Functionalized few-layer MXene, preparation method and high-conductivity proton exchange membrane

Abstract

The invention discloses functionalized few-layer MXene, a preparation method and a high-conductivity proton exchange membrane, and the preparation method comprises the following steps: etching treatment, alkalization treatment, ultrasonic treatment, rotary evaporation concentration and optional modification treatment to obtain a functionalized few-layer MXene (less than five layers) concentrated solution; the functional few-layer MXene and the protonated polymer are compounded to prepare the high-conductivity proton exchange membrane f-MXene / PA-PBI, so that the mechanical property and the proton conductivity of the PA-PBI membrane are well improved, and particularly the proton conductivity at low temperature is improved. According to the invention, the high stability of the interlayer intercalation water of the functionalized few-layer MXene at high temperature is utilized, so that the high-temperature and high-conductivity proton exchange membrane fuel cell stack can realize multiple times of high-temperature and low-temperature start-stop switching, and the practical application of the PA-PBI high-temperature proton exchange membrane fuel cell is greatly facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of MXene nanomaterials, and specifically relates to a preparation method of functionalized few-layer MXene, functionalized few-layer MXene and a high-conductivity proton exchange membrane. Background Art

[0002] The proton exchange membrane fuel cell (PEMFC) is a clean energy device that efficiently converts hydrogen directly into electricity. It has attracted considerable attention for its high efficiency and environmental friendliness. The proton exchange membrane (PEM) is a core component of the fuel cell, playing a key role in isolating reactant gases (preventing hydrogen and oxygen from diffusing into each other), conducting protons, loading catalysts, and participating in water management. The performance of the PEM has a crucial impact on the efficiency and lifespan of the fuel cell, and therefore, improving the PEM has been a key research focus for PEMFCs.

[0003] Compared to traditional low-temperature proton exchange membrane fuel cells (LT-PEMFC), high-temperature proton exchange membrane fuel cells (HT-PEMFC) offer significant advantages. Currently, high-temperature proton exchange membranes are primarily polybenzimidazole (PBI)-type high-temperature resistant membranes (PA-PBI) doped with phosphoric acid (PA), operating at temperatures between 120 and 180°C. As a good proton solvent, PBI, when doped with phosphoric acid, can ionize the hydrogen ions of the phosphoric acid, freeing the electrolyte membrane from its dependence on solvent water and enabling rapid proton transport at temperatures exceeding 100°C. However, PA-PBI membranes also have some drawbacks. The main drawback is that after phosphoric acid doping, the mechanical properties of PBI decrease, the proton conductivity is inferior to that of low-temperature Nafion membranes, and the phosphoric acid is easily dissolved and lost in water.

[0004] Increasing the phosphoric acid doping level (ADL) in PBI is the primary method for improving proton conductivity, but increasing the ADL reduces the strength of the PBI membrane, so there's a trade-off between the membrane's mechanical strength and reduced proton conductivity. In PA-PBI membranes, proton migration can occur without the involvement of water. A large number of hydrogen bond networks form between PA molecules, and protons are primarily transferred through the Grotthuss mechanism, whereby protons are transported through the membrane through the rearrangement of intermolecular hydrogen bonds. Of course, at high temperatures, some PA molecules and a very small amount of water molecules in the membrane can diffuse through the membrane via a carrier mechanism to transfer protons. Although PA-PBI proton conduction does not require the participation of water molecules, relative humidity can still affect the membrane's proton conductivity because water is a stronger proton solvent than PBI. When H2O molecules participate in proton transport through the Grotthuss mechanism, proton transport is faster.

[0005] At low temperatures (<80°C), PA has poor fluidity and may even condense into a solid (<42°C). The PA-PBI membrane's proton transport capacity is weak, and protons can only be transported through the hydrogen bond network between water molecules within the membrane. However, after operating at high temperatures, the water in the PA-PBI membrane evaporates, and the water molecule content within the membrane is very low, resulting in very low proton transport efficiency during low-temperature restart. The stack cannot rely on its own reaction heat to heat up to the rated operating temperature (160°C), so external auxiliary heating is generally required. This brings great inconvenience to the application of PA-PBI high-temperature proton exchange membrane fuel cells.

[0006] On the other hand, MXene, as an emerging two-dimensional nanolayered material, has attracted much attention due to its superior electrical properties and abundant hydrophilic groups (such as fluorine-F, oxygen-O, and hydroxyl-OH). MXene is obtained by etching the "A" element layer in MAX phase materials using chemical reagents containing hydrogen fluoride (HF). MXene has the following significant characteristics:

[0007] Research has shown that even after drying overnight at 200°C under vacuum, the intercalated water remains intact, contributing to MXene's excellent water retention. Furthermore, while the interlayer size effect of MXene makes it difficult for hydrated ions to pass through, the intercalated water can form fast water molecule channels through hydrogen bonds, significantly facilitating proton transport. Finally, the hydroxyl groups on the MXene surface serve not only as a medium for proton transport but also as active sites for chemical modification, endowing it with a wider range of functionalization potential. These characteristics suggest that MXene has potential applications in proton exchange membranes, particularly in improving the membrane's water absorption and retention properties and high-temperature proton conductivity.

