A m-n-c monatomic catalyst coated with m-os2 and application thereof in lithium-air battery

Abstract

The application discloses a kind of MoS2-coated porous M-N-C single-atom catalyst and its application in lithium-air battery, first by chelating agent transition metal ion chelation and anchor on porous carbon carrier, then mixed with nitrogen source precursor and calcined, obtain with porous nitrogen-doped carbon as carrier, load transition metal single atom M Material, again by hydrothermal sulfidation method and high-temperature calcination layer MoS2 Nanometer sheet, obtain target catalyst material.The composite material obtained by the application has higher mass transfer efficiency, higher oxygen reduction activity and stability in acidic and alkaline medium, and has lower overvoltage, high discharge specific capacity and excellent cycle performance when used as lithium-air battery catalyst, and has good research prospect.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation, specifically to a MoS2-coated porous MNC single-atom catalyst and its application in lithium-air batteries. Background Technology

[0002] Electric vehicles (EVs) have broad application prospects as they can reduce greenhouse gas emissions and the use of petroleum-derived fuels. However, the lithium-ion batteries commonly used in existing EVs suffer from insufficient energy density to meet demand. Rechargeable lithium-air batteries offer performance far exceeding that of traditional lithium-ion batteries and, due to their ultra-high energy density, hold the promise of becoming the "star of tomorrow" in the EV field. However, lithium-air batteries also face numerous challenges, such as low cycle performance, high overvoltage, and electrolyte instability. In non-aqueous lithium-air batteries, the oxidation reaction (ORR, O2 + 2Li)... + +2e - →Li2O2) and redox reactions (OER, Li2O2→O2+2Li + +2e - Both play a crucial role in the kinetics, but both are subject to limitations. For these reasons, developing an effective electrocatalyst is urgently needed for the development of lithium-air batteries.

[0003] Transition metal single-atom nitrogen-coordinated carbon-based (MNC, where M is one or two transition metals such as Fe, Co, and Ni) materials have been widely prepared and have exhibited high catalytic activity and unique selectivity in electrocatalytic applications. Existing MNC materials are mostly prepared using MOF-derived single-atom catalysts, but these catalysts generally suffer from unstable active sites. Therefore, researching new processes for preparing MNC materials is of great significance.

[0004] Meanwhile, designing a protective layer that can confine and protect the active sites of the catalyst to maintain its stability and prevent detachment and aggregation, while also possessing excellent catalytic activity and the ability to synergistically catalyze with MNCs, is also an effective way to solve the above problems. Molybdenum disulfide (MoS2) is a typical two-dimensional layered compound of transition metals with a graphene-like layered structure. Its S-Mo-S "sandwich" structure determines that the bond energy between adjacent sulfur atom layers is weak and the surface energy is low, while the binding energy of the S-Mo-S bond is very strong. The bond valence of the Mo and S atoms at the edges is unsaturated, with many dangling bonds, exhibiting a chemically unstable state. This results in a high surface energy at the edges of the MoS2 crystal. Therefore, forming a MoS2 protective layer on the surface of MNC materials through a suitable method, and creating an internal heterostructure between the two, is a feasible approach to improve the stability of the active sites and the electrochemical activity of MNC materials. Summary of the Invention

[0005] To address the shortcomings of existing cathode catalyst materials for lithium-air batteries, the present invention aims to provide a MNC@MoS2SACs composite material that can be prepared by a simple process, exhibits good conductivity and catalytic activity, and has stable catalytic active sites, for use in lithium-air batteries to improve their performance.

[0006] To solve the technical problem, the present invention adopts the following technical solution:

[0007] This invention first discloses a method for preparing a MoS2-coated porous MNC single-atom catalyst, characterized by:

[0008] First, transition metal ions are chelated and anchored onto a porous carbon support using a chelating agent. Then, the carbon support is mixed with a nitrogen source precursor and calcined to obtain a material, denoted as MN-CSACs, with porous nitrogen-doped carbon as the support and a single transition metal atom M loaded onto it. During calcination, a new MN-based catalyst is formed, which can improve the stability and activity of the catalyst. x Furthermore, chelated metal complexes can fix metal atoms to certain positions in the decomposition residue during calcination and pyrolysis, thereby further improving their stability.

