KR101111224B1 - SOFC unit cell for hydrocarbon and the manufacturing method of the same - Google Patents

Abstract

The present invention relates to a SOFC unit cell for hydrocarbons and a method for manufacturing the same, and more particularly, to a fuel cell of a fuel cell by adding Li ₂ TiO ₃ as a catalyst to nickel-YSZ or nickel oxide-YSZ. Minimize poisoning and ensure that stability is maintained despite long operation time of fuel cell.

To this end, the present invention comprises the steps of mixing nickel oxide, YSZ, carbon black, Li ₂ TiO ₃ catalyst to prepare a slurry for the anode; Molding the slurry by a tape casting method to produce an anode molded body; Stacking the anode compact with a solid electrolyte compact; Preparing a primary fired body by primary firing the laminated molded body by a simultaneous firing method; Stacking or screen-printing an air cathode molded body on the primary plastic body; It provides a method for producing a hydrocarbon SOFC unit cell comprising a primary firing body and a cathode assembly combined secondary firing; and a SOFC unit cell for a hydrocarbon produced by the same method comprising a. .

SOFC, unit cell, anode, nickel, YSZ, Li2TiO3, carbon poisoning, porosity, electrical conductivity, operating time, stability

Description

SOFC unit cell for hydrocarbons and its manufacturing method {SOFC unit cell for hydrocarbon and the manufacturing method of the same}

The present invention relates to a SOFC unit cell for hydrocarbons and a method for manufacturing the same, and more particularly, to a fuel cell of a fuel cell by adding Li ₂ TiO ₃ as a catalyst to nickel-YSZ or nickel oxide-YSZ. Minimize poisoning and ensure that stability is maintained despite long operation time of fuel cell.

To this end, the present invention comprises the steps of mixing nickel oxide, YSZ, carbon black, Li ₂ TiO ₃ catalyst to prepare a slurry for the anode; Molding the slurry by a tape casting method to produce an anode molded body; Stacking the anode compact with a solid electrolyte compact; Preparing a primary fired body by primary firing the laminated molded body by a simultaneous firing method; Stacking or screen-printing an air cathode molded body on the primary plastic body; It provides a method for producing a hydrocarbon SOFC unit cell comprising a primary firing body and a cathode assembly combined secondary firing; and a SOFC unit cell for a hydrocarbon produced by the same method comprising a. .

Fuel cell technology is a technology that has a large ripple effect to other industries, such as the power generation industry as a home or industrial power generation device, the automobile industry as a driving device to replace the existing internal combustion engine, and the electronics industry as a conventional battery replacement power source. Among these, solid oxide fuel cell (SOFC) has the highest energy efficiency among the fuel cell methods, and has a large degree of freedom in size, shape, and capacity. It has a very wide application range from very small power supplies to large combined cycle power generation systems. In particular, SOFC is easy to modularize, and can be developed for almost all energy sources, ranging from ultra-small power supplies in the mW class to large-scale power generation systems in the hundreds of MW to replace existing grid-type power generation systems.

SOFC is also the only fuel cell technology that can be applied to existing fossil fuel systems. Hydrogen used in most fuel cells is the ideal fuel of the future, but the production and storage of hydrogen limits the range of fuel cell applications. Therefore, considering the economic feasibility of fuel cells as an energy source in the domestic situation where there is no hydrogen supply infrastructure, efficient utilization of hydrocarbon fuels such as LPG and LNG is very important for market creation and long-term fuel cell development / distribution. Have In particular, internal reforming SOFCs do not use expensive external reforming, which can simplify the system and make use of existing infrastructure for fuel supply.

On the other hand, when hydrocarbon fuel is injected directly into the anode, the nickel-based fuel electrode is quickly deactivated because nickel catalyzes carbon deposition. In other words, carbon poisoning may be a problem. In the case of a hydrocarbon fuel-compatible anode, metal catalysts resistant to carbon poisoning other than nickel, such as copper, ruthenium, silver, gold, and various alloys (nickel-copper, copper-cobalt, etc.) Although it is used, the development of a new ceramic composite negative electrode composition exhibiting better catalytic activity is required first.

