Proton ceramic reversible cell, and water vapor electrolytic cell and fuel cell containing the same.

Abstract

To provide a proton ceramic reversible cell capable of exhibiting better characteristics than the conventional art.SOLUTION: A proton ceramic reversible cell comprises an air electrode, an air electrode interface function layer, a proton conductivity ceramic layer, and a fuel electrode in this order, and the air electrode interface function layer includes a metal oxide with a perovskite structure and / or the hydrate thereof. The metal oxide and / or the hydrate meets the following expression (1) ([Ba]+[R1]+[R2]+[Fe]) / [A1]≥0.75---(1) In the expression, R1 is one or more kinds selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to a proton ceramic reversible cell, and to a steam electrolytic cell and fuel cell containing the same. [Background technology]

[0002] Electrochemical cells containing a proton-conducting ceramic layer (hereinafter referred to as "proton ceramic reversible cells") are, for example, one of the most efficient devices for producing hydrogen from renewable energy when used as a steam electrolysis cell. Proton ceramic reversible cells are also useful as fuel cells.

[0003] Patent Document 1 discloses an electrochemical cell for steam electrolysis that uses a proton-conducting solid oxide and a perovskite-type oxide containing a transition metal as the anode. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-209441 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, proton ceramic reversible cells, such as those disclosed in Patent Document 1, do not possess sufficient properties, and further improvements are needed.

[0006] This disclosure has been made in view of the above circumstances, and one of its objectives is to provide a proton ceramic reversible cell, as well as a steam electrolytic cell and a fuel cell containing the same, which can exhibit better characteristics than the prior art (for example, a high electrolytic current density at 600°C and 1.3V as a steam electrolytic cell, and a low voltage drop associated with the increase in current density at 600°C as a fuel cell). [Means for solving the problem]

[0007] Aspect 1 of the present invention is a proton ceramic reversible cell having an air electrode, an air electrode interface functional layer, a proton conductive ceramic layer, and a fuel electrode in this order, where the air electrode interface functional layer contains a metal oxide having a perovskite structure and / or its hydrate, and the metal oxide and / or its hydrate satisfies the following formula (1), and satisfies the following formula (2b) when satisfying the following formula (2a), and satisfies the following formula (3b) when satisfying the following formula (3a). ([Ba] + [R a , 2 , a , 2 , , b , a , 1 , b , a , 2 , 2 , b , 1 , b , 1 , 1 , 1 , b , 1 , 1 , , b , a , , 2 , a , 1 , a , 2 , a , b , b + [R 2 + [Fe]) / [A 1 ≥ 0. seventy-five ···(1) [Ba] + [R 1 ≤ [Fe] + [M 1 y + [M 2 ···(2a) [Ba] : [R 1 : [R 2 : [Fe] : [M 1 : [M 2 = (1 - x a - y a ) : x a : y a : c(1 - l a - m a ) : cl a : cm a ···(2b) [Ba] + [R 1 > [Fe] + [M 1 + [M 2 ···(3a) n [Ba] : [R 1 : [Fe] : [M 1 : [M 2 : [R 2 = (1 - x b ) : x b : c(1 - l b - m b - n b ) : cl b : cm b : cn b...(3b) In equations (1) to (3b), R 1 is one or more selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, and R 2 is one or more selected from the group consisting of Sc, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and A 1 M consists of all elements except oxygen and hydrogen. 1 is one or more selected from the group consisting of Li, Na, Mg, Al, Ca, Cu, Zn, Ga, Ag, Cd, In, Hg, and Tl, M 2 [Ba], [R] 1 ], [R 2 ], [Fe], [A 1 ], [M 1 ] and [M 2 ] represents Ba and R in mol% respectively. 1 , R 2 Fe, A 1 M 1 and M 2 This indicates the content, and 0≦(x a +y a )<1.0, 0<(l a +m a )≦0.3, 0≦m a <0.3, 0.90≦c≦1.10, 0≦x b <1.0, 0<(l b +m b +n b )≦0.3, 0≦m b The relationship <0.3 is satisfied.

[0008] Aspect 2 of the present invention is, R 1 The proton ceramic reversible cell according to Embodiment 1 is one or more selected from the group consisting of La, Ce, Pr, Nd, Pm, and Sm.

[0009] A third aspect of the present invention is: M 1The proton ceramic reversible cell according to embodiment 1 or 2 is one or more selected from the group consisting of Li, Mg, Al, Cu, Zn, Ga, Cd, In, and Tl.

[0010] Aspect 4 of the present invention is This is a water vapor electrolytic cell containing a reversible proton ceramic cell as described in any one of embodiments 1 to 3.

[0011] Aspect 5 of the present invention is A fuel cell comprising a reversible proton ceramic cell according to any one of claims 1 to 3. [Effects of the Invention]

[0012] According to embodiments of the present invention, it is possible to provide a reversible proton ceramic cell that exhibits better characteristics than the prior art (for example, as a steam electrolytic cell, a high electrolytic current density at 600°C and 1.3V, and as a fuel cell, a low voltage drop associated with the increase in current density at 600°C), as well as a steam electrolytic cell and a fuel cell containing the same. [Brief explanation of the drawing]

