Preparation method and application of a metal oxide-gangue catalyst with an amorphous-crystalline structure

Abstract

Preparation method and application of an amorphous-polycrystalline structured metal oxide-coal gangue catalyst, belonging to the technical field of organic system lithium-oxygen batteries. The surface of the gangue is activated by weak base calcination to promote the formation of silicate, and then the surface of the coal gangue is purified and modified by acid leaching to prepare a gangue precursor rich in SiO<subgt;2< / subgt> on the surface. At the same time, strong acid further etches and pores the surface of the coal gangue to optimize the surface structure of the coal gangue. After that, a layer of metal oxide nanoparticles is loaded on the surface of the gangue carrier rich in SiO<subgt;2< / subgt> through high-temperature hydrothermal reaction to enhance the overall stability of the composite material. And heteroatom N is introduced to dope the metal oxide lattice to form a Metal-N chemical bond with high electrochemical activity to further improve the electrocatalytic performance of the coal gangue. At the same time, the loading reaction of the metal oxide under hydrothermal conditions can promote the lattice instability of SiO<subgt;2< / subgt> on the surface of the gangue, forming a special heterogeneous structure with coexistence of amorphous and polycrystalline phases.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic system lithium-oxygen batteries, and specifically discloses a preparation method and application of an amorphous-polycrystalline structure metal oxide-gangue catalyst. Background Art

[0002] Benefiting from a high theoretical energy density of >3500 Wh kg -1 of lithium-oxygen batteries are considered as next-generation new energy storage devices that can replace lithium-ion batteries. However, the kinetics of the oxygen reduction-evolution reaction (ORR-OER) occurring at the cathode is too slow, resulting in a high polarization potential and poor cycle durability of lithium-oxygen batteries, thus limiting their large-scale practical applications. The introduction of an efficient and stable cathode catalyst can significantly increase the reaction rates of ORR and OER, which is the key to solving the above problems of lithium-oxygen batteries.

[0003] As a solid waste generated during coal mining and washing, the unreasonable discharge and accumulation of gangue have caused great pollution and waste. However, the multi-active-component coexisting layered structure of gangue can not only improve the dispersion of catalytic active sites but also promote the diffusion and transport of carriers during the catalytic process. Therefore, gangue can be used as an ideal precursor for nano-scale cathode materials. However, natural gangue has a dense structure, complex mineral composition, poor structural controllability, and low catalytic activity. At the same time, there is little research on the catalytic utilization of gangue in lithium-oxygen batteries, especially in the high-potential-organic electrolyte environment of the battery. The internal evolution process and the electrochemically active regulation mechanism of the formation of a highly active energy storage material through the structural regulation of gangue at the molecular-level microscale are not clear. Therefore, the rational design of gangue-based electrocatalysts remains a great challenge. Summary of the Invention

[0004] Technical Problem: Aiming at the deficiencies in the prior art, a preparation method and application of an amorphous-polycrystalline structure metal oxide-gangue catalyst are provided, which show high catalytic performance and excellent stability in the application of lithium-oxygen batteries, have a simple preparation process, low raw material cost, and broad application prospects.

[0005] Technical solution: To achieve the above technical objectives, a preparation method of an amorphous-crystalline structure metal oxide-gangue catalyst of the present invention activates the surface of gangue by weak base calcination to promote the formation of silicate, and then uses acid leaching to purify and modify the surface of gangue to prepare a gangue precursor rich in SiO2 on the surface. At the same time, strong acid further etches and pores the surface of gangue to optimize the surface structure of gangue and improve its intrinsic activity in electrochemical energy storage applications. Then, a layer of metal oxide nanoparticles is loaded on the surface of the gangue carrier rich in SiO2 through high-temperature hydrothermal reaction to enhance the overall stability of the composite material, and heteroatom N is introduced to dope the metal oxide lattice to form a Metal-N chemical bond with high electrocatalytic activity to further improve the electrocatalytic performance of gangue. At the same time, the loading reaction of metal oxide under hydrothermal conditions can promote the lattice instability of SiO2 on the surface of gangue, forming a special heterostructure with coexistence of amorphous and polycrystalline, providing a potential way for the high-value application of gangue in energy storage devices.

