A high entropy double perovskite structure IT-SOFC cathode and preparation method thereof

Abstract

The present invention discloses a high entropy double perovskite structure IT-SOFC cathode and a preparation method, belonging to the field of cathode materials. The technical scheme is: a high entropy double perovskite structure IT-SOFC cathode, characterized in that the general formula of the high entropy double perovskite structure IT-SOFC cathode is: G y Q 1‑x Q′ x M 1‑z M′ z O 6‑δ , wherein the value range of x is 0<x<1, the value range of z is 0.3<z<0.4, and δ is the oxygen vacancy content; the high entropy double perovskite structure IT-SOFC cathode is a double perovskite structure. The beneficial effects of the present invention are: the high entropy double perovskite structure IT-SOFC cathode provided by the present invention has a double perovskite structure, good electrochemical performance at a medium and low temperature solid oxide fuel cell operating temperature of 600 to 800°C, simple preparation process, low cost, good repeatability, and broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of medium- and low-temperature SOFC cathode materials, and in particular to a high-entropy double perovskite structure IT-SOFC cathode and a preparation method thereof. Background Art

[0002] The four keywords "clean", "low-carbon", "safe" and "efficient" are the fundamental requirements for China's energy development in the new era. To promote the development of clean and low-carbon energy, we must rely on breakthroughs in new energy technologies, among which hydrogen energy is the most important energy carrier in the future. Solid oxide fuel cells can convert hydrogen energy and existing fossil fuel energy cleanly and efficiently, and are compatible with my country's existing energy supply system, and will definitely shoulder a very important historical mission.

[0003] Traditional solid oxide fuel cells need to work at higher operating temperatures (800-1000°C) to achieve the best energy conversion effect. However, higher operating temperatures also bring about problems such as mismatched thermal expansion coefficients between electrode materials and electrolyte materials, and severe degradation of cathode electrochemical performance, which reduces the long-term stability and service life of solid oxide fuel cells and greatly limits the commercial development of solid oxide fuel cells. In this regard, lowering the operating temperature of solid oxide fuel cells can fundamentally solve these problems. However, at medium and low temperatures (600-800°C), the polarization resistance of commonly used solid oxide fuel cell cathode materials is usually large, and the performance degrades rapidly. Therefore, it is of great significance to develop high-performance cathode materials suitable for medium and low temperature solid oxide fuel cells.

[0004] Perovskite oxide is a material with mixed ionic and electronic conductivity. It has good electrochemical properties at low temperatures and has received widespread attention. However, its stability as a cathode for solid oxide fuel cells is inconsistent with its electrochemical performance. When the electrochemical performance is good, the stability will be poor, and when the stability is improved by reducing the thermal expansion coefficient, the electrochemical performance will decrease. Although double perovskite oxides have improved relatively, they are still insufficient for commercial use. In this regard, doping with other elements to achieve simultaneous improvement of the electrochemical performance and stability of the material has become a current research hotspot.

[0005] High entropy oxide refers to an oxide with a perovskite structure formed by combining 5 or more elements in the same or similar proportions. The higher construction entropy in the system makes the crystal structure of the high entropy oxide have excellent stability and can inhibit the segregation of cations. At present, there have been studies on the use of high entropy oxides in the cathode of solid oxide fuel cells. For example, patent CN202211590615.5 provides a high entropy oxide nanostructured SOFC cathode and its preparation method. The chemical formula of the material is: (Ln 0.6 Ba0.2 Sr 0.2 )Co 0.2 Fe 0.8 O 3-δ , wherein Ln is selected from La, Y, Nd, Sm or Gd. By introducing lanthanide metal elements in equal molar ratios at the A position, the structural stability of the material is improved, the Sr segregation on the cathode surface of the solid oxide fuel cell and the coarsening of the cathode particles are inhibited, thereby significantly improving the catalytic activity and long-term stability of the cathode, and effectively slowing down the attenuation of the cathode electrochemical performance. Summary of the invention

[0006] In order to solve the problems in the above-mentioned prior art, the present invention provides a high-entropy double perovskite structure IT-SOFC cathode which combines a high-entropy oxide with a double perovskite structure, has good electrochemical performance at a medium- and low-temperature solid oxide fuel cell operating temperature of 600 to 800°C, has a simple preparation process, low cost, good repeatability, and broad application prospects.

