Electrolyte membrane, membrane electrode assembly, electrochemical cell, method for manufacturing electrolyte membrane

Abstract

The electrolyte membrane of the present disclosure comprises a plurality of crystal domains, wherein at least one crystal domain comprises a first sub-crystal domain and a second sub-crystal domain in its interior, the first sub-crystal domain and the second sub-crystal domain respectively comprise Ba, Zr, M, O, M is a trivalent element, and the concentration of M in the first sub-crystal domain is different from the concentration of M in the second sub-crystal domain.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrolyte membrane, a membrane electrode assembly, and a method for manufacturing an electrolyte membrane for an electrochemical cell. BACKGROUND

[0002] As an electrolyte material having proton conductivity, a perovskite-type ion conductor of a chemical formula of BaZr 1-x M x O 3-α (M is a trivalent substitution element) is known.

[0003] Patent Document 1 discloses a BaZr 1-x M x O 3-α (M is at least one element selected from Sc, In, Lu, and Yb, and 0 < x < 1).

[0004] PRIOR ART DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-88384 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] An object of the present disclosure is to provide an electrolyte membrane having high proton conductivity.

[0008] MEANS FOR SOLVING THE PROBLEMS

[0009] The electrolyte membrane of the present disclosure includes a plurality of crystal domains, wherein at least one crystal domain includes a first sub-crystal domain and a second sub-crystal domain in the inside thereof, the first sub-crystal domain and the second sub-crystal domain each include Ba, Zr, M, O, M is a trivalent element, and the concentration of M in the first sub-crystal domain is different from the concentration of M in the second sub-crystal domain.

[0010] The method for manufacturing an electrolyte membrane of the present disclosure includes mixing a material including BaZr 1-d M d O 3-δ’ and a material including BaM2O4, wherein M is a trivalent element, 0 < d < 1 and 0 < δ' < 1 are satisfied.

[0011] EFFECTS OF THE INVENTION

[0012] The present disclosure provides an electrolyte membrane having high proton conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A cross-sectional STEM of the electrolyte membrane of the embodiment is schematically shown.

[0014] Figure 2Ais a cross-sectional view of a membrane electrode assembly of an embodiment.

[0015] Figure 2B is a cross-sectional view of an electrochemical cell of an embodiment.

[0016] Figure 3 shows a fuel cell system of an embodiment.

[0017] Figure 4 shows the production steps of the electrolyte membrane, membrane electrode assembly, and electrochemical cell of the example and comparative examples.

[0018] Figure 5 is a cross-sectional STEM image of the electrolyte membrane of Example 1.

[0019] Figure 6A is FE-EPMA data of the Yb element of the membrane electrode assembly of Example 1 (unit: counts).

[0020] Figure 6B is FE-EPMA data of the Yb element of the membrane electrode assembly of Example 1 (unit: wt%).

[0021] Figure 7 shows the proportion of Yb of each analysis point of the membrane electrode assembly of Example 1.

[0022] Figure 8 shows the Cole-Cole chart of the cell of Example 1.

[0023] Figure 9 is a cross-sectional STEM image of the electrolyte membrane of Example 2.

[0024] Figure 10A is FE-EPMA data of the Yb element of the membrane electrode assembly of Example 2 (unit: counts).

[0025] Figure 10B is FE-EPMA data of the Yb element of the membrane electrode assembly of Example 2 (unit: wt%).

[0026] Figure 11 shows the proportion of Yb of each analysis point of the membrane electrode assembly of Example 2.

[0027] Figure 12 is a cross-sectional STEM image of the electrolyte membrane of Comparative Example 1.

[0028] Figure 13A is FE-EPMA data of the Yb element of the membrane electrode assembly of Comparative Example 1 (unit: counts).

[0029] Figure 13BFE-EPMA data of Yb element (unit: weight %) of the membrane electrode assembly of Comparative Example 1.

[0030] Figure 14 The proportion of Yb of each analysis point of the membrane electrode assembly of Comparative Example 1 is shown. DETAILED DESCRIPTION

[0031] (Definitions of Terms)

[0032] The term "STEM" used in the present specification means a scanning transmission electron microscope.

[0033] The term "FE-EPMA" used in the present specification means an electron beam microanalyzer.

[0034] The term "EDX" used in the present specification means an energy dispersive X-ray.

[0035] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0036] (Embodiment 1)

[0037] Figure 1 A cross-sectional STEM image of the electrolyte membrane 11 of Embodiment 1 is schematically shown.

[0038] A cross-sectional STEM image of the electrolyte membrane 11 obtained in Example 1 and Example 2 described later is schematically shown. Figure 5 and Figure 9 As shown in

[0039] The plurality of crystal domains 100 include a first crystal domain 100a and a second crystal domain 100b.

[0040] As shown in Figure 1 Each crystal domain 100 is composed of a first sub-crystal domain 101 and a second sub-crystal domain 102. In other words, at least one crystal domain 100 includes the first sub-crystal domain 101 and the second sub-crystal domain 102 in its interior.

[0041] A crystal boundary gb is formed between two adjacent crystal domains 100 (for example, between the first crystal domain 100a and the second crystal domain 100b). The crystal boundary gb defines the boundary of the two adjacent crystal domains. Each crystal domain 100 is surrounded by a plurality of crystal boundaries gb in the STEM image. In other words, each crystal domain 100 is defined by a plurality of crystal boundaries gb in the STEM image.

[0042] The first sub-crystal region 101 and the second sub-crystal region 102 each contain Ba, Zr, M, O, and M is an element having a valence of 3. M may be, for example, at least one element selected from Sc, In, Lu, and Yb. The concentration of M in the first sub-crystal region 101 is different from the concentration of M in the second sub-crystal region 102. In Embodiment 1, for example, the concentration of M in the first sub-crystal region is higher than the concentration of M in the second sub-crystal region, and in addition, the first sub-crystal region 101 is surrounded by the second sub-crystal region 102 inside each crystal region 100.

