A gadolinium oxide-doped cerium oxide material and a method for producing the same

Abstract

The application relates to a preparation method of a gadolinium oxide doped cerium oxide material (GDC), which comprises the following steps: preparing an ammonium benzoate precipitator solution and a nitrate raw material solution; mixing the ammonium benzoate precipitator solution and the nitrate raw material solution, stirring, repeatedly filtering and washing the obtained precipitate, and then drying to obtain a fiber rod-shaped precursor powder; grinding and crushing the precursor powder and calcining to obtain a light yellow GDC pure phase powder; placing the GDC pure phase powder in a ball mill tank, mixing with a liquid medium and a calcium salt solution, ball milling, and then heat treating, so that the calcium salt solvent is fully decomposed into nano calcium oxide and coated on the surface of the GDC pure phase powder, and finally, the nano gadolinium oxide doped cerium oxide material is obtained; wherein the addition amount of the calcium oxide is controlled to be less than or equal to 2 wt%.

Description

Technical Field

[0001] This invention relates to the field of solid oxide fuel cell technology, specifically to a gadolinium oxide-doped cerium oxide material and its preparation method. Background Technology

[0002] Solid oxide fuel cells (SOFCs), as electrochemical conversion devices that efficiently convert chemical energy into electrical energy, possess advantages such as high energy conversion efficiency, wide fuel adaptability, and environmental friendliness, showing broad application prospects in distributed power generation, residential combined heat and power (CHP), and transportation. However, traditional SOFCs require operation at medium to high temperatures (700-850℃), and problems such as difficult battery sealing, oxidation and corrosion of connectors, rapid performance degradation, and high material costs hinder their commercialization. Therefore, there is an urgent need to develop medium- and low-temperature SOFCs (≤650℃) to improve battery life, reduce battery costs, and promote their commercial application.

[0003] CeO2-based electrolyte materials exhibit high oxygen ion conductivity at medium and low temperatures, and demonstrate good chemical compatibility and thermal expansion matching with electrode materials, making them a promising class of electrolyte materials for medium and low temperature SOFCs. Many CeO2-doped materials (such as GdO2)... 3+ Sm 3+ Y 3+ In electrolyte materials, Gd 3+ CeO2-doped electrolyte materials (also known as gadolinia-doped cerium oxide, or GDC for short) have the characteristics of high ionic conductivity, readily available raw materials, low cost, and good chemical compatibility with commonly used electrode materials, and are considered to be one of the most promising electrolyte materials for medium and low temperature SOFCs.

[0004] However, GDC materials exhibit poor sintering activity. GDC prepared by traditional solid-state methods often requires high temperatures (≥1600℃) to achieve dense sintering, limiting its practical application. Secondly, the high grain boundary resistance of GDC leads to low ionic conductivity of the electrolyte in the mid-to-low temperature range, hindering the performance of SOFC batteries. The morphology and chemical composition of GDC electrolyte powder significantly affect its sintering activity and ionic conductivity; therefore, the preparation technology of highly active GDC powder materials is a key research focus in this field.

[0005] Currently, the preparation methods for GDC electrolyte powder are mainly divided into solid-phase methods and liquid-phase methods. Liquid-phase methods include sol-gel methods, combustion methods, hydrothermal methods, and co-precipitation methods. Among these, co-precipitation is a very suitable technology for large-scale preparation of GDC powder due to its simple process, low production cost, and suitability for mass production. However, during co-precipitation, problems such as powder agglomeration and inaccurate composition control can easily occur, leading to poor sintering activity and low ionic conductivity.

[0006] In addition, to improve the sintering activity of GDC, sintering aids are often added to lower the sintering temperature. Currently, oxides such as lithium oxide, iron oxide, cobalt oxide, and copper oxide are commonly used as sintering aids for GDC, which can effectively reduce the sintering temperature. However, lithium oxide has high volatility and can pollute the preparation equipment, while transition metals such as Fe, Co, and Cu can cause electronic conductivity in GDC, making the electrolyte internally conductive, reducing the open-circuit voltage of SOFC cells, and thus reducing the energy conversion efficiency of fuel cells.

