Cobalt-based pyrochlore material as well as preparation method and application thereof

Abstract

The invention relates to a cobalt-based pyrochlore material as well as a preparation method and application thereof, belongs to the technical field of new materials, and is used for solving at least one of the problems of high pressure, harsh reaction conditions, low yield, high cost and the like of a cobalt-based pyrochlore material prepared by an existing method. According to the method disclosed by the invention, the physical pressure required by sample preparation is reduced by introducing the chemical pressure through a strategy of coordinated regulation and control of the chemical pressure and the physical pressure. According to the method, the Pb2Co2-xRuxO7 material is synthesized under a relatively low pressure condition by adopting Ru element to partially replace Co element and introducing a chemical pressure regulation mode, the pressure required by sample synthesis is remarkably reduced, the Pb2Co2-xRuxO7 material is prepared under a relatively mild condition, and a foundation is laid for subsequent electro-catalysis research of the Pb2Co2-xRuxO7 material.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to a cobalt-based pyrochlore material and a preparation method and application thereof. Background Art

[0002] 3d transition metal Co not only has variable valence states (+2, +3, +4 and corresponding mixed valence states) and spin states (low spin LS, medium spin IS, high spin HS), but also has flexible and variable coordination environments, which makes cobalt oxides have rich and diverse crystal structures, such as perovskite, spinel and pyroxene. The strong correlation in cobalt oxides and the mutual coupling of multiple degrees of freedom such as charge, spin, orbital, lattice, etc. make them present novel and interesting chemical and physical properties, such as pressure-induced spin state transition, unconventional superconductivity, thermoelectric effect and multiferroelectricity, etc. Therefore, the creation of new cobalt oxide materials and the study of their properties are important research directions in condensed matter physics and materials science. In particular, in recent years, cobalt oxide materials have received great attention in the field of energy and environment as catalysts for electrocatalytic decomposition of water and oxygen evolution. For example, new cobalt oxide materials such as CaCoO3 and BiCoO3 prepared by high pressure and high temperature synthesis technology show excellent electrocatalytic performance in water splitting, have potential application prospects, and have been widely studied.

[0003] Pb-based cobalt oxide material Pb2Co2O7 is a new material reported in recent years. This material has a pyrochlore structure and Co 3+ / Co 4+ Mixed valence state is a potential catalyst for electrocatalytic reactions. However, due to the low matching degree of ion radius and serious crystal structure distortion in this material, it is difficult to prepare it under conventional conditions and must be prepared by a high-pressure and high-temperature synthesis method with external "physical pressure". At present, the synthesis of Pb2Co2O7 materials requires a pressure of 8GPa (1GPa~10,000 atmospheres) and a high temperature of 1400℃. The synthesis conditions are very harsh and must be prepared using a two-stage propulsion high-temperature and high-pressure synthesis device with complex technology, high cost and low efficiency. Limited by the small cavity and low efficiency of the two-stage propulsion high-temperature and high-pressure synthesis device, the size of the Pb2Co2O7 material sample prepared in a single time is only 2-3 mm, and the sample amount is only in the milligram level, which restricts the large-scale preparation of Pb2Co2O7 materials and is not conducive to the electrocatalytic application research of Pb2Co2O7 materials.

[0004] Therefore, how to prepare Pb2Co2O7 materials under low pressure or even mild conditions such as normal pressure while ensuring that the material performance is not reduced is a technical difficulty in the field of cobalt-based oxide electrocatalytic material preparation, and is also of great significance for its application research. For example, once the preparation pressure of the above materials is reduced to less than 5GPa, they can be prepared using a six-sided large cavity high temperature and high pressure synthesis device, and the preparation efficiency and yield of the materials can be greatly improved to meet the needs of practical research and application. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a cobalt-based pyrochlore material and a preparation method and application thereof, so as to solve at least one of the problems of high pressure, harsh reaction conditions, low yield and high cost of the cobalt-based pyrochlore material prepared by the existing method.

[0006] In a first aspect, the present invention provides a cobalt-based pyrochlore material, wherein the molecular formula of the cobalt-based pyrochlore material is Pb2Co 2-x Ru x O7, where 0.1≤x≤1.9.

[0007] In a second aspect, the present invention provides a method for preparing a cobalt-based pyrochlore material, comprising the following steps: uniformly mixing PbO, CoO, RuO2 and an oxidant, pressing to obtain a flake sample, sealing the surface of the flake sample, placing it in a high-pressure synthesis device, performing a high-temperature and high-pressure synthesis reaction to obtain a product; and grinding the product to obtain the cobalt-based pyrochlore material.

