Oxide proton-conducting fuel battery cell

Abstract

To provide an oxide proton-conducting fuel battery cell capable of improving output density.SOLUTION: The present invention provides an oxide proton-conducting fuel battery cell including an electrolyte formed of a proton conducting material, an air electrode, and a dense thin film layer provided between the electrolyte and the air electrode and having a thickness of 10-600 nm. The thin film layer is an ABO-type perovskite oxide, and is formed of an oxide material (1) containing one or more elements selected from the group consisting of Sc, Sn, Mo, Y, Yb and Mg at a B site.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an oxide proton conducting fuel cell. [Background technology]

[0002] In recent years, rapid industrialization and fossil fuel consumption have led to the serious problem of greenhouse gas emissions, such as CO2, which can cause serious environmental pollution. Hydrogen, a promising new energy source, has been attracting attention, as it can produce energy without emitting greenhouse gases, prompting the innovative and advanced application of hydrogen fuel cells. These fuel cells have been recognized for their efficient energy conversion without emitting CO2, and interest in solid oxide fuel cells (SOFCs) has been growing due to their high energy conversion efficiency (>60%) and impressive power output. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-6322 Summary of the Invention [Problem to be solved by the invention]

[0004] However, solid oxide fuel cells have high operating temperatures (700 to 1000°C), which tend to cause drawbacks such as rapid performance degradation, electrode agglomeration, and high overvoltage. In contrast, proton-conducting ceramic fuel cells (PCFCs) can be operated at lower temperatures than solid oxide fuel cells (SOFCs) by using a proton-conducting electrolyte, and as a result, they have been widely studied as energy conversion devices (for example, Patent Document 1). Specifically, proton-conducting ceramic fuel cells can exhibit excellent ionic conductivity with a low activation energy for proton conduction (Ea: 0.4 to 0.5 eV when BZCY is used as the electrolyte). Furthermore, while solid oxide fuel cells (SOFCs) have the problem of fuel dilution due to water generation on the anode side (fuel electrode side), proton-conducting ceramic fuel cells can avoid this problem because water is generated on the cathode side (air electrode side).

[0005] Although proton-conducting ceramic fuel cells have these advantages, further improvements in performance are required. Specifically, proton-conducting ceramic fuel cells can experience relatively large interfacial resistance and electrode overvoltage on the air electrode side, resulting in a need for further improvements in power density (for example, power density at low temperatures).

[0006] Therefore, an object of the present invention is to provide an oxide proton conducting fuel cell capable of improving the output density. [Means for solving the problem]

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have surprisingly found that by providing a specific thin film layer between the electrolyte and air electrode of an oxide proton conducting fuel cell, it is possible to reduce the relatively large interfacial resistance on the air electrode side and the electrode overvoltage, thereby improving proton conductivity from the electrolyte to the air electrode and solving the above-mentioned problems. That is, the present invention is as follows.

[0008] [1] An oxide proton conducting fuel cell, an electrolyte formed of a proton-conducting material; an air electrode; a dense thin film layer having a thickness of 10 to 600 nm provided between the electrolyte and the air electrode; Equipped with The thin film layer is an oxide proton conducting fuel cell, which is formed from an oxide material (1) that is an ABO type perovskite oxide and contains one or more elements selected from the group consisting of Sc, Sn, Mo, Y, Yb, and Mg at the B site. [2] The oxide proton conducting fuel cell according to [1], wherein the oxide material (1) of the thin film layer contains Sr or Ba at the A site. [3] The oxide proton conducting fuel cell according to [1] or [2], wherein the oxide material (1) of the thin film layer is a perovskite oxide material represented by the following general formula (1): (A 1 1-x1 B 1 x1 )(Sc 1-y1 C 1 y1) )O 3―δ1 ···(1) (In general formula (1), A 1 is at least one of La, Pr, Nd, Sm, Ba, Sr, and Ca, B 1 is at least one of Sr, Ba, and Ca, C 1 is at least one of Mg, Y, Yb, Ga, Al, In, Mo, and Sn, x1 is 0.0 to 0.4, y1 is 0.0 to 0.4, δ1 is the amount of oxygen deficiency. [4] The oxide material (1) of the thin film layer is La 1-X Sr X The oxide proton conducting fuel cell according to any one of [1] to [3], wherein the perovskite oxide material is represented by ScO3, and x is in the range of 0.05 to 0.4. [5] The oxide proton conducting fuel cell according to any one of [1] to [4], wherein the thin film layer has a thickness of 10 to 500 nm. [6] The oxide proton conducting fuel cell according to any one of [1] to [5], wherein the thin film layer has a density of 90% or more of the theoretical density. [7] An oxide proton conducting fuel cell, an electrolyte formed of a proton-conducting material; an air electrode; a dense thin film layer having a thickness of 10 to 600 nm and formed of a proton-conductive material, disposed between the electrolyte and the air electrode; Equipped with An oxide proton conducting fuel cell in which the overvoltage of the air electrode catalyst is reduced by maintaining a high proton concentration at the interface between the air electrode and the proton conducting material in the proton conducting material forming the thin film layer. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an oxide proton conducting fuel cell capable of improving the output density. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram schematically illustrating an oxide proton conducting fuel cell according to Example 1. FIG. [Figure 2] 2(a) and 2(b) are graphs showing the power generation characteristics of oxide proton conducting fuel cells of an example and a comparative example in Test Example 1, where FIG. 2(a) shows the results measured at 700°C and FIG. 2(b) shows the results measured at 500°C. [Figure 3] 2A and 2B are graphs showing the results of measurement of oxide proton conducting fuel cells of Examples and Comparative Examples in Test Example 1 by electrochemical impedance spectroscopy (EIS), where FIG. 2A shows the results measured at 700°C and FIG. 2B shows the results measured at 500°C. [Figure 4]1 is a graph showing the power generation characteristics of oxide proton conducting fuel cells of an example and a comparative example in Test Example 2, and a graph showing the results of measurements by electrochemical impedance spectroscopy (EIS). [Figure 5] 10 is a graph showing the power generation characteristics of an oxide proton conducting fuel cell of a comparative example in Test Example 3, and a graph showing the results of measurements by electrochemical impedance spectroscopy (EIS). [Figure 6] 10 is a graph showing the power generation characteristics of an oxide proton conducting fuel cell according to an embodiment of Test Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following exemplary embodiments. In this specification, "A to B" (A and B are numerical values) means "greater than or equal to A and less than or equal to B."

