CN110400937B - Preparation method and application of manganese cobalt oxide with porous spherical hollow structure - Google Patents

Abstract

The invention relates to a preparation method and application of a manganese cobalt oxide material with a uniform porous spherical structure. It uses manganese acetate and cobalt acetate as manganese sources and cobalt sources, ethylene glycol and methanol as organic solvents, and prepares manganese-cobalt oxide materials with a porous spherical hollow structure with uniform size by one-step organic solvent combustion method. By adjusting the ratio of manganese and cobalt Mn ₃ O ₄ with porous spherical core-shell structure, CoMn ₂ O 4 with porous spherical shell structure, MnCo ₂ O ₄ with porous spherical hollow structure and Co ₃ O ₄ with uniform solid spherical structure _were obtained respectively. The porous material manganese cobalt oxide has good catalytic performance for ORR OER, and the method of the invention has the characteristics of simple operation, low process cost, regular morphology, etc., and is suitable for the large-scale industrial production of porous spherical manganese cobalt oxide and Practical applications are of great significance.

Description

Preparation method and application of manganese cobalt oxide with porous spherical hollow structure

technical field

The invention belongs to the technical field of zinc-air battery catalysts, and relates to a preparation method of a manganese-cobalt oxide with a porous spherical hollow structure and its application in ORR and OER electrocatalysis.

Background technique

With the rapid development of society, people's demand for energy is increasing. At present, most energy sources are derived from fossil fuels. These traditional energy sources cause serious environmental pollution and threaten human health. It is necessary to develop the next generation of renewable energy equipment to replace fossil fuels in a clean way. Electrochemical energy storage and conversion is considered an ideal way to develop efficient and clean energy devices. Among them, zinc-air batteries are expected to become a new generation of energy storage devices due to their low cost, safety, and environmental friendliness. The discharge process of zinc-air batteries involves oxygen reduction reaction (ORR), while the charging process involves oxygen evolution reaction (OER). At present, commercial catalysts are mainly noble metals such as Pt, Ir, and Ru, but their scarcity, poor stability, and high price limit their further application. Therefore, the development of low-cost, high-efficiency, and stable non-precious metal catalysts is of great significance for the commercialization of Zn-air batteries.

Spinel-structured manganese-cobalt metal oxides exhibit good electrocatalytic activity and catalytic stability in both ORR and OER processes, and are effective and promising bifunctional catalysts. Studies have shown that manganese-cobalt metal oxides with different morphologies show great differences in catalytic performance. Hollow metal oxides are widely used in energy storage and conversion, catalysis, and drug delivery due to their controllable size, composition, and structure [Adv. Mater. 2017, 29, 1605902]. Literature has reported porous hollow-structured MnCo ₂ O ₄ and CoMn ₂ O ₄ spinel oxides with high specific capacity and good cycling performance in Li-ion batteries [Nanoscale, 2013, 5, 2045–2054], but In the synthesis process, carbonate precursors need to be hydrothermally synthesized, and then calcined at high temperature to be decomposed into manganese cobalt oxides, and the synthesis process is relatively complicated. Li et al. obtained hollow spherical MnCo ₂ O ₄ materials with different structures by adjusting different heating rates, and applied them to lithium-ion batteries, but in this method, PVP was used as the structure directing agent to condense and reflux to obtain MnCo-glycolic acid The precursor is then calcined at high temperature to obtain manganese cobalt oxide [ACS Appl. Mater. Interfaces 2014, 6, 24−30]. The above-mentioned two synthetic methods have complicated processes and many influencing factors, which are not conducive to industrialized production. Therefore, it is very important to find a simple and controllable method to prepare hollow manganese cobalt oxides.

