ZIF-derived composite bifunctional electro-catalytic material as well as preparation method and application thereof

Abstract

The invention discloses a ZIF-derived composite bifunctional electro-catalytic material as well as a preparation method and application thereof, and belongs to the field of new energy materials. The material is synthesized by stirring an organic ligand 2-methylimidazole, metal sources of zinc nitrate, cobalt nitrate and ferric acetylacetonate and a sulfur source of thioacetamide at room temperature, the preparation method is simple, and the reaction conditions are mild and environment-friendly. Under the synergistic effect of the bimetallic alloy and heteroatoms, the catalytic material shows efficient oxygen reduction and oxygen evolution electrochemical properties. The zinc-air battery assembled by the zinc-air composite material has an open-circuit voltage of 1.48 V, and the attenuation of the battery is small after 500 cycles, so that the zinc-air composite material can be compared favorably with a commercial material.

Description

Technical Field

[0001] The present invention belongs to the field of new energy materials, and specifically relates to a method for preparing a transition metal and heteroatom doped composite carbon material based on ZIF-L derived under different iron sources and its application in zinc-air batteries. Background Art

[0002] With the rapid development of modern society, the resource depletion and environmental problems caused by the continuous increase in energy consumption have attracted more and more attention. At present, 70% of the world's energy consumption is provided by non-renewable fossil fuels. Although the energy released by their combustion can meet the large demand of human activities, fossil energy has also caused serious environmental problems while promoting social and economic development. Therefore, researchers are committed to developing more efficient, renewable and clean energy conversion and storage devices. Electrochemical technology is an effective means to convert renewable energy from chemical energy to electrical energy, and is considered to be one of the most promising energy technologies. Among them, rechargeable zinc-air batteries (ZABs) combine the key characteristics of secondary batteries and fuel cells, which can meet the requirements of high energy density for power batteries and high safety and economic benefits for consumer batteries. The performance of rechargeable ZABs mainly depends on the oxygen reduction reaction (ORR) at the cathode during battery discharge and the oxygen evolution reaction (OER) at the anode during charging. However, at the complex liquid-gas-solid three-phase interface, the ORR / OER reaction kinetics are slow and the durability is poor. Rechargeable ZABs still have problems such as low round-trip efficiency and poor stability. Based on the above analysis, the design and use of efficient bifunctional electrocatalysts that have both ORR and OER catalytic behaviors and strong environmental adaptability are the key to achieving high-performance zinc-air batteries.

[0003] In order to develop efficient and low-cost ORR / OER bifunctional catalysts, an effective method is to assemble transition metal and heteroatom-doped carbon-based catalysts. Zeolite imidazolate frameworks (ZIFs) are a new type of metal-organic framework (MOFs) material. They use metal ions to coordinate with imidazole to form a complex structure. They have the characteristics of large specific surface area and high porosity. Their pyrolysis products are MNCs. They are often used as catalytic materials due to their high atomic utilization and metal catalytic centers. However, the structure and morphology of ZIFs are greatly affected by their synthesis conditions. Surfactants are often added to control their growth direction to form ZIF precursors with controllable morphology. Iron and cobalt are the most commonly used transition metals for the preparation of bifunctional catalysts, and different coordination structures and even different types of substances can be obtained under the action of different metal sources. The types of these derived substances determine the catalytic performance of the material. Among them, the synergistic effect between Fe and Co in FeCo alloys provides a large number of binary active centers and electronic valence states, which can promote the formation of ORR active sites. However, the OER activity of most alloy catalysts is not sufficient to meet their application in rechargeable zinc-air batteries. The structure and charge distribution of carbon materials can be adjusted by heteroatom doping (such as B, N, P, S, Se) to improve the OER activity. Therefore, regular and morphologically controllable precursors can be synthesized, the effects of different iron sources on ZIF material-derived substances can be explored, and the dual functionality of catalytic materials can be improved by combining transition metals with heteroatom-doped carbon substrates. Summary of the invention

[0004] In response to the research needs in this field, the purpose of the present invention is to provide a bimetallic alloy / N, S co-doped carbon material derived from ZIF under different iron sources to improve the catalytic performance of the catalyst and solve the problem of slow air cathode kinetics in zinc-air batteries.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for preparing a ZIF-derived composite bifunctional electrocatalytic material, wherein an aqueous solution of zinc nitrate and dimethylimidazole is stirred at room temperature to obtain ZIF-L, and then different iron sources and heteroatom doping are added to form a precursor, and finally a final product is obtained by high-temperature pyrolysis. The specific steps are as follows:

[0007] (1) dissolving zinc nitrate in water to obtain solution A, dissolving 2-methylimidazole and surfactant P123 in water to obtain solution B, mixing A and B, and filtering the obtained precipitate, washing, and drying to obtain ZIF-L;

[0008] (2) adding cobalt nitrate and ferric acetylacetonate to water and stirring evenly, adding ZIF-L obtained in step (1) and stirring for 10 min, then adding a mixed solution of 2-methylimidazole and thioacetamide, stirring, filtering, washing, and drying to obtain a CoFe(acac)3-ZIF-L / S precursor;

[0009] (3) The obtained precursor is pyrolyzed under an inert atmosphere to obtain the final composite material Co-Co 0.7 Fe 0.3 / S@NC.

[0010] In step (1), the molar ratio of zinc nitrate to 2-methylimidazole is 2:16, and the molar ratio of P123 to zinc nitrate is 0.0005-0.002:1, preferably 0.001:1.

[0011] The molar ratio of cobalt nitrate to ferric acetylacetonate in step (2) is 1:(0.1-0.3), preferably 1:0.2, the molar ratio of ZIF-L to cobalt nitrate is (0.5-2):1, preferably 1-1.5:1, the molar ratio of cobalt nitrate to 2-methylimidazole is 1:8, and the molar ratio of cobalt nitrate to thioacetamide is 1:0.8.

[0012] Preferably, the stirring time in step (1) and step (2) is 4 hours.

[0013] Preferably, the pyrolysis temperature in step (3) is 900° C., the heating rate is 5° C. / min, and the holding time is 2 h.

[0014] Application of a ZIF-derived composite bifunctional electrocatalytic material obtained by the present invention, Co-Co derived from ZIF-L 0.7 Fe 0.3 / S@NC composite material was used as cathode catalyst of zinc-air battery to prepare working electrode for electrocatalytic reduction reaction of O2 and H2O and evolution of O2.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The surfactant P123 in the present invention can adjust the morphology of ZIF, and the introduction of ferric acetylacetonate promotes the 0.7 Fe 0.3 Alloy formation.

[0017] (2) The catalyst of the present invention exhibits excellent oxygen reduction performance, and its half-wave potential of oxygen reduction reaction is 0.9 V vs. RHE. The nitrogen-doped carbon material derived from the zeolite imidazole framework can improve the stability and conductivity of the material.

[0018] (3) The preparation process of the composite material of the present invention is simple and mild. The zinc-air battery assembled with the composite material as the air cathode exhibits a high open circuit voltage, good cycle stability and considerable power density, showing certain practical application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Scanning electron microscope image of ZIF-L in the present invention;

[0020] Figure 2 X-ray powder diffraction patterns of samples prepared in Example 1 of the present invention and Comparative Examples 1-2;

[0021] Figure 3 Linear sweep voltammetric curves of electrocatalytic oxygen reduction (a) and oxygen evolution (b) of the samples prepared in Examples 1-3 of the present invention under alkaline conditions (a-0.1M KOH, b-1M KOH);

[0022] Figure 4 Linear sweep voltammetric curves of electrocatalytic oxygen reduction (a) and oxygen evolution (b) of the samples prepared in Example 1 of the present invention and Comparative Examples 1-3 under alkaline conditions (a-0.1M KOH, b-1M KOH); Figure 5 The open circuit voltage curve (a), polarization curve and power density curve (b) and cycle stability (c) of the zinc-air battery of the samples prepared in Example 1 of the present invention and Comparative Example 3 under alkaline conditions (6M KOH+0.2MZn(CH3COO)2). DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and examples, but the scope of protection claimed by the present invention is not limited to the scope of protection of the examples.