[0009] Then, by hydrothermal sulfidation and high-temperature calcination, layered MoS2 nanosheets were coated onto the MNC SACs material to obtain a MoS2-coated porous MNC single-atom catalyst, denoted as MNC@MoS2SACs.

[0010] The preparation method of MNC@MoS2SACs described in this invention specifically includes the following steps:

[0011] Step 1: Calcine 5-15g of carbon source precursor at 500-1000℃ for 1-10 hours to obtain porous carbon nanosheets;

[0012] Step 2: Dissolve 1-5g of chelating agent and 0.08-0.30g of transition metal salt in deionized water and stir evenly. Then add 0.05-0.2g of porous carbon nanosheets and disperse evenly by ultrasonication. Let stand for 12-24h, then centrifuge and dry. Mix the resulting powder with the nitrogen source precursor at a mass ratio of 1:2.5-10 and grind. Then calcine at 500-1500℃ for 1-10 hours to obtain MN-CSACs.

[0013] Step 3: Disperse 0.1-0.3g of molybdenum source, 0.2-0.4g of sulfur source and 0.1-0.2g of MNC SACs obtained in Step 2 evenly in 20mL of distilled water, transfer to a reaction vessel, and react at 180-200℃ for 15-36h. After the reaction is completed, wash and dry the product, and then calcine it at 500-1000℃ for 2-4h to obtain the target product MNC@MoS2 SACs composite material.

[0014] Furthermore, the carbon source precursor is potassium phytate, anhydrous potassium citrate, or plant fiber, preferably anhydrous potassium citrate (which has the characteristics of being porous and having a large specific surface area).

[0015] Furthermore, the chelating agent is glucose.

[0016] Further, the transition metal is at least one of Fe, Co and Ni, and the transition metal salt is a nitrate, sulfate, acetate, oxalate or chloride of the transition metal, preferably a nitrate.

[0017] Furthermore, the nitrogen source precursor is dicyandiamide, melamine, or urea, preferably melamine.

[0018] Further: the sulfur source is thiourea, sulfur, thiol or thioamino acid, preferably thiourea; the molybdenum source is ammonium molybdate tetrahydrate, molybdenum trioxide, calcium molybdate or molybdenum hexafluoride, preferably ammonium molybdate tetrahydrate.

[0019] Furthermore, the calcination in steps 1 to 3 is carried out under inert gas protection.

[0020] The present invention also discloses the MNC@MoS2 SACs composite material prepared by the above preparation method, which can be used as a positive electrode catalyst material for lithium-air batteries.

[0021] Compared with existing technologies, this invention provides a novel method for preparing MoS2-coated porous MNC single-atom catalysts, the advantages of which are reflected in:

[0022] 1. This invention first proposes a template-free integration procedure for preparing non-polymerized, high-specific-surface-area oxygen-rich porous carbon nanosheets, which is simple and economical. In the preparation of porous carbon nanosheets, anhydrous potassium citrate is preferably used as the carbon source precursor. The resulting nanosheets are interconnected and form a desert rose nanosheet structure, thereby improving the ion diffusion rate. In contrast, products obtained using other carbon sources are flat carbon nanoparticles with disordered aggregation between particles.

[0023] 2. This invention utilizes glucose as a chelating agent to chelate and anchor transition metal ions onto an oxygen-rich porous carbon support with a high specific surface area, thereby effectively isolating the transition metal ions (primary protection) and stably binding them to the carbon support through interactions with O-containing groups. Simultaneously, excess glucose can bind to the supporting surface, resulting in physical isolation of the transition metal complex (secondary protection). Glucose can further fix metal atoms by decomposing residues at certain temperatures. Furthermore, when melamine is used as a nitrogen source precursor, glucose can decompose with melamine at higher temperatures to form carbon-nitrogen species (such as C3N4) that can capture active metal single atoms, and further combine with metal atoms to form M-Nx species. These multiple principles synergistically prevent the aggregation of metal atoms.

[0024] 3. This invention utilizes the special structure of porous MoS2, embedding porous MoS2 within the shell of MNC. The confinement effect of the micropores and the anchoring effect of the functionalized surface can prevent the detachment and aggregation of metal atom active sites during the preparation process, stabilize the uniform distribution of active sites on the carrier, and improve the density of active sites.