[0007] In order to achieve the above-mentioned invention object, the present invention provides a high entropy double perovskite structure IT-SOFC cathode, the general formula of the high entropy double perovskite structure IT-SOFC cathode is: y Q 1-x Q′ x M 1-z M′ z O 6-δ , wherein the value range of x is 0<x<1, the value range of z is 0.3<z<0.4, and δ is the oxygen vacancy content; the high entropy double perovskite structure IT-SOFC cathode is a double perovskite structure, G is an alkaline earth metal element, Q, Q′, M, and M′ are transition metal elements, respectively. In the double perovskite structure, the ionic radii of the Q, Q′, and M′ elements are of the same order of magnitude, and the ionic radius of the M element is larger than the ionic radii of the Q, Q′, and M′ elements, respectively. Preferably, the ionic radius of the M element is larger than the ionic radius of the Q, Q′, and M′ elements, respectively.

[0008] Furthermore, in the general formula, G is Sr element, M is Mo element, M′ is Ni element, and y=2, z=0.35.

[0009] Furthermore, in the general formula, Q is Fe element, and Q′ is Co element.

[0010] A method for preparing the high entropy double perovskite structure IT-SOFC cathode comprises the following steps:

[0011] Step 1: Weigh nitrates and / or ammonium salts containing elements G, Q, Q′, M, and M′ in a stoichiometric ratio, respectively, and dissolve to obtain a solution A, and stir the solution A under heating conditions, wherein the heating temperature is 80 to 100° C. and the heating time is 1 to 2 hours; preferably, the heating temperature is 80° C.;

[0012] Step 2: Ethylenediaminetetraacetic acid and citric acid are weighed in a stoichiometric ratio and dissolved in deionized water, and then the pH value of the mixed solution is adjusted to 9-10 with aqueous ammonia to obtain solution B, and the solution B is stirred under heating conditions, wherein the heating temperature is 80-100° C. and the heating time is 1-2 h; preferably, the heating temperature is 80° C.;

[0013] Step 3: adding the solution A dropwise into the solution B to obtain a clear mixed solution, adjusting the pH to 9-10 with aqueous ammonia, sealing the container containing the mixed solution, and stirring the mixed solution under heating conditions;

[0014] Step 4: opening the sealed container, increasing the heating temperature, and continuing to stir until the mixed solution forms a gel;

[0015] Step 5: transferring the gel to an oven and igniting it under heating conditions until the gel is completely transformed into a foamy solid, and grinding the foamy solid after cooling to obtain a solid powder;

[0016] Step 6: Sinter the solid powder at high temperature to obtain a solid block, take out the solid block after cooling, and grind it again to obtain the high entropy double perovskite structure IT-SOFC cathode powder.

[0017] Preferably, the stirring in the above steps 1 to 4 is uniform magnetic stirring.

[0018] Furthermore, the metal nitrate containing the elements G, Q, Q', M, and M' is dissolved in a dilute nitric acid solution to obtain the solution A.

[0019] Furthermore, the ratio of the total molar amount of the G, Q, Q', M, M' elements to the molar amount of the ethylenediaminetetraacetic acid is 1:2 to 1:5, preferably 1:1; the ratio of the total molar amount of the G, Q, Q', M, M' elements to the molar amount of the citric acid is 1:1 to 1:4, preferably 1:2.

[0020] Furthermore, the heating conditions for stirring the mixed solution in step 3 are: heating temperature of 80-120° C., heating time of 12-16 h, preferably, the heating temperature is 80° C.

[0021] Furthermore, the heating conditions during stirring after opening the sealed container in step 4 are: heating temperature is 165-180° C., and heating time is 10-12 h.

[0022] Furthermore, the heating conditions for igniting the gel in step 5 are: a heating temperature of 285-300° C. and a heating time of 2-3 hours. Preferably, the heating temperature is 285° C.

[0023] Furthermore, the conditions for high temperature sintering in step 6 are: high temperature sintering temperature is 600-900°C, high temperature calcination time is 6-12h, and high temperature calcination heating / cooling rate is 5-10°C / min. Preferably, high temperature calcination time is 6h, and high temperature calcination heating / cooling rate is 5°C / min.

[0024] The beneficial effects of the present invention are:

[0025] (1) The high entropy double perovskite structure IT-SOFC cathode provided by the present invention combines the double perovskite structure with the high entropy oxide, which can be designed with rich and flexible components to reduce the dependence on a single element. At the same time, the electronic structure can be regulated by changing the stoichiometric ratio to further improve the electrochemical performance.

[0026] (2) The high entropy double perovskite structure IT-SOFC cathode provided by the present invention has a very stable crystal structure due to the thermodynamic high entropy effect and the kinetic hysteresis diffusion effect. Combined with the double perovskite structure, it has good stability and electrochemical performance when used as a cathode material for medium and low temperature solid oxide fuel cells.