[0006] The specific steps are as follows:

[0007] S1. Mix coal gangue powder with sodium carbonate, and then calcine the mixture at high temperature. At high temperature, silicon dioxide in coal gangue reacts with sodium carbonate to generate sodium aluminosilicate, realizing the preliminary activation of coal gangue.

[0008] S2. Add the calcined product to dilute sulfuric acid for acid leaching and stirring, adjust the pH value of the acid leaching solution to 2 and then centrifuge. Sulfuric acid dissolves the impurity components on the surface of gangue, and the impurity components include aluminum and iron. After washing with deionized water and alcohol, collect the precipitate, and then dry the precipitate in an oven to obtain the active coal gangue precursor.

[0009] S3. Add (NH4)6Mo7O 24 ·4H2O, glucose and the prepared active coal gangue precursor into deionized water, stir evenly and then add them into a hydrothermal autoclave for high-temperature hydrothermal reaction. Under high-temperature and high-pressure environment, (NH4)6Mo7O 24 ·4H2O will be used as an effective molybdenum source and nitrogen source to form MoO2 nanoparticles on the surface of the active coal gangue precursor to further enhance the stability of gangue. The nitrogen source will also be doped into the MoO2 lattice to form a highly active Mo-N chemical bond. At the same time, the loading reaction of MoO2 under hydrothermal conditions can promote the lattice instability of silicon dioxide on the surface of gangue, forming a special heterostructure with coexistence of amorphous and polycrystalline; Replace (NH4)6Mo7O 24 ·4H2O with cerium nitrate, and keep other conditions including reaction mass ratio, reaction steps and reaction time unchanged to prepare the CeO2@coal gangue electrocatalyst; Replace (NH4)6Mo7O 24 ·4H2O with potassium hexacyanoferrate, and keep other conditions unchanged to prepare the Co3O4@coal gangue electrocatalyst; Replace (NH4)6Mo7O24 Replace 4H₂O with potassium ferricyanide, and other conditions remain unchanged, then the Fe₂O₃@coal gangue electrocatalyst can be prepared.

[0010] S4. Take out the precipitate in the hydrothermal reactor, wash it by centrifugation with deionized water and ethanol, collect the washed precipitate and dry it to obtain the MoO₂@coal gangue electrocatalyst.

[0011] Furthermore, the mass mixing ratio of coal gangue powder to sodium carbonate Na₂CO₃ is 10:6.

[0012] Furthermore, in step S1, the temperature for high-temperature roasting of the mixture is 700 - 1000 °C, and the roasting time is controlled within 2 - 3 h.

[0013] Furthermore, in step S2, the H₂SO₄ solution added to the dried acid-leached product has a concentration of 6 mol·L, and the mass ratio of the H₂SO₄ solution to the acid-leached product is about 3:1.

[0014] Furthermore, the mixed solution added to the hydrothermal reactor includes: (NH₄)₆Mo₇O 24 ·4H₂O, glucose, and the active coal gangue precursor are dissolved in deionized water at a mass ratio of 20:5:4, and the mass of the active coal gangue precursor is controlled within 30 - 80 mg.

[0015] Furthermore, the hydrothermal reaction temperature of the mixed solution added to the hydrothermal reactor is controlled within 160 - 200 °C, and the reaction time is 10 - 14 hours.

[0016] Furthermore, the drying temperature is all 60 °C.

[0017] Application of an amorphous - polycrystalline structure metal oxide - coal gangue catalyst: Spray the metal oxide - coal gangue electrocatalysts: MoO₂@coal gangue, CeO₂@coal gangue, Co₃O₄@coal gangue, Fe₂O₃@coal gangue on the cathode surface of the lithium - oxygen battery as a catalytic medium to promote the electrode reaction kinetics and reduce the cycle overpotential, and significantly improve the ionic interaction during the electrode reaction process to optimize the performance of the lithium - oxygen battery.

[0018] A lithium - oxygen battery is provided with a layer of amorphous - polycrystalline structure metal oxide - coal gangue catalyst coating on the cathode surface of the battery.

