Nano-porous Mn alloy / MnO2 anode with core-shell structure as well as preparation method and application of nano-porous Mn alloy / MnO2 anode

Abstract

The invention discloses a nano-porous Mn alloy / MnO2 anode with a core-shell structure and a preparation method and application thereof, and relates to the technical field of new materials.The preparation method comprises the steps that manganese powder serves as a main material, an auxiliary material I, an auxiliary material II and a pore forming agent are added, and uniform mixing is conducted to obtain a mixture; pressing into a blank; sintering the sample blank; and performing post-oxidation treatment in an air or oxygen atmosphere to obtain the catalyst. The auxiliary material I comprises at least one of Re, Co, Fe, Ni, Ag, Ce, La and Nd; the auxiliary material II comprises at least one of Ti, Ta, Ca, Sr, K, Na, Y, Eu and Dy; the pore-forming agent comprises at least one of magnesium powder, aluminum powder, stearic acid and urea. The nano-porous Mn alloy / MnO2 anode material has the beneficial effects that the nano-porous Mn alloy / MnO2 anode material with a three-dimensional open-pore structure, high permeability, high strength, large specific surface area and excellent conductivity is obtained by adding synergistic catalytic and synergistic stable elements and combining a specific preparation process.

Description

Technical Field

[0001] The present invention relates to the field of new materials, and in particular to a nanoporous Mn alloy / MnO2 anode with a core-shell structure, and a preparation method and application thereof. Background Art

[0002] Insoluble anodes (also called dimensionally stable anodes, DSA) for oxygen evolution in acidic media such as hydrometallurgy, proton exchange membrane (PEM) water electrolysis, organic synthesis, sewage treatment, and cathodic protection are indispensable key core materials in the field of electrochemical engineering. Traditionally, lead alloys, graphite, and precious metals (such as platinum) anodes are mainly used. Platinum is expensive and scarce, and graphite and lead alloy anodes have large oxygen evolution overpotentials and low electrocatalytic activity. Beer et al. developed titanium-based precious metal oxide insoluble anodes. For example, ruthenium-based oxide anodes have good electrocatalytic properties for chlorine evolution and have been used by more than 90% of chlor-alkali companies in the world. The service life is more than 10 years, but the service life in acidic media is extremely short. Iridium dioxide (IrO2) or Ir-based oxides (such as IrO2+Ta2O5 anodes, etc.) have excellent oxygen evolution stability in acidic media, and the dissolution and precipitation of iridium and other substances on the electrode are very small, and no secondary pollution will be generated. However, the scarcity of Ir limits its wide application, so it is urgent to develop new low-cost insoluble anodes suitable for acidic media.

[0003] Rutile MnO2 (10 -1 ~10 -2 Ωcm) has the advantages of low price, abundant resources, and environmental friendliness. The basic structural unit is a tunnel structure composed of [MnO6] octahedrons shared by the vertices of adjacent double chains. There are many types such as α, β, γ, ε, δ and λ. As an acidic medium oxygen evolution electrocatalyst, it has certain electrocatalytic activity and stability and is considered to be one of the most likely materials to replace rare metal oxides. However, in the acidic oxygen evolution reaction, MnO2 as an anode has two main problems: the first is the serious Jahn-Teller effect in the acidic (pH <9) medium oxygen evolution process, that is, the Mn in the material has a certain electrocatalytic activity and stability. 3+ A disproportionation reaction will occur to generate Mn 2+ and Mn 4+ , and then dissolves into the electrolyte (manganese dissolution), resulting in an unstable material structure; secondly, poor electrical conductivity and low electrocatalytic activity lead to its low electron transport capacity and high oxygen evolution overpotential.

[0004] Regarding how to simultaneously improve the electrocatalytic activity and stability of MnO2 anode materials for industrial oxygen evolution in acidic media, current research has failed to make substantial progress. Therefore, designing and developing new MnO2 anode structure systems is an effective way to achieve breakthroughs. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a nanoporous Mn alloy / MnO2 anode with a core-shell structure and a preparation method and application thereof. Through alloying, post-oxidation and anti-disproportionation treatment, the prepared Mn alloy / MnO2 anode has the advantages of porous structure, high permeability, high strength, large specific surface area, excellent conductivity and the like.

