CN119674153A - Growth regulation method of cerium oxide-doped electrolyte film - Google Patents

Abstract

The present invention discloses a growth regulation method for a doped cerium oxide electrolyte film, the steps of which are: placing a half-cell in a soluble salt solution of Ce and X, ensuring that the zirconium oxide-based electrolyte of the half-cell is in contact with the soluble salt solution, adding methanol, transferring to a reactor, performing hydrothermal solution crystallization film formation at a certain temperature, and forming a doped cerium oxide electrolyte ceramic film after a period of time. The present invention combines the hydrothermal solution crystallization in-situ film-forming technology, and changes the physical properties of the precursor solution by adding an appropriate amount of methanol, such as polarity, dielectric constant, surface tension, etc., to accurately control the doping amount of the doping elements of the electrolyte ceramic film, and directionally modify the grain size and morphology.

Description

Method for regulating growth of doped cerium oxide electrolyte film

Technical Field

The invention relates to a strategy for adjusting the growth of a solid oxide fuel cell isolating layer, and belongs to the field of solid oxide fuel film electrolyte preparation.

Background

Solid oxide fuel cells (Solid Oxide Fuel Cell, SOFC) are an efficient clean energy technology that converts chemical energy directly into electrical energy. The core principle is that chemical energy in fuel (such as hydrogen, carbon monoxide or hydrocarbon) is converted into electric energy and heat energy through oxidation-reduction reaction. SOFCs mainly include a porous anode, a porous cathode, and a dense electrolyte. The electrolyte is the most important part of a solid oxide fuel cell, and the key function of the solid electrolyte in an SOFC is to prevent electrons from diffusing in its body, acting as a separator between the fuel and the oxidant. The oxidizing ions (or protons) must have a high ionic conductivity when they pass through the electrolyte to undergo a redox reaction with the fuel. In SOFCs, yttrium Stabilized Zirconia (YSZ) is commonly used as an electrolyte because it has excellent mechanical properties, high stability and higher ionic conductivity at high temperatures (800-1000 ℃). However, zirconia-based electrolyte is easy to have poor chemical compatibility with a plurality of high-activity cathodes, is easy to react in the high-temperature long-term operation process, generates La ₂Zr₂O₇、SrZrO₃ with high resistance phase, and the like, and seriously affects the performance and the service life of the battery.

The design and preparation of the barrier layer becomes particularly important in order to improve the performance and stability of the SOFC. The separator layer is located between the electrolyte and the electrode and has the main functions of reducing interdiffusion between the electrolyte and the electrode material, avoiding performance degradation caused thereby, and improving interface contact to increase oxygen ion conductivity. A commonly used spacer material is CeO ₂ based material, such as GDC (Gd _xCe_1-xO_2-δ)、SDC(Sm_xCe_1-xO_2-δ) and the like. At present, the traditional preparation method is a silk screen sintering method, and research has proved that the isolation performance is considerable, but the high temperature of more than 1500 ℃ is required, and the problems that the co-sintering of GDC and YSZ is difficult to realize, the ohmic impedance is possibly increased and the like limit the further application of the preparation method. The preparation method of the specific film such as pulse laser deposition and physical vapor deposition has the advantages and disadvantages shown in the table, and the thickness of the isolation layer prepared by the methods is a micron or submicron-level film, so that the high-performance transportation of the SOFC single cell is realized. However, the advanced coating technology still faces the problems of high cost, severe process conditions, poor amplification uniformity and the like, so how to obtain a compact high-performance CeO ₂ -based isolation layer at low temperature is one of the leading edge and the key point of research in the field.

The compact and uniform ceramic film can be prepared on the electrolyte surface of the half cell as an isolation layer by adopting a hydrothermal in-situ growth method at a low temperature of 180 ℃. However, the growth rate is slow, the doping amount of the elements is small, and in the test process, the diffusion of part of the elements is found through long-term high-temperature operation, so that the attenuation rate is high. Therefore, it is a problem to be solved at present if the doping amount of the doping element, the growth rate and the service life of the single cell are further improved.

Disclosure of Invention

Based on the problems existing in the prior art, the invention provides a method for precisely regulating the growth of a doped cerium oxide electrolyte ceramic film. The invention adopts nitrate solution as hydrothermal precursor liquid, adds proper content of methanol, and adopts a hydrothermal in-situ growth method on the electrolyte of the half cell to prepare the continuous compact cerium oxide-based electrolyte film.

