Solid Oxide Fuel Cell with a Loaded Anode Base Promoter

Abstract

A solid oxide fuel cell according to the present invention can provide a solid oxide fuel cell with improved performance by loading a base promoter in the anode.

Description

Technical Field

[0001] The present invention relates to a solid oxide fuel cell having improved performance by loading a base promoter in an anode. Background Art

[0002] A SOFC (solid oxide fuel cell) is an energy conversion device that directly converts chemical energy into electrical energy and is composed of an oxygen ion-conducting electrolyte and a cathode and an anode positioned on both sides thereof.

[0003] If air and fuel are supplied to each electrode of the solid oxide fuel cell, in the cathode, oxygen is reduced to generate oxygen ions, and the generated oxygen ions move through the electrolyte to the anode and react with hydrogen supplied in the anode to generate water. Among them, since electrons are generated in the anode and electrons are consumed in the cathode, if the two electrodes are connected to each other, it operates in such a way that an electric current flows.

[0004] Since the solid oxide fuel cell operates at a high temperature, research on reducing the operating temperature is in progress, and it is generally related to the performance of the cathode and the anode. Although various cathode materials having high electron-ion conductivity are being developed, excellent anode materials that can replace Ni have not been developed so far.

[0005] Therefore, there is a need to develop an anode that has high performance even when the operating temperature of the solid oxide fuel cell is reduced.

[0006] Disclosure

[0007] Technical Problem

[0008] An object of the present invention is to provide a solid oxide fuel cell having improved performance by loading a base promoter in an anode.

[0009] Technical Solution

[0010] To solve this problem, the solid oxide fuel cell includes a cathode, an anode, and an electrolyte between the cathode and the anode, wherein at least a part of the pores of the anode contains a promoter as an alkali metal compound.

[0011] Since the solid oxide fuel cell operates at a high temperature, in particular, the performance of the cathode and the anode should be improved to reduce the operating temperature, and the present invention is characterized by improving the performance of the anode.

[0012] Previously, the material or shape of the anode was controlled to improve the performance of the anode, but the performance improvement was limited and it was difficult to reproduce the technology. However, the present invention improves the performance of the anode by introducing an alkali metal precursor while using the material or shape of the previously used anode as it is.

[0013] As used herein, the term 'promoter' is used to improve the performance of the anode, and it is loaded in the anode to improve the performance without destroying the components or shape of the anode. In this regard, the component loaded in the anode is referred to as 'promoter' herein.

[0014] The promoter according to the present disclosure is present in the pores of the anode, and when the solid oxide fuel cell is operated, the gases introduced into the anode, such as hydrogen, hydrocarbon fuel, etc. contact the promoter. Thus, the description "at least a part of the pores of the anode contains a promoter" as used herein means that the promoter is inserted into at least a part of the pores of the anode, and when the solid oxide fuel cell is operated, the gases introduced into the anode can contact the promoter in the pores of the anode. Meanwhile, the method for loading the promoter in the anode will be explained later.

[0015] The promoter herein means an alkali metal compound. Preferably, the alkali metal compound means an alkali metal oxide, an alkali metal hydroxide or a combination thereof.

[0016] Specifically, when the alkali metal of the alkali metal compound is M, the alkali metal oxide can be represented by M2O, and the alkali metal hydroxide can be represented by MOH. As examples of the alkali metal (M), mention may be made of lithium (Li), sodium (Na), potassium (K) or cesium (Cs).

[0017] Although there is no limitation in theory, the promoter is present in the pores of the anode and simultaneously contacts the anode. Therefore, when the surface of the anode is partially oxidized and moisture is introduced into the pores of the anode, a large amount of moisture is adsorbed on the surface of the anode. Thus, the promoter relieves the strong bond between the anode and the hydrogen introduced into the anode, thereby promoting the oxidation of hydrogen in the anode and broadening the region of hydrogen reaction, thus improving the performance of the anode. In addition, it can inhibit the deposition of carbon on the anode during the operation of the solid oxide fuel cell.

[0018] In this regard, the anode is preferably a metal-ceramic composite anode. More preferably, the metal of the metal-ceramic composite is Ni. Most preferably, the anode is a composite of Ni and GDC (Gd-doped CeO2).

