Growth regulation and control method for cerium oxide-doped electrolyte ceramic film

Abstract

The invention discloses a growth regulation and control method for a doped cerium oxide-based electrolyte ceramic film. According to the method, a hydrothermal in-situ growth technology is combined, and the pH value of the hydrothermal solution is effectively regulated and controlled by adding the pH regulator, so that decomposition of precursor salt is promoted, the growth rate of the ceramic film is remarkably increased and reaches-20 nm / h, and meanwhile, the element doping amount in the cerium oxide-based ceramic film is remarkably increased.

Description

Technical Field

[0001] The invention relates to a method for preparing a solid oxide fuel cell isolation layer, and belongs to the field of solid oxide fuel film electrolyte preparation. Background Art

[0002] Solid oxide fuel cell (SOFC) technology can provide an important supplement to intermittent renewable energy sources such as solar and wind power, and is a key technological approach to promoting the development of a clean, low-carbon, safe, and efficient modern energy system. Its main components include an anode, cathode, and electrolyte. The electrolyte, as a core component, primarily functions to conduct ions and form a conductive path between the cathode and anode. Zirconia-based electrolytes, such as Y2O3-stabilized ZrO2 (YSZ), maintain excellent chemical stability and mechanical strength in both reducing and oxidizing atmospheres and are the most widely used electrolyte materials. However, they also have certain drawbacks, including poor chemical compatibility with many highly active cathode and anode perovskite materials; and the tendency to react during high-temperature preparation and long-term operation, generating low-conductivity phases such as La2Zr2O7 and SrZrO3, which severely impact battery performance and lifespan.

[0003] To address the above challenges, the mainstream approach currently adopted is to use a denser isolation layer between the cathode and the electrolyte to prevent interdiffusion. This not only inhibits the electrode / electrolyte interface reaction and element diffusion, preventing the formation of high-resistance products, but also has an expansion coefficient located between the electrode and the electrolyte, which can improve the thermal expansion matching between the two. The isolation layer material is commonly used CeO2-based oxide intermediate layer, such as cerium-containing materials doped with 10 mol% Gd [Ce 0.9 Gd 0.1 O 1.95 , CGO or GDC]. There are many methods for preparing isolation layers, such as pulsed laser deposition, spray pyrolysis, physical vapor deposition, magnetron sputtering, etc., which can produce denser GDC isolation layers. However, the above methods have problems such as high production cost, complex process, and difficulty in large-area preparation. At the same time, they are also less adaptable to non-flat electrolyte surfaces, such as tubular, conical, corrugated and other structures. Compared with the above methods, the hydrothermal in situ growth method has low cost, simple operation, and strong plasticity. It can prepare continuous, uniform and dense GDC isolation layers, which can be applied to SOFC single cells of various complex configurations and sizes. 2021113588134 discloses a solid oxide battery isolation layer, a single cell and a preparation method, in which the solid oxide battery electrolyte is immersed in a soluble salt solution of Ce and one of the lanthanide rare earth elements, and reacts at a certain temperature for a certain time to form an isolation layer, but it has the problems of low Gd element doping and slow growth rate.

[0004] Therefore, optimizing the lanthanide doping amount and increasing the growth rate of the GDC isolation layer are the bottlenecks that need to be broken through at present. Summary of the Invention

[0005] To address the challenges of the existing technology, the present invention provides a method for regulating the growth of ceramic thin films using a ceria-doped electrolyte. This method utilizes a precursor salt solution of a ceria-doped electrolyte as a hydrothermal solution, adds a pH adjuster at an appropriate concentration, and hydrothermally in situ grows a continuous, dense ceria-based electrolyte film on a NiO-YSZ anode support. This method effectively blocks elemental migration and deposition between the cathode and electrolyte, reduces sheet resistance, and improves the electrochemical performance of the single cell.

[0006] The technical solutions proposed by the present invention to solve the problems of the prior art are as follows:

[0007] A method for controlling the growth of a cerium oxide-doped electrolyte ceramic film comprises the following steps:

[0008] The solid oxide battery electrolyte is immersed in a soluble salt solution of Ce and X, a pH adjuster is added, and the solution is transferred to a reactor for hydrothermal reaction at a certain temperature. After a period of reaction, an electrolyte ceramic film is formed, wherein X is one or two of the lanthanide rare earth elements Gd, Sm, La, and Pr.

