KR101274592B1 - MCFC cathode coated with mixed conducting oxide - Google Patents

Abstract

The present invention provides a cathode for a molten carbonate fuel cell prepared by pouring or dipping a slurry prepared by dispersing mixed-conducting oxide on a nickel-formed electrode plate and coating the inner pores, thereby increasing the oxygen reduction reaction rate of the cathode. It is possible to obtain a cathode electrode having a longer life than the cathode for a molten carbonate fuel cell while increasing the performance of the anode.

Description

MFC cathode coated with mixed conducting oxide

In general, the fuel cell is a device that directly converts the chemical energy of the chemical fuel into electrical energy. Fuel cells operating at a high temperature of more than 600 ℃ are molten carbonate fuel cell (MCFC) and solid oxide type And fuel cells. The molten carbonate fuel cell has an advantage that cannot be expected in a low temperature fuel cell such as a phosphoric acid type or a polymer fuel cell because it is operated at a high temperature of 650 ° C. In other words, the rapid electrochemical reaction at high temperature enables the use of inexpensive nickel instead of expensive platinum, which is advantageous in economics, and even carbon monoxide acting as a coating material on the platinum electrode can be used as fuel through the water gas shift reaction. Can be. In addition, the characteristics of the nickel electrode has a variety of fuel selectivity, such as coal gas, natural gas, methanol, biomass, has the advantage of very economical compared to other fuel cells.

Below are the chemical formulas for hydrogen oxidation and oxygen reduction in molten carbonate fuel cells.

_{^{Anode: H 2 + CO 3 2 -}} → H 2 O + CO 2 + 2e - ( a hydrogen oxidation reaction)

_{Cathode: 1/2 O 2 + CO 2 +} 2e - → CO 3 2 - ( oxygen reduction reaction)

Electrons are donated as hydrogen is oxidized in the anode, and electrons are donated as oxygen is reduced in the cathode. At this time, the oxygen reduction reaction of the cathode is much slower than the hydrogen oxidation of the anode, which is a major cause of battery performance reduction.

Conventional cathodes for molten carbonate fuel cells are used through in-situ oxidation and lithium lithiation after a nickel plate is made to produce a cell. In other words, the Ni-formed electrode mounted in the cell is oxidized by oxygen, which is a fuel gas, and reacts with lithium carbonate supplied to the electrolyte to change into porous lithiated NiO, and the electrical conductivity is rapidly increased by lithiation of lithium. Lithiated NiO, which is a cathode for a molten carbonate fuel cell, has the advantage of using a variety of fuels. However, when the oxygen reduction reaction is slower than the hydrogen oxidation of the anode, the operating temperature is lowered.

Therefore, it can be said that the invention of a new air electrode that can maintain a fast oxygen reduction reaction rate is very important. However, there is a lack of research on the air cathode which can improve the performance of molten carbonate fuel cell by reducing the polarization resistance through the fast oxygen reduction reaction rate even at low operating temperature and stably use the battery even in long time operation. . Japanese Laid-Open Patent Publication No. 1994-275283 has disclosed such a study. However, in the case of the above patent, since the entire air electrode is composed of an oxide having an expensive perovskite structure, it is economically inferior, and thus, there is a problem in mass production, and thus it is not currently applied in a commercially available MCFC system. Therefore, there is a great need for the development of cathodes which can be manufactured in an economical and mass-producible manner.

Molten carbonate fuel cells have the characteristic of operating at high temperatures of 650 ° C. If this high operating temperature is lowered to 600 ° C. to 620 ° C., it is advantageous for long time operation and has the advantage of reducing operating costs. On the other hand, the redox reaction rate that occurs at the air electrode is significantly lowered, causing a decrease in operating performance. In the present invention, in order to compensate for the decrease in performance due to the increased polarization resistance of the cathode generated when the operating temperature is lowered, mixed conducting oxide, which is known to have both electrical conductivity and oxygen ion conductivity at the surface of the existing air cathode lithiated NiO, among other perovskites When the molten carbonate fuel cell is operated by coating the sky material, the redox reaction rate of the cathode is significantly slower than that of the anode, so that it is stable and has high performance even at a low operating temperature, and can be operated for a long time.

