Preparation and application of manganese-doped oxide composite catalyst with gamma-Fe2O3 as precursor

Abstract

The application relates to a preparation and application of a manganese-doped oxide composite catalyst loaded on the surface of carbon nanotubes and taking gamma-Fe2O3 as a doping precursor. A mixed solution of a gamma-Fe2O3 precursor and carbon nanotubes is added into anhydrous ethanol; a manganese nitrate solution is continuously added and heated and stirred to be evaporated to dryness to obtain a black powder; the black powder is placed into a crucible, the crucible is placed in a muffle furnace for heat treatment; after cooling, the manganese-doped gamma-Fe2O3 composite catalyst loaded on the surface of the carbon nanotubes is obtained by cleaning with alcohol and deionized water and drying. The manganese-doped gamma-Fe2O3 composite catalyst loaded on the surface of the carbon nanotubes is prepared by taking gamma-Fe2O3 as a preparation precursor, is composed of manganese-doped gamma-Fe2O3 and carbon nanotubes, and the manganese-doped gamma-Fe2O3 particles are uniformly distributed on the carbon nanotubes. The preparation device is simple, the operation is convenient, the conditions are controllable, the repeatability is high, the cost is low, and the factory large-scale production can be realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials and chemical synthesis, and particularly relates to preparation and application of a manganese-doped oxide composite catalyst with gamma-Fe2O3 as a precursor, and provides a preparation method with simple process and low cost. BACKGROUND

[0002] Since the 21st century, people have paid more and more attention to energy security and environmental problems, and the demand for new green, safe and renewable energy and energy conversion devices has increased, and their development and utilization are imminent. As a representative of new energy conversion devices, metal-air batteries are expected to be widely used due to their high energy density and environmental friendliness. Metal-air batteries include air electrodes, electrolytes and metal anodes, and their working principle is that oxygen in the air electrode is reduced to combine with electrons generated by the oxidation reaction of the negative electrode metal, and the electrons pass through the external circuit to reach the positive electrode to output electric energy to the outside system. The rate of oxygen reduction reaction at the positive electrode is the key to determining the efficiency of the metal-air battery. However, its slow reaction kinetics results in low efficiency, which restricts the commercial development of metal-air batteries, and designing a reasonable oxygen reduction catalyst to improve its reaction kinetics is the current main research direction. Platinum-based noble metal materials are currently the most commonly used commercial oxygen reduction catalyst, but their high price and low reserves limit their large-scale application. Therefore, it is of great scientific significance and practical value to develop non-noble metal oxygen reduction catalysts with high efficiency, low price and stable performance.

[0003] In practical applications and catalytic processes, spinel transition metal oxides, especially iron-based oxides, have been widely studied as non-noble oxygen reduction catalysts due to their low cost and the potential to provide various active sites. Introducing heteroatoms into spinel oxides is an important strategy to improve their catalytic activity. Since the electronic interaction between multiple metal atoms can induce a synergistic effect, it plays a crucial role in regulating the adsorption and desorption energy of reaction intermediates, thereby optimizing the reaction pathway. The +2 and +3 valence metals in the spinel structure occupy tetrahedral or octahedral sites, and the octahedral site is considered to be a superior active site due to its greater electron-donating ability. Therefore, doping heteroatoms into the octahedral site will be more beneficial to improve catalytic activity. However, heteroatoms are currently doped into the oxide lattice during the synthesis of the oxide substrate, because when the substrate atoms crystallize, the heteroatoms randomly occupy the octahedral and tetrahedral sites. This results in highly active heteroatoms that will be randomly doped into the inactive tetrahedral sites, limiting their efficiency in the active octahedral sites. Due to the lack of directional induction, it is a challenge to avoid entering the inert tetrahedral site while doping heteroatoms into the octahedral site of the spinel. At the same time, the commonly used method is to use various metal salts as precursors, and through various heat treatment processes in liquid or solid phase, often needing to go through high temperature and high pressure heat treatment process, not only the energy consumption is high, but also the product phase is uncontrollable, and impurities are easy to produce. Therefore, it is a very effective method to improve catalytic activity to enhance oxygen reduction catalytic activity by doping heteroatoms into the highly active octahedral site of the spinel. On the other hand, the conductivity of oxide catalysts is generally poor, and structural optimization is needed to improve their conductivity.

