KR20120139384A - Reforming composite material, and anode structure for fuel cell and solid oxide fuel cell including the material - Google Patents

Abstract

PURPOSE: A reforming composite material capable of improving coke resistance of cathode, a cathode structure for fuel cells and a solid oxide fuel cell adopting the same are provided to drastically increase conductivity. CONSTITUTION: A reforming composite material comprises supported catalyst which includes nickel metal, alkali series metal, lanthanum based metal and group 11 transition metals. The cathode structure for the fuel cells comprises a negative electrode layer, and a reforming layer is placed on one or more sides and includes a reforming layer. The solid oxide fuel cell contains cathod, positive electrode, and solid oxide elctrolyte.

Description

Reforming composite material, and anode structure for fuel cell and solid oxide fuel cell including the material}

A reforming composite material, a cathode structure for a fuel cell and a solid oxide fuel cell employing the same are provided.

A solid oxide fuel cell (SOFC) is a device that generates electricity by flowing a fuel of hydrogen or hydrocarbon to the anode (cathode) and oxygen to the cathode (anode) using a solid oxide as an electrolyte. The anode of SOFC plays the role of electrochemical oxidation and electron transfer of fuel. Ni-YSZ ceramics (ceramic-metallic composites) are widely used as anodes in systems using YSZ as an electrolyte and CO and H ₂ as fuels.

As a fuel cell for low temperature, SOFC has the advantage of wide choice of fuel in that not only hydrogen but also hydrocarbon fuel can be used. Currently, the use of fossil fuels in low-temperature fuel cells requires additional purification after the reforming of the fossil fuels, but SOFC can use the modified fossil fuels directly without refining. This is because some hydrocarbons are contained in the fuel. Furthermore, SOFC can also directly use fossil fuels such as LNG without reforming reaction.

Ni-YSZ ceramic alloy, the most commonly used SOFC anode material, is used as a good electrocatalyst when using hydrogen fuel, but has low hydrocarbon reforming activity when using hydrocarbon fuel, and carbon deposition. There is a problem in that durability is reduced by coking formation due to deposition). In order to solve such low hydrocarbon reforming activity, a method of introducing a reforming layer such as Ru-CeO ₂ or Ni-Al ₂ O ₃ onto the cathode layer has been proposed. However, these catalysts have a problem in that the electrical conductivity is low, so that the function as a current collector of the fuel cell is reduced.

Therefore, in addition to improving the low reforming activity of the Ni-YSZ cathode catalyst and improving the coke resistance under the conditions of directly using hydrocarbon fuels, the new anode (cathode) structure and material with high electrical conductivity can be obtained. Development is needed.

One aspect of the present invention is to provide a reforming composite material having excellent hydrocarbon reforming activity, high coking resistance, and high electrical conductivity.

Another aspect of the present invention is to provide a negative electrode structure for a fuel cell employing the reforming composite material.

Another aspect of the present invention is to provide a solid oxide fuel cell having the anode structure for the fuel cell as a cathode.

According to one aspect of the invention,

A supported catalyst comprising a nickel (Ni) metal, an alkali metal and a lanthanum metal; And

There is provided a reforming composite material comprising a Group 11 transition metal.

According to another aspect of the present invention,

Cathode layer; And

A negative electrode structure for a fuel cell is provided, comprising: a reforming layer disposed on at least one surface of the cathode layer and including the reforming composite material.

According to another aspect of the present invention,

A negative electrode including the negative electrode structure;

An anode disposed to face the cathode; And

There is provided a solid oxide fuel cell comprising a; solid oxide electrolyte disposed between the cathode and the anode.

The reforming composite material according to an embodiment of the present invention has a high hydrocarbon reforming activity, high coke resistance, and very high electrical conductivity, so that the solid oxide fuel cell directly uses a hydrocarbon-based fuel. It can be usefully applied as a cathode functional layer on the cathode layer in the.

1 is a cross-sectional view schematically showing the structure of a solid oxide fuel cell according to one embodiment.
2 is an X-ray diffraction pattern measurement results of the reforming composite material of Preparation Example 1-3 and the LiLaNi-Al ₂ O ₃ catalyst of Comparative Example 1.
3 is a catalytic activity measurement result for partial oxidation of methane of the reforming composite material obtained in Preparation Example 1-3.
4 is a catalytic activity measurement result for steam reforming of methane of the reforming composite material obtained in Preparation Example 1-3.
FIG. 5 shows catalytic activity results for CO ₂ reforming of methane of the reforming composite material obtained in Preparation Example 1-3.
FIG. 6 shows the results of hydrogen temperature-programmed reduction (H ₂ -TPR) of the reforming composite materials of Preparation Examples 1 to 3 and the LiLaNi-Al ₂ O ₃ catalyst of Comparative Example 1. FIG.
7 is a graph showing methane conversion and CO selectivity according to reaction time after partial oxidation of methane is performed on the reforming composite material of Preparation Example 1. FIG.
8 is a result of Oxygen temperature-programmed oxidation (O ₂ -TPO) of the reforming composite material of Preparation Example 1-3 and the LiLaNi-Al ₂ O ₃ catalyst of Comparative Example 1.
9 is a Raman spectrum analysis of the samples of Preparation Example 1 and Comparative Example 1 after the O ₂ -TPO.
10 to 12 show the IV and IP measurement results of the fuel cell of Example 1 operated at CH ₄ -O ₂ , CH ₄ -H ₂ O, and CH ₄ -CO ₂ , respectively.
13 to 15 are IV and IP measurement results of the fuel cell of Comparative Example 1 operated at CH ₄ -O ₂ , CH ₄ -H ₂ O, and CH ₄ -CO ₂ , respectively.
16 is a graph illustrating a result of measuring the voltage and the power density over time by operating the fuel cell of Example 1 with a CH ₄ -O ₂ mixed gas at a temperature of 850 ° C. for 400 minutes.
FIG. 17 is a photograph of a cross section of a fuel cell of Example 1 observed after scanning using a scanning electron microscope (SEM). FIG.

