Medium-entropy alloy phosphide / black phosphorene electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a medium-entropy alloy phosphide / black phosphorene electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of hydrogen evolution electrocatalysts. The catalyst is prepared by the following steps: carrying out acid pickling treatment on three foam metals (foam nickel, foam cobalt and foam iron), respectively taking black phosphorus crystals as an anode and a cathode, placing the foam metals and the black phosphorus crystals in an electrolytic bath containing propylene carbonate and tetrabutylammonium tetrafluoroborate, and applying 12-20V voltage to realize black phosphorus stripping and metal ion in-situ loading, and carrying out a solvothermal reaction at 160-180 DEG C for 3-4 hours to form a heterostructure. The catalyst is a heterostructure of black phosphorus nanosheet loaded medium entropy alloy phosphide, can efficiently separate hydrogen in alkaline and chloride ion-containing electrolyte, solves the problems of complex process, high cost, poor stability and the like of the existing catalyst, and is simple in process and excellent in performance.

Description

Technical Field

[0001] This invention relates to the field of hydrogen evolution electrocatalyst technology, specifically to an electrocatalyst based on a heterostructure of medium-entropy alloy phosphide and black phosphorusene, its preparation method, and its application in alkaline electrolytes and chloride-containing electrolytes. Background Technology

[0002] Hydrogen energy, as a clean and efficient green energy source, has become a research hotspot. Electrocatalytic water splitting technology is key to achieving efficient hydrogen production; however, this technology currently faces many challenges in terms of catalysts.

[0003] While noble metal catalysts (such as Pt / C) possess excellent catalytic activity, their high cost severely restricts their large-scale application. Transition metal-based catalysts, although relatively inexpensive, suffer from insufficient activity and poor stability. In seawater electrolysis for hydrogen production, the situation is even more severe, with issues such as chloride ion corrosion, high overpotential, and low stability significantly limiting the development of water electrolysis hydrogen production technology.

[0004] Black phosphorus (BP), as a novel two-dimensional material, is considered an ideal catalyst substrate material due to its advantages such as tunable band gap, high carrier mobility, and intrinsic hydrophilicity. However, pure black phosphorus nanosheets suffer from low intrinsic activity and structural instability, which makes its industrial application extremely difficult.

[0005] To improve the performance of electrocatalysts, constructing heterogeneous interfaces has become an effective strategy. By constructing heterogeneous interfaces, charge transfer resistance can be reduced, allowing more active sites to be exposed, thereby increasing the activity of the electrocatalyst. However, existing methods for improving performance through heterogeneous interface construction have significant drawbacks. For example, patent CN113235107A uses an electrochemical stripping method to simultaneously reduce metal salts (such as NiCl2 and FeCl3). In practice, this method not only requires precise control of the salt molar ratio (x:y=4), but also suffers from high metal salt costs and low reduction efficiency, undoubtedly increasing the difficulty and cost of preparation. Patent CN111517294A utilizes an H-type electrolytic cell to dope metals through an ion exchange membrane, avoiding oxygen defects, but only forming a metal-doped black phosphorus heterostructure rather than a phosphide heterostructure. Furthermore, this method requires specialized equipment, limiting its widespread application.

[0006] In conclusion, developing a hydrogen evolution catalyst that is simple to process, low in cost, and can simultaneously achieve high activity and high stability is key to overcoming the bottleneck of hydrogen production through seawater electrolysis, and has significant research value and practical application value. Summary of the Invention

[0007] This invention aims to solve the problems of complex processes, high costs, and insufficient activity and stability of hydrogen evolution catalysts in the prior art, and provides a medium-entropy alloy phosphide / black phosphorus electrocatalyst, its preparation method and application.