[0024] Example 1:

[0025] (1) 2 mmol Zn(NO3)2·6H2O was dissolved in 40 ml water to form solution A, 16 mmol 2-methylimidazole and 0.002 mmol P123 were dissolved in an equal amount of water to form solution B, then solutions A and B were mixed and stirred for 4 h, the obtained product was filtered and dried in a vacuum oven at 70 °C for 12 h to obtain ZIF-L;

[0026] (2) Weigh 1 mmol Co(NO3)2·6H2O and 0.2 mmol Fe(acac)3 and dissolve them in 20 ml water. After stirring, add 1 mmol ZIF-L and stir for 10 min. Then add 20 ml of an aqueous solution of 8 mmol 2-methylimidazole and 0.8 mmol thioacetamide. Filter the obtained product and dry it in a vacuum oven at 60 °C for 12 h to obtain the precursor CoFe(acac)3-ZIF-L / S.

[0027] (3) The precursor CoFe(acac)3-ZIF-L / S was pyrolyzed in an argon atmosphere at a heating rate of 5°C / min and kept at 900°C for 2 h to obtain Co-Co 0.7 Fe 0.3 / S@NC composite materials.

[0028] Example 2:

[0029] (1) Same as step (1) of Example 1;

[0030] (2) Weigh 1 mmol Co(NO3)2·6H2O and 0.2 mmol Fe(acac)3 and dissolve them in 20 ml water. After stirring evenly, add 0.5 mmol ZIF-L and stir for 10 min. Add 20 ml of an aqueous solution of 8 mmol 2-methylimidazole and 0.8 mmol thioacetamide. Filter the obtained product and dry it in a vacuum oven at 60 °C for 12 h to obtain the precursor CoFe(acac)3-ZIF-L / S-0.5.

[0031] (3) The precursor CoFe(acac)3-ZIF-L / S-0.5 was pyrolyzed in an argon atmosphere at a heating rate of 5°C / min and kept at 900°C for 2 h to obtain Co-Co 0.7 Fe 0.3 / S@NC-0.5 composite material.

[0032] Example 3:

[0033] (1) Same as step (1) of Example 1;

[0034] (2) Weigh 1 mmol Co(NO3)2·6H2O and 0.2 mmol Fe(acac)3 and dissolve them in 20 ml water. After stirring, add 1.5 mmol ZIF-L and stir for 10 min. Add 20 ml of an aqueous solution of 8 mmol 2-methylimidazole and 0.8 mmol thioacetamide. Filter the obtained product and dry it in a vacuum oven at 60 °C for 12 h to obtain the precursor CoFe(acac)3-ZIF-L / S-1.5.

[0035] (3) The precursor CoFe(acac)3-ZIF-L / S-1.5 was pyrolyzed in an argon atmosphere at a heating rate of 5°C / min and kept at 900°C for 2 h to obtain Co-Co 0.7 Fe 0.3 / S@NC-1.5 composite material.

[0036] Comparative Example 1:

[0037] (1) Same as step (1) of Example 1;

[0038] (2) Weigh 1 mmol Co(NO3)2·6H2O and 0.2 mmol ferric citrate and dissolve them in 20 ml water. After stirring, add 1 mmol ZIF-L and stir for 10 min. Then add 20 ml of an aqueous solution of 8 mmol 2-methylimidazole and 0.8 mmol thioacetamide. Filter the obtained product and dry it in a vacuum oven at 60 °C for 12 h to obtain the precursor Co(NMS)Fe-ZIF-L / S.

[0039] (3) The pyrolysis process was the same as in Example 1 to obtain the Co-FeS@NC composite material.

[0040] Comparative Example 2:

[0041] (1) Same as step (1) of Example 1;

[0042] (2) Weigh 1 mmol Co(NO3)2·6H2O and 0.2 mmol K3[Fe(CN)6] and dissolve them in 20 ml water. Stir evenly and then add 1 mmol ZIF-L. Stir for 10 min. Add 8 mmol 2-methylimidazole and 20 ml of 0.8 mmol thioacetamide aqueous solution. Filter the obtained product and dry it in a vacuum oven at 60 °C for 12 h to obtain the precursor CoFe(QHJ)-ZIF-L / S.

[0043] (3) The pyrolysis process was the same as in Example 1 to obtain the Co / S@NC composite material.

[0044] Comparative Example 3:

[0045] 20wt%PtC.

