The invention relates to Maps. 1.33 R < 0.67 > Maps < s >; carrying out apos; the invention relates to a 2AlC3 MAX phase synthesis method and two-dimensional Mapos. 1.33 Maps, 1.33 Maps; carrying out apos; preparation method of 2C3 MXene material

Abstract

The invention relates to the technical field of preparation of transition metal carbide materials, in particular to a synthesis method of an M '1.33 R0. 67 M ''2AlC3 MAX phase and a preparation method of a two-dimensional M' 1.33 M'' 2C3 MXene material. Aiming at specific synthesis obstacles caused by high stability of carbides of high-inertia M elements such as Ta and the like, an R element is introduced as a phase forming accelerant, and a high-purity ordered MAX phase containing Mo and Ta elements, which cannot be obtained before, is successfully synthesized. The auxiliary phase forming effect of rare earth is critical and indispensable, and the effect is not necessary in an M element (such as Nb) system with high activity. The two-dimensional M '1.33 M ''2C3 MXene material which is prepared from the specific precursor, has an ordered vacancy structure and is high in performance has excellent conductivity, can be used as a carrier to be compounded with metal phosphide, and provides excellent electrocatalytic oxygen evolution performance.

Description

Technical Field

[0001] This invention relates to the field of transition metal carbide material preparation technology, specifically to an M' 1.33 R 0.67 Methods for synthesizing M''2AlC3MAX phase and two-dimensional M'' 1.33 A method for preparing M''2C3MXene materials, a controllable method for preparing highly inert metal ordered MAX phases based on the key role of rare earth elements, and two-dimensional derivatives. Background Technology

[0002] MAX phase materials are a class of ternary carbides or nitrides with a nanolayered structure, and have the general chemical formula M. n+ 1AX n In this system, M represents pre-transition metals from groups IIIB, IVB, VB, and VIB; A primarily represents elements from groups IIIA and IVA; and X represents carbon or nitrogen. The MAX phase unit cell consists of M... n+1 X n The phases are formed by alternating stacking of unit cells and A-plane atoms, with n = 1, 2, 3, or 4, and are commonly referred to as the 211, 312, 413, and 514 phases. M n+1 X n The atoms within the unit cell are connected by strong covalent bonds, M n+1 X n The unit cell and the A layer are connected by weak metallic bonds, and this bond strength difference makes it possible to etch two-dimensional transition metal carbides. Previous studies have largely focused on traditional ternary MAX phases represented by M2AlC (M = Ti, V, Nb, Ta), M3AlC2 (M = Ti), and M4AlC3 (M = V, Nb, Ta) [Martin Dahlqvist, Michel W. Barsoum, Johanna Rosen, Materials Today 2024, 72, 1-24]. In recent years, researchers have successfully prepared multi-transition metal MAX phase solid solutions containing two or more transition metals (e.g., M', M'') using M-site element alloying methods. In systems with n ≥ 2, under certain specific element combinations and ratios, different types of transition metal atoms are no longer randomly distributed but tend to occupy specific crystallographic positions (M', M'' atoms occupy M... n+1 X n The outer and inner layers of the unit cell are used to form out-of-plane ordered phases (o-MAX) with the chemical formulas M'2M''AlC2 and M'2M''2AlC3. By etching and intercalating these out-of-plane ordered MAX phases, two-dimensional out-of-plane ordered carbides (o-MXene) of M'2M''C2 and M'2M''2C3 can be obtained. This atomically ordered site occupancy makes it possible to precisely customize the physicochemical properties of MXene.

[0003] However, these out-of-plane ordered carbides (n=3) exist only in combination with certain specific elements, and their numbers are very limited. Currently, only the MAX phases of Mo₂Ti₂AlC₃, Mo₂Nb₂AlC₃, Cr₂V₂AlC₃, and Cr₂Ti₂AlC₃ have been successfully reported for synthesis. This is likely due to the significant differences in reactivity among different transition metal elements. This reactivity mainly depends on the bond energy (or formation enthalpy or formation energy) and atomic diffusion ability of their carbides. For example, in exploring novel MAX phases, researchers naturally attempted to replace Nb in the known system Mo₂Nb₂AlC₃ with its family member Ta in order to obtain Mo₂Ta₂AlC₃. However, this seemingly simple family element substitution encountered unexpected failure, the fundamental reason being the critical difference in thermodynamic stability between the Nb and Ta carbides. According to the Materials Project database, the predicted formation energy of tantalum carbide (TaC) with space group Fm-3m