In addition, one of the difficulties encountered in commercializing fuel cells is that the manufacturing cost of the unit cell is very high, and this manufacturing cost currently accounts for 30% of the total stack cost, and thus, development of a low-cost process is considered essential. Currently, SOFC advanced companies are focusing on process development that can be mass-produced at low cost, easy to control process, and can manufacture large area unit cells. From this point of view, the tape casting process is the most widely used process, and it is expected to be cost-effective and very advantageous for large area because it can be mass-produced and automated.

The present invention has been made to solve the above problems, the present invention is applied to a new catalyst of Li ₂ TiO ₃ as a catalyst for a fuel cell for hydrocarbons, the practical use of a fuel cell comprising a Ni-YSZ-based anode Aims to make it possible.

In addition, the present invention, by adding Li ₂ TiO ₃ as a catalyst to the Ni-YSZ-based anode to minimize the carbon poisoning through the carbon bond decomposition or carbon adsorption suppression effect to enhance the durability of the fuel cell, in the operation of the fuel cell Another aim is to ensure long-term stability.

In order to achieve the above object, the present invention provides a hydrocarbon SOFC unit cell in which Li ₂ TiO ₃ is added as a catalyst to the anode of the unit cell.

The anode has an electrical conductivity of 1400 ~ 1200 S / cm in the operating temperature range of 600 ~ 800 ℃.

Preferably, the anode has a porosity of about 35 to 45%.

In addition, the present invention comprises the steps of mixing a starting material containing a nickel oxide, YSZ, Li2TiO3 catalyst in order to achieve the object as described above to prepare a slurry for the anode; Molding the slurry by a tape casting method to produce an anode molded body; Stacking the anode compact with a solid electrolyte compact; Preparing a primary fired body by primary firing the laminated molded body by a simultaneous firing method; Stacking or screen-printing an air cathode molded body on the primary plastic body; It provides a SOFC unit cell for a hydrocarbon comprising a; and the secondary firing of the primary firing body and the cathode molded body combination to produce a unit cell.

In addition, the present invention comprises the steps of mixing a starting material containing a nickel oxide, YSZ, Li2TiO3 catalyst in order to achieve the object as described above to prepare a slurry for the anode; Molding the slurry by a tape casting method to produce an anode molded body; Stacking a solid electrolyte compact and a cathode compact on the anode compact; And firing the laminated molded body to produce a unit cell.

The Li ₂ TiO ₃ is mixed with Li ₂ CO ₃ and at least one selected from TiO ₂ or Ti [OCH (CH ₃ ) ₂ ] ₄ as a starting material, heat treatment for 6 to 24 hours at a temperature range of 700 ~ 900 ℃ It is preferable to synthesize | combine by.

Carbon black is further added to the starting material including the nickel oxide, YSZ, and the Li ₂ TiO ₃ catalyst, and the carbon black is preferably added in an amount of 10% by weight based on the mixed weight of the nickel oxide, YSZ, and carbon black.

The firing temperature for producing the primary fired body is in the range of 1300 ~ 1400 ℃, the firing temperature for producing the secondary fired body is preferably in the range of 1100 ~ 1200 ℃.

The firing temperature of the laminated fired body is preferably in the range of 1200 ~ 1350 ℃.

According to the present invention as described above, it is expected that the SOFC fuel cell having a Ni-YSZ-based fuel electrode as one component can be put to practical use for hydrocarbons.

In addition, by using Li ₂ TiO ₃ as a catalyst of the anode, the carbon poisoning phenomenon of the fuel cell is minimized, and thus, the effect of securing long-term stability during operation is expected by improving the durability of the fuel cell.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

The present invention minimizes carbon poisoning by using Li ₂ TiO ₃ as a catalyst in a Ni-YSZ anode where carbon poisoning frequently occurs in a hydrocarbon fuel cell, and also a fuel electrode, a solid electrolyte, a fuel electrode, and a solid It is characterized by simplifying the process and reducing the process cost by the method of simultaneously firing the electrolyte and the cathode.

In general, Ni (40 vol%)-YSZ cermet, which is a fuel electrode, has a phenomenon in which a fuel electrode is destroyed while carbon deposition amount is increased by 12 wt% or more. This is due to the formation of carbon in the form of filaments around Ni by the methane pyrolysis reaction and the sidewalk reaction during the reforming reaction of the anode system used as a problem, which causes a problem of cell destruction.

(1) Synthesis of Li ₂ TiO ₃

1 shows a synthesis process of Li ₂ TiO ₃ as a catalyst for an anode according to the present invention.

