KR101534607B1 - Porous cathode composite for solid oxide regenerative fuel cell, fabrication method thereof and solid oxide regenerative fuel cell comprising the same - Google Patents

Abstract

The present invention relates to a porous cathode composite for a solid oxide regenerative fuel cell comprising a porous composite of perovskite and fluorite and a nanocatalyst formed on the surface of the porous composite electrode. The performance of the conventional solid oxide regenerative fuel cell (SORFC) wateuna is greatly limited by the polarization of the air electrode, there is a nano-catalyst in the pores inside the porous composite cathode is uniformly penetrate O ₂ reduction and O ₂ according to the ^invention the air electrode surface reactions for oxidation is promoted, whereby the solid by Oxide fuel cell (SOFC) / solid oxide electrolytic cell (SOEC) performance can be greatly improved at the same time. In addition, since the method of manufacturing the air electrode composite for a solid oxide recycle fuel cell according to the present invention is applicable to various conventional solvent injection techniques, it is easy to introduce into the production process, and since the air electrode composite is crystallized at 800 ° C, Since the crystallization can proceed at the beginning of the operation of the solid oxide fuel cell (SORFC) without the heat treatment process, it can contribute to the simplification of the manufacturing process.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous cathode composite for a solid oxide regeneration fuel cell, a method for producing the same, and a solid oxide regenerative fuel cell comprising the solid oxide regenerative fuel cell,

The present invention relates to a porous cathode composite for a solid oxide regenerative fuel cell and a method of manufacturing the same.

As a next-generation fuel cell technology, a fuel cell - a unitized regenerative fuel cell (URFC) technology, which is an integrated energy conversion and storage system, is emerging as the most promising research topic to lead fuel cell research .

The integrated regenerative fuel cell (URFC) is constituted by a fuel cell mode and an electrolyzer mode. In the fuel cell mode, electrical energy is generated in the same manner as the conventional fuel cell driving mode. In the electrolytic cell mode, And a system for generating hydrogen and oxygen again by electrolyzing water produced as a by-product in a fuel cell reaction. In this case, the technology of re-supplying the regenerated hydrogen and oxygen to the fuel cell to obtain the electric energy is the core of the URFC technology and the use efficiency of the hydrogen fuel of the existing fuel cell is greatly improved to about 10-15% .

Solid Oxide Regenerative Fuel Cell (SORFC), which is the most efficient technology among URFCs, is a solid oxide fuel cell (SOFC) for high-efficiency clean energy conversion and its reverse operation It is a battery that incorporates the corresponding Solid Oxide Electrolysis Cell (SOEC) for hydrogen production. It can supply large capacity electricity and produce / store / utilize hydrogen. Therefore, unequal low quality electricity of renewable energy It is a technology suitable for stable supply. That is, hydrogen can be manufactured and stored by using surplus power of new and renewable energy in a time when power demand is low, and power can be supplied by using it as fuel when power demand is high. Since it operates at a high temperature region of 800 ° C, it has thermodynamic and kinetic advantages compared to the low-temperature type regenerative fuel cell and has relatively high efficiency and performance. Therefore, it is possible to solve the reaction problems between the materials and develop new materials, Driving test evaluation are emerging as key issues in major research and development.

However, when the SOFC technology is applied to SOEC for the hydrogen production, the performance is remarkably low, and a large part of the performance loss is caused by polarization at the air electrode. Therefore, for commercialization of the technology, it is necessary to develop a system having performance similar to that of operating in the SOFC and SOEC modes, such as long life, high-performance large-area electrolytes and electrode fabrication, The development of an air electrode having a composition and structure is desperately required.

Disclosure of Invention Technical Problem [6] The present invention provides a solid oxide fuel cell and a method of manufacturing the same, which can greatly improve both the solid oxide fuel cell and the solid oxide electrolysis performance by promoting the surface reaction of the air electrode.

