Patent Application
20180138533
The present disclosure relates to a membrane electrode assembly and a solid oxide fuel cell for use in an electrochemical device.
Solid oxide fuel cells are known as one of electrochemical devices including electrolyte materials formed of solid oxides. In general, oxide ionic conductors, typically stabilized zirconia, are widely used as electrolyte materials for solid oxide fuel cells. Oxide ionic conductors have lower ionic conductivity at lower temperature. Because of this property, for example, solid oxide fuel cells that include stabilized zirconia as an electrolyte material need to operate at temperatures of 700° C. or higher.
However, when electrochemical devices that include an electrolyte material formed of a solid oxide, such as solid oxide fuel cells, operate at high temperatures, an expensive special heat-resistant metal is needed for a metal material used in the structural component. The use of such a metal increases the costs of the entire system and tends to result in cracks when starting and stopping the system because of differences in thermal expansion between the structural components, which causes problems associated with low reliability of the entire system. Therefore, a common practical approach for using electrochemical devices is to lower their operating temperature.
A solid electrolyte stacked body that permits operation at low temperatures and includes a solid electrolyte having proton conductivity has been proposed (e.g., Patent Literature 1, Japanese Patent No. 5936898). More specifically, Patent Literature 1 discloses a solid electrolyte layer stacked body that includes a solid electrolyte layer formed of yttrium-doped barium zirconate (BZY) and a cathode electrode layer formed of a lanthanum strontium cobalt compound (LSC).
One non-limiting and exemplary embodiment provides a membrane electrode assembly and a solid oxide fuel cell that achieve improved power-generation efficiency.
In one general aspect, the techniques disclosed here feature a membrane electrode assembly that includes an electrode consisting of at least one compound selected from the group consisting of lanthanum strontium cobalt complex oxide, lanthanum strontium cobalt iron complex oxide, and lanthanum strontium iron complex oxide, or consisting of a composite of the at least one compound and an electrolyte material, and a first solid electrolyte membrane represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). The electrode is in contact with the first solid electrolyte membrane.
The membrane electrode assembly the present disclosure has the above-described structure and thus has an effect of improving power-generation efficiency.
Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.
The inventors of the present disclosure have diligently studied the related solid electrolyte layer stacked body (membrane electrode assembly) disclosed in Patent Literature 1. As a result, the following finding has been obtained. That is, the inventors have devised a membrane electrode assembly that provides higher power-generation efficiency than the membrane electrode assembly disclosed in Patent Literature 1 when used in an electrochemical device.
Specifically, the inventors have found that there is a problem in which high power-generation efficiency is not obtained when a membrane electrode assembly in an electrochemical device, as disclosed in Patent Literature 1, includes a combination of an electrode formed of a lanthanum strontium cobalt compound (hereinafter referred to as LSC) and a solid electrolyte membrane represented by BaZr1−xYxO3−δ. Therefore, the inventors have diligently studied combinations of an electrode and a solid electrolyte membrane that provide high power-generation efficiency and, as a result, the present disclosure has been made.
First, the inventors have studied the power-generation efficiency for membrane electrode assemblies obtained by replacing the electrode in the structure of the membrane electrode assembly of Patent Literature 1 with an electrode consisting of any one of lanthanum strontium cobalt iron complex oxide (hereinafter referred to as LSCF), which has often been reported as a cathode material, and lanthanum strontium iron complex oxide (hereinafter referred to as LSF).
Specifically, the inventors have studied the power-generation efficiency for membrane electrode assemblies obtained by replacing the solid electrolyte membrane (BaZr1−xYxO3−δ) in the membrane electrode assembly of Patent Literature 1 with a solid electrolyte membrane having a different composition and replacing the electrode with an electrode consisting of at least one compound selected from the group consisting of LSC, LSCF, and LSF.
As a result of these studies, it has been found that, when a membrane electrode assembly includes a combination of an electrode containing at least one compound selected from the group consisting of LSC, LSCF, and LSF, and a solid electrolyte represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1), the membrane electrode assembly provides higher power-generation efficiency than the membrane electrode assembly of Patent Literature 1. It has also been found that the above-described membrane electrode assembly provides higher power-generation efficiency than membrane electrode assemblies obtained by replacing the electrode in the structure of the membrane electrode assembly of Patent Literature 1 with an electrode consisting of at least one compound selected from the group consisting of LSC, LSCF, and LSF.
This is probably because the contact resistance, which is a resistance between the electrode and the solid electrolyte membrane, is lower in a membrane electrode assembly including a combination of an electrode consisting of at least one compound selected from the group consisting of LSC, LSCF, and LSF and a solid electrolyte represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1) than in the membrane electrode assembly disclosed in Patent Literature 1 and other membrane electrode assemblies. This may result in a low ohmic resistance (IR resistance) of the entire membrane electrode assembly.
The above-mentioned finding, which was first revealed by the inventors, has novel technical features that enable new challenges to be identified and significant operational advantages to be realized. Specifically, the present disclosure provides the aspects described below.