[225] is -0.659 eV / atom, while that of niobium carbide (NbC) is -0.536 eV / atom. This data clearly indicates that TaC is thermodynamically more stable than NbC. In the high-temperature solid-state reaction of MAX phase synthesis, this critical difference in thermodynamic stability leads to drastically different results: for Nb-based systems, the reaction pathway can lead to the formation of quaternary MAX phases; while for Ta-based systems, there is a strong tendency to preferentially form extremely stable TaC binary compounds, thereby completely suppressing the complex quaternary layered reaction between molybdenum, aluminum, tantalum, and carbon.

[0004] In the current research field of MAX phase materials, achieving high-quality synthesis of ordered MAX phases of highly inert multi-transition metals (such as tantalum Ta) remains a significant technical bottleneck. Traditional synthesis methods often fail to achieve atomic-level ordered arrangement when dealing with highly inert metals due to problems such as large differences in chemical potential between elements, mismatched diffusion rates, and the ease with which competitive impurities (such as carbides or intermetallic compounds) are formed. This results in products with low purity, numerous structural defects, and poor uniformity of element distribution.

[0005] Currently, although research teams both domestically and internationally have made some progress in expanding the composition of MAX phases through high-entropy strategies or solid-state reaction methods, such as synthesizing M4AlC3 phases containing multiple transition metals, their focus is mostly on increasing configurational entropy to stabilize disordered solid solutions, or limited to highly reactive metal elements. For high-melting-point, highly inert metals like Ta, achieving precise control of long-range ordered arrangement at the M site is particularly difficult, effective synthetic routes are scarce, and related reports are few and far between.

[0006] Against this backdrop, the novel rare-earth-assisted synthesis method of this invention introduces rare-earth elements as phase-forming promoters. Utilizing their unique chemical reactivity and electronic properties, this method effectively lowers the diffusion barrier of highly inert metal atoms, promoting the ordered occupancy of multiple transition metals (including Ta) in the MAX phase lattice. This strategy not only overcomes the limitations of traditional methods in element selectivity and order control, providing a novel and efficient solution for the synthesis of precisely structured ordered MAX phases of multiple transition metals (such as Ta-containing MAX phases), but also lays a solid material foundation for the application of such materials in extreme environments.

[0007] Based on the knowledge of the similarity of chemical properties of Nb-Ta, those skilled in the art would find it difficult to predict that the two would exhibit such a huge and decisive difference in the synthesis of MAX phases. This is precisely the long-standing technical bias and cognitive blind spot that this invention aims to overcome. Summary of the Invention

[0008] (a) Purpose of the invention The purpose of this invention is to overcome the technical bias that "elements M'' in the same group have similar properties, so their MAX phases can be synthesized by analogy," and in particular, to overcome the unique synthesis obstacles caused by the high stability of carbides of highly inert M'' elements such as Ta. This invention provides a feasible method for preparing ordered MAX phases of dual or multiple transition metals using rare earth element-assisted synthesis. Another objective of this invention is to provide a two-dimensional M'' phase with an ordered vacancy structure and high performance, prepared from this specific precursor. 1.33 M''2C3MXene material, this two-dimensional derivative can only be prepared by rare earth-assisted synthesis of a specific MAX phase as a precursor.

[0009] (II) Technical Solution A kind of M' 1.33 R 0.67 The M''2AlC3MAX phase synthesis method uses rare earth element R as a phase formation promoter; M' is derived from group VIB, and M'' is derived from groups IVB-VB. The specific steps include: Step 1: Mix the ingredients according to the atomic molar ratio of M':R:M'':Al:C = 1.33:0.67:2:(1~2):(2.2~3) and mix thoroughly. Step 2: Press the mixed powder into shape; Step 3: Under vacuum or inert atmosphere, heat to 1300℃~1600℃ at a heating rate of 5℃ / min~20℃ / min and hold for 0.5 hours~10 hours. The rare earth element R reduces the energy barrier of the synthesis reaction, inhibits the preferential formation of M''C impurity phase, and promotes the formation of the target MAX phase. Step 4: Cooling to obtain high-purity M'1.33 R 0.67 M''2AlC3MAX phase.