[0012] (First embodiment) The oxide proton conducting fuel cell (hereinafter also referred to as fuel cell) of the first embodiment is a fuel cell comprising an electrolyte made of a proton conducting material, an air electrode, and a dense thin film layer having a thickness of 10 to 600 nm provided between the electrolyte and the air electrode. Furthermore, in the oxide proton conducting fuel cell of the first embodiment, the thin film layer is formed from an oxide material (1) that is an ABO-type perovskite oxide and contains an element selected from the group consisting of Sc, Sn, Mo, Y, Yb, and Mg at the B site. Furthermore, in the first embodiment, the oxide proton conducting fuel cell comprises a fuel electrode on the opposite side of the electrolyte from the air electrode. The fuel cell of the first embodiment can improve power density. Hereinafter, each component of the oxide proton conducting fuel cell of the first embodiment will be described.

[0013] (electrolyte) In the first embodiment, the electrolyte is made of a proton-conductive material. More specifically, the electrolyte is a perovskite-type oxide, and has a dense layer to prevent gas cross-leakage, and the entire electrolyte may be a dense layer. The relative density of the dense layer of the electrolyte may be 90 to 100% by volume, and the thickness of the dense layer of the electrolyte may be 0.1 μm to 500 μm. In order to make the electrolyte thin while preventing gas cross-leakage, it is desirable that the entire electrolyte be a dense layer.

[0014] The proton-conducting material of the electrolyte is not particularly limited and may be any conventionally known material. For example, the proton-conducting material of the electrolyte may be an oxide represented by the following formula (2), or a mixture or solid solution of oxides represented by the following formula (2). A 2 a B 2 b C 2 1-b O 3-δ2 Formula (2) In the above formula (2), A 2 represents at least one element selected from the group consisting of Ba, Ca, and Sr. In the above formula (2), B 2 represents at least one element selected from the group consisting of Ce and Zr. In the above formula (2), C 2 represents at least one element selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In, Sn, Mo, and Sc. In particular, B 2 is preferably Ce, which results in higher proton conductivity in the electrolyte.

[0015] In the above formula (2), a can be set to 0.9 to 1.1, and more preferably, a is set to 0.9 to 1.0. In the above formula (2), b can be 0.50 or more and less than 1, more preferably 0.70 to 0.9, and even more preferably 0.75 to 0.90. When b is 0.50 or more, precipitation of a phase that inhibits proton conduction can be suppressed. Furthermore, when b is less than 1, the conductivity of the electrolyte is further increased. In the above formula (2), δ is the amount of oxygen deficiency, which is determined depending on the values ​​of a and b and the atmosphere.

[0016] The proton-conducting material of the electrolyte is Ba, among the compounds represented by the formula (2). d Zr e Ce f M 1-e-f O 3-δ3 , or Sr d Zr e Ce f M 1-e-f O 3-δ3 (wherein M is a trivalent cation and a rare earth element, and is preferably Y or Yb. M may be both Y and Yb; d is a number satisfying 0.85≦d≦1; e is a number satisfying 0≦e≦1; f is a number satisfying 0≦f≦1; δ3 is the amount of oxygen vacancy; and e and f cannot be 0 at the same time.)

[0017] The thickness of the electrolyte is not particularly limited, and may be, for example, about 0.5 μm or more and 100 μm or less. By making the thickness of the electrolyte 0.5 μm or more, it is possible to increase the strength and prevent gas leakage. Furthermore, by making the thickness of the electrolyte 100 μm or less, it is possible to reduce the resistance. From these viewpoints, the lower limit of the thickness of the electrolyte is preferably 3 μm or more, more preferably 4 μm or more, and even more preferably 5 μm or more. Furthermore, the upper limit is preferably 50 μm or less, and more preferably 10 μm or less. The electrolyte may be formed in multiple layers using multiple types of materials.

[0018] (air electrode) In the first embodiment, the air electrode (cathode) is provided on the opposite side of the electrolyte from the fuel electrode, and air or oxygen gas, etc., can be supplied to the air electrode during operation of the fuel cell. Any conventionally known material can be used for the air electrode, as long as it has catalytic function, electronic conductivity, gas permeability, stability under high-temperature conditions, etc. The material for the air electrode is not particularly limited, but examples thereof include lanthanum strontium cobalt iron composite oxide (LSCF), lanthanum strontium manganese composite oxide (LSM), lanthanum strontium cobalt composite oxide (LSC), lanthanum strontium iron composite oxide (LSF), samarium strontium cobalt composite oxide (SSC), barium lanthanum cobalt composite oxide (BLC), praseodymium nickel cobalt composite oxide, and mixtures thereof. In the first embodiment, the cathode may be, for example, a lanthanum strontium cobalt iron composite oxide, a barium lanthanum cobalt composite oxide, or a praseodymium nickel cobalt composite oxide, more specifically, La(Sr)Fe(Co)O3, Ba(La)CoO3, or PrNi(Co)O3. If necessary, other materials or the proton conductor of formula (2) may be added to the cathode. The thickness of the air electrode can be adjusted depending on the application of the oxide proton conducting fuel cell.

[0019] (Fuel electrode) In the first embodiment, the fuel electrode (anode) is provided on the opposite side of the electrolyte from the air electrode, and hydrogen gas or the like can be supplied to the anode during operation of the fuel cell. Any conventionally known material can be used for the fuel electrode, as long as it has catalytic activity for redox reactions, electronic conductivity, gas permeability, stability under high-temperature conditions, and the like. The material for the fuel electrode is not particularly limited, but may be, for example, Ni, Pd, Pt, Ru, Ni-Fe alloy, Ni-Co alloy, Fe-Co alloy, Ni-Cu alloy, Pd-Pt alloy, a mixture of nickel and zirconia-based oxide, a mixture of nickel and ceria-based oxide, or a mixture of nickel and barium zirconate-based oxide. In the first embodiment, the fuel electrode is preferably made of Ni, Pd, etc. If necessary, other materials may be added to the fuel electrode. The thickness of the fuel electrode can be adjusted depending on the application of the oxide proton conducting fuel cell.

