Bifunctional catalyst, preparation method and application thereof

Abstract

The present application relates to a bifunctional catalyst, a preparation method thereof and an application. The method includes: S1. Providing a metal precursor, a metal salt solution, a polymer and an organic solvent. Among them, the metal precursor and the metal salt solution contain cobalt element and manganese element, and the cobalt element and manganese element in the metal precursor and the metal salt solution have the same molar ratio; S2. Dissolving the metal precursor in an organic solution containing a polymer and an organic solvent, and stirring to obtain a precursor solution; S3. Performing electrospinning treatment on the precursor solution to obtain a nanofiber membrane; S4. Adding the nanofiber membrane into the metal salt solution to in-situ grow MOFs; S5. Pyrolyzing and activating the nanofiber membrane grown with MOFs to obtain a Co / Co2Mn3O8 carbon fiber catalyst. The bifunctional catalyst obtained by this method can not only be used as a stable support carrier but also provide effective electron conduction. Moreover, it has the characteristics of ORR / OER bifunctional catalysis and can be applied to zinc-air batteries.

Description

Technical Field

[0001] The present application relates to a bifunctional catalyst, a preparation method and application thereof, and belongs to the technical field of zinc-air batteries. Background Art

[0002] As one of the renewable energy devices, rechargeable zinc-air battery has become one of the ideal candidates for the new generation of energy due to its inherent safety, low cost and high energy density. Its charging and discharging process involves two important catalytic processes, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), respectively. Due to the complex four-electron transfer pathways of OER and ORR, they usually show slow kinetics and require higher overpotentials to drive the catalytic reactions. In recent years, researchers have significantly improved the activity of unidirectional oxygen reaction catalysts by increasing the density of active sites, improving intrinsic activity, and optimizing pore structure. However, the active sites in bifunctional catalysts generally include dual-coupled active sites that are effective for each ORR and OER or single bifunctional active sites that can bidirectionally catalyze oxygen reactions. Although decoupling electrocatalysts in ORR or OER alone can improve the energy efficiency and cycle stability of zinc-air batteries, the configuration of bifunctional active sites is structurally complex and may lead to a loss in battery energy density and power density. At present, precious metal catalysts with excellent half-reaction catalytic activity, such as Pt-based catalysts and RuO2 / IrO2 catalysts, do not show ideal bifunctional catalytic properties and do not have economic competitive advantages. Therefore, the lack of ORR / OER bifunctional catalysts is still an important factor restricting the large-scale application of rechargeable zinc-air batteries.

[0003] The catalytic reaction mechanism of a single metal active center is relatively simple, which is not conducive to increasing the probability of coupled catalysis, and it is even more difficult to form active sites with ORR / OER dual-functional catalysis. Fortunately, alloys allow the integration of the functions of a single metal and generate unique new functions through intermetallic forces. Therefore, alloy materials are conducive to the generation of multiple active centers and provide active sites with different characteristics for ORR / OER catalytic processes, which have unique structural advantages in achieving ORR / OER dual-functional catalysis.

[0004] Based on the above situation, this application is hereby filed. Summary of the invention

[0005] The purpose of the present invention is to provide a bifunctional catalyst, a preparation method and application thereof, which can not only serve as a stable supporting carrier but also provide effective electron conduction, and has the characteristics of ORR / OER bifunctional catalysis and can be applied to zinc-air batteries.

[0006] In order to achieve the above objectives, this application provides the following technical solutions:

[0007] In a first aspect, the present application provides a method for preparing a bifunctional catalyst, comprising:

[0008] S1. Providing a metal precursor, a metal salt solution, a polymer and an organic solvent, wherein the metal precursor and the metal salt solution contain cobalt and manganese, and the cobalt and manganese elements in the metal precursor and the metal salt solution have the same molar ratio;

[0009] S2, dissolving the metal precursor in an organic solution containing the polymer and an organic solvent, and stirring to obtain a precursor solution;

[0010] S3, subjecting the precursor solution to electrospinning to obtain a nanofiber membrane;

[0011] S4, adding the nanofiber membrane into the metal salt solution to in-situ grow metal organic frameworks (MOFs);

[0012] S5, pyrolyzing and activating the nanofiber membrane grown with the MOFs to obtain Co / Co 2 Mn 3 O 8 Carbon fiber catalyst.

[0013] Through the technical solution of the embodiment of the present application, Co / Co 2 Mn 3 O 8 On the one hand, the unique one-dimensional core-shell structure of carbon fiber catalyst has a larger specific surface area of ​​electrocatalyst, which is conducive to the exposure of active sites and orderly conduction of electrons; on the other hand, Co / Co 2 Mn 3 O 8 The electron transition between metals with different valence states can promote the oxygen electrocatalytic reaction. At the same time, the addition of Mn inhibits the hydrogen peroxide (H 2 O 2 ) is generated, which improves the stability of the catalyst.

[0014] In some possible embodiments, the metal precursor and the metal salt solution further contain zinc element, and the MOFs are Co / Mn / Zn zeolitic imidazolate framework materials (Zeolitic Imidazolate Frameworks, ZIFs), that is, Co / Mn / Zn-ZIF.