[0009] Preferably, the pH adjuster is a substance that becomes alkaline after being hydrolyzed by heating, including but not limited to urea and thiourea.

[0010] Preferably, the molar ratio of Ce to X is 6:4 to 9:1. When the molar ratio is less than 6:4, the conductivity of the thin film electrolyte isolation layer decreases and the charge transfer rate decreases significantly. When the molar ratio is greater than 9:1, the oxygen vacancy concentration in the thin film electrolyte isolation layer is low, which is not conducive to oxygen ion conduction.

[0011] Preferably, when the concentration of the pH regulator in the hydrothermal reaction system is 0.025-0.1 mol / L (preferably 0.1 mol / L), the pH value in the hydrothermal reaction system is 2-6. If the concentration of the pH regulator is too low, the pH change during the hydrothermal process is not significant, and the isolation layer grown after hydrothermal treatment is not effective. If the concentration is too high, the powder-forming ability of the precursor is greater than the film-forming ability, and no electrolyte film is generated.

[0012] Preferably, the hydrothermal reaction temperature is 160-200°C, and the reaction time is not less than 24 hours.

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] By adjusting the pH value during the hydrothermal process, a doped ceria electrolyte is hydrothermally grown in situ on the surface of a zirconium oxide-based electrolyte, significantly increasing the growth rate of the doped ceria electrolyte film while also increasing the doping level of the ceria electrolyte. The growth rate of the doped ceria electrolyte film is increased by at least 2 times, reaching no less than 20 nm / h. The ceria electrolyte contains a doping level greater than 10%, which increases the oxygen vacancy concentration and provides more vacancies for oxygen ion conduction. This results in high density, low sheet resistance, and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the thickness of the GDC isolation layer in Cell-91, Cell-82, and Cell-64.

[0016] Figure 2 is the thickness of the GDC isolation layer in Cell-91U, Cell-82U, and Cell-64U.

[0017] Figure 3 Schematic diagram of the configuration of the Cell-82 battery (a) in the comparative example and the Cell-82U battery (b) in Example 1.

[0018] Figure 4 (a) XRD patterns of the GDC surface after adding different amounts of urea in Example 2 and (b) an enlarged view of the peak.

[0019] Figure 5 This is a diagram showing the pH change of the solution after the hydrothermal reaction in Example 2.

[0020] Figure 6 (a) is the SEM image of the cross section of the single cell after adding different amounts of urea in Example 1, and (b) is the thickness change line graph.

[0021] Figure 7 The power density comparison diagram of Cell-1 and Cell-4 at 800℃ in Example 2 (a) and Cell-4 at 700℃-300mA / cm 2 Lower long-term operation curve (b). DETAILED DESCRIPTION

[0022] In order to better understand the technical content of the present invention, specific embodiments are given and described below with reference to the accompanying drawings.

[0023] Various aspects of the present invention are described herein with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present invention are not necessarily intended to encompass all aspects of the present invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, may be implemented in any of a number of ways, as the concepts and embodiments disclosed herein are not limited to any particular implementation. In addition, some aspects disclosed herein may be used alone or in any appropriate combination with other aspects disclosed herein.

[0024] Comparative Example

[0025] The anode support half cell was prepared by sintering at 1350℃ for 3h, in which the anode support and functional layer were NiO-YSZ (NiO-Zr 0.84 Y 0.16 O 2-δ ), the electrolyte is YSZ(Zr 0.84 Y 0.16 O 2-δ ), and its half-cell structure is NiO-YSZ||YSZ.