The preparation methods of hollow-structured micro-nano materials mainly include: hard film plate method, soft film plate method and template-free method. The hard coating method first needs to synthesize a template with a certain morphology, mainly silicon dioxide, carbon materials, etc., and then cover the target material on the template by various methods, and finally remove the template by selective etching or high-temperature calcination The material obtains a hollow-structured micro-nano material. Although the material obtained by this method is relatively uniform, the operation process is complicated, and the template cannot be completely removed, which brings great difficulties to the later large-scale application. The soft template method is mainly to prepare oxide materials with hollow structures in one step by combining non-covalent bond forces with the assistance of some other means (such as electrochemistry, precipitation, etc.). However, this method has many influencing factors and poor controllability in the synthesis process, so it is difficult to adapt to industrial needs. The template-free method has been widely studied due to its advantages of no need to introduce a template agent, mild reaction conditions, and simple operation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing manganese cobalt oxide with a porous hollow spherical structure with simple process, no template and low cost. The method can simply and quickly obtain the manganese cobalt oxide with a porous spherical hollow structure, and its porous properties are conducive to the exposure of more active sites, and have a good industrial application prospect.

The invention provides a preparation method and application of a manganese cobalt oxide material with a uniform porous spherical structure. The chemical composition of the manganese cobalt oxide is: Mn _3-x Co _x O ₄ , x=0-3;

When x=0, it is Mn ₃ O ₄ with a uniform porous spherical core-shell structure;

When x=1, it is CoMn ₂ O ₄ with uniform porous spherical shell structure;

When x=2, it is MnCo ₂ O ₄ with a uniform porous spherical hollow structure;

When x=3, it is Co ₃ O ₄ with uniform solid spherical structure;

The preparation method comprises the following steps:

1) In the mixed solution of ethylene glycol and anhydrous methanol, add at least one of manganese acetate and cobalt acetate to dissolve, and mix evenly;

2) Dry the obtained mixed solution in an oven at 80°C for 8-12h;

3) Transfer the dried solution in step 2) to a crucible, and heat at a gradient of 2°C/min and heat at 400°C for 5-6 hours.

The molar ratios of cobalt acetate and manganese acetate described in step 1) are respectively 0:3, 1:2, 2:1, and 3:0.

The volume ratio of ethylene glycol and anhydrous methanol described in step 1) is 3:2.

In step 3), the filling degree of the solution in the crucible is 3 vol.%-10 vol.% or 20 vol.%-60 vol.%.

The present invention provides the manganese cobalt oxide material obtained by the above preparation method. Among them, in the manganese cobalt oxide material

The diameter of the outer shell of the Mn ₃ O ₄ is 0.40 μm-1.60 μm, and the diameter of the inner core is 0.45 μm-0.90 μm;

The outer diameter of the CoMn ₂ O ₄ with the uniform porous spherical shell structure is 0.40 μm-1.60 μm;

The diameter of the MnCo ₂ O ₄ of the uniform porous spherical hollow structure is 0.10 μm-0.50 μm;

The diameter of the Co ₃ O ₄ of the uniform solid sphere structure is 0.10 μm-0.30 μm;

When x=0 and the filling degree of the crucible is 20 vol.%-60 vol.%, it is Mn ₃ O ₄ with a porous flower-like structure; the diameter is 1.20 μm-3.00 μm.

The invention provides the electrocatalytic application of the manganese cobalt oxide material in oxygen evolution reaction and oxygen reduction reaction.

The invention provides a preparation method and application of a manganese cobalt oxide material with a uniform porous spherical structure. It uses manganese acetate and cobalt acetate as manganese source and cobalt source, ethylene glycol and methanol as organic solvents, and prepares CoMn ₂ O ₄ metal oxide with porous spherical shell structure in one step by organic solvent combustion method, and its outer diameter is 0.40 μm -1.60μm. By changing the molar ratio of manganese salt to cobalt salt, spherical manganese-cobalt metal oxides with different structures can be effectively prepared. When Co:Mn=0:3, a porous spherical core-shell structure of Mn ₃ O ₄ can be obtained. , it is CoMn ₂ O4 with a uniform porous spherical shell structure, and its outer diameter is 0.40 μm-1.60 μm; when Co:Mn=2:1, a porous spherical hollow structure of Mn ₂ CoO ₄ can be obtained, and its outer diameter is 0.10 μm-0.50μm; when Co:Mn=3:0, Co ₃ O ₄ with uniform solid spherical structure can be obtained, and its diameter is 0.10 μm-0.30 μm.

