor ,
The cathode is
A conductive metal layer (2A) composed of first particles (21) containing silver as a main component and in contact with a raw material gas (G) containing carbon dioxide and water vapor;
a composite oxide layer (2B) composed of second particles (22) mainly composed of a composite oxide containing a transition metal element and in contact with the oxide ion conductor;
An electrochemical cell having a structure in which an intermediate layer (2C) provided between the conductive metal layer and the composite oxide layer and composed of the first particles and the second particles is laminated. be.

Another aspect of the present invention is a hydrocarbon production apparatus (100) using the electrochemical cell according to the above aspect,
A hydrocarbon production section (10) in which the electrochemical cell is arranged so as to close one end of a cylindrical gas flow section (101),
The gas flow part has a gas inlet part (102) and a gas outlet part (103) provided facing the cathode of the electrochemical cell,
the gas introduction unit supplies the raw material gas to the cathode with a direction perpendicular to the cathode as a gas introduction direction;
The gas lead-out part is arranged on the outer peripheral side of the gas lead-in part, and leads the reaction product at the cathode to the outside of the gas flow part, with the direction opposite to the gas lead-in direction as the gas lead-out direction. Located in a hydrocarbon production unit.

When a raw material gas containing carbon dioxide and water vapor is introduced into the cathode of the three-layer structure of the electrochemical cell, first, in the conductive metal layer containing the first particles mainly composed of silver, electrolysis of water vapor Hydrogen is produced and diffuses into the intermediate layer. The intermediate layer contains first particles and second particles whose main component is a composite oxide containing a transition metal element, and electrolysis of water vapor further progresses, and carbon monoxide is produced by electrolysis of carbon dioxide. It is thought that the intermediate layer has a hydrogen-rich atmosphere due to the hydrogen diffusing from the conductive metal layer. Furthermore, it is believed that the catalytic action of the second particles electroreduces the precursor and converts it to hydrocarbons. At this time, since it has not been confirmed that hydrocarbons are produced only in the intermediate layer or the composite oxide layer, by including both layers, the production of the precursor and its electrolytic reduction proceed step by step, resulting in carbonization. It is speculated that hydrogen production will become possible.

A hydrocarbon production apparatus using such an electrochemical cell is provided with a gas flow section having a gas outlet section on the outer periphery of the gas introduction section, and when the electrochemical cell is arranged on one end side of the gas flow section, compact and efficient carbonization can be achieved. A hydrogen production unit can be configured. In the gas flow part with this structure, the gas introduction part faces the cathode of the electrochemical cell, and the raw material gas is introduced in the vertical direction, while the gas flow is in the opposite direction in the gas outlet part. While the reaction progresses, the precursor-containing gas that has reached the composite oxide layer tends to remain without flowing out. Further, in the intermediate layer, electrolysis, which is an endothermic reaction, progresses and the temperature is lowered, which is suitable for the progress of methane production in the adjacent composite oxide layer. Therefore, the electrolytic reduction of the precursor is facilitated, and the conversion rate of methane can be increased.

As described above, according to the above aspect, it is possible to provide an electrochemical cell capable of converting carbon dioxide and water vapor into hydrocarbons by an electrochemical process, and a hydrocarbon production apparatus using the electrochemical cell.
It should be noted that the symbols in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the embodiments described later, and limit the technical scope of the present invention. not a thing

1 is an overall cross-sectional view schematically showing the configuration of an electrochemical cell in Embodiment 1. FIG. FIG. 3 is a cross-sectional view schematically showing the structure of the cathode, which is the main part of the electrochemical cell, in Embodiment 1, and is an enlarged cross-sectional view of part A in FIG. 2 ; FIG. 2 is an enlarged cross-sectional view of a main part for explaining the reaction at the cathode of the electrochemical cell in Embodiment 1; FIG. 2 is an enlarged cross-sectional view of a main part showing a configuration example of a gas distribution section of a hydrocarbon production section using an electrochemical cell in Embodiment 1; FIG. 5 is an enlarged cross-sectional view of a main part for explaining the raw material gas flow supplied to the cathode of the electrochemical cell in Embodiment 1, and is an enlarged cross-sectional view of part B in FIG. 4 ; 1 is an overall configuration diagram of a hydrocarbon production apparatus using an electrochemical cell in Embodiment 1. FIG. FIG. 7 is an enlarged cross-sectional view of a main part showing a configuration example of the gas introduction part of the hydrocarbon production apparatus in Embodiment 1, and is an enlarged cross-sectional view of part C in FIG. 6 ; FIG. 5 is an enlarged cross-sectional view of a main portion corresponding to the configuration of FIG. 4, for explaining the gas flow in the gas introduction portion of the hydrocarbon production apparatus in Embodiment 1; FIG. 8 is an enlarged cross-sectional view of a main part corresponding to the configuration of FIG. 7, for explaining the gas flow in the gas introduction portion of the hydrocarbon production apparatus in Embodiment 1; FIG. 2 is a columnar graph showing a comparison of methane conversion rates in methane production tests using hydrocarbon production equipment in Examples. FIG. 4 is a graph showing the relationship between the methane production rate and the pressure in the methane synthesis reaction in Reference Example.

(Embodiment 1)
Embodiments of an electrochemical cell and a hydrocarbon production apparatus will be described with reference to FIGS. 1 to 9. FIG. As shown in FIG. 1, an electrochemical cell 1 comprises an oxide ion conductor 11 and a cathode 2 and an anode 3 provided on two opposite sides 12 , 13 of the oxide ion conductor 11 . The cathode 2 and the anode 3 face each other with a flat plate-shaped oxide ion _{conductor 11} interposed therebetween. is supplied.

As shown in FIGS. 2 and 3, the cathode 2 includes a conductive metal layer 2A composed of first particles 21 containing silver (Ag) as a main component and a composite oxide containing a transition metal element as a main component. and an intermediate layer 2C composed of first particles 21 and second particles 22 are laminated in this order.

At this time, the conductive metal layer 2A is provided in contact with the space 4 into which the raw material gas G is introduced, and constitutes the outermost layer of the cathode 2. As shown in FIG. Surface 20 is shown as a virtual plane parallel to oxide ion conductor 11 . Composite oxide layer 2B is provided in contact with surface 12 of oxide ion conductor 11 on the source gas G side, and constitutes the innermost layer of cathode 2 . The intermediate layer 2C is located between the conductive metal layer 2A and the composite oxide layer 2B and is provided integrally with these layers. Gaps formed between particles in the conductive metal layer 2A, the composite oxide layer 2B and the intermediate layer 2C communicate with each other, and diffusion paths 23 through which the source gas G and the produced gas containing reaction products can diffuse. forming

Thus, the cathode 2 has a three-layer structure, and the intermediate layer 2C containing both the first particles and the second particles is formed between the conductive metal layer 2A and the composite oxide layer 2B. , in each layer, the co-electrolysis of CO ₂ and H ₂ O contained in the raw material gas G and the reaction of the electrolysis products proceed step by step, making it possible to produce hydrocarbons. When only the conductive metal layer 2A and the composite oxide layer 2B do not have the intermediate layer 2C, or when only the conductive metal layer 2A and the intermediate layer 2C do not have a structure corresponding to the composite oxide layer 2B , no hydrocarbon formation is observed.
Next, the detailed structure of the cathode 2 and the overall structure of the electrochemical cell 1 will be described.