[0008] To achieve the above objectives, the specific solution adopted by the present invention is as follows: On one hand, this invention discloses a method for preparing a medium-entropy alloy phosphide / black phosphorus electrocatalyst, comprising the following steps: Step (1): Cut the three foam metals, nickel foam, cobalt foam, and iron foam, into sheets and remove surface oxides and impurities by acid washing; Step (2): Black phosphorus crystals are used as cathodes and foam metal treated in step (1) is used as anodes. They are placed together in an electrolytic cell containing organic solvents and electrolytes to provide a reaction environment for simultaneous stripping and loading. Step (3): Apply a preset voltage to cause the black phosphorus crystals at the cathode to undergo interlayer exfoliation to form black phosphorus nanosheets and disperse them in the electrolyte. At the same time, the foam metal at the anode is oxidized and dissolved into metal cations. Under the drive of the electric field, the metal cations can be loaded in situ onto the surface of the black phosphorus nanosheets, thus obtaining a mixed system containing solid suspensions. Step (4): After ultrasonically breaking and dispersing the mixed system obtained in step (3), it is subjected to a solvothermal reaction at 160-180℃ for 3-4 hours to allow the metal cations to undergo a phosphating reaction with black phosphorus. After naturally cooling to room temperature, it is taken out and then centrifuged and dried to obtain the medium entropy alloy phosphide / black phosphorus electrocatalyst.

[0009] Furthermore, in step (2), the organic solvent is propylene carbonate and the electrolyte is tetrabutylammonium tetrafluoroborate.

[0010] Furthermore, in step (3), the preset voltage applied is 12-20V.

[0011] Furthermore, during the preparation process, each 30-50 mg of black phosphorus crystals corresponds to 30-45 ml of organic solvent and 400-600 mg of electrolyte.

[0012] On the other hand, the present invention discloses a medium-entropy alloy phosphide / black phosphorus electrocatalyst, which is prepared by the above method. Its structure is a black phosphorus nanosheet substrate loaded with medium-entropy alloy phosphide nanoparticles, and the two form a heterogeneous interface.

[0013] Furthermore, the medium-entropy alloy phosphide / black phosphorus electrocatalyst is NiCoFeP / BP, where BP is black phosphorus nanosheets.

[0014] In another aspect, the present invention discloses the application of a medium-entropy alloy phosphide / black phosphorus electrocatalyst for electrocatalyzing hydrogen evolution reaction, wherein the hydrogen evolution reaction is carried out in an alkaline electrolyte or a chloride-containing electrolyte.

[0015] This invention constructs a highly active and stable heterostructure electrocatalyst through a three-step synergistic process of "pretreatment – ​​electrochemical stripping and loading – solvothermal phosphating". The core mechanisms of each step are as follows: (1) In step (1), ultrasonic cleaning with HCl mixture can remove the oxide layer on the surface of the foamed metal through chemical reaction. The removal of the oxide layer ensures that the metal can be efficiently oxidized and dissolved into cations in subsequent steps. If the oxide layer remains, it will hinder the contact between the metal and the electrolyte, resulting in a reduced metal cation generation rate and uneven distribution. At the same time, ultrasonic vibration can enhance solution convection and accelerate the removal of oxidation products from the metal surface, laying the foundation for uniform loading in the subsequent process.

[0016] (2) In steps (2)-(3), the electrolytic cell uses propylene carbonate as the organic solvent and tetrabutylammonium tetrafluoroborate as the electrolyte to form a low-water-content system, which can reduce the oxidation of black phosphorus nanosheets. When a voltage of 12-20V is applied, black phosphorus acts as the cathode and undergoes interlayer stripping: there are weak van der Waals forces between the black phosphorus layers, and the electric field generated by the voltage causes uneven distribution of electron clouds between the layers, forming electrostatic repulsion, which promotes the separation of the layers into nanosheets. At the same time, the anode foam metal is oxidized, and the generated metal cations migrate to the cathode under the drive of the electric field. The surface of the black phosphorus nanosheets is weakly negative due to the lone pair electrons of phosphorus atoms, which form an electrostatic adsorption effect with the metal cations (positively charged), so that the metal cations are uniformly preloaded on the surface of black phosphorus. This preloading does not require metal salts and directly uses foam metal as the ion source, avoiding the problems of low metal salt reduction efficiency and high cost in CN113235107A. Moreover, the metal ion loading can be controlled by voltage and reaction time to achieve simultaneous "stripping-loading".