[0043] In Embodiment 1, M is, for example, Yb, and the first sub-crystal region and the second sub-crystal region each consist of BaZr 1-a Yb a O 3-δ and BaZr 1-b Yb b O 3-δ represented by BaZr

[0044] As demonstrated in Example 1 and Example 2 described later, in the case where the concentration of M in the first sub-crystal region 101 is different from the concentration of M in the second sub-crystal region 102, the electrolyte membrane 11 of Embodiment 1 has a high proton conductivity at a temperature of 500 degrees Celsius or higher and 700 degrees Celsius or lower. In Example 1 and Example 2, an example in which Yb is used as M is shown, but even in the case where another element is used, if the concentration of M in the first sub-crystal region 101 is different from the concentration of M in the second sub-crystal region 102, a high proton conductivity at a temperature of 500 degrees Celsius or higher and 700 degrees Celsius or lower is obtained.

[0045] If there is no sub-crystal region, that is, in the case where the concentration of M in the first sub-crystal region 101 is substantially the same as the concentration of M in the second sub-crystal region 102, as demonstrated in Comparative Example 1 described later, the proton conductivity at a temperature of 500 degrees Celsius or higher and 700 degrees Celsius or lower is 0.22 (10 -2 S·cm -1 or less. Thus, in the case where there is no sub-crystal region, the proton conductivity is low when compared under the same temperature conditions.

[0046] Here, "the concentration of M in the first sub-crystal region is substantially the same as the concentration of M in the second sub-crystal region" means that any one of the following is satisfied:

[0047] (i) BaZr 1-a M a O 3-δ contained in the first sub-crystal region and BaZr 1-b M b O 3-δ contained in the second sub-crystal region, (a - b) ≤ 0.156;

[0048] (ii) the value of "maximum value of weight % of M - average value of weight % of M" per unit area of data output by analyzing a 3 x 3 μm range of the electrolyte membrane with an electron beam microanalyzer is 2.0% or less;

[0049] (iii) the proportion of M calculated by FE-EPMA analysis is within the range of the value of the average composition + 0.1 (i.e., c + 0.1 ≥ x).

[0050] In this case, "the concentration of M in the first subcrystalline domain is different from the concentration of M in the second subcrystalline domain" means:

[0051] (i) BaZr 1-a M a O 3-δ contained in the first subcrystalline domain and BaZr 1-b M b O 3-δ contained in the second subcrystalline domain, (a - b) > 0.156;

[0052] (ii) the value of "maximum value of weight % of Yb - average value of weight % of Yb" per unit area of data output by analyzing a 3 x 3 μm range of the electrolyte membrane with an electron beam microanalyzer is more than 2.0%;

[0053] (iii) the proportion of Yb calculated by FE-EPMA analysis is not within the range of the value of the average composition + 0.1 (i.e., c + 0.1 < x).

[0054] As demonstrated in Example 1 and Example 2 described later, in the case where the value of (a - b) is 0.28 or more, the electrolyte membrane 11 of Embodiment 1 has a high proton conductivity at a temperature of 500 degrees Celsius or more and 700 degrees Celsius or less.

[0055] In the case where the value of (a - b) is less than 0.28, for example, in the case where (a - b) ≤ 0.156, as demonstrated in Comparative Example 1 described later, the proton conductivity at a temperature of 500 degrees Celsius or more and 700 degrees Celsius or less is 0.22 (10 -2 S·cm -1 ) or less. In the case where the value of (a - b) is less than 0.28, the proton conductivity is low when compared under the same temperature conditions.

[0056] More specifically, at a temperature in the range of 500 degrees Celsius or higher and 700 degrees Celsius or lower, the electrolyte film having a value of (a-b) of 0.28 or higher (i.e., the electrolyte film of Embodiment 1) has a high proton conductivity compared to the electrolyte film having a value of (a-b) of less than 0.28. For example, at a temperature of 600 degrees Celsius, the electrolyte film having a value of (a-b) of 0.28 or higher (i.e., the electrolyte film of Embodiment 1) has a high proton conductivity of 0.24 (10 -2 S-cm -1 ) or more, whereas the electrolyte film having a value of (a-b) of less than 0.28 has a proton conductivity of 0.21 (10 -2 S-cm -1 ).

[0057] It is preferable that the mathematical expression (a-b) ≥ 0.30 be satisfied. It is more preferable that the mathematical expression (a-b) ≥ 0.35 be satisfied. The value of a is the amount of deficiency of Zr (in other words, the amount of doping of Yb). The value of δ is the amount of oxygen deficiency. The value of δ satisfies 0 < δ < 1.

[0058] The cross section of the electrolyte film 11 of Embodiment 1 was analyzed by FE-EPMA, and as demonstrated in Example 1 and Example 2 described later, the electrolyte film 11 contains a barium zirconate compound doped with ytterbium. The value of "maximum value of weight % of Yb - average value of weight % of Yb" per unit area of the data output by the FE-EPMA analysis (hereinafter sometimes referred to as "difference in Yb") is 5% or more. At a temperature in the range of 500 degrees Celsius or higher and 700 degrees Celsius or lower, the electrolyte film having a difference in Yb of 5% or more has a high proton conductivity compared to the electrolyte film having a difference in Yb of less than 5%. For example, at a temperature of 600 degrees Celsius, the electrolyte film having a difference in Yb of 0.24 (10 -2 S-cm -1 ) or more. In the case where the difference in Yb is less than 5%, for example, in the case where it is 2.0% or less, as demonstrated in Comparative Example 1, at a temperature of 600 degrees Celsius, the electrolyte film has a low proton conductivity of 0.21 (10 -2 S-cm -1 ).