[0015] In some possible implementations, in the metal precursor and the metal salt solution, the zinc element has the same molar ratio as the cobalt element and the manganese element.

[0016] In some possible implementations, the metal precursor includes cobalt acetylacetonate, manganese acetylacetonate, and zinc acetylacetonate.

[0017] In some possible embodiments, the preparation method further comprises:

[0018] The pyrolysis-activated material is placed in a protective atmosphere above 900° C. for 1-3 hours.

[0019] Through the technical solution of the embodiment of the present application, heat treatment is carried out in an environment above 900°C, Zn will volatilize to form micropores, and at the same time, MOF particles are evenly distributed on the surface and inside of the nanofibers, and have a good bonding force with them, which effectively reduces the shedding of MOF particles during the reaction process, thereby ensuring the stability of the catalyst in recycling.

[0020] In some possible embodiments, the polymer includes polyacrylonitrile, polyvinyl pyrrolidone and melamine, the polyacrylonitrile, polyvinyl pyrrolidone and melamine have the same mass ratio, and the bifunctional catalyst is Co / Co 2 Mn 3 O 8 Nitrogen-doped carbon fibers (NCFs), namely Co / Co 2 Mn 3 O 8 @NCFs carbon-based composite electrocatalysts.

[0021] In some possible embodiments, the polymer includes polyacrylonitrile and polyvinyl pyrrolidone, the polyacrylonitrile and polyvinyl pyrrolidone have the same mass ratio, and the bifunctional catalyst is Co / Co 2 Mn 3 O 8 Carbon Fibers (CFs) are Co / Co 2 Mn 3 O 8 @CFs carbon-based composite electrocatalyst.

[0022] In some possible implementations, in step S4, adding the nanofiber membrane to the metal salt solution to in-situ grow MOFs comprises:

[0023] The nanofiber membrane is immersed in the imidazole ligand, and then the metal salt solution is added to react to obtain the MOFs.

[0024] In some possible embodiments, the imidazole ligand is an aqueous solution of 2-methylimidazole.

[0025] In some possible implementations, the metal salt solution is a hexahydrate nitrate solution of a metal.

[0026] Through the technical solution of the embodiment of the present application, the in-situ growth method is used to make MOFs grow uniformly, densely and stably on the surface of the nanofiber membrane, so as to obtain a larger specific surface area of ​​the electrocatalyst, greatly expanding the effective reaction area; thereby, the catalyst can not only serve as a stable supporting carrier but also provide effective electron conduction, and its surface shell is conducive to fully exposing the metal active sites. This layered structure promotes the efficient and orderly progress of the catalytic reaction.

[0027] In some possible implementations, in step S5, pyrolysis activation of the nanofiber membrane grown with the MOFs includes:

[0028] The nanofiber membrane grown with the MOFs is placed in a tubular furnace, and the temperature is raised to 250-300° C. at a rate of 2° C. / min under a protective atmosphere for 1-3 hours.

[0029] In a second aspect, the present application provides a bifunctional catalyst prepared according to the preparation method described in the first aspect, wherein the bifunctional catalyst is Co / Co 2 Mn 3 O 8 @NCFs carbon-based composite electrocatalyst or Co / Co 2 Mn 3 O 8 @CFs carbon-based composite electrocatalyst.

[0030] In a third aspect, the present application provides use of the bifunctional catalyst according to the second aspect in the preparation of an air electrode or an air battery.

[0031] In some possible embodiments, the air electrode contains Co / Co 2 Mn 3 O 8 @NCFs as catalyst.

[0032] In some possible embodiments, the air electrode contains Co / Co 2 Mn 3 O 8 @CFs as catalysts.

[0033] In some possible embodiments, the air battery comprises an anode, a cathode and an electrolyte, wherein the cathode comprises Co / Co 2 Mn 3 O 8 @NCFs as catalysts for air electrodes.

[0034] In some possible embodiments, the air battery comprises an anode, a cathode and an electrolyte, wherein the cathode comprises Co / Co 2 Mn 3 O 8 @CFs as air electrode catalyst.

[0035] In some possible implementations, the air battery further includes a battery housing.

[0036] In some possible implementations, the battery housing is made of PMMA material, the anode material is a polished zinc sheet, and the electrolyte is KOH and Zn(Ac) 2 Mix the solution.

[0037] Through the technical solution of the embodiment of the present application, Co / Co 2 Mn 3 O 8 @NCFs as cathode electrocatalyst for rechargeable zinc-air batteries have ORR / OER bifunctional catalytic properties and exhibit high peak power density (118.19 mW / cm 2 ), high energy density (968.10Wh / kg) and excellent cycle stability (at 10mA / cm 2 Stable cycle charge and discharge for 120h).