The conductive metal layer 2A of the cathode 2 is a porous conductive metal layer composed of only the first particles 21 aggregated, and mainly has the effect of electrolyzing water vapor contained in the raw material gas G. As shown in FIG. At this time, as indicated by [I] in FIG. 3, it is considered that a reaction proceeds to generate hydrogen (H ₂ ) gas by electrolysis of water vapor. Hydrogen generated in the conductive metal layer 2A diffuses into the intermediate layer 2C together with the raw material gas G containing unreacted water vapor.

The first particles 21 are conductive metal particles containing silver as a main component metal, and may contain other catalyst metals within a range that does not interfere with the electrode reaction in the conductive metal layer 2A and the intermediate layer 2C. Preferably, the first particles 21 can be conductive metal particles containing only silver as the metal component.

The intermediate layer 2C is a porous mixed material layer formed between the conductive metal layer 2A and the composite oxide layer 2B, and the composite oxide layer 2B is composed of only the second particles 22 aggregated. It is a porous composite oxide layer. Like the conductive metal layer 2A, the intermediate layer 2C contains the first particles 21 containing silver as a main component, and like the composite oxide layer 2B, it contains a composite oxide containing a transition metal element as a main component. It is configured including the second particles 22 .

As indicated by [II] in FIG. 3, in the intermediate layer 2C, the electrolytic reaction of the raw material gas G and the reaction of the electrolysis product to generate a methane precursor proceed. That is, as with the conductive metal layer 2A, unreacted water vapor is electrolyzed to generate H ₂ , and CO ₂ gas contained in the raw material gas G is electrolyzed to produce carbon monoxide (CO) gas. Generate. Furthermore, a methane precursor is produced from the produced CO and H ₂ supplied from the conductive metal layer 2A or H ₂ produced in the intermediate layer 2C.

At this time, H ₂ generated in advance in the conductive metal layer diffuses into the intermediate layer 2C, and the intermediate layer _2C becomes in a hydrogen-rich state. exists around. As a result, it is thought that when CO is produced, the reaction with surrounding H ₂ proceeds rapidly, and methane precursors can be produced from a CO molecule and a plurality of H ₂ molecules as follows.
CO+ _2H2 →CO( _H2 ) ₂
CO( _H2 ) ₂ : methane precursor

As indicated by [III] in FIG. 3, in the composite oxide layer 2B, a reaction proceeds to generate methane (CH ₄ ) gas from the methane precursor. That is, when the generated gas containing the methane precursor generated in the intermediate layer 2C diffuses into the composite oxide layer 2B, the catalytic action of the second particles 22 electrolytically reduces the methane precursor as follows, resulting in CH It is assumed that it is converted to ₄ .
CO( _H2 ) ₂ +2e ^-- > _CH4 + ^O2-
Oxide ions (O ²⁻ ) generated by the electrolytic reduction of the methane precursor pass through the oxide ion conductor 11 in contact with the composite oxide layer 2B and are released to the anode 3 side.

The second particles 22 are particles of a composite oxide containing at least one element selected from transition metals, have electrical conductivity, function as an electrolytic electrode in the intermediate layer 2C, and function in the composite oxide layer 2B. It functions as a reduction catalyst for methane precursors. Preferably, it is a composite oxide having mixed conductivity of electrons and oxide ions. As a composite oxide having such functions, a perovskite-type composite oxide containing a transition metal element, a ceria-based composite oxide containing a transition metal element, and the like are used.

A perovskite-type composite oxide containing a transition metal element is a composite oxide having a perovskite structure represented by the general formula ABO ₃ as a basic composition and containing at least one transition metal element. A similar structure including a perovskite structure, for example, a composite oxide represented by [(A1) BO ₃ +(A2) O] or the like may be used. In that case, the A1 or A2 element may contain at least one selected from rare earth elements such as lanthanide elements and alkaline earth metal elements, and the B element may contain at least one selected from transition metal elements. As the A1 or A2 element and the B element, for example, one or more of the following are preferably selected.
A1 or A2; La, Sm, Sr, Ca, Ba
B: V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd

Preferably, a lanthanum-based composite oxide containing lanthanum (La) can be used as the perovskite-type or similar structure composite oxide. Examples of such lanthanum-based composite oxides are preferably (La,Sr)CoO ₃ , (La,Sr)(Co,Fe)O ₃ , from the viewpoint of electronic conductivity and ionic conductivity. LaSr(Co,Fe)O ₄ or the like is used. Specific examples of such composite oxides include LaSrCo _0.8 Fe _0.2 O ₄ and the like. However, it is not limited to this.

Specifically, the ceria-based composite oxide containing a transition metal element can be a composite oxide represented by a composition formula of Ce _1-x (M1) _x O ₂ (where 0<x<1). can. The M1 element in the formula is a transition metal element, and for example, one or two or more elements shown below are selected. Preferably, X is a value selected from the range of 0.1 to 0.4.
M1: V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd
Examples of such ceria-based composite oxides include Ce _1-x (Co, Fe) _x O ₃ and the like from the viewpoint of electronic conductivity and ionic conductivity. _0.75 Co _0.2 Fe _0.05 O ₂ and the like. However, it is not limited to this.

A ceria-based composite oxide containing a transition metal element has an electronic structure that is metallic and electrically conductive by substituting a part of Ce with a transition metal in contrast to cerium oxide (CeO ₂ ), which has good ion conductivity. is given. At this time, for example, if Co is selected as the M1 element, a larger amount of Ce can be substituted, which is advantageous for enhancing electrical conductivity. In addition, in order to impart catalytic function as well as electrical conductivity, it is necessary to adsorb the methane precursor, supply electrons, and reduce it. Having a structure is preferred. When the M1 element described above is selected, it is believed that such a reaction field is advantageously formed within the electrode, and it is preferable that a plurality of transition metal elements be included.

Preferably, in the intermediate layer 2C, the first particles 21 are formed so as to be continuous with the first particles 21 of the conductive metal layer 2A, and extend to the surface of the second particles 22 to form an integrated structure. It is preferable that In that case, the average particle size of the first particles 21 is preferably smaller than the average particle size of the second particles 22, and the intermediate layer 2C is an aggregate of the second particles 22 having the first particles 21 attached to the surface. constructed as a body. For example, the primary particle size of the material of the first particles 21 can be 0.1 μm or less, and the primary particle size of the material of the second particles 22 can be 1 μm or less. The plurality of first particles 21 on the surface of the second particles 22 are electrically connected to each other to form a belt-like series, one end of which is electrically connected to the first particles 21 of the conductive metal layer 2A. be done. Adjacent particles of the second particles 22 to which the first particles 21 are attached are electrically connected to each other, and are formed so as to be continuous with the second particles 22 of the composite oxide layer 2B and integrated. is preferred.

As a result, in the cathode 2, the first particles 21 or the second particles 22 are connected to each other, making it easier to form a three-dimensional mesh-like conduction path, thereby improving electronic conductivity or ionic conductivity. In addition, in the intermediate layer 2C, the area where the first particles 21 and the second particles 22 are in contact with each other expands, the electrode reaction proceeds more easily, the first particles 21 become smaller, and the second particles 22 The gaps between the particles are ensured, and the gas diffusibility of the diffusion path 23 is improved.

