Cerium oxide-based isolation layer and preparation method and application thereof

Abstract

The invention discloses a cerium oxide-based isolation layer and a preparation method and application thereof, and belongs to the technical field of batteries. According to the technical scheme, a Ce-M alloy is used as a target material, a cerium oxide-based isolation layer is prepared on the surface of an electrolyte layer of a solid oxide fuel cell half cell by adopting a magnetron sputtering process, then a cathode is printed on the surface of the cerium oxide-based isolation layer, and after cathode slurry is dried, co-firing is performed to obtain a single cell, so that a metal magnetron sputtering technical route is improved, and the production cost is reduced. A certain amount of oxygen is introduced into a sputtering cavity at the same time to achieve reactive magnetron sputtering, the processing temperature of a thin film and an LSCF electrode after sputtering is optimized by optimizing technological parameters such as current, oxygen flow and bias voltage in the sputtering process, a compact cerium oxide-based isolation layer is effectively obtained, and the performance and long-term stability of the SOC are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a cerium oxide-based isolation layer and a preparation method and application thereof. Background Art

[0002] Solid oxide cell (SOC) technology is a new type of electrochemical energy conversion technology. When working in fuel cell mode, it is a solid oxide fuel cell (SOFC), which can generate electricity using hydrogen or other hydrocarbons as fuel; when working in water electrolysis mode, it is a solid oxide electrolysis cell (SOEC), which can use electricity to convert water into hydrogen through the water electrolysis process, or electrolyze carbon dioxide to convert carbon dioxide into carbon monoxide, or co-electrolyze water and carbon dioxide to generate a synthesis gas composed of hydrogen and carbon monoxide. SOC is green, environmentally friendly, efficient, pollution-free and noise-free. SOC consists of three parts: fuel electrode, electrolyte and air electrode. The commonly used electrolyte material is yttria-stabilized zirconia (YSZ), the commonly used fuel electrode is a metal-ceramic composite material composed of metal nickel (Ni) and YSZ, and the commonly used air electrode material is a doped lanthanum cobalt oxide perovskite material with a perovskite structure, such as La 1-x Sr x Co 1-y Fe y O 3-δ (LSCF), or a composite electrode composed of LSCF and gadolinium-doped cerium oxide (GDC). The preparation of the cerium oxide-based isolation layer of traditional solid oxide fuel cells involves screen printing and high-temperature sintering. On the one hand, high-temperature sintering is prone to cause interface stress and interface element diffusion, resulting in performance degradation, and on the other hand, it is difficult to obtain a dense structure.

[0003] In order to make the YSZ electrolyte dense enough, high-temperature sintering at around 1400°C is generally required. However, since YSZ and LSCF are prone to react to form the SrZrO3 second phase at the preparation and operating temperature of SOFC, a layer of GDC is often added between the YSZ electrolyte and the LSCF electrode as an isolation layer. The traditional preparation of the GDC isolation layer is to deposit the GDC slurry on the YSZ electrolyte by a tape casting method and sinter it at a high temperature of 1200°C. However, the GDC isolation layer prepared by this method is not completely dense, and the high-temperature sintering at 1200°C easily leads to the formation of an element diffusion layer at the interface between YSZ and GDC, which reduces the ionic conductivity of the electrolyte and the electrochemical performance of the SOC.

[0004] CN104934614A discloses a doped cerium oxide catalytic film with preferential orientation and its preparation and application. The film is prepared by a magnetron reactive sputtering method, but the patent is mainly aimed at the preparation of the catalyst layer or porous electrode of the solid oxide fuel cell, so the density of the catalytic film is not required, and it is not suitable for the preparation of a dense isolation layer film used to block element migration and reaction in the battery. CN112695285A discloses a method for preparing a cerium oxide-based isolation layer based on magnetron reactive sputtering. The film is prepared by magnetron sputtering a cerium-based alloy target in an electrolyte to prepare a cerium-based metal film, and then sintering the cerium-based metal film in air to oxidize the cerium oxide-based oxide isolation layer. Although this method can prepare a dense cerium oxide-based isolation layer, the method first prepares the metal layer and then oxidizes it into an oxide, which is easy to form microcracks at the interface during the oxidation process, affecting the long-term stability of the isolation layer. In addition, the invention is only applicable to the preparation of cerium oxide-based isolation layers, and does not have the preparation of other ceramic films such as YSZ. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to propose a cerium oxide-based isolation layer and a preparation method and application thereof, improve the metal magnetron sputtering technical route, realize reactive magnetron sputtering by simultaneously introducing a certain amount of oxygen into the sputtering chamber, optimize the process parameters such as current, oxygen flow, bias voltage during the sputtering process, optimize the processing temperature of the film and LSCF electrode after sputtering, effectively obtain a dense cerium oxide-based isolation layer, and further improve the performance and long-term stability of the SOC.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention is to provide a method for preparing a cerium oxide-based isolation layer, comprising the following steps:

[0008] Ce-M alloy was used as the target material, and a cerium oxide-based isolation layer was prepared on the surface of the electrolyte layer of the solid oxide fuel cell half-cell by magnetron sputtering process;

[0009] Wherein, M is at least one of gadolinium, manganese, cobalt and zirconium, the Ce content is 80-90%, and the M content is 10-20%.