[0004] It is feasible to use oxides as precursors to induce heteroatom doping into more active octahedrons, which is different from previous strategies aimed at achieving heteroatom doping during the synthesis of the oxide substrate. However, it is challenging to achieve heteroatom doping based on the oxide lattice as a precursor, with two main reasons. First, the stability of the oxide structure leads to a lack of stable doping sites, making it difficult to achieve the substitution of substrate atoms by heteroatoms or the formation of interstitial heteroatoms by introducing doping atoms. Second, the atomic incompatibility between the matrix and the heteroatom makes it difficult to maintain the stable existence of the heteroatom in the matrix crystal structure. Therefore, it is a very meaningful work to find a simple and feasible preparation method using oxide substrates as precursors. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art, and provides a preparation and application of a manganese-doped oxide composite catalyst using gamma-Fe2O3 as a precursor, wherein octahedral site intrinsic vacancy defect-containing gamma-Fe2O3 is selected as a doped precursor, manganese with a similar atomic radius and outer electron arrangement as the base iron atom is selected as a doped heteroatom, and multi-walled carbon nanotubes are compounded to improve the conductivity of the catalyst; the preparation process is simple, convenient to operate, and has high repeatability; the manganese atoms are uniformly distributed on the gamma-Fe2O3, and the oxide particles are uniformly distributed on the carbon nanotubes; the catalyst has high catalytic activity, simple process, high stability, and excellent energy catalytic application prospect.

[0006] The object of the present application is achieved by the following technical solutions.

[0007] The present application provides a manganese-doped oxide composite catalyst material, which is composed of manganese-doped gamma-Fe2O3 particles and carbon nanotubes, and the manganese-doped gamma-Fe2O3 particles are uniformly distributed on the carbon nanotubes. The manganese-doped precursor is octahedral site intrinsic vacancy defect-containing gamma-Fe2O3. Other metal precursors, such as ferric nitrate, ferric citrate, ferric ammonium citrate, ferric oxalate, ferric ammonium oxalate, ferrous lactate, and ferrous acetate, or alpha-Fe2O3 cannot achieve the effect of inducing high-activity heteroatoms to be doped into high-activity octahedral sites, because the metal salt precursors crystallize to form Fe2O3 through a phase change process, and the alpha-Fe2O3 lattice does not contain metal cation vacancies.

[0008] In some embodiments, the purchased gamma-Fe2O3 is washed and dried with deionized water and anhydrous ethanol multiple times, the precursor is used as a manganese-doped base, carbon nanotubes, a manganese source, and PVP are added, one-step heat treatment is performed in a muffle furnace, and manganese-doped gamma-Fe2O3 particles are uniformly distributed on the carbon nanotubes.

[0009] The present application also provides a preparation method of a manganese-doped oxide composite catalyst, which comprises mixing gamma-Fe2O3 as a precursor, carbon nanotubes, a manganese source, PVP, and a solvent, and then performing heat treatment.

[0010] As an embodiment of the present application, the method specifically comprises the following steps:

[0011] S1, gamma-Fe2O3, carbon nanotubes, a manganese source, and PVP are stirred in a solvent, evaporated and dried, and ground;

[0012] S2, heat treatment;

[0013] S3, the heat treatment product is washed, dried, and the composite catalyst is obtained.

[0014] If the manganese source is not added in step S1, but the product of step S3 is washed and dried, and then immersed in a manganese source solution (such as manganese nitrate solution), and dried to obtain the final product. Since the heat-treated product is not γ-Fe2O3, it does not contain cation vacancies in its crystal lattice, and therefore cannot achieve the effect of inducing high-activity heteroatoms to be doped into high-activity octahedral sites.

[0015] As an embodiment of the present application, in step S1, the γ-Fe2O3 is cleaned multiple times by ultrasonic waves using deionized water and anhydrous ethanol, and dried. The ultrasonic cleaning time is 20-60 min; the drying temperature is 40-100°C, and the drying time is 6-24 h.

[0016] As an embodiment of the present application, the manganese source is selected from manganese nitrate, manganese sulfate, and manganese chloride.

