MXene-based conductive hydrogel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nano generators, and particularly relates to MXene-based conductive hydrogel as well as a preparation method and application thereof.The MXene-based conductive hydrogel comprises a rigid network constructed by dynamic physical crosslinking of carboxymethyl chitosan, ferric ions coordinated with the carboxymethyl chitosan network and a flexible network constructed by covalent crosslinking of acrylamide, and MXene nanosheets bonded to the polymer network by hydrogen bonds. Compared with the prior art, the problem that in the prior art, due to the fact that hydrogel can only achieve single-performance improvement of mechanical performance or electrical performance, the performance of the flexible friction nano-generator is poor is solved. According to the scheme, a three-dimensional conductive path is formed through a constructed carboxymethyl chitosan rigid network and a constructed polyacrylamide flexible network in cooperation with introduced MXene nanosheets, and the coordination effect of Fe < 3 + > ions is achieved, so that high stretchability of the hydrogel and high output voltage of hydrogel-based TENG are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanogenerators, and in particular relates to a MXene-based conductive hydrogel and a preparation method and application thereof. Background Art

[0002] The rapid development of flexible wearable electronic technology has placed higher demands on energy supply systems that combine flexible adaptability with dynamic reliability. Although lithium-ion batteries and supercapacitors have achieved significant breakthroughs in energy density and power density, their rigid packaging architecture, multi-process integration, and insufficient cycle durability make it difficult to meet the dual requirements of wearable scenarios for mechanical deformation compatibility and long-term stability. More importantly, such devices are unable to achieve an in-situ capture and storage loop for low-frequency mechanical energy (such as human motion and airflow disturbances) in the environment, resulting in the system's continued reliance on external energy supply networks.

[0003] In this context, the flexible triboelectric nanogenerator (TENG), with its unique contact electrochemical-electrostatic induction coupling mechanism, has become a cutting-edge direction for breaking through the bottleneck of traditional energy supply. Through the spatiotemporal modulation of the interface charge density and the synergistic optimization of the dynamic potential gradient, high energy conversion efficiency is achieved under broadband mechanical excitation, with output power ranging from microwatts to milliwatts. Its core advantages are reflected in the flexibility of the material system, which is compatible with heterogeneous substrates such as fabrics and skin; its self-driven energy supply characteristics, which enable the construction of an integrated sensing-energy supply system without an external power supply, and the ability to capture a wide spectrum of environmental mechanical energy, making it suitable for energy collection in multiple scenarios such as biokinetic energy and wind energy.

[0004] In recent years, hydrogels have become an ideal substrate for flexible triboelectric nanogenerator electrodes due to their excellent biocompatibility, high stretchability, and tissue compatibility. However, traditional single-network hydrogels generally suffer from the dual drawbacks of insufficient mechanical strength and poor electrical performance, which severely restricts their energy conversion efficiency under high-load scenarios. In order to break through the bottleneck of mechanical properties, the double-network cross-linking strategy can increase the fracture strength of hydrogels to the order of hundreds of kPa by constructing an energy dissipation mechanism. For example, CN111004400B discloses an alkali-soluble chitosan-polyacrylamide-polyaniline conductive hydrogel material with an adjustable conductive polymer network structure, which has a tensile strength of up to 0.80 MPa and an elongation at break of up to 365%. However, its electrical conductivity reaches a maximum of 2.89 S / m. In addition, CN114479125B discloses a double-network conductive hydrogel, a preparation method thereof, and a flexible wearable electronic device, which has a maximum electrical conductivity of up to 0.107 S / cm, a tensile strength of up to 0.18 MPa, and an elongation at break of up to 644.54%. At the same time, researchers often introduce conductive fillers such as graphene and carbon nanotubes to enhance electrical properties, but such materials are prone to phase separation or aggregation. For example, CN111748107A discloses a MXene material-reinforced conductive hydrogel with a conductivity of nearly 30×10 -4 S / cm, while its compressive stress is lower than 150kPa; for example, CN115418005A discloses a preparation method and application of an antifreeze pectin-based conductive hydrogel based on the synergistic effect of a conductive polymer and multivalent salt ions, the conductivity of which can reach 8.085S / m, while its compressive stress is lower than 0.12MPa and its tensile performance is 800%; this shows that the currently disclosed hydrogels have an imbalance in mechanical-electrical properties.