[0019] Beneficial effects:

[0020] The advantages of the lithium-oxygen battery coal gangue-based positive electrode catalyst disclosed in the present invention are as follows: i) The active gangue substrate with an amorphous layered structure can optimize the structural stability of the composite material and provide sufficient space for the deposition of discharge products; ii) N-doped metal oxide nanoparticles, as active sites, enhance the interaction between ions in the electrode reaction and optimize the formation process of charge-discharge products; iii) The overpotential is significantly reduced, the rate performance is excellent, and the cycle stability is greatly improved. Our invention mainly optimizes the surface chemical properties of coal gangue materials through simple physical and chemical reactions, and for the first time demonstrates that modified gangue can be used as a cathode electrocatalyst for lithium-oxygen batteries to improve electrochemical performance, providing a potential way for the high-value application of coal gangue in energy storage devices.

[0021] This method uses coal-based solid waste gangue as a precursor for functional modification, and successfully loads a layer of N-doped metal oxide nanoparticles on its surface to further improve the electrochemical activity of coal gangue. This gangue modification method has the advantages of simple operation and low cost. Taking the MoO2@coal gangue-based cathode as an example, its cyclic voltammetry (CV) curve has a higher oxygen reduction reaction (ORR) onset potential (2.86 V) than the coal gangue electrode, showing higher ORR catalytic activity. In addition, the MoO2@coal gangue-based cathode has a lower oxygen evolution reaction (OER) onset potential of 3.34 V and a larger anodic peak area, having good OER electrocatalytic performance. The MoO2@coal gangue composite material shows excellent bifunctional electrocatalytic performance. At the same time, the discharge specific capacity of the lithium-oxygen battery assembled with MoO2@coal gangue (9748 mAh g -1 ) is significantly higher than the battery capacity assembled with single coal gangue (9106 mAh g -1 ). Moreover, MoO2@coal gangue has a lower charging voltage platform, which is beneficial to improving the durability of discharge-charge, and can effectively slow down the decomposition of the organic electrolyte of the lithium-oxygen battery. The lithium-oxygen battery assembled with MoO2@coal gangue shows excellent rate performance. Even after charging and discharging at a high current of 1000 mA g -1 , the overpotential still remains at about 1.7 V. Moreover, the MoO2@coal gangue-based cathode can be continuously and stably cycled for 2200 hours without obvious performance degradation, and even maintains a relatively stable overpotential (1.70 V) after 2100 hours. While the single coal gangue-based cathode can only maintain less than 400 hours, and the discharge-charge overpotential increases from 1.42 V (the first cycle) to 2.70 V (the 19th cycle), further indicating that MoO2@coal gangue has excellent catalytic performance and stability in lithium-oxygen batteries.

[0022] Explanation of the attached drawings

[0023] Figure 1 It is a schematic diagram of the structural characterization of the MoO2@coal gangue material in the embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram of the electrochemical performance of a lithium-oxygen battery prepared with MoO2@coal gangue as the positive electrode catalyst in the embodiments of the present invention. Specific implementation method

[0025] The method of the present invention will be further described below in conjunction with the accompanying drawings and examples:

[0026] The present invention starts from the direction of energy storage utilization of coal gangue. First, the industrial solid waste coal gangue is acid-leached and purified, and the surface of the coal gangue is etched to create voids to improve the intrinsic activity of the coal gangue in electrochemical energy storage applications. Then, a nanoscale metal oxide particle layer is successfully loaded on the surface of the coal gangue through a hydrothermal reaction, and heteroatom N is introduced to dope its crystal structure to further improve the electrocatalytic performance of the coal gangue. Finally, the metal oxide-coal gangue is sprayed onto a carbon paper current collector as the cathode to successfully assemble a 2032-type button battery. The results show that the metal oxide-coal gangue material has excellent electrocatalytic activity and stability in lithium-oxygen batteries, and can significantly improve the ion interaction in the electrode reaction process to optimize the performance of lithium-oxygen batteries.