Thus, in the cathode 2, by appropriately arranging the intermediate layer 2C between the conductive metal layer 2A and the composite oxide layer 2B, it is possible to produce hydrocarbons with a single electrochemical cell 1. Become. Preferably, a ratio t1/ It is preferable that t is 1% or more, and CH ₄ can be generated by co-electrolysis of the raw material gas G. More preferably, by setting the ratio t1/t to 5% or more, a practically sufficient methane conversion rate can be obtained. Incidentally, the methane conversion rate is obtained by the following formula.
Methane conversion rate = (concentration of methane in generated gas) / [(CO ₂ concentration in source gas) - (CO ₂ concentration in generated gas)]

On the other hand, even if the ratio t1/t exceeds 5% and increases to about 50%, the effect of improving the methane conversion rate is limited, and if it is increased to about 95%, the methane conversion rate tends to decrease. be done. Also, as the ratio t1/t increases, the amount of the first particles 21 used increases. It is preferable to appropriately select such that the desired methane conversion rate is obtained.

Although the thickness of the cathode 2 is not particularly limited, it is generally preferable that the thickness for acting as an electrode is, for example, about 20 μm to 30 μm or more. Preferably, the total layer thickness t of the intermediate layer 2C and the composite oxide layer 2B is set in the range of 20 μm or more and 30 μm or less, and the layer thickness of the conductive metal layer 2A is appropriately selected from the viewpoint of electronic conductivity. preferably. Preferably, the layer thickness of the conductive metal layer 2A can be set to about 10 μm or more to obtain sufficient electron conductivity.

The layer thickness t1 of the intermediate layer 2C is determined by adjusting the viscosity and the like of the printing paste for forming the conductive metal layer 2A and by adjusting the penetration depth when applied to the surface of the composite oxide layer 2B. Desired thickness can be controlled. The thickness of each layer of the cathode 2 can be measured, for example, by image observation of a sample cross section using an electron microscope. In that case, the region where the second particles 22 having the first particles 21 adhered to the surface is the intermediate layer 2C, and both sides thereof are the conductive metal layer 2A or the composite oxide layer 2B, each having a thickness of a plurality of places. can be taken as the thickness of each layer.

The oxide ion conductor 11 is a dense solid electrolyte layer arranged between the cathode 2 and the anode 3, and allows oxide ions (O ²⁻ ) generated on the cathode 2 side to pass through to the anode 3 side. . The O ²⁻ transmitted to the anode 3 emits electrons (e ⁻ ) to generate oxygen (O ₂ ) gas. Although the material of the oxide ion conductor 11 is not necessarily limited, it is preferable to use stabilized zirconia, non-oriented or oriented apatite type compound from the viewpoint of withstand voltage, oxide ion conductivity, etc. can be done.

Stabilized zirconia is a zirconia-based oxide that is stabilized by dissolving an oxide such as a rare earth element as a stabilizer in zirconium oxide (ZrO ₂ ) having a fluorite-type crystal structure. Examples of stabilizers include yttria (Y ₂ O ₃ ) and scandia (Sc ₂ O ₃ ). Zirconium chloride (YSZ) can mainly be used.

The apatite-type compound is a compound having a hexagonal apatite-type crystal structure, and is a non-oriented compound having no orientation axis, or an oriented apatite-type compound including uniaxial orientation and biaxial orientation. be able to. In the case of an oriented apatite type compound, it preferably has c-axis orientation. An apatite-type compound generally has a higher oxide ion conductivity than stabilized zirconia, so the electrode reaction proceeds more easily, and more generated gas can be obtained. Moreover, those having orientation have higher oxide ion conductivity than non-orientation, contributing to the improvement of the methane conversion rate.

Examples of apatite-type compounds include compounds having a basic composition of phosphate-based apatite represented by the compositional formula (M2) ₁₀ (PO ₄ ) ₆ (X) ₂ . The M2 site includes, for example, one or more selected from the following monovalent or divalent metal ions, etc., and the X site includes, for example, one selected from the following anions, H ₂ O, etc. Two or more types can be included.
M2: Li ⁺ , Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , Ba ²⁺ , Mn ²⁺ , Fe ²⁺ , Cu ²⁺
X: OH ⁻ , F ⁻ , Cl ⁻ , CO ₃ ²⁻ , H ₂ O
Phosphate-based apatite containing Na ⁺ and Ca ²⁺ at the M2 site and OH ⁻ and CO ₃ ²⁻ at the X site is preferably used from the viewpoint of improving oxide ion conductivity. Examples of such apatite type compounds include Ca10 _{- xNa2x/3} ( _PO4 ) ₅ ( _CO3 ) _x ( _H2O ) _x (OH) _2-x/3 . However, it is not limited to these.

An apatite-type composite oxide represented by the following (1) can also be used as the apatite-type compound. i.e.
Formula (1): A _9.3+x [T _6.0-y M _y ] O _26.0+z
(A in the formula is from the group consisting of La, Ce, Y, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr and Ba One or more selected elements, where T is an element containing Si or Ge or both, and M is Mg, Al, Sc, Ti, V, Cr, Mn , Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, W and Mo.
x in the formula is a number of -1.4 or more and 1.5 or less, y in the formula is a number of 0.0 or more and 3.0 or less, and z in the formula is -5.0 or more and 5.2 The oxide ion conductor 11 is a composite oxide having an apatite-type structure in which the ratio of the number of moles of A to the number of moles of T (A/T) is 1.4 or more and 3.7 or less. can be used as

In Formula (1), the A element is a lanthanide or alkaline earth metal that becomes a positively charged ion and can form an apatite-type hexagonal crystal structure. Among these, a combination of one or more elements selected from the group consisting of La, Nd, Ba, Sr, Ca and Ce is preferable from the viewpoint of further increasing the oxide ion conductivity. Among them, one of La or Nd, or a combination of La and one or more elements selected from the group consisting of Nd, Ba, Sr, Ca and Ce is preferable.
Moreover, T in the formula (1) may be an element containing Si or Ge or both.

The M element in the formula (1) is introduced by reaction with a metastable precursor (A _2+x TO _5+z ) in the gas phase when forming an oriented apatite structure, and as a result, The precursor can be changed to an apatite structure and crystals can be oriented in one direction.
From this point of view, any element may be used as the M element as long as it becomes a vapor phase at a temperature of 1000° C. or higher at which the precursor assumes an apatite structure, and can obtain the required vapor pressure. The "necessary vapor pressure" means a vapor pressure that can move in the gaseous state in the atmosphere and diffuse from the surface of the precursor to the grain boundary or intragranular to promote the reaction. .
Therefore, from such a point of view, the M element can be, for example, one or more elements selected from the group consisting of B, Ge, Zn, W, Sn and Mo. Among them, B, Ge and Zn are particularly preferable in terms of high degree of orientation and high productivity (orientation speed).

In the formula (1), x is preferably −1.4 or more and 1.5 or less, especially 0.00 or more and 0.70 or less, from the viewpoint of being able to increase the degree of orientation and oxygen ion conductivity. Among them, it is preferably 0.45 or more and 0.65 or less.
From the viewpoint of filling the T element position in the apatite crystal lattice, y in the formula (1) is preferably 0.0 or more and 3.0 or less, especially 1.0 or more and 2.0 or less, especially 1 .0 or more and 1.6 or less.
From the viewpoint of maintaining electrical neutrality in the apatite-type crystal lattice, z in formula (1) is preferably -5.0 or more and 5.2 or less, especially -1.5 or more and 1.5. In the following, it is preferably -1.0 or more and 1.0 or less.

