TWI694634B - Cathode layer and membrane electrode assembly of solid oxide fuel cell - Google Patents

Abstract

A cathode layer and a membrane electrode assembly of solid oxide fuel cell are provided. The cathode layer consists of a plurality of perovskite crystal films, and an average change rate of the liner thermal expansion coefficient of these perovskite crystal films is 5% to 40% along a thickness direction. The membrane electrode assembly includes above cathode layer, and the liner thermal expansion coefficient of these perovskite crystal films decreases towards a solid electrolyte layer of the membrane electrode assembly.

Description

Cathode layer and membrane electrode assembly of solid oxide fuel cell

The present invention relates to a solid oxide fuel cell technology, and particularly to a cathode layer and a membrane electrode assembly (MEA) of a solid oxide fuel cell.

Solid Oxide Fuel Cell (SOFC) is a fuel cell technology that uses solid ceramic materials as electrolytes. The operating temperature of the entire system is between 500°C and 1000°C, and it is a high-temperature fuel cell, so it has good flexibility in fuel selection. The fuels that can be selected include methane, natural gas, city gas, biomass, diesel, and other carbon. Hydrogen compounds.

However, because the solid electrolyte and the electrodes (cathode layer and anode layer) in the fuel cell membrane electrode group have a large difference in coefficient of thermal expansion (CTE), the solid electrolyte and electrode are easily damaged and cracked due to cyclic thermal stress, resulting in solid state There is a problem with the operation of the oxide fuel cell.

The invention provides a cathode layer of a solid oxide fuel cell, which can reduce the generation of thermal stress.

The invention also provides a membrane electrode assembly of a solid oxide fuel cell, which can greatly reduce the influence of thermal stress on the battery performance.

The cathode layer of the solid oxide fuel cell of the present invention is composed of a plurality of perovskite crystal layers, and the average linear thermal expansion coefficient of the perovskite crystal layer in the thickness direction is 5% to 40%.

The membrane electrode assembly of the solid oxide fuel cell of the present invention includes a cathode layer, an anode layer, and a solid electrolyte layer interposed between the cathode layer and the anode layer. The cathode layer is composed of a plurality of perovskite crystal layers described above. The cathode layer is formed, and the linear thermal expansion coefficient of the perovskite crystal layer decreases toward the solid electrolyte layer.

Based on the above, the present invention constitutes a cathode layer by a plurality of perovskite crystal layers, and reduces the linear thermal expansion coefficient of each layer toward the solid electrolyte layer. Therefore, the membrane electrode assembly can have high resistance to thermal shock and greatly reduce the thermal cycle The effect of stress on the performance of solid oxide fuel cells.

In order to make the above-mentioned features and advantages of the present invention more obvious and understandable, the embodiments are specifically described below in conjunction with the accompanying drawings for detailed description as follows.

Please refer to the following embodiments and accompanying drawings to understand the present invention more fully, but the present invention can still be practiced in many different forms and should not be interpreted as being limited to the embodiments described herein. In the drawings, for the sake of clarity, the components and their relative sizes may not be drawn according to the actual scale.

1 is a schematic cross-sectional view of a cathode layer of a solid oxide fuel cell according to the first embodiment of the present invention.