[0027] (4) In the preparation method of the high-entropy double perovskite structure IT-SOFC cathode provided by the present invention, the pH of the mixed solution is adjusted by ammonia water, which can change the original acidic system of the mixed solution, avoid the inhibition of ionization of citric acid, poor complexation of citrate ions with metal ions, resulting in the re-precipitation of metal nitrates and sinking to the bottom of the container in the form of crystals, which is almost unable to induce high-temperature sintering and the reaction is incomplete. At the same time, the pH value range can be accurately controlled to ensure that the reaction proceeds according to the designed route of the components, achieving sufficient complexation and complete high-temperature sintering.

[0028] (5) The high-entropy double perovskite structure IT-SOFC cathode provided by the present invention has good electrochemical performance and long-term stability at the medium and low temperature solid oxide fuel cell operating temperature of 600-800°C, and has a simple preparation process, low cost, good repeatability and broad application prospects. It can be used in both solid oxide fuel cells and solid oxide electrolyzers. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1XRD diagram of the high entropy double perovskite structure IT-SOFC cathode prepared in Examples 1, 2, and 3 of the present invention;

[0030] Figure 2 It is an EIS comparison diagram of a half-cell having a high entropy double perovskite structure IT-SOFC cathode in Examples 1, 2, and 3 of the present invention and a half-cell having a LSCF cathode material as a cathode;

[0031] Figure 3 The polarization impedance-time diagrams are of a half-cell having a high entropy double perovskite structure IT-SOFC cathode prepared in Examples 1, 2, and 3 of the present invention and a half-cell having a LSCF cathode material as a cathode;

[0032] Figure 4 SEM images and EDS spectra of a half-cell having a high-entropy double perovskite structure IT-SOFC cathode prepared in Example 1 of the present invention before and after a 1000 h long-term electrochemical test at 600°C. DETAILED DESCRIPTION

[0033] In order to clearly explain the technical features of this solution and better understand the above technical solution, this solution is described below through specific implementation methods. The above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The embodiment of the present invention provides a high entropy double perovskite structure IT-SOFC cathode, and the general formula of the high entropy double perovskite structure IT-SOFC cathode is: y Q 1-x Q′ x M 0.65 M′ 0.35 O 6-δ , wherein the value range of x is 0<x<1, δ is the oxygen vacancy content; in the general formula, G is Sr element, Q is Fe element, Q′ is Co element, M is Mo element, M′ is Ni element, wherein y=2; preferably, the general formula is: Sr2Fe 1-x Co x Mo 0.65 Ni 0.35 O 6-δ .

[0036] A method for preparing a high entropy double perovskite structure IT-SOFC cathode comprises the following steps:

[0037] Step 1: Weigh the nitrates and / or ammonium salts containing the elements G, Q, Q', M, and M' in a stoichiometric ratio, respectively, and dissolve them in a dilute nitric acid solution to obtain a solution A, and subject the solution A to magnetic stirring under heating conditions, wherein the heating temperature is 80-100°C and the heating time is 1-2h; preferably, the heating temperature is 80°C; Mo element is usually obtained by ammonium salts such as (NH4)6Mo7O 24 ·4H2O is introduced, while (NH4)6Mo7O 24 4H2O is insoluble in deionized water solution but soluble in dilute nitric acid solution;

[0038] Step 2: Ethylenediaminetetraacetic acid and citric acid are weighed in a stoichiometric ratio and dissolved in deionized water, and then the pH value of the mixed solution is adjusted to 9-10 with aqueous ammonia to obtain solution B, and solution B is magnetically stirred under heating conditions, wherein the heating temperature is 80-100° C. and the heating time is 1-2 h; preferably, the heating temperature is 80° C.; the ratio of the total molar amount of G, Q, Q′, M, and M′ elements to the molar amount of ethylenediaminetetraacetic acid is 1:2-1:5, preferably 1:1; the ratio of the total molar amount of G, Q, Q′, M, and M′ elements to the molar amount of citric acid is 1:1-1:4, preferably 1:2;

[0039] Step 3: adding solution A dropwise into solution B to obtain a clarified mixed solution, adjusting the pH to 9-10 with aqueous ammonia, sealing the container containing the mixed solution, and subjecting the mixed solution to magnetic stirring under heating conditions; the heating temperature is 80-120° C., the heating time is 12-16 hours, preferably, the heating temperature is 80° C.;

[0040] Using ammonia water to adjust the pH value of the mixed solution can change the original acidic system of the mixed solution, avoid the phenomenon that the ionization of citric acid is inhibited, the citrate ions and metal ions are poorly complexed, causing the metal nitrate to re-precipitate and sink to the bottom of the container in the form of crystals, which is almost unable to induce high-temperature sintering, and the reaction is not complete. At the same time, the pH value range can be accurately controlled to ensure that the reaction proceeds according to the route designed by the components, and sufficient complexation and complete high-temperature sintering are achieved;

[0041] Sealed stirring can inhibit the volatilization of ammonia in the solution and ensure that the pH value of the solution is stably maintained at 9-10 during the stirring process, thereby avoiding the precipitation of precipitates and the generation of impurity phases due to the decrease in pH value.

