KR101637917B1 - Protonic conducting solid oxide fuel cell and method for preparing thereof - Google Patents

Abstract

The present invention relates to a proton-conducting solid oxide fuel cell and a method of manufacturing the proton-conducting solid oxide fuel cell. The proton-conductive solid oxide fuel cell includes a step of preparing a fuel electrode, a step of forming a yttrium-doped barium zirconate Forming a first electrolyte layer including a BZY solid oxide, forming a second electrolyte layer including a yttrium-doped barium sulfate based (BCY) solid oxide on the first electrolyte layer, , Sintering the fuel electrode, the first electrolyte layer and the second electrolyte layer at the same time, and forming the air electrode on the second electrolyte layer.

Description

Technical Field [0001] The present invention relates to a proton conducting solid oxide fuel cell and a method for preparing the same,

The present invention relates to a proton-conducting solid oxide fuel cell and a method of manufacturing the same.

The depletion of fossil fuels and rising prices, the environmental pollution caused by the combustion reaction of fossil fuels, the global warming problem, and the consequent climate change treaties are urgently required to develop fuel cells that produce clean energy.

The fuel cell is composed of an alkaline fuel cell (AFC) using an alkaline aqueous solution, a polymer electrolyte membrane fuel cell (PEMFC) using a polymer electrolyte, a phosphoric acid type using phosphoric acid as an electrolyte (MCFC), which uses molten carbonate as an electrolyte, and a solid oxide fuel cell (SOFC), which uses solid oxide as an electrolyte. ) Are usually divided into five. Of these, the fuel cells using liquid electrolyte are AFC, PAFC and MCFC, and the fuel cells using solid electrolyte are PEMFC and SOFC.

When a liquid electrolyte is used, a porous matrix capable of impregnating the electrolyte is required, and the amount of the electrolyte may be reduced with time due to corrosion of the material by the electrolyte and volatility of the electrolyte. When a solid electrolyte is used, the problems in the liquid electrolyte can be avoided. That is, a support for holding the electrolyte is not required, and there is no corrosion or volatility caused by the electrolyte, so that the decrease of the electrolyte does not occur. In addition, the advantage of the solid electrolyte is that the contact with the catalyst surface dispersed in the electrode can be easily controlled, thereby greatly increasing the performance.

There are two types of solid electrolytes that are currently being developed and used: hydrogen ion conductive polymer electrolytes and oxygen ion conductive oxides. Since the solid polymer electrolyte exhibits sufficient ion conductivity only when moisture is present therein, the solid polymer electrolyte is used at a temperature of 100 ° C or lower. The oxygen ion conductive solid oxide electrolyte exhibits sufficient ion conductivity at a high temperature of 600 ° C or higher, .

In the case of low operating temperature, the usable catalyst has a disadvantage that it is limited to noble metal of platinum system. In case that the operating temperature is high, usable materials are limited to expensive ceramics and disadvantages such as stack instability due to thermal stress .

Korean Patent Publication No. 10-2007-0037254

Therefore, in order to promote commercialization of a high performance fuel cell, it is necessary to develop a solid electrolyte capable of overcoming the problems of the liquid electrolyte and solving problems at low and high temperature operating temperatures. .

The present invention provides a method for producing a hydrogen-ion conductive solid oxide fuel cell, comprising the steps of:

1) preparing a fuel electrode,

2) forming a first electrolyte layer including yttrium-doped barium zirconate (BZY) solid oxide on the anode,

3) forming a second electrolyte layer including a yttrium doped barium cerate (BCY) solid oxide on the first electrolyte layer,

4) simultaneously sintering the fuel electrode, the first electrolyte layer and the second electrolyte layer to produce a semi-conductive paper,

5) forming an air electrode on the second electrolyte layer.

The present invention also provides a proton-conducting solid oxide fuel cell comprising a fuel electrode, an electrolyte layer and an air electrode, wherein the electrolyte layer comprises a solid oxide represented by the following formula 3, And the Ce / Zr ratio has a continuous gradient in the thickness direction.

(3)

Ba (Zr _{1 -x- y} Ce _y Y _x ) O _{3 -?}

In the above formula 3, x is 0 < x? 0.2, y is 0 < y? 0.8, and 0 is 0 <

The present invention also provides a proton-conducting solid oxide fuel cell comprising a fuel electrode, an electrolyte layer and an air electrode.

Wherein the electrolyte layer comprises two or more electrolyte layers comprising different solid oxides, wherein the solid oxide is selected from the group consisting of yttrium doped barium zirconate (BZY) solid oxide, yttrium doped barium sulfate a yttrium doped barium cerate (BCY) solid oxide and a solid oxide represented by the above formula (3).

The electrolyte of the conventional hydrogen ion conductive solid oxide fuel cell has been dependent on BZY, BZCY or BCY single phase. The BZY electrolyte has a low sintering property and low fronton conductivity, but has very excellent chemical stability. As the Ce / Zr ratio of the electrolyte increases compared to the BZY electrolyte, the Pronton conductivity tends to increase but still has a disadvantage of low sinterability. On the other hand, BCY electrolytes have high proton conductivity and good sinterability but have poor chemical stability.

