KR20190130835A - Solid oxide fuel cell and electrolyte thereof - Google Patents

Abstract

The present invention is to provide a solid oxide fuel cell comprising an electrolyte made of composite structures and materials so as to maximize electrochemical reactivity and shielding performance. A solid oxide fuel cell according to the present invention comprises: a board; a first electrode stacked on the board; an electrolyte stacked on the first electrode; and a second electrode stacked on the electrolyte so as to be spaced apart from the first electrode with the electrolyte interposed therebetween. The electrolyte may comprises: a first electrolyte layer configured to be in contact with the first electrode and the second electrode, respectively; and a second electrolyte layer formed inside the first electrolyte layer so as to be spaced apart from the first electrode and the second electrode, respectively, and configured to shield pin holes formed in the thickness direction of the first electrolyte layer.

Description

Solid oxide fuel cell and electrolyte thereof {SOLID OXIDE FUEL CELL AND ELECTROLYTE THEREOF}

TECHNICAL FIELD The present invention relates to solid oxide fuel cells, and more particularly, to electrolyte configurations in which electrochemical reactivity and shielding ability are improved.

A solid oxide fuel cell (SOFC), which is one type of fuel cell, is a fuel cell operated by using a solid ceramic as an electrolyte, and generally has advantages such as high power density and efficiency, and simple system configuration. In addition, above all, the relatively high driving temperature is possible to internally reform itself, there is an advantage that can be used directly hydrocarbon fuel, such as natural gas.

In general, a solid oxide fuel cell is operated at a high temperature of 800 to 1000 ℃, recently, research has been conducted on a low temperature driven solid oxide fuel cell that can be operated at a low temperature by lowering the operating temperature.

In such a low temperature driven solid oxide fuel cell, there is a problem that the ion conductivity in the electrolyte is lowered and the ohmic loss is greatly increased in a low temperature environment of 500 ° C. or lower. To improve this, a solid oxide fuel cell having a thin film electrolyte has been introduced, and this thin film structure can be supported on a porous substrate for mechanical strength reinforcement and sufficient scale.

On the other hand, the electrolyte of the low-temperature driving type solid oxide fuel cell having a thin film structure requires high ion conductivity and surface reactivity in order to minimize resistance loss, and must block the movement of electrons and gases (electric shielding and gas shielding).

Electrolyte materials in consideration of these characteristics include doped ceria and yittria stabilized zirconia (YSZ). The doped ceria is characterized by excellent ion conductivity and electrochemical reactivity, but may exhibit low open circuit voltage (OCV) characteristics due to its electrical conductivity even at a low temperature below 500 ° C. In addition, yttria stabilized zirconia can secure electrical shielding ability, but there is a possibility that the ion resistance and the surface reaction rate of charge transfer are low, thereby increasing the electrical resistance.

Therefore, it is necessary to specify and optimize the structure of the electrolyte of the low temperature driven solid oxide fuel cell so as to block the electric and gas movement while ensuring ion conduction and electrochemical reactivity.

KR 10-2017-0003280 A (published Jan. 9, 2017)

An object of the present invention is to provide a solid oxide fuel cell comprising an electrolyte composed of a complex structure and material to maximize the electrochemical reactivity and shielding ability.

In order to achieve the object of the present invention, a solid oxide fuel cell according to the present invention includes a substrate; A first electrode stacked on the substrate; An electrolyte stacked on the first electrode; And a second electrode stacked on the electrolyte so as to be spaced apart from the first electrode with the electrolyte interposed therebetween, wherein the electrolyte comprises: a first electrolyte layer configured to be in contact with the first electrode and the second electrode, respectively; And a second electrolyte layer formed inside the first electrolyte layer so as to be spaced apart from the first electrode and the second electrode, respectively, and shielding a pin hole formed in the thickness direction of the first electrolyte layer. do.

The second electrolyte layer may be formed to conformally cover the surface of the first electrolyte layer.

The second electrolyte layer may be formed by atomic layer deposition (ALD).

The first electrolyte layer may be formed by sputtering.

The first electrolyte layer is made of doped ceria, the second electrolyte layer is made of yttria stabilized zirconia (YSZ), and has a thickness of 20 to 70 nm in the stacking direction. Can have

The first electrolyte layer may be formed to have a thickness of 180 nm on both surfaces of the second electrolyte layer in a lamination direction, and the second electrolyte layer may have a thickness of 25 nm.