[0013] [Figure 1A] Figure 1A is a surface SEM image of the air electrode interface functional layer (BLFZ) of Example 1 formed on a Si substrate. [Figure 1B] Figure 1B shows the XRD pattern of the air electrode interface functional layer (BLFZ) of Example 1 formed on a Si substrate. [Figure 2] Figure 2 shows a cross-sectional SEM image (left) and a magnified image (right) of Example 1. [Figure 3A] Figure 3A is an HRTEM image of Example 1 (before air electrode formation). [Figure 3B] Figure 3B shows magnified images of two different locations in Figure 3A. [Figure 3C] Figure 3C shows the EDX mapping for Example 1 (before air electrode formation). [Figure 4]Figure 4 shows the open-circuit voltage (OCV) at each temperature for Example 1, Comparative Example 1, and Reference Examples 1 to 6. [Figure 5] Figure 5 shows the IV characteristics at each temperature for Comparative Example 1. [Figure 6] Figure 6 shows the IV characteristics at each temperature of Example 1. [Figure 7] Figure 7 shows the electrolytic current density measured at 1.3V at each temperature for Example 1, Comparative Example 1, and Reference Examples 1 to 6. [Figure 8] Figure 8 shows the IV characteristics at each temperature for Example 2. [Figure 9] Figure 9 shows the IV characteristics at each temperature in Example 3. [Figure 10] Figure 10 shows the IV characteristics at each temperature of Example 4. [Figure 11A] Figure 11A shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Comparative Example 1 at 600°C and 314 mA / cm2. [Figure 11B] Figure 11B shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Comparative Example 1 at 500°C and 70 mA / cm2. [Figure 12A] Figure 12A shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Example 1 at 600°C and 570 mA / cm2. [Figure 12B] Figure 12B shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Example 1 at 500°C and 214 mA / cm2. [Figure 13] Figure 13 shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Reference Example 6. [Figure 14] Figure 14 shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Reference Example 5. [Figure 15A] Figure 15A shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Example 4 at 600°C and 743 mA / cm2. [Figure 15B] Figure 15B shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Example 4 at 600°C and 1143 mA / cm2. [Figure 15C] Figure 15C shows the time evolution of voltage, hydrogen release rate, and Faraday efficiency for Example 4 at 500°C and 214 mA / cm2. [Figure 16] Figure 16 shows the relationship between electrolytic current density and Faraday efficiency for Examples 1 and 4, Comparative Example 1, and Reference Examples 2, 5, and 6. [Modes for carrying out the invention]

[0014] The inventors investigated various aspects to realize a reversible proton ceramic cell that exhibits better properties than the conventional technology.

[0015] When a proton ceramic reversible cell is used as a water vapor electrolysis cell, the following reaction occurs at the air electrode (also called the oxygen electrode). H2O + 2h + → 2H + +1 / 2O2···(4) In equation (4), h + H is a positive hole, + This is a proton. This proton, generated at the air electrode, is conducted through the proton-conducting ceramic layer to the fuel electrode (also called the hydrogen electrode), where it is reduced to hydrogen. Furthermore, when a proton ceramic reversible cell is used as a fuel cell, the opposite reaction to the one described above occurs.

[0016] The inventors hypothesized that the reaction in formula (4) occurs via the following steps 1 to 8. (Step 1) H2O(g) → H2O(TPB) (Step 2) H2O(TPB)→OH - (TPB) + H + (TPB) (Step 3) OH - (TPB) → O 2- (TPB) + H + (TPB) (Step 4) H + (TPB) → H+ (ele) (Step 5) O 2 (TPB) + h + → O - (TPB) (Step 6) O - (TPB) → O - (air) (Step 7) O - (air) + h + → O(air) (Step 8) 2O(air) → O2(g) Here, (g) means gas. For example, H2O(g) means water vapor. (TPB) means the three-phase boundary (i.e., the reaction field) of the gas phase / electron conduction layer / proton conduction layer. For example, H2O(TPB) means water molecules present (or adsorbed) in the reaction field. (ele) means the electrolyte layer. For example, H + (ele) means protons present in the electrolyte layer. (air) means the air electrode. For example, O - (air) means O present in the air electrode[[ID=XX]] - ions.

[0017] In order to promote the reactions of Steps 1 to 8 above, the inventors considered inserting another layer different from them (hereinafter referred to as the "air electrode interface functional layer") between the air electrode and the proton conductive ceramic layer. And as the air electrode interface functional layer, it contains a metal oxide (and / or its hydrate) having a perovskite structure represented by the general formula ABO3. As the metal oxide, a layer satisfying the formulas (1) to (3b) described in the above Aspect 1 (hereinafter referred to as the "Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ layer" or "Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2cmb R 2 cnb O 3-δ By selecting a layer (also referred to as a "layer"), we were able to realize a reversible proton ceramic cell that exhibits better properties than conventional technologies.

[0018] The reason we were able to achieve the above cell is, "Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ "Layer" or "Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2 cmb R 2 cnb O 3-δ This is thought to be because the "layer" has the following functions. (i) To enable the conduction of protons, oxide ions, and electrons (holes), thereby expanding the reaction field in steps 1 to 6 above. (ii) The inclusion of Ba promotes the adsorption of water molecules into the reaction field (i.e., promotes step 1) and improves proton conductivity (i.e., promotes steps 3 and 4). (iii) Due to the high Fe content, the oxidation equilibrium constant K is given by the following equation (5). ox For the hydration equilibrium constant K hyd This allows for increased size and suppression of leakage current.

[0019]

number

[0020] As described in (i) to (iii) above, when the proton ceramic reversible cell according to the embodiment of the present invention is used as a water vapor electrolytic cell, the electrolytic current density can be increased, and the Faraday efficiency can also be improved. Similarly, when the proton ceramic reversible cell according to the embodiment of the present invention is used as a fuel cell, the voltage drop associated with the increase in current density can be reduced, and the open-circuit voltage can also be increased. Furthermore, the above mechanism does not limit the technical scope of the embodiments of the present invention.

[0021] The details of each requirement defined in the embodiments of the present invention are shown below.