According to the present invention, it is possible to form a BZCY electrolyte having a single solid solution composition by simultaneously sintering a half-cell including a BZY-BCY double-layer electrolyte, or to form a double layer such as BZY-BCY, BZCY- BCY, BZY-BZCY, BZY-BZCY- It is possible to provide a proton conductive solid oxide fuel cell including a triple layer electrolyte, and it is possible to improve the chemical stability and the sinterability while having an excellent hydrogen ion conductivity.

Further, according to the present invention, it is possible to form a BZCY electrolyte having a composition gradient in which both end portions of the electrolyte in contact with the fuel electrode and the air electrode are continuously changed from Zr-rich to Ce-rich, It is possible to form a single phase solid solution BZCY electrolyte having a constant Ce / Zr composition ratio.

Therefore, even when operating with fuel such as syngas, CO ₂ The stability of the electrolyte for H ₂ O can be maintained to maintain the long-term stability of the fuel cell. By lowering the polarization resistance of the air electrode through the Ce-rich BZCY electrolyte in contact with the air electrode having high hydrogen ion conductivity, Can be improved.

1 is a conceptual diagram schematically showing the pseudo-symmetric sintering shrinkage behavior of the proton-conducting solid oxide fuel cell of the present invention.
FIG. 2 is a graph plotting optimization (temperature and time) of co-firing process conditions in a method of manufacturing a proton-conductive solid oxide fuel cell according to the present invention.
FIG. 3A and FIG. 3B are the results of performance evaluation of a hydrogen ion conductive solid oxide fuel cell manufactured by making the ratio of the lower electrolyte layer (BZY) to the upper electrolyte layer (BCY) 1: 2 according to an embodiment of the present invention .
4A and 4B are graphs showing performance evaluations of a hydrogen ion-conducting solid oxide fuel cell manufactured with a ratio of a lower electrolyte layer (BZY) to an upper electrolyte layer (BCY) of 2: 1 according to an embodiment of the present invention .
5A to 5F are SEM images showing an electrolyte layer manufactured according to an embodiment of the present invention.
6A to 6C are SEM images showing the surface of the upper electrolyte layer BCY after the heat treatment process according to an embodiment of the present invention.
FIG. 7 is a graph showing the results of confirming electrolyte layer components when the ratio of the lower electrolyte layer (BZY) to the upper electrolyte layer (BCY) is 1: 1 according to an embodiment of the present invention.
FIG. 8 is a graph showing the results of confirming electrolyte layer components when the ratio of the lower electrolyte layer (BZY) to the upper electrolyte layer (BCY) is 1: 3 according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail.

A future type of fuel cell that can be realized from the viewpoint of developing a high performance fuel cell is a hydrogen ion conductive solid oxide fuel cell (PCFC). PCFC is a fuel cell which is expected to be able to overcome the disadvantages of conventional solid polymer electrolytes and solid oxide electrolytes at a middle temperature of 100-600 ° C since there is no disadvantage of liquid electrolyte because it uses solid electrolyte.

The electrolyte used in the proton conductive solid oxide fuel cell is mainly composed of yttrium doped barium zirconate (BZY), yttrium doped barium cerate (BCY) Chain BZCY are the most commonly used. The BZY generally has about 10 times lower hydrogen ion conductivity than BCY, but CO ₂ It has excellent chemical stability to gas.

In order to improve the hydrogen ion conductivity of BZY, the solid solution of Zr of BZY substituted with Ce has been actively researched and developed. As a result, BZCY, which has excellent hydrogen ion conductivity and secures chemical stability against CO ₂ gas, High possibility is recognized. The hydrogen ion conductivity of the BZCY tends to increase almost linearly as the Ce / Zr ratio increases. Most of the BZCY powders were prepared by solid phase reaction or solution coprecipitation method, but the calcination temperature for obtaining the crystal phase is high, but the sintering temperature for forming the electrolyte is also very high.

The electrolyte of the conventional hydrogen ion conductive solid oxide fuel cell has been dependent on BZY, BZCY or BCY single phase. The BZY electrolyte has a low sintering property and low fronton conductivity, but has very excellent chemical stability. As the Ce / Zr ratio of the electrolyte increases compared to the BZY electrolyte, the Pronton conductivity tends to increase but still has a disadvantage of low sinterability. On the other hand, BCY electrolytes have high proton conductivity and good sinterability but have poor chemical stability.

Accordingly, the present inventors have studied a method capable of improving chemical stability and sinterability with excellent proton conductivity, and completed the present invention.

The method for producing a proton conductive solid oxide fuel cell according to the present invention includes the steps of 1) preparing a fuel electrode, 2) forming a yttrium-doped barium zirconate (BZY) solid oxide on the anode, 3) forming a second electrolyte layer comprising a yttrium doped barium cerate (BCY) solid oxide on the first electrolyte layer, 4) forming a second electrolyte layer on the first electrolyte layer, Sintering the anode, the first electrolyte layer, and the second electrolyte layer simultaneously to form a half-cell; and 5) forming an air electrode on the second electrolyte layer.