In formula (1), the ratio of the number of moles of A to the number of moles of T (A/T), in other words, 9.3+x/6.0-y in formula (1) is the space in the apatite crystal lattice. From the viewpoint of maintaining a reasonable occupation rate, it is preferably 1.4 or more and 3.7 or less.
desirable

As the apatite-type composite oxide represented by the above formula (1), for example, a rare earth silicate-based composite oxide in which A in the formula is a rare earth element and T in the formula is Si can be used. . Examples of rare earth silicate-based composite oxides include La _9.3+x (Si _6.0-y B _y )O _26.0+z , La _9.3+x (Si _6.0-y Ge _y )O _26.0+z , La _9.3+x (Si6.0 _{-yZny ) O26.0+z} and the like. However, it is not limited to these.

In the case of producing a non-oriented apatite-type composite oxide, an oxide containing each constituent element is used as a raw material by a usual method, wet-mixed, formed into a sheet, heated and sintered, and compositely oxidized. A sintered body can be obtained. In the case of producing an oriented apatite-type composite oxide, a sintered precursor of a desired apatite-type composite oxide excluding a specific element is similarly produced, and then a sintered body containing a specific element is prepared. A specific element and a precursor can be reacted by a gas phase-solid phase diffusion process of heating in a gas phase to form an oriented apatite structure having a desired composition.

Thus, by adopting a manufacturing method including a vapor phase-solid phase diffusion process, a composite oxide having an apatite structure in which crystals are oriented in one direction can be obtained. In addition, since the occurrence of cracks or the like in the crystal can be suppressed, the oriented apatite type oxide ion conductor 11 having a larger area can be manufactured.

The constituent material of the anode 3 is not necessarily limited, but for example, a perovskite-type composite oxide containing a transition metal element can be used. Specifically, the perovskite-type composite oxide containing a transition metal element has, at the A site of the perovskite structure represented by the general formula _ABO3 , one or two elements selected from lanthanoid elements, alkaline earth metal elements, rare earth elements, and the like It is a composite oxide containing one or more elements and one or more transition metal elements at the B site. Preferably, (Ba, Sr)CoO ₃ or the like containing Ba and Sr at the A site and Co at the B site can be used. Examples of such composite oxides include Ba _0.6 Sr _0.4 CoO ₃ and the like. However, it is not limited to these.

As shown in FIG. 4 , the electrochemical cell 1 having such a configuration can constitute a hydrocarbon production section 10 having a gas flow section 101 . In the hydrocarbon production section 10 , the gas distribution section 101 includes a gas introduction section 102 to which the raw material gas G is supplied, and a gas outlet section 103 to which the produced gas in the electrochemical cell 1 is led out. The gas flow section 101 is configured as a pipe having a gas flow path inside, and here, a single-tube-shaped gas introduction section 102 and gas outlet section 103 are connected at an angle of 90°. , has a structure in which the gas flow path is bent at 90° at a connecting portion in the middle.

In the electrochemical cell 1, the cathode 2 forms a part of the inner wall of the gas circulation part 101 at the bent connection part of the gas circulation part 101, and the source gas is supplied to the surface 20 of the cathode 2 from the gas introduction part 102. It is arranged so that the introduction of G and the derivation of the produced gas can be performed smoothly. For example, the angle (gas introduction angle) θ1 formed between the gas flow direction of the raw material gas G and the cathode 2 indicated by the white arrow in the figure has an inclination of 45°, and the gas flow direction of the generated gas and the cathode 2 The angle (gas lead-out angle) .theta.2 formed with .theta.2 can have an inclination of 135.degree. In that case, the gas flow direction of the raw material gas G and the gas flow direction of the generated gas are perpendicular to each other. The angle formed with the cathode 2 is the angle with respect to the cathode surface, for example, the surface 20 which is a virtual plane, with the surface 12 of the oxide ion conductor 11 on the source gas G side as a reference.

As schematically shown in FIG. 5, in the electrochemical cell 1, a raw material gas G is supplied from a gas introduction part 102 toward the surface 20 of the cathode 2, and passes from the conductive metal layer 2A through the intermediate layer 2C. While diffusing into the oxide layer 2B, CH ₄ is generated by the co-electrolysis of CO ₂ and H ₂ O in the source gas G and the reaction of the electrolysis products as described above. The generated gas containing CH ₄ diffuses laterally from inside the composite oxide layer 2B, goes to the gas lead-out portion 103, and is taken out to the outside.

A hydrocarbon production unit 10 having a gas distribution unit 101 constitutes a main part of a hydrocarbon production apparatus 100, an example of which is shown in FIG. The configuration of the gas distribution section 101 of the hydrocarbon production section 10 and the arrangement of the electrochemical cell 1 are not limited to those shown in FIGS. 4 and 5, and can be changed as appropriate. For example, as shown in FIGS. 6 and 7, if the gas flow part 101 is not provided with a bending connection part and the gas introduction direction and the gas discharge direction are arranged perpendicular to the electrochemical cell 1, the efficiency can be improved. Allows production of good hydrocarbons.

In FIG. 6 , the hydrocarbon production section 10 includes a double tubular gas circulation section 101 . The inner cylinder of the gas circulation part 101 constitutes the gas introduction part 102 , and the outer cylinder surrounding the outer circumference of the inner cylinder constitutes the gas outlet part 103 . The electrochemical cell 1 is arranged so as to close one end side of the gas circulation part 101 . One end side of the gas flow section 101 extends outside from the housing 10a of the hydrocarbon production section 10, and the gas introduction section 102 and the gas discharge section 103 are separated at the branch section 10b. Heaters H are arranged around the casing 10a of the hydrocarbon production unit 10, and the separated gas introduction unit 102 and gas discharge unit 103, so that they can be heated to a predetermined temperature or kept warm.

The gas introduction section 102 includes a CO ₂ introduction passage 102a through which CO ₂ is introduced, and an N ₂ introduction passage 102b through which nitrogen (N ₂ ) serving as a base gas is introduced. In the N ₂ introduction path 102b, a water vapor concentration control tank 102c in which water (H ₂ O) is stored is arranged upstream of the connection with the CO ₂ introduction path 102a, and passes through the inside of the water vapor concentration control tank 102c. By doing so, the water vapor concentration is adjusted. A gas sampling pipe 104 is connected in the middle of the gas lead-out portion 103 so that the generated gas can be analyzed by a gas chromatograph analyzer 105 .

In FIG. 7 , the gas flow portion 101 has a gas introduction portion 102 facing the central portion of the surface 20 of the cathode 2 and a gas outlet portion 103 facing the outer peripheral portion of the surface 20 . As indicated by the white arrow in the drawing, the raw material gas G is introduced toward the surface 20 of the cathode 2 with the gas flow direction being the direction perpendicular to the surface 20 of the cathode 2 . The flow direction of the produced gas is opposite to the gas introduction direction, and the produced gas is led out in parallel and opposite to the flow of the raw material gas G away from the surface 20 of the cathode 2 . In that case, the angle θ between the gas flow direction and the cathode 2 is 90°, and is the same on the gas introduction side and the gas discharge side (angle θ=gas introduction angle θ1=gas discharge angle θ2).