[0017] As an embodiment of the present application, the solvent is selected from anhydrous ethanol, water, and isopropanol.

[0018] As an embodiment of the present application, the heat treatment temperature is 150-400°C, and the reaction time is 1-6 h.

[0019] As an embodiment of the present application, the purity of the γ-Fe2O3 is 80.0-99.999%. The purity of the anhydrous ethanol used as the solvent is 80.0-99.7%. The purity of the carbon nanotubes is 80.0-99.7%. The purity of the PVP is 80.0-99.7%. The purity of the manganese nitrate solution is 40-99.7%.

[0020] As an embodiment of the present application, in the mixture formed by stirring in step S1, the concentrations of the γ-Fe2O3, carbon nanotubes, PVP, and manganese nitrate are 0.1-40 g / L, respectively.

[0021] As an embodiment of the present application, in step S1, the stirring speed is 600-2000 r / min, and the stirring time is 5-20 h.

[0022] As an embodiment of the present application, in step S1, the temperature for evaporative drying is 30-80°C.

[0023] As an embodiment of the present application, in step S3, the washing is performed using deionized water and alcohol.

[0024] As an embodiment of the present application, in step S3, the drying is performed at 40-100°C for 6-24 h.

[0025] In some embodiments, the preparation of the manganese-doped oxide composite catalytic material comprises the following steps:

[0026] (1) Weigh commercial γ-Fe2O3, and clean it in ultrapure water and anhydrous ethanol for several times, and dry it overnight;

[0027] (2) Weigh the cleaned commercial γ-Fe2O3, carbon nanotubes, PVP and manganese nitrate solution obtained in step (1), and stir them in anhydrous ethanol, evaporate and grind them uniformly;

[0028] (3) Put the product obtained in step (2) into a crucible, and place the crucible in a muffle furnace for one-step heat treatment;

[0029] (4) Rinse the powder prepared in step (3) with deionized water and alcohol, and dry it at 60°C to obtain a manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor.

[0030] (5) Mix the powder prepared in step (4), carbon powder, isopropanol and Nafion solution to obtain a slurry, and drop it on a carbon cloth to dry overnight to obtain an electrode for standby use.

[0031] The application also provides an electrode for an oxygen reduction reaction, which contains the manganese-doped oxide composite catalyst or the manganese-doped oxide composite catalyst prepared by the method.

[0032] As an embodiment of the application, the preparation of the electrode comprises: mixing the manganese-doped oxide composite catalyst, carbon powder, isopropanol and Nafion solution to obtain a slurry, and dropping it on a carbon cloth to dry to obtain an electrode for standby use.

[0033] As an embodiment of the application, the purity of the composite catalyst is 80.0-99.7%. The purity of the carbon powder is 80.0-99.7%. The purity of the isopropanol is 80.0-99.7%. The purity of the Nafion is 2-99.7%.

[0034] As an embodiment of the application, the concentration of the composite catalyst and the carbon powder in the slurry is 0.1-10 kg / L, and the concentration of the isopropanol and the Nafion is 0.2-8 mol / L.

[0035] As an embodiment of the application, the carbon cloth is a commercial carbon cloth.

[0036] As an embodiment of the application, the drying temperature is 40-100°C, and the drying time is 6-24 h.

[0037] The application also provides a three-electrode system for an oxygen reduction reaction, wherein the working electrode contains the manganese-doped oxide composite catalyst or the manganese-doped oxide composite catalyst prepared by the method, a carbon rod is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, and a (0.1 mol / L) KOH solution is used as an electrolyte.

[0038] In some embodiments, the manganese-doped oxide composite catalyst with gamma-Fe2O3 as a precursor of the present application is preferably used as a test electrode for oxygen reduction reaction as described in step (5) above.

[0039] The electrode prepared by the manganese-doped oxide composite catalyst with gamma-Fe2O3 as a precursor is used as a working electrode, a carbon rod is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, and a 0.1 mol / L KOH solution is used as an electrolyte to form a three-electrode system for oxygen reduction reaction.

