A mxene / iron oxalate composite material and a preparation method thereof

Abstract

The application relates to the technical field of supercapacitor electrode materials, in particular to a MXene / iron oxalate composite material and a preparation method thereof. The preparation method comprises the following steps: preparing MXene nanosheets; mixing, stirring and then placing MXene suspension, FeSO4.7H2O, ascorbic acid and H2C2O4.2H2O into a muffle furnace to perform a hydrothermal reaction to obtain the MXene / iron oxalate composite material. The MXene and the iron oxalate are compounded by the hydrothermal method, the conductivity of the MXene is improved, a three-dimensional conductive network is generated after the in-situ compounding of the MXene and the iron oxalate, the conductivity of the composite material is further improved, the crystallinity of the iron oxalate is increased with the increase of the temperature under the hydrothermal condition, the ion transmission rate is improved after the cross-compounding of the MXene and the iron oxalate, and the performance of the composite material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of supercapacitor electrode materials, and in particular to a MXene / ferric oxalate composite material and a preparation method thereof. Background Art

[0002] Supercapacitors offer advantages such as high output power, rapid charge and discharge capabilities, a wide operating temperature range, and ultra-long cycle times. However, their application is limited by their low energy density. Electrode materials are a component of supercapacitors, and their selection and optimization are crucial to improving their performance.

[0003] In recent years, MXene materials have become a hot topic in supercapacitor electrode material research due to their excellent electrochemical properties. MXene is a two-dimensional material composed of transition metal carbides, nitrides, or carbonitrides. MXene exhibits metal-like conductivity, significantly improving the rate capability of supercapacitors. Its two-dimensional layered structure provides abundant active sites, facilitating ion adsorption and storage. MXene surfaces often bear active groups such as -OH, -F, and -O. These groups can store more charge in pseudocapacitive reactions, further enhancing specific capacity.

[0004] However, due to its two-dimensional lamellar structure, MXene is prone to interlamellar stacking during use, resulting in a reduction in active surface area and impeded ion transport, thus affecting its electrochemical performance. Interlamellar stacking can also cause mechanical instability, reducing the cycle life of supercapacitors. Ferric oxalate has gradually become a popular capacitor material due to its low cost, porous structure, and high specific capacity. However, ferric oxalate also suffers from poor conductivity, and its rate performance and charge-discharge speed are limited when used alone as an electrode material.

[0005] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to provide a MXene / ferric oxalate composite material and a preparation method thereof, wherein MXene and ferric oxalate are compounded by a hydrothermal method, and ferric oxalate is loaded on the surface and interlayer of MXene under high temperature and high pressure, so that MXene and ferric oxalate are cross-compounded to form an interwoven three-dimensional conductive network, further improving the conductivity of the material, increasing the ion transmission rate, and achieving an improvement in the electrochemical performance of the material.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A preparation method of a MXene / iron oxalate composite material, comprising the following steps:

[0009] S01: preparing MXene nanosheets: LiF and Ti3AlC2 are slowly added into an HCl solution in sequence and stirred uniformly, and then transferred to an oil bath pot for heating and stirring etching; the solution obtained after the etching is completed is centrifuged and washed with HCl and deionized water respectively, and then placed in an ultrasonic crusher for ice bath ultrasonic treatment under protection, and then placed in a centrifuge for centrifugation to obtain the upper suspension;

[0010] In the method, Ti3AlC2 (MAX phase) is etched by using an HCl solution and LiF, and the aluminum element is removed from Ti3AlC2 to generate layered MXene nanosheets (Ti3C2Tx, Tx represents surface groups such as -OH, -F, etc.). Then, the MXene layers are further peeled off by ultrasonic crushing to obtain MXene nanosheets with high specific surface area and rich active surface sites. These sites provide more active reaction areas for subsequent iron oxalate composites.

[0011] Preferably, in step S01, the mass ratio of LiF to Ti3AlC2 is 1:1-1.2. LiF releases F - in the HCl solution - , which cooperates with H + to selectively etch the Al layer in Ti3AlC2 to generate MXene nanosheets. If the amount of LiF is too small, F - is insufficient, which may lead to incomplete etching of the Al layer and affect the yield and quality of MXene. By setting the mass ratio of LiF to Ti3AlC2 to 1:1-1.2, sufficient F - can be ensured to participate in the etching, while avoiding excessive waste of LiF.