EMBODIMENT OF THE INVENTION Hereinafter, specific embodiment of this invention is described in detail.

The reforming composite material according to an aspect of the present invention includes a supported catalyst including nickel (Ni), an alkali metal and a lanthanum metal, and a Group 13 transition metal.

The reforming composite material is to improve the low hydrocarbon reforming activity of the Ni cermet anode material generally used in fuel cells, and includes an alkali metal and a lanthanum metal based on nickel (Ni) as a main component. A catalyst metal is supported on a carrier such as alumina to improve coking resistance with high reforming activity, and low electricity due to insulation of a carrier supporting a supported catalyst including a Group 13 transition metal having high electrical conductivity as an electron carrier. It solves the problem of conductivity. By using the reforming composite material to form a reforming layer on the cathode layer as a cathode functional layer, reforming efficiency, stability, durability, and the like of the SOFC for hydrocarbon fuel can be directly improved.

The supported catalyst has a form in which active ingredients such as nickel (Ni), an alkali metal and a lanthanum metal having catalytic activity are supported on a carrier. The carrier is not particularly limited as long as it is mechanically, thermally, chemically stable, and has a porous or large surface area to disperse and support the active ingredients. For example, metal oxides such as Al ₂ O ₃ , SiO ₂ , MgO, MnO, ZnO, TiO ₂ , ZrO ₂ , CeO _2, and the like may be used as the carrier, and these metal oxides may be used alone, It is also possible to use a mixture of two or more kinds. According to one embodiment, Al ₂ O ₃ may be used as the carrier.

The nickel (Ni) metal is a main component for imparting reforming activity in the reforming composite material, and the content of nickel (Ni) metal may be 20 to 50 parts by weight based on 100 parts by weight of the supported catalyst. For example, the nickel (Ni) metal may be 25 to 45 parts by weight based on 100 parts by weight of the supported catalyst, and more specifically 25 to 35 parts by weight. With respect to the reforming reaction such as partial oxidation of methane (partial oxidation), steam reforming (steam reforming), CO ₂ reforming (CO ₂ reforming) in the above content range it can exhibit excellent catalytic activity.

By further including an alkali-based metal and a lanthanum-based metal in the supported catalyst together with the nickel metal, coking resistance can be improved without inhibiting the reforming catalyst activity of the nickel metal. Nickel metal may be deteriorated in activity due to carbon deposition during the reforming of hydrocarbon-based fuels, while the supported catalyst may include alkali-based metals and lanthanide-based metals so that the surface of the supported catalyst is basic. It promotes nickel metal, and this basic surface can effectively prevent the carbon deposition phenomenon.

The alkali metal includes Group 1 elements such as Li, Na, K, and Rb, and may be used alone or in the form of a mixture or alloys of two or more thereof, or oxide forms thereof. For example, the alkali metal may be Li. Such alkali-based metals can bring about steric effect and electronic modification in the supported catalyst.

The content of the alkali metal is not particularly limited, and may be determined within an appropriate range capable of imparting coking resistance with the lanthanum metal. For example, the content of the alkali metal may be 0.1 to 2 parts by weight, specifically 0.5 to 1.5 parts by weight, and more specifically 0.8 to 1.2 parts by weight based on 100 parts by weight of the supported catalyst.

The lanthanum-based metal includes lanthanide elements such as La, Ce, Pr, Nd, Sm Gd, Tb, Dy, and Yb, and may be used alone or in a mixture or alloy form of two or more thereof. Also available. For example, the lanthanum metal may be La. According to one embodiment, in the case of using an alumina carrier, such lanthanum-based metal may delay the transition of the crystal structure of the alumina carrier from γ-A1 ₂ O ₃ to α-A1 ₂ O ₃ having a low surface area.

The content of the lanthanum-based metal is not particularly limited, and may be determined within an appropriate range capable of imparting coking resistance with the alkali-based metal. For example, the content of the lanthanum-based metal may be 1 to 10 parts by weight, specifically 2 to 8 parts by weight, and more specifically 4 to 6 parts by weight based on 100 parts by weight of the supported catalyst.