As shown, Li ₂ TiO ₃ is a starting material, at least one selected from Li ₂ CO ₃ and TiO ₂ or Ti [OCH (CH ₃ ) ₂ ] ₄ is mixed with ethanol as a solvent, and then dried. , Synthesized through heat treatment process. At this time, the mixture was ball milled for 4 hours in the mixing process, as an optimal synthesis condition, the heat treatment temperature was set to a temperature range of 700 ~ 900 ℃, the heat treatment time was to maintain 6 ~ 24 hours.

This is because if the heat treatment temperature is lower than 700 ° C., a substance that remains unreacted in the starting materials is detected. If the heat treatment temperature is higher than 900 ° C., the result is an unnecessarily high temperature for the synthesis of Li ₂ TiO ₃ . The range is critical in the above range.

In addition, the above heat treatment time range is set in the process of selecting an optimized heat treatment time at each temperature in order to prevent unreacted residues from occurring, and it is critical to prevent unreacted residues from forming. Has

X-ray analysis results according to the heat treatment temperature of Li ₂ TiO ₃ prepared by one embodiment of the present invention is shown in FIG.

(a) is a case where the heat treatment holding time for synthesis is 3 hours and the heat treatment temperature is 500 ° C., 600 ° C., and 700 ° C., respectively, and as shown, when the heat treatment temperatures are 500 ° C. and 600 ° C. It was found that unreacted residues were detected in Li ₂ CO ₃ and TiO ₂ as starting materials, but unreacted residues were hardly detected at 700 ° C.

However, the heat treatment holding time was maintained at 6 hours in order to react the total amount of the unreacted substance in a very small amount, which is shown in (b). As shown, when the heat treatment for 6 hours it can be seen that no unreacted residual material was detected. At this time, the heat treatment temperature was 700 degreeC, 800 degreeC, and 900 degreeC, respectively.

On the other hand, the heat treatment temperature for the synthesis was fixed to 700 ℃, the heat treatment holding time was extended to 24 hours, the experimental results are shown in (c), as expected, unreacted residual material was not detected at all.

Therefore, the heat treatment temperature and the heat treatment time will be well represented the characteristics of the present invention in the range as described above.

(2) Carbon Poisoning Reaction of Fuel Cell Prepared with Li ₂ TiO ₃ as Catalyst

Next, a fuel electrode was manufactured using Li ₂ TiO ₃ as a catalyst, and carbon poisoning reaction of a fuel cell including the fuel electrode as a component was shown in FIG. 3.

As shown, when Li ₂ TiO ₃ directly synthesized by the present invention is not added to the Ni-YSZ anode, the carbon poisoning amount is increased by 18.62% by weight relative to the weight of the anode, while Li ₂ TiO ₃ is 1 weight by weight of the anode. % Added, 13.86% by weight of the anode weight, 4% by weight of the anode weight, 3.41% by weight of the anode weight of about 1/6 of the carbon poisoning generated in the anode without Li ₂ TiO ₃ added It was supported that the carbon poisoning phenomenon can be minimized.

The mechanism for preventing Li ₂ TiO ₃ carbon from depositing on Ni is to evenly place Li ₂ TiO ₃ between Ni particles to prevent carbon from being deposited into a filamentary form, or to form carbon in a solid state. It appears to be due to the further activation of gaseous carbon formation to prevent carbon from depositing.

Meanwhile, in FIG. 4, FIG. 4 is a particle size distribution graph showing comparisons of particle sizes of commercial Li ₂ TiO ₃ and particle sizes of Li ₂ TiO ₃ synthesized according to the present invention. As shown, commercial Li ₂ TiO ₃ The particle size of was measured to have an average value of about 1.9㎛, the particle size is widely distributed over a variety of sizes, the particle size of Li ₂ TiO ₃ synthesized by the present invention has an average value of about 0.44㎛ It was measured and the particle size distribution is relatively narrow, indicating that the size of the particle size is more uniform.

That is, in the case of Li ₂ TiO ₃ synthesized by the present invention, it can be said that the catalytic activity effect according to the specific surface area is greater than that of the commercial powder, thereby having a superior carbon poisoning prevention effect.