[0010] Cerium oxide has excellent oxygen ion conductivity. By doping M metal, more oxygen vacancies can be created in the structure, but if the doping is too much, the material structure will be unstable and the performance will be degraded. Therefore, the content of M metal is limited to 10-20%.

[0011] Preferably, a mixed atmosphere of oxygen and argon is used in the magnetron sputtering process.

[0012] More preferably, the volume fraction of oxygen is 15-25%, and the balance is argon.

[0013] Oxygen can combine with metal atoms excited on the metal target to generate metal oxides, thereby achieving the purpose of depositing metal oxides using metal materials as targets.

[0014] Preferably, the electrolyte layer is yttria-stabilized zirconia.

[0015] A second aspect of the present invention is to provide a cerium oxide-based isolation layer.

[0016] The third aspect of the present invention is to provide a use of a cerium oxide-based isolation layer in a fuel cell.

[0017] In some embodiments, the cathode is printed on the surface of the cerium oxide-based isolation layer, and after the cathode slurry is dried, it is co-fired to obtain a single cell.

[0018] Preferably, the cathode is a lanthanum cobalt oxide perovskite material doped with a perovskite structure or a composite electrode comprising a lanthanum cobalt oxide perovskite material doped with a perovskite structure.

[0019] Preferably, co-firing is divided into four stages: in the first stage, the heating rate is controlled at 2-5°C / min, and the temperature rises to 800-1000°C; in the second stage, after reaching 800-1000°C, it is maintained for 1-10h; in the third stage, the temperature begins to cool down at a cooling rate of 1-3°C / min, and the temperature drops to 500-700°C; in the fourth stage, it is placed in a natural environment at a temperature below 300°C until it cools to room temperature.

[0020] It should be noted that the second stage of insulation can ensure the full densification and interface bonding of the material; the third stage of cooling duration is adjusted according to the specific characteristics of the sample to ensure that the material does not crack or produce excessive stress during the initial cooling process; the fourth stage of natural cooling can ensure the stability of the sample's structure and performance.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention directly deposits a dense and uniform cerium oxide-based isolation layer on the surface of the YSZ electrolyte through a sputtering process, achieving densification at a relatively low temperature (800-1000°C), significantly improving the density and functionality of the isolation layer, overcoming the problem of insufficient density of the isolation layer in the traditional tape casting method, effectively blocking the direct contact between YSZ and LSCF, preventing the generation of second phases such as SrZrO3 under high temperature conditions, and avoiding the decrease in electrolyte ion conductivity caused by chemical reactions at the interface. Low-temperature preparation not only avoids element diffusion at the interface between the YSZ and GDC isolation layers, effectively retains the high ion conductivity of the YSZ electrolyte, reduces the interface resistance, and reduces the interface degradation phenomenon caused by high temperature, thereby significantly improving the electrochemical performance and operating stability of SOFC.

[0023] 2. The present invention does not need to perform high-temperature sintering on the isolation layer separately after sputtering, but completes the preparation by co-firing with the cathode material. Through reasonable temperature control and optimization of the heating and cooling rate, a good combination between the isolation layer and the cathode material is achieved, the mechanical strength and chemical stability are improved, the sintering steps are reduced, and the stability of the interface structure is further improved. Compared with the traditional process, this method omits the high-temperature treatment step of sintering the isolation layer separately, significantly shortens the production process, reduces production costs, and avoids the potential damage to the performance of the YSZ electrolyte and electrode materials by multiple sintering, further improving the structural integrity and long-term stability of SOFC. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The current-voltage-power curves of SOFC monomers prepared by sintering at different temperatures.

[0025] Figure 2 The cross-sectional SEM images of SOFC monomers prepared by sintering at different temperatures: (a) sintering temperature 800°C; (b) sintering temperature 1000°C; (c) sintering temperature 1200°C.

[0026] Figure 3 Surface XRD patterns of SOFC monomers prepared by co-firing at different temperatures.

[0027] Figure 4 This is a graph showing the variation of the logarithm of the maximum power density of step-by-step sintering and co-firing versus the inverse of the sintering temperature. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0029] Example 1

[0030] A method for preparing a cerium oxide-based isolation layer comprises the following steps:

[0031] The NiO-YSZ|YSZ half-cell substrate was placed in a magnetron sputtering device, and a Gd-Ce alloy target (the atomic ratio of Gd and Ce was 20 / 80) was used as the target. The working atmosphere was an Ar / O2 mixed gas, in which the volume fraction of oxygen was 20%, and a dense GDC isolation layer with a thickness of about 300nm was formed on the surface of the electrolyte layer of the half-cell.