[0026] In situ hydrothermal growth of gadolinium oxide-doped ceria (GDC-CeO) on YSZ surface x Gd 1-x O 2-δ ), the precursor solution is 0.1 mol / L aqueous solution of gadolinium nitrate and cerium nitrate, wherein Ce 3+ :Gd 3+ The molar ratios are 9:1, 8:2, and 6:4, respectively, and the half-cells prepared are numbered Cell-91, Cell-82, and Cell-64, respectively. The specific process is: fix the anode support half-cell on a polytetrafluoroethylene protective mold and immerse it in the above solution, wherein the YSZ electrolyte surface is completely exposed to the solution, and other parts such as the anode support are all protected by the mold. Seal and lock the hydrothermal autoclave and keep it in an oven at 180°C (corresponding to a water vapor pressure of approximately 1MPa) for 36 hours, then cool it naturally. Take out the half-cell, rinse it with deionized water, and place it on an 80°C heating plate to dry. The hydrothermal half-cell was characterized by SEM-EDS, and the results are as follows Figure 1 In terms of GDC isolation layer thickness, the thickness of Cell-91, Cell-82, and Cell-64 are all between 350-400 nm, with no significant difference in thickness, indicating that changing Ce 3+ With Gd 3+ The molar ratio of has little effect on the thickness of the GDC isolation layer after hydrothermal growth. Figure 3As shown in (a) in Table 1, in terms of Gd doping, the Gd doping amount in Cell-91, Cell-82 and Cell-64 is less than 5%, which indicates that although Gd in the precursor solution 3+ The ion concentration gradually increases, but the proportion of Gd atoms after hydrothermal film formation is still very small, indicating that the addition of Gd in the precursor solution 3+ The ion concentration has almost no essential effect on the doping amount of Gd element in GDC film.

[0027] Example 1

[0028] In situ hydrothermal growth of gadolinium oxide-doped ceria (GDC-CeO) on YSZ surface x Gd 1-x O 2-δ ), the precursor solution is 0.1 mol / L aqueous solution of gadolinium nitrate and cerium nitrate, wherein Ce 3+ :Gd 3+ The molar ratios were 9:1, 8:2, and 6:4, respectively. At the same time, 0.1 mol / L urea was added to the precursor solution. The half-cells were named Cell-91U, Cell-82U, and Cell-64U, respectively. The subsequent steps were consistent with the comparative example. The hydrothermal half-cells were characterized by SEM-EDS. The results are shown in the figure. Figure 2 As shown in FIG, after adding urea to the precursor solution, as the urea decomposes during the hydrothermal process, it is more conducive to the formation of a GDC isolation layer. Specifically, the thickness of the GDC isolation layer in Cell-91U, Cell-82U, and Cell-64U (0.8±0.02μm, 0.85±0.02μm, 0.5±0.02μm) is greater than that in the comparative examples (Cell-91, Cell-82, and Cell-64) (0.39±0.02μm, 0.5 ... 0.38±0.02μm, 0.36±0.02μm) grow thicker in the same time, that is, the growth rate is faster, which helps to solve the growth cost and improve production efficiency; on the other hand, as shown in Table 2, due to the addition of urea in the hydrothermal precursor, the urea decomposes during the hydrothermal process, which significantly increases the doping amount of the Gd element. Compared with the comparative example, the Gd element content is significantly improved. The increase in the doping amount of the Gd element makes the oxygen vacancies more abundant, which is more conducive to oxygen ion conduction, and is specifically manifested in better electrochemical performance. Among them, the structural schematic diagram of Cell-82U is shown in FIG. Figure 3 As shown in (b) in .

[0029] Example 2

[0030] In situ hydrothermal growth of gadolinium oxide-doped ceria (GDC-CeO) on YSZ surface x Gd 1-x O 2-δ), the precursor solution is 0.1 mol / L aqueous solution of gadolinium nitrate and cerium nitrate, wherein Ce 3+ :Gd 3+ The molar ratio is 8:2. At the same time, different amounts of urea are added to the precursor solution, such as 0 mol / L, 0.025 mol / L, 0.05 mol / L, 0.075 mol / L, 0.10 mol / L, 0.15 mol / L, 0.2 mol / L, etc. The subsequent steps are consistent with the comparative example. The pH test of the precursor solution after hydrothermal treatment is performed. The results are as follows: Figure 5 As shown in the figure, with 0.1 mol / L urea content as the dividing line, when the added urea content is less than 0.1 mol / L, the pH value of the solution after hydrothermal treatment gradually increases to 6 as the urea content increases; when the urea content is greater than 0.1 mol / L, the pH value of the solution after hydrothermal treatment gradually increases and becomes alkaline. At this time, the powder-forming ability of GDC is greater than its film-forming ability, and no GDC film is formed. Finally, the half-cell after hydrothermal treatment was characterized by XRD, and the results are shown in the figure. Figure 4 As shown in the figure, with 0.1mol / L urea as the dividing line, when the urea content in the hydrothermal precursor solution is less than 0.1mol / L, the diffraction peak of doped cerium oxide appears at 2θ of 28.6°, indicating that with the addition of urea, GDC can still gradually form a film during the hydrothermal process and finally form a GDC isolation layer. When the urea content is greater than 0.1mol / L, according to the XRD pattern, the diffraction peak of doped cerium oxide cannot be detected at 2θ of 28.6°. Figure 5 This indicates that the pH of the solution after hydrothermal treatment is alkaline. 3+ 、Gd 3+ The ion powder-forming ability is greater than the film-forming ability, and no doped cerium oxide film is formed. This is because the urea concentration is too high. It begins to decompose continuously above 70°C, making the solution system alkaline. The products of urea hydrolysis under alkaline conditions are carbonate ions. At this time, cerium ions associate with water molecules and carbonate ions to form hydrated cerium oxycarbonate powder and hydrated basic cerium carbonate, etc., and no GDC film is formed on the YSZ surface.