[0007] Therefore, for GDC materials, solving the agglomeration problem in the manufacturing process, improving sintering activity and ionic conductivity, and thus enhancing energy conversion efficiency are of great significance for their commercial application. Summary of the Invention

[0008] To address the above problems, this invention provides a method for preparing gadolinium oxide-doped cerium oxide (GDC) materials, comprising the following steps:

[0009] S1: Preparation of precipitant solution: Prepare ammonium benzoate precipitant solution using deionized water as solvent;

[0010] S2: Prepare raw material solution: Prepare gadolinium oxide or gadolinium nitrate and cerium nitrate hexahydrate according to the stoichiometric ratio of GDC, add them to deionized water, and add nitric acid to dissolve the solute to prepare nitrate raw material solution;

[0011] S3: Mixed precipitation: The nitrate raw material solution in step S2 is mixed with the ammonium benzoate precipitant solution in step S1 to obtain a mixed solution, and the mixture is stirred. The resulting precipitate is filtered and washed multiple times, and then dried to obtain fibrous rod-shaped precursor powder.

[0012] S4: Heat treatment: The precursor powder obtained in step S3 is crushed and calcined to obtain light yellow GDC pure phase powder.

[0013] S5: Mechanical ball milling: Place the fibrous rod-shaped GDC pure-phase powder in step S4 into a ball milling tank, add a liquid medium that does not react with the powder and is easy to remove, and a calcium salt solution for mixed ball milling, and then perform heat treatment to make the calcium salt fully decompose into nano-calcium oxide and coat it on the surface of the GDC pure-phase powder, finally obtaining a gadolinium-doped cerium oxide nano-material; wherein, the addition amount of calcium oxide is controlled within 2 wt%.

[0014] Preferably, in step S2, by controlling the dosage of nitric acid, the pH value of the solution after mixing the nitrate raw material solution and the ammonium benzoate precipitant solution in step S1 is between 2 and 5.

[0015] Preferably, in the above step S4, the calcination temperature is 400°C to 600°C, and the time is 2 to 4 hours.

[0016] Preferably, the heat treatment method in step S5 is to heat for 2 hours in an environment of 300°C to 600°C.

[0017] Preferably, in step S1, the concentration of the ammonium benzoate precipitant solution is 1 to 2 mol / L.

[0018] Preferably, in step S2, the concentration of the nitrate raw material solution is 0.25 to 0.5 mol / L.

[0019] Preferably, in step S3, the concentration of the nitrate raw material solution is 0.25 to 0.5 mol / L.

[0020] Preferably, the liquid medium in step S5 is deionized water, alcohol, acetone or isopropanol.

[0021] The present invention also provides a gadolinium-doped cerium oxide material with the chemical formula Gd x Ce1- x O 2-x / 2 (GDC), where 0 < x ≤ 0.2, prepared by the above method.

[0022] The present invention also provides a fuel cell, including a solid electrolyte material, and the solid electrolyte material includes the above gadolinium-doped cerium oxide material.

[0023] In the method for preparing GDC materials in this invention, the precursor is fibrous rod-shaped particles. These fibrous particles intertwine to form a loose and porous structure. Compared with other morphologies such as plate-shaped or spherical particles, this method can effectively reduce the heat treatment temperature (400℃-600℃) of the precursor and requires a shorter heat treatment time (2h). Secondly, it facilitates the crushing of the powder into fine and uniform nanoparticles during ball milling, while simultaneously forming a large number of highly active fresh surfaces. These fresh surfaces have a large surface energy, which is beneficial for improving the sintering activity of the GDC electrolyte. Thirdly, the calcium salt is decomposed in situ into calcium oxide through in-situ ball milling and low-temperature heat treatment. By controlling the mass percentage of calcium oxide to within 2%, the sintering activity of the powder can be effectively improved, the number of GDC grain boundaries can be reduced, the grain boundary conductivity of the material can be increased, and the total ionic conductivity of the electrolyte can be improved. The electrolyte prepared from the obtained GDC powder has high density, low grain boundary resistance, and high ionic conductivity. Attached Figure Description

[0024] Figure 1 This is a SEM image of the precursor powder of this invention;

[0025] Figure 2 This is a SEM image of the precursor powder under mixed solution pH>5 conditions;

[0026] Figure 3 This is a SEM image of the nano-GDC powder of this invention;

[0027] Figure 4 These are SEM comparison images of the surface cross sections of electrolytes prepared from fibrous precursors and sheet precursors.