[0042] Step 4: Open the sealed container, increase the heating temperature, and continue magnetic stirring until the mixed solution forms a gel; the heating temperature is 165-180° C., and the heating time is 10-12 hours.

[0043] Step 5: Transfer the gel to an oven and ignite it under heating conditions until the gel is completely transformed into a foamy solid. After cooling, grind the foamy solid to obtain a solid powder; the heating temperature is 285-300°C and the heating time is 2-3h. Preferably, the heating temperature is 285°C.

[0044] Step 6: Sinter the solid powder at high temperature to obtain a solid block, take out the solid block after cooling, and grind it again to obtain a high-entropy double perovskite structure IT-SOFC cathode powder; the high-temperature sintering conditions in step 6 are: high-temperature sintering temperature is 600-900°C, high-temperature calcination time is 6-12h, and high-temperature calcination temperature rise / fall rate is 5-10°C / min. Preferably, the high-temperature calcination time is 6h, and the high-temperature calcination temperature rise / fall rate is 5°C / min.

[0045] The general formula of the double perovskite structure can be expressed as A2B′B"O6, the coordination number of the A-type ion is 8, and the coordination number of the B-type ion is 6. The crystal structure of the double perovskite is a cubic system with a body-centered cubic structure. The standard A2B′B"O6 type oxide can be regarded as a regular alternating arrangement of different BO6 octahedra. Generally, B′ and B" are different transition metal ions. The stability of the B′B"O6 octahedron in the double perovskite structure plays an important role in the stability of the entire structure. The more stable the oxides corresponding to the B' and B" ions are, the more stable the double perovskite structure is. The relationship between different ions at the B position (B' position, B" position) in the double perovskite structure can largely determine whether they can form an ordered arrangement.

[0046] The Sr2Fe provided in the embodiment of the present invention 1-x Co x Mo 0.65 Ni 0.35 O 6-δ The crystal structure of the high-entropy double perovskite structure IT-SOFC cathode is a double perovskite structure, δ is the oxygen vacancy content, where Sr corresponds to the A-type ion in the general formula of the double perovskite structure, and Fe, Co, Mo, and Ni correspond to the B-type ions in the general formula of the double perovskite structure, where Fe and Co correspond to the B' position, and Mo and Ni correspond to the B" position. At high temperatures, the oxides formed by the B-type ions Fe, Co, Mo, and Ni have excellent stability. It can be seen that in this double perovskite structure, the B′B"O6 octahedron has strong stability, and Sr2Fe 1-x Co x Mo 0.65 Ni 0.35 O 6-δ The double perovskite structure formed by the high-entropy double perovskite structure IT-SOFC cathode is stable.

[0047] The high entropy effect in thermodynamics means that in a high entropy alloy, the more main elements there are, the greater the total entropy value of the high entropy alloy. 1-x Co x Mo 0.65 Ni 0.35 O 6-δ The crystal structure of the high-entropy double perovskite structure IT-SOFC cathode is a double perovskite structure, δ is the oxygen vacancy content, and the main element is more than the most widely used IT-SOFC cathode material LSCF. The total entropy value of the high-entropy double perovskite structure IT-SOFC cathode is large. At high temperatures, the mixing entropy plays a leading role, allowing the formation of a solid solution phase with a lower Gibbs free energy. In addition, the high entropy effect may have a negative effect on the electronegativity difference, which can inhibit the formation of intermetallic compounds, and can also make the mixing of elements easier, making it easier to form a simple and stable solid solution phase;

[0048] At the same time, the kinetic hysteresis diffusion effect refers to the different molar ratios of various elements in the high entropy alloy and the difference in ion size of various elements, which causes serious lattice distortion in the high entropy alloy. In the high entropy double perovskite cathode material, the ion radius of Fe, Co, and Ni is quite different from that of Mo, resulting in serious lattice distortion inside it, which makes the element diffusion channel and diffusion activation energy in the high entropy alloy very different from those of traditional alloys. The large fluctuation of lattice potential energy between lattice points causes the diffusion of elements in high entropy alloys to be relatively slow, and a large number of low lattice potential energy points restrict and hinder the diffusion of atoms, making the lattice more stable, which is the so-called hysteresis diffusion.