The supported catalyst may be prepared by, for example, GNP (Glycine Nitrate Process). The GNP method is useful in that the exposure time to high temperature is short and the particle size can be kept small while effectively promoting the interaction between NiO and the carrier.

The reforming composite material includes a Group 13 transition metal together with the supported catalyst.

Group 13 transition metals such as Cu have a low cracking reaction activity and high electrical conductivity, thereby overcoming the low electrical conductivity problem of the supported catalyst, for example, can increase the electrical conductivity to about 10 ¹⁰ times. . Therefore, the reforming composite material may perform a current collector function in the anode structure of the fuel cell.

In addition, the Group 13 transition metal can increase the proportion of amorphous carbon than crystalline carbon such as graphite when caulking occurs, which is more reactive than graphite and easier to remove from the catalyst surface. Therefore, catalyst regeneration can be improved by the addition of the Group 13 transition metal.

The Group 13 transition metal may include Cu, Ag, Au, alloys thereof, or oxides thereof, or may be used alone or in a mixed form of two or more thereof. The Group 13 transition metal may be introduced by physical mixing with a supported catalyst, for example, to form a continuous percolate phase in the reforming material and contribute to the improvement of electrical conductivity. According to one embodiment, in the reforming composite material obtained after physically mixing the supported catalyst using an alumina carrier with the Group 13 transition metal and calcining, the Group 13 transition metal is a nickel (Ni) metal, an alkali metal, and It was confirmed through X-ray diffraction analysis that the lanthanum-based metal may be present in the form of a monometallic oxide, a binary oxide with aluminum, or a combination thereof without forming an alloy.

The content of the Group 13 transition metal is not particularly limited, but may be determined in a range capable of improving electrical conductivity by forming a continuous percholate phase without reducing the performance of the fuel cell. For example, the content ratio of the supported catalyst and the Group 13 transition metal may be 80:20 to 20:80 by weight. Specifically, the content ratio of the supported catalyst and the Group 13 transition metal may be 70:30 to 30:70 by weight, and more specifically, 60:40 to 40:60.

As described above, the reforming composite material includes a supported catalyst including nickel (Ni), an alkali metal and a lanthanide metal, and a group 13 transition metal, thereby improving the reforming activity and increasing the coking resistance and the electrical conductivity. Can be.

According to one embodiment, it can have a high electrical conductivity of 1.0 Scm ^-1 or more of the reforming composite material.

In another aspect of the invention, the cathode layer; And a reforming layer including the above-described reforming composite material disposed on at least one surface of the cathode layer.

The anode structure for the fuel cell is to form a reforming layer including the reforming composite material on at least one surface of the cathode layer to improve the reforming efficiency of the SOFC for direct hydrocarbon fuel, and to enable stable operation of the cell without reducing performance. Can be. The negative electrode structure will be described together in a solid oxide fuel cell to be described later.

In another aspect of the invention, the negative electrode comprising the negative electrode structure; An anode disposed to face the cathode; And a solid oxide electrolyte disposed between the cathode and the anode.

1 is a cross-sectional view schematically showing the structure of a solid oxide fuel cell according to one embodiment. Referring to FIG. 1, in the solid oxide fuel cell 100, an anode 120 and a cathode 110 are disposed on both sides of the solid oxide electrolyte 130. The cathode 110 is a cathode structure composed of a cathode layer 111 and a reforming layer 112.

The solid oxide electrolyte 130 should be dense so as not to mix air and fuel, and should have high oxygen ion conductivity and low electron conductivity. In addition, since the positive electrode 120 and the negative electrode 110 having a large oxygen partial pressure difference are positioned at both sides of the electrolyte 130, it is necessary to maintain the above physical properties in a wide oxygen partial pressure region.

The material constituting the solid oxide electrolyte 130 is not particularly limited as long as it can be generally used in the art, and is selected from, for example, zirconia-based, ceria-based, bismuth oxide-based, and lanthanum gallate-based solid electrolytes. It may include at least one. For example, the solid oxide electrolyte 130 may be zirconia-based or doped with at least one of yttrium, scandium, calcium, and magnesium; Ceria based or not doped with at least one of gadolinium, samarium, lanthanum, ytterbium and neodymium; Bismuth oxide based or doped with at least one of calcium, strontium, barium, gadolithium and yttrium; And it may include at least one selected from the group consisting of lanthanum gallate (doped or not doped with at least one of strontium and magnesium. Specific examples of the solid oxide electrolyte 130 include yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), samaria doped ceria (SDC), gadolinia doped ceria (GDC), and the like.

The solid oxide electrolyte 130 may have a thickness of about 10 nm to about 100 μm. For example, the thickness of the solid oxide electrolyte 130 may be 100 nm to 50 μm.