[0059] It is more preferable that the difference in Yb be 6% or more. At a temperature in the range of 500 degrees Celsius or higher and 700 degrees Celsius or lower, the electrolyte film having a difference in Yb of 6% or more has a high proton conductivity of 0.24 (10 -2 S-cm -1 ) or more. In the case where the difference in Yb is less than 6%, as demonstrated in Example 2 and Comparative Example 1, at a temperature of 500 degrees Celsius, the electrolyte film has a low proton conductivity of 0.19 (10 -2 S-cm -1 ) or less.

[0060] A cross section of the electrolyte membrane 11 of Embodiment 1 was analyzed, and as demonstrated in Example 1 and Example 2, there was a region of 3 x 3 μm square on the electrolyte membrane represented by the composition formula BaZr 1-x Yb x O 3-δ (where 0 < c < 1, (c + 0.1) < x, 0 < δ < 1) indicates a 3 x 3 μm square region. Here, the value of x is the amount of Zr deficiency (in other words, the amount of Yb doping). In addition, x < 1 can be satisfied. Here, the value of c indicates the ratio of Yb with respect to the sum of Zr and Yb. This ratio is calculated from the feed amount of the starting material. The value of c satisfies the formula: 0 < c < 1. The value of c can also satisfy the formula: 0 < c < 0.4. The electrolyte membrane 11 of the present embodiment has a high proton conductivity of 0.24 (10 -2 S-cm -1 ) or more at a temperature of 600 degrees Celsius. In the case where there is no region on the electrolyte membrane that satisfies the mathematical formula (c + 0.1) < x, as demonstrated in Comparative Example 1, the proton conductivity is low at 0.21 (10 -2 S-cm -1 ) at a temperature of 600 degrees Celsius.

[0061] The electrolyte material is synthesized by a citric acid complex method, a solid phase sintering method, a coprecipitation method, a nitrate method, or a spray granulation method.

[0062] (Embodiment 2)

[0063] Figure 2A A cross section of the membrane electrode assembly 10 of Embodiment 2 is shown. The membrane electrode assembly 10 is provided with an electrolyte membrane 11 and an electrode 12. In other words, the electrode 12 is provided on one main surface of the electrolyte membrane 11.

[0064] The electrolyte membrane 11 is described in Embodiment 1. The thickness of the electrolyte membrane 11 is, for example, 1 to 50 μm.

[0065] The electrode 12 mainly contains at least one compound among the following.

[0066] (i) an electrolyte material contained in the electrolyte membrane, and a mixture of one or more metals selected from Co, Fe, Pt, and Pt and Ni (i.e., a metal ceramic)

[0067] (ii) a composite oxide containing lanthanum

[0068] (iii) a composite oxide containing barium

[0069] (iv) a composite oxide containing strontium

[0070] Electrode 12 has a thickness of, for example, 1 to 1000 μm. When electrode 12 also serves as a support for the unit cell, electrode 12 preferably has a thickness of 100 μm to 500 μm. When a structure other than electrode 12 serves as a support for the unit cell, electrode 12 preferably has a thickness of 10 μm to 20 μm.

[0071] Figure 2A In this configuration, the electrolyte membrane 11 and the electrode 12 are in contact. However, other layers may also be present between the electrolyte membrane 11 and the electrode 12. Examples of other layers include functional layers. Functional layers are layers that facilitate the movement of electrons or protons between the electrolyte membrane 11 and the electrode 12. Functional layers may be composed, for example, of composite materials of cermets and composite oxides.

[0072] Electrolyte membranes are fabricated using methods such as strip casting, spin coating, dip coating, sputtering, and PLD (Pulse Laser Deposition). Electrolyte membranes are made by using BaZr-containing... 1-d M d O 3-δ’ The material is mixed with a material containing BaM₂O₄ to prepare an electrolyte ceramic slurry containing the mixed material, which is then manufactured by a blade coating method. The slurry satisfies 0 < d < 1 and 0 < δ' < 1, and M is a trivalent element, which can be at least one element selected from Sc, In, Lu, and Yb. By manufacturing in this way, it is possible to produce electrolyte materials in which the concentration of M in the first subdomain differs from the concentration of M in the second subdomain. The manufacture of the electrolyte membrane may, for example, include mixing BaZr… 1-d M d O 3-δ The powder contains BaM2O4 powder.

[0073] (Implementation Method 3)

[0074] Figure 2B A cross-section of an electrochemical unit 20 having a membrane electrode assembly 10 is shown.

[0075] The electrochemical unit 20 includes an electrode 12, an electrolyte membrane 11, and a counter electrode 13.

[0076] The membrane electrode assembly 10 was described in Embodiment 2.

[0077] like Figure 2B As shown, the electrochemical unit 20 consists of an electrode 12, an electrolyte membrane 11, and a counter electrode 13 stacked sequentially. That is, the electrolyte membrane 11 is sandwiched between the electrode 12 and the counter electrode 13. In other words, the electrolyte membrane 11 is disposed between the electrode 12 and the counter electrode 13.

[0078] When the counter electrode 13 functions as an air electrode, it comprises a composite compound. For example, the counter electrode 13 primarily comprises lanthanum strontium cobalt oxide. The counter electrode 13 can be fabricated on the membrane electrode assembly 10 by screen printing.

[0079] like Figure 2B As shown, the counter electrode 13 is disposed in contact with the electrolyte membrane 11, but this is not a limitation. Other layers may also be disposed between the counter electrode 13 and the electrolyte membrane 11.

[0080] Other types of layers include, for example, functional layers. Functional layers are described in Implementation 2.

[0081] Electrochemical unit 20 can be used in fuel cells, electrochemical hydrogen pumps, hydrogen sensors, and water electrolysis devices.

[0082] (Implementation Method 4)

[0083] Figure 3 A fuel cell system 1000 with an electrochemical unit is schematically shown.

[0084] Electrochemical unit 20 is described in embodiment 3.

[0085] Electrochemical units 20 are stacked to obtain a laminate 30. The resulting laminate 30 is housed in a housing 1014.