A membrane electrode assembly according to a first aspect of the present disclosure includes an electrode consisting of at least one compound selected from the group consisting of lanthanum strontium cobalt complex oxide, lanthanum strontium cobalt iron complex oxide, and lanthanum strontium iron complex oxide or consisting of a composite of the at least one compound and an electrolyte material, and a first solid electrolyte membrane represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). The electrode is in contact with the first solid electrolyte membrane.
In the membrane electrode assembly according to the first aspect of the present disclosure having the above-mentioned structure, the electrode consisting of the at least one compound or consisting of a composite of the at least one compound and an electrolyte material is in contact with the first solid electrolyte membrane represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). This structure can reduce the contact resistance between the electrode and the first solid electrolyte membrane. As a result, this structure can reduce the resistance of the entire membrane electrode assembly. Therefore, the membrane electrode assembly according to the first aspect of the present disclosure has an effect of improving power-generation efficiency.
In a membrane electrode assembly according to a second aspect of the present disclosure, the membrane electrode assembly according to the first aspect further includes a second solid electrolyte membrane represented by BaZr1−x1M1x1O3−δ where M1 represents at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Sc, Mn, Fe, Co, Ni, Al, and Ga, and x1 satisfies 0<x1<1. The first solid electrolyte membrane may have a first surface in contact with the electrode and a second surface, which is a surface opposite to the first surface, in contact with the second solid electrolyte membrane. The electrode, the first solid electrolyte membrane, and the second solid electrolyte membrane may be stacked in this order.
According to the above-described structure, the solid electrolyte membrane in contact with the electrode is the first solid electrolyte membrane. This structure can reduce the contact resistance between the electrode and the first solid electrolyte membrane. Furthermore, when a solid electrolyte membrane includes a first solid electrolyte membrane and a second solid electrolyte membrane having higher conductivity than the first solid electrolyte membrane, the solid electrolyte membrane has higher conductivity than a solid electrolyte membrane composed only of the first solid electrolyte membrane, provided that these solid electrolyte membranes have the same thickness. Therefore, the membrane electrode assembly according to the second aspect of the present disclosure can improve power-generation efficiency.
In addition, when the solid electrolyte membrane is composed only of the first solid electrolyte membrane and, for example, a member that produces large contact resistance in the interface between the member and the first solid electrolyte membrane represented by BaZr1−xLuxO3−δ (0<x<1) needs to be disposed on the second surface of the first solid electrolyte membrane opposite to the first surface in contact with the electrode, the efficiency of the electrochemical device may deteriorate. However, the membrane electrode assembly according to the second aspect of the present disclosure includes the second solid electrolyte membrane disposed on the second surface of the first solid electrolyte membrane. Therefore, when a member that produces large contact resistance in the interface between the member and BaZr1−xLuxO3−δ (0<x<1) needs to be disposed on the second surface of the first solid electrolyte membrane, the member can be prevented from being disposed directly on the first solid electrolyte membrane, which can suppress decreases in the efficiency of the electrochemical device.
In a membrane electrode assembly according to a third aspect of the present disclosure, the electrode in the membrane electrode assembly according to the first aspect is a cathode electrode, and the membrane electrode assembly according to the first aspect further includes an anode electrode containing Ni and a compound represented by any one composition formula selected from the group consisting of BaZr1−x2M2x2O3−δ, BaCe1−x3M3x3O3−δ, and BaZr1−x4−y4Cex4M4y4O3−δ, where M2, M3, and M4 each represent at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Sc, Mn, Fe, Co, Ni, Al, Ga, In, and Lu, and x2, x3, x4, and y4 satisfy 0<x2<1, 0<x3<1, 0<x4<1, and 0<y4<1, respectively. The first solid electrolyte membrane has a first surface in contact with the cathode electrode and a second surface, which is a surface opposite to the first surface, in contact with the anode electrode. The cathode electrode, the first solid electrolyte membrane, and the anode electrode are stacked in this order.
According to this structure, the electrode consisting of the at least one compound or consisting of the at least one compound and an electrolyte material, namely, the cathode electrode, is in contact with the first solid electrolyte membrane represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). This structure can reduce the contact resistance between the cathode electrode and the first solid electrolyte membrane and, as a result, can reduce the resistance of the entire membrane electrode assembly including the cathode electrode, the first solid electrolyte membrane, and the anode electrode. Therefore, the membrane electrode assembly according to the third aspect of the present disclosure can improve power-generation efficiency.
In a membrane electrode assembly according to a fourth aspect of the present disclosure, the electrode in the membrane electrode assembly according to the second aspect may be a cathode electrode, and the membrane electrode assembly according to the second aspect may further include an anode electrode containing Ni and a compound represented by any one composition formula selected from BaZr1−x2M2x2O3−δ, BaCe1−x3M3x3O3−δ, and BaZr1−x4−y4Cex4M4y4O3−δ where M2, M3, and M4 each represent at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Sc, Mn, Fe, Co, Ni, Al, Ga, In, and Lu, and x2, x3, x4, and y4 satisfy 0<x2<1, 0<x3<1, 0<x4<1, and 0<y4<1, respectively. The second solid electrolyte membrane may have a first surface in contact with the first solid electrolyte membrane and a second surface, which is a surface opposite to the first surface, in contact with the anode electrode. The cathode electrode, the first solid electrolyte membrane, the second solid electrolyte membrane, and the anode electrode may be stacked in this order.