[0020] (thin film layer) In the first embodiment, the thin film layer is provided between (at the interface between) the electrolyte and the air electrode. The thin film layer has a thickness of 10 to 600 nm and is a dense layer. The thin film layer can be a proton-conducting oxide thin film layer formed from an oxide material (1) that is an ABO-type perovskite oxide and contains an element selected from the group consisting of Sc, Sn, Mo, Y, Yb, and Mg at the B site. In the first embodiment, the oxide proton-conducting fuel cell is provided with the above thin film layer, thereby making it possible to improve the power density (including the power density at low temperatures).

[0021] Specifically, without being bound by theory, it is believed that the inclusion of a thin film layer between the air electrode and the electrolyte in a fuel cell results in the following effect. Specifically, because the oxide material (1) forming the thin film layer contains elements such as Sc, the material (1) absorbs a large amount of water vapor, potentially increasing the water vapor partial pressure at the interface. As a result, it is believed that the reaction between protons and oxygen activated at the air electrode (at the interface) between the air electrode and the thin film layer can be promoted. Furthermore, the promotion of the reaction between protons and oxygen can significantly reduce the interfacial resistance and overvoltage at the air electrode, thereby improving proton conductivity from the electrolyte to the air electrode. Therefore, the inclusion of a thin film layer in a fuel cell can improve power density and achieve excellent power generation characteristics.

[0022] If the thickness of the thin film layer is relatively large, excessive absorption of water vapor may occur, resulting in cracking of the expanded thin film layer. Alternatively, if the proton conductivity of the thin film layer itself is not sufficiently high (e.g., if its conductivity is lower than that of the electrolyte), the effect of improving proton conductivity at the interface may not be achieved (may be offset) by the conductivity of the thin film layer itself. In contrast, in the first embodiment, the thickness of the thin film layer is 600 nm or less, thereby effectively improving proton conductivity. While there is no particular lower limit to the thickness of the thin film layer, a thickness of 10 nm or more facilitates the formation of a more appropriate membrane. Furthermore, since the thin film layer is a dense layer, it is possible to suppress gas cross-leakage during operation of the oxide proton conducting fuel cell, and also to improve the water vapor partial pressure. Furthermore, when the oxide proton conducting material forming the electrolyte contains Ba and the oxide material (1) of the thin film layer contains Sc, the Ba may react with carbon dioxide, gradually deactivating the oxide proton conducting material of the electrolyte. However, since the Sc of the oxide material (1) of the thin film layer is highly resistant to carbon dioxide, the stability of the oxide proton conducting fuel cell against carbon dioxide can be improved.

[0023] In the first embodiment, the element at the A site of the oxide material (1) is not particularly limited, but it is preferable that Sr or Ba is contained at the A site, which can increase the proton concentration and improve the conductivity. In the first embodiment, the oxide material (1) contains one or more elements selected from the group consisting of Sc, Sn, Mo, Y, Yb, and Mg at the B site. More preferably, the oxide material (1) contains one or more elements selected from the group consisting of Sc, Y, Sn, and Mo. Still more preferably, the oxide material (1) contains one or more elements selected from the group consisting of Sc, Sn, and Mo. Most preferably, the oxide material (1) contains Sc at the B site. This allows for more effective improvement of the power density. Furthermore, when the oxide proton-conductive material forming the electrolyte contains Ba, the inclusion of Sc can improve the stability of the fuel cell against carbon dioxide. The oxide material (1) may be one type or a combination of two or more types.

[0024] In the first embodiment, the oxide material (1) of the thin film layer may be a perovskite-type oxide material represented by the following general formula (1). (A 1 1-x1 B 1 x1 )(Sc 1-y1 C 1 y1) )O 3―δ1 ···(1) (In general formula (1), A 1 is at least one of La, Pr, Nd, Sm, Ba, Sr, and Ca, B 1 is at least one of Sr, Ba, and Ca, C 1 is at least one of Mg, Y, Yb, Ga, Al, In, Mo, and Sn, x1 is between 0.0 and 0.4, y1 is 0.0 to 0.4, δ1 is the amount of oxygen deficiency. This makes it possible to more effectively improve the power density. In the general formula (1), A 1 lists "Ba, Sr, Ca" as selectable elements, and B 1also contains "Ba, Sr, Ca". This is because, for example, A 1 and B 1 This means that the same element can be selected. 1 and B 1 Therefore, the A site of the oxide material (1) is A 1 the amount of the selected element in B 1 There will be a sum of the amount of the selected element in 1 and B 1 If only Sr is selected in the A site, then one species of Sr will be present at the A site. 1 and B 1 If different elements are selected from Ba, Sr, and Ca for the A site, then multiple different types of alkaline earth metals will be present at the A site. Furthermore, x1 is preferably in the range of 0.05 to 0.4, more preferably in the range of 0.07 to 0.3, and even more preferably in the range of 0.1 to 0.25.

[0025] In the first embodiment, among the oxide materials (1) having the above-mentioned composition, perovskite-type oxide materials represented by the following general formula (11) may be used. (A 11 1-x11 B 11 x11 )(Sc 1-y11 C 11 y11) )O 3―δ11 ···(11) (In general formula (11), A 11 is at least one of La, Pr, Nd, Sm, Ba, Sr, and Ca, B 11 is at least one of Sr, Ba, and Ca, C 11 is at least one of Mg, Y, Ga, Al, In, Mo, and Sn, x11 is 0.0 to 0.4, y11 is 0.0 to 0.4, δ11 is the amount of oxygen deficiency. Furthermore, x11 is preferably in the range of 0.05 to 0.3, and more preferably in the range of 0.1 to 0.25.