[0086] The housing 1014 may be constructed from heat-insulating components. Oxidant gas is supplied to the counter electrode 13 of the stacked electrochemical unit 20.

[0087] Specifically, oxidant gas is supplied from oxidant gas supplier 1021 to the counter electrode 13 (i.e., cathode) of multiple electrochemical units 20 via oxidant gas path 1024.

[0088] The following reaction (1) is carried out on electrode 13.

[0089] O2+4H + +4e - →2H2O (1)

[0090] Oxidizing gases, for example, are air.

[0091] Raw materials are supplied from the raw material feeder 1022 to the electrode 12 through the raw material gas path 1023.

[0092] The following reaction (2) takes place at electrode 12.

[0093] 2H2→4H + +4e - (2)

[0094] The raw material is, for example, hydrogen molecules.

[0095] Hydrogen can be generated by a reforming reaction. Alternatively, hydrogen can also be generated by water electrolysis.

[0096] In this way, the fuel cell system 1000 operates. The fuel cell system 1000 generates electricity.

[0097] (Examples)

[0098] (Production of cells of examples and comparative examples and evaluation of characteristics)

[0099] The present disclosure will be described in more detail below with reference to examples and comparative examples. As described below, in Example 1, Example 2, and Comparative Example 1, electrolyte membranes and membrane electrode assemblies / cells using the electrolyte membranes were produced. Also, analysis of each electrolyte membrane and evaluation of characteristics of each membrane electrode assembly / cell were performed.

[0100] (Example 1)

[0101] (Production of electrolyte membranes and membrane electrode assemblies / cells using the electrolyte membranes)

[0102] Reference Figure 4 The production of electrolyte membranes and membrane electrode assemblies / cells using the electrolyte membranes will be described.

[0103] (1) Production of electrolyte green sheets

[0104] (1A) Preparation of electrolyte ceramic slurry (Reference S100)

[0105] First, the preparation of the ceramic slurry used to obtain electrolyte green sheets will be described.

[0106] As starting materials for the electrolyte material, the following materials were prepared.

[0107] Ba(N03)2 (manufactured by Kanto Chemical Co., Inc.) 0.100 mol

[0108] ZrO(N03)2-2H20 (manufactured by Kanto Chemical Co., Inc.) 0.085 mol

[0109] Yb(N03)3-xH20 (2 < x < 6, manufactured by Takasago Pure Chemical Industries, Ltd.) 0.015 mol

[0110] The above starting materials were added to distilled water to obtain a mixture, and the mixture was then stirred.

[0111] Next, citric acid monohydrate (0.1 mol, manufactured by Kanto Chemical Co., Inc.) and ethylenediaminetetraacetic acid (0.2 mol, manufactured by Kanto Chemical Co., Inc., hereinafter, "ethylenediaminetetraacetic acid" is written as EDTA) were added to the mixed solution. Thereafter, the mixed solution was stirred at a temperature of 90°C.

[0112] Then, ammonia water (28% by weight, manufactured by Kanto Chemical Co., Inc.) was added to the mixed solution. Next, the pH of the mixed solution was adjusted to 7 using a pH meter (manufactured by Horiba Ltd.) at a temperature of 90°C.

[0113] After the pH of the mixed solution was adjusted to 7, the temperature of the mixed solution was raised from 95°C to 240°C using a hot stirrer, and the solvent (i.e., water) was evaporated. In this way, water was removed from the mixed solution, and a solid substance was obtained.

[0114] After the obtained solid substance was pulverized in a mortar, debinding was performed at a temperature of about 400°C. In this way, a powder was obtained.

[0115] The obtained powder was pressed into a cylindrical shape using an oil pressure pump (manufactured by Enplas Corporation) and a powder molding mold having a diameter of 30 mm. In this way, a cylindrical shaped molded product was obtained.

[0116] Next, the obtained cylindrical shaped molded product was calcined at 900°C for 10 hours in an atmosphere. In this way, a calcined powder was obtained.

[0117] Then, the calcined powder was pulverized. Next, the pulverized powder was moved to a plastic container together with zirconia balls.

[0118] Then, ethanol (100 g, manufactured by Kanto Chemical Co., Inc.) was added to the plastic container. In this way, a mixed solution was obtained. Next, the mixed solution was pulverized for 4 days using a ball mill.

[0119] After pulverization by the ball mill, the mixed solution was dried using a lamp, and ethanol was removed from the mixed solution. In this way, a powder was obtained.

[0120] The obtained powder was main calcined at 1200°C for 5 hours in an atmosphere. At this stage, a substance equivalent to BaZr 1-d M d O 3-δ’ (M is Yb) was produced. Further, to the main calcined powder, a powder of BaYb2O4 (3 mol% with respect to the main calcined powder) was added, and an electrolyte material of Ba 0.97 Zr 0.80 Yb 0.20 O 3-δ (δ is an oxygen deficiency, 0 < δ < 1.0) was produced.

[0121] Next, an electrolyte ceramic slurry was prepared by mixing the following materials (refer to S100).

[0122] Ba 0.97 Zr 0.80 Yb 0.20 O 3-δ Electrolyte material 50 g

[0123] Polyvinyl butyral (manufactured by Seiko Epson Corporation) 5 g

[0124] Butyl benzyl phthalate (manufactured by Showa Denko K.K.) 1.25 g

[0125] Mixed solvent 40 g

[0126] The mixed solvent was composed of butyl acetate (20 g, manufactured by Showa Denko K.K.) and 1-butanol (20 g, manufactured by Showa Denko K.K.). Thus, an electrolyte ceramic slurry was prepared.

[0127] (1B) Preparation of electrolyte green sheet (refer to S101 and S102)

[0128] Next, a film of the electrolyte ceramic slurry was formed on a support sheet made of a polyethylene terephthalate film having a thickness of about 50 μm by a doctor blade method (refer to S101). The resulting film of the slurry was heated at a temperature of 80°C to evaporate the solvent. Thus, an electrolyte green sheet was prepared (refer to S102). The electrolyte green sheet had a thickness of about 21 μm.