[0008] Document 1 (Michael Naguib et al, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials Adv. Mater. 2014, 26, 992-1005) points out that the interlayer spacing of MXene changes with etching conditions, especially the concentration of HF and etching time. For MXene Ti3C2(OH)2 with hydroxyl as the end group, hydrazine molecules N2H4 can be intercalated between Ti3C2 layers. The molecular plane of hydrazine is parallel to the Ti3C2 layer plane, but molecular dynamics calculations show that the monolayer Ti3C2(OH)2 is not a most stable state. Document 2 (Michael A. Hope et al, NMR reveals the surface functionalisation of Ti3C2 MXene, Phys. Chem. Chem. Phys., 2016, 18, 5099-5102) points out that the MXene Ti3C2T produced by the conventional LiF-HCl etchant and vacuum drying method x The terminal groups T are mainly F and O. Reference 3 (Michael Ghidiu et al, Ion-Exchange and Cation Solvation Reactions in Ti3C2 MXene, Chem. Mater. 2016, 28, 3507-3514) believes that when etching, if there are appropriate cations, such as Li + , K + , Na +The expansion of interlayer spacing is related to humidity and the hydration enthalpy of cations. Based on the technical findings of the aforementioned literature, the present invention utilizes a method of dynamically increasing the etching reagent concentration by flowing a carrier gas during etching, and a method of converting F and O end groups to OH end groups by alkalization after etching. This allows planar water molecules to quickly and reversibly enter the MXene interlayers, achieving two objectives: first, efficiently exfoliating the MAX phase to form a structurally stable 2-4-layer MXene through intercalation of water molecules; second, ensuring that the interlayers of the exfoliated MXene contain thermally stable structural water capable of proton transfer at high temperatures. Prior art, such as patent CN119170840A, discloses a MXene-assisted cation exchange membrane for electrodialysis desalination and its preparation method. This invention improves the membrane's ion exchange capacity and desalination performance by filling a sulfonated polymer matrix with small-platelet-sized MXene nanosheets. However, the proton conductivity of its core matrix, sulfonated polyvinyl alcohol, is low, and it is prone to dehydration and performance degradation under high temperature conditions, making it difficult to meet the needs of high-temperature proton exchange membrane fuel cells (HT-PEMFCs).

[0009] Invention CN114221003B discloses a method for preparing a proton exchange membrane, comprising the following steps: S1. Mixing a strong acid solution and a fluoride salt to obtain a mixed solution, then adding a MXene precursor to the mixed solution for etching; S2. Ultrasonic treatment of the etched MXene precursor to produce a MXene material; S3. Mixing the MXene material with a cerium salt for a hydrothermal reaction to produce a CeO2 / MXene composite material; and S4. Membrane formation using the CeO2 / MXene composite material and Nafion as raw materials. Although this invention uses a mixture of a strong acid solution and a fluoride salt to etch the MXene precursor to produce a morphologically intact MXene material, the highly corrosive properties of the strong acid and fluoride salt can alter the chemical environment on the MXene surface and between layers. The layered structure of MXene relies on the interaction between fluoride salts and metal elements. The chemical interaction between the strong acid and fluoride salt may weaken the interlayer bonding strength of the MXene, leading to dissociation or inhomogeneity of the interlayer structure, which may affect water retention and proton conduction channels.

[0010] Therefore, how to functionalize MXene to improve its proton conductivity, water absorption and water retention, while enhancing its interfacial bonding with the matrix material, so as to prepare a proton exchange membrane with excellent high-temperature proton conduction performance and chemical stability, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0011] In response to the defects in the above-mentioned prior art, the present invention provides a high-temperature proton exchange membrane based on functionalized few-layer MXene and a preparation method thereof. By surface functionalization modification of MXene (such as sulfonation, hydroxylation or amination), its proton conductivity, water absorption and water retention are significantly improved. By synergistically enhancing with a matrix material (such as polybenzimidazole), a proton exchange membrane with high-temperature proton conduction performance, mechanical strength and chemical stability is prepared, overcoming the problems of insufficient proton conductivity, poor high-temperature stability and phosphoric acid loss of existing membranes.

[0012] In a first aspect, the present invention provides a method for preparing a functionalized few-layer MXene, characterized in that it comprises the following steps:

[0013] S1 etching:

[0014] dissolving a fluoride salt in a strong acid solution to obtain a mixed solution;

[0015] Add MAX phase powder into the mixed solution for etching;

[0016] The precipitate was collected by centrifugation and washed, filtered, and freeze-dried to obtain a few-layer MXene powder;

[0017] S2 alkalization treatment:

[0018] The MXene powder is added to an alkaline reagent solution for alkalization treatment;

[0019] The precipitate was collected by centrifugation and washed, filtered, and freeze-dried to obtain high-hydroxyl and low-fluorine MXene powder;

[0020] S3 ultrasonic treatment: ultrasonically treat the high hydroxyl low fluorine MXene powder, take the supernatant, and obtain a high hydroxyl low fluorine MXene colloidal solution;

[0021] S4 rotary evaporation concentration: The high-hydroxyl, low-fluorine MXene colloidal solution is rotary evaporated to obtain a functionalized few-layer MXene concentrate.

[0022] The alkalization treatment of MXene powder in the present invention is an important step in the preparation method of functionalized few-layer MXene. The F end group is converted into an OH end group, which reduces the concentration of surface fluorine groups and increases hydrophilic groups such as hydroxyl groups. These hydroxyl groups can promote proton conduction through hydrogen bonding, facilitate the insertion of water molecules between MAX phase layers, and make the subsequent ultrasonic stripping process more efficient. At the same time, the intercalated water retained between the layers has good stability under high temperature conditions, so that a rapid proton transmission channel is formed between the MXene layers. The alkalization treatment also provides structural conditions for a variety of subsequent modification treatments, such as the optional sulfonation treatment, hydroxylation treatment, and amination treatment, which are mainly used to regulate the type of MXene surface end groups, thereby optimizing the interfacial interaction force between it and the polymer matrix. If the alkalization treatment is lacking as a prerequisite, the subsequent modification treatment will not be able to give full play to its structural and performance advantages.

[0023] Preferably, step S1 satisfies at least one of the following conditions:

[0024] (1) The fluoride salt is selected from at least one of LiF and NaF, the strong acid solution is selected from at least one of HCl solution and H2SO4 solution, the concentration of the strong acid solution is 4-12M, and the MAX phase is an etching product of the MAX phase in which A is Al;

[0025] (2) A protective gas is flowed throughout the etching process, wherein the protective gas is selected from at least one of an inert gas and a reducing gas;

[0026] (3) Etching is performed at 40-50°C and a stirring rate of 200-400 rpm for 8-48 hours.

[0027] Preferably, the preparation method satisfies at least one of the following conditions:

[0028] In step S1, 0.6-1.2 g of fluoride salt and 0.5-1.5 g of MAX phase powder are added to every 20-35 mL of strong acid solution;

[0029] In step S2, the alkaline reagent solution is selected from at least one of a KOH solution and a NaOH solution, with a concentration of 0.5-3M;

[0030] In step S3, ultrasonic treatment is performed under inert gas protection for more than 30 minutes, and the solid content of the high-hydroxyl low-fluorine MXene colloidal solution is greater than 80%;

[0031] In step S4, rotary evaporation is performed at 45-55° C. under vacuum for more than 30 minutes.