[0019] As explained above, since the anode of the solid oxide fuel cell according to the present disclosure contains a promoter loaded therein, the electrode resistance is lower compared to the anode of a solid oxide fuel cell that does not contain a promoter. The comparison of the electrode resistance is carried out under the same conditions except for the loading amount of the promoter, such as the same structure of the solid oxide fuel cell, the same operating conditions, etc.

[0020] Preferably, the electrode resistance of the anode of the solid oxide fuel cell is 10% or less of the electrode resistance of the anode of the solid oxide fuel cell not containing the promoter, and more preferably 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, or 5% or less.

[0021] In addition, as described in the examples below, it can be confirmed that for the long-term operation of the solid oxide fuel cell, the electrode resistance of the anode according to the loading amount of the promoter is stably maintained.

[0022] There is also provided a method for manufacturing the solid oxide fuel cell explained above. Specifically, there is provided a method for preparing the solid oxide fuel cell explained above, the method including the steps of: introducing an alkali metal precursor into at least a part of the pores of the anode (step 1); and producing a promoter from the alkali metal precursor (step 2).

[0023] In order to load the promoter in the pores of the anode of the solid oxide fuel cell, the promoter should be loaded while the pores are formed in the anode, and thus, it is difficult to directly load the promoter in the pores of the anode. Therefore, in the present disclosure, the alkali metal precursor is introduced into at least a part of the pores of the anode, and then the promoter is produced from the alkali metal precursor by a chemical reaction.

[0024] Preferably, the alkali metal precursor is an alkali metal carbonate or an alkali metal nitrate. As explained above, when the alkali metal is M, as examples of the alkali metal (M), mention may be made of lithium (Li), sodium (Na), potassium (K), or cesium (Cs), the alkali metal carbonate may be represented by M2CO3, and the alkali metal nitrate may be represented by MNO3.

[0025] Preferably, step 1 is carried out by coating a solution containing the alkali metal precursor on the surface of the anode, or dipping the anode into a solution containing the alkali metal precursor. Thereby, the solution containing the alkali metal precursor can be introduced into the pores of the anode. This method can be applied in the case where the operation of the solid oxide fuel cell is stopped and the temperature is lowered to room temperature and during the manufacture of the anode of the solid oxide fuel cell.

[0026] Preferably, step 1 can be carried out by introducing a solution containing the alkali metal precursor into the gas pipeline for introducing fuel into the anode. The solid oxide fuel cell has a gas pipeline for introducing fuel into the anode, and if a solution containing the alkali metal precursor is introduced into the gas pipeline, the solution containing the alkali metal precursor can be introduced into the pores of the anode. Such a method can be applied during the operation of the solid oxide fuel cell.

[0027] Preferably, step 1 can be carried out by bonding a current collector containing an alkali metal precursor to the surface of the anode. In a solid oxide fuel cell, the anode contacts the current collector, and thus, by including the alkali metal precursor in the current collector, the alkali metal precursor can be introduced into the anode. Among them, the alkali metal precursor can be applied in the form of powder and in the form of solution. Such a method can be applied during the manufacture of the solid oxide fuel cell.

[0028] Preferably, step 2 is carried out by introducing fuel or moisture into the gas pipeline for introducing fuel into the anode. If fuel or moisture is introduced, it reacts with the alkali metal precursor present in the pores of the anode, and thus the alkali metal precursor is converted into the promoter explained above. In addition, it is preferable that the fuel contains hydrogen.

[0029] Meanwhile, for other configurations except for using the anode explained above of the present disclosure, the previously applied configurations of the solid oxide fuel cell can be applied.

[0030] Beneficial effects

[0031] As explained above, if a promoter is loaded in the anode according to the present disclosure, the performance of the solid oxide fuel cell can be significantly improved without changing the material or shape of the anode.

[0032] Description of the drawings

[0033] Figure 1 Shows the XPS results according to Example 1.

[0034] Figure 2 Shows the shape and cross-section of the half-cell used in Example 2.

[0035] Figure 3 Shows the performance evaluation in the half-cell according to Example 2.

[0036] Figure 4 Schematically shows the method for loading the promoter in the half-cell in Example 3.

[0037] Figure 5 Shows the performance evaluation in the half-cell according to Example 3.

[0038] Figure 6 Shows the performance evaluation in the full cell according to Example 4.

[0039] Figure 7 Shows the performance evaluation in the full cell according to Example 5.

[0040] Mode of the invention

[0041] In the following, embodiments and experimental examples of the present invention will be explained in detail. These embodiments and experimental examples are presented to more specifically explain the present invention, and the scope of the present invention is not limited thereto.