In order to solve the above problems,

There is provided a porous cathode composite for a solid oxide regeneration fuel cell comprising a porous composite of perovskite and fluorite represented by the following Chemical Formula 2 and a nanocatalyst represented by the following Chemical Formula 1 formed on the surface of the composite.

(2)

_{A 1- X B X C 1 -} Y D Y O 3 -δ ( _{perovskite) - E 1 - Z F Z} O 2 -δ ( fluorite)

In the above formula 2, A is one element of La, Ba and Y, B is one element of Sr and Ca, C and D are elements of one of Mn, Co, Fe and Ni, E X is a real number of 0 <X <1, Y is a real number of 0 <Y <1, and Z is a real number of 0 < 0 < Z &lt; 1, [delta] is a real number of 0 &lt;

[Chemical Formula 1]

_{G x H 1 - x IO 3} -δ

In the above formula 1, G and H are elements of one of Sm, Sr, La, Ca and Ba, I is one element of Co, Mn and Fe, X is a real number of 0 < , and? is a real number of 0???? 1.

According to an embodiment of the present invention, the nanocatalyst may be formed by penetrating the inner pore surface of the porous composite.

According to one embodiment of the present invention, in the X-ray diffraction analysis, the porous composite and the nanocatalyst have a perovskite or fluorite crystal structure.

The present invention also provides a method of manufacturing a porous cathode composite for a solid oxide regenerative fuel cell, comprising the steps of: forming a uniform nanocatalyst on the inner surface of the pores of the porous cathode composite.

(a) dissolving a metal precursor compound in an aqueous alcohol solution, adding urea, and mixing to prepare a nanocatalyst precursor solution represented by the following formula (1)

(b) immersing the nanocatalyst precursor solution in a porous composite electrode represented by the following formula (2), followed by performing a urea decomposition process,

(c) firing the urea decomposition process.

(2)

_{A 1- X B X C 1 -} Y D Y O 3 -δ ( _{perovskite) - E 1 - Z F Z} O 2 -δ ( fluorite)

In the above formula 2, A is one element of La, Ba and Y, B is one element of Sr and Ca, C and D are elements of one of Mn, Co, Fe and Ni, E X is a real number of 0 <X <1, Y is a real number of 0 <Y <1, and Z is a real number of 0 < 0 < Z &lt; 1, [delta] is a real number of 0 &lt;

[Chemical Formula 1]

_{G x H 1 - x IO 3} -δ

In the above formula 1, G and H are elements of one of Sm, Sr, La, Ca and Ba, I is one element of Co, Mn and Fe, X is a real number of 0 < , and? is a real number of 0???? 1.

According to one embodiment of the present invention, the metal precursor may be nitrate or acetate.

According to an embodiment of the present invention, the alcohol aqueous solution may have a volume ratio of alcohol: water of 0.5-3: 1, and the alcohol may be at least one selected from methanol, ethanol, propanol and butanol.

According to one embodiment of the present invention, the molar ratio of urea in the precursor solution to the precursor material cation may be 5-15: 1.

According to an embodiment of the present invention, the urea decomposition process of step (b) may be performed at 70-100 ° C.

According to an embodiment of the present invention, the firing in the step (b) may be performed at 700-1,000 ° C.

The solid oxide reproduction fuel cell (SORFC) performance wateuna is greatly limited by the polarization of the air electrode, in accordance with the present invention is a nano-catalyst penetrate evenly pores inside of the porous composite cathode's O ₂ reduction and O ₂ ^- for the oxidation The surface reaction of the cathode is promoted, thereby greatly enhancing the performance of the SOFC / SO oxidizing tank (SOEC) at the same time. In addition, since the method of manufacturing the air electrode composite for a solid oxide recycle fuel cell according to the present invention is applicable to various conventional solvent injection techniques, it is easy to introduce into the production process, and since the air electrode composite is crystallized at 800 ° C, Since the crystallization can proceed at the beginning of the operation of the solid oxide regenerative fuel cell without the heat treatment process, it can contribute to simplification of the manufacturing process.