At this time, as shown in FIG. 8, in the electrochemical cell 1 shown in FIG. 5, the direction in which the source gas G is introduced is inclined with respect to the surface 20. In a region R (for example, a region surrounded by a dotted line in FIG. 8) where many electrolytic reactions occur, the gas containing the methane precursor tends to flow together with the gas flow. Here, in the region R, the electrolysis reaction, which is an endothermic reaction, occurs more frequently, so the temperature is lowered and the region is a low temperature region advantageous for methane production. However, since the gas containing the methane precursor flows downstream, it may move away from the region R, making it difficult for methane production to proceed. The generated gas containing CO, H ₂ and CH ₄ is led out of the cathode 2 as it is.

On the other hand, as shown in FIG. 9, in the electrochemical cell 1 shown in FIG. 7, the raw material gas G is introduced from the vertical direction, so the region where the amount of the raw material gas G introduced is large (for example, In region R enclosed by a dotted line in FIG. 9 , after many electrolytic reactions occur, the gas containing the methane precursor stays in the composite oxide layer 2B and tends to stay in the vicinity of region R, which is a low-temperature region. Therefore, the state is favorable for the electrolytic reduction of the methane precursor, and the production of methane is facilitated. As a result, the _CH4 ratio in the generated gas containing CO, _H2 , and _CH4 becomes higher, and the efficient hydrocarbon production apparatus 100 can be realized. Moreover, since the gas circulation portion 101 has a double-cylinder structure, the structure can be made compact.

The electrochemical cell 1 is heated by a heater H arranged around the hydrocarbon production section 10 to a temperature suitable for these series of reactions, for example, in the range of 300°C to 800°C. A low temperature side (eg, 300° C. to 600° C.) is advantageous for the methanation reaction, and a high temperature side (eg, 500° C. to 800° C.) is advantageous for the catalytic activity of the electrode surface. Preferably, the electrode temperature in the cell is in a temperature range that is advantageous for both (for example, 500° C. to 600° C.), and the temperature around the cell is adjusted in consideration of the temperature drop due to electrolysis, which is an endothermic reaction. Heater control is preferred.

(Examples 1 to 4)
An electrochemical cell 1 having a configuration similar to that of Embodiment 1 was produced, and a methane production test was performed using the hydrocarbon production apparatus 100 shown in FIG. 6 to evaluate the methane conversion rate. Electrochemical cell 1 is produced in the following manner by preparing an electrolyte sheet serving as oxide ion conductor 11 and applying a cathode forming material serving as cathode 2 and an anode forming material serving as anode 3 on both sides of the sheet. It was applied by printing and heat-treated.

<Production of electrolyte sheet>
As a material for the electrolyte sheet, zirconia (ZrO ₂ ) added with yttria (Y ₂ O ₃ ) so as to have a content of 8 mol % was prepared. A slurry was prepared by adding polyvinyl butyral to the obtained yttria-stabilized zirconia powder and mixing it with isoamyl acetate, 2-butanol and ethanol as a mixed solvent in a ball mill. As shown in Table 1, yttria-stabilized zirconia containing 8 mol % Y ₂ O ₃ is hereinafter abbreviated as “8YSZ”.

The average particle size of the 8YSZ powder was 0.8 µm. Here, the average particle diameter is the particle diameter (diameter) d50 when the volume-based cumulative frequency distribution measured by the laser diffraction/scattering method shows 50%, and the same applies hereinafter.

The prepared slurry was applied in layers on a resin sheet using a known doctor blade method and dried. After that, the resin sheet was peeled off and baked in the air at 1450° C. for 2 hours to obtain an electrolyte sheet made of 8YSZ.

<Preparation of cathode material>
LaSrCo _0.8 Fe _0.2 O ₄ , which is a lanthanum-based composite oxide, was used as the composite oxide containing a transition metal element, which is the material for the composite oxide layer 2B of the cathode 2 (in Table 1, LaSr-based show). As raw materials, single oxides of constituent elements of lanthanum-based composite oxides (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.; test reagents) were used and weighed to obtain desired compositions. Next, the weighed raw materials were mixed in a ball mill in ethanol to which 1% by mass of polyvinyl alcohol was added as a dispersant. Mixing by a ball mill was performed for 16 hours using zirconia beads with a diameter of 10 mm, after which the mixed raw material was taken out into a vat and dried. By heat-treating this dry powder at 1100° C., a composite oxide powder containing a transition metal element was obtained (average particle size 0.5 μm).

The obtained composite oxide powder was mixed with a ball mill in terpineol to which 1% by mass of an acrylic resin was added as a dispersant. Mixing by a ball mill was performed for 16 hours using zirconia beads with a diameter of 10 mm, and then the mixture was kneaded to obtain a paste for printing, which is a material for forming the composite oxide layer 2B.

Silver (Ag) was used as the material of the conductive metal layer 2A of the cathode 2, and printing pastes with different viscosities were prepared. First, a commercially available paste-like silver frit (manufactured by Daiken Chemical Industry Co., Ltd.; "NAG-10") is prepared, added to terpineol to dilute it, or an acrylic resin is added and dissolved to obtain the desired amount. A silver paste for printing adjusted to a viscosity of . The silver frit used had an average particle size of 0.02 μm.

<Preparation of anode material>
Ba _0.6 Sr _0.4 CoO ₃ , which is a perovskite-type composite oxide, was used as the composite oxide material for the anode 3 . In the same manner as for the composite oxide layer 2B of the cathode 2, the single oxides of the constituent elements as raw materials are weighed so as to have a desired composition, dispersed in a vehicle of acrylic resin and terpineol, and ball-milled. After mixing, it was dried to obtain a dry powder. By heat-treating this dry powder, a composite oxide powder was obtained (average particle size: 0.5 μm). The powder of the obtained composite oxide was ball mill-mixed in the same manner and viscous by kneading to prepare a printing paste for forming an anode.

<Preparation of electrochemical cell 1>
A printing paste prepared for forming the composite oxide layer 2B was applied to one surface of the electrolyte sheet obtained as described above by printing, and then dried. After that, baking is performed by heat-treating at 1000° C. for 10 minutes. A composite oxide layer 2B was formed. Furthermore, a silver paste for printing prepared for forming the conductive metal layer 2A is printed on the surface of the composite oxide layer 2B and heat-treated to form the intermediate layer 2C, and a conductive metal layer is formed on the surface of the intermediate layer 2C. 2A was formed to serve as cathode 2 .

At that time, the layer thickness t1 of the intermediate layer 2C was adjusted for each sample by adjusting the penetration depth into the composite oxide layer 2B by using silver pastes with different viscosities. In addition, the layer thickness of the conductive metal layer 2A is 10 μm for all samples, and when using a silver paste with a low viscosity, after printing, a silver paste that has not been subjected to viscosity adjustment is printed to obtain a layer thickness of 10 μm. was adjusted to be The layer thickness of the composite oxide layer 2B was set to 25 μm.