[0042] Example 1: Confirmation of the Loading of the Promoter

[0043] In order to confirm whether the promoter according to the present disclosure is loaded in the anode, the following experiment was conducted.

[0044] A mixed powder of CsNO3, NiO, and GDC (10% Gd-doped CeO2) (1:5.4:3.6 weight ratio) was heat-treated at 450 °C for 10 hours in a 3% humidified 10% hydrogen atmosphere (3% H2O + 10% H2 + 87% Ar), and then XPS (Cs3d) was measured, and the results are shown in Figure 1 as follows.

[0045] As Figure 1 shown, the presence of Cs can be confirmed, and thus it can be confirmed that the Cs precursor is loaded in the anode as a promoter.

[0046] Example 2: Performance Evaluation in a Half-Cell

[0047] Step 1) Fabrication of the Half-Cell

[0048] After molding GDC (10% Gd-doped CeO2) powder, it was sintered at 1450 °C for 5 hours. Furthermore, then, the surface was flattened using sandpaper, thus fabricating a GDC sample.

[0049] A mixed powder of NiO and GDC in a weight ratio of 6:4, an ink carrier (Fuelcellmaterialscompany), and ethanol were mixed in a weight ratio of 1:1:0.5 to prepare a paste, and it was applied to both sides of the sintered GDC sample by screen printing, and then it was sintered at 1400 °C for 10 hours. Finally, it was reduced and heat-treated at 650 °C in a 4% hydrogen atmosphere (4% H2 + 96% Ar) to finally fabricate a porous Ni-GDC electrode (thickness of about 8 μm). The fine structure of the fabricated half-cell is as Figure 2 shown.

[0050] Step 2) Performance Evaluation in the Half-Cell

[0051] In the half-cell fabricated above, at room temperature (23 °C), 10 μL of an aqueous solution of CsNO3 (0.023 M) was directly introduced into the porous Ni-GDC electrode using a pipette, and then the half-cell was loaded into the measurement system, and the change in the electrode resistance according to temperature was observed. Among them, as the applied gas atmosphere, 3% humidified 10% hydrogen (3% H2O + 10% H2 + 87% Ar) was used, and the measurement results are shown in Figure 3 For comparison, half-cells without the promoter were measured together, and the half-cells without the promoter were designated as 'Ni-GDC', and the half-cells with the promoter were designated as 'p-Ni-GDC'.

[0052] As Figure 3 shown in, in the case of the electrode with the promoter (p-Ni-GDC), compared with the ordinary half-cell control (Ni-GDC), the resistance was significantly reduced, and a stable resistance value was presented at 450 °C for 10 hours. Such a method can be applied when the operation of the solid oxide fuel cell is stopped and the temperature is reduced to room temperature.

[0053] Example 3: Performance evaluation in half-cells

[0054] The half-cell of Step 1 of Example 2 was loaded onto the measurement system, and then during operation, 2 mL of an aqueous solution of CsNO3 (0.1 M) was directly introduced into the half-cell through the gas pipeline using an injection pump to evaluate the performance.

[0055] First, as Figure 4 shown in, at the beginning, 3% humidified 10% hydrogen (3% H2O + 10% H2 + 87% Ar) was introduced, and then 2 mL of distilled water was introduced into the gas pipeline heated to above 120 °C as a control.

[0056] As Figure 5 shown in, the resistance change caused by water (sky blue) was not shown. Thereafter, the inside of the device was dried to apply the same conditions, and then 2 mL of an aqueous solution of CsNO3 (0.1 M) was introduced under the same conditions, and compared with the control, the electrode resistance (blue) decreased rapidly, showing a resistance reduction of 100 times or more.

[0057] Figure 5 The Nyquist plots on the right side of show the values after 10 hours of introducing distilled water and an aqueous solution of CsNO3, respectively, and a rapid performance improvement (resistance reduction) can be confirmed. Such a method can be applied when operating a solid oxide fuel cell.