According to this structure, the cathode electrode consisting of the at least one compound or consisting of the at least one compound and an electrolyte material is in contact with the first solid electrolyte membrane represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). This structure can reduce the contact resistance between the cathode electrode and the first solid electrolyte membrane. Furthermore, when a solid electrolyte membrane includes a first solid electrolyte membrane and a second solid electrolyte membrane having higher conductivity than the first solid electrolyte membrane, the solid electrolyte membrane has higher conductivity than a solid electrolyte membrane composed only of the first solid electrolyte membrane, provided that these solid electrolyte membranes have the same thickness.
Therefore, the membrane electrode assembly according to the fourth aspect of the present disclosure achieves low resistance of the entire membrane electrode assembly including the cathode electrode, the first solid electrolyte membrane, the second solid electrolyte membrane, and the anode electrode, and can improve power-generation efficiency.
A solid oxide fuel cell according to a fifth aspect of the present disclosure includes an electrode consisting of at least one compound selected from the group consisting of lanthanum strontium cobalt complex oxide, lanthanum strontium cobalt iron complex oxide, and lanthanum strontium iron complex oxide, or consisting of a composite of the at least one compound and an electrolyte material, and a first solid electrolyte membrane represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). The electrode is in contact with the first solid electrolyte membrane.
This structure can reduce the resistance of the entire membrane electrode assembly. Therefore, the solid oxide fuel cell according to the fifth aspect of the present disclosure has high power-generation efficiency.
Embodiments of the present disclosure will be described below with reference to the drawings. Hereinafter, the same or corresponding structural components are provided with the same reference symbols throughout the figures, and the description thereof may be omitted.
A membrane electrode assembly 10 according to a first embodiment of the present disclosure will be described with reference to
The electrode 11 is formed by using an oxide ion-electron mixed conductor consisting of at least one compound selected from the group consisting of lanthanum strontium cobalt complex oxide (LSC), lanthanum strontium cobalt iron complex oxide (LSCF), and lanthanum strontium iron complex oxide (LSF). That is, the electrode 11 may be formed only of the above-mentioned compound (oxide ion-electron mixed conductor) or may be formed of a combination of the above-mentioned compounds (oxide ion-electron mixed conductors). Furthermore, the electrode 11 may be formed of, for example, a composite of the above-mentioned compound (oxide ion-electron mixed conductor) and an electrolyte material (e.g., BaZrLuO3). When the electrode 11 is used, for example, as a cathode electrode for a solid oxide fuel cell, the electrochemical reduction reaction of oxygen in a gas phase occurs. Because of this, the electrode 11 may be a porous body to ensure paths through which oxygen diffuses and to promote the reaction.
The first solid electrolyte membrane 12 has a composition represented by BaZr1−xLuxO3−δ (0<x<1), which has proton conductivity. When the molar ratio of Zr to Lu is, for example, 8:2, BaZrLuO3 has a proton conductivity of about 8.0×10−3 S/cm at 600° C. When the first solid electrolyte membrane 12 is used as a solid electrolyte membrane of the membrane electrode assembly 10 in an electrochemical device, it is possible to minimize the thickness of the first solid electrolyte membrane 12 in order to reduce the ohmic resistance (IR resistance) of the first solid electrolyte membrane 12.
When an electrochemical device that includes the membrane electrode assembly 10 is, for example, a solid oxide fuel cell, power is produced by supplying air to the first surface of the first solid electrolyte membrane 12 having the electrode 11 and supplying a hydrogen-containing gas to the second surface having no electrode 11. Therefore, when the electrochemical device is a solid oxide fuel cell, the first solid electrolyte membrane 12 needs to be gas-tight.
Since the membrane electrode assembly 10 according to the first embodiment has a structure in which the electrode 11 is stacked on the first surface of the first solid electrolyte membrane 12, the contact resistance, which is a resistance between the electrode 11 and the first solid electrolyte membrane 12, is low. This structure can improve the power-generation efficiency of electrochemical devices, such as solid oxide fuel cells.
A membrane electrode assembly 20 according to a second embodiment of the present disclosure will be described with reference to
The electrode 11 in the membrane electrode assembly 20 according to the second embodiment, as in the first embodiment, is formed by using an oxide ion-electron mixed conductor that is at least one compound selected from the group consisting of lanthanum strontium cobalt complex oxide (LSC), lanthanum strontium cobalt iron complex oxide (LSCF), and lanthanum strontium iron complex oxide (LSF). The electrode 11 may be formed only of the above-mentioned compound (oxide ion-electron mixed conductor) or may be formed of a combination of the above-mentioned compounds (oxide ion-electron mixed conductors). Furthermore, the electrode 11 may be formed of, for example, a composite of a compound (oxide ion-electron mixed conductor) and an electrolyte material (e.g., BaZrLuO3). When the electrode 11 is used, for example, as a cathode electrode for a solid oxide fuel cell, the electrochemical reduction reaction of oxygen in a gas phase occurs, as in the first embodiment. Because of this, the electrode 11 may be a porous body to ensure paths through which oxygen diffuses and to promote the reaction.