The technical proposal for solving the problems in the prior art is as follows:

A method for precisely regulating the growth of a doped cerium oxide electrolyte ceramic film comprises the following steps:

Putting the half cell in a soluble salt solution of Ce and X, ensuring that only zirconia-based electrolyte of the half cell is completely contacted with the soluble salt solution, adding methanol at other parts, transferring to a reaction kettle, and performing hydrothermal in-situ self-crystallization for a period of time at a certain temperature to form a doped ceria-electrolyte ceramic film, wherein X is one or two of lanthanide rare earth elements.

Preferably, in the soluble salt solution of Ce and X, the molar ratio of Ce to X is 90-70:10-30, and the total molar ratio is 100%.

More preferably, X is one or more of Gd, sm and Pr.

Preferably, the ambient temperature of the solution is 160-200 ℃ and the time is not less than 6 hours.

Preferably, the methanol is added in an amount of not more than 5% by volume of the soluble salt solution of Ce and X.

Preferably, the support of the half cell includes, but is not limited to, an anode support, an electrolyte support, a metal support, and the like.

Compared with the prior art, the invention has the advantages that:

The physical property of the precursor liquid is changed by adding proper content of methanol, the doped cerium oxide electrolyte is grown on the surface of the electrolyte in situ by means of hydrothermal method, the doping amount of doped elements in the cerium oxide electrolyte is precisely controlled, meanwhile, the size of GDC crystal grains is obviously changed, and the crystal grain arrangement is changed from small-size compact arrangement to large-size staggered arrangement. In terms of service life of single cells, element diffusion is obviously hindered, and durability of long-term operation of single cells is improved.

Drawings

FIG. 1 shows the results of scanning (a) and (b) of a SEM image of a surface of a precursor solution without adding methanol Gd-0.

FIG. 2 is a SEM image of the Gd-1 surface after adding 2.5% volume fraction methanol to the precursor (a) and EDS results (b).

FIG. 3 is a SEM image of the Gd-2 surface after adding 5.0% volume fraction methanol to the precursor (a) and EDS results (b).

FIG. 4 is a SEM image of the Gd-1 surface after adding 7.5% volume fraction methanol to the precursor (a) and EDS results (b).

FIG. 5 shows the electrochemical impedance spectra EIS curves (a) and the electrochemical performance j-P-V curves (b) of Gd-0, gd-1 and Gd-2 single cells.

Fig. 6 shows Gd-2 constant current for 1000 hours long run curve (a) and SEM image of cell cross section after long run (b) and EDS scan result of cell cross section (c).

FIG. 7 is a SEM image of the Gd-4 surface after 2.5% volume fraction methanol addition to the precursor (a) and EDS scan results (b).

FIG. 8 is a SEM image of Gd-5 surface after addition of 2.5% ethanol by volume of precursor (a) and EDS scan results (b).

Detailed Description

In order to better understand the technical content of the present invention, specific embodiments are specifically described below with reference to the drawings.

Aspects of the invention are described herein with reference to the drawings, in which illustrative embodiments are shown. Embodiments of the invention are not necessarily intended to include all aspects of the 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 disclosed concepts and embodiments are not limited to any implementation. Additionally, some aspects of the disclosure may be used alone or in any suitable combination with other aspects of the disclosure.

Comparative example 1

The green anode-supported half cell was sintered at 1320 ℃ for 3 hours to prepare an anode-supported half cell in which the anode support and functional layer were NiO-YSZ (NiO-Zr _0.84Y_0.16O_2-δ) and the electrolyte was YSZ (Zr _0.84Y_0.16O_2-δ).