[0017] (3) In step (4), ultrasonic crushing makes the black phosphorus nanosheets preloaded with metal cations more uniformly dispersed, avoiding agglomeration. Under solvothermal conditions of 160-180℃, phosphorus atoms in the black phosphorus nanosheets gain sufficient diffusion energy due to the high temperature, and undergo phosphating reaction with the metal cations preloaded on the surface. This reaction takes place in situ on the surface of the black phosphorus nanosheets, so that the generated medium-entropy alloy phosphide forms a heterogeneous interface with close contact with the black phosphorus substrate. The formation of the heterogeneous interface is the key to improving performance: the medium-entropy alloy phosphide has a multi-metal synergistic effect, and its d-band center position is closer to the Fermi level, which can optimize the adsorption energy for H; the high carrier mobility of black phosphorus accelerates the interface charge transfer and reduces the charge transfer resistance (Rct). At the same time, the lattice matching of the heterogeneous interface (XRD confirms the coexistence of BP and M2P crystal planes) inhibits the agglomeration of black phosphorus and the shedding of metal phosphides, solving the problem of poor stability of pure black phosphorus (superior to the structure formed by only metal doping in CN111517294A).

[0018] Compared with the prior art, the medium-entropy alloy phosphide / black phosphorusene hydrogen evolution electrocatalyst of the present invention has the following advantages: (1) Simple process: The preparation method of the present invention uses pure foam metal (foam nickel, foam cobalt and foam iron) as the electrochemical stripping anode. During the electrochemical stripping of black phosphorus, metal cations are introduced in situ, avoiding the use of metal salts and simplifying the operation steps. Subsequently, the medium-entropy alloy phosphide / black phosphorus heterostructure electrocatalyst is directly obtained through a one-step solvothermal method. Compared with the complex multi-step operation and precise condition control in the prior art, this method is simpler to operate and reduces the preparation difficulty and cost.

[0019] (2) High activity: Medium-entropy alloy phosphides possess high intrinsic activity, effectively promoting the hydrogen evolution reaction. Simultaneously, the black phosphorus substrate exhibits high carrier mobility, facilitating rapid electron transport. The presence of the black phosphorus substrate also promotes the uniform distribution of medium-entropy alloy phosphide nanoparticles, exposing more active sites and significantly enhancing catalyst activity. For example, in 1M KOH electrolyte, NiCoFeP / BP at a current density of 10 mA•cm -2 (η 10 The overpotential of the catalyst is only 197mV, while the overpotential of pure black phosphorus nanosheets (BP) is as high as 393mV, which fully demonstrates the high activity advantage of the catalyst of this invention.

[0020] (3) High stability: The heterogeneous interface formed between the medium-entropy alloy phosphide and black phosphorus can effectively enhance the structural stability of the catalyst. During the electrocatalytic hydrogen evolution process, the heterogeneous interface can inhibit the structural changes and degradation of black phosphorus, allowing black phosphorus to maintain good structural integrity during the reaction. Taking the hydrogen evolution reaction in simulated seawater (1M KOH + 0.5M NaCl) electrolyte as an example, NiCoFeP / BP can still maintain a low overpotential (206mV) under this complex environment, and its performance is stable during long-term reaction, showing good resistance to chloride ion corrosion and structural stability, which is difficult for existing catalysts to match. Attached Figure Description

[0021] Figure 1 This is a SEM image of the NiCoFeP / BP prepared in Example 1, showing the morphology of the two-dimensional nanosheets and the phosphide particles on the surface.

[0022] Figure 2 The image shows the XRD pattern of the NiCoFeP / BP prepared in Example 1.

[0023] Figure 3 This is the XPS full spectrum of the NiCoFeP / BP prepared in Example 1.

[0024] Figure 4 These are the LSV curves of different catalysts in 1M KOH electrolyte.