In the present invention, the step 1) may include the steps of forming a fuel electrode substrate and forming an anode functional layer on the anode substrate.

In the present invention, the anode substrate should serve as a support for a multi-layered unit cell, so that it must have mechanical properties and satisfy electrochemical properties for oxidation reaction of the fuel. In addition, electrical conductivity and gas permeability should be excellent.

The mechanical properties of the anode may be such that the strength of the substrate itself as well as the thermal expansion coefficient of the electrolyte membrane on the substrate can be matched with each other so as to prevent the occurrence of defects during a thermal cycle during the manufacturing process or operation. The fuel electrode can not only use a simple metal material as a fuel electrode because it plays a role not only as a carrier to extract electricity but also to enable the oxidation reaction of fuel at the fuel electrode. In order to activate the oxidation reaction of the fuel, not only the active catalyst component should be included in the anode but also the concentration of the active reaction point must be maintained high in the anode. Further, since the fuel electrode substrate smoothly supplies the fuel to the reaction point where the electrochemical reaction of the fuel occurs, the oxidized hydrogen ions in the fuel electrode go to the air electrode through the electrolyte and react with the oxygen ions reduced in the air electrode to generate water. It should have a porous structure containing pores as passages for facilitating the movement of the product.

In order to simultaneously satisfy these properties, the anode substrate mainly uses a metal complex having an electrochemical activity with an ion conductive oxide and an excellent electron conductivity, wherein the composition of the oxide-metal complex is controlled to adjust the mechanical strength and the thermal expansion coefficient, In addition, the composition is adjusted so that the combination of the electrical conductivity and the gas permeability, which are opposite physical properties, is optimized. Also, the porosity of the composite is determined in consideration of mechanical properties and gas permeability, and the active reaction point of the fuel should be adjusted to the maximum in the allowable porosity range.

A preferred anode composition in the present invention comprises a transition metal and a hydrogen ion conductor, wherein the transition metal has catalytic activity for the fuel and electron conductivity, and the hydrogen ion conductor has ion conductivity as an oxide.

In the present invention, the composition of the anode substrate as a support is determined as follows according to requirements. In the initial configuration of the anode substrate (and the anode function layer described later), NiO in the form of an oxide and BZY in the form of an ion conductive oxide form a composite body, and Ni- do. Also, according to an embodiment of the present invention, the structure of the anode substrate may be a composite of BZYCu and NiO in which a part of Zr is substituted with Cu in BZY.

In the present invention, the raw material composition of the fuel electrode substrate has a volume ratio of NiO to BZY in the range of 70-50: 50-30, preferably 65-55: 45-35. At this time, if NiO is too much, the ability to transfer ions to the electrolyte may be deteriorated. If too little NiO is present, there is a problem in that it is insufficient as a catalyst for oxidizing the fuel.

The average particle size ratio of BZY and NiO powder may be 10: 1 to 5: 1. This is to smoothly supply the fuel through the pores of the anode after the final cell is manufactured.

In order to maintain the mechanical strength of the single cell support, the volume fraction of BZY, which is an oxide component, can be adjusted in the range of from 40% to 70% relative to Ni, which is a metal component after reduction. In this case, as the volume fraction of the oxide component increases, the mechanical strength increases and the coefficient of thermal expansion between the electrolyte layers becomes similar. Preferably, the volume fraction of the metal: ion conductive oxide in the reduced state is 55-65: 35-45. In order to obtain the electrical conductivity value (100 S / cm level at the operating temperature) of the anode, the higher the volume fraction of the metal component is, the more the glass component is. However, the volume fraction of the metal phase in the Ni- Or less. At this time, the composition should be such that the volume fraction of the metal phase is as low as possible and the electrical conductivity can be maintained, so that the desired thermomechanical properties of the fuel electrode substrate can be secured and the electrical conductivity value required for the fuel electrode substrate can be reduced by up to 30% can do.

The metal component may be a transition metal having a catalytic activity such as Cu, Co, Fe, etc. in addition to Ni. The particle size of the metal component may be 1-5 μm, and preferably, the average particle size ratio of the transition metal oxide to the fine powder is 1: 10 to 1: 5.

The fuel electrode substrate may be formed by a screen printing process or a tape casting process using a slurry for manufacturing the fuel electrode substrate.

The slurry for preparing the fuel electrode substrate may further include a pore precursor. The pore precursor may form pores in the anode substrate after sintering to promote gas movement. Specific examples of the pore precursor include, but are not limited to, polymethyl methacrylate (PMMA) and the like.

The fuel electrode substrate preferably has a porosity of 25 to 50% for smooth fuel supply.

In addition, the slurry for producing the fuel electrode substrate may further include at least one of a solvent, a dispersant, a plasticizer, a binder, and the like.

