KR20150073647A - Segmented solid oxide fuel cell - Google Patents

Abstract

According to an embodiment of the present invention, a segmented solid oxide fuel cell comprises a porous tubular supporting body; a barrier layer formed on the porous tubular supporting body; and a plurality of unit cells formed on the barrier layer wherein the surface roughness of the barrier layer is smaller than that of the porous tubular supporting body.

Description

[0001] SEGMENTED SOLID OXIDE FUEL CELL [0002]

The present invention relates to a segmented solid oxide fuel cell, and more particularly, to a segmented solid oxide fuel cell having improved structure.

A solid oxide fuel cell (SOFC) is a fuel cell that produces electricity by electrochemical reaction of fuel (for example, hydrogen) and oxygen at a high temperature using solid phase ceramic as an electrolyte. It is economical.

Since the solid oxide fuel cell is in a solid state, it can be manufactured in various forms such as a flat plate or a cylindrical shape. The flat plate type solid oxide fuel cell is excellent in power density and productivity and can be made thinner than electrolyte. On the other hand, gas sealing using a separate sealing material is required and the metal (for example, chromium) constituting the connecting material at high temperatures may be volatilized, leading to deterioration of electrode efficiency and low resistance to thermal cycling. The cylindrical solid oxide fuel cell is advantageous in that it does not require gas sealing, has excellent mechanical strength, and is highly reliable. On the other hand, there is a disadvantage that the current path is long and the internal resistance is high and the output density is low.

A segmented solid oxide fuel cell has been proposed as one of the improved cell types that overcomes such disadvantages. The segmented solid oxide fuel cell has a structure in which conventional single cell tubular cells are divided into a plurality of cells in a node shape. Since such a segmented solid oxide fuel cell is a module in which unit cells are connected in series, it is possible to generate high efficiency with a high voltage and a low current output, reduce the volume of the stack, and simplify the system. In addition, various processes that are low in manufacturing cost and capable of mass production can be applied.

However, the segmented solid oxide fuel cell may not uniformly reach the anode electrode due to uneven pore distribution and uneven surface of the support. Then, there may occur a problem that output and efficiency of the cells are not uniform.

The present invention seeks to provide a segmented solid oxide fuel cell capable of equalizing output and efficiency in a plurality of cells.

A segmented solid oxide fuel cell according to an embodiment of the present invention includes: a porous tubular support; A barrier layer formed on the porous tubular support; And a plurality of unit cells formed on the barrier layer, wherein the barrier layer has a surface roughness smaller than that of the porous tubular support.

The surface roughness of the barrier layer may be between 0.2 um and 0.5 um.

The barrier layer includes yttria-stabilized zirconia, and the yttria content of the barrier layer may be 5 wt% to 13 wt% with respect to 100 wt% of the barrier layer.

Wherein each of the plurality of unit cells comprises: an anode electrode formed on the barrier layer; An electrolyte layer formed on the anode electrode; And a cathode electrode formed on the electrolyte layer. Wherein the barrier layer comprises yttria-stabilized zirconia, the electrolyte layer comprises yttria-stabilized zirconia, and the yttria content of the barrier layer may be less than the yttria content of the electrolyte layer.

The electrical conductivity of the barrier layer may be less than the electrical conductivity of the electrolyte layer.

The gas permeability of the barrier layer may be greater than the gas permeability of the electrolyte layer.

In the fuel cell according to the present embodiment, a barrier layer having a surface roughness smaller than that of the porous tubular support is formed between the porous tubular support and the anode electrode so that the fuel can be uniformly diffused to the anode electrode formed on the barrier layer. In addition, the pores are uniformly distributed by the barrier layer, so that the fuel can be more uniformly diffused to the anode electrode. Thus, the power generation efficiency and output in each unit cell can be maximized and equalized. Thus, the efficiency and the output of the fuel cell can be maximized.

Further, the thermal expansion coefficient of the barrier layer is made similar to that of the electrolyte layer of the unit cell to reduce the thermal stress and make the electric conductivity smaller than that of the electrolyte layer, thereby preventing unnecessary electric current flow.

1 is a perspective view schematically illustrating a segmented solid oxide fuel cell according to an embodiment of the present invention.
2 is a cross-sectional view taken along the line II-II in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it is needless to say that the present invention is not limited to these embodiments and can be modified into various forms.

In the drawings, the same reference numerals are used for the same or similar parts throughout the specification. In the drawings, the thickness, the width, and the like are enlarged or reduced in order to make the description more clear, and the thickness, width, etc. of the present invention are not limited to those shown in the drawings.

