High-entropy bismuth oxide ceramic as well as preparation method and application thereof

Abstract

The invention discloses high-entropy bismuth oxide ceramic as well as a preparation method and application thereof. The chemical general formula of the high-entropy bismuth oxide ceramic is ((Sm < 0.25 > Gd < 0.25 > Pr < 0.25 > Yb < 0.25 >) x Bi < 1-x >) 2O3, wherein x is equal to 0.3 to 0.5. The preparation method comprises the following steps: weighing citric acid, dissolving the citric acid in deionized water, adding ammonia water to adjust the pH value, sequentially adding Sm (NO3) 3.5 H2O, Gd (NO3) 3.6 H2O, Pr (NO3) 3.6 H2O, Yb (NO3) 3.5 H2O and Bi (NO3) 3.5 H2O according to the stoichiometric ratio of ((Sm < 0.25 > Gd < 0.25 > Pr < 0.25 > Yb < 0.25 >) x Bi < 1-x >) 2O3, and continuously heating and stirring to obtain gel; pre-calcining the gel to obtain precursor powder; the high-entropy bismuth oxide ceramic is obtained after the precursor powder is subjected to compression molding and sintering, the high-entropy bismuth oxide ceramic can be used as an electrolyte of an SOFC, and a stable cubic fluorite structure is still kept at the medium and low temperature of 600 DEG C, so that oxygen ions are efficiently conducted, the conversion efficiency of an SOFC device is remarkably improved, and the service life of the SOFC device is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of ceramic technology, and more specifically, to a high-entropy bismuth oxide ceramic, its preparation method, and its application. Background Technology

[0002] In the field of solid oxide fuel cells (SOFCs), bismuth oxide-based (Bi2O3) solid electrolytes have potential application value due to their efficient oxygen ion transport. However, Bi2O3 exhibits various crystal forms depending on temperature: δ-Bi2O3 is the dominant phase, possessing a cubic fluorite crystal structure with a high oxygen vacancy concentration of up to 25%, enabling efficient oxygen ion transport. Its drawback is its extremely narrow stable temperature range, existing only between 730 ℃ and 825 ℃. Once the temperature drops below 730 ℃, δ-Bi2O3 undergoes a crystal transformation, losing its original advantageous properties. To improve the structural stability of the δ-Bi2O3 phase at low temperatures, modification is often carried out through the "high entropy effect" of multi-element doping. The "high entropy effect" is manifested at both thermodynamic and mechanical levels.

[0003] At the thermodynamic level, the configurational entropy of the material is greatly increased through multi-element synergistic doping. According to the Gibbs free energy formula G=HT•S, the surge in configurational entropy will significantly enhance the contribution of the "T•S" term. Even in low-temperature environments, it can effectively lower the Gibbs free energy of the cubic fluorite phase, keeping it consistently lower than competing crystal forms such as α-Bi2O3, thus avoiding spontaneous phase transitions from an energy perspective.

[0004] At the structural level, due to the ionic radius of the dopant element and Bi... 3+ There are differences, replacing Bi 3+ Once inside the crystal lattice, it forms uniform and minute lattice distortions. These distortions raise the energy barrier required for the phase transition, hindering the orderly rearrangement of atoms into a low-entropy crystal form and further suppressing the occurrence of the phase transition.

[0005] Currently, the preparation of high-entropy bismuth oxide mainly relies on solid-state methods, such as the common co-precipitation and ball milling methods. The co-precipitation method uses ammonia as a precipitant to prepare a precursor of metal hydroxides. This precursor powder is then pressed and sintered to obtain high-entropy bismuth oxide. The main drawback of this technique is that during the co-precipitation stage, the pH values ​​corresponding to the precipitation of each metal ion differ, making it difficult to achieve simultaneous precipitation and good mixing. The ball milling method uses the component metal oxides as precursors, adding them to a ball mill in a predetermined ratio. After prolonged mechanical grinding to achieve component mixing, high-entropy bismuth oxide is prepared through a pressing and sintering process. The main shortcomings of this method are the high energy consumption of mechanical grinding and the low mixing uniformity.