[0006] The technical solution of the present invention is as follows: The first aspect of the present invention provides a method for preparing a nanoporous Mn alloy / MnO2 anode material having a core-shell structure, comprising the following steps: S1, taking manganese powder as the main material, adding auxiliary material 1, auxiliary material 2 and pore-forming agent, mixing evenly to obtain a mixture; S2, pressing the mixed material into a blank to obtain a blank sample; S3, sintering the sample to obtain a nanoporous manganese alloy; S4, post-oxidizing the nanoporous manganese alloy in air or oxygen atmosphere to obtain a nanoporous Mn alloy / MnO2 anode material with a core-shell structure; Wherein, the auxiliary material 1 includes at least one of Re, Co, Fe, Ni, Ag, Ce, La and Nd; The auxiliary material 2 includes at least one of Ti, Ta, Ca, Sr, K, Na, Y, Eu and Dy; The pore-forming agent includes at least one of magnesium powder, aluminum powder, stearic acid and urea.

[0007] The present invention adds auxiliary material 1 for synergistic catalysis and adds auxiliary material 2 for synergistic stabilization of Mn 3+ By combining experiments and simulations, the types and contents of alloying elements are optimized to enhance the electrocatalytic activity and stability of the anodic acidic oxygen evolution reaction; and pore-forming agents are added to form a more complex pore structure through the combined use of magnesium powder, aluminum powder, stearic acid, etc.

[0008] The present invention adopts a high-temperature sintering + post-oxidation treatment process. On the one hand, metal magnesium powder, aluminum powder, etc. are used as pore-forming agents. The liquid phase Mg in the high-temperature sintering process can form a solid-liquid interface with other powders, greatly improving the diffusion rate of atoms / vacancies, the diffusion interface area, the grain boundary migration rate, and reducing the sintering temperature of the interface, which is conducive to the formation and regulation of nano Kirkendall pores. On the other hand, an oxide layer can be generated on the surface or inside of the material through post-oxidation to improve the performance of the material (such as corrosion resistance, wear resistance, catalytic activity, etc.). During sintering or porous material preparation, the post-oxidation process can further regulate the microstructure and performance of the material. Specifically, after sintering, magnesium powder may remain in a single substance form. Through post-oxidation treatment, the residual magnesium powder can be oxidized to MgO, further improving the stability and mechanical properties of the material. Similarly, the residual aluminum powder can be generated by post-oxidation treatment to generate aluminum oxide, thereby enhancing the hardness and corrosion resistance of the material. Stearic acid will thermally decompose during the sintering process to generate carbon and gas. Through post-oxidation treatment, the residual carbon can be oxidized to CO2, further cleaning the pores and regulating the pore structure. For porous materials, post-oxidation can generate an oxide layer on the pore surface and improve the surface properties of the material (such as catalytic activity, adsorption performance, etc.).

[0009] Optionally, in step S1, calculated as a molar percentage, Manganese powder 50-80%, auxiliary material 1 3-20%, auxiliary material 2 3-15%, pore-forming agent 5-25%.

[0010] Optionally, in step S1, the amount of each raw material added is calculated in molar percentage as follows: Manganese powder 50-80%, Re 0.5-2.5%, Co 0.5-2.5%, Fe 0.5-2.5%, Ni 0.5-2.5%, Ag 0.5-2.5%, Ce 0.2-0.8%, La 0.2-0.8%, Nd 0.2-0.8%, Ti 0.5-1.5%, Ta 0.5-1.5%, Ca 0.5-1.5%, Sr 0.5-1.5%, K 0.5-1.5%, Na 0.5-1.5%, Y 0.1%-0.5%, Eu 0.1-0.5%, Dy 0.1-0.5%, magnesium powder 3-5%, aluminum powder 3-5%, stearic acid 3-5%, urea 3-11%.

[0011] Optionally, in step S2, the pressing pressure is 100-500 MPa, and the holding time is 10-50 seconds.