On the other surface of the electrolyte sheet obtained as described above, a printing paste prepared for forming the anode 3 was applied by printing and then dried. After that, baking is performed by heat-treating at 1000° C. for 10 minutes. A composite oxide layer to be the anode 3 was formed. The layer thickness of the anode 3 was set to 25 μm.

Furthermore, a lead wire made of platinum (Pt) for power supply was joined to each of the cathode 2 and the anode 3 by melting the silver frit. The silver frit on the anode 3 was placed by printing silver frit paste without viscosity adjustment and heat treating at 800° C. for 10 minutes.

In this way, samples of the electrochemical cell 1 were obtained in which the cathode 2 and the anode 3, which are porous electrodes, were laminated on both sides of the dense oxide ion conductor 11 (Examples 1 to 4). At this time, as shown in Table 1, in the sample of Example 1, the ratio t1/t between the layer thickness t1 of the intermediate layer 2C and the total layer thickness t of the composite oxide layer 2B was 1%. is adjusted to Further, the samples of Examples 2 to 4 were electrochemical cells 1 having intermediate layers 2C in which the ratios t1/t were adjusted to 5%, 50% and 95%, respectively. The oxide ion conductor 11 had a porosity of 5% or less, and the porous electrode had a porosity of 50%.

<Evaluation method>
A methane production test using the hydrocarbon production apparatus 100 was conducted on the electrochemical cells 1 of Examples 1 to 4. The hydrocarbon production unit 10 has a configuration including the gas flow unit 101 shown in FIG. It was taken out from the gas lead-out part 103 . The gas flow direction of the gas flow part 101 was connected so that the gas introduction angle θ1=45°, and the gas outlet part 103 was connected so that the gas outlet angle θ2=135°. Table 1 shows these gas directions as gas introduction angle θ1 (45°)/gas discharge angle θ2 (135°).

The raw material gas G is a gas containing CO ₂ and water vapor, the remainder being N ₂ , and is converted to N ₂ containing water vapor by bubbling of N ₂ passing through the water vapor concentration control tank 102c from the N ₂ introduction passage 102b, It was mixed with CO ₂ introduced from the CO ₂ introduction passage 102 a and supplied to the gas introduction section 102 . The raw material gas G is adjusted so that the concentrations of CO ₂ and water vapor are in a molar ratio suitable for the production of CH ₄ , and is placed in the hydrocarbon production section 10 from a gas introduction section 102 that is appropriately kept warm. It was supplied to the electrochemical cell 1 in which it was carried out and co-electrolyzed. The gas flow rate of the raw material gas G, the water vapor concentration and the CO ₂ concentration in the raw material gas G, the electrode areas of the cathode 2 and the anode 3 of the electrochemical cell 1, and the applied voltage between both electrodes are shown below as methane production conditions.
Methane production conditions Gas flow rate: 50 ml/min
Water vapor concentration: 0.6% (bubbling temperature: 0°C)
_CO2 concentration: 0.3%
Electrode area: ^2cm2
Applied voltage: -1.6V

The gas flow rate was adjusted so that the ratio of the raw material gas amount per unit time to the electrode volume (space velocity SV) was in the range of about 1000 to 10000 (for example, SV=3600). The electrochemical cell 1 was entirely heated by a heater H arranged around the hydrocarbon producing section 10, and the internal temperature of the hydrocarbon producing section 10 was controlled to be around 700.degree. At this time, due to the electrolytic reaction (endothermic reaction) of CO ₂ and H ₂ O, the cell temperature becomes lower than the ambient temperature, which is 500° C. to 600° C. which is favorable for both the surface catalytic activity and the methanation reaction at the cathode 2. maintained to some extent.

The generated gas taken out to the gas lead-out part 103 is obtained by sampling 1 ml of the gas over 10 seconds from the gas sampling tube 104 connected in the middle of the gas lead-out part 103, and analyzing it with a gas chromatograph (manufactured by Agilent Technologies; GC490). A component analysis was performed. For component analysis, each gas concentration (mol%/L) in the produced gas was measured. In addition, the methane conversion rate was calculated based on the measurement results, and the results are also shown in Table 1. Also, FIG. 10 shows a columnar graph comparing methane conversion rates.
Methane conversion rate = (concentration of methane in generated gas) / [(CO ₂ concentration in source gas) - (CO ₂ concentration in generated gas)]

(Comparative Examples 1 and 2)
For comparison, an electrochemical cell 1 adjusted so that the intermediate layer 2C was not formed on the cathode 2, that is, the ratio t1/t was 0%, was produced by the same manufacturing process as in Example 1. Example 1. Further, in the cathode 2, the electrochemical cell 1 was adjusted so that the ratio t1/t of the intermediate layer 2C was 100%, that is, the complex oxide layer 2B was not formed, and this was used as Comparative Example 2. .

The electrochemical cells 1 of Comparative Examples 1 and 2 were subjected to a methane production test using the hydrocarbon production apparatus 100 in the same manner as in Example 1, and the produced gas was analyzed by gas chromatography. The results are also shown in Table 1 and FIG. As shown in these results, in both the electrochemical cells 1 of Comparative Examples 1 and 2, the production of CO and H ₂ by electrolysis was observed, but the production of CH ₄ was not confirmed.

In contrast, the generation of CH ₄ was confirmed in all of the electrochemical cells 1 of Examples 1-4. Specifically, in Example 1, where the ratio t1/t is 1%, a methane conversion of 20% is obtained, and in Example 2, where the ratio t1/t is 5%, the methane conversion is greatly increased to 80%. bottom. Example 3 with a ratio t1/t of 50% further increased the methane conversion to 85%. In Example 4 in which the ratio t1/t is 95%, the methane conversion rate is 35%, which is lower than in Examples 2 and 3, but higher than in Example 1.

From these results, the cathode 2 has a single It was confirmed that in the electrochemical cell 1, CH ₄ can be produced efficiently. Although the reason for this is not necessarily clear, the intermediate layer 2C is in a H ₂ -rich state due to the H ₂ produced by the electrolysis of water vapor in the raw material gas G in the conductive metal layer 2A. It is thought that As a result, in the intermediate layer 2C, when the CO ₂ in the source gas G is further electrolyzed to generate CO, the electrolysis products react rapidly to generate a methane precursor, and the electrode reduction reaction proceeds. , selectively proceeding in the complex oxide layer 2B, it is speculated that CH ₄ can be produced.

Such an effect is obtained at 1% or more on the lower limit side of the ratio t1/t, and the methane conversion rate becomes 20% or more. As the layer thickness t1 of the intermediate layer 2C increases, the methane conversion rate increases, reaching 80% or more in the range of 5% to 50%. On the other hand, the upper limit of the ratio t1/t is 95%, and a methane conversion rate of 35% or more can be obtained, and it is considered that a methane conversion rate corresponding to the ratio t1/t can be obtained.

Here, as shown in FIG. 11 as a reference example, the methane production rate in the reaction for synthesizing methane from H ₂ and CO ₂ has a correlation with pressure. Since this synthesis reaction is a reaction under reduced pressure, it is known that synthesis under high pressure conditions increases the methane production rate. At this time, when comparing the curves for the methane production rate of 30% to 70% at normal pressure, if the methane production rate is 50% at normal pressure, it reaches 95% at a pressure of 3 MPa, and the methane production rate at normal pressure If it is 70%, it reaches 95% at a pressure of 1 MPa. The methane production rate of 95% is based on the Wobbe index, which is an index that indicates the injection heat input, and the maximum combustion speed, which is an index that indicates the combustion speed, among the indices that indicate gas combustibility. This is the value at which the generated gas after the reaction can be put into a gas pipeline or the like without going through a process such as purification when performing management.