The solvent, the dispersant, the plasticizer and the binder may be materials known in the art and are not particularly limited.

The amount of the dispersing agent may vary depending on the particle size, and may be generally in the range of 2-3% by weight of the powder.

In order to more effectively disperse and mix the binder, a solid binder may be dissolved in a part of a solvent and then added in a liquid phase.

The thickness of the fuel electrode substrate may be 600-1,000 mu m, but the thickness of the fuel electrode substrate is preferably such that the upper and lower electrodes can withstand the pressure externally applied to the interconnector Only the thickness having the mechanical strength of the film is required.

In the present invention, the anode function layer plays an important role in expanding the triple phase boundary occupying the reaction area of most of the fuel cell of the present invention. The three-phase interface refers to a region in which the reaction is most actively generated between the fuel electrode and the electrolyte. Therefore, in order to further expand the three-phase interface, a functional layer is coated between the anode substrate and the electrolyte layer to widen the reaction area between the anode substrate and the electrolyte layer. The anode functional layer expands the three phase interface to promote the electrochemical reaction, prevents the electrolyte layer from being sucked into the vacant space of the pore precursor in the subsequent electrolyte process, and free sintering the upper electrolyte at the pore precursor site. Thereby ensuring uniformity of sintering behavior of the electrolyte layer, thereby ensuring interfacial stability.

The anode functional layer may include NiO and BZY as well as the anode substrate described above.

Unlike the anode substrate, the anode functional layer has the main purpose of improving the mechanical properties of the anode, which can change the mechanical properties of the anode functional layer depending on the particle size characteristics of the ion conductive oxide.

In the present invention, as the ion conductive oxide, a core particle having an average particle size ratio of 5-9: 1-1.5 and a nano particle can be mixed and used. When only fine powder is used, the mechanical strength of the anode functional layer is high, but the sintering shrinkage ratio of the anode functional layer is too high compared to the electrolyte layer under the high volume fraction condition, and defects may occur during the anode / electrolyte layer simultaneous sintering process. On the other hand, when only the coarse powder is used, the strength of the functional layer of the anode function becomes too low, and a problem of generating a porosity higher than necessary arises. Therefore, when the coarse powder having a low degree of sintering and the fine powder having a high degree of sintering are appropriately mixed, it is possible to meet the required mechanical properties. In the present invention, the mixing ratio of the coarse powder and the fine powder can be adjusted in the range of about 7: 3 to about 5: 5. Simultaneous sintering of the anode and the electrolyte layer is facilitated when the mixing ratio is close to 7: 3. When the mixing ratio is close to 5: 5, it is easy to make the thickness to 15 to 5 탆 according to the contraction ratio of the anode function layer. The preferable volume fraction of the coarse powder to the fine powder of the ion conductive oxide of the anode functional layer is 55: 45 - 45: 55.

The thickness of the anode function layer may be 1-20 [mu] m, but is not limited thereto.

In the present invention, the step 2) is a step of forming a first electrolyte layer including a yttrium-doped barium zirconate (BZY) solid oxide on a fuel electrode.

The yttrium-doped barium zirconate (BZY) solid oxide may be represented by the following formula (1).

[Chemical Formula 1]

Ba (Zr _{1 - x} Y _x ) O _{3 -?}

In the above formula (1), x is 0 < x? 0.2 and? Is 0 <

In the present invention, step 3) is a step of forming a second electrolyte layer including a yttrium-doped barium cerate (BCY) solid oxide on the first electrolyte layer to produce a semi-conductive paper.

The yttrium-doped barium cerate (BCY) solid oxide may be represented by the following formula (2).

(2)

Ba (Ce _{1 - x} Y _x ) O _{3 -?}

In the above formula (2), x is 0 < x? 0.2 and? Is 0 <

In the present invention, it is preferable that the thickness ratio of the first electrolyte layer: the second electrolyte layer is 1: 1-3 and the thickness of the second electrolyte layer is larger than the thickness of the first electrolyte layer. The thicknesses of the first electrolyte layer and the second electrolyte layer may independently be 4-10 탆.

In the present invention, the fuel electrode, the first electrolyte layer, and the second electrolyte layer may be formed by a screen printing process, respectively.

Each of the anode, the first electrolyte layer, and the second electrolyte layer is formed as a separate film by a tape casting process, and the individual films are laminated by a warm isostatic pressing method, Can be manufactured.

In the present invention, the step 4) is a step of simultaneously sintering the fuel electrode, the first electrolyte layer and the second electrolyte layer.

In the present invention, in order to densely sinter a BZY or BZCY electrolyte layer having a relatively slow sintering speed compared to a fuel electrode having a BZY-NiO or BZCY-NiO composition, if a double layer electrolyte having a BCY electrolyte layer thereon is used, And the shrinkage behavior is shown, so that a dense electrolyte can be obtained.

The pseudo-symmetric sintering shrinkage behavior is schematically shown in FIG.