[0012] Preferably, in step S01, the heating time of the oil bath pot is 48-52 h, and the heating temperature of the oil bath pot is 38-42℃. The etching reaction of Ti3AlC2 is a relatively slow process, which requires time for F - and H + ions to fully diffuse and chemically react with the Al layer in Ti3AlC2. Under appropriate temperature and time conditions, the etching reaction can proceed relatively smoothly, reducing excessive damage to the layered structure of MXene. If the temperature is too high or the time is too long, F - may further etch the Ti3C2 matrix, leading to interlayer accumulation and reduction of active sites. By optimizing this interval, the layered characteristics and high specific surface area of MXene can be preserved.

[0013] As preferred, in step S01, when using HCl for centrifugal washing, the centrifugal speed of HCl is 3000-4000 rpm; the centrifugal time is 3-5 min. The main purpose of HCl centrifugal washing is to remove the by-products generated in the etching reaction. If the centrifugal speed is too low, the impurities may not be effectively separated, resulting in an increase in the number of subsequent washing, wasting resources; if the centrifugal speed is too high or the time is too long, it may generate a large shear force on the sheet layer, causing the sheet layer to be damaged or stacked, affecting the specific surface area and active sites of the material.

[0014] As preferred, in step S01, when using deionized water for centrifugal washing, the centrifugal speed of deionized water is 3500-6000 rpm; the centrifugal time is 4-6 min. After completing the HCl washing, there may still be some acidic impurities, Al 3+ ions, salt by-products and a small amount of residual HCl in the solution. Using deionized water for washing can neutralize and completely remove these impurities, improving the purity of the MXene suspension.

[0015] As preferred, in step S01, the ice bath ultrasonic time is 2-2.5 h; when centrifuging the upper suspension, the centrifugal speed of the centrifuge is 3500-4000 rpm; the centrifugal time is 40-50 min. Ultrasonic waves can produce high-intensity vibrations and cavitation effects, significantly weakening the interlayer bonding force of MXene, thereby achieving the full exfoliation of MXene sheets. The low temperature in the ice bath environment can reduce the detachment of surface groups (such as -OH, -F, etc.) caused by temperature rise, thereby maintaining the chemical activity of MXene. Through ultrasonic crushing and ice bath protection, the exfoliated MXene nanosheets have high specific surface area and abundant active surface sites, providing an ideal basis for subsequent composite reactions.

[0016] S02: After mixing and stirring the MXene suspension with FeSO4·7H2O, ascorbic acid and H2C2O4·2H2O, it is placed in a muffle furnace for hydrothermal reaction; after centrifugal washing, it is placed in a vacuum drying box for drying, and finally the MXene / iron oxalate composite material is obtained.

[0017] In this step, by mixing the MXene suspension with FeSO4·7H2O, H2C2O4·2H2O (oxalic acid) and ascorbic acid, iron oxalate (FeC2O4·2H2O) particles are generated under hydrothermal reaction conditions. Iron oxalate particles gradually crystallize in the reaction and combine with the active surface sites of MXene to form a cross-linked three-dimensional network structure. Among them, ascorbic acid as a reducing agent can effectively inhibit the oxidation of Fe 2+ to Fe 3+ , thereby ensuring the stable and pure formation of iron oxalate.

[0018] Preferably, in step S02, the molar ratio of FeSO4·7H2O, H2C2O4·2H2O and ascorbic acid is 50:25:1, and the ratio of FeSO4·7H2O to H2C2O4·2H2O is 2:1, ensuring that Fe 2+ and oxalate ions (C2O4 2- ) The reaction is complete to form ferric oxalate, which not only avoids the formation of by-products caused by excessive oxalate ions, but also ensures that the reactants are efficiently utilized. The molar ratio of ascorbic acid is set to 1, which acts as a reducing agent, thereby improving the purity and quality of ferric oxalate and avoiding the formation of mixtures or impurities.