Like the first solid electrolyte membrane 12 according to the first embodiment, the first solid electrolyte membrane 12 has a composition represented by BaZr1−xLuxO3−δ (0<x<1) having proton conductivity. The second solid electrolyte membrane 13 is a proton conductor represented by a composition formula of BaZr1−x1M1x1O3−δ where M1 represents at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Sc, Mn, Fe, Co, Ni, Al, Ga, and In, and x1 satisfies 0<x1<1. In the membrane electrode assembly 20 according to the second embodiment of the present disclosure, both the first solid electrolyte membrane 12 and the second solid electrolyte membrane 13 may be formed to have a reduced thickness in order to reduce the IR resistance.
When the electrochemical device that includes the membrane electrode assembly 20 is, for example, a solid oxide fuel cell, power is produced in a stacked body including the electrode 11, the first solid electrolyte membrane 12, and the second solid electrolyte membrane 13 by supplying air to the electrode 11 side of the stacked body and a hydrogen-containing gas to the second solid electrolyte membrane 13 side of the stacked body. Since the electrode 11 is desirably a porous body, at least one of the first solid electrolyte membrane 12 and the second solid electrolyte membrane 13 needs to be gas-tight.
In the second embodiment, the solid electrolyte membrane has a stacked structure including the first solid electrolyte membrane 12 and the second solid electrolyte membrane 13. The second solid electrolyte membrane 13 may be a proton conductor having higher proton conductivity than BaZrLuO3, which is a proton conductor of the first solid electrolyte membrane 12. As the solid electrolyte membrane including a combination of the first solid electrolyte membrane 12 and the second solid electrolyte membrane 13 having higher proton conductivity than the first solid electrolyte membrane 12 is compared with a solid electrolyte membrane composed of the first solid electrolyte membrane 12, the former solid electrolyte membrane has higher proton conductivity than the latter solid electrolyte membrane, provided that these solid electrolyte membranes have the same thickness. To achieve good proton conductivity, it is possible to minimize the thickness of the first solid electrolyte membrane 12 having low proton conductivity. Even if the first solid electrolyte membrane 12 is too thin to maintain gas-tight properties, the second solid electrolyte membrane 13 can compensate for the gas-tight properties.
Therefore, the solid electrolyte membrane including a combination of the first solid electrolyte membrane 12 and the second solid electrolyte membrane 13 achieves low IR resistance and has an advantage of improving the power-generation efficiency of the electrochemical device compared with a solid electrolyte membrane composed of the first solid electrolyte membrane 12 having gas-tight properties.
In addition, when a member that produces large contact resistance in the interface between the member and the first solid electrolyte membrane 12 needs to be disposed on the second surface of the first solid electrolyte membrane 12 opposite to the first surface in contact with the electrode 11, the efficiency of the electrochemical device may deteriorate. However, the membrane electrode assembly 20 according to the second embodiment includes the second solid electrolyte membrane 13 disposed on the second surface of the first solid electrolyte membrane 12. With this structure, the member that produces large contact resistance in the interface between the member and BaZrLuO3 can be prevented from being disposed directly on the first solid electrolyte membrane 12. This can suppress decreases in the efficiency of the electrochemical device.
As described above, the membrane electrode assembly 20 according to the second embodiment has a structure in which the electrode 11, the first solid electrolyte membrane 12, and the second solid electrolyte membrane 13 are stacked in this order. As in the first embodiment, this structure can reduce the contact resistance between the electrode 11 and the first solid electrolyte membrane 12 and can improve the power-generation efficiency of electrochemical devices, such as fuel cells.
A membrane electrode assembly 30 according to a third embodiment of the present disclosure will be described with reference to
As illustrated in
As illustrated in
That is, in the membrane electrode assembly 40 according to the modification of the third embodiment, the membrane electrode assembly 20 according to the second embodiment further includes the anode electrode 14. Otherwise, it can also be said that the membrane electrode assembly 30 according to the third embodiment further includes the second solid electrolyte membrane 13.
In the membrane electrode assembly 40, the electrode 11 (cathode electrode), the first solid electrolyte membrane 12, and the second solid electrolyte membrane 13 have structures similar to those of the electrode 11, the first solid electrolyte membrane 12, and the second solid electrolyte membrane 13 in the membrane electrode assembly 20 according to the second embodiment, and thus description of these members is omitted.
The anode electrode 14 may contain, for example, Ni and a compound having proton conductivity and represented by any one composition formula selected from BaZr1−x2M2x2O3−δ, BaCe1−x3M3x3O3−δ, and BaZr1−x4−y4Cex4M4y4O3−δ where M2, M3, and M4 each represent at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Sc, Mn, Fe, Co, Ni, Al, Ga, In, and Lu, and x2, x3, x4, and y4 satisfy 0<x2<1, 0<x3<1, 0<x4<1, and 0<y4<1, respectively.
When the anode electrode 14 is used as, for example, an anode electrode in a solid oxide fuel cell, the oxidation reaction of hydrogen in a gas phase into protons occurs in the anode electrode 14. Because of this, the anode electrode 14 may be formed of a composite of Ni having electron conductivity and a hydrogen-oxidizing activity and the compound having proton conductivity in order to promote the oxidation reaction of hydrogen into protons. The anode electrode 14 may be a porous body to ensure paths through which hydrogen gas diffuses.