[0027] After the modified coal gangue-based composite material is sprayed on the cathode surface of the lithium-oxygen battery, it will play a key role in promoting electrode reaction kinetics and reducing the cycle overpotential as an important catalytic medium. However, the catalytic characteristics of the gangue material are not only related to the intrinsic characteristics such as the morphology structure and chemical components, but also more affected by the complex environment of high overpotential and organic electrolyte in the lithium-oxygen battery. During the cycling process of the lithium-oxygen battery, a large overpotential will be generated, and at high overpotentials, the existing ether or sulfone organic electrolytes are prone to decomposition and react with the gangue to form by-products. At this time, the gangue catalyst will be in a high-potential oxygen-rich free radical environment, and be affected by the strong nucleophilic negative action of oxygen free radicals and the passivation accumulation of insoluble product Li2O2. Since the gangue-based electrode material belongs to a multi-component coexisting porous medium, the complex high-potential organic battery system can not only change the physical and chemical properties of the gangue itself, but also the infiltration of the organic electrolyte will accelerate the dissolution of the micro-components inside the gangue material and the expansion of pores, and cause the rearrangement of the gangue electrode skeleton structure, thus affecting the catalytic activity of the gangue material for the electrode reaction of the lithium-oxygen battery. Therefore, in the lithium-oxygen battery environment, the gangue-based cathode will exhibit more complex electrocatalytic performance. The present invention mainly studies the main control factors for the microstructure regulation of coal gangue hidden at the molecular level, and clarifies the controllable preparation, strong interaction mechanism and modification mechanism of N-doped metal oxides loaded on the surface of coal gangue.

[0028] Example 1

[0029] 1. Synthesis of active coal gangue precursor

[0030] Mix the coal gangue powder with sodium carbonate (Na2CO3) at a mass ratio of 10:6, and then calcine it at 875 °C for 2.5 h. Next, stir the calcined product in a dilute sulfuric acid solution for 30 minutes, wash it 3-4 times with deionized water and alcohol respectively, and dry it in an oven at 60 °C overnight. Then, put the dried product into a H2SO4 solution (6 mol / L), pour in deionized water, mix it evenly and adjust the pH value of the solution to 2. Finally, centrifuge and wash the above solution, collect the final precipitate, and dry it at 60 °C.

[0031] 2. Synthesis of MoO2@coal gangue composite

[0032] Weigh (NH4)6Mo7O 24 ·4H2O, glucose, and the active coal gangue precursor in a mass ratio of 20:5:4, dissolve them in 30 ml of deionized water, and continuously stir until homogeneous. Then pour the mixed solution into a hydrothermal autoclave and react at 160 - 200 °C under high temperature and high pressure for 10 - 14 hours. Next, centrifuge and wash the obtained precipitate with deionized water and ethanol. Finally, collect the precipitate and dry it at 60 °C to obtain the MoO2@coal gangue composite. Weigh (NH4)6Mo7O 24 ·4H2O, glucose, and the active coal gangue precursor in a mass ratio of 15:5:4, and the material prepared according to the previous steps is denoted as comparative sample 1. Then weigh (NH4)6Mo7O 24 ·4H2O, glucose, and the active coal gangue precursor in a mass ratio of 25:5:4, and the material prepared according to the previous steps is denoted as comparative sample 2.

[0033] Replace (NH4)6Mo7O 24 ·4H2O with cerium nitrate, and keep other conditions unchanged, including the reaction mass ratio, reaction steps, and reaction time, then the CeO2@coal gangue electrocatalyst can be prepared; replace (NH4)6Mo7O 24 ·4H2O with potassium hexacyanoferrate(II), and keep other conditions unchanged, then the Co3O4@coal gangue electrocatalyst can be prepared; replace (NH4)6Mo7O 24 ·4H2O with potassium hexacyanoferrate(III), and keep other conditions unchanged, then the Fe2O3@coal gangue electrocatalyst can be prepared.

[0034] 3 Synthesis of other coal gangue-based composites

[0035] Replace (NH4)6Mo7O 24 ·4H2O in step 2 with cerium nitrate, and keep other conditions unchanged (reaction mass ratio, reaction steps, reaction time, etc.), then the CeO2@coal gangue electrocatalyst can be prepared. Replace (NH4)6Mo7O 24· Replace 4H₂O with potassium hexacyanoferrate(II), and other conditions remain unchanged to prepare the Co₃O₄@coal gangue electrocatalyst. Replace (NH₄)₆Mo₇O in Step 2 24 · Replace 4H₂O with potassium hexacyanoferrate(III), and other conditions remain unchanged to prepare the Fe₂O₃@coal gangue electrocatalyst.