[0032] Preferably, after step S4, the functionalized few-layer MXene concentrate is subjected to a modification treatment, wherein the modification treatment includes at least one of sulfonation treatment, hydroxylation treatment, and amination treatment.

[0033] Sulfonation introduces sulfonic acid groups (-SO3H), hydroxylation enhances surface hydrophilicity and proton conductivity, and amination further improves its composite properties with the matrix by providing hydrogen bonding and electrostatic interactions. The presence of surface groups creates a proton transport "hopping mechanism," effectively improving proton conduction efficiency.

[0034] Preferably, the modification treatment includes sulfonation treatment, comprising the following steps:

[0035] A1: mixing the functionalized few-layer MXene concentrate, the sulfonation reagent and the solvent;

[0036] A2: React at 105-125°C for 1-3 hours;

[0037] A3: Filtration, washing, and drying to obtain sulfonated few-layer MXene powder.

[0038] Preferably, the modification treatment includes a hydroxylation treatment, comprising the following steps:

[0039] B1: Add the functionalized few-layer MXene concentrate to an alkaline aqueous solution and ultrasonicate for 2-4 hours under inert gas protection;

[0040] B2: react at 50-65°C for 45-60 hours;

[0041] B3: Centrifugation, washing, and drying to obtain hydroxylated few-layer MXene powder.

[0042] Preferably, the modification treatment includes an amination treatment, comprising the following steps:

[0043] C1: Add the functionalized few-layer MXene concentrate to the amination reagent and stir for 1-5 minutes;

[0044] C2: Stir at 400-500 rpm for 20-30 hours at room temperature;

[0045] C3: After washing, the precipitate is centrifuged and treated with ultrasound in an organic solvent for 2-4 hours, and then dried to obtain aminated few-layer MXene powder.

[0046] In a second aspect, the present invention further provides a functionalized few-layer MXene, which is prepared by the preparation method described above. The number of layers of the functionalized few-layer MXene is less than 5 layers, preferably 2-5 layers, and more preferably 3-4 layers.

[0047] In a third aspect, the present invention also provides a high-conductivity proton exchange membrane, comprising the aforementioned functionalized few-layer MXene and a protonated polymer. Optionally, the high-conductivity proton exchange membrane is a phosphoric acid-doped protonated polymer membrane composited with the functionalized few-layer MXene.

[0048] In the high conductivity proton exchange membrane of the present invention, the intercalated water retained between the functionalized few-layer MXene layers has good stability under high temperature conditions, and the doped phosphoric acid penetrates into the pores between the polymer chains to form a stable acid-base pair, so that free H + The conductive site shows high temperature resistance, high conductivity, high phosphate retention and other properties. For example, the proton conductivity at 40-160℃ is above 40mS / cm; the current density (0.6V, 40℃) is 100mA / cm 2 Above, the current density (0.6V, 160℃) is 400mA / cm 2 Above; Maximum power density (40℃) is 100mW / cm 2 Above, the maximum power density (160℃) is 600mW / cm 2 The phosphate retention rate (120h, 160°C) is above 70%, preferably above 80%, and more preferably above 85%. In addition, protonated polymers, such as PBI, can provide good temperature resistance and mechanical strength. After adding functionalized few-layer MXene, especially f-MXene modified by sulfonation, the temperature resistance and mechanical properties of the high-conductivity proton exchange membrane can be improved as a whole. For example, the tensile strength can be increased to above 50MPa, preferably above 55MPa, and more preferably above 60MPa. This results in a proton exchange membrane with both high-temperature proton conductivity, mechanical properties, and chemical stability, overcoming the problems of insufficient proton conductivity, poor high-temperature stability, and phosphoric acid loss in existing membranes.

[0049] The high conductivity proton exchange membrane comprises a basic protonated polymer, which refers to a polymer that can be protonated (binding protons) or deprotonated (releasing protons) under certain conditions, preferably including but not limited to at least one of polyacrylic acid (PAA) and its derivatives, polyethyleneimine (PEI), polyaniline and its derivatives, chitosan and its derivatives, poly-N-isopropylacrylamide (PNIPAM), polydopamine (PDA) and imidazole ring polymers (such as polybenzimidazole (PBI)) and its derivatives (such as aromatic ether polybenzimidazole (oPBI), poly 2,2'-(m-phenyl)-5,5'-bibenzimidazole) (mPBI), poly (2,5-benzimidazole) (AB-PBI), etc.).

[0050] In a fourth aspect, the present invention further provides a method for preparing a high-conductivity proton exchange membrane, wherein the protonated polymer includes an imidazole ring polymer, and the high-conductivity proton exchange membrane is a functionalized few-layer MXene composite phosphoric acid-doped imidazole ring polymer membrane, comprising the following steps:

[0051] Step 1: dissolving the protonated polymer in an organic solvent, adding the functionalized few-layer MXene and ultrasonically dispersing the mixture to obtain a casting solution;

[0052] Step 2: Coating the casting solution on the substrate and removing the organic solvent to obtain the f-MXene / protonated polymer composite membrane;

[0053] Step 3: Soaking the f-MXene / protonated polymer composite membrane in a phosphoric acid aqueous solution with a temperature of 100-125° C. and a concentration of 75-90 wt % to obtain the high conductivity proton exchange membrane.