As described above, the membrane electrode assembly 30 according to the third embodiment has a structure in which the electrode 11, the first solid electrolyte membrane 12, and the anode electrode 14 are stacked in this order. As in the first embodiment, this structure can reduce the contact resistance between the electrode 11 and the first solid electrolyte membrane 12 and can improve the power-generation efficiency of electrochemical devices, such as fuel cells. Similarly, the membrane electrode assembly 40 according to the third embodiment has a structure in which the electrode 11, the first solid electrolyte membrane 12, the second solid electrolyte membrane 13, and the anode electrode 14 are stacked in this order. As in the first and second embodiments, this structure can reduce the contact resistance between the electrode 11 and the first solid electrolyte membrane 12 and can improve the power-generation efficiency of electrochemical devices, such as fuel cells.
Next, the following description will provide, as Examples, the evaluation method for concluding that the power-generation efficiency is high when the membrane electrode assemblies 10, 20, 30, and 40 according to the first, second, and third embodiments and the modification of the third embodiment include a combination of the electrode formed by using at least one compound (oxide ion-electron mixed conductor) selected from the group consisting of LSC, LSCF, and LSF, and the first solid electrolyte membrane 12 represented by a composition formula of BaZr1−xLuxO3−δ (0<x<1). The present disclosure is not limited by Examples described below.
First, an evaluation membrane electrode assembly 100 illustrated in FIG. 5 was prepared in order to carry out this evaluation method.
Oxide ion-electron mixed conductors having typical compositions of La0.6Sr0.4CoO3−δ for LSC, La0.6Sr0.4Co0.2Fe0.8O3−δ for LSCF, and La0.6Sr0.4FeO3−δ for LSF were used to form the electrodes 11. In addition to these conductors, LaNi0.6Fe0.4O3−δ (hereinafter referred to as LNF) and La2NiO4+δ, which are promising materials for cathode electrodes in solid oxide fuel cells, were also added to evaluation targets in these Examples.
BaZrLuO3 having a typical composition of BaZr0.8Lu0.2O2.90 was used to form the first solid electrolyte membrane 12. The cases where the first solid electrolyte membrane 12 was formed of BaZrYO3, which was another example of the solid electrolyte having proton conductivity, were also added to evaluation targets. BaZrYO3 having a typical composition of BaZr0.8Y0.2O2.90 was used.
As described below, three evaluation membrane electrode assemblies in Examples 1 to 3 were prepared as evaluation targets.
Evaluation membrane electrode assembly 100 including electrodes 11 made of La0.6Sr0.4CoO3−δ and first solid electrolyte membrane 12 made of BaZr0.8Lu0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La0.6Sr0.4Co0.2Fe0.8O3−δ and first solid electrolyte membrane 12 made of BaZr0.8Lu0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La0.6Sr0.4FeO3−δ and first solid electrolyte membrane 12 made of BaZr0.8Lu0.2O2.90
Evaluation membrane electrode assemblies in Comparative Examples 1 to 7 were prepared as targets to be compared with those in Examples 1 to 3 and evaluated.
Evaluation membrane electrode assembly 100 including electrodes 11 made of LaNi0.6Fe0.4O3−δ and first solid electrolyte membrane 12 made of BaZr0.8Lu0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La2NiO4+δ and first solid electrolyte membrane 12 made of BaZr0.8Lu0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La0.6Sr0.4CoO3−δ and first solid electrolyte membrane 12 made of BaZr0.8Y0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La0.6Sr0.4Co0.2Fe0.8O3−δ and first solid electrolyte membrane 12 made of BaZr0.8Y0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La0.6Sr0.4FeO3−δ and first solid electrolyte membrane 12 made of BaZr0.8Y0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of LaNi0.6Fe0.4O3−δ and first solid electrolyte membrane 12 made of BaZr0.8Y0.2O2.90
Evaluation membrane electrode assembly 100 including electrodes 11 made of La2NiO4+δ and first solid electrolyte membrane 12 made of BaZr0.8Y0.2O2.90
Hereinafter, a method for producing evaluation membrane electrode assemblies 100 in Examples 1 to 3 and Comparative Examples 1 to 7 will be described.
BaZr0.8Lu0.2O2.90 to form the first solid electrolyte membrane 12 was prepared by a citric acid complex method using a powder of Ba(NO3)2 (available from Kanto Chemical Co., Inc.), a powder of ZrO(NO3)2.2H2O (available from Kanto Chemical Co., Inc.), and a powder of Lu(NO3)3.5H2O (available from Kojundo Chemical Laboratory Co., Ltd.) as starting materials. In the preparation of BaZr0.8Y0.2O2.90, Y(NO3)3.6H2O (available from Kojundo Chemical Laboratory Co., Ltd.) was used as a starting material instead of Lu(NO3)3.5H2O. A predetermined amount of each powder was dissolved in distilled water, and 1.0 equivalent of citric acid monohydrate (available from Kanto Chemical Co., Inc.) and 0.7 equivalents of ethylenediaminetetraacetic acid (EDTA) (available from Kanto Chemical Co., Inc.) based on the metal cations were added. The pH was then adjusted to 7 by using ammonia water (28%) (available from Kanto Chemical Co., Inc.). After pH adjustment, the solvent was removed at 90° C. by using a hotplate stirrer. The obtained solid was ground with a mortar, followed by degreasing at about 600° C.