[0005] Therefore, constructing a flexible friction nanogenerator with high stretchability and high electrical output performance has become one of the urgent problems to be solved. Summary of the Invention

[0006] The purpose of the present invention is to provide a MXene-based conductive hydrogel and its preparation method and application in order to solve at least one of the above problems, so as to solve the problem that the hydrogel-based flexible triboelectric nanogenerator in the prior art can only achieve a single performance improvement of mechanical properties or electrical properties (it cannot achieve a simultaneous improvement of mechanical and electrical properties), resulting in weak performance of the flexible triboelectric nanogenerator. This solution constructs a rigid network of carboxymethyl chitosan and a flexible network of polyacrylamide, and combines the introduction of MXene nanosheets to form a three-dimensional conductive path, as well as Fe 3+ The coordination effect of ions enables the high stretchability of the hydrogel and the high output voltage of the hydrogel-based TENG.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention discloses a MXene-based conductive hydrogel, comprising:

[0009] A rigid network constructed by dynamic physical cross-linking of carboxymethyl chitosan (CMC), and

[0010] ferric ions coordinated to the carboxymethyl chitosan network, and

[0011] A flexible network constructed by covalent crosslinking of acrylamide, and

[0012] MXene nanosheets bound to polymer networks (including carboxymethyl chitosan rigid networks and polyacrylamide flexible networks) through hydrogen bonding;

[0013] Wherein, the polymer network is a double network structure formed by a rigid network and a flexible network.

[0014] A second aspect of the present invention discloses a method for preparing the MXene-based conductive hydrogel as described above, comprising the following steps:

[0015] S1: Preparation of MXene:

[0016] Disperse LiF in hydrochloric acid solution, add MAX powder and continue stirring to adjust the pH of the solution to weak acidity;

[0017] The precipitate was taken and redispersed, and after ultrasonic treatment, the supernatant was collected by centrifugation to obtain a MXene suspension;

[0018] S2: Preparation of MXene-based conductive hydrogels:

[0019] Prepare carboxymethyl chitosan solution, add MXene suspension and acrylamide and continue stirring until completely dissolved, then transfer to an ice bath environment, and add ammonium persulfate, N,N-methylenebisacrylamide and tetramethylethylenediamine in sequence and continue stirring;

[0020] The obtained solution is allowed to stand for gelation, and then immersed in a trivalent iron salt solution to obtain the MXene-based conductive hydrogel.

[0021] Preferably, in step S1, the ratio of LiF to hydrochloric acid solution is 2 g:40 mL, the concentration of the hydrochloric acid solution is 9 M, and the MAX powder is titanium aluminum carbide powder.

[0022] Preferably, in step S1, the step of adjusting the pH of the solution to weak acidity is:

[0023] Deionized water was added to the mixed solution containing MAX powder, and the mixture was centrifuged. The centrifugation step was repeated until the pH of the supernatant stabilized to 6.

[0024] Preferably, in step S1, the ultrasonic treatment is performed under nitrogen atmosphere for 1 hour.

[0025] Preferably, in step S2, the concentration of the carboxymethyl chitosan solution is 4 wt %, and the concentration of the MXene nanosheets in the MXene suspension is 0.25-1.25 wt %.

[0026] Preferably, in step S2, the ratio of carboxymethyl chitosan to acrylamide in the carboxymethyl chitosan solution and MXene nanosheets in the MXene suspension is 2 g:2.84 g:1 mL.

[0027] Preferably, step S2 includes one or more of the following:

[0028] i) the mass ratio of carboxymethyl chitosan to ammonium persulfate in the carboxymethyl chitosan solution is 2:0.05;

[0029] ii) the mass ratio of carboxymethyl chitosan to N,N-methylenebisacrylamide in the carboxymethyl chitosan solution is 2:0.001;

[0030] iii) The ratio of carboxymethyl chitosan to tetramethylethylenediamine in the carboxymethyl chitosan solution is 2 g:10 μL.