That is, the sintering shrinkage ratio of the second electrolyte layer including the anode and the BCY is similar to improve the symmetry of the sintering shrinkage as a whole, thereby improving the flatness of the reverse electrode.

According to the present invention, when the BZY-BCY bilayer electrolyte having a bilayer structure is subjected to a sintering process at a temperature of 1,300-1,500 ° C. for 1-5 hours, the Ce / Zr ratio in the electrolyte layer has a continuous concentration gradient in the thickness direction A BZCY electrolyte layer can be formed. More specifically, the Ce ion diffused from the second electrolyte layer containing BCY can improve hydrogen ion conductivity while moving the solid solution composition to Ce-rich composition while substituting Zr ions of BZY of the first electrolyte layer, The densification of the first electrolyte layer including the slow BZY can be promoted.

By the above-described sintering process, by forming the electrolyte layer BZCY the Ce content of the high CO ₂ contained in the while having excellent proton conductivity than the electrolyte layer, the fuel gas BZY And an electrolyte layer excellent in chemical resistance to H ₂ O can be formed. In addition, in the sintering process, the Zr ions diffuse to the surface of the air electrode, and the Ce ions diffuse toward the anode, and the Ce / Zr ratio increases continuously from the anode toward the cathode. While the chemical stability is enhanced by the effect of high Zr, the composition of the electrolyte layer on the air electrode side is relatively high in the content of Ce, thereby lowering the polarization resistance of the air electrode.

In the present invention, the step 5) is a step of forming an air electrode on the second electrolyte layer.

The air electrode is mainly composed of a material having an ionic conductivity and a material of an air electrode, as in a fuel electrode. In this case, an oxide-oxide complex should be used instead of a metal-oxide composite.

The most typical cathode composition is a complex between the ion conductive oxide applied to the electrolyte and the electron conductive oxide of the air electrode. In this case, the ratio between the ion conductor and the electron conductor should be controlled so that the concentration of the active reaction point necessary for the electrochemical reaction in the air electrode is maximized, and the composition should be controlled so as to have excellent interfacial bonding with the electrolyte. In addition, the composition should be determined so as to buffer the discrepancy in the physical and chemical properties between the air electrode and the electrolyte.

A composite between BZCY and LSCF (La _{0 .6} Sr _{0 .4} Co _{0 .2} Fe _{0 .8} O ₃ ), an electron conductive oxide as an air electrode material, as a material having good electron conductivity, catalytic role and ionic conductivity for the oxygen gas Can be applied. LSCF addition _{PrBaCuFeO 5, Ba 0.5 Sr 0.5 Co} 0.2 Fe 0.8 O 3, Sm 0 .5 Sr 0 .5 CoO 3, Ba 0 .5 Pr 0 .5 CoO 3, La 0 .5 Sr 0 .5 CoO 3, La _{0 .6} Ba _{0 .4} may be used _{CoO 3, La 0.7 Sr 0.3 FeO} 3 or the like.

The average particle size ratio of the electron conductive oxide and the ion conductive oxide may be 2: 1 - 3: 1. The characteristics of the raw material powder may be an average particle size of powder of 200-300 nm in the case of LSCF and a fine powder of 100-150 nm in average particle size used in the case of BZCY as an electrolyte.

In the case of the air electrode, the mixing ratio of LSCF and BZCY is in the range of 30:70 to 70:30 by weight. As with the anode function layer, the advantages and disadvantages are given according to the mixing ratio. The closer the mixing ratio of LSCF and BZCY is to 30: 70, the better the bonding between the electrolyte and the air electrode, Is reduced. On the other hand, as the mixing weight ratio is closer to 70: 30, the electrical conductivity and the electrochemical activity of the air electrode are increased, thereby reducing the active polarization loss in the air electrode. On the other hand, the porosity of the air electrode is 20-25% lower as the mixing ratio of LSCF and BZCY becomes closer to 30: 70, and the porosity becomes higher as 70: 30, which is up to 40%. However, since the air electrode is formed with a thickness of 20 to 40 탆, the porosity does not need to be high, and the optimum air electrode composition is 55: 45 - 45: 55.

In the present invention, it is preferable that the air electrode is formed so as to be surrounded by the center portion of the tubular electrolyte membrane for performance measurement.

Also, in the case of the air electrode, unlike in the case of the fuel electrode, the thickness is not so large, so that the restriction on the porosity is not large, and the preferable porosity is 30-35%. However, since the activity of the oxide electrode is not so high as compared with that of the metal electrode, and smooth gas supply to the air electrode is performed, polarization loss in the air electrode can be minimized, so that the microstructure of the air electrode itself needs to be controlled.

Also, the hydrogen-ion conductive solid oxide fuel cell according to an embodiment of the present invention includes a fuel electrode, an electrolyte layer, and an air electrode, wherein the electrolyte layer includes a solid oxide represented by the following Formula 3, And the Ce / Zr ratio has a continuous gradient in the thickness direction.