The invention provides a preparation method of a manganese-cobalt metal oxide material that is environment-friendly, controllable in shape and beneficial to industrial production, with low cost, simple required equipment, easy large-scale synthesis, and the obtained manganese-cobalt oxide material is crystalline It has good properties, uniform morphology, and has good applications in electrocatalytic ORR and OER.

Description of drawings

The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

FIG. 1 is an XRD image of the porous spherical structure manganese cobalt oxide material of the present invention.

FIG. 2 is the SEM, TEM and particle size distribution images of the porous core-shell structured Mn ₃ O ₄ material synthesized in Example 1 of the present invention.

3 is the SEM, TEM and particle size distribution images of the porous spherical shell structure CoMn ₂ O ₄ material synthesized in Example 2 of the present invention.

4 is the SEM, TEM and particle size distribution images of the porous spherical hollow structure MnCo ₂ O ₄ material synthesized in Example 3 of the present invention.

5 is the SEM, TEM and particle size distribution images of the solid spherical structure Co ₃ O ₄ material synthesized in Example 4 of the present invention.

FIG. 6 is the SEM, TEM and particle size distribution images of the porous flower-like Mn ₃ O ₄ material synthesized in Example 5 of the present invention.

FIG. 7 is the ORR linear potential scan graph of the example and the comparative example.

FIG. 8 is an OER linear potential scan diagram of the example and the comparative example.

Detailed ways

The features of the present invention will be further described below through examples, and the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The structure and morphology of the manganese-cobalt oxide prepared by the present invention are analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). analysis. Note that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

At room temperature, 30 ml of ethylene glycol was mixed with 20 ml of anhydrous methanol, and a homogeneous solution was obtained after stirring for 10 min. 2 mmol of manganese acetate was weighed and added to the above solution, and a dark brown mixed solution was obtained after stirring at room temperature for 24 h. The manganese acetate solution was dried in an oven at 80° C. for 10 hours, and the solution obtained above was transferred to a crucible so that the filling degree in the crucible was 3vol.%-10vol.%. The crucible containing the solution was placed in a muffle furnace, heated to 400°C at a heating rate of 2°C/min and kept for 6 hours to obtain a brown-black sample. As shown in Figure 1, the product is Mn ₃ O ₄ with a pure phase spinel structure; as shown in Figure 2, the obtained product is a porous core-shell structure with an outer diameter of 0.40μm-1.60μm and an inner diameter of 0.45μm-0.90μm .

The metal oxide materials obtained above were used as electrode catalyst materials to study their ORR and OER properties. The specific operations are as follows:

1) Weigh 5 mg of Mn ₃ O ₄ and 5 mg of nitric acid-treated conductive carbon black (Vulcan XC-72), add it to a mixed solution of 950 μL of absolute ethanol and 50 μL of 5% Nafion®, and sonicate for 30 min to obtain a dispersion;

2) Measure 15 μL of the above dispersion liquid and drop it evenly on a 5 mm glassy carbon electrode, and dry it naturally to obtain a working electrode.

3) Test its ORR and OER linear potential scan curves in an oxygen-saturated 0.1M KOH solution with an electrochemical workstation (Shanghai Chenhua), the results are shown in Example 1 in Figure 7 and Figure 8, wherein Figure 7 is in ORR linear potential scan of oxygen-saturated 0.1 MKOH at 1600 rpm, Figure 8 is an OER linear potential scan of oxygen-saturated 0.1 M KOH at 1600 rpm.