[0031] Preferably, in step S2, the immersion time is 30 minutes, and the concentration of the trivalent iron salt solution is 0.5M.

[0032] The third aspect of the present invention discloses an application of the MXene-based conductive hydrogel as described above in a flexible tribonanogenerator.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] In the prior art, CN111748107A constructs a single-network hydrogel containing a hydroxyl matrix, realizes cross-linking with MXene nanosheets by means of hydrogen bonds, and then uses metal cations to assist in reinforcement; CN111004400B uses chitosan / graphene oxide and polyacrylamide to build a double-network hydrogel structure, but the conductive component polyaniline selected is only dispersed in the network as an ordinary conductive filler. The hydrogel network of the present invention is composed of a double-network structure consisting of a dynamically physically cross-linked carboxymethyl chitosan rigid network and a covalently cross-linked polyacrylamide flexible network. The introduced MXene nanosheets can further form a three-dimensional conductive path through the hydrogen bonding between the surface hydroxyl groups and the polymer chains, thereby improving the electrical output performance of the hydrogel-based TENG. In addition, Fe 3+The coordination of ions within the CMC network not only enhances the network crosslinking density but also improves the electrical output performance of the hydrogel-based TENG through ionic conductivity. The resulting conductive hydrogel not only exhibits a high stretchability of 1654%, but also boasts an output voltage of up to 143V. Therefore, this approach offers significant advantages in multiple dimensions compared to existing technologies in terms of performance and design logic (the specific mechanism is analyzed below):

[0035] First of all, in terms of performance, the hydrogel prepared by this scheme has achieved a double improvement in mechanical and electrical properties. The existing technology has obvious limitations: the CN111004400B scheme has limited stretchability due to polyaniline filling (elongation at break is only 365%); the CN111748107A scheme is limited to a single network structure and has insufficient compressive stress (<150kPa). This scheme uses a rigid network of carboxymethyl chitosan (Fe 3+ The dual network structure of polyacrylamide (PMMA) and the flexible network of polyacrylamide, combined with the mechanical enhancement of MXene nanosheets, achieves an ultra-high stretchability of 1654%. 3+ The synergistic effect of ionic conductivity makes the output voltage of the hydrogel-based TENG as high as 143V, which is significantly better than the performance of existing hydrogel-based TENG.

[0036] Secondly, in terms of conductive mechanism, compared with CN111748107A which only utilizes the intrinsic conductivity of MXene, this scheme anchors MXene to the polymer network through hydrogen bonding to form a continuous and stable conductive network; in addition, the Fe 3+ Ions not only act as cross-linking agents to enhance mechanical properties, but their ionic conductivity complements the electronic conductivity of MXene, further improving the electrical output of TENG. However, the CN111004400B solution relies on the single conductive mechanism of polyaniline, and the ionic conductivity in the CN111748107A solution has limited contribution, making it difficult to achieve the performance effect of the present application solution.

[0037] Finally, in terms of dynamic cross-linking mechanism design and focused application scenarios, this scheme combines carboxymethyl chitosan with Fe 3+ The dynamic coordination and cross-linking mechanism imparts fatigue resistance to the hydrogel. By optimizing the mechanical-electrical balance, it can adapt to high-frequency mechanical deformation (e.g., TENG for energy harvesting from human motion). This proposal focuses on flexible triboelectric nanogenerator applications, addressing the low energy conversion efficiency of existing TENGs due to insufficient hydrogel performance. However, CN111004400B and CN111748107A are more targeted towards sensors or biomaterials, and do not address the design of TENGs for interfacial charge regulation and dynamic potential gradient optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 PAM / CMC / MXene prepared in Example 1 1.00% Mechanical properties test results of the hydrogel and the PAM / CMC hydrogel prepared in the comparative example;

[0039] Figure 2 PAM / CMC / MXene prepared in Example 1 1.00% Electrical properties test results of hydrogel;

[0040] Figure 3 PAM / CMC / MXene / Fe prepared in Examples 1-5 3+ Mechanical properties test results of hydrogel;

[0041] Figure 4 PAM / CMC / MXene / Fe prepared in Examples 1-5 3+ Electrical properties test results of hydrogel. DETAILED DESCRIPTION

[0042] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] The present invention will be described in detail below with reference to specific embodiments, but the present invention is by no means limited thereto.