[0026] Furthermore, in the first embodiment, among the oxide materials (1) having the above-mentioned composition, La 1-X2 Sr X2 It is preferable that the perovskite oxide material is represented by ScO3, and x2 is in the range of 0.05 to 0.4. By using such a composition, the power density can be improved more effectively. More preferably, x2 is in the range of 0.07 to 0.3, even more preferably, x2 is in the range of 0.1 to 0.25, and most preferably, La 0.85 Sr 0.15 It is ScO3.

[0027] In the first embodiment, the thin film layer has a thickness of 10 to 600 nm. The upper limit of the thickness of the thin film layer is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 250 nm or less. Furthermore, the thinner the thin film layer, the more likely it is that even if the proton conductivity of the thin film layer itself is not sufficiently high (for example, if it is lower than the conductivity of the electrolyte), the more likely it is that the effect of providing the thin film layer (promotion of the reaction between protons and oxygen at the interface between the thin film layer and the air electrode) can be obtained while suppressing this influence. Therefore, the lower limit of the thickness of the thin film layer is not particularly limited, but from the viewpoint of facilitating the formation of a more appropriate film, the lower limit is 10 nm or more, may be 50 nm or more, or may be 100 nm. The thickness of the thin film layer can be determined by observing the cross section of the thin film layer with a scanning electron microscope or a field emission scanning electron microscope.

[0028] In the first embodiment, the thin film layer is a dense layer, which can suppress gas cross-leakage during operation of the oxide proton conducting fuel cell. Furthermore, the thin film layer is a dense layer, which can increase the concentration of water vapor at the interface and promote the reactivity between protons permeating from the electrolyte and oxygen activated at the air electrode. In the first embodiment, a thin film layer being a dense layer can mean, for example, that the thin film layer has a density of 90% or more of the theoretical density, or 92.5% or more, 95.0% or more, or 97.5% or more. If the density of the thin film layer is low, it tends to be difficult to increase the concentration of water vapor at the interface, but by making the density 90% or more of the theoretical density, the concentration of water vapor at the interface can be increased.

[0029] The density of the thin film layer means a relative density, which is calculated from the ratio of the density of the sintered body measured by Archimedes' method to the theoretical density.

[0030] Furthermore, in the oxide proton conducting fuel cell of the first embodiment, the overvoltage measured at 700°C was 0.1 Ω / cm 2 It may be the following: The overvoltage can be measured by an electrochemical impedance method.

[0031] (Method of manufacturing an oxide proton conducting fuel cell) The oxide proton conducting fuel cell of the first embodiment can be manufactured arbitrarily using materials constituting the oxide proton conducting fuel cell, and can be manufactured as follows, although not particularly limited thereto. A method for manufacturing an oxide proton conducting fuel cell may include the steps of (i) forming an anode and an electrolyte on the surface of the anode, (ii) forming a thin film layer on the cathode side surface of the electrolyte (on the surface of the electrolyte opposite to the anode side), and (iii) forming an anode on the surface of the thin film layer opposite to the electrolyte side. An example of a method for manufacturing an oxide proton conducting fuel cell will be described in more detail below.

[0032] The method for manufacturing an oxide proton conducting fuel cell first involves (i) forming an anode and an electrolyte on the surface of the anode, which can be formed by a known method using materials for forming the anode and the electrolyte. For example, first, the raw materials for forming the anode are mixed to prepare a mixture for the anode. The prepared mixture is then used to obtain a fired body. The fired body can be obtained from the mixture by any method, including pressing into a predetermined shape and firing. Alternatively, if necessary, the fired body can be fired in a reducing atmosphere (e.g., an inert gas atmosphere containing hydrogen) when obtaining the fired body or when further firing the obtained fired body. The anode can be formed by such a process. The firing temperature may be any temperature that allows the formation of a ceramic layer. The firing temperature can be, for example, 1000 to 1500°C.

[0033] Next, an electrolyte is formed on the surface of the fuel electrode. The method for forming the electrolyte is not particularly limited, but for example, it can be obtained by forming a film by physical vapor deposition. Examples of physical vapor deposition methods include vacuum deposition, laser ablation, ion beam, and sputtering, with laser ablation being preferred. The material to be subjected to physical vapor deposition can be a fired body obtained by preparing a mixture of raw materials for forming the electrolyte, firing the mixture, press-molding, and then firing the mixture. It can also be prepared using a wet method. In the wet method, electrolyte powder is combined with an organic additive, and a film is formed by a method such as screen printing, tape casting, or inkjet printing, followed by firing. The firing temperature can be, for example, 1000 to 1500°C.

[0034] (i) In the step of forming the fuel electrode and the electrolyte on the surface of the fuel electrode, instead of the above, raw materials for forming the fuel electrode and the electrolyte may be mixed to prepare a mixture for the fuel electrode and a mixture for the fuel electrode, respectively, and a laminate may be formed in which a first layer containing the mixture for the fuel electrode and a second layer containing the mixture for the electrolyte are stacked, followed by co-firing, thereby forming the fuel electrode and the electrolyte in a stacked state. Furthermore, the formation of the anode during the step (i) may be limited to the formation of a precursor of the anode in that step, depending on the type of material of the anode, or a step of forming the anode from a precursor of the anode (for example, a reduction step or a step of firing the pre-fired body) may be additionally performed in a separate step (for example, after laminating the anode, electrolyte, thin film layer, and air electrode).

[0035] Next, in the method for producing an oxide proton conducting fuel cell, a step (ii) of forming a thin film layer on the surface of the electrolyte opposite to the fuel electrode side can be carried out. In this step, the film can be formed by, for example, physical vapor deposition, although not particularly limited thereto. Examples of physical vapor deposition include vacuum deposition, pulsed laser beam deposition, laser ablation, ion beam, and sputtering, with laser ablation being preferred. The material to be subjected to physical vapor deposition can be a sintered body obtained by sintering a mixture prepared from raw materials for forming the thin film layer, press-molding, and then further sintering the mixture. By forming the thin film layer using physical vapor deposition, a dense, thin layer can be obtained.