[0036] Figure 1 a It can be seen that the untreated coal gangue has a structure with large particles and uneven morphology. After acid immersion hydrothermal treatment, the surface of the coal gangue is loose and porous, and is evenly loaded with nanoparticles, and the size of the nanoparticles is between 50 - 100 nm ( Figure 1 b). In Comparative Samples 1 and 2, nanoscale particles of MoO₂ could not be formed and evenly loaded on the surface of the coal gangue due to incorrect ratios ( Figure 1 c and d). Therefore, a suitable precursor material ratio is required to prepare the highly active MoO₂@coal gangue electrocatalytic material.

[0037] Figure 2 a. Rate performance of the lithium - oxygen battery assembled based on MoO₂@coal gangue at different discharge - charge current densities; b. The lithium - oxygen battery assembled based on MoO₂@coal gangue at 100 mA g -1 The cut - off capacity at a current density of is 1000 mAh g -1 of the cycle stability

[0038] The 2032 - type LOB was assembled by the above - mentioned method to evaluate the activity of the MoO₂@coal gangue catalyst in the lithium - oxygen battery. We evaluated the cycle stability of the prepared lithium - oxygen at a current density of 100 mA g -1 and a cut - off specific capacity of 1000 mAh g -1 . As shown in Figure 2 b, the MoO₂@coal gangue cathode successfully operated for 2200 hours, and there was no attenuation in the discharge and charge capacities, and maintained a relatively stable voltage difference of about 1.70 V. In contrast, the single coal gangue cathode could only last for 400 hours. Figure 2 a shows the rate performance of the MoO₂@coal gangue - based lithium - oxygen battery prepared at different current densities (100, 200, 500, and 1000 mA g -1 ). The cut - off capacity is 1000 mAh g -1 . The MoO₂@coal gangue - based battery showed excellent recovery ability after cycling. At the same time, we can also observe that at all working current densities, the MoO₂@coal gangue - based battery has a low charge - discharge voltage polarization.

[0039] This method uses coal-based solid waste gangue as a precursor for functional modification, and successfully loads a layer of N-doped metal oxide nanoparticles on its surface to further improve the electrochemical activity of coal gangue. This gangue modification method has the advantages of simple operation and low cost. Taking the MoO2@coal gangue-based cathode as an example, its cyclic voltammetry (CV) curve has a higher oxygen reduction reaction (ORR) onset potential (2.86 V) than the coal gangue electrode, showing higher ORR catalytic activity. In addition, the MoO2@coal gangue-based cathode has a lower oxygen evolution reaction (OER) onset potential of 3.34 V and a larger anodic peak area, exhibiting good OER electrocatalytic performance. Therefore, the MoO2@coal gangue composite shows excellent bifunctional electrocatalytic performance. At the same time, the discharge specific capacity of the lithium-oxygen battery assembled with MoO2@coal gangue (9748 mAh g -1 ) is significantly higher than the battery capacity assembled with single coal gangue (9106 mAh g -1 ). Moreover, MoO2@coal gangue has a lower charging voltage plateau, which is beneficial to improving the durability of discharge-charge, and can effectively slow down the decomposition of the organic electrolyte in the lithium-oxygen battery. The lithium-oxygen battery assembled with MoO2@coal gangue exhibits excellent rate performance, and the overpotential still remains at about 1.7 V even after charging and discharging at a high current of 1000 mA g -1 . Most importantly, the MoO2@coal gangue-based cathode can continuously and stably cycle for 2200 hours without obvious performance degradation, and even maintains a relatively stable overpotential (1.70 V) after 2100 hours. While the single coal gangue-based cathode can only maintain less than 400 hours, and the discharge-charge overpotential increases from 1.42 V (the 1st cycle) to 2.70 V (the 19th cycle), further indicating that MoO2@coal gangue has excellent catalytic performance and stability in the lithium-oxygen battery.