The anode 120 reduces the oxygen gas to oxygen ions and maintains a constant oxygen partial pressure by continuously flowing air to the anode 120. As the material of the anode 120, for example, metal oxide particles having a perovskite crystal structure can be used, and (La, Sr) MnO ₃ , (La, Ca) MnO ₃ , (Sm, Sr ) CoO _3, there may be mentioned _{(La, Sr) CoO 3,} (La, Sr) (Fe, Co) O 3, ( the metal oxide particles, such as La, Sr) (Fe, Co , Ni) O 3 as an example. The metal oxide particles described above may be used alone or in combination of two or more kinds thereof. As the material for forming the cathode layer, it is also possible to use precious metals such as platinum, ruthenium and palladium.

The thickness of the anode 120 may be typically 1 to 100 μm. For example, the thickness of the first anode 120 may be 5 to 50 μm.

Between the anode 120 and the solid oxide electrolyte 130 may further include a cathode functional layer to more effectively prevent the reaction between them as needed. Such an anode functional layer may include, for example, at least one selected from the group consisting of gadolinium doped ceria (GDC), samarium doped ceria (SDC), and yttrium doped ceria (YDC). The bipolar functional layer may have a thickness in the range of 1 to 50 μm, for example, 2 to 10 μm.

The cathode 110 (fuel electrode) includes a cathode structure composed of the cathode layer 111 and the reforming layer 112. The cathode layer 111 plays a role of electrochemical oxidation and charge transfer of the fuel. Therefore, it is preferable to use a cathode catalyst which is chemically stable and has a similar thermal expansion coefficient to the electrolytic material.

The cathode layer 110 may include a Ni cermet in which a material for forming the solid oxide electrolyte 130 and nickel oxide are mixed. For example, when YSZ is used as an electrolyte, a Ni / YSZ composite (ceramic-metallic composite) may be used as the cathode layer 111. In addition, pure metals such as Ni, Co, Ru, and Pt may be used as the material of the cathode layer 111, but is not limited thereto. The negative electrode layer 111 may further include activated carbon as necessary. The cathode 111 may have a porosity so that the fuel gas can be diffused well.

The negative electrode layer 111 may have a thickness of about 1 μm to 1000 μm. For example, the thickness of the cathode layer 111 may be 5 to 100 μm.

The reforming layer 112 includes the reforming composite material, and as described above with respect to the reforming composite material, a detailed description thereof will be omitted herein.

The thickness of the reforming layer 112 may be 1 to 100 μm. For example, the thickness of the cathode layer 111 may be 5 to 50 μm.

The solid oxide fuel cell may be manufactured using conventional methods known in various literatures in the art. In addition, the solid oxide fuel cell may be applied to various structures such as a cylindrical stack, a flat tubular stack, and a planar type stack.

Hereinafter, the present invention will be exemplified by the following examples, but the protection scope of the present invention is not limited only to the following examples.

Manufacturing example  One: Reforming  Production of composite materials (1)

LiLaNi-Al ₂ O ₃ catalyst powder consisting of 1 wt% Li ₂ O, 5 wt% La ₂ O ₃ , 30 wt% Ni and the remaining amount of Al ₂ O ₃ was synthesized using a glycine nitrite process (GNP) method. First, chemical equivalents of nickel nitrate, lithium nitrate, lanthanum nitrate and alumina nitrate were dissolved in deionized water and glycine was added at a ratio of 2.0 to the metal cation. The solution was heated on a hotplate with continued stirring to evaporate all the water in the solution and form a liquid precursor. The liquid precursor was transferred to an electric oven at 240 ° C. for automatic combustion. The powder obtained here was sintered at 850 ° C. for 5 hours to obtain a final LiLaNi-Al ₂ O ₃ catalyst powder.

The LiLaNi-Al ₂ O ₃ catalyst and copper oxide (Shanghai zhenxin reagents Co., Ltd., China) were mixed in a weight ratio of 50:50 and physically mixed by grinding using agate mortar and pestle. After physical mixing, the catalyst was sintered at 850 ° C. for 5 hours to obtain a LiLaNi-Al ₂ O ₃ / Cu reforming composite material.

Manufacturing example  2: Reforming  Production of composite materials (2)

A reforming composite material was obtained in the same manner as in Preparation Example 1, except that the mixing ratio of the LiLaNi-Al ₂ O ₃ catalyst and the copper oxide in Preparation Example 1 was 40:60 by weight.

Manufacturing example  3: Reforming  Manufacture of composite materials (3)

A reforming composite material was obtained in the same manner as in Preparation Example 1, except that the mixing ratio of the LiLaNi-Al ₂ O ₃ catalyst and the copper oxide in Preparation Example 1 was 20:80.

Comparative example  One

As a control, LiLaNi-Al ₂ O ₃ supported catalyst obtained by synthesis of GNP (glycine nitrite process) in Preparation Example 1 without mixing copper was used as Comparative Example 1.

Comparative example  2

In order to compare the electrical conductivity of the reforming composite material of Preparation Example 1-3, the measurement result of the electrical conductivity of the Ni-YSZ cermet negative electrode was set as Comparative Example 2.

