Electrochemical etching preparation method and application of Fe-based MBene two-dimensional material

Abstract

The application belongs to the technical field of functional composite materials, and relates to an electrochemical etching preparation method and application of Fe-based MBene two-dimensional material. The existing chemical etching technology has the problems of insufficient etching selectivity, severe reaction conditions and difficult regulation and control when preparing Fe-based MBene, which leads to defects such as oxidation of Fe element, residual Al layer, damage of Fe-B skeleton and collapse of two-dimensional morphology. Technical scheme: a three-electrode system is constructed by taking a conductive substrate loaded with Fe2AlB2 powder as a working electrode, a platinum sheet as a counter electrode and Ag / AgCl as a reference electrode; the three-electrode system is placed in a 70 DEG C, 15% to 20% sodium hydroxide solution, and electrochemical etching is carried out at a constant current density of 0.5 mA / cm2; after etching, the Fe-based MBene two-dimensional material is obtained through ultrasonic peeling in N-methyl pyrrolidone, magnetic separation, deionized water washing and freeze-drying.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials technology, and provides an electrochemical etching preparation method and application of Fe-based MBene two-dimensional materials. Background Technology

[0002] Two-dimensional materials exhibit unique advantages in electromagnetic wave absorption due to their atomic-level thickness, extremely large specific surface area, tunable electronic band structure, and abundant interfacial polarization and defect effects. In recent years, a novel class of two-dimensional transition metal boride materials called MBene has gradually come into the research spotlight. Their structure is similar to MXene, but boron (B) replaces carbon / nitrogen, forming stronger M–B covalent bonds. Among them, Fe-based MBene, derived from Fe2AlB2 as a precursor, is particularly noteworthy. This material not only inherits the multiple scattering and interfacial polarization effects brought about by the two-dimensional layered structure, but also possesses good electrical conductivity and intrinsic magnetism due to the presence of Fe, which is expected to synergistically achieve a dual mechanism of dielectric loss and magnetic loss, significantly improving the attenuation efficiency of electromagnetic waves. More importantly, compared to the disadvantage of traditional MXene being easily oxidized and unstable in air, the strong M–B bonds in MBene endow it with higher thermodynamic and chemical stability, allowing it to maintain structural integrity in humid, saline, and even weakly acidic and alkaline environments, exhibiting excellent corrosion resistance potential. This ability to integrate wave absorption and corrosion protection into the same material system makes it a promising candidate to become a truly intrinsic "wave absorption-corrosion protection" integrated material.

[0003] However, despite the numerous theoretical advantages of Fe2AlB2-based MBene, its practical preparation still faces significant challenges, with the core difficulty lying in the controllability and feasibility of the selective etching process. MBene is typically obtained by selectively removing the intermediate Al atomic layer from ternary layered ceramics (such as Fe2AlB2). However, Al atoms form strong metal-covalent mixed bonds with Fe and B in the crystal lattice, resulting in low selective etching efficiency of Al in conventional etching systems used for MXene synthesis (such as HF hydrofluoric acid, lithium fluoride + LiF + HCl, or alkaline NaOH solution). Even more problematic is that Fe is highly susceptible to dissolution, oxidation, or phase transformation in acidic or oxidizing etching environments. This can not only lead to insufficient Fe content in the target product but also generate non-target oxidation byproducts such as Fe2O3 and FeOOH, severely damaging the original crystal structure and weakening its conductivity and magnetism. Furthermore, improper etching processes can easily lead to problems such as insufficient interlayer peeling, lamellar aggregation, and structural collapse, further reducing the material's specific surface area and interfacial activity, thus limiting its performance in microwave absorption and corrosion protection. Therefore, designing a mild, efficient, and highly selective etching path—capable of precisely removing the Al layer while maximizing the preservation of the Fe–B framework's integrity and functionality—has become a key bottleneck in propelling Fe2AlB2-based MBene from the laboratory to engineering applications. Future research urgently needs to systematically optimize etching mechanisms, solvent systems, reaction kinetics, and post-processing techniques to achieve controllable preparation of high-quality MBene, laying the material foundation for its multifunctional integrated applications in complex environments. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing chemical etching techniques (such as hydrofluoric acid, lithium fluoride + hydrochloric acid, or conventional alkaline solution etching) in the preparation of Fe-based MBene. These shortcomings include insufficient etching selectivity, harsh reaction conditions, and difficulty in precise control, leading to defects such as Fe element oxidation and dissolution / phase transformation, insufficient Al layer removal, damage to the Fe-B framework structure, collapse of two-dimensional layered morphology, lamellar aggregation, or excessive corrosion. Consequently, it is difficult to obtain high-quality Fe-B MBene nanosheets with intact structure, few defects, and stable function. This restricts their application in microwave absorption and anti-corrosion integrated coatings to effectively construct a "maze barrier" physical barrier and exert the synergistic performance of intrinsic corrosion resistance and electromagnetic loss.