[0049] The high entropy double perovskite structure IT-SOFC cathode and the specific preparation process of the present invention are described below by combining Examples 1-3 and a comparative example:

[0050] Example 1

[0051] In the high entropy double perovskite structure IT-SOFC cathode provided in this embodiment, the chemical formula of the high entropy double perovskite structure IT-SOFC cathode is: Sr2Fe 0.5 Co 0.5 Mo 0.65 Ni 0.35 O 6-δ , (i.e. x=0.5), the preparation method comprises the following steps:

[0052] Step 1: Weigh strontium (Sr), iron (Fe), cobalt (Co), nickel (Ni) nitrate and (NH4)6Mo7O in stoichiometric ratios. 24·4H2O, specifically: 0.025mol Sr(NO3)2, 0.009375mol Fe(NO3)3·9H2O, 0.009375mol Co(NO3)2·6H2O, 0.004375mol Ni(NO3)2·6H2O and 0.00160714mol (NH4)6Mo7O 24 ·4H2O. Dissolve the above drugs in deionized water, add 30ml of dilute nitric acid to prepare solution A, and stir solution A magnetically under heating conditions at 80℃ for 1h;

[0053] Step 2: Add 230 ml of deionized water and 20 ml of ammonia water to a beaker, and then weigh citric acid and ethylenediaminetetraacetic acid and add them thereto, wherein ethylenediaminetetraacetic acid and citric acid are weighed according to the ratio of the total molar amount of metal elements (Sr, Fe, Co, Ni, Mo) to the molar amount of ethylenediaminetetraacetic acid being 1:1 and the ratio of the total molar amount of metal elements (Sr, Fe, Co, Ni, Mo) to the total molar amount of citric acid being 1:2, that is, 0.1 mol of anhydrous citric acid and 0.05 mol of ethylenediaminetetraacetic acid are added in sequence, and then the pH value of the mixed solution is adjusted to 9-10 with ammonia water to obtain solution B, and solution B is magnetically stirred under heating conditions, and the heating temperature is 80°C.

[0054] Step 3: Add solution A dropwise into solution B to obtain a clear mixed solution, adjust the pH to 9-10 with aqueous ammonia, seal the container containing the mixed solution, and stir the mixed solution magnetically at 80° C. for 12 h.

[0055] Step 4: Open the sealed container, increase the heating temperature to 165°C, and continue magnetic stirring until the mixed solution forms a gel with a skeleton structure.

[0056] Step 5: Transfer the gel formed in step 4 to an oven and ignite it at a heating temperature of 285° C. until the gel is completely transformed into a foamy solid. After cooling to room temperature, use an agate mortar to fully grind the foamy solid to obtain a solid powder.

[0057] Step 6: Pour the fixed powder into a crucible, place it in a tube furnace and perform high-temperature sintering in an air atmosphere. Specifically, heat the temperature to 900°C at a rate of 5°C / min and keep it for 6 hours to obtain a block solid. After cooling, take out the block solid, take it out after the temperature drops to room temperature, and then use an agate mortar to fully grind it to obtain a chemical formula of Sr2Fe 0.5 Co 0.5 Mo 0.65 Ni 0.35 O 6-δ High entropy double perovskite structure IT-SOFC cathode powder.

[0058] Example 2

[0059] In the high entropy double perovskite structure IT-SOFC cathode provided in this embodiment, the chemical formula of the high entropy double perovskite structure IT-SOFC cathode is: Sr2Fe 0.9 Co 0.1 Mo 0.65 Ni 0.35 O 6-δ , (i.e. x=0.1), the preparation method comprises the following steps:

[0060] Step 1: Weigh strontium (Sr), iron (Fe), cobalt (Co), nickel (Ni) nitrate and (NH4)6Mo7O in stoichiometric ratios. 24 ·4H2O, specifically: 0.025mol Sr(NO3)2, 0.01125mol Fe(NO3)3·9H2O, 0.00125mol Co(NO3)2·6H2O, 0.004375mol Ni(NO3)2·6H2O and 0.00160714mol (NH4)6Mo7O 24 ·4H2O. Dissolve the above drugs in deionized water, add 30ml of dilute nitric acid to prepare solution A, and stir solution A magnetically under heating conditions at 80℃ for 1h;

[0061] Step 2: Add 230 ml of deionized water and 20 ml of ammonia water to a beaker, and then weigh citric acid and ethylenediaminetetraacetic acid and add them thereto, wherein ethylenediaminetetraacetic acid and citric acid are weighed according to the ratio of the total molar amount of metal elements (Sr, Fe, Co, Ni, Mo) to the molar amount of ethylenediaminetetraacetic acid being 1:1 and the ratio of the total molar amount of metal elements (Sr, Fe, Co, Ni, Mo) to the total molar amount of citric acid being 1:2, that is, 0.1 mol of anhydrous citric acid and 0.05 mol of ethylenediaminetetraacetic acid are added in sequence, and then the pH value of the mixed solution is adjusted to 9-10 with ammonia water to obtain solution B, and solution B is magnetically stirred under heating conditions, and the heating temperature is 80°C.