[0044] In the following description, unless otherwise specified, the reagents used are conventional commercial products, the methods used are well known in the art, and matters not covered may be based on existing technologies.

[0045] Example 1

[0046] A method for preparing a MXene-based conductive hydrogel flexible triboelectric nanogenerator:

[0047] Step 1: Preparation of MXene

[0048] 2g of LiF was dispersed in 40mL of 9M hydrochloric acid solution and stirred at room temperature for 30 minutes until completely dissolved. Then, 2g of MAX powder (titanium aluminum carbide powder) was slowly added and stirred at 40°C for 24 hours. Deionized water was then added and the mixture was centrifuged at 4000 rpm for 5 minutes. This centrifugation was repeated until the pH of the supernatant stabilized to 6. The resulting precipitate was dispersed in deionized water and sonicated under nitrogen for 1 hour. Finally, the supernatant was separated by centrifugation for 30 minutes to obtain a MXene suspension. This suspension was diluted with water to 1wt% (10mg / mL) and stored at low temperature until further use.

[0049] Step 2: Preparation of MXene-based conductive hydrogel

[0050] Carboxymethyl chitosan (CMC, 2 g) was dissolved in deionized water (48 g) and heated and stirred to form a uniform CMC solution (4 wt%). Subsequently, 1 mL of MXene suspension containing 1 wt% MXene nanosheets and acrylamide (AM, 2.84 g) were added in sequence and stirred continuously until completely dissolved. The mixed solution was transferred to an ice bath environment, and ammonium persulfate (APS, 0.05 g), N,N-methylenebisacrylamide (MBAA, 0.001 g) and tetramethylethylenediamine (TEMED, 10 μL) were added in sequence and stirred continuously for 5 minutes. After the solution was injected into the mold, it was allowed to stand at 60 ° C for 2 hours to complete gelation to obtain PAM / CMC / MXene. 1.00% The hydrogel was further immersed in 0.5 M FeCl3 solution for 30 minutes to obtain PAM / CMC / MXene. 1.00% / Fe 3+ hydrogel.

[0051] Step 3: Preparation of MXene-based conductive hydrogel flexible triboelectric nanogenerator

[0052] First, the A and B components of Ecoflex 00-30 silicone rubber (commercially available) were mixed in a mass ratio of 1:1 (according to the steps in the product manual), injected into the mold and allowed to stand for 2 hours to fully cure. Then, the conductive hydrogel (PAM / CMC / MXene prepared in step 2) pre-connected with the copper conductive tape was placed in the mold. 1.00% / Fe 3+ The hydrogel was placed on the surface of the cured silicone rubber, and then the Ecoflex 00-30 silicone rubber mixed in equal proportions was injected again. The mixture was left to stand for 2 hours to complete the secondary curing, thus completing the MXene-based conductive hydrogel flexible friction nanogenerator (hydrogel-based flexible friction nanogenerator).

[0053] Comparative Example

[0054] This comparative example is PAM / CMC, and its preparation method is:

[0055] Carboxymethyl chitosan (CMC, 2 g) was dissolved in deionized water (48 g) and heated with stirring to form a homogeneous CMC solution (4 wt%). Acrylamide (AM, 2.84 g) was then added and stirred until completely dissolved. The mixed solution was transferred to an ice bath, and ammonium persulfate (APS, 0.05 g), N,N-methylenebisacrylamide (MBAA, 0.001 g), and tetramethylethylenediamine (TEMED, 10 μL) were added sequentially and stirred for 5 minutes. The solution was then poured into a mold and allowed to stand at 60°C for 2 hours to complete gelation, resulting in a PAM / CMC hydrogel.

[0056] Mechanical testing method: Dumbbell-shaped specimens (size 4 mm × 3 mm, thickness of each specimen was measured before testing) were subjected to uniaxial tensile tests using an electronic universal testing machine (ZWICK, Germany). The loading rate was set to 50 mm∙min. -1 .

