SOLID OXIDE FUEL CELL COMPRISING ANODE ALKALINE-BASED PROMOTER LOADED

Abstract

A solid oxide fuel cell according to this invention can provide a solid oxide fuel cell with improved performance, by loading an alkali-based promoter in an anode.

Claims

1. A solid oxide fuel cell comprising: a cathode, an anode, and an electrolyte between the cathode and anode, wherein at least a part of the pores of the anode comprises a promoter, and the promoter is an alkali metal compound.

2. The solid oxide fuel cell according to claim 1, wherein the alkali metal compound is alkali metal oxide, alkali metal hydroxide, or a combination thereof.

3. The solid oxide fuel cell according to claim 1, wherein the alkali metal is lithium (Li), sodium (Na), potassium (K), or cesium (Cs).

4. The solid oxide fuel cell according to claim 1, wherein the promoter is M.sub.2O, MOH, or a combination thereof, and the M is lithium (Li), sodium (Na), potassium (K), or cesium (Cs).

5. The solid oxide fuel cell according to claim 1, wherein the anode is a metal-ceramic composites

6. The solid oxide fuel cell according to claim 1, wherein the anode of the solid oxide fuel cell has lower electrode resistance, compared to an anode of a solid oxide fuel cell that does not comprise the promoter.

7. A method for manufacturing the solid oxide fuel cell according to claim 1, comprising steps of: introducing an alkali metal precursor in at least a part of the pores of the anode (step 1); and producing the promoter from the alkali metal precursor (step 2).

8. The method according to claim 7, wherein the alkali metal precursor is alkali metal carbonate or alkali metal nitrate.

9. The method according to claim 8, wherein the alkali metal precursor is M.sub.2CO.sub.3, or MNO.sub.3, and the M is lithium (Li), sodium (Na), potassium (K), or cesium (Cs).

10. The method according to claim 7, wherein the step 1 comprises coating a solution comprising the alkali metal precursor on the surface of the anode, or immersing the anode in a solution comprising the alkali metal precursor.

11. The method according to claim 7, wherein the step 1 comprises introducing a solution comprising the alkali metal precursor in a gas line for introducing fuel in the anode.

12. The method according to claim 7, wherein the step 1 comprises bonding a current collector comprising the alkali metal precursor on the surface of the anode.

13. The method according to claim 8, wherein the step 2 comprises introducing fuel or moisture in a gas line for introducing fuel in the anode.

Description

DESCRIPTION OF DRAWINGS

[0028] FIG. 1 shows the XPS results according to Example 1.

[0029] FIG. 2 shows the shape and cross-section of the half cell used in Example 2.

[0030] FIG. 3 shows the performance evaluation in the half cell according to Example 2.

[0031] FIG. 4 schematically shows a method for loading a promoter in the half cell in Example 3.

[0032] FIG. 5 shows the performance evaluation in the half cell according to Example 3.

[0033] FIG. 6 shows the performance evaluation in the full cell according to Example 4.

[0034] FIG. 7 shows the performance evaluation in the full cell according to Example 5.

MODE FOR INVENTION

[0035] Hereinafter, examples and experimental examples of the invention will be explained in detail. These examples and experimental examples are presented to explain the invention more specifically, and the scope of the invention is not limited thereby.

EXAMPLE 1

Confirmation of Loading of Promoter

[0036] In order to confirm whether or not the promoter according to this disclosure is loaded in an anode, the following experiments were conducted.

[0037] Mixed powder of CsNO.sub.3, NiO, GDC (10% Gd doped CeO.sub.2) (1:5.4:3.6 weight ratio) was heat treated at 450° C. for 10 hours under 3% humidified 10% hydrogen atmosphere (3% H.sub.2O+10% H.sub.2+87% Ar), and then, XPS (Cs3d) was measured and the result was shown in FIG. 1.

[0038] As shown in FIG. 1, the existence of Cs can be confirmed, and it can be confirmed therefrom that a Cs precursor is loaded in an anode as a promoter.

EXAMPLE 2

Performance Evaluation in Half Cell

[0039] Step 1) Manufacture of Half Cell

[0040] After molding GDC (10% Gd doped CeO.sub.2) powder, it was sintered at 1450° C. for 5 hours. Further then, the surface was planarized using a sandpaper, thus manufacturing a GDC specimen.

[0041] Mixed powder of NiO and GDC at a weight ratio of 6:4, Ink vehicle (Fuelcellmaterials company), and ethanol were mixed at a weight ratio of 1:1:0.5 to make paste, and it was applied on both sides of the sintered GDC specimen by screen printing, and then, it was sintered at 1400° C. for 10 hours. Finally, it was reduced and heat treated at 650° C. under 4% hydrogen atmosphere (4% H.sub.2+96% Ar) to finally manufacture a porous Ni-GDC electrode (thickness about 8 um). The fine structure of the manufactured half cell was as shown in FIG. 2.

[0042] Step 2) Performance Evaluation in Half Cell

[0043] In the above manufactured half cell, at room temperature (23° C.), 10 uL of an aqueous solution in which CsNO.sub.3 is dissolved (0.023 M) was directly introduced with a pipette in the porous Ni-GDC electrode, and then, the half cell was loaded in measurement system, and change in electrode resistance according to temperature was observed. Wherein, as applied gas atmosphere, 3% humidified 10% hydrogen (3% H.sub.2O+10% H.sub.2+87% Ar) was used, and the measurement result was shown in FIG. 3. For comparison, a half cell to which the promoter was not applied was measured together, and the half cell to which the promoter was not applied was designated as ‘Ni-GDC’, and the half cell to which the promoter was applied was designated as ‘p-Ni-GDC’

[0044] As shown in FIG. 3, in the case of an electrode to which the promoter was applied (p-Ni-GDC), compared to common half cell control (Ni-GDC), resistance was significantly decreased, and stable resistance value was exhibited at 450° C. for 10 hours. Such a method can be applied in case the operation of a solid oxide fuel cell is stopped and the temperature is decreased to room temperature.