[0019] The preferred mass ratio of FeSO4·7H2O to MXene is 1:1 to 6. A mass ratio of 1:1 results in a lower iron oxalate content, which better preserves the conductive properties of MXene and is suitable for applications requiring high conductivity. A mass ratio of 1:6 results in a higher iron oxalate content, which enhances the structural stability and ion transport capabilities of the composite material and is suitable for applications requiring higher ion storage performance.

[0020] Preferably, in step S02, during the hydrothermal reaction, the muffle furnace temperature is 60-100°C, and the holding time is 10-12 hours. The hydrothermal reaction is a time-dependent process, and a 10-12-hour holding time provides sufficient growth time for the iron oxalate crystals, forming uniform and well-distributed particles. The mild hydrothermal conditions of 60-100°C allow the iron oxalate particles to evenly bond with the MXene surface and interlayers during the formation process, preventing particle shedding or uncontrolled crystallization caused by high temperatures. This allows for the construction of a more stable three-dimensional conductive network, improving the uniformity and stability of the composite material.

[0021] Preferably, in step S02, during centrifugal washing, the centrifugal speed is 6000~7000rpm, the centrifugal time is 3~5min, and then the centrifugal material is placed in a vacuum drying oven at a temperature of 40~60°C and the drying time is 10~12h. Through appropriate centrifugal speed and time, the MXene / ferric oxalate composite material can be quickly settled without the loss of fine particles due to excessive centrifugal force or too long time, thereby improving the recovery rate and yield of the material. After removing impurities and residual moisture, the chemical properties of the composite material are more stable. During long-term use, the composite material can better resist capacity decay and structural collapse, and exhibit better cycle stability.

[0022] The present invention improves the conductivity of MXene and generates a three-dimensional conductive network after in-situ compounding with ferric oxalate, thereby further improving the conductivity of the composite material, reducing the interlayer stacking effect of MXene, and enhancing the structural stability of the composite material during charge and discharge cycles; under hydrothermal conditions, the crystallinity of ferric oxalate increases with increasing temperature, and after cross-compounding with MXene, the ion transmission rate is improved, thereby improving the performance of the composite material.

[0023] A second objective of the present invention is to provide a MXene / ferric oxalate composite material prepared according to the above-mentioned preparation method. The two-dimensional MXene sheets and the ferric oxalate particles are interlaced to form a three-dimensional conductive network structure. The ferric oxalate particles act as a proppant, reducing the interlayer stacking effect of the MXene, thereby improving the ion transport rate and the electrochemical performance of the composite material.

[0024] The beneficial effects of the present invention are:

[0025] The present invention increases the conductivity of MXene by compounding MXene and ferric oxalate, and under hydrothermal conditions, increases the O functional groups on the surface of MXene and reduces the OH functional groups. After compounding with ferric oxalate, the ferric oxalate first forms a nanosheet structure at low temperature. As the temperature rises, the ferric oxalate evolves into an adhesion structure and a microrod structure, adhering to the interlayer and surface of MXene. MXene and ferric oxalate cross-compound to form an interwoven three-dimensional conductive network, further improving the conductivity of the material, increasing the ion transmission rate, and achieving an improvement in the electrochemical performance of the material.

[0026] Due to the layered structure of MXene, some active surface sites are easily lost during stacking. When compounded with ferric oxalate, the ferric oxalate particles act as "space support," effectively reducing the interlayer stacking effect, thereby increasing the specific surface area and the number of active sites in the material. Through in-situ compounding with MXene, the ferric oxalate particles embed themselves between layers and on the surface, forming ion transport channels and further optimizing the overall electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is the XRD pattern of the MXene / ferric oxalate composite material synthesized in Example 1.

[0029] Figure 2 This is the SEM image of the iron oxalate synthesized in Comparative Example 1.

[0030] Figure 3 SEM image of MXene synthesized for Comparative Example 2.

[0031] Figure 4 SEM image of MXene / iron oxalate composite material synthesized for Example 2.

[0032] Figure 5 Comparison of rate performance according to CV curves for Example 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0033] In order to make the above objectives, features and advantages of the present application more apparent, the present application will be described in detail below with reference to the accompanying drawings and specific examples.