[0012] Optionally, in step S3, the sintering is microwave vacuum sintering, and the specific steps of the microwave vacuum sintering include: The sample was placed in a vacuum microwave sintering furnace and the vacuum degree was set to 10-2 - 10 -3 Pa, microwave power is 500-1000 W, heating to 700-1200°C at a heating rate of 10-50°C / min in air or oxygen atmosphere, and keeping warm for 10-60min to obtain nanoporous manganese alloy.

[0013] Optionally, in step S3, the sintering is conventional atmosphere sintering, and the specific steps of the conventional atmosphere sintering include: The sample is placed in an inert atmosphere for pre-sintering at a temperature of 300-500° C. for 1-2 hours; Then, the nanoporous manganese alloy is obtained by heating the alloy to 700-1200° C. at a heating rate of 10-50° C. / min in air or oxygen atmosphere and keeping the temperature for 10-60 minutes.

[0014] Optionally, in step S3, the sintering is plasma sintering, and the specific steps of the plasma sintering include: The sample is placed in a graphite mold of a plasma sintering device, heated to 700-1200° C. at a heating rate of 10-50° C. / min under an inert gas and a pressure of 30-50 MPa, and kept warm for 10-60 minutes to obtain a nanoporous manganese alloy.

[0015] Optionally, in step S4, the specific steps of the post-oxidation treatment include: The nanoporous manganese alloy is placed in an oxygen atmosphere, heated to 200-500° C. at a heating rate of 10-30° C. / min, and kept warm for 60-120 min to obtain a nanoporous Mn alloy / MnO2 anode system with a core-shell structure.

[0016] After extensive research, the applicant found that the effect of post-oxidation depends on process parameters such as temperature, atmosphere, time and heating rate. Among them, temperature is the key factor affecting the oxidation rate and the thickness of the oxide layer. The applicant found that a temperature of 200~500°C is more conducive to the formation of a core-shell structure; air or oxygen-rich atmosphere (such as O2, O2 / N2 mixed gas) is usually used as an oxidizing medium, which helps to generate an oxide layer on the surface or inside of the material to improve the performance of the material (such as corrosion resistance, wear resistance, catalytic activity, etc.). The oxidation time affects the thickness and uniformity of the oxide layer. The applicant found that keeping the temperature for 60~120min is more conducive to the formation of the oxide layer. The heating rate affects the uniformity of the oxide layer. The applicant found that a heating rate of 10~30°C / min helps to form a uniform oxide layer.

[0017] The second aspect of the present invention provides a nanoporous Mn alloy / MnO2 anode material with a core-shell structure, which is obtained by the above-mentioned preparation method.

[0018] The third aspect of the present invention provides the use of the nanoporous Mn alloy / MnO2 anode material in hydrometallurgy or proton exchange membrane water electrolysis or organic synthesis or sewage treatment, wherein the nanoporous Mn alloy / MnO2 anode material is used as an anode and graphite is used as a cathode, and a scanning voltage of -1.7 V to 1.7 V vs. RHE is controlled in a 0.5 M H2SO4 electrolyte to achieve Mn 3+ electrochemically captures and stabilizes it at the center of the tetrahedron.

[0019] The present invention adopts electrochemical induced anti-disproportionation reaction method to achieve Mn by scanning voltage range regulation. 3+ The electrochemical capture of manganese and stabilization of it at the center of the tetrahedron inhibits manganese dissolution during the acidic oxygen evolution process at the anode and enhances its electrocatalytic activity.

[0020] The present invention has at least one of the following beneficial effects: 1. Improved material performance: By adding synergistic catalytic and synergistic stabilizing elements and combining them with a specific preparation process, a nanoporous Mn alloy / MnO2 anode material with a three-dimensional open pore structure, high permeability, high strength, large specific surface area and excellent conductivity is obtained, which can effectively improve the performance of the material in related applications.

[0021] 2. Catalytic activity optimization: Adding organic compounds such as stearic acid and urea as pore-forming agents can dope the anode with C and N, thereby achieving the regulation and modification of its catalytic activity, which is beneficial to improving the efficiency of the electrochemical reaction.