1 is an XRD pattern of a porous cathode composite comprising a nanocatalyst on the pore inner surface of a porous composite according to an embodiment of the present invention.
2 is a SEM image showing a structure of a solid oxide fuel cell (SORFC) according to an embodiment of the present invention, wherein (a) is a SORFC cross section, (b) is an LSCF- GDC porous composite cathode, (SSC) structure uniformly formed in the porous composite cathode.
FIG. 3 is a graph showing the effect of a nanocatalyst (SSC) according to an embodiment of the present invention on the performance of a fuel cell, wherein (a) shows the relationship between the SOFC permeated with nanocatalyst (SSC) (B) is a graph comparing the performance of a SORFC in which a nanocatalyst (SSC) is impregnated.
FIG. 4 is a graph showing impedance measurement results of a fuel cell according to an embodiment of the present invention, wherein (a) is an OCV, (b) is an SOFC mode (0.7 V) This is the measured result.

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

One aspect of the present invention relates to a porous cathode composite for a solid oxide regeneration fuel cell comprising a nanocatalyst represented by the following formula (1) on a pore inner surface of a porous composite represented by the following formula (2).

(2)

(Perovskite) -E _{1 -Z} F _Z O _2-隆 (fluorite) -A _{1 -X} B _X C _{1 -Y} D _Y O _3-δ

In the above formula 2, A is one element of La, Ba and Y, B is one element of Sr and Ca, C and D are elements of one of Mn, Co, Fe and Ni, E X is a real number of 0 <X <1, Y is a real number of 0 <Y <1, and Z is a real number of 0 < 0 < Z &lt; 1, [delta] is a real number of 0 &lt;

[Chemical Formula 1]

G _x H _1-x IO _{3 -?}

In the above formula 1, G and H are elements of one of Sm, Sr, La, Ca and Ba, I is one element of Co, Mn and Fe, X is a real number of 0 < , and? is a real number of 0???? 1.

Wherein the nano catalyst is formed by uniformly infiltrating the inner surface of the pores of the porous composite, wherein the porous porous material composite including the nanocatalyst on the pore inner surface has a perovskite structure or a fluorite structure . The porous cathode composite according to the present invention is characterized in that the nanocatalyst is uniformly formed in the pores of the porous composite.

The present invention also relates to a method for producing a porous cathode composite for a solid oxide regenerative fuel cell, which comprises the steps of: forming a uniform nanocatalyst on the pore inner surface of the porous composite;

(a) dissolving a metal precursor compound in an aqueous alcohol solution, adding urea, and mixing to prepare a nanocatalyst precursor solution represented by the following formula (1)

(b) immersing the nanocatalyst precursor solution in a porous composite electrode represented by the following formula (2), followed by performing a urea decomposition process,

(c) firing the urea decomposition process.

(2)

_{A 1- X B X C 1 -} Y D Y O 3 -δ ( _{perovskite) - E 1 - Z F Z} O 2 -δ ( fluorite)

In the above formula 2, A is one element of La, Ba and Y, B is one element of Sr and Ca, C and D are elements of one of Mn, Co, Fe and Ni, E X is a real number of 0 <X <1, Y is a real number of 0 <Y <1, and Z is a real number of 0 < 0 < Z &lt; 1, [delta] is a real number of 0 &lt;

[Chemical Formula 1]

_{G x H 1 - x IO 3} -δ

In the above formula 1, G and H are elements of one of Sm, Sr, La, Ca and Ba, I is one element of Co, Mn and Fe, X is a real number of 0 < , and? is a real number of 0???? 1.

First, after the metal precursor compound is dissolved in an aqueous alcohol solution, urea is added and mixed to prepare a nanocatalyst precursor solution.

The metal precursor compound may be a nitrate salt or an acetate compound.