[0034] Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described can be included in at least one implementation of the present application. The appearances of "in one embodiment" at various places in the specification do not necessarily all refer to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

[0035] Example 1

[0036] A MXene / iron oxalate composite material and a preparation method thereof are as follows:

[0037] S01: 1 g of LiF was slowly added to a 20 ml solution of HCl (concentration of 9 M), and then 1 g of Ti3AlC2 was slowly added thereto, and the reaction was carried out at 290 rpm under the condition of an oil bath at 40°C for 48 h. The product after the reaction was first centrifuged at 8 ml of 12.1 M HCl at a rotation speed of 3500 rpm for 5 min, and after centrifugation twice, deionized water was used to increase the rotation speed from 3500 rpm to 6000 rpm by 500 rpm each time, and each time the centrifugation was carried out for 5 min. The centrifugation was continued until the pH of the supernatant was neutral, and the solution was ultrasonicated for 2 h under N2 atmosphere while stirring in an ice bath, and then centrifuged at 3500 rpm for 40 min, and the upper suspension was collected to obtain layered MXene nanosheets.

[0038] S02: 0.193 g of FeSO4·7H2O and 0.0024 g of ascorbic acid were dissolved in 15 ml of deionized water to form solution A, 0.0876 g of H2C2O4·2H2O was dissolved in 5 ml of anhydrous ethanol, H2C2O4·2H2O was added dropwise to solution A, and 0.1 g of MXene was added dropwise to the mixed solution, and after mixing and stirring for 1 h, it was placed in a muffle furnace and heated at 100°C for 12 h, and then centrifuged and washed at 6000 rpm, and then placed in a vacuum drying oven at 60°C for 12 h.

[0039] Example 2

[0040] A MXene / ferric oxalate composite material and a preparation method thereof are as follows:

[0041] S01: 1g of LiF was slowly added to a 20ml 9M HCl solution, followed by 1g of Ti3AlC2. The reaction was continued at 290 rpm and 40°C in an oil bath for 48 hours. The product was then centrifuged at 3500 rpm for 5 minutes with 8ml of 12.1M HCl. After two centrifugations, the slurry was centrifuged from 3500 rpm to 6000 rpm in deionized water, increasing the rpm by 500 rpm each time for 5 minutes each. Centrifugation was continued until the supernatant reached a neutral pH. The solution was then stirred and ultrasonicated in an ice bath under a nitrogen atmosphere for 2 hours. The supernatant was then centrifuged at 3500 rpm for 40 minutes. The supernatant was collected to yield lamellar MXene nanosheets.

[0042] S02: Dissolve 0.386g FeSO4·7H2O and 0.0049g ascorbic acid in 15ml deionized water, recorded as solution A, dissolve 0.174g H2C2O4·2H2O in 5ml anhydrous ethanol, drop the H2C2O4·2H2O solution into solution A, drop 0.1g MXene into the mixed solution, mix and stir for 1h, place it in a muffle furnace, heat it at 100℃ for 12h, centrifuge it at 6000rpm, and then dry it in a vacuum drying oven at 60℃ for 12h.

[0043] Comparative Example 1

[0044] The preparation method of ferric oxalate is as follows:

[0045] S01: Dissolve 10 mmol FeSO4·7H2O and 0.2 mmol ascorbic acid in 45 ml deionized water, recorded as solution A. Dissolve 5 mmol H2C2O4·2H2O in 15 ml anhydrous ethanol. Add the H2C2O4·2H2O solution dropwise into solution A. After mixing and stirring for 30 minutes, heat the mixture at 100°C in a muffle furnace for 12 hours, centrifuge and wash at 6000 rpm, and then dry it in a vacuum drying oven at 60°C for 12 hours.

[0046] Comparative Example 2

[0047] The MXene preparation method is as follows:

[0048] S01: 1g of LiF was slowly added to a 20ml 9M HCl solution, followed by 1g of Ti3AlC2. The reaction was continued at 290 rpm and 40°C in an oil bath for 48 hours. The product was then centrifuged at 3500 rpm for 5 minutes with 8ml of 12.1M HCl. After two centrifugations, the slurry was centrifuged from 3500 rpm to 6000 rpm in deionized water, increasing the rpm by 500 rpm each time for 5 minutes each. Centrifugation was continued until the supernatant reached a neutral pH. The solution was then stirred and ultrasonicated in an ice bath under a nitrogen atmosphere for 2 hours. The supernatant was then centrifuged at 3500 rpm for 40 minutes. The supernatant was collected to yield lamellar MXene nanosheets.