[0025] 4. The composite material prepared by this invention has higher mass transfer efficiency, higher oxygen reduction activity and stability in acidic and alkaline media, and exhibits lower overvoltage, higher discharge specific capacity and excellent cycle performance when used as a lithium-air battery catalyst. The results show that, under high-purity oxygen conditions, deep battery performance testing (2.0-4.5V) shows that the initial discharge specific capacity at a current density of 100mA / g is 24896.46mAh / g, the overvoltage is maintained at around 1.01V, and it can stably operate for 210 cycles at a current density of 500mA / g, demonstrating excellent performance. Attached Figure Description

[0026] Figure 1 The X-ray diffraction (XRD) patterns of the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2 are shown.

[0027] Figure 2 The EDS spectrum of the Co-NC@MoS2SACs composite material prepared in Example 1 is shown below.

[0028] Figure 3 The images shown are high-resolution transmission electron microscopy (HRTEM) images of the Co-NC@MoS2SACs composite material prepared in Example 1, where (a) and (b) are TEM images at different magnifications, (c) is an HRTEM image, and (d) is a partial magnified view of (c).

[0029] Figure 4 The porous carbon nanosheets prepared in Example 1 ( Figure 4 (a) in Co-NC SACs Figure 4(b) of the above, and MoS2 prepared in Comparative Example 2 ( Figure 4 (c) and Co-NC@MoS2SACs prepared in Example 1 Figure 4 Scanning electron microscope (SEM) image of (d) in the image.

[0030] Figure 5 The first charge-discharge performance of lithium-air batteries assembled with the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2 is shown in the figure.

[0031] Figure 6 The graph shows the cycle performance of lithium-air batteries assembled with the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2.

[0032] Figure 7 The overvoltage diagram shows the lithium-air batteries assembled with the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2.

[0033] Figure 8 The graphs show the ORR performance test results of the materials prepared in Examples 1-3 and Comparative Examples 1-2, where a-e represent the materials obtained in Examples 1-3 and Comparative Examples 1-2, respectively. Detailed Implementation

[0034] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] Example 1

[0036] Step 1: Place 5g of anhydrous potassium citrate in a crucible and transfer it to a tube furnace. Calcinate at 800℃ for 1 hour under argon protection to obtain porous carbon nanosheets.

[0037] Step 2: Dissolve 1.33g glucose and 0.0873g cobalt nitrate hexahydrate in 5mL distilled water, stir well, add 60mg porous carbon nanosheets, sonicate for 30min, let stand for 24h, then centrifuge, wash with water several times, vacuum dry, mix the resulting powder with melamine at a mass ratio of 1:5 and grind, then calcine at 800℃ for 2 hours under argon protection to obtain Co-NC SACs material.

[0038] Step 3: Dissolve 0.1g ammonium molybdate tetrahydrate, 0.2g thiourea and 0.12g Co-NC SACs material obtained in Step 2 in 20mL of distilled water, stir, sonicate until homogeneous, and then transfer to a reaction vessel. React at 200℃ for 24h. After the reaction is completed, wash and dry the product, and then calcine it at 700℃ for 2h under argon protection to obtain the target product Co-NC@MoS2 SACs composite material.

[0039] Example 2

[0040] In this embodiment, Co-NC@MoS2 SACs composite material was prepared using the same method as in Example 1, except that the mass of cobalt nitrate hexahydrate in step 2 was 0.176 g.

[0041] Example 3

[0042] In this embodiment, Co-NC@MoS2 SACs composite material was prepared using the same method as in Example 1, except that the mass of the Co-NC SACs material in step 3 was 0.24 g.

[0043] Comparative Example 1

[0044] This comparative example uses the Co-NC SACs material prepared in step 2 of Example 1 as a catalyst.

[0045] Comparative Example 2

[0046] This comparative example uses separately prepared MoS2 nanomaterials as a catalyst, and the preparation steps are as follows:

[0047] Dissolve 0.1g ammonium molybdate tetrahydrate and 0.2g thiourea in 20mL of distilled water, stir, sonicate until homogeneous, and then transfer to a reaction vessel. React at 200℃ for 24h. After the reaction is complete, wash and dry the product, and then calcine it at 700℃ for 2h under argon protection to obtain the target product MoS2 material.