[0036] The next step in the manufacturing method for an oxide proton conducting fuel cell is (iii) the step of forming an air electrode on the surface of the thin film layer opposite the electrolyte side. In this step, the raw materials for forming the air electrode are mixed to prepare a mixture for the fuel electrode. Next, a third layer containing the mixture can be formed on the surface of the thin film layer that will form the air electrode using existing methods such as screen printing, spray coating, spin coating, and dip coating. The third layer is then fired. The air electrode can be obtained through these steps.

[0037] (Second embodiment) Next, an oxide proton conducting fuel cell according to the second embodiment will be described. Below, the description of the same configuration as the oxide proton conducting fuel cell according to the first embodiment will be omitted as appropriate. The oxide proton conducting fuel cell of the second embodiment comprises an electrolyte made of an oxide proton conducting material, an air electrode, and a dense thin film layer having a thickness of 10 to 600 nm, which is made of a proton conducting material and is provided between the electrolyte and the air electrode. Furthermore, in the second embodiment, the proton conducting material forming the thin film layer maintains a high proton concentration at the interface between the air electrode and the proton conducting material, thereby reducing the overvoltage of the air electrode catalyst. In this way, in the second embodiment, during operation of the oxide proton conducting fuel cell, the proton concentration at the interface between the air electrode and the proton conducting material in the thin film layer is kept high, and the overvoltage of the air electrode catalyst is reduced, thereby improving proton conductivity from the electrolyte to the air electrode, improving the output density at low temperatures, and achieving excellent power generation characteristics.

[0038] Maintaining a high proton concentration at the interface between the air electrode and the proton-conductive material in the thin film layer can be achieved, for example, by using a proton-conductive material that can absorb a large amount of water vapor as the proton-conductive material forming the thin film layer, although this is not particularly limited. Examples of such materials include, but are not limited to, the oxide material (1) described in the first embodiment above, which is an ABO-type perovskite oxide and contains an element selected from the group consisting of Sc, Sn, Mo, Y, Yb, Mg, Zr, and Ce at the B site.

[0039] The water vapor absorption of an oxide material can be measured by a thermogravimetric electronic balance method.

[0040] In the second embodiment, the features of the electrolyte, fuel electrode, air electrode, thin film layer, etc. included in the oxide proton conducting fuel cell may be the same as those of the electrolyte, fuel electrode, air electrode, thin film layer, etc. of the oxide proton conducting fuel cell of the first embodiment. Furthermore, the oxide proton conducting fuel cell of the first embodiment may have the features of the oxide proton conducting fuel cell of the second embodiment.

[0041] Although the embodiments of the present invention have been described above, the oxide proton conducting fuel cell of the present invention is not limited to the above examples, and appropriate modifications can be made to the oxide proton conducting fuel cell of the present invention. [Example]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0043] <Test Example 1> In Test Example 1, a fuel cell without a thin film layer was compared with a plurality of fuel cells with a thin film layer, the composition of which was varied, to evaluate the performance of the fuel cell.

[0044] [Example 1] As Example 1, the following fuel cell was manufactured. (Fuel electrode) First, porous Ni-Fe metal pellets were fabricated as anodes using NiO-NiFe2O4 composite powders synthesized by the impregnation method. Specifically, to prepare the mixed powder, 12.6 g of Fe(NO3)3·9H2O (99%, Fujifilm Wako Pure Chemical Industries, Ltd.) and 20 g of NiO (99%, Fujifilm Wako Pure Chemical Industries, Ltd.) precursors were dissolved in 200 mL of distilled water, covered with a glass lid, and continuously stirred at 150 °C to prevent rapid evaporation. After gelation and combustion at 600 °C for 4 h, during which nitrate decomposition occurred, 10 wt% Fe2O3 coated the NiO. The mixed powder was then calcined in air at 1200 °C for 6 h. To obtain uniform and fine particle size, the mixed powder was then milled in ethanol for 5 h using zirconia balls (φ: 10 mm). The resulting dried powder was then pressed into pellets (20 mm diameter) using a 270 MPa cold isostatic press (CIP) at 30 MPa for 30 min. The resulting pellets were sintered at 1000 °C for 6 h. The pellets were polished and sintered at 1450 °C for 6 h to obtain dense NiO-NiFeO pellets with sufficient porosity to be reduced to Ni-Fe in a hydrogen (H) atmosphere.

[0045] (Electrolyte and thin film layers) Next, the electrolyte and thin film layer were formed. 0.46 Ce 0.34 Y 0.2 The electrolyte was formed of a proton-conducting material having a composition of La0.9Sr0.1ScO3 (hereinafter, the composition of the electrolyte is also referred to as BZCY), and the thin film layer was formed of a proton-conducting oxide material (1) having a composition of La0.9Sr0.1ScO3 (hereinafter, the composition of the thin film layer is also referred to as LSS). Note that BZCY is a preferred electrolyte rich in Ce and Y dopants for its proton conductivity, as opposed to Zr, which is selected for its chemical stability. First, BZCY powder for the electrolyte was prepared using the Pechini method (with the addition of citric acid) and a nitrate solution. The BZCY raw materials were 7.95 g of Ba(NO3)2, 7.12 g of ZrO(NO3)2 / 2H2O, 3.56 g of Ce(NO3)3·6H2O, and 2.3 g of Y(NO3)3·nH2O. Each raw material and the above metal nitrates were dissolved in 200 mL of distilled water. Next, EDTA and citric acid were added as chelating agents, and the mixture was stirred at 290 °C. The mixture was covered with a glass lid to prevent incomplete reaction due to rapid evaporation. At this stage, gel formation was observed as a result of metal complexation. Upon completion of gelation, the magnetic bar was removed. The powder was then heated until it turned black. The resulting powder was pre-calcined at 400 °C for 2 hours and then further heat-treated at 1450 °C for 6 hours to obtain BZCY powder. The prepared BZCY powder was pressed into pellets (20 mm diameter) using a cold isostatic press (CIP) at 270 MPa for 30 min and sintered at 1450 °C for 6 h.

