MXene prepared by oxygen-free etching and its preparation method and application

Abstract

The present invention relates to the technical field of material preparation, and specifically discloses a MXene prepared by oxygen-free etching, and its preparation method and application. The preparation method comprises the following steps: adding a MAX phase material into a corrosion-resistant sealed container, introducing a halogen fluoride gas and a fluorine gas to a preset pressure, and etching by heating to obtain a MXene material. The present invention uses a fluorine-containing gas or a fluorine gas to perform high-pressure etching on the MAX phase material under closed pressurized conditions. The surface of the prepared MXene material does not contain oxygen-containing functional groups and has good conductivity. The supercapacitor prepared by using the MXene material as an electrode material has excellent capacitance performance and cycle stability. At the same time, the preparation process is simple, does not require the use of a hydrofluoric acid solution, and the process is safe and reliable. It has broad application prospects in high-performance supercapacitors.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and in particular to a MXene prepared by oxygen-free etching, and a preparation method and application thereof. Background Art

[0002] In the 1960s, Nowotny et al. first proposed the concept of ternary transition metal carbides or nitrides. After that, some compounds with similar structures were discovered. n+1 AX n , such as TiSiC2, Ti3AlC2, Ti3GeC2, etc. In 2011, the Gogotsi team at Drexel University selectively etched the Al layer of the ternary layered carbide Ti3AlC2 with a hydrofluoric acid solution to obtain Ti3C2T with a graphene-like two-dimensional structure. x , where T x represents the surface functional groups (such as -O, -OH, -F, etc.), and it is named MXene.

[0003] Because hydrofluoric acid etching is simple and easily scalable, the resulting MXene sheet structure is relatively complete, making it more suitable as a substrate. Therefore, hydrofluoric acid etching remains the mainstream method for preparing MXene. However, during etching and subsequent processing, MXene inevitably oxidizes, reducing its conductivity and hindering its application. In addition, hydrofluoric acid is a highly toxic and hazardous substance. At the same time, its reaction with MAX releases a large amount of heat, posing a risk of explosive boiling. The process is therefore unsafe and environmentally friendly. Therefore, there is an urgent need to develop a new MXene preparation process to improve the performance of the prepared MXene and expand its application areas. Summary of the Invention

[0004] In response to the problems of poor conductivity of MXene materials prepared by existing methods for preparing MXene materials, as well as poor process safety and environmental protection, the present invention provides MXene prepared by oxygen-free etching, and its preparation method and application.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A method for preparing MXene by oxygen-free etching comprises the following steps:

[0007] The MAX phase material is added to a corrosion-resistant sealed container, halogen fluoride gas and fluorine gas are introduced to a preset pressure, and the temperature is increased for etching to obtain the MXene material.

[0008] Compared with the prior art, the method for preparing MXene by oxygen-free etching provided by the present invention uses fluorine-containing gas or fluorine gas to perform high-pressure etching on the MAX phase material under closed and pressurized conditions, which can allow F atoms to be intercalated into the MXene interlayer. After etching, the active sites exposed by the Ti atoms form Ti-F bonds with F, avoiding combining with O to form Ti-O bonds and causing oxidation. The strong intermolecular repulsion between the Ti-F bonds can increase the interlayer spacing of MXene, making it easier for the electrolyte to infiltrate, increasing the specific surface area, and increasing the active sites. It can also ensure the stability of the MXene structure in long-term cycle periods, thereby giving it good rate performance and cycle stability; more importantly, gas etching is carried out under closed and oxygen-free conditions to avoid the formation of oxygen-containing functional groups on its surface, thereby maximizing the capacitance performance of the MXene material.

[0009] The MXene material prepared by the present invention has high electrical conductivity, high lamellar structure stability, and excellent electrochemical properties. The supercapacitor prepared by using it as an electrode material has high specific capacity and long cycle life, providing a superior electrode material for supercapacitors. The preparation process is simple and easy, and large-scale production can be carried out. It has opened up a new process for the preparation and performance optimization of high-performance MXene materials and has broad application prospects.

[0010] Specifically, the etching process in the present invention is performed according to the following equation:

[0011] M n+1 AlX n +5 / 2F2=AlF3+M n+1 X n F2

[0012] Furthermore, the halogen fluoride gas is first continuously introduced into the sealed container, and after a preset time, the fluorine gas is introduced until the preset pressure is reached, and the introduction of the halogen fluoride gas and the fluorine gas is stopped at the same time.

[0013] First, halogen fluoride is introduced into a sealed container and sealed with the MAX phase material and allowed to stand for a certain period of time to pre-fluorinate the MAX phase material. Then fluorine gas is introduced to improve the etching effect and allow fluorine atoms to be intercalated into the MXene interlayer. The fluorine atoms inserted into the interlayer can reduce the self-stacking effect of the MXene material, increase the interlayer spacing, increase the insertion and extraction rate of anions and cations in the interlayer and the electrochemical active sites, and significantly improve the electrochemical performance of the MXene material.