[0022] 3. Advantages of pore structure regulation: Metal magnesium powder, aluminum powder, etc., as pore-forming agents, can form a solid-liquid interface during high-temperature sintering, greatly improving the diffusion rate of atoms / vacancies, etc., which is beneficial to the formation and regulation of nano-Kirkendall pores, and can accurately control the pore structure of the material to meet the needs of different application scenarios.

[0023] 4. Inhibit manganese dissolution: The electrochemical induced anti-disproportionation reaction method is used for anti-disproportionation treatment, which can inhibit manganese dissolution during the acidic oxygen evolution process of the anode, improve the stability and service life of the material, improve the electrocatalytic activity of the anode, and enhance the reliability of the material in practical applications.

[0024] 5. Strong process adaptability: In the preparation process, a variety of sintering methods such as microwave vacuum sintering, conventional atmosphere sintering, plasma sintering, and a combination of various process parameters such as temperature and time are used, which makes the preparation process highly adaptable and adjustable, and is easy to optimize according to actual production conditions and needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1This is the SEM image of the nanoporous Mn alloy / MnO2 anode obtained in Example 2.

[0026] Figure 2 This is the TEM image of the nanoporous Mn alloy / MnO2 anode obtained in Example 2. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Example 1 According to the atomic ratio, weigh Mn (15g, 0.364mol), Re, Co, Fe, Ni, Ag (0.0124mol each), Ce, La, Nd (0.0027mol each), Ti, Ta, Ca, Sr, K, Na (0.0059mol each), Y, Eu, Dy (0.0016mol each), magnesium powder (0.0126mol), aluminum powder (0.0126mol), stearic acid (6.15g), urea (about 2.6g). After mixing evenly, use a tablet press to press at a pressure of 300MPa for 30 seconds to form a blank. Then put the blank into a microwave vacuum sintering furnace and set the vacuum degree to 10 -2 Pa, microwave power of 500 W, heating at a heating rate of 30 ° C / min to 900 ° C, and keeping it warm for 30 minutes to obtain a nanoporous manganese alloy. Then post-oxidation treatment: the obtained manganese alloy is placed in a muffle furnace, heated to 350 ° C at 20 ° C / min in an oxygen atmosphere, and kept warm for 90 minutes to obtain a nanoporous Mn alloy / MnO2 anode system.

[0029] Example 2 According to the atomic ratio, Mn (15g, 0.364mol), Re, Co, Fe, Ni, Ag (0.0124mol each), Ce, La, Nd (0.0027mol each), Ti, Ta, Ca, Sr, K, Na (0.0059mol each), Y, Eu, Dy (0.0016mol each), magnesium powder (0.0126mol), aluminum powder (0.0126mol), stearic acid (6.15g), urea (about 2.6g) were weighed. After mixing evenly, the mixture was pressed into a blank at a pressure of 280MPa for 30 seconds using a tablet press. The blank was then placed in a microwave vacuum sintering furnace, heated to 1000℃ at a heating rate of 30℃ / min, and kept warm for 30min to obtain a nanoporous manganese alloy. Then, a post-oxidation treatment is performed: the obtained manganese alloy is placed in a muffle furnace, and the temperature is raised to 350° C. at a rate of 20° C. / min in an oxygen atmosphere, and kept at this temperature for 90 minutes to obtain a nanoporous Mn alloy / MnO2 anode system.

[0030] Example 3 According to the atomic ratio, Mn (15g, 0.364mol), Re, Co, Fe, Ni, Ag (0.0124mol each), Ce, La, Nd (0.0027mol each), Ti, Ta, Ca, Sr, K, Na (0.0059mol each), Y, Eu, Dy (0.0016mol each), magnesium powder (0.0126mol), aluminum powder (0.0126mol), stearic acid (6.15g), urea (about 2.6g) were weighed. After mixing evenly, the mixture was pressed into a blank at a pressure of 260MPa for 30 seconds using a tablet press. The blank was then placed in a microwave vacuum sintering furnace, heated to 1100℃ at a heating rate of 30℃ / min, and kept warm for 30min to obtain a nanoporous manganese alloy. Then, a post-oxidation treatment is performed: the obtained manganese alloy is placed in a muffle furnace, and the temperature is raised to 350° C. at a rate of 20° C. / min in an oxygen atmosphere, and kept at this temperature for 90 minutes to obtain a nanoporous Mn alloy / MnO2 anode system.