The alcohol aqueous solution may have a volume ratio of alcohol to water of 0.5-3: 1, and the alcohol may be at least one selected from methanol, ethanol, propanol, and butanol.

Water is needed to dissolve the nitrate or acetate compound, and an organic solvent such as alcohol is needed to lower the surface tension of the precursor solution so that the precursor solution can be injected into the micro pores.

According to a preferred embodiment of the present invention, an alcohol is used as an organic solvent to dissolve using a mixed solution of alcohol and water, more preferably, a mixed solution having a volume ratio of alcohol and water of 0.5: 3: 1 is used .

Also, the molar ratio of urea in the precursor solution to the cation derived from the precursor compound may be 5-15: 1.

Next, the nanocatalyst precursor solution obtained in step (a) is in-situ impregnated into the pores of the porous composite cathode material by impregnation and then subjected to a urea decomposition step, wherein the urea decomposition step is carried out at 70-100 Lt; 0 &gt; C.

The urea serves as a complexing agent in the preparation of the nanocatalyst precursor solution, and when heated at a temperature of 70-100 ° C after the permeation process, the urea decomposes and the metal hydroxide / metal carbonate precipitates by decomposition. Scope is important.

In the case of heating to a higher temperature range, a drying process takes place instead of urea decomposition, and the capillary force brings the precursor solution to the surface of the porous composite, thereby causing concentration of the nanoparticles close to the upper surface of the electrode. There may be a problem in that non-uniform particle growth occurs on the surface of the inner pore, thereby deteriorating the performance of the battery.

Finally, the step of firing at 700-1,000 ° C after the urea decomposition step is performed to crystallize the porous cathode composite.

The porous cathode composite according to the present invention produced through the above firing step has improved thermal stability together with the porous composite in which the nanocatalyst formed on the inner surface of the pores of the porous composite is crystallized to become a backbone.

In the method of manufacturing the porous cathode composite according to the present invention, the heat treatment process plays a crucial role in manufacturing the nanocatalyst particles in a desired size, shape, and crystal structure.

In addition, since the crystallization process can be performed at a temperature not higher than the operating temperature of the solid oxide recycle fuel cell, the crystallization can proceed at the beginning of the operation of the solid oxide recycle fuel cell without a separate heat treatment process, thereby contributing to simplification of the manufacturing process. Particle growth and unnecessary chemical bonding can be prevented.

In addition, the manufacturing method according to the present invention can be applied to various conventional solvent injection techniques, and is easily introduced into a production process.

In addition, the present invention relates to a solid oxide play a fuel cell comprising a porous cathode composite, O ₂ reduction and O ₂ ^- and wherein the better the air electrode surface reactions for oxidation, the ohmic than the conventional solid oxide regeneration fuel cell The resistance is lowered, and the electrode polarization resistance is remarkably reduced, so that the performance is improved by 60% or more than that of the conventional solid oxide regenerative fuel cell.

Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. However, it should be understood that the scope and content of the present invention are not construed to be limited or limited by the embodiments, and that based on the teachings of the present invention including the following examples, It will be apparent that those skilled in the art can easily carry out the present invention.

Manufacturing example  1. Porosity according to the present invention Air pole  Manufacture of Composites

(1) Preparation of Nanocatalyst (SSC)

For the production of nano-catalyst _{1 mol / L Sm 0 .5 Sr} 0 .5 CoO 3 (SSC) precursor solution Sm (NO ₃₎ in a solvent mixture of water and ethanol _{3 · 6H 2 O, Sr (} NO 3 ) ₂ , Co (NO ₃ ) ₂ .6H ₂ O and urea were mixed to obtain Sm _{0 .5} Sr _{0 .5} CoO ₃ catalyst. The [urea] / [cation] ratio was 10, and the volume ratio of the [water] / [ethanol] solution was 1.7.

(2) Preparation of porous cathode composite

Infiltration using a micro-syringe was performed to form the porous cathode composite by forming the nanocatalyst obtained in the above (1) on the surface of the porous material.