[0014] Specifically, the sealed container used in the present invention is a sealed container resistant to fluorine gas corrosion, and is provided with an inlet for the halogen fluoride gas and an inlet for the fluorine gas.

[0015] Exemplarily, the sealed container is a reactor made of Monel alloy or nickel alloy.

[0016] As a specific embodiment of the present invention, the halogenated fluoride gas inlet is first opened to pass the halogenated fluoride gas into the sealed container. After a preset time, the fluorine gas inlet is opened again to pass the fluorine gas and the halogenated fluoride gas into the sealed container at the same time. After reaching the preset pressure, the halogenated fluoride gas inlet and the fluorine gas inlet are closed at the same time.

[0017] It should be noted that before the halogen fluoride gas is introduced, the sealed container may be purged with an inert gas to ensure an oxygen-free environment in the sealed container.

[0018] The above-mentioned inert gas can be selected from conventional inert gases in the art, such as nitrogen, argon, etc.

[0019] Preferably, the preset time is 1 hour to 2 hours.

[0020] Preferably, the preset pressure is 59KPa-118KPa.

[0021] Preferably, when the preset pressure is reached, the volume ratio of the halogen fluoride gas to the fluorine gas in the sealed container is 2:1-4:1.

[0022] Preferably, the temperature of the temperature-elevated etching is 200° C.-400° C., and the time is 6 h-24 h.

[0023] The preferred etching conditions allow the fluorine-containing gas or fluorine gas to fully etch the MAX phase material, preparing a multilayer MXene material with an accordion-like structure, a smooth surface and no wrinkles, and facilitate the intercalation of fluorine atoms into the MXene interlayer, thereby improving the electrochemical properties of the MXene material.

[0024] Preferably, the halogen fluoride gas is at least one of IF5, ClF3 or BF3.

[0025] Specifically, the MAX phase material includes Ti3AlC2, Ti2AlC, Nb2AlC or V2AlC.

[0026] The oxygen-free etching method provided by the present invention is suitable for etching MAX phase materials with M2AlX, M3AlX2 and M4AlX3 structures.

[0027] Specifically, after the etching reaction is completed, the temperature is lowered, the etched product is taken out, washed with anhydrous ethanol and deionized water, and dried to obtain the MXene material.

[0028] The present invention also provides a MXene material, which is prepared by any of the above-mentioned methods for preparing MXene by oxygen-free etching.

[0029] The present invention also provides the use of the above-mentioned MXene material in supercapacitors.

[0030] The present invention also provides an electrode comprising the above-mentioned MXene material.

[0031] The present invention also provides a supercapacitor comprising the above-mentioned electrode.

[0032] The MXene material prepared by the present invention does not contain oxygen-containing functional groups on the surface and has good conductivity. The fluorine atoms intercalated between MXene layers can increase the interlayer spacing and improve the stability of the MXene layer structure. The supercapacitor prepared using it as an electrode material has excellent capacitance performance and cycle stability. At the same time, the preparation process is simple and does not require the use of hydrofluoric acid solution. The process is safe and reliable, suitable for large-scale production and application, and has broad application prospects in high-performance supercapacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is an SEM image of the MXene material prepared in Example 1 of the present invention;

[0034] Figure 2 This is an SEM image of the MXene material prepared in Comparative Example 1 of the present invention;

[0035] Figure 3 The XPS graphs of the MXene materials prepared in Example 1 and Comparative Example 1 of the present invention are shown;

[0036] Figure 4 CV curves of MXene materials prepared in Example 1 and Comparative Examples 1-3 of the present invention, wherein (a) Comparative Example 1, (b) Comparative Example 2, (c) Comparative Example 3, and (d) Example 1, are 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, 500 mV / s, and 1000 mV / s from bottom to top according to the direction of the arrows;

[0037] Figure 5 GCD curves of MXene materials prepared in Example 1 and Comparative Examples 1-3 of the present invention, wherein (a) Comparative Example 1, (b) Comparative Example 2, (c) Comparative Example 3, and (d) Example 1, from left to right according to the direction of the arrows, are 20 A / g, 10 A / g, 5 A / g, 2 A / g, and 1 A / g;

[0038] Figure 6 This is the GCD curve of the MXene material prepared in Example 1 of the present invention after 200 cycles of cycle testing at a current density of 5 A / g. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] In order to better illustrate the present invention, further examples are given below.

[0041] Example 1

[0042] A method for preparing MXene by oxygen-free etching comprises the following steps:

[0043] Step 1: Place 2 g of Ti3AlC2 powder in a sealed container made of nickel alloy and purge the container with nitrogen for 5 minutes to ensure an oxygen-free environment.