(3)

Ba (Zr _{1 -x- y} Ce _y Y _x ) O _{3 -?}

In the above formula 3, x is 0 < x? 0.2, y is 0 < y? 0.8, and 0 is 0 <

In the present invention, the solid oxide represented by the above formula (3) will be referred to as BZCY.

In the present invention, the Ce / Zr ratio in the electrolyte layer may continuously increase toward the air electrode in the thickness direction.

According to another aspect of the present invention, there is provided a hydrogen-ion conducting solid oxide fuel cell including a fuel electrode, an electrolyte layer, and an air electrode, wherein the electrolyte layer includes two or more electrolyte layers containing different solid oxides, The solid oxide is selected from the group consisting of a yttrium doped barium zirconate (BZY) solid oxide, a yttrium doped barium cerate (BCY) solid oxide, and a solid oxide represented by the above formula &Lt; / RTI &gt;

In the present invention, it is preferable that the electrolyte layer has a double-layer structure including an electrolyte layer including a BZY solid oxide and an electrolyte layer including a BCY solid oxide, an electrolyte layer including a BZY solid oxide, and a solid Layer structure including a double layer structure including an electrolyte layer containing an oxide, or an electrolyte layer including a solid oxide represented by the above formula (3) and an electrolyte layer comprising a BCY solid oxide. Also, the electrolyte layer may be a triple layer structure including an electrolyte layer including a BZY solid oxide, an electrolyte layer including a solid oxide represented by Formula 3, and an electrolyte layer including a BCY solid oxide.

The electrolyte of the conventional hydrogen ion conductive solid oxide fuel cell has been dependent on BZY, BZCY or BCY single phase. The BZY electrolyte has a low sintering property and low fronton conductivity, but has very excellent chemical stability. As the Ce / Zr ratio of the electrolyte increases compared to the BZY electrolyte, the Pronton conductivity tends to increase but still has a disadvantage of low sinterability. On the other hand, BCY electrolytes have high proton conductivity and good sinterability but have poor chemical stability.

According to the present invention, it is possible to form a BZCY electrolyte having a single solid solution composition by simultaneously sintering a half-cell including a BZY-BCY double-layer electrolyte, or to form a double layer such as BZY-BCY, BZCY- BCY, BZY-BZCY, BZY-BZCY- It is possible to provide a proton conductive solid oxide fuel cell including a triple layer electrolyte, and it is possible to improve the chemical stability and the sinterability while having an excellent hydrogen ion conductivity.

Further, according to the present invention, it is possible to form a BZCY electrolyte having a composition gradient in which both end portions of the electrolyte in contact with the fuel electrode and the air electrode are continuously changed from Zr-rich to Ce-rich, It is possible to form a single phase solid solution BZCY electrolyte having a constant Ce / Zr composition ratio.

Therefore, even when operating with fuel such as syngas, CO ₂ The stability of the electrolyte for H ₂ O can be maintained to maintain the long-term stability of the fuel cell. By lowering the polarization resistance of the air electrode through the Ce-rich BZCY electrolyte in contact with the air electrode having high hydrogen ion conductivity, Can be improved.

Hereinafter, preferred embodiments of the present invention will be described in order to explain the present invention in more detail. The following examples are only illustrative of the present invention, and the scope of the present invention and its effects are not limited by the following description, which is obvious to those skilled in the art.

< Example >

One) Anode  Fabrication of Substrate

An anode substrate was prepared using the slurry composition shown in [Table 1] below.

During the preparation of the slurry for preparing the anode substrate, BZY having a relatively small particle size was first ball-milled for 8 hours to release coagulation. NiO powder was added to the coagulated BZY, and after mixing for 8 hours, the pore precursor (PMMA) was added and milling was further performed for 8 hours. At this time, the solvent was mixed with ethanol and toluene in a ratio of 6: 4 to form an azeotrope, and 2.45 wt% of the dispersant was added to the powder. The NiO powder had a size of d50 = 1 占 퐉, the BZY powder had d50 = 0.3 占 퐉, and the pore precursor (PMMA) had a size of d50 = 3 占 퐉. After milling for 24 hours, plasticizer was added and mixed for 2 hours. After thorough mixing, the binder was added. At this time, in order to prevent aggregation of the binder, the mixture was divided into three portions at intervals of 2 hours at a ratio of 50: 30: 20, followed by sufficient mixing for 24 hours.

The slurry and ball for fuel electrode substrate were thoroughly mixed using a screen, and the separated slurry was deaerated for about 10 minutes and deaired for 8 hours or more through co-milling at low speed. The air-removed slurry was cast in a tape casting machine at a rate of 15 cm / min to a thickness of about 200-300 μm and air-dried.

Fuel electrode substrate Slurry composition Content (g) NiO 50.8 BZY 42.0 Pore precursor (PMMA) 7.2 ethanol 36.7 toluene 27.2 Dispersant 2.45 Plasticizer 9 bookbinder 9

2) Anode Functional layer  Produce

The anode functional layer was prepared using the slurry composition shown in Table 2 below.