[0022] A proton ceramic reversible cell according to an embodiment of the present invention comprises an air electrode, an air electrode interface functional layer, a proton-conducting ceramic layer, and a fuel electrode in this order, wherein the air electrode interface functional layer comprises a metal oxide and / or hydrate having a perovskite structure, and the metal oxide and / or hydrate satisfies the following formula (1) and either of the following formulas (2a) and (3a), and when formula (2a) is satisfied, formula (2b) is further satisfied, and when formula (3a) is satisfied, formula (3b) is further satisfied, thus forming a proton ceramic reversible cell. ([Ba]+[R 1 ] +[R 2 ]+[Fe]) / [A 1 ]≧0.75 ···(1) [Ba]+[R 1 ]≦[Fe]+[M 1 ]+[M 2 ] ···(2a) [Ba]:[R 1 ]:[R 2 ]:[Fe]:[M 1 ]:[M 2 ]=(1-x a -y a ):x a :y a :c(1-l a -m a ):cl a :cm a ...(2b) [Ba]+[R1 ]>[Fe]+[M 1 ]+[M 2 ] ···(3a) [Ba]:[R 1 ]:[Fe]:[M 1 ]:[M 2 ]:[R 2 ]=(1-x b ):x b :c(1-l b -m b -n b ):cl b :cm b :cn b ...(3b) In equations (1) to (3b), R 1 is one or more selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, and R 2 is one or more selected from the group consisting of Sc, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and A 1 M consists of all elements except oxygen and hydrogen. 1 is one or more selected from the group consisting of Li, Na, Mg, Al, Ca, Cu, Zn, Ga, Ag, Cd, In, Hg, and Tl, M 2 [Ba], [R] 1 ], [R 2 ], [Fe], [A 1 ], [M 1 ] and [M 2 ] represents Ba and R in mol% respectively. 1 , R 2 Fe, A 1 M 1 and M 2 This indicates the content, and 0≦(x a +y a )<1.0, 0<(l a +m a )≦0.3, 0≦m a <0.3, 0.90≦c≦1.10, 0≦x b <1.0, 0<(l b +m b +nb )≦0.3, 0≦m b The relationship <0.3 is satisfied. The above air electrode interface functional layer is referred to as "Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ "Layer" or "Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2 cmb R 2 cnb O 3-δ It is sometimes referred to as a "layer."

[0023] The proton ceramic reversible cell according to an embodiment of the present invention contains a metal oxide and / or hydrate thereof having a perovskite structure represented by the general formula ABO3. The perovskite structure is not particularly limited and may include cubic, hexagonal, orthorhombic, monoclinic, or tetragonal crystals, but cubic perovskite is stable and therefore preferred. Whether or not these perovskite structures are present can be confirmed by obtaining an electron diffraction pattern using a field emission transmission electron microscope (FE-TEM).

[0024] In one embodiment, the air electrode interface functional layer may contain 50 area % or more, 75 area % or more, or 90 area % or more of a metal oxide and / or hydrate having a perovskite structure in a cross-sectional view parallel to the lamination direction. Furthermore, the air electrode interface functional layer may have a portion in which the metal oxide and / or hydrate having a perovskite structure extends continuously from one surface to the other in the lamination direction. These can be confirmed by cross-sectional TEM observation.

[0025] The left-hand side of equation (1) increases, for example, when there are fewer impurity elements. From the viewpoint of reducing impurities, it is preferable that the left-hand side of equation (1) is 0.80 or higher. It is also preferable that the following equation (6) is satisfied. ([Ba]+[R 1 ]+[R 2 ]+[Fe]) / [A 2 ]≧0.60 ···(6) Here, A 2 These are all elements except oxygen. The left-hand side of equation (6) also increases, for example, if there are fewer impurity elements. From the perspective of reducing impurities, it is more preferable for the left-hand side of equation (6) to be 0.65 or higher.

[0026] If equation (2a) is satisfied (i.e., Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ In the case of a layer, Ba forms a divalent cation, and R forms a trivalent cation. 1 and / or R 2 By substituting with, unstable Fe 4+ Fe 3+ This can be done, and it is preferable that the perovskite structure can be made more stable. From the viewpoint of stabilizing the perovskite structure, it is preferable that 0 < (x a +y a ) < 1.0, and more preferably 0.5 ≤ (x a +y a ) < 1.0, and more preferably 0.7 ≤ (x a +y a ) < 1.0. Similarly, if equation (3a) is satisfied (i.e., Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2 cmb R 2cnb O 3-δ In the case of a layer, Ba forms a divalent cation, and R forms a trivalent cation. 1 By substituting with, unstable Fe 4+ Fe 3+ This can be done, and it is preferable that the perovskite structure can be made more stable. From the viewpoint of stabilizing the perovskite structure, it is preferable that 0 <x b <1.0, and more preferably 0.5 ≤ x b <1.0, and more preferably 0.7≦x b < 1.0. Also, R 1 By selecting one or more elements from the group consisting of La, Ce, Pr, Nd, Pm, and Sm, the perovskite structure can be made more stable. On the other hand, by reducing the amount of substitution and increasing the amount of Ba, more water molecules can be adsorbed, and proton conductivity may be improved. From the viewpoint of water adsorption, if equation (2a) is satisfied, preferably 0 ≤ (x a +y a ) ≤ 0.5, and more preferably 0 ≤ (x a +y a ) ≤ 0.3. Similarly, if equation (3a) is satisfied, preferably 0 ≤ x b ≤ 0.5, and more preferably 0 ≤ x b The value is ≤ 0.3.

[0027] If equation (2a) is satisfied (i.e., Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ (In the case of layers), Fe is M 1 (One or more selected from the group consisting of Li, Na, Mg, Al, Ca, Cu, Zn, Ga, Ag, Cd, In, Hg, and Tl) or M 1 and M 2(One or more metals selected from the group consisting of metals in periods 4-6 and groups 4-10 of the periodic table) can be substituted. Similarly, if equation (3a) is satisfied (i.e., Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2 cmb R 2 cnb O 3-δ (In the case of layers), Fe is M 1 M 2 and R 2 It can be replaced by one or more of the group consisting of (however, M 2 (Cannot be replaced by this alone.) M 1 and R 2 Its ionic charge is lower than that of Fe. Therefore, Fe is M 1 and / or R 2 By substituting with Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ Layer or Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2 cmb R 2 cnb O 3-δ Oxygen vacancies can occur within the layers (i.e., δ can be made > 0). These layers possess oxygen vacancies, which allows for the conduction of various elements (oxide ions, protons, etc.). Note that M 1 and / or R 2 In addition, M, which has a similar ionic charge to Fe 2 Fe may be substituted with [another component].