1, the cathode layer 100 of the first embodiment is composed of a plurality of perovskite crystal layers 102a and 102b, and the average change rate of the linear thermal expansion coefficient of the perovskite crystal layers 102a and 102b in the thickness direction is 5 % To 40%, for example, 10% to 35%, 20% to 35%, 10% to 25%, or 10% to 20%. The so-called "average rate of change of linear thermal expansion coefficient in the thickness direction" means that if there are N perovskite crystal layers, first obtain the (N-1) values of the linear thermal expansion coefficient values of the two adjacent layers in the thickness direction Change rate, and then divide the sum of these change rates by (N-1) to get the average value of change rate. The materials of the perovskite crystal layers 102a and 102b are, for example, lanthanum strontium cobalt iron oxide, lanthanum strontium iron oxide, or lanthanum strontium manganese oxide, and the porosity of the perovskite crystal layers 102a and 102b may be similar or consistent. The perovskite crystal layers 102a and 102b can be basically the same or different perovskite materials; if the perovskite crystal layers 102a and 102b are the same material, such as lanthanum strontium cobalt iron oxide (La _1-x Sr _x Co _{1 -y} Fe _y O ₃ , where x=0.1~0.9, y=0.3~1.0, or x=0.2~0.8, y=0.2~1.0), you can adjust the ratio of strontium (Sr) and cobalt (Co) Changing the linear thermal expansion coefficient, such as increasing Sr or Co, can obtain a perovskite crystal layer material with a larger linear thermal expansion coefficient. In another embodiment, if the perovskite crystal layers 102a and 102b are the same material, such as lanthanum strontium manganese oxide (La _1-z Sr _z MnO ₃ , where z=0.1~0.5), or lanthanum strontium iron oxide (La _1-w Sr _w FeO ₃ , w=0.1~0.5), the linear thermal expansion coefficient can be changed by adjusting the ratio of Sr. For example, increasing Sr can obtain a perovskite crystal layer material with a large linear thermal expansion coefficient.

In the first embodiment, the perovskite crystal layer 102b contacts the solid electrolyte layer 104, and the perovskite crystal layer 102a does not contact the solid electrolyte layer 104, so the coefficient of thermal expansion of the perovskite crystal layer 102b is higher than that of the perovskite crystal layer 102a. The coefficient of thermal expansion is small, for example, the linear thermal expansion coefficient of the uppermost layer (perovskite crystal layer 102a) in the thickness direction is, for example, 1.2×10 ⁻⁵ /K to 2×10 ⁻⁵ /K, or 1.8×10 ⁻⁵ /K to 2×10 ^-5 /K, the linear thermal expansion coefficient of the lowermost layer (perovskite crystal layer 102b) in the thickness direction is, for example, 9×10 ^-6 /K to 1.5×10 ^-5 /K, or 1.2× 10 ^-5 /K to 1.5×10 ^-5 /K, but the present invention is not limited to this.

2 is a schematic cross-sectional view of a cathode layer of a solid oxide fuel cell according to a second embodiment of the present invention, in which the element symbols of the first embodiment are used to denote the same or similar components, and the description of the same components can be referred to The first embodiment will not be repeated here.

2, the difference between the cathode layer 200 of the second embodiment and the first embodiment is the number of perovskite crystal layers. The number of the perovskite crystal layers of the first embodiment is two, the second embodiment The example perovskite crystal layer has three layers, including the uppermost perovskite crystal layer 202a in the thickness direction, the perovskite crystal layer 202b, and the lowermost perovskite crystal layer 202c in the thickness direction.

As for the average change rate of the linear thermal expansion coefficient of the perovskite crystal layers 202a~c in the thickness direction and the selection of materials, refer to the first embodiment, in which the linear thermal expansion of the uppermost layer (perovskite crystal layer 202a) in the thickness direction The coefficient is, for example, 1.2×10 ^-5 /K to 2×10 ^-5 /K, or 1.8×10 ^-5 /K to 2×10 ^-5 /K, and the lowest layer in the thickness direction (perovskite crystal layer 202c) The linear thermal expansion coefficient of is, for example, 9×10 ⁻⁶ /K to 1.5×10 ⁻⁵ /K, or 1.2×10 ⁻⁵ /K to 1.4×10 ⁻⁵ /K. In the second embodiment, the perovskite crystal layer 202c contacts the solid electrolyte layer 104, the perovskite crystal layers 202b and 202a do not contact the solid electrolyte layer 104, and the perovskite crystal layer 202b is located in the perovskite crystal layer 202a and Between 202c, so the thermal expansion coefficient of the perovskite crystal layer 202c (third layer) is smaller than the thermal expansion coefficient of the perovskite crystal layer 202b (second layer) and the thermal expansion coefficient of the perovskite crystal layer 202b (second layer) It is smaller than the thermal expansion coefficient of the perovskite crystal layer 202a (first layer); for example, the linear thermal expansion coefficients of two adjacent layers in the perovskite crystal layers 202a~c differ by 2×10 ^-6 /K to 5× 10 ^-6 /K, but the invention is not limited to this.