[0129] (2) Preparation of electrode green sheet

[0130] The electrode green sheet was prepared in the same manner as the method of preparing the electrolyte green sheet except for the matters described below.

[0131] (2A) Preparation of electrode ceramic slurry (refer to S200)

[0132] Instead of the starting material of the electrolyte material, the following materials were prepared as the starting material of the electrode, and the electrolyte material was prepared in the same manner as the method of preparing the electrolyte material of Ba 1.00 Zr 0.85 Yb 0.15 O 3-δ (δ is the oxygen deficiency, 0 < δ < 1.0).

[0133] Ba(NO3)2(manufactured by Showa Denko K.K.) 0.097 mol

[0134] ZrO(NO3)2-2H2O (manufactured by Showa Denko K.K.) 0.08 mol

[0135] Yb(NO3)3-xH2O (2 < x < 6, manufactured by High Purity Chemical Laboratory, Inc.) 0.02 mol

[0136] Thus, instead of Ba 1.00 Zr 0.85 Yb 0.15 O 3-δ (δ is the oxygen deficiency, 0 < δ < 1.0), a Ba 0.97 Zr 0.8 Yb 0.2 O 3-δ electrolyte material was obtained.

[0137] The electrode ceramic slurry was prepared by mixing the following materials.

[0138] Ba 0.97 Zr 0.8 Yb 0.2 O 3-δ electrolyte material 20 g

[0139] Polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd.) 5 g

[0140] Butyl benzyl phthalate (manufactured by Showa Chemical Co., Ltd.) 1.25 g

[0141] NiO (manufactured by Sumitomo Metal Mining Co., Ltd.) 30 g

[0142] Mixed solvent 40 g

[0143] The mixed solvent was composed of butyl acetate (20 g, manufactured by Showa Chemical Co., Ltd.) and 1-butanol (20 g, manufactured by Showa Chemical Co., Ltd.).

[0144] (2B) Preparation of the electrode green sheet (refer to S201 and S202)

[0145] Next, a film of the electrode ceramic slurry was formed on a support sheet made of a polyethylene terephthalate film having a thickness of about 50 μm by a doctor blade method (refer to S201). The film of the slurry had a thickness of about 30 μm. The resulting film of the slurry was heated at a temperature of 80°C. Thus, the electrode green sheet was prepared (refer to S102).

[0146] (3) Lamination of the sheets (refer to S300 to S303)

[0147] The electrolyte green sheet was cut to obtain one cut electrolyte green sheet. Next, the polyethylene terephthalate film was peeled off from the electrolyte green sheet. The one cut electrolyte green sheet had a size of 140 mm x 140 mm. The electrode green sheet was cut to obtain one cut electrode green sheet. The one cut electrode green sheet had a size of 140 mm x 140 mm.

[0148] The cut plurality of electrode green sheets were stacked to obtain a laminate. The obtained laminate had a thickness of about 700 μm.

[0149] Then, the laminate was hot-pressed. The hot-pressing was performed under conditions of 85°C and 13 MPa. In this way, an electrode was produced.

[0150] Further, one cut electrolyte green sheet was stacked on one main surface of the electrode to obtain a laminate (see S300). Then, the obtained laminate was hot-pressed.

[0151] The hot-pressing was performed under conditions of 80°C and 13 MPa. In this way, a molded body was obtained.

[0152] The obtained molded body was further pressed at a pressure of 50 MPa (manufactured by San-Oh Industrial Co., Ltd.) to obtain a laminate (see S301). The thickness was hardly changed and was about 700 μm.

[0153] The laminate was cut to a size of 20 mm x 20 mm (see S302).

[0154] Finally, the cut laminate was fired at 1400°C in an atmospheric atmosphere for 2 hours. In this way, a membrane-electrode assembly of Example 1 was produced (see S303, one of the cut laminates is shown in the figure). The membrane-electrode assembly was a combination of an electrolyte membrane and an electrode.

[0155] (4) Formation of a counter electrode (see S304 and S305)

[0156] Further, a counter electrode was provided on the obtained membrane-electrode assembly. The method of providing the counter electrode is described below. As a starting material for the counter electrode, the following materials were prepared.

[0157] NiO (manufactured by Sumitomo Metal Mining Co., Ltd.) 5 g

[0158] Polyethylene glycol 400 (manufactured by Wako Pure Chemical Industries, Ltd.) 1 g

[0159] Ethanol (manufactured by Showa Denko K.K.) 40 g

[0160] The various starting materials were added to a ball mill and mixed. In this way, a mixture was obtained. Then, the obtained mixture was heated to 150°C using a hot stirrer. In this way, a paste of NiO was obtained.

[0161] Next, on one main surface of the membrane-electrode assembly on which the electrolyte membrane was exposed, the paste of NiO was applied by a screen printing method (see S304). The applied paste of NiO had a diameter of 10 mm. In this way, a precursor of a unit was obtained.

[0162] Then, the precursor of the unit was fired at 1400°C under an atmospheric atmosphere for 2 hours. Thus, the unit of Example 1 was produced (see S305).

[0163] (Analysis 1 of the unit: STEM analysis, EDX analysis)

[0164] The electrolyte membrane of the unit of Example 1 was analyzed by STEM. Specifically, the obtained membrane-electrode assembly was cut, and the cross section of the membrane-electrode assembly was analyzed by STEM. Hereinafter, the analysis by STEM is sometimes referred to as "STEM analysis".

[0165] The STEM used for the analysis was JEM-F200 (manufactured by JEOL Ltd.). The STEM analysis was performed at an acceleration voltage of 200 kV.

[0166] Figure 5 is a bright-field STEM image of the electrolyte membrane. Figure 5 The circular marks shown are sites analyzed by EDX. Hereinafter, the analysis by EDX is sometimes referred to as "EDX analysis".