NiO powder was added to BZY and mixed and milled for 8 hours. At this time, ethanol was used as the solvent and 2.45 wt% of the dispersing agent was added to the powder. After milling for 8 hours, plasticizer was added and mixed for 2 hours. After thorough mixing, the binder was added. At this time, in order to prevent aggregation of the binder, the mixture was divided into three portions at intervals of 2 hours at a ratio of 50: 30: 20, followed by sufficient mixing for 14 hours.

The slurry and the ball for the fuel electrode functional layer sufficiently mixed were separated using a screen. The separated low viscosity slurry was stirred with a hot plate and the solvent was evaporated. After defoaming for 5 minutes at the viscosity just before the coagulation of the binder, the mixture was cast to a thickness of about 10-20 탆 at a rate of 15 cm / min using a comma coat, followed by natural drying.

Anode function layer Slurry composition Content (g) NiO 54.7 BZY 45.3 ethanol 100 Dispersant 2.45 Plasticizer 9 bookbinder 10

3) Lower Of the electrolyte layer  Produce

A lower electrolyte layer was prepared using the slurry composition shown in [Table 3] below.

Ethanol and dispersant were added to BZY and milled. At this time, 2.45 wt% of dispersant was added to the powder. After milling for 16 hours, plasticizer was added and mixed for 2 hours. After thorough mixing, the binder was added. At this time, in order to prevent aggregation of the binder, the mixture was divided into three portions at intervals of 2 hours at a ratio of 50: 30: 20, followed by sufficient mixing for 14 hours.

The slurry for the lower electrolyte layer and the ball were thoroughly mixed using a sieve. The separated low viscosity slurry was stirred with a hot plate and the solvent was evaporated. The binder was degassed for 5 minutes at the viscosity immediately before agglomeration, cast using a comma coat at a speed of 15 cm / min to a thickness of about 4-10 μm, and air-dried.

The lower electrolyte layer Slurry composition Content (g) BZY 100 ethanol 100 Dispersant 2.45 Plasticizer 9 bookbinder 10

3) Top Of the electrolyte layer  Produce

A lower electrolyte layer was prepared using the slurry composition shown in Table 4 below.

The BCY was milled with ethanol and a dispersant. At this time, 2.45 wt% of dispersant was added to the powder. After milling for 16 hours, plasticizer was added and mixed for 2 hours. After thorough mixing, the binder was added. At this time, in order to prevent aggregation of the binder, the mixture was divided into three portions at intervals of 2 hours at a ratio of 50: 30: 20, followed by sufficient mixing for 14 hours.

The prepared slurry was tape casted and dried to prepare an upper electrolyte layer.

The upper electrolyte layer Slurry composition Content (g) BCY 100 ethanol 100 Dispersant 2.45 Plasticizer 9 bookbinder 10

4) Lamination  fair

The prepared anode substrate, the anode functional layer, the lower electrolyte layer, and the upper electrolyte layer were laminated through a warm isostatic pressing (WIP) method so as to have a sequential structure.

The anode substrate was laminated at a temperature of 80 캜 for about 10-15 minutes at a pressure of 5 MPa per unit area. At this time, lamination was performed using a closed frame so that the total thickness was 600-1,000 mu m.

The anode functional layer and the lower electrolyte layer were laminated. The temperature and time were the same as in the lamination of the anode substrate, and the pressure was applied at a load of 100 MPa per unit area.

A stacked body of the anode functional layer and the lower electrolyte layer was laminated on the anode substrate. At this time, the temperature and time were the same as the lamination of the anode substrate, and the pressure was applied at a load of 4 MPa per unit area.

Thereafter, the upper electrolyte layer was laminated for about 20 minutes under a load of 4 MPa at a temperature of 80 캜.

5) Sintering process

In order to remove organic matters such as a dispersant, a plasticizer, and a binder, heat treatment was performed with a schedule as shown in FIG.

More specifically, holding at 200 ° C and 600 ° C to remove plasticizers, dispersants and binders, the shrinkage behavior of BCY starts at around 1,150 ° C, so that the occurrence of peeling or microcracking between the BZY interface and the anode functional layer In order to minimize the spalling defects, the holding time was set so that the shrinkage occurred gradually. Next, the shrinkage behavior of BZY starts around the temperature of 1,250 ° C. By putting the holding time at the temperature near the start of the shrinkage behavior as in BYC, stress between the lower anode function layer and the upper BYC electrolyte layer can be minimized.

Since the BZY of the lower electrolyte layer can not reach the full density at a temperature of 1,375 ° C., the BZY of the lower electrolyte layer is used to promote densification by using the compressive stresses of the upper layer BYC and the lower layer NiO- I gave the holding time. In addition, annealing was performed to minimize micro cracks and thermal shock due to the difference in thermal expansion coefficient between the interfaces at the time of cooling.

6) Production of unit cell

An air electrode was screen-printed on the sintered laminate, and then heat-treated to prepare a proton-conductive solid oxide fuel cell including an electrolyte layer according to the present invention.