[0005] To achieve the above objectives, the present invention employs the following technical means:

[0006] This invention provides an electrochemical etching method for preparing Fe-based MBene two-dimensional materials, comprising the following steps: constructing a three-electrode system using a conductive substrate loaded with Fe2AlB2 powder as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode; placing the three-electrode system in an alkaline electrolyte at a temperature of 60–80 °C, wherein the alkaline electrolyte is a 15–20 wt% sodium hydroxide solution, and performing electrochemical etching at a constant current density of 0.25–1 mA·cm⁻²; after etching, ultrasonically peeling the working electrode in N-methylpyrrolidone, followed by magnetic separation, washing with deionized water, and freeze-drying to obtain the Fe-based MBene two-dimensional material.

[0007] In the above scheme, the conductive substrate is nickel foam.

[0008] In the above scheme, the three-electrode system is placed in an alkaline electrolyte at a temperature of 70°C.

[0009] In the above scheme, electrochemical etching is performed at a constant current density of 0.5 mA·cm⁻².

[0010] In the above scheme, the concentration of the alkaline electrolyte is 20 wt%.

[0011] The present invention also provides a Fe-based MBene two-dimensional material, which is prepared by the method described above. The Fe-based MBene has a two-dimensional layered nanosheet structure with a smooth sheet surface, no iron oxide byproducts, and exhibits uniform wrinkles and layered textures under a scanning electron microscope.

[0012] The present invention also provides an anti-corrosion coating, which is composed of a thermoplastic polyurethane matrix and a filler uniformly dispersed in the matrix, wherein the filler is the Fe-based MBene two-dimensional material.

[0013] This invention also provides the application of Fe-based MBene two-dimensional material in the preparation of an integrated coating that combines electromagnetic wave absorption and long-term corrosion protection of metal substrates.

[0014] Because the present invention employs the above-mentioned technical means, it has the following beneficial effects:

[0015] This invention employs electrochemical selective etching technology, using alkaline NaOH solution as the etching medium, and applying a constant current density of 0.5 mA·cm⁻² at a constant temperature of 70℃. By utilizing the preferential dissolution reaction of Al in an alkaline environment (Al + 4OH⁻ → [Al(OH)₄]⁻ + 3e⁻), the Al atomic layer is precisely removed. This solves the technical problems of low Al selectivity, easy oxidation and dissolution of Fe components, and structural collapse in traditional HF or LiF+HCl etching systems. It achieves high-purity and controllable preparation of Fe₂AlB₂-based MBene, achieving efficient Al removal and complete preservation of the Fe-B framework, significantly improving the structural stability of the material.

[0016] This invention solves the problems of easy agglomeration, impurity residue and structural damage of etched products by combining post-processing techniques such as ultrasonic stripping, magnetic separation and freeze drying. It achieves uniform dispersion, efficient purification and maintenance of the integrity of the material's microstructure, and further improves the electromagnetic loss performance and corrosion resistance potential of Fe2AlB2-based MBene.

[0017] This invention combines electrochemical selective etching with post-processing techniques such as ultrasonic stripping, magnetic separation, and freeze-drying to produce a synergistic effect: electrochemical etching precisely removes the Al atomic layer, ultrasonic stripping effectively prevents the collapse of the layered structure, magnetic separation achieves efficient purification, and freeze-drying maintains the porous structure and high specific surface area of ​​the material. This synergistically improves the material's structural stability, electromagnetic loss performance, and corrosion resistance potential, solving the technical problem of traditional methods that struggle to balance efficient etching with structural integrity, and demonstrating significant inventiveness. Attached Figure Description

[0018] Figure 1 SEM images: (a) Fe2AlB2; (b) M-5; (c) M-10; (d) M-15; (e) M-20; (f) M-25;

[0019] Figure 2 EIS impedance spectra of Q235 steel coated with various composite coatings (ag) after immersion in 3.5 wt.% sodium chloride solution for 3, 5 and 7 days; (h) curve of lg|Z|f=0.01Hz value as a function of number of days (f) M-25. Detailed Implementation

[0020] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0021] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without these specific details.