[0028] As mentioned above, due to the high Fe content, the oxidation equilibrium constant K shown in equation (5) oxFor the hydration equilibrium constant K hyd This allows for a larger value, thereby suppressing leakage current. Equation (5) will be explained in detail below. The mobile proton defects in the proton-conducting ceramic layer, described later, are thought to arise from hydration equilibrium due to the association of oxygen vacancies and water vapor, as shown in equation (7) below.

[0029]

number

[0030] Simultaneously with equation (7), equilibrium is also achieved in the association of oxygen vacancies and oxygen shown in equation (8) below.

[0031]

number

[0032] The defect equilibrium in equations (7) and (8) generates electron-holes in the electrolyte, which move from the air electrode to the fuel electrode, causing electron leakage. As a result, the performance of the steam electrolysis cell (e.g., Faraday efficiency) may decrease. Similarly, the performance of a fuel cell, where the opposite reaction occurs (e.g., open-circuit voltage and / or hydrogen utilization rate), may also decrease. Based on the above properties, the electron-hole concentration in the electrolyte during water vapor electrolysis is expressed by equation (5).

[0033]

number

[0034] K hyd -1 / 2 K ox 1 / 2 The larger the term, that is, K ox Large and K hyd The smaller K is, the higher the relative rate of electron-hole injection into the electrolyte, resulting in an increase in the electron-hole concentration in the electrolyte. hyd -1 / 2 K ox 1 / 2The term is small, that is, K ox small and K hy The larger the value, the higher the proton injection rate into the electrolyte, the lower the electron-hole concentration, and the better the performance (e.g., Faraday efficiency). Ba 1-xa-ya R 1 xa R 2 ya Fe c(1-la-ma) M 1 cla M 2 cma O 3-δ Layer or Ba 1-xb R 1 xb Fe c(1-lb-mb-nb) M 1 clb M 2 cmb R 2 cnb O 3-δ The layer, due to its high Fe content, has an oxidation equilibrium constant K ox For the hydration equilibrium constant K hyd Because it is very large, it can improve performance such as Faraday efficiency and open-circuit voltage.

[0035] From the perspective of improving cell performance, the amount of Fe substitution needs to be kept relatively low. Therefore, 0 < (l a +m a )≦0.3, 0≦m a <0.3, 0<(l b +m b +n b )≦0.3, 0≦m a Let <0.3. Preferably 0.05 ≤ (l a +m a )≦0.25, 0≦m a <0.25, 0.05≦(l b +m b +n b )≦0.25, 0≦m b <0.25.

[0036] M 1It is preferable that the perovskite structure be stabilized in terms of ionic radius if it is one or more elements selected from the group consisting of Li, Mg, Al, Cu, Zn, Ga, Cd, In, and Tl. 1 It is more preferable that the element is one or more selected from the group consisting of Mg, Al, Cu, Zn, and Ga, as this can make the perovskite structure more stable in terms of ionic radius.

[0037] M 2 It is preferable that the perovskite structure be stable in terms of ionic radius, as it can be selected from one or more of the following metals: Ti, V, Cr, and metals from periods 5-6 and groups 4-10 of the periodic table.

[0038] In embodiments of the present invention, whether formulas (1) to (3b) are satisfied can be determined, for example, by general compositional analysis (FE-TEM / EDS, etc.). Although impurities other than those specified above may be detected in the compositional analysis, they are included in embodiments of the present invention as long as formulas (1), (2a) and (2b), or formulas (1), (3a) and (3b) are satisfied. Furthermore, although measurement errors may occur in compositional analysis, the c value is set taking this into consideration, and if 0.90 ≤ c ≤ 1.10, it is included in embodiments of the present invention.

[0039] In embodiments of the present invention, the air electrode interface functional layer can be formed by known methods. The thickness of the air electrode interface functional layer is not particularly limited. In one embodiment, the thickness of the air electrode interface functional layer may be, for example, 5 to 500 nm, 10 to 200 nm, or 30 to 170 nm.

[0040] In embodiments of the present invention, the air electrode and fuel electrode are not particularly limited and can be made of known materials and formed by known methods. For example, the air electrode can be made of a conductive material, a semiconductor material, or a dual conductive material (La) that conducts oxide ions and electrons (holes). 1-x Sr x OO 3-δ (LSC), LaSrCoO 4+δ (LSC4), LaNiO3-δ (LNO), La 1-x Sr x Co 1-y Fe y O 3-δ (LSCF), La 1-x Sr x MnO 3-δ (LSM), Sm x Sr 1-x OO 3-δ (SSC, etc.), or triple conductive materials that conduct protons, oxide ions, and electrons (holes) (BaCo 1-x-y-z Fe x Zr y Y z O 3-δ (BCFZY), BaPr 1-x Y x O 3-δ (BPY), PrNi 1-x Co x O 3-δ (PNC), PrBa 1-x Sr x Co 2-y Fe y O 5+δ (PBSCF), NdBa 1-x Sr x Co 2-y Fe y O 5+δ (NBSCF), PrBa 1-x Ca x Ho2O 5+δ (PBCC), Ba 1-x Gd 0.8 La 0.2+x Ho2O 6-δ Materials such as (BGLC) can be used. To obtain a proton ceramic reversible cell with better properties, it is preferable, and more preferable, that the air electrode contains one or more of the biconducting materials and / or one or more of the triplicating materials.

[0041] In embodiments of the present invention, the proton-conducting ceramic layer is not particularly limited and can be made of a known ceramic material that conducts protons, and can be formed by a known method.

