Sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane, preparation method thereof and application of sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane in vanadium redox flow battery

Abstract

The invention belongs to the technical field of vanadium redox flow batteries, and relates to a proton exchange membrane of a vanadium redox flow battery, in particular to a sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane, a preparation method of the sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane and application of the sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane in the vanadium redox flow battery. Comprising a polymer matrix, the polymer matrix contains a hybrid, and the hybrid is formed by sulfonated cellulose nanocrystals and an MXene material according to the mass ratio of 50: (5-25). The hybrid proton exchange membrane provided by the invention not only has low vanadium permeability, high proton conductivity and high ion selectivity, but also has good mechanical properties, so that the prepared vanadium redox flow battery has comprehensive and excellent battery performance.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery technology, and relates to proton exchange membranes for vanadium redox flow batteries, specifically to sulfonated cellulose nanocrystal / MXene hybrid proton exchange membranes, their preparation methods, and their application in vanadium redox flow batteries. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Vanadium redox flow batteries (or all-vanadium flow batteries, VRFB) offer advantages such as environmental friendliness, high efficiency, long cycle life, and safety and reliability, making them one of the preferred technologies for large-scale, high-efficiency energy storage. VRFB achieves the conversion of chemical energy into electrical energy through the redox reactions of vanadium ions with different valence states (V(IV) / V(V) in the positive electrode cell and V(III) / V(II) in the negative electrode cell. The proton exchange membrane (PEM) is a key component of VRFB, allowing proton exchange and preventing electrolyte cross-contamination. The overall performance of VRFB depends on the proton conductivity, vanadium ion permeability, chemical stability, and electrochemical stability of the PEM. High proton conductivity can improve voltage efficiency (VE) by increasing the ratio of discharge voltage to charge voltage, while vanadium ion cross-permeability reduces coulombic efficiency (CE) and accelerates the self-discharge process.

[0004] However, the high proton conductivity of proton exchange membranes often comes at the cost of vanadium ion resistance. For example, the widely commercialized perfluorosulfonic acid-based Nafion membranes possess high proton conductivity and excellent stability, but still suffer from high cost and low vanadium permeation resistance. Therefore, balancing proton conductivity and vanadium ion permeability to design VRFB proton exchange membranes with high ion selectivity is a challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide sulfonated cellulose nanocrystals.

[0006] The MXene hybrid proton exchange membrane and its preparation method, along with its application in vanadium redox flow batteries, provide a hybrid proton exchange membrane that not only has low vanadium permeability, high proton conductivity, and high ion selectivity, but also excellent mechanical properties, enabling the prepared vanadium redox flow batteries to have comprehensive and superior battery performance.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, a sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane includes a polymer matrix containing a first sulfonated cellulose nanocrystal and a hybrid, wherein the hybrid is formed by a second sulfonated cellulose nanocrystal and an MXene material, and the mass ratio of the first sulfonated cellulose nanocrystal to the hybrid is 50:5 to 25.

[0009] The first sulfonated cellulose nanocrystal and the second sulfonated cellulose nanocrystal described in this invention are both sulfonated cellulose nanocrystals.

[0010] Through experimental discovery, this invention found that when the first sulfonated cellulose nanocrystals and the hybrid formed by the second sulfonated cellulose nanocrystals and MXene material are incorporated into the polymer matrix at a mass ratio of 50:5 to 25, not only can the vanadium ion permeability be greatly reduced, but the proton conductivity, ion selectivity and ion exchange capacity can also be significantly increased.

[0011] Furthermore, further research has shown that when the mass ratio of the first sulfonated cellulose nanocrystals to the hybrid is 50:9 to 15 (especially 50:9 to 11), the mechanical properties of the hybrid proton exchange membrane can be greatly improved.

[0012] Secondly, a method for preparing the above-mentioned sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane includes the following steps:

[0013] The dispersion of second sulfonated cellulose nanocrystals was mixed with the dispersion of multilayer MXene material, and ultrasonic treatment was performed under inert atmosphere and ice bath conditions. Then, the supernatant was obtained by first centrifugation to obtain the hybrid.

[0014] First sulfonated cellulose nanocrystals and hybrids are added to a polymer matrix solution and mixed evenly to obtain a membrane-forming solution, which is then used to form a hybrid proton exchange membrane.