3 is a schematic cross-sectional view of a cathode layer of a solid oxide fuel cell according to a third embodiment of the present invention, in which the element symbols of the first embodiment are used to denote the same or similar components, and the description of the same components can be referred to The first embodiment will not be repeated here.

3, the difference between the cathode layer 300 of the third embodiment and the first embodiment is the number of perovskite crystal layers. The number of the perovskite crystal layers of the first embodiment is two, the third embodiment The example perovskite crystal layer has four layers, including the uppermost perovskite crystal layer 302a in the thickness direction, the perovskite crystal layer 302b, the perovskite crystal layer 302c, and the lowermost perovskite layer in the thickness direction Crystalline layer 302d.

For the average change rate of the linear thermal expansion coefficient of the perovskite crystal layers 302a~d in the thickness direction and the selection of materials, refer to the first embodiment, in which the linear thermal expansion of the uppermost layer (perovskite crystal layer 302a) in the thickness direction The coefficient is, for example, 1.2×10 ^-5 /K to 2×10 ^-5 /K, or 1.8×10 ^-5 /K to 2×10 ^-5 /K, and the lowest layer in the thickness direction (perovskite crystal layer 302d) The linear thermal expansion coefficient of is, for example, 9×10 ⁻⁶ /K to 1.5×10 ⁻⁵ /K, or 9×10 ⁻⁶ /K to 1.3×10 ⁻⁵ /K. In the third embodiment, the perovskite crystal layer 302d contacts the solid electrolyte layer 104, the perovskite crystal layers 302a-c do not contact the solid electrolyte layer 104, and the perovskite crystal layer 302c is located on the perovskite crystal layer 302b and Between 302d, the perovskite crystal layer 302b is located between the perovskite crystal layers 302a and 302c, so the thermal expansion coefficient of the perovskite crystal layer 302d (fourth layer) is smaller than that of the perovskite crystal layer 302c (third layer ), the thermal expansion coefficient of the perovskite crystal layer 302c (third layer) is smaller than the thermal expansion coefficient of the perovskite crystal layer 302b (second layer), the thermal expansion coefficient of the perovskite crystal layer 302b (second layer) It is smaller than the thermal expansion coefficient of the perovskite crystal layer 302a (first layer); for example, the linear thermal expansion coefficients of two adjacent layers in the perovskite crystal layers 302a~d differ by 1×10 ^-6 /K to 4.5× 10 ^-6 /K, but the invention is not limited to this.

4 is a schematic cross-sectional view of a membrane electrode assembly of a solid oxide fuel cell according to a fourth embodiment of the present invention.