[0006] In summary, the existing solid-state method for preparing high-entropy bismuth oxide has common drawbacks, including the difficulty in achieving atomic-level mixing of precursors and poor system uniformity. Therefore, more stringent calcination conditions are often required to achieve high entropy. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a high-entropy bismuth oxide ceramic, its preparation method and application, at least to achieve the purpose of improving the oxygen ion conductivity and stability of the material at medium and low temperatures.

[0008] To solve the above technical problems, according to one aspect of the present invention, a high-entropy bismuth oxide ceramic is provided, the general chemical formula of which is: ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x )2O3, x=0.3~0.5.

[0009] As a preferred embodiment, the high-entropy bismuth oxide ceramic has a cubic fluorite crystal structure at room temperature.

[0010] According to another aspect of the present invention, a method for preparing the above-described high-entropy bismuth oxide ceramic is provided, comprising: Step 1: Weigh citric acid and dissolve it in deionized water. Add ammonia to adjust the pH, then according to ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O were added in stoichiometric proportions to obtain a gel under continuous heating and stirring. Step 2: Pre-calcine the gel to obtain precursor powder; Step 3: Press the precursor powder into shape and sinter it to obtain the high-entropy bismuth oxide ceramic.

[0011] In a preferred embodiment, in step one, the amount of citric acid dissolved in deionized water is 25-50 g / 100 ml of deionized water.

[0012] In a preferred embodiment, in step one, the pH is adjusted to 5-7 after adding ammonia.

[0013] In a preferred embodiment, in step one, the total number of moles of each metal nitrate is 0.01~0.03 mol.

[0014] As a preferred embodiment, in step two, the pre-calcination procedure is as follows: heat to 100~150 ℃ at 5 ℃ / min and hold for 6 h, then heat to 400~500 ℃ at 5 ℃ / min and hold for 12 h.

[0015] As a preferred embodiment, in step three, the pressing conditions are: holding pressure at 10~20 MPa for 2 min.

[0016] As a preferred embodiment, in step three, the sintering conditions are: heating at 5 ℃ / min to 900~1000 ℃ and holding for 12~24 h.

[0017] According to another aspect of the present invention, the application of the high-entropy bismuth oxide ceramic described above in the fabrication of solid oxide fuel cells (SOFCs) is provided. This ceramic can serve as an electrolyte for SOFCs, maintaining a stable cubic fluorite structure even at medium-low temperatures up to 600°C, thereby efficiently conducting oxygen ions and significantly improving the conversion efficiency and lifespan of SOFC devices.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method proposed in this invention can achieve atomic-level mixing of each component through the complexation of citric acid, which greatly improves the uniformity of the system; by taking advantage of the intense exothermic reaction of the combustion of the complex system, the diffusion and migration of doped metal ions are promoted, thereby greatly reducing the difficulty of high entropy.

[0019] (2) The precursor powder obtained by the preparation method proposed in this invention has abundant hydroxyl groups on its surface, which can serve as the basis for subsequent modifications such as ion exchange and surface grafting to improve its overall performance.

[0020] (3) The ((Sm) prepared by this invention 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x The high-entropy bismuth oxide ceramic (2O3) has a dense structure and can be used as an electrolyte in SOFCs. Its oxygen ion conductivity at medium and low temperatures is significantly improved compared with the traditional solid-state method. Attached Figure Description

[0021] Figure 1 The XRD patterns are of the high-entropy bismuth oxide ceramics prepared in Examples 1-3 and Comparative Example 1.

[0022] Figure 2 Electrical conductivity (a) and Arrhenius plot (b) of the high-entropy bismuth oxide ceramics prepared for Example 1 and Comparative Example 1.

[0023] Figure 3The infrared spectrum of the precursor in Example 1.

[0024] Figure 4 The surface (a) and cross-section (b) of the high-entropy bismuth oxide ceramic in Example 3 are shown in SEM images. Detailed Implementation

[0025] A typical embodiment of the present invention provides a high-entropy bismuth oxide ceramic, the general chemical formula of which is: ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x )2O3, x=0.3~0.5. It has a cubic fluorite crystal structure at room temperature.