[0042] Without departing from the object of the embodiments of the present invention, the proton ceramic reversible cell may include other layers. For example, the air electrode and the air electrode interface functional layer may be in direct contact, but they may not be in contact; that is, there may be other layers between the air electrode and the air electrode interface functional layer. The air electrode interface functional layer and the proton-conducting ceramic layer may be in direct contact, but they may not be in contact; that is, there may be other layers between the air electrode interface functional layer and the proton-conducting ceramic layer. The proton-conducting ceramic layer and the fuel electrode may be in direct contact, but they may not be in contact; that is, there may be other layers between the proton-conducting ceramic layer and the fuel electrode.

[0043] A proton ceramic reversible cell according to an embodiment of the present invention can be used as a water vapor electrolysis cell. Furthermore, a proton ceramic reversible cell according to an embodiment of the present invention can also be used as a fuel cell. That is, a water vapor electrolysis cell (or fuel cell) according to an embodiment of the present invention includes a proton ceramic reversible cell according to an embodiment of the present invention. [Examples]

[0044] The embodiments of the present invention will be described in more detail below with reference to examples. The embodiments of the present invention are not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit described above and below, and all such modifications are included within the technical scope of the embodiments of the present invention.

[0045] Table 1 shows the layer configurations of the proton ceramic reversible cells for Examples 1-4, Comparative Example 1, and Reference Examples 1-6. In Table 1, "←" means "same as above," and "-" means that the corresponding layer is not present. Also, in the following descriptions, including Table 1, "LSCF" means "La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ " and "BLFZ" is "Ba 0.95 La 0.05 Fe 0.8 Zn 0.2 O 3-δ" and "BZCYYb" (or "BZCYYb6211") is "BaZr 0.6 Ce 0.2 Y 0.1 Yb 0.1 O 3-δ " and "BCFZY" is "BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-δ " and "BPY" is "BaPr 0.8 Y 0.2 O 3-δ " and "LNO" is "LaNiO 3-δ " and "LSC" is "La 0.5 Sr 0.5 OO 3-δ " and "PBSCF" is "PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ " and "LSC4" is "LaSrCoO 4+δ " and "SSC" is "Sm 0.5 Sr 0.5 OO 3-δ " and "ATO" is "Sb 0.1 "SnO2" is used, "AFL" stands for "Air Electrode Interface Functional Layer", and "NoAFL" refers to Comparative Example 1, which lacks an air electrode interface functional layer.

[0046] [Table 1]

[0047] The following describes the methods for fabricating reversible proton ceramic cells in Examples 1-4, Comparative Example 1, and Reference Examples 1-6.

[0048] <Fabrication of the fuel electrode> First, porous NiO and BaZr 0.6 Ce 0.2 Y 0.1 Yb 0.1 O 3-δMixed pellets with (BZCYYb) were prepared. BZCYYb powder was prepared by the following method. First, the following materials were mixed in predetermined ratios: BaCO3 (purity 99.95%, manufactured by Koshu Chemical Laboratory); ZrO2 (purity 98%, manufactured by Koshu Chemical Laboratory); CeO2 (purity 99.99%, manufactured by Koshu Chemical Laboratory); Y2O3 (purity 99.99%, manufactured by Koshu Chemical Laboratory); and Yb2O3 (purity 99.9%, manufactured by Koshu Chemical Laboratory). The mixed materials were ball-milled for 10 hours, then calcined in air at 1300°C for 10 hours. This milling and calcination process was repeated twice to obtain BZCYYb powder.

[0049] NiO (99.97% purity, manufactured by Kojun Chemical Laboratory), BZCYYb powder obtained by the method described above, and starch (manufactured by Kanto Chemical) were mixed in ethanol in a weight ratio of 60:40:10 for 10 hours using a ball mill. This mixed powder was subjected to a uniaxial press (20 MPa, 1 minute) and a hydrostatic press (100 MPa, 1 minute) to obtain NiO-BZCYYb green pellets with a diameter of 15 mm and a thickness of approximately 1 mm. As described later, after all layers had formed, the NiO was reduced to form the Ni-BZCYYb fuel electrode.

[0050] <Formation of a proton-conducting ceramic layer> Among proton-conducting ceramic layer materials, BaZr exhibits excellent thermodynamic stability under high H2O partial pressure. 0.6 Ce 0.2 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) was selected. BZCYYb powder was obtained by the method described above. BZCYYb powder containing 1 wt% NiO was dispersed in a 1:1 mixed solution of a binder (5 wt% ammonium stearate dissolved in α-terpineol) and a polyethyleneimine solution (20 wt% polyethyleneimine (Mw: 28000) dissolved in α-terpineol) to prepare a slurry. This slurry was spin-coated onto both sides of the green pellets described above. A proton-conducting ceramic layer was formed by sintering at 1500°C for 10 minutes, followed by 1450°C for 8 hours. Finally, the back surface was polished with SiC paper.