[0015] This invention enables the incorporation of sulfonated cellulose nanocrystals and MXene materials into a polymer matrix by ultrasonic treatment under inert atmosphere and ice bath conditions followed by centrifugation.

[0016] Thirdly, the application of the above-mentioned sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane in vanadium redox flow batteries.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention prepares a hybrid proton exchange membrane of one-dimensional SCNC and two-dimensional MXene by incorporating one-dimensional sulfonated cellulose nanocrystals (SCNC) / two-dimensional MXene hybrids into a polymer matrix. This membrane exhibits low vanadium permeability (as low as 4.92 × 10⁻⁶).- 9 cm 2 ·min -1 High proton conductivity (up to 15.8 mS·cm) -1 ) and high ion selectivity (up to 3.21 × 10⁻⁶) 6 S·min·cm -3 It exhibits excellent mechanical properties (tensile strength up to 53.38 MPa, strain up to 0.79%). The synergistic effect between one-dimensional SCNC and two-dimensional MXene nanosheets significantly enhances the performance of VRFB within the range of 40–120 mA·cm⁻¹. -2 At current densities of [specific values ​​not specified], the coulombic efficiency is 97.0–98.2%, the voltage efficiency is 83.07–93.44%, and the energy efficiency is 81.6–90.7%, exhibiting higher coulombic and energy efficiencies than the commercially available Nafion 212 membrane. Furthermore, the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane demonstrates good cycle stability in 90 charge-discharge cycles. The SCNC / MXene / PVDF-HFP hybrid proton exchange membrane prepared in this invention exhibits a comprehensive range of excellent battery performance, making it a potential candidate material for proton exchange membranes in VRFB (Vibration-Reverse Fusion Battery). Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a schematic diagram illustrating the fabrication of the SCNC / MXene / PVDF-HFP proton exchange membrane for a vanadium redox flow battery (VRFB) in an embodiment of the present invention.

[0021] Figure 2 The images shown are characterization diagrams of the synthesized SCNC in this embodiment of the invention; A is a transmission electron microscope (TEM) image, and the inset is an optical image of the SCNC dispersion under polarized light; B is an atomic force microscope (AFM) image.

[0022] Figure 3 The multilayer Ti3C2T synthesized in the embodiments of the present invention X Characterization diagram; A is a scanning electron microscope (SEM) image; B is an X-ray diffraction (XRD) pattern.

[0023] Figure 4 The images shown are characterization diagrams of the synthesized SCNC / MXene in this embodiment of the invention; A is a low-magnification atomic force microscope (AFM) image; B is a high-magnification AFM image, and the inset is a height profile along the indicator line; C is a TEM image.

[0024] Figure 5 The images shown are SEM images of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane prepared in the embodiments of the present invention; A is a surface SEM image, the inset is an optical image of the membrane; B is a cross-sectional SEM image.

[0025] Figure 6 The figure shows the test results of the physicochemical properties of the SCNC / MXene / PVDF-HFP hybrid proton exchange membranes containing 50% SCNC and different MXene contents (0-25%) prepared in the embodiments of the present invention; A is the vanadium ion permeability over 72 hours; B is the proton conductivity and ion selectivity; C is the stress-strain curve; D is the ion exchange capacity (IEC).

[0026] Figure 7 Figure A shows the electrochemical performance test results of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane prepared in the embodiments of the present invention; Figure B shows the current rate performance of the all-vanadium redox flow battery (VRFB) assembled using SCNC / MXene / PVDF-HFP, SCNC / PVDF-HFP and commercial Nafion 212 membrane; Figure C shows the current rate performance of SCNC / MXene / PVDF-HFP at different current densities (40, 60, 80, 100 and 120 mA cm⁻¹). -2 Charge-discharge curves of SCNC / MXene / PVDF-HFP and Nafion 212 at different current densities (40, 60, 80, 100 and 120 mA cm⁻¹); C represents the charge-discharge curves of SCNC / MXene / PVDF-HFP and Nafion 212 at different current densities (40, 60, 80, 100 and 120 mA cm⁻¹). -2 Coulomb efficiency (CE) at different current densities (40, 60, 80, 100, and 120 mA cm⁻¹); D represents the coulomb efficiency (CE) of SCNC / MXene / PVDF-HFP and Nafion212 at different current densities (40, 60, 80, 100, and 120 mA cm⁻¹). -2 Energy efficiency (EE) at different current densities (40, 60, 80, 100, and 120 mA cm⁻¹); E represents the energy efficiency of SCNC / MXene / PVDF-HFP and Nafion 212 at different current densities (40, 60, 80, 100, and 120 mA cm⁻¹). -2 Voltage efficiency (VE) under )

