CATHODE MATERIAL INCLUDING BISMUTH-DOPED MANGANITE-BASED PEROVSKITE AND SOLID OXIDE FUEL CELL INCLUDING SAME

Abstract

The present disclosure relates to a cathode material including bismuth-doped manganite-based perovskite and having excellent electrochemical properties and long-term stability, and a solid oxide fuel cell including the same. A cathode material according to an embodiment includes bismuth-doped manganite-based perovskite which is represented by Formula 1 below and in which praseodymium strontium manganite is deponed with bismuth:

##STR00001## wherein in the Formula 1, x is in a range of 0<X<0.5, and ? is in a range of 0<?<2.

Claims

1. A cathode material comprising bismuth-doped manganite-based perovskite which is represented by Formula 1 below and in which praseodymium strontium manganite is deponed with bismuth: ##STR00006## wherein in the Formula 1, x is in a range of 0<X<0.5, and ? is in a range of 0<?<2.

2. The cathode material of claim 1, wherein in the Formula 1, x is in a range of 0.2<X<0.4.

3. The cathode material of claim 1, wherein the cathode material is used to for a bidirectional solid oxide fuel cell.

4. A method for manufacturing a cathode material comprising the steps of: preparing a precursor mixture by mixing a praseodymium precursor, a bismuth precursor, a strontium precursor, a manganese precursor, and glycine with distilled water; preparing a dried precursor by drying the precursor mixture, heating the dried precursor, and then combusting the dried precursor to prepare a combustion product; and calcining the combustion product to manufacture a cathode material including a bismuth-doped manganite-based perovskite represented by Formula 1 below: ##STR00007## wherein in the Formula 1, x is in a range of 0<X<0.5, and ? is in a range of 0<?<2.

5. The method of claim 4, wherein in the Formula 1, x is in a range of 0.2<X<0.4.

6. A bidirectional solid oxide fuel cell comprising: a cathode manufactured with the cathode material of claim 1; an electrolyte layer located on the cathode; and an anode located on the electrolyte layer.

7. The bidirectional solid oxide fuel cell of claim 6, wherein when 350 mA/Cm.sup.2 is applied to the cathode at 700? C., a degradation rate of 6.3?10.sup.?7 V/h for 480 hours is exhibited.

8. The bidirectional solid oxide fuel cell of claim 6, wherein a power density of 0.58 to 2.24 W/Cm.sup.2 at 600 to 750? C. is exhibited.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a process diagram illustrating a method for manufacturing a cathode according to an embodiment.

[0023] FIG. 2 is a diagram illustrating the results of X-ray diffraction pattern analysis for powder samples (PSM, PBSM1, PBSM3, and PBSM5) manufactured by a method according to Example.

[0024] FIG. 3 is a diagram illustrating the results of evaluating the electrical properties of a half-cell in which a cathode manufactured with powder samples (PSM, PBSM1, and PBSM3) according to Example was applied to YSZ electrolyte.

[0025] FIG. 4 is a diagram illustrating the results of analyzing the microstructure of a half cell in which a cathode manufactured with a powder sample (PBSM3) according to Example was applied to YSZ electrolyte.

[0026] FIG. 5 is a diagram illustrating the results of evaluating the performance a unit cell including a cathode manufactured with a powder sample (PBSM3) according to Example in fuel cell and electrolytic cell modes at each temperature.

[0027] FIG. 6 is a diagram illustrating the results of evaluating the long-term stability of a unit cell including a cathode manufactured with a powder sample (PBSM3) according to Example.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to accompanying drawings. However, it should be understood that the present disclosure can be implemented in various forms, and that it is not intended to limit the present disclosure to the exemplary embodiments. Also, in the drawings, descriptions of parts unrelated to the detailed description are omitted to clearly describe the present disclosure. Throughout the specification, like numbers refer to like elements.

