KR101969767B1 - Interconnect layer having stable conducting behavior in solid oxide fuel cell stack and fabrication method of the unit cell using the same - Google Patents

Abstract

The present invention relates to a connecting material layer having stable conduction characteristics in a solid oxide fuel cell stack and a method of forming the layer in a unit cell, and more particularly, to a cathode- Type connecting material layer is used for the positive electrode exposed surface or the positive electrode surface, and a p-type connecting material layer having conductivity only in the oxidizing atmosphere is used, and the two connecting material layers and the exposed surface of the positive electrode or negative electrode are bonded to each other, And the unit cell is attached. The connecting material layer shown in the present invention exhibits stable conductivity irrespective of changes in the hydrogen concentration of the cathode surface in the unit cell and the oxygen concentration in the anode surface, and the uniform and stable performance is obtained regardless of the position of the inlet or outlet of the stacked unit cell It is expected.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a solid oxide fuel cell stack having a stable conductive property and a unit cell forming method using the solid oxide fuel cell stack.

It is an object of the present invention to provide a method for forming a connecting material layer for connecting a cathode and an anode surface between unit cells in the stacking of unit cells for stacking solid oxide fuel cells, And a method for manufacturing the same.

Generally the solid oxide fuel cells operate at high temperatures, usually above 700 ℃, anode, electrolyte, conventional Ni / YSZ the cathode layer cermet, YSZ (Yttria Stabilized Zirconia) of the unit cell used, and LSM (La _{0. 8} Sr _{0 . 2} MnO ₃₎ respectively made of a material such as to produce a unit cell. Such a solid oxide fuel cell unit cell produces an open circuit voltage of 1 V or more, but it can increase the capacity by increasing the voltage by fabricating a stack by electrically connecting a plurality of unit cells. Therefore, the stack must electrically connect the anode of one unit cell with the anode of a neighboring unit cell adjacent to the unit cell. In this case, a dense membrane is formed on the exposed surface of the cathode or anode to prevent gas intermixing, It is an interconnect.

In the solid oxide fuel cell system, fuel gas (mainly hydrogen) and air (mixed gas containing oxygen) are supplied to the anode and the cathode, respectively. Therefore, the anode material of the unit cell and the cathode material of the adjacent unit cell are electrically connected to each other It should be formed of dense membrane without pores so that fuel gas and air are not mixed.

In addition, since both sides of the membrane are simultaneously exposed to different environments (oxidation / reduction), electrical conduction performance must be observed in both the atmospheres. The main material used as the connecting material is a ceramic material in the form of a metal oxide, which is advantageous because the anode, cathode and electrolyte of the solid oxide fuel cell are also mainly in the form of a metal oxide, and also in terms of adhesion and thermal matching.

LaCrO ₃ -based materials have been known as ceramic interconnecting materials of typical ABO ₃ perovskite structure, which have stable and conformal conduction characteristics in oxidation and reduction atmosphere and are easy to match with other constituent materials. However, it is difficult to form a thin and dense thin film due to the sinterability due to the volatility of Cr at high temperature, and the low electric conductivity value in the reducing atmosphere due to the p-type conduction behavior acts as a weak point. On the other hand, the La-doped SrTiO ₃ (LST) material is very easy to form a dense film due to its excellent sinterability and exhibits excellent electrical conductivity in a reducing atmosphere due to n-type conduction behavior, It acts as a weak point. Recently, the development of a coupling material which is simultaneously exposed to an oxidizing and reducing atmosphere has been carried out in various directions.

Korean Unexamined Patent Publication (Kokai) No. 10-2013-0040311 discloses a double layer structure of an n-type conductive layer and a p-type conductive layer, which overcomes the above drawbacks. The anode exposed to the oxidizing atmosphere (which comes into contact with the cathode of the unit cell) is composed of a thin film exhibiting p-type conduction behavior. The side exposed to the reducing atmosphere (in contact with the anode of another adjacent unit cell) type conduction type thin film is formed as a double layer. However, when the double-layered connecting material layer is formed of a thin film to improve the conduction performance, it may experience two types of performance deterioration as shown in FIG.