[0026] By doping four rare earth elements—Sm (samarium), Gd (gadolinium), Pr (praseodymium), and Yb (ytterbium)—into the lattice of δ-Bi₂O₃ using the sol-gel method, the configurational entropy and lattice distortion of the material are significantly improved, thereby enhancing the stability of its cubic fluorite crystal structure at medium and low temperatures and even room temperature, as well as its oxygen ion conductivity.

[0027] Another typical embodiment of the present invention provides a method for preparing the above-mentioned high-entropy bismuth oxide ceramic, which adopts the sol-gel method and includes the following steps one to three.

[0028] Step 1, Gel Preparation Weigh 50-100 g of citric acid and dissolve it in 200 mL of deionized water. Add ammonia to adjust the pH to 5-7. The total molar amount of each metal nitrate is 0.01-0.03 mol. Then, according to ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O were added in stoichiometric proportions to obtain a gel by heating and concentrating under stirring at 80~120 °C.

[0029] Step 2, Pre-calcination The gel was pre-calcined to obtain precursor powder. The pre-calcination procedure was as follows: the temperature was increased to 100~150℃ at 5℃ / min and held for 6 h, and then the temperature was increased to 400~500℃ at 5℃ / min and held for 12 h.

[0030] Step 3, pressing and sintering The precursor powder is pressed into shape and sintered to obtain the high-entropy bismuth oxide ceramic.

[0031] The compression conditions are: hold pressure at 10~20 MPa for 2 min; The sintering conditions are: heating at 5 ℃ / min to 900~1000 ℃ and holding for 12~24 h.

[0032] According to the above implementation method, when the metal-citric acid complex solution is heated, several types of physical and chemical changes occur sequentially. The first is the dehydration stage: as the temperature rises, water molecules in the complex are gradually removed, and the solution viscosity gradually increases, eventually forming a sol with a certain viscosity. Upon further heating, the sol further transforms into a gel. During this process, intermolecular interactions are enhanced, leading to the formation of a three-dimensional network structure with uniformly distributed elements.

[0033] When the temperature reaches a certain threshold, the gel initiates a combustion reaction: at this point, the metal-citric acid complex acts as fuel, undergoing a violent redox reaction with oxygen (or oxidizing gases produced by the decomposition of nitrates) within the system. This reaction is a violently exothermic process, with a large amount of heat being released rapidly, providing additional impetus for the migration of metal ions, prompting them to migrate or diffuse rapidly into the cubic fluorite crystal structure of bismuth oxide, and ultimately forming a single solid solution with a specific crystal phase structure under the influence of the "high entropy effect".

[0034] The above preparation method employs the sol-gel method, achieving atomic-level mixing of components through complexation, significantly improving system homogeneity and thus substantially reducing the difficulty of achieving high entropy. Furthermore, the powder obtained after calcining the gel at a suitable temperature contains abundant hydroxyl groups on its surface, facilitating modifications such as ion exchange and surface grafting to improve overall performance.

[0035] The prepared high-entropy bismuth oxide ceramic can serve as the electrolyte for SOFCs, forming SOFCs with electrodes on both the fuel and air sides. The performance of this device largely depends on the electrolyte's ability to conduct oxygen ions, and lowering the operating temperature can significantly improve the device's lifespan. The high-entropy bismuth oxide ceramic prepared in this invention can stably maintain its advantageous cubic fluorite structure at medium-low temperatures up to 600℃, efficiently conducting oxygen ions. This provides a reliable foundation for the development of long-lifetime, high-efficiency SOFC devices.

[0036] The technical solutions claimed in this invention will be further described below through some embodiments. However, the embodiments and comparative examples are for explaining the implementation schemes of this invention and do not exceed the scope of the subject matter of this invention. The scope of protection of this invention is not limited by the embodiments. Unless otherwise specified, the materials and reagents used in this invention can be obtained from commercially available products in the art. Example 1

[0037] ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.3 Bi 0.7 Preparation method of high-entropy bismuth oxide solid electrolyte 2O3 (1) First, weigh 50 g of citric acid and dissolve it in 200 mL of deionized water. Stir to dissolve, then add ammonia to adjust the pH to 5. Fix the total molar amount of each metal nitrate to 0.01 mol, and then follow ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.3 Bi 0.7 Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O were added in stoichiometric proportions to 2O3. After stirring, the mixture was dissolved and then heated and concentrated at 80 °C with continuous stirring. The solution gradually turned into a sol and eventually transformed into a gel with very poor flowability.