[0167] The ratio (i.e., the weight ratio) of the elements of Zr and Yb was calculated from the characteristic X-ray intensity obtained by EDX analysis, using the Cliff-Lorimer method as a known method. Table 1 shows the ratio of Zr and Yb at all analysis sites.

[0168] (Analysis 2 of the unit: analysis by FE-EPMA)

[0169] The electrolyte membrane of Example 1 was analyzed by FE-EPMA. Hereinafter, the analysis by FE-EPMA is sometimes referred to as "FE-EPMA analysis".

[0170] The FE-EPMA used for the analysis was EPMA-8050G (manufactured by Shimadzu Corporation). The analysis by FE-EPMA was performed at an acceleration voltage of 15 kV and an irradiation current of 100 nA. A range of 40 x 30 μm including the electrolyte membrane was analyzed.

[0171] Figure 6A and Figure 6B is data output from FE-EPMA. Figure 6A The column on the right side of shows the count of Yb on the basis of the weight of each element. Further, the obtained count is an absolute value. Figure 6A The column on the right side of shows the count of Yb on the basis of the weight of each element. Further, the obtained count is an absolute value. Figure 6A The column on the right side of shows the relationship between the density (shading) on and the count.

[0172] The column on the right side of shows the relationship between the density (shading) on and the count. Figure 6AThe graph obtained by converting to relative values (i.e., weight%) is Figure 6B .

[0173] In addition, the average, maximum, and minimum of the weight% of Yb in a 3 x 3 μm square region of the electrolyte membrane were output by EPMA-8050G (HITACHI, LTD.).

[0174] Table 2 is data showing the average, maximum, and minimum of the weight% of Yb in a 3 x 3 μm square region of the electrolyte membrane.

[0175] From the data of Figure 6A , the concentration of each analysis point of Zr and Yb was calculated.

[0176] From the data of Figure 6A , the counts were converted to concentrations (i.e., weight%) using a standard curve method. The number of analysis points was 15000 points.

[0177] The value of Yb / (Zr+Yb) (i.e., the composition ratio of Yb) was calculated based on the weight% of 15000 analysis points. Further, the average of 15000 analysis points was corrected so that Yb / (Zr+Yb) = 0.2 (i.e., the average composition of the electrolyte membrane, sometimes represented as c). This average composition of the electrolyte membrane was calculated from the feed amount of the starting material.

[0178] Then, the value of Yb / (Zr+Yb) of each analysis point, and the proportion of 15000 analysis points that became a predetermined value of Yb / (Zr+Yb) were calculated.

[0179] Figure 7 is a graph showing the value of Yb / (Zr+Yb) of each analysis point, and the proportion of 15000 analysis points that became a predetermined value of Yb / (Zr+Yb).

[0180] Figure 7 "Yb Proportion" shown in Figure 7 "Frequency (%) " is the proportion of the electrolyte membrane that became a predetermined value of Yb / (Zr+Yb).

[0181] (Analysis 3 of the cell: proton conductivity of the electrolyte membrane)

[0182] Using the cell of Example 1, the proton conductivity of the electrolyte membrane was calculated from the resistance of the electrolyte membrane and the thickness of the electrolyte membrane. The resistance of the electrolyte membrane was based on the alternating current impedance method. The calculation method of the proton conductivity in the electrolyte membrane is described below.

[0183] Using ModuLab XM ECS (manufactured by Solartron Analytical), an alternating current was applied to the cell in a frequency range of 1 MHz to 0.01 Hz with an amplitude of 10 mV (conditions: temperature of 600°C under a humidified hydrogen atmosphere). Then, a Cole-Cole chart was output (refer to Figure 8 ). From the circular arc in the frequency range of 100 kHz to 0.01 Hz of the output Cole-Cole chart (refer to Figure 8 ), the focus of the circular arc and the real axis was calculated. The real axis refers to the axis where the value of the Y axis in the chart of Figure 8 is 0. Then, the intersection point on the high frequency side among the calculated intersection points was taken as the IR resistance (refer to Figure 8 ).

[0184] Based on the calculated IR resistance and the thickness of the electrolyte membrane, the proton conductivity in the electrolyte membrane of the cell (unit: 10 -2 S-cm -1 ) was calculated.

[0185] Further, the resistance of the electrolyte membrane was measured at each of the temperatures of 500°C and 700°C.

[0186] Table 3 shows the proton conductivity (unit: 10 -2 S-cm -1 ) of the electrolyte membrane at each temperature.

[0187] (Example 2)

[0188] In Example 2, the electrolyte membrane of Example 2 and the membrane electrode assembly / cell using the electrolyte membrane were produced by the same method as in Example 1 except for the following procedure. Then, the electrolyte membrane was analyzed. Next, the characteristics of the membrane electrode assembly / cell were evaluated. Figure 9 and Table 1 are the results of STEM analysis / EDX analysis. Figure 10A , Figure 10B and Table 2 are the results of FE-EPMA analysis. Table 3 is the result of calculating the proton conductivity of the cell.

[0189] (1) As starting materials for the electrolyte material, the following materials were prepared.

[0190] Ba(N03)2 (manufactured by Kanto Chemical Co., Inc.) 0.098 mol

[0191] ZrO(N03)2-2H20 (manufactured by Kanto Chemical Co., Inc.) 0.081 mol

[0192] Yb(N03)3-xH20 (3 < x < 6, manufactured by Takasago Pure Chemical Industries, Ltd.) 0.019 mol

[0193] (2) In the process of preparing the electrolyte ceramic slurry, the amount of the powder of BaYb2O4 added to the powder that was fired to completion was set to 1 mol%.