[0027] Figure 8 The figure shows the stability test results of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane prepared in the embodiments of the present invention; A represents the stability test results at 100 mA cm⁻¹. -2The discharge capacity, coulombic efficiency (CE), and energy efficiency (EE) of SCNC / MXene / PVDF-HFP after 90 consecutive charge-discharge cycles at a given current density are shown in Figure 1. B is a schematic diagram of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane. C is a schematic diagram of the proton transport path through the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] Given that current proton exchange membranes are difficult to simultaneously possess properties such as low vanadium ion permeability, high proton conductivity, and high ion selectivity, thus affecting the electrochemical performance of VRFB, this invention proposes a sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane, its preparation method, and its application in vanadium redox flow batteries.

[0031] A typical embodiment of the present invention provides a sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane, comprising a polymer matrix containing a first sulfonated cellulose nanocrystal and a hybrid, wherein the hybrid is formed by a second sulfonated cellulose nanocrystal and an MXene material, and the mass ratio of the first sulfonated cellulose nanocrystal to the hybrid is 50:5 to 25.

[0032] Studies have shown that the hybrid proton exchange membrane provided by this invention has properties such as low vanadium ion permeability, high proton conductivity, high ion selectivity and high ion exchange capacity, and the vanadium redox flow battery prepared with it has comprehensive and excellent battery performance.

[0033] Specifically, the mass percentage of the first sulfonated cellulose nanocrystals in the hybrid proton exchange membrane is 45-55%.

[0034] In some embodiments, the mass ratio of the first sulfonated cellulose nanocrystals to the hybrid is 50:9 to 15, preferably 50:9 to 11. Studies have shown that this condition can significantly improve the mechanical properties of the hybrid proton exchange membrane.

[0035] MXene materials are two-dimensional transition metal carbides, nitrides, or carbonitrides. In some embodiments, the MXene material is Ti3C2T. x Ti3C2T x As one of the most commonly used MXene materials, this invention uses Ti3C2T x Experiments have shown that adding a hybrid of sulfonated cellulose nanocrystals and MXene material in a specific ratio to a polymer matrix can enable the resulting hybrid proton exchange membrane to have the effects claimed in this invention.

[0036] In some embodiments, the polymer matrix is ​​made of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). This invention uses PVDF-HFP as the polymer matrix to verify that a hybrid formed by adding sulfonated cellulose nanocrystals and MXene material in a specific ratio can enable the resulting hybrid proton exchange membrane to possess the effects claimed in this invention.

[0037] Another embodiment of the present invention provides a method for preparing the above-mentioned sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane, comprising the following steps:

[0038] The dispersion of second sulfonated cellulose nanocrystals was mixed with the dispersion of multilayer MXene material, and ultrasonic treatment was performed under inert atmosphere and ice bath conditions. Then, the supernatant was obtained by first centrifugation to obtain the hybrid.

[0039] First sulfonated cellulose nanocrystals and hybrids are added to a polymer matrix solution and mixed evenly to obtain a membrane-forming solution, which is then used to form a hybrid proton exchange membrane.

[0040] In some embodiments, the mass ratio of the second sulfonated cellulose nanocrystals to the multilayer MXene material is 1:45 to 55.

[0041] In some embodiments, the ultrasonic treatment time is 0.5 to 2 hours.

[0042] In some embodiments, the supernatant is subjected to a second centrifugation to obtain a hybrid, which is then added to an organic solvent and dispersed evenly. A third centrifugation is then performed, and the supernatant from the third centrifugation is added to a solution of the polymer matrix. Specifically, the hybrid is added to N,N-dimethylformamide (DMF) and dispersed evenly. Using N,N-dimethylformamide to disperse the hybrid allows for better mixing of the hybrid with the polymer matrix.

[0043] In some embodiments, the hybrid proton exchange membrane is prepared by casting and vacuum drying.