Wherever certain parts of the specification are referred to as "comprising ", the description does not exclude other parts and may include other parts, unless specifically stated otherwise. Also, when a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, it also includes the case where another portion is located in the middle as well as the other portion. When a portion of a layer, film, region, plate, or the like is referred to as being "directly on" another portion, it means that no other portion is located in the middle.

Hereinafter, a segmented solid oxide fuel cell according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view schematically showing a segmented solid oxide fuel cell according to an embodiment of the present invention, and FIG. 2 is a sectional view cut along a line II-II in FIG.

1 and 2, a segmented solid oxide fuel cell (hereinafter "fuel cell") 100 according to the present embodiment includes a porous tubular support 10, A barrier layer 20, and a plurality of unit cells 30 formed on the barrier layer 20. Each of the unit cells 30a, 30b and 30c includes an anode electrode 32 formed on the barrier layer 20, an electrolyte layer 34 formed on the anode electrode 32, an electrolyte layer 34, And the plurality of unit cells 30 may be connected to each other in series by the coupling member 38. [ This will be explained in more detail.

The porous tubular support 10 is formed of a porous material having a tubular shape having a hollow 10a therein and having a plurality of first pores 10b. The fuel (for example, hydrogen) flowing through the hollow 10a can be moved toward the anode electrode 32 through the porous tubular support 10 by the porosity of the porous tubular support 10. The porous tubular support 10 may comprise a ceramic material capable of withstanding high temperatures. For example, the porous tubular support 10 may comprise an aluminum-based material or a zirconia-based material. However, the present invention is not limited thereto. The porous tubular support 10 can support a plurality of unit cells 30, and various materials capable of flowing gas can be used.

The surface of the barrier layer 20 formed on the porous tubular support 10 is planarized to uniformize the pores so that the fuel flowing through the hollow 10a can be uniformly moved to the anode electrode 32. [ When the barrier layer 20 has the same or similar thermal expansion coefficient as the electrolyte layer 34, the fuel cell 100 can have high stability at a high temperature. Thus, the barrier layer 20 may comprise a material that can planarize the surface of the porous tubular support 10 and have the same or similar thermal expansion coefficient as the electrolyte layer 34. In order to prevent unnecessary electric current flow, it is advantageous that the barrier layer 20 has a low electric conductivity and excellent mechanical properties. Further, the barrier layer 20 may have a gas permeability higher than that of the electrolyte layer 34 so that the fuel gas can move.

More specifically, the surface roughness of the barrier layer 20 may be less than the surface roughness of the porous tubular support 10. For example, the surface roughness Ra of the porous tubular support 10 may be 0.6 to 0.7 um, and the surface roughness Ra of the barrier layer 20 may be 0.5 um or less. If the surface roughness of the barrier layer 20 exceeds 0.5 mu m, the surface planarization characteristic may not be sufficient. The smaller the surface roughness of the barrier layer 20 is, the better, the lower limit is not particularly limited, but it may be difficult to realize a surface roughness of less than 0.2 um. The surface roughness of the barrier layer 20 may be from 0.2 um to 0.4 um to make the surface more planar. However, the present invention is not limited thereto, and the surface roughness of the barrier layer 20 may have various values.

The barrier layer 20 may have the same or similar thermal expansion coefficient as the electrolyte layer 34 and the electrical conductivity may be smaller than the electrolyte layer 34 to prevent unnecessary electric current flow. Accordingly, the barrier layer 20 includes the same material as the electrolyte layer 34, but may have a different composition. This will be described in more detail later. Since the fuel gas must permeate through the barrier layer 20 and reach the anode electrode 34, it is advantageous that the barrier layer 20 has a high gas permeability and the electrolyte layer 34 has a low gas permeability. Thus, the gas permeability of the barrier layer 20 may be greater than that of the electrolyte layer 34. For this purpose, the pore size, pore density and the like of the barrier layer 20 may be larger than that of the electrolyte layer 34.

In one example, the barrier layer 20 may comprise metal oxide stabilized zirconia. Metal oxide stabilized zirconia is a material that can maintain stability at room temperature by adding metal oxide to zirconia. If the metal oxide is contained in a large amount, the amount of the metal oxide should be limited considering that the metal oxide stabilization zirconia can move easily due to vacancy at a temperature above a predetermined temperature (for example, 800 ° C or higher) .