[0028] Figure 5 This is a comparison chart of the relative compaction of electrolytes prepared from fibrous precursors and sheet-like precursors;

[0029] Figure 6 The relative density of the GDC electrolytes with different calcium oxide contents after sintering at a specific temperature according to the present invention;

[0030] Figure 7 The total conductivity of electrolytes with different calcium oxide contents prepared in this invention at 600°C. Detailed Implementation

[0031] This invention provides a method for preparing a gadolinium oxide-doped cerium oxide (GDC) solid electrolyte material, comprising the following steps:

[0032] S1: Preparation of precipitant solution: Using deionized water as solvent, prepare an ammonium benzoate precipitant solution with a concentration of 1-2 mol / L;

[0033] S2: Prepare raw material solution: Prepare gadolinium oxide or gadolinium nitrate and cerium nitrate hexahydrate according to the stoichiometric ratio of GDC, add them to deionized water, and add nitric acid to dissolve the solute, and finally prepare a nitrate raw material solution with a concentration of 0.25-0.5 mol / L.

[0034] S3: Mixed precipitation: The nitrate raw material solution prepared in step S2 is added to the ammonium benzoate precipitant solution in step S1 to obtain a mixed solution. The solution is stirred and the precipitate is filtered and washed multiple times. Then it is dried to obtain fibrous rod-shaped precursor powder.

[0035] S4: Heat treatment: The precursor powder obtained in step S3 is crushed and placed in an alumina crucible, and calcined in a muffle furnace at 400℃~600℃ for 2~4h to obtain light yellow fibrous rod-shaped GDC pure phase powder.

[0036] S5: Mechanical ball milling: The fibrous rod-shaped GDC pure phase powder from step S4 is placed in a ball mill jar, and a liquid medium that does not react with the powder and is easy to remove, as well as a calcium salt solution, are added. Ball milling is then performed, and the mixture is heated in a muffle furnace at 300℃~600℃ for 2 hours to fully decompose the calcium salt solution into nano-calcium oxide, which is then coated on the surface of the GDC pure phase powder to finally obtain nano-gadolinium oxide-doped cerium oxide material; wherein the amount of calcium oxide added is controlled to be less than 2wt%.

[0037] The main innovation of this invention lies in controlling the amount of nitric acid used in step S2, so that the pH value of the mixed solution after mixing with the precipitant solution in step S1 is controlled between 2 and 5. Research has shown that this allows the precursor generated in step S3 to exhibit fibrous rod-shaped particles (see...). Figure 1 Compared to other morphologies such as plate-like or spherical particles, this type of fibrous rod-shaped particle interweaves, resulting in a more fluffy precursor with no severe aggregation between particles and high density (see [link to original text]). Figure 5 Furthermore, during subsequent heat treatment, the precursor can have sufficient contact with air, which can effectively reduce the heat treatment temperature of the precursor (400℃-600℃) and the required heat treatment time is shorter (2-4h).

[0038] Correspondingly, if the pH of the mixed solution in step S3 is greater than 5, the resulting precursor powder will exhibit a plate-like structure (see...). Figure 2This leads to severe precursor agglomeration and high powder bulk density, requiring prolonged heat treatment at 650℃ (over 4 hours) to completely remove the organic matter from the precursor. High powder calcination temperatures also reduce the sintering activity of the powder and hinder efforts to reduce energy consumption and save manufacturing costs. Furthermore, the flake-like precursor powder is difficult to grind into nanoparticles during subsequent ball milling, resulting in poor sintering activity and very low density of the electrolyte prepared from the powder (see...). Figure 5 ).

[0039] By controlling the pH value of the mixed solution, fibrous rod-shaped precursor powder is obtained. After heat treatment, the GDC pure phase powder will maintain a fibrous rod structure with a very large aspect ratio, which is beneficial for the powder to be broken into fine and uniform powder particles during ball milling. At the same time, a large number of highly active fresh surfaces are formed. The fresh surfaces have a large surface energy, which is beneficial for improving the sintering activity of GDC electrolyte.