[0038] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic flow chart of a method for preparing a bifunctional catalyst according to an embodiment of the present application;

[0040] Figure 2 This is a schematic structural framework diagram of an air battery shown in an embodiment of the present application;

[0041] Figure 3 This is the surface morphology of Co / Mn / Zn-ZIFs@PAN / PVP / ML shown in Example 1 of the present application;

[0042] Figure 4 The Co / Co shown in Example 1 of this application 2 Mn 3 O 8 @Surface morphology of NCFs;

[0043] Figure 5 and Figure 6 The Co / Co shown in Example 1 of this application2 Mn 3 O 8 High-resolution transmission images of @NCFs;

[0044] Figure 7 This is the surface morphology of Co / Mn / Zn-ZIFs@PAN / PVP shown in Example 2 of the present application;

[0045] Figure 8 The Co / Co shown in Example 2 of this application 2 Mn 3 O 8 @Surface morphology of CFs;

[0046] Fig. 9 This is the surface morphology of Co / Zn-ZIFs@PAN / PVP shown in Example 3 of the present application;

[0047] Fig.10 This is the surface morphology of Co@CFs shown in Example 3 of the present application;

[0048] Fig.11 This is the surface morphology of Mn / Zn-ZIFs@PAN / PVP shown in Example 4 of the present application;

[0049] Fig.12 This is the surface morphology of MnO@CFs shown in Example 4 of the present application;

[0050] Fig.13 X-ray diffraction patterns of the carbon-based composite electrocatalysts shown in Examples 1 to 4 of the present application;

[0051] Fig.14 The X-ray photoelectron spectrum of Co2p corresponding to the carbon-based composite electrocatalyst shown in Examples 1 to 3 of the present application;

[0052] Fig.15 The X-ray photoelectron energy spectrum of the carbon-based composite electrocatalyst corresponding to Mn2p shown in Examples 1, 3, and 4 of the present application;

[0053] Fig.16 The total polarization curve diagram corresponding to the carbon-based composite electrocatalyst shown in Examples 1 to 4 of the present application;

[0054] Fig.17 Polarization curves of the carbon-based composite catalyst and the commercial Pt / C catalyst shown in Example 1 of the present application before and after 5000 CV test cycles;

[0055] Fig.18 Polarization curves of the carbon-based composite electrocatalysts shown in Examples 2 and 3 of the present application before and after 5000 CV test cycles;

[0056] Fig.19 is the electron transfer number n and H of the carbon-based composite electrocatalyst and the commercial Pt / C catalyst shown in Examples 1 to 4 of the present application 2 O 2 Schematic diagram of yield;

[0057] Fig. 20 The Co / Co shown in Example 1 of this application 2 Mn 3 O 8 @NCFs catalyst and commercial Pt / C catalyst corresponding to the discharge polarization and power density curve of zinc-air battery;

[0058] Fig.21 The Co / Co shown in Example 1 of this application 2 Mn 3 O 8 Schematic diagram of the specific capacity of Zn-air batteries corresponding to @NCFs catalysts and commercial Pt / C catalysts; the inset is a photo of the corresponding series-powered diode;

[0059] Fig. 22 The Co / Co shown in Example 1 of this application 2 Mn 3 O 8 @NCFs catalyst and commercial Pt / C catalyst for Zn-air battery at 10 mA / cm 2 Constant current charge-discharge cycle curve at current density. DETAILED DESCRIPTION

[0060] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0061] It should be noted that the terms “upper”, “lower”, “left”, “right”, “inner”, “outer”, etc. in the present invention are only used to illustrate the present invention with reference to the drawings and are not intended to be limiting terms.

[0062] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units that are inherent to these processes, methods, products or devices. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances. In addition, in the description of the present application, unless otherwise specified, "multiple" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships can exist, for example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the objects associated before and after are in an "or" relationship.

[0063] The terms "first", "second", "third", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0064] On the one hand, the present application provides a method for preparing a bifunctional catalyst. Figure 1 A schematic flow chart of the preparation method is shown.

[0065] like Figure 1 As shown, the preparation method comprises the following steps:

[0066] S1. Providing a metal precursor, a metal salt solution, a polymer and an organic solvent, wherein the metal precursor and the metal salt solution contain cobalt and manganese, and the cobalt and manganese elements in the metal precursor and the metal salt solution have the same molar ratio;

[0067] S2, dissolving the metal precursor in an organic solution containing the polymer and an organic solvent, and stirring to obtain a precursor solution;

[0068] S3, subjecting the precursor solution to electrospinning to obtain a nanofiber membrane;

[0069] S4, adding the nanofiber membrane to the metal salt solution to grow MOFs in situ;

[0070] S5, pyrolyzing and activating the nanofiber membrane grown with the MOFs to obtain Co / Co 2 Mn 3 O 8 Carbon fiber catalyst.

[0071] Specifically, in the embodiment of the present application, the metal precursor and the metal salt solution also contain zinc element, and the MOFs is Co / Mn / Zn-ZIF.

[0072] Optionally, in an embodiment of the present application, in the metal precursor and the metal salt solution, the zinc element has the same molar ratio as the cobalt element and the manganese element.

[0073] As an example but not limitation, in the embodiment of the present application, the metal precursor includes cobalt acetylacetonate, manganese acetylacetonate and zinc acetylacetonate.

[0074] Specifically, the preparation method further comprises: placing the pyrolyzed activated material in a protective atmosphere at a temperature above 900° C. for 1-3 hours. The material is heat treated in this process, so that Zn can be volatilized to form micropores.