In the first case, if the concentration of oxygen supplied to the p-type conduction layer that is bonded to the cathode becomes small and enters a certain decomposition point 115 or less, the p-type conduction layer starts to be reduced from the interface 103, Which leads to a deterioration in the overall conductivity of the connecting material.

In the second case, if the concentration of hydrogen supplied to the n-type conduction layer connected to the anode of the adjacent unit cell becomes small, the inside of the n-type conduction layer is exposed to a relatively high oxygen partial pressure, The conductivity of the n-type conductive layer having the characteristic is reduced, and the conductive property of the entire conductive layer is lowered.

In the case of the double layer consisting of the conventional n-type conductive layer and the p-type conductive layer, resistance was increased as the concentration of supplied hydrogen was decreased as in Comparative Example 1, The stack structure may cause a sudden performance deterioration at the fuel outlet where the fuel concentration is low.

Another method is to use an amphoteric type of conductive material that exhibits conductivity both under oxidizing and reducing conditions. Unfortunately, these materials are extremely low in conductivity and should be used under very thin film conditions. In this thin film condition, It is structurally unstable and thus impossible to be practically applied.

A problem to be solved by the present invention is to provide a novel double-layered connecting layer capable of realizing constant and stable high conductivity irrespective of the concentration of oxygen supplied to the anode in which the connecting material is exposed or the concentration of hydrogen supplied to the anode, and a method for manufacturing the same. .

In order to solve the above problems,

An amphoteric perovskite conducting layer having conductivity in an oxidizing and reducing atmosphere; And

And a p-type perovskite conducting layer having conductivity in the oxidized region is bonded,

The amorphous perovskite conducting layer is in contact with the negative electrode of the unit cell,

And the p-type perovskite conductive layer is in contact with the anode of the unit cell.

The present invention, in one aspect,

1. A solid oxide fuel cell in which unit cells and electrical connecting materials are alternately stacked,

An amphoteric perovskite conducting layer having conductivity in an oxidizing and reducing atmosphere; And

And a p-type perovskite conducting layer having conductivity in the oxidized region is bonded,

The amorphous perovskite conducting layer is in contact with the negative electrode of the unit cell,

And the p-type perovskite conducting layer is in contact with the anode of the unit cell.

According to another aspect of the present invention,

The present invention relates to an amphoteric type perovskite material having conductivity both in an oxidizing and reducing atmosphere, comprising the steps of: forming a very thin thin film connecting material layer on a cathode side or a cathode exposed side; And a p-type perovskite material having conductivity only in the oxidized region is formed on the anode exposed surface or the anode surface side. Finally, the two connecting material layers and the cathode or anode exposed surface are jointed together with the dense film, And a method for manufacturing a unit cell using the same.

In the present invention, the perovskite material may be expressed as a metal oxide ceramic material as follows.

A _x A ' _1-x B _{1 -y} B' _y O ₃

Wherein A is a halide metal, A 'is an alkaline earth metal, B and B' are transition metals, wherein the metal halide is selected from La and Y, the alkaline earth metal is selected from Ca, Sr and Ba, The transition metals are selected from among Ti, V, Cr, Mn, Fe, Co, Ni and Cu.

In the preferred embodiment of the present invention, the connecting material layer formed on the cathode surface or the exposed surface of the negative electrode is selected from the group consisting of La as the lead metal A, Sr as the alkaline earth metal A, Sr as the transition metal, Ti as the transition metal, (La _x Sr _{1 - x} Ti _{1 - y} Mn _y O ₃ ), and the material exhibits conduction characteristics simultaneously in an oxidizing atmosphere and a reducing atmosphere.