[0046] Next, the thin-film layer LSS powder was prepared using a solid-state method. The LSS raw materials were 2.07 g of Sc2O3, a specified amount of SrCO3 (0.05 g for the optimal Sr = 0.15), and 4.15 g of La2O3. The calculated precursors were pre-calcined at 900 °C to remove powder impurities (La2O3, Sr carbonate, Sc2O3). The precursors were mixed in an ethanol solution for 1 hour and 30 minutes using a ball mill (Mixer Mill MM500 nano, Retsch) with zirconia balls (diameter: 10 mm). The prepared thin-film layer powder was pressed into 30 MPa pellets (diameter: 20 mm) by CIP at 270 MPa for 30 minutes and sintered at 1450 °C for 6 hours.

[0047] Electrolyte and thin film layers were grown on dense NiO-NiFe2O4 composite substrates using a pulsed laser beam (PLD-7, Pascal Corporation). The pulsed laser beam system consisted of a vacuum chamber with a base pressure of 5-10 Pa. The electrolyte and thin film layers were deposited using a pulsed laser beam generated by a KrF excimer laser with a wavelength of 248 nm. First, the electrolyte was deposited by focusing a pulsed laser onto a target surface prepared at 800 °C under different oxygen partial pressure conditions (energy 180 mJ / pulse, repetition rate 10 Hz, oxygen partial pressure 1.0 Pa). The target and substrate were rotated at an appropriate speed to obtain a uniform electrolyte film (10 μm thick). Next, a thin film layer was obtained on the electrolyte surface in the same manner, except that the oxygen partial pressure was changed to 0.67 Pa. The deposited layer was then calcined at 800 °C to match the deposition conditions.

[0048] (air electrode) Next, the air electrode was formed. 0.5 Sr 0.5 The cathode was made of a mixed conductive material with a composition of SmO, SrCO, and CoO (hereinafter, the cathode composition will also be referred to as SSC). The raw materials were prepared by evaporating SmO, SrCO, and Co(NO) and then baking them at 800°C to obtain SSC. The powder (50 mg) was dispersed in a mixture of a small amount of 3-hydroxy-2,2,4-trimethylpentyl isobutyrate and ethyl cellulose (0.06 g) to obtain Sm0.5Sr 0.5A slurry of CoO (SSC) was prepared. The slurry was screen printed onto the surface of the thin film layer (surface area: 0.19625 cm). 2 ) and calcined at 800°C for 1 hour.

[0049] (Fuel cell) Using the laminate prepared as described above, a test fuel cell was fabricated as shown in Figure 1. Specifically, a platinum electrode was used as the reference electrode and placed on the air electrode side. Platinum mesh was used as a current collector, and the surfaces of both the anode and cathode were covered with the platinum mesh. Platinum lead wires were used to establish connections between the electrodes and the electrochemical device. The cell thus fabricated was placed inside a mullite tube with a double-wall structure. Specifically, the cell was placed inside the outer tube and fixed with a glass seal. Next, the inner tube was placed inside the outer tube so that the cell was sandwiched between the air electrode and the fuel electrode. This configuration allows hydrogen gas or oxygen gas passed through the inner tube to permeate the fuel electrode and the air electrode, and then passes through the outer tube to discharge residual gas and water vapor. These gases were supplied in a humidified state through a bubbler, with a total flow rate of 100 mL / min consistent on both sides of the electrodes. Prior to each measurement described below, a fuel electrode (precursor) with a composition of NiO-NiFe2O4 was reduced in the assembled cell by exposure to H2 at 700°C for 1 hour to form a Ni-Fe fuel electrode. The test fuel cell thus produced was evaluated by the method described below.

[0050] [Examples 2, 3, and 4] In Example 2, an oxide proton conducting fuel cell was produced using the same production method as in Example 1, except that the composition of the LSS in the thin film layer was changed from La0.9Sr0.1ScO3 to La0.8Sr0.2ScO3. In Example 3, an oxide proton conducting fuel cell was produced in the same manner as in Example 1, except that the composition of the LSS in the thin film layer was changed from La0.9Sr0.1ScO3 to La0.75Sr0.25ScO3. In Example 4, an oxide proton conducting fuel cell was produced using the same manufacturing method as in Example 1, except that the composition of the LSS in the thin film layer was changed from La0.9Sr0.1ScO3 to La0.85Sr0.15ScO3.

[0051] [Comparative Example 1] In Comparative Example 1, a fuel cell was produced using the same production method as in Example 1, except that no thin film layer was provided. Note that in Example 1, the air electrode was produced on the surface of the thin film layer, but in Comparative Example 1, the air electrode was produced on the surface of the electrolyte.

[0052] [Characteristics analysis] (measuring the thickness of thin film layers) The thickness of the thin film layer was determined by observing the cross section of the thin film layer with a scanning electron microscope (SEM, manufactured by Keyence Corporation, product number V-7800) or a field emission scanning electron microscope (FE-SEM, manufactured by FEI Corporation, product number versa3D). The oxide proton conducting fuel cells of Examples 1 to 4 had a thin film layer thickness of 200 nm.

[0053] (thin film layer density) The density of the thin film layer means a relative density, and was calculated from the ratio of the density of the sintered body measured by Archimedes' method to the theoretical density. The density of the thin film layers in Examples 1 to 4 was 95% or more.

[0054] [Performance evaluation of oxide proton conducting fuel cells] The oxide proton conducting fuel cells of Examples 1 to 4 and Comparative Example 1 were used to evaluate electrochemical performance. (Power generation characteristics) The power generation characteristics were measured using the oxide proton conducting fuel cells of Examples 1 to 4 (cells in which the composition ratio of La to Sr in the oxide material (1) was changed to 0.9:0.1, 0.8:0.2, 0.75:0.25, and 0.85:0.15, respectively) and the oxide proton conducting fuel cell of Comparative Example 1 without a thin film layer. In the measurement, hydrogen gas humidified at 25°C was supplied to the fuel electrode at 100 mL / min, and oxygen gas humidified at 25°C was supplied to the air electrode at 100 mL / min, and measurements were performed at temperatures of 700°C and 500°C. A constant current was applied to each of the cells of Examples 1 to 4 and Comparative Example 1 using a galvanostat (HA-301, manufactured by Hokuto Denko Corporation), and the cell voltage at that time was measured using a digital multimeter (R6451A, manufactured by Advantest Corporation).