[0038] (2) The gel was calcined in a muffle furnace to obtain the precursor. The program was set as follows: the temperature was increased from room temperature to 100 ℃ at 5 ℃ / min and held for 6 h; then the temperature was increased to 400 ℃ at 5 ℃ / min and held for 12 h. After natural cooling, the product was collected as the precursor.

[0039] (3) The precursor powder is kept at 10 MPa for 2 min in a tablet press, and then the pressed discs are sent to a muffle furnace and heated to 900 °C at 5 °C / min and kept for 12 h. After natural cooling, a high-entropy bismuth oxide ceramic electrolyte with good density can be obtained. Example 2

[0040] ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.4 Bi 0.6 Preparation method of high-entropy bismuth oxide solid electrolyte (2O3) (1) First, weigh 100 g of citric acid and dissolve it in 200 mL of deionized water. Stir to dissolve, then add ammonia to adjust the pH to 7. Fix the total molar amount of each metal nitrate to 0.03 mol, and then follow ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.4 Bi0.6 Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O were added in stoichiometric proportions to 2O3. After stirring, the mixture was dissolved and then heated and concentrated at 120 °C with continuous stirring. The solution gradually turned into a sol and eventually transformed into a gel with very poor flowability.

[0041] (2) The gel was calcined in a muffle furnace to obtain the precursor. The program was set as follows: the temperature was increased from room temperature to 150 ℃ at 5 ℃ / min and held for 6 h; then the temperature was increased to 500 ℃ at 5 ℃ / min and held for 12 h. After natural cooling, the product was collected as the precursor.

[0042] (3) The precursor powder is kept at 20 MPa for 2 min in a tablet press, and then the pressed discs are sent to a muffle furnace and heated to 1000 ℃ at 5℃ / min and kept for 24 h. After natural cooling, a high-entropy bismuth oxide ceramic electrolyte with good density can be obtained. Example 3

[0043] ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.5 Bi 0.5 Preparation method of high-entropy bismuth oxide solid electrolyte (2O3) (1) First, weigh 75 g of citric acid and dissolve it in 200 mL of deionized water. Stir to dissolve, then add ammonia to adjust the pH to 6. Fix the total molar amount of each metal nitrate to 0.02 mol, and then follow ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.5 Bi 0.5 Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O were added in stoichiometric proportions to 2O3. After stirring, the mixture was dissolved and then heated and concentrated at 100 °C with continuous stirring. The solution gradually turned into a sol and eventually transformed into a gel with very poor flowability.

[0044] (2) The gel was calcined in a muffle furnace to obtain the precursor. The program was set as follows: the temperature was increased from room temperature to 125 ℃ at 5 ℃ / min and held for 6 h; then the temperature was increased to 450 ℃ at 5 ℃ / min and held for 12 h. After natural cooling, the product was collected as the precursor.

[0045] (3) The precursor powder is kept at 15 MPa for 2 min in a tablet press, and then the pressed discs are sent to a muffle furnace and heated to 950 °C at 5 °C / min and kept for 18 h. After natural cooling, a high-entropy bismuth oxide ceramic electrolyte with good density can be obtained.

[0046] Comparative Example 1 (1) High-entropy bismuth oxide solid electrolyte was prepared by co-precipitation. The total molar amount of each metal nitrate was fixed at 0.02 mol, and the electrolyte was prepared according to ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) 0.3 Bi 0.7 Calculate the stoichiometric ratio of Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O.

[0047] (2) First, measure 200 mL of deionized water, add Bi(NO3)3·5H2O, and then add 5 mL of concentrated nitric acid to promote the dissolution of bismuth nitrate. Then add other nitrates, and after they are completely dissolved, add ammonia dropwise until the pH reaches 9, so that the metal ions are completely precipitated. After standing for 5 h, filter the solution and wash the filter cake with a large amount of deionized water. Finally, collect the filter cake and vacuum dry it to obtain hydroxide precursor powder.