[0025] Figure 5 These are the LSV curves of different catalysts in simulated seawater (1M KOH + 0.5M NaCl electrolyte). Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0027] On one hand, this invention discloses a method for preparing a medium-entropy alloy phosphide / black phosphorus electrocatalyst, the preparation method specifically including the following steps: Step (1) Processing transition metal foam: Cut nickel foam, cobalt foam, and iron foam into sheets with dimensions of 1.2-2.3 cm in length, 0.3-0.5 cm in width, and 0.15 cm in thickness. Then mix 35-45 ml of deionized water with 1-2 ml of HCl solution (38% concentration) to obtain an acid pickling solution. Place the foamed metal in the acid pickling solution and ultrasonically clean for 20-30 minutes. This can effectively remove oxides and impurities from the surface of the foamed metal, ensuring efficient dissolution of metal ions in the subsequent process. Step (2), constructing the electrochemical stripping system: Black phosphorus crystals (30-50 mg) are used as the cathode, and foam metal treated in step (1) is used as the anode (foam metal is taken in sheets, one sheet of each type of foam metal, for a total of three sheets), and placed together in an electrolytic cell containing propylene carbonate (30-45 ml) and tetrabutylammonium tetrafluoroborate (400-600 mg). Propylene carbonate serves as the organic solvent, and tetrabutylammonium tetrafluoroborate serves as the electrolyte, both providing a suitable reaction environment for simultaneous stripping and loading; Step (3), Synchronous Exfoliation and Metal Ion Loading: A DC voltage of 12-20V is applied to the electrolytic cell. Under the action of the electric field, the black phosphorus crystals on the cathode undergo interlayer exfoliation, forming black phosphorus nanosheets that are dispersed in the electrolyte. Simultaneously, the foamed metal on the anode undergoes oxidative dissolution, generating metal cations (Ni... 2+ Co 2+ Fe 2+ These metal cations can migrate to the surface of black phosphorus nanosheets under the drive of an electric field, resulting in a mixed system containing black phosphorus nanosheets and metal ions; Step (4) In-situ phosphating to form a heterogeneous structure: The mixed system obtained in step (3) is ultrasonically broken for 10-15 min to make the system more uniform; then, a solvothermal reaction is carried out at 160-180℃ for 3-4 h. During this process, the metal cations react with black phosphorus to generate medium-entropy alloy phosphide, which grows in situ on the black phosphorus substrate to form a heterogeneous structure; after the reaction is completed, it is naturally cooled to room temperature, and then the medium-entropy alloy phosphide / black phosphorus electrocatalyst can be obtained by centrifugation, drying and other operations.

[0028] Next, this invention discloses the prepared medium-entropy alloy phosphide / black phosphorus electrocatalyst, the structure of which consists of medium-entropy alloy phosphide nanoparticles supported on a black phosphorus nanosheet substrate, forming a heterogeneous interface between the two. Specifically, the electrocatalyst is NiCoFeP / BP, where BP represents black phosphorus nanosheets.

[0029] Furthermore, this invention discloses the application of a medium-entropy alloy phosphide / black phosphorus electrocatalyst, which can be used for the electrocatalytic hydrogen evolution reaction, and the hydrogen evolution reaction can be carried out in an alkaline electrolyte (such as 1M KOH) or a chloride-containing electrolyte (such as simulated seawater: 1M KOH + 0.5M NaCl).