[0062] Step 3: Add solution A dropwise into solution B to obtain a clear mixed solution, adjust the pH to 9-10 with aqueous ammonia, seal the container containing the mixed solution, and stir the mixed solution magnetically at 80° C. for 12 h.

[0063] Step 4: Open the sealed container, increase the heating temperature to 165°C, and continue magnetic stirring until the mixed solution forms a gel with a skeleton structure.

[0064] Step 5: Transfer the gel formed in step 4 to an oven and ignite it at a heating temperature of 285° C. until the gel is completely transformed into a foamy solid. After cooling to room temperature, use an agate mortar to fully grind the foamy solid to obtain a solid powder.

[0065] Step 6: Pour the fixed powder into a crucible, place it in a tube furnace and perform high-temperature sintering in an air atmosphere. Specifically, heat the temperature to 900°C at a rate of 5°C / min and keep it for 6 hours to obtain a block solid. After cooling, take out the block solid, take it out after the temperature drops to room temperature, and then use an agate mortar to fully grind it to obtain a chemical formula of Sr2Fe 0.9 Co 0.1 Mo 0.65 Ni 0.35 O 6-δ High entropy double perovskite structure IT-SOFC cathode powder.

[0066] Example 3

[0067] In the high entropy double perovskite structure IT-SOFC cathode provided in this embodiment, the chemical formula of the high entropy double perovskite structure IT-SOFC cathode is: Sr2Fe 0.1 Co 0.9 Mo 0.65 Ni 0.35 O 6-δ , (i.e. x=0.9), the preparation method comprises the following steps:

[0068] Step 1: Weigh strontium (Sr), iron (Fe), cobalt (Co), nickel (Ni) nitrate and (NH4)6Mo7O in stoichiometric ratios. 24 ·4H2O, specifically: 0.025mol Sr(NO3)2, 0.00125mol Fe(NO3)3·9H2O, 0.00125mol Co(NO3)2·6H2O, 0.004375mol Ni(NO3)2·6H2O and 0.00160714mol (NH4)6Mo7O 24 ·4H2O. Dissolve the above drugs in deionized water, add 30ml of dilute nitric acid to prepare solution A, and stir solution A magnetically under heating conditions at 80℃ for 1h;

[0069] Step 2: Add 230 ml of deionized water and 20 ml of ammonia water to a beaker, and then weigh citric acid and ethylenediaminetetraacetic acid and add them thereto, wherein ethylenediaminetetraacetic acid and citric acid are weighed according to the ratio of the total molar amount of metal elements (Sr, Fe, Co, Ni, Mo) to the molar amount of ethylenediaminetetraacetic acid being 1:1 and the ratio of the total molar amount of metal elements (Sr, Fe, Co, Ni, Mo) to the total molar amount of citric acid being 1:2, that is, 0.1 mol of anhydrous citric acid and 0.05 mol of ethylenediaminetetraacetic acid are added in sequence, and then the pH value of the mixed solution is adjusted to 9-10 with ammonia water to obtain solution B, and solution B is magnetically stirred under heating conditions, and the heating temperature is 80°C.

[0070] Step 3: Add solution A dropwise into solution B to obtain a clear mixed solution, adjust the pH to 9-10 with aqueous ammonia, seal the container containing the mixed solution, and stir the mixed solution magnetically at 80° C. for 12 h.

[0071] Step 4: Open the sealed container, increase the heating temperature to 165°C, and continue magnetic stirring until the mixed solution forms a gel with a skeleton structure.

[0072] Step 5: Transfer the gel formed in step 4 to an oven and ignite it at a heating temperature of 285° C. until the gel is completely transformed into a foamy solid. After cooling to room temperature, use an agate mortar to fully grind the foamy solid to obtain a solid powder.

[0073] Step 6: Pour the fixed powder into a crucible, place it in a tube furnace and perform high-temperature sintering in an air atmosphere. Specifically, heat the temperature to 900°C at a rate of 5°C / min and keep it for 6 hours to obtain a block solid. After cooling, take out the block solid, take it out after the temperature drops to room temperature, and then use an agate mortar to fully grind it to obtain a chemical formula of Sr2Fe 0.1 Co 0.9 Mo 0.65 Ni 0.35 O 6-δ High entropy double perovskite structure IT-SOFC cathode powder.