[0008] Furthermore, the molar ratio of PbO, CoO, RuO2 and the oxidant is 2:2-x:x:y, wherein 0.1≤x≤1.9, 0.5≤y≤2.

[0009] Furthermore, the oxidant includes at least one of KClO4 or NaClO4.

[0010] Furthermore, the thickness of the sheet sample is 0.5-1 cm.

[0011] Furthermore, the sheet sample is sealed by using a gold capsule or a platinum capsule.

[0012] Furthermore, in the high temperature and high pressure synthesis reaction, the pressure is 1-5 GPa, the temperature is 800-1500°C, and the reaction time is 0.1-10h.

[0013] Furthermore, after grinding, it also includes cleaning and drying.

[0014] Furthermore, the drying temperature is 100-200° C., and the drying time is 1-2 hours.

[0015] Furthermore, the high-pressure synthesis device is a six-sided top press.

[0016] In a third aspect, the present invention provides an application of the above-mentioned cobalt-based pyrochlore material in electrochemistry.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0018] (1) The method of the present invention adopts the strategy of coordinated regulation of "chemical pressure" and "physical pressure" to reduce the physical pressure required for sample preparation by introducing chemical pressure; specifically, Ru element is used to partially replace Co element, and Pb2Co is synthesized under lower pressure conditions by introducing chemical pressure regulation. 2-x Ru x O7 material, the pressure required for sample synthesis is significantly reduced, and Pb2Co can be prepared under relatively mild conditions 2-x Ru x O7 material, for subsequent Pb2Co 2-x Ru x It laid the foundation for the research on electrocatalysis of O7 materials;

[0019] (2) The method of the present invention can significantly reduce the pressure of synthesizing cobalt-based pyrochlore materials, and has the advantages of higher yield and lower cost.

[0020] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0022] Figure 1 This is an X-ray diffraction pattern of the cobalt-based pyrochlore material prepared in Example 1 of the present invention;

[0023] Figure 2 This is a crystal structure diagram of the cobalt-based pyrochlore material prepared in Example 1 of the present invention;

[0024] Figure 3 This is the magnetic susceptibility-temperature curve of the cobalt-based pyrochlore material prepared in Example 1 of the present invention;

[0025] Figure 4 This is an X-ray diffraction pattern of the cobalt-based pyrochlore material prepared in Example 2 of the present invention;

[0026] Figure 5 This is an X-ray diffraction pattern of the cobalt-based pyrochlore material prepared in Example 3 of the present invention;

[0027] Figure 6 This is an X-ray diffraction pattern of the cobalt-based pyrochlore material prepared in Example 4 of the present invention;

[0028] Figure 7 The X-ray diffraction pattern of the product prepared in Comparative Example 1 of the present invention;

[0029] Figure 8 The X-ray diffraction pattern of the product prepared in Comparative Example 2 of the present invention;

[0030] Fig. 9 This is the X-ray diffraction pattern of the product prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0032] A specific embodiment of the present invention discloses a cobalt-based pyrochlore material, wherein the molecular formula of the cobalt-based pyrochlore material is Pb2Co 2-x Ru x O7, wherein 0.1≤x≤1.9, for example, x is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8.

[0033] Another specific embodiment of the present invention discloses a method for preparing a cobalt-based pyrochlore material, comprising the following steps:

[0034] (1) mixing PbO, CoO, RuO2 and an oxidant uniformly to obtain an initial mixed powder;

[0035] (2) pressing the initial mixed powder into a sheet to obtain a sheet sample;

[0036] (3) sealing the surface of the sheet sample, placing it in a high-pressure synthesis device, and performing a high-temperature and high-pressure synthesis reaction to obtain a product;

[0037] (4) Grinding the product to obtain the cobalt-based pyrochlore material.

[0038] Since the cobalt-based pyrochlore material Pb2Co2O7 has a low ion radius matching degree and a serious crystal structure distortion, it must be prepared by a high-pressure and high-temperature synthesis method that applies "physical pressure", and the required preparation conditions are harsh. The method of the present invention adopts a strategy of coordinated regulation of "chemical pressure" and "physical pressure" to reduce the physical pressure required for sample preparation by introducing chemical pressure. Specifically, Ru element is used to partially replace Co element, and Pb2Co is synthesized under lower pressure conditions by introducing chemical pressure regulation. 2-x Ru x O7 material, the pressure required for sample synthesis is significantly reduced, and Pb2Co can be prepared under relatively mild conditions 2-x Ru x O7 material, for subsequent Pb2Co 2-x Ru x This laid the foundation for the research on O7 material electrocatalysis.