[0075] Optionally, in an embodiment of the present application, the polymer includes polyacrylonitrile, polyvinyl pyrrolidone and melamine, the polyacrylonitrile, polyvinyl pyrrolidone and melamine have the same mass ratio, and the bifunctional catalyst is Co / Co 2 Mn 3 O 8 @NCFs carbon-based composite electrocatalysts.

[0076] Optionally, in an embodiment of the present application, the polymer includes polyacrylonitrile and polyvinyl pyrrolidone, the polyacrylonitrile and polyvinyl pyrrolidone have the same mass ratio, and the bifunctional catalyst is Co / Co 2 Mn 3 O 8 @CFs carbon-based composite electrocatalyst.

[0077] In step S4, the nanofiber membrane is added to the metal salt solution, and the in-situ growth of MOFs includes: immersing the nanofiber membrane in an imidazole ligand, and then adding the metal salt solution to react to obtain the MOFs. The in-situ growth method is used to make MOFs grow uniformly, densely and stably on the surface of the nanofiber membrane to obtain a larger specific surface area of ​​the electrocatalyst, greatly expanding the effective reaction area, and facilitating the exposure of more metal active sites.

[0078] Optionally, in an embodiment of the present application, the imidazole ligand is an aqueous solution of 2-methylimidazole.

[0079] Optionally, in an embodiment of the present application, the metal salt solution is a hexahydrate nitrate solution of a metal.

[0080] In step S5, the pyrolysis activation of the nanofiber membrane grown with the MOFs includes: placing the nanofiber membrane grown with the MOFs in a tubular furnace, heating the temperature to 250-300° C. at a rate of 2° C. / min for 1-3 hours under a protective atmosphere.

[0081] Through the technical solution of the embodiment of the present application, the bifunctional catalyst prepared by the above method can be used in an air electrode or an air battery.

[0082] By way of example and not limitation, Figure 2 The Co / Co 2 Mn 3 O 8 NCFs as cathode electrocatalysts for zinc-air batteries.

[0083] like Figure 2 As shown, the zinc-air battery includes an anode 101, a cathode 102 and an electrolyte 103. As an example but not a limitation, the material of the anode 101 is a polished zinc sheet, and the electrocatalyst material of the cathode 102 is Co / Co 2 Mn 3 O 8 @NCFs, electrolyte 103 is KOH and Zn(Ac) 2 Mix the solution.

[0084] Optionally, the zinc-air battery can be used in sustainable energy products, such as new energy vehicles.

[0085] Furthermore, when applied in sustainable energy products, the zinc-air battery may further include a battery casing; and, as an example but not a limitation, the battery casing may be made of PMMA material.

[0086] The present application will be further described in detail below in conjunction with specific embodiments.

[0087] Embodiment 1

[0088] Co / Co 2 Mn 3 O 8 Preparation of @NCFs

[0089] First, 0.8 g of polyacrylonitrile (PAN), 0.8 g of polyvinyl pyrrolidone (PVP) and 0.8 g of melamine (ML) were added to 10 mL of DMF solution and stirred for 12 hours. Then 1 mmol of cobalt acetylacetonate, 1 mmol of manganese acetylacetonate and 1 mmol of zinc acetylacetonate were added to the above solution, ultrasonically dispersed for 30 minutes and stirred for more than 8 hours to obtain a precursor solution.

[0090] A cobalt acetylacetonate / manganese acetylacetonate / zinc acetylacetonate / PAN / PVP / ML (Co / Mn / Zn-PAN / PVP / ML) composite nanofiber membrane was prepared by a single-needle electrospinning device. In this embodiment, single-needle electrospinning is an existing conventional technology, and its process is not described in detail here. The relevant electrospinning parameters are as follows: voltage 16kV, spinning solution flow rate 0.6mL / h, receiving distance 16cm, temperature 25°C, humidity 50%. Finally, the electrospun composite nanofiber membrane was dried at 60°C for 8 hours.

[0091] 150 mg of the composite nanofiber membrane was first immersed in 50 mL of an aqueous solution containing 0.1 mol / L 2-methylimidazole for 2 minutes, and then 50 mL of a mixed aqueous solution of 0.8 mol / L cobalt nitrate hexahydrate / manganese nitrate hexahydrate / zinc nitrate hexahydrate (molar ratio of 1:1:1) was added. After shaking for 5 minutes, the mixture was allowed to stand for 1 hour. After being taken out, it was washed three times with deionized water and dried at 60°C for 12 hours. It was marked as Co / Mn / Zn-ZIFs@PAN / PVP / ML.

[0092] Figure 3 The surface morphology of Co / Mn / Zn-ZIFs@PAN / PVP / ML of this embodiment is shown. It can be seen from the figure that the multi-metal ZIFs material on the surface of Co / Mn / Zn-ZIFs@PAN / PVP / ML exhibits a uniform nanosheet structure and densely wraps the fiber surface.