Example  1-3: Manufacture of Fuel Cell

A fuel cell is _{La 0 .8 Sr 0 .2 MnO 3} (LSM) _{cathode, (Y 2 O 3) 0.1} (ZrO 2) 0.9 (YSZ) that is not the electrolyte and reduction NiO + YSZ anode (NiO: YSZ = 60: 40 , Weight ratio). LSM was synthesized according to the EDTA-citrate complex sol-gel method. In the above procedure, metal nitrate (analytical reagent) was used as a raw material, and commercial NiO (Chengdu Shudu Nano-science Co., Ltd.) and YSZ (Tosoh) were used as negative electrode materials.

The negative electrode substrate was prepared by tape-casting, and the organic solvent was removed by heat treatment in air at 1100 ° C. for 2 hours. In order to deposit the electrolyte layer, a colloidal suspension (solid content of 5 wt%) in which fine YSZ powder was dispersed in ethylene glycol through high energy ball milling (Fritcsch, Pulverisettle 6) for 0.5 h at 400 rpm was spray deposited on the negative electrode substrate. It was deposited to prepare an electrolyte layer. The double layer green cell obtained above was sintered in air at 1400 ° C. for 5 hours to increase the density of the electrolyte layer. An LSM + YSZ composite anode (LSM: YSZ = 70: 30, weight ratio) was deposited on the YSZ electrolyte at a surface area of 0.48 cm ² by the spray deposition method, and then sintered in air at 1100 ° C. for 2 hours to give a positive electrode. A layer was formed. The negative electrode functional layer was prepared by forming each of the reforming materials obtained in Preparation Examples 1 to 3 by screen painting on the negative electrode and sintering at 850 ° C. for 1 hour.

Comparative example  3: Manufacture of Comparative Fuel Cell

Except for using the LiLaNi-Al ₂ O ₃ catalyst of Comparative Example 1 as the negative electrode functional layer in Example 1, the same procedure as in Example 1 was carried out to prepare a fuel cell of the control.

Evaluation example  1: X-ray diffraction  analysis

X-ray diffraction patterns using CuKα rays were measured for the reforming composite material of Preparation Example 1-3 and the LiLaNi-Al ₂ O ₃ catalyst of Comparative Example 1, and the results are shown in FIG. 2.

As shown in FIG. 2, g-Al ₂ O ₃ and NiAl ₂ O ₄ crystal phases were observed in all samples, and the peaks of La ₂ O ₃ and Li ₂ O were observed in the reforming composite material of Preparation Example 1-3. It can be seen that La ₂ O ₃ and Li ₂ O are well dispersed in the catalyst. In addition, it is understood that Cu does not form an alloy with Ni, Li, and La, and exists in the form of CuO or CuAl ₂ O ₄ .

Evaluation example  2: Reforming  Catalytic Activity Assessment

In order to evaluate the catalytic activity of the reforming composites obtained in Preparation Examples 1 to 3 for partial oxidation, steam reforming and CO2 reforming of methane, a size of 40-60 mesh About 2.0 g of catalyst particles were introduced into a tubular quartz-tube reactor with an inner radius of about 8 mm and gas flow was controlled by AFC 80MD digital mass flow controllers (Qualiflow) during each reforming reaction. The gas mixture was introduced to the top of the reactor, and the exhaust gas was transferred from the bottom of the reactor to a Varian 3800 gas chromatograph (GC) for composition analysis at 600-850 ° C. GC was equipped with Hayesep Q, Poraplot Q, 5Å molecular sieve capillary column and a thermal conductivity detector, and detected by separating H ₂ , O ₂ , CO, CO ₂ and CH ₄ . Prior to the reforming reaction, all catalysts were reduced in a hydrogen atmosphere at 850 ° C. for 1 hour. The methane flow rate was fixed at 10 m / min during the measurement and helium was fixed at a flow rate of 80 ml / min and applied as a carrier gas. Partial oxidation, steam reforming and CO ₂ reforming reactions of methane were carried out at 600-850 ° C. and proceed as shown in the following scheme. The gas used for each reaction was a 2: 1, 1: 1 and 1: 1 ratio of methane to O ₂ / H ₂ O / CO ₂ , respectively.

(Partial oxidation) CH ₄ + 0.5H _2- > CO + 2H ₂

(Steam reforming) CH ₄ + H ₂ O-> CO + 3H ₂

(CO ₂ reforming) CH ₄ + CO _2- > 2CO + 2H ₂

The conversion of methane in partial oxidation and steam reforming of methane (X (%)) was calculated according to Equation 1 below, and the conversion of methane in CO2 reforming was calculated according to Equation 2 below. In addition, the selectivity (S1 (%) and S2 (%)) of CO and H2 was calculated according to the following equations 3 and 4, respectively.

[식 1]

[Formula 1]

[식 2]

[Formula 2]

[식 3]

[Equation 3]

[식 4]

[Formula 4]

The catalytic activity results for partial oxidation, steam reforming and CO ₂ reforming of the methane of the reforming composite material obtained in Preparation Examples 1 to 3 are shown in FIGS. 3 to 5, respectively. .