An electrolyte according to the present invention, which provides an ion migration passage of a solid oxide fuel cell, is interposed between a first electrode stacked on a substrate and a second electrode spaced apart from the first electrode, wherein the first and second electrodes are disposed. A first electrolyte layer configured to be in contact with each electrode; And a second electrolyte layer formed inside the first electrolyte layer so as to be spaced apart from the first and second electrodes, respectively, and configured to shield pin holes formed in the thickness direction of the first electrolyte layer.

According to the present invention, when a second electrolyte layer is provided between the first electrolyte layers to shield the pinhole of the first electrolyte layer, the first electrolyte layer ensures reactivity with the electrode and the second electrolyte layer is a gas between the material electrodes. Improved performance can be achieved by complementing the electrolyte properties such as ensuring the ability to shield the film.

In addition, since the second electrolyte layer is conformally covered on the surface of the first electrolyte layer by atomic layer deposition, an electrolyte structure in which shielding ability is secured even at a thin thickness may be realized.

Further, by optimizing the thickness of the second electrolyte layer made of yttria stabilized zirconia, the production cost and performance of the fuel cell may be maximized by complementary complement of the electrolyte components.

1 is a cross-sectional view of a solid oxide fuel cell according to the present invention.
FIG. 2 shows the pinhole shielding effect of the yttria stabilized zirconia layer formed by atomic layer deposition.
FIG. 3 is a detailed view illustrating a laminated structure and a second electrolyte layer position of a comparative example of the solid oxide fuel cell illustrated in FIG. 1.
FIG. 4 is a diagram illustrating an open circuit voltage (OCV) value of one embodiment and a comparative example of FIG. 3.
FIG. 5 is a diagram illustrating a polarization curve of one embodiment and a comparative example of FIG. 3.
FIG. 6 is a view showing area-specific resistances (ASRs) of the example and the comparative example of FIG. 3.
FIG. 7 illustrates resistance and OCV values according to the thickness of the second electrolyte layer illustrated in FIG. 1.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, throughout the specification, when a part is said to "include" a certain component, it means that it may further include other components, without excluding the other components unless otherwise stated.

1 is a cross-sectional view of a solid oxide fuel cell 100 according to the present invention. The solid oxide fuel cell 100 according to the present invention is characterized by having a sandwich type composite electrolyte structure. Referring to FIG. 1, a solid oxide fuel cell 100 according to the present invention includes a substrate 110, a first electrode 120, an electrolyte 130, and a second electrode 140.

Specifically, the substrate 110 may support the solid oxide fuel cell 100 according to the present invention to secure mechanical strength. In addition, the substrate 110 in the present invention may be made of a porous, specifically, may be provided with a porous portion 111 penetrating up and down in the thickness direction. The porous portion 111 may be a passage through which gas (hydrogen) passes when the solid oxide fuel cell 100 is driven according to the present invention.

The first electrode 120 may be stacked on the surface of the substrate 110. The first electrode 120 may be an anode of the solid oxide fuel cell 100 according to the present invention, and in the cathode, hydrogen gas, which is a fuel supplied through the porous portion 111 of the substrate 110, may be formed. It is ionized to decompose into hydrogen ions and electrons.

An electrolyte 130 may be stacked between the first electrode 120 and the second electrode 140 corresponding thereto. The electrolyte 130 blocks the movement of electrons between the first electrode 120 and the second electrode 140 and serves to provide a passage through which ions move. That is, oxygen ions generated at the second electrode 140 may move to the first electrode 120 through the electrolyte 130, while electrons flow to an external circuit.

A solid ceramic material may be used for the electrolyte 130 of the solid oxide fuel cell 100 according to the present invention. The structure and characteristics of the electrolyte 130 according to the present invention will be described later.

The second electrode 140 positioned to be spaced apart from the first electrode 120 by the electrolyte 130 is a cathode, and electrons generated in the first electrode 120 are transferred to the second electrode 140 through an external circuit. Inflow). In the second electrode 140, electrons and oxygen introduced through an external circuit meet and oxygen is reduced to form oxygen ions. Oxygen ions may move through the electrolyte 130 to the first electrode 120 to react with hydrogen ions to generate water. As shown, the second electrode 140 may have a structure stacked on the electrolyte 130.

As mentioned above, the electrolyte 130 may block the movement of electrons to allow electrons to flow to an external circuit to produce current, and also to rapidly transfer oxygen ions therein, and a chemical reaction may occur at a surface that meets an electrode. It is desirable to get up quickly.