The porous electrode (LSCF-GDC) was impregnated with a chemical solution containing the SSC nitrate precursor and urea having the [urea] / [cation] ratio of 10 obtained in the above (1) (The above penetration and heat treatment steps were repeated three times) and then fired at 800 ° C.

The temperature control in this process plays a crucial role in realizing the desired crystal structure in the size and shape of the nanocatalyst particles. It is desirable to crystallize the nanocatalyst at a temperature that is not significantly higher than the operating temperature of the solid oxide regenerative fuel cell. In addition, a simple in-situ crystallization process is possible during fuel cell operation, preventing excessive particle growth and also preventing unwanted chemical bonding.

Example  1. Solid oxide regeneration fuel cell

(1) Production of hydrogen electrode substrate

(NiO), yttria stabilized zirconia (YSZ), and poly (methyl methacrylate) (PMMA) pore-forming materials were prepared in ethanol containing dispersants, binders and plasticizers Mixed for 24 hours by ball-milling, and spray dried to obtain a granule. The volume ratio of NiO, YSZ and PMMA was 0.37: 0.33: 0.3 and the substrate (2 cm x 2 cm) was prepared by uniaxial compression of granules at 60 MPa.

(2) Production of slurry

The slurry contains a hydrogen electrode functional layer (NiO / YSZ), an electrolyte (YSZ), an interdiffusion barrier layer (GDC), an air electrode functional layer (LSCF + GDC), and an air electrode collector layer (LSCF) A ceramic powder containing dissolved dispersant, binder and plasticizer was prepared using a planetary ball mill followed by subsequent screen printing. The hydrogen electrode functional layer and the electrolyte were subjected to screen-printing and then immediately co-sintered at 1370 ° C. The GDC interdiffusion barrier layer was screen printed on the batch fired YSZ electrolyte and sintered at 1250 ° C. The LSCF-GDC air electrode functional layer and the LSCF current collector layer were then screen-printed and sintered at 1050 ° C in air. The effective electrode area is 1 cm x 1 cm.

Experimental Example .

First, the crystal structure of the porous cathode composite particles according to the present invention was confirmed by X-ray diffraction (XRD).

Following the process of Example with respect to the hydrogen electrode of the battery 1 using a H ₂ containing 3-50% H ₂ O, and the air electrode, using the air generated powder between 700-800 ℃ temperature and hydrogen-producing mode, Respectively. The gas flow rate was fixed at 200 sccm for all electrodes. The electrochemical properties were measured using a Solartron 1260/1287 oscillator and a constant voltage.

After the electrochemical property test, the battery was divided, and a part of the battery was cured by injecting epoxy in a vacuum state and then polished to 0.25 탆 or less. The cross section of the surface was confirmed by scanning electron microscope (SEM).

Experimental Example  One.

In order to measure the crystallization behavior of the nanocatalyst (SSC) and the porous material (LSCF-GDC), LSCF particles were dispersed in the SSC precursor solution and heat-treated at 80 ° C. for 2 hours and at 800 ° C. for 1 hour , And X-ray diffraction (XRD) were used to measure the crystal structure of the porous cathode composite particles according to the present invention.

As shown in FIG. 1, all major peaks in the XRD pattern were identified as SSC and LSCF perovskite, and secondary state formation was not measured within instrument sensitivity.

In the urea cracking process, the crystallization behavior was found to be strongly affected by the [urea] / [cation] ratio since urea was provided as a precipitant as well as a complexing agent.

Specifically, the urea composite was mixed with metal cations and decomposed at a temperature of 80 캜 or higher, then cooled slowly, and the release of ammonia and carbon dioxide was controlled through the solution.

CO (H ₂ N) ₂ + 3H ₂ O? CO ₂ + 2NH ₃ + 2H ₂ O (1)

As a result, the pH of the solution continued to increase, and a steady supply of OH ^- and CO ₃ ^{2 -} led to the precipitation of metal hydroxides and hydroxycarboxylic acid as precipitants for the formation of the desired ceramic state in the sequential firing process.

