Mn-Co3O4@CNTs-O electrocatalyst and preparation method and application thereof

Abstract

The application discloses an Mn-Co3O4@CNTs-O electrocatalyst and a preparation and application thereof, and the electrocatalyst takes oxygen-containing group modified carbon nanotubes as a carrier and takes Mn-Co3O4 as an active component; in the catalyst, the loading amount of the active component is 10%-60%; the molar ratio of Mn and Co is 0.1-0.8; and the particle size of Mn-Co3O4 is 3-7nm. The Mn-Co3O4@CNTs-O electrocatalyst provided by the application has higher activity and stability compared with Co3O4 electrocatalyst, wherein the doping of manganese increases the number of active sites Co 3+ in the catalyst, which is beneficial to the improvement of catalytic activity. Moreover, compared with the existing preparation method, the preparation method has the advantages of mild conditions, low cost, green environmental protection and the like.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to an oxygen reduction and oxygen evolution catalyst for metal-air fuel cells and other alkaline conditions, as well as its preparation and application. Background Technology

[0002] Metal-air batteries have attracted considerable attention from researchers due to their theoretically high energy density, low cost, portability, and environmental friendliness, and have become a popular research direction in recent years. Compared to other metal-air batteries, zinc / air batteries have a more environmentally friendly electrolyte, a reversible zinc anode, a low self-discharge rate, and a high coulombic efficiency. Therefore, zinc / air batteries are more likely to be used to realize rechargeable batteries. However, in actual operation, a high overpotential is generated between the oxygen reduction and oxygen evolution reactions at the air cathode, which reduces the actual operating voltage of zinc / air batteries to less than 1.4V, resulting in a cycle efficiency of only 55-65%. To address this issue, researchers have used non-noble metal oxides as bifunctional oxygen electrocatalysts.

[0003] In recent years, due to the unique spinel structure of Co3O4, multiple valence states (Co... 2+ and Co 3+ The coexistence of catalytic activity and structural stability under alkaline conditions has made it a current research hotspot. Su et al. prepared cubic Co3O4 nanostructures, synthesized via hydrothermal assisted defect engineering, which exhibited good electrocatalytic activity (J. Alloys Compd. 2019, 799, 160-168). However, due to the low electrical conductivity of Co3O4, its catalytic activity and stability still have room for improvement in practical applications. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing an oxygen reduction and oxygen evolution catalyst for rechargeable metal-air fuel cells and other alkaline conditions, as well as its preparation and application.

[0005] To achieve the above objectives, the present invention employs the following specific solutions:

[0006] On one hand, the present invention provides a Mn-Co3O4@CNTs-O electrocatalyst, which uses carbon nanotubes modified with oxygen-containing groups as a support and Mn-Co3O4 as the active component; Mn-Co3O4 nanoparticles are uniformly supported on it, and the loading of the active component in the catalyst is 10%-60%; the molar ratio of Mn to Co is 0.1-0.8.

[0007] Based on the above scheme, preferably, the molar ratio of Mn to Co is 0.3-0.6; the loading of the active component is 35wt%-45wt%; and the particle size of the Mn-Co3O4 is 3-7nm, more preferably 5nm.

[0008] On the other hand, the present invention provides a method for preparing the above-mentioned Mn-Co3O4@CNTs-O electrocatalyst, comprising the following preparation steps,

[0009] (1) Mix carbon nanotubes with white fuming nitric acid, ultrasonically disperse for a period of time, then heat under reflux, let stand overnight, pour off the supernatant, filter to separate carbon nanotubes, wash with ultrapure water and anhydrous ethanol multiple times, and then dry in a forced-air drying oven to obtain the carbon nanotubes modified with oxygen groups.

[0010] (2) Place cobalt acetate and manganese acetate in a single-necked round-bottom flask, stir for a period of time, add ammonia water and continue stirring, transfer it to an oil bath and heat under reflux, stop stirring after a period of time to obtain Mn-Co(OH)2 colloidal solution. No precipitate was formed in the Mn-Co(OH)2 colloidal solution after a period of time.