Referring to FIGS. 3 to 5, samples having LiLaNi-Al ₂ O ₃ : Cu ratios of 5: 5 and 4: 6 exhibited significant catalytic performance in the range of 750-850 ° C., and the performance of the samples having 2: 8 is It was the lowest in all three responses. For example, when steam reforming, the methane conversions of samples containing 50%, 60% and 80% Cu were 99.8%, 99.1% and 94.8% at 850 ° C, respectively. It tended to decrease more.

In addition, as shown in Figures 3 to 5, it can be seen that while the hydrogen selectivity decreases with temperature reduction in partial oxidation and steam reforming, the hydrogen selectivity remains almost stable in CO ₂ reforming. The lower the copper content is, the better the catalytic activity, but in terms of electrical conductivity it is necessary to contain a sufficient amount of copper will be described later.

Evaluation example  3: with metal oxide Al ₂ O ₃ carrier  The interaction between

Hydrogen temperature-programmed reduction (H ₂ -TPR) was performed to confirm the chemical interaction between NiO / CuO and Al ₂ O ₃ carriers. First, the reforming composite materials of Preparation Examples 1 to 3 and the LiLaNi-Al ₂ O ₃ supported catalyst of Comparative Example 1 were each placed in a U-type quartz reactor having an inner radius of about 3 mm by 3 g each, and 400 ° C. in an argon atmosphere. Pretreated at 30 ml / min for 30 minutes. After cooling the reactor to room temperature the atmosphere was changed to 10 vol% H ₂ / Ar and the reactor was heated to 930 ° C. at a rate of 10 ° C./min. The consumption of hydrogen was monitored in real time with a TCD detector, and the results are shown in FIG. 6.

As shown in FIG. 6, all samples showed peaks at 800 ° C., which is a temperature at which reduction of NiAl ₂ O ₄ spinels occurs. In the LiLaNi-Al ₂ O ₃ supported catalyst of Comparative Example 1, in which Cu was not added, no peak was observed at 330 ° C, and a broad peak was observed at 513 ° C. 330 ° C is the temperature at which free NiO reduction occurs, which means no free NiO, and the peak at 513 ° C is related to the high Ni content of LiLaNi-Al ₂ O ₃ (30%). Will follow. The TPR signal was quantified for the Cu-containing sample shown in FIG. 6 and the results are shown in Table 1 below.

As shown in Table 1, it can be seen that the amount of free NiO decreases with the addition of Cu, which indicates that the addition of Cu inhibits Ni particle growth by increasing the interaction of Ni and Al ₂ O ₃ carriers. .

Catalyst The ratios of H ₂ consumption below 500 and above 600 ℃ (R ₁ ) The mole ratios of copper to nickel in the as-prepared catalysts (R ₂ ) Calculated
Free NiO / total NiO ratios (R) Production Example 1 LiLaNi-Al ₂ O ₃ / Cu (50:50) 5.0 3.08 0.320 Production Example 2 LiLaNi-Al ₂ O ₃ / Cu (40:60) 6.7 4.62 0.270 Production Example 3 LiLaNi-Al ₂ O ₃ / Cu (20:80) 16.8 12.3 0.251

Evaluation example  4: catalyst durability evaluation

In order to evaluate the effect of copper on the operating stability of the LiLaNi-Al ₂ O ₃ supported catalyst, the reforming composite material of Preparation Example 1 for 300 hours at 850 ℃ under a condition of 2: 1 CH ₄ : O ₂ ratio Partial oxidation of methane was carried out. Methane conversion and CO selectivity according to the reaction time of the reforming composite material are shown in FIG. 7.

As shown in FIG. 7, there was no decrease in performance over the entire run time, methane conversion was stable at about 98%, and CO selectivity reached 100%. Such excellent catalyst durability is due to the strong interaction between NiO / CuO and Al ₂ O ₃ carriers as described in Evaluation Example 3 above.

Evaluation example  5: electrical conductivity evaluation

The electrical conductivity of the reforming composite material of Preparation Example 1-3 and the LiLaNi-Al ₂ O ₃ supported catalyst of Comparative Example 1 was analyzed using a 4-probe DC method. The silver paste was painted on the catalyst layer at a predetermined interval S to form current and voltage electrodes, and each silver line was used for electrode contact and voltage contact. The constant current was applied and the response of the voltage line was measured using a Keithley 2420 source meter, and electrical conductivity was measured by the following equation.

[식 5]

[Formula 5]

(ρ: electrical conductivity (S cm ^-1 ), S: distance between probes (cm), V: voltage (V), I: current (A))

Electrical conductivity measurement results are shown in Table 2 below. For comparison, the electrical conductivity (comparative example 2) of the Ni-YSZ cermet negative electrode is shown in Table 2 together.