Referring to FIG. 4, the membrane electrode group 400 of this embodiment includes a cathode layer 402, an anode layer 404, and a solid electrolyte layer 406 disposed between the cathode layer 402 and the anode layer 404. The cathode layer 402 is any one of the cathode layers in the first to third embodiments; for example, the cathode layer 402 is composed of perovskite crystal layers 408a and 408b, and the perovskite crystal layers 408a and 408b are linear The average change rate of the coefficient of thermal expansion in the thickness direction is 5% to 40%, and examples may be 10% to 35%, 20% to 35%, 10% to 25%, or 10% to 20%. Moreover, the linear thermal expansion coefficients of the perovskite crystal layers 408a and 408b decrease toward the solid electrolyte layer 406, so that the linear thermal expansion coefficient of the perovskite crystal layer 408b close to the solid electrolyte layer 406 is close to the linear thermal expansion coefficient of the solid electrolyte layer 406, The perovskite crystal layer 408a far away from the solid electrolyte layer 406 has a linear thermal expansion coefficient that is significantly different from the linear thermal expansion coefficient of the solid electrolyte layer 406, thus reducing the generation of thermal stress in the membrane electrode assembly 400 and making the cathode layer 402 and solid state The electrolyte layer 406 is in direct contact. In this embodiment, the material of the solid electrolyte layer 406 may include zirconium oxide (ZrO ₂ ), cerium oxide (CeO ₂ ), bismuth oxide (Bi ₂ O ₃ ), lanthanum strontium gallium magnesium oxide (La(Sr)Ga( Mg)O ₃ ) or a combination thereof. In some embodiments, the zirconia may include undoped zirconia, yttria stabilized zirconia (YSZ), cerium oxide stabilized zirconia, scandium oxide stabilized zirconia, or a combination thereof, but the present invention Not limited to this. In some embodiments, the cerium oxide may include undoped cerium oxide, samarium-doped cerium oxide (Sm-doped Ceria), gadolinium-doped cerium oxide (Gd-doped Ceria), or a combination thereof, but the present invention does not use this Limited. In this embodiment, the material of the anode layer 404 may include at least one material of nickel oxide and solid electrolyte, wherein the material of the solid electrolyte is as described above, for example, the anode layer 404 may be yttrium oxide stabilized zirconia containing nickel oxide or Samarium containing nickel oxide is doped with cerium oxide, but the invention is not limited thereto. In addition, the technology currently available for the membrane electrode assembly of the solid oxide fuel cell can also be combined with the cathode layer of the present invention having a specific linear thermal expansion coefficient change rate in the thickness direction.

The following lists experiments to verify the efficacy of the present invention, but the present invention is not limited to the following.

<Preparation Examples 1 to 6>

The present invention utilizes the pulsed laser deposition method (PLD) to quickly prepare the characteristics of samples, and prepares and deposits different proportions of perovskite crystal layers on the YSZ substrate. The steps are as follows.

First apply silver glue to the test piece holder and place the YSZ substrate (linear thermal expansion coefficient is 9.9×10 ^-6 /K) on top. After light pressing and heating, the silver glue is completely solidified and the sample can be placed into the PLD Cavity. Then adjust the oxygen pressure, laser focal length and substrate temperature in the chamber to the required conditions, such as a pressure of 80 mTorr~100 mTorr and a temperature of about 600 ºC~700 ºC.

Then, according to the number of layers in Table 1 below and the corresponding perovskite crystal layer material, use high-energy laser to strike the target uniformly (dual target experiment: LaCoO ₃ , LaFeO ₃ , SrCoO _2.5 , SrFeO ₃ ), and by adjusting The laser strikes the number of different targets to achieve the purpose of controlling the components. In addition, the perovskite crystal layers of the present invention can also be formed by screen printing, and are not limited to experimental steps.

The prepared sample was taken out for the following analysis.

<X-ray diffraction with variable temperature>

Using a X-ray Diffraction (X-ray Diffraction) to analyze the crystal structure of the sample: the measurement process uses Cu-Kα with a wavelength of 0.154 nm, a scanning angle (2θ) from 30º to 32º, a scanning speed of about 0.03º/sec, etc. Conditions, measured at room temperature, 100 ºC, 200 ºC, 300 ºC, 400 ºC, 500 ºC (hold the temperature for 5-10 minutes before the measurement to make the sample reach the thermal equilibrium state), through the change of 2θ at different temperatures, it can be inferred The change of the inter-surface distance, and then calculate the linear thermal expansion coefficient of the material, and record the results in Table 1 below.

Table 1

From Table 1, it can be seen that the difference in ΔCTE of the single-layer cathode structure (Preparation Example 6) reaches 47.6%; but the difference in ΔCTE of each layer of the four-layer progressive multilayer cathode structure (Preparation Example 5) can be reduced to <22%.