A p-type layer to be bonded to the consolidated LSTM consolidated layers in a preferred embodiment of the present invention are La, A` by A in teugye perovskite material of the Sr, the transition metals of B is selected, only La Mn (LSM _x Sr _{1 - x} MnO ₃ , where x = 0.8) and exhibits excellent conduction properties in an oxidizing atmosphere.

In the present invention, the thickness of the cathode-side side amphoteric type layer constituting the double-layer connection material is coated to 50 μm or less, preferably 10 μm or less, and the thickness of the connection layer (p-type) Or less, preferably 50 m, more preferably 10 m or less.

In the practice of the present invention, it is possible to easily form the connecting material layer on the exposed surface of the porous cathode support or the anode support by a general wet coating method such as a dip coating method and a spray coating method The remaining connecting material layer is directly coated with spray coating or the like, and the sintering furnace of the double layer can be stably formed at a final temperature of about 1400 ° C.

In order to overcome the problem of lowering the conductivity in a low concentration hydrogen atmosphere of an n-type / p-type double-layer connection material used for connecting unit cells of a conventional solid oxide fuel cell stack, In the oxidation / reduction atmosphere, a conductive amphoteric-type material is thinly coated, and a conductive p-type having a high level is bonded only in an oxidizing atmosphere, so that it is structurally stabilized and a high pressure oxygen / low pressure hydrogen atmosphere, It is proposed to use a double-layered connecting material, which exhibits stable conductivity even in a hydrogen atmosphere, with a dense film. In the present invention, the double layer connection material has a hydrogen concentration of 97% to 2%, an oxygen concentration of 21% to 1% and an oxygen concentration of 800 Lt; RTI ID = 0.0 > C, < / RTI >

FIG. 1 is a graph showing oxygen partial pressure behavior formed in accordance with a change in oxygen concentration or hydrogen concentration in an oxidizing / reducing atmosphere in a double filler. FIG.
FIG. 2 is a graph showing a specific area resistance value according to a change in hydrogen concentration on a cathode surface or an oxygen concentration on a cathode surface using a double layer connection material developed by the present invention on a cathode support.
3 is a graph showing a specific area resistance value according to the oxygen concentration of the anode surface or the hydrogen concentration of the cathode surface using the double layer connection material of the conventional n-type conductive layer / p-type conductive layer conducted in Comparative Example 1

Hereinafter, the present invention will be described in detail with reference to examples. It should be noted that the following examples are not intended to limit the invention and are intended to illustrate the invention.

(Example 1)

In order to evaluate stable double-layered joints under the conditions of the oxidation / reduction atmosphere variation proposed in the present invention, a porous NiO-YSZ anode support was first prepared. First, NiTi (YT Baker) and YSZ (Y ₂ O ₃ stabilized ZrO _{2 ,} Tosho) were mixed at 55 wt.%: 45 wt.%, And graphite corresponding to 25 wt. The mixture was mixed with ethanol and zirconia balls and ball milling was performed for about 24 hours. After drying the obtained sample, an appropriate amount of powder was pressed using a press and sintered at 1200 ° C for 3 hours to form a button-like porous anode support.

In order to replace the double layer existing in the n-type conductive layer of the consolidated developed in the present invention _{LST (La 0. 4 Sr 0} . 6 TiO 3) a La (LSTM an appropriate amount of Mn is partially substituted for _0.4 Sr _0.6 Ti _0.6 Mn _0.4 O ₃ ), solid phase synthesis was used, and an equivalent ratio of La ₂ O ₃ (Sigma-aldrich, 99.99%), SrCO ₃ (Sigma-aldrich, 98%) , TiO 2 (Acros, 98%) and MnCO ₃ (Sigma-aldrich, 99.9%) were milled together with ethanol and zirconia balls for 24 hours, dried and heat treated at 1400 ° C for 3 hours, Milling was used to obtain a suitable size of powder, and dip coating was used as an example for dense film formation. For the preparation of the dip coating slurry, the synthesized LSTM powder is added to the organic solvent, the binder and various additives at a predetermined ratio, followed by ball milling. One surface of the sintered anode support was coated with a desired thickness through a dip coating method using the obtained slurry to form a 1st conductive layer. Since the thin film coating of the 2nd conductive layer was used for the p-type of _{LSM (La 0. 8 Sr 0} . 2 MnO 3, Fuel Cell Materials , Inc.) powder. In this case, organic solvents, binders and various additives were mixed in order to apply a coating using a spray method, and then uniformly coated on the 1st conductive layer through a spray device. The sintering furnace is heated at a rate of 2 ° C / min and finally sintered at 1400 ° C for about 3 hours. The sintered compact has a dense structure and a thickness of about 10 μm and a total thickness of about 20 μm The thickness of the double-layer connection material of the present invention can be formed.