[0049] Test data

[0050] A three-electrode system was assembled using Examples 1-2 and Comparative Examples 1-2 as working electrodes, activated carbon as a counter electrode, Ag / AgCl as a reference electrode, and 40% H₂SO₄ as the electrolyte. CV measurements were performed using an electrochemical workstation (Shanghai CHI660E).

[0051] from Figure 1 It can be seen that MXene and iron oxalate are successfully composited.

[0052] from Figure 2 It can be seen that iron oxalate presents a multi-layer rod-like structure.

[0053] from Figure 3 It can be seen that MXene has a layered structure.

[0054] from Figure 4 It can be seen that MXene and iron oxalate are successfully cross-compounded.

[0055] from Figure 5 It can be seen that the specific capacity of Example 2 at 1 mV / s is 387 F / g, while the specific capacity of Comparative Example 1 at 1 mV / s is 67 F / g, and the specific capacity of Comparative Example 2 at 1 mV / s is 317 F / g. Figure 4 It can be seen that the MXene / ferric oxalate composite material prepared by the present invention can obtain a higher specific capacitance, and the electrode material used for supercapacitors can improve its performance.

[0056] Those skilled in the art will appreciate that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a MXene / ferric oxalate composite material, characterized in that: The following steps are involved: S01: Preparation of MXene nanosheets: LiF and Ti3AlC2 were slowly added to the HCl solution in sequence and stirred evenly, then transferred to an oil bath for heating and stirring etching; the resulting solution was centrifuged and washed with HCl and deionized water respectively, then placed in an ultrasonic crusher with protective gas and ultrasonicated in an ice bath, and then placed in a centrifuge to obtain the upper suspension; S02: The suspension is mixed with FeSO4·7H2O, ascorbic acid and H2C2O4·2H2O, and then placed in a muffle furnace for hydrothermal reaction; during the hydrothermal reaction, the temperature of the muffle furnace is 60~100℃, and the insulation time is 10~12h. After centrifugal washing, it is placed in a vacuum drying oven for drying to finally obtain a MXene / ferric oxalate composite material.

2. The method for preparing a MXene / ferric oxalate composite material according to claim 1, wherein: In step S01, the mass ratio of the LiF to the Ti3AlC2 is 1:1-1.

2.

3. The method for preparing a MXene / ferric oxalate composite material according to claim 1, wherein: In step S01, the heating time of the oil bath is 48-52 hours, and the heating temperature of the oil bath is 38-42°C.

4. The method for preparing a MXene / ferric oxalate composite material according to claim 1, wherein: In step S01, when HCl is used for centrifugal washing, the centrifugal speed of the HCl is 3000-4000 rpm; and the centrifugal time is 3-5 min.

5. The method for preparing a MXene / ferric oxalate composite material according to claim 1, wherein: In step S01, when deionized water is used for centrifugal washing, the centrifugal speed of the deionized water is 3500-6000 rpm; and the centrifugal time is 4-6 minutes.

6. The method for preparing a MXene / ferric oxalate composite material according to claim 1, wherein: In step S01, the ice bath ultrasonication time is 2 to 2.5 hours; when the upper suspension is centrifuged, the centrifugal speed of the centrifuge is 3500 to 4000 rpm; and the centrifugation time is 40 to 50 minutes.

7. The method for preparing a MXene / ferric oxalate composite material according to claim 1, characterized in that: In step S02, the molar ratio of the FeSO4·7H2O, the H2C2O4·2H2O and the ascorbic acid is 50:25:1, and the mass ratio of the FeSO4·7H2O to the MXene is 1:1-6.

8. The method for preparing a MXene / ferric oxalate composite material according to claim 1, characterized in that: In step S02, during centrifugal washing, the centrifugal speed is 6000-7000 rpm, the centrifugal time is 3-5 minutes, and then the product is placed in a vacuum drying oven at a temperature of 40-60° C. for a drying time of 10-12 hours.

9. A MXene / ferric oxalate composite material prepared according to the preparation method according to any one of claims 1 to 8.

Images