[0054] f-MXene is a brief representation of the functionalized few-layer MXene material obtained by the functionalized few-layer MXene preparation method of the present invention. MXene is a two-dimensional transition metal carbide / nitride with a general chemical formula of M (n+1) X n T x (M is a transition metal such as Ti, V, etc., X is carbon or nitrogen, T x is the surface end group). In the present invention, MXene is obtained by etching the MAX phase (such as Ti3AlC2) with a mixed solution of fluoride salt and strong acid, and then the surface fluorine (-F) end group is partially converted into hydroxyl (-OH) by alkalinization treatment, and specific functional groups (such as sulfonic acid group -SO3H, amino group -NH2) can be optionally further introduced through modification steps such as sulfonation, hydroxylation or amination. This functionalization process significantly reduces the fluorine content of MXene, improves its hydrophilicity, proton conductivity and interfacial bonding performance with the polymer matrix. The intercalated water retained between the MXene layers is stable at high temperatures, and the hydrogen bond network formed by the surface functional groups constructs a rapid proton transport channel (such as a hopping mechanism), thereby giving f-MXene excellent high-temperature proton conductivity and structural stability.

[0055] Preferably, the imidazole ring polymer includes at least one of polybenzimidazole (PBI), aromatic ether polybenzimidazole (oPBI), poly-2,2'-(m-phenyl)-5,5'-bibenzimidazole (mPBI), and poly(2,5-benzimidazole) (AB-PBI). When polybenzimidazole (PBI) is used as the protonated polymer, the resulting high-conductivity proton exchange membrane can be represented as f-MXene / PA-PBI (functionalized few-layer MXene composite phosphoric acid-doped polybenzimidazole membrane), a high-temperature proton exchange membrane prepared by doping with phosphoric acid (H3PO4) using polybenzimidazole (PBI) as the protonated polymer matrix. PBI is a heterocyclic polymer that is resistant to high temperatures and has high mechanical strength, but its intrinsic proton conductivity is low. In the present invention, f-MXene and PBI are first dissolved in an organic solvent to form a composite casting solution. After film formation, an f-MXene / PBI composite membrane is obtained, which is then immersed in a high-temperature (100-125°C) and high-concentration (75-90wt%) phosphoric acid aqueous solution. Phosphoric acid molecules penetrate into the pores between PBI chains and form stable acid-base pairs with the imidazole rings on the molecular chains (such as the hydrogen bond between NH and H3PO4), forming free H + The introduction of f-MXene further enhances the performance of the PA-PBI membrane. In particular, after modification, its surface sulfonic acid or hydroxyl groups form a synergistic hydrogen bond network with phosphoric acid, which not only improves proton conduction efficiency but also inhibits the high-temperature loss of phosphoric acid molecules through interfacial bonding. Ultimately, f-MXene / PA-PBI can still maintain high proton conductivity (>0.1S / cm) and long-term stability in low-humidity environments above 120°C, making it suitable for high-temperature proton exchange membrane fuel cells.

[0056] The technical solution provided by the present invention has at least the following beneficial effects:

[0057] (1) The present invention performs a series of functionalization treatments on MXene materials (such as Ti3AlC2) to prepare functionalized few-layer MXene (f-MXene) with less than 5 layers, which is then compounded with protonated polymers (such as PBI, oPBI, mPBI, AB-PBI, etc.) and doped with PA to prepare a composite PEM. Due to the rich hydroxyl end groups and high-temperature stable intercalated water of the functionalized few-layer MXene (f-MXene), the low-temperature startup performance of the composite PEM is greatly improved, the proton conductivity at 40-160°C is increased to above 40 mS / cm, and the maximum power density reaches 600 mW cm -2 (160℃) and above, and the tensile strength of the composite PEM is also greatly improved.

[0058] (2) Based on the previous functionalization treatment, the present invention further grafts functional groups such as sulfonic acid groups on the end groups of the functionalized few-layer MXene (f-MXene) through modification treatments such as sulfonation, which is beneficial to improving the dispersion uniformity of the functionalized few-layer MXene in the polymer matrix and the bonding force between the functionalized few-layer MXene and the polymer matrix. While improving the mechanical properties, it also improves the low-temperature starting performance and high-temperature conductivity of the composite PEM. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a flow chart for preparing the high conductivity proton exchange membrane of the present invention;

[0060] Figure 2 This is a photo of the MXene and its high-conductivity proton exchange membrane prepared in Example 4 of the present invention, wherein:

[0061] (a) Scanning electron micrograph of clay-like multilayer MXene just after etching.

[0062] (b) Scanning electron micrograph of the few-layer MXene after alkalization and ultrasonication.

[0063] (c) Polarized light micrograph of the MXene concentrate after rotary evaporation.

[0064] (d) Scanning electron micrograph of the f-MXene / oPBI composite membrane of functionalized few-layer MXene and oPBI after sulfonation treatment. DETAILED DESCRIPTION

[0065] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0066] The terms used in the embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "a," "an," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, and unless the context clearly indicates otherwise, "a plurality" generally includes at least two.

[0067] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the product or device comprising the element.

[0068] See attached Figure 1 A high-conductivity proton exchange membrane comprising the functionalized few-layer MXene is prepared by a method comprising:

[0069] Step 1: Preparation of functionalized few-layer MXene with less than 5 layers:

[0070] S1. Etching: Add concentrated hydrochloric acid, fluoride salt, and MAX phase powder to a reaction kettle, adding 0.6-1.2 g of fluoride salt and 0.5-1.5 g of MAX phase powder for every 20-35 mL of strong acid solution; the fluoride salt is selected from at least one of LiF and NaF, and the strong acid solution is selected from at least one of HCl solution and H2SO4 solution, and the concentration of the strong acid solution is 4-12 M, preferably 9 M;

[0071] The MAX phase is an etching product of a MAX phase in which A is Al, such as Ti3AlC2, Ti2AlC, etc.

[0072] Stir at room temperature to completely dissolve the fluoride salt, then place the reactor in a 0°C ice-water bath, slowly add the MAX phase powder, cover, and degas by bubbling argon. Then transfer the reactor to a 45°C oil bath and magnetically stir at 300 rpm to perform MAX phase etching. Etching is performed at 40-50°C and a stirring rate of 200-400 rpm for 8-48 hours. A protective gas is flowed throughout the etching process at a flow rate of 500-2000 sccm. The protective gas is selected from at least one of an inert gas or a reducing gas, preferably argon at 1000 sccm. After the etching reaction is completed, the supernatant of the reaction solution is removed by centrifugation, and the precipitate is rinsed with dilute hydrochloric acid to remove excess Li+ ions. It is then washed with deionized water until the pH value of the supernatant is 6.0. Filtering is then performed to obtain a MXene clay cake, which is freeze-dried to obtain a thin layer of MXene powder.