[0011] (3) The carbon nanotubes modified with oxygen-containing groups obtained in step (1) were ultrasonically dispersed in anhydrous ethanol, and the colloid obtained in step (2) was added. The mixture was stirred at room temperature for a period of time, transferred to a beaker, and the ethanol solvent was evaporated in an oil bath. The resulting black powder was calcined in a muffle furnace to finally obtain Mn-Co3O4@CNTs-O in different proportions.

[0012] Based on the above scheme, preferably, in step (1), the fuming nitric acid is 4-5 mol / L, the ultrasonic time is 30-60 min, the reflux temperature is 80-100℃, the reflux time is 6-8 hours, the drying temperature is 100-120℃, and the drying time is 10-12 hours. As a further preferred embodiment, the fuming nitric acid is 5 mol / L, the ultrasonic time is 30 min, the reflux temperature is 90℃, the reflux time is 8 hours, the drying temperature is 120℃, and the drying time is 12 hours.

[0013] Based on the above scheme, preferably, in step (2), the ammonia water is 25 wt.% and the stirring time is 4-6 hours. As a further preferred option, the stirring time is 4 hours.

[0014] Based on the above scheme, preferably, in step (2), the heating reflux temperature is 80-100℃ and the heating reflux time is 4-6 hours. As a further preferred option, the heating reflux temperature is 90℃ and the heating reflux time is 4 hours.

[0015] Based on the above scheme, preferably, in step (3), the mass ratio of the Mn-Co(OH)2 colloid to the carbon nanotube is 0.1 to 0.6.

[0016] Based on the above scheme, preferably, in step (3), the calcination temperature is 200-400℃ and the calcination time is 2-4 hours. As a further preferred option, the calcination temperature is 300℃ and the calcination time is 2 hours.

[0017] The Mn-Co3O4@CNTs-O electrocatalyst is a catalyst for oxygen reduction and oxygen evolution under alkaline conditions, used in metal-air fuel cells (such as rechargeable zinc / air batteries) and other alkaline conditions.

[0018] Compared with the prior art, the Mn-Co3O4@CNTs-O of the present invention has the following advantages:

[0019] 1. The Mn-Co3O4@CNTs-O electrocatalyst provided by this invention exhibits high activity and stability. The manganese doping increases the number of active Co sites in the catalyst. 3+ The amount of manganese is important for the catalytic activity of ORR / OER, and the manganese content needs to be controlled within a certain range. If the manganese doping amount is too low, it is not conducive to the active sites of Co. 3+ Increasing the quantity will lead to a decrease in the crystallinity of the catalyst and a reduction in its catalytic performance.

[0020] 2. The catalyst of the present invention uses carbon nanotubes modified with oxygen-containing groups as a support, and the proportion of the support is controlled within a certain range, which can improve the stability and conductivity of the catalyst. If the amount of carbon nanotubes is too small, it is not conducive to the stability of the catalyst and affects the uniform distribution of the active ingredients, making it impossible to expose more catalytic sites. If the amount is too large, the content of active ingredients will be relatively low, which is also not conducive to catalytic activity.

[0021] 3. The present invention uses ethanol as a solvent for cobalt acetate and manganese acetate because ammonia has a low degree of dissociation in ethanol, which can control the size of the crystals formed.

[0022] 4. The preparation method of this invention is simple, safe, and avoids prolonged reaction at high temperatures. Attached Figure Description

[0023] Figure 1 XRD spectra of 40% Mn-Co3O4@CNTs-O prepared according to Example 4 and Co3O4@CNTs-O prepared according to Comparative Example 1;

[0024] Figure 2 TEM image of 40% Mn-Co3O4@CNTs-O prepared according to Example 4;

[0025] Figure 3ORR polarization curves of 30% Mn-Co3O4@CNTs-O prepared according to Example 3, 40% Mn-Co3O4@CNTs-O prepared according to Example 4, 60% Mn-Co3O4@CNTs-O prepared according to Example 6, and Co3O4@CNTs-O of Comparative Example 1 in oxygen-saturated 0.1M KOH electrolyte;

[0026] Figure 4 OER polarization curves of 30% Mn-Co3O4@CNTs-O prepared according to Example 3, 40% Mn-Co3O4@CNTs-O prepared according to Example 4, 60% Mn-Co3O4@CNTs-O prepared according to Example 6, and Co3O4@CNTs-O of Comparative Example 1 in oxygen-saturated 1M KOH electrolyte.