[0055] FIG. 2 shows the current density (mA / cm) of the cells of Examples 1 to 4 and Comparative Example 1. 2 ), voltage (V) and power density (W / cm 2 ) shows the relationship between the cell current density and voltage. The roughly straight line (open marker) in Figure 2 shows the relationship between the cell current density and voltage, and the curve (filled marker) in Figure 2 shows the relationship between the cell current density and power density. Figure 2(a) shows the measurement at 700°C, and Figure 2(b) shows the measurement at 500°C. Table 1 shows the measurement results at 700°C, and Table 2 shows the measurement results at 500°C. As can be seen from Table 1 and the graph in Figure 2(a), compared to the cell of Comparative Example 1 which does not have a thin film layer, the cells of Examples 1 to 4 which have a thin film layer exhibited a high open circuit voltage and a large maximum power density at 700°C. Furthermore, as can be seen from Table 2 and the graph in Figure 2(b), which show the results of measurements at a relatively low temperature of 500°C, the cells of Examples 1 to 4 exhibited good open circuit voltages and maximum power densities, even at the relatively low temperature of 500°C, compared to the cell of Comparative Example 1, which does not have a thin film layer.

[0056] (Measured by electrochemical impedance spectroscopy (EIS)) Electrochemical impedance spectroscopy (EIS) measurements were performed at 700°C and 500°C using the cells of Examples 1 to 4 and Comparative Example 1. Specifically, impedance spectra of single cells were obtained under open circuit voltage (OCV) conditions using an impedance / gain phase analyzer (Solartron, Type 1260) combined with an electrochemical interface (Solartron, Type 1270). The measurement conditions were a frequency range of 0.1 Hz to 100 kHz and a signal amplitude of 10 mV. Figure 3(a) shows the results at 700°C, and Figure 3(b) shows the results at 500°C. Table 1 shows the results at 700°C, and Table 2 shows the results at 500°C. As can be seen from Table 1 and the graph in Figure 3(a), the cells of Examples 1 to 4, which have a thin film layer, showed a significant decrease in ohmic resistance compared to the cell of Comparative Example 1, which does not have a thin film layer. The improved ohmic resistance of the cells of Examples 1 to 4 thus indicates improved proton conduction in the thin film layer, and it is clear that this enhanced interfacial reaction. Note that in Comparative Example 1, the resistivity was 1.15 (Ohm cm 2 ), which is consistent with the low maximum power density measured above. Furthermore, as can be seen from Table 2 and the graph in Figure 3(b), which show the results of measurements at a relatively low temperature of 500°C, the cells of Examples 1 to 4 showed a decrease in ohmic resistance compared to the cell of Comparative Example 1, which does not have a thin film layer, even at the relatively low temperature of 500°C.

[0057] [Table 1]

[0058] [Table 2]

[0059] <Test Example 2> In Test Example 2, the performance of the fuel cell was evaluated by comparing oxide proton conducting fuel cells in which the thickness of the thin film layer was changed. [Example 5] The oxide proton conducting fuel cell of Example 5 was manufactured so that the thickness of the thin film layer was 200 nm. Specifically, in Example 5, raw materials were prepared so that the LSS composition of the thin film layer of Example 1 was La0.8Sr0.2ScO3, and then the resulting pellets for thin film layer formation were used as a target to form a thin film layer on the surface of the electrolyte at 800°C using a laser ablation method. After the thin film layer was formed, it was annealed in air at 800°C for 1 hour. In Example 5, the oxide proton conducting fuel cell was manufactured in the same manner as in Example 1, except for these operations.

[0060] [Example 6] In Example 6, an oxide proton conducting fuel cell was manufactured in the same manner as in Example 5, except that the thin film layer was manufactured to have a thickness of 500 nm.

[0061] Comparative Example 2 In Comparative Example 2, an oxide proton conducting fuel cell was produced in the same manner as in Example 5, except that no thin film layer was provided.

[0062] [Characteristics analysis] (measuring the thickness of thin film layers) The thickness of the thin film layer was determined in the same manner as above. The oxide proton conducting fuel cells of Examples 5 and 6 had thin film layers of thicknesses of 200 nm and 500 nm, respectively, and it was found that thin film layers of the desired thicknesses were formed.

[0063] (thin film layer density) The density of the thin film layer was determined in the same manner as above. The density of the thin film layer in Examples 5 and 6 was 95% or more.

[0064] [Performance evaluation of oxide proton conducting fuel cells] The oxide proton conducting fuel cells of Examples 5 and 6 and Comparative Example 2 were used to evaluate electrochemical performance. (Power generation characteristics) The power generation characteristics were measured at 500° C. using the same method as in the above measurement. The measurement results are shown in Table 3. As a result, as shown in Figure 4(a) and Table 3, it was found that the thinner the thin film layer, the better the open circuit voltage and the higher the maximum power density.

[0065] (Measured by electrochemical impedance spectroscopy (EIS)) EIS measurements were carried out at 500°C using the same method as in the measurements above. The measurement results are shown in Table 3. As a result, as shown in Figure 4(b) and Table 3, it was found that the thinner the thin film layer, the lower the ohmic resistance.

[0066] [Table 3]

[0067] <Test Example 3> In Test Example 3, as Comparative Example 3, the oxide material (1) forming the thin film layer was mixed with the oxide material forming the air electrode to produce an oxide proton conducting fuel cell without a thin film layer, and the performance of the fuel cell was evaluated.

[0068] (Comparative Example 3) In Comparative Example 3, a fuel cell was produced using the same manufacturing method as in Example 1, except for the following changes to the configuration. In Comparative Example 3, a laminate was produced by laminating an anode and an electrolyte using the same production method as in Example 1. Next, in Comparative Example 3, the LSS powder for forming the thin film layer in Example 1 was mixed with the SCC powder for forming the cathode in Example 1 to produce an cathode on the surface of the electrolyte. Specifically, 0.18 g of SSC powder and 0.02 g of LSSc powder were mixed by hand using a pestle and mortar, and then a slurry was prepared in the same manner as in the production method for the cathode in Example 1, and a film was formed by screen printing.