[0030] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0031] Example 1 (Preparation of FeCoNiP / BP catalyst) Step (1) Processing transition metal foam: Cut nickel foam, cobalt foam and iron foam (equal mass), then prepare pickling solution, mix 40ml of deionized water with 1.5ml of 38% HCl, and use the pickling solution to ultrasonically clean the cut foam metal. Set the cleaning time to 25min to fully remove oxides and impurities from its surface. Step (2) Constructing the electrochemical stripping system: Add 35 ml of propylene carbonate and 450 mg of tetrabutylammonium tetrafluoroborate to the electrolytic cell to construct the reaction environment. Use 40 mg of black phosphorus crystals as the cathode and the treated foam metal as the anode, and fix them at the corresponding positions in the electrolytic cell respectively; Step (3), Synchronous Exfoliation and Metal Ion Loading: Apply 18V to the electrolytic cell to carry out the exfoliation / loading reaction for 30 minutes. During this process, black phosphorus crystals undergo interlayer exfoliation under the action of the electric field, forming nanosheets dispersed in the electrolyte. At the same time, foam metal oxidizes and dissolves to generate cations, which migrate to the surface of black phosphorus nanosheets under the drive of the electric field, resulting in a mixed system. Step (4) In-situ phosphating to form a heterogeneous structure: The above mixed system was ultrasonically broken up for 12 minutes to make the system more uniform; then it was placed in an environment of 170°C for a solvothermal reaction for 3.5 hours. After the reaction was completed, the FeCoNiP / BP catalyst was finally obtained by centrifugation, drying and other operations.

[0032] Comparative Example 1 (Preparation of Ni2P / BP catalyst) The difference between this comparative example and Example 1 is that the anode is replaced with nickel foam, that is, a piece of nickel foam is used as the anode; the catalyst obtained in step (4) is Ni2P / BP.

[0033] Comparative Example 2 (Preparation of NiCoP / BP catalyst) The difference between this comparative example and Example 1 is that the anode is replaced with nickel foam + cobalt foam (mass ratio 1:1), that is, one piece of nickel foam and one piece of cobalt foam are used as the anode to obtain NiCoP / BP.

[0034] The catalysts obtained in Example 1 and Comparative Examples 1-2 were characterized structurally and tested for performance.

[0035] Figure 1 The image shows the SEM image of NiCoFeP / BP obtained in Example 1. It can be clearly observed from the image that NiCoFeP / BP presents a two-dimensional nanosheet morphology with certain undulations on the surface. These undulations are the supported NiCoFeP phase, which shows the microstructure characteristics of the material.

[0036] Figure 2 The XRD pattern of NiCoFeP / BP obtained in Example 1 shows that the diffraction peaks of NiCoFeP / BP at 16.836°, 26.452°, 34.126°, 34.923°, 52.265°, 55.903°, and 56.761° correspond to the (020), (021), (040), (111), (060), (151), and (132) crystal planes of BP (PDF#73-1358). The diffraction peaks at 40.08° and 42.833° correspond to the (111) and (201) crystal planes of Ni2P (PDF#03-0953) and Fe2P (PDF#76-0089), and the (111) and (021) crystal planes of Co2P (PDF#54-0413). This strongly proves that M2P (M=Ni, Co, Fe) metal phosphides have been formed, providing an important basis for the phase composition of the material.

[0037] Figure 3The image shows the XPS full spectrum of NiCoFeP / BP obtained in Example 1. This image demonstrates that the phosphorinated Ni, Co, and Fe elements were successfully loaded onto the BP nanosheets, visually illustrating the element loading situation.

[0038] Figure 4 The figures show the LSV curves of the products obtained in Example 1 and Comparative Examples 1-2 in 1M KOH electrolyte. As can be seen from the figures, in 1M KOH electrolyte, at a current density of 10 mA·cm⁻¹, -2 (η 10 When the overpotential of NiCoFeP / BP prepared in Example 1 was 197 mV, the overpotential of Ni2P / BP prepared in Comparative Example 1 was 251 mV, the overpotential of NiCoP / BP prepared in Comparative Example 2 was 237 mV, and the overpotential of BP was 393 mV, it can be seen that the overpotential of NiCoFeP / BP is significantly lower than that of NiCoP / BP, Ni2P / BP, and BP. This indicates that NiCoFeP / BP prepared in Example 1 exhibits excellent electrocatalytic hydrogen evolution performance in alkaline electrolyte.