Furthermore, the change rate of the linear thermal expansion coefficient of the two-layer perovskite crystal layer of Preparation Example 1 in the direction away from the solid electrolyte layer (thickness direction) was 21.2%, and the change rate of the first perovskite crystal layer and the electrolyte layer was 33.6 %; the change rate of the linear thermal expansion coefficient of the two-layer perovskite crystal layer of Preparation Example 2 in the direction away from the solid electrolyte layer (thickness direction) is 33.9%, and the change rate of the first perovskite crystal layer and the electrolyte layer is 20.8 %; the average change rate of the linear thermal expansion coefficient of the three perovskite crystal layers of Preparation Example 3 in the direction away from the solid electrolyte layer (thickness direction) is 18.6%, and the change of the first perovskite crystal layer and the electrolyte layer The rate is 20.8%; the average change rate of the linear thermal expansion coefficient of the four perovskite crystal layers of Preparation Example 4 in the direction away from the solid electrolyte layer (thickness direction) is 12.8%. The first perovskite crystal layer and the electrolyte The change rate of the layer is 20.8%; the average change rate of the linear thermal expansion coefficient of the four-layer perovskite crystal layer of Preparation Example 5 in the direction away from the solid electrolyte layer (thickness direction) is 19.3%. The rate of change of the electrolyte layer is 0.2%.

<Preparation Examples 7-8>

The double-layer perovskite crystal layer in the following Table 2 was prepared on the YSZ substrate in the same manner as in Preparation Example 1, wherein the dual targets used in Preparation Examples 7 to 8 were "LaMnO ₃ , SrMnO ₃ "and "LaFeO ₃ , SrFeO ₃ ". Then, using the same analysis method as in Preparation Example 1, the linear thermal expansion coefficient of the material was calculated, and the results are described in Table 2 below.

Table 2

It can be obtained from Table 2 that the change rate of the linear thermal expansion coefficient of the two-layer perovskite crystal layer of Preparation Example 7 in the direction away from the solid electrolyte layer (thickness direction) is 7.9%. The difference between the first perovskite crystal layer and the electrolyte layer The rate of change was 14.7%; the change rate of the linear thermal expansion coefficient of the two-layer perovskite crystal layer of Preparation Example 8 in the direction away from the solid electrolyte layer (thickness direction) was 35.8%. The difference between the first perovskite crystal layer and the electrolyte layer The rate of change was 18.9%.

<Experimental Examples 1~7>

Take the samples of Preparation Examples 1~5 and 7~8, and perform the thermal cycle test at room temperature to 800 ^o C to simulate the operating conditions. After five thermal cycle tests, the resistance change rate of the membrane electrode group is shown in Figure 5. The resistance change rate is the resistance value measured by the current (thermal cycle) divided by the resistance value measured by the first thermal cycle and then multiplied by 100 (the unit is %).

<Comparative example>

Taking the sample of Preparation Example 6, the above five thermal cycle tests were also conducted, and the resistance change rate of the membrane electrode group was shown in FIG. 5.

It can be seen from FIG. 5 that the resistance value of the cathode layer of the single-layer structure of the comparative example is as high as 99%; in comparison, the experimental examples 1 to 2, 6 to 7 (that is, the preparation examples 1 to 2 and 7 to 8) The change of the resistance value of the cathode layer of the layer structure is less than 5%, and the change of the resistance value of the cathode layer of the four-layer structure of Experimental Example 4 (ie, Preparation Example 4) is less than 1%, thus confirming that the present invention can greatly reduce the thermal cycle stress on the solid state The effect of oxide fuel cell performance.

In summary, the cathode layer of the present invention is composed of a plurality of perovskite crystal layers with a linear coefficient of thermal expansion with a specific rate of change in the thickness direction, so it has high resistance to thermal shock and can greatly reduce the thermal cycling stress The effect of solid oxide fuel cell performance.

Although the present invention has been disclosed as above with examples, it is not intended to limit the present invention. Any person with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present invention. The scope of protection of the present invention shall be subject to the scope defined in the appended patent application.