The conductivity was measured using the double-layered connector of the present invention. The anode support surface is exposed to an atmosphere in which hydrogen gas is supplied (reducing atmosphere) and an anode surface of the p-type conductive layer (or second conductive layer) is exposed to an atmosphere (oxygen atmosphere) in which oxygen gas is supplied. Should not be mixed through complete sealing. The ASR (area specific resistance) value was measured by the DC 4-probe method. The temperature was maintained at 800 ° C for 24 hours. The concentrations of oxygen and hydrogen supplied to the oxidizing atmosphere and the reducing atmosphere were controlled through mixing with nitrogen gas, and the oxygen concentration in the oxidizing atmosphere was adjusted to 21% to 1% and the hydrogen concentration in the reducing atmosphere was adjusted to 97% to 2% . In experiments where the supplied oxygen concentration was changed, the opposite side of the hydrogen supply was maintained at a concentration of 97%. On the other hand, when the supplied hydrogen concentration was changed, the oxygen supply of the opposite side was maintained at 21%. As shown in the first figure, the oxygen concentration of the anode surface showed a constant conductivity value in the range of 21% to 1%. Also, as shown in the second figure, the specific area resistance was kept constant at 0.157 Ω cm 2 even though the hydrogen concentration was decreased from 97% to 2% under the condition that the anode surface was exposed to 21% oxygen.

(Comparative Example 1)

For the conventional n-type conduction layer structure, La _0.4 Sr _0.6 TiO ₃ (LST) material with n-type conductivity is synthesized by solid phase synthesis method. Equivalent ratio of La ₂ O ₃ (Sigma-aldrich, 99.99%), SrCO ₃ (Sigma-aldrich, 98%) and TiO ₂ (Acros, 98%) powder was milled together with ethanol and zirconia balls for 24 hours, dried and heat treated at 1400 ° C for 3 hours to form LST. Using the synthesized LST powder, a dense n-type 1st conductive layer thin film coating is coated on one side of the anode support by dip coating in the same manner as in Example 1. [ Then, the p-type second conductive layer was uniformly coated using the same spraying method as that of the LSM material in Example 1. The sintering furnace was heated at a rate of 2 ° C / min as in Example 1, and finally sintered at 1400 ° C for 3 hours to form a dense structure having a thickness of about 10 μm, Lt; RTI ID = 0.0 > 20 um. ≪ / RTI >

Conductivity measurement results As shown in FIG. 3, in the experiment of oxygen concentration change (21% ~ 1%), the conduction characteristics of the double layer connection material did not change much, which means that the concentration of oxygen decreases from 21% to 1% The oxygen partial pressure environment formed in the p-type conductive layer does not reach the decomposition point. The LSM material used as the p-type conduction layer has a constant conductivity in the range of 1 atm to 10 ^-8 atm, which means that even if the oxygen concentration is reduced from 21% to 1%, oxygen inside the LSM conduction layer It is considered that the partial pressure environment is still exposed to the environment of 10 ^-8 atm or more. On the other hand, in the experiment of hydrogen concentration change in the second figure, the resistance increases with the decrease of the hydrogen concentration, and the resistance increases abruptly at the concentration of 20%. This is because the inside of the first conductive layer is exposed to a relatively high oxygen partial pressure environment as the hydrogen concentration is reduced as shown in FIG. 1 and relatively oxidized from the interface 103. The LST material used as the n-type conductive layer generally exhibits low conductivity as the oxygen partial pressure is high, and as a result, the overall resistance value of the connection material increases. Therefore, the conventional n-type / p-type The double layer connection of the stack will inevitably have a decrease in the performance of the stack due to the increase in resistance at the outlet of the stack where the hydrogen concentration is decreased.