Sample Surface conductivity (S cm ^-1 ) Comparative Example 1 LiLaNi-Al ₂ O ₃ 5.23 × 10 ^-10 Production Example 1 LiLaNi-Al ₂ O ₃ / Cu (50:50) 1.60 Production Example 2 LiLaNi-Al ₂ O ₃ / Cu (40:60) 1.62 Production Example 3 LiLaNi-Al ₂ O ₃ / Cu (20:80) 1.75 Comparative Example 2 Ni-YSZ 1.91

As shown in Table 2, Comparative Example 1 without the addition of Cu exhibited a low electrical conductivity of 5.23 × 10 ⁻¹⁰ S cm ⁻¹ because the Al ₂ O ₃ carrier was an insulator. On the other hand, Production example 1-3 of Cu is added, it showed a high electric conductivity of each of ^{1.60 S cm -1, 1.62 S cm} -1 and 1.75 S cm ^-1, around 10 in comparison to Comparative Example 1 Cu is not added ^The electrical conductivity increased by about ¹⁰ times. This indicates that copper increased the electrical conductivity while forming a percolate phase in the catalyst layer. On the other hand, the Ni-YSZ cermet negative electrode also showed a significant electric conductivity value (1.91 S cm ⁻¹ ).

Evaluation example  6: Caulking  Resistance coke resistance ) evaluation

In order to evaluate the coking resistance of the reforming composite material of Preparation Examples 1-3 and the LiLaNi-Al ₂ O ₃ supported catalyst of Comparative Example 1, a carbon deposition test was performed.

First, the reduced reforming composite material of Preparation Example 1-3 and the LiLaNi-Al ₂ O ₃ supported catalyst of Comparative Example 1 were each placed in a tubular quartz-tube reactor, each about 2 g, and pure methane at a flow rate of 40 ml / min. The atmosphere was treated at 750-850 ° C. for 5 hours, and the reactor was cooled to room temperature under an inert atmosphere. Next, about 2 g of carbon-deposited catalyst was placed in a U-type quartz reactor having an inner radius of about 3 mm, and pure oxygen at a flow rate of 20 ml / min was added to the top of the reactor for 30 minutes in order to perform Oxygen temperature-programmed oxidation (O2-TPO). Supplied. The reactor was then heated to 800 ° C. at 10 ° C./min. Carbon deposited on the catalyst surface was gradually oxidized to CO ₂ . The exhaust gas from the reactor was connected to a mass spectrometer (Hiden QIC-20) to monitor the CO ₂ concentration, and the results are shown in FIG. 8.

As shown in FIG. 8, the coking resistance of the sample to which 50% of Cu was added was similar to that of the sample to which no addition was made. The caulking of the sample added with 60% Cu increased slightly, and the caulking of the sample added with 80% increased approximately twice as much as the sample without addition.

In addition, the samples of Preparation Example 1 and Comparative Example 1 using a Raman spectrometer (HR800 UV Raman micro spectrometer, JOBIN YVON, France) in order to confirm the carbon deposited on the sample to which Cu and the sample is not added Raman spectrum analysis was performed and the results are shown in FIG. 9.

As shown in FIG. 9, the carbon of the sample to which 50% of Cu was added was relatively high in amorphous carbon, and the carbon of the sample in which Cu was not added was relatively high in graphite form. This means that amorphous carbon is more reactive than graphite and is easier to remove from the catalyst surface, making it easier to regenerate the catalyst by the addition of Cu.

Evaluation example  7: Current-Voltage and Power Density Measurements

The fuel cells of Example 1 and Comparative Example 3 were subjected to IV and IP measurements using a Keithley 2420 source meter in 4-probe mode. During the measurement, hydrogen fuel and CH ₄ -O ₂ , CH ₄ -H ₂ O or CH ₄ -CO ₂ fuel were supplied to the cathode chamber and external air was supplied to the anode chamber as oxidizing gas. The flow rates of hydrogen and methane were maintained at 80 ml / min. IV and IP measurement results of the fuel cell of Example 1 operated at CH ₄ -O ₂ , CH ₄ -H ₂ O and CH ₄ -CO ₂ 10 and 12, respectively, show IV and IP measurement results of the fuel cell of Comparative Example 1 operated at CH ₄ -O ₂ , CH ₄ -H ₂ O, and CH ₄ -CO ₂ . Each is shown in FIGS. 13-15. In FIG. 10-15, the white dot is the graph which plotted the IV relationship at each measurement temperature, and the black dot is the graph which plotted the output density computed from the IV graph.

As shown in Figures 10-15, the performance of the SOFC appeared similar before and after the Cu addition. In other words, it can be seen that addition of Cu did not reduce the power density as compared to LiLaNi-Al ₂ O ₃ catalyst without addition of Cu.

Evaluation example  8: Cell durability rating

In order to evaluate the durability (stability) of the fuel cell of Example 1, the fuel cell was operated for 400 minutes at a temperature of 850 ° C. with a CH ₄ -O ₂ mixed gas having a molar ratio of CH ₄ : O ₂ of 4: 1. Voltage and power density measurement results are shown in FIG. 16.