Gadolinium oxide doped cerium oxide (GDC-Ce _xGd_1-xO_2-δ) which is a GDC isolation layer is grown on the surface of YSZ in situ by means of hydrothermal method, wherein the precursor solution is a mixed aqueous solution of gadolinium nitrate and cerium nitrate with the mol/L of 0.1, the mol ratio of Ce ³⁺:Gd³⁺ is 80:20, and the prepared half cell number is Gd-0. The method comprises the steps of fixing an anode support half cell on a polytetrafluoroethylene protection mold, immersing the anode support half cell in the precursor liquid, and ensuring that zirconia-based electrolyte of the half cell is in contact with the precursor liquid and other parts of the half cell are not in contact. Placing the hydrothermal kettle in a 180 ℃ oven (corresponding to the water vapor pressure of about 1 MPa), preserving heat for 36 hours, naturally cooling, taking out the half cell, flushing with deionized water, and then placing in a 80 ℃ heating plate for drying. SEM-EDS characterization was performed on the hydrothermal half-cell, and as shown in FIG. 1, the (a) in FIG. 1 shows that the GDC grains are small in size and closely arranged, and the grain boundaries are distinct. In terms of doping elements in the GDC isolation layer, (b) in fig. 1 shows that the doping amount of Gd element is less than 5%, which is far from the content of Gd element of 20% in the precursor solution, and the atomic economy is extremely low.

In addition, a LSCF (La _0.6Sr_0.4Co_0.2Fe_0.8O_2-δ) cathode is screen-printed on the Gd-0 surface, calcined at 1075 ℃ for 2 hours, a silver current collecting layer is screen-printed on the cathode surface after the calcination is finished, calcined at 600 ℃ for 2 hours, and finally a single cell is prepared. Cell impedance and electrochemical performance were tested for the comparative examples and the results are shown in fig. 4. FIG. 4 (a) shows that Gd-0 has a polarization impedance of 0.560 Ω cm ² at 700 ℃. FIG. 4 (b) shows that Gd-0 has a maximum power density of 0.386W/cm ² at 700 ℃.

Example 1

Gadolinium oxide doped cerium oxide (GDC-Ce _xGd_1-xO_2-δ) is grown on the surface of YSZ in situ by means of hydrothermal method, the precursor solution is a mixed aqueous solution of gadolinium nitrate and cerium nitrate with the mol/L of 0.1, the mol ratio of Ce ³⁺:Gd³⁺ is 80:20, 2.5%, 5.0% and 7.5% of methanol with the volume fraction (calculated by the volume of the precursor solution) are added into the precursor solution, and the prepared half-cell numbers are named Gd-1, gd-2 and Gd-3 respectively. Subsequent hydrothermal treatment steps were consistent with the comparative examples and SEM-EDS characterization was performed on the hydrothermal half-cells, and the results are shown in fig. 2, 3 and 4. As can be seen from fig. 2 (a), fig. 3 (a) and fig. 4 (a), in terms of the morphology of GDC grains, compared with Gd-0, the grain sizes of Gd-1 and Gd-2 are larger and the grains are staggered, and submicron-sized gaps appear on the surface of Gd-3, which negatively affect the density of the isolation layer, so that the content of added methanol should be less than 5% of the volume fraction of the precursor solution. As can be seen from fig. 2 (b), fig. 3 (b) and fig. 4 (b), the distribution of the elements in the Gd-1, gd-2 and Gd-3 bulk phases (within the tolerance range) achieves the same precise doping as the proportion of the elements in the precursor solution as compared with the comparative example Gd-0, and the doping element is significantly improved compared with Gd-0, so that the oxygen vacancies are significantly increased compared with Gd-0, which is more favorable for oxygen ion conduction and is particularly excellent in electrochemical performance. The methanol is added into the hydrothermal precursor solution, so that the polarity of the solution is changed to enhance the solvent effect of the precursor solution, and the change of the polarity reduces the activation energy of the ion doping process. Therefore, the enhanced solvent effect realizes the accurate doping of Gd element, and greatly improves the atom economy.

Since the Gd-3 surface has obvious submicron-level gaps, we select Gd-1 and Gd-2 (the preparation method of the complete single cell is the same as that of the comparative example) to carry out the subsequent single cell impedance and electrochemical performance test. The impedance and electrochemical performance tests were performed on both single cells and the results are shown in fig. 5. FIG. 5 (a) shows that at 700 ℃, the polarization impedance of Gd-1 is 0.244 Ω cm ², and the polarization impedance of Gd-2 is 0.294 Ω cm ², gd-1 and Gd-2 being reduced by 56% and 47% respectively compared to Gd-0. This is because the size of the GDC grains on the surfaces of Gd-1 and Gd-2 is larger than Gd-0, and the larger grain size increases the contact sites between the GDC grains and the LSCF cathode, increases the active sites where the cathode contacts the isolation layer, and further obviously reduces the polarization impedance. FIG. 5 (b) shows that Gd-1 has a maximum power density of 0.768W/cm ² and Gd-2 has a maximum power density of 0.692W/cm ² at 700℃and Gd-1 and Gd-2 are elevated by a factor of 2 and 1.8, respectively, compared to Gd-0.