[0074] The high entropy double perovskite structure IT-SOFC cathode powder prepared in Example 1-3 was subjected to XRD test. Figure 1 The high entropy double perovskite structure IT-SOFC cathode powders prepared in Examples 1-3 are all pure Sr2NiMoO6 phases without impurity phases.

[0075] Half cells with high entropy double perovskite structure IT-SOFC cathodes prepared in Examples 1-3 and a half cell with LSCF cathode material as cathode (as a control example) were prepared. Specifically:

[0076] Firstly, a pineneol-ethyl cellulose solution was prepared as the solvent of high entropy double perovskite cathode slurry according to the mass ratio of pineneol to ethyl cellulose of 94:6. A certain amount of high entropy double perovskite structured IT-SOFC cathode powder / LSCF cathode material powder was weighed and put into an agate mortar. After adding an appropriate amount of pineneol-ethyl cellulose solution, the powder was manually ground for 2 hours to obtain high entropy double perovskite cathode slurry / LSCF cathode slurry.

[0077] Secondly, the high entropy double perovskite cathode slurry / LSCF cathode slurry was brushed onto the center of the GDC electrolyte sheet using a screen printing process, with an area of ​​approximately 0.5 cm 2 , then transferred to a blast drying oven and dried at 150°C for 15 minutes, and then brushed the second layer of high entropy double perovskite cathode slurry / LSCF cathode slurry on the same position and then dried, and repeated the previous steps, brushing 3 layers of high entropy double perovskite cathode slurry / LSCF cathode slurry on the upper and lower surfaces of the GDC electrolyte. The GDC electrolyte sheet brushed with high entropy double perovskite cathode slurry / LSCF cathode slurry was transferred to a high-temperature box-type muffle furnace, sintered at 1100°C for 2 hours, and then taken out to obtain a half-cell.

[0078] The half-cells prepared above using the high entropy double perovskite structure IT-SOFC cathode / LSCF cathode materials prepared in Examples 1-3 as cathodes were subjected to 1000 h long-term electrochemical testing, and EIS graphs and impedance-time graphs were plotted.

[0079] like Figure 2 As shown in the figure, in order to facilitate the comparison with the electrochemical performance of LSCF cathode materials, the EIS data were normalized, the ohmic resistance part was subtracted, and only the polarization resistance RP was retained. According to the test results, at 600℃ ( Figure 2 (a)), Sr2Fe 1-x Co x Mo 0.65 Ni 0.35 O 6-δ (x is 0.1, 0.5 and 0.9 respectively) The polarization resistance of the half-cell as the cathode is 4.5Ω / cm 2 , 3.4Ω / cm 2 and 5.7Ω / cm 2 , which are both smaller than the polarization resistance of 6.7Ω / cm of the half-cell with LSCF cathode material as cathode 2 , that is, the half-cell with the high entropy double perovskite structure IT-SOFC cathode prepared in Examples 1-3 has higher electrochemical performance, wherein Sr2Fe 0.5 Co x0.5 Mo 0.65 Ni 0.35 O 6-δThe half-cell with (x=0.5, referred to as SFCMN) as the cathode has the best performance.

[0080] After 1000h of long-term testing, Figure 2 (b) The polarization resistance of the half-cell with four cathode materials as cathodes is reduced, but Sr2Fe 1-x Co x Mo 0.65 Ni 0.35 O 6-δ The polarization resistance of the half-cell with the cathode material (x is 0.1, 0.5 and 0.9 respectively) is always smaller than the polarization resistance of the half-cell with the LSCF cathode material as the cathode.

[0081] The polarization resistance of the symmetrical half-cell with different cathode materials as cathode is changed over time during the long-term test at 600℃ for 1000h. Figure 3 As shown, at 600°C, compared with the half-cell with LSCF cathode material as cathode, Sr2Fe 1-x Co x Mo 0.65 Ni 0.35 O 6-δ (x is 0.1, 0.5 and 0.9 respectively) The stability and electrochemical performance of the half-cell in long-term testing as the cathode are better.

[0082] In addition, at an operating temperature of 600°C, the high-entropy double perovskite structure IT-SOFC cathode developed by the present invention has better electrochemical performance. Compared with the cathode material in the disclosed patent CN202211590615.5, not only is the area specific polarization resistance smaller, but the polarization resistance does not decay over time, and has better stability, which is of great significance for reducing the operating temperature of SOFC. It is a very promising medium and low temperature solid oxide fuel cell (IT-SOFC) cathode material.