EXAMPLE 3

Performance Evaluation in Half Cell

[0045] The half cell of step 1 of Example 2 was loaded on measurement system, and then, during the operation, 2 mL of an aqueous solution of CsNO.sub.3 (0.1 M) was directly introduced in the half cell through a gas line using a syringe pump, thus evaluating the performance.

[0046] First, as shown in FIG. 4, at the beginning, 3% humidified 10% hydrogen (3% H.sub.2O+10% H.sub.2+87% Ar) was introduced, and then, 2 mL of distilled water was introduced in a gas line heated above 120° C. as control.

[0047] As shown in FIG. 5, resistance change by water (sky blue) was not shown. Thereafter, the inside of device was dried so as to apply the same conditions, and then, 2 mL of an aqueous solution of CsNO.sub.3 (0.1 M) was introduced under the same conditions, and electrode resistance (blue) rapidly decreased showing resistance decrease of 100 times or more as compared to control.

[0048] The Nyquist plot of the right of FIG. 5 shows values 10 hours after introducing distilled water and an aqueous solution of CsNO.sub.3, respectively, and rapid performance improvement (resistance decrease) can be confirmed. Such a method can be applied while a solid oxide fuel cell is operated.

EXAMPLE 4

Performance Evaluation in Full Cell

[0049] Step 1) Manufacture of Full Cell

[0050] NiO and GDC were mixed at the mass ratio of 6:4 through a ball mill (72 hours, 200 rpm) to prepare mixed powder for manufacturing an anode. The mixed powder was subdivided (about 0.4 g) and uniaxial-pressurized (2 MPa) to manufacture a molded product using a mold and extruder. Further then, it was heat treated at 900° C. for 1 hour to pre-sinter. In order to prepare an electrolyte, GDC powder was mixed with an ethanol-based solvent containing a dispersant and binder through a ball mill (48 hours, 180 rpm) and then, an electrolyte layer was deposited by drop coating. Further then, it was heat treated at 1500° C. for 5 hours to remove organic materials inside and prepare a dense electrolyte with a thickness of about 10 um. Further then, a cathode layer was prepared using material for preparing a cathode (PrBa.sub.0.5Sr.sub.0.5Ce.sub.1.5Fe.sub.0.5O.sub.5+δ) by screen printing, and then, sintered at 900° C. for more than 10 hours to prepare a cathode with a thickness of about 10 um, thus finally manufacturing a full cell.

[0051] Step 2) Performance Evaluation in Full Cell

[0052] In order to minimize contact resistance with an anode of SOFC Full Cell and wire connected outside, a small amount of CsNO.sub.3 powder was mixed with silver paste used as a current collector and bonded to an electrode. For this purpose, 30 mg of CsNO.sub.3 and silver paste were uniformly mixed using a mortar, and then, applied using a brush so as to completely cover the anode surface. The full cell was loaded on measurement system, and as commonly used gas conditions, air was introduced in the cathode, and 3% humidified hydrogen (3% H.sub.2+97% H.sub.2) was supplied to the anode, and then, the performance according to operation temperature was evaluated, and the result was shown in FIG. 6 and the following Table 1. For comparison, a fuel cell without CsNO.sub.3 powder was also measured, and the fuel cell without CsNO.sub.3 powder was designated as ‘Fuel Cell’, and the fuel cell using CsNO.sub.3 powder was designated as ‘Promoted Fuel Cell’.

TABLE-US-00001 TABLE 1 Maximum Maximum performance of performance of control (common promoter applied Performance Temperature Full Cell) full cell improvement 300° C. 7 mW/cm.sup.2  12 mW/cm.sup.2 +71% 350° C. 25 mW/cm.sup.2  44 mW/cm.sup.2 +76% 400° C. 76 mW/cm.sup.2 117 mW/cm.sup.2 +54% 450° C. 193 mW/cm.sup.2 229 mW/cm.sup.2 +19% 500° C. 393 mW/cm.sup.2 391 mW/cm.sup.2 —

[0053] As shown in FIG. 6 and Table 1, the application of a promoter resulted in about 19% performance improvement at the operation temperature of 450° C., and particularly, as the temperature decreased, performance improvement by the promoter was remarkably exhibited. Particularly, at the medium-low temperature region of 400° C. or less, high performance improvement of 50% or more was exhibited. This method can be applied as a dry process when a solid oxide fuel cell is manufactured and loaded.

EXAMPLE 5

Performance Evaluation in Full Cell

[0054] For the Fuel Cell and Promoted Fuel Cell manufactured in Example 4, performances were evaluated as follows.

[0055] After confirming stable performance in 3% humidified hydrogen (3% H.sub.2O+97% H.sub.2) at 450° C., the fuel was converted into 3% humidified methane (3% H.sub.2O+97% CH.sub.4) and performance change was confirmed. Wherein, 0.8 V bias was applied, and the result was shown in FIG. 7.

[0056] As shown in FIG. 7, in the case of Fuel Cell as control, performance was deteriorated within 5 hours and it was difficult to operate (green), while the Promoted Fuel Cell exhibited stable performance (red). Further, as the result of observing each anode, in the case of Fuel Cell as control, carbon fiber was produced in a large quantity by carbon deposition, while in the Promoted Fuel Cell, carbon deposition was not generated within the operation time. Thus, it can be confirmed that carbon deposition in the anode was also inhibited by the promoter according to this disclosure.