Example 2

At room temperature, 30 ml of ethylene glycol was mixed with 20 ml of anhydrous methanol, and a homogeneous solution was obtained after stirring for 10 min. 0.67 mmol of cobalt acetate and 1.33 mmol of manganese acetate were weighed into the above solution, and stirred at room temperature for 24 h to obtain a dark brown mixed solution. The manganese-cobalt mixed solution was dried in an oven at 80°C for 10 hours, and the solution obtained above was transferred to a crucible so that the filling degree in the crucible was 3vol.%-10vol.%. The crucible containing the solution was placed in a muffle furnace, heated to 400°C at a heating rate of 2°C/min and kept for 6 hours to obtain a brown-black sample. As shown in Fig. 1, the product is a pure phase spinel structure CoMn ₂ O ₄ ; as shown in Fig. 3, the obtained product is a porous spherical shell structure with an outer diameter of 0.40 μm-1.60 μm.

The ORR and OER properties of CoMn ₂ O ₄ with a porous spherical shell structure were tested by the same method as in Example 1, and the results are shown in Example 2 in FIG. 7 and FIG. 8 .

Example 3

At room temperature, 30 ml of ethylene glycol was mixed with 20 ml of anhydrous methanol, and a homogeneous solution was obtained after stirring for 10 min. 1.33 mmol of cobalt acetate and 0.67 mmol of manganese acetate were weighed and added to the above solution, and a dark red mixed solution was obtained after stirring at room temperature for 24 h. The manganese-cobalt mixed solution was dried in an oven at 80°C for 10 hours, and the solution obtained above was transferred to a crucible so that the filling degree in the crucible was 3vol.%-10vol.%. The crucible containing the solution was placed in a muffle furnace, heated to 400°C at a heating rate of 2°C/min and kept for 6 h to obtain a black sample. As shown in Figure 1, the product is a pure phase spinel structure MnCo ₂ O ₄ ; as shown in Figure 4, the obtained product is a porous spherical hollow structure with an outer diameter of 0.10 μm-0.50 μm.

The ORR and OER properties of MnCo ₂ O ₄ with a porous hollow spherical structure were tested by the same method as in Example 1, and the results are shown in Example 3 in FIG. 7 and FIG. 8 .

Example 4

At room temperature, 30 ml of ethylene glycol was mixed with 20 ml of anhydrous methanol, and a homogeneous solution was obtained after stirring for 10 min. 2 mmol of cobalt acetate was weighed and added to the above solution, and a dark red mixed solution was obtained after stirring at room temperature for 24 h. The cobalt acetate solution was dried in an oven at 80° C. for 10 hours, and the solution obtained above was transferred to a crucible so that the filling degree in the crucible was 3vol.%-10vol.%. The crucible containing the solution was placed in a muffle furnace, heated to 400°C at a heating rate of 2°C/min and kept for 6 hours to obtain a black-gray sample. As shown in Fig. 1, the product is a pure phase spinel structure Co ₃ O ₄ ; as shown in Fig. 5 , the obtained product is a solid sphere structure with a diameter of 0.10 μm-0.30 μm.

The ORR and OER properties of the solid spherical structure Co ₃ O ₄ were tested by the same method as in Example 1, and the results are shown in Example 4 in FIG. 7 and FIG. 8 .

Example 5

At room temperature, 30 ml of ethylene glycol was mixed with 20 ml of anhydrous methanol, and a homogeneous solution was obtained after stirring for 10 min. 2 mmol of manganese acetate was weighed and added to the above solution, and stirred at room temperature for 24 h to obtain a dark brown mixed solution. The manganese acetate solution was dried in an oven at 80° C. for 10 hours, and the solution obtained above was transferred to a crucible so that the filling degree in the crucible was 20vol.%-60vol.%. The crucible containing the solution was placed in a muffle furnace, heated to 400°C at a heating rate of 2°C/min and kept for 6h to obtain a brown-black sample. As shown in Figure 6, the obtained samples exhibited porous flower-like structures with diameters ranging from 1.20 μm to 3.00 μm.