The metal of the metal oxide stabilized zirconia may include at least one of aluminum (Al), scandium (Sc), magnesium (Mg), hafnium (Hf), cerium (Ce) and yttrium (Y). Thus, the barrier layer 20 can be formed from any of alumina stabilized zirconia (ASZ), scandia stabilized zirconia (SSZ), magnesium stabilized zirconia (MSZ), hafnia stabilized zirconia ), Ceria stabilized zirconia (CSZ), and yttria stabilized zirconia (YSZ). Among them, the yttria-stabilized zirconia is low in electric conductivity, high in mechanical strength and low in price, so that the barrier layer 20 may contain yttria-stabilized zirconia.

When the barrier layer 20 contains yttria stabilized zirconia, a paste in which a ceramic powder, a binder, an additive, etc. composed of yttria stabilized zirconia is added to a solvent and is mixed is applied on the porous tubular support 10 And the barrier layer 20 can be formed by baking it.

At this time, the ceramic powder composed of yttria-stabilized zirconia may contain 5 wt% to 13 wt% yttria. When the paste is applied and then baked, the solvent, the binder and the like disappear, and the yttria-stabilized zirconia is mainly left. Therefore, the barrier layer 20 may also contain yttria by 5 wt% to 13 wt%. If the yttria content is less than 5 wt%, the difference in the yttria content between the yttria content and the electrolyte layer 34 higher than the barrier layer 20 becomes large, and therefore the difference in thermal expansion coefficient between the yttria content and the electrolyte layer 34 have. Therefore, cracks may occur due to thermal stress at a high temperature. If the content of yttria is larger than 13 wt%, the yttria content increases and the manufacturing cost can be increased and the electric conductivity can be increased. However, the present invention is not limited thereto, and the content of yttria may have various values.

At this time, the ceramic powder may be contained in an amount of 65 to 85 parts by weight based on 100 parts by weight of the paste. If the weight percentage of the ceramic powder is less than 65, the thickness that can be applied by a single coating process is reduced, and it is difficult or difficult to form the barrier layer 20 to a desired thickness. If the weight percentage of the ceramic powder exceeds 85 parts by weight, the viscosity of the paste may be increased and the surface roughness of the barrier layer 20 may be lowered. At this time, considering the thickness and surface roughness of the barrier layer 20, the weight of the ceramic powder may be 70 to 80 parts by weight. However, the present invention is not limited thereto, and the weight portion of the ceramic powder may be variously modified.

The binder may include various materials capable of enhancing the bonding force between the ceramic powders. For example, ethyl cellulose may be used as the binder. However, the present invention is not limited thereto, and various known binders can be used. The binder may be contained in an amount of 1 wt% to 10 wt% with respect to 100 wt% of the paste, but the present invention is not limited thereto.

The additive may be selected from a wide variety of additives that can improve various properties. For example, the additive may include a leveling agent capable of reducing the surface tension and improving the leveling property, and the leveling agent may include a fluorine-based material. However, the present invention is not limited thereto, and various additives known in the art may be used. Leveling agent and the like can be included in an amount of 0.2 wt% to 5 wt% with respect to 100 wt% of the paste, but the present invention is not limited thereto.

As the solvent, various materials capable of evenly dispersing the ceramic powder, the binder and the additives and mixing them together can be used. For example, the solvent may be an alcohol-based material having excellent printability. However, the present invention is not limited thereto, and various solvents known can be used.

The viscosity of the paste described above may be from 30,000 cps to 60,000 cps. If the viscosity of the paste is less than 30,000 cps, the viscosity may be low and the paste may flow down and the workability may be deteriorated. If the viscosity of the paste exceeds 60,000 cps, the viscosity may be high and it may be difficult to planarize the surface. However, the present invention is not limited thereto, and the viscosity of the paste may have various values.

The paste may be fired at a temperature of a certain temperature (e.g., 1000 to 1500 ° C) to form the barrier layer 20. At this time, the binder, the solvent, and the like are removed by high heat, and the pores are located in the portion, so that the barrier layer 20 can have a relatively large gas permeability. The thickness of this barrier layer 20 may be between 10 um and 25 um. If the thickness of the barrier layer 20 is less than 10 탆, the effect of flattening the surface may not be sufficiently exhibited. When the thickness of the barrier layer 20 exceeds 25 mu m, the solid content (especially, the content of the ceramic powder) contained in the paste increases, and the viscosity becomes high, and the surface roughness may be lowered. However, the present invention is not limited thereto, and the thickness of the barrier layer 20 may have various values.

A plurality of unit cells 30 are formed on the barrier layer 20. Each unit cell 30 may include an anode electrode 32, an electrolyte layer 34, and a cathode electrode 36. The anode electrode 32 of one unit cell 30 and the cathode electrode 36 of the adjacent unit cell 30 are connected by the connecting material 38 so that a plurality of unit cells 30 are connected in series .