Therefore, in practice, it is sufficient if a methane conversion rate of 50% or more is obtained at normal pressure, and a methane conversion rate of 70% or more is more preferable. Therefore, in the electrode configurations of Examples 1 to 4, the ratio t1/t is about 5% or more, and more preferably about 50% or less.

(Comparative Example 3)
For comparison, electrochemical A cell 1 was produced and referred to as Comparative Example 3. In the electrochemical cell 1 of Comparative Example 3, the ratio t1/t of the intermediate layer 2C is 1%, and the direction of gas flow in the gas flow section 101 is the gas introduction angle θ1 (45°)/gas discharge angle θ2 (135°). ).

The electrochemical cell 1 of Comparative Example 3 was subjected to a methane production test using the hydrocarbon production apparatus 100 in the same manner as in Example 1, and the generated gas was analyzed by gas chromatography. The results are also shown in Table 1 and FIG. As shown in these results, when the electrochemical cell 1 of Comparative Example 3 is used, even in the configuration having both the intermediate layer 2C and the composite oxide s2B. No generation of _CH4 was confirmed. The reason for this is not necessarily clear, but it is presumed that when Pt is used as the conductive metal, even if a methane precursor is produced, electrolytic reduction does not proceed and methanation does not occur.

(Example 5)
As Example 5, _Ca9.00Na0.67 ( _PO4 ) ₅ ( _CO3 )( _H2 ), which is non-oriented phosphate-based apatite, was used instead of 8YSZ _of Example 1 for the material of the oxide ion conductor 11. An electrochemical cell 1 was prepared in which O)(OH) was _1.67 and the cathode 2 and anode 3 had the same construction as in Example 1. The non-oriented phosphate-based apatite was obtained by weighing calcium phosphate [Ca ₃ (PO ₄ ) ₂ ] and sodium hydrogen carbonate (NaHCO ₃ ) so as to have a desired composition as raw materials. The raw materials were mixed, dried, and heat-treated by the same manufacturing process as for the composite oxide material to obtain a compound powder having a phosphate-based apatite structure.

A slurry containing the obtained compound powder was prepared in the same manner as for 8YSZ in Example 1, and coated on a resin sheet. Next, the resin sheet was peeled off, and sintering was performed at 1350° C. for 2 hours in an air atmosphere adjusted to contain 5% of water vapor to form an electrolyte sheet to be the oxide ion conductor 11 .

Materials for the cathode 2 and the anode 3 were applied to the resulting electrolyte sheet in the same manner as in Example 1, and the sheet was fired to obtain an electrochemical cell 1. As in Example 1, the electrochemical cell 1 of Example 5 was subjected to a methane production test using the hydrocarbon production apparatus 100, and the produced gas was analyzed. The results are also shown in Table 1 and FIG.

(Example 6)
As Example 6, Ca _9.00 Na _0.67 (PO ₄ ) ₅ (CO ₃ ) ( An electrochemical cell 1 was produced in the same manner as in Example 5, except that H ₂ O)(OH) was _1.67 . In that case, first, only calcium phosphate as a raw material was weighed so as to have a desired amount, and in the same manner as in Example 5, a sheet-forming powder and slurry were prepared and coated on a resin sheet. A processed sheet was produced.

After that, the resin sheet of the obtained sheet was peeled off and buried in the sodium hydrogen carbonate powder. Then, heat treatment was performed at 1300° C. for 50 hours in an air atmosphere adjusted to contain 5% of water vapor. Through such a gas phase-solid phase diffusion process, calcium phosphate and sodium bicarbonate are reacted to form a c-axis oriented phosphate-based apatite compound, thereby forming an electrolyte sheet that serves as an oxide ion conductor 11. formed.

Materials for the cathode 2 and the anode 3 were applied to the resulting electrolyte sheet in the same manner as in Example 1, and the sheet was fired to obtain an electrochemical cell 1. As in Example 1, the electrochemical cell 1 of Example 6 was subjected to a methane production test using the hydrocarbon production apparatus 100, and the produced gas was analyzed. The results are also shown in Table 1 and FIG.

(Example 7)
As Example 7, Example 1 except that La _9.3 Si _5.3 B _0.7 O ₂₅ , which is a non-oriented apatite-type composite oxide, was used as the material of the oxide ion conductor 11 instead of 8YSZ in Example 1. An electrochemical cell 1 was produced in the same manner. In that case, first, the single oxide of the constituent element as the raw material is weighed so as to have a desired composition, and after ball mill mixing, the dried powder obtained by drying is heat-treated to obtain a sheet. A composite oxide powder for forming was obtained. Using this composite oxide powder, a slurry was prepared in the same manner as 8YSZ in Example 1, and the slurry was coated on a resin sheet. Next, the resin sheet was peeled off, and sintering was performed at 1600° C. for 2 hours in an air atmosphere to form an electrolyte sheet serving as the oxide ion conductor 11 .

Materials for the cathode 2 and the anode 3 were applied to the resulting electrolyte sheet in the same manner as in Example 1, and the sheet was fired to obtain an electrochemical cell 1. As in Example 1, the electrochemical cell 1 of Example 7 was subjected to a methane production test using the hydrocarbon production apparatus 100, and the produced gas was analyzed. The results are also shown in Table 1 and FIG.

(Example 8)
As Example 8, the material of the oxide ion conductor 11 was replaced with 8YSZ of Example 1, and La _9.3 Si _5.3 B _0.7 O ₂₅ , which is a c-axis oriented apatite-type composite oxide, was used. An electrochemical cell 1 was produced in the same manner as in Example 1. In that case, as a raw material, a single oxide of the constituent elements excluding B is weighed so as to have a desired composition, mixed in a ball mill, and then dried to obtain a dry powder. A precursor powder for sheet formation was obtained. Using this precursor powder, a slurry was prepared in the same manner as 8YSZ of Example 1, and coated on a resin sheet. Then, the resin sheet was peeled off, and baking was performed at 1600° C. for 2 hours in an air atmosphere.

Thereafter, the resin sheet of the obtained sheet was peeled off, and heat treatment was performed at 1550° C. for 50 hours in a boron oxide (B ₂ O ₃ ) vapor atmosphere. Through such a gas phase-solid phase diffusion process, the precursor and boron oxide were reacted to form a c-axis oriented apatite-type composite oxide, forming an electrolyte sheet to be the oxide ion conductor 11. .

Materials for the cathode 2 and the anode 3 were applied to the resulting electrolyte sheet in the same manner as in Example 1, and the sheet was fired to obtain an electrochemical cell 1. As in Example 1, the electrochemical cell 1 of Example 6 was subjected to a methane production test using the hydrocarbon production apparatus 100, and the produced gas was analyzed. The results are also shown in Table 1 and FIG.