[0093] Finally, Co / Mn / Zn-ZIFs@PAN / PVP / ML was placed in a tube furnace under N 2 The temperature was raised to 280°C at a rate of 2°C / min and kept for 2 hours, and then raised to 900°C at a rate of 5°C / min and kept for 2 hours to obtain Co / Co 2 Mn 3 O 8 @NCFs carbon-based composite electrocatalysts.

[0094] Figure 4 The Co / Co ratio of this embodiment is shown. 2 Mn 3 O 8 @NCFs surface morphology, as shown in the figure, the Co / Co2 Mn 3 O 8 @NCFs has a unique one-dimensional core-shell structure, and a large number of nanoparticles are evenly distributed on the surface of the nanofibers. Analysis shows that the particles are Co / Co generated by the combination of cobalt and manganese. 2 Mn 3 O 8 alloy.

[0095] Figure 5 and Figure 6 The Co / Co ratio of this embodiment is shown. 2 Mn 3 O 8 High-resolution transmission images of @NCFs. See Figure 5 , Co in the image 2 Mn 3 O 8 The (022) and (013) planes of Co 2 Mn 3 O 8 In addition, Figure 6 It can be seen that Co / Co 2 Mn 3 O 8 There are also many long-range ordered Co metal crystals in @NCFs, most of which are distributed at the edges of the nanoparticles. This is because N doping forms more edge defects in the carbon fiber matrix, which can easily capture metal elements and form Co-Nx structural sites with high activity.

[0096] Embodiment 2

[0097] Co / Co 2 Mn 3 O 8 Preparation of @CFs

[0098] First, 0.8 g of polyacrylonitrile (PAN) and 0.8 g of polyvinyl pyrrolidone (PVP) were added to 10 mL of DMF solution and stirred for 12 hours. Then 1 mmol of cobalt acetylacetonate, 1 mmol of manganese acetylacetonate and 1 mmol of zinc acetylacetonate were added to the above solution, ultrasonically dispersed for 30 minutes and stirred for more than 8 hours to obtain a precursor solution.

[0099] A cobalt acetylacetonate / manganese acetylacetonate / zinc acetylacetonate / PAN / PVP (Co / Mn / Zn-PAN / PVP) composite nanofiber membrane was prepared by a single-needle electrospinning device. In this embodiment, single-needle electrospinning is an existing conventional technology, and its process is not described in detail here. The relevant electrospinning parameters are as follows: voltage 16kV, spinning solution flow rate 0.6mL / h, receiving distance 16cm, temperature 25°C, humidity 50%. Finally, the electrospun composite nanofiber membrane was dried at 60°C for 8 hours.

[0100] 150 mg of the composite nanofiber membrane was first immersed in 50 mL of an aqueous solution containing 0.1 mol / L 2-methylimidazole for 2 minutes, and then 50 mL of a mixed aqueous solution of 0.8 mol / L cobalt nitrate hexahydrate / manganese nitrate hexahydrate / zinc nitrate hexahydrate (molar ratio of 1:1:1) was added. After shaking for 5 minutes, the mixture was allowed to stand for 1 hour. After being taken out, it was washed three times with deionized water and dried at 60°C for 12 hours. It was marked as Co / Mn / Zn-ZIFs@PAN / PVP.

[0101] Figure 7 The surface morphology of Co / Mn / Zn-ZIFs@PAN / PVP of this embodiment is shown. It can be seen from the figure that the multi-metal ZIFs material on the surface of Co / Mn / Zn-ZIFs@PAN / PVP exhibits a uniform nanosheet structure and densely wraps the fiber surface.

[0102] Finally, Co / Mn / Zn-ZIFs@PAN / PVP was placed in a tube furnace under N 2 The temperature was raised to 280°C at a rate of 2°C / min and kept for 2 hours, and then raised to 900°C at a rate of 5°C / min and kept for 2 hours to obtain Co / Co 2 Mn 3 O 8 @CFs carbon-based composite electrocatalyst.

[0103] Figure 8 The Co / Co ratio of this embodiment is shown. 2 Mn 3 O 8 @CFs surface morphology, as shown in the figure, the Co / Co 2 Mn 3 O 8 @CFs has a unique one-dimensional core-shell structure, and a large number of nanoparticles are evenly distributed on the surface of the nanofibers. Analysis shows that the particles are Co / Co generated by the combination of cobalt and manganese. 2 Mn 3 O 8 alloy.

[0104] Embodiment 3

[0105] Preparation of Co@CFs

[0106] First, 0.8 g of polyacrylonitrile (PAN) and 0.8 g of polyvinyl pyrrolidone (PVP) were added to 10 mL of DMF solution and stirred for 12 hours. Then 1 mmol of cobalt acetylacetonate and 1 mmol of zinc acetylacetonate were added to the above solution, ultrasonically dispersed for 30 minutes and stirred for more than 8 hours to obtain a precursor solution.

[0107] A cobalt acetylacetonate / zinc acetylacetonate / PAN / PVP (Co / Zn-PAN / PVP) composite nanofiber membrane was prepared by a single-needle electrospinning device. In this embodiment, single-needle electrospinning is an existing conventional technology, and its process is not described in detail here. The relevant electrospinning parameters are as follows: voltage 16kV, spinning solution flow rate 0.6mL / h, receiving distance 16cm, temperature 25°C, humidity 50%. Finally, the electrospun composite nanofiber membrane was dried at 60°C for 8 hours.