[0048] (3) Press the powder into a disc at 10 MPa for 2 min, then put it into a muffle furnace, heat it to 600 ℃ at 5 ℃ / min, hold it for 2 h; then heat it to 1000 ℃ at 5 ℃ / min, hold it for 24 h and sinter to obtain high entropy bismuth oxide ceramic.

[0049] from Figure 1 As can be seen, the powder material prepared by the sol-gel method matches well with the standard PDF card (PDF#27-0052) corresponding to δ-Bi2O3, indicating that the sol-gel method can successfully prepare high-entropy δ-Bi2O3 ceramics with stable structure at room temperature.

[0050] from Figure 2 As can be seen from the above, the high-entropy bismuth oxide ceramic prepared by the sol-gel method in Example 1 has a much higher conductivity than the high-entropy bismuth oxide ceramic prepared by the co-precipitation method in Comparative Example 1.

[0051] from Figure 3 As can be seen from the results, the precursor surface in Example 1 is rich in hydroxyl groups, which can serve as the basis for subsequent modifications such as ion exchange and surface grafting to improve its overall performance.

[0052] from Figure 4 As can be seen, the surface and cross-section of the high-entropy bismuth oxide ceramic in Example 3 are very dense, with a continuous structure and no obvious faults or large pores. This dense structure is beneficial for improving its ionic conductivity as an SOFC electrolyte and for increasing the operating life of SOFC devices.

[0053] The scope of protection claimed by this invention is not limited to the specific embodiments described above. For those skilled in the art, this invention can have various modifications and alterations. Any modifications, improvements, and equivalent substitutions made within the concept and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A high-entropy bismuth oxide ceramic, characterized in that, Its general chemical formula is: ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x )2O3,x=0.3~0.

5.

2. The high-entropy bismuth oxide ceramic according to claim 1, characterized in that: It has a cubic fluorite crystal structure at room temperature.

3. The method for preparing high-entropy bismuth oxide ceramic according to claim 1 or 2, characterized in that, include: Step 1: Weigh citric acid and dissolve it in deionized water, add ammonia to adjust the pH, and then according to ((Sm 0.25 Gd 0.25 Pr 0.25 Yb 0.25 ) x Bi 1-x Sm(NO3)3·5H2O, Gd(NO3)3·6H2O, Pr(NO3)3·6H2O, Yb(NO3)3·5H2O and Bi(NO3)3·5H2O were added in stoichiometric proportions to obtain a gel under continuous heating and stirring. Step 2: Pre-calcine the gel to obtain precursor powder; Step 3: Press the precursor powder into shape, and sinter it to obtain the high-entropy bismuth oxide ceramic.

4. The method for preparing high-entropy bismuth oxide ceramic according to claim 3, characterized in that: In step one, the amount of citric acid dissolved in deionized water is 25-50 g / 100 ml of deionized water.

5. The method for preparing high-entropy bismuth oxide ceramic according to claim 3 or 4, characterized in that: In step one, after adding ammonia, the pH is adjusted to 5-7.

6. The method for preparing high-entropy bismuth oxide ceramic according to claim 5, characterized in that: In step one, the total number of moles of each metal nitrate is 0.01~0.03 mol.

7. The method for preparing high-entropy bismuth oxide ceramic according to claim 1 or 6, characterized in that: In step two, the pre-calcination procedure is as follows: heat up to 100~150 ℃ at 5 ℃ / min and hold for 6 h, then heat up to 400~500 ℃ at 5 ℃ / min and hold for 12 h.

8. The method for preparing high-entropy bismuth oxide ceramic according to claim 3, characterized in that: In step three, the pressing conditions are: holding pressure at 10~20 MPa for 2 minutes.

9. The method for preparing high-entropy bismuth oxide ceramic according to claim 3, characterized in that: In step three, the sintering conditions are: heating at 5 ℃ / min to 900~1000 ℃ and holding for 12~24 h.

10. The application of the high-entropy bismuth oxide ceramic according to claim 1 or 2 in the preparation of solid oxide fuel cells.

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