[0029] Throughout this specification, when a part is mentioned as being connected (accessed, contacted, coupled) to another part, this means that the part may not only be directly connected to the other part but may also be indirectly connected to the other part through another member interposed therebetween. In addition, when a part is mentioned as including a specific component, this does not preclude the possibility of the presence of other component(s) in the part which means that the part may further include the other component(s), unless otherwise stated.

[0030] The terms used herein are only used to describe specific embodiments but are not intended to limit the present disclosure. Singular forms are intended to include plural forms unless the context clearly indicates otherwise. In the specification, it should be understood that the terms such as include or have may be construed to denote a certain feature, number, step, operation, constituent element, component or a combination thereof, but may not be construed to exclude the existence of or a possibility of addition of one or more other features, numbers, steps, operations, constituent elements, components or combinations thereof.

[0031] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0032] The cathode material including bismuth-doped manganite-based perovskite according to an embodiment has a structure which is represented by the following Formula (1) and in which praseodymium strontium manganite (PrSrMnO) is deponed with bismuth (Bi).

##STR00004##

[0033] Accordingly, the above cathode material has a structure with improved electrochemical properties and long-term stability by the bismuth doping.

[0034] In order to exhibit the above characteristics, in Formula 1, x may be in the range of 0<x<0.5, and ? may be in the range of 0<?<2.

[0035] In Formula 1, if x is 0, it is difficult to expect improvement in physical properties because bismuth is not doped, and if x exceeds 0.5, the amount of bismuth doping is large so that there is risk that physical properties may degrade due to the formation of secondary phases such as Pr.sub.1.1Bi.sub.0.9Mn.sub.4O.sub.10. That is, the bismuth-doped manganite-based perovskite preferably has a bismuth doping amount of more than 0 and less than 0.5 mol.

[0036] In particular, in Formula 1, x may be 0.2<X<0.4.

[0037] The bismuth (Bi)-doped manganite-based perovskite as described above can be used as a cathode material, and in particular, it can be used as a cathode material for a bidirectional solid oxide fuel cell.

[0038] The doping of bismuth (Bi) may be performed by a process of artificially implanting a dopant, such as diffusion or ion implantation, but is not limited thereto.

[0039] Meanwhile, FIG. 1 is a process diagram illustrating a method for manufacturing a cathode material according to an embodiment.

[0040] Referring to FIG. 1, a method for manufacturing a cathode material including bismuth-doped manganite-based perovskite represented by the following Formula 1 through a glycine nitrate process according to an embodiment includes the steps of preparing a precursor mixture (S100); preparing a combustion product (S200); and manufacturing a cathode material (S300).

##STR00005##

[0041] The method for manufacturing a cathode material will be described in detail. First, in the step of preparing the precursor mixture (S100), the precursor mixture may be prepared by mixing a praseodymium precursor, a bismuth precursor, a strontium precursor, a manganese precursor, and glycine with distilled water.

[0042] As the praseodymium precursor, the bismuth precursor, the strontium precursor, and the manganese precursor, various types of conventional precursors used for producing perovskite compounds may be used.

[0043] Specifically, as a representative example of the praseodymium precursor, there is praseodymium nitrate (Pr(NO.sub.3).sub.36H.sub.2O), as a representative example of the bismuth precursor is bismuth nitrate (Bi(NO.sub.3).sub.35H.sub.2O), as a representative example of the strontium precursor, there is strontium nitrate (Sr(NO.sub.3).sub.2), and as a representative example of the manganese precursor, there is nitric acid. Manganese (Mn(NO.sub.3).sub.24H.sub.2O).

[0044] In this step, the precursor mixture may be prepared by mixing the praseodymium precursor, bismuth precursor, strontium precursor, and manganese precursor in distilled water according to the stoichiometric ratio, then adding glycine to the mixture and mixing the mixture uniformly. The precursor mixture may be mixed by heating to a temperature of 50 to 90? C. so that the precursors and glycine may be uniformly mixed. Thereafter, moisture may be removed from the precursor mixture and the dried precursor may be combusted in the step to be described later to prepare a combustion product.