(3) Porosity and electrical conductivity of anode

The porosity of the anode prepared in the firing temperature range of 1300 ~ 1400 ℃ by the present invention was measured to be 35% or more, for example, when firing at 1325 ℃ showed a porosity of about 56%.

In FIG. 5, the electrical conductivity of the anode in which Li ₂ TiO ₃ prepared by the embodiment of the present invention is added as a catalyst is shown in comparison with the anode without the above catalyst. As shown, it can be seen that the electrical conductivity according to the operating temperature appearing in the anode having no catalyst added and the electrical conductivity according to the operating temperature appearing in the anode including the catalyst according to the present invention is almost the same.

Therefore, it was found that the anode including the catalyst according to the present invention can be applied to a commercial fuel cell.

(4) Performance evaluation of fuel cell

FIG. 6 shows the results of measuring the maximum output density of the anode including Li ₂ TiO ₃ prepared by one embodiment of the present invention as a catalyst, and the change in voltage and output density according to long-term operation.

As shown in the top view, Li ₂ TiO ₃ The unit cell prepared by the addition of the maximum power density of 0.4 W / cm ² at the operating temperature of 800 ℃, the voltage showed a nearly linear behavior according to the current density, as shown in the lower drawing 800 In spite of operating for more than 50 hours at the operating temperature of ℃, there was almost no change in voltage and power density, it can be seen that the fuel cell manufactured by the present invention operates stably in the long term. This is because the carbon poisoning phenomenon generated in the anode of the present invention as described above is minimized, and is due to the durability of the fuel cell as the carbon poisoning phenomenon is minimized.

(5) Manufacturing process of fuel cell

7 is a flowchart illustrating a manufacturing process of a fuel cell according to an embodiment of the present invention.

As shown, the above manufacturing process, first, a starting material containing a nickel oxide, YSZ, Li ₂ TiO ₃ catalyst is mixed to prepare a slurry for the anode. In this case, ethanol was used as the solvent, and in addition to ethanol, the solvent may be variously modified.

Here, Li ₂ TiO ₃ can be used as a catalyst, Li ₂ TiO ₃ has a melting point of 1535 ℃, this temperature is the firing temperature of the electrolyte material such as YSZ (1300 ~ 1400 ℃) in the unit cell fabrication This is because it is higher, so that it is possible to sinter the anode and the electrolyte together by the co-firing method by adding it directly to the general ceramic process, that is, when manufacturing the anode.

The slurry thus prepared is adjusted to have a viscosity suitable for tape casting, preferably mixing nickel oxide and YSZ in equal volume percent and adding a small amount of Li ₂ TiO ₃ to it. Here, the amount of Li ₂ TiO ₃ is preferably added 1 to 4% by weight based on the weight of the anode. As the amount of Li ₂ TiO ₃ is increased, the carbon deposition amount will decrease due to the decrease of the reaction surface of Ni, but the reforming reaction can be reduced, resulting in a decrease in unit cell performance. The optimum content range determined in consideration of performance has its critical significance in the above range.

In addition, a small amount of carbon black is further added thereto. In this embodiment, the carbon black is added in an amount of 10 wt% based on the total content of nickel oxide, YSZ, and carbon black.

The mixed starting materials are prepared into a slurry by a ball milling method for 24 hours, and a binder is added to the slurry thus prepared to be suitably prepared by tape casting, and then mixed by a ball milling method or the like.

Then, the anode molded body is manufactured by the tape casting method using the above slurry, and the manufactured molded body is laminated with a separately prepared solid electrolyte molded body through a drying process.

Here, the solid electrolyte may also be manufactured by a tape casting method. The stacked anode fuel cell and the solid electrolyte molded body may be press-molded by CIP (Cold Isostatic Pressing) or WIP (Warm Isostatic Pressing).

After calcining the molded article press-molded in this way, the binder is first fired by a simultaneous firing method to prepare a primary fired body, and the firing temperature is preferably in the range of 1300 to 1400 ° C. It baked at 1325 degreeC.

The unit cell may be manufactured by combining the cathode molded body by laminating or screen printing on the primary fired body manufactured as described above, and firing it again to manufacture the secondary fired body. At this time, the secondary firing temperature is preferably applied in the temperature range of 1100 ~ 1200 ℃, in this embodiment 1150 ℃ as the firing temperature.