[0031] According to the above experimental results, four half-cells with different urea contents of 0 mol / L, 0.025 mol / L, 0.05 mol / L, and 0.10 mol / L were prepared by screen printing on the surface of LSCF cathode, and co-fired with GDC isolation layer at 1075 ° C for 2 h to obtain a complete single cell. Finally, silver grids (the effective working area of ​​the cathode is 0.5 cm) were screen printed on the surface of the anode and cathode of the above single cell. 2) and calcined at 600℃ for 1h as the current collecting layer, respectively named Cell-1 (0mol / LU), Cell-2 (0.025mol / LU), Cell-3 (0.05mol / LU), Cell-4 (0.10mol / LU). SEM characterization was performed on them, and the results were as follows Figure 6 As shown in Figure 3, it was found that with the increase of urea content, the thickness of the GDC isolation layer grown after hydrothermal growth also increased, from 0.38 μm to 0.85 μm, and the growth rate increased from ~100 nm / 10 h to ~200 nm / 10 h.

[0032] Cell-1 and Cell-4 were reduced at 800℃ for 5h (fuel gas was 3% H2O-97% H2) and then the electrochemical performance was tested. Figure 7 As shown in (a), the peak power density of Cell-4 is 0.98W / cm 2 Compared with Cell-1 (0.88W / cm 2 ) increased by ~12%; ohmic resistance at 0.8V is 0.070Ω·cm 2 Compared with Cell-1 (0.082Ω·cm 2 ) is reduced by ~15%. The reason for the improvement of the electrochemical performance of Cell-4 is that, on the one hand, the isolation layer becomes thicker and denser, which hinders the diffusion of elements such as Sr in the cathode; on the other hand, the higher amount of Gd doping provides more oxygen vacancies, which is conducive to oxygen ion conduction.

[0033] The single cell prepared by Cell-4 was placed in a constant current discharge at 700℃ for 180h, and the discharge voltage-time was as follows: Figure 7 As shown in (b), during the discharge process, the battery voltage decays from 0.847 V to 0.824 V, with a decay rate of 0.023 V / h, and the battery exhibits good long-term stability.

[0034] Table 1 Ce and Gd atomic ratios on the hydrothermal GDC surface

[0035]

[0036] Table 2 Ce and Gd atomic ratios on the hydrothermal GDC surface after adding urea

[0037]

[0038]

[0039] Table 3 Ce and Gd atomic ratios on the surface of hydrothermal GDC with different urea contents

[0040]

Claims

1. A method for controlling the growth of a cerium oxide-doped electrolyte ceramic film, characterized in that: The steps include: The solid oxide battery electrolyte is immersed in a soluble salt solution of Ce and X, a pH adjuster is added, and the solution is transferred to a reactor for hydrothermal reaction at a certain temperature. After a period of reaction, an electrolyte ceramic film is formed, wherein X is one or two of the lanthanide rare earth elements Gd, Sm, La, and Pr.

2. The method according to claim 1, wherein The pH adjuster is a substance that becomes alkaline after being hydrolyzed by heating.

3. The method according to claim 1, wherein The pH adjuster is one or both of urea and thiourea.

4. The method according to claim 1, wherein The molar ratio of Ce to X is 6:4~9:

1.

5. The method according to claim 1, wherein The concentration of the pH regulator in the hydrothermal reaction system is 0.025~0.1 mol / L.

6. The method according to claim 1, wherein The hydrothermal reaction temperature is 160~200 o C, reaction time is not less than 24 h.

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