In order to satisfy such characteristics, the electrolyte 130 of the solid oxide fuel cell 100 according to the present invention has a sandwich structure including a first electrolyte layer 131 and a second electrolyte layer 132. Here, the first electrolyte layer 131 may provide excellent characteristics in ion conduction and surface reaction, and the second electrolyte 130 may serve to provide excellent characteristics in blocking the movement of electrons and gases.

In detail, the first electrolyte layer 131 may be positioned to contact the first and second electrodes 120 and 140, respectively. The second electrolyte layer 132 may be located inside the first electrolyte layer 131 so as to be spaced apart from the first and second electrodes 120 and 140, respectively. The second electrolyte layer 132 may be formed to shield pin holes 131a formed in the thickness direction of the first electrolyte layer 131.

Here, the pinhole 131a means a minute hole formed in the deposited layer in the thickness direction (lamination direction). When the first electrode 120 and the first electrolyte layer 131 are sequentially stacked on the substrate 110, the pinhole 131a may be formed by a porous part (such as sputtering) in which deposition is performed in a thickness direction. 111) may not be completely covered. When the pinhole 131a is present in the first electrolyte layer 131, electrons and hydrogen may pass through the pinhole 131a, and electrical and gas shielding capabilities required for the electrolyte 130 may be reduced.

According to the present invention, when the second electrolyte layer 132 capable of shielding the pinhole 131a of the first electrolyte layer 131 is interposed inside the first electrolyte layer 131, the first electrolyte layer 131 is an electrode. The second electrolyte layer 132 and the second electrolyte layer 132 are complementary to each other, such as to secure the ability to shield the gas between the material electrodes, so that complex electrolyte characteristics can be obtained. That is, the first electrolyte layer 131 has excellent reaction characteristics with the electrode, and the second electrolyte layer 132 may be designed to effectively shield electrons and gases, thereby improving overall performance of the electrolyte 130. Can be. In addition, by comparing the ionic conductivity of the first and second electrolyte layers 131 and 132, a layer having a low ion conductivity may be designed to minimize the thickness thereof.

2 is a view showing the pinhole 131a shielding effect of the yttria stabilized zirconia layer formed by atomic layer deposition. Hereinafter, referring to FIGS. 1 and 2, a method of forming a first electrolyte layer 131 and a second electrolyte layer 132 that can shield the pinhole 131a of the first electrolyte layer 131 and the resulting The shielding structure will be described.

 Specifically, the yittria stabilized zirconia (YSZ) layer shown in FIG. 2 may be used for the second electrolyte layer 132 of the solid oxide fuel cell 100 according to the present invention. FIG. 2 (a) shows the yttria stabilized zirconia layer deposited on the platinum layer by plasma enhanced atomic layer deposition (PEALD), which is one of atomic layer deposition (ALD) methods. will be. In comparison, (b) of FIG. 2 shows the yttria stabilized zirconia layer deposited on the platinum layer by sputtering. In both cases there may be pinholes in the platinum layer.

Comparing FIGS. 2A and 2B, the yttria zirconia layer formed by plasma atomic layer deposition can shield pinholes that can be formed in platinum, while the yttria zirconia layer formed by sputtering is platinum It will have a structure that does not shield the pinhole that can be formed in. That is, it can be seen that the pinhole penetrating the platinum electrode, the porous substrate positioned below the platinum electrode, and the electrolyte layer formed by sputtering is formed in the structure of FIG. 2 (b).

The reason why the layer formed by the atomic layer deposition method can shield the pinhole is that the deposition of the material by the atomic layer deposition method forms a structure that conformally covers the surface on which the material is to be deposited. . That is, the sputtering process proceeds by stacking materials deposited mainly in a vertical direction (thickness direction) with respect to the surface on which the material is to be deposited, whereas the atomic layer deposition method stacks materials in the thickness direction and the surface direction with respect to the surface on which the material is to be deposited. Can proceed.

In the solid oxide fuel cell 100 according to the present invention, the first electrolyte layer 131 may be deposited by sputtering. Sputtering has the advantage that the process speed and the manufacturing cost can be reduced compared to atomic layer deposition.