[0027] Figure 5 Charge-discharge polarization curves and corresponding power density curves are shown for the rechargeable zinc / air batteries assembled from 40% Mn-Co3O4@CNTs-O prepared according to Example 4 and Co3O4@CNTs-O of Comparative Example 1. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to these specific embodiments.

[0029] Example 1

[0030] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.0492g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0031] 5g of carbon nanotubes were oxidized with 350mL of HNO3, first ultrasonically dispersed for 2 hours, and then refluxed at 90℃ for 8 hours. After standing overnight, the mixture was filtered and washed three times with ultrapure water to obtain a filter cake. The filter cake was dried in a 120℃ forced-air drying oven for 12 hours to obtain oxygen-modified carbon nanotubes.

[0032] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 10% Mn-Co3O4@CNTs-O.

[0033] Example 2

[0034] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.0984g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0035] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0036] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 20% Mn-Co3O4@CNTs-O.

[0037] Example 3

[0038] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.1476g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0039] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0040] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 30% Mn-Co3O4@CNTs-O.

[0041] Example 4

[0042] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.1762g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0043] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0044] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 40% Mn-Co3O4@CNTs-O.

[0045] Example 5

[0046] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.2460g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0047] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0048] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 50% Mn-Co3O4@CNTs-O.

[0049] Example 6

[0050] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.2643g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0051] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0052] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 60% Mn-Co3O4@CNTs-O.

[0053] Example 7

[0054] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.3524g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0055] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0056] Weigh 0.0664 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 80% Mn-Co3O4@CNTs-O.

[0057] Example 8

[0058] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.1762g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0059] The preparation methods for oxygen-modified carbon nanotubes are the same as in Example 1.

[0060] Weigh 0.1 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 40% Mn-Co3O4@CNTs-O-0.3.

[0061] Example 9

[0062] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.1762g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0063] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0064] Weigh 0.0442 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 40% Mn-Co3O4@CNTs-O-0.5.

[0065] Example 10

[0066] Preparation method of Mn-Co3O4@CNTs-O: Weigh 0.5g cobalt acetate and 0.1762g manganese acetate, disperse them in 25mL anhydrous ethanol and stir until the solution is clear pink; then add 2.5mL 25wt.% ammonia water, keep stirring until the solution is clear dark brown, transfer to an oil bath, heat and reflux at 90℃ for 4h, stop heating and reflux, and Mn-Co(OH)2 colloid can be obtained.

[0067] The preparation method of oxygen-modified carbon nanotubes is the same as in Example 1.

[0068] Weigh 0.1777 g of oxygen-modified carbon nanotubes, disperse them in 35 mL of anhydrous ethanol, and sonicate for 30 min. While stirring, add 5 mL of Mn-Co(OH)2 colloid, stir at room temperature for 4 h, transfer to a beaker, and evaporate the ethanol solvent in an oil bath at 70 °C to obtain a black powder. Place the powder in a muffle furnace and calcine at 300 °C for 2 h to obtain 40% Mn-Co3O4@CNTs-O-0.2.

[0069] Comparative Example 1

[0070] The comparative example is undoped Co3O4@CNTs-O, see the preparation method of 40% Mn-Co3O4@CNTs-O in Example 4.

[0071] Figure 1The XRD patterns are shown for 40% Mn-Co3O4@CNTs-O prepared according to Example 4 and Co3O4@CNTs-O of Comparative Example 1. Comparing the two curves, it can be seen that the sample prepared in Example 4 has characteristic peaks of Co3O4.

[0072] Figure 2 The image shows a TEM image of the 40% Mn-Co3O4@CNTs-O sample prepared according to Example 4. The image shows that the nanoparticles are uniformly distributed on the carbon nanotubes in the sample prepared in Example 4.

[0073] Figure 3 The ORR polarization curves of 30% Mn-Co3O4@CNTs-O prepared according to Example 3, 40% Mn-Co3O4@CNTs-O prepared according to Example 4, 60% Mn-Co3O4@CNTs-O prepared according to Example 6, and Co3O4@CNTs-O of Comparative Example 1 in oxygen-saturated 0.1M KOH electrolyte are shown. Comparison revealed that the ORR overpotential of 40% Mn-Co3O4@CNTs-O was lower than that of the other samples, indicating higher ORR catalytic activity.