[0044] Step 2: IF5 gas is introduced into the sealed container. After 1.5 hours of ventilation, fluorine gas is introduced until the pressure of the sealed container reaches 100 kPa. Then, the introduction of IF5 gas and fluorine gas is stopped;

[0045] Step 3: Place the sealed container in a muffle furnace, heat to 200°C, etch at a constant temperature for 18 hours, cool to room temperature, take out the product, and wash it with anhydrous ethanol and deionized water until neutral, vacuum filter, and dry it at 60°C in a vacuum to obtain MXene material.

[0046] In this embodiment, the flow rates of IF5 gas and fluorine gas are such that the volume ratio of IF5 gas to fluorine gas in the final closed container is 3:1.

[0047] The SEM image of the MXene material prepared in this example is as follows Figure 1 shown.

[0048] Example 2

[0049] A method for preparing MXene by oxygen-free etching comprises the following steps:

[0050] Step 1: Place 2 g of Ti2AlC powder in a sealed container made of nickel alloy and purge the container with nitrogen for 5 minutes to ensure an oxygen-free environment.

[0051] Step 2: introduce ClF3 gas into the sealed container. After ventilating for 1 hour, introduce fluorine gas until the pressure of the sealed container reaches 59 kPa, and then stop introducing ClF3 gas and fluorine gas;

[0052] Step 3: Place the sealed container in a muffle furnace, heat to 250°C, etch at a constant temperature for 24 hours, cool to room temperature, take out the product, and wash it with anhydrous ethanol and deionized water until neutral, vacuum filter, and dry it at 60°C in a vacuum to obtain MXene material.

[0053] In this embodiment, the flow rates of IF5 gas and fluorine gas are such that the volume ratio of IF5 gas to fluorine gas in the final closed container is 2:1.

[0054] Example 3

[0055] A method for preparing MXene by oxygen-free etching comprises the following steps:

[0056] Step 1: Place 2 g of V2AlC powder in a sealed container made of nickel alloy and purge the container with nitrogen for 5 minutes to ensure an oxygen-free environment.

[0057] Step 2: BF3 gas is introduced into the sealed container. After 2 hours of ventilation, fluorine gas is introduced until the pressure of the sealed container reaches 80 kPa. Then, the introduction of BF3 gas and fluorine gas is stopped;

[0058] Step 3: Place the sealed container in a muffle furnace, heat to 400°C, etch at a constant temperature for 6 hours, cool to room temperature, take out the product, and wash it with anhydrous ethanol and deionized water until neutral, vacuum filter, and dry it at 60°C in a vacuum to obtain MXene material.

[0059] In this embodiment, the flow rates of IF5 gas and fluorine gas are such that the volume ratio of IF5 gas to fluorine gas in the final closed container is 4:1.

[0060] Example 4

[0061] A method for preparing MXene by oxygen-free etching comprises the following steps:

[0062] Step 1: Place 2 g of Nb2AlC powder in a sealed container made of nickel alloy and purge the container with nitrogen for 5 minutes to ensure an oxygen-free environment.

[0063] Step 2: IF5 gas is introduced into the sealed container. After 1 hour of ventilation, fluorine gas is introduced until the pressure of the sealed container reaches 118 kPa. Then, the introduction of IF5 gas and fluorine gas is stopped;

[0064] Step 3: Place the sealed container in a muffle furnace, heat to 350°C, etch at a constant temperature for 15 hours, cool to room temperature, take out the product, and wash it with anhydrous ethanol and deionized water until neutral, vacuum filter, and dry it at 60°C in a vacuum to obtain MXene material.

[0065] In this embodiment, the flow rates of IF5 gas and fluorine gas are such that the volume ratio of IF5 gas to fluorine gas in the final closed container is 3.5:1.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing MXene, comprising the following steps:

[0068] 2.0 g of Ti3AlC2 powder was slowly added to 20 mL of HF solution and heated in a constant temperature water bath at 35 °C for 24 h. The reaction product was then placed in a centrifuge and centrifuged at 3500 r / min for 5 min. The supernatant was centrifuged until it was neutral. The centrifugation was stopped and the centrifuged product was filtered with an organic filter membrane. It was then placed in a 60 °C oven and dried for 6 h to obtain MXene material.

[0069] The SEM image of the MXene material prepared in this comparative example is as follows Figure 2 shown.

[0070] Comparative Example 2

[0071] This comparative example provides a method for preparing MXene, comprising the following steps:

[0072] After mixing 0.67g LiF and 10mL 6mol / L hydrochloric acid solution evenly, slowly add 2.0g Ti3AlC2 powder, then place it in a 40℃ water bath and heat it for 24h. Place the reaction product in a centrifuge and centrifuge at 3500r / min for 5min. Centrifuge until the supernatant is neutral, stop the centrifugation, filter the centrifuged product with an organic filter membrane, and then place it in a 60℃ oven to dry for 6h to obtain MXene material.