The anode electrode 32 may be formed on the barrier layer 20 in parallel with each other with a certain pattern (for example, a stripe pattern extending long along the circumferential direction of the porous tubular support 10). For example, the anode electrode 32 may include a Ni-YSZ series cermet. However, the present invention is not limited thereto, and the anode electrode 32 may include various materials.

The electrolyte layer 34 is formed on the anode electrode 32 in parallel with each other with a certain pattern (for example, a stripe pattern extending long in the circumferential direction of the porous tubular support 10) on the anode electrode 32 . The electrolyte layer 34 may be positioned to expose a part of the anode electrode 32 (the left part of the anode electrode 32 in the figure). In one example, the electrolyte layer 34 may comprise YSZ and the content of yttria may be greater than the barrier layer 20. For example, the electrolyte layer 34 may have a yttria content of more than 13 wt% and 30 wt%. Then, the electrolyte layer 34 has an electric conductivity superior to that of the barrier layer 20 and can have excellent electrical characteristics, and the thermal expansion coefficient of the electrolyte layer 34 and the barrier layer 20 are made similar to each other, Can be prevented. In addition, the electrolyte layer 34 may include CYZ, LaGaO ₃ -based materials, SYZ, and the like. The present invention is not limited thereto, and the electrolyte layer 34 may have various other materials.

When the electrolyte layer 34 includes YSZ, it may be formed by a method similar to that of the barrier layer 20. However, since the gas permeability of the electrolyte layer 34 should be relatively low, the ceramic powder composed of YSZ may be uniformly distributed on the solvent so that the ceramic powders can be positioned with high lamination density after sintering. This minimizes gas permeability and prevents gas from passing unnecessarily. The gas permeability of the electrolyte layer 34 and the barrier layer 20 can be made different from each other although the same material is contained by various methods.

The cathode electrode 36 is formed on the electrolyte layer 34 in parallel with each other with a certain pattern (for example, a stripe pattern extending long along the circumferential direction of the porous tubular support 10) on the electrolyte layer 34 . A part of the cathode electrode 36 is formed in an area not overlapping the anode electrode 32 so that it can be easily connected to the neighboring anode electrode 32. The cathode electrode 36 is formed of a composite of LSM (La _{1 - x} Sr _x MnO ₃ ) -YSZ layer (where a <x <1) of a perovskite structure and YSZ of a fluorite structure . &Lt; / RTI &gt;

The connection member 38 may have various shapes and materials for connecting the anode electrode 32 of one unit cell 30 and the cathode electrode 36 of the adjacent unit cell 30. For example, the connecting member 38 may include a cathode electrode 36 in a portion that does not overlap with the anode electrode 32 of one unit cell 30 (i.e., the first unit cell 30a positioned on the left side of FIG. 2) And the anode electrode 32 of the portion not covered by the electrolyte layer 34 in the unit cell adjacent to the first unit cell 30a (i.e., the second unit cell 30b positioned in the middle of FIG. 2) You can connect. The cathode electrode 36 of the second unit cell 30b and the anode electrode 36 of the other cell adjacent to the second unit cell 30b (i.e., the third unit cell 30c positioned on the right side of FIG. 2) ) Can be connected. Thus, a plurality of unit cells 30 can be connected in series. The connecting material 38 may be a LaGaO ₃ -based material having a perovskite structure. However, the present invention is not limited thereto, and the shapes and materials of the connection member 38 may be variously modified.

In this fuel cell 100, a fuel (for example, hydrogen) is supplied to the hollow 10a inside the porous tubular support 10 and the outside of the porous tubular support 10 (that is, Lt; / RTI &gt; The hydrogen supplied to the anode electrode 32 through the porous tubular support 10 and the barrier layer 20 is separated into hydrogen ions and electrons and hydrogen ions are moved to the cathode electrode 36 through the electrolyte layer 34 To form a reaction product (water). Then, the electrons separated from the hydrogen migrate to the cathode electrode 36 through the external circuit, whereby electricity flows.