[0051] <Formation of the functional layer at the air electrode interface> The functional layer at the air electrode interface was formed by pulsed laser deposition (PLD). Various target materials used in the PLD method were prepared as follows. First, powders of air electrode interface functional layer materials (BLFZ, BCFZY, BPY, LNO, LSC, PBSCF, and LSC4) were synthesized using the citric acid precursor method. Specifically, citric acid (C6H7O·H2O, 99.5% purity, manufactured by Kanto Chemical Co., Ltd., hereinafter referred to as "CA") was used as a chelating agent, so that the total number of moles of CA to metal atoms was 2:1, and the concentration of metal atoms was 2 mol / dm³. 2 The precursor solution was prepared to achieve the following. The precursor solution was prepared by adding and dissolving the following materials in Milli-Q® water in the required stoichiometric ratio: La(NO3)3·1.5H2O (purity 99.99%, manufactured by Kanto Chemical); Sr(NO3)2 (purity 98%, manufactured by Kanto Chemical); Co(NO3)2·6H2O (purity 98%, manufactured by Kanto Chemical); Ba(NO3)2 (purity 99%, manufactured by Kanto Chemical); Pr(NO3)3·3H2O (purity 99%) 0.5%, manufactured by Fujifilm Wako Pure Chemical Industries); Ni(NO3)2·6H2O (98% purity, manufactured by Kanto Chemical Co., Ltd.); Fe(NO3)3·9H2O (99.9% purity, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.); Y(NO3)3·6H2O (99.99% purity, manufactured by Kanto Chemical Co., Ltd.); ZrO(NO3)2·2H2O (99% purity, manufactured by Kanto Chemical Co., Ltd.); and Zn(NO3)2·6H2O (99.9% purity, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Furthermore, a predetermined amount of CA was added to the precursor solution to prepare it. This precursor solution was heated and stirred at 80°C to evaporate H2O and promote polymerization to obtain a precursor gel. After calcining the gel at 500°C for 1 hour, the pulverized precursor powder was calcined in air at 1000°C for 8 hours to obtain each air electrode interface functional layer material powder. The obtained material powders were molded into pellets with a diameter of 25 mm and a thickness of 5 mm, and then sintered at 1100°C for 6 hours to obtain targets for use in the PLD method.

[0052] Functional layers at each air electrode interface were formed on the surface of a proton-conducting ceramic layer using a PLD system (ULVAC UPS-10000S ultra-vacuum chamber system). For deposition, using the targets obtained above, ablation was performed for 10 minutes at a substrate temperature of 700°C with a KrF excimer laser (248 nm, Coherence Comp109), an energy of 102 mJ / pulse, an oxygen pressure of 21 Pa, and a repetition rate of 5 Hz. Separately, for structural analysis, functional layers at each air electrode interface were also formed on a Si substrate under the same conditions.

[0053] <Formation of the air pole> For Example 1, Comparative Example 1, and Reference Examples 1-6, an air electrode was formed by screen printing a commercially available LSCF ink (manufactured by Fuelcellmaterials) onto the surface of the air electrode interface functional layer (in Comparative Example 1, the surface of the proton-conducting ceramic layer). For Examples 2-4, a slurry was prepared by dispersing the PBSCF powder, SSC powder (commercially available), or ATO powder (commercially available) obtained as described above in a 1:1 mixed solution of a binder (5 wt% ammonium stearate dissolved in α-terpineol) and a polyethyleneimine solution (a solution of 20 wt% polyethyleneimine (Mw: 28000) dissolved in α-terpineol). This slurry was then screen printed onto the surface of the air electrode interface functional layer to form an air electrode.

[0054] Subsequently, the laminate described above was baked at 800°C, and then the fuel electrode side and air electrode side were exposed to gases with 60% H2 / Ar=60 / 40 and 3% H2O / Ar=3 / 97, respectively, at 700°C to reduce the NiO in the fuel electrode, thereby obtaining the proton ceramic reversible cells of Examples 1-4, Comparative Example 1, and Reference Examples 1-6.

[0055] <Structural analysis> Figure 1A is a surface SEM image of the air electrode interface functional layer (BLFZ) of Example 1 formed on a Si substrate, acquired using a field emission scanning electron microscope (FE-SEM, SIGMA500, ZEISS). From Figure 1A, the air electrode interface functional layer (BLFZ) of Example 1 was a dense film with a particle size of several tens of nanometers. The top of Figure 1B is the XRD pattern of the air electrode interface functional layer (BLFZ) of Example 1 formed on a Si substrate, acquired using thin-film XRD (Rigaku, RINT-2000), and the bottom of Figure 1B is the literature value XRD pattern (BaFeO 3-δ (PDF#75-0426). From Figure 1B, the XRD pattern of the BLFZ film in Example 1 is in good agreement with the literature value, indicating that the BLFZ film in Example 1 is single-phase. Similarly, the air electrode interface functional layers in Reference Examples 1 to 6 were also confirmed to be single-phase and dense films.

[0056] The left side of Figure 2 shows a cross-sectional SEM image of Example 1, acquired using a field emission scanning electron microscope (FE-SEM, SIGMA500, ZEISS), and the right side of Figure 2 shows a magnified image thereof. From the left of Figure 2, a high-density BZCYYb6211 electrolyte membrane (14 μm thick), which is a proton-conducting ceramic layer, was uniformly formed on the porous Ni-BZCYYb6211, which is the fuel electrode. The LSCF, which is the air electrode, was a porous layer of sub-100 μm. Cross-sectional SEM images of Comparative Example 1 and Reference Examples 1-6 were also acquired, and it was confirmed that the air electrode, proton-conducting ceramic layer, and fuel electrode were similarly formed. From the right of Figure 2, the BLFZ membrane, which is the functional layer at the air electrode interface, was a dense membrane with a thickness of approximately 140 nm and covered the surface of the BZCYYb6211 electrolyte membrane. Similarly, it was confirmed that the functional layers at the air electrode interface of Reference Examples 1-6 were also uniform membranes.