[0073] Comparative Example 3

[0074] This comparative example provides a method for preparing MXene, comprising the following steps:

[0075] 0.5 g of Ti3AlC2 powder was added to 10 mL of 2 mol / L NH4HF2 solution and stirred at room temperature for 24 h. The reaction product was placed in a centrifuge and centrifuged at 3500 r / min for 5 min until the supernatant was neutral. The centrifugation was stopped and the centrifuged product was filtered with an organic filter membrane and then placed in a 60 ° C oven to dry for 6 h to obtain MXene material.

[0076] Performance Testing

[0077] 1.XPS

[0078] The XPS test results of the MXene materials prepared in Example 1 and Comparative Example 1 are as follows: Figure 3 shown.

[0079] In Ti3C2T xCharacteristic peaks corresponding to C1s, Ti 2p, O 1s, and F1s were observed in the sample spectrum at 284eV, 461eV, 532eV, and 686eV. The O1s peak intensity of the MXene sample prepared in the absence of oxygen in Example 1 was significantly lower, demonstrating the absence of oxygen during the preparation of Example 1.

[0080] 2. Electrochemical performance test

[0081] The MXene materials prepared in Example 1 and Comparative Examples 1-3 were mixed with carbon black and PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, added to N-methylpyrrolidone, mixed evenly, and coated on a 1×1 cm 2 The coating amount was 1±0.2 mg on a stainless steel sheet, dried under vacuum at 60°C, and then the electrochemical performance was tested in a 1 mol / L sulfuric acid solution. The voltage range of the cyclic voltammetry test was -0.2V-0.4V, and the scan rate was 10mV / s-1000mV / s. The results are as follows: Figure 4 As shown; the voltage range of the constant current discharge test is -0.2V-0.4V, the current density is 1A / g-20A / g, and the results are as follows Figure 5 and as shown in Table 1.

[0082] Table 1 Capacitance at different current densities (F / g)

[0083]

[0084] from Figure 4 As can be seen, the area of ​​the CV curve measured for the MXene material prepared in Example 1 of the present invention is significantly larger than that of Comparative Examples 1-3, indicating that the MXene material prepared in Example 1 of the present invention has superior capacitive performance. As the scan rate increases, the CV curve maintains a symmetrical rectangular shape, demonstrating that the MXene material prepared in Example 1 of the present invention has a relatively fast electron transfer rate and good conductivity.

[0085] Depend on Figure 5 Table 1 further demonstrates that the capacitance performance of the MXene material prepared in Example 1 of the present invention is significantly better than that of Comparative Examples 1-3.

[0086] The MXene prepared in Example 1 was subjected to a constant current discharge test at a current density of 5 A / g, and the GCD curve of the cycle number was 200. Figure 6 shown.

[0087] As can be seen from the figure, after 200 cycles, the MXene prepared in Example 1 still maintains 98.76% of its capacity, indicating that the supercapacitor prepared using the MXene material prepared in this embodiment of the present invention has good rate performance and ultra-long service life.

[0088] The MXene materials prepared in Examples 2-4 can achieve effects substantially equivalent to those in Example 1.

[0089] 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 or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing MXene by oxygen-free etching, characterized in that: The steps include: The MAX phase material is added to a corrosion-resistant sealed container, halogen fluoride gas and fluorine gas are introduced to 59KPa-118KPa, and the temperature is raised to 200℃-400℃ for etching to obtain MXene material; The MAX phase material includes Ti3AlC2, Ti2AlC, Nb2AlC or V2AlC.

2. The method for preparing MXene by oxygen-free etching according to claim 1, wherein: First, the halogen fluoride gas is continuously introduced into the sealed container. After a preset time, the fluorine gas is introduced and the pressure reaches a preset value. At the same time, the introduction of the halogen fluoride gas and the fluorine gas is stopped.

3. The method for preparing MXene by oxygen-free etching according to claim 2, wherein: The preset time is 1 hour to 2 hours.

4. The method for preparing MXene by oxygen-free etching according to claim 1 or 2, wherein: When the preset pressure is reached, the volume ratio of the halogen fluoride gas to the fluorine gas in the sealed container is 2:1-4:

1.

5. The method for preparing MXene by oxygen-free etching according to claim 1 or 2, wherein: The etching time is 6h-24h; and / or The halogen fluoride gas is at least one of IF5, ClF3 or BF3.

6. A MXene material, characterized in that The MXene is prepared by the method for preparing MXene by oxygen-free etching according to any one of claims 1 to 5.

7. Use of the MXene material according to claim 6 in a supercapacitor.

8. An electrode, characterized in that Including the MXene material according to claim 6.

9. A supercapacitor, characterized in that: Comprising the electrode according to claim 8.

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