[0032] The cerium oxide-based isolation layer prepared above is applied in a solid oxide fuel cell (SOFC). The SOFC includes a NiO-YSZ|YSZ half-cell substrate, a cerium oxide-based isolation layer, and a commercial LSCF cathode. The working area of ​​the half-cell substrate is 2 cm 2 (diameter 1.6cm); the LSCF cathode is printed on the surface of the GDC isolation layer by screen printing. The thickness of the cathode after printing is about 10μm. After printing, the cathode slurry is dried and then a single cell is obtained by co-firing. The temperature is raised to 1000℃ at a heating rate of 2℃ / min and maintained for 2 hours. The temperature is then lowered to 500℃ at a rate of 3℃ / min. Then, the cell is placed in a natural environment at a temperature below 300℃ until it cools to room temperature.

[0033] Example 2

[0034] The preparation method and application are consistent with those in Example 1, except that in the co-firing process, the temperature is increased to 800° C. at a heating rate of 2° C. / min.

[0035] Comparative Example 1

[0036] The preparation method and application are consistent with those in Example 1, except that in the co-firing process, the temperature is increased to 1200° C. at a heating rate of 2° C. / min.

[0037] Comparative Example 2

[0038] The preparation method and application are consistent with Example 1, with the only difference being that: step-by-step sintering is adopted, the prepared GDC isolation layer is sintered at 1000°C, and then the LSCF cathode is printed on the surface of the isolation layer by screen printing, sintered at 1000°C, and cooled to room temperature after sintering.

[0039] In order to prove that the cerium oxide-based isolation layer provided by the present invention and the co-firing process with the cathode can effectively improve the energy density of SOFC and improve the battery performance, performance tests are performed on Examples 1-2 and Comparative Examples 1 and 2 as follows.

[0040] The single cells prepared in Examples 1-2 and the single cells in Comparative Example 1 were tested at 600-800°C. The test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the energy density of the batteries in the examples is higher than that in the comparative example 1.

[0041] The cross-section of the single cell of Example 1-2 and Comparative Example 1 was tested by scanning electron microscope to further understand the reason why Example 1 has a higher power density from a microscopic perspective. The test method is: the single cell interface is tested by scanning electron microscope (SEM), the scanning electron microscope model is S3700, the electron gun acceleration voltage is 20.0KV, the distance between the battery sample and the bottom of the objective lens is 9.3MM, and the magnification is 2000 times. The test results are as follows: Figure 2 shown. Figure 2 In Examples 1 and 2, at sintering temperatures of 800°C and 1000°C, the GDC layer presents a dense structure, but when the sintering temperature is 1200C, closed pores are generated in the GDC layer, which will reduce the conductivity of the layer to a certain extent, thereby reducing the performance of the battery, indicating that the co-firing temperature is very important for the GDC isolation layer and SOCF.

[0042] XRD detection was performed on the cross-section of the single cell prepared in Examples 1, 2 and Comparative Example 1 to further understand the reasons why the examples have higher power density from a microscopic perspective. The detection results are as follows Figure 3 As shown, XRD characterization shows that the samples sintered at different temperatures all formed the GDC phase, but with the increase of sintering temperature, the crystallinity of the GDC layer increased. The increase in crystallinity can reduce the disordered area at the grain boundary, increase the migration efficiency of oxygen ions in the lattice, and further improve the ionic conductivity of the material.

[0043] Figure 4 The variation law of the logarithm of the maximum power density with the inverse of the sintering temperature is given in FIG. Compared with the distributed sintering in Example 2 and the co-sintering in Example 1, it can be seen that the co-sintering has better performance than the step sintering, and the activation energy is lower, which means the low temperature performance is better. In addition, the co-sintering process has fewer steps and lower costs.

[0044] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a cerium oxide-based isolation layer, characterized in that: The following steps are involved: Ce-M alloy was used as the target material, and a cerium oxide-based isolation layer was prepared on the surface of the electrolyte layer of the solid oxide fuel cell half-cell by magnetron sputtering process; Wherein, M is at least one of gadolinium, manganese, cobalt and zirconium, the Ce content is 80-90%, and the M content is 10-20%.

2. The preparation method according to claim 1, characterized in that: The magnetron sputtering process uses a mixed atmosphere of oxygen and argon.

3. The preparation method according to claim 2, characterized in that: The volume fraction of oxygen is 15-25%, and the balance is argon.

4. The preparation method according to claim 1, characterized in that: The electrolyte layer is yttria-stabilized zirconia.

5. A cerium oxide-based isolation layer prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the cerium oxide-based isolation layer according to claim 5 in a fuel cell.

7. The use according to claim 6, characterized in that: The cathode is printed on the surface of the cerium oxide-based isolation layer, and after the cathode slurry is dried, it is co-fired to obtain a single cell.

8. The use according to claim 7, characterized in that: The cathode is a lanthanum cobalt oxide perovskite material doped with a perovskite structure or a composite electrode containing a lanthanum cobalt oxide perovskite material doped with a perovskite structure.

9. The use according to claim 7, characterized in that: The co-firing is divided into four stages: in the first stage, the heating rate is controlled at 2-5°C / min, and the temperature rises to 800-1000°C; in the second stage, after reaching 800-1000°C, it is maintained for 1-10 hours; in the third stage, the temperature begins to drop at a cooling rate of 1-3°C / min, and the temperature drops to 500-700°C; in the fourth stage, it is placed in a natural environment at a temperature below 300°C until it cools to room temperature.

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