The complete formation of the perovskite nano catalyst (SSC) was confirmed in FIG. 1, and it was confirmed that crystallization at 800 ° C. was sufficient when the [urea] / [cation] ratio was 10. In addition, no additional reactants or major peak migration were identified due to chemical bonding with LSCF, which means that the SSC nanocatalyst and LSCF structure are chemically compatible.

Thus, in-situ crystallization allows the formation of SSC nanocatalysts in the early stages of the SORFC device, simplifying the fabrication process and preventing grain boundary coarsening caused by exposure to very high temperatures.

Experimental Example  2.

As shown in Fig. 2, the detailed structure of the SORFC used in this study is shown in Fig. 2 (a). The cell comprised a porous Ni-YSZ hydrogen electrode substrate (not less than 800 μm), a fine, porous Ni-YSZ hydrogen electronic functional layer (not more than 7 μm), dense YSZ electrolyte (not more than 8 μm), a partially dense GDC interdiffusion barrier layer 6 μm or less), a fine porous LSCF-GDC air electronic functional layer (12 μm or less), and a porous LSCF air current collector layer (16 μm or less).

In Fig. 2 (b), the backscattered electron image of the LSCF-GDC composite air electrode was separated into two separated states. The results of energy dispersive spectroscopy showed that LSCF was gray and GDC was white, and the average particle diameter was 0.4 Both LSCF and GDC are homogeneously mixed with a very fine size of 탆 or less.

The volume fraction of the voids and the average pore diameter are, based on image analysis, 80% or more and 0.7 탆 or less. The very fine structure of the air electrode is advantageous in that the active portion capable of electrochemical reaction is increased, but the problem is emphasized that the wetting characteristic of the chemical solution is important since the solution is caused by impregnation with ultrafine pores .

Due to the high polarity of the water, the aqueous solution exhibits low wetting properties in perovskite electrodes and electrolytes due to the high surface tension of water (72.0 mN / m at 25 ° C), although it is mostly an excellent solution for metal nitrate precursors. The surface tension of such an aqueous solution was determined by adding an organic solution having a low surface tension such as ethanol (22.3 mN / m at 25 ° C), acetone (23.7 mN / m at 25 ° C) and isopropanol (21.7 mN / m at 25 ° C) Can be reduced. In the present invention, ethanol was used as a co-solvent in consideration of surface tension, miscibility with water and boiling temperature. In penetration experiments using porous LSCF-GDC electrodes, wetting properties significantly increased due to the addition of ethanol. In particular, it has been found that a solution having a [water] / [ethanol] volume ratio of 1.7 is sufficient to control the penetration of nitrate precursors and ultrafine size pores.

FIG. 2C shows the SSC nanocatalyst formed on the surface of the porous LSCF-GDC air electrode by chemical dissolution and in-situ crystallization infiltration at a temperature of 800 ° C., which is an initial stage of battery operation.

As shown in Fig. 2c, it can be confirmed that the uniform dispersion of the particles over the entire air electrode is due to the low surface wettability with which the liquid beads can be formed, and both LSCF and GDC have excellent wettability of the precursor solution. In addition, SSC nanocatalysts have diameters in the range of 40-80 nm with uniform particle morphology and distribution, which is an advantage of the urea cracking process according to the present invention, which regulates the nucleation process.

Further, in the urea decomposition process according to the present invention, the urea is mixed in the solution and decomposed slowly as soon as it is heated to a temperature of 80 캜 or lower, and the ligand through the solution is uniformly provided to initiate uniform precipitation. Therefore, the dynamics of nanoparticle morphology is well controlled, and as shown in Fig. 2 (c), the size and morphology of nanocatalyst particles have excellent homogeneity.