[0039] Specifically, in step (1), the molar ratio of PbO, CoO, RuO2 and the oxidant is 2:2-x:x:y, wherein 0.1≤x≤1.9, for example, x is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 0.5≤y≤2, for example, y is 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9.

[0040] It should be noted that y represents the oxidant ratio, which is used to control the oxygen content. When it is less than 0.5, the sample cannot be synthesized due to lack of oxygen. When it is greater than 2, the sample can be synthesized, but there is too much residual KCl or NaCl in the product, which is not conducive to increasing the yield.

[0041] Specifically, in step (1), the oxidant includes at least one of KClO4 or NaClO4.

[0042] Specifically, in step (2), the thickness of the sheet sample is 0.5-1 cm, for example, 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm.

[0043] It should be noted that the thickness of the sheet sample is selected within the above range because if it is too low, it will affect the sample yield, and if it is too high, the longitudinal temperature gradient of the sample will be large during synthesis, resulting in uneven synthesized samples.

[0044] Specifically, in step (3), the sheet sample is sealed by using a gold capsule or a platinum capsule.

[0045] It should be noted that the gold capsule or platinum capsule described in the present invention refers to a capsule-shaped hollow structure made of gold or platinum, and the sheet sample is placed in the capsule for sealing. The purpose of sealing and wrapping the sheet sample is to ensure that the oxygen released by the oxidant during the reaction does not overflow and fully participates in the sample synthesis reaction.

[0046] Specifically, in step (3), in the high temperature and high pressure synthesis reaction, the pressure is 1-5 GPa, for example, 1 GPa, 1.5 GPa, 2.0 GPa, 2.5 GPa, 3.0 GPa, 3.5 GPa, 4.0 GPa, 4.5 GPa, the temperature is 800-1500°C, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, and the reaction time is 0.1-10h, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h.

[0047] It should be noted that the present invention adopts the above synthesis temperature because high or low temperature affects the purity of the product. In addition, if the reaction time is too short, the reaction is not sufficient, which affects the purity of the product. If the reaction time is too long, the product can be prepared, but the synthesis efficiency is affected.

[0048] Specifically, in step (4), after grinding, the process also includes cleaning and drying.

[0049] Specifically, the cleaning is performed with deionized water, and preferably, the cleaning is performed with deionized water 1-3 times.

[0050] It should be noted that the purpose of washing with deionized water is to remove residual KCl or NaCl in the product and improve the purity of the product.

[0051] Specifically, the drying temperature is 100-200°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and the drying time is 1-2h, for example, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h.

[0052] It should be noted that the above-mentioned drying temperature can ensure that the product does not decompose and has a higher drying efficiency. If the drying time is too short, the drying is insufficient, residual moisture will remain, and a long drying time will affect the preparation efficiency.

[0053] Specifically, in step (4), the molecular formula of the cobalt-based pyrochlore material is Pb2Co 2-x Ru x O7, where 0.1≤x≤1.9.

[0054] Specifically, in step (4), the high-pressure synthesis device is a six-sided top press.

[0055] The invention adopts a six-sided top press to synthesize the cobalt-based pyrochlore material into a cylindrical shape with a diameter of 0.5-1 cm, a height of 0.5-1 cm and a weight of 0.5-6 g at one time.

[0056] The method of the present invention can significantly reduce the pressure of synthesizing the cobalt-based pyrochlore material, and has the advantages of higher yield, low cost, etc.

[0057] Another specific embodiment of the present invention discloses an application of the above-mentioned cobalt-based pyrochlore material in electrochemistry.

[0058] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0059] Example 1

[0060] A method for preparing a cobalt-based pyrochlore material in this embodiment comprises the following steps:

[0061] (1) In an inert gas argon atmosphere glove box, PbO, CoO, RuO2 and KClO4 oxidant were mixed uniformly in a molar ratio of 2:1:1:0.5 to obtain an initial mixed powder;

[0062] (2) pressing the initial mixed powder into a sheet so that the powder particles are fully in contact with each other to obtain a sheet sample, wherein the thickness of the sheet sample is 5 mm;

[0063] (3) placing the sheet sample in a gold capsule, sealing and wrapping it, placing it in the cavity of a six-sided press, and performing a high-temperature and high-pressure synthesis reaction at a pressure of 5 GPa, a temperature of 1100° C., and a reaction time of 0.5 h to obtain a product;

[0064] (4) The product was taken out from the gold capsule, ground into a uniform powder, washed with deionized water for 3 times, and dried at 100° C. for 1 h to obtain the cobalt-based pyrochlore material.