Experimental Example  One.

5A to 5F are SEM images showing the electrolyte layer manufactured according to the above embodiment, and it can be seen that the electrolyte layer has a uniform density. This is because the upper and lower layers (the upper electrolyte layer and the anode layer) of the lower electrolyte layer BZY are formed by screen printing the upper electrolyte layer BCY having good sinterability above the lower electrolyte layer BZY having a small sintering property, By applying a constrain to the lower electrolyte layer (BZY), the sinterability is promoted, and as a result, the electrolyte layer has an even higher density.

6A to 6C are SEM images showing the surface of the upper electrolyte layer BCY after the heat treatment step. It can be seen that the surface of the BCY layer is uniformly grown on the entire surface, and it can be seen that there is no phenol phenomenon.

Experimental Example  2.

In order to investigate the characteristics of the electrolyte layer alone, the anode and the cathode were maintained in the same composition and thickness, and the performance was evaluated by varying the ratio of the electrolyte layer only.

Figs. 3A and 3B show the performance evaluation results when the ratio of BZY: BCY is 1: 2, and Figs. 4A and 4B show the performance evaluation results when the ratio of BZY: BCY is 2: 1.

When the ratio of BZY: BCY is 1: 2 and 2: 1, the power density (power density (mW / ㎠) of 501 at a temperature of 650 for 1: 2 is 336 Of power density (mW / ㎠). When comparing the overall power density (mW / ㎠) by temperature range, it can be seen that BZY: BCY ratio is much higher at 1: 2 in all temperature ranges. That is, the power density (mW / cm2) as well as the current density (mA / cm2) are 1: 2 higher.

It can be seen that the Ohmic resistance of each electrolyte layer does not differ greatly with the change of temperature, and the Ohmic resistance is smaller at the ratio of 1: 2 thick BCY layer which is superior in proton conductor. The overall resistance also shows that the ratio of BZY: BCY is smaller at 1: 2.

Experimental Example  3.

FIG. 7 is a graph showing the electrolyte layer composition when the thickness ratio of the BZY layer and the BCY layer is 1: 1. The amount of Ce on the cathode side decreases as the anode direction increases Able to know.

On the contrary, the amount of Zr decreases inversely. In this case, it can be seen that Ce and Zr are substituted with each other in accordance with the difference in thickness ratio (1: 1) between the BZY layer and the BCY layer to form a whole structure in a gradient type. The electrolyte in the functional layer of the anode has a structure in which the Zr is rich, thereby maximizing the stability in the reducing atmosphere, and the electrolyte in the air electrode is rich in Ce to maximize the performance.

FIG. 8 is a graph showing the electrolyte layer composition when the thickness ratio of the BZY layer and the BCY layer is 1: 3. The total thickness of the electrolyte is less than 10 micrometers, and the BCY layer accounts for most of the electrolyte . In this case, the electrolytic BZY on the anode side, which is a reducing atmosphere, also has a gradient type electrolyte structure, which enhances the high resistance to the reduction and the BCY layer on the air electrode side maximizes the performance.

Claims (15)

1) preparing a fuel electrode;
2) forming a first electrolyte layer including yttrium-doped barium zirconate (BZY) solid oxide on the anode;
3) forming a second electrolyte layer including a yttrium-doped barium cerate (BCY) solid oxide on the first electrolyte layer;
4) The anode, the first electrolyte layer and the second electrolyte layer are simultaneously sintered at 1,300-1,500 ° C for 1-5 hours to form an electrolyte layer containing a solid oxide represented by the following formula ; And
5) forming an air electrode on an electrolyte layer containing a solid oxide represented by the above formula 3,
The Ce / Zr ratio in the electrolyte layer containing the solid oxide represented by the above formula 3 continuously increases in the thickness direction toward the air electrode,
The thickness ratio of the first electrolyte layer to the second electrolyte layer is 1: 1-3,
Wherein the thickness of the first electrolyte layer and the thickness of the second electrolyte layer are independently 4-10 탆.
(3)
Ba (Zr _{1-x y} Ce _y Y _x ) O _3-隆
In the above formula 3,
x is 0 < x? 0.2, y is 0 < y? 0.2, and? is 0 < The method according to claim 1,
The step 1) may include forming a fuel electrode substrate; And forming a fuel electrode functional layer on the fuel electrode substrate. &Lt; Desc / Clms Page number 20 &gt; 3. The method of claim 2,
Wherein the fuel electrode substrate and the anode functional layer comprise a yttrium doped barium zirconate (BZY) solid oxide and NiO. The method according to claim 1,
Wherein the fuel electrode, the first electrolyte layer, and the second electrolyte layer are formed by a screen printing process, respectively. The method according to claim 1,
The fuel electrode, the first electrolyte layer, and the second electrolyte layer are each formed as a separate film by a tape casting process,
Wherein the individual films are laminated by a hot isostatic pressing method to produce a semi-conductive paper. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; delete delete delete delete delete delete delete delete delete delete

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