[0194] (Comparative Example 1)

[0195] In Comparative Example 1, the electrolyte membrane of Comparative Example 1 and the membrane electrode assembly / cell using the electrolyte membrane were produced by the same method as in Example 1 except for the following process. Then, the electrolyte membrane was analyzed. Next, the characteristics of the membrane electrode assembly / cell were evaluated. Figure 12 Table 1 is the results of STEM analysis / EDX analysis. Figure 13A 、 Figure 13B Table 2 is the results of FE-EPMA analysis. Table 3 is the results of calculating the proton conductivity of the cell.

[0196] (1) As the starting material of the electrolyte material, the following materials were prepared.

[0197] Ba(NO3)2 (manufactured by Kanto Chemical Co., Inc.) 0.097 mol

[0198] ZrO(NO3)2·2H2O (manufactured by Kanto Chemical Co., Inc.) 0.080 mol

[0199] Yb(NO3)3·xH2O (3 < x < 6, manufactured by Takuma Pure Chemicals Co., Ltd.) 0.020 mol

[0200] (2) In the process of preparing the electrolyte ceramic slurry, no powder of BaYb2O4 was added to the powder that was fired to completion.

[0201] (Results of the characteristic evaluation)

[0202] (Analysis 1 of the cell: STEM analysis / EDX analysis)

[0203] Based on Figure 5 、 Figure 9 、 Figure 12 Table 1, the results of STEM analysis and EDX analysis are described. As shown in Figure 5 and Figure 9 , the electrolyte membranes of Example 1 and Example 2 were crystalline. The crystalline electrolyte membranes were composed of a plurality of crystal domains. Each crystal domain was composed of a first sub-crystal domain and a second sub-crystal domain. The first sub-crystal domain was surrounded by the second sub-crystal domain. In other words, the first sub-crystal domain was located near the center of each crystal domain. On the other hand, the second sub-crystal domain was located near the periphery of each crystal domain.

[0204] As shown in Figure 5As shown, analytical regions 1-1, 1-3, and 1-5 are visually observed to be black. These analytical regions are the first subdomains. Analysis of these first subdomains using EDX, as shown in Table 1, reveals that the concentration of Yb is higher than that of Zr. On the other hand, as... Figure 5 As shown, analytical regions 1-2, 1-4, and 1-6 are visually white. These analytical regions are the second subdomains. Analysis of these second subdomains using EDX, as shown in Table 1, reveals that the concentration of Zr is higher than that of Yb.

[0205] like Figure 9 As shown, analytical regions 2-1 and 2-3 are visually observed to be black. These analytical regions are the first subdomains. Analysis of these first subdomains using EDX, as shown in Table 1, reveals that the concentration of Yb is higher than that of Zr. On the other hand, as... Figure 9 As shown, analytical regions 2-2 and 2-4 are visually white. These regions are the second subdomains. Analysis of these second subdomains using EDX, as shown in Table 1, reveals that the Zr concentration is higher than that of Yb. Analytical regions 2-5 and 2-6 are also visually white. Therefore, the domains in analytical regions 2-5 and 2-6 do not possess subdomains.

[0206] like Figure 12 As shown, the crystal domains constituting the electrolyte membrane of Comparative Example 1 do not have sub-domains. Analysis of the electrolyte membrane of Comparative Example 1 by EDX showed that the concentration of Zr was higher than the concentration of Yb in any analytical region.

[0207] Therefore, the electrolyte membrane of Comparative Example 1 is an electrolyte membrane with a uniform concentration of Yb compared to the electrolyte membranes of Example 1 and Example 2.

[0208] In other words, the electrolyte membranes of Examples 1 and 2 have regions where the concentration of Yb is uneven (variable) compared to Comparative Example 1.

[0209] According to Examples 1 and 2, in an electrolyte membrane with uneven Yb concentration, the difference in Yb / (Zr+Yb) measured in each domain is 0.28 or more. Specifically, the difference in Yb / (Zr+Yb) is 0.29 or more.

[0210] Therefore, the electrolyte membranes of Examples 1 and 2 comprise multiple crystal domains. Furthermore, at least one crystal domain contains a first sub-crystal domain and a second sub-crystal domain within it. The concentration of M in the first sub-crystal domain differs from the concentration of M in the second sub-crystal domain. The concentration of M in the first sub-crystal domain is higher than the concentration of M in the second sub-crystal domain. The first sub-crystal domain is surrounded by the second sub-crystal domain. The first sub-crystal domain is composed of the chemical formula BaZr. 1-a Yb a O 3-δ This indicates that the second subdomain is composed of the chemical formula BaZr. 1-bYb b O 3-δ represents. In the formulae, 0 < a < 1, 0 < b < 1, 0 < δ < 1, and a - b ≥ 0.28.

[0211] (Analysis 2 of the unit: analysis by FE-EPMA)

[0212] Based on Figure 7 , Figure 11 and Figure 14 , the results of the FE-EPMA analysis will be described.

[0213] According to Yb / (Zr + Yb) = 0.2 (i.e., the Yb ratio in the average composition, in other words, the composition formula BaZr 0.8 Yb 0.2 O 3-δ (δ is the oxygen deficiency, 0 < δ < 1) of Yb), the Yb ratio that deviates the most from the value is Example 1: Yb / (Zr + Yb) = 0.49, Example 2: Yb / (Zr + Yb) = 0.32, and Comparative Example 1: Yb / (Zr + Yb) = 0.30.

[0214] As shown in Comparative Example 1, an electrolyte membrane in which the concentration of Yb is more uniform than in Examples 1 and 2 was produced, and the Yb ratio obtained by FE-EPMA analysis was in the range of the value of the average composition (i.e., 0.2) + 0.1.

[0215] On the other hand, in Examples 1 and 2, the Yb ratio obtained by FE-EPMA analysis was not in the range of the value of the average composition + 0.1. In other words, in Examples 1 and 2, at least a part of the Yb ratio obtained by FE-EPMA analysis had a value larger than the value of the average composition + 0.1. From this, it was found that the distribution of the Yb concentration of the electrolyte membranes of Examples 1 and 2 was more non-uniform than in Comparative Example 1 (i.e., the Yb concentration was non-uniform in the electrolyte membrane, and the Yb concentration was different between the 1st sub-crystalline domain and the 2nd sub-crystalline domain).