After degreasing, the resulting powder was press-molded in a cylindrical shape and calcined at 1200° C. for 10 hours. After calcination, the roughly ground powder was placed in a plastic container together with zirconia balls, and ethanol was added, followed by grinding with a ball mill for 3 days or longer.
After grinding with the ball mill, the solvent was removed by lamp drying, and the obtained powder was vacuum-dried at 200° C. In the preparation of BaZr0.8Lu0.2O2.90 and BaZr0.8Y0.2O2.90 after vacuum drying, the powder was formed into pellets by cold isostatic pressing at a press pressure of 200 MPa and fired at 1750° C. for 24 hours to obtain a sintered product. The obtained sintered product was then machined into a disk shape, and the surface of the disk-shaped product was polished with a wrapping film sheet coated with 3-μm abrasive grains to obtain a first solid electrolyte membrane 12.
La0.6Sr0.4CoO3−δ to form the electrodes 11 in Example 1 and Comparative Example 3 was prepared by a citric acid complex method using a powder of La(NO3)3.6H2O (available from Kanto Chemical Co., Inc.), a power of Sr(NO3)2 (available from Kanto Chemical Co., Inc.), and a power of Co(NO3)2.6H2O (available from Kanto Chemical Co., Inc.) as starting materials. A predetermined amount of each powder was dissolved in distilled water, and 1.0 equivalent of citric acid monohydrate (available from Kanto Chemical Co., Inc.) and 0.7 equivalents of ethylenediaminetetraacetic acid (EDTA) (available from Kanto Chemical Co., Inc.) based on the metal cations were added. The pH was then adjusted to 7 by using ammonia water (28%) (available from Kanto Chemical Co., Inc.). After pH adjustment, the solvent was removed at 90° C. by using a hotplate stirrer. The obtained solid was ground with a mortar, followed by degreasing at about 600° C.
After degreasing, the obtained powder was calcined at 850° C. for 5 hours. After calcination, the roughly ground powder was placed in a plastic container together with zirconia balls, and polyethylene glycol 400 (available from Wako Pure Chemical Industries) and isopropyl alcohol were added, followed by grinding with a ball mill for 24 hours or longer.
After grinding with the ball mill, isopropyl alcohol was removed by heating to 120° C. with a hotplate stirrer to obtain a slurry of La0.6Sr0.4CoO3−δ.
La0.6Sr0.4Co0.2Fe0.8O3−δ to form the electrodes 11 in Example 2 and Comparative Example 4 was prepared by a citric acid complex method using a powder of La(NO3)3.6H2O (available from Kanto Chemical Co., Inc.), a power of Sr(NO3)2 (available from Kanto Chemical Co., Inc.), a power of Co(NO3)2.6H2O (available from Kanto Chemical Co., Inc.), and a powder of Fe(NO3)3.9H2O (available from Kanto Chemical Co., Inc.) as starting materials. A predetermined amount of each powder was dissolved in distilled water, and 1.0 equivalent of citric acid monohydrate (available from Kanto Chemical Co., Inc.) and 0.7 equivalents of ethylenediaminetetraacetic acid (EDTA) (available from Kanto Chemical Co., Inc.) based on the metal cations were added. The pH was then adjusted to 7 by using ammonia water (28%) (available from Kanto Chemical Co., Inc.). After pH adjustment, the solvent was removed at 90° C. by using a hotplate stirrer. The obtained solid was ground with a mortar, followed by degreasing at about 600° C.
After degreasing, the obtained powder was calcined at 850° C. for 5 hours. After calcination, the roughly ground powder was placed in a plastic container together with zirconia balls, and polyethylene glycol 400 (available from Wako Pure Chemical Industries) and isopropyl alcohol were added, followed by grinding with a ball mill for 24 hours or longer. After grinding with the ball mill, isopropyl alcohol was removed by heating to 120° C. with a hotplate stirrer to obtain a slurry of La0.6Sr0.4Co0.2Fe0.8O3−δ.
La0.6Sr0.4FeO3−δ to form the electrodes 11 in Example 3 and Comparative Example 5 was prepared by a citric acid complex method using a powder of La(NO3)3.6H2O (available from Kanto Chemical Co., Inc.), a power of Sr(NO3)2 (available from Kanto Chemical Co., Inc.), and a power of Fe(NO3)3.9H2O (available from Kanto Chemical Co., Inc.) as starting materials. A predetermined amount of each powder was dissolved in distilled water, and 1.0 equivalent of citric acid monohydrate (available from Kanto Chemical Co., Inc.) and 0.7 equivalents of ethylenediaminetetraacetic acid (EDTA) (available from Kanto Chemical Co., Inc.) based on the metal cations were added. The pH was then adjusted to 7 by using ammonia water (28%) (available from Kanto Chemical Co., Inc.). After pH adjustment, the solvent was removed at 90° C. by using a hotplate stirrer. The obtained solid was ground with a mortar, followed by degreasing at about 600° C.