[0010] M' is one or more of molybdenum (Mo), chromium (Cr), and tungsten (W).

[0011] M'' is one or more of titanium (Ti), zirconium (Zr), hafnium (Hf), and tantalum (Ta).

[0012] The M' 1.33 R 0.67 The M' and M'' combinations of the M''2AlC3MAX phase do not include Mo-Ti, Cr-Ti, or Cr-V.

[0013] A kind of M' 1.33 R 0.67 Application of the M''2AlC3MAX phase as a precursor for the preparation of two-dimensional M' 1.33 M''2C3MXene material.

[0014] A two-dimensional M' 1.33 M''2C3MXene material preparation method, using M' 1.33 R 0.67 Using the M''2AlC3MAX phase as a precursor, the precursor is etched by a solution containing fluoride ions or a molten salt containing fluoride ions to remove the Al atomic layer and R atoms, forming surface-bonded negative ion functional groups T. x And a two-dimensional M' with ordered vacancies 1.33 M''2C3MXene material.

[0015] A two-dimensional M' 1.33 Using M''2C3MXene material as a support, FeCoNi-based MOFs were grown in situ via electrostatic self-adsorption, and (FeCoNi)P / M'' was obtained through annealing and phosphating processes. 1.33 M''2C3 composite material.

[0016] (III) Beneficial Effects of the Invention Solved a specific technical problem: Taking the Mo2Ta2AlC3 system as an example, this invention reveals for the first time that rare earth element R is the key to solving the synthesis problem of highly inert M" elements (such as Ta), and successfully synthesizes high-purity ordered MAX phase containing Mo and Ta elements that could not be obtained before.

[0017] The present invention discovers that the role of element R in solving the synthesis problem of highly inert element systems such as Ta-based system is crucial and indispensable, while this role is not necessary in highly reactive M-element (such as Nb) system, and is therefore not obvious to those skilled in the art.

[0018] The derived material exhibits excellent properties: the obtained two-dimensional Mo 1.33 Ta2C3MXene exhibits advantages in conductivity and other aspects due to its unique ordered vacancies, and shows good oxygen evolution performance when combined with metal phosphides. Attached Figure Description

[0019] Figure 1 For M'2M''2AlC3 and M' 1.33 R 0.67 XRD results of products prepared from two M''2AlC3 systems; (a) is the M'2M''2AlC3 system, (b) is the M' 1.33 R 0.67 M''2AlC3 system; Figure 2 for Mo 1.33 Y 0.67 High-angle annular dark-field image of Ta2AlC3MAX phase under transmission electron microscopy; Figure 3 for Mo 1.33 Y 0.67 Secondary electron micrographs of the Ta2AlC3MAX phase before etching and X-ray energy dispersive spectra of Mo, Y, Ta, and Al; (a) is a secondary electron micrograph, (b) is the X-ray energy dispersive spectrum of Mo, (c) is the X-ray energy dispersive spectrum of Y, (d) is the X-ray energy dispersive spectrum of Ta, and (e) is the X-ray energy dispersive spectrum of Al. Figure 4 for Mo 1.33 Y 0.67 Secondary electron micrographs of the Ta2AlC3MAX phase after etching and X-ray energy dispersive spectra of Mo, Y, Ta, and Al; (a) is a secondary electron micrograph, (b) is the X-ray energy dispersive spectrum of Mo, (c) is the X-ray energy dispersive spectrum of Y, (d) is the X-ray energy dispersive spectrum of Ta, and (e) is the X-ray energy dispersive spectrum of Al. Figure 5 for Mo 1.33 Scanning electron microscope image of the cross section of the filter plate for Ta2C3MXene suspension; Figure 6 for Mo 1.33 Bright-field image of Ta2C3MXene lyophilized powder under a transmission electron microscope; Figure 7 for Mo 1.33 Ta2C3MXene, (FeCoNi)P, and (FeCoNi)P / Mo 1.33 Ta2C3-200 in 1M L -1 Polarization curves in KOH. Detailed Implementation