The ORR and OER properties of flower-like Mn ₃ O ₄ were tested by the same method as in Example 1, and the results are shown in Example 5 in Figure 7 and Figure 8 .

Comparative Example 1

As a comparative example, a commercial platinum-carbon catalyst (Pt/C 20%, Sigma Aldrich) was used as the comparative catalyst, and the electrocatalytic performance testing process was as follows:

1) Weigh 2 mg of 20% Pt/C, add it to a mixed solution of 950 μL of absolute ethanol and 50 μL of 5% Nafion®, and sonicate for 30 min to obtain a dispersion;

2) Measure 15 μL of the above dispersion liquid and drop it evenly on a 5 mm glassy carbon electrode, and dry it naturally to obtain a working electrode.

3) Test its ORR and OER linear potential scan curves in an oxygen-saturated 0.1M KOH solution with an electrochemical workstation (Shanghai Chenhua). The results are shown in Figure 7 and Comparative Example 1 in Figure 8. ORR linear potential scan of oxygen-saturated 0.1 MKOH at 1600 rpm, Figure 8 is an OER linear potential scan of oxygen-saturated 0.1 M KOH at 1600 rpm.

The above results show that MnCo ₂ O ₄ and Co ₃ O ₄ have excellent ORR activities, and the ORR current density of MnCo ₂ O ₄ is even better than that of platinum carbon; while Co ₃ O ₄ not only has excellent ORR activity, but also has the best ORR activity. It has excellent OER activity and is a potential bifunctional electrocatalyst.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims (4)

1. A preparation method of a manganese cobalt oxide material with a spherical structure is characterized in that the manganese cobalt oxide material comprises the following chemical components: mn (Mn)_3-xCo_xO₄,x=0-3；

Mn of porous spherical core-shell structure when x =0₃O₄Said Mn₃O₄The diameter of the outer shell is 0.40-1.60 μm, and the diameter of the inner core is 0.45-0.90 μm;

CoMn with uniform porous spherical shell structure when x =1₂O₄The CoMn₂O₄The outer diameter of (A) is 0.40-1.60 μm;

MnCo with uniform porous spherical hollow structure when x =2₂O₄Said MnCo₂O₄The diameter of (A) is 0.10-0.50 μm;

co of uniform solid sphere structure when x =3₃O₄Said Co₃O₄The diameter of (A) is 0.10-0.30 μm;

the preparation method comprises the following steps:

1) adding at least one of manganese acetate and cobalt acetate into a mixed solution of ethylene glycol and anhydrous methanol for dissolving, and uniformly mixing;

2) drying the obtained mixed solution in an oven at 80 ℃ for 8-12 h;

3) Transferring the dried solution obtained in the step 2) into a crucible, heating at a gradient of 2 ℃/min and calcining for 5-6h at 400 ℃; the solution filling degree in the crucible is 3-10 vol%;

the volume ratio of the ethylene glycol to the anhydrous methanol in the step 1) is 3: 2.

2. The method according to claim 1, wherein the molar ratios of cobalt acetate and manganese acetate in step 1) are:

when x =0, the molar ratio of cobalt acetate to manganese acetate is 0: 3;

when x =1, the molar ratio of cobalt acetate to manganese acetate is 1: 2;

when x =2, the molar ratio of cobalt acetate to manganese acetate is 2: 1;

when x =3, the molar ratio of cobalt acetate to manganese acetate is 3: 0.

3. manganese cobalt oxide material obtainable by the process according to any one of claims 1 to 2.

4. The manganese cobalt oxide material of claim 3, wherein: the manganese cobalt oxide material is applied to electrocatalysis in oxygen evolution reaction and oxygen reduction reaction.

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