[0073] S2. Alkalization: Add an appropriate amount of MXene powder to 50 ml of an alkaline solution (at least one of KOH and NaOH, with a concentration of 0.5-3 M). Magnetic stirring is performed for 30 minutes, followed by centrifugation and washing, repeated multiple times until the pH reaches a neutral pH of 7.0. Filter and freeze-dry to obtain high-hydroxyl, low-fluorine MXene powder.

[0074] S3. Ultrasonic exfoliation: Pour an appropriate amount of the high-hydroxyl, low-fluorine MXene powder into a gas washing bottle, add 80 ml of deionized water, and first deoxygenate with inert gas for at least 30 minutes. Then, place in an ice bath and ultrasonicate for at least 30 minutes, maintaining the protective gas state during the ultrasonication process. After the ultrasonication is completed, centrifuge at 3500 rpm for at least 30 minutes, and collect the supernatant to obtain a high-hydroxyl, low-fluorine MXene colloidal solution. The high-hydroxyl, low-fluorine MXene colloidal solution has a solid content greater than 80% and is stored in a refrigerator below 4°C.

[0075] S4. Rotary evaporation concentration: Pour 100 ml of the MXene colloidal solution into a 500 ml round-necked flask, connect a rotary evaporator to a 45-55°C water bath, and perform rotary evaporation under vacuum for at least 30 minutes until the solution thickens and clings to the wall. The resulting MXene concentrate is sealed in a container under a protective atmosphere and stored in a refrigerator below 4°C. The protective atmosphere may be argon, helium, hydrogen, or nitrogen, preferably argon.

[0076] Step 2: dissolving polybenzimidazole (PBI) or aryl ether polybenzimidazole (oPBI) in an organic solvent, adding the functionalized few-layer MXene and ultrasonically dispersing the mixture to obtain a casting solution;

[0077] Step 3: The casting solution is coated on the substrate and placed in a 60°C oven to dry for 24 hours to remove the solvent. The membrane is then immersed in ethanol and stirred for 24 hours to remove the residual solvent. The membrane is then immersed in a 120°C oven for 1 hour to remove water to obtain an f-MXene / PBI composite membrane or f-MXene / oPBI composite membrane;

[0078] The organic solvent is dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), preferably dimethylacetamide; the amount of MXene added is 1 to 7 wt% of the mass of PBI / oPBI, preferably 3 to 5 wt%.

[0079] Step 4: Soaking the f-MXene / PBI composite membrane or f-MXene / oPBI composite membrane in a phosphoric acid aqueous solution at a temperature of 100-125° C. and a concentration of 75-90 wt % to obtain a high conductivity proton exchange membrane f-MXene / PA-PBI or f-MXene / PA-oPBI.

[0080] Example 1

[0081] A high-conductivity proton exchange membrane comprising the functionalized few-layer MXene is prepared by the following method:

[0082] Step 1: Preparation of functionalized few-layer MXene:

[0083] (1) Etching: Add 1g LiF to 30ml 9M hydrochloric acid and stir for 10 minutes. Then slowly add 1g Ti3AlC2 powder to the reactor under ice water bath, cover it, bubble with argon to degas, and then transfer it to a 45℃ oil bath and stir it magnetically at 300 rpm. The entire etching reaction process is protected by argon, which also acts as a carrier gas to remove the volatile liquid phase in the reactor. The flow rate is 1000sccm. After the specified 24-hour etching time, remove the solution in the reactor and centrifuge to remove the supernatant; rinse the precipitate with 1M hydrochloric acid to remove excess Li + ions, and then washed with deionized water until the pH of the supernatant is about 6.0, and then filtered to obtain a Ti3AlC2 clay cake. A portion of the Ti3AlC2 clay cake was freeze-dried to prepare a multilayer Ti3AlC2 powder sample for later use.

[0084] (2) Alkalization: Add an appropriate amount of Ti3AlC2 clay cake or Ti3AlC2 powder to 50ml of 1M KOH solution, stir magnetically for 30 minutes, then wash and centrifuge, and repeat the above steps until the pH is close to neutral. During this alkalinization process, Ti3AlC2 will swell again. The washed alkalinized Ti3AlC2 clay cake is dispersed again in deionized water, placed in a test tube and vacuum filtered to obtain alkalinized low-F multilayer MXene Ti3AlC2. After freeze-drying, Ti3AlC2 powder is obtained and is ready for testing.

[0085] (3) Ultrasonic exfoliation: Pour an appropriate amount of Ti3AlC2 powder into a gas washing bottle, add 80 ml of deionized water, and pass argon for 30 minutes to deoxygenate. Then, ultrasonicate for 30 minutes. Keep the argon flow and ice bath during the ultrasonication process. After the ultrasonication, centrifuge at 3500 rpm for 30 minutes. Take the supernatant, which is the low-fluorine few-layer Ti3AlC2 colloidal solution, and store it in a refrigerator below 4°C until it is concentrated.

[0086] (4) Rotary evaporation concentration: Pour 100 ml of Ti3AlC2 colloidal solution into a round-mouth flask, connect a rotary evaporator, and place it in a 50°C water bath. Rotary evaporate under vacuum for 30 minutes until the solution thickens and hangs on the wall. The Ti3AlC2 concentrated solution is obtained, sealed in a container with an argon atmosphere, and stored in a refrigerator at 4°C for later use.

[0087] Step 2: Dissolve 0.35 g of oPBI [4,4′-diphenylether]-5,5′-bibenzimidazole] in 12 ml of 60°C DMAC, add about 5 wt% of Ti3AlC2 concentrate to the solution, and then sonicate for 1 hour to disperse evenly to obtain a casting solution;

[0088] Step 3: The slurry was coated on a 10×10 cm horizontal glass plate and dried in a 60°C oven for 24 hours to remove the solvent. The resulting membrane was immersed in ethanol and stirred for 24 hours to further remove the residual solvent. The membrane was then dried in a 60°C oven for 1 hour to remove water, resulting in an f-MXene / oPBI composite membrane.