Claims

1. A preparation method of an amorphous-crystalline structured metal oxide-gangue catalyst, characterized in that, The specific steps are as follows: S1. Mix the coal gangue powder with sodium carbonate, and then calcine the mixture at a high temperature. At high temperature, the coal gangue reacts with sodium carbonate to form sodium aluminosilicate, realizing the preliminary activation of the coal gangue. S2. Add the calcined product to dilute sulfuric acid for acid leaching and stirring. After washing the acid leached product with deionized water and alcohol, dry it in an oven. Add dilute sulfuric acid to the dried acid leached product again for acid leaching. Adjust the pH value of the acid leaching solution to 2 and then centrifuge. Sulfuric acid dissolves the impurity components on the surface of the coal gangue, and the impurity components include aluminum and iron. After washing with deionized water and alcohol, collect the precipitate, and then dry the precipitate in an oven to obtain the active coal gangue precursor. S3. Add (NH4)6Mo7O 24 ·4H2O, glucose and the prepared activated coal gangue precursor into deionized water. After stirring evenly, add them together into a hydrothermal autoclave for high-temperature hydrothermal reaction. The hydrothermal reaction temperature of the mixed solution added to the hydrothermal autoclave is controlled at 160 - 200 °C, and the reaction time is 10 - 14 hours. Under the high-temperature and high-pressure environment, (NH4)6Mo7O 24 ·4H2O will form MoO2 nanoparticles on the surface of the activated coal gangue precursor as an effective molybdenum source and nitrogen source to further enhance the stability of coal gangue. The nitrogen source will also be doped into the MoO2 lattice to form highly active Mo-N chemical bonds. At the same time, the loading reaction of MoO2 under hydrothermal conditions can promote the lattice instability of silica on the surface of the gangue, forming a special heterostructure with coexistence of amorphous and polycrystalline phases; (NH4)6Mo7O 24 ·4H2O can be replaced by cerium nitrate, potassium hexacyanoferrate or potassium hexacyanoferrate(II). Other conditions including the reaction mass ratio, reaction steps and reaction time remain unchanged; S4. Take out the precipitate in the hydrothermal kettle, wash it by centrifugation with deionized water and ethanol, collect the washed precipitate and dry it to obtain the MoO2@coal gangue electrocatalyst, CeO2@coal gangue electrocatalyst, Co3O4@coal gangue electrocatalyst, and Fe2O3@coal gangue electrocatalyst.

2. The preparation method of the amorphous-crystalline structured metal oxide-gangue catalyst according to claim 1, characterized in that: The mass mixing ratio of the coal gangue powder to sodium carbonate (Na2CO3) is 10:

6.

3. The preparation method of a metal oxide-gangue catalyst with an amorphous-crystalline structure according to claim 1, characterized in that: In step S1, the temperature for high-temperature calcination of the mixture is 700 - 1000 °C, and the calcination time is controlled within 2 - 3 h.

4. The preparation method of a metal oxide-gangue catalyst with an amorphous-crystalline structure according to claim 1, characterized in that: In step S2, the concentration of the H2SO4 solution added to the dried acid leached product is 6 mol / L, and the mass ratio of the H2SO4 solution to the acid leached product is about 3:

1.

5. The preparation method of a metal oxide-gangue catalyst with an amorphous-polycrystalline structure according to claim 1, characterized in that: The mixed solution added to the hydrothermal autoclave includes: (NH4)6Mo7O 24 ·4H2O, glucose, and the active coal gangue precursor are dissolved in deionized water at a mass ratio of 20:5:4, and the mass of the active coal gangue precursor is controlled at 30-80 mg.

6. The preparation method of a metal oxide-gangue catalyst with an amorphous-polycrystalline structure according to claim 1, characterized in that: The drying temperature in both S2 and S4 is 60 °C.

7. Use of the amorphous-polycrystalline structured metal oxide-gangue catalyst according to claim 1, characterized in that: Spray the metal oxide - coal gangue electrocatalysts: MoO2@coal gangue, CeO2@coal gangue, Co3O4@coal gangue, Fe2O3@coal gangue on the surface of the cathode of the lithium - oxygen battery as a catalytic medium to promote the electrode reaction kinetics and reduce the cycle overpotential.

8. A lithium-oxygen battery, characterized in that: There is a coating containing the amorphous - polycrystalline structured metal oxide - coal gangue catalyst prepared by the preparation method described in claim 1 on the surface of the battery cathode.

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