[0083] SEM images and EDS spectra were taken for the half-cell with the high entropy double perovskite structure IT-SOFC cathode prepared in Example 1 before and after a 1000 h long-term electrochemical test at 600°C. Figure 4 As shown, before and after the long-term test, according to the SEM image, the high-entropy double perovskite cathode layer presents a porous structure, and the cathode layer is in good contact with the electrolyte layer. According to the EDS energy spectrum, the five metal elements Sr, Fe, Co, Mo, and Ni are evenly distributed in the cathode layer before and after the long-term test.

[0084] The present invention is not limited to the above-described embodiments, and those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high entropy double perovskite structure IT-SOFC cathode, It is characterized in that The general formula of the high entropy double perovskite structure IT-SOFC cathode is: y Q 1-x Q ′ x M 1-z M z ′ O 6-δ , wherein the value range of x is 0<x<1, the value range of z is 0.3<z<0.4, and δ is the oxygen vacancy content; the high entropy double perovskite structure IT-SOFC cathode is a double perovskite structure, G is an alkaline earth metal element, Q, Q ′ , M, M ′ are transition metal elements. In the double perovskite structure, Q, Q ′ 、M ′ The ionic radii of the elements are of the same order of magnitude, and the ionic radii of element M are larger than those of Q and Q respectively. ′ 、M ′ The ionic radius of the element; M is Mo element, M′ is Ni element; Q, Q', M, and M' correspond to B-type ions in the general structure of double perovskite, Q and Q' correspond to the B' position, and M and M' correspond to the B" position.

2. The high entropy double perovskite structure IT-SOFC cathode according to claim 1, It is characterized in that In the general formula, G is Sr element, wherein y=2, z=0.

35.

3. The high entropy double perovskite structure IT-SOFC cathode according to claim 1 or 2, It is characterized in that In the general formula, Q is Fe element, Q ′ It is the Co element.

4. A method for preparing a high entropy double perovskite structure IT-SOFC cathode according to any one of claims 1 to 3, It is characterized in that The following steps are involved: Step 1: Weigh the G, Q, and Q ′ , M, M ′ nitrates and / or ammonium salts of the element, and dissolving them to obtain a solution A, and stirring the solution A under heating conditions; Step 2: Ethylenediaminetetraacetic acid and citric acid are weighed in a stoichiometric ratio and dissolved in deionized water, and then the pH value of the mixed solution is adjusted to 9-10 with aqueous ammonia to obtain a solution B, and the solution B is stirred under heating conditions; Step 3: adding the solution A dropwise into the solution B to obtain a clear mixed solution, adjusting the pH to 9-10 with aqueous ammonia, sealing the container containing the mixed solution, and stirring the mixed solution under heating conditions; Step 4: opening the sealed container, increasing the heating temperature, and continuing to stir until the mixed solution forms a gel; Step 5: transferring the gel to an oven and igniting it under heating conditions until the gel is completely transformed into a foamy solid, and grinding the foamy solid after cooling to obtain a solid powder; Step 6: Sinter the solid powder at high temperature to obtain a solid block, take out the solid block after cooling, and grind it again to obtain the high entropy double perovskite structure IT-SOFC cathode powder.

5. The preparation method according to claim 4, It is characterized in that Contains G, Q, Q ′ , M, M ′ The metal nitrate of the element is dissolved in a dilute nitric acid solution to obtain the solution A.

6. The preparation method according to claim 4 or 5, It is characterized in that The G, Q, Q ′ , M, M ′ The ratio of the total molar amount of the elements to the molar amount of the ethylenediaminetetraacetic acid is 1:2 to 1:5; the G, Q, Q ′ , M, M ′ The ratio of the total molar amount of the elements to the molar amount of the citric acid is 1:1 to 1:

4.

7. The preparation method according to any one of claims 4 to 6, It is characterized in that The heating conditions for stirring the mixed solution in step 3 are as follows: heating temperature is 80-120° C., and heating time is 12-16 hours.

8. The preparation method according to any one of claims 4 to 7, It is characterized in that The heating conditions during stirring after opening the sealed container in step 4 are as follows: the heating temperature is 165-180° C. and the heating time is 10-12 hours.

9. The preparation method according to any one of claims 4 to 8, It is characterized in that The heating conditions for igniting the gel in step 5 are: a heating temperature of 285 to 300° C. and a heating time of 2 to 3 hours.

10. The preparation method according to any one of claims 4 to 9, It is characterized in that The conditions for high temperature sintering in step 6 are: high temperature sintering temperature is 600-900° C., high temperature calcination time is 6-12 hours, and high temperature calcination temperature rise / fall rate is 5-10° C. / min.

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