[0108] 150 mg of the composite nanofiber membrane was first immersed in 50 mL of an aqueous solution containing 0.1 mol / L 2-methylimidazole for 2 minutes, and then 50 mL of a mixed aqueous solution of 0.8 mol / L cobalt nitrate hexahydrate / zinc nitrate hexahydrate (molar ratio of 1:1) was added. After shaking for 5 minutes, it was allowed to stand for 1 hour. After being taken out, it was washed three times with deionized water and dried at 60°C for 12 hours. It was marked as Co / Zn-ZIFs@PAN / PVP.

[0109] Fig. 9 The surface morphology of Co / Zn-ZIFs@PAN / PVP of this embodiment is shown. It can be seen from the figure that the multi-metal ZIFs material on the surface of Co / Zn-ZIFs@PAN / PVP exhibits a uniform nanosheet structure and wraps the fiber surface.

[0110] In this embodiment, compared with Embodiments 1 and 2, the amount of ZIFs material is relatively less and the density is relatively smaller.

[0111] Finally, Co / Zn-ZIFs@PAN / PVP was placed in a tube furnace under N 2 The temperature was raised to 280°C at a rate of 2°C / min in an atmosphere and kept for 2 hours, and then raised to 900°C at a rate of 5°C / min and kept for 2 hours to obtain the Co@CFs carbon-based composite electrocatalyst.

[0112] Fig.10 The surface morphology of Co@CFs of this embodiment is shown. It can be seen from the figure that the Co@CFs has a small amount of nanoparticles distributed on the surface of the nanofibers, and the number and density of nanoparticles are significantly lower than those of the materials prepared in Implementation 1 and Implementation 2.

[0113] Embodiment 4

[0114] Preparation of MnO@CFs

[0115] First, 0.8 g of polyacrylonitrile (PAN) and 0.8 g of polyvinyl pyrrolidone (PVP) were added to 10 mL of DMF solution and stirred for 12 hours. Then 1 mmol of manganese acetylacetonate and 1 mmol of zinc acetylacetonate were added to the above solution, ultrasonically dispersed for 30 minutes and stirred for more than 8 hours to obtain a precursor solution.

[0116] A composite nanofiber membrane of manganese acetylacetonate / zinc acetylacetonate / PAN / PVP (Mn / Zn-PAN / PVP) was prepared by a single-needle electrospinning device. In this embodiment, single-needle electrospinning is an existing conventional technology, and its process is not described in detail here. The relevant electrospinning parameters are as follows: voltage 16kV, spinning solution flow rate 0.6mL / h, receiving distance 16cm, temperature 25°C, humidity 50%. Finally, the electrospun composite nanofiber membrane was dried at 60°C for 8 hours.

[0117] 150 mg of the composite nanofiber membrane was first immersed in 50 mL of an aqueous solution containing 0.1 mol / L 2-methylimidazole for 2 minutes, and then 50 mL of a mixed aqueous solution of 0.8 mol / L manganese nitrate hexahydrate / zinc nitrate hexahydrate (molar ratio of 1:1) was added. After shaking for 5 minutes, it was allowed to stand for 1 hour. After being taken out, it was washed three times with deionized water and dried at 60°C for 12 hours. It was marked as Mn / Zn-ZIFs@PAN / PVP.

[0118] Fig.11 The surface morphology of Mn / Zn-ZIFs@PAN / PVP of this embodiment is shown. It can be seen from the figure that the multi-metal ZIFs material on the surface of Mn / Zn-ZIFs@PAN / PVP exhibits a uniform nanosheet structure and densely wraps the fiber surface.

[0119] Finally, Mn / Zn-ZIFs@PAN / PVP was placed in a tube furnace under N 2 The temperature was raised to 280°C at a rate of 2°C / min in an atmosphere and kept for 2 hours, and then raised to 900°C at a rate of 5°C / min and kept for 2 hours to obtain a MnO@CFs carbon-based composite electrocatalyst.

[0120] Fig.12 The surface morphology of MnO@CFs of this embodiment is shown. It can be seen from the figure that after carbonization, Mn / Zn-ZIFs@PAN / PVP exhibits irregular polyhedral particles. This morphological change is mainly due to the change in the structural phase caused by the uneven growth of grains due to the aggregation of microcrystals of primary nanoparticles at high temperature.

[0121] also, Fig.13 The X-ray diffraction patterns of the carbon-based composite electrocatalysts of Examples 1 to 4 are shown. 2 Mn 3 O 8 and the presence of MnO crystalline phase.