[0216] From this, the electrolyte membranes of Examples 1 and 2 contained a barium zirconate compound doped with ytterbium. Also, there were regions represented by the composition formula BaZr 1-x Yb x O 3-δ (0 < c < 1, c + 0.1 < x, 0 < δ < 1) on the electrolyte membrane.

[0217] Next, the results of the FE-EPMA analysis will be described based on Table 2.

[0218] The data were output by FE-EPMA analysis. Then, the maximum value, the minimum value, the average value, and the value of "maximum value - average value" of the weight % of Yb in a 3 μm x 3 μm region on the electrolyte membrane were calculated. In Example 1 and Example 2, the value of "maximum value - average value" was 5 or more. Specifically, the value of "maximum value - average value" was 6.2 in Example 1 and 5.6 in Example 2. On the other hand, in Comparative Example 1, the value of "maximum value - average value" was 2.0. From this, it was found that the electrolyte membranes of Example 1 and Example 2 had a larger difference in Yb concentration than the electrolyte membrane of Comparative Example 1. In other words, the electrolyte membranes of Example 1 and Example 2 contained a barium zirconate compound doped with ytterbium. As a result of the electrolyte membrane of Comparative Example 1, it can be said that the concentration of M in the 1st subcrystal domain was substantially the same as the concentration of M in the 2nd subcrystal domain. Then, a 3 x 3 μm range of the electrolyte membrane was analyzed by an electron beam microanalyzer, and data were output. The value of "maximum value of weight % of Yb - average value of weight % of Yb" per unit area of the output data was 5% or more.

[0219] (Analysis 3 of the cell: proton conductivity of the cell)

[0220] Based on Table 3, the proton conductivity of the electrolyte membrane will be described.

[0221] The cells of Example 1 and Example 2 had a high proton conductivity at each temperature (i.e., 500°C, 600°C, and 700°C) compared to the cell of Comparative Example 1. From this, it was found that the electrolyte membrane having a Yb concentration unevenness and the cell made of the electrolyte membrane had an improved proton conductivity.

[0222] Table 1

[0223]

[0224] Table 2

[0225]

[0226] Table 3

[0227] 500℃ 600℃ 700℃ Example 1 0.24 0.26 0.26 Example 2 0.19 0.24 0.24 Comparative Example 1 0.18 0.21 0.22

[0228] Industrial applicability

[0229] The electrolyte membrane of the present disclosure can be applied to an electrochemical cell and a fuel cell.

[0230] Explanation of reference signs

[0231] 10 membrane electrode assembly

[0232] 11 electrolyte membrane

[0233] 100 crystal domain

[0234] 100a first crystal domain

[0235] 100b second crystal domain

[0236] 101 first sub-crystal domain

[0237] 102 second sub-crystal domain

[0238] gb grain boundary

[0239] 12 electrode

[0240] 13 counter electrode

[0241] 20 electrochemical cell

[0242] 1000 fuel cell system

[0243] 1014 cell body

[0244] 1021 oxidant gas supplier

[0245] 1022 raw material supplier

[0246] 1023 raw material gas path

[0247] 1024 oxidant gas path

Claims

1. An electrolyte membrane comprising a plurality of crystal domains, wherein at least one of the crystal domains comprises a first sub-crystal domain and a second sub-crystal domain in its interior, The first sub-crystal domain is represented by the chemical formula BaZr 1-a Yb a O 3-δ and The 2nd sub-crystal domain is represented by the chemical formula BaZr 1-b Yb b O 3-δ indicates, wherein 0 < a < 1, 0 < b < 1, 0 < δ < 1, and (a - b) ≥ 0.28 are satisfied.

2. The electrolyte membrane according to claim 1, the first sub-crystal domain is surrounded by the second sub-crystal domain.

3. The electrolyte membrane according to claim 1, the mathematical formula (a - b) ≥ 0.30 is satisfied.

4. The electrolyte membrane according to claim 3, the mathematical formula (a - b) ≥ 0.35 is satisfied.

5. The electrolyte membrane according to any one of claims 1 to 4, wherein a value of "maximum value of weight % of Yb - average value of weight % of Yb" per unit area of data outputted by analyzing a range of 3 x 3 μm with an electron beam microanalyzer is 5% or more.

6. The electrolyte membrane according to claim 5, a value of "maximum value of weight % of Yb - average value of weight % of Yb" per unit area of data outputted by analyzing a range of 3 x 3 μm with an electron beam microanalyzer is 6% or more.

7. The electrolyte film according to any one of claims 1 to 4, a 3 x 3 μm square region represented by the compositional formula BaZr 1-x Yb x O 3-δ is present, wherein, 0 < c < 1, c + 0.1 < x, 0 < δ < 1, the value of c represents a ratio of Yb to the sum of Zr and Yb, and the ratio is calculated from a feeding amount of starting materials.

8. The electrolyte membrane according to claim 7, There is a 3 x 3 pm square region represented by the composition formula BaZr 1-x Yb x O 3-δ indicates, wherein, 0 < c < 1, c + 0.2 < x, 0 < δ < 1.

9. A membrane electrode assembly comprising the electrolyte membrane according to any one of claims 1 to 8, and an electrode provided to the electrolyte membrane.

10. An electrochemical cell comprising an electrode, the electrolyte membrane according to any one of claims 1 to 8, and a counter electrode, wherein the electrolyte membrane is provided between the electrode and the counter electrode.

11. A method for producing the electrolyte membrane according to any one of claims 1 to 8, comprising mixing a material containing BaZr 1-d M d O 3-δ’ with a material containing BaM2O4. wherein M is a trivalent element, 0 < d < 1, and 0 < δ' < 1 are satisfied.

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