The cathode of the molten carbonate fuel cell according to the present invention is prepared by pouring or immersing a slurry prepared by dispersing mixed-conducting oxide on a nickel-formed electrode plate and then coating the inner pores.

Various materials may be used as the mixed-conducting oxide that may be used in the present invention. For example, a perovskite-based material having an ABO ₃ structure having electrical conductivity and oxygen ion conductivity at 600 to 800 ° C. may be used.

The perovskite structure, generally named ABO ₃ , is a very basic structure. The A site, which is a vertex of a cubic unit, is generally filled with cations such as rare earth metals or alkaline earth metals such as La, Sr, Ca, Gd, Ba, and Mg, which have large and low valences. These atoms, along with oxygen, have 12 coordination numbers. The B site in the center of the cube is filled with small, generally high valence cations (potential metals such as Ti, Cr, Mn, Ni, Fe, Co, Cu and Zr). These atoms are coordinated by six oxygen ions in the octahedral coordination. Perovskite structures are known to be highly resilient because they allow doping and partial substitution of A or B cations. Therefore, Lanthanum strontium manganese oxide (LSM), Lanthanum strontium cobalt ferrite (LSCF), Lanthanum strontium gallium magnesium oxide (LSGM), Lanthanum strontium nickel ferrite (LSNF), Lanthanum calcium nickel ferrite (LCNF), Lanthanum strontium copper oxide , GSC (Gadolinium strontium cobalt oxide) is possible.

As the perovskite material of the ABO ₃ structure of the present invention, La _x Sr _{1 - x} Co _y Fe _{1 - y} O ₃ (where 0.5 ≦ x ≦ 0.9 and 0.1 ≦ y ≦ 0.5) is preferable. LSCF other than this composition tends to have low electrical conductivity and inferior electrochemical catalyst properties, and thus it is difficult to achieve the object of the present invention.

The content of the coating layer including the ABO ₃ structure of the perovskite material is preferably 30% by weight or less based on the weight of the porous nickel substrate in consideration of the economical characteristics of the cathode of the molten carbonate fuel cell and economical efficiency.

In addition, the size of the perovskite particles of the present invention to penetrate into the pores of the nickel base electrode and finally adsorbed to the nickel particles is preferably 5 μm or less, considering the pore size of the air electrode.

In order for the molten carbonate fuel cell of the present invention to have a perovskite coating layer, a) dispersing the perovskite material in a solvent, b) applying the dispersed perovskite coating solution on a porous nickel substrate, c) After the applied coating liquid penetrates into the internal pores, it should include the step of drying.

When the perovskite material is dispersed in a solvent, it is preferable to add 1 to 10% by weight of the dispersant relative to the perovskite material to prepare a coating solution.

In the present invention, since the slurry in which the perovskite material is dispersed in the nickel base electrode is poured or soaked into the internal pores and then adsorbed to Ni, the pore size of the existing electrode has a pore size of 5 to 10 μm and porosity of 60 to 80%. The polarization resistance of the cathode may be reduced by increasing the redox reaction rate of the cathode as a catalyst for the oxygen reduction reaction of the mixed conducting oxide while maintaining the same level as a conventional cathode. The viscosity of the prepared perovskite slurry is preferably 100 ~ 5,000cp. Adsorption here is a concept including a coating, and the following methods are possible in this regard.

As a method of coating the perovskite material on the nickel base electrode, most coating methods such as the Sol-gel method, the deep coating method, the spray coating method, and the vacuum deposition method are used. Can be.

FIG. 1 shows a schematic view and a SEM photograph of an air electrode 100 formed by adsorbing porous nickel particles 120 and perovskite particles 110 of a nickel base electrode.

By manufacturing the cathode for the molten carbonate fuel cell according to the method of the present invention, it is possible to uniformly coat the mixed-conducting oxide on the surface of the cathode and the inner pore surface, thereby increasing the oxygen reduction reaction rate of the cathode to increase the performance of the electrode In addition, it is possible to obtain a cathode electrode having a longer life than the conventional cathode for molten carbonate fuel cells.