After degreasing, the obtained powder was calcined at 850° C. for 5 hours. After calcination, the roughly ground powder was placed in a plastic container together with zirconia balls, and polyethylene glycol 400 (available from Wako Pure Chemical Industries) and isopropyl alcohol were added, followed by grinding with a ball mill for 24 hours or longer. After grinding with the ball mill, isopropyl alcohol was removed by heating to 120° C. with a hotplate stirrer to obtain a slurry of La0.6Sr0.4FeO3−δ.
LaNi0.6Fe0.4O3−δ to form the electrodes 11 in Comparative Example 1 and Comparative Example 6 was prepared by a citric acid complex method using a powder of La(NO3)3.6H2O (available from Kanto Chemical Co., Inc.), a powder of Ni(NO3)2.6H2O (available from Kanto Chemical Co., Inc.), and a powder of Fe(NO3)3.9H2O (available from Kanto Chemical Co., Inc.) as starting materials. A predetermined amount of each powder was dissolved in distilled water, and 1.0 equivalent of citric acid monohydrate (available from Kanto Chemical Co., Inc.) and 0.7 equivalents of ethylenediaminetetraacetic acid (EDTA) (available from Kanto Chemical Co., Inc.) based on the metal cations were added. The pH was then adjusted to 7 by using ammonia water (28%) (available from Kanto Chemical Co., Inc.). After pH adjustment, the solvent was removed at 90° C. by using a hotplate stirrer. The obtained solid was ground with a mortar, followed by degreasing at about 600° C.
After degreasing, the obtained powder was calcined at 850° C. for 5 hours. After calcination, the roughly ground powder was placed in a plastic container together with zirconia balls, and polyethylene glycol 400 (available from Wako Pure Chemical Industries) and isopropyl alcohol were added, followed by grinding with a ball mill for 24 hours or longer. After grinding with the ball mill, isopropyl alcohol was removed by heating to 120° C. with a hotplate stirrer to obtain a slurry of LaNi0.6Fe0.4O3−δ.
La2NiO4+δ to form the electrodes 11 in Comparative Example 2 and Comparative Example 7 was prepared by a citric acid complex method using a powder of La(NO3)3.6H2O (available from Kanto Chemical Co., Inc.) and a power of Ni(NO3)2.6H2O (available from Kanto Chemical Co., Inc.) as starting materials. A predetermined amount of each powder was dissolved in distilled water, and 1.3 equivalents of citric acid monohydrate (available from Kanto Chemical Co., Inc.) and ethylenediaminetetraacetic acid (EDTA) (available from Kanto Chemical Co., Inc.) based on the metal cations were added. The pH was then adjusted to 7 by using ammonia water (28%) (available from Kanto Chemical Co., Inc.). After pH adjustment, the solvent was removed at 90° C. by using a hotplate stirrer. The obtained solid was ground with a mortar, followed by degreasing at about 600° C.
After degreasing, the obtained powder was calcined at 900° C. for 5 hours. After calcination, the roughly ground powder was placed in a plastic container together with zirconia balls, and polyethylene glycol 400 (available from Wako Pure Chemical Industries) and isopropyl alcohol were added, followed by grinding with a ball mill for 24 hours or longer. After grinding with the ball mill, isopropyl alcohol was removed by heating to 120° C. with a hotplate stirrer to obtain a slurry of La2NiO4+δ.
As described above, the first solid electrolyte membranes 12 and the electrodes 11 for use in Examples 1 to 3 and Comparative Examples 1 to 7 were produced. The slurry for the electrodes 11 was then applied to both sides of the first solid electrolyte membrane 12 by screen printing. The coating area for the electrode 11 was 0.785 cm2. The electrodes 11 were attached to the first solid electrolyte membrane 12 by firing at 950° C. for 2 hours to produce an evaluation membrane electrode assembly 100.
In actual measurement of the contact resistance in the first solid electrolyte membrane 12, the evaluation membrane electrode assembly 100 illustrated in
Next, a method for measuring the contact resistance between the electrode 11 and the first solid electrolyte membrane 12 in the evaluation membrane electrode assembly 100 produced by the above-mentioned production method will be described with reference to
Specifically, the contact resistance was measured for Examples 1 to 3 and Comparative Examples 1 to 7 as described below. First, evaluation membrane electrode assemblies 100 each including the electrodes 11 made of Ag were prepared. These evaluation membrane electrode assemblies 100 each including the electrodes 11 made of Ag and further including the first solid electrolyte membrane 12 having a different thickness were prepared and measured for the contact resistance by an alternating-current impedance method. Next, evaluation membrane electrode assemblies 100 having the same thickness were prepared for Examples 1 to 3 and Comparative Examples 1 to 7. The evaluation membrane electrode assemblies 100 according to Examples 1 to 3 and Comparative Examples 1 to 7 were measured for the contact resistance by an alternating-current impedance method. The thickness of the first solid electrolyte membrane 12 targeted for measurement was in the range from about 250 μm to about 1000 μm.