[0031] Comparative Example 1 Weigh 15 grams of manganese powder (65%), and then weigh 7% magnesium powder (about 1.62g), 7% aluminum powder (about 1.62g), 7% stearic acid (about 1.62g), and 14% urea (about 3.23g) by mass percentage. After these materials are fully mixed, put them into a tablet press and press them at a pressure of 300MPa for 30 seconds to make a sample. Then put the sample into a microwave vacuum sintering furnace, heat it to 900℃ at a heating rate of 30℃ / min, and keep it warm for 30min to prepare nanoporous manganese material. Post-oxidation: Put the sintered manganese material into a muffle furnace, heat it to 350℃ at a heating rate of 20℃ / min in an oxygen atmosphere, and keep it warm for 90min to obtain a nano MnO2 anode system.

[0032] Comparative Example 2 The difference from Example 1 is that no post-oxidation treatment is performed, and the rest is the same as Example 1.

[0033] Comparative Example 3 The difference from Example 1 is that in the post-oxidation treatment, the heating rate is changed to 40° C. / min, and the rest is the same as Example 1.

[0034] Results and Characterization: The Mn alloy / MnO2 anode prepared in Example 2 was characterized by the following specific method: (1) Structural analysis: The core-shell structure and porosity were observed by SEM and TEM.

[0035] The results are as follows Figure 1~2 As shown by Figure 1~2 It can be seen that the structure of the Mn alloy / MnO2 anode prepared in Example 2 has macropores, mesopores and micropores, and the Mn alloy / MnO2 anode prepared in Examples 1 to 3 has a small amount of macropores with a size of 0.5-2 microns, which is mainly due to the large space left by the agglomerates of magnesium powder and aluminum powder after the reaction, and the large pores formed in some areas when stearic acid decomposes and are interconnected. A large number of pore sizes are concentrated between 100-500 nanometers (mesopores), which are the spaces left after the oxidation reaction of magnesium powder and aluminum powder, as well as the joint action of stearic acid decomposition and partial reaction of the matrix material. There are also some micropores with a size of 20-80 nanometers, distributed at the boundaries and grain boundaries of MnO2 and Mn particles, mainly due to defects in the crystal growth process, irregular atomic arrangement and other factors.

[0036] (2) Electrochemical performance: The electrochemical performance was evaluated by cyclic voltammetry and constant current charge and discharge tests.

[0037] The Mn alloy / MnO2 electrode obtained from each experimental sample was used as the anode and graphite as the cathode for electrolysis in 0.5MH2SO4 solution with an anode current density of 100 mA / cm 2 The data obtained are shown in Table 1: Table 1 It can be seen from Table 1 that the life of the Mn alloy / MnO2 electrodes prepared in Examples 1 to 3 is more than 1300 h, and the anode overpotential is less than 420 mV; while the life of the Mn alloy / MnO2 electrodes prepared in Comparative Examples 1 to 3 is less than 425 h, and the anode overpotential is more than 543 mV; it can be seen that, compared with Comparative Examples 1 to 3, the life of Examples 1 to 3 is significantly better than that of Comparative Examples 1 to 3, and the anode overpotential is less than that of Comparative Examples 1 to 3, indicating that whether auxiliary material 1 and auxiliary material 2 are added, whether post-oxidation treatment is performed, and the heating rate of post-oxidation will affect the electrochemical properties of the prepared Mn alloy / MnO2 electrodes.