(Example 9)
In Example 9, the material of the composite oxide layer 2B was Ce _0.75 Co _0.2 Fe _0.05 O ₂ , which is a ceria-based composite oxide, instead of the lanthanum-based composite oxide of Example 1 (see Table 1, An electrochemical cell 1 was fabricated in the same manner as in Example 1, except for Ce(Co, Fe) O). For the ceria-based composite oxide, a single oxide of the constituent elements is used as a raw material, and the raw materials are mixed, dried, and heat-treated in the same manufacturing process as the composite oxide material of Example 1 to obtain a ceria-based composite oxide. I got the powder of the thing.

Using the obtained composite oxide powder, in the same manner as in Example 1, a printing paste was prepared as a material for forming the composite oxide layer 2B. The cathode 2 and anode 3 materials containing the prepared printing paste were applied to an electrolyte sheet using 8YSZ similar to that of Example 1 and fired to obtain an electrochemical cell 1 . As in Example 1, the electrochemical cell 1 of Example 9 was subjected to a methane production test using the hydrocarbon production apparatus 100, and the produced gas was analyzed. The results are also shown in Table 1 and FIG.

As shown in the results of Examples 5 to 8 in Table 1 and FIG. 9, by using an apatite type compound as the material of the oxide ion conductor 11, the methane conversion rate can be improved to 50% or more. . In that case, the methane conversion rate of the c-axis oriented apatite type compound was higher than that of the non-oriented apatite type compound, and a methane conversion rate of 70% or more was obtained. Moreover, a higher methane conversion rate was obtained in Examples 7 and 8 using the apatite-type composite oxide than in Examples 5 and 6 using the phosphate-based apatite-type compound. Further, as shown in the results of Example 9, the methane conversion rate was improved to 90% by using the ceria-based oxide as the material of the second particles 22 constituting the intermediate layer 2C and the composite oxide layer 2B. bottom.

(Example 10)
As Example 10, the electrochemical cell 1 produced in the same manner as in Example 1 was attached to the hydrocarbon production section 10 shown in FIG. 7, and a methane production test was conducted. The hydrocarbon production section 10 has a double-cylinder gas circulation section 101 which is connected so that the gas flow direction of the gas circulation section 101 is perpendicular to the cathode 2 . In Table 1, the gas directions (gas introduction angle θ1/gas discharge angle θ2) are shown as 90°/90°. Also, the results of a methane production test conducted in the same manner as in Example 1 are shown in Table 1 and FIG.

As shown in the results of Table 1 and FIG. 10, by changing the direction of gas flow in the electrochemical cell 1 having the same structure as in Example 1, the methane conversion rate was improved to 52%. Although the reason for this is not necessarily clear, as shown in FIG. 9, by introducing the gas from the vertical direction and discharging the gas in the direction opposite to the gas introduction direction, the methane precursor stays in the easily heated region. Therefore, it is presumed that the electrolytic reduction proceeds efficiently.

Thus, in the electrochemical cell 1, when the ratio t1/t is 1% or more, the materials of the cathode 2 and the oxide ion conductor 11 are appropriately selected, or the hydrocarbon production section 10 By appropriately setting the direction of gas flow in the gas flow section 101, it is possible to realize the hydrocarbon production apparatus 100 that exhibits a practically sufficient methane conversion rate.

According to the electrochemical cell 1 having the above configuration, the cathode 2 has a three-layer structure having the intermediate layer 2C between the conductive metal layer 2A and the composite oxide layer 2B, thereby forming a single electrochemical cell. 1 allows the production of hydrocarbons. The conductive metal layer 2A contains Ag as a main component, the composite oxide layer 2B contains a composite oxide containing a transition metal element as a main component, and the intermediate layer 2C contains both of these components. , a high catalytic activity at the cathode 2 is obtained. Moreover, by using such an electrochemical cell 1, it is possible to realize a highly practical hydrocarbon production apparatus.

The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the scope of the invention. For example, when configuring the hydrocarbon production section 10 using the electrochemical cells 1, a plurality of electrochemical cells 1 may be stacked. Moreover, the configuration of the gas distribution unit 101 of the hydrocarbon production unit 10 and the configuration of the hydrocarbon production apparatus 100 including the hydrocarbon production unit 10 are not limited to the configurations described above, and can be changed according to the application.

REFERENCE SIGNS LIST 1 electrochemical cell 11 oxide ion conductor 12, 13 face 2 cathode 3 anode 21 first particle 22 second particle 2A conductive metal layer 2B composite oxide layer 2C intermediate layer

Claims (9)

In an electrochemical cell (1) comprising an oxide ion conductor (11) and a cathode (2) and an anode (3) provided on two opposite sides (12, 13) of said oxide ion conductor ,
The cathode is
A conductive metal layer (2A) composed of first particles (21) containing silver as a main component and in contact with a raw material gas (G) containing carbon dioxide and water vapor;
a composite oxide layer (2B) composed of second particles (22) mainly composed of a composite oxide containing a transition metal element and in contact with the oxide ion conductor;
An electrochemical cell having a structure in which an intermediate layer (2C) provided between the conductive metal layer and the composite oxide layer and composed of the first particles and the second particles is laminated. 2. The electrochemical cell according to claim 1, wherein a ratio t1/t between the layer thickness t1 of the intermediate layer and the total layer thickness t of the intermediate layer and the composite oxide layer is 1% or more. 3. The electrochemical cell according to claim 1, wherein a ratio t1/t of the layer thickness t1 of the intermediate layer and the total layer thickness t of the intermediate layer and the composite oxide layer is 95% or less. The electrochemical cell according to any one of claims 1 to 3, wherein the oxide ion conductor is composed of at least one selected from stabilized zirconia, non-oriented or oriented apatite type compounds. . 5. The electrochemical cell according to claim 4, wherein the apatite-type compound is a phosphate-based apatite-type compound or an apatite-type composite oxide. The apatite-type composite oxide has the following formula;
A _9.3+x [T _6.0-y M _y ] O _26.0+z
(A in the formula is from the group consisting of La, Ce, Y, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr and Ba One or more selected elements, where T is an element containing Si or Ge or both, and M is Mg, Al, Sc, Ti, V, Cr, Mn , Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, W and Mo.
x in the formula is a number of -1.4 or more and 1.5 or less,
y in the formula is a number of 0.0 or more and 3.0 or less,
z in the formula is a number of -5.0 or more and 5.2 or less,
6. The electrochemical cell according to claim 5, wherein the ratio of the number of moles of A to the number of moles of T in the formula (A/T) is 1.4 or more and 3.7 or less. The electrochemical cell according to any one of claims 1 to 6, wherein the composite oxide containing the transition metal element is a lanthanum-based composite oxide or a ceria-based composite oxide. 8. The electrochemical cell according to claim 7, wherein the composite oxide containing transition metal elements is a ceria-based composite oxide containing a plurality of transition metal elements. A hydrocarbon production apparatus (100) using the electrochemical cell according to any one of claims 1 to 8,
A hydrocarbon production section (10) in which the electrochemical cell is arranged so as to close one end of a cylindrical gas flow section (101),
The gas flow part has a gas inlet part (102) and a gas outlet part (103) provided facing the cathode of the electrochemical cell,
the gas introduction unit supplies the raw material gas to the cathode with a direction perpendicular to the cathode as a gas introduction direction;
The gas lead-out part is arranged on the outer peripheral side of the gas lead-in part, and leads the reaction product at the cathode to the outside of the gas flow part, with the direction opposite to the gas lead-in direction as the gas lead-out direction. Hydrocarbon production equipment.

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