The alternating-current impedance was measured at 600° C. in a 20° C. humidified air atmosphere. Alternating current was applied by using model 1287, available from Solartron Metrology, at an amplitude of 10 mV and frequencies from 100 kHz to 0.01 Hz.
Before obtaining the contact resistance between each electrode 11 and each first solid electrolyte membrane 12 for Examples 1 to 3 and Comparative Examples 1 to 7, various evaluation membrane electrode assemblies 100 each including the electrodes 11 made of Ag and the first solid electrolyte membrane 12, the thickness of each first solid electrolyte membrane 12 being different for each respective evaluation membrane electrode assembly 100, were first prepared and measured for the contact resistance by an alternating-current impedance method. Next, evaluation membrane electrode assemblies 100 according to Examples 1 to 3 and Comparative Examples 1 to 7 were measured for the contact resistance by an alternating-current impedance method.
The electrolyte resistance included in the IR resistance increases in proportion to the thickness of the first solid electrolyte membrane 12. The correlation between the IR resistance and the thickness of the first solid electrolyte membrane 12 was determined for the evaluation membrane electrode assemblies 100 each including the electrodes 11 made of Ag by measuring the IR resistance as a function of the thickness of the first solid electrolyte membranes 12. As a result, as shown in
Subsequently, the evaluation membrane electrode assemblies 100 according to Examples 1 to 3 and Comparative Examples 1 to 7 were evaluated for the IR resistance C at the thickness d of the first solid electrolyte membrane 12 (α(d, C) in
The results obtained by the method for measuring the contact resistance are shown in Table of
A low contact resistance results in a low IR resistance in the membrane electrode assembly. Therefore, when the membrane electrode assembly including a combination of the electrode 11 described in Examples 1 to 3 and the first solid electrolyte membrane 12 is used, for example, in a solid oxide fuel cell, the power-generation efficiency is high.
As a result, the membrane electrode assembly 10 according to the first embodiment, the membrane electrode assembly 20 according to the second embodiment, the membrane electrode assembly 30 according to the third embodiment, and the membrane electrode assembly 40 according to the modification of the third embodiment are low in contact resistance, which is a resistance between the electrode 11 and the first solid electrolyte membrane 12. A low contact resistance can lead to improved power-generation efficiency of electrochemical devices, such as solid oxide fuel cells.
The detailed reason for differences in contact resistance is not clear. However, the differences in contact resistance imply that the diffusion behavior of cations in the interface between the electrode 11 and the first solid electrolyte membrane 12, or a change in IR resistance due to the diffusion behavior differs greatly depending on the type of cations in the electrode 11 and the first solid electrolyte membrane 12.
In Examples 1 to 3 described above, the cases where the electrodes 11 were formed of any one compound selected from LSC, LSCF, and LSF were evaluated. The contact resistance is low even when the electrodes 11 are formed of at least one compound selected from the group consisting of LSC, LSCF, and LSF.
In Examples, the electrode 11 and the first solid electrolyte membrane 12 were synthesized by using the citric acid complex method, but the synthesis method is not limited to this method. For example, the oxides may be synthesized by a solid phase sintering method, a coprecipitation method, a nitrate method, a spray granulation method, or other methods.
The first solid electrolyte membrane 12 is not necessarily strictly made only of a composition of BaZr0.8Lu0.2O2.90. The first solid electrolyte membrane 12 may further contain a small amount of BaZr1−x1M1x1O3−δ where M1 represents at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Sc, Mn, Fe, Co, Ni, Al, Ga, and In.
In the method for producing the evaluation membrane electrode assembly 100 in Examples, the evaluation membrane electrode assembly 100 is produced as follows: obtaining the first solid electrolyte membrane 12 from the sintered product of BaZrLuO3; and then applying the slurry for the electrodes 11 to the first solid electrolyte membrane 12 by screen printing, followed by baking. However, the production method is not limited to this method. For example, the evaluation membrane electrode assembly 100 may be produced by, for example, a method involving stacking, as powders or slurries, BaZrLuO3 and the second solid electrolyte membrane 13 or a composite of Ni and BaZrLuO3, followed by co-sintering. The electrodes 11 are not necessarily formed by screen printing and may be formed by a tape casting method, a dip coating method, a spin coating method, or other methods.
These methods are not limited to wet methods, and a deposition method, such as a CVD method or a sputtering method, may be employed. Thermal spraying may be used for production.
The membrane electrode assembly 10 of the present disclosure can be used in applications of electrochemical devices, such as fuel cells, gas sensors, hydrogen pumps, and water electrolysis devices.
It will be apparent to those skilled in the art from the above description that the present disclosure includes many modifications and other embodiments. The above description should be considered illustrative only and is provided for the purpose of teaching those skilled in the art the best modes for carrying out the present disclosure. The details of the structure and/or function of the present disclosure can be substantially modified without departing from the spirit of the present disclosure.
The membrane electrode assembly according to the present disclosure can be used in applications pertaining to electrochemical devices, such as fuel cells, gas sensors, hydrogen pumps, and water electrolysis devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-224088 | Nov 2016 | JP | national |