However, in the present invention, the second electrolyte layer 132 may have a structure formed to conformally cover the surface of the first electrolyte layer 131. That is, the second electrolyte layer 132 may have a structure in which the second electrolyte layer 132 is equally grown and deposited in the surface direction as well as the thickness direction from the surface of the first electrolyte layer 131. As described above, the second electrolyte layer 132 may be formed by atomic layer deposition.

The solid oxide fuel cell 100 according to the present invention has a structure divided into first and second electrolyte layers 131 and 132, so that only the second electrolyte layer 132, which is a layer which serves as an electron and gas shielding role, is an atomic layer. It may be formed by vapor deposition. That is, since only a portion of the layer is formed by atomic layer deposition, there is an advantage that the electrolyte 130 layer having excellent shielding ability can be formed thinly and at low cost.

FIG. 3 is a detailed view of the laminated structure and the position of the second electrolyte layer 132 of the comparative example of the solid oxide fuel cell 100 shown in FIG. 1. 4 is a graph showing an open circuit voltage (OCV) value of the embodiment and the comparative example of FIG. 3, FIG. 5 is a graph showing a polarization curve of the example and the comparative example of FIG. Is a graph showing the area-specific resistances (ASRs) of the Examples and Comparative Examples of FIG. 3.

Hereinafter, the difference in performance according to the arrangement of the first and second electrolyte layers 131 and 132 will be described with reference to FIGS. 3 to 6.

Referring to FIG. 3, in the solid oxide fuel cell 100 according to an embodiment of the present invention, the substrate 110 is anodized aluminum oxide (AOA), and the first electrode 120 and the second electrode. 140 may be made of platinum (Pt).

In addition, the first electrolyte layer 131 constituting the electrolyte 130 is a samaria-doped ceria (SDC) formed by sputtering, and the second electrolyte layer 132 is formed by atomic layer deposition. It may consist of yittria stabilized zirconia (YSZ).

As described above, in the present embodiment, the second electrolyte layer 132 may be positioned at the center of the first electrolyte 130 to be spaced apart by the same distance from the first and second electrodes 120 and 140, respectively (CZC). ). In addition, an example (ZC) in which an atomic layer deposited yttria stabilized zirconia layer 232 is positioned between the first electrode 120, which is a cathode, and the samaria doped ceria layer, and the second electrode 140, which is an anode, and samaria doped Comparative example is an example (CZ) in which the yttria stabilized zirconia layer 332 deposited atomically between two ceria layers is positioned. In addition, FIG. 4 shows an example (Ref.) In which only the samaria doped ceria layer is present and the yttria stabilized zirconia layer does not exist in the electrolyte 130.

4 to 6, it can be seen that the structure of the electrolyte 130 including the first and second electrolyte layers 131 and 132 according to the exemplary embodiment is an optimized layer arrangement. First, referring to FIG. 4, in the case where an yttria stabilized zirconia layer is present (ZC, CZC, CZ) without significant influence on the position, the result is secured close to a theoretical OCV value of 1.1 V at 450 ° C. That is, it can be seen that the electrical shielding role is performed by the second electrolyte layer 132 made of yttria stabilized zirconia formed by atomic layer deposition.

Next, referring to FIGS. 5 and 6, it can be seen that the performance curve shows the best result in the case of the present embodiment (CZC) compared to the comparative examples (ZC, CZ). This result may be due to the difference in that the second electrolyte layer 132 made of yttria stabilized zirconia is not disposed in contact with the first and second electrodes 120 and 140. In particular, in the case of Comparative Example (CZ) in which the yttria stabilized zirconia layer is in contact with the anode, it can be seen that the resistance loss due to the activation energy required for the chemical reaction at the anode is large (Cathodic Activation Resistance of FIG. 6).

7 is a diagram illustrating resistance and OCV values according to the thickness of the second electrolyte layer 132 illustrated in FIG. 1. Hereinafter, referring to FIG. 7, an optimum thickness of the first and second electrolyte layers 131 and 132 included in the electrolyte 130 of the present invention will be described.

In the sandwich structure of the embodiment of FIG. 7, the change of the OCV value with respect to the thickness of the second electrolyte layer 132 made of atomic layer deposited yttria stabilized zirconia is described. When the thickness of) becomes 20 nm or more, a value close to the theoretical OCV value can be confirmed. That is, when the second electrolyte layer 132 is atomic layer deposited, it is confirmed that the thickness of the second electrolyte layer 132 may be 20 nm or more so that the pinhole 131a that may exist in the first electrolyte layer 131 may be sufficiently shielded. Can be.