[0089] Step 4: Soak the f-MXene / oPBI composite membrane in a phosphoric acid aqueous solution at a temperature of 120° C. and a concentration of 85 wt % to obtain the high conductivity proton exchange membrane f-MXene / PA-oPBI.

[0090] Example 2

[0091] The difference between this embodiment and embodiment 1 is that the alkalization treatment conditions are different. This embodiment uses a 3M KOH alkaline reagent solution, and the other preparation steps and process parameters are the same.

[0092] Example 3

[0093] The difference between this embodiment and embodiment 1 is that the alkalization treatment conditions are different. This embodiment uses a 0.5M KOH alkaline reagent solution, and the other preparation steps and process parameters are the same.

[0094] Example 4

[0095] The difference between this embodiment and embodiment 1 is that the functionalized few-layer MXene concentrate is sulfonated and then a high-conductivity proton exchange membrane is prepared.

[0096] The sulfonation modification method comprises the following steps:

[0097] A1: Take 0.3g of functionalized few-layer MXene concentrate and mix it with 6ml of sulfosuccinic acid solution, pour it into a flask, add 4ml of distilled water, and stir;

[0098] A2: react at 120°C for 2 hours;

[0099] A3: After the reaction is completed, filter and rinse with deionized water for 5 to 10 times, then wash with ethanol for 5 times, and then dry in a 40°C oven for more than 12 hours to obtain sulfonated few-layer MXene powder.

[0100] Step 2: Dissolve 0.35 g of oPBI [4,4′-(diphenylether)-5,5′-bibenzimidazole] in 12 ml of 60°C DMAC, add 3 wt% of sulfonated few-layer Ti3AlC2 powder to the solution, and then sonicate for 1 hour to evenly disperse the powder to obtain a casting solution;

[0101] Step 3: The slurry was coated on a 10×10 cm horizontal glass plate and dried in a 60°C oven for 24 hours to remove the solvent. The resulting membrane was immersed in ethanol and stirred for 24 hours to further remove the residual solvent. The membrane was then dried in a 60°C oven for 1 hour to remove water, resulting in an f-sMXene / oPBI composite membrane.

[0102] Step 4: Soak the f-sMXene / oPBI composite membrane in a phosphoric acid aqueous solution at a temperature of 120° C. and a concentration of 85 wt % to obtain the high conductivity proton exchange membrane f-sMXene / PA-oPBI.

[0103] Example 5

[0104] This embodiment differs from embodiment 1 in that the functionalized few-layer MXene concentrate is hydroxylated and then a high-conductivity proton exchange membrane is prepared. The hydroxylation modification method includes the following steps:

[0105] B1: 0.5 g of functionalized few-layer MXene concentrate was added to 50 ml of 0.5 M NaOH aqueous solution and sonicated for 3 h under argon atmosphere;

[0106] B2: Stir at 60°C for about 50 hours;

[0107] B3: Centrifuge and wash repeatedly until the pH reaches a neutral pH of 7.0, then dry in a 40°C oven for more than 12 hours to obtain hydroxylated few-layer MXene powder.

[0108] Step 2: Dissolve 0.35 g of oPBI [4,4′-diphenylether]-5,5′-bibenzimidazole] in 12 ml of 60°C DMAC, add 3 wt% of hydroxylated few-layer Ti3AlC2 powder to the solution, and then sonicate for 1 hour to evenly disperse the powder to obtain a casting solution;

[0109] Step 3: The slurry was coated on a 10×10 cm horizontal glass plate and dried in a 60°C oven for 24 hours to remove the solvent. The resulting membrane was immersed in ethanol and stirred for 24 hours to further remove the residual solvent. The membrane was then dried in a 60°C oven for 1 hour to remove water, resulting in an f-MXene / oPBI composite membrane.

[0110] Step 4: Soak the f-MXene / oPBI composite membrane in a phosphoric acid aqueous solution at a temperature of 120° C. and a concentration of 85 wt % to obtain the high conductivity proton exchange membrane f-MXene / PA-oPBI.

[0111] Example 6

[0112] This embodiment differs from embodiment 1 in that the functionalized few-layer MXene concentrate is aminated in step 2 (before compounding with oPBI). Other preparation methods and process parameters are the same. The amination modification method includes the following steps:

[0113] C1: 10 mg of functionalized few-layer MXene concentrate was centrifuged at 20,000 rpm to remove surface adsorbents, and then 10 ml of oleylamine was added and stirred for 3 minutes.

[0114] C2: The solution was stirred continuously at 450 rpm for 24 hours at room temperature;

[0115] C3: Wash with 30 ml of ethanol to remove residual amination reagent, centrifuge the washing solution at high speed for 5 minutes, discard the supernatant, collect the bottom sediment, and then ultrasonically treat it in 3 ml of cyclohexane for 3 hours, and then place it in a 40°C oven to dry for more than 12 hours to obtain aminated few-layer MXene powder.

[0116] Step 2: Dissolve 0.35 g of oPBI [4,4′-(diphenylether)-5,5′-bibenzimidazole] in 12 ml of 60°C DMAC, add 5 wt% of aminated few-layer Ti3AlC2 powder to the solution, and then sonicate for 1 hour to evenly disperse the powder to obtain a casting solution;

[0117] Step 3: The slurry was coated on a 10×10 cm horizontal glass plate and dried in a 60°C oven for 24 hours to remove the solvent. The resulting membrane was immersed in ethanol and stirred for 24 hours to further remove the residual solvent. The membrane was then dried in a 60°C oven for 1 hour to remove water, resulting in an f-MXene / oPBI composite membrane.

[0118] Step 4: Soak the f-MXene / oPBI composite membrane in a phosphoric acid aqueous solution at a temperature of 120° C. and a concentration of 85 wt % to obtain the high conductivity proton exchange membrane f-MXene / PA-oPBI.

[0119] Example 7

[0120] This embodiment differs from embodiment 4 in that a different protonated polymer is used, and oPBI in step 2 is replaced by mPBI (poly 2,2'-(m-phenyl)-5,5'-bibenzimidazole). Other preparation methods and process parameters are the same.