101: p-type conductive layer (2nd conductive layer)
102: an n-type conductive layer or an improved conductive layer (or 1st conductive layer)
103: Interface between bilayers
104: Cathode
105: Anode
111: 21% O ₂ / N ₂
112: 1% O ₂ / N ₂
113: 97% H ₂ / N ₂
114: 2% H ₂ / N ₂
115: decomposition oxygen partial pressure of the p-type conductive layer (LSM: 10 ^-8 atm)

Claims (9)

An amphoteric perovskite conducting layer having conductivity in an oxidizing and reducing atmosphere; And
And a p-type perovskite conducting layer having conductivity in an oxidizing atmosphere are bonded to each other,
The amorphous perovskite conducting layer is in contact with the negative electrode of the unit cell,
And the p-type perovskite conducting layer is in contact with the anode of the unit cell. 3. The method of claim 1, wherein the perovskite conductive layer is represented by the following formula:
A _x A ' _1-x B _y B' _{1 -y} O ₃
Wherein A is a halide metal, A 'is an alkaline earth metal, B and B' are transition metals,
The metal halide is selected from La and Y,
The alkaline earth metal is selected from Ca, Sr and Ba,
Wherein the transition metal is selected from Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The amorphous perovskite material according to claim 1, wherein the amorphous perovskite in contact with the cathode is La _x Sr _{1 - x} Ti _{1 - y} Mn _y O ₃ , wherein the values of x and y are 0.2-0.8,
Wherein the p-type perovskite in contact with the anode is La _x Sr _{1 - x} MnO ₃ , wherein the x value is 0.2-0.8. The double electrical connector according to claim 1, wherein the amorphous perovskite conductive layer and the p-type perovskite conductive layer each have a thickness of 10 mu m or less. The solid oxide fuel cell according to any one of claims 1 to 3, wherein the electric connection material and the unit cell are alternately laminated. In the production of a stack of solid oxide fuel cells,
The amorphous-type connecting material layer, which exhibits conductivity both in the oxidizing and reducing atmosphere, and the p-type connecting material layer, which exhibits conductivity only in the oxidizing atmosphere, are double-bonded to the stacked unit cells, and the negative electrode exposed surface The amphoteric-type connecting material layer, which exhibits conductivity both in the oxidizing and reducing atmosphere, is bonded, and the double-connecting material layer of the completed dense membrane is bonded to the anode exposed surface (in the case of the anode support) Wherein the unit cells are alternately stacked. The method according to claim 6, wherein the material of the anode side facing material layer and the cathode side facing material layer is represented by the following formula:
A _x A ' _1-x B _y B' _{1 -y} O ₃
Where A is a halide metal, A 'is an alkaline earth metal, B and B' are transition metals, wherein the metal halide is selected from La and Y, the alkaline earth metal is selected from Ca, Sr and Ba, V, Cr, Mn, Fe, Co, Ni and Cu. The positive electrode material according to claim 6 or 7, wherein the cathode side binder is a perovskite-based La _x Sr _1-x Ti _1-y Mn _y O ₃ wherein x and y are in the range of 0.2-0.8, Wherein the linking material is a perovskite-based La _x Sr _1-x MnO ₃ and the x value is 0.2-0.8. The method according to claim 6, wherein the thickness of the cathode side side amphoteric type coating layer is 10 μm or less and the thickness of the anode side p-type coating layer is 50 μm or less.

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