[0020] This invention provides an example of M' 1.33 R 0.67 Methods for synthesizing M''2AlC3MAX phase and two-dimensional M'' 1.33 Preparation method of M''2C3MXene material, whose chemical formula is M' 1.33 R 0.67 M''2AlC3, in which the transition metals M' and M'' come from Group VIB (M' = molybdenum Mo, chromium Cr and tungsten W) and Groups IVB-VB (M'' = titanium Ti, zirconium Zr, hafnium Hf, vanadium V, tantalum Ta), and other elements are Group IIIB rare earth R (Sc, Y or lanthanides), Group IIIA aluminum Al and Group IVA carbon C.

[0021] The preparation method of this type of MAX phase precursor is as follows: after uniform mixing according to the ratio of M':R:M'':Al:C = 1.33:0.67:2:(1~2):(2.2~3), the mixture is cold-pressed into sheets. Alternatively, a rare earth-aluminum master alloy can be used, but the final element ratio before uniform mixing and sintering remains the same as above. Then, the mixture is heated at a heating rate of 5℃ / min to 20℃ / min and held under vacuum at 1300℃ to 1600℃ for 0.5 to 10 hours, and then naturally cooled to room temperature to obtain the precursor.

[0022] The method for preparing two-dimensional derivatives of the MAX phase involves etching the MAX phase with a fluorine-containing etchant at 25 ℃-200 ℃ for 2 h~48 h to remove Al and R atoms, forming a multilayer carbide (ML-MXene); further, a few-layer two-dimensional ordered carbide (MXene) is obtained by intercalation with an intercalating agent.

[0023] The etching agent is an aqueous solution of HF, a mixed solution of fluorine-containing salts (LiF, NaF, KF, NH4HF2, NH4F) and hydrochloric acid, or NH4HF2 salt; the intercalating agent is tetramethylammonium hydroxide (TMAOH) or tetrabutylammonium hydroxide (TBAOH).

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings. Example 1: Mo 1.33 R 0.67 Synthesis of Ta2AlC3MAX phase; Powder with a molar ratio of Mo:Y:Ta:Al:C = 1.33:0.67:2:1.3:2.7 was placed in a ball mill jar and ball-milled for 7 hours. After the powder was uniformly mixed, it was cold-pressed into sheets, then heated at a heating rate of 10℃ / min and held under vacuum at 1500℃ for 1 hour. The sheets were then allowed to cool naturally to room temperature to obtain the MAX phase. Figure 1As shown in b, XRD indicates the formation of the corresponding phases and crystal structures. Transmission electron microscopy reveals, as shown... Figure 2 As shown, an out-of-plane ordered layered structure of (Mo+Y) atoms and Ta atoms is formed.

[0025] Example 2: Cr 1.33 R 0.67 Synthesis of Ta2AlC3MAX phase; Powder with a molar ratio of Cr: Y: Ta: Al: C = 1.33: 0.67: 2: 1.3: 2.7 was placed in a ball mill jar and ball-milled for 7 hours. After the powder was uniformly mixed, it was cold-pressed into sheets, then heated at a heating rate of 10℃ / min and vacuum-held at 1500℃ for 1 hour. The sheets were then allowed to cool naturally to room temperature. Figure 1 As shown in b, the MAX phase is obtained.

[0026] Comparative Example 1: An Attempt to Synthesize Mo2Ta2AlC3 Without Rare Earth Elements Take powder with a molar ratio of Mo: Ta: Al: C = 2: 2: 1.3: 2.7, put the powder into a ball mill jar and ball mill for 7 hours. After the powder is uniformly mixed, cold press it into a sheet, then heat it at a heating rate of 10℃ / min, hold it under vacuum at 1500℃ for 1 hour, and then let it cool naturally to room temperature. Figure 1 XRD patterns showed that the main phases of the product were TaC and MoC with strong diffraction peaks, and no diffraction peaks of the MAX phase were detected. This result contrasts sharply with the success of Example 1, directly confirming that for Ta-based systems, due to the extremely high stability and slow kinetics of the Ta-C bond, the reaction strongly tends to generate simple binary carbides without the introduction of R elements, and the target MAX phase cannot be synthesized.