[0040] The mechanism of action of the present application is that gamma-Fe2O3 is a reversed spinel structure with a high vacancy content of about 11% iron vacancies in the octahedral position. These vacancies can provide the necessary doping sites for the introduction of foreign atoms and reduce the binding energy of the substrate atoms. Therefore, this is conducive to the migration of foreign atoms in the substrate lattice and the preferential doping of the octahedral position. In addition, based on the similar ionic radius and outer electron arrangement of iron and manganese atoms, manganese is used as a suitable heterogeneous doping atom, which helps the dopant manganese atoms to stably exist in the original iron position of the gamma-Fe2O3 lattice, avoiding significant internal lattice stress caused by significant differences in atomic size and mismatch in the number of coordination atoms. In addition, the difference in adsorption energy of manganese and iron on the oxygen reduction reaction intermediates can lead to a beneficial synergistic effect. In addition, in order to overcome the inherent conductivity limitation of gamma-Fe2O3, highly conductive carbon nanotubes are integrated with the catalyst. The unsaturated state and enhanced metal support interaction can improve the intrinsic activity of the active sites. The synergistic effect of the two aspects is conducive to improving the performance of the catalyst. At the same time, it is abundant in source, cheap and easy to obtain, which can effectively reduce the cost of the catalyst.

[0041] Compared with the prior art, the present application has the following advantages:

[0042] (1) The oxygen reduction half-reaction catalytic material provided by the present application has uniform morphology and is composed of manganese-doped gamma-Fe2O3 and carbon nanotubes. The oxide particles are uniformly distributed on the carbon nanotubes, and the unique microstructure is conducive to the exposure of active sites and the increase of conductivity, thereby promoting the improvement of electrochemical performance;

[0043] (2) The preparation method proposed by the present application has the advantages of simple equipment, easy operation, controllable conditions, high repeatability, low preparation cost, and is suitable for factory large-scale production;

[0044] (3) The γ-Fe2O3 containing vacancies is used as a precursor to induce the doped heteroatoms into the inverse spinel octahedral position, so as to improve the utilization efficiency, and the carbon nanotubes can provide a one-dimensional conductive network channel, so that the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor has high conductivity and good intrinsic catalytic activity, and has a relatively optimal reaction kinetics. Meanwhile, the binding force between the manganese-doped γ-Fe2O3 and the carbon nanotubes is firm, the contact resistance is reduced, the structure is more stable, and the agglomeration of the nanoparticles is reduced. Benefiting from these advantages, the electrode exhibits excellent oxygen reduction activity and stability in an alkaline solution, and has a wide application prospect in metal-air batteries and the like. BRIEF DESCRIPTION OF DRAWINGS

[0045] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, when read in conjunction with the accompanying drawings:

[0046] Figure 1 A scanning electron microscope picture of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application;

[0047] Figure 2 A transmission electron microscope picture and a high-resolution transmission electron microscope picture of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application;

[0048] Figure 3 Various element distribution maps of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application;

[0049] Figure 4 An XRD curve of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application;

[0050] Figure 5 An LSV graph of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application in oxygen reduction in a 0.1M KOH electrolyte;

[0051] Figure 6 A long-period oxygen reduction stability test result graph of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application in a 0.1M KOH electrolyte;

[0052] Figure 7 A morphology graph of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application after a stability test in a 0.1M KOH electrolyte. DETAILED DESCRIPTION

[0053] The application will be described in detail below in conjunction with specific embodiments and corresponding drawings. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the application. These all belong to the protection scope of the application.

[0054] Example 1

[0055] (1) Commercial γ-Fe2O3 was weighed at a concentration of 0.1 g / L, ultrasonically cleaned several times in ultrapure water or anhydrous ethanol, and dried; the ultrasonic time was 40 min; the drying temperature was 60°C, and the drying time was 12 h;

[0056] (2) Commercial γ-Fe2O3 and 0.1 g / L carbon nanotubes, 0.1 g / L PVP, and 0.1 g / L manganese nitrate solution cleaned and dried were mixed in anhydrous ethanol at room temperature and magnetically stirred at a speed of 1200 r / min for 10 h, uniformly mixed, and then continuously stirred and evaporated at 80°C and uniformly ground;

[0057] (3) The product prepared in step (2) was placed in a crucible, and the crucible was placed in a muffle furnace and kept at 300°C for 5 h;

[0058] (4) The product prepared in step (3) was washed with deionized water and alcohol, and air-dried at 60°C for 12 h to obtain a manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor.