Also, if the formation of the precipitate is initiated by a drying process instead of a urea decomposition process, the capillary forces will bring the precursor solution to the surface of the porous matrix and cause concentration of the nanoparticles close to the top surface of the electrode.

Experimental Example  3.

The current density voltage (IV) curve and the corresponding power density were compared with the SOFC standard cell as shown in Fig. 3 (a). The measurement was carried out at a temperature of 750 ° C using air as fuel and wet H ₂ (3% H ₂ O) as the oxidant.

The maximum output density of the standard cell is 1.05 W / cm ^2, and the cell in which the nanocatalyst according to the present invention is impregnated is 1.62 W / cm ² . The output density of the standard cell at 0.7 V is 0.86 W / cm ^2, and the cell into which the nanocatalyst according to the present invention is impregnated is 1.39 W / cm ² . This was increased by more than 60% under SOFC operating conditions through the penetration of SSC nanocatalyst into conventional LSCF-GDC air electrode.

Further, for the same battery with a feed of 50% H ₂ O in the air to the H ₂ and the air electrode on the hydrogen electrode, it was tested at 750 ℃ SOFC and SOEC mode (Fig. 3 (b) below). It is reported that the amount of steam is optimum for the Ni-YSZ hydrogen electrode under the SOEC operating condition considering both performance and stability. The amount of steam supplied from the hydrogen electrode is fixed to 50%, and the amount of steam There is a problem in that partial oxidation of Ni is caused at a high vapor content. The OCV of 0.96 V measured for the two cells is in good agreement with the theoretical value according to certain operating conditions and indicates that the desired amount of vapor was supplied to the hydrogen electrode.

On the other hand, in the SOEC mode, the hydrogen generation rate at the thermal neutral voltage is important because the endothermic heat of vapor decomposition is compensated by the ohmic heating, and the hydrogen generation reaction can last without the external heat supplier located above the potential , The thermal neutral voltage of the cell according to the invention was 1.29 V at 750 ° C and the current density increased from 0.9 to 1.8 A / cm ² due to the penetration of the SSC nanocatalyst, and the doubling of the H ₂ production rate was achieved under realizable SOEC operating conditions 3.7 to 7.4 Nm ³ / m ² hr.

Experimental Example  4.

The penetration effect of the nanocatalyst (SSC) according to the present invention was analyzed using the impedance spectrum performed under various operating conditions of the SORFC. In the Nyquist plot of the impedance spectrum, the high-frequency intercept is consistent with the ohmic resistance of the cell, and the low-frequency intercept is described by the total cell resistance including ohmic resistance and electrode polarization resistance. Thus, the electrode polarization resistance can be obtained by the difference between the low-frequency section and the high-frequency section (see FIG. 4).

The impedance spectrum measured at the OCV in FIG. 4 (a) shows that the ohmic resistance is slightly lowered by SSC penetration and the electrode polarization resistance is remarkably lowered. The slight reduction in ohmic resistance due to SSC penetration results from the local network of SSC nano-particles formed on the surface of the LSCF-GDC electrode, which provides an additional conduction path to the current, which is SSC (1000 S / cm), because the electrical conductivity is generally higher than LSCF (about 300 S / cm at 800 ° C).

In order to explain the drastic decrease in the electrode polarization resistance due to the SSC penetration, it is necessary to understand the fundamental reaction path related to the frequency response of the impedance spectrum. The impedance spectrum of the air electrode is known to consist of a number of flat arcs overlapping reflecting the physical and / or chemical processes associated with the electrode response. Each single step represents their inherent characteristic frequency and reacts differently depending on the type of cell material and structure.

As shown in FIG. 4 (a), the board diagram (Bode polt) clearly shows that the impedance spectrum of the tested cell is composed of two dominants having a specific frequency of 10 ² -10 ³ Hz and 1-10 Hz . It has been found that the size of the low-frequency arc (1-10 Hz) is significantly reduced by SSC penetration, while the high-frequency arc (10 ² -10 ³ Hz) is relatively insensitive to air electrode deformation. 4B and 4C, it was confirmed that the SOFC (0.7 V) and the SOEC (1.2 V) show a similar tendency collectively under all the operating conditions.