[0057] like Figure 1 As shown in the figure, the elongation at break of PAM / CMC hydrogel is 883% and the fracture stress is 92 kPa; 1.00% The elongation at break of the hydrogel is 1412% and the stress at break is 278 kPa. It can be seen that the mechanical properties of the PAM / CMC hydrogel prepared in the comparative example are significantly inferior to those of the PAM / CMC / MXene prepared in Example 1. 1.00% hydrogel.

[0058] Example 2

[0059] This example is basically the same as Example 1, with the main difference being that the concentration of MXene nanosheets added is 0.25 wt%. The final product is PAM / CMC / MXene. 0.25% / Fe 3+ hydrogel.

[0060] Example 3

[0061] This example is basically the same as Example 1, with the main difference being that the concentration of MXene nanosheets added is 0.50 wt%. The final product is PAM / CMC / MXene. 0.50% / Fe 3+ hydrogel.

[0062] Example 4

[0063] This example is basically the same as Example 1, with the main difference being that the concentration of MXene nanosheets added is 0.75 wt%. The final product is PAM / CMC / MXene. 0.75% / Fe 3+ hydrogel.

[0064] Example 5

[0065] This example is basically the same as Example 1, with the main difference being that the concentration of MXene nanosheets added is 1.25 wt%. The final product is PAM / CMC / MXene. 1.25% / Fe 3+ hydrogel.

[0066] Electrical testing method: First, a copper conductive tape was attached to the hydrogel electrode of the TENG. The copper conductive tape was then connected to the clamp end of a Keithley multimeter (Keithley 6514) to obtain an electrical signal. An electrometer and multimeter (Keithley DMM 6500) were used to measure the open-circuit voltage and short-circuit current.

[0067] like Figure 2 As shown, the PAM / CMC / MXene prepared in Example 1 1.00% The open circuit voltage of the hydrogel is 83 V under the conditions of working pressure of 40 kPa and working frequency of 1 Hz.

[0068] like Figure 3 As shown, the PAM / CMC / MXene / Fe prepared by Examples 1-5 3+ The mechanical properties of the hydrogel increase with the increase of MXene concentration and reach the maximum value when the MXene concentration is 1 wt%. 0.25% / Fe 3+ The elongation at break of the hydrogel is 1213%, and the fracture stress is 168 kPa; PAM / CMC / MXene 0.50% / Fe 3+ The elongation at break of the hydrogel is 1367%, and the fracture stress is 214 kPa; PAM / CMC / MXene 0.75% / Fe 3+ The elongation at break of the hydrogel is 1483%, and the fracture stress is 269 kPa; PAM / CMC / MXene 1.25% / Fe 3+ The elongation at break of the hydrogel is 1356% and the breaking stress is 262 kPa. 3+ The introduction of PAM / CMC / MXene 1.00% / Fe 3+ The mechanical properties of hydrogel are significantly better than those of PAM / CMC / MXene 1.00% Hydrogel, PAM / CMC / MXene 1.00% / Fe 3+ The elongation at break of the hydrogel was 1654%, and the breaking stress was 343 kPa.

[0069] like Figure 4 As shown, when Fe 3+ After that, the electrical output performance of TENG was greatly improved, PAM / CMC / MXene 0.25% / Fe 3+ The open circuit voltage output of hydrogel-based TENG is 78 V; PAM / CMC / MXene 0.50% / Fe3+ The open circuit voltage output of hydrogel-based TENG is 92 V; PAM / CMC / MXene 0.75% / Fe 3+ The open circuit voltage output of hydrogel-based TENG is 126 V; PAM / CMC / MXene 1.25% / Fe 3+ The open circuit voltage output of hydrogel-based TENG is 142 V; PAM / CMC / MXene 1.00% / Fe 3+ The hydrogel-based TENG has the highest electrical output performance, with an open-circuit voltage output of 143V.

[0070] Test results: The hydrogel not only has a high stretchability of 1654%, but the hydrogel-based TENG also has an open-circuit voltage output of up to 143V.