[0059] (5) The product prepared in step (4) 10 mg, carbon powder 10 mg, isopropyl alcohol 0.965 ml, and Nafion solution 0.035 ml were mixed to obtain a slurry, which was dropped on a carbon cloth and dried at 60°C overnight to obtain an electrode for testing.

[0060] Figure 1 The scanning electron microscope picture of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application shows that the manganese-doped oxide particles are uniformly distributed on the carbon nanotubes and have a one-dimensional structure.

[0061] Figure 2 The transmission electron microscope picture of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application shows that the material has a one-dimensional nanostructure, and the manganese-doped oxide particles are closely combined with the carbon nanotubes, which is beneficial to the improvement of the electrochemical performance.

[0062] Figure 3 The element distribution picture of the manganese-doped oxide composite catalyst with γ-Fe2O3 as a precursor prepared in the application shows that the elements are uniformly distributed in the nanosheet.

[0063] Figure 4 The XRD spectrum of the manganese-doped oxide composite catalyst prepared in the application with γ-Fe2O3 as the precursor has the phases of γ-Fe2O3 and carbon nanotubes, and no phase of manganese exists, which means that manganese is doped into the crystal lattice of γ-Fe2O3 and no heterogeneous phase is formed.

[0064] Figure 5 The LSV graph of the manganese-doped oxide composite catalyst prepared in the application with γ-Fe2O3 as the precursor for oxygen reduction in 0.1M KOH electrolyte shows that the manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor can improve the oxygen reduction half-wave potential to 0.83V, and can effectively improve the energy conversion efficiency.

[0065] Figure 6 The long-period oxygen reduction stability test result graph of the manganese-doped oxide composite catalyst prepared in the application with γ-Fe2O3 as the precursor in 0.1M KOH electrolyte shows that the material can still maintain good stability after 10000 cycles of CV scanning in an alkaline environment, indicating that it has good stability.

[0066] Figure 7 The morphology graph of the manganese-doped oxide composite catalyst prepared in the application with γ-Fe2O3 as the precursor after stability test in 0.1M KOH electrolyte shows that the composite structure has excellent structural stability.

[0067] Example 2

[0068] (1) Commercial γ-Fe2O3 was weighed at a concentration of 0.1g / L, and ultrasonic cleaning was performed several times in ultrapure water and anhydrous ethanol, and then dried; the ultrasonic time was 40min; the drying temperature was 60℃, and the drying time was 12h;

[0069] (2) 0.1g / L of the cleaned commercial γ-Fe2O3, 0.1g / L of carbon nanotubes, 0.1g / L of PVP, and 0.1g / L of manganese nitrate solution were weighed in anhydrous ethanol, and magnetic stirring was performed at a speed of 1200r / min at room temperature for 10h, and then mixed uniformly, and then dried by continued stirring at 80℃, and then ground uniformly;

[0070] (3) The product prepared in step (2) was placed in a crucible, and the crucible was placed in a muffle furnace, and then heat preservation was performed at 200℃ for 5h;

[0071] (4) The product prepared in step (3) was washed with deionized water and alcohol, and then air-dried at 60℃ for 12h to obtain the manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor.

[0072] (5) The product prepared in step (4) 10 mg and carbon powder 10 mg, isopropyl alcohol 0.965 ml, Nafion solution 0.035 ml were mixed to obtain a slurry by ultrasonic, which was dropped on carbon cloth overnight and dried at 60 ℃ to obtain an electrode for testing.

[0073] The results of the morphology and structure characterization by scanning, transmission electron microscopy and XRD show that the manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor is prepared. The manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor prepared in this embodiment is composed of γ-Fe2O3 and carbon nanotubes, and the manganese-doped oxide particles are uniformly distributed on the carbon nanotubes, having a one-dimensional structure.

[0074] The manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor prepared in this embodiment was tested for oxygen reduction reaction activity in a 0.1M KOH electrolyte, which proved that the oxygen reduction half-wave potential of the manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor was about 0.80V, which can effectively improve the energy conversion efficiency.