[0121] Example 8

[0122] The difference between this embodiment and embodiment 7 is that mPBI in step 2 is replaced by AB-PBI (poly(2,5-benzimidazole)), and other preparation methods and process parameters are the same.

[0123] Comparative Example 1

[0124] This comparative example differs from Example 1 in that no alkalization treatment is performed, and other preparation methods and process parameters are the same.

[0125] Comparative Example 2

[0126] The difference between this comparative example and comparative example 1 is that the functionalized few-layer MXene concentrate is subjected to sulfonation modification, and the sulfonation modification steps are the same as those in Example 4.

[0127] Control group 1

[0128] oPBI without MXene was used as a control for testing.

[0129] Control group 2

[0130] mPBI without MXene was used as a control for testing.

[0131] Control group 3

[0132] AB-PBI without MXene was used as a control for testing.

[0133] Test Method

[0134] 1. ADL (phosphoric acid doping level) and swelling ratio (SR): PBI dry film was cut into 4 cm x 6 cm rectangles and dried in a 120°C drying oven for 2 hours. The film was weighed and its volume was measured. The film was then immersed in an 85 wt% phosphoric acid (PA) aqueous solution at 120°C for 24 hours. The film was removed and the excess PA on the surface was wiped off with tissue paper. The film was then weighed and its volume was measured again. The phosphoric acid doping level and swelling ratio were calculated from the difference in film mass and the change in volume using the following formula:

[0135]

[0136] The results were the average of three parallel tests.

[0137] 2. Wet film tensile strength and elongation: The test was conducted in accordance with the method specified in ISO 1184-1983, "Plastic Films — Determination of Tensile Properties." The film was immersed in PA at 120°C for at least 24 hours, then cut into a 4 mm x 15 mm dumbbell-shaped tensile specimen. The specimen was stretched at room temperature at a rate of 2 mm / min on a SANS-CMT4204 universal testing machine. The tensile strength and elongation (elongation at break) were determined based on the resulting tensile stress-strain curve.

[0138] 3. Phosphoric acid retention (AR): Weigh a 4 cm x 6 cm piece of dry PBI membrane, then soak it in an 85 wt% phosphoric acid solution for 24 hours. Remove it, blot the surface with tissue paper to remove any residual liquid, and weigh it again. Place the saturated phosphoric acid-doped PBI membrane sample in a constant temperature and humidity chamber at 120°C and 100% humidity. Remove the sample every 5 hours, wipe the surface clean with tissue paper, and weigh it again. Calculate the AR after 120 hours:

[0139]

[0140] 4. Proton conductivity: Electrochemical impedance spectroscopy (EIS) was used on an electrochemical workstation CHI760E. The frequency range was 1 to 10 6 Hz, the standing time is 2s, and the AC voltage amplitude is 0.05V. The proton conductivity of the membrane is calculated by the following formula:

[0141] σ=L / (R×A)

[0142] Where L, R, and A represent the electrode spacing, membrane resistance, and membrane cross-sectional area, respectively.

[0143] Before testing, the PBI membrane was immersed in PA for 24 hours for PA doping. After being taken out, the PA on the surface was wiped dry to measure the size of the membrane. The membrane was then placed in a heatable sealed metal mold. The mold was heated to the measurement temperature (40-160°C) and kept warm for 1 hour to make the moisture content in the membrane consistent. The measurement voltage was then applied using a gold-plated electrode.

[0144] 5. Current density @ 0.6V and maximum power density: obtained from the IV curve of a single fuel cell discharge in an anhydrous environment.

[0145] The Pt loading was 1 mg / cm 2 , 15wt% PTFE hydrophobically treated carbon paper electrodes were used as anode and cathode, and the effective catalytic layer area was 2.25×2.25cm 2 The membrane electrode assembly (MEA) was not hot-pressed. The IV curve of the battery was measured using a fuel cell test platform. The test conditions were: 80 mL / min of dry hydrogen was passed through the anode, 160 mL / min of dry air was passed through the cathode, and the battery temperature was 40°C or 160°C.

[0146] Test results

[0147] The test results of Examples 1-8, Comparative Example 1, Comparative Example 2, and Control Groups 1-3 are shown in Table 1:

[0148] Table 1

[0149]

[0150] As can be seen from the data in Table 1, the comprehensive performance of each embodiment is significantly improved compared with the samples of the comparative example and the control group. For example, the proton conductivity at 40-160°C is above 40mS / cm; the current density (0.6V, 40°C) is above 100mA / cm 2 Above, the current density (0.6V, 160℃) is 400mA / cm 2 Above; Maximum power density (40℃) is 100mW / cm 2 Above, the maximum power density (160℃) is 600mW / cm 2 The phosphoric acid retention rate (120h, 160°C) is above 70%, preferably above 80%, more preferably above 85%; the tensile strength can be increased to above 50MPa, preferably above 55MPa, more preferably above 60MPa. Specifically:

[0151] ADL and SR: Compared to Control 1, the oPBI membrane's phosphate saturation loading (ADL) increased by 19% from 320% to 380% after incorporation of sulfonated Ti3AlC2 in Example 4, while its swelling ratio (SR) increased by only 5%. This suggests that incorporation of sulfonated Ti3AlC2 improves oPBI's solubility in PA. However, in Comparative Example 2, which also employed sulfonation modification, the ADL was significantly reduced due to the lack of prior alkalinization treatment.

[0152] Mechanical properties: The tensile test showed that the tensile strength of the samples in the embodiment was significantly improved compared with the samples without PA doping in the control group, especially the composite membrane obtained after sulfonation treatment, which had a significant improvement in tensile strength.

[0153] Conductivity and Durability: Compared to Control 1, the sulfonated Ti3AlC2 composite membrane of Example 4 achieved a phosphoric acid retention rate exceeding 90% after 120 hours at 160°C. Proton conductivity at 40°C increased from 27mS / cm to 45mS / cm, and at 160°C from 35mS / cm to 70mS / cm, demonstrating significant improvements. Proton conductivity at both 40°C and 160°C was also significantly improved for each example compared to the corresponding control.