[0027] Comparative Example 2: An Attempt to Synthesize Cr2Ta2AlC3 Without Rare Earth Elements Take powder with a molar ratio of Cr: Ta: Al: C = 2: 2: 1.3: 2.7, put the powder into a ball mill jar and ball mill for 7 hours. After the powder is uniformly mixed, cold press it into a sheet, then heat it at a heating rate of 10℃ / min, hold it under vacuum at 1500℃ for 1 hour, and then let it cool naturally to room temperature. Figure 1 The XRD pattern shows that the main phase of the product is TaC with strong diffraction peaks, and no diffraction peaks of the MAX phase can be detected at all.

[0028] Comparative Example 3: Mo 1.33 R 0.67 Comparison of the synthesis of Nb2AlC3MAX and Mo2Nb2AlC3MAX phases This comparative example aims to verify the different roles of rare earth element R in different M element systems. Mo was synthesized using the above-described technical scheme. 1.33 R 0.67 The Nb₂AlC₃MAX phase and the Mo₂Nb₂AlC₃MAX phase were synthesized. The results showed that both systems yielded products dominated by the MAX phase. This crucial experiment demonstrates that in Nb-based systems, the MAX phase can still be generated even without the introduction of the rare earth element (R). The introduction of R primarily serves an optimizing role rather than being essential for phase formation. This result stands in stark contrast to Comparative Example 1 (where the Ta-based system cannot form a phase at all without R), strongly proving that: 1) Nb and Ta elements exhibit fundamentally different reaction pathways and difficulties in MAX phase synthesis; 2) the rare earth element R plays a unique and crucial role in solving the synthesis challenges of highly inert Ta-based systems (and similar systems), a role that is not needed in conventional systems such as Nb-based systems.

[0029] Example 3: Performance Comparison Take 1g of Mo ground into powder 1.33 Y 0.67 Ta2AlC3MAX and 6g NH4HF2 were ground and mixed evenly, placed in a polytetrafluoroethylene bottle, and then placed in a stainless steel reactor. The mixture was then kept at 180℃ for 5 hours in a forced-air drying oven. This process selectively etched away the Al and Y atomic layers. After the reaction, the mixture was washed five times with deionized water, and the resulting precipitate was ML-MXene. Scanning electron microscopy revealed the characteristic step-like morphology of the MAX phase before etching, and a distinct "accordion" morphology after etching. Combined X-ray energy dispersive spectroscopy (EDS) before and after etching, this indicates that the MAX phase was successfully etched into ML-MXene. Figure 3 (a) and Figure 3 As shown in (b).

[0030] Add 5 mL of 25 wt% tetramethylammonium hydroxide (TMAOH) to the resulting precipitate and stir in a water bath at 55°C for 1 day. After the reaction is complete, wash three times with anhydrous ethanol, add deionized water to the resulting precipitate, and sonicate for 1 hour to obtain a stable MXene suspension. After vacuum filtration, the cross-section of the fragment still shows a mesoscale layered stacking morphology. Figure 3 As shown in (c), the aerogel powder obtained by freeze-drying the colloidal solution can be clearly observed as layered flakes under a transmission electron microscope. Figure 3 As shown in (d).

[0031] Mix N,N-dimethylformamide (DMF) (64 mL), ethanol (4 mL), water (4 mL), and 200 mg of Mo. 1.33Ta₂C₃Mxene was mixed in a 100 mL polytetrafluoroethylene bottle and stirred until homogeneous. Then, 1.5 mmol of terephthalic acid (1,4-BDC) was dissolved in the mixture, followed by the sequential addition of 0.5 mmol FeCl₃·6H₂O, 0.5 mmol CoCl₂·6H₂O, and 0.5 mmol NiCl₂·6H₂O. The FeCl₃Mxene was then... 3+ Co 2+ and Ni 2+ After the salt was completely dissolved, 1.6 mL of triethylamine (TEA) was rapidly injected. The solution was stirred for 5 minutes to form a homogeneous colloidal suspension, and then stirred continuously for 4 hours under sealed conditions. Finally, the product was washed 3-5 times with ethanol, centrifuged to separate the product, and then lyophilized under vacuum. The lyophilized sample was then annealed in a tube furnace under an argon atmosphere at a heating rate of 5 °C / min at 600 °C for 1 hour to obtain FeCoNi@C / Mo. 1.33 Ta2C3-200. Subsequently, a crucible containing 500 mg of NaH2PO2·H2O powder was placed upstream of a tube furnace, along with 50 mg of FeCoNi@C / Mo. 1.33 The Ta2C3-200 crucible was located downstream of a tube furnace for phosphating under an argon atmosphere. The tube furnace was heated to 400°C at a rate of 2°C / min and held at that temperature for 2 hours. After the sample cooled to room temperature, (FeCoNi)P / Mo was collected. 1.33 Ta2C3-200 sample. For comparison, (FeCoNi)P was synthesized using the same procedure without the addition of MXene.