[0048] Figure 1 The X-ray diffraction (XRD) patterns of the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2 are compared with the MoS2 (PDE#75-1539) standard card. The peaks at 14.1°, 39.5°, and 49.7° correspond to the three strongest peaks on the card, indicating that the obtained materials successfully composited Co-NC SACs and MoS2.

[0049] Figure 2 The image shows the EDS energy spectrum of the Co-NC@MoS2 SACs composite material prepared in Example 1. It can be seen from the image that the five elements C, N, Co, Mo and S in the composite material are uniformly distributed.

[0050] Figure 3 Here is a high-resolution transmission electron microscope (HRTEM) image of the Co-NC@MoS2 SACs composite material prepared in Example 1. Figure 3 (a) and (b) show that the material has a nanosheet structure. Figure 3 (c) and (d) show the lattice fringes in the selected region, revealing the presence of few-layer pure 2H-MoS2 nanosheets with an increased interlayer spacing (0.632 nm).

[0051] Figure 4 The porous carbon nanosheets prepared in Example 1 ( Figure 4 (a) in Co-NC SACs Figure 4 (b) of the above, and MoS2 prepared in Comparative Example 2 ( Figure 4 (c) and Co-NC@MoS2 SACs prepared in Example 1 Figure 4 Scanning electron microscope (SEM) image of (d) in the image. Figure 4 (a) and (b) show that both porous carbon nanosheets and Co-NC SACs are in the form of nanosheets. Figure 4 (c) It can be seen that MoS2 is in the form of nanoflowers. Figure 4 (d) It can be seen that the Co-NC@MoS2 composite material is composed of layered MoS2 nanosheets uniformly coated on the outside of the Co-NC SACs material.

[0052] The materials prepared in the above embodiments were used as positive electrode catalyst materials for lithium-air batteries and assembled with lithium sheets to form coin-type lithium-air batteries. The assembly method is as follows: A slurry containing 60% KB, 30% catalyst material, and 10% PVDF was added to a carbon paper current collector. Then, it was dried in a vacuum drying oven at 60°C for 12 hours. The net mass of the dried catalyst on the carbon paper was approximately 0.3–0.5 mg. Using lithium foil as the anode, a glass fiber separator was laid flat, 110 μL of electrolyte was added dropwise, followed by the carbon paper containing the catalyst. Finally, the cathode instrument was covered with nickel foam as a filler, and the battery assembly was completed in an argon-filled glove box. All tests were conducted under pure oxygen conditions.

[0053] Figure 5 The graphs show the initial charge-discharge performance of lithium-air batteries assembled with the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2. It can be seen that the lithium-air battery assembled with the Co-NC@MoS2 SACs composite material prepared in Example 1 achieves a charge-discharge performance of 100 mAg. carbon -1 At a constant current discharge density, the initial discharge specific capacity reached 24896.46 mA hg. carbon -1 In contrast, the lithium-air battery assembled from Co-NC SACs materials in Comparative Example 1 only achieved a first-discharge specific capacity of 19898.17 mA hg. carbon -1 The lithium-air battery assembled with MoS2 material in Comparative Example 2 only achieved a specific capacity of 18218.5 mA hg during the first discharge. carbon -1 .

[0054] Figure 6The graphs show the cycle performance of lithium-air batteries assembled with the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2. It can be seen that the lithium-air battery assembled with the Co-NC@MoS2 SACs composite material prepared in Example 1 achieves a cycle performance of 500 mA g⁻¹. carbon -1 Under constant current discharge density, the capacity decayed after 210 cycles, demonstrating good cycle stability. In contrast, the lithium-air battery assembled with Co-NC SACs material in Comparative Example 1 showed capacity decay after 130 cycles, and the lithium-air battery assembled with MoS2 material in Comparative Example 2 showed capacity decay after 102 cycles.

[0055] Figure 7 The overvoltage diagrams for lithium-air batteries assembled with the catalyst materials prepared in Example 1 and Comparative Examples 1 and 2 show that the lithium-air battery assembled with the Co-NC@MoS2 SACs composite material prepared in Example 1 has an overvoltage of 100 mA g. carbon -1 At a constant current discharge density, the overvoltage is approximately 1.01V. In contrast, the overvoltage of the lithium-air battery assembled with Co-NC SACs material in Comparative Example 1 is 1.31V, and the overvoltage of the lithium-air battery assembled with MoS2 material in Comparative Example 2 is 1.05V.