[0039] Figure 5 The figures show the LSV curves of the products obtained in Example 1 and Comparative Examples 1-2 in a simulated seawater (1M KOH + 0.5M NaCl) electrolyte. As can be seen from the figures, in the simulated seawater electrolyte, at a current density of 10 mA•cm⁻¹, the... -2 (η 10 When the overpotential of NiCoFeP / BP prepared in Example 1 was 206 mV, the overpotential of Ni2P / BP prepared in Comparative Example 1 was 244 mV, the overpotential of NiCoP / BP prepared in Comparative Example 2 was 239 mV, and the overpotential of BP was 623 mV, it can be seen that the overpotential of NiCoFeP / BP is significantly lower than that of NiCoP / BP, Ni2P / BP, and BP, indicating that the catalyst prepared by the method of the present invention has good hydrogen evolution performance in electrolytes containing chloride ions.

[0040] In summary, SEM, XRD, and XPS characterization of the catalysts obtained in Example 1 revealed that all prepared catalysts are heterostructures of medium-entropy alloy phosphide nanoparticles supported on black phosphorus nanosheet substrates. The medium-entropy alloy phosphide is FeCoNiP, and all elements were successfully loaded onto the black phosphorus nanosheets, consistent with the expected structure and laying a structural foundation for the excellent performance of the catalysts. LSV curves of different catalysts in 1M KOH electrolyte and simulated seawater (1M KOH + 0.5M NaCl) electrolyte show that the overpotential of NiCoFeP / BP is lower than that of other catalysts in both electrolytes. This indicates that NiCoFeP / BP exhibits excellent electrocatalytic hydrogen evolution performance in both alkaline and chloride-containing electrolytes, achieving a high hydrogen evolution reaction rate at a lower overpotential, which has significant advantages in practical applications.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a medium-entropy alloy phosphide / black phosphorus electrocatalyst, characterized in that, Includes the following steps: Step (1): Cut the three foam metals, nickel foam, cobalt foam, and iron foam, into sheets and remove surface oxides and impurities by acid washing; Step (2): Black phosphorus crystals are used as cathodes and foam metal treated in step (1) is used as anodes. They are placed together in an electrolytic cell containing organic solvents and electrolytes to provide a reaction environment for simultaneous stripping and loading. Step (3): Apply a preset voltage to cause the black phosphorus crystals at the cathode to undergo interlayer exfoliation to form black phosphorus nanosheets and disperse them in the electrolyte. At the same time, the foam metal at the anode is oxidized and dissolved into metal cations. Under the drive of the electric field, the metal cations can be loaded in situ onto the surface of the black phosphorus nanosheets, thus obtaining a mixed system containing solid suspensions. Step (4): After ultrasonically breaking and dispersing the mixed system obtained in step (3), it is subjected to a solvothermal reaction at 160-180℃ for 3-4 hours to allow the metal cations to undergo a phosphating reaction with black phosphorus. After naturally cooling to room temperature, it is taken out and then centrifuged and dried to obtain the medium entropy alloy phosphide / black phosphorus electrocatalyst.

2. The method according to claim 1, characterized in that, In step (2), the organic solvent is propylene carbonate and the electrolyte is tetrabutylammonium tetrafluoroborate.

3. The method according to claim 1, characterized in that, In step (3), the preset voltage applied is 12-20V.

4. The method according to claim 1, characterized in that, During the preparation process, each 30-50 mg of black phosphorus crystals corresponds to 30-45 ml of organic solvent and 400-600 mg of electrolyte.

5. A medium-entropy alloy phosphide / black phosphorus electrocatalyst, characterized in that, Prepared by the method described in any one of claims 1-4, its structure is a black phosphorus nanosheet substrate loaded with medium-entropy alloy phosphide nanoparticles, the two forming a heterogeneous interface.

6. The electrocatalyst according to claim 5, characterized in that, The medium-entropy alloy phosphide / black phosphorus electrocatalyst is NiCoFeP / BP, where BP is black phosphorus nanosheets.

7. The application of the medium-entropy alloy phosphide / black phosphorus electrocatalyst according to any one of claims 5-6, characterized in that, Used for electrocatalytic hydrogen evolution reaction, wherein the hydrogen evolution reaction is carried out in an alkaline electrolyte or a chloride-containing electrolyte.

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