[0069] [Performance evaluation of oxide proton conducting fuel cells] The electrochemical performance was evaluated using the oxide proton conducting fuel cell of Comparative Example 3. For comparison, the evaluation results also include the evaluation results of the oxide proton conducting fuel cell of Comparative Example 1. (Power generation characteristics) The power generation characteristics at 500°C were measured using the same method as in the above measurement. As a result, as shown in Figure 5(a), the open circuit voltages of the cells of Comparative Examples 1 and 3 were 0.995 V and 0.957 V, respectively. The maximum power densities of the cells of Comparative Examples 1 and 3 were 200 mW / cm 2 , 147mW / cm 2 Therefore, it was found that when the air electrode contains the thin film layer of oxide material (1), both the open circuit voltage and the maximum power density are lower than when the air electrode does not contain oxide material (1).

[0070] (Measured by electrochemical impedance spectroscopy (EIS)) EIS measurements were carried out at 500°C using the same method as in the measurements above. As a result, as shown in Figure 5(b), the ohmic resistance of the cells of Comparative Examples 1 and 3 was 0.43 (Ohm cm 2 ) and 0.83(Ohm cm 2 ) Therefore, it was found that when the air electrode contains the oxide material (1) in a thin film layer, the ohmic resistance is larger than when the air electrode does not contain the oxide material (1). Therefore, the effect of the oxide material (1) containing Sc cannot be obtained by simply mixing it, but a significant effect is obtained when it is inserted into the interface in the form of a thin film.

[0071] <Test Example 4> In Test Example 4, the composition of the cell was changed from that in Test Example 1, and the same evaluation was carried out. [Example 7] First, we fabricated an anode with the composition of NiO-BZYb. 0.8 Yb 0.2 The mixture was thoroughly mixed with O3 (BZYb, fired at 1600°C) in a weight ratio of 6:4 using a ball mill, then molded to a thickness of 0.6 mm and pre-fired at 1000°C. Next, an electrolyte containing BZYb was prepared on the surface of the anode. A BZYb powder slurry in isopropanol, which had been calcined at 1200°C, was screen-printed onto the electrolyte surface to form a film. The film thickness was 10 μm, and the film was calcined at 1430°C to form a half-cell. Then, a thin film layer with the composition of LSSc was fabricated on the surface of the electrolyte using laser ablation. 0.8 Sr 0.2 Thin films of ScO3 were prepared and annealed at 800℃. Furthermore, an air electrode with the composition LBC-BZYb was fabricated on the surface of the thin film layer. 0.6 Ba 0.4 CoO3-BZYb (1:1 weight ratio) was applied to a surface of 6 mm in diameter by screen printing, and then fired at 800°C for 1 hour. Using the laminate produced as described above, a test fuel cell as schematically shown in FIG.

[0072] [Performance evaluation of oxide proton conducting fuel cells] The power generation characteristics were evaluated in the same manner as above using the oxide proton conducting fuel cell of Example 7. The evaluation was carried out at 500° C., 600° C., and 700° C. The results are shown in FIG. As can be seen from FIG. 6 and Table 4, the cell of Example 5 having the thin film layer exhibited a high open circuit voltage and a large maximum power density even when the cell composition was changed.

[0073] [Table 4]

[0074] From the above, Tests 1 to 4, it is clear that the oxide proton-conducting fuel cell of the present invention has an increased power density when it is provided with a thin film layer and the thin film layer has a predetermined thickness. [Industrial Applicability]

[0075] According to the present invention, it is possible to provide an oxide proton conducting fuel cell capable of improving the output density.

Claims

1. An oxide proton conducting fuel cell, an electrolyte formed of a proton-conducting material; an air electrode; a dense thin film layer having a thickness of 10 to 600 nm provided between the electrolyte and the air electrode; Equipped with The thin film layer is an oxide proton conducting fuel cell, and is formed from an oxide material (1) that is an ABO-type perovskite oxide and contains one or more elements selected from the group consisting of Sc, Sn, Mo, Y, Yb, and Mg at the B site.

2. 2. The oxide proton conducting fuel cell according to claim 1, wherein the oxide material (1) of the thin film layer contains Sr or Ba at the A site.

3. 3. The oxide proton conducting fuel cell according to claim 1, wherein the oxide material (1) of the thin film layer is a perovskite oxide material represented by the following general formula (1): (A １ １－ｘ１ B １ ｘ１ )(Sc １－ｙ１ C １ ｙ１） )O ３―δ１ ・・・(1) (In general formula (1), A １ is at least one of La, Pr, Nd, Sm, Ba, Sr, and Ca, B １ is at least one of Sr, Ba, and Ca, C １ is at least one of Mg, Y, Yb, Ga, Al, In, Mo, and Sn, x1 is 0.0 to 0.4, y1 is 0.0 to 0.4, δ1 is the amount of oxygen deficiency.

4. The oxide material (1) of the thin film layer is La １－Ｘ Sr Ｘ ScO ３ 3. The oxide proton conducting fuel cell according to claim 1, wherein the perovskite oxide material is represented by the formula: where x is in the range of 0.05 to 0.

4.

5. 3. The oxide proton conducting fuel cell according to claim 1, wherein the thin film layer has a thickness of 10 to 500 nm.

6. 3. The oxide proton conducting fuel cell according to claim 1, wherein the thin film layer has a density of 90% or more of the theoretical density.

7. An oxide proton conducting fuel cell, an electrolyte formed of a proton-conducting material; an air electrode; a dense thin film layer having a thickness of 10 to 600 nm and formed of a proton-conductive material, disposed between the electrolyte and the air electrode; Equipped with An oxide proton conducting fuel cell in which the overvoltage of the air electrode catalyst is reduced by maintaining a high proton concentration at the interface between the air electrode and the proton conducting material in the proton conducting material forming the thin film layer.

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