[0056] Testing showed that the lithium-air battery assembled based on the Co-NC@MoS2 SACs composite material of Example 2 performed well at 500 mA g. -1 At a constant current discharge density, capacity decayed after 88 cycles. A lithium-air battery assembled based on the Co-NC@MoS2 SACs composite material of Example 3 exhibited capacity decay at 500 mA g⁻¹. -1 Under constant current discharge density, the capacity decays after 135 cycles.

[0057] Figure 8 The ORR performance test graphs for the materials prepared in Examples 1-3 and Comparative Examples 1-2 are shown, where a-e represent the materials obtained in Examples 1-3 and Comparative Examples 1-2, respectively. The sample preparation and testing methods are as follows: 10 mg of catalyst, 2 mg of XC-72, and 40 μL of naphthol were dissolved together in 2 mL of isopropanol aqueous solution (V... 异丙醇 V 水 In a mixture of 1:4, the solution was sonicated for 1 hour to form a homogeneous mixture. 10 μL of this solution was dropped onto a glassy carbon electrode and air-dried for 2 hours to form a catalyst layer. LSV (Limited Current Vibration) was measured on a disc electrode. The figure shows that the catalyst prepared in Example 1 achieved the highest limiting current density and exhibited the best catalytic effect during testing.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a MoS2-coated porous MNC single-atom catalyst for use as a cathode catalyst material in lithium-air batteries, characterized in that: First, transition metal ions are chelated and anchored onto a porous carbon support using glucose as a chelating agent. Then, they are mixed with melamine, a nitrogen source precursor, and calcined to obtain a material MN-CSACs, denoted as MN-CSACs, with porous nitrogen-doped carbon as the support and a single transition metal atom M supported thereon. The transition metal is at least one of Fe, Co, and Ni. Next, through hydrothermal sulfidation and high-temperature calcination, layered MoS2 nanosheets are coated onto the MN-CSACs material to obtain a MoS2-coated porous MNC single-atom catalyst, denoted as MNC@MoS2SACs. The specific steps include the following: Step 1: Calcine 5-15g of anhydrous potassium citrate, a carbon source precursor, at 500-1000℃ for 1-10 hours to obtain porous carbon nanosheets. Step 2: Dissolve 1-5g of chelating agent glucose and 0.08-0.30g of transition metal salt in deionized water and stir evenly. Then add 0.05-0.2g of porous carbon nanosheets and disperse evenly by ultrasonication. Let stand for 12-24h, then centrifuge and dry. Mix the resulting powder with the nitrogen source precursor melamine at a mass ratio of 1:2.5-10 and grind. Then calcine at 500-1500℃ for 1-10 hours to obtain MN-CSACs. Step 3: Disperse 0.1-0.3g of molybdenum source, 0.2-0.4g of sulfur source and 0.1-0.2g of MN-CSACs obtained in Step 2 evenly in 20mL of distilled water, transfer to a reaction vessel, and react at 180-200℃ for 15-36h. After the reaction is completed, wash and dry the product, and then calcine it at 500-1000℃ for 2-4h to obtain the target product MNC@MoS2SACs composite material.

2. The method for preparing the MoS2-coated porous MNC single-atom catalyst according to claim 1, characterized in that: The transition metal salt is a nitrate, sulfate, acetate, oxalate, or chloride of a transition metal.

3. The method for preparing the MoS2-coated porous MNC single-atom catalyst according to claim 1, characterized in that: The sulfur source is thiourea, sulfur, thiols, or thioamino acids, and the molybdenum source is ammonium molybdate tetrahydrate, molybdenum trioxide, calcium molybdate, or molybdenum hexafluoride.

4. A MoS2-coated porous MNC single-atom catalyst prepared by the preparation method according to any one of claims 1 to 3, which can be used as a positive electrode catalyst material for lithium-air batteries.

5. The application of the MoS2-coated porous MNC single-atom catalyst according to claim 4, characterized in that: It is used as a positive electrode catalyst material for lithium-air batteries.

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