[0045] Next, in the step of preparing a combustion product (S200), moisture may be removed from the precursor mixture as described above, and then the precursor mixture may be combusted at a temperature of 200 to 500? C. In this step, a combustion product including manganite-based perovskite may be formed through a glycine nitrate process that induces an exothermic reaction between glycine and nitrate.

[0046] Next, in the step of manufacturing a cathode material (S300), the combustion product may be obtained and the obtained combustion product may be calcined to prepare a composite powder in which manganite-based perovskite is doped with bismuth. In this step, a calcination process may be performed at a temperature of 800 to 1,200? C. for 0.5 to 24 hours to prepare the composite powder including bismuth-doped manganite-based perovskite.

[0047] Thereafter, the bismuth-doped manganite-based perovskite as described above may be pulverized and prepared in powder form. Specifically, a commonly used method such as ball milling may be used for the pulverization, and the composite powder may be mixed with ethanol and then prepared into nanometer-sized particles through a ball milling process.

[0048] Meanwhile, a solid oxide fuel cell according to an embodiment may have a structure including a cathode manufactured with the above cathode material, an electrolyte layer located on the cathode, and an anode located on the electrolyte layer.

[0049] The solid oxide fuel cell having the above structure includes a cathode manufactured using the bismuth-doped manganite-based perovskite and exhibits improved electrochemical properties and long-term stability.

[0050] Specifically, in the solid oxide fuel cell, when 250 mA/Cm.sup.2 is applied to the cathode at 700? C., it can exhibit a degradation rate of 6.3?10.sup.?7 V/h for 480 hours, showing excellent long-term stability.

[0051] In addition, the solid oxide fuel cell can exhibit a power density of 0.58 to 2.24 W/Cm.sup.2 at 600 to 750? C. in a fuel cell mode, and a current density of 0.6 to 2.7 A/Cm.sup.2 in an electrolytic cell mode, showing excellent electrical characteristics.

[0052] In particular, the solid oxide fuel cell may be a bidirectional solid oxide fuel cell, and the bidirectional solid oxide fuel cell may be doped with less than 0.5 mol of bismuth to form a cathode that exhibits high performance in a fuel cell mode and an electrolytic cell mode.

[0053] The cathode material according to the above-described embodiment exhibits high electrochemical properties and excellent long-term stability by doping bismuth (Bi) into a perovskite structure based on praseodymium strontium manganite, and thus, the cathode material can be used to manufacture a cathode for a solid oxide fuel cell.

[0054] Hereinafter, the present disclosure will be described in more detail through Examples.

[0055] The presented Examples are only specific examples of the present disclosure and are not intended to limit the technical scope of the present disclosure.

Example

[0056] Nano-powder including praseodymium strontium manganite-based compound (Pr.sub.0.8-xBi.sub.xSr.sub.0.2MnO.sub.3-?) having the composition shown in Table 1 was synthesized using a high-temperature continuous reaction method using a combustion material including glycine. Nano-powder was synthesized through the glycine nitrate process, which is a type of combustion synthesis process.

TABLE-US-00001 TABLE 1 PSM Pr.sub.0.8Sr.sub.0.2MnO.sub.3-? PBSM1 Pr.sub.0.7Bi.sub.0.1Sr.sub.0.2MnO.sub.3-? PBSM3 Pr.sub.0.5Bi.sub.0.3Sr.sub.0.2MnO.sub.3-? PBSM5 Pr.sub.0.3Bi.sub.0.5Sr.sub.0.2MnO.sub.3-?