[0065] The cobalt-based pyrochlore material prepared in this example is cylindrical, with a diameter of 0.5 cm, a height of 0.5 cm, and a weight of 0.6 g.

[0066] The molecular formula of the cobalt-based pyrochlore material prepared in this embodiment is Pb2CoRuO7. The X-ray diffraction of the cobalt-based pyrochlore material prepared in this embodiment is tested. The results are as follows: Figure 1 shown.

[0067] The crystal structure of the cobalt-based pyrochlore material prepared in this example is as follows: Figure 2 As shown, it indicates that the material is a cobalt-based pyrochlore material structure.

[0068] The magnetic properties of the cobalt-based pyrochlore material prepared in this embodiment were tested using a vibrating sample magnetometer, and the magnetic susceptibility-temperature curve was as follows: Figure 3 As shown, the results show that the material is paramagnetic.

[0069] Example 2

[0070] A method for preparing a cobalt-based pyrochlore material in this embodiment comprises the following steps:

[0071] (1) In an inert gas argon atmosphere glove box, PbO, CoO, RuO2 and NaClO4 oxidant were mixed uniformly in a molar ratio of 2:1.5:0.5:1 to obtain an initial mixed powder;

[0072] (2) pressing the initial mixed powder into a sheet so that the powder particles are fully in contact with each other to obtain a sheet sample, wherein the thickness of the sheet sample is 8 mm;

[0073] (3) placing the sheet sample in a gold capsule, sealing and wrapping it, placing it in the cavity of a six-sided press, and performing a high-temperature and high-pressure synthesis reaction at a pressure of 3 GPa, a temperature of 1000° C., and a reaction time of 2 h to obtain a product;

[0074] (4) Taking the product out of the gold capsule and grinding it into a uniform powder to obtain the cobalt-based pyrochlore material.

[0075] The cobalt-based pyrochlore material prepared in this example is cylindrical, with a diameter of 0.8 cm, a height of 0.8 cm, and a weight of 2.4 g.

[0076] The molecular formula of the cobalt-based pyrochlore material prepared in this example is Pb2Co 1.5 Ru 0.5 O7, test the X-ray diffraction of the cobalt-based pyrochlore material prepared in this example, the result is as follows Figure 4 shown.

[0077] The crystal structure and magnetic properties of the cobalt-based pyrochlore material prepared in this example are basically the same as those in Example 1, and are not listed one by one due to limited space.

[0078] Example 3

[0079] A method for preparing a cobalt-based pyrochlore material in this embodiment comprises the following steps:

[0080] (1) In an inert gas argon atmosphere glove box, PbO, CoO, RuO2 and KClO4 oxidant were mixed uniformly in a molar ratio of 2:0.3:1.7:2.0 to obtain an initial mixed powder;

[0081] (2) pressing the initial mixed powder into a sheet so that the powder particles are fully in contact with each other to obtain a sheet sample, wherein the thickness of the sheet sample is 10 mm;

[0082] (3) placing the sheet sample in a platinum capsule, sealing and wrapping it, placing it in the cavity of a six-sided press, and performing a high-temperature and high-pressure synthesis reaction at a pressure of 1 GPa, a temperature of 1200° C., and a reaction time of 3 h to obtain a product;

[0083] (4) Taking the product out of the platinum capsule and grinding it into a uniform powder to obtain the cobalt-based pyrochlore material.

[0084] The cobalt-based pyrochlore material prepared in this example is cylindrical, with a diameter of 1 cm, a height of 1 cm, and a weight of 5.5 g.

[0085] The molecular formula of the cobalt-based pyrochlore material prepared in this example is Pb2Co 0.3 Ru 1.7 O7, test the X-ray diffraction of the cobalt-based pyrochlore material prepared in this example, the result is as follows Figure 5 shown.

[0086] The crystal structure and magnetic properties of the cobalt-based pyrochlore material prepared in this example are basically the same as those in Example 1, and are not listed one by one due to limited space.