The barrier layer 20 having a surface roughness smaller than that of the porous tubular support 10 is formed between the porous tubular support 10 and the anode electrode 32 in the fuel cell 100 according to the present embodiment, So that the fuel can be uniformly diffused into the anode electrode 32 formed on the anode electrode 32. Further, the pores are uniformly distributed by the barrier layer 20, so that the fuel can be more uniformly diffused into the anode electrode 32. [ Thus, the power generation efficiency and output of each unit cell 30 can be maximized and equalized. Thus, the efficiency and the output of the fuel cell 100 can be maximized. The thermal expansion coefficient of the barrier layer 20 is similar to that of the electrolyte layer 34 of the unit cell 30 to reduce the thermal stress and make the electric conductivity smaller than that of the electrolyte layer 34 to prevent unnecessary electric current flow .

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited thereto.

Example  One

A porous tubular support having a centerline average roughness of 0.60 um was prepared.

% Of ytterbium (YSZ), 8 wt% of an ethylcellulose-based binder, 2 wt% of a fluorine-based leveling agent, and the remaining alcohol-based solvent were mixed to prepare a paste. The porous tubular substrate was coated by printing. And baked at 1200 DEG C to form a barrier layer on the porous tubular support.

Example  2

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 70 wt%.

Example  3

The barrier layer was formed in the same manner as in Example 1, except that the content of YSZ was 75 wt%.

Example  4

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 80 wt%.

Example  5

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 85 wt% and the content of the binder was 2 wt%.

Comparative Example  One

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 90 wt% and the content of the binder was 1 wt%.

Comparative Example  2

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 60 wt%.

Comparative Example  3

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 55 wt%.

Comparative Example  4

The barrier layer was formed in the same manner as in Example 1 except that the content of YSZ was 50 wt%.

The thickness and surface roughness (centerline average roughness) of the barrier layer formed by Examples 1 to 5 and Comparative Examples 1 to 4 were measured and the results are shown in Table 1 below. The centerline average roughness of the porous tubular support was 0.60 um.

Thickness [um] Centerline Average Roughness [um] Example 1 11.5 0.27 Example 2 13.6 0.26 Example 3 17.3 0.34 Example 4 19.4 0.32 Example 5 22.1 0.43 Comparative Example 1 24.2 0.96 Comparative Example 2 9.5 0.25 Comparative Example 3 8.4 0.22 Comparative Example 4 7.8 0.23

Referring to Table 1, it can be seen that the barrier layer prepared according to Examples 1 to 5 has a centerline average roughness smaller than that of the porous tubular support and has excellent surface characteristics, and the thickness of the barrier layer is also 10um or more, As shown in FIG. Accordingly, it can be seen that the barrier layers having excellent surface characteristics and sufficient thickness can be formed by one printing process according to the first to fifth embodiments.

On the other hand, the barrier layer prepared according to Comparative Example 1 had a greater center line average roughness than the porous tubular support, indicating that the surface flattening effect did not appear. It can be seen that the barrier layer prepared according to Comparative Examples 2 to 4 has a low content of YSZ and thus does not have a sufficient thickness of the barrier layer. Then, the barrier layer may not have sufficient surface planarization effect or pore-uniformizing effect. If the barrier layer is formed by a plurality of prints in order to compensate for this, the productivity may be lowered.

Features, structures, effects and the like according to the above-described embodiments are included in at least one embodiment of the present invention, and the present invention is not limited to only one embodiment. Further, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

100: Segment-type solid oxide fuel cell
10: Porous tubular support
20: barrier layer
30: Unit cell
32: anode electrode
34: electrolyte layer
36: cathode electrode
38: connecting material

Claims (6)

A porous tubular support;
A barrier layer formed on the porous tubular support; And
And a plurality of unit cells
/ RTI &gt;
Wherein the barrier layer has a surface roughness smaller than that of the porous tubular support. The method according to claim 1,
Wherein the barrier layer has a surface roughness of 0.2 [mu] m to 0.5 [mu] m. The method according to claim 1,
Wherein the barrier layer comprises yttria-based stabilized zirconia,
And the yttria content of the barrier layer is 5 wt% to 13 wt% with respect to 100 wt% of the barrier layer. The method according to claim 1,
Wherein each of the plurality of unit cells includes:
An anode electrode formed on the barrier layer;
An electrolyte layer formed on the anode electrode; And
The cathode layer formed on the electrolyte layer
/ RTI &gt;
Wherein the barrier layer comprises yttria-based stabilized zirconia,
Wherein the electrolyte layer comprises yttria-based stabilized zirconia,
Wherein the yttria content of the barrier layer is smaller than the yttria content of the electrolyte layer. 5. The method of claim 4,
And the electrical conductivity of the barrier layer is smaller than the electrical conductivity of the electrolyte layer. 5. The method of claim 4,
And the gas permeability of the barrier layer is larger than the gas permeability of the electrolyte layer.

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