As shown in FIG. 16, at a current density of 1000 mA cm ⁻² for the entire operating time, the voltage was stable at 0.75 V and the corresponding power density was stable at 750 mW cm ⁻² . The stability of the cell is due to the coking resistance of the Cu-added LiLaNi-Al ₂ O ₃ catalyst.

After cell performance and stability tests were performed at 750-850 ° C. for 15 hours, the cross section of the fuel cell was observed using a scanning electron microscope (SEM), and the SEM photograph is shown in FIG. 17.

As shown in FIG. 17, the cathode functional layer (forming layer) is well adhered to the surface of the cathode, and the reforming composite material of 1 has thermal and mechanical compatibility with the cathode of the fuel cell. It can be seen that. In addition, no carbon deposition was observed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, . Accordingly, the scope of protection of the present invention should be determined by the appended claims.

100: solid oxide fuel cell 110: cathode (cathode structure)
111: cathode layer 112: reforming layer
120: anode 130: solid oxide electrolyte

Claims (19)

A supported catalyst comprising a nickel (Ni) metal, an alkali metal and a lanthanum metal; And
Group 11 transition metal; reforming composite material comprising a. The method of claim 1,
The supported catalyst is a carrier in which the nickel (Ni) metal, the alkali metal and the lanthanum metal are selected from Al ₂ O ₃ , SiO ₂ , MgO, MnO, ZnO, TiO ₂ , ZrO ₂ , CeO _2, and combinations thereof. Reforming composite material with a supported form. The method of claim 1,
Wherein said alkali-based metal comprises at least one selected from Li, Na, K, Rb, alloys thereof, oxides thereof, and combinations thereof. The method of claim 1,
The lanthanum-based metal is a reforming composite material comprising at least one selected from La, Ce, Pr, Nd, Sm Gd, Tb, Dy, Yb, alloys thereof, oxides thereof, and combinations thereof. The method of claim 1,
A reforming composite material including 20 to 50 parts by weight of the nickel (Ni) metal, 0.1 to 2 parts by weight of the alkali metal, and 1 to 10 parts by weight of the lanthanum metal, based on 100 parts by weight of the supported catalyst. The method of claim 1,
The Group 11 transition metal includes at least one selected from Cu, Ag, Au, alloys thereof, oxides thereof, and combinations thereof. The method of claim 1,
The Group 11 transition metal does not form an alloy with the nickel (Ni) metal, the alkali metal and the lanthanum metal. The method of claim 1,
The Group 11 transition metal is a reforming composite material present in the form of a monometallic oxide, a binary oxide with aluminum, or a combination thereof. The method of claim 1,
The content ratio of the supported catalyst and the Group 11 transition metal is 80:20 to 20:80 by weight ratio. The method of claim 1,
The reforming composite material is a reforming composite material comprising a LiLaNi-Al ₂ O ₃ supported catalyst and Cu. The method of claim 1,
The reforming composite material has an electrical conductivity of 1.0 Scm ^-1 or more. Cathode layer; And
12. A negative electrode structure for a fuel cell, comprising: a reforming layer disposed on at least one surface of the cathode layer and comprising a reforming composite material according to any one of claims 1 to 11. The method of claim 12,
The cathode layer is a fuel cell anode structure comprising a Ni cermet (cermet). The method of claim 13,
The Ni cermet may be zirconia-based or undoped with at least one of yttrium, scandium, calcium and magnesium; Ceria based or not doped with at least one of gadolinium, samarium, lanthanum, ytterbium and neodymium; Bismuth oxide based or doped with at least one of calcium, strontium, barium, gadolithium and yttrium; And a lanthanum gallate-based or at least one selected from the group consisting of lanthanum gallates doped or not doped with at least one of strontium and magnesium. The method of claim 13,
The Ni cermet is a negative electrode structure for a fuel cell Ni / YSZ (Yttria-stabilized zirconia) composite. A negative electrode comprising the negative electrode structure according to claim 12;
An anode disposed to face the cathode; And
And a solid oxide electrolyte disposed between the cathode and the anode. 16. The method of claim 15,
The anode includes (La, Sr) MnO ₃ , (La, Ca) MnO ₃ , (Sm, Sr) CoO ₃ , (La, Sr) CoO ₃ , (La, Sr) (Fe, Co) O ₃ , (La , Sr) (Fe, Co, Ni) O ₃ , and a solid oxide fuel cell comprising at least one selected from the group consisting of noble metals. 16. The method of claim 15,
The solid oxide electrolyte is zirconia-based or not doped with at least one of yttrium, scandium, calcium and magnesium; Ceria based or not doped with at least one of gadolinium, samarium, lanthanum, ytterbium and neodymium; Bismuth oxide based or doped with at least one of calcium, strontium, barium, gadolithium and yttrium; And a lanthanum gallate system, which is doped or not doped with at least one of strontium and magnesium. 16. The method of claim 15,
And said solid oxide electrolyte is yttria stabilized zirconia (YSZ).

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