[0057] Specifically, the bismuth-doped praseodymium strontium manganite-based compound (Pr.sub.0.8-xBi.sub.xSr.sub.0.2MnO.sub.3-?) and praseodymium strontium manganite-based compound (Pr.sub.0.8Sr.sub.0.2MnO.sub.3-?) were each prepared as follows. First, the precursor materials including praseodymium nitrate (Pr(NO.sub.3).sub.36H.sub.2O, Sigma aldrich, 99.9%), bismuth nitrate (Bi(NO.sub.3).sub.35H.sub.2O, Alfa aesar, 98%), strontium nitrate (Sr(NO.sub.3).sub.2, Alfa aesar, 99.0%), manganese nitrate (Mn(NO.sub.3).sub.24H.sub.2O, Sigma aldrich, 97.0%) were prepared respectively, and the prepared precursor materials were mixed in distilled water according to the stoichiometric ratio and then stirred to prepare a mixture. Glycine was added to the prepared mixture and stirred at 80? C. to prepare a homogeneous mixed solution. Afterwards, the mixed solution was dried at 120? C. to evaporate all moisture, and then heated to 300? C. to induce a combustion reaction. After the combustion reaction, the remaining ash was pulverized using a mortar and pestle to prepare powder. The prepared powder was calcined at 1000? C. for 2 hours. Zirconia balls and ethanol were added to the obtained calcined material, and a ball-milling process was performed for 24 hours. After mixing and grinding, each of black final powder samples (PSM, PBSM1, PBSM3, and PBSM5) was obtained.

<Experimental Example> (1) Crystal Structure Analysis

[0058] Powder XRD measurements were performed using an X-ray diffraction analyzer (RIGAKU, SmartLab) in the 20 range from 20 to 80? with Cu K? radiation (2=1.5418 ?). The crystal structure of the powder was refined using HighScore software.

[0059] FIG. 2 shows the results of X-ray diffraction pattern analysis for powder samples (PSM, PBSM1, PBSM3, and PBSM5) prepared by the method according to Example.

[0060] As shown in FIG. 2, in the case of PBSM1, PBSM3, and PBSM5 in which PSM was doped with Bi, it was confirmed that an orthorhombic perovskite phase was formed. In addition, it was observed that the main peak around 32 to 33? shifted to a lower angle as the doping amount of bismuth increased. This result is due to the fact that the radius (1.13 ?) of the bismuth (Bi3.sup.+) ion is larger than the radius (1.17 ?) of the praseodymium (Pr.sup.3+) ion.

[0061] In addition, it was confirmed that in the case of PBSM5 with a bismuth doping amount of 0.5 mol or more, a secondary phase, Pr.sub.1.1Bi.sub.0.9Mn.sub.4O.sub.10, was formed.

(2) Manufacturing of Half-Cell and Unit Cell

[0062] To manufacture a half-cell, yttria-stabilized Zirconia (YSZ, TOSHO) powder was placed in a mold, a pressure of 50 MPa was applied to the mold using uniaxial pressing, and then the mold was sintered at 1400? C. for 10 hours to form a YSZ pellet.

[0063] Tape casting and screen printing techniques were used to sequentially stack an anode support layer, an anode functional layer, and an electrolyte layer that constitute the unit cell.

(3) Evaluation of Electrochemical Properties

[0064] Electrochemical properties of half-cells and unit cells were evaluated using a potentiostat (Bio-Logic, VMP-300). In this case, in the case of half cells, electrochemical property evaluation was performed in the air, and in the case of unit cells, hydrogen (3% wet) and air were injected into the anode and cathode, respectively.

[0065] In addition, the ionic conductivity of the prepared EYZB pellet was measured in a temperature range of 550 to 750? C. using a potentiostat. In addition, the long-term durability evaluation of the material was conducted at a temperature of 600? C.

[0066] In addition, XRD measurements of the pellets for long-term durability evaluation were performed using an X-ray diffraction analyzer (RIGAKU, SmartLab) in the 20 range from 20 to 80? with Cu K? radiation (?=1.5418 ?). The crystal structure of the corresponding pellet was refined using HighScore software.

[0067] FIG. 3 shows the results of evaluating the electrical properties of a half-cell in which a cathode manufactured with powder samples (PSM, PBSM1, and PBSM3) according to Example was applied to YSZ electrolyte.