Meanwhile, the impedance spectrum of the air / hydrogen electrode was analyzed using a separate half cell technique closely related to the fuel cell data.

The performance of the LSCF-GDC air electrode has been confirmed by low frequency impedance (1-10 Hz) and is associated with surface chemical exchange, and due to the small contribution of oxygen ion diffusion, the high vibration range (10 ² -10 ³ Hz). On the other hand, in the case of the Ni-YSZ hydrogen electrode, the main impedance arc appeared at 10 ² -10 ³ Hz due to the gas-solid interconnection, and the low- A frequency-impedance arc (1-10 Hz) was identified. The results can be directly applied to the description of the fuel cell impedance.

In particular, as shown in Fig. 4, the high-frequency arc (10 &lt; ^{2 &gt;} -10 ³ Hz) has a relatively small effect of oxygen ion diffusion on the LSCF- GDC air electrode, And the low-frequency arc (1-10 Hz) consists of gas diffusion through the LSCF-GDC air electrode and the Ni-YSZ hydrogen electrode substrate. Thus, the surface chemical exchange is proposed to regulate the LSCF-GDC air electrode reaction, which is consistent with conventional results, and the binding of the SSC nano-catalyst, as shown in Figures 4 (a) - (c) And lowering the low-frequency impedance arc can effectively increase the electrode performance.

On the other hand, oxygen reduction occurs at the air electrode in the power generation mode, and oxygen gas generation occurs at the hydrogen production mode. Therefore, O ₂ reduction (see Fig. 4b) and O ₂ ^- Surface Chemical Exchange via oxidation (see Fig. 4c) is porous LSCF-GDC air electrode SSC nano-can be significantly accelerated by the combination of the catalyst and, as a result SOFC And SOEC performance can be significantly increased.

Claims (10)

delete delete (a) dissolving a nanocatalyst precursor compound in an alcohol aqueous solution, adding urea, and mixing to prepare a nanocatalyst precursor solution represented by Formula 1 below;
(b) immersing the nanocatalyst precursor solution in a porous composite electrode represented by the following formula (2), followed by performing a urea decomposition process at 70 to 90 캜; And
(c) firing the urea decomposition process,
Wherein the molar ratio of urea to cation in the precursor solution is 5-15: 1.
(2)
(Perovskite) -E _{1 -Z} F _Z O _2-隆 (fluorite) -A _{1 -X} B _X C _{1 -Y} D _Y O _3-δ
In the above formula 2, A is one element of La, Ba and Y, B is one element of Sr and Ca, C and D are elements of one of Mn, Co, Fe and Ni, E X is a real number of 0 <X <1, Y is a real number of 0 <Y <1, and Z is a real number of 0 < 0 < Z < 1, [delta] is a real number of 0 <
[Chemical Formula 1]
G _x H _1-x IO _3-隆 (SSC)
In the above formula 1, G and H are elements of one of Sm, Sr, La, Ca and Ba, I is one element of Co, Mn and Fe, X is a real number of 0 &lt; , and? is a real number of 0???? 1.
The method of claim 3,
Wherein the precursor compound is nitrate or acetate. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
The method of claim 3,
Wherein the alcohol aqueous solution is at least one selected from the group consisting of methanol, ethanol, propanol, and butanol, and the alcohol has a volume ratio of water to water of 0.5: 3: 1, and the alcohol is at least one selected from methanol, ethanol, propanol and butanol.
delete delete The method of claim 3,
Wherein the calcination in step (b) is performed at 700-1000 &lt; 0 &gt; C.
A porous cathode composite prepared by the method of any one of claims 3 to 5 and 8.
A solid oxide regenerative fuel cell comprising the porous cathode composite according to claim 9.

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