100, 200, 300, 402‧‧‧ Cathode layers 102a, 102b, 202a, 202b, 202c, 302a, 302b, 302c, 302d, 408a, 408b ‧‧‧ perovskite crystal layers 104, 406‧‧‧ solid electrolyte layer 400‧‧‧Membrane electrode group 404‧‧‧Anode layer

1 is a schematic cross-sectional view of a cathode layer of a solid oxide fuel cell according to the first embodiment of the present invention. 2 is a schematic cross-sectional view of a cathode layer of a solid oxide fuel cell according to a second embodiment of the present invention. 3 is a schematic cross-sectional view of a cathode layer of a solid oxide fuel cell according to a third embodiment of the present invention. 4 is a schematic cross-sectional view of a membrane electrode assembly of a solid oxide fuel cell according to a fourth embodiment of the present invention. 5 is a graph of resistance values obtained by thermal cycle testing of the membrane electrode groups of Experimental Examples 1-7 and Comparative Examples.

100‧‧‧Cathode layer

102a, 102b ‧‧‧ perovskite crystal layer

104‧‧‧Solid electrolyte layer

Claims (13)

A cathode layer of a solid oxide fuel cell, characterized in that the cathode layer is composed of a plurality of perovskite crystal layers, wherein the material of the perovskite crystal layer includes lanthanum strontium cobalt iron oxide, lanthanum strontium Iron oxide or lanthanum strontium manganese oxide, and the average change rate of the linear thermal expansion coefficient of the plurality of perovskite crystal layers in the thickness direction is 5% to 40%. The cathode layer of the solid oxide fuel cell as described in item 1 of the patent application range, wherein the number of the plurality of perovskite crystal layers is two to four layers. The cathode layer of the solid oxide fuel cell as described in item 1 of the patent application range, wherein the plurality of perovskite crystal layers are La _1-x Sr _x Co _1-y Fe _y O ₃ , x=0.1~0.9 , Y=0.3~1.0. The cathode layer of the solid oxide fuel cell as described in item 1 of the patent application range, wherein the plurality of perovskite crystal layers are La _1-w Sr _w FeO ₃ , w=0.1~0.5. The cathode layer of the solid oxide fuel cell as described in item 1 of the patent application range, wherein the plurality of perovskite crystal layers are La _1-z Sr _z MnO ₃ , z=0.1~0.5. The cathode layer of the solid oxide fuel cell as described in item 1 of the patent application range, wherein the linear thermal expansion coefficient of the uppermost layer in the thickness direction of the plurality of perovskite crystal layers is 1.2×10 ^-5 /K To 2×10 ^-5 /K, the linear thermal expansion coefficient of the lowermost layer is 9×10 ^-6 /K to 1.5×10 ^-5 /K. The cathode layer of the solid oxide fuel cell as described in item 6 of the patent application range, wherein the number of the plurality of perovskite crystal layers is three, and the two adjacent layers of the perovskite crystal layer The linear thermal expansion coefficients differ by 2×10 ^-6 /K to 5×10 ^-6 /K. The cathode layer of the solid oxide fuel cell as described in item 6 of the patent application range, wherein the number of the plurality of perovskite crystal layers is four, and the two adjacent layers of the perovskite crystal layer The linear thermal expansion coefficients differ by 1×10 ^-6 /K to 4.5×10 ^-6 /K. The cathode layer of a solid oxide fuel cell as described in item 1 of the patent application range, wherein the plurality of perovskite crystal layers have the same porosity. A membrane electrode assembly of a solid oxide fuel cell, comprising: a cathode layer; an anode layer; and a solid electrolyte layer disposed between the cathode layer and the anode layer, wherein the cathode layer is the first in the patent application The cathode layer of the solid oxide fuel cell according to any one of items 9 to 9, wherein the linear thermal expansion coefficients of the plurality of perovskite crystal layers decrease toward the solid electrolyte layer. The membrane electrode assembly of a solid oxide fuel cell as described in item 10 of the patent application range, wherein the material of the solid electrolyte layer includes zirconia, cerium oxide, bismuth oxide, lanthanum strontium gallium magnesium oxide, or a combination thereof. The membrane electrode assembly of a solid oxide fuel cell according to item 11 of the patent application range, wherein the material of the anode layer includes nickel oxide and at least one of the materials of the solid electrolyte layer. The membrane electrode assembly of a solid oxide fuel cell as described in item 10 of the patent application range, wherein the cathode layer is in direct contact with the solid electrolyte layer.

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