[0071] like Figure 2 As shown, the PAM / CMC / MXene prepared in Example 1 1.00% hydrogels; e.g. Figure 3 、 4 As shown, the PAM / CMC / MXene / Fe prepared by Examples 1-5 3+ hydrogel.

[0072] This scheme consists of a dynamic physically cross-linked carboxymethyl chitosan rigid network and a covalently cross-linked polyacrylamide flexible network. The introduced MXene nanosheets form a three-dimensional conductive path through the hydrogen bonding between the surface hydroxyl groups and the polymer chains, and Fe 3+ The coordination of ions within the CMC network not only enhances the network's crosslinking density but also, through synergy with MXene, improves the electrical output performance of the hydrogel-based TENG. The improved hydrogel not only exhibits a high stretchability of 1654%, but also boasts an open-circuit voltage output of up to 143V.

[0073] In summary, the MXene-based conductive hydrogel flexible friction nanogenerator of the present invention can be used as a self-powered element to convert mechanical energy into electrical energy, and can solve the inherent rigidity defects of components such as batteries, meeting the dual requirements of wearable devices for mechanical deformation compatibility and long-term stability.

[0074] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A MXene-based conductive hydrogel, characterized in that include: A rigid network constructed by dynamic physical cross-linking of carboxymethyl chitosan, and ferric ions coordinated to the carboxymethyl chitosan network, and A flexible network constructed by covalent crosslinking of acrylamide, and MXene nanosheets bound to the polymer network via hydrogen bonds; Wherein, the polymer network is a double network structure formed by a rigid network and a flexible network.

2. A method for preparing a MXene-based conductive hydrogel according to claim 1, characterized in that: The steps include: S1: Preparation of MXene: Disperse LiF in hydrochloric acid solution, add MAX powder and continue stirring to adjust the pH of the solution to weak acidity; The precipitate was taken and redispersed, and after ultrasonic treatment, the supernatant was collected by centrifugation to obtain a MXene suspension; S2: Preparation of MXene-based conductive hydrogels: Prepare carboxymethyl chitosan solution, add MXene suspension and acrylamide and continue stirring until completely dissolved, then transfer to an ice bath environment, and add ammonium persulfate, N,N-methylenebisacrylamide and tetramethylethylenediamine in sequence and continue stirring; The obtained solution is allowed to stand for gelation, and then immersed in a trivalent iron salt solution to obtain the MXene-based conductive hydrogel.

3. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: In step S1, the ratio of LiF to hydrochloric acid solution is 2 g:40 mL, the concentration of the hydrochloric acid solution is 9 M, and the MAX powder is titanium aluminum carbide powder.

4. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: In step S1, the step of adjusting the pH of the solution to weak acidity is: Deionized water was added to the mixed solution containing MAX powder, and the mixture was centrifuged. The centrifugation step was repeated until the pH of the supernatant stabilized to 6.

5. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: In step S1, the ultrasonic treatment is performed under nitrogen atmosphere for 1 hour.

6. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: In step S2, the concentration of the carboxymethyl chitosan solution is 4 wt%, and the concentration of the MXene nanosheets in the MXene suspension is 0.25-1.25 wt%.

7. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: In step S2, the ratio of carboxymethyl chitosan to acrylamide to MXene suspension in the carboxymethyl chitosan solution is 2 g:2.84 g:1 mL.

8. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: Step S2 includes one or more of the following: i) the mass ratio of carboxymethyl chitosan to ammonium persulfate in the carboxymethyl chitosan solution is 2:0.05; ii) the mass ratio of carboxymethyl chitosan to N,N-methylenebisacrylamide in the carboxymethyl chitosan solution is 2:0.001; iii) The ratio of carboxymethyl chitosan to tetramethylethylenediamine in the carboxymethyl chitosan solution is 2 g:10 μL.

9. The method for preparing a MXene-based conductive hydrogel according to claim 2, wherein: In step S2, the immersion time is 30 minutes, and the concentration of the ferric salt solution is 0.5M.

10. Use of the MXene-based conductive hydrogel as claimed in claim 1 in a flexible triboelectric nanogenerator.

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