[0044] The sulfonated cellulose nanocrystals described in this invention can be obtained commercially or in-house. In some embodiments, the preparation method of the sulfonated cellulose nanocrystals is as follows: cellulose nanocrystals are oxidatively aldehyde-treated to obtain aldehyde-treated cellulose nanocrystals, and then the aldehyde-treated cellulose nanocrystals are subjected to a sulfonation reaction to obtain sulfonated cellulose nanocrystals. Specifically, the oxidant used for aldehyde treatment is sodium periodate. Specifically, the sulfonating reagent used for the sulfonation reaction is sodium bisulfite.

[0045] In one or more embodiments, cellulose nanocrystals are obtained by hydrolyzing microcrystalline cellulose with sulfuric acid.

[0046] In some embodiments, the multilayer MXene material is Ti3C2T. x Ti3C2T x The preparation method is as follows: Ti3AlC2 is obtained by selective etching with hydrochloric acid-lithium fluoride.

[0047] In some embodiments, the polymer matrix is ​​made of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0048] A third embodiment of the present invention provides an application of the above-described sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane in a vanadium redox flow battery.

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0050] Example

[0051] The process for preparing the VRFB proton exchange membrane (sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane) in this embodiment is as follows: Figure 1 As shown, cellulose nanocrystals (CNCs) are first extracted from abundant renewable biomass materials via acid hydrolysis. Then, the CNCs are sulfonated through a combination of oxidation and sulfonation steps, introducing sulfonic acid groups and transforming them into SCNCs. Sulfonation of CNCs helps to establish more hydrogen proton transport channels. Ti3C2T x Preparation such as Figure 1 As shown in B, etching the MAX phase with HCl / LiF resulted in delamination and the formation of Ti3C2T. x MXene. Then, SCNC is introduced into the MXene stripping process to obtain an SCNC / MXene hybrid. Finally, as... Figure 1 As shown in Figure C, this SCNC / MXene hybrid was incorporated into the PVDF-HFP matrix to prepare a VRFB proton exchange membrane with enhanced battery performance characteristics.

[0052] Specifically, the preparation process is as follows:

[0053] Synthesis of SCNC:

[0054] Cellulose nanocrystals (CNCs) were prepared by hydrolyzing microcrystalline cellulose (MCC) with sulfuric acid. 15 g of MCC was added to a mixture of 150 mL H₂SO₄ and 154 mL H₂O, and the mixture was vigorously stirred mechanically at 45 °C for 60 min. The reaction was then terminated by adding 1000 mL of deionized water. The sulfuric acid-hydrolyzed CNCs were collected by centrifugation at 8000 rpm for 5 min, and this process was repeated 3-4 times to remove residual acid and impurities. The turbid suspension was sonicated at 450 W for 1 h, and then dialyzed with deionized water until the pH reached 3.5.

[0055] SCNC was then obtained by aldehyde and sulfonation of CNC. The CNC suspension and an aqueous sodium periodate solution (39.5 mL, 3.8 mg / mL) were added to a round-bottom flask and reacted with continuous stirring at 50 °C for 4 h to obtain aldehyde-modified CNC. The reaction was carried out in the dark to prevent photolysis of sodium periodate. The aldehyde-modified CNC was then diluted to 1 mg / mL and immediately sulfonated with an equal mass of sodium bisulfite at room temperature for 3 h. After the reaction was complete, the sulfonating agent was removed by continuous filtration to obtain an SCNC dispersion, which was then analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Figure 2 The preparation of A-2B was characterized, proving its success.

[0056] Synthesis of MXene:

[0057] Layered Ti3C2T was synthesized by selectively etching Al from Ti3AlC2. x First, 0.666 g of lithium fluoride (LiF) was dispersed in 10 mL of 6 M hydrochloric acid (HCl) and magnetically stirred for 35 min at room temperature to ensure thorough mixing. Next, 1 g of Ti3AlC2MAX powder was slowly added (for 30 min) with continuous stirring (500 rpm). The mixture was reacted at 35 °C for 35 h. Then, the resulting product was centrifuged and washed with deionized water until the pH value was greater than 6. The layered MXene was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the results are as follows: Figure 3 As shown. The XRD pattern of the prepared layered MXene is shown in the figure. Figure 3 As shown in Figure B, after LiF / HCl etching, the characteristic (104) peak (2θ = 39.1°) of Ti3AlC2 MAX disappeared, indicating that the Al layer was successfully etched. The (002) peak of the layered MXene broadened and shifted to 6.6° (d = 1.134 nm), indicating an increase in interlayer spacing.