[0122] Fig.14 The X-ray photoelectron spectra of Co2p corresponding to the carbon-based composite electrocatalysts of embodiments 1 to 3 are shown. The high-resolution fine spectrum of Co2p shows that the cobalt elements in the samples mainly include Co 0 、Co 2+ Two valence states, Co 0 Among them, unlike Co@CFs, Co / Co 2 Mn 3 O 8 @CFs and Co / Co 2 Mn 3 O 8 @NCFs in Co 2+ Has a significantly higher proportion, and Co 2+ The corresponding binding energy peak position shifts toward the high energy level, which is due to the presence of Co in the alloy. 2 Mn 3 O 8 or Co-Nx, and Co 2 Mn 3 O 8 The electrons in Co 2+ To Mn 4+ The transition causes the transfer of electrons between metals of different valence states, resulting in charge redistribution, which is beneficial to improving the adsorption of oxygen and forming OER / ORR dual-functional active centers.

[0123] Fig.15 The X-ray photoelectron spectra of the carbon-based composite electrocatalysts of Examples 1, 3, and 4 corresponding to Mn2p are shown. The high-resolution fine spectrum of Mn2p shows that the manganese element in MnO@CFs is mainly Mn 2+ , while Co / Co 2 Mn 3 O 8 @CFs and Co / Co 2 Mn 3 O 8 The manganese element in @NCFs is mainly Mn 4+ .

[0124] Fig.16 The total polarization curves of the carbon-based composite electrocatalysts of Examples 1 to 4 are shown. Fig.16, Table 1 is shown for demonstrating the bifunctional catalytic activity of the carbon-based composite electrocatalysts of Examples 1 to 4. Among them, the current density in OER is 10 mA / cm 2 The potential E J＝10 The half-wave potential E 1 / 2 The difference ΔE is used to evaluate the bifunctional catalytic activity of the sample. The smaller the ΔE, the better the OER / ORR bifunctional catalytic activity of the sample. Fig.16 The total OER / ORR LSV curves of the samples are shown, and the corresponding ΔE is calculated. Fig.16 As shown in Table 1, Co / Co 2 Mn 3 O 8 The ΔE of the @NCFs sample is the smallest, and the corresponding OER / ORR bifunctional catalytic activity is also the best; Co / Co 2 Mn 3 O 8 The ΔE of @CFs samples is only greater than that of Co / Co 2 Mn 3 O 8 @NCFs samples, their corresponding OER / ORR bifunctional catalytic activity is also stronger than that of other samples.

[0125] Table 1 Bifunctional activity of carbon-based composite electrocatalysts in Examples 1 to 4

[0126] sample <![CDATA[E 1 / 2 (V vs RHE)]]> <![CDATA[E J＝10 (V vs RHE)]]> ΔE(V) Pt / C 0.83 1.695 0.865 <![CDATA[Co / Co 2 Mn 3 O 8 @NCFs]]> 0.826 1.612 0.786 <![CDATA[Co / Co 2 Mn 3 O 8 @CFs]]> 0.823 1.65 0.827 Co@CFs 0.81 1.689 0.879 MnO@CFs 0.78 1.68 0.90

[0127] The present application also evaluates the stability of the catalyst by measuring the LSV curve of the test sample before and after 5000 CV cycles and using the attenuation of the half-wave potential. Fig.17 The Co / Co ratio in Example 1 is shown. 2 Mn 3 O 8 Polarization curves of @NCFs samples and commercial Pt / C catalysts before and after 5000 cycles of CV test. Fig.18 The polarization curves of the catalyst samples in Examples 2 and 3 before and after 5000 CV test cycles are shown. Fig.19 The electron transfer number n and H of the carbon-based composite electrocatalysts of Examples 1 to 4 and the commercial Pt / C catalyst are shown. 2 O 2 Yield

[0128] Depend on Fig.17 It can be seen that after 5000 cycles, Co / Co 2 Mn 3 O 8 The half-wave potential of @NCFs decayed by only 25 mV, which was significantly less than the 58 mV of Pt / C catalyst, indicating that the Co / Co 2 Mn3 O 8 @NCFs catalyst has good stability. Fig.18 It can be seen that Co / Co 2 Mn 3 O 8 The stability of @CFs is also greatly improved compared to Co@CFs. On the one hand, the surface of the alloy particles is protected by the graphite carbon layer, which avoids the Co / Co 2 Mn 3 O 8 On the other hand, the presence of the alloy promotes the occurrence of the 4-electron transfer path, which fully reduces the oxygen and reduces the H 2 O 2 The generation of oxidative corrosion reduces the probability of the catalyst being oxidized. Fig.19 shown.

[0129] This application measures the implementation of a Co / Co 2 Mn 3 O 8 The open circuit voltage of the Zn-air battery corresponding to the NCFs catalyst is 1.45 V, which is slightly lower than the equilibrium potential of the Zn-air battery (1.65 V). Fig. 20 The Co / Co ratio in Example 1 is shown. 2 Mn 3 O 8 @NCFs catalyst and commercial Pt / C catalyst corresponding to the discharge polarization and power density curve of zinc-air battery. 2 Mn 3 O 8 The @NCFs battery exhibited a maximum power density of 118.19 mW / cm2, which was also higher than that of the battery corresponding to the Pt / C catalyst (63.88 mW / cm2).