[0075] Example 3

[0076] (1) The commercial γ-Fe2O3 with a concentration of 0.1g / L was ultrasonically cleaned several times in ultrapure water and anhydrous ethanol, and dried; the ultrasonic time was 40 min; the drying temperature was 60℃, and the drying time was 12h;

[0077] (2) 0.1g / L of the cleaned commercial γ-Fe2O3 and 0.1g / L of carbon nanotubes, 0.1g / L of PVP, and 0.1g / L of manganese nitrate solution were magnetically stirred at a speed of 1200r / min for 10h at room temperature in anhydrous ethanol, and were mixed uniformly, and were further stirred at 80℃ and evaporated to dryness, and were ground uniformly;

[0078] (3) The product prepared in step (2) was placed in a crucible, and the crucible was placed in a muffle furnace, and was kept at 400℃ for 5h;

[0079] (4) The product prepared in step (3) was washed with deionized water and alcohol, and was dried at 60℃ by air blowing for 12h to obtain a manganese-doped oxide composite catalyst with γ-Fe2O3 as the precursor.

[0080] (5) The product prepared in step (4) 10 mg and carbon powder 10 mg, isopropyl alcohol 0.965 ml, Nafion solution 0.035 ml were mixed to obtain a slurry by ultrasonic, which was dropped on carbon cloth overnight and dried at 60 ℃ to obtain an electrode for testing.

[0081] The characterization results of the morphology and structure of the manganese-doped oxide composite catalyst prepared by taking γ-Fe2O3 as the precursor by means of scanning, transmission electron microscopy and XRD show that the manganese-doped oxide composite catalyst prepared by taking γ-Fe2O3 as the precursor is composed of γ-Fe2O3 and carbon nanotubes, and the manganese-doped oxide particles are uniformly distributed on the carbon nanotubes, having a quasi-one-dimensional structure.

[0082] The manganese-doped oxide composite catalyst prepared by taking γ-Fe2O3 as the precursor in this embodiment was subjected to oxygen reduction reaction activity test in 0.1M KOH electrolyte, proving that the oxygen reduction half-wave potential of the manganese-doped oxide composite catalyst prepared by taking γ-Fe2O3 as the precursor is about 0.78V, which can effectively improve the energy conversion efficiency.

[0083] Comparative Example 1

[0084] (1) A commercial α-Fe2O3 with a concentration of 0.1g / L was ultrasonically cleaned several times in ultrapure water and anhydrous ethanol, and dried; the ultrasonic time was 40min; the drying temperature was 60℃, and the drying time was 12h;

[0085] (2) 0.1g / L of the cleaned commercial α-Fe2O3, 0.1g / L of carbon nanotubes, 0.1g / L of PVP and 0.1g / L of manganese nitrate solution were magnetically stirred at a speed of 1200r / min for 10h at room temperature in anhydrous ethanol, and were uniformly mixed, and were further stirred at 80℃ until dry and were uniformly ground;

[0086] (3) The product prepared in step (2) was placed in a crucible, and the crucible was placed in a muffle furnace, and was kept at 400℃ for 5h;

[0087] (4) The product prepared in step (3) was washed with deionized water and alcohol, and was air-dried at 60℃ for 12h to obtain a manganese-doped oxide composite catalyst taking α-Fe2O3 as the precursor.

[0088] (5) 10mg of the product prepared in step 4, 10mg of carbon powder, 0.965ml of isopropyl alcohol and 0.035ml of Nafion solution were mixed and ultrasonically treated to obtain a slurry, which was dropped on a carbon cloth and dried at 60℃ overnight to obtain an electrode for test.

[0089] The characterization results of the morphology and structure of the manganese-doped oxide composite catalyst prepared by taking α-Fe2O3 as the precursor by means of scanning, transmission electron microscopy and XRD show that the manganese-doped oxide composite catalyst prepared by taking α-Fe2O3 as the precursor is composed of α-Fe2O3 and carbon nanotubes, and the manganese-doped oxide particles are uniformly distributed on the carbon nanotubes, having a quasi-one-dimensional structure.