[0058] Synthesis of SCNC / MXene:

[0059] Add 5 mL of SCNC (2 mg / mL) to 5 mL of layered Ti3C2T (100 mg / mL). x In the dispersion, the final concentration of SCNC was 1 mg / mL, and the layered Ti3C2T was prepared. x The final concentration was 50 mg / mL. The mixture was sonicated at 450 W for 1 h in an ice bath under argon protection. The homogeneous supernatant was then collected by centrifugation at 3500 rpm for 1 h to obtain the exfoliated SCNC / MXene hybrid. To transfer the SCNC / MXene hybrid to an N,N-dimethylformamide (DMF) dispersion, the supernatant was centrifuged at 15000 rpm for 1 h, the precipitate was carefully collected, and redispersed in DMF. After sonication at 450 W for 30 min, the SCNC / MXene / DMF dispersion was centrifuged at 3500 rpm for 1 h to collect a homogeneous supernatant (concentration ~15 mg / mL). The mixture was characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM and TEM images showed that the lateral dimensions of the SCNC / MXene hybrid nanosheets ranged from 160 nm to 1 μm, and the thickness ranged from 7 nm to 9.4 nm. Figure 4 It contains A-4C and can be dispersed uniformly and stably.

[0060] Preparation of SCNC / MXene hybrid proton exchange membranes:

[0061] A certain amount of SCNC and SCNC / MXene nano-assemblies were mixed with 10 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) / N,N-dimethylformamide (DMF) solution. The resulting homogeneous solution was then poured into a glass container and dried in a vacuum oven at 60 °C to prepare an SCNC / MXene hybrid proton exchange membrane. The mass percentages of SCNC, MXene, and PVDF-HFP are shown in Table 1. The surface of the membrane was then examined using a scanning electron microscope (SEM). Figure 5 A) and cross-section ( Figure 5 Observation using B-5D revealed a uniform microstructure. Cross-sectional image ( Figure 5 B) It was confirmed that the thickness of the membrane was 40.5 micrometers.

[0062] Table 1. Mass percentage of each component in the SCNC / MXene hybrid proton exchange membrane.

[0063] Serial Number SCNC (%) SCNC / MXene (%) PVDF-HFP (%) 1 50 0 50 2 50 1 49 3 50 2 48 4 50 5 45 5 50 10 40 6 50 25 25

[0064] Proton exchange membrane performance testing:

[0065] 1. Vanadium ion permeability:

[0066] VO was evaluated using a diffusion cell. 2+ The permeability of the membrane (with an effective area of ​​2.01 cm²) 2 The solution was placed between two diffusion half-cells. The left chamber contained 25 mL of a solution of 1 M VOSO4 / 2 M H2SO4, while the right chamber contained 25 mL of a solution of 1 M MgSO4 / 2 M H2SO4. Both chambers were continuously stirred to minimize concentration polarization. Every 12 hours, the concentration of VO4 in the right chamber was measured at 756 nm using a UV-Vis spectrophotometer (UV-2700, Shimadzu, Japan). 2+ The concentration of VO is then calculated using the following formula. 2+ Permeability:

[0067]

[0068] Among them, V B It is VO 2+ Volume of solution; C B (t) is the VO of the right ventricle at time t (minutes). 2+ Concentration. A is the effective area (2.01 cm²). 2 ), d is the membrane thickness. P is the VO. 2+ The permeability of C A Indicates VO in the left ventricle 2+ The initial concentration.

[0069] 2. Proton conductivity:

[0070] The membrane (effective area S = 2.01 cm²) was measured by electrochemical impedance spectroscopy (EIS) using a PARSTAT 2273 electrochemical workstation. 2 The proton conductivity (σ) of a conductive cell containing 2M H₂SO₄ solution was determined. The cell was divided into two chambers by a membrane. The resistances with and without the membrane (R₁) were measured by ESI at 25°C in the frequency range of 1MHz to 0.1Hz. The area resistivity of the membrane was calculated using the following formula: R = (R₁ - R₂) × S. The proton conductivity (σ) was then calculated using the following formula: σ = L / R, where L (cm) represents the membrane thickness and R (Ωcm) represents the total resistance. 2 ) indicates its area resistivity.