[0022] This invention aims to explore the effective etching of aluminum by Fe-based MBene. The core objective is to overcome the key preparation bottleneck in the transformation from the three-dimensional MAB phase to two-dimensional MBene, seeking to obtain high-quality, defect-free Fe-B MBene nanosheets by developing an etching strategy with higher selectivity and less damage to the layered framework. The research will systematically investigate the influence of key parameters such as etchant concentration and temperature on etching selectivity and product structural integrity, and utilize microscopy to precisely characterize the layered structure and surface state of the etched product. Only by achieving precise and controllable preparation of its two-dimensional structure can a solid material foundation be laid for integrated functional coatings that provide long-lasting physical / chemical corrosion barriers.

[0023] This invention focuses on the controllable preparation of Fe-based MBene (Fe2AlB2), with the core being the development of a highly selective, low-damage electrochemical etching strategy for precise removal of Al from the crystal lattice. The experiment uses an alkaline NaOH solution as the etching medium, applying a constant current density of 0.5 mA·cm⁻² at a constant temperature of 70°C. By adjusting key parameters such as the NaOH concentration, the aim is to utilize the preferential solubility of Al in an alkaline environment (Al + 4OH⁻) to achieve the desired effect. - → [Al(OH)4] - + 3e - This method achieves selective exfoliation of the Al layer while minimizing the oxidation, dissolution, or structural collapse of the Fe component. After etching, the target product is obtained through ultrasonic exfoliation, magnetic separation, and freeze-drying. This strategy aims to overcome the structural defects and performance degradation caused by the non-selective reaction of traditional etching methods while preserving the integrity and intrinsic functions (such as ferromagnetism and dielectric response) of the Fe–B framework. It provides a high-quality two-dimensional MBene base material for the subsequent construction of integrated functional coatings with excellent electromagnetic loss capability and long-term corrosion resistance.

[0024] Example 1

[0025] 1. Preparation of Fe2AlB2 powder working electrode: First, 0.1g of Fe2AlB2 powder was immersed in 50mL of 1M hydrochloric acid solution and gently shaken for 30s to remove surface alumina. After washing with deionized water three times, it was vacuum dried at 40℃ for 12h. After drying, the powder was mixed and ground with 0.03g of superconducting carbon black (SUPER P) and 0.015g of polyvinylidene fluoride (PVDF), while adding a few drops of N-methylpyrrolidone (NMP). After grinding for ten minutes, the mixed active material was evenly coated on one side of a foam nickel mesh with a size of 1cm×1.2cm×0.5mm and dried in an oven at 50℃ for 6h.

[0026] 2. Fe2AlB2 powder etching: A three-electrode system was formed by using a Fe2AlB2-coated nickel foam electrode as the working electrode, a platinum sheet as the counter electrode, and a silver chloride electrode (Ag / AgCl) as the reference. The electrolytic cell was placed on a heating stage, the temperature was set to 70℃, the constant current was set to 0.5 mA·cm⁻², and the electrolyte used was a 5wt%, 10wt%, 15wt%, 20wt%, and 25wt% sodium hydroxide solution.

[0027] After electrochemical etching, the nickel foam mesh was ultrasonically treated in NMP solution for 30 minutes, followed by magnetic separation to separate the etched particles. The mesh was then washed repeatedly with NMP and deionized water, and finally freeze-dried for 24 hours to obtain Fe–BMBene. The samples were then named M-5, M-10, M-15, M-20, and M-25 according to the electrolyte concentration gradient.

[0028] 3. Polyurethane Coating Preparation: 1.8 g of thermoplastic polyurethane (TPU) was dissolved in 2 mL of N,N-dimethylformamide by heating to obtain a uniformly dispersed polyurethane solution. 0.2 g of powder was added to the polyurethane solution and stirred thoroughly for 30 min. After degassing, the solution was spin-coated onto a Q235 steel sheet. The coatings were named Fe2AlB2, M-5, M-10, M-15, M-20, and M-25. Pure TPU films were prepared using the same method.