[0038] 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 technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a nanoporous Mn alloy / MnO2 anode material with a core-shell structure, characterized in that: The following steps are involved: S1, taking manganese powder as the main material, adding auxiliary material 1, auxiliary material 2 and pore-forming agent, mixing evenly to obtain a mixture; S2, pressing the mixed material into a blank to obtain a blank sample; S3, sintering the sample to obtain a nanoporous manganese alloy; S4, post-oxidizing the nanoporous manganese alloy in air or oxygen atmosphere to obtain a nanoporous Mn alloy / MnO2 anode material with a core-shell structure; Wherein, the auxiliary material 1 includes at least one of Re, Co, Fe, Ni, Ag, Ce, La and Nd; The auxiliary material 2 includes at least one of Ti, Ta, Ca, Sr, K, Na, Y, Eu and Dy; The pore-forming agent includes at least one of magnesium powder, aluminum powder, stearic acid and urea.

2. The preparation method according to claim 1, characterized in that: In step S1, the amount of each raw material added is calculated in molar percentage: Manganese powder 50-80%, auxiliary material 1 3-20%, auxiliary material 2 3-15%, pore-forming agent 5-25%.

3. The preparation method according to claim 1, characterized in that: In step S1, the amount of each raw material added is calculated in molar percentage: Manganese powder 50-80%, Re 0.5-2.5%, Co 0.5-2.5%, Fe 0.5-2.5%, Ni 0.5-2.5%, Ag 0.5-2.5%, Ce 0.2-0.8%, La 0.2-0.8%, Nd 0.2-0.8%, Ti 0.5-1.5%, Ta 0.5-1.5%, Ca 0.5-1.5%, Sr0.5-1.5%, K 0.5-1.5%, Na 0.5-1.5%, Y 0.1%-0.5%, Eu 0.1-0.5%, Dy 0.1-0.5%, magnesium powder 3-5%, aluminum powder 3-5%, stearic acid 3-5%, urea 3-11%.

4. The preparation method according to claim 1, characterized in that: In step S2, the pressing pressure is 100-500 MPa, and the holding time is 10-50 seconds.

5. The preparation method according to claim 1, characterized in that: In step S3, the sintering is microwave vacuum sintering, and the specific steps of the microwave vacuum sintering include: The sample was placed in a vacuum microwave sintering furnace and the vacuum degree was set to 10 -2 - 10 -3 Pa, microwave power is 500-1000 W, heating to 700-1200°C at a heating rate of 10-50°C / min in air or oxygen atmosphere, and keeping warm for 10-60min to obtain nanoporous manganese alloy.

6. The preparation method according to claim 1, characterized in that: In step S3, the sintering is performed in a conventional atmosphere, and the specific steps of the conventional atmosphere sintering include: The sample is placed in an inert atmosphere for pre-sintering at a temperature of 300-500° C. for 1-2 hours; Then, the nanoporous manganese alloy is obtained by heating the alloy to 700-1200° C. at a heating rate of 10-50° C. / min in air or oxygen atmosphere and keeping the temperature for 10-60 minutes.

7. The preparation method according to claim 1, characterized in that: In step S3, the sintering is plasma sintering, and the specific steps of the plasma sintering include: The sample is placed in a graphite mold of a plasma sintering device, heated to 700-1200° C. at a heating rate of 10-50° C. / min under an inert gas and a pressure of 30-50 MPa, and kept warm for 10-60 minutes to obtain a nanoporous manganese alloy.

8. The preparation method according to claim 1, characterized in that: In step S4, the specific steps of the post-oxidation treatment include: The nanoporous manganese alloy is placed in an oxygen atmosphere, heated to 200-500° C. at a heating rate of 10-30° C. / min, and kept warm for 60-120 min to obtain a nanoporous Mn alloy / MnO2 anode system with a core-shell structure.

9. A nanoporous Mn alloy / MnO2 anode material with a core-shell structure, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 8.

10. The use of the nanoporous Mn alloy / MnO2 anode material according to claim 9 in hydrometallurgy or proton exchange membrane water electrolysis or organic synthesis or sewage treatment, characterized in that: The nanoporous Mn alloy / MnO2 anode material was used as the anode and graphite as the cathode. The MnO2 was electrochemically controlled by scanning voltage between -1.7 V and 1.7 V vs. RHE in 0.5 M H2SO4 electrolyte. 3+ electrochemically captures and stabilizes it at the center of the tetrahedron.

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