[0071] 3. Ion selectivity:

[0072] Ion selectivity is defined as the relationship between proton conductivity and VO2max. 2+ The ratio of permeability, calculated using the following formula: Ion selectivity = σ / P, where σ represents proton conductivity and P represents VO2max.2+ Its permeability.

[0073] 4. Ion exchange capacity test:

[0074] The ion exchange capacity (IEC) of the membrane was determined using classical titration. The membrane was dried at 60°C for 24 hours, and its weight (W) was recorded. dry Then, the sample was immersed in 2.0 M H₂SO₄ for 24 hours to ensure complete protonation. Afterward, the membrane was immersed in 1.0 M NaCl solution for 24 hours. Next, 0.01 M NaOH was used to remove H₂ from the solution. + The concentration is determined by titration. IEC is calculated using the following formula: IEC = C NaOH ×V NaOH / W dry C NaOH and V NaOH W represents the concentration and volume of the NaOH solution used in the titration, respectively. dry This indicates the dry weight of the membrane.

[0075] 5. Water absorption rate:

[0076] After drying in a vacuum oven, the membrane is immersed in water for 24 hours, and then excess surface moisture is absorbed using filter paper. Water absorption rate (WU) is calculated using the following formula:

[0077] WU = (W wet -W dry ) / W dry

[0078] Among them, W dry and W wet The weights are those of the dried film and the film after water absorption, respectively.

[0079] Performance test results:

[0080] The physicochemical properties of the proton exchange membrane, such as vanadium ion permeability, proton conductivity, ion selectivity, mechanical properties, and ion exchange capacity, all affect the efficiency and durability of the battery. This example tests the physicochemical properties of the prepared hybrid proton exchange membrane, and the results are as follows: Figure 6 As shown.

[0081] Figure 6The results show that as the concentration of the SCNC / MXene hybrid increases, its vanadium ion permeability, proton conductivity, ion selectivity, mechanical properties, and ion exchange capacity change. Overall, the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane exhibits excellent vanadium ion resistance, high proton conductivity and ion selectivity, and superior mechanical properties, thus showing great potential in vanadium flow battery membrane applications. With an SCNC mass concentration of 50%, a SCNC / MXene hybrid mass concentration of 5–25% can significantly reduce the vanadium ion permeability of the hybrid proton exchange membrane while significantly improving its proton conductivity, ion selectivity, and ion exchange capacity. Among these, a SCNC / MXene hybrid mass concentration of 10% results in better mechanical properties, with a tensile strength of 53.38 MPa and a strain of 0.79%. At this concentration, the membrane exhibits low vanadium permeability (4.92 × 10⁻⁶ MPa). -9 cm 2 ·min -1 High proton conductivity (15.8 mS·cm) -1 ) and high ion selectivity (3.21×10 6 S·min·cm -3 Therefore, an SCNC / 10% MXene / PVDF-HFP hybrid proton exchange membrane was used in a vanadium redox flow battery (VRFB) for subsequent performance testing.

[0082] Based on its excellent proton conductivity and vanadium ion resistance, this embodiment assembled a single vanadium redox flow battery (VRFB, where the positive electrode is 1.5 MV(IV) / V(V), 3M H2SO4; the negative electrode is 1.5 MV(II) / V(III), 3M H2SO4) to evaluate the performance of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane. Nafion and SCNC / PVDF-HFP membranes were used as controls at 40-120 mA cm⁻¹. -2 The current rate performance was tested within a current density range, with five consecutive cycles performed at each current density. Figure 7 A). At 40, 60, 80, 100, and 120 mA cm -2 At the given current densities, the battery capacities were 41.9, 40.6, 39.6, 38.8, and 37.9 Ah L, respectively. -1 When the current density returns to its initial value of 40 mA cm⁻¹ -2 At that time, the battery capacity was 40.4 Ah L. -1 The capacity retention is 96.4% of the original capacity. Compared to Nafion 212, the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane exhibits higher capacity retention due to its lower vanadium ion permeability. Figure 7 A). Figure 6 B showed 40 to 120 mA cm -2 Charge-discharge curves at current densities. At higher current densities, the overpotential increases due to increased ohmic losses and mass transport limitations, leading to a decrease in battery capacity. The coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) of Nafion, SCNC / PVDF-HFP membranes, and SCNC / MXene / PVDF-HFP hybrid proton exchange membranes are shown below. Figure 7 As shown in C-7E. Increasing the current density can shorten the charge / discharge time, thereby improving the CE value. The CE of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane is higher than that of the Nafion 212 membrane (97.0%-98.2% vs 93.4%-94.9%). Figure 7 C), which can be attributed to the low vanadium ion permeability of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane.