Furthermore, the cathode electrode according to the present invention serves to lower the polarization resistance generated in the cathode by accelerating the oxygen reduction reaction of the cathode even at a low operating temperature to provide an improved cathode that can be applied to long-term operation of the molten carbonate fuel cell. can do.

1 shows a schematic and SEM photograph of LSCF coated.
2 shows a unit cell operation result using the LSCF-coated cathode.
Figure 3 shows the unit cell operation results using the cathode without the LSCF coating.
FIG. 4 illustrates a change in battery performance after operating the unit cell using the LSCF-coated cathode for 1,000 hours while changing the operating temperature from 600 ° C. to 700 ° C. FIG.
FIG. 5 illustrates changes in cell performance at 610 ° C., 630 ° C., and 650 ° C. operating temperature of a unit cell using a cathode without LSCF.

< Example >

Lanthanum strontium cobalt ferrite oxide (LSCF) was added to a solution containing ethanol and a dispersant and dispersed for 1 hour with an ultrasonic disperser. At this time, the amount of LSCF was 5% by weight based on the weight of the cathode used in the unit cell, and BYK-110 was used as a dispersant. The prepared dispersion was coated on a Ni molded electrode by vacuum adsorption. Subsequently, in order to effectively penetrate the LSCF into the internal pores, the vacuum adsorption state was maintained for 30 minutes, followed by drying in an oven at 100 ° C. for one hour to complete the coated electrode.

< Experimental Example >

As shown in FIG. 2, the unit cell operation result using the LSCF-coated cathode was found to be about 35 to 40 mV higher than that of the cathode in which the coating layer of FIG. 3 was not formed. In addition, when comparing internal resistance (IR), LSCF-coated cathode internal resistance showed 4.1mΩ on average, which was significantly lower than that of uncoated cathode (4.7mΩ). Confirmed that. This can be seen as a decrease in internal resistance that is exhibited by the high electrical conductivity of the LSCF has a characteristic of the air electrode having high electrical conductivity as a result. In addition, when the unit cell was operated for about 2000 hours, it was confirmed that the cathode electrode coated with LSCF had no problem even for long time operation by maintaining the performance of 0.83V or more.

In addition, the operation temperature was changed after 1,000 hours of operation in a unit cell using the LSCF-coated cathode. The battery performance was observed while changing the operating temperature from 600 ° C. to 700 ° C., and is shown in FIG. 4. For comparison, after 1,000 hours of operation even in a unit cell using an uncoated cathode, the performance was measured together at 610 ° C., 630 ° C., and 650 ° C., and the results are shown in FIG. 5.

In the unit cell using the LSCF-coated cathode, the performance was 0.781V when the operating temperature was 600 ° C. In the unit cell using the uncoated cathode, the performance was 0.751V at 610 ° C. Despite the lower performance. It can be seen that LSCF indirectly plays a role of reducing the decrease in performance due to the temperature decrease by increasing the rate of oxygen reduction reaction at low temperature to accelerate the electric reduction reaction in air.

Description of the Related Art
100: air electrode 110: perovskite particles
120: nickel particles

Claims (10)

A nickel base electrode formed of nickel particles and having a porous structure by the gap between the nickel particles; And
Perovskite type oxide particles adhered to the nickel particles; Lt; / RTI &gt;
The perovskite oxide particles are La _x Sr _1-x Co _y Fe _1-y O ₃ (wherein 0.5 ≤ x ≤ 0.9, 0.1 ≤ y ≤ 0.5) cathode for molten carbonate fuel cell.
delete The cathode for a molten carbonate fuel cell according to claim 1, wherein the content of perovskite particles is 30% by weight or less based on the weight of the porous nickel base electrode.
delete The cathode for the molten carbonate fuel cell of claim 1, wherein the porosity of the cathode is 60 to 80%.
The cathode for a molten carbonate fuel cell according to claim 1, wherein the size of all the pores of the cathode is 5 to 10 µm.
The cathode of claim 1, wherein the size of the perovskite particles is 5 µm or less.
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