[0029] According to scanning electron microscopy (SEM) Figure 1 The method (af) can systematically analyze the effects of different concentrations of NaOH electrolyte on the electrochemical etching effect of Fe2AlB2 powder. Figure 1 In sample a, the unetched original sample exhibits a dense, irregular blocky morphology, displaying a typical three-dimensional MAB phase structure. With a NaOH concentration of 5 wt% ( Figure 1 (b) Slight roughening and localized depressions began to appear on the particle surface, indicating that etching had started, but to a weak degree. When the concentration was increased to 10 wt% ( Figure 1In step c), obvious grooves and layered exfoliation marks appeared on the particle surface, and some areas exhibited a preliminary two-dimensional layered stacking structure, indicating that the dissolution of Al atomic layers gradually increased and the crystal structure began to be destroyed. In 15 wt% NaOH ( Figure 1 In the middle (d), the etching depth is significantly increased, and numerous deep cracks and wrinkles form on the particle surface. Some areas exhibit characteristics resembling "curling" or "peeling," demonstrating a strong dealloying effect and a more pronounced layered structure. Further increasing to 20 wt% ( Figure 1 In the middle (e), the exposure of elongated sheet-like structures was observed, with clear edges and obvious layered texture, indicating that the Al layer had been effectively removed, the Fe-B framework was released and partially unfolded, forming a two-dimensional nanosheet-like structure. However, under a high concentration of 25 wt% NaOH ( Figure 1 Although the layered structure is still maintained (f), the overall morphology tends to be fragmented and loose. Excessive corrosion or intensified side reactions lead to the formation of byproducts on the surface, resulting in decreased skeleton integrity and weakened layered stacking structure. In summary, NaOH concentration has a significant regulatory effect on the etching process. The optimal balance between layered exfoliation and structural integrity is achieved at 20 wt%, while excessively high or low concentrations are detrimental to obtaining high-quality Fe–B MBene.

[0030] like Figure 2As shown in the electrochemical impedance spectroscopy (EIS) results, the Fe2AlB2 filler obtained by etching with different NaOH concentrations has a significant impact on the long-term corrosion resistance of the polyurethane coating in 3.5 wt.% NaCl solution. The pure TPU coating, lacking a functional barrier, exhibits rapid impedance decay during immersion, resulting in limited corrosion resistance. While the unetched Fe2AlB2 composite coating shows slight improvement, the increase is not significant. In contrast, the samples treated with alkaline etching exhibit significantly enhanced corrosion resistance, especially those etched with 10–20 wt% NaOH. Among them, the 20 wt% NaOH etched sample (M-20) maintained the highest low-frequency impedance value and the slowest decay rate after immersion for 3, 5, and 7 days, indicating that it imparts excellent long-term protective capabilities to the coating. This performance improvement is primarily attributed to the etching-induced two-dimensional layered MBene structure. Its high aspect ratio nanosheets, uniformly dispersed in the coating, create a typical "maze effect," significantly extending the diffusion path of corrosive media to the metal substrate and effectively inhibiting penetration and electrochemical corrosion reactions. Crucially, unlike traditional MXenes which are easily oxidized and unstable in air, the strong covalent Fe-B bonds in Fe-B MBene endow it with higher thermodynamic and chemical stability, allowing it to maintain structural integrity even in humid, saline, and even weakly acidic / alkaline environments, exhibiting excellent intrinsic corrosion resistance. When the NaOH concentration increases to 25 wt%, the impedance performance decreases, possibly due to excessive etching leading to layer breakage, stacking, or increased defects, weakening the continuity and density of the maze barrier. In summary, moderate alkaline etching successfully exfoliated high-quality two-dimensional Fe-BMBene, whose unique layered morphology constructs an efficient physical barrier network within the polymer matrix, fully demonstrating the crucial role of the "maze effect" of two-dimensional materials in long-lasting anti-corrosion coatings.

Claims

1. A method for electrochemical etching preparation of Fe-based MBene two-dimensional materials, characterized in that, Includes the following steps: A three-electrode system was constructed using a conductive substrate loaded with Fe2AlB2 powder as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The three-electrode system was placed in an alkaline electrolyte at a temperature of 60-80°C, wherein the alkaline electrolyte was a sodium hydroxide solution with a concentration of 15-20 wt%, and electrochemical etching was performed at a constant current density of 0.25-1 mA·cm⁻². After etching, the working electrode was ultrasonically peeled in N-methylpyrrolidone, and then subjected to magnetic separation, washing with deionized water and freeze drying to obtain the Fe-based MBene two-dimensional material.

2. The preparation method according to claim 1, characterized in that, The conductive substrate is nickel foam.

3. The preparation method according to claim 1, characterized in that, The three-electrode system was placed in an alkaline electrolyte at a temperature of 70°C.

4. The preparation method according to claim 1, characterized in that, Electrochemical etching was performed at a constant current density of 0.5 mA·cm⁻².

5. The preparation method according to any one of claims 1 or 2, characterized in that, The concentration of the alkaline electrolyte is 20 wt%.

6. A Fe-based MBene two-dimensional material, characterized in that, Prepared by the method described in any one of claims 1–3.

7. An anti-corrosion coating, characterized in that, It is composed of a thermoplastic polyurethane matrix and a filler uniformly dispersed in the matrix, wherein the filler is the Fe-based MBene two-dimensional material as described in claim 6.

8. The Fe-based MBene two-dimensional material of claim 6 is used in the preparation of an integrated coating that combines electromagnetic wave absorption and long-term corrosion protection of metal substrates.

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