[0068] Referring to FIG. 3, in the case of a half cell in which PSM, PBSM1, and PBSM3 cathodes were applied to the YSZ electrolyte, it was confirmed that the electrode resistance decreased as the doping amount of bismuth increased, thereby improving the electrical characteristics.

(4) Microstructure Analysis

[0069] Microstructural analysis of the unit cell was performed using a scanning electron microscope (SEM, Hitachi SU8230).

[0070] FIG. 4 shows the results of analyzing the microstructure of a half cell in which a cathode manufactured with a powder sample (PBSM3) according to Example was applied to YSZ electrolyte.

[0071] Referring to FIG. 4, it was confirmed that the cell was entirely constituted with a cathode, an electrolyte, and an anode, the electrolyte had a dense structure with a thickness of approximately 5 ?m, and it was confirmed that the cathode and the electrolyte were each bonded without peeling.

(5) Evaluation of Electrochemical Properties of Unit Cell

[0072] FIG. 5 shows the results of evaluating the performance of a unit cell including a cathode manufactured with a powder sample (PBSM3) according to Example in fuel cell and electrolytic cell modes at each temperature.

[0073] Referring to FIG. 5, it was confirmed that the powder density was 2.24, 1.90, 1.26, and 0.58 W/Cm.sup.2 in a fuel cell mode, respectively, and 2.7, 1.9, 0.9, and 0.6 W/Cm.sup.2 in an electrolytic cell mode, respectively, at 750? C., 700? C., 650? C., and 600? C.

[0074] FIG. 6 shows the results of evaluating the long-term stability of a unit cell including a cathode manufactured with a powder sample (PBSM3) according to Example.

[0075] As shown in FIG. 6, it was confirmed that when 250 mA/Cm.sup.2 was applied at 700? C., a degradation rate of 6.3?10.sup.?7 V/h was observed for 480 hours.

[0076] Through the above results, it was determined that the cathode material could be used as an oxygen electrode material for a reversible solid oxide battery with excellent performance and stability without a buffer layer on a popularly used YSZ electrolyte.

[0077] In addition, through crystallographic analysis, it was confirmed that impurities were formed when more than 0.5 mol of bismuth was doped into the manganite-based perovskite structure, and the perovskite with an orthorhombic structure was free of impurities when bismuth was doped to less than 0.5 mol.

[0078] In addition, as a result of evaluating the electrochemical properties of the half-cell to which the developed cathode was applied, it was confirmed that PBSM3 had the lowest electrode resistance. As a result of measuring the performance of the electrode in the fuel cell and electrolytic cell modes, it was confirmed to have high performance of 1.90 W/Cm.sup.2 and 1.91 A/Cm.sup.2, respectively, at 700? C. In addition, as a result of conducting a long-term stability evaluation at 700? C. in the fuel cell mode, it was confirmed that the degradation rate was 6.3?10.sup.?7 V/h over 480 hours.

[0079] Therefore, it was confirmed that the electrode had high performance and long-term stability when operating in the fuel cell and electrolytic cell modes on the most popularly used YSZ electrolyte without lamination of a buffer layer. In particular, it was confirmed that PBSM3 was a very promising material for reversible Solid oxide Cells.

[0080] The cathode material according to an embodiment exhibits high electrochemical properties and excellent long-term stability by doping bismuth (Bi) into a perovskite structure based on praseodymium strontium manganite. Accordingly, the cathode material may be used for manufacturing the cathode of a solid oxide fuel cell.

[0081] It should be understood that the effects of the present disclosure are not limited to the effects described above, but include all effects that can be deduced from the detailed description of the present disclosure or the constitution of the disclosure described in the claims.

[0082] Although the technical idea of the present disclosure described above has been described in detail in preferred embodiments, it should be noted that the above-described embodiments are for illustrative purposes only and are not intended for limitation. In addition, those skilled in the art of the present disclosure will understand that various embodiments are possible within the scope of the technical idea of the present disclosure. Therefore, the true technical protection scope of the present disclosure should be determined by the technical spirit of the attached claims.