[0040] In step S5 above, the calcium salt solvent is a calcium salt that easily decomposes into calcium oxide during subsequent heat treatment, such as calcium nitrate or calcium acetate, which facilitates the decomposition at low temperatures to obtain calcium oxide. Secondly, as another innovation of this invention, research has found that controlling the mass percentage of calcium oxide (calcium oxide / (calcium oxide + GDC)) to within 2 wt% can effectively eliminate grain boundary impurities (such as SiO2), further improve the sintering activity of the powder, increase the total ionic conductivity of the electrolyte, and the resulting electrolyte prepared from the GDC powder has high density (see...). Figure 6 High ionic conductivity (see) Figure 7 It is an ideal medium- and low-temperature SOFC electrolyte material.

[0041] In a preferred embodiment, in step S3 above, the nitrate raw material solution is added to the ammonium benzoate precipitant solution by a peristaltic pump at a speed of 1.5 to 7.5 r / min, and stirred for 12 hours by a mechanical stirrer at a speed of 200 to 400 r / min; the precipitate is filtered and washed 3 times.

[0042] In a preferred embodiment, in step S5 above, the ball mill jar rotates at a speed of 300-400 r / min and the ball milling is performed for 6-12 hours; the liquid medium is deionized water, alcohol, acetone, or isopropanol, etc.

[0043] The chemical formula of the GDC powder material prepared by the above method is Gd. x Ce 1-x O 2-x / 2 , of which 0 <x≤0.2。

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing gadolinium oxide-doped cerium oxide material, characterized in that, Includes the following steps: S1: Preparation of precipitant solution: Prepare ammonium benzoate precipitant solution using deionized water as solvent; S2: Prepare raw material solution: Prepare gadolinium oxide or gadolinium nitrate, or cerium nitrate hexahydrate according to the stoichiometric ratio of gadolinium oxide doped with cerium oxide, add them to deionized water, and add nitric acid to dissolve the solute to prepare nitrate raw material solution; S3: Mixed precipitation: The nitrate raw material solution in step S2 is mixed with the ammonium benzoate precipitant solution in step S1 to obtain a mixed solution, and the mixture is stirred. The resulting precipitate is filtered and washed multiple times, and then dried to obtain fibrous rod-shaped precursor powder. S4: Heat treatment: The precursor powder obtained in step S3 is crushed and calcined to obtain pale yellow gadolinium oxide-doped cerium oxide pure phase powder. S5: Mechanical ball milling: The fibrous rod-shaped gadolinium oxide-doped cerium oxide pure phase powder from step S4 is placed in a ball mill jar, and a liquid medium that does not react with the powder and is easy to remove, along with a calcium salt solution, is added for mixing and ball milling. Then, heat treatment is performed to fully decompose the calcium salt into nano-calcium oxide, which then coats the surface of the gadolinium oxide-doped cerium oxide pure phase powder, ultimately obtaining nano-gadolinium oxide-doped cerium oxide material; wherein, the amount of calcium oxide added is controlled to be less than 2 wt%. In step S2, by controlling the amount of nitric acid, the pH value of the solution after mixing the nitrate raw material solution and the ammonium benzoate precipitant solution in step S1 is between 2 and 5.

2. The method according to claim 1, characterized in that, In step S4 above, the calcination temperature is 400℃~600℃ and the time is 2~4 hours.

3. The method according to claim 2, characterized in that, The heat treatment method in step S5 is to heat at 300~600 ℃ for 2 hours.

4. The method according to claim 3, characterized in that, In step S1, the concentration of the ammonium benzoate precipitant solution is 1~2 mol / L.

5. The method according to claim 4, characterized in that, In step S2, the concentration of the nitrate raw material solution is 0.25~0.5mol / L.

6. The method according to claim 1, characterized in that, In step S3, the concentration of the nitrate raw material solution is 0.25~0.5mol / L.

7. The method according to claim 1, characterized in that, The liquid medium in step S5 is deionized water, alcohol, acetone or isopropanol.

8. A fuel cell, characterized in that, Includes a solid electrolyte material, wherein the solid electrolyte material is a gadolinium oxide-doped cerium oxide material prepared according to any one of claims 1-7.

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