[0083] The EE of the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane is 81.6%-90.7%, which is higher than that of the Nafion 212 membrane (79.2%-88.1%). Figure 7 D). As the current density increases from 40 to 120 mA / cm² -2 The obtained VE decreased from 93.44% to 83.07%, mainly due to higher overpotential and ohmic resistance at higher current densities. Compared with commercial Nafion 212 membranes (VE ranging from 83.43% to 94.24%), the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane has comparable VEs, ranging from 83.07% to 93.44%. Figure 7 )

[0084] To further evaluate the stability of the membrane, a constant current density of 100 mA cm⁻¹ was used. -2 The single battery underwent 90 charge-discharge cycles. Figure 8 A). During 90 charge-discharge cycles, the battery exhibited a stable coulombic efficiency (CE) of 97.4%–98%, an energy efficiency (EE) of 84.4%, and retained 71% of its initial capacity. Figure 8The schematic diagram shown in B-8C illustrates this superior performance, which benefits from the proton transport channels formed between the SCNC and MXene nanosheets, enhancing proton conduction. Simultaneously, the high aspect ratio of SCNC and the large specific surface area and abundant titanium in MXene effectively prevent vanadium ion cross-penetration, thereby improving battery performance. Overall, the SCNC / MXene / PVDF-HFP hybrid proton exchange membrane exhibits superior overall battery performance, indicating its potential as a proton exchange membrane for all-vanadium redox flow batteries (VRFB).

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane, characterized in that, The invention includes a polymer matrix containing first sulfonated cellulose nanocrystals and a hybrid, the hybrid being formed by second sulfonated cellulose nanocrystals and MXene material, wherein the mass ratio of the first sulfonated cellulose nanocrystals to the hybrid is 50:5 to 25.

2. The sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane as described in claim 1, characterized in that, The first sulfonated cellulose nanocrystals have a mass percentage content of 45-55% in the hybrid proton exchange membrane; Alternatively, the mass ratio of the first sulfonated cellulose nanocrystals to the hybrid is 50:9 to 15, preferably 50:9 to 11.

3. The sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane as described in claim 1, characterized in that, The MXene material is Ti3C2T. x ; Alternatively, the polymer matrix may be made of polyvinylidene fluoride-hexafluoropropylene.

4. A method for preparing the sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane according to claim 1, characterized in that, Includes the following steps: The dispersion of second sulfonated cellulose nanocrystals was mixed with the dispersion of multilayer MXene material, and ultrasonic treatment was performed under inert atmosphere and ice bath conditions. Then, the supernatant was obtained by first centrifugation to obtain the hybrid. First sulfonated cellulose nanocrystals and hybrids are added to a polymer matrix solution and mixed evenly to obtain a membrane-forming solution, which is then used to form a hybrid proton exchange membrane.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the second sulfonated cellulose nanocrystals to the multilayer MXene material is 1:45-55; Alternatively, the ultrasonic treatment time is 0.5 to 2 hours.

6. The preparation method according to claim 4, characterized in that, The supernatant is centrifuged a second time to obtain a hybrid, which is then added to an organic solvent and dispersed evenly. A third centrifugation is then performed, and the supernatant from the third centrifugation is added to the polymer matrix solution.

7. The preparation method according to claim 4, characterized in that, Hybrid proton exchange membranes were fabricated using a casting and vacuum drying method.

8. The preparation method according to claim 4, characterized in that, The preparation method of sulfonated cellulose nanocrystals is as follows: cellulose nanocrystals are oxidized and aldehyde-treated to obtain aldehyde-treated cellulose nanocrystals, and then the aldehyde-treated cellulose nanocrystals are subjected to sulfonation to obtain sulfonated cellulose nanocrystals.

9. The preparation method according to claim 4, characterized in that, The multilayer MXene material is Ti3C2T. x ; Alternatively, the polymer matrix may be made of polyvinylidene fluoride-hexafluoropropylene.

10. The application of the sulfonated cellulose nanocrystal / MXene hybrid proton exchange membrane according to any one of claims 1 to 3 in a vanadium redox flow battery.

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