[0057] Figure 3A is a high-resolution TEM (HRTEM) image of Example 1 (before air electrode formation) acquired using a field emission transmission electron microscope (FE-TEM, Titan3™ G2 60-300). From Figure 3A, it can be seen that the interface between the air electrode interface functional layer (BLFZ film) and the proton-conducting ceramic layer (BZCYYB6211 film) is very sharp and no interdiffusion has occurred. The upper left and lower left of Figure 3B are magnified images of two different locations in Figure 3A, and the upper right and lower right show the contrast along lines perpendicular to the lattice fringes seen in the upper left and lower left figures, respectively. From Figure 3B, lattice fringes with intervals of 0.29 nm and 0.40 nm, corresponding to the (110) and (100) crystal plane spacings of BLFZ, respectively, can be seen, indicating that the crystallinity of the BLFZ film in Example 1 is high. These grid patterns were observed almost entirely, and in the air electrode interface functional layer of Example 1, the area ratio of metal oxides with a perovskite structure (BLFZ) in a cross-sectional view parallel to the stacking direction was at least 90 area %. Furthermore, in the air electrode interface functional layer of Example 1, the metal oxides with a perovskite structure (BLFZ) had a continuous portion from one surface to the other in the stacking direction. Figure 3C is an energy-dispersive X-ray spectroscopy (EDX) mapping of Example 1 (before air electrode formation) obtained using the EDS device attached to the FE-TEM described above. The air electrode interface functional layer of Example 1 is Ba 0.95 La 0.05 Fe 0.8 Zn 0.2 O 3-δ It was found to be a film, with its metal atoms (Ba, La, Fe, and Zn) uniformly distributed, and no braided segregation or similar processes had occurred.

[0058] <Evaluation of Proton Ceramic Reversible Cell Properties> The proton ceramic reversible cell characteristics of the examples, comparative examples, and reference examples were evaluated using a test station (Solartron 1260A / 1287) equipped with an electrochemical evaluation device. In all measurements, a 20% O2 / Ar=20 / 80 mixed gas was passed through 70°C water at a total flow rate of 40 sccm to prepare air containing 30% H2O gas, which was then introduced to the air electrode. Humidified hydrogen gas, prepared by bubbling a 10% H2 / Ar=10 / 90 mixed gas in 25°C water at a total flow rate of 30 sccm, was supplied to the fuel electrode side for measurement.

[0059] Figure 4 shows the open-circuit voltage (OCV) at each temperature for Example 1 (BLFZ), Comparative Example 1 (NoAFL), Reference Example 1 (BCFZY), Reference Example 2 (BPY), Reference Example 3 (LNO), Reference Example 4 (LSC), Reference Example 5 (PBSCF), and Reference Example 6 (LSC4). As shown in Figure 4, Example 1 showed a higher OCV at each temperature than Comparative Example 1 (i.e., an example without an air electrode interface functional layer, corresponding to the prior art), indicating good fuel cell characteristics (for example, at 600°C, the OCV of Example 1 was 0.94V compared to 0.91V for Comparative Example 1). This is due to Example 1 having less electron leakage than Comparative Example 1.

[0060] Figure 5 shows the current-voltage (IV) characteristics of Comparative Example 1, and Figure 6 shows the current-voltage (IV) characteristics of Example 1. Note that the IV characteristics as a fuel cell are shown on the negative current density side, and the IV characteristics as a steam electrolysis cell are shown on the positive current density side.

[0061] First, looking at the negative current density side (fuel cell), Example 1 (Figure 6) showed better fuel cell characteristics than Comparative Example 1 (Figure 5) at each temperature from 500 to 700°C, with a smaller voltage drop associated with increasing current density (to the left in the figure).

[0062] Next, looking at the positive current density side (water vapor electrolytic cell), Example 1 (Figure 6) had a higher electrolytic current density than Comparative Example 1 (Figure 5) at each temperature from 500 to 700°C, and exhibited better characteristics as a water vapor electrolytic cell (for example, at 600°C, the electrolytic current density of Example 1 at 1.3V was 570 mA / cm²). 2 This value was higher than the corresponding electrolytic current density in Comparative Example 1.

[0063] Figure 7 shows a comparison of the electrolytic current density at 1.3V for Example 1 (BLFZ), Comparative Example 1 (NoAFL), Reference Example 1 (BCFZY), Reference Example 2 (BPY), Reference Example 3 (LNO), Reference Example 4 (LSC), Reference Example 5 (PBSCF), and Reference Example 6 (LSC4). Example 1 (BLFZ), including the reference examples, showed the highest electrolytic current density below 550°C. Above 600°C, Reference Examples 5 (PBSCF) and 6 (LSC4) showed higher electrolytic current densities than Example 1 (BLFZ). However, as will be discussed later, Reference Examples 5 and 6 had low Faraday efficiency, and considering Faraday efficiency, Example 1 showed better characteristics as a water vapor electrolytic cell. In Comparative Example 1, changing the air electrode (LSCF) to BLFZ did not result in good characteristics.

[0064] Next, the air electrode (dual conductive material LSCF) of Example 1 was replaced with an n-type semiconductor ATO (Example 2), a dual conductive material SSC (Example 3), and a triple conductive material PBSCF (Example 4), and the IV characteristics of the water vapor electrolysis cell were evaluated. Figure 8 shows the IV characteristics of Example 2 (air electrode: ATO). Compared to Example 1, the electrolytic current density was lower. Figure 9 shows the IV characteristics of Example 3 (air electrode: SSC). Compared to Example 1, the electrolytic current density was approximately the same. Figure 10 shows the IV characteristics of Example 4 (air electrode: PBSCF). Compared to Example 1, the electrolytic current density was higher. From these results, it was found that it is preferable for the air electrode to contain one or more of the biconducting materials and / or one or more of the triplicating materials, and more preferable to contain one or more of the triplicating materials.

[0065] Next, the Faraday efficiency (η) was evaluated by quantifying the amount of hydrogen generated (hydrogen release rate) under constant current conditions of 500 and / or 600°C. Figure 11A shows Comparative Example 1 at 600°C and 314 mA / cm². 2 Figure 11B shows the time evolution of the hydrogen release rate (left of the two right axes, plotted with "+") and the Faraday efficiency (right of the two right axes, plotted with "〇") at 500°C and 70 mA / cm². 2 This figure shows the time evolution of the hydrogen release rate and Faraday efficiency. The current value was set so that the voltage value (left axis), shown by the solid line, was 1.3V. As can be seen from Figures 11A and 11B, Comparative Example 1 had a Faraday efficiency of 31% at 600°C and 46% at 500°C. Figure 12A shows the results of Example 1 at 600°C and 570 mA / cm². 2 Figure 12B shows the time evolution of hydrogen release rate and Faraday efficiency at 500°C and 214 mA / cm². 2 The time evolution of the hydrogen release rate and Faraday efficiency is shown. The current value was set so that the voltage value shown by the solid line was 1.3V. As can be seen from Figures 12A and 12B, Example 1 showed better characteristics than Comparative Example 1, with a Faraday efficiency of 45% at 600°C and 75% at 500°C.