[0090] The manganese-doped oxide composite catalyst prepared by using α-Fe2O3 as the precursor in the present comparative example was subjected to the oxygen reduction reaction activity test in 0.1M KOH electrolyte, and it was proved that the oxygen reduction half-wave potential of the manganese-doped oxide composite catalyst prepared by using α-Fe2O3 as the precursor was about 0.70V, and it was proved that the catalytic efficiency of the catalyst prepared by using the substrate α-Fe2O3 without vacancies as the precursor was obviously lower than that of the catalyst prepared by using the precursor γ-Fe2O3 with vacancies.

[0091] The manganese-doped oxide composite catalyst prepared by using γ-Fe2O3 as the precursor and the preparation method thereof disclosed and presented in the present application can be realized by the technical personnel in the field through referring to the content of the present application, and appropriately changing the conditions, routes and other links, although the method and the preparation technology of the present application have been described through the preferred example, and the relevant technical personnel can obviously make changes or recombination to the method and the technical route described in the present application without departing from the content, spirit and scope of the present application, to realize the final preparation technology. It is particularly pointed out that all the similar substitutions and changes are obvious to the technical personnel in the field, and they are considered to be included in the spirit, scope and content of the present application.

Claims

1. A manganese-doped oxide composite catalyst, characterized in that, The composite catalyst is composed of manganese-doped γ-Fe2O3 particles and carbon nanotubes, wherein the manganese-doped γ-Fe2O3 particles are uniformly distributed on the carbon nanotubes. The preparation method of the manganese-doped oxide composite catalyst includes using γ-Fe2O3 as a precursor, mixing it with carbon nanotubes, a manganese source, PVP and a solvent, and then heat-treating it.

2. A method for preparing the manganese-doped oxide composite catalyst as described in claim 1, characterized in that, The method includes using γ-Fe2O3 as a precursor, mixing it with carbon nanotubes, a manganese source, PVP, and a solvent, followed by heat treatment.

3. The method for preparing the manganese-doped oxide composite catalyst according to claim 2, characterized in that, The method specifically includes the following steps: S1, γ-Fe2O3, carbon nanotubes, manganese source, and PVP were stirred in a solvent, evaporated to dryness, and then ground. S2, heat treatment; S3. The composite catalyst is obtained by washing and drying the heat-treated product.

4. The method for preparing the manganese-doped oxide composite catalyst according to claim 2 or 3, characterized in that, In step S1, the γ-Fe2O3 is ultrasonically cleaned and dried multiple times with deionized water and anhydrous ethanol; the ultrasonic time is 20-60 min; the drying temperature is 40-100 ℃ and the drying time is 6-24 h; the manganese source is selected from manganese nitrate, manganese sulfate and manganese chloride; the solvent is selected from anhydrous ethanol, water and isopropanol.

5. The method for preparing the manganese-doped oxide composite catalyst according to claim 2 or 3, characterized in that, The heat treatment temperature is 150~400 ℃, and the heat treatment time is 1~6 h.

6. The method for preparing the manganese-doped oxide composite catalyst according to claim 3, characterized in that, In step S1, the stirring speed is 600-2000 r / min, the stirring time is 5-20 h, and the evaporation temperature is 30℃-80℃; in step S3, the washing is done by rinsing with deionized water and alcohol, and the drying is done at 40-100℃ for 6-24 h.

7. An electrode for an oxygen reduction reaction, characterized in that, The electrode contains the manganese-doped oxide composite catalyst as described in claim 1, or the manganese-doped oxide composite catalyst prepared by any one of claims 2-6.

8. The electrode for the oxygen reduction reaction according to claim 7, characterized in that, The preparation of the electrode includes: mixing the manganese-doped oxide composite catalyst with carbon powder, isopropanol, and Nafion solution, ultrasonically obtaining a slurry, and then dripping it onto carbon cloth and drying it to obtain the electrode for later use.

9. A three-electrode system for oxygen reduction reaction, characterized in that, In the three-electrode system, the working electrode contains the manganese-doped oxide composite catalyst as described in claim 1, or the manganese-doped oxide composite catalyst prepared by any one of claims 2-6, with a carbon rod as the counter electrode, a saturated calomel electrode as the reference electrode, and KOH solution as the electrolyte.

Images