[0032] 10 mg of powder was placed in a mixed solution of 700 μL water, 250 μL isopropanol, and 50 μL naphthol, and sonicated in an ice-water bath for 30 min to completely dissolve the powder. Then, 3.5 μL of the solution was pipetted onto a 3 mm diameter glassy carbon electrode. After air drying, the electrocatalytic oxygen evolution performance was tested in 1 M KOH solution using Hg / HgO as the reference electrode and a Pt sheet as the counter electrode.

[0033] The results show that the composite material (FeCoNi)P / Mo 1.33 Ta2C3-200 exhibits a significant performance improvement compared to pure (FeCoNi)P phosphide, reaching 10 mA / cm². 2 The current density overpotential decreased from 350 mV to 290 mV, such as Figure 4 As shown.

Claims

1. A kind of M' 1.33 R 0.67 The method for synthesizing the M''2AlC3 MAX phase is characterized by, Rare earth elements R As a phase formation promoter; M' is derived from group VIB, and M'' is derived from group IVB-VB, specifically including the following steps: Step 1, according to M': R The atomic molar ratio of M'': Al: C = 1.33 : 0.67 : 2 : (1~2) : (2.2~3) was used to prepare the mixture and made homogeneous. Step 2: Press the mixed powder into shape; Step 3: Under vacuum or inert atmosphere, heat to 1300℃~1600℃ at a heating rate of 5℃ / min~20℃ / min, and hold at that temperature for 0.5 hours~10 hours, through the rare earth elements... R Lowering the energy barrier of the synthesis reaction, suppressing the preferential formation of the M''C hetero phase, and promoting the formation of the target MAX phase; Step 4: Cooling to obtain high-purity M' 1.33 R 0.67 M''2AlC3 MAX phase.

2. The M' according to claim 1 1.33 R 0.67 The method for synthesizing the M''2AlC3 MAX phase is characterized by, M' is one or more of molybdenum (Mo), chromium (Cr), and tungsten (W).

3. M' according to claim 1 1.33 R 0.67 The method for synthesizing the M''2AlC3 MAX phase is characterized by, M'' is one or more of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), and tantalum (Ta).

4. M' according to claim 1 1.33 R 0.67 The method for synthesizing the M''2AlC3 MAX phase is characterized by, The M' 1.33- x R 0.67 The M' and M'' combinations of the M''2AlC3 MAX phase do not include Mo-Ti, Cr-Ti, or Cr-V.

5. A method for preparing M' by any one of claims 1-4 1.33 R 0.67 The application of the M''2AlC3 MAX phase is characterized by, Used as a precursor for the preparation of two-dimensional M' 1.33 M''2C3 MXene material.

6. A two-dimensional M' 1.33 The method for preparing M''2C3 MXene material is characterized by, M' prepared by any of the preparation methods described in claims 1-4 1.33 R 0.67 Using the M''2AlC3 MAX phase as a precursor, the precursor is etched by a solution containing fluoride ions or a molten salt containing fluoride ions to remove the Al atomic layer and R atoms, forming surface-bonded negative ion functional groups T. x And a two-dimensional M' with ordered vacancies 1.33 M''2C3 MXene material.

7. A two-dimensional M' prepared by the preparation method of claim 6 1.33 M''2C3 MXene material, characterized in that, As a carrier, FeCoNi-based MOFs were grown in situ via electrostatic self-adsorption, and (FeCoNi)P / M' was obtained through annealing and phosphating processes. 1.33 M''2C3 composite material.

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