[0130] at the same time, Fig.21 The Co / Co ratio in Example 1 is shown. 2 Mn 3 O 8 @NCFs catalyst and commercial Pt / C catalyst corresponding to the specific capacity of zinc-air battery. As shown in the figure, using Co / Co 2 Mn 3 O 8 The battery assembled with @NCFs catalyst also exhibited a specific capacity of 841.83 mAh / g (corresponding to an energy density of 968.10 Wh / kg) when discharged at a current density of 10 mA / cm2, which is higher than the 748.52 mAh / g of Pt / C (corresponding to an energy density of 830.86 Wh / kg), normalized to the mass of zinc consumed.

[0131] More importantly, Fig. 22 The Co / Co ratio in Example 1 is shown. 2 Mn 3 O 8 @NCFs catalyst and commercial Pt / C catalyst corresponding to the constant current charge-discharge cycle curve of zinc-air battery at a current density of 10mA / cm2. 2 Mn 3 O 8 The battery with @NCFs catalyst can stably charge and discharge for 120h (the voltage difference increased by 0.1V after 540 cycles), while the battery with Pt / c catalyst has a charge and discharge voltage difference increase of 0.4V after 340 cycles (only 75h), indicating that Co / Co 2 Mn 3 O 8 @NCFs catalyst batteries have good charge and discharge cycle stability.

[0132] In addition, the inventors also found that the tandem-based Co / Co 2 Mn 3 O 8 @NCFs' zinc-air battery can provide enough power to illuminate a red LED ( Fig.21 Inset), showing the Co / Co 2 Mn 3 O 8 @NCFs catalysts have great potential in practical energy applications.

[0133] In summary, through the technical solution of the embodiment of the present application, Co / Co 2 Mn 3 O 8 @NCFs as cathode electrocatalyst for rechargeable zinc-air batteries have ORR / OER bifunctional catalytic properties and exhibit high peak power density (118.19 mW / cm 2 ), high energy density (968.10Wh / kg) and excellent cycle stability (at 10mA / cm 2 Stable cycle charge and discharge for 120h).

[0134] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a bifunctional catalyst, characterized in that: include: S1. Providing a metal precursor, a metal salt solution, a polymer and an organic solvent, wherein the metal precursor and the metal salt solution contain cobalt and manganese, and the cobalt and manganese in the metal precursor and the metal salt solution have the same molar ratio; S2, dissolving the metal precursor in an organic solution containing the polymer and an organic solvent, and stirring to obtain a precursor solution; S3, subjecting the precursor solution to electrospinning to obtain a nanofiber membrane; S4, adding the nanofiber membrane to the metal salt solution to grow MOFs in situ; S5, pyrolyzing and activating the nanofiber membrane on which the MOFs are grown to obtain a Co / Co2Mn3O8 carbon fiber catalyst; wherein, In step S4, the step of adding the nanofiber membrane to the metal salt solution to in-situ grow MOFs comprises: The nanofiber membrane is immersed in the imidazole ligand, and then the metal salt solution is added to react to obtain the MOFs, which present a uniform nanosheet structure and densely wrap the fiber surface.

2. The method for preparing a bifunctional catalyst according to claim 1, characterized in that: The metal precursor and the metal salt solution also contain zinc element, and the MOFs are Co / Mn / Zn-ZIFs.

3. The method for preparing a bifunctional catalyst as claimed in claim 2, characterized in that: In the metal precursor and the metal salt solution, the zinc element has the same molar ratio as the cobalt element and the manganese element; and / or the metal precursor includes cobalt acetylacetonate, manganese acetylacetonate and zinc acetylacetonate.

4. The method for preparing a bifunctional catalyst as claimed in claim 3, characterized in that: The preparation method further comprises: The pyrolysis-activated material is placed in a protective atmosphere above 900° C. for 1-3 hours.

5. The method for preparing a bifunctional catalyst according to claim 1 or 4, characterized in that: The polymer comprises polyacrylonitrile, polyvinyl pyrrolidone and melamine, wherein the polyacrylonitrile, polyvinyl pyrrolidone and melamine have the same mass ratio, and the bifunctional catalyst is a Co / Co2Mn3O8@NCFs carbon-based composite electrocatalyst; or, The polymer includes polyacrylonitrile and polyvinyl pyrrolidone, the polyacrylonitrile and polyvinyl pyrrolidone have the same mass ratio, and the bifunctional catalyst is a Co / Co2Mn3O8@CFs carbon-based composite electrocatalyst.

6. The method for preparing a bifunctional catalyst according to claim 5, characterized in that: The imidazole ligand is a 2-methylimidazole aqueous solution; and / or the metal salt solution is a hexahydrate nitrate solution of a metal.

7. The method for preparing a bifunctional catalyst according to claim 1, characterized in that: In step S5, the pyrolysis activation of the nanofiber membrane grown with the MOFs comprises: The nanofiber membrane grown with the MOFs is placed in a tubular furnace, and the temperature is raised to 250-300° C. at a rate of 2° C. / min under a protective atmosphere for 1-3 hours.

8. The bifunctional catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The bifunctional catalyst is a Co / Co2Mn3O8@NCFs carbon-based composite electrocatalyst or a Co / Co2Mn3O8@CFs carbon-based composite electrocatalyst.

9. Use of the bifunctional catalyst according to claim 8 in the preparation of an air electrode or an air battery.

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