In addition, gd-1 was tested for long-term operation stability at 700℃and SEM-EDS characterization of the cell cross section after long-term operation, as Gd-1 had better electrochemical performance than Gd-2 in terms of cell life, and the results are shown in FIG. 6. FIG. 6 (a) shows that the cell decay rate was only 3.9mV/kh after 1000 hours and 0.3A/cm ² constant current operation, and that there was little apparent diffusion of Sr/Zr and other elements after operation, as shown in FIG. 5 (b-c). The solvent effect of the solution is enhanced after the methanol is added into the precursor liquid, so that the size of GDC crystal grains is enlarged and the crystal grains are staggered, the phenomenon effectively prevents cathode/electrolyte elements from mutually diffusing in the high-temperature long-term operation process, and the service life of the SOFC single cell is greatly prolonged.

Example 2

According to the method of example 1, gadolinium oxide doped cerium oxide (GDC-Ce _xGd_{1- x}O_2-δ) was grown hydrothermally in situ on the YSZ surface, the precursor solution was a mixed aqueous solution of gadolinium nitrate and cerium nitrate of 0.1mol/L, wherein the molar ratio of Ce ³⁺:Gd³⁺ was 85:15, and at the same time, 2.5% by volume (based on the volume of the precursor solution) of methanol was added to the precursor solution, and the prepared half cell number was named Gd-4. The subsequent hydrothermal treatment steps were consistent with the comparative examples and SEM-EDS characterization was performed on the hydrothermal half-cells, with the results shown in fig. 7. Compared with the comparative example, the proportion of the elements in Gd-4 is the same as that in the precursor solution like Gd-1, gd-2 and Gd-3, so that the accurate doping of the doping elements in the cerium oxide-based electrolyte can be realized by adding methanol into the precursor solution.

Comparative example 2

According to the method of example 2, gadolinium oxide doped ceria (GDC-Ce _xGd_{1- x}O_2-δ) was grown hydrothermally in situ on the YSZ surface, except that Ce ³⁺:Gd³⁺ was 80:20 molar ratio and ethanol was added at a volume fraction (based on the precursor volume) of 2.5%, the half cell number made was named Gd-5. SEM-EDS characterization was performed on the hydrothermal half-cell, and the results are shown in fig. 8. Fig. 8 (a) shows that submicron-sized gaps appear on the surface of the GDC isolation layer after ethanol is added to the hydrothermal precursor solution, and fig. 8 (b) shows that the doping amount of Gd element is 20% and is consistent with the Gd content in the precursor solution, but the apparent gaps appear on the surface, which is unfavorable for prolonging the service life of the battery, and is contrary to the dense electrolyte film required in the industry, so that the addition of ethanol to the precursor solution is not selected to change the physical properties of the solution.

Claims (6)

1. The method for precisely regulating the growth of the doped cerium oxide electrolyte ceramic film is characterized by comprising the following steps of:

Putting the half cell in a soluble salt solution of Ce and X, ensuring that only zirconia-based electrolyte of the half cell is completely contacted with the soluble salt solution, adding methanol at other parts, transferring to a reaction kettle, and performing hydrothermal in-situ self-crystallization for a period of time at a certain temperature to form a doped ceria-electrolyte ceramic film, wherein X is one or two of lanthanide rare earth elements.

2. The method of claim 1, wherein the molar ratio of Ce to X in the soluble salt solution of Ce and X is 90-70:10-30, the molar total being 100%.

3. The method of claim 1, wherein X is one or more of Gd, sm, pr.

4. The method of claim 1, wherein the temperature of the solution environment is 160-200 ^o C for a time not less than 6 h.

5. The method of claim 1, wherein the methanol is added in an amount of no more than 5% by volume of the soluble salt solution of Ce and X.

6. The method of claim 1, wherein the support of the half cell is an anode support, an electrolyte support, or a metal support.