[0087] Example 4

[0088] A method for preparing a cobalt-based pyrochlore material in this embodiment comprises the following steps:

[0089] (1) In an inert gas argon atmosphere glove box, PbO, CoO, RuO2 and KClO4 oxidant were mixed in a molar ratio of 2:1:1:1 to obtain an initial mixed powder;

[0090] (2) pressing the initial mixed powder into a sheet so that the powder particles are fully in contact with each other to obtain a sheet sample, wherein the thickness of the sheet sample is 5 mm;

[0091] (3) placing the sheet sample in a platinum capsule, sealing and wrapping it, placing it in the cavity of a six-sided press, and performing a high-temperature and high-pressure synthesis reaction at a pressure of 3 GPa, a temperature of 1400° C., and a reaction time of 2 h to obtain a product;

[0092] (4) Taking the product out of the platinum capsule and grinding it into a uniform powder to obtain the cobalt-based pyrochlore material.

[0093] The cobalt-based pyrochlore material prepared in this example is cylindrical, with a diameter of 0.5 cm, a height of 0.5 cm, and a weight of 0.6 g.

[0094] The molecular formula of the cobalt-based pyrochlore material prepared in this embodiment is Pb2CoRuO7. The X-ray diffraction of the cobalt-based pyrochlore material prepared in this embodiment is tested. The results are as follows: Figure 6 shown.

[0095] The crystal structure and magnetic properties of the cobalt-based pyrochlore material prepared in this example are basically the same as those in Example 1, and are not listed one by one due to limited space.

[0096] Comparative Example 1

[0097] The preparation method of a cobalt-based pyrochlore material in this comparative example is the same as that in Example 1, except that in step (1), the raw material ratio is changed to PbO:CoO:KClO4=2:2:0.5, and other conditions remain unchanged, that is, Ru is not doped. The synthesized sample is tested for X-ray diffraction, and the results are as follows: Figure 7 As shown, the product contains a large amount of impurities such as PbO2, and no Pb2Co2O7 sample was synthesized.

[0098] Comparative Example 2

[0099] The preparation method of a cobalt-based pyrochlore material in this comparative example is the same as that in Example 1, except that in step (1), y is 0.4.

[0100] The product prepared in this comparative example was subjected to an X-ray diffraction test, and the results were as follows: Figure 8 As shown, the product contains more unknown impurities.

[0101] Comparative Example 3

[0102] The preparation method of a cobalt-based pyrochlore material in this comparative example is the same as that in Example 1, except that in step (3), the pressure is 0.5 GPa and the temperature is 700°C.

[0103] The product prepared in this comparative example was subjected to an X-ray diffraction test, and the results were as follows: Fig. 9 As shown, the products are PbO2 and Co3O4, etc., and no Pb2CoRuO7 material is prepared.

[0104] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A cobalt-based pyrochlore material, characterized in that: The molecular formula of the cobalt-based pyrochlore material is Pb2Co 2- x Ru x O7, where 0.1≤x≤1.

9.

2. A method for preparing a cobalt-based pyrochlore material, characterized in that: The method comprises the following steps: uniformly mixing PbO, CoO, RuO2 and an oxidant, pressing to obtain a flake sample, sealing the surface of the flake sample, placing the sample in a high-pressure synthesis device, performing a high-temperature and high-pressure synthesis reaction to obtain a product; and grinding the product to obtain the cobalt-based pyrochlore material.

3. The method for preparing a cobalt-based pyrochlore material according to claim 2, characterized in that: The molar ratio of PbO, CoO, RuO2 and the oxidant is 2:2-x:x:y, wherein 0.1≤x≤1.9 and 0.5≤y≤2.

4. The method for preparing a cobalt-based pyrochlore material according to claim 3, characterized in that: The oxidant includes at least one of KClO4 and NaClO4.

5. The method for preparing a cobalt-based pyrochlore material according to claim 2, characterized in that: The thickness of the sheet sample is 0.5-1 cm.

6. The method for preparing a cobalt-based pyrochlore material according to claim 2, characterized in that: The sheet sample is sealed by using a gold capsule or a platinum capsule.

7. A method for preparing a cobalt-based pyrochlore material according to any one of claims 2 to 6, characterized in that: In the high temperature and high pressure synthesis reaction, the pressure is 1-5GPa, the temperature is 800-1500°C, and the reaction time is 0.1-10h.

8. The method for preparing a cobalt-based pyrochlore material according to any one of claims 2 to 6, characterized in that: After grinding, it also includes cleaning and drying.

9. The method for preparing a cobalt-based pyrochlore material according to any one of claims 2 to 6, characterized in that: The high-pressure synthesis device is a six-sided top press.

10. Use of the cobalt-based pyrochlore material according to claim 1 or the cobalt-based pyrochlore material prepared by the method of any one of claims 2 to 9 in electrochemistry.

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