[0074] Figure 4 The OER polarization curves of 30% Mn-Co3O4@CNTs-O prepared according to Example 3, 40% Mn-Co3O4@CNTs-O prepared according to Example 4, 60% Mn-Co3O4@CNTs-O prepared according to Example 6, and Co3O4@CNTs-O of Comparative Example 1 in oxygen-saturated 1M KOH electrolyte are shown. Comparison revealed that the OER overpotential of 40% Mn-Co3O4@CNTs-O was lower than that of the other samples, indicating higher OER catalytic activity.

[0075] Figure 5 The charge-discharge polarization curves and corresponding power density curves of the rechargeable zinc / air batteries assembled from 40% Mn-Co3O4@CNTs-O prepared according to Example 4 and Co3O4@CNTs-O of Comparative Example 1 are shown in the figures. It can be seen from the figures that the power density of the rechargeable zinc / air battery assembled from 40% Mn-Co3O4@CNTs-O is around 180 mA cm⁻¹. -2 It reached 116mW cm -2 It is superior to the rechargeable zinc / air battery assembled with Co3O4@CNTs-O.

Claims

1. An electrocatalyst, characterized in that, The electrocatalyst uses oxygen-containing modified carbon nanotubes as a support and Mn-Co3O4 as the active component; the loading of the active component in the catalyst is 10wt%-60wt%; the molar ratio of Mn to Co is 0.1-0.8; the electrocatalyst is prepared by the following method, the specific steps of which are as follows: (1) Carbon nanotubes and fuming nitric acid are mixed and then subjected to ultrasonic dispersion, heating and reflux, standing, filtering, washing and drying in sequence to obtain the carbon nanotubes modified with oxygen-containing groups. (2) Dissolve cobalt acetate and manganese acetate in ethanol, add ammonia water and stir until the solution turns blackish-brown, then heat under reflux for a period of time to obtain Mn-Co(OH)2 colloidal solution; (3) The carbon nanotubes modified with oxygen-containing groups were dispersed in anhydrous ethanol, and the Mn-Co(OH)2 colloid was added. The mixture was stirred at room temperature for a period of time, and then dried and calcined to obtain the catalyst.

2. The electrocatalyst according to claim 1, characterized in that, The molar ratio of Mn to Co is 0.3-0.6; the loading of the active component is 35wt%-45wt%; and the particle size of the Mn-Co3O4 is 3-7nm.

3. A method for preparing the catalyst according to any one of claims 1-2, characterized in that, The method includes the following steps: (1) Carbon nanotubes and fuming nitric acid are mixed and then subjected to ultrasonic dispersion, heating and reflux, standing, filtering, washing and drying in sequence to obtain the carbon nanotubes modified with oxygen-containing groups. (2) Dissolve cobalt acetate and manganese acetate in ethanol, add ammonia water and stir until the solution turns blackish-brown, then heat under reflux for a period of time to obtain Mn-Co(OH)2 colloidal solution; (3) The carbon nanotubes modified with oxygen-containing groups were dispersed in anhydrous ethanol, and the Mn-Co(OH)2 colloid was added. The mixture was stirred at room temperature for a period of time, and then dried and calcined to obtain the catalyst.

4. The preparation method according to claim 3, characterized in that, In step (1), the fuming nitric acid is 4-5 mol / L, the ultrasonic time is 30-60 min, the reflux temperature is 80-100℃, the reflux time is 6-8 hours, the drying temperature is 100-120℃, and the drying time is 10-12 hours.

5. The preparation method according to claim 3, characterized in that, In step (2), the ammonia water is 25 wt.% and the stirring time is 4-6 hours.

6. The preparation method according to claim 3, characterized in that, In step (2), the heating reflux temperature is 80-100℃ and the heating reflux time is 4-6 hours.

7. The preparation method according to claim 3, characterized in that, In step (3), the mass ratio of the Mn-Co(OH)2 colloid to the carbon nanotube is 0.1 to 0.

6.

8. The preparation method according to claim 3, characterized in that, In step (3), the roasting temperature is 200-400℃ and the roasting time is 2-4 hours.

9. The application of the electrocatalyst according to any one of claims 1-2 in metal-air fuel cells and in oxygen reduction and oxygen evolution reactions under alkaline conditions.

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