[0066] Figure 13 shows Reference Example 6 (LSC4) at 500°C and 128 mA / cm². 2 Figure 14 shows the time evolution of hydrogen release rate and Faraday efficiency in Reference Example 5 (PBSCF) at 500°C and 142 mA / cm². 2The time evolution of hydrogen release rate and Faraday efficiency is shown. As mentioned above, in the IV characteristic evaluation at 600°C or higher, Reference Example 5 (PBSCF) and Reference Example 6 (LSC4) showed higher electrolytic current density than Example 1 (BLFZ). However, as can be seen from Figures 13 and 14, the Faraday efficiency was 30% (Reference Example 6) and 27% (Reference Example 5), which were lower than that of Example 1. Therefore, considering the Faraday efficiency, Example 1 can be said to have shown better characteristics as a water vapor electrolytic cell.

[0067] Figures 15A to 15C show the results for Example 4 (air electrode: PBSCF, air electrode interface functional layer: BLFZ) at 600°C and 743 mA / cm². 2 (Figure 15A), 600℃, 1143mA / cm² 2 (Figure 15B) and 500°C, 214 mA / cm² 2 Figure 15C shows the time evolution of the hydrogen release rate and Faraday efficiency. Example 4 showed a higher Faraday efficiency than Example 1 (air electrode: LSCF, air electrode interface functional layer: BLFZ) shown in Figures 12A and 12B, demonstrating even better characteristics as a water vapor electrolytic cell.

[0068] Figure 16 shows the relationship between electrolytic current density and Faraday efficiency for Example 1 (BLFZ-AFL), Example 4 (PBSCF / BLFZ-AFL), Comparative Example 1 (NoAFL), Reference Example 2 (BPY-AFL), Reference Example 5 (PBSCF-AFL), and Reference Example 6 (LSC4-AFL). A higher electrolytic current density and higher Faraday efficiency (i.e., plotted in the upper right of the figure) indicates superior performance as a water vapor electrolytic cell. Generally, as the electrolytic current density increases, leakage current is more likely to occur, and the Faraday efficiency may decrease. However, Example 1, shown as a black circle, showed higher electrolytic current density and higher Faraday efficiency than Comparative Example 1, shown as a black diamond. Furthermore, among the reference examples, Reference Example 2 showed good characteristics, but Example 1 showed even higher electrolytic current density and higher Faraday efficiency. Furthermore, Example 4, in which the air electrode was changed from a dual-conducting material (LSCF) to a triple-conducting material (PBSCF), showed even higher electrolytic current density and higher Faraday efficiency than Example 1.

Claims

1. The device comprises an air electrode, an air electrode interface functional layer, a proton-conducting ceramic layer, and a fuel electrode in this order. The air electrode interface functional layer comprises a metal oxide and / or its hydrate having a perovskite structure, wherein the metal oxide and / or its hydrate satisfies the following formula (1): A reversible proton ceramic cell that satisfies formula (2b) below when formula (2a) below is satisfied, and satisfies formula (3b) below when formula (3a) below is satisfied. ([Ba]+[R １ ]+[R ２ ]+[Fe]) / [A １ ]≧0.75 ・・・(1) [Ba]+[R １ ]≦[Fe]+[M １ ]+[M ２ ] ・・・(2a) [Ba]:[R １ ]:[R ２ ]:[Fe]:[M １ ]:[M ２ ]=(1-x ａ -y ａ ):x ａ :y ａ :c(1-l ａ -m ａ ):cl ａ :cm ａ ・・・(2b) [Ba]+[R １ ]>[Fe]+[M １ ]+[M ２ ] ・・・(3a) [Ba]:[R １ ]:[Fe]:[M １ ]:[M ２ ]:[R ２ ]=(1-x ｂ ):x ｂ :c(1-l ｂ -m ｂ -n ｂ ):cl ｂ :cm ｂ :cn ｂ ・・・(3b) In equations (1) to (3b), R １ is one or more selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, and R ２ is one or more selected from the group consisting of Sc, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu, A １ M consists of all elements except oxygen and hydrogen. １ is one or more selected from the group consisting of Li, Na, Mg, Al, Ca, Cu, Zn, Ga, Ag, Cd, In, Hg, and Tl, M ２ [Ba], [R] １ ] [R ２ ], [Fe], [A １ We, [M １ ] and [M ２ ] represents Ba and R in mol% respectively. １ , R ２ Fe, A １ M １ and M ２ The content is shown, and 0 ≤ (x ａ +y ａ )<1.0, 0<(l ａ +m ａ ) ≤ 0.3, 0 ≤ m ａ <0.3, 0.90 ≤ c ≤ 1.10, 0 ≤ x ｂ <1.0, 0<(l ｂ +m ｂ +n ｂ ) ≤ 0.3, 0 ≤ m ｂ The relationship < 0.3 is satisfied.

2. R １ The proton ceramic reversible cell according to claim 1, wherein is one or more selected from the group consisting of La, Ce, Pr, Nd, Pm, and Sm.

3. M １ The proton ceramic reversible cell according to claim 1 or 2, wherein is one or more selected from the group consisting of Li, Mg, Al, Cu, Zn, Ga, Cd, In, and Tl.

4. A water vapor electrolytic cell comprising a reversible proton ceramic cell according to any one of claims 1 to 3.

5. A fuel cell comprising a proton ceramic reversible cell according to any one of claims 1 to 3.

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