As shown in FIG. 7, the resistance increases as the thickness of the second electrolyte layer 132 increases. Also in this embodiment, as the thickness of the yttria stabilized zirconia layer (second electrolyte layer 132), which has lower ion conductivity than that of the first electrolyte layer 131, is increased, the resistance of the entire electrolyte 130 may also be greatly increased. have.

Meanwhile, FIG. 7 shows the OCV value for the thickness of the single layer structure in which the electrolyte is composed only of the yttria stabilized zirconia layer together with the structure of one embodiment of the present invention. For this structure, it can be seen that the OCV value close to the theoretical level can be obtained when the thickness of the yttria stabilized zirconia layer is 70 nm or more.

In consideration of the resistance of the electrolyte of FIG. 7 and the OCV value of the single layer structure, the thickness of the second electrolyte layer 132 of the present embodiment may be optimized. In the sandwich structure of the present embodiment, when the thickness of the second electrolyte layer 132 is 20 nm or more, sufficient OCV value can be secured. That is, in the present embodiment, since the second electrolyte layer 132 is not in direct contact with the electrodes (each of the first and second electrodes 120 and 140), the surface reaction characteristics may be sufficiently improved. Since the second electrolyte layer jointly blocks the pinholes, the OCV value can be sufficiently secured even with a thinner yttria stabilized zirconia layer thickness compared to the single layer structure.

Thus, in this embodiment where the first electrolyte layer 131 is present on both side surfaces of the second electrolyte layer 132, the thickness of the second electrolyte layer 132 may be optimized to have a thickness of 20 to 70 nm. Can be. That is, the thickness of the second electrolyte layer 132 formed by expensive atomic layer deposition may not be secured more than necessary, and may be secured to a level sufficient to sufficiently perform an electrical shielding role.

According to this optimization, the thickness of each layer of the solid oxide fuel cell 100 according to an embodiment of the present invention can be designed. That is, as shown in FIG. 3, the present embodiment includes a substrate 110 made of 100 μm of anodized aluminum, a first electrode 120 made of platinum of 300 nm, and a second electrode 140 made of platinum of 80 nm. ) In addition, the present embodiment may have a first electrolyte layer 131 made of samaria doped ceria material sputtered at 180 nm to contact the first and second electrodes 120 and 140, respectively. Further, the second electrolyte layer 132 made of yttria stabilized zirconia may be atomic layer deposited at 25 nm to serve as a shield for electrons and hydrogen gas, and unnecessary increase in cost and thickness may be suppressed.

The description of the present invention described above is for illustrative purposes, and those skilled in the art can understand that the present invention can be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. There will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

In addition, the scope of the present invention is shown by the following claims rather than the detailed description, it should be construed that all changes or modifications derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present invention. do.

100: solid oxide fuel cell
110: substrate
111: Perforation
120: first electrode
130: electrolyte
131: first electrolyte layer
131a: pinhole
132: second electrolyte layer
140: second electrode
232, 332: yttria stabilized zirconia layer

Claims (5)

Board;
A first electrode stacked on the substrate;
An electrolyte stacked on the first electrode; And
A second electrode stacked on the electrolyte so as to be spaced apart from the first electrode with the electrolyte interposed therebetween,
The electrolyte,
A first electrolyte layer configured to be in contact with the first electrode and the second electrode, respectively; And
And a second electrolyte layer formed inside the first electrolyte layer so as to be spaced apart from the first electrode and the second electrode, respectively, and configured to shield pin holes formed in the thickness direction of the first electrolyte layer. Solid oxide fuel cell.
The method of claim 1,
And the second electrolyte layer is formed to conformally cover the surface of the first electrolyte layer.
The method of claim 1,
And the second electrolyte layer is formed by atomic layer deposition.
The method of claim 1,
The first electrolyte layer is made of a doped ceria material,
The second electrolyte layer is made of yttria stabilized zirconia (YSZ) material and has a thickness of 20 to 70 nm in the stacking direction.
An electrolyte interposed between a first electrode stacked on a substrate and a second electrode spaced apart from the first electrode to provide an ion migration path of a solid oxide fuel cell,
A first electrolyte layer configured to be in contact with the first electrode and the second electrode, respectively; And
A second electrolyte layer formed inside the first electrolyte layer so as to be spaced apart from the first electrode and the second electrode, and configured to shield a pin hole formed in the thickness direction of the first electrolyte layer; Electrolyte.

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