[0046] Test Results

[0047] Figure 1 The SEM showed that after adding surfactant P123, the precursor was in the shape of a 3D hexagonal star;

[0048] Figure 2 The XRD spectrum in the figure shows that the broad peak at about 25° belongs to graphite carbon. When iron acetylacetonate is used as the iron source, Co and Co are obtained after pyrolysis. 0.7 Fe 0.3 The characteristic peaks of the bimetallic alloy and the nitrogen-carbon composite material were successfully formed. When ferric citrate was used as the iron source, Co and FeS were obtained by pyrolysis. However, when potassium ferrocyanide was used as the iron source, only the characteristic peak of Co appeared.

[0049] Figure 3 The LSV curve in shows that the best catalytic activity is achieved when the addition amount of ZIF-L is 1 mmol;

[0050] Figure 4The LSV curves in the composite material Co-Co 0.7 Fe 0.3 / S@NC has the highest half-wave potential (0.9V vs.RHE) and the lowest overpotential (378mV vs.RHE);

[0051] Figure 5 It shows that the composite material Co-Co 0.7 Fe 0.3 The open circuit voltage of the Zn-air battery assembled with S@NC is 1.48 V and the power density reaches 161 mW cm -2 , and there is no obvious decay after 500 cycles (265h). Its performance is better than that of zinc-air batteries with 20wt% commercial PtC and RuO2 as catalysts under the same conditions, indicating that this composite material has broad application prospects in the practical application of zinc-air batteries.

[0052] In summary, the surfactant P123 is used in the present invention to make ZIF present a regular 3D hexagonal star shape. By regulating the iron source, it is found that the metal source can affect the types of substances derived from ZIF materials. The obtained Co-Co 0.7 Fe 0.3 Due to the synergistic effect between the alloy and the heteroatom-doped carbon substrate, the S@NC composite material has excellent oxygen reduction and oxygen evolution performance under alkaline conditions. The zinc-air battery assembled with it as the air cathode also shows good cycle stability, which has certain practical application potential.

[0053] The above contents are only preferred examples of the present invention and are not limitations on the embodiments of the present invention. Any other equivalent changes, modifications, evolutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a ZIF-derived composite bifunctional electrocatalytic material, characterized in that: The aqueous solution of zinc nitrate and dimethylimidazole is stirred at room temperature to obtain ZIF-L, and then different iron sources and heteroatom doping are added to form a precursor, and finally the final product is obtained by high-temperature pyrolysis. The specific steps are as follows: (1) dissolving zinc nitrate in water to obtain solution A, dissolving 2-methylimidazole and surfactant P123 in water to obtain solution B, mixing A and B, and filtering the obtained precipitate, washing, and drying to obtain ZIF-L; (2) adding cobalt nitrate and ferric acetylacetonate to water and stirring evenly, adding ZIF-L obtained in step (1) and stirring for 10 min, then adding a mixed solution of 2-methylimidazole and thioacetamide, stirring, filtering, washing, and drying to obtain a CoFe(acac)3-ZIF-L / S precursor; (3) The obtained precursor is pyrolyzed under an inert atmosphere to obtain the final composite material Co-Co 0.7 Fe 0.3 / S@NC.

2. The method according to claim 1, characterized in that In step (1), the molar ratio of zinc nitrate to 2-methylimidazole is 2:16, and the molar ratio of P123 to zinc nitrate is 0.0005-0.002:1, preferably 0.001:

1.

3. The method according to claim 1, characterized in that The molar ratio of cobalt nitrate to ferric acetylacetonate in step (2) is 1:(0.1-0.3), preferably 1:0.2, the molar ratio of ZIF-L to cobalt nitrate is (0.5-2):1, preferably 1-1.5:1, the molar ratio of cobalt nitrate to 2-methylimidazole is 1:8, and the molar ratio of cobalt nitrate to thioacetamide is 1:0.

8.

4. The method according to claim 1, characterized in that The stirring time in step (1) and step (2) is 4 hours.

5. The method according to claim 1, characterized in that The pyrolysis temperature in step (3) is 900° C. and the holding time is 2 h. The inert atmosphere in step (3) is argon.

6. A ZIF-derived composite bifunctional electrocatalytic material prepared according to the method of any one of claims 1 to 5.

7. Use of the ZIF-derived composite bifunctional electrocatalytic material prepared by the method according to any one of claims 1 to 5 as a cathode catalyst for preparing a working electrode of a zinc-air battery.

8. The use according to claim 7, for electrocatalytic reduction reaction of O2 and H2O and precipitation of O2.

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