The firing temperature range of the primary firing body has a critical significance as a temperature range for realizing an optimal microstructure and obtaining a dense electrolyte, and the firing temperature range of the secondary firing material realizes a microstructure of the cathode. As the temperature range for the above, when the upper limit of the above temperature range is exceeded, the microstructure changes due to oversintering, and if it is below the lower limit, the plastic body of the cathode cannot have the appropriate strength or pore size. have.

As a simple modification of the above production example, the following process may also be proposed. That is, mixing the starting material containing a nickel oxide, YSZ, Li ₂ TiO ₃ catalyst to prepare a slurry for the anode; Molding the slurry by a tape casting method to produce an anode molded body; Stacking a solid electrolyte compact and a cathode compact on the anode compact; And firing the laminated molded body to produce a unit cell. In the case of firing in this way, it is possible to simultaneously fire the fuel electrode, the solid electrolyte, and the air electrode, thereby contributing to the process economy.

At this time, the firing temperature range may be implemented in the intermediate range of the temperature range of the primary and secondary plastics, for example, 1200 ~ 1350 ℃ considering the firing temperatures of the anode, the solid electrolyte and the cathode. And, although it is not the optimum temperature range, it was found that the present inventors can operate as a fuel cell.

If the temperature is less than 1200 ° C., the sintering does not proceed. If the temperature is 1350 ° C. or more, it is preferable to maintain the temperature in the above range because the microstructure of the cathode is destroyed to such an extent that it cannot be operated as a fuel cell.

Of course, in this case, a sintering aid may be added to lower the firing temperatures of the anode and the solid electrolyte in view of the relatively low firing temperature of the cathode.

1 is a flow chart showing a process for synthesizing Li ₂ TiO ₃ as a catalyst for an anode according to the present invention;

Figure 2 is a graph showing the X-ray analysis results according to the heat treatment temperature of Li ₂ TiO ₃ prepared by one embodiment of the present invention,

FIG. 3 is a graph illustrating an anode prepared using Li ₂ TiO _{3 according} to the present invention and experimenting with carbon poisoning reaction of a fuel cell including the anode as a component; FIG.

4 is a particle size distribution graph comparing the particle size distribution of commercial Li ₂ TiO _{3 and} the particle size of Li ₂ TiO ₃ synthesized according to the present invention;

FIG. 5 is a graph showing the electrical conductivity of an anode in which Li ₂ TiO ₃ prepared by an embodiment of the present invention is added as a catalyst, compared with an anode in which the above catalyst is not added.

Figure 6 is a graph showing the results of measuring the maximum output density of the anode and the change in voltage and output density according to long-term operation of the anode prepared by adding Li ₂ TiO ₃ catalyst according to an embodiment of the present invention,

7 is a flowchart illustrating a manufacturing process of a fuel cell according to an embodiment of the present invention.

Claims (10)

In SOFC unit cell for hydrocarbon, The unit cell is a material containing nickel as a fuel electrode, SOFC unit cell for hydrocarbons, characterized in that Li ₂ TiO ₃ is added to the fuel electrode to suppress carbon poisoning by nickel. The method of claim 1, The anode is a hydrocarbon SOFC unit cell, characterized in that the electrical conductivity of 1400 ~ 1200 S / cm in the operating temperature range of 600 ~ 800 ℃. The method of claim 1, The anode has a SOFC unit cell for a hydrocarbon, characterized in that having a porosity of 35 ~ 45%. The method of claim 1, The Li ₂ TiO ₃ is a SOFC unit cell for a hydrocarbon, characterized in that 1 to 4% by weight based on the weight of the anode. delete delete The method of claim 1, The Li ₂ TiO ₃ is mixed with Li ₂ CO ₃ and at least one selected from TiO ₂ or Ti [OCH (CH ₃ ) ₂ ] ₄ as a starting material, heat treatment for 6 to 24 hours at a temperature range of 700 ~ 900 ℃ SOFC unit cell for a hydrocarbon, characterized in that synthesized by. The method of claim 1, The anode is a SOFC unit cell for a hydrocarbon, characterized in that prepared from the starting material containing a nickel oxide, YSZ, Li ₂ TiO ₃ catalyst. The method of claim 8, Carbon black is further added to the starting material, and the carbon black is a SOFC unit cell for a hydrocarbon, characterized in that 10% by weight is added to the mixed weight of the nickel oxide, YSZ and carbon black. delete

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