[0154] Fuel cell performance: Assembled into fuel cell test, Example 4 sulfonated Ti3AlC2 composite PA-oPBI membrane has a current density of 200mA / cm at 40°C 2 @0.6V, power density reaches 150mW / cm 2 ; The current density reached 800mA / cm at 160℃ 2 @0.6V, power density reaches 750mW / cm 2At the same time, Examples 7 and 8 with different protonated polymers also have good battery stack performance.

[0155] The present invention significantly improves the physical and chemical properties and electrochemical stability of the phosphoric acid-doped membrane through the composite modification of sulfonated Ti3AlC2 and oPBI matrix, combined with an alkalinization pretreatment process. Specifically, the sulfonated composite membrane significantly improves the phosphoric acid adsorption capacity and tensile strength while maintaining a low swelling rate; through surface functional group regulation and interlayer confinement effect, a continuous proton transport channel is constructed, achieving a significant improvement in proton conductivity within a wide temperature range (40-160°C); the assembled fuel cell exhibits excellent current density and power density output under both low and high temperature conditions, and the phosphoric acid retention rate is stable after high-temperature operation, verifying the synergistic optimization effect of material structure design on membrane electrode durability and energy conversion efficiency.

[0156] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the invention. Thus, the present invention is intended to include such changes and modifications as fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing functionalized few-layer MXene, characterized in that: The steps include: S1 etching: dissolving a fluoride salt in a strong acid solution to obtain a mixed solution; Add MAX phase powder into the mixed solution for etching; The precipitate was collected by centrifugation and washed, filtered, and freeze-dried to obtain a few-layer MXene powder; S2 alkalization treatment: The MXene powder is added to an alkaline reagent solution for alkalization treatment; The precipitate was collected by centrifugation and washed, filtered, and freeze-dried to obtain high-hydroxyl and low-fluorine MXene powder; S3 ultrasonic treatment: ultrasonically treat the high hydroxyl low fluorine MXene powder, take the supernatant, and obtain a high hydroxyl low fluorine MXene colloidal solution; S4 rotary evaporation concentration: The high-hydroxyl, low-fluorine MXene colloidal solution is rotary evaporated to obtain a functionalized few-layer MXene concentrate.

2. The preparation method according to claim 1, wherein Step S1 satisfies at least one of the following conditions: (1) The fluoride salt is selected from at least one of LiF and NaF, the strong acid solution is selected from at least one of HCl solution and H2SO4 solution, the concentration of the strong acid solution is 4-12M, and the MAX phase is an etching product of the MAX phase in which A is Al; (2) A protective gas is flowed throughout the etching process, wherein the protective gas is selected from at least one of an inert gas and a reducing gas; (3) Etching is performed at 40-50°C and a stirring rate of 200-400 rpm for 8-48 hours.

3. The preparation method according to claim 1 or 2, wherein The preparation method satisfies at least one of the following conditions: (1) In step S1, 0.6-1.2 g of fluoride salt and 0.5-1.5 g of MAX phase powder were added to every 20-35 mL of strong acid solution; (2) In step S2, the alkaline reagent solution is selected from at least one of a KOH solution and a NaOH solution, with a concentration of 0.5-3 M; (3) In step S3, the ultrasonic treatment is performed under inert gas protection for more than 30 minutes, and the solid content of the high-hydroxyl low-fluorine MXene colloidal solution is greater than 80%; (4) In step S4, rotary evaporation is performed at 45-55° C. under vacuum for more than 30 min.

4. The preparation method according to claim 1 or 2, wherein After step S4, the functionalized few-layer MXene concentrate is subjected to a modification treatment, wherein the modification treatment includes at least one of a sulfonation treatment, a hydroxylation treatment, and an amination treatment.

5. The preparation method according to claim 4, wherein The modification treatment includes sulfonation treatment, which includes the following steps: A1: mixing the functionalized few-layer MXene concentrate, the sulfonation reagent and the solvent; A2: React at 105-125°C for 1-3 hours; A3: Filtration, washing, and drying to obtain sulfonated few-layer MXene powder.

6. The preparation method according to claim 4, wherein The modification treatment includes a hydroxylation treatment, comprising the following steps: B1: Add the functionalized few-layer MXene concentrate to an alkaline aqueous solution and ultrasonicate for 2-4 hours under inert gas protection; B2: react at 50-65°C for 45-60 hours; B3: Centrifugation, washing, and drying to obtain hydroxylated few-layer MXene powder.

7. The preparation method according to claim 4, wherein The modification treatment includes an amination treatment, which includes the following steps: C1: Add the functionalized few-layer MXene concentrate to the amination reagent and stir for 1-5 minutes; C2: Stir at 400-500 rpm for 20-30 hours at room temperature; C3: After washing, the precipitate is centrifuged and treated with ultrasound in an organic solvent for 2-4 hours, and then dried to obtain aminated few-layer MXene powder.

8. A functionalized few-layer MXene, characterized in that Prepared by the preparation method according to any one of claims 1 to 7, the functionalized few-layer MXene has less than 5 layers.

9. A high-temperature, high-conductivity proton exchange membrane, characterized in that: Comprising the functionalized few-layer MXene and protonated polymer according to claim 8, optionally, the high-conductivity proton exchange membrane is a phosphoric acid-doped protonated polymer membrane composited with the functionalized few-layer MXene.

10. A method for preparing a high-temperature, high-conductivity proton exchange membrane according to claim 9, characterized in that: The protonated polymer includes an imidazole ring polymer, and the high conductivity proton exchange membrane is a phosphoric acid-doped imidazole ring polymer membrane composited with a functionalized few-layer MXene, comprising the following steps: Step 1: dissolving the protonated polymer in an organic solvent, adding the functionalized few-layer MXene and ultrasonically dispersing the mixture to obtain a casting solution; Step 2: Coating the casting solution on the substrate and removing the organic solvent to obtain the f-MXene / protonated polymer composite membrane; Step 3: Soaking the f-MXene / protonated polymer composite membrane in a phosphoric acid aqueous solution with a temperature of 100-125° C. and a concentration of 75-90 wt % to obtain the high conductivity proton exchange membrane.

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