[0058] Example 4: Performance evaluation in full-cells

[0059] Step 1) Fabrication of the full cell

[0060] Mix NiO and GDC in a ball mill (72 hours, 200 rpm) at a mass ratio of 6:4 to prepare the mixed powder for fabricating the anode. Subdivide the mixed powder (about 0.4 g) and uniaxially press it (2 MPa) to fabricate a molded product using a mold and an extruder. Furthermore, then, heat-treat it at 900 °C for 1 hour for pre-sintering. To prepare the electrolyte, mix GDC powder with an ethanol-based solvent containing a dispersant and a binder in a ball mill (48 hours, 180 rpm), and then deposit the electrolyte layer by dip coating. Furthermore, then, heat-treat it at 1500 °C for 5 hours to remove the internal organic materials and prepare a dense electrolyte with a thickness of about 10 μm. Furthermore, then, the cathode layer is prepared using the material for preparing the cathode (PrBa 0.5 Sr 0.5 Ce 1.5 Fe 0.5 O 5+δ ) by screen printing, and then, sinter it at 900 °C for more than 10 hours to prepare a cathode with a thickness of about 10 μm, thus finally fabricating the full cell.

[0061] Step 2) Performance evaluation in the full cell

[0062] To minimize the contact resistance of the wire connected to the anode of the SOFC full cell and the outside, mix a small amount of CsNO3 powder with the silver paste used as the current collector and bind it to the electrode. For this purpose, uniformly mix 30 mg of CsNO3 and the silver paste using a mortar, and then apply it using a brush to completely cover the anode surface. Load the full cell on the measurement system and, as the common gas condition, introduce air into the cathode, and supply 3% humidified hydrogen (3% H2 + 97% H2) to the anode, and then, evaluate the performance according to the operating temperature, and the results are shown in Figure 6 and Table 1 below. For comparison, the fuel cell without CsNO3 powder was also measured, and the fuel cell without CsNO3 powder was designated as 'fuel cell', and the fuel cell using CsNO3 powder was designated as 'promoted fuel cell'.

[0063] [Table 1]

[0064]

[0065] As Figure 6As shown in Table 1, the application of the promoter results in a performance improvement of approximately 19% at an operating temperature of 450°C. In particular, as the temperature decreases, the performance improvement by the promoter is significantly presented. In particular, in the medium and low temperature region of 400°C or lower, a high performance improvement of 50% or higher is presented. When manufacturing and loading a solid oxide fuel cell, this method can be applied as a dry process.

[0066] Example 5: Performance Evaluation in a Full Cell

[0067] For the fuel cells and the promoted fuel cells manufactured in Example 4, the performance was evaluated as follows.

[0068] After confirming the stable performance in 3% humidified hydrogen (3% H2O + 97% H2) at 450°C, the fuel was changed to 3% humidified methane (3% H2O + 97% CH4), and the performance change was confirmed. Among them, a 0.8V bias was applied, and the results are shown in Figure 7 as follows.

[0069] As Figure 7 shown, in the case of the fuel cell as a control, the performance deteriorated within 5 hours and was difficult to operate (green), while the promoted fuel cell presented stable performance (red). In addition, as a result of observing each anode, in the case of the fuel cell as a control, a large amount of carbon fiber was generated by carbon deposition, while in the promoted fuel cell, no carbon deposition occurred during the operation time. Therefore, it can be confirmed that carbon deposition in the anode is also inhibited by the promoter according to the present disclosure.

Claims

1. A method for manufacturing a solid oxide fuel cell, the solid oxide fuel cell comprising a cathode, an anode, and an electrolyte between the cathode and the anode, wherein at least a portion of the pores of the anode contains a promoter, and the promoter is an alkali metal compound, the method comprising the steps of: introducing an alkali metal precursor into at least a portion of the pores of the anode (step 1); and producing the promoter from the alkali metal precursor (step 2), wherein the anode is a composite of Ni and GDC (Gd-doped CeO2), and wherein the alkali metal is cesium (Cs), and wherein step 2 includes introducing fuel or moisture into a gas pipeline for introducing fuel into the anode.

2. The method according to claim 1, wherein the alkali metal precursor is an alkali metal carbonate or an alkali metal nitrate.

3. The method according to claim 2, wherein the alkali metal precursor is M2CO3 or MNO3, and M is cesium (Cs).

4. The method according to claim 1, wherein step 1 includes coating a solution containing the alkali metal precursor on the surface of the anode, or immersing the anode in a solution containing the alkali metal precursor.

5. The method according to claim 1, wherein step 1 includes introducing a solution containing the alkali metal precursor into a gas pipeline for introducing fuel into the anode.

6. The method according to claim 1, wherein step 1 includes bonding a current collector containing the alkali metal precursor to the surface of the anode.

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